Microwave_heating

Determination of total mercury in bauxite and bauxite residue by flow injection cold vapour atomic absorption spectrometryNeetu Bansal a ,⁎,James Vaughan a ,Amiel Boullemant b ,Tony Leong ca School of Chemical Engineering,The University of Queensland,Australiab Rio Tinto Alcan Technology QRDC,Australia cQueensland Alumina Limited,Australiaa b s t r a c ta r t i c l e i n f o Article history:Received 9October 2013Received in revised form 4November 2013Accepted 4November 2013Available online 13November 2013Keywords:Mercury determination FI-CV-AAS BauxiteBauxite residueMicrowave digestionA simple method for precise and accurate determination of total mercury in bauxite and bauxite residue was de-veloped by using the flow injection mercury system.Samples of the solid materials were first microwave digested in acidic and oxidising conditions to convert all mercury to an aqueous ionic form.Following filtration and dilution,ionic mercury was reduced to elemental mercury with acidic SnCl 2to produce a cold mercury vapour.The mercury absorbance calibration graph was linear up to 20μg·kg −1with R 2N 0.999.The detection limits were determined to be 23ng·kg −1and 17ng·kg −1for bauxite and bauxite residue respectively.The relative standard deviation for 1μg·L −1mercury standard solution (n =27)was 1.5%.In the absence of a certi fied baux-ite reference material,accuracy of the method was tested with the closest available zinc concentrate reference material.Spiking known amounts of mercury in bauxite and bauxite residue samples was also tested;95–111%recovery was obtained for both samples.The method developed in this paper is recommended for measuring total mercury in bauxite and bauxite residue.©2013Elsevier B.V.All rights reserved.1.IntroductionMercury has long been recognised as a neurotoxic element [1].It is ranked third in the “priority list of hazardous substances ”by the United States Comprehensive Environmental Response,Compensation,and Liability Act [2].The United Nations also finalised the legal document “Minamata Convention of Mercury ”with the aim to reduce mercury emission;140countries are signatories to this convention [3].Recognising the growing international concern over mercury emissions,the International Council on Metals and Mining (ICMM)adopted a Mercury Risk Management Position Statement to position its members in a leadership role on the issue [4].Rio Tinto Alcan and Queensland Alumina Limited began collaboration with the University of Queensland in 2011to develop an improved understanding of mercury in their operations.Mercury can be found both naturally as well as introduced into the environment by anthropogenic activities [5].Reliable monitoring of mercury release and distribution is challenging due to issues with both sampling and measurement.Many instrumental analytical methods can be employed to determine the trace level of mercury in various samples.The most commonly cited techniques are:atomicabsorption spectrometry [6–11],atomic florescence spectrometry [12–15],inductively coupled plasma mass spectrometry (ICP-MS)[16–19],inductively coupled plasma atomic emission spectrometry (ICP-AES)[20],electroanalysis [21,22],and neutron activation analysis [23,24].Cold vapour atomic absorption spectrometry (CV-AAS)is a widely used method because of its high sensitivity and selectivity for mercury.This method involves generation of elemental mercury from an acidi-fied solution with a reducing agent (e.g.SnCl 2,NaBH 4)or by other means such as photoreduction,electrochemical (EC)vapour generation,and ultrasound promoted cold vapour generation [25].The CV-AAS technique requires that the elemental and organic forms of mercury be oxidised into ionic mercury in the feed solution [8].The conversion of complex solids into an aqueous form is accom-plished by heating the samples with concentrated acids.Wet digestion is used most commonly as mercury is lost to the vapour phase during dry ashing.Oxidants are also employed during wet digestion with the most common acids and oxidising agents being HCl,HNO 3,H 2SO 4,HClO 4,KMnO 4,K 2Cr 2O 7and H 2O 2.Elemental mercury,methyl mercury,dimethyl mercury are potential volatile components of the mercury species in a sample.Due to these volatile components,along with the tendency of mercury to adsorb on vessel walls and the requirement for complete digestion of the mercury,care must be taken in the selection of respective digesting agents and overall procedure.The choice of digestion acid depends upon the type of sample and the form of mercury present in the sample.For example,samplesMicrochemical Journal 113(2014)36–41⁎Corresponding author.E-mail address:neetu.bansal@.au (N.Bansal).0026-265X/$–see front matter ©2013Elsevier B.V.All rights reserved./10.1016/j.microc.2013.11.002Contents lists available at ScienceDirectMicrochemical Journalj o u r na l ho m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /m i c r o ccontaining organic mercury need strong oxidising agents such as aqua regia and bromine monochloride solution.Samples high in silica may require hydrofluoric acid for complete solid dissolution.Perchloric acid also has strong oxidising power but can be dangerous for the sam-ple high in organic content and it requires heating N200°C to achieve its maximum oxidising power[26].The sample preparation step in mercury determination is a challeng-ing part of the process,as it consumes time and can result in loss of analyte due to its volatile nature.Pressure microwave digestion is a good alternative to ambient pressure digestion[27].The advantages of pressure digestion are a fast digestion time,greater accuracy,less consumption of reagents,reduced sample size and less contamination [28–31].Bauxite ore is a sedimentary rock that arises due to weathering of volcanic rocks[32].The minerals are generally well oxidised with alu-minium,iron and silicon being the major components.Metallurgical grade alumina is produced from bauxite ore using the Bayer process which involves digestion of bauxite with hot sodium hydroxide under high pressure at temperatures in the range of130°C to280°C depending on the feed material.Bayer process residue(bauxite residue) is the fraction of the bauxite ore that remains undigested.The mercury content of bauxite ore can vary significantly with values of20–100, 500–700and1200–2000μg·kg−1being reported[33].The mercury varies with the geographical origin of bauxite ore[34]and,within a single deposit,mercury content can also vary significantly.To reliably ascertain the total mercury content bauxite ore and bauxite residue,a robust method was developed using microwave digestion andflow injection mercury system(FIMS)on the resulting solution.The main challenges in the development of the procedure are the presence of trace and variable amounts of mercury and complex matrix of bauxite and bauxite residue.2.Experimental2.1.ReagentsDeionised water(greater than1.0MΩcm resistivity)was used to prepare the solutions.All reagents were of analytical grade and checked for trace mercury contamination.A1.2%(w/v)SnCl2reagent was freshly prepared by dissolving12.0g SnCl2.2H2O in30mL HCl and diluted up to1L with deionised water.Mercury stock solution1000mg·L−1in 10%(v/v)HNO3was supplied by Perkin Elmer Australia.Other stock solution was prepared by diluting this mother stock solution with deionised water and1mL BrCl as a preservative for50mL solution. Mercury calibration solutions(0.5to20μg L−1)were prepared from di-lution of the mother stock solution prior to each experiment.Hydrogen peroxide(30%w/w)was supplied by Fluka Analytical,and used as such without further dilution.Bromine monochloride solution was prepared byfirst mixing5.4g of KBr(Sigma Aldrich)in50mL HCl for1h,7.6g KBrO3(Sigma Aldrich)was then added slowly over a period of approx-imately5min to produce the BrCl solution.Hydroxylamine hydrochlo-ride was prepared by dissolving15g NH2OH.HCl in deionised water to a final volume of50mL.Aqua regia(3HCl+1HNO3by volume)was prepared immediately prior to digestion.Argon gas with N99.95%purity (Core gas)was used in all experiments.The concentrated acids(HCl-37%,H2SO4-95%,HNO3-70(w acid/ w solution)%)were supplied by Sigma Aldrich.They are used with-out dilution unless specified.When diluted,the percentage speci-fied throughout the paper refers to volume percentage:100%∗(V concentrated solution/V diluted solution).2.1.1.Reference materialValidation of the method described in the present work was performed using zinc concentrate reference material BCR®-109 (Institute for Reference Material and Measurements).2.2.Instrumental2.2.1.Microwave digesterFor the digestion process a speed wave®4(Berghof products)+ instruments GmbH Germany,digester with DAK-100pressure vessels was used.The pressure vessels are made of TFM-PTFE which has a high chemical resistance and hydrophobicity.The vessels are rated up to100bars with a maximum temperature of300°C.To provide a com-fortable safety margin,the maximum temperature applied in this pro-cedure was230°C.The pressure is monitored continuously by a contact free,optical system along with temperature by an external in-frared based estimate.The microwave digestion of bauxite and bauxite residue was carried out in stages,in thefirst stage,the reactor contents were heated to120°C(maximum pressure60bars)for6min with a ramp up time3min followed by heating at200°C for5min with ramp up time of3min.In the third stage,the solutions were heated at230°C for16min with a ramp up time of5min.The total time required for digestion is about45min(including cooling time in the microwave digester).2.2.2.Flow injection mercury system(FIMS)A Perkin Elmer FIMS400flow injection mercury system is employed for the determination of mercury content of the diluted digestion liquor. This instrument uses a high performance single beam optical system, solar blind detector and low pressure mercury lamp.Thisflow injection system consists of two peristaltic pumps(P1,P2),a24cm long absorp-tion cell with removable quartz window,electrically heated mantle to maintain the cell temperature at approximately50°C.Theflow injec-tion switching valve hasfive ports with variable length sample loops. The tubing is made of PTFE and the gas liquid separator is a membrane also made of PTFE.FIMS is a combination of theflow injection technique with atomic absorption detection.The hardware was controlled using the Perkin Elmer Win Lab32for AA system software.The instrumental operating conditions are given in Table1.SnCl2/HCl was used as reductant and argon gas was used as a carrier of mercury vapour to the absorption cell.2.3.Sample collection and nature of samplesThree different bauxite and two different bauxite residue samples were collected from various alumina refineries and mining sites. Samples were collected and placed in plastic containers and transported to the lab.2.4.Characterization of bauxite residue and bauxiteThe main components of bauxite and bauxite residue samples were quantified by XRF(X-rayfluorescence),the bauxite content was 44–53%Al2O3,14–27%Fe2O3,3.8–7%SiO2,2–2.5%TiO2as wt.%andTable1Characteristic parameters of FIMS.FIMSWave length253.7nmLamp Electrodeless discharge mercury lamp(EDL) Measurement Peak heightFIAS prefill time15sFIASfill time10sFIAS inject time15sRead delay0sRead time15sReductant 1.2%(w/v)SnCl2in3%(v/v)HClCarrier3%(v/v)HClCarrier gas stream ArgonCarrier gasflow rate50mL·min−1Cell temperature50°CSample loop500μL(can be variable)37N.Bansal et al./Microchemical Journal113(2014)36–41bauxite residue content was15–23%Al2O3,27–30%Fe2O3,10–19%SiO2, 4.7–6.5%TiO2as wt.%.The major mineral phases present in the samples were identified by XRD(X-ray diffraction)using the PDF-22012data-base.The results indicate the major components of bauxite-1,bauxite-2and bauxite-3are gibbsite(Al(OH)3),boehmite(γ-AlOOH),hematite (Fe2O3),and kaolinite(Al2Si2O5(OH)4).XRD patterns for the bauxite samples are similar despite coming from various deposits.The baux-ite residue samples showed the presence of mostly hematite and some boehmite.Certain peaks for the bauxite residue XRD patterns remain unidentified.Of the unidentified peaks,some were matching with sodium aluminium silicate compounds but there was no com-plete match with the compounds in the database.The sodium aluminium silicate is the result of a desilication process which ex-plains the elevated sodium content in the residue[35].Calcium and magnesium contents are also elevated in the residue due to addition of lime during the process and a seawater neutralisation process.The literature shows the presence of aluminium hydroxide as major component and iron oxide,clay,titanium oxide,quartz,water and some other minerals as minor components in bauxite samples[36]. On the other hand the bauxite residue samples contain iron oxide and silica as major component and alumina and some other metal oxides as observed here[37].2.5.Sample preparationSample preparation is a critical step in accurate mercury content determination.As bauxite ore has a non-uniform distribution of mineral phases,the sample preparation step becomes important to obtain a representative sample and measure a sufficient quantity of sample to assess the natural variability.2.5.1.Mineral processing20kg bauxite samples were rotary split to about2.5kg fractions and one of the2.5kg fraction was then riffle split to about300g.Before splitting,the coarse fraction of the bauxite was crushed with a mortar and pestle.Finally,bauxite samples were staged pulverised for two cy-cles of5s to minimise mercury loss due to heat produced.The material was then sieved through a300μm mesh screen.The oversized material was re-pulverised for5s until all the material passed through the 300μm mesh.2.5.2.Digestion of samplesTo dissolve the sample matrix,wet digestion was carried out using a combination of acids at high temperature in the microwave digester. The hot,wet digestion can solubilise both inorganic and organic matter. Microwave digestion may enhance contact between acid and particle by fracturing particle that results in providing a new surface for acid attack [38].Careful selection of acid is required for optimal digestion.A combi-nation of aqua regia and hydrogen peroxide worked well for digesting bauxite and bauxite residue samples leaving behind a silica rich residue. Addition of H2O2in the digestion mixture facilitates the complete oxida-tion of organic matter.For the digestion of bauxite and bauxite residue, closed vessel microwave digestion with varying combinations of acid was systematically evaluated.From an analytical point of view;it is dif-ficult to solubilise bauxite and bauxite residue due to the high silicates/ silica content without using hydrofluoric acid.Also,increasing the amount of acid used can compromise the measurement using FIMS. Some researchers have claimed that digestion with acid can leach all the mercury from the sample into the acid solution and remove silicates byfiltration[39–41].The use of hydrofluoric acid to solubilise silica was avoided,due to its hazardous nature and its adverse effect on the FIMS [42].As mercury has no tendency to form natural silicate material,it was not deemed necessary to dissolve silica in the digestion mixture [43].2.5.3.Bauxite digestionFor the digestion of bauxite,various combinations of acids were test-ed.In each method0.5g of bauxite was digested with single and/or combination of various acids in the microwave digester.2.5.4.Bauxite residue digestionBauxite residue samples were digested as slurry.Before weighing the sample,bauxite residue was stirred for at least1h to make sure it is homogenous.A3.5g of bauxite residue sample was digested with dif-ferent combinations of acids.Moisture content of the bauxite residue was approximately60%that was measured separately after drying a sample in oven at60°C to constant mass.2.6.Calibration matrixThe mercury standard solution was treated exactly as the sample solutions and underwent every step including microwave digestion with the same reagents.Calibration blanks were also prepared in reagent water containing the exact amount of digestion mixture and preservative with no mercury and treated like a sample.2.7.Analytical procedureA0.5g bauxite or3.5g bauxite residue was weighted directly in the TFM-PTFE in-liner vessel.The digestion procedure was carried out in two steps,predigestion and closed vessel microwave digestion.In the pre-digestion step,for bauxite samples,3mL HCl and1mL HNO3 were added followed by drop by drop addition of1mL H2O2over a time period of approximately1min.These samples were kept over-night to ensure the oxidation of all organic matter and total degassing in solution prior to microwave digestion to prevent the build-up of extra pressure due to generation of carbon dioxide gas.For the bauxite residue samples,the same procedure was adopted,except that the amount of acid was3.75mL HCl and1.25mL HNO3.During the pre-digestion step,the PTFE vessels were loosely capped.The following day water was added to the pre-digested sample to a total volume of 15mL.The in-liners were then placed in the pressure vessels and the digestion procedure was carried out.After digestion,the pressure vessels were cooled(to room temperature)for a minimum of2h.After cooling,750μL of BrCl was added as a mercury preservative and also to assist with the conversion of any remaining organically com-plexed mercury into ionic mercury.After3–4h,the digested samples were transferred to a50mL centrifuge tube along with the washings from the TFM-PTFE in-liner.All the samples were centrifuged for 15min at5000rpm.After centrifuging,the solution was carefully transferred to another centrifuge tube leaving behind a white silica rich residue.The bauxite sample typically had less residue compared to the bauxite residue sample,this was attributed to the relatively high silica content of the residue.The digested decanted sample solution was thenfiltered through0.2μm PTFE syringefilter,and diluted to50mL with deionised water for analysis by FIMS.15min prior to the analysis,hydroxylamine hydrochloride solution was added to neutralise remaining BrCl.3.Results and discussionFIMS sensitivity is highly dependent on cold vapour generation which in turn depends on the experimental conditions.To determine the optimum conditions for the given method from the FIMS,physical and chemical variables were studied at10μg·L−1mercury.3.1.Chemical parameters3.1.1.Effect of SnCl2The effect of SnCl2on recovery of10μg·L−1mercury was studied. The concentration of SnCl2was varied from0.01%(w/v)to7%(w/v).38N.Bansal et al./Microchemical Journal113(2014)36–41The best recovery(100%)was obtained between1.0and2.0%SnCl2.This is in close agreement with the recommended concentration given by the supplier of FIMS.Reductant concentrations below1.0%and above 2.0%result in decreased recovery of mercury.1.2%SnCl2was chosen as the optimum value.3.1.2.Effect of HCl concentration in SnCl2To obtain clear solutions for aqueous SnCl2required dissolution in dilute HCl.Hydrochloric acid concentrations were varied from0.1% (v/v)to7.0%(v/v).Results showed100%recovery when the HCl content of the SnCl2solution was in the range of3.0%to4.0%.3%HCl was selected for experiments.3.1.3.Effect of HCl as a carrierThe concentration was varied between0.01%(v/v)and10%(v/v). The optimal range was determined to be3–4%HCl for10μg·L−1 mercury and3%HCl was selected for study.3.2.Physical parameters3.2.1.Argonflow rateArgon was used as carrier gas,the effect of gasflow rate was de-termined over the range of30to130mL·min−1(Fig.1).Argon flow rate also plays an important role in the sensitivity of the instru-ment as this carrier gas is responsible for carrying mercury vapour from the gas liquid separator to the absorption cell.Absorbance of the mercury signal was increased with argonflow rate from30mL·min−1 to50mL·min−1and reaches a maximum value at50mL·min−1and again decreases with increasingflow rate.At high argonflow rates the sensitivity decreases considerably due to reduction in residence time and dilution of the mercury vapour by argon gas.50mL·min−1was se-lected as the optimum value.3.2.2.Reagentflow rateThe maximum absorbance was observed when acid and reducing agentflow rates were10and6mL·min−1respectively.3.2.3.Effect of sample volumeThe effect of the sample volume was studied from20μL to 1000μL for absorbance of10μg·L−1mercury.Absorbance increased with increasing volume size from20–500μL,but from500–1000μL the absorbance plateaued.Results are shown in Fig.1.500μL was se-lected for further parison of oxidising agentsTo determine the optimum digestion working conditions for bauxite and bauxite residue samples,different combinations and amounts of digestion mixture were tested for microwave digestion. Total solubilisation of bauxite and bauxite residue was not required as mercury has no tendency to form silicates due to its large ionic radii [44].Initially,different individual acids and combinations of oxidising agent and acid at various amounts were tested.A result showed be-tween4and5mL acid/acid combinations was sufficient and efficient to digest0.5g bauxite in the microwave digester.Next about5mL of acid or combinations of different oxidising agents were tested.This study has been performed on the bauxite-1samples.A single factor Anova test was carried out at95%confidence interval.For one type of study,samples from a specific refinery were selected and taken from one container only.3.3.1.Aqua regia digestionIn this series of digestions,0.5g of bauxite was mixed with increas-ing amounts of aqua regia.The same procedure was followed as given in Section2.7including addition of BrCl.It is desirable to minimise the aqua regia required for digestion,as large amounts of aqua regia in-creases the detection limit of the assay.The results show(not included) 4mL aqua regia is sufficient to digest0.5g bauxite ore.The optimal value of4mL aqua regia was also verified for a second bauxite sample (results not shown).The lower observed recovery of mercury for higher aqua regia concentration could be related to decreased absorbance in FIMS.3.3.2.Other digestionsOther methods tested for digestion of bauxite are,4mL aqua regia+1mL H2O2,5mL HNO3,4mL HNO3+1mL H2SO4, 4mL HNO3+1mL HCl, 2.5mL HNO3+2.5mL HCl, 2.5mL HNO3+2.5mL HCl+1mL H2O2.In all these digestion the same pro-cedure given in Section2.7was followed.After testing different diges-tion mixtures,results showed that to digest0.5g bauxite,4mL aqua regia and1mL H2O2gave the best recovery of total mercury.Likewise, for the digestion of bauxite residue samples,different combinations of aqua regia and H2O2were tested.The highest recovery of mercury from bauxite residue samples using3.5mL slurry needed5mL aqua regia and1mL H2O2.3.4.Effect of sample drying temperature on recovery of mercury in bauxite sampleThe effect of drying temperature on bauxite-3was studied for a temperature range of40–240°C.For each temperature,sampleswere0.12Sample volume (µL)AbsorbanceforHgArgon gas flow rate [ mL. min-1]samplevolumeFig.1.Effect of argonflow rate and sample volume on absorbance at10μg·L−1mercuryconcentration(error barsrepresents the standard deviation of triplicate data point).[Hg]µg.kg-1Temperature in ⁰CFig.2.Effect of drying temperature of bauxite-3on mercury recovery(duplicate samples).39N.Bansal et al./Microchemical Journal113(2014)36–41dried for48h in the oven.Fig.2shows that increasing the temperature results in a minor loss in mercury concentration from40to80°C. Further increasing the temperature from80to120°C,there is a sharp decrease in the recovery of mercury that shows a major loss of the volatile mercury that occurs in this region.3.5.Validation of the method and analytical results of samplesFive point calibration curves with R2N0.999were constructed with the microwave digested mercury standard solution using the same amount of digesting mixture.In the absence of an appropriate bauxite reference material,the method was tested using a zinc ore reference material(Certified reference material BCR109)and by using spike and recovery experiments.The certified value for mercury was 960±120μg·kg−1(mean±standard deviation).Measured value for reference material in this study was973±34(mean±standard deviation)for9replicates.Two statistical tests were conducted to com-pare our results of the certified reference material to the certified value provided by the supplier.A t-test[45]compares the sample mean valueto the standard value.In the t-test,t calc was1.14and t tab was1.83at95% confidence interval for9degrees of freedom.As t tab N t calc,there is not sufficient evidence to reject the null hypothesis,which proves that both of the values are statistically similar.In another test,the confidence interval calculated for the certified value was960±98μg·kg−1at95% confidence interval and the measured value(973μg·kg−1)is within range.Bauxite and bauxite residue samples analysed by FI-CV-AAS are given in Table2.Fig.3shows the variability of the mercury content. For quality control,a known concentration mercury solution was analysed after every four samples.Accuracy was determined by 80–120%mercury recovery.To evaluate the variability of mercury concentration within the samples a single factor Anova[45]test was performed on all samples. Results showed in all the samples that there was enough evidence to reject the null hypothesis at≈100%confidence interval as F N F critical, this proves that there is natural variability in the samples.In another attempt an Anova test with Tukey method[46]was performed to compare the mercury contents in all samples.Results showed that the mercury content of bauxite-1and bauxite-2are not statistically differ-ent and the same results were seen in bauxite residue-1with bauxite residue-2.On the other hand the mercury content of bauxite-3is statistically different from bauxite-1and bauxite-2.Mercury present in bauxite is also statistically different and considerably greater than in the bauxite residues.For validation of the method,spike and recovery experiments were done by adding increasing concentrations of mercury to bauxite-1samples and bauxite residue-1samples with digestion of the mixture in the microwave digester.The procedure was repeated for each addition as described in Section2.7.Results are given in Table3.The recoveries for spiked bauxite and bauxite residue samples were between95and111%.3.6.Analyticalfigure of meritThe analyticalfigure of merit of the proposed method was calculated under optimised condition.The calibration curve was linear up to 20μg·L−1with standard solutions of mercury.The precision was calcu-lated as repeatability of the signal.It was determined from the analysis of27replicate sample of microwave digested mercury standard solu-tion containing1μg·L−1mercury with a relative standard deviation of1.5%.The method detection limit(MDL)was calculated by a U.S. EPA method[47].MDL was calculated for the bauxite and bauxite resi-due matrix.Bauxite-1sample was heated to150°C for24h to produce low mercury bauxite.This bauxite sample was used to calculate detection limits as its mercury concentration was reduced between one tofive times the estimated detection limit[47].The detection limit calculated for12samples of the bauxite at95%confidence interval was23ng·kg−1.The detection limit for bauxite residue matrix was determined to be17ng·kg−1at95%confidence interval based on10 samples from the same batch of residue.4.ConclusionA simple and accurate method for the determination of total mercu-ry in bauxite and bauxite residue samples by FI-CV-AAS was developed. The method yields lower detection limits than those stated in the liter-ature for the CV-AAS method and is sufficiently low for measurement of mercury in both bauxite and bauxite residue.Satisfactory relative stan-dard deviation values were obtained for standard solution of mercury and the method was also validated using a zinc concentrate mercury reference material.Method performance and validation were checked by quantitative recovery of mercury from spiked bauxite and bauxite residue samples.This method was successfully applied to assess the natural variability of mercury in the samples.Based on the outcomesTable2Results of bauxite and bauxite residue by FI-CV-AAS.Sample Measured value(μg·kg−1)a No.of samples Tukey method groupinginformation at95%confidence intervalBauxite-144±1224A Bauxite-246±1216A Bauxite-3135±2118B Bauxite residue-110±326C Bauxite residue-27±18Ca Mean±standard deviation.b au xi t eb au xi t eb au xi t eb au xi t er es i du eb au xi t er es i du e[Hg](µg•kg-1)Fig.3.Variability of mercury in bauxite and bauxite residue samples.Table3Analytical results of mercury in spiked bauxite and bauxite residue sample.Samples Hg added(μg·kg−1)Hg found(μg·kg−1)aHg recovered(μg·kg−1)aRecovery(%)aBauxite-1042––150195152101±3275339297108±4650765723111±3 Bauxite residue-109––556859107±112512811995±1286306297104±1a n=3,mean±mean deviation.40N.Bansal et al./Microchemical Journal113(2014)36–41。

ORIGINAL PAPERSilicon-hybrid carbon dots strongly enhance the chemiluminescence of luminolZhen Lin&Xiangnan Dou&Haifang Li&Qiushui Chen&Jin-Ming LinReceived:3October2013/Accepted:18December2013#Springer-Verlag Wien2014Abstract We report on a4-min microwave pyrolytic meth-od for the preparation of fluorescent and water-soluble silicon-hybrid carbon dots(C-dots)with high fluorescent quantum yield.The material is prepared by preheating aminopropyltriethoxysilane and ethylene diamine tetraacetic acid for1min,then adding a mixture of poly(ethylene glycol)and glycerin to the solution and heating for another 3min.It is found that the hybrid carbon dots strongly enhance the chemiluminescence(CL)of the luminol/N-bromosuccinimide system.A study on the enhancement mechanism via CL,fluorescence and electron paramagnetic resonance spectroscopy showed that the effect most proba-bly is due to electrostatic interaction between the C-dots and the luminol anion which facilitates electron transfer from luminol anion to the N-bromosuccinimide oxidant.CL in-tensity is linearly related to the concentration of the C-dots in the range between1.25and20μg mL−1.The detection limit is0.6μg mL−1(at an S/N of3).Keywords Carbon dots.Chemiluminescence.Luminol. Bromosuccinimide IntroductionFluorescent carbogenic nanoparticles hardly photobleach and display low toxicity to living cells and tissue[1].They have attracted tremendous attentions recently and could be an al-ternative for traditional heavy metal contained nanoparticles. Carbon dots is a kind of a new emerging star among various fluorescent carbogenic nanoparticles.Since the first report in 2004[2],the preparation method and their luminescence mechanism have gained great attentions[3].The methods for the preparation of carbon dots consist of “bottom up”and“top down”methods.In“top down”method, materials such as graphite[4],multiwalled carbon nanotubes [5],candle soots[6]were oxidized or exfoliated into carbon nanoparticles with diameter in the range of2to10nm.In “bottom up”route,small chemical compounds,such as citrate acid[7],ascorbic acid[8],were pyrolized to produce fluores-cent carbon dots.The quantum yields of the carbon dots and the surface modification were challenging and worthwhile.In the present work,we report an economic and fast microwave pyrolysis method to prepare luminescence carbon dots with high quantum yield within4min.The carbon dots contain silicon related group on the surface and are water-soluble, which are convinient for surface modification and their po-tential applications in many fields.Some new properties of carbon dots,such as enzy-matics mimetics[9,10],flurescent probe[11,12]and photocatalyst[13,14],have been reported recently by several groups.Our group firstly used chemiluminescence(CL)gen-erated through a chemical reaction to study the optical proper-ties of carbon dots.Their CL properties in the prescence of oxidant,such as KMnO4,Ce(IV)[15]as well as peroxynitrous acid(ONOOH)[16]have been found.Radiative recombina-tion of the injected electrons and holes was supposed to con-tribute to the CL emission.The exploring of new CL properties of carbon dots is still an interesting and challengingwork. Electronic supplementary material The online version of this article(doi:10.1007/s00604-013-1153-x)contains supplementary material,which is available to authorized users.Z.LinDepartment of Pharmaceutical Analysis,Faculty of Pharmacy,Fujian Medical University,Fuzhou350004,ChinaZ.Lin:X.Dou:H.Li(*):Q.Chen:J.<M.Lin(*)Department of Chemistry,Beijing Key Laboratory for MicronalyticalMethods and Instrumentation,The Key Laboratory of BioorganicPhosphorus Chemistry&Chemical Biology,Tsinghua University,Beijing100084,Chinae-mail:lihaifang@e-mail:jmlin@Microchim ActaDOI10.1007/s00604-013-1153-xLuminol(3-aminophthalhydrazide)is a famous CL re-agent,which has been successfully utilized in bioanalysis or sensitive detectors for high-performance liquid chromatogra-phy or capillary electrophoresis.The effective catalysts for this reagent include metal ions,metal nanoparticles,and en-zymes[17,18].The CL enhanced property of the carbon dots in luminol system has been firstly found in the present study, which extends the range of the enhancer for the luminol CL system.Futhermore,the CL emission spectra,fluorescence spectra and electron paramagnetic resonance(EPR)spectra were employed to investigate the CL enhancement mecha-nism,which provided us new insight into the CL properties of carbon dots.Experimental sectionReagents and materialsAll chemicals used were of analytical grade and used as received.Ethylene diamine tetraacetic acid(EDTA)and glyc-erin was from Sinopharm Chemical Reagent Co.,Ltd(Shang-hai,China,).(3-Aminopropyl) triethoxysilane(APTES),luminol and N-bromosuccinimide were obtained from Alfa Aesar China Ltd(China,www. ).Polyethylene glycol1500(PEG1500)were purchased from Merck Company(Darmstadt,Germany, ).ApparatusThe CL kinetic curves were recorded by a BPCL lumines-cence analyzer(Institute of Biophysics,Chinese Academy of Sciences,Beijing,China).CL signal from the flow injection was measured with a LumiFlow LF-800detector(NITI ON, Funabashi,Japan).Transmission electron microscopy image was recorded by a JEM2010electron microscope(JEOL, Japan).The CL spectra and fluorescence spectra were mea-sured with a fluorescence spectrophotometer(F7000,Hitachi, Japan).EPR spectra were measured on a Bruker spectrometer (ESP300E,Bruker,Germany).Fourier transform infrared (FTIR)spectrum was recorded on a PerkinElmer100FTIR spectrometer(Massachusetts,USA).The zeta potential was performed by Zetasize3000HSa(Malvern UK).The X-ray photoelectron spectrum(XPS)was measured by a PHI Quantera SXMTM Scanning X-ray MicroprobeTM using Al-Kαas the exciting source(1486.6ev)and binding energy calibration was based on C1s at284.8eV.Synthesis of silicon-hybrid carbon dotsFive hundredμL APTES were preheated with0.1g EDTA for 1min by mircowave-heating.The amino group on the APTES was conjugated with the carboxylic group on the EDTA,then mixture of PEG1500(1mL)and glycerin(1mL)was injected into the solution.The microwave treatment for3min caused the dehydration and pyrolysis of the mixture,and then made them broken into small luminescent carbon dots.PEG1500 and glycerin provided high boiling media for the reaction. Carbon dots were dialyzed against pure water before the experiment.CL systemCL kinetic curves were obtained by batch experiments,which were carried out in the glass cuvette.The CL profiles were displayed and integrated for0.1s interval.A microliter sy-ringe was used for the injection of the solution from the upper injection port.The effect of the carbon dots on the CL from luminol-N-bromosuccinimide system has been investigated by both batch experiment and flow injection system.The manifolds of the flow injection system were shown in Fig.S1.H2O was used as the carrier for carbon dots solution. Carbon dots were firstly mixed with luminol at the three-way channel.The mixture finally mixed with N-bromosuccinimide at the flow cell,where the CL signal was collected by the LF-800detector.The peak height of the signal recorded was measured as CL intensity.Results and discussionSynthesis and characterization of carbon dotsThe microwave-heating of APTES and EDTA induced the amino group on the APTES to be conjugated with the carbox-ylic group on the EDTA.After the injection of the mixture of PEG1500and glycerin into the solution,the further micro-wave treatment for3min caused the dehydration and pyroly-sis of the mixture,and then made them broken into small luminescent carbon dots.Transmission electron microscopy(TEM)image showed that the carbon dots had an average diameter of3nm(Fig.1a). The carbon dots showed excitation wavelength-dependence fluorescence emission with the excitation wavelength higher than360nm.Different from previously reported carbon dots [19],the emission wavelength of the silicon hybrid carbon dots did not shift with the excitation wavelength lower than360nm (Fig.1b),which may be because that the surface energy traps for the carbon dots were modified by the silicon element. Furthermore,the quantum yield of the silicon-carbon dots was calculated as24%with quinine sulfate as the reference, which was higher than some water-soluble carbon dots.The microwave heating time has some influence on the size and the fluorescence of the carbon dots.3min heating could make the carbon dots own the suitable structure with highestZ.Lin et al.fluorescence intensity.Heating time longer than 3min caused little effect on the size of the carbon dots,which was con-firmed by the TEM image.The effect of the weight ratio between APTES and EDTA on the fluorescence of the carbon dots has been investigated.Five hundre μL APTES and 0.1g EDTA could obtain the homogenous carbon dots with high fluorescence intensity.X-ray photoelectron spectroscopy (XPS)spectrum (Fig.2a )showed that the prepared carbon dots contained C,N,O and Si in a weight ratio of 61.11:5.77:24.62:8.50.Fourier trans-form infrared spectroscopy (FT-IR)(Fig.2b )revealed func-tional groups,such as ≥C-OH (hydroxyl),≥C-O-C ≤(ether),=C=O,≥Si-OH and ≥Si-O-Si ≤,could be formed on the car-bon dots.Hydroxyl group and silicon hydroxyl group on the carbon dots are beneficial for their conjugation with biomol-ecules.The X-ray diffraction pattern indicated that the carbon dots were amorphous (Fig.S2).The enhanced CL from luminol-N-bromosuccinimide system by carbon dotsIn alkaline media,N-bromosuccinimide could hydrolyze into HBrO and oxidize luminol to excited 3-aminophthalate dianion,which returned to basic state with CL emission (Fig.3a (1)).The injection of N-bromosuccinimide into the mixture of carbon dots and luminol brought in almost ten fold enhancement compared with the CL from luminol-N-bromosuccinimide system (Fig.3a (2)).The CL reaction between N-bromosuccinimide and car-bon dots in the absence of luminol was also investigated to get further insights into the interaction of the reagent.It was found that the CL reaction between N-bromosuccinimide and carbon dots could be observed in the absence of luminol in alkaline media (Fig.3b )under high recording voltage (−1.2kv),although its CL intensity was much lower com-pared with the CL from carbon dots-luminol-N-bromosuccinimide system.The CL emission arousedfromFig.1a TEM image of the carbon dots and b fluorescence spectra for carbon dots excited at wavelengths from 280nm to 460nm with 20nmincrementFig.2a X-ray photoelectron spectrum and b the IR spectrum of the silicon hybrid-carbon dotSilicon-hybrid carbon dots strongly enhance the chemiluminescencethe injection of N-bromosuccinimide to carbon dots-NaOH solution had the similar intensity compared with that from the injection of carbon dots to the mixture of NaOH and N-bromosuccinimide (Curve 1and 2in Fig.3b ).The injection of N-bromosuccinimide to carbon dots in the absence of NaOH only resulted in low CL emission (Curve 3in Fig.3b ).NaOH herein was to adjust the pH value of the system for the hydration of the N-bromosuccinimide to HBrO that acted as the oxidant in the CL reaction.It is suspected that the CL between the carbon dots and N-bromosuccinimide is similar with previous research which used KMnO 4,Ce(IV)as well as peroxynitrous acid as the oxidant [15,16],except that the CL reaction should take place in alkaline media.The CL mechanism illustrationThe enhancement role of the nanoparticle in the CL system has gained great attentions in recent years.Nanoparticle could act as catalyst that facilitated the generation CL related spe-cies,as the energy acceptors receiving the energy releasing from the excited species,or as participator that is involved in the oxidation or reduction reaction.In the presence of oxidant,such as acidic potassium per-manganate and cerium(IV),carbon dots acts as the electron acceptor.The radiative recombination of oxidant-injected holes and electrons in the carbon dots accounts for the CL emission [15].In order to verify the role of carbon dots in the N-bromosuccinimide-luminol system,EPR was utilized to investigate the ground-state properties of luminescent species in the carbon dots.The EPR signal of carbon dots at g =1.9990revealed singly occupied orbital in ground-state carbon dots.The EPR spectra of the carbon dots after their reaction with N-bromosuccinimide in the absence of luminol were presented in Fig.4and the g value of the carbon dots shifted from 1.9990to 1.9982,which suggested the electron transfer between the carbon dots and N-bromosuccinimide in the absence of luminol.While in N-bromosuccinimide -luminol-carbon dots system,the g value of the carbon dots presented little shift,which indicated that new role rather than electron donor of the carbon dots.Luminol with low reductant potential is reason-able to serve as the electron donor in N-bromosuccinimide-luminol-carbon dots system.The fluorescence of the carbon dots exhibited severely decreased after their reaction with N-bromosuccinimide.The pr ese nce of lum inol with c arb on d ots a nd N-bromosuccinimide alleviated the decreasing of the fluores-cence of carbon dots,which also indicated that luminol com-peted with carbon dots to react with N-bromosuccinimideandFig.3CL profiles in the batch system:a (1)50μL of 10−6M luminol+50μL of H 2O+N-bromosuccinimide;(2)(1)50μL of 10−6M luminol+50μL of carbon dots+N-bromosuccinimide;b (1)injection of N-bromosuccinimide into the mixture of NaOH and carbon dots;(2)injec-tion of carbon dots into the mixture of NaOH and N-bromosuccinimide;(3)injection of N-bromosuccinimide into carbon dots;(4)The mixture in (3)+NaOH.a and b were recorded with PMT voltage of −0.9kV and −1.2kV ,respectivelyFig.4The EPR signal of the carbon dots before and after CL reaction with N-bromosuccinimideZ.Lin et al.confirmed the role of electron donor of luminol on N-bromosuccinimide-luminol-carbon dots system.CL spectrum of one CL reaction is beneficial for us to get further insight into the CL emitters in the system.CL spectrum was measured by a fluorescence spectrometer with the xenonlamp turned off.In view of the weak CL emission from N-bromosuccinimide-carbon dots system,high-energy cutoff filters of various wavelengths were also used to determine the CL spectrum of the system (Blue line in Fig.5).Both methods showed that the maximum CL emission for carbon dots-N-bromosuccinimide CL system located in 550nm (Fig.5a ),which could be attributed to the oxidation of carbon dots by N-bromosuccinimide.However,the maximum CL emission for the luminol-carbon dots-N-bromosuccinimide system was around in 425nm,which was characteristic wave-length of excited 3-aminophthalate (Fig.5b ).The shift of g value of carbon dots and the sharply decrease of fluorescence indicated the reaction between carbon dots and N-bromosuccinimide.The CL emission spectra further confirmed that carbon dots acted as CL emitter in carbon dots-N-bromosuccinimide system,which was similar with the sit-uation that carbon dots reacted with some other oxidant [15].The coexistence of luminol in carbon dots-N-bromosuccinimide system not only reduced the shift of g value of carbon dots,but also reduced the decrease of FL.In addition,the CL spectra revealed the CL emitter in luminol-carbon dots-N-bromosuccinimide system was excited 3-aminophthalate,which indicated that carbon dots played a new role rather than the CL emitter in the luminol-carbon dots-N-bromosuccinimide system.pH value has significant effect on the CL emission of the CL system.The highest CL emission for carbon dots-luminol-N-bromosuccinimide system is observed in the solution with a pH value of 7.0(Fig.S3).Under the pH condition,the Zeta value of the carbon dots is 14.7mV .The pKa for luminol is 6and 13[20].Luminol is negatively charged in media with a pH value of 7.0.Therefore,it is reasonable to assume electro-static interaction between the carbon dots and luminol anion,which facilitates the electron transfer from luminol anion to the N-bromosuccinimide oxidant.As a result,the carbon dots enhance the CL intensity of thesystem.Fig.5The CL spectra of the carbon dots-N-bromosuccinimide system (a )and carbon dots-luminol-N-bromosuccinimide system (b)Fig.6Schematic illustration of CL mechanism of carbon dots-N-bromosuccinimide-luminol systemSilicon-hybrid carbon dots strongly enhance the chemiluminescenceThe contribution of 1O 2to the CL emission was excluded by investigating effects of different radical scavengers on the CL system.4-Diazabicyclo [2,2,2]octane (DABCO)was known to be a quencher of 1O 2,which could deactivate O 2(1Σg +)through electronic-to-vibrational (e-v)process [21].0.01M DABCO showed no inhibition of the CL.NaN 3,as a specific scavenger for 1O 2[22,23],with a concentration of 0.001M still could not decrease the CL signal.Based on the discussion above,the enhancement of the carbon dots on N-bromosuccinimide-luminol system could be explained as follows.The carbon dots with positive zeta potential resulted in the concentrating of the luminol anion (Fig.6),which facilitated the oxidation of luminol by HBrO that hydrolyzed from the N-bromosuccinimide.Luminol was oxidized by HBrO to excited 3-aminophthalate,which turned to its basic state by CL emission in 425nm.The application of the systemIn carbon dots-N-bromosuccinimide and carbon dots-luminol-N-bromosuccinimide systems,the CL intensity showed a linear relationship with the concentration of the carbon dots (Fig.7)in the range from 1.25×10−3to 2.00×10−2mg mL −1(Fig.4b )with a correlation coefficient of 0.9985.The detection limit was as low as 6.00×10−4mg mL −1(S /N =3).The CL system could be developed as a method for the determination of carbon dots.The carbon dots prepared by the present method contained hydroxyl group and silicon hydroxyl group on the surface that were easy for modification.It is expected that carbon dots could be conjugated with various biomolecules,such as protein,or DNA via covalent bond.These biomolecules could be quan-tified through the concentration of carbon dots.ConclusionsIn summary,microwave pyrolysis method 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摘要随着社会经济的不断发展和人们生活水平的不断提高，微波炉在我们的日常生活中得到普及，微波包装食品的消费量也在全球范围内呈现出逐年增长的趋势，新型绿色微波食品包装材料是国内外包装技术发展的一个方向。

微波加热对于包装材料和容器的性能要求较高，要具有良好的耐热性、耐油性、耐寒性、隔热性、卫生性等，目前微波包装较为先进的材料有微波穿透材料、微波吸收材料和微波反射等材料。

微波加热当今被广泛应用于人们的日常生活中，起到对食品加热、杀菌、解冻等作用，所以国内微波包装材料市场需求非常广阔。

虽然生产厂家较多, 但由于受包装材料和研发能力的限制产品技术水平仍有待提高, 很多时候无法满足客户的特殊需求, 如产品性能的要求, 包装形式的要求, 成本的要求等方面。

因此, 开发新型微波食品包装材料很有必要。

对于微波食品包装材料和容器的研发前景较为广阔，多层复合材料、聚醋膜及材料、新型的微波感受薄膜、经过处理的玻璃容器等都将发挥巨大的作用。

微波食品包装材料和容器的研发是促进微波食品技术进步的重要内容之一，运用科学技术改进微波食品包装材料和容器的性能，将会有力推动微波食品的发展，各种新型的微波食品包装材料和容器也会使得微波食品市场极大丰富。

关键词：微波食品；包装；材料AbstractWith the increasing development of social economy and people's living standards, Microwave gained popularity in our daily lives, microwave packaged food consumption worldwide are showing increasing trend year by year, new green microwave food packaging material domestic and foreign packaging technology development direction. Microwave heating performance requirements for packaging materials and containers higher, to have good heat resistance, oil resistance, cold resistance, insulation, sanitation, etc., is currently more advanced microwave packaging material microwave barrier materials, microwave absorbing microwave reflective material and other materials. Microwave heating today is widely used in people's daily lives, play on the food heating, sterilization, thawing and so on, so the domestic market demand for microwave packaging material is very broad. While many manufacturers, but because of packaging materials and R & D capacity constraints still to be improved level of technology products, we are often unable to meet the specific needs of customers, such as product performance requirements, packaging form requirements, cost requirements and so on. Therefore, the development of new microwave food packaging materials is necessary. Prospects for the development of microwave food packaging materials and containers a wider, multi-layered composite material, polyester film material, a new type of microwave susceptor films, treated glass containers and so will play a huge role. R & D of microwave food packaging materials and containers is to promote the progress of one of the important contents of microwave food technology, the use of science and technology to improve the performance of microwave food packaging materials and containers, will boost the development of microwave food, a variety of new microwave food packaging materials and also makes microwave food container market greatly enriched.Keywords: microwave food, packaging, material目录前言 (4)1、微波在食品及包装上的应用 (4)1.1在食品方面的应用 (4)1.2在食品包装上的应用 (4)2、微波食品包装材料 (4)2.1微波食品的包装 (4)2.2微波食品包装的材料 (5)3、微波食品包装容器 (6)3.1可以用于微波食品包装的容器 (6)3.2不可以用于微波食品包装的器皿 (6)4、微波食品包装的主要特点 (6)4.1易于控制，工艺先进 (7)4.2节能高效 (7)4.3选择性加热 (7)5、微波食品包装应该注意的问题 (7)5.1耐热性 (8)5.2耐油性 (8)5.3耐寒性 (8)5.4廉价性 (8)5.5卫生性 (8)5.6隔热性 (8)6、微波食品包装材料和容器的开发及应用 (9)6.1多层复合材料成为主流 (9)6.2聚醋膜及材料成为微波食品包装主要材料 (9)6.3新型的微波感受薄膜成为微波食品包装材料新秀 (10)6.4传统的玻璃包装容器也将发挥作用 (10)6.5未来的材料开发将着重于食品、材料、微波三方配合原则进行 (10)7、微波食品包装的发展前景 (10)8、结语 (12)参考文献 (13)前言随着微波炉的普及及使用,利用原包装在微波炉直接加热的食品越来越多。

微波炉的工作原理（The working principle of microwave oven）The working principle of microwave ovenIn 1946, Spence was a fellow of Raytheon Corporation in the United states. By chance, he found that the microwave dissolved the candy. It has been proved that microwave radiation can cause molecular vibrations in food and produce heat. In 1947, the first microwave oven came out.As the name suggests, the microwave oven is to use microwave to cook cook. Microwave is an electromagnetic wave. This electromagnetic energy than radio waves are often much larger, but also a strong "personality", microwave an encounter took place reflective metal, the metal there is no way to absorb or transfer it; microwave can pass through glass, ceramics, plastics and other insulating materials, but it will not consume energy; and water containing food, microwave not only through its energy but will be absorbed.Microwave ovens are made with these characteristics of microwaves. The outer shell of the microwave oven is made of stainless steel and other metal materials, and the microwave can be prevented from escaping from the furnace so as not to influence the health of the people. Food containers are made of insulating material. The heart of a microwave oven is a magnetron. The electron tube, called a magnetron, is a microwave generator that produces microwaves with a frequency of 2 billion 450 million vibrations per second. This invisible microwave can penetrate the food to 5cm depth, and also move the water molecules in the food. Intense movement produces a large amount of heat energy, so the food is cooked. This is theprinciple of microwave heating. When cooking food from an ordinary stove, heat is always coming from the outside of the food into the food. Microwave cooking, the heat is directly into the food inside, so the cooking speed faster than other stoves 4 to 10 times, thermal efficiency of more than 80%. At present, the thermal efficiency of other stoves can not be compared with that of other stoves.The microwave oven, for its short cooking time, can keep the vitamins and natural flavors in the food very well. For example, cooking green peas in a microwave can almost do without vitamin C. In addition, the microwave can also disinfect and sterilize.The use of microwave ovens should be careful not to empty "burning", because the "empty" "burning" when the microwave energy can not be absorbed, so that it is easy to damage the magnetron. In addition, the human body contains a lot of moisture, must be stopped after the magnetron, and then open the door to extract food.Basic structure of microwave ovenBasic shape and structure of microwave ovenDoor safety interlock switch - to ensure that the door is open, microwave oven can not work, the door closed, microwave oven can work;Screen window - with metal screen, can observe the cooking of food through the mesh;Ventilation - ensure good ventilation during cooking;Turntable support - drive glass turntable rotation;Glass turntable - packed food containers placed on the turntable, heating turntable rotation, so that food cooking evenly;The control panel control stall cooking;The door switch: this switch, the door is open.Working principle(1) furnace chamber. The furnace cavity is a microwave resonant cavity, which is a space where microwave energy is changed into heat energy to heat food. In order to make the food in the furnace heated evenly, a special device is arranged in the cavity of the microwave oven. The microwave oven originally produced is equipped with metal fan pages at the top of the furnace cavity, that is, microwave mixers to interfere with the propagation of microwave in the furnace cavity, thus heating the food more evenly. At present, it is loaded by a micro motor driven glass turntable at the bottom of the oven cavity of the microwave oven, the food is heated on the turntable and the disk around the motor shaft rotation, the high frequency electromagnetic field and the furnace for the relative movement, to achieve the purpose of uniform heating furnace of food. The original automatic lifting turntable makes the heating more uniform and the cooking effect more ideal.(2) the furnace door: the door is the import and export of food, and also an important part of the chamber of the microwave oven. It is very demanding, that is, from outside the door can observe the heating of food in the furnace cavity, but also can not let the microwave leak out. The furnace door is made up of metal frames and glass viewing windows. The glass interlayer in the observation window has a layer of metal microporous net, which can see the food through it and prevent the microwave leakage.Because the mesh size of the metal mesh in the glass interlayer is carefully calculated, the penetration of the microwave can be prevented completely.In order to prevent the leakage of microwave, the switch system of microwave oven is composed of multiple safety interlocking micro switch device. When the door is not closed, the microwave oven can not be worked, and the microwave oven doesn't work, so there is no microwave leakage.In order to prevent the microwave oven door shut after microwave from the gap between the door and the leaking out of the cavity, the microwave oven door around with an anti groove structure, or a microwave absorbing material, such as silicone rubber by doing door seals, a small amount of microwave can be absorbed leakage. Anti groove is a groove shaped structure is arranged inside the door, it has guided microwave phase reversal effect. In the anti microwave groove at the entrance, it will be the reverse reflection wave offset, so microwave will not leak.Because the door seal is easy to damage or aging effects caused by anti leakage reduction, so now most microwave ovens are usedto prevent microwave leakage anti groove structure, rarely used silicone rubber door seals. Anti groove structure is the principle of microwave radiation on the method of preventing the leakage of microwave stable *. Guangdong Galanz enterprise (Group) by using Galanz microwave oven production company is the most advanced anti groove structure and production process, with the development of multiple anti leakage microwave technology, microwave leakage control technology has reached the international advanced level.(3) electric circuit: the electric circuit divides the high voltage circuit, the control circuit and the low voltage circuit three parts.(a) high voltage circuit: after high-voltage transformer secondary winding circuit is high voltage circuit, mainly including magnetron, high-voltage capacitor, high voltage transformer, high voltage diode.(b) magnetron: the magnetron is the heart of the microwave oven, and microwave energy is produced and emitted by it. Magnetron operation requires a high pulsating DC anode voltage and a cathode voltage of 3 to 4V. The voltage doubler rectifier circuit composed of high voltage transformer, high voltage capacitor and high voltage diode provides the working voltage for magnetron to meet the above requirements.(c) low voltage circuit: the circuit between the primary winding of the high voltage transformer and the microwave power inlet is a low voltage circuit, and also includes a control circuit. It mainly includes safety tube, thermal circuitbreaker protection switch, interlocking micro switch, lighting lamp, timer and power distributor switch, turntable motor, fan motor, etc..(4) timer. Microwave ovens usually have two timing modes, namely mechanical timing and computer timing. The basic function is to select the set working time. After setting the time, the timer automatically cuts off the main circuit of the microwave oven.(5) power divider. The power divider is used to adjust the average operating time of the magnetron (i.e., the ratio of "work" and "stop" time) during the intermittent operation of the magnetron, so as to achieve the purpose of regulating the average output power of the microwave oven. The mechanical control type usually has 3~6 scale bits, and the computer controlled microwave oven can have 10 adjusting positions.(6) interlock microswitch. The interlocking micro switch is a group of important safety devices in microwave oven. The utility model has the function of multiple interlocking, and is controlled by the door button on the door of a furnace door or the door opening button on a door handle. When the furnace door is not closed or the furnace door is opened, the circuit is disconnected so that the microwave oven stops working.(7) thermal circuit breaker. A thermal circuit breaker is a component used to monitor the operating temperature of a magnetron or furnace chamber. When the operating temperature exceeds a certain limit, the thermal circuit breaker will immediately cut off the power supply, so that the microwave ovenwill stop working.Taboos on the use and maintenance[microwave] should be placed in the ventilation area, do not have magnetic material nearby, so as not to disturb the uniform state of the magnetic field in the furnace cavity, so that the work efficiency is reduced. Also with the TV, radio, a certain distance away, otherwise it will affect the visual and listening effects.[two] do not work with electricity when the cooking food is not in the oven. The microwave oven can not be operated without load, otherwise it will damage the magnetron. In order to avoid the negligence and cause the no-load operation, a glass filled with water can be installed in the furnace cavity.[three] all metal cutlery,Bamboo, plastic container, lacquer and other heat-resistant glass, concave and convex, are not suitable for use in microwave oven. Porcelain dishes must not be lined with gold or silver lace. The containers for the food must be placed in a microwave oven, not in the chamber.[four] microwave oven heating time depends on the amount of material and dosage, but also with food freshness, moisture content. As the heating time of various foods is different, it is necessary to take a shorter time when the heating time of the food is not certain. After heating, the heating time can be added to the degree of the cooked food. Otherwise, if thetime is too long, it will make the food become hard and lose its fragrance, color and flavor. Adjust the timing and power (temperature) knob according to the type and cooking requirements of the food. You can read the instructions carefully and learn more about them.[five] eggs with shells, sealed packaged food, can not be cooked directly. In case of explosion.[six] be sure to close the door and make sure that the interlock switch and the safety switch are closed. After the microwave oven is switched off, it is not advisable to take out the food immediately. Therefore, there is still waste heat in the oven and the food can be cooked again. It should be taken out after 1 minutes.Seven) the furnace should be kept clean. After breaking off the power supply, use a damp cloth and a neutral detergent to wipe off, do not flush, do not let the water flow into the furnace.[eight] regularly check the door around the door and the door, if damaged or closed bad, should stop using, in case of microwave leakage. Should not be close to the microwave oven window, to prevent eye damage due to microwave radiation. Should not be a long time by microwave irradiation, in order to prevent dizziness, dizziness, fatigue, weight loss, hair loss and other symptoms, so that the human body damage.9 taboos in using microwave ovens1., avoid using ordinary plastic containers: first, hot foodwill make plastic containers deformed; two, ordinary plastic will release toxic substances, pollution of food, endanger human health. Use a special microwave oven to hold the food and heat it in a microwave oven,2., avoid using metal utensils: because the furnace into the iron, aluminum, stainless steel, enamel and other vessels, microwave heating will produce sparks and reflect microwave, both damage furnace and heating unfamiliar food.3., avoid using closed containers: heating liquid should use wide mouth containers, because in closed containers, the heating of food is not easy to emit, so that the pressure in the container is too high, easy to cause blasting accidents. Even in the boiling shelled food, but also advance the shell punctured with a needle or chopsticks, to avoid heating caused by the burst, splashing dirty furnace wall, or spill wounding.4. avoid over heating: food into the microwave defrosting or heating, if forgotten to take out, if the time is more than 2 hours, should be thrown away, do not avoid food poisoning.5., avoid heating the meat to half cooked, then microwave heating: because in the half cooked food, bacteria will still grow, second times and then microwave heating, because the time is short, it is impossible to kill all bacteria. Frozen meat must be thawed in a microwave oven before being heated for cooked food.6. meat then frozen by microwave thawing: because meat after thawing in the microwave oven, actually has the outside layerof low temperature heating, this temperature bacteria are capable of reproduction, though again refrigerant can make its reproduction stop, but not live bacteria killing. The meat which has been thawed by microwave oven must be heated to full cooked if it is frozen in the refrigerator.7. avoid fried food: because of high temperature oil will splash, lead to fire. In case of accidentally causing fire in the furnace, be sure not to open the door, but should first turn off the power supply, wait until the fire is extinguished, then open the door to cool down.8. avoid placing the micro heater in the bedroom, and be careful not to cover the cooling windows of the microwave oven with articles.9. avoid long time in front of microwave oven: after opening micro furnace, people should stay away from microwave oven or person, at least 1 meters away from microwave oven.How to remove the dirt of microwave ovenAfter the use of microwave oven if not immediately wipe easily in the internal form of grease, so I had to use special cleaning tricks: a container with hot water in the microwave heat for two or three minutes, so that the microwave oven is filled with steam,This can cause the stubborn dirt to become soft and easy to remove because of the moisture content.When cleaning, wipe it again with water diluted neutral detergent, then washed with water and dry cloth cloth for final cleaning, if you still can not get rid of the stubborn dirt, can use plastic cards to scrape, do not use metal scraping, so as not to hurt inside. Finally, don't forget to turn on the microwave oven door and let the inside air dry thoroughly.Microwave oven principleSummaryMicrowave energy is produced by microwave generator, microwave generator includes microwave tube and microwave tube power supply two parts. Among them, the microwave tube power supply (referred to as power or microwave source) is the role of the common AC energy into DC energy, microwave tubes for the work of the creation of conditions. Microwave tube is the core of microwave generator. It converts DC energy into microwave energy.Microwave tubes have two major categories: microwave transistors and microwave transistors. Microwave transistors have less power output, and are generally used in measurement and communications. There are many kinds of microwave tubes, such as magnetron, klystron, TWT and so on. They are widely used in radar, navigation, communications, electronic countermeasures and heating, scientific research and so on, because of their different working principles, different structures and different performances. Because of its simple structure, high efficiency, low operating voltage, simple power supply and strong adaptability to load change, magnetronis especially suitable for other applications of microwave heating and microwave energy. Magnetron can be divided into two categories: pulsed magnetron and continuous wave magnetron because of their different working conditions. Microwave heating equipment mainly works in continuous wave state, so multi use continuous wave magnetron.Magnetron is an electric vacuum device used to generate microwave energy. Essentially a diode in a constant magnetic field. The tube in electronic control perpendicular constant magnetic field and constant electric field, interact with the high frequency electromagnetic field, the energy into microwave energy from the constant electric field, so as to achieve the purpose of generating microwave energy.There are many kinds of magnetron, and the multi cavity continuous wave magnetron is mainly introduced here.The magnetron consists of a tube core and a magnetic steel (or electromagnet). The structure of the core includes anode, cathode, energy output and magnetic circuit system, etc. four parts. Maintain a high vacuum inside the pipe. The following sections introduce the structure and function of each part.1 anodeThe anode is one of the major components of the magnetron, which together with the cathode constitutes the space between electrons and the high frequency electromagnetic field. Under the influence of a constant magnetic field and a constant electric field, electrons perform the task of energy conversionin this space. The anode of the magnetron collects electrons as well as the anode of the common diode, and plays a decisive role in the oscillation frequency of the high frequency electromagnetic field.The anode is composed of conductive metal material good (such as copper) is made, and a plurality of resonant cavity, resonant cavity must be an even number, the more the number of high frequency tube more. The type of anode resonant cavity is usually hole, groove, fan and groove fan. Each small resonant cavity on the anode is equivalent to a parallel 2C oscillation loop. Taking the slot fan cavity as an example, it can be considered that the groove part of the cavity mainly constitutes the capacitance of the oscillating loop, while the fan part mainly constitutes the inductance of the oscillating circuit. According to the microwave technology theory, the resonant frequency of the resonant cavity is inversely proportional to the geometrical size of the cavity. The larger the cavity is, the lower its operating frequency is. As a result, we can estimate the working frequency of the cavity according to the size of the cavity. The anode of a magnetron is coupled together by many resonant cavities to form a complex resonant system. The resonant cavity frequency of this system is mainly determined by the resonant frequency of each resonant cavity, and we can estimate the operating frequency band of the magnetron according to the size of the small resonant cavity.The anode resonant system of magnetron can produce the required electromagnetic oscillation, and can also generate many kinds of electromagnetic oscillations with different characteristics. In order to make the magnetron stable work inthe desired mode, commonly used "isolation belt" to isolate the interference pattern. The isolation belt anode wing an interval of a connection, in order to increase the frequency interval between the working mode and the adjacent interference pattern.In addition, due to the electron energy exchange also has a certain energy, these electrons hit the anode anode temperature, more electrons collected (i.e. the anode current is larger), or more electron energy (energy conversion rate is low), anode temperature is higher, therefore, the anode need cooling capacity good. The power generally adopts forced air cooling tube, the anode with heat sink. Then use water cooling pipe of high power, a cooling water jacket on the anode.2 cathode and its leadThe cathode of a magnetron, the emitter of electrons, is a part of the interaction space. The performance of the cathode has a great effect on the operating characteristics and life of the pipe and is regarded as the heart of the whole pipe.There are many kinds of cathodes with different properties. A direct heated cathode used in a continuous wave magnetron. It is formed from a tungsten filament or a pure tungsten filament into a spiral shape. The current is heated to a prescribed temperature and has the ability to emit electrons. The cathode has many advantages, such as short heating time and high electron bombardment resistance, and has been widely used in continuous wave magnetron.The cathode heating current is large, requiring the cathodelead to be short and thick, and the connecting parts should be in good contact. The cathode leads of high power tubes work at high temperature and are usually cooled by forced air cooling. When the magnetron works, the cathode is connected to negative high voltage, so the lead wire part should have good insulation performance and meet the requirement of vacuum sealing. In order to prevent the anode from overheating due to the electronic bombardment, the magnetron should be operated to reduce the cathode current so as to extend the service life.3 energy output deviceAn energy output device is a device that delivers microwave energy from an interaction space to a load. The function of the energy output device is that the vacuum sealing of the pipe is ensured through the microwave without loss and without breakdown. Meanwhile, the device can be conveniently connected with the external system. Small power continuous wave magnetron mostly uses coaxial output in the high frequency magnetic field of anode resonant cavity. A coupling loop is placed to generate high-frequency induction currents on the ring when the flux across the torus is so high that the high-frequency power is introduced out of the ring. The larger the coupling ring area is, the stronger the coupling is.An axial energy output device is commonly used in high-power continuous wave magnetron. The output antenna is connected to the anode fin through the hole of the pole shoe. The antenna is usually made of bars or round rods or cones. The whole antenna is sealed by the output window.The output window is usually made of glass or ceramic with low loss characteristics. It does not have to guarantee the microwave energy to pass without loss and has a good vacuum tightness. The output window of a large power tube is usually forced to cool down to reduce the heat generated by dielectric loss.4 magnetic circuit systemWhen the magnetron works normally, it requires a strong constant magnetic field, and its magnetic induction intensity is usually thousands of Gauss. The higher the working frequency, the stronger the magnetic field. The magnetic circuit system of a magnetron is a device for generating a constant magnetic field. The magnetic circuit system is divided into two major categories: permanent magnetic and electromagnetic. The permanent magnet system is generally used for small power tubes, and the magnetic steel and the tube core are firmly combined into a whole to form the so-called packing type. A large power tube electromagnet is used to generate a magnetic field, and the tube core and the electromagnet are used together. The upper and lower pole boots are arranged in the tube core to fix the distance of the magnetic gap. When magnetron works, the output power and working frequency can be adjusted conveniently by changing the magnitude of the magnetic field. In addition, the anode current can be fed into an electromagnetic wire package to improve the stability of the pipe.Proper use of 5 magnetronMagnetron is the heart of microwave equipment, so the correctuse of magnetron is the necessary condition to maintain the normal operation of microwave equipment. When using magnetron, we should pay attention to the following problems:First, the load should match.Whatever device requires the output load of the magnetron to match as much as possible, that is, its voltage to the Bobbi should be as small as possible. Large standing wave not only reflects large power, reduces the actual power of the material to be processed, but also causes the jump of the magnetron and the overheating of the cathode, and seriously damages the pipe. When the die is switched on, the anode current suddenly falls. Causes of skip die except for the small degree of separation of the pipe itself,The main aspects are as follows:(1) the internal resistance of the power supply is too large, and the non load mode causes non PI mode.(2) the load is seriously mismatched, and the reflection of the unfavorable phase weakens the interaction between the high frequency field and the electron flow, but can not sustain the normal mode oscillation.(3) insufficient heating of the filament causes insufficient emission, or because of the outgassing in the tube, the cathode poisoning causes insufficient emission, and the pipe current required for the oscillation of the PI mode can not be provided.In order to avoid the occurrence of skip mode, the internal resistance of the power supply should not be too large, the load should match, and the heating current of the filament should comply with the requirements of the instructionTwo, cooling.Cooling is one of the normal working conditions of the magnetron tube, common anode cooling high power magnetron, the cathode filament leads and output ceramic window simultaneously forced air cooling, some also use air-cooled or water-cooled electromagnet. Poor cooling will overheat the pipe and will not work properly. It will burn out the pipe in serious condition. Should not work under the condition of insufficient cooling.Three. Adjust the cathode heating power reasonably.When the magnetron is started, the cathode is overheated due to the unfavorable electron returning cathode, and the cathode overheating will aggravate the material evaporation, shorten the service life, and burn the cathode when serious. The way to prevent the cathode from overheating is to adjust the cathode heating power according to the regulation.Four 、 installation and debugging.目前常用的微波加热设备中磁控管放在激励腔上直接?だ 湎低场＜だ 患词悄芰考だ 爸茫 质谴 湎低车囊徊糠帧Ｒ虼思だ 坏男阅芏源趴毓艿墓ぷ饔跋旒 蟆＜だ 挥δ芙 苣诓 奈⒉ 芰坑行У拇 涓 涸亍Ｎ 锎四康模 だ 槐旧淼纳杓仆猓 茏釉诩だ 簧系淖芭淝榭龆怨ぷ鞯奈榷ㄐ杂跋旒 蟆Ｕ ９ぷ魇惫茏拥难艏 爰だ 唤哟ゲ糠钟泻艽蟮母咂档缌魍ü 咧 浔匦胗辛己玫慕哟ィ 哟ゲ涣冀 鸶咂荡蚧稹Ｌ煜卟迦爰だ 坏纳疃戎苯佑跋炷芰康拇 浜凸茏拥墓ぷ髯刺 Π此得魇楣娑ň 淖芭洹?Five. Preservation and transportationThe electrode material of magnetron is oxygen free copper, which can be easily oxidized in acid, alkali and moisture. Therefore, the preservation of the magnetron should be moisture-proof and avoid the acid-base atmosphere. Prevent high temperature oxidation. The packaging type magnetron shall be made of magnetic steel, and the magnetic changes of the magnetic steel shall be prevented. There shall be no ferromagnetic substance within 10 cm of the tube when it is present. In the course of pipe transportation, special vibration proof packing box shall be put in order to avoid damage caused by vibration and impact.。

化工进展Chemical Industry and Engineering Progress2022年第41卷第1期微波加热用透波材料的研究进展白永珍1，尚小标1，2，3，刘美红1，魏聪1，张富程1，肖利平1，李广超1，陈君若4（1昆明理工大学机电工程学院，云南昆明650500；2非常规冶金教育部重点实验室，云南昆明650093；3微波能工程应用及装备技术国家地方联合工程实验室，云南昆明650093；4昆明理工大学城市学院，云南昆明650051）摘要：微波加热技术因其绿色环保、体积加热、选择性加热等优势，已被广泛应用于化工强化、金属冶炼、陶瓷烧结、食品加工等众多领域，但微波在反应器内普遍存在透波效果差、微波利用率低等问题。

随着微波加热技术的不断发展，微波加热设备中透波材料的选用越来越受到大家的关注。

本文主要针对透波材料在微波加热领域中的应用现状进行综述，对透波材料的种类进行简要介绍，分别从微波加热用容器和保温材料两方面进行论述。

详细介绍了氧化物、氮化物、硅酸盐、磷酸盐等高温透波材料及聚四氟乙烯、玻纤增强树脂基、环氧树脂等中、低温透波材料的研究进展，并具体论述了目前微波加热常用纤维棉、纤维毯和纤维板等各种陶瓷纤维制品的介电特性和透波性能，最后指出了目前微波加热用透波材料普遍存在的问题，并对透波材料的应用和发展作出了展望。

关键词：微波加热；透波材料；容器；隔热耐火材料中图分类号：TB35文献标志码：A文章编号：1000-6613（2022）01-0253-11Research progress of wave-transmitting materials for microwave heatingBAI Yongzhen 1，SHANG Xiaobiao 1，2，3，LIU Meihong 1，WEI Cong 1，ZHANG Fucheng 1，XIAO Liping 1，LI Guangchao 1，CHEN Junruo 4(1Faculty of Mechanical and Electrical Engineering,Kunming University of Science and Technology,Kunming 650500,Yunnan,China;2Key Laboratory of Unconventional Metallurgy of Ministry of Education,Kunming 650093,Yunnan,China;3National Local Joint Laboratory of Engineering Application of Microwave Energy and Equipment Technology,Kunming650093,Yunnan,China;4City College,Kunming University of Science and Technology,Kunming 650051,Yunnan,China)Abstract:Microwave heating technology has been widely used in many fields,such as chemical strengthening,metal smelting,ceramic sintering,food processing and so on,because of its advantages of green environmental protection,volume heating and selective heating.However,there are many problems in microwave reactor,such as poor transmission effect and low utilization rate of microwave.With the continuous development of microwave heating technology,more and more attention has been paid to the selection of wave-transmitting materials in microwave heating equipment.This research mainly reviewesthe application status of wave-transmitting materials in the field of microwave heating.The types of wave-transmitting materials are briefly introduced,and the microwave heating containers and thermal insulation综述与专论DOI ：10.16085/j.issn.1000-6613.2021-0142收稿日期：2021-01-20；修改稿日期：2021-03-24。

不同加热方式对冷冻豆沙包食用品质及挥发性物质的比较分析王秋玉1，章海风1，2，朱文政1，2，薛盼盼1，沙文轩1，苏嘉敏1，周晓燕1，2（1.扬州大学旅游烹饪学院，江苏扬州 225100）（2.江苏省淮扬菜产业化工程中心，江苏扬州 225100） 摘要：为探究加热方式对冷冻豆沙包成熟后的食用品质及挥发性物质的影响，采用万能蒸烤箱蒸制、传统蒸笼蒸制、微波加热三种方式分别对冷冻豆沙包进行加热，测定豆沙包的水分迁移、质构、色泽、比容、蒸煮特性以及挥发性风味物质。

结果表明：不同加热方式对冷冻豆沙包的食用品质和挥发性风味物质相对含量影响显著差异（p<0.05）。

从水分分布分析，微波加热的豆沙包质子迁移率的变化最小；经质构分析，传统蒸笼蒸制的豆沙包硬度和咀嚼性最低；微波加热的豆沙包的L*值最低，a*值最高；传统蒸笼蒸制的豆沙包比容最大，失水率最小；pH值最大的是微波加热的豆沙包。

通过固相微萃取技术（SPME）和气相色谱-质谱联用技术（GC-MS）从万能蒸烤箱加热的豆沙包中分离鉴定出52种、传统蒸笼加热55种、微波加热54种挥发性风味物质，其成分类别主要包括醇类、酸类、酯类、醛类、酮酚类以及其他类化合物。

综合以上指标，充分显示传统蒸笼蒸制更适宜冷冻面团的加热，该实验结果可为冷冻面团加热方式的选择与控制提供理论依据。

关键词：豆沙包；水分分布；加热方式；品质；风味物质文章篇号：1673-9078(2021)06-266-275 DOI: 10.13982/j.mfst.1673-9078.2021.6.1122 Effects of Heating Methods on Quality and Volatile Substance Contents ofFrozen Red Bean Paste BunsW ANG Qiu-yu1,ZHANG Hai-feng1,2, ZHU Wen-zheng1,2, XUE Pan-pan1, SHA Wen-xuan1, SU Jia-min1,ZHOU Xiao-yan1,2(1. School of Tourism and Cuisine, Y angzhou University, Yangzhou 225100, China)(2.Huaiyang Cuisine Industrialization Engineering Center, Jiangsu Province, Y angzhou 225100, China)Abstract: The effects of heating methods on the quality and volatile substance contents of frozen red bean paste buns were examined. Frozen red bean paste buns were heated using three methods, namely, steaming using a multifunction oven, steaming using a traditional food steamer, and microwave heating. Changes in quality parameters such as water content, texture, color, specific volume, heating characteristics, and volatile flavor substance contents of the heated red bean paste buns were determined. The results show ed that heating methods had significant effects on the quality and relative contents of volatile flavor substances of frozen red bean paste buns (p<0.05). According to water content analysis, microwave heating had the smallest effect in the proton migration rate. Texture analysis revealed that heating using a traditional food steamer yielded the least hard and chewy buns. L* values of the buns heated using microwave were the lowest whereas their a* values were the highest. The specific volume of buns heated using a traditional food steamer was the largest, with the lowest water loss rate. In addition, buns heated using microwave had the highest pH values. Solid phase microextraction and gas chromatography-mass spectrometry assays identified 52, 55, and 54 types of volatile flavor substances from buns heated using the three methods. The identified volatile flavor substances were 引文格式：王秋玉,章海风,朱文政,等.不同加热方式对冷冻豆沙包食用品质及挥发性物质的比较分析[J].现代食品科技,2021,37(6):266-275 W ANG Qiu-yu, ZHANG Hai-feng, ZHU Wen-zheng, et al. Effects of heating methods on quality and volatile substance contents of frozen red bean paste buns [J]. Modern Food Science and Technology, 2021, 37(6): 266-275收稿日期：2020-12-02基金项目：国家自然科学基金资助项目（31701634）；四川省高等学校烹饪科学重点实验室开放课题（PRKX201913）作者简介：王秋玉（1997-），女，硕士研究生，研究方向：营养与食品卫生通讯作者：周晓燕（1964-），男，教授，研究方向：烹饪科学及烹饪工艺标准化266mainly alcohols, acids, esters, aldehydes, ketones, and phenols. The results further indicated that heating using a traditional food steamer was the most suitable method for frozen dough. These findings shall provide a theoretical basis for the selection and control of heating methods for frozen dough.Key words: red bean paste bun; water content; heating method;quality;flavor substance豆沙包是我国传统发酵面制品，也逐步成为中华美食文化的重要组成部分[1]。