High-entropy alloys as high-temperature thermoelectric materials
Samrand Shafeie, Sheng Guo, Qiang Hu, Henrik Fahlquist, Paul Erhart, and Anders Palmqvist
Citation: Journal of Applied Physics 118, 184905 (2015); doi: 10.1063/1.4935489
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High-entropy alloys as high-temperature thermoelectric materials
Samrand Shafeie,1,2Sheng Guo,1,a)Qiang Hu,3Henrik Fahlquist,4Paul Erhart,5and Anders Palmqvist 2,b)
1
Surface and Microstructure Engineering Group,Materials and Manufacturing Technology,Chalmers University of Technology,SE-41296Gothenburg,Sweden 2
Department of Chemistry and Chemical Engineering,Chalmers University of Technology,SE-41296Gothenburg,Sweden 3
Institute of Applied Physics,Jiangxi Academy of Sciences,Nanchang 330029,People’s Republic of China 4
Bruker AXS Nordic AB,17067Solna,Sweden 5
Department of Applied Physics,Chalmers University of Technology,SE-41296Gothenburg,Sweden
(Received 27August 2015;accepted 26October 2015;published online 12November 2015)Thermoelectric (TE)generators that ef?ciently recycle a large portion of waste heat will be an important complementary energy technology in the future.While many ef?cient TE materials exist in the lower temperature region,few are ef?cient at high temperatures.Here,we present the high temperature properties of high-entropy alloys (HEAs),as a potential new class of high temperature TE materials.We show that their TE properties can be controlled signi?cantly by changing the va-lence electron concentration (VEC)of the system with appropriate substitutional elements.Both the electrical and thermal transport properties in this system were found to decrease with a lower VEC number.Overall,the large microstructural complexity and lower average VEC in these types of alloys can potentially be used to lower both the total and the lattice thermal conductivity.These ?ndings highlight the possibility to exploit HEAs as a new class of future high temperature TE
materials.V
C 2015AIP Publishing LLC .[https://www.doczj.com/doc/f918749356.html,/10.1063/1.4935489]INTRODUCTION
Waste heat recovery technologies are important future
complements to renewable energy sources.1During the last two decades,renewed interest in thermoelectric (TE)materi-als for ef?cient waste heat recovery has spawned research within nanostructured materials.2In the search for TE mate-rials with high conversion ef?ciency,the dimensionless TE ?gure-of-merit zT has been used to estimate the performance.It is de?ned as
zT ?S 2r
k tot
T ;(1)
where S is the Seebeck coef?cient,r is the electrical conduc-tivity,T is the absolute temperature in Kelvin,and j tot is the total thermal conductivity.Maximizing the power factor (PF ?S 2r )while minimizing j tot is the most widely employed strategy;however,due to the fundamentally inter-connected nature of the three material parameters (S,r ,j s o s ),the general approach for a speci?c material boils down to a strongly nonlinear optimization problem.1To this end,new approaches related to low dimensional materials and nanostructuring for decoupling and changing the parameters independently have led to signi?cant improvements in the zT of current state-of-the-art TE materials.2
To reach industrially feasible materials for global use,high performance TE materials must contain low cost earth abundant elements with low toxicity.Yet,most high perform-ing TE materials at low to medium temperatures ranging up to
$600 C (e.g.,Bi 2Te 3,PbTe,and (Bi 1àx Sb x )2(Se 1ày Te y )3)contain toxic or scarce elements based on p -block elements,and recent focus has therefore shifted towards using new structure types (e.g.,half-Heusler alloys 3)to meet this prereq-uisite.For high temperature (HT)applications with T >800 C,the aforementioned materials based on p -block elements will quickly degrade,and therefore attention has been directed towards thermally more stable materials,e.g.,oxides,magnesium silicides,and Zintl compounds.1,4,5The advantages of HT TE materials are many (e.g.,lower zT is required to recover the same amount of energy compared with lower temperatures,and large scale industrial waste heat re-covery is possible),though few materials at the moment deliver high performance (zT >1)at T >800 C.1,2,6Among the state-of-the-art metallic compounds and alloys with n -type conductivity,very few examples are known to exhibit high enough zT values that can compete with the state-of-the-art n -type SiGe compounds 1at T !800 C with zT %1(e.g.,half-Heusler type materials 3,7,8).The main drawback of half-Heusler compounds have long been their large lattice (j latt )and electrical thermal conductivity (j e )that hamper their use as commercial HT-TE materials (zT at least $1at $600–700 C).8Some high performance half-Heusler com-pounds also contain costly precious metals such as Pd,9or are only ef?cient at very low temperatures.10
Recently,high entropy alloys (HEAs)have been proposed as novel types of alloys with many intriguing structural and functional properties.11–13HEAs are constituted of at least 5different elements in equimolar or close to equimolar amounts,and the enhanced con?gurational entropic contribution,partic-ularly at elevated temperatures,can thermodynamically stabi-lize the formation of solid solutions.14Apart from the
a)
E-mail:sheng.guo@chalmers.se
b)
E-mail:anders.palmqvist@chalmers.se
0021-8979/2015/118(18)/184905/10/$30.00V
C 2015AIP Publishing LLC 118,184905-1
JOURNAL OF APPLIED PHYSICS 118,184905
(2015)
formation of solid solutions,the complex phase space of these alloys15–17can potentially be used as a means to achieve exceptional properties in areas where nanostructuring is of im-portance.2,18,19As a result,HEAs are currently being evaluated for,e.g.,their mechanical properties.11,20–22Many new and unexplored avenues still remain for these types of materials (e.g.,superconductivity23and soft magnetic materials24,25).
Generally,the reduction of j latt is an important step towards a high zT of a TE material.This usually requires the use of three key strategies:?rst,the scattering of phonons on atomic length scales through rattling atoms,vacancies, impurities,interstitials,or substitutional atoms(all related to point defects in the material);second,the concept of “phonon-glass electron crystal”(PGEC)26should ideally be ful?lled,i.e.,phonons are scattered by complexity or disor-der in the crystal structure,while electrons move freely as in an“electron-crystal”(associated with the long range order in the material);and third,through interfaces,e.g.,mesoscale grain and phase boundaries.1,19,27
In HEAs,all of the above phonon scattering strategies can in principle be achieved simultaneously through the intrinsi-cally complex nature of the materials.In general,HEAs offer large amounts of complexity through severe lattice distortions, point defects,or the precipitation of secondary phases in order to scatter phonons effectively,while maintaining a high mobil-ity of the conduction electrons.In addition to effective means for phonon scattering,HEAs possess mostly high symmetry crystal structures such as simple face centered cubic close packing(FCC)or body centered cubic close packing(BCC), or in some cases hexagonal cubic close packing(HCP).They are,therefore,also likely to achieve a high convergence of the bands close to the Fermi level to obtain high Seebeck coef?-cient values.28The challenge in achieving high zT in these materials is at the moment,therefore,related to the decrease in the electrical conductivity that has a large negative impact on the total thermal conductivity,and also on the Seebeck coef?-cient due to the excessive number of charge carriers.
Controlling the properties with high accuracy in HEAs is a great challenge.However,some well-established rules for prediction of solid solutions in HEAs have been reported,29,30and are based on the following parameters:
VEC?X n
i?1
c ieVECTi;(2)
d?
????????????????????????????????????????????????????
X n
i?1
c i1à
r i
P n
j?1
c j r j
2
s
;(3)
D H mix?X n
i?1;j?i
4c i c j D H AàB:(4)
Here,the valence electron concentration(VEC)is the total number of valence electrons including d-electrons,d is the weighted atomic radii mismatch,and D H mix is the total weighted D H A-B(based on Miedema’s values for binary alloys31).In the above equations,c i and c j are the atomic per-centages of elements i and j,and r i and r j are their atomic radii,respectively.
To our knowledge,HEAs have not been reported before in the context of TE,and therefore,offer completely new possibilities regarding the exploration for HT-TE materi-als.32,33Due to the dif?culty of tuning the charge carrier con-centration in metals,many alloys have not been considered for TE applications due to their large electron concentration and low Seebeck coef?cients.Nevertheless,the possibility to form complex microstructures in HEAs(see,e.g.,Refs.16 and17)offers opportunities for the reduction of the thermal conductivity by phonon scattering.
Here,we present the investigation of a model HEA sys-tem with the composition Al x CoCrFeNi(0.0x 3.0, where x is the atomic portion)as a potential HT-TE material. We show that for this system(for which only electrical and thermal conductivities at intermediate temperatures for 0.0x 2.0have previously been reported32),the VEC (which is a well-established parameter for estimating the sta-bility of FCC and BCC phase regions among HEA systems) can be used as a general parameter to change the electrical conductivity and Seebeck coef?cients of these materials into suitable ranges for TE materials.As a result of the addition of Al,which is inserted in order to decrease the VEC of the system,we observed a signi?cant decrease in electrical con-ductivity.This decrease in electrical conductivity was fol-lowed by an increase in the absolute value of the Seebeck coef?cient.Overall,we also observed a signi?cant decrease in j tot(?j etj latt),primarily due to a lower electrical contri-bution,j e.Possible causes for the enhanced zT are discussed mainly for compositions in the range of2.0x 3.0. EXPERIMENTAL SECTION
Ingots of Al x CoCrFeNi with0.0x 3.0and D x?0.25 were prepared from commercially pure elements(puri-ty!99.9wt.%).The raw elements were alloyed by arc-melting in a Ti-gettered high-purity argon atmosphere.The melting of the ingots with intermediate?ipping was repeated at least?ve times in order to achieve a good homogeneity of the alloys.The ingots were grinded and polished to obtain a smooth and clean surface.Phase constitutions of the ingots were obtained with a Bruker x-ray diffractometer(XRD)D8 Advance diffractometer equipped with a Cr a target (k a1?1.5406A?and k a2?1.54439A?),operated at a voltage of35kV and a current of40mA.Data were acquired in the 2h range of10 –135 with a step size of0.08 /step and6s/ step.To observe if additional phases were formed,samples with x?0.25,0.75,1.25,and3.0were analyzed by XRD af-ter the electrical transport measurements.Differential scan-ning calorimetry(DSC)measurements were performed on small pieces of as-cast samples($40–50mg)placed in an Al2O3crucible and heated in a Netzsch STA449F3.Heating and cooling were performed in?owing Argon gas with a temperature ramp of10 C minà1from30to900 C.The high temperature thermal conductivity,j tot,of the ingots (x?0.0,2.0,2.25,2.5,2.75,and3.0)was measured in a Hot Disk Thermal Constant Analyser TPS2500S.The data were analyzed by using the Hot Disk Thermal Constant Analyser (Version7.1.22)software.A Hot Disk sensor C5465with a radius of3.189mm and a double spiral made of Ni were used for the measurements.Due to the Curie transition (355 C)of the Nickel sensor,data were not measured
between300and450 C in order to obtain physically sensi-ble results.Measurements were made in helium atmosphere by means of the transient plane source(TPS)method34 between105and505 C with4measurements at each tem-perature to obtain better accuracy.The presented results are averages of the4measurement points,where the correspond-ing standard deviation at each temperature is indicated with an error bar in the?gures.For all samples,a measurement time of2s with an applied power output between150and 250mW was used with a waiting time between40and 60min between each measurement.Single sided measure-ments were made with the sensor sandwiched between the ?at polished ingot sample surface and thermally insulating quartz?ber.The error for the measurement points is esti-mated to be$3%–5%on average among measured points at each temperature.
Temperature dependent electrical resistivity(1/r)and Seebeck coef?cients(S)for different samples were measured using as-cast samples in an ULVAC ZEM-3instrument. Sample dimensions ranged between$6and11mm in length, with an average side length/diameter of$2–3mm. Measurements were performed from room temperature to $900 C with$0.1bar helium gas in the measurement chamber.In the ULVAC ZEM-3,the resistivity(1/r)was measured with a standard4-point probe method by sending the current through the sample rod,while simultaneously measuring the voltage difference along the length of the rod. The Seebeck coef?cient was simultaneously obtained by heating one end of the sample,while measuring the gener-ated voltage between the probes.For each measured temper-ature point of the Seebeck coef?cient,temperature differences of D T?20,30,and40 C were used in order to minimize measurement errors.All measurements were per-formed using heating and cooling cycles in order to observe possible hysteresis effects in the as-cast samples.The hyster-esis effect from the?rst heating in the samples has been excluded due to irreversible changes when starting from an as-cast state;the presented values are thus represented as average values for the measured temperature ranges with an estimated total error of $3%between two consecutive measurements.For comparison,remeasured values for x?0.0and1.75are shown in the supplementary material for the electrical conductivity(Figure S1,supplementary mate-rial),Seebeck coef?cients(Figure S2,supplementary mate-rial),and power factors(Figure S3,supplementary material); in addition,the thermal conductivity(Figure S4,supplemen-tary material)for x?2.25was remeasured after remelting to check the reproducibility of the thermal conductivity values for the same sample.35In addition,the total,electronic,and lattice thermal conductivities are also included for x?2.0, 2.25,2.5,2.75,and3.0as additional information(Figures S5–S9,supplementary material).35Overall,it should be noted that the1st heating from room temperature up to 900 C is excluded,due to a hysteresis effect in the electrical conductivity and Seebeck coef?cients that can be related to microstructural changes as well as local compositional changes.It was,however,noted that after reaching900 C such effects were not observed in the2nd and3rd cycles.We observed that for some compositions with large x>2,the hysteresis could start already at$100 C,thus indicating that equilibration might start already at those temperatures.The measurement time at$800–900 C was estimated to be5h from the time stamps in the raw data,and the total time for3 cycles at T>500 C was$20h.Assuming that the equilibra-tion starts already at$100 C,equilibration has taken place for$90h during the3cycles that were used.Hence,the av-erage of those“equilibrated”measurements has been shown in this report.The microstructural effects of before and after annealing at the maximum temperature will be reported else-where and are not the focus of this investigation. RESULTS
Phase identification
The XRD patterns of polished samples from the Al x CoCrFeNi ingots with0.0x 3.0are shown in Figure 1.It is observed that compositions with x?0and0.25 (8.25!VEC!7.94)appear to be close to pure FCC phase. Traces of secondary cubic phases are,however,observed in the XRD data as evident from the right shoulder at$80.6 2h.Traces of tetragonal Ni1.2Al0.8type intermetallic com-pounds are also observed at$41.35 2h.With
larger FIG.1.Results from x-ray diffraction data for0.0x 3.0on polished as-cast samples and samples after Seebeck measurements at900 C(xS)are presented together with their corresponding VEC value.The data are shown using a logarithmic y-scale in order to enhance minor features that would otherwise not to be seen on a linear y-scale.The different phases are marked as1?FCC,2?BCC,and3?B2,while r-phases are marked with arrows and r.Red asterisks(*)mark the phases close in composition.
amounts of Al,with x?0.5and0.75(7.67!VEC!7.42), additional phases are present.These include disordered(A2) and ordered(B2)BCC type https://www.doczj.com/doc/f918749356.html,positions in the range1.0x 3.0(7.2!VEC!6)are observed to form a mixture of A2and B2phases.For Al0.75CoCrFeNi,a (re)measurement after exposure to T900 C during electri-cal resistivity and Seebeck coef?cient measurements(0.75S in Figure1)indicates the formation of minor intermetallic phases(r-phase).Due to the strong preferred orientation (seen in the XRD data as strong variations in the relative in-tensity between peaks)commonly observed for HEAs,36the determination of the actual weight fractions of different phases from XRD is subject to large errors,and it is therefore not presented in this study.
Thermal analysis
From the DSC measurements on samples with0.0 For x?0.25and0.5,no observable anomaly in the heat?ow is observed.For0.75x 1.5(mixed FCCtBCC region), discernable endothermic features,however,start to appear in the temperature range500 C Electrical conductivity The average electrical conductivity for FCC,BCC tFCC,and BCC related phases are shown in Figure3.We observed that the samples in this system are prone to the formation of a thin surface layer that can affect the electri-cal conductivity values to a slight extent($5%–15%).As a result,they do not follow an entirely systematic behavior between compositions close in Al content.The situation is further complicated by phase transformations(observed through DSC)involving the formation of intermetallic phases that change the matrix composition from its nominal value(see Figure2).It is observed that x?0.0 shows the highest conductivity among not only the FCC phases but all the investigated compositions in this study. Among the FCC phases,the decrease in the electrical con-ductivity is followed by x?0.5and0.25.In the FCCtBCC region,the electrical conductivity for Al con-centrations0.75x 1.25follows closely both qualita-tively and quantitatively. At higher Al contents(x>1.25),the electrical conduc-tivity behavior becomes less systematic in the range 1.5x 2.25(i.e.,the electrical conductivity is varying sig-ni?cantly between some compositions close in Al content). Again,the observed variations are most probably due to in-evitable changes in the matrix composition and surface dur-ing heating,as well as preferential enrichment of elements with low melting points and high chemical af?nity for each other.For compositions with x>2.25,the electrical conduc-tivity behavior follows a systematic trend of decreasing elec-trical conductivity with increasing amount of Al.It is also observed that the compositions with high Al contents!2.0 display a remarkably constant conductivity from room tem-perature up to high temperatures$600–650 C. Seebeck coefficient The average Seebeck coef?cient values for FCC, BCCtFCC,and BCC phases as a function of temperature are shown in Figure4.It is observed that for samples with the FCC structure,the absolute value of the Seebeck coef?-cient increases with the increasing Al content for x!0.25. Most compositions appear to be n-type.Positive values are, FIG.2.Representative DSC curves of the samples with0.0 however,observed for x?0.0at all measured temperatures, and in a smaller temperature range also for x?0.25.The trend of an increasing absolute value of the Seebeck coef?-cient continues with increasing x throughout the FCCtBCC region,and the BCC region up to x?2.75where a maximum value of$à24l V Kà1is reached for the Seebeck coef?cient at700 C.Moreover,the absolute value of the Seebeck coef?cients for this system increase over a wide temperature range from room temperature up to900 C for x 2.5,whereas for x>2.5,the temperature range around the maxima in the Seebeck coef?cients becomes narrower and the slope becomes steeper below600 C.Overall,a trend of an increasing absolute value for the Seebeck coef?cient is thus observed,when the VEC is decreased(i.e.,in the direc-tion of higher Al content). Thermal conductivity Thermal conductivity was measured between105–505 C for ingots with compositions x?0.0,2.0,2.25,2.5,2.75and 3.0.Sample with x?0.0was chosen as a reference point, while the samples with x>1.75were selected for their lower electrical conductivities.In Figure5,j tot for the measured samples is found to decrease signi?cantly in comparison with the unsubstituted sample(x?0.0).It is furthermore observed that j tot decreases from$14.5W mà1Kà1for x?0.0to $12.5W mà1Kà1for x?2.25at505 C.In addition,j tot seems to vary to some extent among different compositions at 505 C,in contrast to the values at105 C,for which the j tot values do not follow the initial order of x?0.0,2.0,2.75, 2.25,2.5,and3.0. Due to interchanges during heating,the compositions end up in the order x?0.0,2.75,2.0,2.5,3.0,and3.0at 505 C.These variations,although coming from small com-positional and/or microstructural differences,fall within ex-perimental errors of$3%–5%from the real values(see Figure S4,supplementary material).35DISCUSSION From the XRD and DSC data(see Figures1and2, respectively),the connection between the formation of minor phases with different Al contents can be more clearly observed.In agreement with XRD data(see0.75S in Figure 1),which indicates the formation of a r-phase after heat treatment during resistivity and Seebeck coef?cient measure-ments,the DSC curves indicate a clear endothermic feature with an onset temperature at$580 C for0.5x 1.75. These endothermic features have been reported as the forma-tion of a r-phase at around600 C and its dissolution around $930–960 C depending on the Al content.37Furthermore, XRD data agree well with DSC data for samples with x!1.75(i.e.,no observable endothermic features at around 600 C),hence indicating the absence of intermetallic sec-ondary phases(e.g.,3.0S in Figure1).From the XRD pat-terns a shoulder is however sometimes observed for the main BCC peaks of0.75 FIG.4.Average Seebeck coef?cients for0.0x 3.0as a function of temperature.FIG.5.Thermal conductivity values for samples with x?0.0,2.0,2.25,2.5, 2.75,and 3.0between105and505 C.Errors within each measurement tem- perature for an average of4points are shown as error bars. the smaller transition metal atoms($1.25A?).32Finally,it can be assumed that the increasing Al content gradually increases the formation of local clusters of(Co,Ni)Al rich phases with ordered B2structure(due to the large negative D H Al-Ni?à22kJ molà1and D H Al-Co?à19kJ molà1),and will consequently contribute to the preference for the ordered B2structure for high Al content. From the electrical conductivity data,we observe that compositions with low Al content,starting from x?0.0,pos-sess a high electrical conductivity($0.85MS mà1).The electrical conductivity decreases(to$0.36MS mà1)with increasing amounts of Al up to x?3.0(see Figure3).The observed trend is however not entirely systematic and shows small variations between different compositions(see Figure3). It is evident that the measurement technique and experi-mental sample preparation method in?uence the?nal electri-cal conductivity values to a certain extent( $10%).For our investigated samples,we re-melted and re-casted some annealed samples and re-measured the properties,and no no-ticeable differences were observed in?nal results.In addi-tion,we also tested samples cut from different directions of an ingot for Seebeck coef?cient and electrical conductivity measurements.We found that after the1st heating cycle all samples behaved in the same way(irrespective of which direction was used from the ingot),as the properties “equilibrated”during annealing.Thermal conductivity was, however,only measured for ingots.Re-melted samples were also tested,and they behaved in the same way as the original samples(see Figure S4).Comparison with values reported at $30,$80,and$130 C in Ref.32(see Figure6)shows a strong variation of the values at the reported temperatures; these strong variations between our results and the reported values are,however,mainly in the FCCtBCC region.We attribute these variations to different experimental prepara-tion methods and annealing procedures.This is further sup-ported by the variations observed as a consequence of different preparation methods(e.g.,as-cast,annealing and quenching,and cold deformation by rolling),which can shift the electrical conductivity values by up to$30%for,e.g., x?0.0.33These variations in the measured values for the same composition can be compared with our results for,e.g., x?0.0,with electrical conductivity values changing between $0.86and0.93MS mà1for two different measurements at room temperature(see Figure S1,supplementary material).35 Additionally,the surface of the alloys also changes slightly by the diffusion of different elements with lower melting points to the surface or a slight oxidation.This change in sur-face is observed as a slight coloring of the surface from a dark greenish color without Al(x?0.0)to slightly metallic pinkish color for intermediate Al content to increasing blue-ish/greenish color for high Al content(0.0 The high electrical conductivity values that are expected as a result of an excessive number of charge carriers are believed to be a major contributor to the low absolute value of the Seebeck coef?cient and the high thermal conductivity in the present system.A comparison of r and S for different x values can be made by grouping the compositions into FCC,FCCtBCC,and BCC phases.In Figure3,the FIG.6.A comparison between the electrical conductivity at$30,80,and 130 C from this study and Ref.32. conductivity curves for FCC phase samples are observed to decrease by$35%upon the introduction of Al($0.85MS mà1for x?0.0and$0.55MS mà1for x?0.25).The elec-trical conductivity values for x?0.25and0.5are slightly different($0.55and$0.6MS mà1at room temperature, respectively),and can be ascribed to either the aforemen-tioned effects from defects and/or to the formation of small amounts of secondary phases(minor BCC phases in x?0.5).37A small change in the composition of the main phase will consequently affect the value for the electrical conductivity.The Seebeck coef?cient is,however,changing in a systematic order(following the increasing Al content) with an absolute value of$1l V Kà1for x?0.0(100 C T900 C),which increases to$5.5l V Kà1for x?0.5 over the temperature range400 C T800 C.The change in the Seebeck coef?cient from positive(for x?0.0)to nega-tive(see Figure4)can at this point be ascribed to a change in the shape of the band structure close to the Fermi level due to the introduction of Al.Additionally,different scatter-ing mechanisms may enhance the n-type conductivity in relation to the p-type conductivity.33Furthermore,the decreasing ferromagnetic behavior with higher Al content is also indicative of an ordered(see Figure1)Al-Ni rich phase.33Such an ordered phase would,for Al contents below 44%(x?3.0corresponds to$43%),be expected to show a negative Seebeck coef?cient,very similar to what is observed in pure b-NiAl.17,40 Reported values of the Hall measurements33from x?0.0to1.25indicate a continuous decrease in the number of charge carriers with increasing Al,while an increased car-rier mobility is observed.These reported results indicate the important effect of Al on the charge carrier density and mo-bility in this system. For higher Al contents(0.5 S?8p2k2B 3eh2 m? pl e 3r 2=3 ;(5) where n is the carrier concentration(where the mobility can be de?ned as l?r/en)and m*is the density-of-states effec-tive mass of the carrier.1 In accordance with Equation(5),assuming that the total number of charge carriers decreases(with a factor of$1.9 for0.25x 1.25)33with increasing x,the mobility of the n-type carriers should be increased relative to the p-type car-riers in order to cause an increase in the negative Seebeck coef?cient.Additionally,the electrical conductivity for higher Al-content(2.0x 3.0)is found to systematically decrease with increasing x,while behaving nearly constant from room temperature up to$600 C.For samples with x?1.5and1.75the electrical conductivity deviates slightly from the trend and can be ascribed to small amounts of sec-ondary phases that form during annealing,which appear as small features in the DSC data at higher temperatures $600 C(see Figure2).These features are,however,not observed for higher Al-content.Overall,it is worth noting that the absolute value of the Seebeck coef?cients at T>650 C closely follows the trend of increasing x(i.e.,j S j increases),although the maximum occurs for x?2.75and not3.0. The formation of AlNi-rich domains as mentioned ear-lier can be expected to in?uence the overall Seebeck coef?-cient towards values closer to pure AlNi,which at room temperature is$13–14l V Kà1for Al0.4Ni0.6.This can be expected to occur for higher x-values,where the total Al-content in the system reaches$43%and the probability of forming regions rich in Al and Ni is higher.17 Ideally,we can assume the conduction electrons to scat-ter with unpaired localized electrons(e.g.,in magnetic atoms or ions)in narrow d-bands as in Kondo-like systems.41In the CoCrFeNi system with strongly ferromagnetic atoms,lower-ing the VEC by the introduction of Al will inevitably,at some threshold concentration,create local clusters of magnetic tran-sition metal atoms(i.e.,Co and Ni)surrounded by non-magnetic Al,with substantial differences between dendritic (D)and interdendritic(ID)phases(see energy-dispersive x-ray spectroscopy results of as-cast samples for2x3in Refs.37and42).For as-cast samples with compositions of, e.g.,x?2,it is clearly observed that Al prefers to accumulate in either the D or the ID phase;however,with larger x-values the preference of Al seems less pronounced.For large Al con-centrations(e.g.,x!2),the d-bands of the3d-element clusters will effectively appear similar to defects,with the width of the d-bands varying with cluster size and degree of insulation by surrounding Al atoms.Thus,the formation of a local compos-ite between magnetic and non-magnetic atoms for x!2.0 (with ordered BCC structure)becomes signi?cant enough for the appearance of the Kondo-effect at T?280K(T K%90K, 120K,and280K for Fe,Co,and Ni,respectively).43These clusters of transition metal atoms will,in these compositions, presumably interact with conduction electrons via sp-d cou-pling.41,43A Kondo-like effect has been reported for x?2.0 in these materials,33and also in our previous?ndings for higher x values x>2.0we have observed a nearly constant re-sistivity behavior that can be related to the Kondo-like effect in this system. In general,the conductivity in the system decreases from$0.85MS mà1to0.36MS mà1when moving from x?0.0to x?3.0,hence indicating that the underlying elec-trical conductivity in the system can be changed using the simple VEC concept.For compositions where signi?cant precipitation or phase transition is observed(indicated by DSC measurements),though the electrical conductivity val-ues are affected and deviate from the trend. It is assumed from the lowering of the electrical conduc-tivity that the electrical contribution to the thermal conduc-tivity also follows a gradual decrease.This is observed from our thermal conductivity measurements,indicating a gradual reduction in the thermal conductivity from12.5to9.5W mà1Kà1at room temperature.However,the order between different samples of varying Al content changes,and at 505 C the samples with x?2.25and3.0achieve very simi-lar thermal conductivities.The electrical contribution to the thermal conductivity in a metal can be estimated from the Wiedemann-Franz(W-F)law k e?L r T;(6) where L is the Lorenz number(2.44?10à8W X Kà2),r is the electrical conductivity,and T is the absolute temperature. The ratio of k e/k latt(see Figure7)shows that the electrical contribution to the thermal conductivity decreases gradually from x?2.0to x?3.0in relation to the initial value for x?0.0,which serves as the reference point.From the inset in Figure7,it is observed that the k e/k latt ratio is close to unity for x>2.25.As the electrical conductivity values do not change signi?cantly between the three samples(x?2.5, 2.75,and3.0),the electrical conductivity values most prob-ably reach a minimum at x>2.0for this particular system (0x3). In comparison with previously reported thermal conduc-tivity values32for samples x?0.0–2.0,our system behaves slightly different.For the reported thermal conductivity val-ues,32BCC samples are responsible for the highest thermal conductivities in this system from room temperature up to 300 C,which is the maximum measurement temperature. Due to the complexity of multiprincipal element systems such as HEAs,differences in preparation might affect the ?nal properties signi?cantly. We ascribe the difference in sample preparation to most of the differences observed(apart from the measurement technique).In Ref.32,40–50g of material was used,which was melted and?ipped at least3times,and furthermore, annealed for24h at1100 C,followed by water quenching. This preparation is different in comparison with our samples that were in total$60g per ingot and?ipped at least5–6 times to ensure homogeneity.Samples that were cut out or cast as cylinders from pieces of the ingots were then annealed during the resistivity and Seebeck coef?cient meas-urements from room temperature up to900 C,and were cycled until no hysteresis effects were observed in resistivity and Seebeck coef?cients($5h total time at800–900 C). Moreover,the ingot samples in our study were melted and cooled directly on the water cooled copper plate and were annealed in a similar way as for the samples for resistivity and Seebeck coef?cient measurements.As reported in Ref. 37,the r-phase already starts to form at$600 C and disap-pears at$930 C depending on Al content.The dissolution of the r-phase above$930 C would therefore affect the phase constitution in the reported values from Ref.32,in combination with the quenching procedure that freezes in the existing phases at the annealing temperature.Although r-phases are highly electrically conductive phases,they will also act as phonon scattering centers,and can be assumed to affect the thermal conductivity values by lowering the pho-non contribution(j latt)and thus decrease j tot(this can be assumed to happen in our samples where a maximum anneal-ing temperature of900 C was used).It can be assumed that the highest thermal conductivity value for x?1.5in Ref.32 therefore can be related to the lowest r-phase content in rela-tion to our samples.This is partly re?ected in the observed DSC curves for mainly x?1.0–1.5(see Figure2)and the large differences in electrical conductivity values for the same compositions(see Figure S1,supplementary mate-rial).35In Ref.32,it is reported that their samples are annealed at1100 C for24h,which should be above the tem-perature for the decomposition of r-phases before water quenching.This should produce much lower contribution from secondary phases,especially in the compositions where more than one phase is formed,e.g.,0.5 From the power factors in Figure8,it is observed that the highest absolute values of the Seebeck coef?cients do not automatically render the best power factor(e.g.,x?2.75 with S max%à24l V Kà1at T%700 C),but mainly the com-positions with a reasonable combination of high Seebeck coef?cients and high conductivity(e.g.,x?2.0and2.75).In addition,one interesting feature of the investigated HEAs seems to be the broad range for which a high power factor is FIG.7.Ratios between the calculated electrical and lattice thermal conduc-tivity contributions are shown to illustrate the decrease in the electrical con-tribution with increasing x.For clarity,only samples with x?2.5,2.75,and 3.0are shown in the inset. maintained for most samples(e.g.,x>0.75).Most samples with higher Al content(x!2.0)seem to show a constant re-sistivity behavior,which is a desirable property for thermo-electric applications as this enables a larger operating temperature range.We believe that this constant resistivity property might arise from electron scattering from a complex microstructure(e.g.,spinodal structure)and magnetic clus-ters.We are therefore currently trying to investigate it fur-ther,and results will be reported elsewhere.Furthermore,the zT of the compositions are improved from$0for x?0.0 towards0.015for x?2.0and2.25at505 C(see Figure9), thus indicating that higher zT is achievable at higher temper-atures close to the maxima between600and800 C for the Seebeck coef?cient of the different compositions.The tem-perature range that is presented here as the optimum for this HEA system closes an important gap between half-Heusler compounds and most n-type materials(T%400–650 C)as well as SiGe type materials(T%850–1000 C)that work at temperatures below and above the investigated HEAs, respectively.The numerous possibilities of HEAs from a compositional point of view will open the door towards new high temperature TE materials.In comparison with half-Heusler alloys,HEAs allow microstructural and composi-tional design based on several well established parameters: (1)VEC,(2)atomic size differences,and(3)D H f between different https://www.doczj.com/doc/f918749356.html,bining these three parameters,one can anticipate the design of high performance high tempera-ture TE materials for future high temperature applications. Additionally,one would expect from the band structures of FCC and BCC that there should be a difference between the two structures regarding the Seebeck coef?cient;however, the extent of this impact on the trends in a complex system as the presented one is not straightforward without too many simpli?cations.We therefore believe that it is necessary to combine both photoemission spectroscopy and inverse pho-toemission spectroscopy(from synchrotron sources)with band structure calculations,in order to understand the overall effects on the electronic properties from the changes in com-position and structure. From the results we conclude that the phonon contribu-tion in these HEA materials can reach relatively low values of$3W mà1Kà1at RT for x>2.25relative to alloys like, e.g.,constantan($5W mà1Kà1).For the investigated HEA system,the k latt is already comparable with values achieved for common half-Heusler compounds.In comparison with other systems1with some of the lowest k latt values for high temperatures,e.g.,La3àx Te4($0.5W mà1Kà1),clathrates ($1–2W mà1Kà1),and skutterudites($1–3W mà1Kà1), the presented HEAs have still considerable room for improvement left.However,serious efforts should be directed towards maximizing and optimizing the Seebeck coef?cients and the electrical conductivity in HEAs in order to make them applicable as high temperature TE materials. Especially a Seebeck coef?cient of at least100–200l V Kà1 should be aimed for to reach reasonable performance.Future optimization of HEAs in regard to TE properties is indeed a challenge,which if successful,might lead to high perform-ance alloys that are more compatible with TE generators than materials such as SiGe,Mg2Si,where good electrical contacts are often a concern.The potential to use refractory elements with high melting points in TE HEAs might also open the possibility to use TE materials for ultra-high tem-perature in demanding air/space applications.Additionally, there are substantial possibilities left for decreasing the lat-tice thermal conduction further(e.g.,by adding heavier ele-ments,by precipitating suitable intermetallic phases,or by using powder metallurgical routes to introduce additional microstructural complexity for phonon scattering). Furthermore,it is observed that there is a correlation between the electrical conductivity and the Seebeck coef?-cient with the overall VEC value of the system.This correla-tion opens the possibility to investigate a broad range of HEAs based on appropriate VEC values as starting points for good thermoelectric properties at high temperatures. FIG.8.Calculated power factors for all compositions.A maximum at x?2.0and2.25is reached followed by samples with x?2.75and2.5.It is worth noting the broad maxima of most samples in the HEA system. FIG.9.The thermoelectric?gure-of-merit zT for the samples with x>1.75. CONCLUSIONS High entropy alloys within the Al x CoCrFeNi-system (0.0x 3.0)have been investigated for TE properties in the temperature range of100–900 C.We found that the addition of Al improves the TE properties through an increase in the maximum absolute value of the Seebeck coef-?cient($1l V Kà1for x?0.0to$23l V Kà1for x?3.0), and a simultaneous decrease in the electrical conductivity (from$0.85MS mà1for x?0.0to$0.36for x?3.0).The thermal conductivity is in addition decreasing from$15W mà1Kà1for x?0.0to$12.5–13W mà1Kà1for x?2.25 and3.0,which is indicative of the lower electrical contribu-tion(k e),to the total thermal conductivity.This is also re?ected in the ratio between the electrical and lattice ther-mal conductivity(k e/k latt),which decreases towards unity for high Al contents(i.e.,x?2.5,2.75,and3.0).Moreover,it is found that the investigated compositions reach a zT%0.015 for x?2.0and2.25at T%505 C,which was the upper limit for our thermal conductivity measurements.The zT values follow the power factors for the different compositions with x?0.0,2.0,2.25,2.5,2.75,and3.0.We therefore conclude that the potential to reach an intrinsically low lattice thermal conductivity through complexity in the microstructure for HEAs(e.g.,by spinodal decompositions and mass?uctuation through substitutional elements),in combination with a sys-tematic control of the electrical conductivity and the Seebeck coef?cient through carefully chosen combinations of elements will open the possibility towards the design of high performance bulk TE materials for applications at high temperatures. ACKNOWLEDGMENTS The authors acknowledge the?nancial support from the Area of Advance Materials Science at Chalmers University of Technology.S.G.thanks the start-up funding from Area of Advance Materials Science at Chalmers.P.E.was partially supported by a Young Researcher Grant from the Swedish Research Council. 1G.J.Snyder and E.S.Toberer,Nat.Mater.7,105(2008). 2M.S.Dresselhaus,G.Chen,M.Y.Tang,R.Yang,H.Lee,D.Wang,Z. Ren,J.P.Fleurial,and P.Gogna,Adv.Mater.19,1043(2007). 3S.Chen and Z.Ren,Mater.Today16,387(2013). 4J.de Boor,T.Dasgupta,H.Kolb,https://www.doczj.com/doc/f918749356.html,pere,K.Kelm,and E.Mueller, Acta Mater.77,68(2014). 5J.G.Noudem,S.Quetel-Weben,R.Retoux,G.Chevallier,and C. Estourne`s,Scr.Mater.68,949(2013). 6C.J.Vineis,A.Shakouri,A.Majumdar,and M.G.Kanatzidis,Adv. Mater.22,3970(2010). 7H.Xie,H.Wang,Y.Pei,C.Fu,X.Liu,G.J.Snyder,X.Zhao,and T.Zhu, Adv.Funct.Mater.23,5123(2013). 8S.Chen,K.C.Lukas,W.Liu,C.P.Opeil,G.Chen,and Z.Ren,Adv. Energy Mater.3,1210(2013). 9Q.Shen,L.Chen,T.Goto,T.Hirai,J.Yang,G.P.Meisner,and C.Uher, Appl.Phys.Lett.79,4165(2001). 10S.Populoh,M.H.Aguirre,O.C.Brunko,K.Galazka,Y.Lu,and A. Weidenkaff,Scr.Mater.66,1073(2012). 11Y.Zhang,T.T.Zuo,Z.Tang,M.C.Gao,K.a.Dahmen,P.K.Liaw,and Z.P.Lu,Prog.Mater.Sci.61,1(2014). 12L.J.Santodonato,Y.Zhang,M.Feygenson,C.M.Parish,M.C.Gao,R.J. K.Weber,J.C.Neuefeind,Z.Tang,and P.K.Liaw,https://www.doczj.com/doc/f918749356.html,mun.6, 5964(2015). 13O.N.Senkov,J. https://www.doczj.com/doc/f918749356.html,ler,D. B.Miracle,and C.Woodward,Nat. Commun.6,6529(2015). 14D.Miracle,https://www.doczj.com/doc/f918749356.html,ler,O.Senkov,C.Woodward,M.Uchic,and J.Tiley, Entropy16,494(2014). 15F.Zhang,C.Zhang,S.L.Chen,J.Zhu,W.S.Cao,and U.R.Kattner, CALPHAD:Comput.Coupling Phase Diagrams Thermochem.45,1 (2014). 16C.Tong,Y.-L.Chen,J.Yeh,S.Lin,S.Chen,T.Shun,C.Tsau,and S. Chang,Metall.Mater.Trans.A36,881(2005). 17A.Manzoni,H.Daoud,R.V€o lkl,U.Glatzel,and N.Wanderka, Ultramicroscopy132,212(2013). 18R.Valiev,Nat.Mater.3,511(2004). 19L.-D.Zhao,V.P.Dravid,and M.G.Kanatzidis,Energy Environ.Sci.7, 251(2014). 20B.Gludovatz,A.Hohenwarter,D.Catoor,E.H.Chang,E.P.George,and R.O.Ritchie,Science345,1153(2014). 21K.M.Youssef,A.J.Zaddach,C.Niu,D.L.Irving,and C.C.Koch, Mater.Res.Lett.3,95(2015). 22M.J.Yao,K.G.Pradeep,C.C.Tasan,and D.Raabe,Scr.Mater.72–73,5 (2014). 23P.Ko z elj,S.Vrtnik, A.Jelen,S.Jazbec,Z.Jaglicˇic′,S.Maiti,M. Feuerbacher,W.Steurer,and J.Dolin s ek,Phys.Rev.Lett.113,107001 (2014). 24Y.Zhang and W.J.Peng,Procedia Eng.27,1169(2012). 25M.-H.Tsai,Entropy15,5338(2013). 26G.A.Slack,in CRC Handbook Thermoelectrics,edited by D.M.Rowe (CRC Press,1995),pp.407–440. 27K.Biswas,J.He,I.D.Blum,C.-I.Wu,T.P.Hogan,D.N.Seidman,V.P. Dravid,and M.G.Kanatzidis,Nature490,570(2012). 28Y.Pei,X.Shi,https://www.doczj.com/doc/f918749356.html,Londe,H.Wang,L.Chen,and G.J.Snyder,Nature 473,66(2011). 29S.Guo,C.Ng,J.Lu,and C.T.Liu,J.Appl.Phys.109,103505(2011). 30S.Guo,Q.Hu,C.Ng,and C.T.Liu,Intermetallics41,96(2013). 31F.R.de Boer,R.Boom,W.C.M.Mattens,A.R.Miedema,and A.K. Niessen,Cohesion in Metals:Transition Metal Alloys(Cohesion and Structure)(North Holland,1989). 32H.P.Chou,Y.S.Chang,S.K.Chen,and J.W.Yeh,Mater.Sci.Eng.,B 163,184(2009). 33Y.-F.F.Kao,S.K.Chen,T.-J.J.Chen,P.-C.C.Chu,J.-W.W.Yeh,and S.-J.J.Lin,J.Alloys Compd.509,1607(2011). 34S.E.Gustafsson,Rev.Sci.Instrum.62,797(1991). 35See supplementary material at https://www.doczj.com/doc/f918749356.html,/10.1063/1.4935489for additional material on thermoelectric properties. 36S.Guo,C.Ng,Z.Wang,and C.T.Liu,J.Alloys Compd.583,410(2014). 37W.R.Wang,W.L.Wang,and J.W.Yeh,J.Alloys Compd.589,143 (2014). 38F.Findik,Mater.Des.42,131(2012). 39D.K€o nig,C.Eberling,M.Kieschnick,S.Virtanen,and A.Ludwig,Adv. Eng.Mater.17,1365(2015). 40H.Jacobi,B.Vassos,and H.-J.Engell,J.Phys.Chem.Solids30,1261 (1969). 41J.Kondo,Prog.Theor.Phys.32,37(1964). 42C.Li,J.C.Li,M.Zhao,and Q.Jiang,J.Alloys Compd.504,S515(2010). 43M.R.Calvo,J.Fern a ndez-Rossier,J.J.Palacios,D.Jacob,D.Natelson, and C.Untiedt,Nature458,1150(2009). 创作编号：BG7531400019813488897SX 创作者：别如克* 经纬仪的使用方法 经纬仪是测量工作中的主要测角仪器。由望远镜、水平度盘、竖直度盘、水准器、基座等组成。测量时，将经纬仪安置在三脚架上，用垂球或光学对准器将仪器中心对准地面测站点上，用水准器将仪器定平，用望远镜瞄准测量目标，用水平度盘和竖直度盘测定水平角和竖直角。按精度分为精密经纬仪和普通经纬仪；按读数设备可分为光学经纬仪和游标经纬仪；按轴系构造分为复测经纬仪和方向经纬仪。此外，有可自动按编码穿孔记录度盘读数的编码度盘经纬仪；可连续自动瞄准空中目标的自动跟踪经纬仪；利用陀螺定向原理迅速独立测定地面点方位的陀螺经纬仪和激光经纬仪；具有经纬仪、子午仪和天顶仪三种作用的供天文观测的全能经纬仪；将摄影机与经纬仪结合一起供地面摄影测量用的摄影经纬仪等。 一、经纬仪的结构 DJ6经纬仪是一种广泛使用在地形测量、工程及矿山测量中的光学经纬仪。主要由水平度盘、照准部和基座三大部分组成。 1、基座部分 用于支撑基照准部，上有三个脚螺旋，其作用是整平仪器 2、照准部 照准部是经纬仪的主要部件，照准部部分的部件有水准管、光学对点器、支架、横轴、竖直度盘、望远镜、度盘读数系统等。 3、度盘部分 DJ6光学经纬仪度盘有水平度盘和垂直度盘，均由光学玻璃制成。水平度盘沿着全圆从0°～360°顺时针刻画，最小格值一般为1°或30′ 二、经纬仪的安置方法 1）三脚架调成等长并适合操作者身高，将仪器固定在三脚架上，使仪器基座面与三脚架上顶面平行。 2）将仪器舞摆放在测站上，目估大致对中后，踩稳一条架脚，调好光学对中器目镜（看清十字丝）与物镜（看清测站点），用双手各提一条架脚前后、左右摆动，眼观对中 七段数码管引脚图 《七段数码管引脚图》 数码管使用条件： a、段及小数点上加限流电阻 b、使用电压：段：根据发光颜色决定；小数点：根据发光颜色决定 c、使用电流：静态：总电流 80mA（每段 10mA）；动态：平均电流 4-5mA 峰值电流 100mA 上面这个只是七段数码管引脚图，其中共阳极数码管引脚图和共阴极的是一样的，4位数码管引脚图请在本站搜索我也提供了，有问题请到电子论坛去交流. 数码管使用注意事项说明： （１）数码管表面不要用手触摸，不要用手去弄引角； （２）焊接温度：２６０度；焊接时间：５Ｓ （３）表面有保护膜的产品,可以在使用前撕下来。 这类数码管可以分为共阳极与共阴极两种，共阳极就是把所有LED的阳极连接到共同接点com，而每个LED的阴极分别为a、b、c、d、e、f、g及dp（小数点）；共阴极则是把所有LED的阴极连接到共同接点com，而每个LED的阳极分别为a、b、c、d、e、f、g及dp（小数点），如下图所示。图中的8个LED分别与上面那个图中的A~DP各段相对应，通过控制各个LED的亮灭来显示数字。 那么，实际的数码管的引脚是怎样排列的呢？对于单个数码管来说，从它的正面看进去，左下角那个脚为1脚，以逆时针方向依次为1~10脚，左上角那个脚便是10脚了，上面两个图中的数字分别与这10个管脚一一对应。注意，3脚和8脚是连通的，这两个都是公共脚。 还有一种比较常用的是四位数码管，内部的4个数码管共用 a~dp这8根数据线，为人们的使用提供了方便，因为里面有4个数码管，所以它有4个公共端，加上a~dp，共有12个引脚，下面便是一个共阴的四位数码管 浅谈小学科学教学论文 复兴小学严光利随着信息化程度的提高和全球信息化的实现，作为未来人才培养基地的教育系统首先受到巨大的冲击，当代信息技术带给教育系统的小仅是手段与方法的变革，而且也包括教育观念与教育模式在内的一场历史性变革。教育系统受到信息革命的冲击，最突出的是现代信息技术在教育实践中的应用，这给教育带来了新的格局和新的气象。特别是它对课程改革中新兴的课程一一小学科学课，产生了根本性的改变。 网络环境中的科学课堂教育丰富了教学资源，拓展了教学模式。它将过去传统的、静态的、封闭的课堂变成了现代的、动态的、开放的课堂教学模式，使科学课堂更形象生动，更富感染力，更能激发学生的学习兴趣和求知欲。让学生在有限的教学时间内，轻松地学到更多的知识。为此，我就网络环境下小学科学教学谈一点个人的想法。 一、巧用电教，化难为易 科学课上有很多学生自主探究的素材，要求学生在教师的指导或引导下去进行调查、考察或实验，但有些活动课堂上是无法用实验的形式完全展现的，如《植物怎样喝水》这一课，反反复复讲解理论学生都很难理解，这时我们就可以借助网络技术和多媒体技术，虚实互补，让学生“看到”植物根的水与植物茎、叶脉向上输送的水缓缓流动的情景，再在重点处点拨，植物“喝水” 这一难点就解决了。再比如《地球的公转和自转》等一系列天文知识课文，《食物链》等表现多种生物类课文，都可以利用网络和多媒体教学，生动、形象地展示给学生观看，使学生的科学探究活动小限于课堂上，实现学习时空的拓展。另外在科学课的教学中有许多新知识、新思维的传授，受到了安全性等方面的限制，小可能在课堂进行实际演示，为了增强学生的感性认识，可以通过各种现代教育技术手段在教学过程中对这些实验、现象进行模拟演示达到仿真效果，或对现象进行放大、延时等操作，进而使学生在没有障碍的演示、实验环境中进行愉快地学习，获取知识。 二、提高兴趣，增强感知 传统教学方式主要靠粉笔、黑板、挂图或模型，学生兴趣小大，而网络环境中的科学课堂生动、形象、直观，学生兴趣浓厚。如教学《昆虫》一课，在学生掌握了昆虫的概念以后，训练学生能否在众多的动物中判断哪些是昆虫。这时可以在电脑上出示“送昆虫回家”的题目，让学生以游戏的形式“拖拽”昆虫到相应的栏里，学生既引发了兴趣，又强化了知识。 三、丰富资源，深化探究 《科学课程标准》在课程“基本理念”中指出“科学课程要面向全体学生。”①“科学学习要以探究为核心。......科学课程应向学生提供充分的科学探究机会，使他们在像科学家那样进行科学探究的过程中，体验学习科学的乐趣，增长科学探究能力，获取科学知识，形成尊重事实、善于质疑的科学态度，了解科学发 引用在这里经纬仪操作方法步骤详解图解添加日志标题 经纬仪操作方法步骤详解图解 步骤图解 1、连接螺旋:旋紧连接螺旋， 将仪器固定在三脚架上。 2、调节三脚架:将三脚架打开， 调节高度适中，三条架腿分别 处于测站周围。如果地面松软， 应将架腿踩实。 3、光学对中器:调节光学对中 器的目镜和物镜，使地面清晰 成像。 4、脚螺旋:调节脚螺旋，将仪器精确整平。 5、水平制动螺旋:旋紧水平制动螺旋，照准部被固定。望远镜无法在水平方向转动。 6、水平微动螺旋:水平制动螺旋旋紧后，旋转水平微动螺旋，照准部在水平方向微微转动。 7、竖直制动螺旋:旋紧竖直制动螺旋，望远镜被固定在支架上无法转动。 8、目镜调焦螺旋:转动目镜调焦螺旋，使十字丝清晰。 9、水平度盘反光镜:调整水平度盘反光镜，读书窗数字明亮。 10、竖直度盘反光镜:调整竖直度盘反光镜，使读数窗读数明亮。 11、读数显微镜：调节读数显微镜，使读书清晰。 12、配盘手轮:调整配盘手轮， 改变水平度盘读数。 水准仪操作步骤方法详解图解 发布: 2009-10-06 09:32 | 作者: admin | 查看: 4次水准仪操作步骤方法详解图解 步骤图解 1、安放三角架:调节三脚架腿至适当 高度，尽量保持三脚架顶面水平。如 果地面松软，应将架腿踩入土中。 2、连接螺旋:旋紧连接螺旋， 将水准仪和三脚架连接在一 起。 3、脚螺旋:调节脚螺旋，使圆水准气泡居中。 4、制动螺旋:旋紧制动螺旋，望远镜被固定。 5、水平微动螺旋:在制动螺旋旋紧后，调节水平微动螺旋，望远镜在水平方向微小转动。 6、目镜调焦螺旋:调节目镜调焦螺旋，使十字丝清晰成像。 内部的四个数码管共用a~dp这8根数据线，为人们的使用提供了方便，因为里面有四个数码管，所以它有四个公共端，加上a~dp，共有12个引脚，下面便是一个共阴的四位数码管的内部结构图（共阳的与之相反）。引脚排列依然是从左下角的那个脚（1脚）开始，以逆时针方向依次为1~12脚，下图中的数字与之一一对应。 数码管使用条件： a、段及小数点上加限流电阻 b、使用电压：段：根据发光颜色决定；小数点：根据发光颜色决定 c、使用电流：静态：总电流 80mA（每段 10mA）；动态：平均电流 4-5mA 峰值电流 100mA 上面这个只是七段数码管引脚图，其中共阳极数码管引脚图和共阴极的是一样的，4位数码管引脚图请在本站搜索我也提供了数码管使用注意事项说明： （１）数码管表面不要用手触摸，不要用手去弄引角； （２）焊接温度：２６０度；焊接时间：５Ｓ （３）表面有保护膜的产品,可以在使用前撕下来。 数码管测试方法与数字显示译码表 ARK SM410501K SM420501K 数码管引脚图判断 数码管识别 ARK SM410501K 共阳极数码管 ARK SM420501K 共阴极数码管 到百度搜索下，这两种数码管只有销售商，并无引脚图。 对于判断引脚，对于老手来说，很简单，可是对于新手来讲，这是件很难的事情，因为共阴、 共阳表示的含义可能还不太懂 ZG工作室只是将该数码管的引脚图给出，并让大家一起分享。 注：SM410501K 和SM420501K 的引脚排列是一模一样的。 这张图很明确给出该数码管的引脚排列。 数字一面朝向自己，小数点在下。左下方第一个引脚为1、右下方第二个引脚为5，右上方第一个引脚为6。见图所示。 其中PROTEL图中K 表示共阴、A表示共阳。 能显示字符的LED数码管(三) 常用LED数码管的引脚排列图和内部电路图 CPS05011AR(1位共阴/红色 0.5英寸)、SM420501K(红色 0.5英寸)、 SM620501(蓝色0.5英寸)、SM820501(绿色0.5英寸) 小学科学教师转岗培训教学论文 科学课中学生问题意识的培养 内容提要：小学科学中含有丰富的问题因素，是培养学生问题意识的极好阵地。我们应加强对学生问题意识的培养，让他们敢问，多问，善于发问。 关键词：科学课培养问题意识 记得一位著名教育家说过：“不会提问的学生，不是一个好学生。”现代教育的学生观要求“学生能独立思考，有提出问题的能力。”在建构主义的课程观中也强调，用情节真实复杂的故事呈现问题，营造问题解决的环境，以帮助学生在解决问题的过程中活化知识，让事实性知识成为解决问题的工具。因此，我觉得学生问题意识的培养是十分重要而且是十分必要的。它既能促进学生的思维发展，又是促使学生学会学习的重要途径。我们应加强对学生问题意识的培养，让他们敢问，多问，才能善于发问。 一、“敢问”意识的激起 教育可以成为创新的摇篮，也可以成为创新的坟墓。那种不民主的、压抑的教学气氛是窒息创新火花的主要因素。 在课堂教学中要让学生积极主动地参与教学行为，敢于质疑，敢于释疑，就要让学生冲破思想牢笼，做到不唯书是从，不唯师长是从。心理学研究和实践证明，自由、宽松、安全的气氛可以使人的智慧得到充分的发挥。 1、创设师生民主平等的环境 有这么一个案例：在上《奇妙的指纹》时，一位教师利用影片《警察的证据》成功地引出了课题《奇妙的指纹》，也充分调动了学生的兴趣，顺理成章地提出了问题“我们今天就来研究奇妙的指纹，大家都先看看自己的指纹是怎么样的？学生在观察完后争先恐后地回答。“我的指纹是一条条的”、“我的是一圈圈的”……突然有一个学生说到“老师，我能把指纹印到纸上……”话还没有说完，教师马上问道：“你在回答哪个问题？”这学生被震住了，倒也“识趣”，自己“乖乖”地坐了下去就不再言语了。最终，到下课结束，他都再也没有站起来回答过一次问题。 上面案例中的学生是的如此可怜，他的眼中教师又是多么“威严”。教师应该牢固树立“言者无罪”的意识。学生答错了允许重答；答得不完整的允许补充；没想好的地方允许再想；不明白的地方允许发问；有不同意见的允许争论；教师自己要是有错允许学生向教师提出意见；对一些性格内向、不敢当众提问的学生，教师则可到他们的身边去征求问 §3.2 精密光学经纬仪的构造及使用方法 控制测量中，需用经纬仪进行大量的水平角和垂直角观测。使用经纬仪进行角度观测，最重要的环节是：仪器整平、照准和读数。我们围绕这三个环节，对光学经纬仪的构造和使用方法作如下介绍。 3.2.1 水准器 由前节可知，测角时必须使经纬仪的垂 直轴与测站铅垂线一致。这样，在仪器结 构正确的条件下，才能正确测定所需的角 度。要满足这一要求，必须借助于安装在 仪器照准部上的水准器，即照准部水准器。 照准部水准器一般采用管状水准器。管水 准器是用质量较好的玻璃管制成，将玻璃 管的内壁打磨成光滑的曲面，管内注入冰 点低，流动性强，附着力较小的液体，并 留有空隙形成气泡，将管两端封闭，就成 为带有气泡的水准器，如图3-3所示。 1. 水准轴与水准器轴 为了便于观察水准器的倾斜量，在水准管的外壁上刻有若干个分划，分划间隔一般为2mm ，其中间点称为零点。 水准器安置在一个金属框架内，并安装在经纬仪照准部支架上，所以把这种管状水准器称为照准部水准器。照准部水准器框架的一端有水准器校正螺旋，通过校正螺旋，使照准部水准器的水准器轴与仪器垂直轴正交。 所谓水准器轴，就是过水准器零点O ，水准管内壁圆弧的切线，如图3-3所示。另外，由于水准管内的液体比空气重，当液体静止时，管内气泡永远居于管内最高位置，如图3-3中的'O 位置。显然，过'O 作圆弧的切线，此切线总是水平的，我们称此切线为水准轴由此可知，使其水准轴与水准器轴相重合，即气泡最高点'O 与水准器分划中心O 重合，这时经纬仪的垂直轴与测站铅垂线重合，这个过程称为整置仪器水平。 2. 水准器格值 我们知道，当水准器倾斜时，水准 管内的气泡便会随之移动。不同的水准 器，虽然倾斜的角度完全相同，各自的 气泡移动量不会完全相同。这是因为不 同的水准器，它们的灵敏度不同。灵敏 度以水准器格值表示。所谓水准器格值， 就是当水准气泡移动一格时，水准器轴 所变动的角度，也就是水准管上的一格 所对应的圆心角。 如前所述，水准管的内壁是一圆弧，圆弧的曲率半径愈大，水准管上一格所对应的圆图3-3 水准轴与水准器轴 由于很多多都需要这个数码管引脚图，于是今天专门用qq截了图，请大家记好引角的顺序 《七段数码管引脚图》 数码管使用条件： a、段及小数点上加限流电阻 b、使用电压：段：根据发光颜色决定；小数点：根据发光颜色决定 c、使用电流：静态：总电流 80mA（每段 10mA）；动态：平均电流 4-5mA 峰值电流 100mA 上面这个只是七段数码管引脚图，其中共阳极数码管引脚图和共阴极的是一样的，4位数码管引脚图请在本站搜索我也提供了数码管使用注意事项说明： （１）数码管表面不要用手触摸，不要用手去弄引角； （２）焊接温度：２６０度；焊接时间：５Ｓ （３）表面有保护膜的产品,可以在使用前撕下来。 数码管测试方法与数字显示译码表 图 三、测试：同测试普通半导体二极管一样。注意!万用表应放在R×10K档，因为R×1K档测不出数码管的正反向电阻值。对于共阴极的数码管，红表笔接数码管的“-”，黑表笔分别接其他各脚。测共阳极的数码管时，黑表笔接数码管的vDD，红表笔接其他各脚。另一种测试法，用两节一号电池串联，对于共阴极的数码管，电池的负极接数码管的“-”，电池的正极分别接其他各脚。对于共阳极的数码管，电池的正极接数码管的VDD，电池的负极分别接其他各脚，看各段是否点亮。对于不明型号不知管脚排列的数码管，用第一种方法找到共用点，用第二种方法测试出各笔段a-g、Dp、H等。 uchar bit_secl=0x01; for(n=0;n<8;n++) //显示数字 {P0=bit_secl; P2=0x03; delay_ms(1500); } return; } void display4(void) {uchar n; uchar bit_secl=0x01; for(n=0;n<8;n++) //显示数字{P0=bit_secl; P2=0x04; bit_secl=bit_secl<<1; delay_ms(1500); } return; } void display5(void) {uchar n; uchar bit_secl=0x01; for(n=0;n<8;n++) //显示数字{P0=bit_secl; P2=0x05; bit_secl=bit_secl<<1; delay_ms(1500); } return; } void display6(void) {uchar n; uchar bit_secl=0x01; for(n=0;n<8;n++) //显示数字{P0=bit_secl; P2=0x06; bit_secl=bit_secl<<1; delay_ms(1500); } return; } void display7(void) {uchar n; uchar bit_secl=0x01; for(n=0;n<8;n++) //显示数字{P0=bit_secl; P2=0x07; It + will be + 时间段 + before等表示“在……之后……才”的句型总结 一、用于句型“It + will be + 时间段 + before...”句型中，表示“要过多久才…”，也可用于“It + may be + 时间段 + before...”，表示“也许要过多久才……”。Before 后的句子中用一般现在时态。 其否定形式“It will/would not be +时间段+ before…”表示“不久就……，过不了多久就……”。 【典型考例】 （1）The field research will take Joan and Paul about five months; it will be a long time _____ we meet them again.（2007安徽卷） A. after B. before C. since D. when （2）—How long do you think it will be ______China sends a manned spaceship to the moon? （2006福建卷） —Perhaps two or three years. A. when B. until C. that D. before （3）It ________ long before we _______ the result of the experiment.( 上海春招2002) A. will not be...will know B. is...will know C. will not be...know D. is...know (4) Scientists say it may be five or six years_________ it is possible to test this medicine on human patients. （2004福建） A. since B. after C. before D. when 解析：答案为BDCC。考题 （1）(2)before 用于肯定的“It + will be + 时间段 + before...”句型中，表示“要过多久…才…”。 （3）before在本题中用于否定句,意为“过不了多久就会……”, 状语从句要用一般现在时代替一般将来时，可知C项为正确答案,句意是:要不了多久我们就会知道试验的结果了。 （4）宾语从句中含有句型“It + may be + 时间段 + before...”，表示“也许要过多久才……”，故选择答案C。 二、用于句型“it was +时间段+ before …”表示“过了（多长时间）才……”。其否定形式“ it was not +时间段+ before …”意为“不久就……”, “没过（多长时间）就……”。 【典型考例】 It was some time ___________we realized the truth. （2005山东） A. when B. until C. since D. before 解析：答案为D。before用于句型“it was +时间段+ before …”表示“过了（多长时间）才……”。该题题意是“过了一段时间我们才意识到事情的真相”。故正确答案为C项。 中文名称：电子经纬仪使用方法，以及如何放线经纬仪英文名称：theodolite;transit 定义1：测量水平和竖直角度的测绘仪器。应用学科：测绘学（一级学科）；测绘仪器（二级学科）定义2：测量水平和垂直角度和方位的仪器。应用学科：机械工程（一级学科）；光学仪器（二级学科）；大地测量仪器-经纬仪（三级学科）定义3：测量水平角、垂直角以及为视距尺配合测量距离的仪器。应用学科：水利科技（一级学科）；水利勘测、工程地质（二级学科）；水利工程测量（三级学科）以上内容由全国科学技术名词审定委员会审定公布 求助编辑百科名片 经纬仪，测量水平角和竖直角的仪器。是根据测角原理设计的。目前最常用的是光学经纬仪。 目录 构造 分类 用途和工作原理 自制方法 编辑本段构造 经纬仪结构机器部件一、经纬仪的结构（主要常用部件）：经纬仪 1望远镜制动螺旋2 望远镜3 望远镜微动螺旋4 水平制动5 水平微动螺旋6 脚螺旋9 光学瞄准器10物镜调焦11目镜调焦12 度盘读数显微镜调焦 13 竖盘指标管水准器微动螺旋14 光学对中器15 基座圆水准器16 仪器基 座17 竖直度盘18 垂直度盘照明镜19 照准部管水准器20水平度盘位置变换手轮望远镜与竖盘固连，安装在仪器的支架上，这一部分称为仪器的照准部，属于仪器的上部。望远镜连同竖盘可绕横轴在垂直面内转动，望远镜的视准轴应与横轴正交，横轴应通过水盘的刻画中心。照准部的数轴（照准部旋转轴）插入仪器基座的轴套内，照准部可以作水平转动。 编辑本段分类 经纬仪根据度盘刻度和读数方式的不同，分为游标经纬仪，光学经纬仪和电子经纬仪。目前我国主要使用光学经纬仪和电子经纬仪，游标经纬仪早已淘汰。电子经纬仪光学经纬仪光学经纬仪电子经纬仪光学经纬的水 平度盘和竖直度盘用玻璃制成，在度盘平面的周诶边缘刻有等间隔的分经纬仪划线，两相邻分划线间距所对的圆心角称为度盘的格值，又称度盘的最小分格值。一般以格值的大小确定精度，分为：DJ6 度盘格值为1° DJ2 度盘格值为20′ DJ1 （T3）度盘格值为4′ 按精度从高精度到低精度分： DJ07,DJ1,DJ2,DJ6,DJ30等（D,J分别为大地和经纬仪的首字母）经纬仪是测量任务中用于测量角度的精密测量仪器，可以用于测量角度、工程放样以及粗略的距离测取。整套仪器由仪器、脚架部两部分组成。应用举列(已知A、B两点的坐标，求取C点坐标)：是在已知坐标的A、B两点中一点架设仪器（以仪器架设在A点为列），完成安置对中的基础操作以后对准另一个已知点（B点），然后根据自己的需要配置一个读数1并记录，然后照准C点（未知点）再次读取读数2。读数2与读书1的差值既为角BAC的角度值，再精确量取AC、BC的距离，就可以用数学方法计算出C点的精确坐标。一些建设项目的 before用法知多少？ 在高考中，状语从句是每年高考单项填空部分必考的题目之一，考查的重点是考生容易混淆并且近似的连词在逻辑行文和语篇结构中的使用。before作连词的用法一直是高考的重点，也是学生感觉掌握起来比较头疼的地方。下面选取近几年各省市的高考试题进行归纳分析，使考生通过典型实例，把握高考对before所引导的句型的命题规律，帮助同学们更好地解答此类题目。 1. before作为连词时的基本意义是“在……之前”，用于表示时间或顺序。 You can’t borrow books from the school library ______ you get your student card. (2009上海，32) A. before B. if C. while D. as 【解析】选A。考查连词，该句的意思是：在你得到你的学生卡之前你不能从学校图书馆借书。before表示先后顺序。 2. 表示“过了多久才……”，说明主句的持续时间比较长而从句的动作缓缓来迟。 (1) The American Civil War lasted four years _______ the North won in the end. (2005广东，30) A. after B. before C. when D. then 【解析】选B。本题考查连词before表示“在多久之后才……”的用法，根据本句含义“美国南北战争持续了四年，北方才最终取得胜利”，可知本题应选B。 (2) Several weeks had gone by I realized the painting was missing. (2004宁夏，39) A. as B. before C. since D. when 【解析】选B。before表示“过多久才……”。句意：几个星期已经过去了，我才意识到油画丢了。内含的意思是油画丢了好几个星期了，我才意识到。 3. 表示从句动作还没来得及发生或完成，主句动作就已经发生或完成了，意为“尚未……就”，“没来得及……就”，常用于before sb. can/ could…。 —Why didn’t you tell him about the meeting? ( 2006四川，35) — He rushed out of the room _________ I could say a word. A. before B. until C. when D. after 【解析】选A。本题考查连词before表示“还没来得及……就……”的用法。句意为：我还没来得及说一句话，他就冲出了房间。 4. 表示“以免，以防，趁……还没有……”，强调动作的必要性，以避免或防止从句动作的发生。 He made a mistake, but then he corrected the situation _____ it got worse.（2003北京） A. until B. when C. before D. as 【解析】选C。由made a mistake和转折词but可知本题句意是“他犯了一个错误，但在事情进一步恶化之前他改变了形势。”故答案正确答案为C项。 小学科学电教论文《科学课中的电化教学手段》 摘要：电化教育所追求的，不是教育的机械化，而是教育的最优化。在小学科学课教学中，根据学生、教学内容的实际情况，正确在运用好实物投影、幻灯、电视、收录机、摄像机、数码相机、多媒体、网络等电化教学手段，来优化教学环境，拓宽教师教和学生学的思路，从而提高教学效果。 关键词：素质教育；电化教学手段；教学环境；教学环境 小学《科学课》是一门科学启蒙性学科。它侧重于让学生在探索中学习，在研究学习中保持或发展儿童与生俱来的探究兴趣；教材侧重于提供大量的科学信息，图文并茂，有许多实物彩色图片、形象的模型图与优美的文字相结合，从而将科学知识生动直观地展示出来。此外，一堂40分钟的《科学课》是有多个实验活动—问题—实验活动组成的，如在教学中充分地利用好幻灯、投影、录像、多媒体等各种电化教学手段，使抽象的概念具体化，枯燥的知识趣味化，优化了教学环境，拓宽了教师教和学生学的思路，从而提高教学效果。 电化教育，就是在现代教育思想的指导下，主要采用现代教育媒体和媒体教学法，进行教育活动，以实现教育的过程的最优化。国家教委电化教育办公室在《全国中小学现代教育技术实验学校工作实施意见》中对现代教育技术实验的内容给了科学的、全面的界定：“在实验中，要巩固和发展以投影和音像技术为基础的课堂多媒体优化组合教学；充分利用现有的广播电视教育节目资源；积极发展计算机教育及辅助教学，推动电脑多媒体技术在教学中的作用；实验研究交互网络在学校教学中的应用，以及进行有关虚拟现实的研究实验工作”。在这个精神中，我们知道投影、幻灯、录音、录像、广播还有计算机、多媒体、网络等都是现代教育技术手段之一。下面，笔者就这些电化教学手段如何在《科学课》教学中运用谈谈自己的一些看法。 一、实物投影、幻灯 在《科学课》教学中，实物投影、幻灯是应用最简单、最实用、最广泛的一种电化教学手段。 1、将模糊变清晰 如在教学浙教版三下《科学课》中第六单元《物体的热涨冷缩》一课，关于空气的热涨冷缩实验：烧瓶口装上一个插着玻璃管的塞子，在管里滴一滴带颜色的水，外面用线做个标记，然后用热毛巾捂住玻璃瓶，瓶内空气逐渐变热，管里的小水滴就会向管口移动，放开热毛巾，瓶里空气变冷，管里的小水滴向相反方向移动。这个实验可见度小，且移动距离短，弄不好小水滴会窜出玻璃管外。可以把玻璃弯成“W”或“V”形，这样实际距离长了，就避免了小水滴溢出，将它平放在投影器的工作面上，再照上法实验，实物投影或幻灯放大的图像十分清晰，小水滴在玻璃管里的移动，学生一目了然。 2、将枯燥变生动 实验可使学生动起手来，激发学生爱自然、学自然的兴趣。但在教学中，实验也会受到仪器、演示可见度等诸多方面因素的限制，讲解时也会变枯燥、乏味。如浙教版四下教材《电流》一课，要让学生学会组装简单电路，但没有演示板，如老师在讲台上边讲边组装，学生看不到老师的操作，或站起来争着看从而影响纪律，或只能凭想象。特别是讲解并联时，学生更是莫名其妙。不如直接把干电池、开关、小灯座、导线等放在幻灯机的工作面上进行操作示范，把其黑影打在银幕上，使学生直接看到了老师做的情况，简单明了。当然在实物投影上操作则效果更佳。 又如浙教版四下教材《磁铁》一课的教学中，教师要示范磁铁性质之一：同极相斥异极相吸，示范时如把两辆小车放在实物投影上进行演示，老师就是嘴里什么都不说，学生通过观看演示，也能知道磁铁的性质了；再如《鱼》一课，讲解鱼体构造及鱼鳍作用时，也可把鱼缸放到幻灯机工作面上，（注意当心把水溅出来）鱼影一下子投影到银幕上，生龙活虎。剪去鱼鳍的鱼游动情况也直接显现 J2-2光学经纬仪实验操作方法 目录 ○1仪器用途 ○2仪器主要技术参数 ○3仪器结构 ○4仪器使用方法 ○5仪器的调整 ○6仪器的维护 ○7可供附件 仪器用途 J2-2经纬仪是一种精密光学测角仪器，此种仪器在国防建设、大地测量中占很重要的地位。可以广泛应用于国家和城市的三、四等三角测量。同时亦可用于铁路、公路、桥梁、水利、矿山以及大型企业的建筑，大型机器的安装和计量等工作。 仪器主要技术参数 一测回水平方向标准偏差±2″ 一测回垂直角测量标准偏差±6″ 望远镜正象 物镜通光口径φ40mm 放大倍率30 视场（1000m处）24m 最短视距离2m 乘常数100 加常数不清0 度盘和测微器具 水平度盘直径90mm 垂直度盘直径70mm 全园刻度值勤360 度盘最小格值勤20′ 测微器最小格值勤1′ 自动归零补偿器 补偿精度过±0.3″ 补偿范围±3′ 读数显微镜 水平系统放大率48 x 垂直系统放大率62 x 水准器 长水准器20″/2mm 圆水准器具8′/2mm 光学对点器 视场角7°30′ 调焦范围0.3～6m 仪器重量 净重6kg 毛重9kg 一、望远镜 望远镜成正像、采用了双胶合一分离的物镜和对称式目镜。此种结构的望远镜，其成象质量以及在亮度和清晰方面均较好。 望远镜镜筒的上、下二面均装光学粗瞄准器，以便于在正倒镜观测时均可用其进行粗瞄。筒内装有反光板，以便于夜间观测时用其照明分划板。 望远镜分划板上附有保护玻璃片，以便于当分划板有污点时，可以清除，而不致于有十字丝脱色和其他损伤现象。 逆时针方向转动卡环（7），可根据用户所需，置换不同倍率的目镜。 二、竖轴系 本仪器采用的是半运动轴系。此种轴系的幌动角比标准园式园柱小（在同样参数条件下），轴系中的钢珠和轴套锥面具有自动归心作用，所以间隙的大小对轴的幌动影响不大。 半运动式轴系的优点的摩擦力矩小，耐磨性好，当轴套锥面磨损后，在更换直径不同的钢珠后仍可继续使用。同时温度对其影响也较小。 三、读数系统 本仪器采用了对径符合数字读数方式。因此，我们选用了透射工式度盘和1：1透镜式转象系统。并用移动光楔测微器作为测微系统。 移动光楔测微器的原理是光线通过光楔时，光线会发生转角不变。因此通过光楔移动后，由于光线的偏转点改变了而偏转角不变。因此，通过光楔的光线就产生了平行位移地动以这实现其测微的目的。 四、竖盘指标自动归零补偿器 本仪器采用了悬摆补偿器，它能消除仪器整平后的乘余误差给竖盘读数带来的影响，其原理是当仪器竖轴有一小倾角时，悬挂平板相应地的反向摆转一角度，使得通过平板的光线产生偏移，以此来消除竖轴倾斜时对竖盘读数的影响。支架上的按钮（图2），是用来检查补偿器是否正常工作的，整平仪器后，揿一下按钮，竖盘刻线（读数窗中）互相摆开，然后缓慢回复到初始位置，则补助偿工作正常。否则应排除故障。 仪器使用方法 本仪器配用三爪式基座。 一、置中 1、垂球对中 将三脚架架于测站点之上，悬挂垂球于三脚架三角基座下面的中心固定螺旋的弦线上，并使之对准站点中心，压脚架之脚尖入土中，使三脚架稳固。 仪器从箱中取出，一手握扶照准部，一手握住三角基座，小心地放于三角架头上，转动中心固定螺旋，将仪器轻轻地固定于脚架上，再转动脚螺旋（16），使园水泡（20）居中，将仪器在三角架上精细地移动，使垂球尖端正确对测站点，然后拧紧中心固定螺旋。 若对仪器上面的高点定中心，可自该点挂一垂球，当仪器整平和望远镜视准轴在水平位置时，使粗瞄准器上的红点对准垂球尖端。 2、光学对点器对中 精确的对则使用光学对点器，操作如下：先旋转对点器（18）目镜，使分划板清晰，再拉伸对点器镜管，使对中标志清晰。 滑动仪器，使测站点居于分划板的小圆圈中央。 将仪器照准部转动180°后检查仪器对中情况，然后拧紧中心固定螺旋。 仪器整平后再精细对中一次。 由于很多多都需要这个数码管引脚图，下边介绍几种常用的二极管数码管引脚 《七段数码管引脚图》 数码管使用条件： a、段及小数点上加限流电阻 b、使用电压：段：根据发光颜色决定；小数点：根据发光颜色决定 c、使用电流：静态：总电流 80mA（每段 10mA）；动态：平均电流 4-5mA 峰值电流 100mA 上面这个只是七段数码管引脚图，其中共阳极数码管引脚图和共阴极的是一样的，4位数码管引脚图请在本站搜索我也提供了数码管使用注意事项说明： （１）数码管表面不要用手触摸，不要用手去弄引角； （２）焊接温度：２６０度；焊接时间：５Ｓ （３）表面有保护膜的产品,可以在使用前撕下来。 数码管测试方法与数字显示译码表 图 三、测试：同测试普通半导体二极管一样。注意!万用表应放在R×10K档，因为R×1K档测不出数码管的正反向电阻值。对于共阴极的数码管，红表笔接数码管的“-”，黑表笔分别接其他各脚。测共阳极的数码管时，黑表笔接数码管的vDD，红表笔接其他各脚。另一种测试法，用两节一号电池串联，对于共阴极的数码管，电池的负极接数码管的“-”，电池的正极分别接其他各脚。对于共阳极的数码管，电池的正极接数码管的VDD，电池的负极分别接其他各脚，看各段是否点亮。对于不明型号不知管脚排列的数码管，用第一种方法找到共用点，用第二种方法测试出各笔段a-g、Dp、H等。 数码管引脚图，一般都是一样的。 数字对应数码管显示控制转换字节 （共阴编码） 显示－－HGFE,DCBA－－编码 0 －－0011,1111－－0x3F; 1 －－0000,0110－－0x06; 2 －－0101,1011－－0x5B; 3 －－0100,1111－－0x4F; 4 －－0110,0110－－0x66; 5 －－0110,1101－－0x6D; 6 －－0111,1101－－0x7D; 7 －－0000,0111－－0x07; 8 －－0111,1111－－0x7F; 9 －－0110,1111－－0x6F; 共阳为编码取反即可， 接线为高低端口对应接法。 备注：第一脚的识别很简单，看管脚的底部，有一个方块型的就是第一脚。或者正面（就是显示那面）超你，左下角第一个为第一脚。 but和than引导定语从句的用法 一、but可被看作关系代词，引导定语从句，在句中作主语，在意义上相当于 who not或that not，即用在否定词或具有否定意义的词后，构成双重否定。 如：①There is no mother but loves her children．没有不爱自己孩子的母亲。 ②There was no one present but knew the story already．在场的人都知道这个故事。 二、than作关系代词时，一般用在形式为比较级的复合句中，其结构为形容词比较级（more）．．．than＋从句，than在从句中作主语，相当于that，代表它前面的先行词。（这时，它兼有连词和代词的性质，也有学者认为这种用法的than是连词，后面省略了主语what。） 如：①The indoor swimming pool seems to be a great deal more luxious than is necessary．室内游泳池过于豪华。 ②He got more money than was wanted．他得到了更多的钱。运用上述知识翻译下列句子： 1．任何人都喜欢被赞扬。（but） 2．我们大家都想去桂林。（but） 3．没有人不同情那些嗷嗷待哺的孩子。（but） 4．我们班上没有一个人不想帮你。（but） 5．无论多么荒凉，多么难以行走的地方，人们也能把它变成战畅（but）6．这件事情比想象的要复杂。（than） 7．这个广告的效果比预想的要好。（than） 8．这个问题看起来容易，实际上很难。（than） 9．他爸妈给他的零用钱总是超过他的需要。（than） 10．因为这项工程非常困难，所以需要投入更多的劳动力。（than） 答案： 1．There is no one but likes to be praised． 2．There is no one of us but wishes to visit Guilin． 3．There is no man but feels pity for those starving children．4．There is no one in our class but wants to help you． 5．There is no country so wild and difficult but will be made a theatre of war． 6．This matter is more complex than is imagined． 7．This advertisement is more affective than is expected． 8．The problem may be more difficult in nature than would appear．9．He got more pocket money from his parents than was demanded． 科学教学论文 ——让学生在快乐中学习《科学》 作者：谢世平小学科学是在自然的基础上更全面，更科学地培养学生发现问题、解决问题、探究科学真谛能力的一门学科。科学学习要以探究为核心探究既是科学学习的目标又是科学学习的方式亲自经历以探究为主的学习活动是学生学习科学的重要途径在教学中我们如何引导学生经历和寻找得出结论的过程并在过程中获取知识的方法体验自主探究的乐趣切实带领孩子们一起去领略科学探究中的乐趣呢？一、“探究”让学生学会合作交流 小学三年级学生是《科学》课初始阶段，对于他们来说是一件极为兴奋的事情，学生对科学教材产生有浓厚的兴趣，有强烈的学习欲望，愿意主动参与到科学探究活动中来。因此，教师首先要培养学生积极动脑，认真思考，勇跃发言及合作交流的习惯，让学生真正参与课堂教学，主动探究新知识形成的过程。针对很多科学探究都是通过实践来总结、验正的。,如:分一分、摆一摆、画一画、测一测等，再通过联系课内所获知识,认真仔细地观察事物、分析现象、思考问题,顺水推舟，让学生动手做够，动口说够，动口问够，动脑想够，动眼看够。所以在这一环节中培养学生动手操作能力显得更为重要。因此，合作交流是现代人应该具备的基本能力，一个知道学习需要合作的孩子往往是个幸运的孩子，他会因此而找到探究的兴趣与共事的伙伴；一个善于合作与交流的孩子往往是能干的孩子，一个乐于合作 与交流的孩子往往是成功的孩子，他会因此而学会科学学习乃至科学探究，并且从中享受到学习科学的乐趣。如我在教学《改变浮和沉》时，为了使一些物体改变浮沉状况更为直观、形象，特意引导学生小组内进行交流和讨论，鼓励每人都要敢于发表自己的意见，并注意倾听它人的看法，敢于失败，敢于竞争。学生在自己已有知识经验的基础上大胆提出了很多种不同方案，然后经充分讨论选出最佳探究观察和想象能手。在合作与交流过程中，教师能主动做好事件的引探，并注意到小组各成员的分工与协同作用，使每一小组的同学人人都有事可干。取得了人人参与、人人有收获的喜人效果。 二、“电化教学”让学生更主动积极参与 小学《科学课》是一门科学启蒙性学科。它侧重于让学生在探索中学习，在研究学习中保持或发展儿童与生俱来的探究兴趣；教材侧重于提供大量的科学信息，图文并茂，有许多实物彩色图片、形象的模型图与优美的文字相结合，从而将科学知识生动直观地展示出来。此外，一堂40分钟的《科学课》，是由多个实验活动—问题—实验活动组成的，如在教学中充分地利用好幻灯、投影、录像、多媒体等各种电化教学手段，使抽象的概念具体化，枯燥的知识趣味化，优化了教学环境，拓宽了教师教和学生学的思路，从而提高教学效果。如教《物体的热胀冷缩》时，我设计了一个小课件，开始是小朋友烧开水的生活情景动画录像，当放到“盛满水”和“烧时茶壶溢水“等几个情节时，在“茶壶溢水”的画面的小朋友头脑上出现一个个的“？”，这样引导学生发现、提出问题，通过研讨、实验，使学生先 水 准 测 量 基本知识 1.水准测量原理 工程上常用的高程测量方法有几何水准测量、三角高程测量、GPS 测高及在特定对象和条件下采用的物理高程测量，其中几何水准测量是目前高程测量中精度最高、应用最普遍的测量方法。 如图2-1所示，设在地面A 、B 两点上竖立标尺（水准尺），在A 、B 两点之间安置水准仪，利用水准仪提供一条水平视线，分别截取A 、B 两点标尺上读数a 、b ，显然 A B H a H b +=+ A 、 B 两点的高差h AB 可写为 AB h a b =- A 点高程H A 已知， 求出 B 点高程 B A AB H H h =+ 我们规定A 点水准尺读数a 为后视读数，B 点水准尺读数b 为前视读数。 图 2-1 如果A 、B 两地距离较远时，可以用连续水准测量的方法。中间可设置转点TP （临时高程传递点，须放置尺垫），如图2-2所示 11h a =， 333h a b =-，……， n n n h a b =-。 123......AB n i h h h h h h =+++=∑ 于是，可以求得A 、B 之间的高程差 AB i i h a b =-∑∑ B 点高程 B A AB H H h =+. 图 2-2 2.水准仪介绍： 水准仪是提供水平视线的仪器，按精度分，水准仪通常有DS 05、DS 1、DS 3等几种。其中“D ”和“S ”分别为“”和“水准仪”首字汉语拼音的首字母，而下标是仪器的精度指标，即每千米测量中的偶然误差（以mm 为单位）。目前常用的水准仪从构造上可分为两大类：利用水准管来获得水平视线的“微倾式水准仪”和利用补偿器来获得水平视线的“自动安平水准仪”。此外，还有一种新型的水准仪——“电子水准仪”，它配合条形码标尺，利用数字化图像处理的方法，可自动显示高程和距离，使水准测量实现了自动化。 水准仪主要由望远镜、水准器、基座三部分组成。 （1） DS 3微倾式水准仪 1.仪器介绍经纬仪的使用方法
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