Printed in Great Britain. # 2006 TEMPUS Publications.

Tribology International Vol.31,No.10,pp.597–599,1998©1999Elsevier Science Ltd.All rights reservedPrinted in Great Britain 0301–679X/98/$19.00ϩ0.00PII:S0301–679X(98)00080–2Tribology science,technology and education in ArmeniaA.K.Pogosian*State of the art in the field of tribology in Armenia is discussed.The main problem in research,education and technology transfer to industry are considered.©1999Elsevier Science Ltd.All rights reserved.Keywords :tribology,Armenia,technology transfer,industryAs far back as the 1950s in Armenia,investigations in the field of providing wear resistance and durability of cutting tools were set up.Considerable impulse of work development in the field of tribology was the necessity to create new wear resistant high-friction and low-friction materials,friction nodes and types of lubricants for machines for various purposes.Self-lubricating materials on polymer and cermet bases were made.Tribological problems are actual in machine-tool industry,agricultural machine building industry,automotive industry,instrument engineering,electrical machine industry,composite tribomaterial science,material cutting etc.In the direction of creating optimal friction nodes,forecasting their wear resistance and introduction into production a lot of work is carried out,first of all,at the Yerevan Polytechnic Institute (now State Engineering University of Armenia).One of the most prosperous directions of tribological studies is the calculation and design of machine parts and friction nodes on the basis of composite polymer materials instead of conventional metal parts.Scientific principles of creating of new polymer-based self-lubricating composites,calculating methods on the selection of materials and estimation of wear resistance of friction nodes,as well as physical simulation of friction and wear processes on the small-sized labora-tory samples and forecasting of serviceability of friction nodes according to the results of accelerated tests,are worked out 1,2.The set of worked out methods of calculation and many years of study in these fields,as well as the results of their application to the study of friction interactions of polymer-based self-lubricating composite materials (PSCM),present themselves as a prosperous scientific direction in the solution of theState Engineering University of Armenia,105Terian Street,Yerevan 375009,Armenia*Tel:ϩ3742-589884;fax:ϩ3742-151068;e-mail:pogosian@seua.amReceived 12February 1998;accepted 14March 1998Tribology International Volume 31Number 101998597problems of creating PSCM and new constructions of friction nodes on their basis in the Republic of Armen-ia.The basic principles of selection of the fillers and polymer matrices for PSCM on the bases of general positive interactions and limiting factors of the fillers properties,as well as optimal combinations of compo-nents of filled systems (compositions),proceeding from the purpose of machine parts and friction nodes pro-duced by PSCM are worked out 1.In the basis of composite design,the principle of a self-lubricating mechanism by using the properties of friction transfer (FT)film is given posite polymer materials are able to form on the friction surfaces the film of FT of some nature,having the properties of lubricant film.Analysis of the conditions of friction film formation and evalution of its influence on the friction interaction processes,make it possible to consider that (together with the abrasion and corrosion),the transfer of material modifies the friction surface of counterbody and,consequently,various types of wear may take place with the intensivity that is characteristic for them.A general phenomenon was discovered:in spite of the fact that the friction surface temperature reaches values that are higher than the polymer melting point,inten-sive wear begins only after destruction (failure)of the FT film 4.At the present stage of Tribology development there is no fundamental physical explaination for the FT process.None of the current theories can adequately take account of this phenomenon,which is explained by difficulties of observation and description of mech-ano-chemical and physico-mechanical phenomena tak-ing place on the real area of contact.An adhesion-energetic model 5has been used to evaluate the transfer film thickness and its effectiveness.In accordance with this concept,in the spots of discrete contact of the rubbing bodies,there develop heat sources because of transformation of the mechanical energy.As a result,the contact surface of the polymer softens under theTribology science,technology and education in Armenia:A.K.Pogosianaction of friction heating and so-called scuffing bridges form,after which mechanical fracture arises in the places of least resistance,i.e.,in the section of the weaker polymer material,and transfer to the metal surface takes place.Analytic relations have been derived for determination of the FT film thickness,and the conditions of its effectiveness have been deter-mined.Such calculations significantly extend the possi-bilities of the analytic method for evaluating transfer film lubricity in the friction of polymer-based materials.The most perspective scientific direction for Armenia is the creation of PSCM with local mineral materials as a filler 6.The bulk supply of numerous mineral materials available in the Republic (tufa,basalt,traver-tine,bentonite et al.),may and must be more effectively used along with the other fillers (graphite,fluoroplastic,coke,molybdenum disulfide et al.).Essential results are obtained in the development of wasteless techno-logies for machine parts production,using non-expens-ive raw materials including fillers with special chemical or heat treating.Eventually,a new class of self-lubri-cated materials for bearings and tooth gears has been developed,called SIPAN.These are characterized by a high wear resistivity (wear intensity 2.2ϫ10−9),a constant and low friction coefficient (0.09–0.12)and a high-precision technology of machine parts production (9–10quality accuracy).The tribological and physico-mechanical comparative tests reveal that the developed materials surpass the widely used materials of the same type (SAM-6,SFD-DM,SFD-BS)in their wear resistivity,load-carrying capacity,accuracy of machine parts production tech-nology and strength.The main exploitation conditions of SIPAN composite materials are as follows:sliding velocity 2.0mps,specific loading 6.0MPa and work temperature 90°C (in the condition of nonlubricated friction).Based on the results of a study of the friction transfer phenomena,the mechanisms of self-lubrication and wear in the conditions of ‘dry’friction are revealed,and proposals are elaborated for the evalu-ation of metalopolymer friction pairs durability (wear-resistance).The optimization of the composition of developed materials via the method of full-factor experiments is puter programs are written for the expert computation of PSCM-made machine parts (e.g.,sliding bearings)in various exploitation modes.Technological packages are developed for the production of SIPAN composite materials and machine parts pressing castings as well.One of the most urgent problems of Armenian econ-omy is the creation and utilization of lubricants based on local materials and industrial waste,as well as restoration of used oils,taking into account the market demands for wasteless technologies,environmental pro-tection and urgent needs of the Republic.New composite lubricants have been developed based on wastes of the oleic acid industry and I-40A type industrial oil.The mechanisms of their impact upon the steel surfaces of friction nodes have been revealed.It has been proved that the newly developed composite lubricants in their physicochemical properties are not worse than those of I-40A type industrial oil,while their tribological characteristics are more advantageous:598Tribology International Volume 31Number 101998the friction coefficient and the wear index are lower for 60p.c.and 10p.c.correspondingly,the grip wear loading is higher for 47p.c.This gives an opportunity to make use of these newly developed composite lubri-cants in the heavy-loaded nodes with boundary lubri-cated friction,replacing the I-40A lubricants that is mainly used at present.In order to increase the efficiency of exploitation of the lubricants,new addi-tives with high antiwear and antiscoring properties have been proposed.The antiwear and antiscoring action mechanisms are revealed for various classes of hal-ogen-,sulphur-and phosphorus-containing additives (monocyclic ketones,bi-and tri-cyclic esters,halogen-and sulphur-containing olefins and esters of phosphoric acid).For all the classes of these composites a general regularity is revealed:the optimal choice of the addition leads to both high antiwear and antigear efficiency.As a result of a large number of experiments,two characteristics of the wear and seizure processes are introduced 7.One characteristic,the wear intensity coef-ficient,is represented as a factor of the exponent in the empirical dependence of wear rate on the length of the friction path.The second value is the relative load of seizure,i.e.,the attitude of the seizure loading to the load at which the given test is carried out,and at which the wear rate is measured.These two values are connected in a generalized dependence,invariant to the load,sliding velocity,system rigidity and lubri-cation medium properties.These observations are of essential interest for the theory and practice of tribology,since a unique corre-lation between antiwear and antisoring properties of lubricants has been demonstrated,opening up the possi-bility of predicting the antiscoring properties of lubri-cants based on the results of comparatively simple wear tests.In recent years in Armenia,significant development has obtained the theory of providing motion stability at friction (stick-slip process).Complex methods of reducing friction oscillations in the guide-ways of machine tools,robots and other machines are worked out 8.For the first time,the task of motion stability conformable to the sliding guide-ways is solved,in general view on the basis of space model of oscillation process of friction nodes of slider-guider type,con-firmably to the machine tools 9.Calculation algorithms of friction oscillations on the computer,permitting an evaluation of the influence of geometrical,physico-mechanical,constructive and tribological parameters on the friction auto-ossillation,have been plex methods of increasing of vibrostability of moving by the guides slip nodes,subject to factors of external action is suggested.The obtained data could be used both for the estimation of accuracy of existing,and for the optimization of,friction nodes of newly designed machines and machine tools.In the direction of providing motion stability at friction,wear resistant composite materials NASPAN for the application on the surface of the guide-ways,promoting a decrease in the scale of vibro-displacements of supports of metal cutting machine tools 3or more times,are created.Based on both model and real tests of car disk brakes,the dynamics of the breaking process,as well as theTribology science,technology and education in Armenia:A.K.Pogosianaction of vibration loading on the wear and friction properties of brake materials (asbo-polymers and asbes-tos-free)are investigated.The problem of creation of the asbestos-free friction (brake)composite materials with mineral fillers of local origin,is of greatest importance and crucial for environmental protection in order to replace the asbes-tos which is harmful for human health.Regretfully at present this is the main (up to 80p.c.)component of the vehicles’brake pads (friction clutches)material in the Republic of Armenia,as well as in the former Soviet Union countries 10.A new class of asbestos-free composite friction materials—BASTENIT—is created along with its varieties.A series of local mineral materials have been investigated as asbestos substitutes,and basalt-and glass-fibers along with tufa powder turned out to be most effective ones.A technology for BASTENIT class composite materials production is developed,aiming to use to the fullest extent,the existing technological process for the present full-scale production of asbo-polymerous materials without any additional investments and equipment.The materials obtained have passed through rational cycles of labora-tory,bench and road tests.The experimental evaluation of tribological characteristics and operational indicators proved their adequacy for main technical requirements:high friction coefficient and provision of stable oper-ational (brake)regimes as well as serviceability of the friction pair,especially at high temperatures (400–600°C).A classification of the materials obtained is carried out in accordance to the operational character-istic properties of the vehicles.Complex methods for high-temperature wear and vibration resistance evaluation and constructions of brake pads are worked out based on investigations of thermal,tribologic and oscillatory processes in brake devices 11,12.The second environmental-protection advantage of BASTENIT from the viewpoint of squeak background decrease,has been revealed by means of the characterization of the squeak (shaking)oscil-lations spectrum.Tribological studies are actual in other fields of Armen-ian machine building.Prosperous are the developments of antifriction composite materials by the methods of powder metallurgy 13,e.g.,on the basis of copper pow-der,doped sulphite and phosphorous.In the study of wear process of cutting instruments and tools in the treatment of various materials (including natural stone,with which the Republic is extremely rich)and alloys,a number of investigations are devoted 14.For the increase of capacity of work on restoring worn parts,Tribology International Volume 31Number 101998599the special design and technical bureau with consider-able economical efficiency is organized.Tribology education in Armenia is mostly carried out at the State Engineering University within the whole scale of the educational system:in BE,ME and PhD programms 15.Obviously the school and new generation of the specialists in the field of tribology in Armenia have already formed.In the development of Tribology in the Republic,a significant role is played by,(organized in 1974)the Armenian Tribology Commit-tee (ATC).More than 20years of professional activities and experience within the field of tribology science,technology and education,whether pure or applied,whole country (Republican)conferences,seminars,competitions,lectures and consultations etc.,and also sufficient fame and authority of the ATC,assure in the ability of the ATC to look after all disciplines comprising tribology in Armenia.The Armenian Tri-bology Committee became a member of the Inter-national Tribology Council (ITC)in 1997.References1.Pogosian,A.K.,Friction and Wear of Filled Polymer Materials .Moscow,1977,139p.2.Pogosian,A.K.,Wear ,1973,26,175–186.3.Briscoe,B.J.,Pogosian,A.K.and Tabor,D.,Wear ,1974,27,19–34.4.Pogosian,A.K.,Tribology in the USA and the Former Soviet Union:Studies and Applications .Allerton Press Inc.,New York,1994.pp.271–283.5.Pogosian,A.K.,Friction and Wear ,1984,5(2),204–211.6.Pogosian,A.K.,Karapetian,A.N.and Oganesian,K.V.,Wear of Materials ,1989,2,521–528.7.Pogosian,A.K.,Arustamian,Y.S.and Gevorkian,G.R.,Wear ,1993,167,85–86.8.Sysoev,P.V.,Bliznetc,M.M.and Pogosian,A.K.,Antifriction Epoxside Composites in Machine Tool Building .Minsk,1990,231p.9.Pogosian,A.K.,Demirchian,A.Z.and Gagian,G.S.,EURO-TRIB .Helsinki,1989.10.Pogosian,A.K.,Sysoev,P.V.,Meliksetian,N.G.and Lamb-arian,N.A.,Polymer-Based Friction Composites .Minsk,1992,218p.11.Pogosian,A.K.and Lambarian,N.A.,J.of Lubric.Tech ,1979,101(4),481–485.12.Pogosian,A.K.and Makarian,V.K.,Friction and Wear ,1993,14(3),539–543.13.Manoukian,N.V.(ed),Composite Materials and Their Treat-ment .Yerevan,1985.14.Kasian,M.V.(ed),The Quality of Machine Parts Surface .Yerevan,1985.15.Pogosian,A.K.,Principles of Tribology (Textbook).Yerevan–Athens,1994–95,296pp.。

Correlation between Microstructure andConductance in NTC Thermistors Produced from Oxide PowdersG.D.C.Csete de Gyo rgyfalva,*A.N.Nolte and I.M.ReaneyDepartment of Engineering Materials,Sir Robert Had®eld Building,University of She eld,She eld,S13JD,UKAbstractA detailed study of spinel-structured Ni 1Àx Mn 2+x O 4formed by a mixed oxide route has shown that when x %0a high proportion of NiO is residual in the sin-tered ceramic.Wickham (Wickham,D.G.,Solid phase equilibria in the system NiO±Mn 2O 3±O 2.J.Inorg.Chem.,1964,26,1369±1377)demonstrated that the spinel phase decomposes in air above 900 C.Sintering in this system is usually per-formed around 1200 C.Decomposition of the spi-nel phase is therefore inevitable.The e ect of decomposition on the microstructure and electrical properties of Ni 1Àx Mn 2+x O 4based ceramics is discussed.#1999Elsevier Science Limited.All rights reservedKeywords :microstructure,electrical conductivity,spinels,thermistors.1IntroductionNegative temperature coe cient (NTC)thermistors are found in an ever increasing number of electrical and electronic products.Ni 1Àx Mn 2+x O 4,where x denotes the deviation from the stoichiometric 1:1NiO:Mn 2O 3ratio,o ers a range of properties that are suitable for most temperature sensing applications.When x =0,(nickel manganite,NiMn 2O 4),the solid solution has an inverse cubic spinel structure,based on a 2Â2Â2array of face centred cubic (fcc)oxygen subunits.When x =1,Mn 3O 4is present which is a tetragonally distorted spinel.The properties routinely used to characterise NTC thermistors are resistance,R 1and R 2,at 25 C (T 1)and 85 (T 2)and a B value (with units of tem-perature in Kelvin)which is a measure of the sensi-tivity of the device over a given temperature range:BT 1T 2T 2ÀT 1ln R 1R 2IThe exact mode of conduction in nickel manga-nite is poorly understood,but several modelsinvoke the small polaron theory.1,2Small polaron conduction is sometimes referred to as a `hopping'mechanism,as it involves the transfer of polarisa-tion from one cation to another.In the nickel manganite system,it has been postulated that the mixed valence,Mn 4+,Mn 3+cations present on the octahedral sites give rise to these small polaron pathways.1The octahedral cations in the spinel structure lie in chains along some <110>direc-tions.These vectors represent the smallest inter-cationic distances within the unit cell.Another important parameter when considering applications for Ni 1Àx Mn 2+x O 4ceramics is their thermal stability or aging characteristics (changes in conductance over long periods,i.e.lifetime of the component).Reports indicate that better ther-mal stability is found in tetragonal ceramics rather than cubic materials though the conductivity of the latter is 10to 100times higher.2,3This could be explained by a reduction in the concentration of Mn 4+compared to Mn 2+and Mn 3+or possibly by the presence of planar defects such as ferroelas-tic domain walls.4Ni 1Àx Mn 2+x O 4ceramics have been prepared by the carbonate and oxalate methods,in addi-tion to the more conventional mixed oxide route.5Irrespective of the preparation route,sintering (typically around 1200 C)is always carried out above the decomposition temperature in air for the system ($900 C)as discussed by Wickham.5Con-sequently,ceramics ®red using conventional pro-cessing will contain multiple phases,e.g.NiO fromJournal of the European Ceramic Society 19(1999)857±860#1999Elsevier Science LimitedPrinted in Great Britain.All rights reservedP I I :S 0955-2219(98)00331-80955-2219/99/$-see front matter857*To whom correspondence should be addressed.Fax:+44-(0)114-222-5943;e-mail:mtp96gdc@she the decomposed spinel and Mn-rich regions,3,6,7in accordance with the equation:xiwn III2y43x xiy 3Àx3xi II 3À3x a 3Àxwn II 2x a 3Àx wn III2O4 x6O2PIt is the intention of this paper to demonstrate how the degree of decomposition from single phase in¯uences conductivity and,in particular,aging. X-ray di raction and transmission electron micro-scopy will be used to monitor the degree of decomposition and accelerated aging tests(470 C) will be performed.2Experimental ProcedureThe NiO and Mn2O3powders in a1:1Mn2O3:NiO molar ratio were weighed out using an electronic balance( 0.01g)and transferred to a poly-propylene vessel with a charge of ZrO2milling media(the weight of ZrO2varied with the weight of the batch being processed).The batch was mil-led for6h to reduce particle size distribution to a mean of6"m and a maximum of12"m then drawn through a suction®lter.The resulting slurry was dried in a70 C oven overnight.The dried powder was calcined in a mullite crucible at900 C for16h and subjected to a further6h milling under the above conditions.One one cm diameter pellets were pressed from the powders and sintered at 1250 C,achieving densities better than95%. Microstructural and structural characterisation were carried out using transmission electron microscopy(TEM)and X-ray di raction(XRD), respectively.XRD was performed on solid cera-mics and loose powders using a Phillips PW1050 di ractometer with a Cu K source.A0.02 step size was used at a scan rate of0.5 minÀ1.TEM samples were prepared by grinding the ceramic to a thickness of20"m and ion beam milling to per-foration.Images were obtained using JEOL200CX and3010TEMs:the latter was equipped with a LINK energy dispersive X-ray detector. Accelerated aging tests were carried out using a non-induction wound furnace held at470 C.Tem-perature¯ux was monitored in the furnace using a thermocouple mounted immediately adjacent to the test piece.Platinum wires leading to a high precision HP4284A LCR meter were used to make contact to the electroded surface of the cera-mic.Changes in the resistance of the leads and contacts as a function of temperature were taken into account by performing a closed circuit run.Typically,temperature varied within a 0.2 C range over10h.3Results and DiscussionWickham,5in his study of the Ni1Àx Mn2+x O4solid solution,demonstrated that above900 C decom-position occurs resulting in the formation of NiO and a Mn-rich spinel phase.The higher the tem-perature above the onset of the decomposition reaction,the more rapid the rate.In order to study the decomposition reaction in more detail and its potential e ect on electrical properties,single phase ceramics(within the sensitivity of conventional XRD)were fabricated,as demonstrated in Fig.1. Figure2shows a series of XRD traces from single phase samples heat treated at1000,1100and 1200 C for1h.The evolution of peaks corres-ponding to NiO can be observed in accordance with the predictions of Wickham.6The relative intensities of the NiO peaks(marked)increase with increasing temperature.Figure3is a bright®eld(BF)TEM image showing a typical region of spinel grains in single phase material.The grain boundaries and interiors are free from second phase.Inset in Fig.3is a <110>zone axis di raction pattern(ZADP)from one of the spinel grains in the image.Figure4isaFig.1.XRD trace of single phase ceramic.Note absence ofNiOpeaks.Fig.2.XRD spectra of samples held at1000,1100,1200 c for1h.NiO peaks are marked.858G.D.C.Csete de GyoÈrgyfalva et al.BFTEM image obtained from a sample decom-posed for9h at1250 C.Inset is a<110>ZADP pattern from the imaged region.The fundamental re¯ections can be indexed according to a<110> zone axis from rock salt structured NiO.The weak re¯ections at half integer positions arise from regions of spinel phase,observed as dark contrast. Rock salt(NiO)and spinel structured compounds invariably exhibit a cube//cube orientation rela-tionship.Oxides with the rock salt structure are based around single fcc oxygen subunits whereas spinel structured compounds have a2Â2Â2fcc oxygen sublattice.In order to study the aging characteristics of the ceramics as a function of decomposition,con-ductance measurements were performed over10h at470 C 0.2 C.Figure5shows the change in conductance normalised to the initial value,against time at470 C for(A)single phase spinel and(B) `partially'decomposed spinel(heat treated for9h at1250 C).The single phase sample showed a negligible drift in resistivity over the test period, whereas the`partially'decomposed sample exhib-ited a steady decline in conductance.Di erences in the absolute starting values can be attributed to small variations in the dimensions of the samples. Figures6and7are XRD traces showing the samples before and after the accelerated aging experiments.Figure6,which corresponds to Fig.5(A)(decomposed),shows a reduction intheFig.4.BFTEM image of spinel regions in a NiO matrix.Insetis a<110>ZADP from the NiO.Faint re¯ections are presentat half integer positions arising from the dark regions ofspinel.Fig.5.Graph showing normalised conductance versus time at470 C for(A)single phase and(B)decomposed(9h at1250 C)material.Fig.6.XRD spectra of single phase sample(A)before and(B)after acceleratedaging.Fig.7.XRD spectra of decomposed sample(A)before and(B)after acceleratedaging.Fig.3.BFTEM image of spinel grains in single phase mate-rial.Inset is a<110>zone axis di raction pattern(ZADP)from a spinel grain.NTC thermistors produced from oxide powders859intensity of the NiO peaks(A)before and(B)after the experiment.However,Fig.7,which corre-sponds to Fig.5(B)(single phase),shows traces that are identical(A)before and(B)after.It is thought that the accelerated aging at470 C leads to NiO being re-absorbed into the ceramic during the lifetime of the experiment.It is proposed that the decomposition reaction occurs homogeneously throughout the ceramic,and the NiO is intimately mixed with the spinel phase,as evidenced by Fig.4. The reverse process may therefore occur relatively quickly because of the short di usion distances involved(of the order of nm according to Fig.4). However,it should be noted that aging at room temperature may be related to di erent phenomena than suggested by these accelerated tests.4Conclusions.The reaction between NiO and Mn2O3pro-ceeds forwards slowly at temperatures less than900 C,but will reverse as temperature increases above this value..The rate of decomposition increases with increasing temperature resulting in amicrostructure of intimately mixed NiO and Mn-rich spinel..Initial investigations indicate that a single phase ceramic gives rise to substantial improvements in thermal stability under accelerated aging.References1.Brabers,V.A.M.and Terhell,J.,Electrical conductivityand cation valencies in nickel manganite.Phys.Stat.Sol.(a),1982,69,325±332.2.Dorris,S.E.and Mason,T.O.,Electrical properties andcation valences in Mn3O4.J.Am.Ceram.Soc.,1988, 71(5),379±385.3.Rousset,A.,Larange,A.,Brieu,M.,Couderc,J.andLegros,R.,In¯uence de la microstructure sur la stabilite electrique des thermistance.C.T.N Journ.de Phys.III, 1992,4,833±845.4.Macklen,E.D.,Electric conductivity and cation distribu-tion in nickel manganite.J.Phys.Chem.Solids,1986, 47(11),1073±1079.5.Wickham,D.G.,Solid phase equilibria in the systemNiO±Mn2O3±O2.J.Inorg.Chem.,1964,26,1369±1377.6.Feltz,A.,Topfer,J.and Schirrmeister,F.,Conductivitydata and preparation routes for NiMn2O4thermistor ceramics.J.Eur.Ceram.Soc.,1992,9,187±191.7.Jung,J.,Topfer,J.,Murbe,J.and Feltz,A.,Micro-structure and phase development in NiMn2O4spinel ceramics during isothermal sintering.J.Europ.Ceram.Soc.,1990,6,351±359.860G.D.C.Csete de GyoÈrgyfalva et al.。

新人教版高中英语必修（1-3）课文英汉对照（Word精校版）必修一Welcome Unit 欢迎单元Reading and ThinkingFIRST IMPRESSION 第一印象Han Jing's World7:00a.m.So this is it-senior high school at last. I'm not outgoing so I’m a little anxious right now. I want to make a good first impression. Will I make any friends? What if no one talks to me? 韩静的世界早上7:00这就是了一一终于到了高中学校!我性格并不外向，所以现在感觉有点焦虑。

我想给别人留下良好的第一印象。

我会交到朋友吗?要是没人跟我说话怎么办呢?12:30p.mI just had my first maths class at senior high school! The class was difficult, but the teacher was kind and friendly. He even told us a funny story and everyone laughed so much! I found most of my classmates and teachers friendly and helpful.中午12:30我刚刚上完高中的第一节数学课!这课(内容)很难，但老师却很友善。

他还给我们讲了笑话,惹得每个人都哈哈大笑!我觉得我的大多数同学和老师都很友好，而且乐于助人。

5:32p.mThis afternoon, we had our chemistry class in the science lab. The lab is new and the lesson was great, but the guy next to me tried to talk to me the whole time. I couldn’t concentrate on the experiment. I really wanted to tell him to please be quiet and leave me alone.下午5:32今天下午，我们在科学实验室上化学课。