《材料专业英语课件： Classification of Materials.docx》由会员分享，可在线阅读，更多相关《材料专业英语课件： Classification of Materials.docx（7页珍藏版）》请在三一文库上搜索。
1、材料专业英语课件： Classification of MaterialsBasic Classifications and Engineering MaterialsSolid materials have been conveniently grouped into three basic classifications： metals，ceramics and polymersThis scheme is based primarily on chemical makeup and atomic structure, and most materials fall into one di
2、stinct grouping or another， although there are some intermediates. In addition，there are three other groups of important engineering materialscomposites， semiconductor， and biomaterials Composites consist of combinations of two or more different materials， whereas semiconductors are utilized because
3、 of their unusual electrical characteristics；biomaterials are implanted into the human bodyA brief explanation of the material types and representative characteristics is offered nextMetals： Metallic materials are normally combinations of metallic elements They have large numbers of nonlocalized ele
4、ctrons；that is，these electrons are not bound to particular atoms. Many properties of metals are directly attributable to these electrons Metals are extremely good conductors of electricity and heat，and are not transparent to visible light：a polished metal surface has a lustrous appearance Furthermor
5、e， metals are quite strong，yet deformable， which accounts for their extensive use in structural applicationsCeramics： Ceramics are compounds between metallic and nonmetallic elements： they are most frequently oxides, nitrides，and carbidesThe widerange of materials that falls within this classificati
6、on includes ceramics that are composed of clay minerals， cement， and glass. These materials are typically insulative to the passage of electricity and heat， and are more resistant to high temperatures and harsh environments than metals and polymersWith regard to mechanical behavior，ceramics are hard
7、 but very brittlePolymers：Polymers include the familiar plastic and rubber materials Many of them are organic compounds that are chemically based on carbon，hydrogen， and other nonmetallic elements； furthermore，they have very large molecular structuresThese materials typically have low densities and
8、may be extremely flexibleComposites： A number of composite materials have been engineered that consist of more than one material typeFiberglass is a familiar example，in which glass fibers are embedded within a polymeric material. A composite is designed to display a combination of the best character
9、istics of each of the component materials Fiberglass acquires strength from the glass and flexibility from the polymer Many of the recent material developments have involved composite materialsSemiconductors： Semiconductors have electrical properties that are intermediate between the electrical cond
10、uctors and insulators Furthermore，the electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms，which concentrations may be controlled over very small spatial regionsThe semiconductors have madepossible the advent of integrated c
11、ircuitry that has totally revolutionized the electronics and computer industries over the past two decadesBiomaterials: Biomaterials are employed in components implanted into the human body for replacement of diseased or damaged body partsThese materials must not produce toxic substances and must be
12、 compatible with body tissue(iemust not cause adverse biological reactions)All of the above materials-metals，ceramics，polymers，composites and semiconductors-may be used as biomaterialsFor example，some of the biomaterials such as CFC(carbon fiberscarbon)and CFPS (polysulfone) are utilized in artifici
13、al hip replacementsAdvanced MaterialsMaterials that are utilized in high-technology (or high-tech) applications are sometimes termed advanced materialsBy high technology we mean a device or product that operates or functions using relatively intricate and sophisticated principles；examples include el
14、ectronic equipment(VCRs，CD players，etc)，computers，fiberoptic systems，spacecraft，aircraft，and military rocketryThese advanced materials are typically either traditional materials whose properties have been enhanced or newly developed，highperformance materialsFurthermore，they may be of all material ty
15、pes(egmetals，ceramics，polymers)，and are normally relatively expensiveModern Materials NeedsIn spite of the tremendous progress that has been made in the discipline of materials science and engineering within the past few years，there still remain technological challenges，including the development of
16、even more sophisticated and specialized materials，as well as consideration of the environmental impact of materials productionSome comment is appropriate relative to these issues so as to round out this perspectiveNuclear energy holds some promise，but the solutions to the many problems that remain w
17、ill necessarily involve materials from fuels to containment structures and facilities for the disposal of radioactive wasteSignificant quantities of energy are involved in transportationReducing the weight of transportation vehicles(automobiles，aircraft，trains，etc)，as well as increasing engine opera
18、ting temperatures，will enhance fuel efficiencyNew high strength，lowdensity structural materials remain to be developed，as well as materials that have highertemperature capabilities，for use in engine componentsFurthermore，there is a recognized need to find new，economical sources of energy，and to use
19、the present resources more efficientlyMaterials will undoubtedly play a significant role in these developmentsFor example，the direct conversion of solar energy into electrical energy uses silicon materialsTo ensure a viable technology，materials that are highly efficient in this conversion process ye
20、t less costly must be developedAdditionally，environmental quality depends on our ability to control air and water pollutionPollution control techniques employ various materials In addition, materials Processing and refinement methods need to be improved so that they produce less environmental degrad
21、ation，that is，less pollution and less despoilage of the landscape from mining of raw materials Also， in some materials manufacturing processes，toxic substances are Produced，and the ecological impact of their disposal must be considered.Many materials that we use are derived from resources that are n
22、oenewable，that is not capable of being regeneratedThese include polymers， for which the prime raw material is oil， and some metalsThese noenewable resources are gradually becoming depleted, which necessitates： (1)the discovery of additional reserves， (2)the development of new materials having compar
23、able properties with less adverse environmental impact， andor (3) increased recycling efforts and the development of new recycling technologies As a consequence of economics of not only production but also environmental impact and ecological factors，it is becoming increasingly important to consider the“cradletogravelife cycle of materials relative to the overall manufacturing process(Selected from Materials Science and Engineering：An Introduction，by William D Callister，2002)【材料专业英语课件： Classification of Materials】7