【正文】 ty are almost always brought about by technological revolutions, In this respect, I remember Sir George Porter stating that James Watt had liberated more slaves from slavery than any politician ever did, just by inventing the steam engine. In fact, by his invention, James Watt initiated the industrial era.Which are the major technologies that lie at the basis of the present transformation? In a study performed by the study Centre for Technology Trends in the Netherlands, but also in many other studies, it was concluded that, at this turn of the centuries, three major waves of technology are affecting society: the silicon technology, the biotechnology and the nanotechnology. Silicon technology took off in the fifties and in fact brought about the former jump. One can say that it changed the world pletely in 50 years. It is expected to level off now and even decline, because further developments will be taken over partly by a new technology: nanotechnology (). In the mean time, another technology developed: biotechnology. Started in the 197039。 munication hardware39。Supramolecular Chemistry39。 natural39。synthetic39。controlled plexity39。diversity39。 technologyLooking at the developments in science and technology, it is clear that the fields of 39。 and 39。 are growing closer and closer together. For instance, it is striking that nature succeeds, despite the limited number of building blocks, in getting adequate structural properties anyway. Nature is able to do so by plete control on the molecular level (molecular weight, molecular weight distribution, sequence, tacticity), by ordering on the nanolevel and by perfect macroscopic design. In this respect we can learn a lot from nature, as well for structural applications of synthetic materials, as for functional applications or a bination of the two. (Selected from Industrial research, which way to go, by Joseph Put,2002) New Words and Expressions miniaturization n. 小型化 synthetic a. 合成的，人造的 biotechnology n. 生物技術，生物工藝學 nanotechnology n. 納米技術 sequence n.（分子的）序列結構 tacticity n. 立構規(guī)整度 life cycle 壽命周期，使用壽命 down scaling 減小尺度 smart material 智能材料 functional material 功能材料 supramolecular chemistry 超分子化學 molecular weight 分子量 molecular weight distribution 分子量分布 Exercises 1. List the tree major waves of technology that had significant influence on our society. 2. Do the following statements agree with the views of the writer in the above passage? Write: YES if the statement agrees with the writer NO if the statement contradicts the writer (1) Polymer scientists are devoting themselves to the synthesis of new monomers and their (co)polymers. (2) In recent years, the diversity in molecules synthesized by living organisms is increased by biotechnology. (3) Thanks to the efforts of chemists, we can now perfectly control the macromolecular structure and function of polymers. (4) The fields of 39。 and 39。 are growing closer and closer. Unit 11 Powder MetallurgyPowder Metallurgy (PM) is a wellestablished manufacturing process which has undergone substantial growth in recent years in terms of allowable loads. This is due to the use of detailed stress analysis which can define the best process parameters, the availability of highly pressed powders, and the accurate design of pacting equipment. It is possible to produce helical, bevel, internal and external gears. Consequently, materials scrap losses are eliminated. Internal and frontal configurations are formed simultaneously with the gear profile. Thereby eliminating subsequent machining operations. Slots, grooves, blind holes, and recesses of varied depths are also obtainable. The PM process provides close dimensional tolerances, minimal machining, good surface finish, and excellent partto part reproducibility. Powder Metallurgy technology Powder metallurgy enpasses a wide range of processing techniques applicable to net and nearnet shape ponents manufacturing. It is a wellestablished technology, especially in the power transmission field and specifically in the automotive industry. The PM process uses powder as a raw material which, in the case of gears, is primarily an atomized ironbased powder. This type of metal powder provides the highest density possible. The metal particles are pacted in dies using mechanical or hydraulic presses. These dies have the desired part reproduced in the negative. During the pacting process, the metal particles are brought into contact with one another and plastically beformed along the joints. After pressing, the parts are put into special furnaces with protective atmosphere at temperatures between 1100`C and 1300`C. This phase, called sintering, causes diffusion of the alloy elements present in the powder and solid aggregation among the particles of the pacted part occurs. During the maximum temperature phase, new crystallites form and grow at the contact points. The edges of the original metal particles disappear. After sintering, there may be additional processes such as sizing, a second sintering, and/or heat treatment to improve the mechanical characteristics of the product. By means of tight process control of variables involved in the PM process, limited dimensional tolerance c an be obtained. Powder metallurgy technology offers a series of distinct advantages when pared with other traditional technologies.● Economy in production of mediumtolarge batches.● The ability to obtain plex shapes which could be difficult or even impossible to produce by machining.● The ability to bine functions and eliminate assemdlies.● Selflubrication properties.● Very good surface finish. The possibility of manufacturing parts with plex forms without additional machine work.18