问题 问答题 简答题

简述新技术应用中刷镀的特点与适用范围。

答案

参考答案:

(1)特点:

①刷镀不仅能增大零件的局部尺寸,还可提高零件的耐磨性、抗腐蚀性和表面导电性。

②由于刷镀过程是在低温下进行,因而基体金属性质几乎不受影响,原先的热处理效果不会改变,零件也不会因受热而发生变形。

③镀层与基体间的结合强度高,与热喷涂相比,修复部位的抗冲击性较好。

(2)适用范围:

①修复磨损量不大的机械零件,特别是精密零件或量具,恢复其几何形状和尺寸。

②修复大型、贵重零件机加工中尺寸超差或修补其表面划伤、凹坑及斑蚀等。

③修补槽镀产品的缺陷或完成槽镀难以完成的作业。

④修复日常生活中的家用器具。

⑤改善材料的表面性能,如改善钎焊性,作为零件局部渗碳、渗氮等的保护层及喷涂层的过渡层等。

⑥在工艺美术、建筑装潢等领域广泛应用。

单项选择题
单项选择题

If there is one thing scientists have to hear, it is that the game is over. Raised on the belief of an endless voyage of discovery, they recoil from the suggestion that most of the best things have already been located. If they have, today’s scientists can hope to contribute no more than a few grace notes to the symphony of science.

A book to be published in Britain this week, The End of Science, argues persuasively that this is the case. Its author, John Horgan, is a senior writer for Scientific American magazine, who has interviewed many of today’s leading scientists and science philosophers. The shock of realizing that science might be over came to him, he says, when he was talking to Oxford mathematician and physicist Sir Roger Penrose.

The End of Science provoked a wave of denunciation in the United States last year. "The reaction has been one of complete shock and disbelief, "Mr. Horgan says.

The real question is whether any remaining unsolved problems, of which there are plenty, lend themselves to universal solutions. If they do not, then the focus of scientific discovery is already narrowing. Since the triumphs of the 1960s—the genetic code, plate tectonics, and the microwave background radiation that went a long way towards proving the Big Bang—genuine scientific revolutions have been scarce. More scientists are now alive, spending more money on research, that ever. Yet most of the great discoveries of the 19th and 20th centuries were made before the appearance of state sponsorship, when the scientific enterprise was a fraction of its present size.

Were the scientists who made these discoveries brighter than today’s That seems unlikely. A far more reasonable explanation is that fundamental science has already entered a period of diminished returns. "Look, don’t get me wrong," says Mr Horgan. "There are lots of important things still to study, and applied science and engineering can go on for ever. I hope we get a cure for cancer, and for mental disease, though there are few real signs of progress.

The best title of this passage can be()

A. Great Scientific Discoveries Will Never Be Possible

B. The Harsh Challenge Has to Be Met by Modern Scientists

C. The State Sponsorship and Scientific Enterprise Are All in Vain

D. The Chance for Great Scientific Discoveries Becomes Scarce