ASTM B920-16由美国材料与试验协会 US-ASTM 发布于 2016。
ASTM B920-16 在中国标准分类中归属于: A29 材料防护。
* 在 ASTM B920-16 发布之后有更新,请注意新发布标准的变化。
5.1 Palladium and gold coatings are often specified for the contacts of separable electrical connectors and other devices. Electrodeposits are the form of gold that is most used on contacts, although it is also employed as inlay or clad metal and as weldments on the contact surface. The intrinsic nobility of gold and palladium alloys enables it to resist the formation of insulating oxide films that could interfere with reliable contact operation.
5.2 In order for these coatings to function as intended, porosity, cracks, and other defects in the coating that expose base-metal substrates and underplates must be minimal or absent, except in those cases where it is feasible to use the contacts in structures that shield the surface from the environment or where corrosion inhibiting surface treatments for the deposit are employed. The level of porosity in the coating that may be tolerable depends on the severity of the environment to the underplate or substrate, design factors for the contact device like the force with which it is mated, circuit parameters, and the reliability of contact operation that it is necessary to maintain. Also, when present, the location of pores on the surface is important. If the pores are few in number and are outside of the zone of contact of the mating surfaces, their presence can often be tolerated.
5.3 Methods for determining pores on a contact surface are most suitable if they enable their precise location and numbers to be determined. Contact surfaces are often curved or irregular in shape, and testing methods should be suitable for them. In addition, the severity of porosity-determining tests may vary from procedures capable of detecting all porosity to procedures that detect only highly porous conditions.
5.4 The present test practice is capable of detecting virtually all porosity or other defects that could participate in corrosion reactions with the substrate or underplate. In addition, it can be used on contacts having complex geometry such as pin-socket contacts (although with deep recesses it is preferred that the contact structures be opened to permit reaction of the vapors with the interior significant surfaces).
5.5 The relationship of porosity levels revealed by particular tests to contact behavior must be made by the user of these tests through practical experience or by other forms of testing. Thus, absence of porosity in the coating may be a requirement for some applications, while a few pores in the contact zone may be acceptable for others. The acceptable number, sizes and locations of the pore corrosion products shall be as specified on the appropriate drawing or specification.
5.6 This test is considered destructive in that it reveals the presence of porosity by contaminating the surface with corrosion products and by undercutting the coating at pore sites or at the boundaries of the unplated areas. Any parts exposed to this test shall not be placed in service.
5.7 The test is simple and inexpensive. The cost associated with the test is very low, using standard basic equipment found in an industrial laboratory. There are minimal waste disposal issues associated with the procedure. The test is very popular because of its very quick means of assessing the likelihood of......
图3 DEN-RuO2形成原理图除了一元金属氧化物外,科研人员将目光转向复合催化剂。他们制备了一种用金和钯纳米粒子修饰微观结构像刺猬一样的α⁃MnO2 材料,将其作为正极催化剂应用于锂氧电池中。3~8nm 的Au和Pd纳米颗粒均匀地分散在垂直排列的α⁃MnO2纳米棒表面,图4为Au/α⁃MnO2和Pd/α⁃MnO2催化剂的XRD图和TEM图。...
不同材料具体制备方案陶瓷涂层金属部件这些合金上的陶瓷涂层可以是氧化锆、氧化铝或微晶玻璃等。最常用的是羟基磷灰石(HA)涂层,但也可以采用磷酸三钙和其他磷酸钙。由于这些涂层是通过热喷涂技术涂覆的,因此其孔隙率、厚度和涂层/基体界面是应检查的关键金相参数。...
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