Coatings, important properties

Other important properties that can be measured in the laboratory include sealabiHty, printabiHty, or coating adhesion. Many of these tests have been developed by the film manufacturer in cooperation with customers and are specifically designed to measure product performance in the end use. Some tests, like sealabiHty, can be standardi2ed to time, pressure, and temperature of sealing with instmment-measured peel values, but other tests are subjective, such as evaluations of printing loss to puUoff by adhesive tape. 

Magnesium anodes usually consist of alloys with additions of Al, Zn and Mn. The content of Ni, Fe and Cu must be kept very low because they favor selfcorrosion. Ni contents of >0.001% impair properties and should not be exceeded. The influence of Cu is not clear. Cu certainly increases self-corrosion but amounts up to 0.05% are not detrimental if the Mn content is over 0.3%. Amounts of Fe up to about 0.01% do not influence self-corrosion if the Mn content is above 0.3%. With additions of Mn, Fe is precipitated from the melt which on solidification is rendered harmless by the formation of Fe crystals with a coating of manganese. The addition of zinc renders the corrosive attack uniform. In addition, the sensitivity to other impurities is depressed. The most important magnesium alloy for galvanic anodes is AZ63, which corresponds to the claims in Ref. 22. Alloys AZ31 and M2 are still used. The most important properties of these alloys are... 

The natural corrosion resistance of zinc is, therefore, its most important property in relation to zinc coatings. The electrochemical property becomes important when the zinc coating is damaged in any way to expose the steel, when sacrificial corrosion of the zinc occurs and the steel is thereby protected. Moreover, the corrosion product of the zinc normally fills the break in the coating and prevents or retards further corrosion of the exposed steel. 

In this paper the planarizing properties of some commercially available resins and monomers are evaluated. Other important properties such as etching resistance, film absorbance and glass transition temperature Tg are reported and discussed. Some of the materials that we evaluated are not marketed for use in the microelectronics industry. Consequently, they are not available as filtered spin coating solutions and may contain high levels of metal impurities that adversely affect device performance. 

The five largest uses for PCBs prior to 1970 were dielectric fluids in capacitors, plasticizers, lubricants, transformer fluids, and hydraulic fluids. They were also used widely in protective coatings, sealers, putty, grinding fluids, printing inks, pattern waxes, carbonless paper, etc. (see Chap. 1). Because of this widespread PCB use they are found throughout the environment [363-365]. A number of important properties of PCBs are discussed below along with information on their distribution and persistence in the environment. 

Thus, in acid solution it appears that an important property of a coating for corrosion protection is its permeability to acid. This variation in permeability is thought to be the reason for the difference in behavior of coatings observed during exposure to acid environments [1 ]. The permeability is also affected by the degradation of the coating as caused by reaction with the acid. 

Perhaps the most important part of a coating is the binder or resin. Binders can be in the form of solutions, where the resin is dissolved in a solvent, or a dispersion, where the resin is suspended in water or an organic liquid with a particle size of 10 microns or less. We will subdivide our discussion of binders into four primary types and summarize their important properties and uses. 

Since polymers are often used as clear plastics or coatings and have many applications where transparency is an important property, knowledge of the optical properties of specific polymers is essential. The radiation scale, of course, includes microwave, IR, UV, and visible... 

Eadie, in Ref 69, reports on a considerable amount of work done on the ability of beeswax and paraffin wax to remain coated on HMX surfaces when immersed in liq TNT. Thru measurements of contact angles, a technique used earlier on RDX/wax systems reported on by Rubin in Ref 23, it was determined that the TNT preferentially wets the HMX and the wax is stripped away. He concludes that the most important property of a desensitizing wax is that it should be readily dispersed uniformly thruout the TNT phase. He also suggests that a better desensitizer for investigation for use would be a wax or substituted hydrocarbon having a low interfacial tension with TNT. The smaller the wax droplet size the more efficiently it will be distributed and the more effectively it should desensitize. Williamson (Ref 64) in his examination of the microstructures of PETN/TNT/wax fusion-casts detected that wax is dispersed thru the cast as isolated descrete globules which he refers to as blebs or irregular or streak-like areas, surrounded by TNT (see also Ref 54)... 

There is no question that the method used and the degree of coating of the wax over the surface of either the RDX or HMX crystals is of prime importance in desensitizing the basic materials to mechanical stimuli. Likewise probably the most important property of a desensitizing wax for use in TNT-based expls is its... 

Other important properties of Cr02 when used as a magnetic pigment are its black color, electrical conductivity (2.5-400 O-1 cm-1 [5.27]) and relatively high crystal hardness (Mohs hardness 8-9 [5.20]). Therefore, coating formulations based on Cr02 require less or even no additives such as carbon black (good conductivity, black color) or refractory oxides such as alumina. 

An important property of a passivating solid coating is that it should be stable in spite of subsequent thermal treatments, such as the sintering of metal connections. The problem of thermal stability is especially worrisome in the case of a-Si H that is known to evolve hydrogen above about 350°C (Pankove and Carlson, 1977). Heating the sample for 30 min at 500°C caused the leakage current to increase by a factor of about three, as shown by the dashed line in Fig. 3. Note that the current for the heated sample is still about one order of magnitude lower than that of the oxide-passivated p-n junction, which is well known for its thermal stability. 

Certain important properties of polymers are directly related to the average chain length and the distribution. One of particular importance is the viscosity. This affects the flowability of the polymer and the kinds of applications where it can be used (injection molding, blow molding, fiber spinning, sheet formation, coating, etc.). 

---