Barrier coatings applications

Ramaswamy P, Seetharamu S, Varma KB, Rao KJ. Thermal barrier coating application of zircon sand. Journal of Thermal Spray Technology. 1999 8 447-453. 

Recent applications of e-beam and HF-plasma SNMS have been published in the following areas aerosol particles [3.77], X-ray mirrors [3.78, 3.79], ceramics and hard coatings [3.80-3.84], glasses [3.85], interface reactions [3.86], ion implantations [3.87], molecular beam epitaxy (MBE) layers [3.88], multilayer systems [3.89], ohmic contacts [3.90], organic additives [3.91], perovskite-type and superconducting layers [3.92], steel [3.93, 3.94], surface deposition [3.95], sub-surface diffusion [3.96], sensors [3.97-3.99], soil [3.100], and thermal barrier coatings [3.101]. 

Ability to form and maintain strong bond with propellant, resist any delamination, cracking or interface separation due to self-stressing. The ability to bond itself with the propellant directly on application by casting technique without any barrier coat is considered an added attribute. 

Interpositioning of barrier coats resistant to NG migration, before application of flexible polymeries as main inhibitor and... 

EP-4 developed by ERDL is a very flexible polyester based on polyethylene glycol with molecular weight-200 (PEG-200), isophthalic acid (IPA) and maleic anhydride (MAn). Before its use, it is blended with styrene monomer (1 1) and cured at room temperature using cobalt naphthenate (as an accelerator) and methyl ethyl ketone (MEK) peroxide (as a catalyst). This meets the requirements of the main inhibitor and is used for inhibition of DB and CMDB propellants after the application of a barrier coat (generally a rigid polyester such as PR-3). However, it is observed during manufacture of EP-4 that there is a lot of batch-to-batch variation in properties in spite of the strict quality control measures adopted during its manufacture. 

Vinylidene chloride polymers are often made in emulsion, bul usually are isolated, clned, and used as conventional resins. Stable latices have been prepared and can be used directly for coatings. The principal applications for these materials are as barrier coatings on paper products and, more recently, on plastic films,... 

Vinylidene Chloride Copolymer Latex. Vinylidene chloride polymers are often made in emulsion, but usually are isolated, dried, and used as conventional resins. Stable latices have been prepared and can be used diiecdy for coatings (171—176). The principal applications for these materials are as barrier coatings on paper products and, more recently, on plastic films. The heat-seal characteristics of VDC copolymer coatings are equally valuable in many applications. They are also used as binders for paints and nonwoven fabrics (177). The use of special VDC copolymer latices for barrier laminating adhesives is growing, and the use of vinylidene chloride copolymers in flame-resistant carpet backing is well known (178—181). VDC latices can also be used to coat polyethylene terephthalate) (PET) bottles to retain carbon dioxide (182). 

For barrier coatings to be effective it is necessary to have (i) good adhesion of the barrier film on the metal surface (this is generally accomplished by multicoat procedure to a certain extent) (ii) proper choice of the polymers to control the permeability of oxygen and (iii) optimum film thickness achieved by multicoats or thin-film system, depending upon the envisaged application. 

Kinetic Monte Carlo and hyperdynamics methods have yet to be applied to processes involved in thermal barrier coating failure or even simpler model metal-ceramic or ceramic-ceramic interface degradation as a function of time. A hindrance to their application is lack of a clear consensus on how to describe the interatomic interactions by an analytic potential function. If instead, for lack of an analytic potential, one must resort to full-blown density functional theory to calculate the interatomic forces, this will become the bottleneck that will limit the size and complexity of systems one may examine, even with multiscale methods. 

A barrier coating may also be required for protection against alpha particles. High-density devices can suffer soft errors when alpha particles emitted from trace quantities of thorium or uranium in packaging materials strike the active surface. Thus, the surface must be protected against this possibility. Polyimides are again recommended for such applications. 

In many cases, the protection provided by a simple barrier coating such as RTV silicone will be suflScient to ensure long-term reliability of the device. Small, ceramic-based, hybrid ICs designed to be inserted into a PWB are often protected in this manner. However, for other applications, additional protection is required to provide impact and shock resistance (RTV silicones are very soft and offer little mechanical protection), better environmental protection, and a well-defined structure for subsequent assembly and handling. Such protection is provided by embedment in a hard plastic by transfer or injection molding as shown in Figure 1.6. The molding process leaves two parallel rows of pins exposed for subsequent connection to the PWB. 

Both columnar and equiaxed microstructures are obtained from polycrystal growth. Columnar micro structure is composed of columnar grains of preferred orientation that grow from the first nucleated location on a substrate surface. The microstructure is attributed to high supersaturation and low temperature and hence more limited diffusion. A columnar microstructure is suitable for high-temperature structural applications, such as thermal barrier coatings. Figure 6.6 shows the typical columnar CVD SiC microstructure in C/SiC composites. 

Initial attempts to use aluminum for automotive trim were unsuccessful due to the corrosion behavior of the metal. It is therefore anodized for automotive trim applications to provide a protective oxide surface which acts as a barrier coating for corrosion pro tec tion. > 2 Aluminum and its alloys are susceptible to pitting and crevice corrosion in chloride containing environments. The corrosion resistance of anodized aluminum is therefore highly dependent on the quality of the anodized surface and the absence of scratches and other damage sites. 

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