Hard coats

Hydrodynamic principles for gas bearings are similar to those involved with Hquid lubricants except that gas compressibility usually is a significant factor (8,69). With gas employed as a lubricant at high speeds, start—stop wear is minimized by selection of wear-resistant materials for the journal and bearing. This may involve hard coatings such as tungsten carbide or chromium oxide flame plate, or soHd lubricants, eg, PTFE and M0S2. 

Ion plating is used to deposit hard coatings of compound materials, adherent metal coatings, optical coatings having high densities, and conformal coatings on complex surfaces. 

Hard-coated poly(methyl methacrylimide) sun-roofs have already been specified for American sports cars, whilst the polymer might be expected to make some inroads into the polycarbonate market, with one specific target being auto headlamp diffusers. 

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]. 

Surface preparation of concrete consists mainly of removing laitence, form oils and air pockets. Laitence is the fine cement powder that floats to the surface of concrete when it is placed. Coatings applied over such a powdery, weak layer will lose adhesion. Form oils are used for the easy stripping of forms or shuttering. Their presence will also cause loss of adhesion of subsequent coatings. Forms should be coated with non-migratory hard coatings and the use of oils or waxes prohibited. 

Hardness Coating hardness is related to the method of measurement. Results reflect the resistance to scratching as well as to indentation. 

DLC coatings are already in production in several areas (optical and IR windows) and appear particularly well-suited for abrasion and wear applications due to their high hardness and low coefficient of friction. They have an extremely smooth surface and can be deposited with little restriction of geometry and size (as opposed to CVD diamond). These are important advantages and DLC coatings will compete actively with existing hard coatings, such as titanium carbide, titanium nitride, and other thin film... 

Hard coating forthe protection of niobium metal. 

The comparative wear rate of some of these materials is shown in Fig. 17.2. The wear was obtained with aluminum oxide powder in a jet abrader.Pl Hard coating materials such as TiB2, TiC, or SiC have extremely small wear rates. 

Evaporation is used extensively for the deposition of aluminum and other low melting-point metals as well as hard coatings such as TiN for cutting tools, decorative coatings (jewelry), and for the metallization of paper and fibers. It is also a major coating... 

Sputtering is an important thin-film process used extensively in the semiconductor and hard-coating industries and for decorative and jewelry coatings. PlP] Excellent coatings of refractory compounds and metals can be readily produced with good adhesion and composition control without the high temperature requirements of CVD. 

Hard coatings for cutting tools and erosion applications. 

Recent trials and long-term field tests have shown that the combined application of plasmanitriding and physical vapor deposited (PVD) hard-coating currently appears to be the best solution, both in terms of improved wear life and antisticking characteristics. 

For the balanced beam-scrape adhesion test, ASTM-2197, weights were added to a commercial balanced beam tester. The kind of scratch produced by the stylus with the different loadings was recorded and served as a measure of film hardness. Coatings which are not scratched to bare metal by 500 g are desirable. 

When exposed to air and light, the latex will further polymerize to a hard coating at a moderate speed. (It dries fast.)... 

The greatly enhanced hardness and impact resistance of enamels made from LC diols is not simply explainable by the monomer raising the Tg of the coating. In fact, Tg of the crosslinked enamels of Ib-lg are abnormally low for hard coatings and are similar to the much softer control enamels (Table II). 

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