Flexible poor oxidation resistance

Sihcone-based coatings are well suited for high temperature and high speed appHcations. They are flexible, tough, and resistant to thermal and oxidative deterioration. They have good surface resistance and are fungus- and flame resistant. However, they possess a high coefficient of thermal expansion and have poor adhesion. 

The borides are extremely hard (9.8—29 GPa (1000—3000 kgf/mm ) Knoop) and, in the case of molybdenum, >39 GPa (4000 kfg/mm ) (see Hardness). However, oxidation resistance is usually poor unless a subsequent coating is formed, such as silicidi ing or chromizing, which imparts oxidation resistance. SiUcides are generally very oxidation resistant, but not as hard as borides. SiUcide coatings formed on molybdenum (51 pm in 3 h) at 675°C have superior oxidation resistance. At these low temperatures, the molybdenum substrate does not embrittle and the coatings are quite flexible. 

Alkyd (oxidation) Excellent exterior durability Low cost Excellent flexibility Excellent adhesion to most surfaces Easy to apply Very good gloss retention Poor chemical and solvent resistance Fair water resistance Poor heat resistance... 

Polysulfldes Disagreeable odor, no cure exotherm, high viscosity Good flexibility and adhesion, excellent resistance to solvents and oxidation, poor physical properties... 

Outstanding resistance to heat and hot oil Excellent resistance to weather, ozone, sunlight and oxidation Very good resistance to oil and gasoline Poor resistance to alcohols and alkalis Limited flexibility at low temperatures Inferior resistance to water and steam... 

Hot asphalts can be softened with heat and have good resistance to water and water vapor transmission when applied to dry surfaces under controlled heating, but have poor bond adhesion to wet surfaces. In addition, they have relatively poor flexibility, are brittle at low temperatures, and oxidize upon exposure to solar radiation. 

Epoxy Solvent, waterborne, powder Air dry, bake Excellent adhesion, chemical resistance, flexibility, abrasion resistance, hardness Rapid chalking on exterior exposure, poor resistance to oxidizing acids, yellows in clears Moderate, hi Mainimance tainte, automotive primers, appliances, metal products... 

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