Acid-hardening resist

Being cross-linked, the resin will not dissolve without decomposition but will be swollen by liquids of similar solubility parameter to the cured resin. The chemical resistance is as much dependent on the hardener as on the resin since these two will determine the nature of the linkages formed. The acidic hardeners form ester groups which will be less resistant to alkalis. 

Acid generation in photoresist films add photogeneration vs. dose, 3233/ acid present after irradiation, 32,34r add present before irradiation, 32 quantum yield, 3234 Acid hardening resin resists cross-linking adivation energy determination, 87,89 cross-linking chemistry, 87 determination of acid generated, 87-88 effect of postexposure bake temperature and time, 87... 

P.R.170 is broad in scope. It is found in wood stains, including solvent-based stains it is blended with carbon black and yellows to produce a variety of interesting shades of brown. The colorations are fast to overcoating in these media and resist nitro and acid hardening varnishes and polyester coatings. Its lightfastness in these media equals step 7 on the Blue Scale. 

P.R.208 is also applied in a variety of specialty media besides the three main groups mentioned, such as in crayons and laundry inks, as well as in solvent-based wood stains. Applied onto a surface, these products may safely be overcoated and are resistant towards nitro varnish, acid hardening varnish, and polyester varnish. The lightfastness in these media equals step 7 on the Blue Scale, which is excellent. 

For example, strongly alkaline or strongly acidic reaction mixtures weaken cellulose filter papers. Acid-hardened grades which are more chemically resistant are commercially available (e.g. Whatman filter papers) but for maximum resistance to chemical attack, glass-fibre paper (e.g. Whatman) or a glass funnel fitted with a fixed sintered glass plate (Section 2.11) may be used. 

In order to overcome the existing problems with the state-of-the-art technology in vegetable oil and free fatty acid hardening, we have investigated hydrogenation reactions in liquid, near-critical, and supercritical C02, as well as C02/propane mixtures with precious-metal fixed-bed catalysts supported on acid-resistant supports. 

Resorcinol resin glues set without the assistance of heat under mildly alkaline conditions. Therefore, no damage is caused to the wood by acid hardeners, and there are no restrictions on the moisture content of the wood up to 18 %. The resins can be cured with paraformaldehyde. Wood-to-wood glue joints with resorcinol resins are among the strongest and are weatherproof and resistant to solvents, oils, and fats. For reasons of economy, mixed condensates of resorcinol and phenol are used instead of pure resorcinol. 

The compositions of the conversion baths are proprietary and vary greatly. They may contain either hexavalent or trivalent chromium (179,180), but baths containing both Cr(III) and Cr(VI) are rare. The mechanism of film formation for hexavalent baths has been studied (181,182), and it appears that the strength of the acid and its identity, as well as time and temperature, influences the film s thickness and its final properties, eg, color. The newly prepared film is a very soft, easily damaged gel, but when allowed to age, the film slowly hardens, assumes a hydrophobic character and becomes resistant to abrasion. The film s stmcture can be described as a cross-linked Cr(III) polymer, that uses anion species to link chromium centers. These anions may be hydroxide, chromate, fluoride, and/or others, depending on the composition of the bath (183). 

The resistance to heat and aging of optimized EPM/EPDM vulcanizates is better than that of SBR and NR. Peroxide-cured EPM can, for instance, be exposed for 1000 h at 150°C without significant hardening. Particularly noteworthy is the ozone resistance of EPM/EPDM vulcanizates. Even after exposure for many months to ozone-rich air of 100 pphm, the vulcanizates will not be seriously harmed. EPM/EPDM vulcanizates have an excellent resistance to chemicals, such as dilute acids, alkaUes, alcohol, etc. This is in contrast to the resistance to aUphatic, aromatic, or chlorinated hydrocarbons. EPM/EPDM vulcanizates swell considerably in these nonpolar media. 

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystalforming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) can be selected for specific chemical exposures. 

The chemical resistance of celluloid is not particularly good. It is affected by acids and alkalis, discolours on exposure to sunlight and tends to harden on aging. More seriously it is extremely inflammable, this being by far the greatest limitation of the material. 

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