Phosphate fluoride surface treatment

The effect of a 3-day water boil on the strength of adhesive specimens of the PPQ in structure 4 is summarized in Table 6. The phosphate fluoride surface treatment is sensitive to moisture and this is reflected in low strengths after 3-day water boil. The anodized surface is significantly more resistant to moisture than the phosphate fluoride surface, but the PPQ apparently absorbed water after the 3-day water boil and became plasticized, exhibiting what appeared to be thermoplastic failure at 288 C. This was surprising since PPQs gen-... 

The general sequence of surface preparation for ferrous surfaces such as iron, steel, and stainless steel consists of the following methods degreasing, acid etch or alkaline clean, rinse, dry, chemical surface treatment, and priming. The chemical surface treatment step is not considered a standard procedure, but it is sometimes used when optimum quality joints are required. It consists of the formation of a corrosion-preventing film of controlled chemical composition and thickness. These films are a complex mixture of phosphates, fluorides, chromates, sulfates, nitrates, etc. The composition of the film may be the important factor that controls the strength of the bonded joint. 

More recent work with the PPQ in Eq. (3) has involved chromic acid and phosphoric acid anodized Ti surface treatments, which result in better moisture resistance but less thermal resistance than the surface from phosphate fluoride treatment. Chromic acid anodized Ti TSS provided strengths of 5000 psi at 25°C (cohesive failure), 2,000 psi at 232°C after 5,000 hours at 232°C in air (mixed failure) and low strengths at 232°C after 10,000 hours at 232°C in air (100% adhesive failure).An anodized Ti surface degrades when bonding temperatures approaching 370 C are employed. This may have been one of the factors which caused lower strengths at 232 C after aging. 

Beside the chemical treatment, anodizing is an effective treatment method too. The magnesium part is the anode in an electrochemical cell and dissolves into magnesium ions. Together with electrolyte, a defined oxide and hydroxide layer is formed on the magnesium surface. If phosphates, fluorides, sflicates, or chromates are present in the electrolyte they will be incorporated into the surface layer. 

Calcium phosphate has become a common problem with the increase in treatment of municipal waste-water for reuse. Surface waters can also contain phosphate. Calcium phosphate compounds can contain hydroxyl, chloride, fluoride, aluminum, and/ or iron. Several calcium phosphate compounds have low solubility, as shown in Table 7.2. Solubility for calcium carbonate and barium sulfate are also shown by comparison. The potential for scaling RO membranes with the calcium phosphate compounds listed in Table 7.2 is high and will occur when the ion product exceeds the solubility constant. This can occur at orthophosphate concentrations as low as 0.5 ppm. Sodium softening or antisealants together with low pH help to control phosphate-based scaling. 

Cr/alumina exhibits a "fast" kinetics profile that is quite different from that of Cr/silica. The polymerization rate develops rapidly, especially when the alumina has been acidified by treatment with silica, fluoride, phosphate, or sulfate. Cr/alumina exhibits polymerization kinetics similar to that of Cr/AlP04, a topic that is discussed in Section 15. The polymerization rate rises quickly when ethylene is added, but later it tends to decay slowly. The rapid initial rise indicates that reduction of Cr(VI), or desorption of redox by-products, and/or alkylation of the chromium, may be more facile on alumina than on silica. Alumina is known as a strong adsorbent in its own right, so that adsorption of by-products from chromium onto the neighboring surface is one possible contributing cause of the rapid development of polymerization rate. 

Various formulations for dental treatment incorporate polymerised phosphonates, which offer certain advantages over phosphates (Section 12.13). Polyvinyl phosphonic add (12.157) and polyethylene phosphonate (12.159) are adsorbed as monolayers on tooth enamel where they resist decay [29]. Copolymers of vinylphosphonic acid and vinylphosphonyl fluoride (12.201) are also adsorbed on tooth surfaces and provide extra resistance to decay by slowly releasing F which can substitute in the tooth hydroxyapatite [30]. 

Chromate conversion solution consists of chromic acid H2Cr04 or H2Cr207, chromate salts and certain activator ions such as sulfates, chlorides, fluorides, phosphates and complex cyanides with pH around 1 2. As the solutions for chromate conversion treatment are acidic which cause the dissolution of Mg into the solutions as Mg, there is a local rise in pH in the immediate vicinity of the metal-solution interface. Mg ions combine with chromate ions to form a compound that is insoluble at the locally higher pH region. This compound precipitates on the metal surface as an adherent coating. Chromate conversion treatment is a very fast process (30-60 s) and can... 

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