Phosphate coatings heating

Znj(P04)2 4H2 0 appears in three crystal forms, a-hopeite (rhombic plates), 3-hopeite (rhombic crystals), and p-hopeite (triclinic crystals). Their transition points are at 105, 140 and 163°C respectively. It has been observed that zinc phosphate coatings heated in the absence of air lose their corrosion resistance at between 150 and 163°C. 

Manganese phosphate coatings heated in the absence of air lose their corrosion resistance at between 200 and 218°C. At these temperatures, between 75 and 80% of the water of hydration is lost and it is assumed that this results in a volume decrease of the coating which causes voids and thereby lowers the corrosion resistance. Fig. 15.4 shows the loss of water of hydration from zinc, iron and iron-manganese phosphate coatings. 

The loss of water from conventional zinc and managanese phosphate coatings heated in air is from 10 to 20% higher than the loss on heating in the absence of air. It is thought that this greater loss may be due to oxidation of the iron phosphate present in the coatings. 

Insoluble Ammonium Polyphosphate. When ammonium phosphates are heated ia the presence of urea (qv), or by themselves under ammonia pressure, relatively water-iasoluble ammonium polyphosphate [68333-79-9] is produced (49). There are several crystal forms and the commercial products, avaUable from Monsanto, Albright WUson, or Hoechst-Celanese, differ ia molecular weight, particle size, solubUity, and surface coating. Insoluble ammonium polyphosphate consists of long chains of repeating 0P(0)(0NH units. 

An MS tank with a wall thickness of 3-4 mm, having a heating arrangement and a thermostat temperature control will be required. No protective lining is necessary as the phosphate coating itself is protective. 

Fig. 15.4 Effecl of heating on phosphate coatings for 16 h at various temperatures, showing loss of water of hydration. Curve A zinc phosphate, B iron phosphate and C iron manganese phosphate (courtesy y./.S./., 170, II (1952))...

Electrochemical methods applied to deposit calcium phosphate coatings require an electrical conductor as a substrate as well as post-depositional heat treatment (Abe, Kokubo and Yamamuro, 1990). Hence, they are not well suited to coat non-conducting ceramics and heat sensitive polymers. 

Luo, Cui and Li (1999) addressed the problem of temperature sensitivity of IBAD of ACPs and their subsequent crystallisation forming hydroxyapatite. Post-depositional annealing temperatures were decreased to 400 °C. The crystallisation of calcium phosphate coating is a hydroxyl ion diffusion-controlled process, thought to be the mechanism responsible for the decrease of the crystallisation temperature. The detailed study of the crystallisation process of calcium phosphate coatings shows that the crystallinity of the hydroxyapatite coating can be well controlled by adjusting the post-heat-treatment time. 

Blalock, T., Bai, X., and Rabiei, A. (2006) A study on microstructure and properties of calcium phosphate coatings processed using ion beam assisted deposition on heated substrates. Surf. Coat. Technol., 201 (12), 5850-5858. 

Triphenyl phosphate [115-86-6] C gH O P, is a colorless soHd, mp 48—49°C, usually produced in the form of flakes or shipped in heated vessels as a hquid. An early appHcation was as a flame retardant for cellulose acetate safety film. It is also used in cellulose nitrate, various coatings, triacetate film and sheet, and rigid urethane foam. It has been used as a flame-retardant additive for engineering thermoplastics such as polyphenylene oxide—high impact polystyrene and ABS—polycarbonate blends. 

Anhydrous monocalcium phosphate, Ca(H2PObe made in a pan mixer from concentrated phosphoric acid and lime. The high heat of reaction furnishes essentially all the necessary thermal input and subsequent drying is minimized. A small amount of aluminum phosphate or a mixture of sodium and potassium phosphates is added in the form of proprietary stabilizers for coating the particles. Heat treatment converts the coating to a protective polyphosphate (19). 

As with chemical etches, developing optimum conversion coatings requires assessment of the microstructure of the steel. Correlations have been found between the microstructure of the substrate material and the nature of the phosphate films formed. Aloru et al. demonstrated that the type of phosphate crystal formed varies with the orientation of the underlying steel crystal lattice [154]. Fig. 32 illustrates the different phosphate crystal morphologies that formed on two heat-treated surfaces. The fine flake structure formed on the tempered martensite surface promotes adhesion more effectively than the knobby protrusions formed on the cold-rolled steel. 

The flame retardant mechanism for phosphorus compounds varies with the phosphorus compound, the polymer and the combustion conditions (5). For example, some phosphorus compounds decompose to phosphoric acids and polyphosphates. A viscous surface glass forms and shields the polymer from the flame. If the phosphoric acid reacts with the polymer, e.g., to form a phosphate ester with subsequent decomposition, a dense surface char may form. These coatings serve as a physical barrier to heat transfer from the flame to the polymer and to diffusion of gases in other words, fuel (the polymer) is isolated from heat and oxygen. 

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