Phosphate coatings mechanism

Liu, Y., Hunziker, E.B., Randall, N.X., de Groot, I<., and Layrolle, P. (2003) Proteins incorporated into biomimetically prepared calcium phosphate coatings modulate their mechanical strength and dissolution rate. Biomaterials, 24 (1), 65-70. 

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. 

A. (2008) Effect of substrate temperature on mechanical properties of calcium phosphate coatings. /. Biomed. Mater. Res. Part... 

Even though the microhardness of calcium phosphate coatings deposited on metallic implant substrates is not considered to be a critical performance parameter for in vivo applications it can serve to mechanically characterise the coatings and thus shed light on their integrity in service. 

Dehydration Drying temperatures for cat-aphoretic paint are on the order of 150 to 200 °C. The dehydration of hopeite occurs in two steps [34] two water molecules are lost in the temperature range of 80 to 120 °C, and the two final water molecules are lost around 250 °C. The first dehydration step is reversible and in the presence of humidity, the tetrahydrate is reformed, but the crystals are finer and the orientations are different [35]. Van Ooij and Sabata [36] have proposed that the rehydration of the dihydrate is an important mechanism in the adherence failure of phosphate coatings. The presence of Mn and Ni substitutions in the hopeite phase increases the temperature of dehydration [37, 38]. In contrast to hopeite, the phosphophyllite phase is transformed into an amorphous phase, and the dehydration is irreversible. 

To prevent corrosion, mechanical fasteners may be plated or coated in some way, again depending on the application. The most common surface treatments are zinc, nickel and cadmium. Phosphate coatings are also used but have limited corrosion resistance. 

Saber-Samandari, S., Alamara, K., Saber-Samandari, S., 2014. Calcium phosphate coatings morphology, micro-structure and mechanical properties. Ceram. Int. 40, 563—572. 

In the case of mild and alloy steels the use of phosphate coatings [126,12S-131] to impart corrosion protection has been employed since about the beginning of the present century. The function of the phosphated layer is to reduce the corrosion of the steel by providing a mechanical layer against aggressive species and such layers do not have any electrochemical or inhibiting... 

Alkyl diphenyl phosphate plasticizers can exert flame-retardant action in vinyl plastics by a condensed-phase mechanism, which is probably some sort of phosphoms acid coating on the char. Triaryl phosphates appear to have a vapor-phase action (29). 

Fitzpatrick et al. [41] used small-spot XPS to determine the failure mechanism of adhesively bonded, phosphated hot-dipped galvanized steel (HDGS) upon exposure to a humid environment. Substrates were prepared by applying a phosphate conversion coating and then a chromate rinse to HDGS. Lap joints were prepared from substrates having dimensions of 110 x 20 x 1.2 mm using a polybutadiene (PBD) adhesive with a bond line thickness of 250 p,m. The Joints were exposed to 95% RH at 35 C for 12 months and then pulled to failure. 

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