Phosphate-modified cement

Fig. 6.3. Free shrinkage strains in repair mortars, (a) Epoxy mortar, (b) Styrene Butadiene Rubber modified mortar, (c) Magnesium phosphate modified mortar, (d) Ordinary Portland cement mortar.

Ma, W., and Brown, P. (1992) Mechanical behaviour and microstractme development in phosphate modified high almnina cement. Cement and Concrete Research 22, 1092-1200. 

Ma, W., Brown, P. W., Hydration of Sodium Phosphate-Modified High Alumina Cement J. Mater. Res., 9 1291-1297 (1994)... 

The heat evolved (over 24 hrs) for calcium pyrophosphate-modified cements is shown in the calorimetric curves in Fig. 31. Phosphate additions of 10, 25, and 40% were used. The modified cements have only a minor effect on the rate of heat evolution. Progressive additions of 2Ca0 P205 reduce the total heat evolved per unit mass of sample. 

Magnesium (or magnesia) phosphate cements are based on the reaction between ignited magnesium oxide and acid phosphates, which are generally modified by the addition of ammonium and aluminium salts. The phosphates may be either in solution or blended in solid form with the magnesium oxide. In the latter form the cement is formed by mixing the powder blend with water. 

Small amounts of modified methylcellulose and mono-substituted sodium phosphate (both 0.1%), may be added to plugging cement [1766]. The mono-substituted sodium phosphate weakens the effect of calcium ions on modified methylcellulose and prevents its coagulation. Stabilization of the plugging solution and increased strength of the cement rock result. 

P. F. Tsytsymushkin, S. R. Khajrullin, A. P. Tamavskij, G. S. Glyant-seva, G. G. Iskandarova, and B. V. Mikhajlov. Plugging solution for oil and gas wells—contains plugging cement, modified methylcellulose, mono-substituted sodium phosphate and water. Patent SU 1740627-A,... 

This definition of CBCs was established by Della Roy and Rustum Roy [6,20,21]. While Della Roy emphasized formation of modified conventional hydraulic cements, Rusmm Roy used CBC to mean formation of more general ceramics made at room temperature by techniques such as ultrasonic signals in aqueous phosphate systems. We extend this generalization further to include all inorganic materials that are consolidated into a hard mass by chemical reactions and not by sintering. 

Inclusion of porosity, with the aim to improve the osteoconductivity, can be introduced by the addition of soluble inclusions such as sucrose, sodium hydrogen carbonate, sodium hydrogen phosphate (Takagi and Chow 2001), or calcium carbonate that reacts to evolve carbon dioxide (Walsh et al. 2001). These reactants produce ionic substitutions in the structure and further improve the resorbability. Another example is that of strontium, which has been shown to be incorporated at low concentrations, while higher concentrations require a heat treatment (Leroux and Lacout 2001b). Since the cement is designed to harden in the body, the composition is modified in situ by reaction with the physiological solutions. 

The zinc phosphate cement dates back to at least 1879, when Rollins reported a formulation based on syrupy orthophosphoric acid [13]. The first really satisfactory cement of this type was reported by Fleck in 1902 [14], His report described a paper based on zinc oxide that had been deactivated by heating, together with a solution of phosphoric acid modified by the inclusion of aluminium and zinc. These two approaches to moderating the reaction led to a setting process that took place at a sufficiently slow speed that a smooth paste could be prepared from the components, and there was time to apply it before hardening took place. 

Acrylic dental adhesives have been modified with a phosphate ester linkage by reaction of a glycidyl methacrylate or hydroxyethyl methacrylate with phosphorus oxychloride (158). One such product, a 3M Scotchbond, adheres to dentine as well as to tooth enamel. Adhesion to enamel can be improved in dental bonding cements by including an acryloxyalkyl- or acryloxyaryl acid phosphate component (159). Japanese products utilize an imsaturated phosphinic acid monomer to improve adhesion (160). 

These cements are based on the reaction product of phosphoric acid with other materials, such as sodium silicate, metal oxides and hydroxides, and the salts of the basic elements. Zinc phosphate is the most important phosphate cement and is widely used as permanent dental cement. It is also modified with silicones to produce dental-filling materials. Compressive strengths of up to 200 MPa are typical of these materials, which are formulated to have good resistance to water. Copper phosphates are used for similar applications, but they have a shorter useful life and are used primarily for their antiseptic qualities. Magnesium, aluminum, chromium, and zirconium phosphates are also used. ... 

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