Calcium oxide is the main ingredient in conventional Portland cements. Since limestone is the most abundant mineral in nature, it has been easy to produce Portland cement at a low cost. The high solubility of calcium oxide makes it difficult to produce phosphate-based cements. However, calcium oxide can be converted to compounds of reduced solubility such as silicates, aluminates, or even hydrophosphates, which then can be used in an acid-base reaction with phosphate, forming CBPCs. The cost of phosphates and conversion to the correct mineral forms add to the manufacturing cost, and hence calcium phosphate cements are more expensive than conventional cements. For this reason, their use has been largely limited to dental and other biomedical applications. Calcium phosphate cements have found applications as structural materials, but only when wollastonite is used as an admixture in magnesium phosphate cements. Because calcium phosphates are also bone minerals, they are indispensable in biomaterial applications and hence form a class of useful CBPCs that cannot be substituted by any other.

Calcium and magnesium oxides are constituents of nearly all glasses and may be determined using EDTA titration. Neither determination is free of interference.

If the glass contains lead and/or barium oxide, the glass should be treated with a mixture of hydrofluoric and sulfuric acids and the insoluble lead and barium sulfates filtered off before the titration. Lead may also be precipitated with hydrogen sulfide. Small amounts of aluminum and iron may be masked with triethanolamine. Greater amounts of aluminum and iron must be preseparated by precipitation as their hydrated oxides in the procedure for gravimetric determination of alumina. If the content of iron oxide, alumina, and titania is large, they can be separated using a 25% solution of urotropin.

In the cement containing MgO the expansion is low up to about 4% addition, after which a steep increase occurs. The expansion values are much higher in disks containing CaO. A molar expansion of 90% for the reaction CaO→Ca(OH)2 compared with 117% for the MgO→Mg(OH)2 reaction cannot explain these differences. If expansions are compared on equivalent molar basis (1 g CaO=0.018 mol and 1gMgO=0.0248 mol), MgO would be expected to show more expansion. It appears that the particle size of the oxides, the crystalline dimensions, and crystalline growth pressures, may be important factors influencing the overall expansion. These results also reveal that in specifications for unsoundness of cement the limitations should be based on the potential expansive nature of CaO and MgO and not just on MgO.

At 4% MgO, the prism expands by about 0.75%, close to the limit specified by ASTM. At this concentration, the expansion in the disk is much higher, being 2.4%. The results demonstrate that disks are much more sensitive to autoclave treatment than the prisms, providing an alternate technique for the determination of unsoundness in cements.