Calcium-based composites

Calcium-based composites rely on their similarity to the mineral component of natural bone— hydroxyapatite (HA). The theory behind their use is that the body will see these materials as tissues that need to be remodeled, allowing them to be integrated with and then replaced by bone. Tricalcium phosphate [TCP, Ca3(P04)2], calcium sulfate [plaster of paris, CaS04], and hydroxyapatite [Ca,o(P04)s(OH)2] are all currently being used to fill bony deflects and stimulate or direct bone formation. Calcium suifate has been used for over a century due to its ready availability and bio-... 

Table 5 Composition of Ammonia, Sodium, Magnesium, and Calcium Base Sulfite Pulping Liquors...

Insulation fiberglass is glass wool used for thermal and acoustic insulation of homes, commercial buildings, industrial equipment, and automobiles. It has a sodium aluminoborosilicate-based composition, often with additional modifiers, such as calcium, magnesium, and potassium, which vary by... 

Domb, A. J., Manor, N., Elmalak, O. (1996). Biodegradable bone cement compositions based on acrylate and epoxide terminated poly(propylene fumarate) oligomers and calcium salt compositions. Biomaterials, 77,411-417. 

The biocompatible CBPC development has occurred only in the last few years, and the recent trend has been to evaluate them as biocompatible ceramics. After all, biological systems form bone and dentine at room temperature, and it is natural to expect that biocompatible ceramics should also be formed at ambient temperature, preferably in a biological environment when placed in a body as a paste. CBPCs allow such placement. We have discussed such calcium phosphate-based cements in Chapter 13. Calcium-based CBPCs, especially those constituting hydroxyapatite (HAP), are a natural choice. HAP is a primary mineral in bone [3], and hence calcium phosphate cements can mimic natural bone. Some of these ceramics with tailored composition and microstructure are already in use, yet there is ample room for improvement. This Chapter focuses on the most recent biocompatible CBPCs and their testing in a biological environment. To understand biocompatible material and its biological environment, it is first necessary to understand the structure of bone and how it is formed. 

Since bone contains mainly calcium phosphate compounds, and in particular HAP as the major mineral, calcium-based CBPC materials can provide the necessary bone composition. 

Mold fluxes are routinely used in both continuous casting and bottom pouring of steel. These fluxes are generally calcium silicate based compositions with alkali oxides [(Li, Na, K)20] and fluorides [CaF2, NaF] added as fluidizers. The compositions frequently use fly ash as the base material because it provides a significant concentration of silica in a prefused form easily dissolved as the powder melts on the liquid steel. 

In the 5 years that followed (1965-70), three additional producers—American Potash, National Lead, and Pittsburgh Plate Glass—opened chloride-process plants. Sales of composite titanium calcium-base pigments continued to drop, as they had done over the previous 5 years in which Du Pont had ceased to produce them. This was due primarily to their adverse effect upon the stability of latex systems and the rapid replacement of alkyd and oleoresinous flat wall paints by flat latex paints. Two so-called "maximum-durability" pigments were introduced during this period—one by Du Pont and the other by National Lead. These pigments, although produced by different methods, both essentially eliminated the photochemical reactivity of the base titanium dioxide. 

Thermal expansion-contraction of inorganic fillers is much lower compared with that of plastics. Therefore, the higher the filler content, the lower the coefficient of expansion-contraction of the composite material (see Chapter 10). Many inorganic nonmetallic fillers decrease thermal conductivity of the composite material. For example, compared with thermal conductivity of aluminum (204 W/deg Km) to that of talc is of 0.02, titanium dioxide of 0.065, glass fiber of 1, and calcium carbonate of 2-3. Therefore, nonmetallic mineral fillers are rather thermal insulators than thermal conductors. This property of the fillers effects flowability of filled plastics and plastic-based composite materials in the extruder. 

As rubber has a much better coefficient of friction compared with polyoleflns, it might be helpful to add rubber powder or small particles into, say, HDPE-based composite matrix. Coarse grades of calcium carbonate could serve the same purpose (this would be again a certain trade-off in properties of the flnal composite material). Additional benefits can be obtained if the same additive/ filler enhances both friction and impact resistance (a rubber might be a good candidate in this case). 

Alexander H., Parsons J.R., Ricci J.L., Bajpai P.K., and Weiss A.B. 1987. Calcium-based ceramics and composites in bone reconstruction. Crit. Rev. 4 43—47. 

A.H. Schuurs, R.J. Gruythuysen, P.R. Wesselink, Pulp capping with adhesive resin-based composite vs calcium hydroxide a review. Ended. Dent. Traumatol. 16 (2000) 240-250. J. Ward, Vital pulp therapy in cariously exposed permanent teeth and its limitations, Aust. Endod. J. 28 (2002) 29-37. 

Low KL, Tan SH, Zein SH, Roether JA, Mourino V, Boccaccini AR. Calcium phosphate-based composites as injectable bone substitute materials a review. J Biomed Mater Res B Appl Biomater 2010 94B(1), 273-286. 

Ignjatovic, N., Plavsic, M., Miljkovic, M., Zivkovic, Lj., and Uskokovic, D., Microstructural characteristics of calcium hydroxyapatite/poly-L-lactide based composites, J. Microsc., 196, 243-249, 1999. 

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