Glass-Ceramic Microspheres

Glass-ceramic microspheres (solid or hollow, 1-100 pm) are finding increasing usage in a range of industrial products, which include plastics, sealants, adhesives, paints and buoyancy materials [65]. 

These spheres will lower the density of a product and improve its viscosity and thermal insulator value. Surface gloss, abrasive resistance, oil and water absorption and other properties can be modified. 

Although phosphates have usually been absent from most reported products, fired hollow ceramic spheroids made from AlP04/Na2Si03/Kaolin/Al203 compositions have been patented [66]. Microcellular siliceous materials have been synthesised and phosphates may prove to have important application in this field. Very-low-density (-0.003 g/cc) silica aerogels may have their AIPO4 counterparts. Phosphate-bonded silica microspheres are promising materials [67,68]. 

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Glass-ceramic Microspheres Impart Yellow Color to Retroreflected Light US Patent 6,479,417, 12 November 2002. 

Phosphate glass ceramic microspheres impregnated with radioactive [40] P are used in some radiation treatments (Chapter 13.5). 

Syntactic foams have been made from organosilicone polymers and glass, ceramic, or polymer microspheres 23,100). They are used mainly for heat insulation and ablation coating101). For the latter, the two components are sprayed together onto the exterior of rockets, and cold setting silicone glues are used to improve ablation102). Syntactic materials with carbon microspheres and silicones have also been proposed 39>. 

Still other ceramics are important in medicine. For example, they are used to febricate artificial bones and to crown damaged teeth. The feet that many ceramics can be easily sterilized and are chemically inert makes ceramic microspheres made of these materials useful as biosensors. Drugs and other chemicals can be carried within microsphere pores to desired sites in the body. SEE ALSO Glass Minerals Semiconductors Superconductors. 

Rather conventional means for the manufacturing of hollow microspheres with diameters between 1 and 1000 pm have been developed [11.9]. Methods include spray drying and dripping as well as emulsion or suspension techniques. The microspheres feature low effective and bulk densities coupled with high specific surfaces. Typical wall thicknesses are in the range 1-10% of the diameter. Potential wall materials include glass, ceramic and mixed oxides, silicates and aluminosilicates, polymers and polycondensates, and metals. Surface phenomena, which may be modified by chemical reactions, additives, and/or post-treatments, play an important role for microsphere formation, properties, and stability. Fig. 11.12 is the photomicrograph of a calcined hollow microsphere [11.9]. 

Another approach to decrease slurry weight can be to add light solids like coal, asphaltite minerals, hollow glass, or ceramic microspheres. Finally, foams can be prepared using air or nitrogen and a cement slurry as the continuous phase to densities as low as 0.8 g/cm3 (24). 

Wood is the most appropriate material for a solid sandwich core and has been used extensively for many applications, such as doors and partitions. For lightweight constructions flat or end grain balsa is still used, although this is being superseded by synthetic materials. Bonded microspheres of inorganic materials, glass, ceramics, etc. to form syntactic foams are useful core materials. 

FIGURE 14.1.27 Hysteresis loops of magnetite-containing glass-ceramic, and magnetite microspheres prepared using a high-frequency induction thermal plasma technique and a solution process. 

Materials/characteri sties Clays, calcium carbonates, talc, silicates. Pigments such as titanium dioxide and carbon black may also have a reinforcing effect. Glass or ceramic microspheres can also offer good properties. 

Mondal, T., Sunny, M.C., Khastgir, D., et al., 2012. Poly (L-lactide-co-epsilon caprolactone) microspheres laden with bioactive glass-ceramic and alendronate sodium as bone regenerative scaffolds. Materials Science and Engineering C 32, 697-706. 

Rapid Thermal Decomposition of Solutions (RTDS) process, 6 850 Rapid thermal processing sintering ceramics processing, 5 663 Rare-earth alloys, 23 262 economic aspects of, 74 645 Rare earth aluminosilicate (REAS) glass microspheres, 72 612... 

Syntactic foamed plastics (from the Greek ovvxa C, to put together) or spheroplastics are a special kind of gas filled polymeric material. They consist of a polymer matrix, called the binder, and a filler of hollow spherical particles, called microspheres, microcapsules, or microballoons, distributed within the binder. Expoxy and phenolic resins, polyesters, silicones, polyurethanes, and several other polymers and oligomers are used as binders, while the fillers have been made of glass, carbon, metal, ceramics, polymers, and resins. The foamed plastic is formed by the microcapsular method, i.e. the gas-filled particles are inserted into the polymer binder1,2). 

The filler microspheres may be glass, polymeric, carbon, ceramic, or metallic. However, the main requirements are that the microspheres are spherical, non-cohesive, strong, intact, moisture and chemically resistant, and hydrolytically stable. They should be... 

Glass, carbon, ceramic, quartz, and polymer microspheres together with inorganic materials such as cement, gypsum, lime, and metals have all been used as fillers37> 88). 

Entrapment provides an alternative to covalent immobilization. IVpically, cells are entrapped in a porous matrix and the cells grow throughout the pores/media to result in high cell densities. Cells may be added to the matrix at the time it is formed, or may be added after matrix formation. Many matrices have been used for entrapment including agarose beads, ceramics and silica, collagen microspheres, polyacrylamide, controlled pore glass, and various membranes [68, 69]. Membrane retention of cells, which has been used for biosensors (table 8.7) is, per se, not an immobilized system since the cells are... 

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