Ceramics, sintered

AI2O3 and Zr02 are considered to be nonbioactive ceramics and are frequently used as the articular heads of total arthroplasties such as total hip prostheses, total shoulder prostheses, and maxillar articular replacements. No unwanted biological effects could be observed in vivo, and no cytotoxic effects have been evidenced in vitro for both compounds except for some formation of granuloma around wear particles of these materials. Oonishi et al. (1997) have also shown small amounts of new bone formation between AI2O3 particles in an experimental rabbit femoral defect model. 

---

Abrasives. Abrasive materials are either bonded or coated. Bonded phenoHc abrasives have superior strength and shock resistance compared to sintered ceramic compositions. The higher stabiUty permits higher rotational speeds for resin-binder wheels however, temperatures are lower than with ceramic wheels. 

Conventional Sintering. Ceramic sintering is usually accompHshed by heating a powder compact to ca two-thirds of its melting temperature at ambient pressure and hoi ding for a given time. Densification can occur by soHd-state, Hquid-phase, or viscous sintering mechanisms. 

If the temperature and supersaturation are sufficiently high in a CVD reaction, the product is primarily powder precipitated from the gas phase (see Ch. 2). Such powders have few impurities provided that the CVD precursors are carefully purified. Their small diameter and great uniformity are important factors in the production of high quality hot-pressed or sintered ceramic bodies with good mechanical and electrical properties. In addition, the sintering temperatures required for CVD powders are lower than those for conventional powders. 

Fig. 3.5.8 Schematic and NMR image of C4F8 gas at 80 kPa in a hybrid phantom containing Vycor glass, a nanoparticulate AI2O3 powder, a nanoparticulate ZnO powder and sintered ceramics made from each of these powders. Dashed boxes indicate the regions of interest (ROIs) from which the isotherms in Figure 3.5.9 were extracted. Adapted from Ref. [21].

A. Caprihan, C. F. M. Clewett, D. O. Kuethe, E. Fukushima, S. J. Glass 2001, (Characterization of partially sintered ceramic powder compacts using fluori-nated gas NMR imaging), Magn. Reson. Imag. 19, 311-317. 

Kumar A, Devi PS, and Maiti HS. A novel approach to develop dense lanthanum calcium chromate sintered ceramics with very high conductivity. Mater. Chem. 2004 16 5562-5563. 

Plasma reactors, for CVD, 5 807-808 Plasma sintering, ceramics processing, 5 663... 

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... 

T0169 Clemson University, Sintered Ceramic Stabilization... 

T0160 Chemfix Technologies, Inc., Chemfix Solidification/Stabilization Technology T0162 Chemical Precipitation of Metals—General T0169 Clemson University, Sintered Ceramic Stabilization... 

T0088 Battelle Pacific Northwest National Laboratory, Terra-VIT Vitrification Technology T0151 Ceramic Immobilization of Radioactive Wastes—General T0169 Clemson University, Sintered Ceramic Stabilization T0178 Constructed Wetlands—General... 

The U.S. Department of Energy (DOE) is researching technologies for the stabilization and immobilization of fly ash contaminated with radionuclides and metals that will reduce waste material volume and consistently satisfy regulatory requirements. The Mixed Waste Focus Area (MWFA), a DOE/EM-50 program, has stated the need for improved stabilization methods that would accept higher ash waste loadings. To address these issues, the MWFA has invested in a sintered ceramic stabilization technique developed by Clemson University. 

Microwave energy has been widely used to process and sinter ceramics and the following advantages compared to conventional heating have been quoted4 ... 

For second-phase sintered ceramics, these phases control the plasticity and they are responsible for the asymmetric behaviour when deformed in tension or compression, because there is a crucial difference in the microstructure evolution associated with tension and compression creep. There are few explanations for this asymmetry. 

---