Sintering microwave ceramics

The microwave ceramics discussed so far are prepared by sintering pellets of pressed power. Usually, the sintering temperatures are very high (typically around 1200 to 1500°C)... 

J. D. Katz, Microwave sintering of ceramics. Annual Review of Materials Science, 22, 153-170 (1992)... 

The primary interest in microwave sintering of ceramics has been in the promise of microstructural engineering of particular materials. For example, microwave sintering of SrO- and MgO-doped LaGaOs... 

Keywords Sintering Microwave dielectric ceramic. Dielectric resonator. 

R. Umemura, H. Ogawa, A. Yokoi, H.Ohsato, A. Kim, Low-temperature sintering-microwave dielectric property relations in Ba3(V04)2 ceramic, J. Alloys Compd. 424 (2006) 388-393. 

The ultimate goal is to simulate the densification of the ceramics during microwave sintering. Microwave sintering is different from the conventional sintering in certain aspects, e.g., inhomogeneity of temperamre distribution in the materials [84]. There have been only limited attempts to simulate the temperamre-... 

Katz JD (1992) Microwave sintering of ceramics. Annu Rev Mater Sci 22 153-170... 

Iskander MF, Smith RL, Andrade AOM, Kimrey H, Walsh LM (1994) FDTD simulation of microwave sintering of ceramics in multimode cavities. TREE Trans Microw Theory Tech 42 793-800... 

Microwave sintering of ceramics is quite straightforward. The ceramic body, usually contained in nonabsorbing or weakly absorbing insulation such as loose, nonconducting powder, is placed within a microwave cavity. It is possible to use... 

D. Agrawal, Microwave Sintering of Ceramics, Composite, Metals, And Transparent... 

D. Agrawal, J. Cheng and R. Roy, "Microwave Sintering of Ceramics, Composites and Metal Powders Recent Development." Innovative Processing/Synthesis Ceramics, Glasses, Composites IV, Am. Ceramic Soc.Publ., p. 273 - 284, (2000). 

Agrawal D. Microwave sintering of ceramics, composite, metals, and transparent materials. Journal of Material Education 1999 19 49-58. 

An additional conclusion which may be drawn from these results is the importance of homogeneity with respect to the density of green samples. A lack of such homogeneity may account for some of the non-uniform heating experienced by researchers attempting to microwave sinter green ceramic pieces (see section 7.5). 

The accurate measurement of sample temperature during heating by a microwave field is seen as one of the major problems to be overcome for the successful exploitation of microwave ceramic processing. Infra-red pyrometry has been used extensively to date, particularly when a single mode applicator forms the basis of the sintering system. However, this technique suffers from the disadvantage that only the surface temperature of the samples is recorded. 

Despite the widespread view discussed above that ceramic materials are essentially transparent to microwave frequencies, perhaps the greatest amount of research effort in the field of microwave ceramic processing is concerned with firing or sintering. Most of this effort, however, has occurred over the last 5 years with a large number of ceramic systems now having received attention. 

The use of plasmas to assist In the sintering of ceramic materials weis first reported by Sennet et A microwave-induced plasma discharge was used to sinter rods and pellets of a range of oxides in several gases at pressures between 130 and 6700 Pa. The results Indicated that plasma sintered samples displayed smaller grain sizes and greater densificatlon compared with samples conventionally sintered under similar temperature, time and atmospheric conditions. 

Johnson, D.L. and Brodwin, M.E., Microwave sintering of ceramics. EM-5890 Research Project 2730-1, Final Report. Northwestern University, Department of Materials Science and Engineering, (1988). 

Chabinsky, I.J., Microwave sintering of ceramics. Presented at the Materials Research Society Symposium, Reno, Nevada, USA. April 5-9, 1988. Not published. 

Xie, Y., Yin, S., Hashimoto, T., Kimura.H. and Sato, T. (2009) Microwave-hydrothermal synthesis of nano-sized Sn2+-doped BaTi03 powdersand dielectric properties of corresponding ceramics obtained byspark plasma sintering method. Journal of Materials Science, 44, 4834—4839. 

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

Perovskites AB)/3C2/303 (A = Ba, Sr, B = Zn, Mg, Co, Ni C = Nb, Ta) are promising compounds for microwave applications. It is important to synthesize these complex oxides as pure perovskite phases because the slightest admixture of a second phase hinders drastically the dielectric properties of ceramics, which sinter only at very high temperatures (1400 to 1500°Q. The precursor chemistry resembles greatly that of BaTi03 formation by alkoxide or alkoxide-hydroxide routes. Below we summarize the 3 approaches to the synthesis of these perovskites by the sol-gel method ... 

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