Solid State Chemistry


 Microwave Syntheses in the Solid State

 © G. Whittaker, 1994 & 2007. This work, or extracts from this work may be reproduced only with the written permission of the author.

 In addition to the physical changes induced in ceramic materials, the microwave dielectric losses of many solid compounds may be used to provide sufficient heat to drive chemical changes. This is particularly true of a number of metal oxides. The high loss factor of copper oxide, for example, has been used alongside those of other materials to synthesise the high Tc superconductor YBa2Cu3Ox . A number of other materials also display excellent heating properties, for example boron and carbon, and whilst they may be used in conjunction with other lossy materials, their heating characteristics are good enough that they may be used as the only significant microwave absorber. In many cases, the microwave induced reactions require only a small percentage of the conventional syntheses. A summary of some of the published reactions is shown in Table 1






V2O5+ C


5min / 500W


V2O5+ 2C


20min / 500W


U3O8+ C


5 min / 500W


Fe3O4+SrCO3 +La2O3


36 min / 500W


Cr + B


27 min (3 stages) 500W


Zr + 2B


5 min / 500W


Cu + In + 2S


1+3+3 min / 400W


Cu + In + 2Se


1+3+3 min / 400W


 Table 1 Inorganic solid state reactions under microwave irradiation


 The use of metals as microwave absorbent materials in solid state reactions is a special case with problems of its own. The improved syntheses of metal chalcogenides under microwave irradiation132 from my own work have been adapted for rapid syntheses of the semiconducting ternary sulphides CuInS2 CuInSe2 and CuInSSe.131, 133 The use of metals has also been recently reported in the synthesis of transition metal borides.

 Other work in this area includes the synthesis of submicron powders. Taking barium and titanium acetates in a 0.4M solution, microwave irradiation first gave a gel, and on further irradiation was pyrolysed via a dark brown phase to give submicron BaTiO3 powder.134 A more general alternative to this method uses a microwave plasma to produce powders from rapid indirect heating of aqueous solutions. A low pressure microwave induced plasma is fed with an aerosol formed from a suitable solution - usually contains the metal nitrate, although chlorides or even suspensions may be used.135 Vaporisation of the solvent and subsequent chemical changes lead to the formation of nanometre-sized particles of ceramic oxides. By using mixed salts, for example, it is possible to form zirconia based ceramics such as (ZrO2)0.77(Y2O3)0.03(Al2O3)0.20.136




 120. C.E. Holcombe & N.L. Dykes. J. Mat. Sci. Lett.9, 425 (1990).

 121. H.D. Kimrey, M.A. Janney & M.K. Ferber. Ceramic Technology Newsletter20, 3 (1988).

 122. S. Das & T.R. Curlee. Amer. Ceram. Soc. Bull.66, 1093 (1987).

 123. C. Shibata & H. Tamai. J. Microwave Power and Electromagnetic Energy25, 81 (1990).

 124. R.B. James, P.R. Bolton, R.A. Alvarez, W.H. Christie & R.E. Valiga.J. Appl. Phys.64, 3243 (1988).

 125. S. Komenarni & R. Roy. Materials Lett.4, 107 (1986).

 126. D. Palaith, R. Silberglitt, C.C.M. Wu, R. Kleiner & E.L. Libelo.MRS Symp. Proc.124, 255 (1988).

 127. H. Fukushima, T. Yamanaka & M. Matsui. MRS Symp. Proc.124, 267 (1988).

 128. D.R. Baghurst. Chemical Applications of Microwave Radiation Oxford, , (1993).

 129. D.R. Baghurst, A.M. Chippendale & D.M.P. Mingos. Nature332, 311 (1988).

 130. D.R. Baghurst & D.M.P. Mingos. Br. Ceram. Trans. J.91, 124-127 (1992).

 131. A.R. Barron & C.C. Landry. Science260, 1653 (1993).

 132. A.G. Whittaker & D.M.P. Mingos. J Chem Soc Dalton Trans 2751-2752 (1992).

 133. R. Kniep. Angew. Chem. Int. Ed. Engl.32, 1411-1412 (1993).

 134. W.F. Klandig & J.E. Horn. Ceramics International16, 99 (1990).

 135. D. Vollath & K.E. Sickafus. J. Mat. Sci.28, 5943-5948 (1993).