Self-Propagating High-Temperature Synthesis (SHS) is an alternative for producing a wide variety of light-weight intermetallic compounds, ceramics and composite materials. The method [1] is exothermic and after ignition the reaction proceeds as a reaction front travelling at speeds of 10-250 mm/s through a compacted powder sample with reaction front temperatures of up to several thousand degrees (Figure 113). The procedure is inexpensive and has large potential for industrial applications. Limited information is available on the actual mechanisms and products involved because of the high temperatures and the fast reactions.

Although pioneering work has been performed at second generation synchrotron X-ray sources [2], these early studies were complicated by limited counting statistics and access only to the surface regions of the sample.

The Materials Science Beamline, ID11, has now been used to study the exothermic reactions of the systems Al-Ni, Al-Ni-C-Ti and Ti-C [3]. Circular pellets of equal amounts of Al, Ni, C and Ti were produced by compressing the powder mixtures using a steel die to about 45% of maximum density. The pellets were 20 mm in diameter and about 2 mm in thickness. The powder samples were ignited by passing a current through a tungsten wire attached to one side of the pellets. An X-ray beam of dimensions 0.2*0.2 mm at a wavelength of 0.295 Å produced by an in-vacuum undulator of 138 magnetic poles and a gap of 8 mm was centred on the middle portion of the sample. X-ray diffraction patterns were collected every 100 ms. 25 ms of exposure time and 75 ms of readout time from a 1024*1024 pixel FRELON CCD camera gave a sequence of diffraction patterns of the reaction as the reaction front passed the X-ray beam. The experimental setup is illustrated in Figure 114.

A sequence of the changes of the patterns is illustrated in Figure 115. for the system Al-Ni-Ti-C. The start of the reaction involves the melting of the Al and the reaction proceeds through an intermediate ternary phase with the life-time of 400-500 msecs. The final products aluminumnickelide and titaniumcarbide finally stabilises 4.3 secs after the onset of the reaction.

These studies firmly establishes synchrotron radiation experiments at the brilliant third generation sources as a new important tool for studies of a large class of solid-state reactions on a millisecond timescale. Other studies of potentially interesting industrial processes are under way.

References
[1] Z.A. Munir, U. Anselmi-Tamburini, Materials Science Report, 3, 277-365 (1989).
[2] and references within: J.F. Javel, M. Dirand, J.J. Kuntz, F.Z. Nassik, J.C. Gachon, J. of Alloys and Compounds, 247, 72-81 (1997).
[3] C. Curfs, I.G. Cano, G.B. Vaughan, M.A. Rodriguez, X. Turrillas, Int. J. of Self-Propagating High-Temperature Synthesis (1999), in press.

Authors
C. Curfs (a), Á. Kvick (a), G.V. Vaughan (a), I.G. Cano (b), M.A. Rodriguez (b), X. Turrillas (c).

(a) ESRF
(b) Instituto de Ceramica y Vidrio, Madrid (Spain)
(c) Instituto Eduardo Torroja, Madrid (Spain)