The kinetics and mechanisms of combustiain reactions in the Ti-C and Ti-C-Ni systems were studied. Samples were produced by igniting compacts of elemental Ti, C, and Ni powders with a tungsten heating coil under an inert argon atmosphere. Using an elementary model aif the process, the "apparent" activation energies of these highly exothermic reactions were determined by measuring combustion wave velocities and combustion temperatures. For the Ti + C 3 TIC reaction, two different combusition regimes were found. The first, for combustion temperatures greater than 2711 K, was postulated to be controlled by the dissolution of carbon into a titanium melt with an apparent activation energy of 124 f 31 kJ . mol-'. The second, for combustion temperatures less than 2711 K, was postulated to be controlled by the diffusion of carbon through1 a solid T i c layer with an apparent activation energy of 364 2 25 kJ . mol-'. For the reaction Ti + C + 25 wt% Ni 3 T i c + 25 wt% Ni the apparent activation energy was meawred to be 133 f 50 kJ . mol-', corresponding to the dissolution of carbon into a Ti-Ni melt. Temperature profile and microstructural information are also presented. [

Phase equilibrium relations in the celsian-silica-alumina portion of the system Ba0-A1203-SiOz were revised on the basis of data obtained from isothermal firing and from the quenching method. These data verify the existence of a celsian-silica compatibility join by reducing the extent of the mullite field shown in previous diagrams and extending the boundaries of the celsian primary field. The system celsian-silica-alumina is divided into two ternary subsystems, one having a eutectic point and the other an invariant reaction point. The eutectic for the subsystem celsian-silica-mullite is located a t BaO 19, Al,0,3 15, and SiO, 66 we% and 1296°r30C. The pertinent invariant point for the subsystem celsian-mullite-alumina, located a t BaQ 26, Al2O3 27, and Si02 47 wt% and 1554"+4OC, is a reaction point.

EXENT studies in this laboratory' indicate that the ternary K phase relations in the system BaO-AlzOn-SiOz, as currently depicted in the literature," need revision. It is the purpose of this and others in a series of papers' "J to provide an experimental basis for revising the Ba0-A120,1-Si0, phase diagram. This study presents the results for the system celsianalumina and the join celsian-mullite. The resulting diagrams are compared with the corresponding diagrams deduced from the Ba0-A120,,-Si0, diagram of Toropov et al. ' The starting materials were the crystalline end-members, celsian, mullite, and corundum, prepared from the chemically pure oxides or carbonates. Batches were homogenized by manual grinding followed by ultrasonic mixing under acetone. The compositions studied are shown in Figs. 1 and 2, with the most significant quenching runs depicted. These samples were fired in accordance with the standard quenching technique," with the exception that the starting batches were not vitrified due to the high firing temperatures necessary. For the quenching runs, firing temperatures in a vertical tube furnace were controlled and measured with calibrated Pt-Rh thermocouples. The quenched samples were analyzed for crystalline products by X-ray diffraction and petrographic microscopy.The equilibrium diagram for the join celsinn-mullite, determined experimentally in this work, is shown in Fig.