The paper examines the effect of physicochemical properties of starting boron nitride and titanium hydride on their reactive activity in the synthesis of the TiN-TiB x composite. There are kinetic data on thermal desorption of the active adsorbate from the BN surface, which precipitated from the gas mixture (20 vol.% O 2 -80 vol.% N 2 under the relative humidity of 80%). Kinetics of hydrogen release from titanium hydride in isothermal conditions and controlled rate of temperature increase in the reactive system is researched. A possible mechanism of chemical transformations of starting compounds and synthesis of the TiN-TiB x composite is considered.Materials with high hardness and wear resistance that are based on titanium nitride and transient-metal borides are of great interest for contemporary technology. Such ceramics are produced by reactive sintering under pressure or electric discharge sintering [1, 2] in self-propagating high-temperature synthesis. Physicochemcal transformations at the interface of hard and gaseous phases play an important role in the above processes; therefore, adsorption and desorption substantially contribute to their kinetics. The surface activation of reagents resulting from desorption of admixtures and chemical adsorption of a gaseous reagent on the surface of fine particles of the hard-phase reagent are inseparable stages of the synthesis to be considered to study the reaction mechanism.This study is focused on the effect of starting BN and TiH 2 on the kinetics of synthesizing titanium boride and nitride and on the mechanism of chemical transformations. Of interest is reactive sintering in the BN-TiH 2 system in which refractory TiN and TiB 2 phases are final products of the synthesis. This raises the question of the role of hydrogen in this interaction. Titanium hydride is known to release active atomic hydrogen when heated. The fine boron nitride powder is capable of enveloping hard particles of titanium hydride. This means that atomic hydrogen will react with BN mixed with TiH 2 when the former decomposes. As a result, reactive surfaces of hard particles of starting TiH 2 and BN and intermediate products from the synthesis of the TiN-TiB 2 composite are formed.Assuming that splitting the hard boron nitride with atomic hydrogen is the most probable synthesis mechanism, we performed preliminary thermodynamic calculations of the following reactions: BN + 2H ↔ HB = NH + 2H → H 2 B−NH 2 +2H → BH 3 + NH 3 , (1) BN + 3H ↔ BH 3 + N,(2) BN + 3H ↔ B + NH 3 ,(3) 2BN + 6H ↔ B 2 H 6 + 2N, (4) BN + 3H ↔ BH 3 + N, (5) BN + 1.5H 2 ↔ BH 3 + 0.5 NH 3 .(6) Figure 1 shows that molecular hydrogen does not react with boron nitride, which is confirmed by the calculations (curve 6). Boron nitride is intensively oxidized by dry oxygen and CO 2 at 700 to 800°C, B 2 O 3 and N 2 being

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