4 WETTING PHASES IN ALN AL AND ALN COMPOSITES AL SYSTEMS, MODELS OF NONREACTIVE, REACTIVE, AND COMPOSITE SYSTEMS

The contact angles between molten aluminum and samples of AlN and AlN composites were measured to establish a way of estimating the wetting of nonreactive systems, reactive systems and composite systems. The experiments were conducted using an improved sessile drop technique which prevented the oxidation of the aluminum. By plotting the results on a logarithmic time scale, it was found that the contact angle value for AlN containing Y2O3 as a sintering agent progressed through four phases (I: original-wetting phase, II: quasiequilibrium phase, III: interfacial-reaction-wetting phase, and IV: equilibrium phase), while the contact angle of purified AlN progressed through only two phases, I and IV. Phase III in the sample containing Y2O3 was caused by the interfacial reactions; the wetting speed in phase III (interfacial-reaction-wetting speed) and the value of the contact angle in phase IV (equilibrium wettability) depend on the interfacial reactions. The contact angle for AlN composite also progressed through the four phases. The contact angle of phase II (original wettability) conformed to Cassie's law, whereas the contact angle of phase IV depended on the condition of the interface. However, Cassie's equation should be applicable throughout phases II through IV when the condition of the interface is understood. Also, the mechanism of the interfacial reaction wetting was explained using Cassie's equation by taking into account the ratio of area of components at the interface in phase III.