การสังเคราะห์โดยการเผาไหม้และการหาลักษณะเฉพาะของวัสดุผสมเซอร์โคเนียมไดบอไรด์ - มัลไลต์

Abstract

The purpose of this research was synthesize the zirconium diboride - mullite composite (ZrB2 - mullite) from the reactant system of zirconium silicate (ZrSiO1), boron oxide (B203) and aluminium (Al), which divided into two sections. In the first part of the research was to study the effect of experiment parameters and characterizations in order to determine the optimal conditions for combustion synthesis. The effect of different of reactant system or the source of zirconium silicate (commercial ZrSiO4 and zircon sand), the synthesis atmosphere (air and inert gas (Ar)), the high-energy milling durations of zircon sand (120, 240, 360 and 480 minute), and the effect of silicon (Si) addition (0.01, 0.02, 0.03 and 0.05 mole) were investigated. In the second part of the research was to prepare composite specimens from appropriate condition of the first part, by hot pressing at 1,450, 1,550 and 1,650 °c with the pressure of 25 MPa under argon atmosphere for 60 minute. In addition, the physical (density and porosity), mechanical (hardness, flexural strength and fracture toughness), and thermal properties (thermal expansion) were also performed. The experimental study results indicated that the using zircon sand milled 360 minute with 0.01 mole of silicon and synthesized under inert gas was the optimal condition for synthesis the zirconium diboride - mullite composite. The chemical composition of the composite in which compose 76.98 wt% of zirconium diboride and 14.96 wt% of mullite. The zirconium diboride - mullite composite hot pressed at 1,450, 1,550 and 1,650 °C had a density in the range between 3.38 -3.42 g/cm3 with insignificant change in porosity. Furthermore, the best mechanical properties including hardness, flexural strength, fracture toughness and coefficient of thermal expansion in this research were 153.25 MPa, 1084 HV, 4.23 MPa.m1/2 and 6.53 x 10-/K, respectively, obtained from the composite hot pressed at 1,650 °C.