Papers by Author: Yong Ting Zheng

Abstract: In this paper, Nd:YAG ceramic was prepared by combustion synthesis with centrifugation casting. Combustion temperature and pressure were calculated under adiabatic hypothesis, and measured experimentally by W/Re thermocouple and piezometer, respectively. The combustion temperature and pressure decreased with increase of the content of diluents (Y₂O₃ and A1₂O₃). The YAG could be obtained as the ratio between the Y₂O₃ and A1₂O₃ reached 3:5. Phase composition and microstructures of the derived products were analyzed by XRD, SEM and EDS. The results show that the other reaction product TiN and a small quantity of gas and oxide impurity were not completely separated from YAG melt under centrifugal force so that transparent YAG ceramic was not obtained in this work.

Abstract: sothermal oxidation behavior of the AlN-TiB₂ conductive ceramics prepared by self-propagating high-temperature synthesis and hot isostatic pressing (SHS-HIP) was evaluated in a temperature range from 900 to 1400 °C for exposure times from 1 to 16 h in air. The oxidation experimental results show that the conductive ceramics have a good oxidation resistance below 1200 °C. The oxidation products on the sample surfaces are mainly composed of Al₂TiO₅, TiO₂ and aluminum borate phases.

Abstract: AlN-SiC-TiB2 ceramics were synthesized by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP) methods. The powder mixtures of Al, 6H-SiC and TiB2 were shaped by isostatic cool pressing method, and then combustion reaction was carried at the pressure of 100-200 MPa N2 by an ignitor. The solid solution of AlN and 2H-SiC in AlN-SiC-TiB2 ceramics was formed. The phase composition and microstructure were investigated by XRD and SEM. The mechanical properties of composite were measured as functions of composition. The maximum value of flexural strength and fracture toughness of composites were 430 MPa and 3.9 MPa⋅m1/2 respectively.

Abstract: The feasibility of fabricating h-BN-SiC high-temperature ceramics by in-situ combustion synthesis was demonstrated by igniting the mixture of boron carbide and silicon powder under 100MPa nitrogen pressure. The reaction thermodynamics and the adiabatic combustion temperature were calculated theoretically. The phase composition, microstructure and mechanical properties of composite were identified by XRD and SEM. The maximum bending strength and fracture toughness of the composite were 65.2 MPa and 1.4 MPa·m1/2 under room temperature, respectively. The effects of h-BN and SiC dilution contents on the mechanical properties of composite were also discussed.

Abstract: DSC/TG analysis was used to investigate the change of TiSi2-SiC-N2 system in the temperature range from room temperature to 1400°C. The relationships between $G and T about the reactions possible occurring in TiSi2-N2 system during combustion synthesis were calculated. In order to study the combustion process in detail, the reaction of TiSi2-SiC-N2 system was stopped at different stages by quenching the samples. The composition and microstructure in different reaction zones were analyzed by means of XRD and SEM, accordingly, reaction kinetic model of TiSi2-SiC-N2 combustion system was established. The result showed that TiSi2 firstly reacted with N2 to form TiN and Si, and subsequently Si were nitrified.

Abstract: The fabrication of AlN-SiC-TiB2 ceramics with powder mixtures of Al, 6H-SiC and TiB2 was investigated by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP). The powder mixtures were shaped by isostatic cool pressing method and the combustion reaction was carried at the pressure of 100-200 MPa N2 by an ignitor. The compositions and morphologies of the combustion product were studied by XRD and SEM. The determined bending strength and the fracture toughness of the ceramics were 350 MPa and 3.5 MPa⋅m1/2 respectively.

Abstract: BN-AlN-TiB2 compound conductive ceramics from powder mixtures of BN, Al, and TiB2 was fabricated by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP). The powder mixtures were shaped by isostatic cool pressing at 5-10MPa and the combustion reaction was carried at 100-200 MPa N2 by an ignitor. XRD experiments confirmed that the reaction was complete and only AlN, BN and TiB2 were detected. Optical microscopy as well as SEM with an electron probe microanalysis was used for microstructural analysis and revealed a relatively uniform distribution of particulates. The temperature-dependence and composition-dependence of the electrical resistivity of BN-AlN-TiB2 ceramics were studied. The results showed that the optimum composition was 5-10wt% BN, 30-55wt% Al and 60-40wt% TiB2, and the products had the density of 90% of the theoretical, resistivity of 80-1000 μ⋅cm and bending strength of 100-200 MPa.

Abstract: Si3N4-TiN-SiC multiphase ceramics was synthesized from TiSi2 and SiC powders by combustion synthesis. The effect of dilute content on conversion percentage was calculated in theory assuming that there is no penetration of nitrogen gas, and combustion synthesis was carried under different conditions. The results show that the increase of diluent content in certain extent is helpful for nitrification of TiSi2 and free silicon were detected in the 30wt% and 40wt% SiC-diluted samples with 45vol% porosity while no silicon were found in 50vol% porosity green parts. The increase in diluent content and porosity of the compacts are favorable for the development of rod-like β-Si3N4 and the long-diameter ratio of β-Si3N4 is increase as the increase of these two values.