Papers by Author: Rui Zhang

Abstract: Polycrystalline cubic boron nitride (PcBN) composites were fabricated by spark plasma sintering (SPS). The SiC, Si₃N₄ and Si/B were used as binder. The effects of SPS sintering process parameters, such as the sintering temperature, holding time, heating rate and binder composition, on the properties of PcBN samples were investigated. PcBN composite with a hardness of 23.12GPa was fabricated efficiently by SPS. The hardness of PcBN sample increased first and then decreased with the increase of sintering temperature. As the holding time was 20 min, the hardness of PcBN sample was the highest. The PcBN performance at the heating rate of 50 °C/min was significantly better than that of 100°C /min. When the binder component of SiC, Si₃N_4, and Si was 63%:27%:10%, the hardness of PcBN was the highest. With an addition of Si, the PcBN samples had higher hardness than that of B.

Abstract: Different molar ratio of HfB₂ and ZrB₂ had been mixed, and 30 vol.% SiC was selected as sintering additives. The mixing powders were sintered by hot pressing at 1900 °C for 1 h under a pressure of 20 MPa in Ar atmosphere. X-ray diffraction, scanning microscopy and Archimedes’s method were used to characterize the phase, microstructure and density of the sintered composites. Meanwhile, the hardness, the fracture toughness and flexural strength of the obtained composites were considered too. It can be found that the (Zr,Hf)B₂ solid solutions were formed by HfB₂ and ZrB₂ during the sintering. The flexural strength of (Zr,Hf)B₂-SiC composites increased with the amount of HfB₂ increasing, which reached (332±40) MPa for the composites content of 70% HfB₂. Which fracture toughness was (2.22±0.25) MPa·m^1/2. The highest Vickers’ harness of was (24.8±3.4) GPa for the composites content of 50% HfB₂.

Abstract: ZTA/cordierite composites were prepared using ZrO₂, Micro-Al₂O₃/Nano-Al₂O₃ and cordierite as raw materials by pressureless sintering. The influence of Nano-Al₂O₃ particles content on phase composition, microstructure and thermal shock resistance of ZTA/cordierite were investigated. The results show that m-ZrO₂, t-ZrO₂ and Al₂O₃ existed in the matrix and t-ZrO₂ content increased with the increase of Nano-Al₂O₃ powders content. By adding Nano-Al₂O₃ powders and ultrasonic dispersion, which can refine grain and promote sintering, the grain size is uniform, the porosity is less and some grains were pulled out, the fracture mode changes from intergranular fracture to intergranular fracture and transgranular fracture. The thermal shock test was carried out at 300°C-1000°C, the critical thermal shock temperature of ZTA ceramic without adding cordierite and Nano-Al₂O₃ particles is 800°C and the residual strength retention rate of the material is only 32.4%. But by adding Nano-Al₂O₃ powers and ultrasonic dispersion 30 min,the residual strength retention rate, relative density, flexural strength and fracture toughness of ZTA/cordierite sintered at 1550°C for 4 h increased greatly and were up to 73.6%, 97.2%, 436 MPa and 4.6 MPa.m^1/2, respectively.

Abstract: The effects of SiC_p addition on the microstructure and mechanical properties of ZTA ceramics was investigated by microwave sintering. Partially stabilized zirconia（3Y-ZrO₂）nanopowder containing SiC_p was prepared by microwave pyrolysing precursor which was was achieved by co-precipitation method. The powders of alumina, yttria partially stabilized zirconia containing SiC_p were mixed to prepare ZTA ceramics green body by die pressing and cold isostatic pressing and subsequently sintered at the range of 1350°C-1550°C for 30min by microwave. XRD revealed that 3Y-ZrO₂/SiC powder contained more tetragonal phase than 3Y-ZrO₂ powder which was also confirmed by SEM and particle size distribution. The phenomenon was because of SiC_p forming the microwave heating spot that promoted pyrolysis progress when 3Y-ZrO₂/SiC powder was prepared by microwave heating. Microstructure showed that the grain of ZTA ceramics had directional growth by microwave sintering. SiC_p firstly absorbed microwave that made more uniform sintering of ZTA ceramics and caused local oriented growth of zirconia and alumina. Thus, the bending strength of ZTA ceramics was higher than ZTA without SiC_p. The ladder type heating mode of microwave sintering ZTA ceramics reduced relatively sintering time by 20min due to the addition of SiC_p.Introduction

Abstract: Tungsten (W) micro-/nanoparticles were synthesized by thermally treating tungstate-based inorganic-organic hybrid nanobelts with a lamellar structure or the mixture of WO3 nanoplates and C6H12O6 in an Ar flow at 1000-1200 oC for 2-6 h. Phase compositions and morphologies of the W particles obtained were characterized by powder X-ray diffraction and scanning electron microscope.

Abstract: Coal gangue was used as the main material to fabricate floor tiles in this paper. The mixture of coal gangue, quartz, feldspar and bentonite, with the weight percentage of 55, 20, 20 and 5, was wetly milled, dried, and then pressed into green compacts. The obtained compacts were sintered at 1180-1240 oC and the floor tiles were obtained. The obtained tiles were characterized by XRD, SEM, linear shrinkage, water absorption, bulk density and flexural strength. The results indicate that the tiles were composed of glassy phases, quartz and mullite phases. The phase composition, microstructure, physico-mechanical properties of the samples change with the sintering temperature. The tile sintered at 1220 oC achieves the linear shrinkage, water absorption and bulk density values of 6.18%, 0.16%, 2.45 g/cm3, respectively. Its flexural strength reaches the maximum of 92.0 MPa.

Abstract: Hierarchical SnO2 (H-SnO2) and particulate SnO2 (P-SnO2) nanostructures were synthesized by a hydrothermal method with and without the aid of sodium 1-dodecanesulfonate (SDS), respectively. X-ray diffraction and scanning electron microscopy were used to characterize the products obtained. The sensing properties of the H-SnO2 and P-SnO2 nanostructures to volatile organic compound gas (VOCs) were measured. The H-SnO2 sensors show better gas-sensing performance than the P-SnO2 sensors due to the hierarchical microstructure.