Hong Xia Lu

Carbothermal Reduction Synthesis of Zirconium Diboride Powders Assisted by Microwave

ZrB2 powder has been prepared through carbothermal reduction boronization of zirconia/boron carbide/carbon mixtures heating assisted by microwave. The powder characteristics were investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), nitrogen absorption (BET model) and scanning electron microscope (SEM). The experiments indicated that excessive B4C is necessary and the carbothermic reaction reacts severely at a higher temperature and complete at 1600oC. The crystallite size has ranged from 50-100 nm, according to the calculated surface area. Highest purity of ZrB2 powder, which was synthesized at 1600oC, is 99.67 wt%. The surface area of ZrB2 powder synthesis at 1600oC is 18.33 m2/g. Vibration of temperature should affect the purity of ZrB2, as the sub reaction acted.

Properties and Processing of Porous Si3N4 Ceramics

Porous silicon nitride (Si3N4) ceramics green were prepared by sol-gel and freeze drying processing. Al2O3 and MgO were selected as sintering additives. Porous Si3N4 ceramics were sintered at 1200~1300 °C. The porosity of porous Si3N4 ceramics reached 60~80%, the pore size of porous Si3N4 ceramics dried by freeze drying is less than 5μm. Two kinds of pores were formed, including open pores with pore size of 1~5μm and closed pores pore size with the nanometer level. The compression strength of porous Si3N4 ceramics was 15~25MPa. Thermal conductivity of porous Si3N4 ceramics was 0.08-0.1 W/m·K.

Preparation of Fe Coating Al2O3 Nanometer Composite Powder and its Mechanical Properties after Hot Press Sintering

Nano-Fe particles coating Al2O3 composite powders were prepared by heterogeneous precipitation method with nanometer -Al2O3 and Fe(NO3)3•9H2O as raw materials. The composite powders were analyzed by DSC-TG, XRD,SEM and Zeta potential. Results showed that Fe coating Al2O3 nanometer composite powders were obtained in the condition of being sintered at 500°C for 30min and reduced at 700°C for 1h in H2. The coating Fe nanometer particles are in the shape of sphericity with diameter about 30nm and the dispersion of the powders is uniform. Al2O3/Fe composite ceramics were obtained by hot-pressing (30MPa). The mechanical properties of the composite were investigated after hot press at different temperatures. With the increasing of Fe content in composite ceramics, the hardness of the composite is decreased. Fracture toughness of 10mol%Fe content is 5.62MPa after sintered at 1400°C, which is increasing 57% high than that of monolithic Al2O3 ceramics.

Use of Angang Slag for the Production of Glass-Ceramic Materials

The characteristic of Angang blast furnace slag was studied by X-ray fluorescence spectrometry, DSC, X-ray diffraction and SEM. SiO2-Al2O3-CaO system glass-ceramics have been obtained successfully from slag with other additives. The properties of slag-based glass-ceramics were analyzed in this paper. It has been found that nucleation temperature is in the range of 600~700 °C, and crystallization temperature is in the range of 850~950 °C. The crystals phase is 2 CaO⋅ Al2O3⋅ SiO2. The chemical and mechanical properties of slag-based glass-ceramics are superior to the properties of clay brick.

Preparation of Al-Based Metal Matrix Composites Reinforced by Cu Coated SiC Particles

In order to improve the interfacial behavior between SiC and Al, a surface layer of Cu was coated on SiC particles. The influence of pH value on the coating process was analyzed. A powder metallurgy method was used to prepare the Al-based metal matrix composites (MMCs). SEM, XRD techniques were used to characterize the sintered compacts. It was found that the optimized pH value during the coating process was 1~2. The specimen showed the maximum density when sintered at 750oC. Inter-metallic compound of Al3.21Si0.47 was detected which contributed to the enhancement at the interface between SiC and Al. The hardness of the composites is improved to 90 MPa.

Effect of Nano-Al2O3 Particles Addition on Thermal Shock Resistance of ZTA/Cordierite Composites

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.m1/2, respectively.

Processing and Properties of (Zr,Hf)B2-SiC Ceramic Composites

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·m1/2. The highest Vickers’ harness of was (24.8±3.4) GPa for the composites content of 50% HfB2.

Processing and Properties of ZrB2-Cu Composites Sintered by Hot-Pressing Sintering

ZrB2-Cu composite is a new electrical contact materials in the integration of high conductivity, high wear resistance and good mechanical strength. In this paper, ZrB2-Cu composites were prepared by hot-pressing sintering at 800~900 °C under a pressure of 20 MPa.The densification of ZrB2-Cu composites was improved by the addition of nickel using an electroless metal plating technique. X-ray diffraction and scan electron microscopy were used to analyze the phase and microstructure of ZrB2-Cu composites. The results showed that ZrB2-Cu composites with 60 vol % Cu which was sintered at 900 °C had a higher relative density, highest flexural strength of 381 MPa and higher hardness of 2.16 GPa(HV). ZrB2-Cu composites with 50 vol % Cu which was sintered at 900 °C had higher flexural strength of 297 MPa and the highest hardness of 2.66 GPa.

Fabrication and Characterization of Ceramic Floor Tiles from Coal Gangue

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.

Preparation of SiCw/3Y-ZrO2/Al2O3 Composites

SiCw/3Y-ZrO2/A12O3 composites were prepared. The composite powders were prepared by a precursor method. Samples were conventionally sintered at 1500°C and 1580°C for 2h in air. The density, phases, microstructure, hardness of the SiCw/3Y-ZrO2/A12O3 composites were investigated. It was found that the relative density of the samples decreased as the increasing content of SiCw. The optimum mechanical properties may be obtained in the SiCw/3Y-ZrO2/A12O3 composites with 5 vol.% SiCw.