Jia Chen Liu

Preparation and Properties of SiO2/Al2O3-SiO2 Fiber Mat Composite Materials

A light weight and heat-resistant composite material was successfully fabricated by impregnation-filtration process in which Al2O3-SiO2 fiber mat was used as the skeleton and silica was applied as reinforcing filler. The effects of both concentration of silica sol and sintering temperature on SiO2/Al2O3-SiO2 fiber composites were studied. The results indicated that the density of composites increased with the concentration of silica sol increasing. The heat-treatment temperature had little effect on the density of composites. As heat-treatment temperature increased, the compressive strength increased firstly and then decreased.

High Temperature Bonding Effect of the Room-Temperature-Curing Phosphate Adhesive for C/C Composites

A heat-resistant phosphate adhesive was developed for joining and repairing of C/C composites. The high-temperature bonding effect for both cured adhesive and 1300°C-calcined adhesive had been evaluated through testing high-temperature shear strength of corresponding joints. The results showed that the bonding strength of cured adhesive decreased from 7.9 MPa at RT to 0.9 MPa at 1300°C, while that of 1300°C-calcined adhesive could maintain about 4 MPa at temperature range from RT to 700°C and then decreased to 1.7 MPa at 1300°C. Besides, with the increasing thermal cycling times at 1300°C, the high-temperature bonding strength at this temperature could maintain at about 2.3 MPa.

Preparation of Porous Lightweight Ceramics and Fibre Joining Materials

The high-temperature resistance compression material of lightweight porous ceramics and fiber joining is becoming a kind of promising seal parts in high-temperature industries and aerospace field. A combination of the lightweight mullite matrix porous ceramics and the elastic 3-D silica woven fibre, a novel joining material was studied. The low cost fly ash cenosphere as raw materials, mullite porous ceramics with density 0.92 g/cm3, and the thermal conductivity 0.13 w/m.K, were prepared. Using microwave selective heating properties, designing the interlayer composition, the bonding materials were attained by microwave sintering. The flexural strength of joint materials was about 23 MPa, which was higher than porous ceramics matrix.

Preparation of Porous Mullite Ceramics Using Al as Foaming Agent

Effects of Al in different added condition on pores shape and mullite configuration were investigated. Three sorts of hole were got by using Al as foaming agent in mullite composites. It was concluded that isolated holes could be formed by Al changing to Al2Ol3 with acidity condition in green state, open holes could be formed by Al changing to Al2O3 directly in sintering process, and mixed hole of isolated and open ones could be formed by Al changing to Al(OH)3 with alkalescence condition in green state followed changing to Al2O3 in sintering process. These holes could supply a position for growth of mullite as well.

Microstructure and Thermal Shock Resistance of LaPO4-ZrO2

LaPO4-ZrO2 composites were prepared by slip casting and pressureless-sintered in air. The effects of LaPO4 addition on microstructure and thermal shock resistance were addressed. The thermal shock resistance of the composites was evaluated by air quenching and a subsequent three-point bending test to determine the strength degradation. Comparisons were made with results from parallel experiments conducted using a ZrO2 ceramic without LaPO4 additions. The reference ZrO2 ceramic showed the expected substantial strength losses when thermally quenched from 470oC above room temperature. By contrast, the LaPO4-ZrO2 ceramics, while displaying reduced strength relative to the reference ZrO2 ceramics, exhibited minimal strength degradation under severe thermal shock conditions.

Microstructure and Mechanical Properties of Mullite Composites via Pressure Molding and by Oxidation of an Al-Si Alloy Powder

A novel technique to synthesize mullite by the oxidation of Al-Si alloy powder was used for the manufacture of mullite via pressure molding. The mixed powder was consisted of powders of Al-Si alloy, Al2O3 and SiO2 and additives or powders of Al-Si alloy, Al2O3, SiO2 and ZrO2 and additives. Those mixed powders were milled in nonaqueous slurry in order to prevent the oxidation of Al-Si alloy. Then the green bodies were pressureless sintered in air at ≥1380 °C. The Oxidation caused an internal volume expansion, resulting in reducing shrinkage stresses during reaction- bonding of composites, which minimized the sensitivity to crack formation. Comparing with non zirconia reinforced mullite composites, the effect of the microstructure and mechanical properties of mullite composites were studied.

Microwave Joining of 95Al2O3 Using Interlayer Containing SiC

A novel technique to join ceramics was described using microwave heating. SiC was added in the interlayer as a microwave-absorbing material, joining of 95 Al2O3 was realized by raising temperature of SiC itself and then inducing microwave-absorbing of oxides. The strength of joining, microstructure of interlayer and mechanism of joining were investigated.

Coating Nano-TiO2 on Optical Fiber with Al(H2PO4)3 Adhesive

To meet the need of optical fiber photoreactor designed by mechanism of TiO2 photocatalysis, nanometer TiO2 was coated on the surface of optical fiber by dipping nude fibers into an Al(H2PO4)3-contained TiO2 slurry. Effects of slurry conditions, including content of TiO2 and addition of Al(H2PO4)3 adhesive, on coating thickness and quality were determined. Coating process, especially the effect of coating times, was also concerned. Based on the experimental results, fitting slurry conditions and process parameters were suggested for obtaining high-quality TiO2 coating on optical fiber surface.

Effect of Process Conditions on Stability of Ni-ZrO2 Composite Electroplating Bath

For the nano-ZrO2 powders, it is difficult to disperse the particles in a highly concentrated electrolyte. Polymer MZN with composite structure was employed as a dispersant in this work. On the basis of having obtained the optimum quantity of dispersant MZN, the effects of process conditions on stability of Ni-ZrO2 composite electroplating bath were investigated via sedimentation experiments and SEM micrograph. The results showed that the charging sequence have a significant influence on the stability of composite electroplating bath, and the optimum process conditions is that the stable aqueous suspension of 2.5g nano-powders in 100 ml water should be prepared at first by milling for 3 hours, and then the electrolytes were added in it. The well-dispersed composite electroplating bath was obtained, which made sure that the nano-ZrO2 smaller than 30nm was found in the Ni matrix.

Kinetic Studies on Crystallization and Grain Growth of Amorphous Al2O3-ZrO2 Powder

Nanocrystalline Al2O3-ZrO2 powders were prepared through controlled crystallization of amorphous phase, and kinetic studies on crystallization and grain growth were carried out. Based on Kissinger equation, the activation energies for crystallization were determined to be 981.8 kJ·mol-1 for (Zr0.94Y0.06)O1.88 and 1364.1 kJ·mol-1 for α-Al2O3. Average size of crystallite was obtained by Scherrer equation according to FWHMs in XRD peaks; the grain growth was slow below 1100°C, and turned severe at higher temperatures. The appropriate calcination temperatures was determined to be 1100°C, at which stable phases were formed and further severe grain growth can be restrained. SEM micrograph of Al2O3-ZrO2 powder after calcination at 1100°C revealed uniform distribution of spherical particles with size of about 20 nm, close to that determined by XRD results.