Papers by Author: Jia Chen Liu

Abstract: A structural-functional integrative wave-transparent material, consisted of BN coating and SiBN substrate, is synthesized through precursor infiltration pyrolysis (PIP) process. Then the technical parameters and procedures are obtained according to the key properties of the precursors. Studies on the microstructures and properties of the composite show that compact substrate and weak interface enhance the strength, and porous structure improves the dielectric performance of the composite. The composite exhibites good bending strength (~95.12 MPa), tensile strength (~34.95 MPa) and compressive strength (~80.92 MPa). Moreover the composite displays a low dielectric constant (4.17) and a low loss tangent (9.7×10^-3) at room temperature. The composite has a low changing rate of dielectric constant (~2.01% per 100°C). These results imply that the composite with excellent mechanical and dielectric properties can be an excellent wave-transparent material applied in the fields of aerospace.

Abstract: 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.

Abstract: The aluminum phosphate adhesive was prepared by aluminum dihydrogen phosphate and ceramic fillers. The mullite, silica and silicon powders were added as the fillers to improve the mechanical property and high temperature property. The specimens were prepared by joining the mullite ceramic/ceramic by phosphate adhesive. The strengths of the specimens treated at different temperatures were studied. The results indicated that the tensile strength at room temperature was 2.02 MPa, and it reached 5.06 MPa when the specimen was treated at 800°C. The bonding effect and bonding property at high temperature were discussed through the SEM analysis. Besides, the bonding mechanism was also explored.

Abstract: AmorphousAl₂O₃ZrO₂powders were synthesized by citric acid gel process. The effects of molar ratio of citric acid to total metal ions concentration and the calcined powders with CA/M=2:1 were investigated through XRD and SEM analysis. Thermal behavior of the dried gel with CA/M=2:1 was studied by DSC/TG. Amorphous Al₂O₃-ZrO₂ powders with particle size of about 3μm were obtained.

Abstract: Highly porous silica ceramics were produced by gel casting with egg white protein (EWP) as a foaming agent and evaluated by measuring the porosity, mechanical strength and microstructure. After drying, the green bodies were debindered and sintered at 1300°C for 4 h. The influences of the EWP content on the open porosity as well as the strength were investigated. The porosity of the obtained porous silica ceramics was within 70.2%-86.1%, the bending strength decreased from 6.81 MPa to 5.48 MPa. It was found that the strength dependence of the porosity was well described by a modified exponential relation of the form σ=σ0exp(-BP), where P is the porosity and B is a constant (B = 1.37 was obtained by fitting the experimental data). This finding is in agreement with other literature data and seems to indicate a common feature of all porous ceramics.

Abstract: Based on the Al2O3-ZrO2-SiO2 system, the conventional pre-sintering samples were reheated by microwave to investigate the influence of microwave to the thermodynamic equilibrium and phase equilibrium relationships. It was found that microwave can accelerate transitions to thermodynamic equilibrium. The phase equilibrium of the samples prepared by microwave heating was identical with the traditional phase diagram. In addition, the amount of tetragonal zirconia in the prepared samples remained constant as the microwave heating time prolonging. All of the observed phenomenon can be explained by microwave nonthermal effects.

Abstract: The mixture of amorphous silica extracted from coal fly ash and fused silica was used to prepare density silica ceramic through slip-casting method. The XRD results showed that a large amount of cristobalite was formed at 1300°C which can weaken mechanical properties. The SEM results showed that glassy phase present from fused silica promoted ceramic densification. According to the experiment results, it was found that the bending strength was highest when mixing 65wt% fused silica and sintering at 1200°C for 4 hours.

Abstract: A new technique of flyash utilization was presented and high-purity silica was prepared by alkali leaching. The flyash was added into sodium hydroxide solution, and then the suspension was heated to 115 °C for 30 min. After filtrated, the filtrate was collected and carbon dioxide was imported into the solution. Finally, the silica would precipitate from the solution. The silica was characterized by scanning electron microscopy, X-ray diffraction and X-ray fluorescence spectrometer. The high-purity silica prepared from flyash was qualified for the rubber reinforcing agent used in shoemaking.

Abstract: 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.

Abstract: A new way to deposit oxide ceramic coating on the metal was prepared by Gel-casting and microwave assisted heating. The oxide ceramic coating was obtained by dipping the metal substrate whose surface carried positive charge through acid treatment to the gel slurry which was composited by oxide powder with negative charge, and then gelating, drying and heating by microwave. It was showed that it was feasible to realize coating of ceramics on metal surface through microwave heating.