Jiqiang Gao

Effect of Surface Modifications on the Bonding Strength of Titanium–Porcelain

Investigations of surface modifications on cast titanium surfaces and titanium–porcelain adhesion were performed. Cast pure titanium was subjected to surface modifications by sandblasting, preoxidation, and SnO x coating by sol-gel process. The adhesion between the titanium and porcelain was evaluated by a three-point flexure bonding test. The X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) results revealed that failure of the titanium–porcelain predominantly occurred at the titanium–oxide interface after sandblasting and preoxidation treatments. The SnO x film with small spherical pores obtained at 300°C served as an effective oxygen diffusion barrier and improved titanium–porcelain adhesion. With the temperature elevated, SnO was oxidized to SnO2 and the film microcracked, which resulted in the decrease of the titanium–porcelain bonding strength.

Mullite Fibers Prepared by Sol-Gel Method Using Aluminum Chloride Aluminum Isopropoxide and Tetraethylorthosilicate

Mullite fibers with good flexibility were prepared from an aqueous water solution of aluminum chloride (AC), aluminum isopropoxide (AIP), tetraethylorthosilicate (TEOS) by the sol-gel process. Aluminosilicate spinnable sol (pH=2) with the stoichiometric mullite composition (Al:Si = 3:1, AIP/AC = 2:1) was prepared. The removal of organic and chlorine was completed at 800°C. The complete transformation to mullite was observed at 1200°C by X-ray diffraction (XRD). The lateral and circumferential cracks were showed in the results of scanning electron microscopy (SEM) when fibers were sintered at 10°C min−1. It was useful for preparation of fibers with smooth surface and uniform diameter by controlling the sintering schedule.

Effect of starch on extrusion behaviour of ceramic pastes

Abstract Starch was used as extrusion aid in the form of solid in different silicon nitride paste formulations. The effect of starch addition on extrusion behaviour of ceramic pastes such as liquid phase migration and extrusion force was investigated. The extrusion behaviours were evaluated by the curves of extrusion force versus extrusion time in a piston-type extruder. The results showed that paste with an appropriate amount of starch can effectively avoid liquid phase migration while surprisingly lowering the extrusion force to a certain extent. The reasons can be attributed to the strong hydrophilic character and lubrication role of starch particles. The mechanism for plasticity improvement of ceramic paste by starch inclusion in the form of solid is put forward for the first time.

Synthesis and characterisation of alumina fibres using organic/inorganic composite sol

Abstract The polyvinyl butyral–Al(NO3)3 composite sols and alumina fibres were synthesised by the sol–gel process in an aqueous solution using the polyvinyl butyral (PVB) and Al(NO3)3.9H2O (AN). The viscosity of PVB–AN composite sol increased with increasing AN content and aging time when it was laid at room temperature. The addition of AN leads to the formation of new weak peak and the deviation of diffraction angle to higher degrees according to the X-ray diffraction patterns (XRD). The exothermic peak of PVB disappeared and a weak endothermic peak was observed in differential scanning calorimetry curves of composite powders. The XRD pattern of fibres sintered at 1200°C showed the formation of α-alumina and the fibres showed smooth surface and uniform diameter.

Resources consumption and wastes emission analysis for two manufacture processes of siliconit

Silicon carbide (SiC) heating elements (siliconits) are widely used at high-temperature fields. The raw materials, manufacture process and application fields of siliconits are all related to heavy energy consumption and pollutions, and bring high environmental loads. The resources consumption and pollution emissions in siliconit manufacture process were quantificationally estimated by input/output method. Difference between two traditional techniques to produce siliconits in China was also compared and analyzed. The results show that siliconit manufacture processes consume large quantities of resources because the furnace is open to environment and too much thermal-protection materials are used. For the thick-end technique is more complicated and the thick-end siliconits have a bigger size and mass, there are more resources and energy consumptions and pollution emissions for thick-end process than that for equal-diameter process. Some suggestions were introduced to improve the traditional techniques and a new process was designed. It is the most important that the open furnace should be replaced by close vacuum furnace. Sintering and siliconizing process can be combined into one high-temperature process. As results of process simplification and vacuum sintering, resources and energy consumption and wastes emission can be decreased remarkably.

Microstructure and properties of Si3N4 ceramics obtained from addition of β-phase seeds and celsian

The silicon nitride based ceramics obtained by the addition of β-Si3-N4 seeds was fabricated using celsian as the additive and by pressureless sintering. The microstructure of the material was observed and analyzed using XRD, SEM, and TEM and the mechanical response of this array microstructure was characterized for flexural strength and fracture behavior. The result shows that the growth of the larger aspect ratio grains initiate mainly from the seeds through the heterogeneous nucleation mechanism during the process of phase transformation, and the intergranular phase BaAl2Si2O8 services as good refractory materials. In contrast to conventional processing, a stable bimodal microstructure and complicated component with a lower cost can be achieved using the above-mentioned process theoretically and practically.