Ying Na Zhao

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 Principle and Crystal Growth Kinetics of Loaded Nanocrystal TiO2

Nanocrystal TiO2 photocatalystic materials were prepared by melt-phase separation technique, and its preparation principle was discussed in this paper. Anatase nanometer TiO2 could be obtained by heat-treatment at 550 °C for 10 min, which is well combined with porous glass carrier and the particles size is about 25 nm. The growth kinetics of TiO2 crystalline analysis results showed that the growth activation energy Q1 was about 63.27 KJ/mol (<600 °C), and Q2 was about 22.78 KJ/mol (>600 °C).TiO2 crystalline growth closely related to glass phase separation. TiO2 particles grew quickly with the glass phase separation size increase, and then the particles growth rate became slow because of being limited by glass phase separation structure.

Rheological Property of Intercalated Modification Clay

In this paper, the clay was intercalated with polyacrylic acid, and then studied the influences of intercalation on rheological property of ceramic billet. The study indicated that the intercalation changed the properties of clay interlayer domains, such as the interlayer bonding water, the content of free water and the bonding force between the layers, etc. The plasticity index of ceramic billet increased significantly when the amount of intercalation is more than 3.0 wt. The plasticity index increased from 1.09m·N to 4.19m·N when the additive is 5.0wt, increased by 383%. And also its yield strength has improved significantly, the fracture pressure increased from 100N to 600N. These phenomena indicate that the machinability of billet improved significantly.

Epoxy Resin (EP) / Nano-SiO2 Composite Material Preparation by Two Processes

Ultrasonic wave (UW) and sol-gel (SG) technology were using to preprocess the nano-SiO2, and the SiO2/EP composites were prepared by adding coupling agent KH-550, curing agent T-31 and different contents SiO2 into EP matrix. Using infrared spectra analysis tested the samples’ structures and the thermal stability of two preparation processes were tested by TG. The results indicated that, the thermal stability of the SiO2/EP composites by UW preprocess was improved about 25 oC -60 oC when compared with pure EP and the SiO2/EP composites by SG. Comparing to the comprehensive evaluation of thermal stability of different SiO2 contents SiO2/EP composites, the most optimum additive of nano-SiO2 was about 10 wt. % by UW process.

Interface Reactions of Joining Al2O3 Ceramics by Microwave Method

Nanometer Si powders were used as interlayer materials, which were expected to be microwave heated rapidly and reacted with the surface of Al2O3 ceramics to form the low eutectoid compound. The phenomena of element migration of joint samples were investigated by energy dispersive spectroscopy (EDS) and the interface phase transition was analyzed by X-ray diffraction (XRD). The results indicated that the low eutectoid compound of the joint interface wetted and penetrated to the ceramic surface. The variation of micro-hardness at the interface across the parent material was measured by micro-hardness instrument and the interfacial microstructure and the fracture surface were investigated by scanning electron microscopy (SEM).

Microwave Joining Alumina Ceramics Using Al-Si Alloy Powders at Low Temperature

Alumina composites were joined in air by microwave heating, along with Al-Si alloy powder as the interlayer. The interfacial microstructure and the fracture surface were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Element and phase components of the interlayer were analyzed by X-ray diffraction (XRD). Experimental results clearly indicated that microwave heating method effectively hampered the oxidation of the interlayer and indirectly promoted adhesion. The molten Al-Si alloy wetted and penetrated to the 95-Al2O3 ceramics surface, which formed the well joining interface.

3D Interconnetive Porous Silica Ceramics Prepared by Gel Casting with Egg White Protein as a Foaming Agent

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.

The Interlayer Designation for ZTM Ceramics and Fibre Joining

The joining materials of density ceramics and the fibre would be potential application value as seal materials at high temperature condition or in aerospace field. According to chemical composition consistent principle of ceramics/interfaces/fibre, the interlayer of mullite ingredient was designed which based on the ZTM ceramics composition. Using the absorber-microwaves properties of Al-Si alloy, the joining of ZTM ceramics and fibre materials with interlayer was achieved by microwave hybrid heating method. The experiment results indicated that the volume expansion of interlayer was about 4.8% when the content of Al-Si was 24 wt % in the compositions. The interlayer ingredients were mullite, zirconia and alumina after sintering. The fibres were better joint with interlayer by microwave sintering than by traditional method.

Microwave Joining 95-Al2O3 Ceramics Used Al-Si Alloy as Interlayer

Absorber-microwave material Al-Si alloy powder was used as interlayer to join the 95-Al2O3 ceramics. The behaviors curves of time-temperature for Al-Si alloy interlayer and 95-Al2O3 ceramics at different microwave power were researched. The interlayer morphology of the joints region was characterized by SEM and the element and phase components were analyzed by EDX and XRD. The results indicated that the loact heating around 95-Al2O3 ceramics could be achieved by microwave sintering. The joint interfaces of Al-Si/95-Al2O3 formed at microwave 2KW/20min→0KW and the joint mechanism of 95-Al2O3 ceramics was transient liquid phase diffusion bond.

Phase Relationships of Al2O3-ZrO2-SiO2 System with Microwave Heating

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.