Lian Meng Zhang

The Preparation and Characterization of 3D-Silica Fiber Reinforced Silica Composites

The Preparation process of fused silica matrix composites reinforced with threedimensional (3-D) braid via liquid phase infiltration deposition was investigated. The results indicate that the densification is significantly enhanced by using infiltration process with suspension of silica and the addition of a non-ionic surfactant. The 3D SiO2f/ SiO2 specimens have density of 1.65g/cm, flexural strength of 75MPa. Flexural testing and scanning electron microscopy of fracture surface were used to determine mechanical properties and fracture mechanisms. Fractography reveals that the fiber and matrix interface debonding and fiber pulling-out absorb the majority of fracture energy, which is regarded as the principal reason for resulting in the pseudo ductility and toughening mechanisms of the composites.

Preparation and Thermoelectric Properties of Bi-Doped Mg2Si Nanocomposites

Nanocomposites and heavy doping both are regarded as effective way to improve materials’ thermoelectric properties. 0.7at% Bi-doped Mg2Si nanocomposites were prepared by spark plasma sintering. Results of thermoelectric properties tests show that the doping of Bi atom effectively improves the electrical conductivity of Mg2Si，and the nanocomposite structures are helpful to reduce thermal conductivity and increase Seebeck coefficient, hence improving the thermoelectric performance. A maximum dimensionless figure of merit of 0.8 is obtained for the Bi-doped Mg2Si nanocomposite with 50 wt % nanopowder inclusions at 823K, about 63% higher than that of Bi-doped Mg2Si sample without nanopowder inclusions and 119% higher than that of microsized Mg2Si sample without Bi-doped, respectively.

Flexural Properties of 3D- SiO2/ SiO2 Composites

Silica fiber preform reinforced fused silica composites were fabricated with the variation of silica fiber content by repeated vacuum-assisted liquid-phase infiltrations. Flexural test was conducted to investigate the effect of silica fiber content and tre atment temperature on the flexural strength of the 3D-SiO 2 /SiO2 composite. Fracture behavior of the composites was investigated to study the relationship with the flexural property data. The flexura l strength improved with the increment of silica fiber content and decreased with the increment of treatment temperature. The flexural strength of the composite showed the maximum value at 50vol % silica fiber content and treatment temperature at 700 C. Fractography revealed that the composite was damaged by microdebonding at the fiber/matrix interface and the fracture of fiber.

Effect of pH Value on the Properties of SnO2 Nano-Cystalline for Dye Sensitized Solar Cells

The study of dye-sensitized solar cells (DSCs) based on nanocrystalline films of high band gap semiconductors is a progressive field of research that is being carried out by scientists in a wide range of laboratories. To improve the conversion efficiency of the DSCs, the SnO2 nanorots photocurrent is prepared via the hydrothermal method, and characterized by XRD, FESEM, BET and Absorption spectrum. Though analysis the results, the conclusion is shown the pure SnO2 is preparation, the SnO2 nanocrystalline both shows the single phase that SnO2 from the sule solution to kalin solution. The prepared SnO2 nanocrystalline under pH=3 shows the particle-shape crystalline, the surface area of SnO2 nanocrystalline is 86.3412m2/g. The prepared SnO2 nanocrystalline under pH=7 shows the short rod-shape crystalline, the surface area of SnO2 nanocrystalline is 58.3408m2/g. The absorbance of SnO2 nanocrystalline shows the strong absorption in the ultraviolet ray range, the absorbance of synthesized SnO2 nanocrystalline under pH=11 shows the highest value.

Preparation and Properties of 0-3 PZT/PVDF Piezoelectric Composite

The 0-3 PZT/PVDF piezoelectric composites were prepared by the solution-mixing method with hydrothermal synthesized PZT powders and ethanol as the appropriate solution. The results of properties measurement show that the piezoelectric and dielectric constants are improved to 65pc/N and 201, respectively, when PZT volume content in PZT/PVDF composites was 60%. Introduction Piezoelectric ceramic-polymer composites with 0-3 connectivity are considered to be important for underwater acoustic transducer and medical diagnostic applications since they can be fabricated in suitable thin and flexible forms to provide enhanced hydrostatic piezoelectric properties and improved acoustic impedance. Among the composites studied so far, attention has been paid to many aspects that affect the properties of the composites, such as the size of ceramic particles, the manufacturing and poling process of the composites. But these composites are not well polarized to have certain distance from industrial application [1-2]. In the present paper, attempts of adopting the PZT powders synthesized by the hydrothermal method to improve the dielectric and the piezoelectric properties of 0-3 PZT/PVDF composites were made. It is known that hydrothermal synthesized PZT powders are of regular geometry shape and narrow particle size range, which enhances the piezoelectricity and thus improves the uniformity and the dielectric properties of the composites. Experimental Hydrothermal synthesis of PZT ceramic powders. Lead acetate (Pb(CH3COO)2), Zirconium oxychloride (ZrOCl2), and tetra-n-butyl titanate (Ti(OC4H9)4, were used as starting materials. The hydrated mixed feedstock was prepared as follows: (Pb(CH3COO)2, aqueous solution(0.5M), ZrOCl2 aqueous solution(0.5M) and (Ti(OC4H9)4 ethanol solution(0.5M) were added into a NaOH solution(5M to 10M) as the reaction medium in desired ratios of Pb/(Zr+Ti)(1.5/1.0) and Zr/Ti(0.58/0.42)[3]. The feedstock was heated at 240C for 2h then the product was filtered and washed successively with deionized water to remove any excess PbO. Finally, the powders were dried at 100 C in air. Selection of appropriate solution for solution mixing. To determine a compatible PVDF solvent used in the powder suspension, toluene, ethanol, and methanol were studied extensively[4]. The adsorption isotherms of polymer onto the ceramic powder in these solvents were measured. The testing began with preparation of solutions containing 5, 10, 15, 25, or 30g of PVDF per litter of the solvent. The ceramic powders were oven-dried and stored in a desiccator to minimize the adsorption of moisture. The resulting slurries were ultrasonically dispersed then centrifuged. The supernatant liquid was removed by decantation and the polymer not strongly adsorbed by particles was removed. The cake was then dried at 110 C in air and the weight loss, after heating at 750 C, was measured to determine the amount of adsorbed polymer. Preparation of composite. PZT powders were added into an ethanol solution with suitable amount of PVDF ceramic powders. The mixing solution was ultrasonically dispersed to produce the composite suspension. Then the suspension was poured onto a glass plate and left for drying at 70C. The composite was molded into disks with a diameter of 25mm and thickness between 11.1mm. After being coated with Ag electrode and treated at 160 C, the sample was poled under Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 249, pp 129-132 doi:10.4028/www.scientific.net/KEM.249.129

Spark Plasma Sintering of α-Si3N4 Ceramics with MgO-Al2O3 as Sintering Additives

In the present study, α-Si3N4 is prepared by using MgO and Al2O3 as the sintering additives and spark plasma sintering (SPS) technique. The SPS sintering mechanism is discussed. The relationship between the content of sintering additives, sintering temperature and relative densities of the samples is analyzed. The results suggest that when the sintering temperature is 1300-1500°C, the content of sintering additives is 6wt.%-10wt.%, the relative density of sintered samples is 64%-96%. When the sintering temperature reaches 1400°C, the content of sintering additives is 10%, the samples can be fully dense sintered and the relative density can be up to 95%. The sintering mechanism is liquid phase sintering. The bending strength of the sintered samples is 50-403MPa and has a close correlation with the relative density.

Densification Mechanism of SnO2 Ceramics Doped with 5.0 mol% MnO2

Dense SnO2 based ceramics are widely used. In this paper, 95SnO2-5MnO2 ceramics were prepared by pressureless sintering in air at different temperatures. Phase compositions and microstructures are examined by XRD, SEM and EDX, respectively. The SEM results show that different morphologies exist at the SnO2 grain boundary of ceramic, which compose of manganese oxidation, testified by EDX. The different manganese oxides phases, found by XRD, are the source of oxygen concentration at the grain boundary during heating and oxygen dissipation when cooling. However, solid solutions of Mn, Sn and O are not observed. The density of 95SnO2-5MnO2 ceramics decreases with increasing the sintering temperature, due to the evaporation of SnO and decreasing concentration of oxygen at grain boundary in the cooling process. Densification of the ceramic is promoted with inhibiting the decomposition of SnO2 by increasing oxygen concentration in the heating process, but it is limited by the dissipation of oxygen at the grain boundary in the cooling process.

Fabrication by SPS and Thermophysical Properties of High Volume Fraction SiCp/Al Matrix Composites

SiCp/Al composites containing high volume fraction of SiC particles were fabricated by spark plasma sintering (SPS), and their thermophysical properties, such as thermal conductivity (TC) and coefficient of thermal expansion (CTE), were characterized. High relative density (R-D) of composites was successfully achieved through the optimization of sintering parameters, such as sintering temperature, sintering pressure and heating rate. The measured TCs of SiCp/Al composites fabricated by SPS are higher than 195W/m.k, no matter the volume fraction of SiC particles is high or low as long as the R-D is higher than 95%. The measured CTEs of SiCp/Al composites are in good agreement with the estimated values based on Kerner,s model. The high volume fraction of SiCp/Al composites are a good candidate material to substitute for conventional thermal management materials in advanced electronic packages due to its tailorable thermophysical properties.

Local Graded Structure in 6.5wt%Si-Fe Alloy and the Effect on Ductility

The changes of phase composition and structure evolvement of Fe and Si powders with the ratio of 6.5wt%Si to 93.5wt%Fe were mainly studied. It is found that, the local graded structure, Fe-Fe(Si)-Fe3Si-(FeSi)-Si, forms due to the obvious diffusion and the alloying reaction between Fe and Si powders when sintering at 900-975oC. The graded structure, in which the high silicon phase based on Fe-Si alloys is packed by the low silicon solution based on Fe, exhibits a graded concentration of Si distribution. And most of the Fe-containing phase remains a state of lower Si content, less than that of 3wt%Si-Fe alloy, thus provides the good deformation behavior of rolling and cutting for the compacts. Therefore, it is feasible for the high silicon iron sheets to be produced by the powder metallurgy method.

Toughening and Strengthening Mechanism of Zirconia-Alumina Multiphase Ceramics

In the present study, the effect of compositions on the mechanical properties of zirconia-alumina multiphase ceramics was studied. The results showed that with the variety of ZrO2 content, the change of bending strength and fracture toughness of the multiphase ceramics exhibited a saddle shape which could be divided into three zones: ZTA, ADZ, and Transition zone. The mechanism of toughening and strengthening in each zone was mainly analyzed, and it was found that stress-induced transformation toughening of ZrO 2 and dispersion strengthening of Al 2O3 were the two main factors. Introduction ZrO2-Al 2O3 multiphase ceramics have attracted much attention because their mechanical properties are more excellent than the single-phase ceramics, and many r esearches have been done on them. Tsukuma et al [1-3], studied the properties of Y-TZP/Al 2O3 materials firstly, and found that the bending strength of Y-TZP reached more than 2GPa after Al 2O3 was added. Kihara et al [4] found that the value of toughness and strength could be improved by 32% and 17% respectively with the adding of a small amount of Al 2O3 (1.0vol%). More researches [5-6] have also shown that there existed a maximal adding value of Al 2O3 which was used to modify the properties of Y-TZP ceramics. All the above researches have agreed on that the toughness of alumina ceramics was improved by zirconia while the strength of zirconia was improved by alumina . But the optimum composition ratio of Al2O3 to ZrO2 for obtaining the best properties of the multiphase ceramics was not confirmed yet. Therefore, in the present study the dependence of struc ture and properties on the content of multiphase ceramics was studied, and the mutual action mechanism betw een zirconia and alumina was also illustrated. Experimental Sample preparation. ZrO2 raw materials with 1.5mol% Y 2O3 and 4mol% CeO2 were prepared by chemical co-precipitation method. Al 2O3 was produced by thermal decomposition method. In order to investigate the mutual action between Al 2O3 and ZrO2, eleven formulae were designed which are listed in Table 1. Table 1 Compositions in weight of the samples Sample AZ0 AZ1 AZ2 AZ3 AZ4 AZ5 AZ6 AZ7 AZ8 AZ9 AZ10 ZrO2 0 10 20 30 40 50 60 70 80 90 100 Al 2O3 100 90 80 70 60 50 40 30 20 10 0 The powders of Al 2O3 and (Y, Ce)-ZrO2 were mixed by ball-milling method, followed by cold isostatic press moulding (300MPa). Then the green bodies were sintered at 1550°C, 1600°C, 1650°C, 1700°C for sample AZ0 to AZ5 with high Al 2O3 content, and sintered at 1500 °C, 1550°C, 1600°C, 1650°C for samples with high content of ZrO 2, in order that all the samples could be fully Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 249, pp 167-170 doi:10.4028/www.scientific.net/KEM.249.167