Guo Qiang Luo

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.

Foaming of CNTs/PMMA Nanocomposite with Supercritical Carbon Dioxide

The CNTs/PMMA Nanocomposite Foams Are a Kind of Novel Multifunctional Foams which Have a Potential Application for Lightweight Conductive and EMI Shielding Materials. In this Work, the CNTs/PMMA Nanocomposite Foams with Different CNTs Contents from 1wt.% to 10wt.% Were Prepared at a Temperature Range of 50-140 °C with Supercritical Carbon Dioxide as Blowing Agent. The Results Suggest that the Fully Heterogeneous Nucleation Is Achieved due to the Contribution of Well-Dispersed CNTs in PMMA. The CNTs/PMMA Nanocomposite Foams Exhibit a Uniform Cell Distribution, and the Cell Density Is Two Orders of Magnitude Higher than that of PMMA Foams. The Cell Size and Cell Density of CNTs/PMMA Nanocomposite Foams Could Be Controlled by Adjusting the Foaming Process and CNTs Contents. It Is Also Suggested that the Foaming Process Plays an Important Role on the Cell Structure Rather than that of CNTs Content when it Is Higher than 1wt.%.

The Structure and Electrical Conductivity of the CNTs/PMMA Nanocomposites Foams

Carbon nanofillers/polymer nanocomposites foam with electrical conductivity was a novel functional material. In this study, the CNTs/PMMA nanocomposites were prepared by the combination of ultrasonic dispersion and anti-solvent precipitation method. Then supercritical foaming method was untilized applied to prepare the foams. The morphology and the electrical conductivity of the foams were investigated. The conductivity of the nanocomposites showed a conductor behavior which was increased t from 1×10-6 S/cm to 1×10-5S/cm with the CNTs content range from 1 wt.% to 2.5 wt.%. After foaming, the cell size of the foams was below 10 μm while the cell density increased 2~3 orders of magnitude compared with PMMA foams. The produced CNTs/PMMA nanocomposites foams exhibited a wide range electricity conductivity of the nanofiller contents. Key words: structure, electrical conductivity, CNTs, nanocomposites foams

Calculation of Tape Thickness for Ceramic Tape Casting

Tape casting play a significant role in industrial area, such as multilayered ceramic (MLC) packages, functionally graded materials (FGM), low temperature co-fired ceramics (LTCC) and so on. For the complexity of the rheology for slurry during tape casing process, the control of tape thickness by experience was unstable. Although few numerical and analytical studies on predicting the tape thickness have been done, but these efforts have focused on Newtonian, Bingham, Power law, respectively. There is no unified equation to calculate the tape thickness among different rheological models. In this paper, the calculation results are characterized by wide adaptability; the blade gap, the casting speed and the slurry rheological property are incorporated into calculation; the effect of parameters in the result is studied; Parameter Pnd can be used as a guide to check which mark patterns of the flow velocity profiles in the channel. The results proposed and the experimental measurements from existing publications are in close agreement. Compared with the prediction of the existing models, the calculation results proposed has good agreement with them.

The Effect of Sb Content on Spark Plasma Sintered High-Density Antimony-Doped Tin Oxide Ceramics

Spark plasma sintering (SPS) is a newly developed technique that enables poorly sinterable tin oxide powder to be fully densified. Sintering without sintering aids is of great importance when SnO2 ceramics are used as electrodes in the glass melting industry and aluminum electrometallurgy. Dense and good-conductive Antimony-doped SnO2 ceramics can be achieved by SPS at a lower sintering temperature and in a shorter time. When the Sb2O3 concentration is 1.0 mol%, the densities of the samples reach their maximum value, which is 98.2% of the theoretical value. When the content of Sb2O3 was 2.44mol%, SnO2 ceramics with densities 97.6% can be obtained at 800°C-1000°C, and the resistivity was about 5.19×10-2Ω.cm at the sintering temperature of 1000°C. Defined amount of Sb3+ used in our research are beneficial to low the sintering temperature and promote the densification of SnO2 ceramics

Fabrication of Ti-Mg System Composite with Graded Density at a Low Temperature by SPS Method

A Ti-Mg system composite with graded density, a kind of functiona lly graded materials (FGM), is fabricated by spark plasma sintering (SPS), whose de nsity changes quasi-continuously along the thickness direction. At first Ti-Mg alloys with different rat ios were sintered respectively. It is found that the Ti-Mg alloys can be nearly fully densified at a low temperature of 833K by SPS, and their densification are analyzed by XRD and EPMA. All the sol id solution reaction between Ti and Mg can occur at this sintering temperature, which enhances t he densification of Ti-Mg alloy at a low temperature. Then by inserting 7 Ti-Mg transient laye rs with gradient ratios between Ti side and Mg side, the Ti-Mg system FGM, with a thickness of 2.4mm. rang e from 1.74×10kg/m to 3.23×10kg/m, is successfully fabricated at 883K by SPS in the present paper. Introduction A new kind of functionally graded materials (FGMs) with density gradient can be used as a flierplate in dynamic high-pressure technology. It can produce quasi-isent ropic compression on target materials, from which extreme experimental conditions such as hi gh pressure or high velocity can be obtained for thermodynamic physics study.[1-2] A full dense W-Mo-Ti gra ded density flier-plate material was successfully fabricated by the method of powder metallurgy[4,5]. The experimental result of the impact on a light gas gun show that dynamic quasi-is entropic compression has been created.[6,7] In the present paper, SPS method was used to prepare Ti -Mg alloy, which makes it possible to sinter and sinter–bond at low temperatures and in short peri ds by charging the intervals between powder particles with electrical energy and effective ly applying a high temperature spark plasma generated momentarily.[8,9] Ultimately Ti-Mg FGM was s uccessfully fabricated at the same experimental conditions. Experimental The fresh powders of Ti and Mg with particle size of 30 m and 70~100 m respectively were used(Table 1). The powders were given in the design ratios (table 2), mixed mechanically and blended for enough time to make them homogeneous. Then the mixture was put into a graphite mould and sintered by SPS. For all Ti-Mg alloy samples, the sint ring temperature of 833K and the pressure of 30Mpa were held constantly for 10min. The size of sinter ed compact was 32mm in diameter and 2mm in height. The size of Ti-Mg system FGM wa s 32mm in diameter and 2.4mm in height. There were 7 Ti-Mg transient layers, which are Mg90Ti 1 , Mg80Ti20, Mg70Ti30, Mg60Ti40, Mg50Ti50, Mg40Ti60, Mg30Ti70 between Ti side and Mg side. The densities of the samples were measured by the water-imme sion method. The phase composition was analyzed by XRD (RIGAKU RAD-C). The microstruc tures of the samples were observed by EPMA (JEOL JXA-8800R). Table 1 Relevant Parameters of materials Material Average particle Purity Theoretical density Size/( m) (%) x03/(g/cm3) Ti powder x0130 x0499 4.51 Mg powder 70~100 x0499.9 1.74 Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 249, pp 291-294 doi:10.4028/www.scientific.net/KEM.249.291

Preparation and Electrical-Conductive Property of SnO2-Based Ceramics

In this study, SnO2-based ceramics, with CuO as sintering aid and Sb2O3 as activator of the electrical conductivity, was obtained by pressure-less sintering at 1100°C ~ 1470°C. Addition of antimony leads to a higher densification temperature. Densification behavior and microstructure development are strongly dependant on CuO and Sb2O3. CuO gives rise to a liquid phase; Sb2O3 retards the formation of liquid phase and hinders the growth of grain. The electrical resistivities of SnO2-based ceramics vary in a wide range from 10-2 to 107 Ω•cm, depending on starting compositions and processing conditions. The electrical resistivities of samples with different amounts of CuO and Sb2O3 show different trends with the increasing of sintering temperature. The addition of antimony rapidly promotes electrical conductivity of SnO2-based ceramics containing CuO as the solid solution reaction of Sb2O3-SnO2. As the additions of CuO and Sb2O3 are the same, the electrical resistivity arrives the minimal value of 4.72×10-2 Ω•cm for 99%SnO2+0.5%CuO +0.5%Sb2O3 at 1470°C. More content of Sb2O3 than CuO causes the degression of density and the rising of electrical resistivity of ceramics.

Preparation and Electrical-Conductive Property of SnO2-Based Ceramics with 0.5% CuO and Sb2O3

In this study, SnO2-based ceramics, with 0.5%CuO as sintering aid and Sb2O3 as activator of the electrical conductivity, was obtained by pressureless sintering at 1450°C for 5 h. Densification behavior and microstructure development strongly depend on Sb2O3. The characteristization of microstructures on Sb2O3 concentrations are analyzed by SEM. A small amount of CuO improves densification; Sb2O3 retards the densification of SnO2-based ceramic. The electrical resistivities of SnO2-based ceramics with different contents of Sb2O3 are measured by the standard four probe method and varied in a wide range. The electrical resistivity arrives the minimal value of 4.964×10-2 0·cm for 99%SnO2+0.5%CuO +0.5%Sb2O3. More content of Sb2O3 than that of CuO causes the degression of density and the increasing of electrical resistivity of ceramics.

In Situ Synthesis of Size-Controlled Silver/Poly(Methyl Methacrylate) Nanocomposite

In this work, monodispersed silver nanoparticles with controllable size have been successfully in situ synthesized in PMMA matrix. NaHS, HCl and poly (vinyl pyrrolidone) (PVP) were used to optimize the nucleation and growth of silver nanocrystalline. UV–vis analysis and transmission electron microscopy (TEM) were used to characterize the size and dispersion of silver nanoparticles in the Ag/PMMA nanocomposites. The results show that silver nanoparticles homogeneously distribute in PMMA/DMF sol and the particle size of silver nanoparticles increase with the increasing of time. The nucleation of Ag atoms can be facilitated through the addition of a trace amount of NaHS to generate Ag2S clusters as heterogeneous nuclei. Introducing a trace amount of Cl- into the reaction system can effectively reduce the growth rate of the nanoparticles and thus generating more uniform silver nanoparticles in PMMA matrix.

Hot-Press Sintering of the W-40wt.%Cu Composite Tape-Casting Film

In this research, the W-40wt.%Cu composite tape-casting films were prepared through the vacuum hot-press sintering method, and the effect of sintering temperature on the microstructures and properties of the W-40wt.%Cu composite samples was studied. Microstructures of the W-40wt.%Cu tape-casting film and the prepared samples were analyzed by field emission scanning electron microscopy (FE-SEM). The phase of the samples was investigated by X-ray diffraction (XRD). The relative density, Vickers hardness, bending strength and electrical conductivity of the samples were investigated. The results show that the relative density of the W-40wt.%Cu composite materials enhances with the increasing of the sintering temperature, at the same time the mechanical and electrical properties are better with the increasing of the sintering temperature. The W-40wt.%Cu composites prepared at the condition of 900°C-200MPa-2h have the relative density of 97%, the bending strength of 507.3MPa, the Vickers hardness of 376.2HV and the electrical conductivity of 32.5% IACS, respectively.