Liao Jiqiao

Particle size characterization of ultrafine tungsten powder

Abstract The aim of this research was to investigate the particle size measurement of as-supplied and lab-milled ultrafine tungsten powders. The ultrafine tungsten powder derived from X-ray diffraction pure WO3 by hydrogen reduction process under “dry” reduction conditions was milled for 1, 2 and 4 h, respectively. Then the as-supplied and lab-milled tungsten powders were used to perform particle size measurement by laser diffraction method and Fisher sub-sieve sizer (FSSS) method and BET method through adsorption isotherms. Results show that the mean particle size values of as-supplied and lab-milled powders measured by laser diffraction method and FSSS method were misleading because of the defects of the measurement system or unsuitability of measurement theory. And the calculated particle size of dBET values from the formula 6/(S BET density ) were smaller than that of by SEM method, which was resulted from the neglect of the effect of surface roughness and pore area on dBET calculation. The fractal dimension D of surface roughness and external surface area St of pores were obtained from adsorption isotherms, which were used to modify dBET calculation formula. The modified formula was d BET ( M ) =k (D/2)×6/(S BET density ), where coefficient k was a constant, it was a function of pores area, D was fractal dimension value of surface roughness. As to the ultrafine tungsten powders in this investigation, k was defined as SBET/St, so modified dBET(M) may be expressed as 3D/( S t density ). By the modified formula, the calculated dBET(M) values of four powders in this study were in good agreement with the SEM sizes.

Influence of porosity and total surface area on the oxidation resistance of C/C composites

Abstract The oxidation tests of five different porosity C/C composites for non-isothermal oxidation and three different porosity samples for isothermal oxidation in O 2 and two samples which had approximate porosity and different total surface area values for static air oxidation were performed. Results show that the oxidation was controlled by the total surface area other than by the open porosity or the densification degree of samples or amount of pore entrance. The oxidation occurred preferentially at the fiber–matrix interface and pyrocarbon–pyrocarbon interface, and then progressed along the micro-cracks between the interfaces.

Influence of tungsten oxides' characteristics on fineness, homogeneity and looseness of reduced ultrafine tungsten powder

This paper deals with the influence of the characteristics of tungsten oxides on fineness, homogeneity and looseness of tungsten powder by conventional hydrogen reduction techniques.

Determination of physical characterization of tungsten oxides

The physical characterization of surface area, micropore volume, micropore size distribution, mesopore volume, average pore diameter and fractal dimensions of four tungsten oxides of ammonium tungsten bronze, (NH4)0.5WO3 (ATB), hydrogen tungsten bronze, H0.33WO3 (HTB), violet tungsten oxide, W18O49 (TVO), and tungsten blue oxide, WO3+WO2.9 (TBO) were evaluated from the analysis of nitrogen adsorption–desorption isotherm data. Analysis of the adsorption–desorption isotherm data suggested that in this study TVO with the largest mesopore volume, the smallest micropore volume, the narrowest micropore size distribution, the lowest fractal dimension value and the biggest average pore diameter was advantageous for hydrogen reduction during fine tungsten powder production process and disadvantageous for doping process; HTB with the largest micropore volume, the widest micropore size distribution, the highest fractal dimension value and the smallest average pore diameter was favorable for doping process, and characterization properties of ATB and TBO in this investigation were just between TVOs and HTBs. Results showed that it was a preferable method to investigate the physical characterization of oxides by using adsorption–desorption isotherms in this study and the physical characterization of tungsten oxides should be taken into account before they are used in reduction process or in doping process.