ABSTRACT
Particle void filling effects (P f) under low pressure and coal matrix compressibility effects (P c) at high pressure should not be ignored when using mercury intrusion porosimetry (MIP) to study the pore size distribution of coal. In this study, two coal samples (FX and HF) collected from western Guizhou were crushed into three different grain sizes; then, the subsamples were analyzed by MIP and low-pressure nitrogen adsorption to study the pore size distribution characteristics. The micro- and transition pore volumes contribute to the total pore volume of the FX and HF subsamples. With decreasing subsample grain sizes, the macropore volume of FX subsamples tends to increase, while mesopore volume decreases; the volumes of micropores and transition pores first increase and then decrease. In regard to the HF subsamples, the volumes of macropores and mesopores do not reveal any distinctive changes, while the 40-60 mesh subsample contains the greatest volume of micropores and transition pores. Fractal theory was introduced to determine P f and P c. P f barely changed as grain size decreased; it ranged from 0.1 to 0.15 MPa. However, P c increased with reduced coal grain sizes. The coal matrix compressibility coefficients of the subsamples were calculated from the cumulative mercury volume curve, and the true pore volume was also modified. The modified volume of macropores does not change markedly, while the volumes of mesopores and transition pores decrease significantly, clearly indicating the coal matrix compressibility under high mercury injection pressure. The modified pore volume shows that the pore (<10,000 nm) still harbors fractal characteristics.
ABSTRACT
Nano-silver particles were synthesized through chemical reduction method, using silver nitrate, m-dihydroxybenzene and polyvinylpyrrolidone as silver source, reduction agent and protective agent respectively; and redundant reactants were removed through centrifugation and washing operation. Then different nano-silver colloids were acquired by dispersing the nano-silver particles in water, ethanol and ethylene glycol respectively through ultrasonic dispersion. For comparison, the nano-silver particles mass fraction of all the colloids was 0.2 Wt% during the research. Nano-silver particles were characterized by laser particle size analyzer, transmission electron microscopy (TEM) and scanning electron microscopy (SEM); and the concentration of nano-silver colloids was confirmed through synchronized thermal analyzer (STA). The size distribution result of laser particle size analyzer showed that nano-silver particles were about 100 nm and had uniform size distribution. The images of TEM and SEM showed that the size of nano-silver particles was in nanoscale as well. To evaluate the dispersion stabilities of different nano-silver colloids, Turbiscan optical analyzer which was based on multiple light scattering analysis had been employed in the research; and the principle factors leading to instabilities of nano-silver colloids were also discussed. Results showed that particle size variation and particle migration were major factors which affected the dispersion stabilities of nano-silver colloids. For the nano-silver colloid dispersed in water phase, the backscattering light signal in middle of the sample cell stayed unchanged with time while the backscattering light signals at top and bottom of the sample cell showed dramatic variation during the measurement, which indicated that particle migration was the main reason why the nano-silver colloids was unstable. But for the nano-silver colloids dispersed in ethanol and ethylene glycol phase, the backscattering light signals in bottom, middle and top of the sample cell presented obvious variation at the end of the tests, which certificated that both particle size variation and particle migration affected the stabilities of nano-silver colloids. At last, by comparing the Turbiscan Stability Index (TSD of three different nano-silver colloids, the stabilities of the systems were outlined by a descending order: ethylene glycol, water and ethanol.
