Pore Fractal Characteristics of Suancigou Long-Flame Coal after Electrochemical Treatment: An Experimental Study through the Implementation of N2 Adsorption and Mercury Intrusion Prosimetry Techniques.

The application of electrochemical treatment in coal seams for enhancing coalbed methane (CBM) recovery can also decrease the risks of outburst disasters. The long-flame coal samples were electrochemically modified with 0, 1, 2, and 4 V/cm electric potential gradients, and the pore structures were measured and analyzed by combined low-temperature nitrogen gas adsorption, mercury intrusion prosimetry, and fractal theory. The experimental test results indicated that the pore volumes of macropores (>50 nm) and mesopores (2-50 nm) increased after electrochemical modification and further increased with the increase in electric potential gradient. The fractal dimensions of pores showed a decreasing trend except for the slight fluctuation of the mesopores with a size of 2-4.5 nm after modification, which indicated that the overall roughness and irregularity index of pores decreased. The evolution mechanisms of pore size distributions and their fractal dimensions were explained by the dissolution of minerals and the falling off of alkane side chains in the coal surface, which would expand and connect the pores during the electrochemical modification process. The results obtained from this work were crucial for CBM exploration via an electrochemical method.

Effect of Electrolyte pH on CH4 Adsorption and Desorption Behavior in Electrochemically Modified Lean Coal.

Practical application of the electrochemical method for enhancing coalbed methane (CBM) extraction is limited due to the insufficiency of in-depth experimental and theoretical research. Therefore, H2SO4, Na2SO4, and NaOH electrolytes with different pH values were selected to electrochemically modify lean coals and their CH4 adsorption and desorption behaviors were tested. The experimental results showed that the amount of CH4 adsorption decreased after modification using H2SO4 and Na2SO4 electrolytes, and increased after electrochemical modification using the NaOH electrolyte. The ratio of CH4 desorption increased from 83.20 to 90.10 and 87.84%, respectively, after electrochemical modification using H2SO4 and Na2SO4 electrolytes, and decreased to 81.71% after electrochemical modification using the NaOH electrolyte. The pore volume and average pore size increased, and the specific surface area decreased with the decrease of electrolyte pH. Lower pH electrolytes perform better and the mechanism was analyzed by the change of surface energy, surface groups, and pore structures. The work will provide a basis for the reasonable selection of electrolyte pH when using in situ electrochemical methods for enhancing CBM extraction.

Effect of Electric Potential Gradient on Methane Adsorption and Desorption Behaviors in Lean Coal by Electrochemical Modification: Implications for Coalbed Methane Development of Dongqu Mining, China.

The application of electrochemical modification for accelerating methane extraction in lean coal seams is limited due to the lack of experimental and theoretical research studies. Therefore, electrochemical modification with different electric potential gradient values was selected to modify lean coals in this study; meanwhile, the amount of methane adsorption and the methane desorption ratio were tested and analyzed. The results showed that the maximum amount of methane adsorption in coal samples decreased after electrochemical modification and the decrease in methane adsorption increased with an increase in electric potential gradient. The methane desorption ratio increased from 83.20% up to 87.84 and 86.90% at the anode and cathode zone, respectively, after electrochemical modification using a 4 V/cm electric potential gradient. A higher electric potential gradient performs better in the electrochemical modification. The mechanism of electrochemical modification using different electric potential gradients was revealed based on the measurements of Fourier transform infrared spectroscopy and liquid nitrogen adsorption. It is due to an increase in acid groups in coal molecular structure and the change of the specific surface area of coal after modification. The results obtained from this work contribute to the methane extraction via the electrochemical method in lean coal seams.

Measurement and modeling of the adsorption isotherms of CH4 and C2H6 on shale samples.

CH4 and C2H6 are two common components in shale gas. Adsorption isotherms of CH4, C2H6, and their binary mixtures on shale samples are significant for understanding the fundamental mechanisms of shale gas storage and the recovery of shale resources from shale reservoirs. In this study, the thermogravimetric method is applied to obtain the adsorption isotherms of CH4, C2H6 and their binary mixtures on two typical shale core samples. A simplified local density theory/Peng-Robinson equation of state (SLD-PR EOS) model is then applied to calculate the adsorption of CH4 and C2H6 on shale, and the efficiency of the SLD-PR EOS model is thus evaluated. The results show that C2H6 exhibits a higher adsorption capacity than CH4 on shale samples, indicating the greater affinity of C2H6 to organic shale. As the molar fraction of C2H6 increases in the CH4/C2H6 mixtures, the adsorption capacity of the gas mixtures increases, indicating the preferential adsorption of C2H6 on shale. Based on the predicted results from the SLD-PR EOS model, a reasonable agreement has been achieved with the measured adsorption isotherms of CH4 and C2H6, validating the reliability of the SLD-PR EOS model for predicting adsorption isotherms of CH4 and C2H6 on shale samples. In addition, the SLD-PR EOS model is more accurate in predicting the adsorption of CH4 on shale than that of C2H6. This study is expected to inspire a new strategy for predicting the adsorption of hydrocarbons on shale and to provide a basic understanding of competitive adsorption of gas mixtures in shale reservoirs.

Formation mechanism and characterization of black silicon surface by a single-step wet-chemical process.

We report a simple single-step etching method for formation of black surface on silicon wafer by using HAuCl4-HF-H2O2 etching solution, in which catalytic Au particles were deposited in situ. The black surface suppresses the reflectivity in a wide spectral region. The formation mechanism involved has been discussed.

Metalorganic chemical vapor deposition growth of InAs/GaSb type II superlattices with controllable AsxSb1-x interfaces.

InAs/GaSb type II superlattices were grown on (100) GaSb substrates by metalorganic chemical vapor deposition (MOCVD). A plane of mixed As and Sb atoms connecting the InAs and GaSb layers was introduced to compensate the tensile strain created by the InAs layer in the SL. Characterizations of the samples by atomic force microscopy and high-resolution X-ray diffraction demonstrate flat surface morphology and good crystalline quality. The lattice mismatch of approximately 0.18% between the SL and GaSb substrate is small compared to the MOCVD-grown supperlattice samples reported to date in the literature. Considerable optical absorption in 2- to 8-µm infrared region has been realized.PACS: 78.67.Pt; 81.15.Gh; 63.22.Np; 81.05.Ea.