The dependence of the nanotribological properties of ultrathin amorphous carbon (a-C) films, deposited on Si(100) substrates by radio frequency sputtering, on their nanomechanical properties was investigated using surface force microscopy. The thickness and nanohardness of the a-C films were found to be in the range of 7–95 nm and 9–44 GPa, respectively. Sharp conical diamond tips with a 90 deg included angle and radius of curvature of about 20 μm and 100 nm were used to perform friction and wear experiments, respectively. The effect of the substrate compliance on the nanomechanical and nanotribological properties of the a-C films is interpreted in terms of the indentation depth and the film thickness. The coefficient of friction and wear rate of the a-C films are related to their nanomechanical properties, thickness, and surface roughness. The dependence of the coefficient of friction on contact load and the dominant friction mechanisms of elastically and plastically deformed films are discussed in light of friction force and surface imaging results. High effective hardness-to-elastic modulus ratio and low surface roughness characterize high wear resistance a-C films. Below a critical load, the steady-state removal rate of the film material is insignificantly small, revealing a predominantly elastic behavior.

Permeability improvement of coal seams by hydraulic fracturing can promote desorption of coalbed methane. However, the water-block effect will restrain desorption of coalbed methane. Based on the essence of the physical adsorption of methane, competitive adsorption, substitution desorption, the capillary effect, and the Jamin effect are analyzed to study the effect of the critical moisture content and liquid water on methane adsorption and desorption. Simultaneously, the effects of the fluid pressure, fracturing fluid, fracturing time, pore pressure, and other variables on methane adsorption and desorption characteristics are analyzed. Then, problems that require further study are described.

Thin films of nitrogenated amorphous carbon (a-CNx) were deposited on Si(100) substrates by reactive radio frequency sputtering using a gas mixture of Ar and N2 at a total working pressure of 3 mTorr. X-ray photoelectron spectroscopy (XPS) showed that the films consisted of amorphous carbon (a-C) containing a β-C3N4-like phase with N atoms bonded to C atoms in tetrahedral coordination (sp3) and a graphite-like phase with N atoms bonded to C atoms in trigonal coordination (sp2). Analysis of the XPS spectra revealed a strong effect of the N2 partial pressure on the concentration and composition of each constituent. The thickness and nanohardness of the a-CNx films were in the ranges of 7–35 nm and 12.5–40 GPa, respectively, depending on the fraction of N2 in the sputtering gas. Conversely to the chemical composition, the growth rate (thickness), microstructure, and nanomechanical properties of the a-CNx films were found to depend on the total mass flow rate. While the N/C atomic ratio increased with the N2 partial pressure, the film nanohardness and in-plane elastic modulus decreased due to the reduced energetic ion bombardment on the growing film surface and the incorporation of soft phases in the sputtered films. Nanoindentation and XPS results are presented to elucidate the deposition kinetics and to interpret the dependence of the resulting film microstructure and nanomechanical properties on the plasma conditions.

The mechanical stability of amorphous carbon (a-C) films deposited on ultrasmooth Si(100) substrates by radio-frequency sputtering under different energetic ion bombardment conditions was investigated in light of results obtained from aging and annealing experiments. The a-C films were annealed at 495 °C in the high-vacuum chamber of an x-ray photoelectron spectroscopy (XPS) system with a base pressure of 10−8 Torr. The annealing process consisted of three sequential heating cycles of temperature 495 °C and duration 5, 10, and 70 min, respectively. Atomic force microscopy and XPS studies were conducted to reveal possible changes in the surface topography, microstructure, and composition of the a-C films. To investigate the effect of annealing on the nanomechanical properties of the a-C films, nanoindentation experiments were performed with a surface force microscope. Only subtle changes in the surface topography, microstructure, composition, and nanomechanical properties of the a-C films were observed after aging for about two years. Film agglomeration during annealing due to residual stress relaxation was found to strongly depend on the kinetics of film deposition. It is shown that the stability of the a-C films is affected by residual stresses produced from the energetic ion bombardment during film growth. The magnitude of the residual stress and the film thickness exhibits a pronounced effect on the thermodynamics and kinetics of film agglomeration. The experimental results demonstrate that increasing the residual stress and/or film thickness decreases the mechanical stability of the a-C films.

Directional rupture is one of the most important and common problems in rock breaking engineering. The purpose of directional rock breaking can be effectively realized by using multihole linear codirectional hydraulic fracturing. In this paper, realistic failure process analysis (RFPA) software is used to verify the experimental results of multihole linear codirectional hydraulic fracturing and investigate its basic law. The following results are demonstrated: (1) RFPA software can be very helpful to study the basic law of multihole linear codirectional hydraulic fracturing; (2) the process of multihole linear codirectional hydraulic fracturing can be divided into four stages: water injection boost, fracture initiation, stable fracture propagation, and fracture connection; and (3) multihole linear codirectional hydraulic fractures propagate along the direction of borehole distribution. Multihole codirectional hydraulic fracturing is influenced by the angle between the direction of the hole distribution and maximum principal stress, the difference of the principal stress, and the spacing of the boreholes. The smaller the angle, the difference value of the principal stress, and the hole spacing, the better the multihole codirectional hydraulic fracturing effect.