Super High-Concentration Si and N Doping of CVD Diamond Film by Thermal Decomposition of Silicon Nitride Substrate.

The high-concentration N doping of diamond film is still a challenge since nitrogen is limited during diamond growth. In this work, a novel method combined with the thermal decomposition of silicon nitride was proposed to form the activated N and Si components in the reactor gas that surrounded the substrate, with which the high-concentration N and Si doping of diamond film was performed. Meanwhile, graphene oxide (GO) particles were also employed as an adsorbent to further increase the concentration of the N element in diamond film by capturing the more decomposed N components. All the as-deposited diamond films were characterized by scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. For the pure diamond film with a growth time of 0.5 h, the N and Si concentrations were 20.78 and 41.21 at%, respectively. For the GO-diamond film, they reached 47.47 and 21.66 at%, which set a new record for super high-concentration N doping of diamond film. Hence, thermal decomposition for the substrate can be regarded as a potential and alternative method to deposit the chemical vapor deposition (CVD) diamond film with high-concentration N, which be favorable for the widespread application of diamond in the electric field.

Effect of flue gas on elemental mercury removal capacity of defective carbonaceous surface: A first-principles study.

The atomic interaction between elemental mercury in the flue gas and defective carbonaceous surface is studied by the first-principles calculation. The defective carbonaceous surface is modeled by a nine-fused benzene cluster with two adjacent atomic vacancies. The results indicate that vacancies can increase the activity of their neighboring carbon atoms. However, the vacant sites present the decrease in mercury removal capacity, which is different from the behavior of the defective carbonaceous surface with only one atomic vacancy. In addition, flue gas molecules (FGMs) including CO, CO2, NO, NO2, SO2 and H2O, are examined to evaluate the influence on the mercury removal of the defective carbonaceous surface. The calculated results demonstrate that different adsorption behaviors for Hg0 occur on the defective carbonaceous surface due to the presence of FGMs. It can be found that CO may enhance the mercury removal capacity of the defective carbonaceous surface when its concentration is higher than that of Hg0. Meanwhile, SO2 presents the remarkable positive effect on the mercury removal efficiency at the vacancy. On the contrary, the presence of CO2, NO, NO2 and H2O leads to the increase in the adsorption energies of mercury on the defective carbonaceous surface.

Influence of Adhesive Strength, Fatigue Strength and Contact Mechanics on the Drilling Performance of Diamond Coating.

Adhesive strength of the coating significantly affects the lifetime of the coating. However, it is still inevitable for the coating, even with strong adhesive strength, to peel off from the substrate after working for a while. In this work, fatigue and wear behaviors were employed to analyze the effect on the mechanics of coating and contribute to a fundamental understanding of peeling of the coating. A small-size Co-cemented tungsten carbide drill bit was selected as the examined substrate to fabricate the diamond coating. Roughening pretreatment with a diamond slurry combined with ultrasonic vibration was performed for the substrate surface to enhance adhesive strength. Meanwhile, a diamond coating without roughening pretreatment was also fabricated for comparison. The lifetime and quality of the coating were evaluated by the drilling test. Although the diamond coating could grow on the substrates with and without roughening pretreatment, the diamond coating with roughening pretreatment possessed a higher lifetime and stronger wear resistance than that without roughening pretreatment. We found that both substrates with and without roughening pretreatment exhibited a coarse surface, whereas the roughening pretreatment could remove the original machined surface of the substrate and thus make the near surface with numerous integrated crystalline grains become the new topmost surface. This increased the contact area and surface energy of the interface, leading to the improvement of adhesive strength. Finally, fatigue strength and contact mechanics were studied to trace the changes in the stress of the diamond coating in the whole process of drilling from a theoretical point of view. We suggest that fatigue strength and contact mechanics may play vital roles on the durability and peeling of the coating.

Automatic Detection of Pearlite Spheroidization Grade of Steel Using Optical Metallography.

To eliminate the effect of subjective factors during manually determining the pearlite spheroidization grade of steel by analysis of optical metallography images, a novel method combining image mining and artificial neural networks (ANN) is proposed. The four co-occurrence matrices of angular second moment, contrast, correlation, and entropy are adopted to objectively characterize the images. ANN is employed to establish a mathematical model between the four co-occurrence matrices and the corresponding spheroidization grade. Three materials used in coal-fired power plants (ASTM A315-B steel, ASTM A335-P12 steel, and ASTM A355-P11 steel) were selected as the samples to test the validity of our proposed method. The results indicate that the accuracies of the calculated spheroidization grades reach 99.05, 95.46, and 93.63%, respectively. Hence, our newly proposed method is adequate for automatically detecting the pearlite spheroidization grade of steel using optical metallography.

Interaction of elemental mercury with defective carbonaceous cluster.

The interaction of elemental mercury with defective carbonaceous clusters is investigated by the density-functional theory calculation. The defective carbonaceous cluster is represented by seven-fused benzene ring and single atomic vacancy at the surface. Also, the non-defective carbonaceous surface is employed for comparison. The defective carbonaceous cluster with chlorine is carried out to evaluate the effect of the statured carbon at the neighboring sites of vacancy on mercury adsorption. The results indicate that vacancy can promote the activity of its neighboring sites, and the defective carbonaceous cluster has much larger mercury adsorption energy than the non-defective carbonaceous cluster with and without chlorine. Cl atom can improve the activity of its neighboring sites on the non-defective carbonaceous surface, but the effect of Cl atom on mercury adsorption of vacancy is very complex, which depends on the Cl concentration. High concentration of Cl decreases the mercury adsorption because Cl competes for the active sites with mercury. Hence, we find that vacancy can be regarded as a potential functional group to improve the mercury adsorption on carbonaceous surface, but the saturated carbon at the neighboring sites of vacancy can rapidly decrease the mercury capture capacity.