Molecular Dynamics Simulations of the Thermal Conductivity of Silicon-Germanium and Silicon-Germanium-Tin Alloys

In this work, we investigate the thermal conductivity properties of Si 1 − x Ge x and Si 0.8 Ge 0 Sn 2 y alloys. The equilibrium molecular dynamics (EMD) is employed to calculate the thermal conductivities of Si 1 − x Ge x alloys when x is different at temperatures ranging from 100 K to 1100 K. Then nonequilibrium molecular dynamics (NEMD) is used to study the relationships between y and the thermal conductivities of Si 0.8 Ge 0.2 Sn 2 y alloys. In this paper, Ge atoms are randomly doped, and tin atoms are doped in three distributing ways: random doping, complete doping, and bridge doping. The results show that the thermal conductivities of Si 1 − x Ge x alloys decrease first, then increase with the rise of x , and reach the lowest value when x changes from 0.4 to 0.5. No matter what the value of x is, the thermal conductivities of Si 1 − x Ge x alloys decrease with the increase of temperature. Thermal conductivities of Si 0.8 Ge 0.2 alloys can be significantly inhibited by doping an appropriate number of Sn atoms. For the random doping model, thermal conductivities of Si 0.8 Ge 0.2 Sn y alloys approach the lowest level when y is 0.10. Whether it is complete doping or bridge doping, thermal conductivities decrease with the increase of the number of doped layers. In addition, in the bridge doping model, both the number of Sn atoms in the [001] direction and the penetration distance of Sn atoms strongly influence thermal conductivities. The thermal conductivities of Si 0.8 Ge 0.2 Sn y alloys are positively associated with the number of Sn atoms in the [001] direction and the penetration distance of Sn atoms.

Quantitative X-ray µCT Measurement of the Effect of Ore Characteristics on Non-Surface Mineral Grain Leaching

In heap (bio)leaching processes, a substantial fraction of the valuable mineral is positioned below the ore particle surface. X-ray micro-computed tomography (μCT) was used to quantify the effect of ore type and structure and operating temperature on the leaching of this mineral, to investigate the rate-controlling factors. Mini-leaching columns containing agglomerated chalcopyrite, pyrite, and malachite ores were scanned by X-ray μCT (13.40 µm resolution) at select time intervals. The leaching of a relatively porous malachite ore was reaction-controlled, with no leaching penetration limitation into the ore particles. For two less porous ore types, the structure and higher porosity of the agglomerate rim and conditions that resulted in the degradation of the full ore matrix structure were found to be the determining variables of the leaching extent and time. In the case of a chalcopyrite ore, an enhancement of copper recovery and sulphide mineral dissolution with increasing temperature was attributable to the increased leaching penetration distance and crack development in addition to thermodynamically expected increased leaching rate. Increasing temperature did not affect the maximum penetration distance for the waste rock containing pyrite, with no crack development observed. Overall increases in iron recovery were due to accelerated leaching rates, though diffusion or mineral access limitations were evident at a higher temperature.

COMPARISON OF DENTINAL TUBULAR PENETRATION OF THREE BIOCERAMIC SEALERS

Objective: The main objective of endodontic treatment is to remove microorganisms from the root canal space and prevents reinfection. Deep penetration of the dentinal tubule is advantageous because it increases the contact area between the root canal filling material and dentin, thereby increasing the sealing quality of the entire root canal system. Bioceramic sealers are biocompatible, nontoxic, non-shrinking, hydrophilic, and stable, do not expand during setting, and can form hydroxyapatite, which then forms chemical bonds with dentin to compare the abilities of three types of bioceramic-based sealers to penetrate the dentinal tubules.Methods: Obturation used three types of bioceramic sealers. Group 1 (calcium phosphate silicate), Group 2 (a mixture of tricalcium silicate and resin), and Group 3 (pure tricalcium silicate) were observed using a scanning electron microscope and measurement of the penetration distance with ImageJ.Results: The bioceramic sealers had statistically significant differences in penetration distance into dentinal tubules (p’s<0.001). The mean penetration value of Group 1 (calcium phosphate silicate) was 115.99 μm, Group 2 (a mixture of tricalcium silicate and resin) was 209.28 μm, and Group 3 (pure tricalcium silicate) was 84.07 μm.Conclusion: Although all three bioceramic sealers penetrated the dentinal tubules, they exhibited differences in their penetration capabilities. Group 2 had the deepest penetration, likely due to the resin content.

A Research on the Effect of Heterogeneities on Sandstone Matrix Acidizing Performance

Matrix acidizing is one of the common methods to enhance production in sandstone reservoirs. Conventional acidizing designs generally neglected the effect of heterogeneities of mineral and flow field distributions both in areal and vertical directions and assumed that the acid front propagates with a piston-like style. However, sandstone formations inevitably have small-scale heterogeneities of minerals and flow properties that may give rise to acid propagation in a manner much different from what is predicted based on homogeneous assumptions. In this paper, we conduct a research to numerically investigate how the heterogeneities affect acidizing performance under in situ conditions. Firstly, a heterogeneity model is built for mineral and porosity distributions by using the semivariogram model of geological statistics, based on which we generate spatially correlated porosity and mineral distributions. Next, a model of radial acid flooding is developed based on mass balance and the chemical reactions between the acids and minerals occurring during the acidizing process. The model is numerically solved to investigate the permeability response, acid distributions, precipitate distributions, and the effect of the heterogeneities on acidizing. The results show that the heterogeneities both in areal and vertical directions have a significant effect on acidizing. The flow field heterogeneities have a more serious impact than the mineral heterogeneities. In a plane, strong porosity heterogeneity can give rise to acid fingering and even channeling, which make the acid penetration distance longer than the homogeneous cases. The secondary precipitate has a significant effect when fast-reacting mineral content is high. Vertically, several-fold permeability contrast creates the acid break through the high-perm zone leaving the low-perm zone understimulated. Both flow field and mineral heterogeneities make it possible to create high-permeability channels during the acidizing process and to obtain a longer acid penetration distance.