Synthesis and slurry spray coating of barium strontium alumino silicate on SiC substrate

Barium strontium alumino silicate (BSAS); (Ba_0.6Sr_0.4Al₂Si₂O₈) was synthesized through solid state reaction between BaCO₃, SrCO₃, Al₂O₃ and SiO₂ subjected to wet milling in isopropanol for about 24 h. The sequence of the solid state reaction was studied by subjecting to DG/DTG from room temperature to 1550 °C. The crystallographic phase evolution was confirmed by X-ray diffraction of the powders calcined in the range 1000 to 1300 °C for 2 h. The monoclinic celsian phase obtained at 1300 °C, pelletized through uniaxial pressing was sinterable to 67 to 78% density in the temperature range of 1300 to 1500 °C. The density improved to 75 to 94% after ball milling for 76 h, while ZrO₂ addition further improved the density by 2%. The celcian phase of BSAS was dispersed in isopropyl alcohol, milled for about 24 h and spray coated on to plain SiC and mullite precoated SiC substrates. Sintering of coated samples and characterization for weight gain/loss, microstructure, scratch test prove that mullite + BSAS coating is more effective than single layer coating of BSAS on SiC substrates.     

Surface modification of superfine SiC powders by ternary modifiers-KH560/sodium humate/SDS and its mechanism

SiC is a promising functional ceramic material with many great properties. High concentrated SiC slurry with excellent rheology and stability is required in some processes of ceramic forming. In this work, the dispersion of SiC powders was obviously improved by ternary modifiers: γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560), sodium humate and sodium dodecyl sulfate (SDS). Modified SiC slurry showed the lowest viscosity of 0.168 Pa s at a solid content of 50 vol%. The maximum absolute value of zeta potential of SiC increased from 47.3 to 61.6 mV by modification. Sedimentation experiments showed that a highly stable suspension of modified SiC was obtained at pH 10. SiC green body with high density of 2.643 g/cm³ was prepared with modified powders by slip casting. X-ray photoelectron spectra (XPS) and thermogravimetry (TG) measurements indicated the adsorption of modifiers on SiC surface. Therefore, modified SiC powders could stably disperse in aqueous media due to the increase of electrosteric repulsion between particles. The novel strategy used in this study could further improve the dispersion of SiC powders.     

Recent progress on the discrete element method simulations for powder transport systems: A review

Powder transport systems are ubiquitous in various industries, where they can encounter single powder flow, two-phase flow with solids carried by gas or liquid, and gas–solid–liquid three-phase flow. System geometry, operating conditions, and particle properties have significant impacts on the flow behavior, making it difficult to achieve good transportation of granular materials. Compared to experimental trials and theoretical studies, the numerical approach provides unparalleled advantages over the investigation and prediction of detailed flow behavior, of which the discrete element method (DEM) can precisely capture complex particle-scale information and attract a plethora of research interests. This is the first study to review recent progress in the DEM and coupled DEM with computational fluid dynamics for extensive powder transport systems, including single-particle, gas–solid/solid–liquid, and gas–solid–liquid flows. Some important aspects (i.e., powder electrification during pneumatic conveying, pipe bend erosion, non-spherical particle transport) that have not been well summarized previously are given special attention, as is the application in some new-rising fields (ocean mining, hydraulic fracturing, and gas/oil production). Studies involving important large-scale computation methods, such as the coarse grained DEM, graphical processing unit-based technique, and periodic boundary condition, are also introduced to provide insight for industrial application. This review study conducts a comprehensive survey of the DEM studies in powder transport systems.     

Citrate- and glycerol triesters as novel dual-functional dispersants and plasticisers for ceramic processing

Short chained triesters of glycerol and citric acid were systematically investigated as novel dual-functional dispersants and plasticisers for use in ceramic processing. Additional systematic studies on a series of diesters having structural similarities with the citrate and glycerol triesters were performed to further assess the significance of specific functional groups for the stabilisation of suspensions.The overall purpose of this work consists in simplifying the formulation for ceramic processing slurries while at the same time limiting the environmental impact and toxicity. The use of multifunctional additives reduces the risk of unwanted interactions between different components. Additionally, the possible use of one additive in more than one role opens the opportunity for an overall reduction in the number and amount of chemicals and therefore reduction of costs and risks.For the citrate ester candidates, different alkoxy groups were tested as well as the acetylation on the hydroxyl group. The glycerol esters differed by the length of the carboxylic chain.Especially triethyl and tributyl citrate are proposed as promising dual-functional additives for ceramic processing. Specifically, for triethyl citrate the dual-function was finally demonstrated by producing a dense piece of 8YSZ through tape casting and subsequent sintering.     

Ultra-smooth BaTiO3 surface morphology using chemical mechanical polishing technique for high-k metal-insulator-metal capacitors

The surface roughness of barium titanate (BTO) following its implication by aerosol deposition method (ADM), is a very important characteristic affecting its potential for use in high-k metal-insulator-metal capacitors. The ADM is the best candidate to deposit ceramic films but has two major problems: macroscopic defects and rough interface effects on the BTO surface. In this work, a chemical mechanical polishing (CMP) technique is applied to obtain an ultra-smooth BTO surface morphology by the optimization of several factors including the slurry type, the head rotational speed, and the down pressure. Statistically, we were able to achieve a root mean square (RMS) value of the BTO surface of 1.746 nm by utilizing a two-step polishing process, applied at a head rotational speed of 70 rpm under 5 kg/cm² of down pressure; this RMS value is improved at least 8 times over previous studies. This analysis is based on representative pattern images, three-dimensional images, line profiles, histograms, and power spectra of selected BTO surface areas, further verified with data from both energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.     

刚果(金)高泥氧化铜矿的絮凝沉降试验研究及技改应用

本文以刚果(金)高泥氧化铜浸出矿浆为试验对象,进行了有机高分子聚丙烯酰胺的选型试验,探究了最佳沉降效果下浸出矿浆浓度、絮凝剂种类和用量等参数指标,再针对浓密机结构进行优化改造,并取得了较好的效果。结果表明：选择1800-2300万分子量的AN905型的絮凝剂,能满足高泥氧化铜矿的生产浓缩作业要求；根据沉降试验,生产浸出矿浆浓度为20%,絮凝剂作用的沉降效果最佳,单耗为100g/吨矿；改造浓密机中心筒高度、改变絮凝剂投加方式和调整絮凝剂添加点,能有效解决高泥氧化铜浸出矿浆在浓缩过程中的絮凝沉降问题,减少有价金属量的溢流损失,降低絮凝剂用量,进一步提高生产矿石处理量,实现企业良好的经济效益。     

A novel ultra-high-temperature oxidation protective MoSi2-TaSi2 ceramic coating for tantalum substrate

To protect refractory metal against oxidation at ultra-high temperatures, a MoSi₂-TaSi₂ ceramic coating was prepared on a pure tantalum (Ta) substrate using a novel three-step process, which included dip-coating with a molybdenum slurry, vacuum sintering, and halide-activated pack cementation (HAPC). The original coating had a MoSi₂-TaSi₂ double-layer structure from the surface to the substrate. After oxidation at 1700°C for 8 h in air, the coating exhibited a complex multi-layer structure composed of SiO₂-Mo₅Si₃-MoSi₂-(Mo,Ta)₅Si₃-TaSi₂-Ta₅Si₃ from the outer layer to the inner layer, due to the high-temperature phase transition and diffusion of Si and O. The coating effectively protected the Ta substrate at 1700°C for 12 h without failure, thereby demonstrating great improvement to its service life in an ultra-high-temperature aerobic environment. The protective effect was attributed to the integrity of the ceramic coating and the formation of a dense, uniform SiO₂ film that effectively lowered the inward oxygen diffusion rate.     

快速进出水煤浆用调配罐的设计与应用

水煤浆是一种煤基流体燃料,是煤炭深加工的新型产品之一。它既是一种新型洁净的环保材料,又具有良好的流动性,因此得到了广泛的使用。设计了一种快速进出水煤浆用调配罐,从而使得水煤浆进出调配罐效率提高,较好的解决了水煤浆制备过程中出现的问题,具有极佳的推广意义。     

Method for calculating horizontal drain induced non-linear and large strain degree of consolidation

Consolidating dredged clay slurries using a combination of vacuum pressure and prefabricated horizontal drains (PHDs) is widely used in practice. This is a large strain problem, but there is no existing large strain theory for PHD induced consolidation. A method with explicit equations has been proposed to consider both mechanical and geometrical non-linearities in analyzing PHD induced consolidation. The method considers stepwise variation of properties using imaginary time concept. An imaginary time is determined by the condition of continuity of degree of consolidation before and after changing the properties. Then the method was applied to analyze a large scale model test of vacuum consolidation with PHD. Two analyses were conducted. One considered both the mechanical and geometrical non-linearity (large strain), and another only considered mechanical non-linearity (small strain). The results of large strain analysis agree with the measured settlement curve and excess pore pressures well. While the small strain analysis under-estimated the rate of consolidation significantly. The results from this study indicate that for analyzing PHD induced consolidation of clay slurries considering the effect of large strain is important, and the proposed method can be a useful design tool.