Aluminum phosphate sealing to improve insulation resistance of plasma-sprayed alumina coating

The insulation resistance of conventional atmospheric plasma-sprayed alumina coatings with 10–15% porosity is ～10¹¹ Ω. The presence of pores, lamellae boundaries, and other non-fillings dampens the insulation resistance of the coating. In the present study, aluminum phosphate was used to seal the surface of plasma-sprayed alumina coating and evaluate the effect of sealing on the insulation resistance and its thermal cycling response. Sealing was carried out with three concentrations of sealant (P/Al molar ratio of 3, 10, and 15). Characterization by X-ray diffraction and scanning electron microscopy revealed the primary sealing phase as aluminum metaphosphate and effective sealing of the pores by the aluminum phosphate phases. Insulation resistance is improved by two orders of magnitude after sealing the coated samples. Sealing with P/Al molar ratio 3 exhibited maximum insulation resistance of ～10¹³ Ω at room temperature. Thermal cycling studies between 650°C and 200°C on the sealed samples showed deterioration in thermal cycling life after sealing.     

Investigation of machining characteristics in rotary ultrasonic machining of alumina ceramic

Alumina ceramic is well documented as a much-demanded advanced ceramic in the present competitive structure of manufacturing and industrial applications owing to its excellent and superior properties. The current article aimed to experimentally investigate the influence of several process variables, namely: spindle speed, feed rate, coolant pressure, and ultrasonic power, on considered machining characteristics of interest, i.e., chipping size and material removal rate in the rotary ultrasonic machining of alumina ceramic. Response surface methodology has been employed in the form of a central composite rotatable design to design the experiments. Variance analysis testing has also been performed with a view to observing the consequence of the considered parameters. The microstructure of machined rod samples was evaluated and analyzed using a scanning electron microscope. This analysis has revealed and confirmed the presence of plastic deformation that caused removal of material along with brittle fractures in rotary ultrasonic machining of alumina ceramic. The validity and competence of the developed mathematical model have been verified with test results. The multi-response optimization of machining responses (material removal rate and chipping size) has also been attempted by employing a desirability approach, and at an optimized parametric setting the obtained experimental values for material removal rate and chipping size were 0.4166?mm³/s and 0.5134?mm, respectively, with a combined desirability index value of 0.849.     

Catalytic ozonation of natural organic matter on alumina

The paper aims to show the potential of catalytic ozonation in the presence of alumina for the removal of natural organic mater from drinking water. An investigation into the efficiency of catalytic ozonation, ozonation by-products formation and their biodegradability was the main goal of the paper. Characterisation of fresh and worn alumina was also conducted. The results clearly indicated the high activity of alumina over a long period of time, which is crucial in water treatment technology. The application of alumina to the ozonation system doubled the efficiency of NOM removal from water when compared to ozonation alone. Furthermore, catalytic ozonation resulted in lower by-products and biodegradable organic carbon formation.     

回转窑烧成带状态混合智能识别方法

针对氧化铝回转窑过程复杂、长期依赖人工看火操作而造成的生产过程不稳定、 产品质量一致性差、能源消耗大等问题,提出了基于烧成带火焰图像特征与关键过程数据融合的烧成带状态自动识别方法, 该方法由烧成带火焰图像的分割、特征提取、 关键过程数据的融合以及二叉树支持向量机分类器模型组成.工业实验表明, 该方法能够较准确地识别烧成带状态,为基于产品质量指标优化的窑温控制器提供决策依据.     

热处理制度对滑板用铝碳材料性能和结构的影响

按板状刚玉(2.361～0.043mm)91.5%,Al粉(<0.044mm)5%,B4C和炭黑(<0.044mm)3.5%,外加4.5%的热塑性酚醛树脂作为结合剂,制成铝碳材料,分别在氮气气氛和埋炭气氛中经800℃、1000℃、1200℃、1450℃保温5h热处理后,测定试样的常温性能、高温抗折强度(1400℃)和抗水化性能,并用XRD和SEM分析试样的物相组成和显微结构。试验结果表明:随热处理温度的升高,铝碳材料的高温抗折强度逐渐下降;在相同温度条件下,这两种保护气氛处理后试样的高温抗折强度水平相当;在800～1000℃的温度段处理时,埋炭保护处理材料的水化程度大,损伤材料结构,明显降低材料的强度。在相同温度条件下,氮气保护处理试样的抗水化性能优于埋炭保护处理试样。     

Sol–gel alumina environmental barrier coatings for SiC grit

SiO₂ surface film is insufficient to protect SiC from the oxidation at widely varying partial pressures of oxygen, in particular in the presence of water vapor (e.g. in gas turbines) and also in other environments, e.g. during brazing for hard “tipping” of turbine blades. This work demonstrates that sol–gel alumina, coated on 0.5 mm coarse SiC grit, may form an acceptable, up to 10 μm thick “environmental barrier coating” EBC for some of these applications. The sol–gel has advantages over other methods (such as CVD) is the simplicity and low cost. We have used NH₄OH pre-treatment to hydroxylate surface of SiC prior to applying alumina coating. Such modified SiC/SiO₂ surface helped to deposit the positively charged alumina sol, and thus allowed to build thick coatings on the SiC grit. There is some indication that these coatings partially convert to mullite through reaction at the interface with the native silica on SiC. Oxidation resistance tests at 1200 °C were performed to show effectiveness of such coated SiC grit.     

赤泥洗液苛化技术应用研究

重点介绍赤泥洗液苛化最佳条件及该技术在伊朗氧化铝公司的具体应用,同时分析了温度、石灰添加量、NT浓度和NT-NC交互项等因素对苛化率的影响。     

电除尘器在氧化铝焙烧系统中的应用

介绍电除尘器在氧化铝焙烧过程中的应用,重点介绍了德国鲁奇公司电除尘器的气流均布板、极板、极线及振打装置等内部结构和高压电气、自控系统的特点以及成功应用。