Surface properties of aged coal and their effects on bubble–particle attachment during flotation

Aged coal after mining often shows poor flotation performance due to the formation of hydrophilic oxygenated functional groups. In this study, different meta-bituminous aged coal was characterized by XPS and SEM analysis, and contact angle, zeta potential and bubble–particle attachment measurements. Following aging process, the changes in flotation behavior of the coal samples were quantified at different diesel dosages. It was found that the percentage of hydrophobic functional groups of the fresh coal was about 1.31 times higher than that in the case of the aged coal. The contact angle of the fresh coal was 78.9° while that for the aged coal was 36.7°. It means that the hydrophilicity of the aged coal samples was significantly higher than that of the fresh coal. The results of zeta potential, FTIR, XPS and SEM measurements agreed well with the contact angle results. The combustible flotation recovery of the fresh coal in the presence of collector was 98% while that of the aged coal was about 20%. Despite the significant differences in the surface properties of the fresh and aged coal, the induction time slightly changed i.e. the induction time for the most hydrophobic coal (i.e the fresh coal in the presence of collector) was 10 ms while that for the least hydrophobic coal (i.e. the aged coal in the absence of collector) was 11.6 ms. The attachment efficiency and flotation rate shows an exponential decay relationship with induction time.     

感应加热对奥氏体不锈钢弯管组织和性能的影响

采用感应加热技术热煨奥氏体不锈钢弯管,对热煨后弯管的组织、性能及外观进行了分析研究.结果表明感应加热的奥氏体不锈钢弯管不仅可以不进行固溶和消除应力处理,而且具有各部分性能相差小、弯管表面氧化层薄,良好的外观和形状,是其它加工方法无法比拟.     

有机前驱体法BN纤维的制备和表征

以聚合环硼氮烷前驱体(PBN)为原料, 通过熔融纺丝、不熔化处理、高温热解陶瓷化等工艺制备了BN中空陶瓷纤维. 利用XRD、SEM、TEM等对BN中空纤维的物相、结构和形貌进行了分析和表征, 同时测量了BN中空纤维的抗氧化性能及介电性能. 研究表明, 升温速率和热解温度是影响BN中空纤维的结构及介电性能的重要因素. 在优化工艺条件下, 制备BN中空纤维介电性能优异, 介电常数ε′和介电损耗正切值tanδ分别小于3.30和0.00064(室温, 7~18 GHz), 在氧化气氛中的使用温度高达950℃.     

Comparison of flotation behavior of middling coal ground by wet-milling with different media

Breakage could promote liberation of minerals and make recovery of coal with low ash content possible by flotation technology. In the research presented in this paper, middling coal was ground by wet-milling with different media, namely wet-milling iron ball (WMIB) and wet-milling zirconia ceramics (WMZC). As the size-reduction of middling coal is a physical process, Fourier transform infrared spectroscopy (FTIR) analyses of ground products indicate no difference in organic functional groups. Exposure of mineral and cover of hydrolysis reaction products of iron ion on the generated surface of products of WMIB increase the hydrophilicity and worsen the flotation selectivity when compared with products of WMZC. Float-sink tests show that ground products of WMIB have a relatively higher cumulative yield at low density. However, the ash content of flotation concentrate in each size fraction of WMIB is higher than that of WMZC, which is mainly caused by the decrease of hydrophobicity and worse floating selectivity of coal ground by WMIB. Combustible matter recovery (CR) shows an increase with the decrease of particle size, but CR in flotation concentrating on each sized products is similar to products ground by different media.     

The Effect of Surface Contamination on the Transient Oxidation of Ni-20Cr

Abstract

When a metal surface is heated in an oxidising environment for the first time, an oxide scale is formed. This scale is not the product of a process that occurs under steady state conditions, but is instead formed over a wide range of temperatures, as the sample heats. The oxides, often referred to as transient scales, that are formed under these conditions are frequently very different from those found after long oxidation times.

The research presented here considers the oxides formed during the heating of a commercial Ni-20%Cr alloy and examines the effect of surface contamination on the oxidation process. Also examined is the role of surface pretreatment on the behaviour of the alloys during oxidation.

The scales formed on these alloys are very thin (<100 nm) and the scales have thus been examined using transmission electron microscopy (TEM) and scanning transmission electron microscopy techniques (STEM). The samples produced were of cross-sections of the metal and oxide.     

Consolidation of polymer-derived SiC matrix composites: processing and microstructure

SiC fiber reinforced SiC matrix composite (SiC/SiC composite) has been developed by polymer impregnation and pyrolysis (PIP) method, which consists of impregnation, curing, consolidation, and re-impregnation and pyrolysis. As a prospective approach to fabricate a high performance composite, consolidation conditions, such as curing temperature to make a green body, pressure and heating rate during consolidation, were systematically controlled for effective consolidation. Because of its advantage in controlling physical characteristic, polyvinylsilane (PVS) that is liquid thermosetting organo-silicic compound was utilized as the matrix precursor. Based on the pyrolytic behavior of PVS, effects of the process conditions on microstructure of the consolidated bodies were accurately characterized. To relate those microstructure with mechanical property, flexural tests were performed for the composites after multiple PIP processing. Consequently, process conditions to make a high performance composite could be appeared. Structural conditions to be optimized for further improvement in mechanical and environmental properties were also discussed.     

氮掺杂碳点在盐酸溶液中对碳钢的缓蚀作用

碳点因其优异的性能在缓蚀剂开发领域具有巨大的应用潜力。本研究以柠檬酸铵为原料,在180℃热解不同时间(1 h、1.5 h、2 h),合成具有不同形貌结构的氮掺杂碳点(N-CDs),分析了碳点制备条件对其作为Q235碳钢缓蚀剂的性能影响规律。采用极化曲线和电化学阻抗谱,结合表面分析技术,说明了N-CDs的缓蚀机理。结果表明,当热解时间为1.5 h时,N-CDs的缓蚀效率最高,200 mg/L N-CDs1.5在1 M HCl溶液中的缓蚀效率达到91.6%。N-CDs作为混合型缓蚀剂能够减缓碳钢的阳极和阴极腐蚀反应,通过物理、化学吸附形成保护膜,并且提高了金属表面的疏水性,从而有效抑制了碳钢的腐蚀萌生与发展。本研究为发展高效、绿色的新型缓蚀剂提供了新的思路。     

Characterisation of modified polypropylene fibres

Due to excellent mechanical properties, high chemical stability and processability polypropylene fibres are mostly used in different technical fields. However, because of low surface energy, lack of reactive sites and sensitivity to photo or thermal oxidation the polymer properties are insufficient for some applications. Therefore several techniques for fibres modification are reported, e.g., plasma treatment, chemical modification etc.To alter the chemical and physical properties hydrophobic polypropylene monofilament fibres were surface modified and the sulphonation with concentrated sulpuric acid was used. The sulfonation was performed at different conditions, e.g., different temperatures and varying period of time and a detailed study of treatment conditions influence on the fibre properties was carried out. The sulphur content on fibres was determined by mass spectroscopy. The sulfonic acid cation exchange polypropylene fibres were characterised in terms of elektrokinetic and mechanical properties.     

干法纺聚酰亚胺纤维氧化处理及其对结构性能的影响

以H2O2为湿化学处理液,利用扫描电镜、热重分析仪、纤维检测系统、单纤维电子强力仪、傅里叶变换红外光谱仪、X射线光电子能谱仪、X射线粉末衍射仪分别研究了H2O2氧化对干法纺聚酰亚胺纤维浸润性能、微观形貌、热失重性能、直径及力学性能、化学结构、表面元素含量和微观聚集态结构的影响。结果表明,H2O2氧化后,纤维表面凹凸不平,比表面积及粗糙度增加,局部发生刻蚀,引入了活性基团,表面能提高,O/C比值增加,浸润性能得到改善,且随着H2O2浓度或温度提高、处理时间延长,浸润性能改善趋势加快,热失重性能保持较好,直径及力学性能略微下降。表面氧化使纤维化学结构变化不大,微观聚集态结构发生改变,非结晶区比例上升,采用适当的H2O2处理工艺,有助于聚酰亚胺纤维表面进行功能化改性。     

Effect of Heat Treatment on Silica Aerogels Prepared via Ambient Drying

Silica aerogels were prepared at ambient drying by using ethanol/trimethylchlorosilane （TMCS）/heptane solution as pore water exchange and surface modification of the wet gel before drying. The obtained silica aerogels exhibit a sponge-like structure with uniform pore size distribution. The effects of heat-treatment on the hydrophobicity, specific surface area and other properties were investigated. The results indicated that the hydrophobicity of silica aerogels could be maintained up to 350℃. With increasing heating temperature, hydrophobicity decreased, and became completely hydrophilic after heat-treatment at 500℃. Brunaueremmitt-teller （BET） surface area results indicated that the specific surface area of silica aerogels increased with increasing heating temperature in the range of 150-500℃. The effects of heat-treatment on the morphology and chemical bonding state of silica aerogels were investigated by scanning electron microscopy （SEM）, differential temperature analysis （DTA） and Fourier-transform infrared spectroscopy （FT-IR）.     

Activation mechanisms of apatite by purifying reagent polyacrylamide for backwater from mineral processing in flotation of rare earths

This study revealed activation mechanisms of apatite by polyacrylamide (PAM) during flotation of rare earth minerals in Bayan Obo Ore. This activation leads to high phosphorus content in rare earth concentrate. Ultraviolet (UV) absorption measurements show that adsorption of PAM on the surfaces of apatite and rare earths follows a pseudo-second-order reaction kinetic model. The isothermal adsorption process follows the Freundlich adsorption model, indicating that the adsorption of PAM on apatite is a multi-layer, non-uniform process, that is, physical and chemical adsorption occurs simultaneously. The measured zeta potential shows that under weakly alkaline conditions, amide groups with a negative charge are adsorbed on the surface of apatite, increasing the electronegativity, so that the potential is shifted negatively; however, the negative shift of the potential on the surface of rare earths is insignificant. Fourier transform infrared (FT-IR) test and X-ray photoelectron spectroscopy (XPS) results imply that PAM is chemically adsorbed on the surface of apatite, while 506E undergoes stronger chemical adsorption than PAM on the surface of rare earth minerals. It is found that multi-layer, non-uniform adsorption of PAM combining physical and chemical adsorption occurs on the surface of apatite and the process is dominated by physical adsorption: the adsorption of PAM on surfaces of apatite is stronger than that on the surface of rare earth minerals. Such adsorption activates the apatite, causing it to float during the flotation of rare earths, which is the reason for the high phosphorus content in the rare earth concentrate.     

热处理对竹材理化性能影响研究进展

目的 归纳国内外现有热处理工艺对竹材理化性能的影响的研究进展,分析不足,并提出热处理竹材作为代木材料在包装领域的未来研究趋势。方法 综述不同热处理竹材工艺(包含时间条件、温度条件、介质种类)的研究现状,总结竹材理化性能的变化特点。结果 当前热处理技术作为环保简易的竹改性技术表现出一定优势,但单一的工艺条件对竹材原有性能会产生负向影响,需对工艺参数和反应条件进行开发改进,并设计相应的制备装置。结论 采用热处理条件多线程综合工艺可以在优化竹材性能的同时,保持甚至降低中高温对竹结构的破坏,从而增加热处理竹材的使用年限,并拓展其使用领域。     

Preparation of carbon nanostructures from medium and high ash Indian coals via microwave-assisted pyrolysis

This study is focused on valorizing low value and low quality Indian coals via microwave pyrolysis to produce good quality carbon nanostructures in the heat-treated coal char. The effects of operating conditions such as coal type, coal:susceptor (Fe) mass ratio, and microwave power on product yield and quality are evaluated. The quality of the heat-treated coal char was assessed using different characterization techniques such as electron microscopy, porosimetry, X-ray diffraction, and Raman spectroscopy. The addition of Fe enhanced the heating rates, and led to the formation of carbon nanotubes and nanoparticles. Increasing the proportion of Fe resulted in increase in size of nanotubes and nanoparticles, which is attributed to the fusion of small tubes and particles caused by enhanced localized heating. The yield of carbon nanostructures was more from medium ash (~45%) than from high ash coal (~37%) due to the high fixed carbon and low ash content in the former. In addition to char, coal tar and non-condensable gases were characterized. The major compounds in the coal tar were aromatic hydrocarbons, simple phenols and aliphatic hydrocarbons. Hydrogen and methane were the major gases from medium ash coal, while hydrogen, methane and CO were produced in significant quantities from high ash coal. Microwave-assisted pyrolysis is shown to be a promising process to produce carbon nanostructures in a short time period as compared to conventional thermal processes.     

Flame resistant glass-epoxy printed wiring boards with no halogen or phosphorus compounds

A highly flame-resistant glass-epoxy laminate-type printed wiring board (PWB) that does not contain such flame-retarding additives as halogen compounds and phosphorus compounds has been developed to overcome environmental problems caused by these flame-retarding additives. The PWB contains a self-extinguishing epoxy resin compound (phenol aralkyl type) and a limited amount of harmless metal hydroxide (aluminum hydroxide). It has high flame-resistance with no inclusion of halogen or phosphorus compounds and shows other good characteristics, including resistance to solder heating and chemical agents in processing, electronic properties, and moldability, which make it a practical FR-4 board. These good characteristics were obtained by utilizing the epoxy resin compounds superior properties, including its pyrolysis resistant, hydrophobicity and non-polar properties, and by minimizing the amount of metal hydroxide. The board is very safe when burned, disposed of, and reused as a filler after pulverizing.     

Combined electron microscopy and spectroscopy characterization of as-received,acid purified,and oxidized HiPCO single-wall carbon nanotubes

Single-wall carbon nanotubes (SWCNTs) are very important materials due to their combination of unique structure, dimension, strength, chemical stability, and electronic properties. Nevertheless, SWCNTs from commercial sources usually contain several impurities, which are usually removed by a purification process that includes reflux in acids and strong oxidation. This strong chemical procedure may alter the nanotube properties and it is thus important to control the extent of functionalization and oxidation during the purification procedure. In this report, we provide a comprehensive study of the structure and physical composition of SWCNTs during each step of the purification process. Techniques such as Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and Infrared spectroscopy were used to track the SWCNTs structure, in terms of length and diameter distribution, and surface chemical modifications during each purification stage.     

Evaluating the adsorption mechanism of a novel thiocarbamate on chalcopyrite and pyrite particles

The selective adsorption of surfactants on minerals can strengthen the differences of physical and chemical properties of mineral surfaces, thereby improving the separation efficiency of the refractory minerals. Herein, a novel surfactant S-carboxyethyl-N-benzoyl thiocarbamate (CEBTB) was prepared and utilized as a collector to selective separation of chalcopyrite from pyrite. The adsorption performances and mechanism of CEBTB on chalcopyrite and pyrite surface were studied. It showed that the functional groups (CO, CS and –COOH) of CEBTB could selectively anchor on the chalcopyrite surface and increase its surface hydrophobicity, whereas the adsorption of CEBTB on pyrite surface was weak with the surface hydrophobicity improved insignificantly. Flotation experimental indicated that CEBTB exhibited superior flotation selectivity for chalcopyrite against pyrite than the common collector of SIBX. Batch adsorption experimental results demonstrated that the adsorption of CEBTB onto chalcopyrite surface was performed by a monolayer chemisorption, as well as the adsorption process was endothermic and spontaneous.     

生物质热解与热解油精制

生物质是人类的第四大能源来源,同时也是绿色可再生资源。热解是生物质最重要的热化学转化方式,包括慢速热解和快速热解,后者是目前研究的重点,主要得到生物油产品。本文中介绍了热解原理和原料性质、温度、加热速率、停留时间及矿物质对热解的影响,综述了热解反应器的性能,并重点介绍了循环流化床和自由落下床两种反应器,讨论了热解催化剂和热解油精制方式(包括催化加氢和催化裂解),最后预测了生物质热解研究的发展趋势。     

深加工对废轮胎裂解炭黑表面性能的影响

本文主要介绍了废轮胎裂解炭黑经深加工处理后表面性能的变化.实验结果证实,粉碎后裂解炭黑的表面能和化学活性均有所提高.在经过表面改性处理后,其分散性有所改善.通过红外光谱实验论证了表面化学改性的机理.将其填充于天然橡胶后性能良好.     

New insights into the effects of particle size on the surface modification by low-temperature plasma from a perspective of surface oxidation degree

Particle size is an important parameter to determine the surface modification degree of sulfide minerals by plasma as well as the floatability of minerals. However, little studies have been reported to quantitatively relate surface oxidation and sample particle size to flotation performance. In this study, X-ray photoelectron spectroscopy (XPS) was used to characterize the surface species of arsenopyrite and pyrite at different plasma modification times. The critical oxidation degree was quantified as the proportion of hydrophilic oxidation species to hydrophobic species and correlated with flotation recovery. The results showed that the flotation recoveries of minerals with different particle sizes were determined by surface oxidation rate and critical oxidation degree. Fine particles were more likely to become hydrophilic under low-temperature plasma modification and yet the critical oxidation degree was also higher. The coarse particles being plasma modification presented a poor flotation recovery due to its low adsorption density of collector, although its oxidation degree was lower than the fine size fraction. The critical oxidation degree of pyrite was expected to be less than arsenopyrite, but its flotation recovery was higher under the same plasma medication time because of its slower oxidation rate.     

Mathematical modeling of the heat treatment and combustion of a coal particle. II. drying stage

This article is a continuation of the previous article in which, with the aid of mathematical modeling, the regime of radiative-convective heating of a coal particle was studied in detail and which was devoted to an analysis of the stage of coal drying, very important in the general picture of coal combustion. The process of coal drying is formulated as the nonlinear Stefan problem with a moving liquid-vapor phase change interface. The rate and time of coal particle drying, the temperature distribution inside a particle, and other parameters of the process have been found approximately analytically depending on the regime of heat supply. A parametric analysis of the influence of physical and regime factors on the dynamics of drying as an integral part of heat treatment of a fuel for its ignition and combustion has been carried out.