Effect of ionic liquid additive [BMIM]HSO<Subscript>4</Subscript> on zinc electrodeposition from impurity-containing sulfate electrolyte. Part I: current efficiency,surface morphology,and crystal orientations

The effects of ionic liquid additive 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ on the current efficiency (CE), surface morphology, and crystallographic orientations during zinc electrodeposition from acidic sulfate solutions containing some common impurities such as copper, iron, cobalt, nickel, and lead were investigated. The results indicated that all the metallic impurities studied exerted a deleterious effect on the zinc electrodeposition process by decreasing the CE, influencing the purity, and inducing changes in morphology of the cathodic deposits. The addition of [BMIM]HSO₄ was observed to relieve the harmful effects of these impurities to some extent, and led to reduce the impurity content in the zinc deposits and improve the CE and the quality of the cathodic deposits. The data obtained from X-ray diffraction revealed that the presence of these impurities alone and in combination with [BMIM]HSO₄ did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.     

Drying characteristics of particles using thermogravimetric analyzer

The drying characteristics (critical moisture content, equilibrium moisture content, constant drying rate and effective diffusivity) of various particles (gypsum, millet, polyvinyl chloride and silica gel) using a thermogravimetric analyzer were measured. The experiments were performed in the gas temperature range of 40 to 100 °C under isothermal conditions. The drying rate curve was mainly dependent on the moisture content, particle size, gas temperature and the internal structure of the solid particles. The equilibrium moisture content of solid particles decreased with increasing gas temperature, while the critical moisture content and the effective dispersion coefficient increased with increasing gas temperature. The effective diffusion coefficients of both PVC and gypsum particles were not able to be determined by Fick’s law since the experimental data were not well matched with the model predicted values, which consisted of the drying time in the falling-rate drying period.     

Chemistry of by-product gypsum and plaster. I. Identity of an important solid solution impurity

An investigation has been made into why calcium sulphate β-hemihydrate, derived from the by-product gypsum of wet-process phosphoric acid manufacture, can, when derived from certain types of phosphate rock, be insensitive to hydration retarders. Aluminium and fluorine, which are common impurities in phosphate rock, form complex aluminofluorides in the phosphoric acid reaction liquor; and gypsum crystallising from this system has its crystal habit and physical properties modified by these complexes. The hemihydrate calcined from the gypsum has a setting time that is less amenable to control by retarder addition than the setting time of pure hemihydrate. The gypsum crystals exhibiting this effect incorporate a solid solution impurity which has been identified as AlF₅^2? substituting for SO₄^2? ions in the crystal lattice.     

Hydrothermal synthesis of calcium sulfate whisker from flue gas desulfurization gypsum

Plenty of flue gas desulfurization (FGD) gypsum generated from coal-fired power plants for sulfur dioxide se-questration caused many environmental issues. Preparing calcium sulfate whisker (CSW) from FGD gypsum by hydrothermal synthesis is considered to be a promising approach to solve this troublesome problem and uti-lize calcium sulfate in a high-value-added way. The effects of particle size of FGD gypsum, slurry concentration, and additives on CSW were investigated in this work. The results indicated that fine particle size of FGD gypsum and moderately high slurry concentration were beneficial for crystal nucleation and growth. Three additives of magnesium chloride, citric acid, and sodium dodecyl benzene sulfonate (SDBS) were employed in this study. It was found that mean length and aspect ratio of CSW were both decreased by the usage of magnesium chloride, while a small quantity of citric acid or SDBS could improve the CSW morphology. When multi-additives of citric acid-SDBS were employed, the mean length and aspect ratio increased more than 20%. Moreover, surface morphology of CSW went better, and the particle size and crystal shape became more uniform.     

Simultaneous control of particle size and morphology of α-CaSO4·1/2H2O with organic additives

Here we reported a method to simultaneously control the particle size and morphology of α-CaSO₄·1/2H₂O (α-HH) prepared from flue gas desulfurization gypsum by adjusting the succinic acid concentration and glycerol content under mild conditions. Succinic acid controlled the crystal morphology by adsorption onto α-HH surfaces, and glycerol controlled the crystal particle size, in which an increase in the maximal relative supersaturation (S_max) and nucleation rate of α-HH was hypothesized to cause the change in α-HH particle size. Then, based on the method, α-HH with different particle sizes but with almost the same morphology was prepared, and the influence of the crystal particle size on the mechanical strength of the α-HH pastes was explored. With decreasing α-HH particle size from about 26 to 5 μm, the dry compressive strength of the pastes made from the α-HH decreased remarkably from 68.02 to 34.85 MPa, which was ascribed to an increase in the internal porosity of the pastes.     

Effect of pH Value on the aqueous precipitation copolymerization of acrylonitrile and vinyl acetate

The aqueous precipitation copolymerization of acrylonitrile (AN) and vinyl acetate (VAc) with NaClO₃/NaHSO₃ redox initiation system is carried out continuously in a 10L pilot‐plant reactor. The effects of pH value on ionization equilibrium of NaHSO₃, polymerization rate, particle morphology, particle size and its distribution, molecular weight and its distribution have been investigated. It has been found that effective concentration of reductant H₂SO₃ increases with the decrease in pH value. On the other hand, deceasing pH value intensifies the coalescence among particles and then reduces diffusion rate of monomer and radicals into particles. Experimental data shows that the increase of pH value results in higher conversion. It indicates that pH value's effect on particle stability prevails its influence on effective concentration of the reductant. This conclusion is verified by the molecular weight, particle size, and particle morphology. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Pore, surface and fillet moisture in centrifuged beds of coarse coal

The moisture content of the coarse coking coal product from the centrifuges of preparation plants was investigated to evaluate the contribution of three types of water: that held internally in pores, that in fillets at points of contacts between the particles, and the moisture covering the surface. A standardised laboratory centrifuge test was used to measure the total non-centrifugable moisture (NCM) content and also the quantity held in internal pores, called NCM_i. The fillet moisture NCM_f was estimated by means of a formulation which relies on experimentally measured holdup volumes, supplemented by a physical model. The surface moisture NCM_s could then be derived by difference. The NCM_f, which depends on the body force, the particle size and the surface tension and contact angle of the liquid, ranges from effectively zero for large particles to 10% for fines. The surface moisture NCM_s is of the order of 0.5% for high rank coals and increases to 1.5% for lower rank coals.     

氯离子对脱硫石膏结晶性能的影响

经过干燥脱水的脱硫石膏主要成分与模具石膏基本相同,其主要晶体成分均为半水石膏,但脱硫石膏的晶体颗粒形态、杂质等因素均会对石膏性能产生影响。DT发电厂脱硫石膏中氯离子含量达到4130ppm,远超过国外脱硫石膏相关标准中氯离子含量100ppm的限值,而过多的氯离子会影响石膏晶体的水化结晶,导致石膏浆体不凝结、无法形成强度。在脱硫石膏资源化利用过程中可采用多次滤洗等方式消除氯离子的不良影响。     

Occurrence forms of major impurity elements in silicon carbide

In this study, the forms of occurrence of impurity elements in silicon carbide (SiC) with different particle sizes were systematically investigated using a combination of X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometry (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that in SiC powders prepared using the Acheson process, the contents of O, free-Si, free-C, and Fe impurities are high, and those of other trace impurity elements follow the order: Ti > Al > Ni > V. Moreover, O impurities mainly cover the SiC particle surface in the form of amorphous SiO₂. Fe impurities exist around SiC particles as Fe₂O₃, Fe_xSi_y, Fe_xSi_yTi_z, and Fe_xAl_ySi_z phases. Impurity elements are often introduced during the smelting of SiC and/or during milling or subsequent storage.     

螯合剂对湿法磷酸制备磷酸二氢钾结晶过程影响

湿法磷酸生产成本低,但杂质含量高,以湿法磷酸为原料制得的磷酸二氢钾(KDP)产品质量低。研究利用中和法,以杂质含量高的工业湿法磷酸为原料,制备柱状大颗粒磷酸二氢钾晶体。研究了螯合剂用量、降温速率和搅拌速率对磷酸二氢钾结晶过程的影响,考察了磷酸二氢钾的质量分数、收率、结晶速率和晶体形貌等指标,并进行了母液循环实验。研究结果表明：螯合剂能有效消除杂质离子对结晶过程的抑制作用。结晶的最适宜工艺条件为螯合剂用量0.70%、搅拌速率100 r·min^-1、降温速率0.1℃·min^-1。在此条件下得到的磷酸二氢钾晶体外观为柱状大颗粒,质量分数99.91%,平均粒度1.38 mm,结晶速率0.128 g·min^-1,达到肥料级磷酸二氢钾优等品标准(HG/T 2321—2016);其中磷的单次收率49.86%。母液循环生产的磷酸二氢钾晶体质量分数、晶型和收率等指标全部达标。     

Filter Cake Washing of Mesoporous Particles

Particle synthesis in liquid phase usually requires a subsequent washing step in order to remove undesirable impurities such as unreacted educts, byproducts, solvents and salts. In particular, the washing of mesoporous particles is a challenging task due to large specific surface areas and void volumes. The filter cake washing of mesoporous SiO₂ particles contaminated either with an adsorbing fluorescent dye or sodium sulfate is presented. The effects of wash liquid mass flow rate, mean particle size, and mean pore size on the wash efficiency were investigated. Especially the interaction between impurities and the solid surface, and thereby the initial impurity distribution within the filter cake, led to distinctive washing behaviors.     

Efficient extraction of impurities from phosphogypsum during crystal regulation of α-hemihydrate gypsum

Phosphogypsum (PG) is a solid waste generated during the “wet phosphoric acid process.” The phosphorus (P) impurities and low-value-added recycling products seriously constrain PG re-utilization, which results in its massive accumulation and thus occupies large land areas and poses a severe pollution threat to the environment. In this study, by regulating gypsum crystal and P species in CaCl₂–HCl solutions under mild conditions, efficient removal of P impurities (leaching efficiency of 97.78%) and synchronous preparation of high-strength α-CaSO₄·0.5H₂O (α-HH) (compressive strength of 35.2 MPa) from PG were achieved during the phase transition from CaSO₄·2H₂O (DH) to α-HH, which was a reaction of DH dissolution, followed by α-HH crystallization. The co-crystalline P was fully released during the dissolution process, which was necessary to efficiently eliminate P impurities. HCl dissolved the released P and transformed them into the protonated specie (H₃PO₄) with less similarity to SO₄²⁻, which prevented the recombination of the released P with gypsum during the crystallization process. Furthermore, α-HH morphology and size were controlled by seeding in the mixed solutions. The formation of regular large α-HH crystals with a low-specific surface area significantly weakened the surface adsorption of P in solutions and further increased the P leaching efficiency. More importantly, the large stumpy α-HH was identified as high-strength gypsum with high added value. This work would provide innovative guidance to efficiently remove impurities from gypsum and pioneer a cost-effective approach for clean and high-value utilization of industrial gypsum residues.     

Effects of ionic impurities on crystallization of cobalamin

In this paper, the influence of two typical ionic impurities (Na⁺ and Mg²⁺) is investigated with the focused beam reflectance measurement (FBRM) technique. In this system, the on-line FBRM is used as a tool for monitoring the crystallization process of cobalamin by measuring the chord length distribution of particles and the particle counts. It is noted that impurity Mg²⁺ has a more significant effect than Na²⁺ in crystal growth of the whole crystallization process. From the microscopic observation of crystals, Mg²⁺ has an obvious effect on the crystal habit, while Na²⁺ has little effect. In addition, the crystal habit changes can be monitored by particle vision measurement (PVM). Understanding these effects is helpful to aid optimization and improve process control.     

Effects of ionic impurities on crystallization of cobalamin

In this paper, the influence of two typical ionic impurities (Na⁺ and Mg²⁺) is investigated with the focused beam reflectance measurement (FBRM) technique. In this system, the on-line FBRM is used as a tool for monitoring the crystallization process of cobalamin by measuring the chord length distribution of particles and the particle counts. It is noted that impurity Mg²⁺ has a more significant effect than Na²⁺ in crystal growth of the whole crystallization process. From the microscopic observation of crystals, Mg²⁺ has an obvious effect on the crystal habit, while Na²⁺ has little effect. In addition, the crystal habit changes can be monitored by particle vision measurement (PVM). Understanding these effects is helpful to aid optimization and improve process control.     

三聚磷酸钠对建筑石膏水化进程的影响及缓凝机理研究

系统研究了三聚磷酸钠对建筑石膏水化进程、液相离子浓度与过饱和度及二水石膏晶体形貌的影响,结合X光电子能谱分析技术对其缓凝机理进行了分析.结果表明:三聚磷酸钠使建筑石膏水化放热变缓,早期水化率降低,诱导期延长;三聚磷酸钠使液相离子浓度和过饱和度降低,二水石膏晶体粗化,晶型由针状转化为短柱状;三聚磷酸钠使二水石膏晶核表面钙元素2p电子结合能发生1.267eV化学位移,它与二水石膏表面的钙元素作用,在其表面形成化学吸附层,阻碍二水石膏晶核生长;三聚磷酸钠形成磷酸钙难溶盐覆盖在建筑石膏表面抑制其溶解和三聚磷酸钠在二水石膏晶核表面形成化学吸附层阻碍其生长是三聚磷酸钠缓凝的内在原因.     

Effects of impurities on particle sizing by acoustic attenuation spectroscopy

It is important to have correct information regarding particle size in order to interpret, control, and optimize many industrial processes. Prior to the recent advent of acoustic attenuation spectroscopy, it was difficult to study particle size distribution online and under real process conditions in processes involving concentrated dispersions (suspensions or emulsions). The technique still needs improvement because it is less known how and under which conditions to employ the technique when dispersions involve impurities that could be soluble, insoluble, in the form of additives, and so on. This lack of understanding has almost halted the advancement in applications of the technique to various processes that essentially involve dispersions with impurities. This study investigates aqueous suspensions of CaCO₃ at different concentrations (i.e., 5%, 10% and 20% mass/mass) with added impurities of MgCO₃ (insoluble impurity), NaNO₃ (soluble impurity) and sodium polyacrylate (soluble additive) at varying proportions (5%, 10%, 20% and 30% of the weight of CaCO₃). The study characterizes and compares dispersion with and without impurity in order to demonstrate the possible ways in which addition of an impurity change the original acoustic attenuation spectrum of a dispersion. The study brings the conditions in which acoustic attenuation spectroscopy is capable of explaining that addition of an impurity will not change original particle size of the disperse medium.     

Particle formation of an edible fat (rapeseed 70) using the supercritical melt micronization (ScMM) process

The supercritical melt micronization (ScMM) process, also known as particles from gas saturated solutions (PGSS) was applied, in a continuous operated pilot plant, for the particle formation of the edible fat, rapeseed 70 (RP70). The effect of variables like the CO₂ concentration, the melt temperature and the atomization pressure were studied in order to investigate particle morphology, density and the particle size distribution. The experiments were performed at CO₂ concentrations between 0 and 50 wt%, atomization pressure between 70 and 180 bar and melt temperature between 60 and 100 °C. Particles obtained as a function of the CO₂ concentration, showed completely solid, spherical–hollow and aggregated particles with a decrease in particle mean size as the concentration of CO₂ was increased. The results obtained as a function of atomization pressure showed no significant influence on particle morphology and size distribution. Experiments carried out as a function of the melt temperature showed distorted, spherical–hollow and aggregated particles. Furthermore, a theory was developed to explain the mechanism for particle formation as a function of the CO₂ concentration and the melt temperature. The crystallinity of the final product of RP70, showed an alpha polymorph with a crystallinity of 84%.     

Microstructure and flexure creep behaviour of SiC-particle reinforced Al2O3 matrix composites

The flexure creep behaviour of monolithic Al₂O₃ and 10 vol% SiC-particle reinforced Al₂O₃ matrix composites was investigated in air atmosphere at 1160 to 1400 °C and under a stress of 40 to 125 MPa. Two kinds of SiC particles with different particle sizes and oxygen contents were used in the composites, one having an average size of 0.6 μm with 1.7 vol% SiO₂ impurities and the other of average size 2.7 μm with 3.4 vol% SiO₂ impurities. Compared with the creep behaviour of monolithic Al₂O₃ the strain rate of the composites with 0.6 μm SiC particles did not decrease; however, the composites with 2.7 μm SiC particles exhibited excellent creep resistance. Microstructure analysis showed that the Al₂O₃ grains in the composites with 0.6 μm SiC particles were mainly equiaxed with most of the SiC particles lying at the grain boundaries or triplegrain junctions, whereas the grain features of the composites with 2.7 μm SiC particles were irregular and elongated and most of the SiC particles were entrapped into Al₂O₃ matrix grains. It was revealed that the entrapment of 2.7 μm SiC particles into Al₂O₃ matrix grains was related to the high SiO₂ impurity content on SiC particle surfaces, and the change of grain morphology and the good high-temperature oxidation resistance were responsible for the creep resistance increase of the composites with 2.7 μm SiC particles.     

Synthesis of the ternary metal carbide solid-solution ceramics by polymer-derived-ceramic route

The polymer-derived-ceramic (PDC) route has been widely used to fabricate the transition-metal carbides (TMCs). Previously reported works focused mainly on the synthesis of the single or binary TMCs, while the synthesis of the ternary or more component TMCs was rarely reported. Herein, a class of the ternary TMCs, namely (Nb_1/3Zr_1/3Ta_1/3)C solid-solution ceramics, was successfully synthesized via PDC route for the first time. The as-synthesized ceramics exhibited the particle-like morphology with an average particle size of ~250 nm and showed a single rock-salt crystal structure of metal carbides. At the same time, they had high compositional uniformity from nanoscale to microscale. In addition, they possessed low-oxygen impurity content of 0.79 wt% and moderate-carbon impurity content of 8.98 wt%. Such work provides a novel route to fabricate the ternary or more component TMCs.     

淘洗六水氯化铝过程中晶体沉降速度与纯化规律分析

针对粉煤灰酸法制氧化铝工艺中六水氯化铝结晶纯度难以控制、需进一步纯化的问题建立液固淘洗过程模拟实验,考察了液相密度、黏度、颗粒粒度及体积分数对颗粒沉降速度的影响,并用液体对颗粒的抵抗阻力对其修正,建立了关于沉降速度的计算模型,相对误差小于10%,能够较好地预测该体系下颗粒的沉降速度。按照淘洗过程模拟实验条件及对应的颗粒沉降速度设计静态实验,考察了钠、钙、镁和钾4种杂质离子随淘洗时间的变化规律,得到较优淘洗时间为60s。实验结果表明,杂质离子脱除率依次为Na⁺>Ca²⁺>Mg²⁺>K⁺,且最高脱除率均可达80%以上,杂质离子脱除率随着液固比的增大而提高,与沉降速度计算模型趋势一致,研究结果可为淘洗工艺的设计计算和优化提供参考。