Preparation of alumina ceramic template by the molten salt method

ABSTRACT

Single-crystal alpha alumina (α-Al₂O₃) platelets were synthesised with aluminium sulphate in the study. Moreover, the effects of the heating temperature, holding time, and different power mixtures of γ-Al₂O₃ and sodium sulphate (Na₂SO₄) on the morphology of as-prepared α-Al₂O₃ platelets were explored. The crystalline phase evolution and morphology of the samples were characterised by X-ray diffraction and scanning electron microscopy. According to the further analysis results, most of α-Al₂O₃ platelets were hexagonal particles. After the power mixture of γ-Al₂O₃ and Na₂SO₄ (1:2) was heated at 1200°C for 1?h, the platelet size became relatively uniform with an average diameter of 3–5?μm and a thickness of 50–100?nm. This method is an easily controllable, simple, and green method to produce high-quality α-Al₂O₃ platelets.     

Effect of cooling rate and alumina dissolution on the determination of temperature of critical viscosity of molten slag

In slagging gasifiers with crystalline slag, the fluctuation in temperature near the temperature of critical viscosity (T_cv) can rapidly increase the molten slag viscosity and cause an accumulation of slag inside the gasifier. In order to prevent operational problems caused by the slag, one therefore needs to obtain an accurate measurement of T_cv. The effects of cooling profile and the extent of alumina dissolution on the experimentally determined T_cv were investigated. A synthetic slag was prepared using a composition of Alaskan Usibelli ash, which exhibited crystalline slag behavior, and T_cv was determined under constant cooling and equilibrium conditions. The T_cv measured under 2°C/min of constant cooling was 33°C lower than the T_cv under equilibrium conditions. The effect of alumina dissolution was determined using a platinum (Pt) lined crucible. At a 2°C/min cooling rate, the T_cv measured using a bare alumina crucible was 23°C higher than that from the Pt-lined crucible, offsetting the difference caused by constant cooling. In order to determine a safe gasification temperature range, however, the measurement of T_cv under constant cooling conditions should be avoided.     

A numerical study of fluidization behavior of Geldart A particles using a discrete particle model

This paper reports on a numerical study of fluidization behavior of Geldart A particles by use of a 2D soft-sphere discrete particle model (DPM). Some typical features, including the homogeneous expansion, gross particle circulation in the absence of bubbles, and fast bubbles, can be clearly displayed if the interparticle van der Waals forces are relatively weak. An anisotropy of the velocity fluctuation of particles is found in both the homogeneous fluidization regime and the bubbling regime. The homogeneous fluidization is shown to represent a transition phase resulting from the competition of three kinds of basic interactions: the fluid-particle interaction, the particle-particle collisions (and particle-wall collisions) and the interparticle van der Waals forces. In the bubbling regime, however, the effect of the interparticle van der Waals forces vanishes and the fluid-particle interaction becomes the dominant factor determining the fluidization behavior of Geldart A particles. This is also evidenced by the comparisons of the particulate pressure with other theoretical and experimental results.     

磷石膏-氨-水固碳反应体系氨浓度对石膏颗粒溶解速率的影响

磷石膏-氨-水固碳反应体系中石膏颗粒的溶解,是三相流化矿化反应系统的控制性步骤。在氨水溶液中石膏颗粒能与氨分子形成N—H…O氢键,导致石膏溶解速率受氨浓度影响。基于已知粒度分布的石膏颗粒群在不同氨浓度下的溶解实验数据,采用种群平衡模型与物料衡算相结合的方法,探究了氨浓度对石膏颗粒群溶解特性的影响规律。结果表明:氨浓度的增加会降低石膏溶解速率,随着溶解的进行,氨对溶解的抑制作用会减弱。此外,随着氨浓度的增大,增加单位氨浓度石膏溶解速率的降幅将变小。结合实验数据拟合关联溶解动力学参数,构建了氨浓度影响下石膏的溶解速率模型,预测了三相流化矿化反应系统中两个串联回路石膏料浆所需的停留时间,为磷石膏-氨-水固碳反应体系矿化烟气CO₂的放大设计提供了理论依据。     

Nanostructural insights into the dissolution behavior of Sr-doped hydroxyapatite

In this study, high-resolution transmission electron microscopy (HRTEM) was employed to characterize the nanostructure of strontium-substituted hydroxyapatite (Sr-HA) and its evolution following in vitro immersion in physiological solutions. HRTEM images showed that the substitution of Sr induced local distortions in the hydroxyapatite (HA) lattice: minor levels of edge dislocations were detected at low doping contents of Sr ions (1 at%); when the Sr content exceeded 10 at%, the density of grain boundaries increased notably and triple junctions were clearly observed. The dissolution of undoped HA was initiated at crystallite surfaces, whereas the dissolution of Sr-HA started around grain boundaries. Acicular nanocrystal reprecipitation was observed on grain surfaces immersed in simulated body fluid (SBF), while not in dilute hydrochloric acid (HCl). These ?ndings suggest appropriate levels of Sr incorporation can introduce imperfections in the crystal structure of apatite and thus enhance its dissolution rate towards enhanced physicochemical performance in biomedical applications.     

粉煤灰制备氢氧化铝晶核生长动力学数学模型

以粉煤灰为原料，从碳化法制备超细氢氧化铝的工艺参数入手，对氢氧化铝晶核生长动力学数学模型的建立进行了研究。通过单因素实验分别构建铝酸钠溶液质量浓度、碳化温度、分散剂用量、二氧化碳体积分数、pH、A试剂加入量、碳化通气速度等各因素对氢氧化铝粒径影响的回归方程，建立氢氧化铝晶核生长动力学数学模型，然后通过正交实验建立方程组确定各因子相关系数。模型检验结果表明，误差在5％以内，具有一定的可信度。     

A thermodynamic model of dissolution and precipitation of calcium silicate hydrates

A thermodynamic incongruent dissolution/precipitation model of calcium silicate hydrate (C-S-H) is proposed, assuming a binary nonideal solid solution of Ca(OH)₂ and SiO₂. Using this model, both dissolution and precipitation of the C-S-H phase, with a continuous change in the Ca / Si ratio of the solid phase, can be predicted. The notable features of the model are its good continuity and simplicity so that calculation can be easily compiled in a calculation code. A series of experiments were carried out. C-S-H precipitates were prepared using two techniques: precipitation by contacting Ca(OH)₂ solution with C-S-H gel and hydrolysis in a mixture of Ca and Si solutions. The equilibria in these experiments were predicted well by the proposed model. A calculation using the model also predicted well the dissolution of ordinary Portland cement hydrate with water exchange.     

A test for phosphate rock reactivity in which solubility and size are combined in a dissolution rate function

A test for phosphate rock (PR) reactivity has been developed based on a representation of certain fundamental properties of the rocks designated the Dissolution Rate Function. The function and properties have been shown to be those important in models of the dissolution rate of PRs in soil. The properties are size or mass distribution with size, solubility product, P content and particle density. In practice the solubility product is measured in terms of the P concentration attained in a standard solution, simulating that in an average soil with respect to pH, Ca and ionic strength.The test compares favourably with those using citric and formic acids, using published results for the relative agronomic effectiveness of 11 PRs, both unground and ground. The agronomic data also indicated that particle sizes < 0.15 mm can be regarded as equivalent to the size range of 0.10 to 0.15 mm.     

Application of the rotating disk method to the study of bitumen dissolution into organic solvents

The rotating disk system is demonstrated as a tool for performing studies of the dissolution rate of bitumen into organic solvents. Mass transfer coefficients to the rotating disk are constant in position and time can be made comparable to coefficients for sand particles in agitated liquids by adjusting the rotation rate. Data is presented for bitumen dissolution into pentane, hexane, heptane, toluene and oleic acid. Increasing the level of dissolved bitumen in the solvent decreases the bitumen dissolution flux primarily due to the increase in solvent viscosity.     

硅铝胶改变膨润土端面电性的机理研究

制备了硅铝胶改性的膨润土,研究了硅铝胶改性对膨润土的重金属离子吸附性能的影响,并用XRD对改性土进行了分析,提出了硅铝胶作为改性剂改变膨润土端面电性的机理,结果表明,硅铝胶改性在膨润土瑞面发生,改性能显著提高膨润土吸附钴离子的能力。     

沉淀法制备纳米氧化铝粉体的新工艺研究

以（NH4）2CO3为沉淀剂，并采用一种高分子分散剂，研制出沉淀法制备纳米氧化铝粉体的新工艺。制备出球形纳米氧化铝粉体，在800℃煅烧得到的颗粒尺寸为5－6nm，在1100℃煅烧得到的颗粒尺寸约为8nm。研究了沉淀pH、溶液浓度、煅烧温度和分散剂用量对纳米氧化铝粉体性能的影响。     

EQCM研究邻氨基苯甲酸/苯胺的共聚膜的溶胀/溶解行为

本文采用电化学石英微天平（EQCM）研究了现场监测了摩尔比不同的邻氨基苯甲酸／苯胺混合溶液的共聚膜在不同pH值B—R缓冲溶液中的不同性质和过程。发现溶液中邻氨基苯甲酸的含量和溶液的PH值对苯胺／邻氨基苯甲酸的共聚膜的溶胀／溶解行为均具有很大的影响。     

Development and application of a holistic model for the steady state growth of porous anodic alumina films

A holistic model was developed and applied to anodic alumina films galvanostatically grown in sulphuric acid solution at different anodising conditions thus characterised by different structural characteristics. The O²⁻ and Al³⁺ species transport numbers near the metal|oxide interface were determined that depended on both temperature and current density. The rate of film thickness growth was found to be proportional to the O²⁻ anionic current through the barrier layer near the metal|oxide interface. The results introduced a new growth mechanism theory embracing the rarefaction of barrier layer oxide lattice towards the metal|oxide interface. The oxide density near the metal|oxide is closely independent of anodising conditions and is related to the transformation of Al lattice to a transient oxide lattice about 37% rarer than that of γ-Al₂O₃ that is further suitably transformed to denser, amorphous or nanocrystalline material as this oxide is shifted to the oxide|electrolyte interface and becomes the pore wall material. This gradual lattice density variability can explain many peculiar properties of anodic alumina films.     

A population model of quartzite particles in a lab-scale fluidized bed due to the thermal fragmentation

A population model has been developed to simulate the size distribution of quartzite particles in a lab-scale fluidized bed. While quartzite particles as a kind of bed materials in the differential density circulating fluidized bed were loaded into the high temperature bed, the size distribution of quartzite particles would be changed due to the thermal fragmentation, which could significantly influence fluidization characteristics and heat transfer.With the purpose of comprehending the population of quartzite particles after thermal fragmentation, a fragmentation experiment of quartzite particles has been carried out in a lab-scale circulating fluidized bed. The results show that the fragmentation of particles mainly occurred on particles surface. Based on this experimental phenomenon, a mathematical population model was established to estimate the particle size distribution. The predicted value from the population model is close to the experimental value.     

A model on attrition of quartzite particles as a bed material in fluidized beds

In this paper, a model on attrition of quartzite particles as an inert bed material in fluidized beds has been established on the particle-particle collision. For the convenience of describing the attrition of quartzite particles in fluidized beds, we chose the attrition rate constant (k_ARC) as one main characteristic parameter to develop the model.In order to verify the validity of the developed model, an attrition experiment of quartzite particles has been carried out in a lab-scale circulating fluidized bed. The predicted results from the population model were close to the experimental data as far as the engineering use is concerned. Finally, a sensitivity analysis was performed by using the developed model to examine effects of initial particle diameter, attrition time, and fluidization number on k_ARC.     

Insights into influence mechanism of polymeric excipients on dissolution of drug formulations: A molecular interaction-based theoretical model analysis and prediction

This study provides an analysis of the dissolution mechanism of poorly water-soluble drugs, indomethacin (IND) and naproxen (NAP), from polyvinyl acetate (PVAc) and polyvinylpyrrolidone/vinyl acetate 64 (PVPVA 64) formulations under the combination of the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) and a chemical-potential-gradient model. Moreover, the dissolution kinetics of both drugs from these polymeric formulations were modeled in conformity with the in vitro experimental data obtained by means of a rotating disk system (USP II). The combination of the thermodynamic model PC-SAFT and a chemical-potential-gradient model was demonstrated to be an efficient approach to explain the drug dissolution mechanism from the drug/PVAc and PVPVA 64 formulations. These results have implications in reducing experimental time and resources for the sustained dissolution kinetics profile determination without compromising accuracy, in particular for the system of the drug/PVAc formulation when obtaining continuous drug dissolution in this work.     

A model for turbulent binary breakup of dispersed fluid particles

Accurate predictions of particle size distributions, and therefore of the underlying processes of fluid particle breakup and coalescence are of vital importance in process design, but reliable procedures are still lacking. The present paper aims at developing a modular formulation for the turbulent particle breakup process. The model is to be included in a population balance model which is formulated such as to facilitate the direct future implementation into a full multifluid CFD model.The breakup process is described without introducing adjustable parameters. The current model is a further development of an existing model by Luo and Svendsen (AIChE J. 42 (5) (1996) 1225), which has been expanded and refined, and where an inherent weakness regarding the breakup rate for small particles and small daughter particle fragments are removed. A new criterion regarding the kinetic energy density of the colliding turbulent eddy causing breakup has been introduced. This new criterion is a novel concept describing the breakup process. The details are thoroughly discussed together with possible further modifications. The results from the new model are encouraging because the breakup rate is greatly reduced when the dispersed fluid particles are reduced in size. Further, the response to changes in system variables is reasonable and the distribution of daughter sizes vary in a reasonable way for the different collision possibilities.     

Accounting for particle movement when assessing the dissolution of slow release fertilizers in field soils

When fine particulate, slow-release fertilizers are applied to pastures, earthworm activity can physically move the particles both horizontally and vertically in the soil. This physical movement needs to be accounted for when researchers attempt to determine the rate of fertilizer dissolution by measuring the quantity of undissolved fertilizer residue remaining in the soil. A hard igneous phosphate rock (Phalaborwa PR) and an inert chromite ore were used as tracers to follow the physical movement of the reactive PR (RPR), NCPR applied to grazed pasture on a Pallic Soil (Aeric Fragiaqualf) isolated in galvanised steel cylindrical cores (150 mm diameter and 100 mm height) with or without nylon mesh sleeve (63 µm) at the bottom. The soil cores were sampled after 113, 270 and 559 days and analysed for PR and chromite residues. Results from both tracers showed that there was a significant movement of particles laterally out of the cores and vertically below 40 mm soil depth. Phalaborwa PR particle movement to 40–60 mm soil depth was 8% in 112 days and 24% in 270 days. Between 270 and 559 days no significant movement of particles was observed. Particle movement appeared to occur in discrete non-continuous events that were associated with the major end-of-autumn peaks in earthworm activity. When corrected for particle movement, the measured rate of NCPR dissolution satisfactorily fitted the rate of dissolution predicted by two models of PR dissolution.     

A study of the dynamics of anodic copper dissolution in a NaCl/KSCN electrolyte

The oscillatory behaviour of the anodic dissolution of copper into an aqueous NaCl solution containing a small amount of thiocyanate ions has been studied experimentally in the absence and in the presence of a magnetic field. The latter has an inhibiting effect on the oscillation and, under specific conditions, it can fully suppress it.     

The mathematical model of the stripping voltammetry hydrogen evolution/dissolution process on Pd layer

The advanced two-plate mathematical model of electrochemical hydrogen evolution/dissolution process has been presented and discussed. The model, with Langmuir adsorption equation, has been experimentally verified by the use of the glassy carbon/Pd layer electrode system at different scan rates. The two cathodic-anodic stages of hydrogen evolution/dissolution process in 0.1 M and 0.001 M HCl solutions have been interpreted and discussed. The thickness of the layer and the way of deposition were also investigated. The fundamental kinetic problem of a change of electrode properties during electrode process as an effect of the elementary hydrogen presence in the solid electrode is presented and interpreted. The isopotential point phenomenon, an electrochemical analog of isosbestic point in absorption spectroscopy, was unexpectedly discovered as experimental effect of hydrogen adsorption and α variability.