纳米BaF2粉体的热稳定性

采用醇/水混合溶剂方法制备了不同粒径的纳米BaF2粉体,研究了粉体的热稳定性.结果表明,纳米BaF2粉体的粒径随着混合溶剂中乙醇含量的提高而减小,粉体的形貌和分散性也都随之改变.根据在不同升温速率下测量的每种粒径纳米BaF2粉体的DSC曲线,由Kissinger方程求出了各晶粒长大激活能.BaF2晶粒长大激活能随着粉体粒径的减小而线性地减小,纳米晶BaF2的热稳定性随着粒径的减小而降低.     

橡胶连续混炼粉料混合均匀性仿真及实验研究

为了提高橡胶连续混炼中混炼胶质量稳定性,实现炭黑等粉体物料精确配比和均匀性混合问题,针对粉体物料在混合和输送过程存在复杂的物理性质,建立了炭黑等混合粉料的球体颗粒模型和Hertz接触力-位移模型,采用EDEM对典型粉体物料混合均匀性进行模拟仿真和粉体物料混合实验,对炭黑等粉体物料在橡胶连续混炼工艺中的混合均匀性进行分析,探求橡胶粉料连续混合和输送机理.研究发现:粉体物料混合仿真与实验测试结果具有较高的拟合性,表明在橡胶连续混炼工艺中可以在保证混合均匀性的前提下实现多粉体混合物的连续称量和输送,同时也验证了运用EDEM数据模拟仿真粉体物料混合的可行性.     

等离子喷涂Al_2O_3-30%TiO_2微米/纳米复合涂层的结构与耐磨性能

采用溶胶-凝胶法合成了不同粒径的Al2O3-30%(质量分数)TiO2纳米复合粉体,用喷雾干燥法对合成粉体进行喷雾造粒,造粒后的粉体通过等离子喷涂制备Al2O3/TiO2复合涂层,最后对涂层结构和性能进行了表征。涂层结构和形貌分析表明制备的涂层具有微米/纳米复合结构,初始粉体粒径对涂层的结构和致密度影响很小;涂层摩擦学性能测试表明复合涂层的磨损率随初始粉体粒径的增大而减小,初始粉体粒径为100nm左右时,复合涂层的磨损率最低。复合涂层的磨损机制为裂纹扩展导致的磨损剥落。     

碳-蒙脱石二维纳米复合粉体制备与提纯

以聚乙烯醇、钙基蒙脱石为原料,通过溶液插层、碳化和气流粉碎工艺和技术制备碳-蒙脱石二维纳米粉体。物相和粒径分析结果表明:在钙基蒙脱石、聚乙烯醇、水的质量比为5∶5∶90的反应体系中,获得层间距d(001)=2.11 nm的聚乙烯醇-蒙脱石插层型复合粉体;400℃碳化该复合粉体获得具有三明治结构特征的碳-蒙脱石复合粉体(d(001)=1.56 nm);将碳-蒙脱石复合粉体气流粉碎可得含碳质量分数为6%左右,平均片径约为2μm,厚度小于30 nm的碳-蒙脱石二维纳米粉体,以管状、单片和多片层堆积等形态存在于体系中。通过梯度离心分离法可以提取不同片径的碳-蒙脱石二维纳米复合粉体。     

溶胶-凝胶法制备纳米ZnO·Al_2O_3复合粉体

采用溶胶 凝胶法制备了纳米ZnO·Al2 O3复合粉体 ,研究了添加剂用量、溶液 pH值和反应温度对制备结果的影响 ,并对不同灼烧温度下所得粉体进行了分析 ,确定了合适的制备工艺 ,制得的纳米ZnO·Al2 O3复合粉体粒径分布均匀、平均粒径为 14nm左右     

纳米氧化铝的相变研究

以硫酸铝为原料,用沉淀法制取纳米氧化铝,研究了其相变过程。用XRD、SEM、AFM及IR等手段对不同温度下煅烧所得的产品进行了表征。结果表明,该方法制备的氧化铝粉体呈球形、团聚程度轻、粒度分布较均匀、γ相和δ相平均粒径20-30nm、α相平均粒径53nm,其物相变化次序为：非晶态Al2O3→γ-Al2O3→δ-A12O3→α-Al2O3。     

粉体粒度分布的分形研究

本文应用分形几何理论，研究了粉体的粒度分布特征，发现在双对数坐标下，许多材料粒径的重量累积百分含量与粒径之间呈直线关系，表明其粒度分布具有分形结构。分维可作为描述粉体位度分布特征的一个序参量，其大小反映了粉体颗粒的粗细程度和集中、不均匀特征，即粉体粒度分布的空间结构性。并在监控粉磨机械效率、估测颗粒级配等方面有重要意义。     

粉体粒度分布的分形研究

本文应用分形几何理论，研究了粉体的粒度分布特征，发现在双对数坐标下，许多材料粒径的重量累积百分含量与粒径之间呈直线关系，表明其粒度分布具有分形结构。分维可作为描述粉体粒度分布特征的一个序参量，其大小反映了粉体颗粒的组细程度和集中、不均匀特征，即粉体粒度分布空间结构性。并在监控粉磨机械效率、估测颗粒级配等方面有重要意义。     

二乙胺法制备含多种添加剂的ZnO粉体与变阻器陶瓷的研究

本文采用二乙胺化学制备方法研制了如下6种成份组成的 ZnO 粉料:97mol%ZnO 0.5mol%Bi_2O_3 0.5mol%CO_2O_3 0.5mol%Cr_2O_3 1.0mol%Sb_2O_3 0.5mol%MnO_(?)。测量了粉体的粒度分布,粒径<1μm 的粉体占70～80%,其平均粒径为0.5μm 左右。测量瓷体的烧结密度和电物理特性-α值,并用SEM 对粉体和陶瓷进行观察。实验结果表明:本法可获得电物理特性优良、成份均匀的粉料,瓷体的烧结密度较高(理论密度的97%),晶粒较细且均匀。实验中还发现:化学制备 ZnO 陶瓷无焦绿石相呈现及消失。表明了制备方法不同,材料的相变化亦不同。     

橡胶基导热复合材料中填充粉体粒径对导热性能的影响

研究了粉体粒径对复合材料导热率的影响,通过电镜分析观察了粒径对粉体分布的影响,通过理论计算,从微观尺寸解释了填充粉体粒径与复合材料导热率的变化关系.通过分析得出:当粉体填充量相同时,粉体粒径对材料的导热率有很大的影响,粉体粒径越小粉体之间的距离越小,越有利于粉体相互发生协同作用形成导热链,且不同粒径的粉体填充时,存在着不同的体积含量临界值.     

基于最大似然原理的电厂混煤均匀性确定

采用传统采样分析法对电厂混煤混合均匀性进行评估存在较大困难。将掺混原煤看作是各种成分符合不同概率分布的混合物,在原煤掺混而成的混煤中,某种成分的概率分布由原煤该成分分布、混合比例以及颗粒混合状态共同决定。以挥发分作为示踪成分,考察了掺混过程中挥发分概率分布的变化,在给定原煤挥发分分布和混煤挥发分样本集的情况下,采用最大似然原理对混煤中各种原煤掺混比例和标准差进行估计,进而对混合状态进行评估。研究表明,掺混模型对实际掺混系统的预测结果与原煤消耗量的统计数据吻合良好;多工况仿真实验也表明,掺混系统混合质量越差,模型的预测精度越高。     

Investigating the upper limit for applying the coarse grain model in a discrete element method examining mixing processes in a rolling drum

Mixing is an essential manufacturing process in various industries. The processing procedure and final product quality depend on the homogeneity of mixing. Because it is difficult to evaluate mixing systems experimentally, the discrete element method is commonly employed. However, as the number of particles increases, this approach incurs huge computational costs. The coarse grain model offers a potential solution, but its applicability has not been widely demonstrated; this study aimed to elucidate the upper limit for applying the coarse grain model. To determine the appropriate simulation parameters, calibrations were performed by comparing the powder bed in experiments versus simulations. Various mixing processes were numerically evaluated, and the mixing characteristics were qualitatively consistent among all coarse-grained ratios. These mixing systems were also evaluated quantitatively based on Lacey’s mixing index, which indicated that the upper limit of the coarse-grained ratio was five times. It is therefore important to secure a sufficient number of particles in each cell and to use an appropriate number of cells. This study clarified the upper application limit and criteria for the coarse grain model and verified the maximum coarse-grained ratio (five times). This approach can be used to determine the coarse-grained ratio and reduce computational costs.     

A Comparison of Interaction and Solvent Deposition Mixing

Abstract

The mixing of microingredients with diluents may be conducted by various methods. The purpose of this report is to compare the uniformity of mixing of finely powdered reserpine after mixing by an interactive and a solvent deposition method. Reserpine was used in concentrations of 0.25% with Avicel PH 102 and Sorbit Instant as carrier materials. The uniformity of the mixtures was compared by coefficients of variation (CV) of the content of powder or tablet samples. The dissolution of powder samples was measured in a rotating bottle apparatus. Interactive mixing with Avicel produced samples with larger variation in reserine content compared to solvent deposition. The variation in content was not significantly different when the drug was mixed interactively or by solvent deposition on Sorbit. Smaller coefficients of variation in content were observed for tablet samples compared to powder samples in most cases. The CVs obtained with powder samples for all the mixtures. except for solvent deposition on Avicel, were larger than 5% and would therefore not comply with pharmaceutical content uniformly standards. The CVs for all tablet samples, however, were less than 5%, and based on these results all the mixtures were sufficiently mixed so that the tablets complied with content uniformity standards. The dissolution profiles were not influenced by mixing method.     

基于TRIZ改善微米氧化锡粉末粒度均匀性

经过高温处理的等离子气化法制备的纳米氧化锡粉末存在一定的硬团聚以及过度长大的颗粒,影响采用粉末冶金法制备Ag/SnO2电接触材料的混粉均匀性.基于TRIZ理论中的功能分析、资源分析、物质能-场分析及冲突分析理论,分析了采用现有LNJ-36A气流分级机存在的问题,通过各创新理论的综合运用,得到了对现有气流分级机的改造方案,改善了气流后氧化锡粒度的均匀性.     

A three-dimensional particle roundness evaluation method

Particle roundness is one of the major shape parameters influencing the micro-and macroscopic mechanical properties of granular materials. Most of the existing particle roundness methods are based on 2D algorithms utilizing particle projections. However, the morphology of a particle projection will be influenced by the subjectively chosen projection angle. Based on the acknowledged Wadell’s definitions of particle corner and particle roundness, an innovative method is proposed to evaluate the 3D roundness of realistic particles in a quantitative and objective manner. This method first reconstructs the particle with a triangular mesh. Then, corner portions are identified by finding the surface vertexes with both a high local curvature and large relative connected area. After corner identification, a sphere-filling method is employed to fill the corner portions with spheres. Finally, the 3D Wadell roundness is computed by comparing the average radius of the filling spheres with the radius of the maximum inscribed sphere. Validation of the proposed 3D roundness evaluation algorithm is conducted by comparing the results of the proposed method with the results from theoretical and other existing approaches. The comparison indicates that the proposed method can be used to accurately and objectively evaluate the roundness of realistic particles.     

A review of current techniques for the evaluation of powder mixing

Blending a mixture of powders to a homogeneous system is a crucial step in many manufacturing processes. To achieve a high quality of the end product, powder mixtures should be made with high content uniformity. For instance, producing uniform tablets depends on the homogeneous dispersion of active pharmaceutical ingredient (API), often in low level quantities, into excipients. To control the uniformity of a powder mixture, the first required step is to estimate the powder content information during blending. There are several powder homogeneity evaluation techniques which differ in accuracy, fundamental basis, cost and operating conditions. In this article, emerging techniques for the analysis of powder content and powder blend uniformity, are explained and compared. The advantages and drawbacks of all the techniques are reviewed to help the readers to select the appropriate equipment for the powder mixing evaluation. In addition, the paper highlights the recent innovative on-line measurement techniques used for the non-invasive evaluation of the mixing performance.     

Simulation of the organic thin film thickness distribution for multi-source thermal evaporation process

A model of multi-source thermal evaporation process was proposed to achieve higher deposition rate and uniformity of organic thin film. In this model, several point type sources were uniformly distributed around a circle and evaporated simultaneously to form a surface-like source. Based on the Monte Carlo method, the evaporation process was simulated, and the effect of the number of point type sources, circle radius and source-substrate distance on the uniformity was analyzed. Based on the method proposed in this paper, the uniformity of the thickness in the organic layer was successfully controlled in 5%.     

On morphometric uniformity of diamond micron powders

The paper presents the findings of characterization of initial diamond powders and products of their flotation separation, analysis of the adequacy of mean values of morphometric characteristics and assessment of powder uniformity by a system-criterion method. The separation is demonstrated to provide a significant improvement of powder uniformity in dimensional characteristics and shape index. The flotation products have been found to feature the best uniformity which explains their higher abrasive ability. The flotation separation method has proved to be a suitable tool for improving morphometric uniformity of diamond micron powders, and the proposed system of computer-aided analytical methods has been demonstrated to offer an efficiency means for quantitative analysis of morhometric characteristics of the powders.     

Pharmaceutical Powder Mixing from Randomization to Homogenization

ABSTRACT

The process of powder mixing is one of the most important unit operations during the production of pharmaceutical solid dosage forms. This presentation will address the principle stages of pharmaceutical powder mixing, including: expansion of solid particles, application of three-dimensional shear force to the powder bed, and randomization of particles and maintenance of randomization (no segregation). Theories of powder mixing will also be discussed including random mixing theory (shear mixing, diffusive mixing, convective mixing), non-random mixing theory and ordered mixing theory. A special emphasis will be put on ordered (interactive) mixing because of its relevance to the pharmaceutical systems. Authors' experience in this field will be highlighted.