团聚体含量对氧化锆粉料烧结性能的影响

用共沉淀－喷雾干燥的方法制得了具有不同团聚性质的氧化锆粉料。粉料成型后团聚体可能破碎，也可能继续存在。通过团聚体对烧结影响的研究发现，烧结过程中团聚体含量是影响烧结密度和显微结构形成的主要因素，而成型后素坯中团聚体含量又取决于团聚体的强度。讨论了团聚体之间及团聚体与基体之间的相互作用对烧结的影响。     

喷雾造粒ZrO2粉料坯体性能的研究

以喷雾造粒ＺｒＯ２粉料为研究对象,通过对粉料的压力－密度曲线及坯体的ＳＥＭ显微结构分析,发现喷雾造粒粉料的粒度分布对坯体密度的影响较小;颗粒强度的大小是获得均匀的坯体结构的关键,颗粒的强度与其大小及环境湿度有关,因此颗粒适当的增塑及去除大颗粒均有利于坯体显微结构的改善。     

喷雾造粒粉制备ZTM陶瓷的结构缺陷与强度研究

结合喷雾料浆,造粒颗粒的相关工艺控制,对喷雾造粒粉制备的ＺＴＭ陶瓷的结构缺陷及强度进行了研究。结果发现：较低固相含量的料浆易形成具有坚硬外壳的空心颗粒,这种颗粒在成型过程中难以破坏,以坯体中形成结构缺陷;颗粒的残余水分对颗粒的变形性具有重要作用,随残余水分的增加,坯体的断裂从沿颗粒向穿过颗粒的形式过渡。研究还表明：较大颗粒间的气孔,如在成型过程未被完全破坏和变形,则会遗留在烧结体中,导致材料强度的     

氧化锆料浆性能对其喷雾造粒粉料性质的影响

本文研究了料浆含固量和粘度对其喷雾造粒粉料性质影响。结果表明：氧化锆料浆含固量是喷雾造粒（ＳＤ．）粉料填充密度的主要控制因素，高含固量料浆能得到高填充密度喷雾造粒粉料，且其颗粒显微结构相对致密；随着ＺｒＯ２料浆含固量、粘度增加，喷雾造粒粉料平均粒径增大，粗颗粒含量增多，细颗粒含量减少。     

基于CFD-DPM的陶瓷料浆喷雾干燥过程数值模拟

针对陶瓷料浆喷雾干燥过程中干燥塔内气固两相流动及传热传质复杂,温度场、速度场、湿度场、颗粒直径分布等难于测量问题,基于CFD方法,采用DPM模型描述陶瓷料浆颗粒运动轨迹,构建陶瓷料浆喷雾干燥过程二维轴对称数学模型,并进行了数值模拟。搭建喷雾干燥试验装置,开展了陶瓷料浆喷雾干燥实验,实验测得颗粒直径分布、颗粒湿含量与模拟结果吻合,验证了该模型的有效性。陶瓷料浆喷雾干燥过程数值模拟得到了干燥塔内空气湿度、速度、温度分布,以及颗粒的运动轨迹、湿含量情况,可为陶瓷料浆喷雾干燥塔的优化设计提供理论指导。     

陶瓷薄板优质粉料制备工艺

本文概述了陶瓷薄板用优质粉料的工艺性能、制备优质粉料的工艺条件、原料球磨、料浆处理,以及制备优质粉料的设备-喷雾干燥塔的控制等工艺技术,从而获得生产陶瓷薄板使用的优质粉料。     

悬浮态干法造粒工艺制备陶瓷墙地砖坯体粉料的工艺参数研究

介绍了一种新型悬浮态干法造粒工艺的工艺参数研究,通过改变悬浮态干法造粒工艺的增湿腔内壁材料、雾化水中粘结剂含量、给料速率和增湿腔截面风速四种参数,以所制备陶瓷砖坯体粉料的收料率、含水率和成粒率为指标,研究不同参数对陶瓷砖坯体粉料生产的影响,用优选出的参数组合,与湿法造粒工艺及优化前的颗粒质量做了对比.结果表明:增湿腔内壁材料对所制备颗粒的收料率和成粒率影响很大,使用聚四氟乙烯作为增湿腔内壁材料制备效果明显好于有机玻璃,粘结剂含量在1%左右时粉料与雾化液滴接触结合的情况为最佳;随着给料速率的增加,收料率随之增大,但是实验结果的含水率及成粒率都呈现先增大后减小的趋势,并在3.1 kg/min时出现最大值;随着增湿腔截面风速的提高,颗粒成粒率和含水率降低,而收料率增加.以优化后参数方案制备的坯体粉料颗粒质量上也得到了进一步优化,颗粒流动性更好,与湿法工艺接近.     

共沉淀喷雾干燥法制备YSZ粉料及其对烧结密度的影响

用共沉淀结合喷雾干燥法制得了可直接用于煅烧、成型的Y_2O_3稳定的ZrO_2粉料。用扫描电镜观察了喷雾干燥得到的粉料团聚体的尺寸、形貌,以及与喷雾干燥条件的关系。发现了共沉淀悬浮液的球磨对喷雾干燥后粉料的热行为的影响。喷雾干燥制得的粉料在1350、1500℃烧结后,相对密度分别达96.5％、97.8％;而烘箱干燥的粉料在相应温度下烧结,相对密度只达88％、93％。     

工艺条件对化学共沉淀法制备SrTiO3粉料性能的影响

采用化学共沉淀法制备了ＳｒＴｉＯ３超细粉料。借助ＳＥＭ、粒度分析、红外光谱等测试手段，探讨了反应溶液浓度、表面活性剂的添加及乙醇脱水等工艺条件对制备粉料性能的影响。结果表明，反应盐溶液浓度越高，所得粉料的颗粒越粗；表面活性剂聚乙二醇（ＰＥＧ）的添加及乙醇脱水处理均可使用粉粒的团聚程度减小。     

高铝瓷球生产工艺若干主参数的优化

本利用佛山地区某高铝瓷球生产线,采用正交法设计安排试验,对生产工艺若干主参数分段进行优化组合。其结果是：料浆含水率48％,料浆喷雾压力2．3MPa－2．7MPa,喷雾干燥尾气温度103℃－105℃为制备优质压形粉料的最佳组合;压形粉料含水率0．4％－0．5％,粉料颗粒分布：＞60目0、150目67％＞、180目18％、＜180目15％,成形压力55MPa及在梭式窑窑车底层（约1510℃－1520℃）,可制备出高性能低成本高铝瓷球。     

Influence of Granule Character and Compaction on the Mechanical Properties of Sintered Silicon Nitride

The influence of granule character and compaction on the mechanical properties of sintered silicon nitride was studied as a function of the pH of the spray-dry slurry. The character and the compaction behavior of the spray-dried silicon nitride granules considerably affect the mechanical properties of the sintered body. Dense and hard granules resulting from a well-dispersed slurry retained their shape in green compacts and caused numerous pore defects in sintered body. Decreasing the slurry pH to a certain value (e.g., 7.9) caused slurry flocculation and reduced the granule density as well as the diametral compression strength of the granules. Sintered bodies fabricated with these weak granules contained fewer defects and showed remarkable strength increase.     

Formation and Control of Agglomerates in Alumina Powder

High-purity alumina powder with submicrometer particle size was colloidally dispersed and classified in either water or ethanol to remove agglomerates from as-received powder. After the slurries were dried, fine alumina particles cohered to form agglomerates, which were "hard" when formed in a water slurry, and "soft" in an ethanol slurry. Firing of the powder compacts with "hard" agglomerates resulted in inhomogeneous microstructures, and homogeneous microstructures were formed with "soft" agglomerates. The reasons for their formation are discussed and experimentally confirmed. In the case of water slurry, a small amount of transition alumina reacted with water at low pH. After drying, alumina gels were formed and acted as a strong binder between α-alumina particles to form "hard" agglomerates.     

Influence of Slurry Flocculation on the Character and Compaction of Spray-Dried Silicon Nitride Granules

The effect of slurry flocculation on the characteristics of silicon nitride granules prepared by the spray drying process is investigated. The flocculation state of an aqueous silicon nitride slurry is controlled by adding nitric acid and evaluated as a function of pH. Dense and hard silicon nitride granules result from a well-dispersed slurry having a high pH (e.g., 10.8). These hard granules retain their shape in green compacts and form detrimental defects. Lowering the pH of the slurry to a certain value (e.g., pH 7.9) results in slurry flocculation. Granules prepared from this flocculated slurry have low density and low diametral compression strength and contribute to the elimination of large pores in green compacts.     

Role of strontium substitution in spray drying of hydroxyapatite: A comparative study on physical properties

Spray drying (SD) has the ability to tailor granule size and morphology, thus, it is used for producing hydroxyapatite (HA) granules. Recently, Sr functionalized HA (SrHA) has been recommended owing to its improved biological properties. The aim of this article was to produce SrHA granules with the combination of nanoparticle synthesis and spray-drying. The effects of substitution on the physical properties of SrHA nanoparticles and spray-dried granules were investigated. TEM analyzes revealed that Sr substitution reduced the mean size of HA nanoparticles from 4.59 nm to 2.31 nm. Besides, Sr substitution increased the viscosity of the prepared slurry for spray drying, which may be attributed to the smaller nanoparticle sizes. The reduced nanoparticle size caused to the agglomeration of the SrHA more than the pure HA nanoparticles. Moreover the 16 mol % Sr substituted HA (16SrHA) slurry were quickly hardened, which hampered the feeding of the slurry to the SD system; eventually the atomizer was blocked. The increase in the viscosity increased the mean granule size of HA from 41.53 µm to 49.18 µm. HA and 8SrHA granules presented HA phase dominantly after the heat treatment at 1000°C, while, 16SrHA decomposed to TCP according to RAMAN and XRD investigations.     

Effect of structural characteristics on impact breakage of agglomerates

The mechanical properties and evolved structure of agglomerates depend strongly on the manufacturing method. There is a great interest in finding a simple way of establishing a rank order in their processing behaviour, e.g., the ease with which they could be dispersed in fluids. For this reason, the breakage propensity of two types of detergent agglomerates produced by different processes but with the same formulation has been evaluated under different conditions by impact testing with a view to diagnose differences in mechanical properties and structure arising from their manufacturing method. The effects of impact velocity, agglomerate size, impact angle, fatigue, humidity, and temperature have been analysed. Both samples show extensive plastic deformation due to the elongation and eventual rupture of the interparticle bridges, especially for the humidified samples. Reducing the temperature increases the extent of breakage substantially. The impact test results of samples kept at −20 °C show brittle failure mode, whilst those of oblique impacts at 45° and ambient conditions show a semi-brittle failure mode by shear deformation. Drying strengthens the agglomerates presumably due to the solidification of bridges. In contrast, humidifying the granules decreases their strength. A general comparison of the impact test results of both samples for different feed sizes shows that, due to the structural differences, the breakage trend of these two types of agglomerate varies with increasing agglomerate size.     

Powder Processing for the Fabrication of Si3N4 Ceramics: I, Influence of Spray-Dried Granule Strength on Pore Size Distribution in Green Compacts

The effect of spray-dried granule strength on the micro-structure of green compacts obtained by isostatic pressing was quantitatively analyzed. The fracture strength of single granules of Si₃N₄ powder made with ultrafine A1₂O₃ and Y₂O₃ powders was measured directly by diametral compression. It was found that fracture strength increased notably with the increasing relative density of the granule and the decreasing size of agglomerates in suspension before spray-drying. Even when green bodies were prepared at an isostatic pressure of 200 MPa, intergranular pores, which negatively affected densification of the sintered bodies, occurred between unfractured granules. The volume and size of these pores in the green compacts increased with the increasing fracture strength of the granules. In the case of closely packed granules, an isostatic pressure of 800 MPa was required to completely collapse the intergranular pores. A simple equation was derived to calculate the isostatic pressure necessary for complete collapse of intergranular pores in the green compacts, and it was determined that granule strength must be kept as low as possible to obtain uniform green compacts.     

Separation of CNF agglomerates from a ceramic suspension by spray drying technique

Aqueous silicon nitride based composite suspensions with the addition of 3.1 wt% of carbon nano-fibers (CNFs) were dried using two different drying techniques: spray drying and freeze drying. The paper deals with optimisation of parameters of the spray drying processwith the aim of maximising the yield and improve the quality of the granulate. Freeze drying was selected as a reference drying method, because no powder separation can occur in the course of the process. Prepared suspensions were spray dried at 4 different temperatures: 80, 110, 140 and 180 °C. After each run, two types of granules were obtained: from the separation flask and from the product vessel. Thermo-gravimetric analysis together with SEM examination show that spray drying results in separation of CNFs agglomerates. The granules from separation flask are always enriched by CNFs agglomerates whilst the granules from product vessel have reduced content of CNFs agglomerates. Sintering of spray-dried granules from the product vessel resulted in the composite with uniform microstructure, low amount of CNFs agglomerates and high relative density.     

Agglomeration of fine particles subjected to centripetal compaction

Agglomeration is a common phenomenon in many processes. The mechanical properties of agglomerates strongly depend on their structures. This paper presents a numerical study of the agglomeration of fine particles down to 1 μm in size based on the discrete element method. The agglomerates were formed with particles initially generated randomly in a spherical space and then packed under an assumed centripetal force. Agglomerate structure, packing density, coordination number and tensile strength were analysed with particular reference to the effect of particle size associated with the van der Waals attraction. The results showed that both the packing density and coordination number of the agglomerates decay exponentially to their limits as agglomerate size increases. The tensile strength of the agglomerates was calculated from the simulations and shown to decrease with the increase of particle size. The strength was also estimated from the Rumpf model supported by the empirical equations formulated based on the present simulation results. The good agreement between the results from the simulations and the estimation indicates that the equations are useful to facilitate engineering applications.     

Particle growth mechanisms in fluidised bed granulation—I: The effect of process variables

Two types of product granule have been identified in an experimental study of batch fluidised bed granulation; agglomerates which consist of two or more, and usually several, initial particles; and layered granules, which consist of single primary particles with dried feed material adhering to the surface. Increasing the excess fluidising gas velocity, in the range U-U_mf = 0.15-0.525 m s^?1, resulted in decreased particle growth rates and, depending upon the binder material, a change in product morphology from agglomerates to layered granules. Similar changes resulted from increasing the mean size of the starting material. Thus, a mechanism of particle growth is proposed in which the strength of inter-particle bridges and the extent of fluid drag and inertial forces on particles determine the equilibrium granule form and size. However, if the initial particles are porous this mechanism may break down since liquid may enter intra-particle pores and be unavailable for the initial formation of liquid bonds.