Pentaerythritol crystallization – Influence of the process conditions on the granulometric properties of crystals

The quality of crystals depends on many factors that determine their granulometric properties. In order to obtain crystals of desired size distribution, proper selection of the operating conditions is of a great importance. Commonly, the unseeded cooling crystallization is controlled by selecting the appropriate cooling profile. The crystallization process can also be controlled by adding a certain number of seed crystals of a uniform size in the crystallizer at the saturation temperature. This paper investigates the influence of the process conditions (mixing intensity, cooling profile, batch time, saturation temperature and seeding) on the granulometric properties of pentaerythritol obtained by batch cooling crystallization. All investigated process conditions influence the crystal size distribution (seeded and unseeded experiments). On the other hand, the shape of crystals was the same for all experimental conditions. Optimal cooling profile, lower retention time, higher mixing rate, and smaller initial seed surface area improves the final crystal size distribution.     

Low-field magnetoresistance in La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> manganite compounds prepared by the spray drying technique

Calcium-substituted lanthanum manganite compounds were synthesized by the spray drying technique. This method—whose main advantages are versatility, high reproducibility and scalability—yields small grain materials of high homogeneity and displaying low-field magnetoresistance effects. We report about the physical and chemical characterizations of these samples in order to investigate the potential interest of spray drying for the production of materials for low-field magnetoresistance applications. We have studied the dependence of the low-field magnetoresistance on the temperature and duration of the thermal treatment applied to the pelletized powders. The issue of the shape anisotropy (demagnetisation effects) influence on the magnetoresistance properties has also been dealt with.     

Properties of copper-detonation nanodiamond composites obtained by spray drying

Nanostructural copper-detonation nanodiamond (DND) composites have been obtained by the method of spray drying. The technological process consists in spraying and drying a mixture of an aqueous copper salt solution and DND suspension, followed by thermal treatment in a reductive atmosphere. The DND content in copper powder was varied from 0.5 to 5.0 mass %. The average DND particle size in suspension was 4–6 nm. Copper-DND nanocomposite powders consist of nearly spherical particles with average size within 20–30 μm. Composition and structure of obtained materials have been studied.     

碳化硼超细微粉团聚及解决方法

对碳化硼超细微粉在干燥时的硬团聚现象进行了分析,并分别采用喷雾干燥和气流破碎两种方法对物料进行处理.喷雾干燥能避免硬团聚现象的发生,但其能耗要比厢式干燥器高,较细的颗粒需要回收.利用气流磨时干燥后的碳化硼超细粉进行解聚,有效地解决了颗粒在干燥过程中发生硬团聚的问题,物料收率高,分级轮的转速很低,几乎没有磨损.     

干燥温度对粉末状聚羧酸系减水剂性能的影响

以甲氧基聚乙二醇、马来酸酐、甲基丙烯磺酸钠等为原料,合成一种聚羧酸系高效减水剂,并与聚乙烯醇和超细SiO2粉体进行搅拌配制成喷雾干燥料液,在离心式喷雾干燥塔中对料液进行干燥,制备一种粉末状聚羧酸系减水剂,探讨干燥温度对粉末状聚羧酸系减水剂性能的影响。结果表明:在雾化盘转速为14 000 r/min,进料速率为80 g/min的条件下,随着干燥温度的升高,粉末状聚羧酸系减水剂的含水率下降,而滤渣率和休止角先下降后升高;干燥温度对粉末状聚羧酸结构没有很大的影响;最佳干燥温度为160～200℃。     

喷雾干燥可控制备生物玻璃微球及其体外生物活性研究

CaO-SiO₂-P₂O₅体系生物玻璃(Bioglass, BG)微球具有良好的生物活性和骨传导性, 在骨组织修复领域得到广泛研究与应用。传统熔融法制备BG粉体的能耗大、粉体形貌不可控、生物活性相对较低; 溶胶-凝胶法制备BG粉体则需大量溶剂、制备周期长、不易量产。为快速、规模化制备形貌、粒径、化学组成可控的BG微球, 本研究以水溶液为溶剂, 以正硅酸四乙酯、磷酸三乙酯、四水硝酸钙为原料, 采用喷雾干燥前驱体溶液方法制备BG微球, 探讨喷雾干燥过程中进气风量、前驱体溶液浓度和进料速率等工艺参数对BG微球粒径的影响; 前驱体溶液化学组成对BG微球的体外诱导磷灰石沉积能力的影响。结果表明, BG微球的粒径范围在40 μm以下可控, 且粒径随前驱体溶液浓度增大而增大, 随进气风量增大而减小, 进料速率则对微球粒径影响较小。不同化学组成的BG微球都具有良好的体外诱导磷灰石沉积能力, 而且随CaO含量的增加而提高。     

Preparation of porous particles by liquid–liquid interfacial crystallization

Liquid–liquid interfacial crystallization was proposed as a novel method of controlling crystal shape and size of precipitated solute particles. The crystallization was performed at interface forming two separate phases of aqueous solution and organic solvent in the present study, and progressed by increase of supersaturation caused by the slightly mutual diffusion at the liquid–liquid system. This crystallization process is possible to precipitate particles at room and constant temperature without cooling or heating sources. The liquid–liquid interfacial crystallization method was able to carry out in changing the shape of the interface.A spherical shape was made by droplets in the present liquid atomization process. Crystallization started when the droplets of the solution sprayed into the organic liquid. Our research involved producing glycine porous particles by atomizing glycine solution into 1-butanol and other organic solvent with 3-fluid nozzle. The collision between the solutions in compressed air produced the micro-size droplets of glycine solution. In using 1-butanol liquid, the glycine crystallized at the glycine solution/1-butanol interface. The spherical aggregated particles were obtained in this spray granulation process. In addition, the transformation occurred from unstable β-structure to metastable α-structure with changing crystallization condition, and it was found that α- and β-structure of glycine coexist in the obtained particles from observation by X-ray powder diffraction.     

Production of stable amorphous form by means of spray drying

Spray drying is a very useful method for manufacturing of amorphous solid materials. This is mainly due to the possibility of fast solvent evaporation that leads to a rapid transformation of solution to a solid state. Besides evaporation kinetics, there are various process parameters that influence physical and chemical characteristics of such obtained material. The possibility of obtaining a stable amorphous structure of the active pharmaceutical ingredient in a spray dryer was examined. A solution of the hydrochloride crystalline structure of the active pharmaceutical ingredient in a mixture of water and acetonitrile was dried at different temperatures and flowrates of nitrogen used for atomization, as well as the flowrates of the solution. The influence of the process conditions on the properties of the product was analyzed. The final dried products were characterized and identified with a variety of analytical and physical methods. The results showed that a stable amorphous structure of the high purity active pharmaceutical ingredient is obtained, and that the optimal conditions of the process are defined. The amorphous structure is stable at temperatures below 200°C when it is transformed into a new crystal structure. Conditions of high relative air humidity lead to partial transformation.     

氧化锆喷雾造粒粉末的制备

为了制备流动性、均匀性好的氧化锆粉末,以氧化钙部分稳定氧化锆为主要原料,采用离心式喷雾造粒干燥机,制备出松装密度为1.945 g/cm3,流动性好且呈球状的氧化锆颗粒。结果表明,均匀稳定性好的氧化锆料浆对制备优良性能的氧化锆颗粒至关重要;喷雾造粒的工艺条件对造粒粉末性能也有较大影响:当雾化器频率为100~110 Hz,进料泵转速为15~20 r/min时,造粒粉末流动性好,颗粒相对均匀,缺陷较少。     

溶胶-凝胶法制超细炭的拉曼光谱和XRD研究

采用不同的原料 ,利用溶胶 -凝胶超临界流体干燥法制得了超细炭原粉。将超细炭原粉在氩气气氛中于1 1 0 0℃和 2 60 0℃分别进行炭化和石墨化处理得到超细炭粉。利用 XRD和拉曼光谱对超细炭粉进行了表征。研究结果表明 ,原料性能对超细炭结构有较大的影响。     

Chemical preparation of spherical lithium tantalate powder

Spherical, micron size lithium tantalate powder was prepared by spray drying a lithium tantalate precursor using a mini spray dryer. Three chemical routes were used to prepare the lithium tantalate precursors, using lithium acetate and tantalum ethoxide as starting materials. The affects of processing parameters, such as solvent, drying temperature, and water, on the properties of the resulting powders were investigated. The as-dried powders were amorphous and became crystalline at a temperature as low as 450° C.     

超细球形空心磷铵灭火粉的制备与应用

采用气流和离心两种喷雾干燥方法制备超细球形空心磷酸二氢铵灭火粉,并添加甲基含氢硅油乳液、氟碳表面活性剂FK-510、羧甲基纤维素钠对粉体进行原位改性。结果表明:气流喷雾制备出的颗粒较细但不均匀,而离心喷雾制备出的颗粒均匀却较粗;表面活性剂甲基含氢硅油、FK-510的添加使粉体疏水性得到了很大提高;羧甲基纤维素钠的添加能使提高颗粒的球形度以及表面光滑度;喷雾干燥过程选择温度较低以及空气相对湿度较小的大气条件有利于制备高品质灭火粉。另外灭火实验结果表明:喷雾干燥制备的超细球形空心磷酸二氢铵灭火粉灭火效果明显优于某些市售灭火粉。     

Improvements in the production of Yb:YAG transparent ceramic materials: Spray drying optimisation

Spray drying parameters have been optimized for the preparation of granulated stoichiometric mixture of oxides. These oxides are used in the production of Yb:YAG laser grade ceramic materials by reactive sintering. The selected compositions were Yb_0.294Y_2.706Al₅O₁₂ and Yb_0.03Y_2.97Al₅O₁₂, i.e. YAG doped with 9.8 and 1.0 at% of Yb with respect to the overall Y + Yb amount. The influence of solid content, drying medium flux, temperature and aspiration rate of the spray drying process on the transparency of the sintered materials has been evaluated. Sintering was conducted under high vacuum and clean atmosphere in the temperature range of 1650-1735 °C and with a soaking time of 16 h. SEM analysis of the microstructure of granulated powders and sintered materials, as well as the transmittance measurement, were used as tools to guide the selection of the best spray drying parameters.     

Air-dictated bottom spray process: impact of fluid dynamics on granule growth and morphology

Background: Growing interest in the use of the less-explored bottom spray technique for fluidized bed granulation provided impetus for this study. Aim: The impact of fluid dynamics (air accelerator insert diameter; partition gap) and wetting (binder spray rate) on granule properties were investigated. Method: In this 3³ full factorial study, the results were fitted to a quadratic model using response surface methodology. The air velocity at the spray granulation zone for the investigated conditions was measured using a pitot tube. Results: Air accelerator insert diameter correlated to measured air velocity at the spray granulation zone and was found to not only dictate growth but also influence granule morphology. The partition gap was found to play important roles in regulating particle movement into the spray granulation zone and optimizing process yields, whereas binder spray rate significantly affected granule morphology but not granule size. Conclusions: Unlike conventional fluidized bed granulation, ease of modulation of fluid dynamics and insensitivity of the bottom spray process to wetting allow flexible control of granule size, shape, and flow. Its good drying ability also indicated potential use in granulating moisture-sensitive materials.     

Preparation of various titanium suboxide powders by reduction of TiO2 with silicon

Various titanium suboxide powders have been produced by solid-state reaction between TiO2 powders or TiO2 coated mica and silicon as reducing agent at temperatures below 1000°C in an inert atmosphere. The process leads to blue-grey powders with colour characteristics depending on the composition and the structure of the materials. Titanium suboxides like Ti2O3, -Ti3O5, Ti4O7, Ti7O13, Ti8O15 or Ti9O17 are formed during the reduction processes. Calcium chloride as an additive, type of atmosphere as well as temperature have an important influence on the composition and on the colour of the powders. The titanium suboxide powders were characterized by XRD.     

Psychrometry as a methodological tool for optimizing the spray drying process

Because psychrometry takes into account a great number of variables reflecting the quality of the drying air, it is an interesting tool to improve the control and the optimization of the spray drying process. In this article the authors study the evolution of the psychrometric variables according to the values taken by four inlet parameters (inlet air temperature, liquid flow rate, solid concentration of the spray dried liquid, and nature of the product). The results highlighted the existence of mathematical models making it possible to optimize the process, but also to underline the influence of the nature of the product on the drying mechanism.     

Synthesis of solid NMC622 particles by spray drying,post-annealing and lithiation

Layered lithium-nickel-manganese-cobalt oxide (NMC) cathode materials are widely used in Li-ion batteries that require high energy densities, such as those used in plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). Here we studied the synthesis of NMC622 particles by spray pyrolysis, which is a simple one-step process for production of spherical particles. However, synthesising NMC powder using spray pyrolysis has a tendency to produce hollow NMC particles. To gain insight into the mechanism behind the formation of the hollow particles, one dimensional numerical simulation of the physical and chemical phenomena taking place during spray drying were carried out. The effects of several process parameters, including drying air temperature, drying air mass flow rate, and liquid feed mass flow rate, on the evaporation and particle formation process were studied. The increased evaporation rate at higher temperatures was found to result in crust formation on the droplet surface during the particle formation, and thus, in lower solid volume fractions in the dried particles. However, by optimizing the process parameters production of solid NMC622 sulphate particles by spray drying was achieved. The produced NMC622 sulphate particles were then oxidised and lithiated in air at 850 °C via the conventional thermal treatment process. Four lithium precursors, LiOH, Li₂CO₃, Li₂SO₄ and LiNO_3, were tested for the lithiation of the oxidized NMC particles. The degree of lithiation and the crystalline phase of the powders were determined using ICP-OES and XRD, respectively.     

Synthesis of ceramic oxide powders by microwave plasma pyrolysis

Ceramic powders prepared pyrolytically exhibit homogeneity and, in most cases, small grain sizes. The energy efficiency of electrically heated systems performing the pyrolysis in a stream of carrier gas is poor. Similar considerations concerning energy demand are valid for spray drying of suspensions. This situation can be improved using a microwave plasma as a source for thermal energy. The process described in this paper works with any aqueous solution of salts used as starting material in ceramics. The process was demonstrated by the synthesis of alumina, zirconia, and zirconia-based ceramic powders; where an energy efficiency of more than 80% was found. For the powder synthesis, aqueous solutions of the nitrates were used as starting materials. Through proper selection of conditions for synthesis, it is possible to obtain nanocrystalline powders, as demonstrated by electron microscopy. Because of the extreme conditions associated with plasma during synthesis, it is possible to prepare nonequilibrium structures and solid solutions in systems in which nearly no equilibrium solubility exists.     

Innovative approach to produce submicron drug particles by vibrational atomization spray drying: influence of the type of solvent and surfactant

Spray drying is a technique used to produce solid particles from liquid solutions, emulsions or suspensions. Buchi Labortechnik developed the latest generation of spray dryers, Nano Spray Dryer B-90. This study aims to obtain, directly, submicron drug particles from an organic solution, employing this equipment and using dexamethasone as a model drug. In addition, we evaluated the influence of both the type of solvent and surfactant on the properties of the powders using a 3² full factorial analysis. The particles were obtained with high yields (above 60%), low water content (below 2%) and high drug content (above 80%). The surface tension and the viscosity were strongly influenced by the type of solvent. The highest powder yields were obtained for the highest surface tension and the lowest viscosity of the drug solutions. The use of ionic surfactants led to higher process yields. The laser diffraction technique revealed that the particles deagglomerate into small ones with submicrometric size, (around 1?µm) that was also observed by scanning electron microscopy. Interaction between the raw materials in the spray-dried powders was verified by calorimetric analysis. Thus, it was possible to obtain dexamethasone submicrometric particles by vibrational atomization from organic solution.     

The influence of precursor powders and processing parameters on the properties of SnO2-based gas sensors

Semiconducting tin oxide precursor powders were synthesized via three different chemical processing routes. The influence of powder processing conditions on the physical properties, e.g., particle size, surface area and phase composition of both uncalcined and calcined materials, was investigated. These powders were used to fabricate gas sensors using thick-film screen-printing technology. The effect of precursor powders, sintering conditions, sensor temperature and Pd catalyst on the carbon monoxide, methane, propane and ethanol gas sensing characteristics of the sensors were investigated. Sensors were also fabricated using tin oxide powders obtained from a commercial source and their gas sensing properties were also investigated. The data indicates that the powder processing methodology, sensor fabrication conditions and Pd catalyst can profoundly influence the physical characteristics as well as the gas sensing properties of the sensors.