Sol-gel processing of tellurite powder

Tellurium ethoxide is highly sensitive to moisture in air and water. The hydrolysis and condensation of tellurium ethoxide exposed under different levers of water and moisture are investigated in this work and the hydrolysis products were characterised by infrared spectrometry and X-ray diffraction. The decomposition process of the product of tellurium ethoxide hydrolysed in air was analysed by differential scanning calorimetry and thermogravimetry. This work also studied the influence of sodium component on the phase transformation of the hydrolysis product in the decomposition process and on the morphology of the heat-treated hydrolysis products.     

Ceramic material processing by electrical discharge in electrolyte

New ceramic materials receive a great deal of attention as machine components, but they are hard to work. So a hybrid processing which combines electrical discharge processing with grinding is proposed. In this study, in order to examine the possibility of this hybrid processing, the electrical discharge processing on four kinds of ceramics was carried out with a needle electrode. The ceramic materials were alumina and three kinds of silicon nitride series to which are added alumina (ASN), magnesia (MSN), yttria and alumina (YASN). The results obtained showed that a pit can be formed on any ceramic and the pit depth apparently varies with the ceramic material. The removal rates of ASN, alumina, YASN and MSN become low in turn, and are independent of their mechanical properties. In the case of the silicon nitride series, the removal rates depended on their sintering additives, and the higher the applied voltage, the greater was the volume removed. High removal rate and low electrode loss are obtained when the needle electrode is negative. The ceramic materials are mainly removed by etching the grain boundary in a high-temperature electrolyte during the discharging process.     

Quality assurance in pharmaceutical powder processing: Current developments

Abstract

Pharmacopoeia1 requirements relating to standardization of the physical performance of oral dosage forms containing powders are usually limited to tests on the final product.

Such tests are aimed at ensuring that all tablets or capsules have the correct, nominal, drug content and that the drug is released into solution within a specified time. Whilst dissolution or disintegration test to assess drug release can only be carried out on a finished dosage form, content uniformity tests currently carried out on tablets or capsules alone could also be usefully carried out earlier on component powders at different stages during processing. The aim of developing a quality assurance procedure for quantifying the homogeneity of powders prior to tablet compaction or encapsulation would be to pin-point more precisely the part of a process where content uniformity problems arise. Secondly, a good quality assurance procedure would provide full mechanistic information about the behaviour of a given powder system, so that appropriate remedies could be applied.

Eleven different methods of testing homogeneity of powder mixes have been cited in pharmaceutically oriented literature and these will be reviewed in terms of their usefulness as routine quality assurance procedures for drug content uniformity. Of these 11 methods, 2 test methods were considered to be especially useful: one based on a flow test and the other on vibration analysis. This techniques has been validated using a complete vibration analysis and testing rig under conditions encountered during routine powder processing.

It would be desirable to see standard powder mixes tested on apparatus of the same design in different laboratories as a means of assessing the reproducibility of the proposed quality assurance method when used by different personnel.     

Quality assurance in pharmaceutical powder processing: Current developments

Pharmacopoeia1 requirements relating to standardization of the physical performance of oral dosage forms containing powders are usually limited to tests on the final product.

Such tests are aimed at ensuring that all tablets or capsules have the correct, nominal, drug content and that the drug is released into solution within a specified time. Whilst dissolution or disintegration test to assess drug release can only be carried out on a finished dosage form, content uniformity tests currently carried out on tablets or capsules alone could also be usefully carried out earlier on component powders at different stages during processing. The aim of developing a quality assurance procedure for quantifying the homogeneity of powders prior to tablet compaction or encapsulation would be to pin-point more precisely the part of a process where content uniformity problems arise. Secondly, a good quality assurance procedure would provide full mechanistic information about the behaviour of a given powder system, so that appropriate remedies could be applied.

Eleven different methods of testing homogeneity of powder mixes have been cited in pharmaceutically oriented literature and these will be reviewed in terms of their usefulness as routine quality assurance procedures for drug content uniformity. Of these 11 methods, 2 test methods were considered to be especially useful: one based on a flow test and the other on vibration analysis. This techniques has been validated using a complete vibration analysis and testing rig under conditions encountered during routine powder processing.

It would be desirable to see standard powder mixes tested on apparatus of the same design in different laboratories as a means of assessing the reproducibility of the proposed quality assurance method when used by different personnel.     

Ceramic composite components with gradient porosity by powder injection moulding

Various components used in the industries may benefit from having layered structures with gradient porosity in each layer. In this paper, bi-layer composite components with gradient porosity made by Powder Injection Moulding (PIM) have been investigated. The ceramic spinel materials of AR7845 having coarse particle size and AR7820 having fine particle size were used. It shows that AR7820 and AR7845 powders have different sintering behaviour with the fine powder having faster shrinkage as compared to coarse powder. Curling or bending is found in the bi-layer rectangular composite component fabricated from these two powders. This is due to induced stress caused mainly by strain rate mismatch of the two materials during sintering. The degree of curling is also related to thickness ratio of two materials in each layer. Composite components can be designed into cylindrical shape so as to avoid curling as observed in rectangular composite components. No interfacial debonding and part cracking are observed in both rectangular and cylindrical composite components. The microstructure shows that continuously straight joining lines along the interfaces are formed in these composite components.     

Preparation of metal alloy powder by semi-solid processing

A laboratory study was carried out, using Pb–15 wt.% Sn alloy on self-made apparatus, to determine the solidification behavior of the semi-solid slurry with the solid fraction beyond 0.6. It is found that the solid–liquid separation is obvious in the samples with the solid fraction beyond 0.6. According to this character of semi-solid processing, a kind of single-crystal powder coated with Pb–Sn eutectic was made during continuous stirring and cooling processes. The analysis and discussion indicated that this approach can reduce the content of oxide and impurity in the powder.     

Sintering of pre-mullite powder obtained by chemical processing

The crystallization and sintering behaviour of a premullite powder which had been synthesized from aluminium sulphate [Al₂(SO₄)₃· 16H₂O] and colloidal silicon dioxide have been studied. Calcination of the mixture at 860 °C for 12 h gives a very active powder (surface area – 188 M²g^–1) in the form of spine] and mullite forms via this spinel phase. The non-mullitized powder can be reactively sintered at 1500–1550°C to 97%–99% density in 3–5 h with a very fine microstructure.     

Thermomechanical processing of a nickel-base superalloy powder compact

Some means by which the grain size and flow strength of nickel-base superalloy powder .compacts can be controlled during processing have been examined. The compacts were prepared by hot isostatic pressing and their flow behaviour studied by constant true strain rate compression testing under conditions simulating isothermal forging. It was found that the selection of a finer starting powder results in slight lowering of flow strength at forging temperatures. Prior cold working of the compact by hydrostatic extrusion also leads to small reductions in strength at these temperatures. Both the . grain size and flow strength may change substantially during plastic deformation at forging temperatures. This depends on the conditions of strain rate and temperature. Under all the testing conditions examined this transient flow behaviour is followed by a stesdy state regime of flow during which neither the grain size nor the flow strength continue to change. These observations and their practical implications are discussed.     

Strengthening bioceramic through an approach of powder processing

Bioactive ceramics, such as calcium phosphate and calcium sulfate, have gained attention with the increase of aged population. Contrast to bio-inert ceramics, such as alumina and zirconia, the strength of bioactive ceramics is much lower. The strength of calcium sulfate (CaSO₄) is the lowest among all. In the present study, two approaches, involving the refinement of microstructure and the addition of nano-particles, are combined to enhance the strength. Various powder-processing treatments are adopted to facilitate these approaches. A pre-grinding treatment is applied first to reduce the matrix CaSO₄ grain size. The nano-silica (SiO₂) particles are then fixed onto the CaSO₄ particles through an attrition milling process. The strength of CaSO₄ is enhanced by 60% by adding only 1 mass% nano-SiO₂ particles. The strength of the SiO₂-CaSO₄ composites follows the Orowan-Petch relationship, indicating that their strength is dominated by the flaws. The addition of nano-particles refines the matrix grain size, consequently, the flaw size.     

Mo-8wt%Cu纳米复合粉末的烧结与加工

用机械合金化法制取Mo-8%Cu(质量分数)纳米复合粉末,采用液相烧结和致密化后处理工艺制备了Mo-8%Cu(质量分数)合金。通过扫描电镜对Mo-Cu液相烧结和变形加工后合金显微组织进行了分析,研究了各种工艺参数对Mo-Cu合金致密性、拉伸强度、延伸率和晶粒尺寸的影响。结果表明,高能球磨的Mo-8%Cu(质量分数)纳米复合粉末坯体,经液相烧结后,其烧结态为Mo、Cu复合网状组织,可获得相对密度高达98.6%的Mo-Cu合金,再经静液挤压变形加工处理后,可获得全致密的Mo-8%Cu(质量分数)合金,在室温静液挤压40%形变率的条件下,拉伸强度可达到576MPa,延伸率5.8%。     

Feedstock powder processing research needs for additive manufacturing development

Additive manufacturing (AM) promises to redesign traditional manufacturing by enabling the ultimate in agility for rapid component design changes in commercial products and for fabricating complex integrated parts. By significantly increasing quality and yield of metallic alloy powders, the pace for design, development, and deployment of the most promising AM approaches can be greatly accelerated, resulting in rapid commercialization of these advanced manufacturing methods. By successful completion of a critical suite of processing research tasks that are intended to greatly enhance gas atomized powder quality and the precision and efficiency of powder production, researchers can help promote continued rapid growth of AM. Other powder-based or spray-based advanced manufacturing methods could also benefit from these research outcomes, promoting the next wave of sustainable manufacturing technologies for conventional and advanced materials.     

Fabrication of nature-inspired bulk laminar composites by a powder processing

Among many kinds of “nano-laminar” composites inspired by the brick and mortar structure of nacre in mollusk shells, a bulky, dense and ceramics–base composite has been a missing piece despite its importance. Here we report that such a composite with a submicron-order layered structure can be fabricated by a simple method, sintering aligned flake-like inorganic powder coated with ductile matrix material. The composites fabricated by this method had crack extension resistance by interface delamination, crack deflection, and ligament bridging by the ductile matrix. They showed non-brittle fracture behavior in a bending test despite a quite high flake volume fraction of over 80%, and had a work of fracture (WOF) of more than 300 J/m², several hundreds times as large as that of monolithic glass.     

Wet powder processing of sol-gel derived mesoporous silica-hydroxyapatite hybrid powders

This paper describes a method by which a porous silica coating layer can be obtained on different apatite particles through a simple sol-gel synthesis route. Sol-gel derived powders of hydroxyapatite (HAP) and beta tricalciumphosphate (beta-TCP) were coated with a mesoporous silica using C16TAB (hexadecyltrimethylammonium bromide) as a template in order to induce mesophase formation. Further calcination of the material removes the template from the mesophase and leaves a highly ordered hexagonal arranged mesoporous silica structure with a core of HAP/beta-TCP. The phase purity of the SiO2/apatite composites has been thoroughly investigated by the means of FT-IR, XRD, and solid state 31P MAS NMR. The phase purity of these materials is shown to be dependent on the solubility properties of the used apatites. The hybrid materials are suitable as a multifunctional biomaterial where osteoconductive properties can be combined with drug delivery.     

Sintering and crystallization of mullite powder prepared by sol-gel processing

Mullite powder with the stoichiometric composition (3Al₂O₃.2SiO₂) was synthesized by a sol-gel process, followed by hypercritical drying with CO₂. Within the limits of detection by X-ray diffraction, the powder was amorphous. Crystallization of the powder commenced at 1200 °C and was completed after 1 h at 1350 °C. In situ X-ray analysis showed no intermediate crystalline phases prior to the onset of mullite crystallization and the pattern of the fully crystallized powder was almost identical to that of stoichiometric mullite. The synthesized powder was compacted and sintered to nearly theoretical density below 1250 °C. The microstructure of the sintered sample consisted of nearly equiaxial grains with an average size of 0.2 m. The effect of heating rate (1–15 °C min^–1) on the sintering of the compacted powder was investigated. The sintering rate increased with increasing heating rate, and the maximum in the sintering curve shifted to higher temperatures. The sintering kinetics below 1150 °C can be described by available models for viscous sintering.     

An overview of the powder processing of soft magnetic composites

The technique of powder metallurgy is becoming increasingly common in the electrical manufacturing industry. It not only eliminates a number of steps in the manufacturing process, but uses less energy and gives near-net shape results which require few, or no finishing steps. The process is suitable for soft magnetic composites, and appropriate heat treatments can further tailor properties to a specific application. This article gives an overview of the technology and makes reference to some advances in the materials used and the processes involved     

The effect of processing parameters in the carbothermal synthesis of titanium diboride powder

The mechanism of the carbothermal method for synthesizing titanium diboride (TiB₂) powder has been studied. Mixtures of TiO₂, H₃BO₃ and carbon were heated in an argon atmosphere at 1000–1600 °C. The effect of the molar ratio and holding time on the phase evolution was studied by X-ray diffraction. The products were also characterized by scanning electron microscopy observations and particle size measurements.For a composition with a molar ratio of TiO₂:H₃BO₃:C = 1:2.4:5 heated for 1 h, the simultaneous presence of TiC and TiB₂ phases at 1100 °C and the transformation of TiO₂ to Ti₂O₃ at 1200 °C and higher confirms that TiB₂ synthesis is based on a TiC formation mechanism, in which TiC may be formed from a reaction between TiO₂ or Ti₂O₃ and carbon. Then TiC may react with liquid B₂O₃ and/or gaseous B₂O₂ to form the TiB₂ phase. The reaction is completed at 1500 °C. Also by increasing the molar ratio of boric acid to 3, the impurities decreased considerably and pressing of the material had an obvious effect on decreasing the impurities, due to an increase of the surface contact of particles, which causes an effective inhibition of boron escape from the reaction chamber. Under these experimental conditions, a relatively narrow size distribution of TiB₂ particles was produced. When the reaction time increased to 1.5–2 h, grain growth of particles occurred. Therefore, a wider distribution of particle size was obtained.     

Chemical processing and characterization of spinel-type thermistor powder in the Mn-Ni-Fe oxide system

The coprecipitated Mn-Ni-Fe oxalate was prepared from the mixed sulfate solution by optimum pH control. The chemical composition agreed well with that of the starting solution, and the thermal decomposition of the Mn-Ni-Fe oxalate in air below 600 °C led to the direct formation of cubic spinel phase with fine particle size. The sinterability of the calcined powder, the stability of cubic spinel phase and the influence of annealing temperature on electrical properties of the sintered bodies, were investigated.