Binder jetting of well-controlled powder agglomerates for breakage studies

Based on the similarity between the solidification process of the Additive Manufacturing (AM) binder jetting technique and wet granulation mechanisms, binder jetting is used to print powder granules with controlled geometry and strength. Powder granules with different strengths were achieved by changing the printing parameters, including the layer thickness and saturation level. The printed powder granules were then characterised for their structural properties such as their porosity and printing accuracy. Different parameter settings were found to have a significant influence on surface roughness. The strength of powder granules was improved by increasing the print saturation level, without compromising the printed geometry. A breakage study was carried out by compression tests of granules printed with different shapes and strengths. The relationship between print setting, structure and strength was established and discussed. This study demonstrates that AM powder granules with designed shapes and well-controlled strengths may act as ideal calibration particles for a range of industrial applications.     

Effect of agglomerates in ZrO2 powder compacts on microstructural development

Ultrafine zirconia powders were prepared by a coprecipitation and spray-drying method. Agglomerates may be fragmented or present in green bodies after compaction. The effect of agglomerates on sintering and microstructural development was studied and it was found that the agglomerate content in compacts was a major factor affecting the microstructure development and the sintered densities. The interaction between agglomerates themselves, and between agglomerates and the primary particle matrix is discussed. It is argued that the hard agglomerates in the powder from the water-washed coprecipitates are formed by oxobridging between non-bridging hydroxyl groups present in the zirconium hydroxide structures due to the effect of hydrogen bonding in the aqueous system. The substitution of organic -OR groups for the non-bridging hydroxyl groups removes this hydrogen-bonding effect between the zirconium hydroxide units and thus eliminates the cause of agglomeration.     

超细球形铜粉的制备

研究了一种新颖的球形铜粉制备方法,即先用葡萄糖还原法制备球形超细Cu2O粉末,然后用氢气还原Cu2O粉末制备球形铜粉.用葡萄糖还原Cu(Ⅱ)可以制备球形的Cu2O粒子.在240℃下用氢气还原球形Cu2O粉末,得到了分散性良好的球形铜粉,铜粉具有良好的导电性和稳定性.铜粉粒径大小和粒径分布取决于前驱体Cu2O粒子的大小和粒径分布.还原后的粉末粒径略有收缩,平均粒径为1.18μm,振实密度为2.1g/ml.     

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.     

Simulation of spherical powder sintering by surface diffusion

The surface diffusion-controlled sintering of monosized spheres is studied by a computer simulation process. The simulation is used to determine the variations in neck size and surface area as functions of both sintering time and powder packing density. Both morphology parameters are shown to be complex functions of the sintering time, contrary to numerous models. This work shows that the exponent method is not sufficient for identifying the dominant sintering mechanism.This work was supported by the United States Energy Research and Development Administration.     

Combustion synthesis and characterization of spherical PZT powder

A simple and effective method for the synthesis of PZT powder is reported. Fine spherical powders of PZT [Zr]/[Ti]=52/48 in mol ratio were prepared by solid-state combustion synthesis method based on the reaction of Pb₃O₄, ZrO₂, and TiO₂, activated by KClO₃+1.5C mixture. The powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and LPSA methods. The PZT powder consists of nearly homogenous and spherical grains with an average diameter of 1 μm. An approximate explanation of spherical shape formation is proposed.     

Rotary powder bed chemical vapour deposition of titanium nitride on spherical iron powder

Titanium nitride (TiN) was coated on to spherical iron powder by the rotary powder bed chemical vapour deposition technique using a reactant gas of the TiCl₄-N₂-H₂ system. The dispersibility of the coated powder was significantly improved by the adsorption of the reactant gas on to the rotating particles during raising the temperature. Polycrystalline TiN film, having a columnar structure of a few micrometres was coated on to the iron powder, typically at a deposition temperature of 1000° C and at a treatment time of 80 min. The TiN-coated iron powder showed an oxidation resistance up to about 650° C.     

Sinterability of magnesium silicon nitride powder with yttrium oxide addition coated using the homogeneous precipitation method

The sinterability of magnesium silicon nitride (MgSiN₂) powder with yttrium oxide (Y₂O₃) addition was examined using the hot-pressing technique (31 MPa and N₂ atmosphere) at 1550°C for 90 min; the MgSiN₂ powder had been coated with 0–4 mass% of Y₂O₃ addition by a (urea-based) homogeneous precipitation method. Relative densities of the hot-pressed MgSiN₂ compacts (ceramics) with and without Y₂O₃ addition were 99.6% apart for the MgSiN₂ceramic with 4 mass% Y₂O₃ addition (98.4%). The thermal conductivities of the MgSiN₂ ceramics with 0–1 mass% Y₂O₃ addition were in the range of 20–21 W · m^–1 · K^–1 whilst the Vickers hardness was 19.7 GPa for the pure MgSiN₂ ceramic and decreased slightly with Y₂O₃ addition. Average fracture toughness values were in the range of 1.2–1.6 MPa · m^1/2 with significant trend being noted with regards to the ceramic containing 0.5 mass% of Y₂O₃. It was concluded that the use of homogeneous precipitation processing resulted in significant advantages regarding the densification, homogeneous microstructure, and fracture toughness despite the amount of Y₂O₃ addition being as low as 0.5 mass%.     

On the micromechanics of composites containing spherical inclusions

Exact solutions for the stress distribution inside a spherical inclusion embedded in an other-wise homogeneous matrix are obtained. Such expressions provide a framework for discussing the load carrying capacity of rubber inclusions and the effect of interfacial bonding on the toughness of such filled systems. Parametric studies of the influence of constituent stiffness ratios on the resultant stress patterns in the inclusion and matrix have been conducted. Results indicate that chemical bonding between the particle and matrix is not necessary for soft inclusions, but is essential for rigid inclusions.     

Epoxy composites containing CFRP powder wastes

The increasing utilisation of carbon materials increases the waste generation. Therefore, it is necessary to analyse recycling alternatives. In this research, carbon powder wastes obtained from the cutting process of laminate composites have been incorporated into epoxy matrix phase in order to improve the mechanical characteristics. Physical and mechanical properties, hardness, abrasion, erosion and thermal behaviour have been analysed. Results show that carbon powder wastes incorporated to new epoxy matrix phases act basically as reinforcement. This allows for the recycling of the residues as well as improves some properties of the composites.     

Synthesis of nanosized spherical cobalt powder by ultrasonic spray pyrolysis

The ultrasonic spray pyrolysis (USP) method has been used to prepare nanosized powders of metallic, intermetallic compounds and ceramic materials. Spherical nanosized cobalt powders were obtained by USP of aqueous solutions of cobalt nitrate followed by thermal decomposition of generated aerosols in hydrogen atmosphere. Particle sizes of the produced cobalt powder can be controlled by the change of the concentration of an initial solution. Non-agglomerated spherical nanosized cobalt particles in the range of 158–1001 nm were obtained at 800 °C. A decrease of the concentration of cobalt nitrate decreases the mean particle diameter from 596 to 480 nm. The discrepancy between the experimentally and theoretically obtained values indicates that the partial coalescence of the droplets occur during the formation of aerosol.     

Synthesis of mullite nanostructured spherical powder by ultrasonic spray pyrolysis

In this paper the synthesis of nanostructured spherical particles of mullite powders by ultrasonic spray pyrolysis is presented. The mullite crystallization and the nanostructure development during heating were examined by infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscope analysis. Comparative analysis of experimentally determined and theoretically calculated particle size distribution, obtained on the basis of three-dimensional (3D) model of spherical/ellipsoidal waves generated by incident ultrasonic field, confirmed that the process of aerosol/powder particle synthesis can be regarded as deterministic process.     

On localization in ductile materials containing spherical voids

Macroscopic properties of a porous ductile medium are analysed on the basis of an axisymmetric numerical model and on the basis of a set of approximate constitutive equations for a voided material suggested by Gurson. Both models are used to analyse bifurcation into a localized mode. A number of predictions obtained by the two different approaches are in reasonable agreement; but it is found under several different loading conditions that the critical strain for localization is considerably overestimated by the approximate continuum model. A relatively simple modification of the constitutive equations for a voided medium results in considerably improved predictions.

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Résumé On analyse les propriétés macroscopiques d'un milieu poreux ductile sur base d'un modèle numérique axysimétrique et d'une série d'équations constitutives représentant avec une approximation suffisante un matériau comportant des vides, ainsi que le suggère Gurson. Ces deux modèles sont utilisés pour analyser la biffurcation dans un model local. Les deux méthodes, qui sont différentes, permettent d'établir plusieurs prédictions qui sont en accord raisonnable. On trouve néanmoins que sous des conditions de charge différentes la déformation critique conduisant à localisation est considérablement surestimée par le modèle d'approximation du continuum. Une modification relativement simple des équations constitutives dans le cas d'un milieu comportant des vides entraîne des prédictions considérablement améliorées.

     

Synthesis of spherical Al2O3 and AlN powder from C@Al2O3 composite powder

A novel approach has been taken to produce (1) spherical Al₂O₃ particles by decarbonisation and (2) spherical AlN particles by nitridation and subsequent decarbonisation of C@Al₂O₃ composite particles. C@Al₂O₃ composite particles have been prepared by heterogeneous nucleation and crystallisation of Al(NO₃)₃ on surfactant encapsulated carbon nano particles followed by evaporative decomposition of the nitrate. Overpressure (0.4 MPa) of nitrogen and a temperature range (1723–1873 K) have been used for nitridation. Whiskers as well as spherical particles of AlN have been observed in the final product. The final product has been characterised by X-Ray Diffraction, Scanning Electron Microscope and Carbon–Hydrogen–Nitrogen content analysis by Elemental Analyser and the mechanism of the nitridation reaction has been analysed. The average size of the spherical AlN particles consisting of crystallites in nano-dimensions (30–50 nm) could be varied from 100 nm to 8 μm by changing the composition of the sol.     

氧化锆空心球形粉末的粒度分布对流动性的影响

采用喷雾造粒和高温球化工艺制备空心球形氧化锆(YSZ-1型)喷涂粉末.研究了各种粒度区间的粉末流动性,将各种粒度区间的粉末进行适当配比,找出了粒度分布在产品标准规定的范围内流动性较好的配比方案,并进一步研究了超细粉末(粒径＜5μm)含量对粉末流动性的影响.     

Sinterability of various high-purity magnesium oxide powders

The sinterability of high-purity MgO powders with different production histories was investigated to make clear the relationship between the powder characterization, the densification processes, and the changes in microstructure both with increasing temperature at a rate of 10° C min^–1 and at a fixed temperature of 1450° C for 5 h. The densification behaviour and the changes in microstructure of these compressed bodies were affected chiefly by their original surface activity and degree of agglomeration, depending on the production histories: (i) the ultra-fine and well-dispersed powder prepared by the vapour-phase oxidation process showed that densification proceeded with an appreciable grain growth with few closed pores remaining; (ii) powder derived from the sea-water magnesia process showed that the densification behaviour was affected by the species of magnesium salt, i.e. basic magnesium carbonate or magnesium hydroxide, used as a precursor; however, whichever magnesium salt was used, its sintered compact showed similar closed porosities and grain-size distributions; (iii) powder derived from the spark-discharge process contained skeletons of the original Mg(OH)₂ particles; however, the densification proceeded gradually with slow grain growth, reflecting the fact that the powder has a moderate surface area (36 m² g^–1). The sintered compact from (iii) had a small closed porosity and the smallest grain-size distribution among the compacts used in this investigation.     

单分散球形MoS2超细粉体材料的制备

采用液相沉淀-高温氢还原两步合成新方法制备单分散球形MoS2超细粉体材料,利用透射能谱、X射线衍射仪(XRD)、冷场扫描电子显微镜(SEM)和马尔文激光粒度仪等研究了反应条件对产物化学组成、晶型的影响以及酸浓度、熟化时间和反应温度对前驱体MoS3平均粒径的影响.研究结果表明:反应条件对 前驱体MoS3的晶型没有影响;M...