Journal of Powder Technology The latest articles from Hindawi Publishing Corporation © 2016 , Hindawi Publishing Corporation . All rights reserved. New Materials for SLS: The Use of Antistatic and Flow Agents Thu, 02 Jun 2016 07:39:05 +0000 Selective laser sintering (SLS) is a process based on the principle of a locally confined energy input by a laser into a powder bed, producing highly complex parts without the use of moulds or any other tools. In order to ensure good results for the processing behaviour of a new material, the powder must perform well during the phase of feeding the material into the process chamber which majorly influences the quality of the spread of the powder into the part bed and thus the mechanical performance of the final parts. In the present study, the principle of modification of fine powders with flow agents is applied aiming to enable the use of powders for SLS which are otherwise unsuitable due to poor flowability. In addition, the influence of antistatic agent on the powder flow and processing behaviour is discussed. The additives are found to strongly improve the flow behaviour at already very small contents and thus allow for processing of the composite material. The development of determining factors shares insight into the mechanisms of dry particle coating and its implementation into a growing market of material development. Matthias Michael Lexow and Dietmar Drummer Copyright © 2016 Matthias Michael Lexow and Dietmar Drummer. All rights reserved. Wall-to-Suspension Heat Transfer in a CFB Downcomer Tue, 08 Sep 2015 13:07:51 +0000 With the development of circulating fluidized beds (CFB) and dense upflow bubbling fluidized beds (UBFB) as chemical reactors, or in the capture and storage of solar or waste heat, the associated downcomer has been proposed as an additional heat transfer system. Whereas fundamental and applied research towards hydrodynamics has been carried out, few results have been reported on heat transfer in downcomers, even though it is an important element in their design and application. The wall-to-suspension heat transfer coefficient (HTC) was measured in the downcomer. The HTC increases linearly with the solids flux, till values of about 150 kg/m2 s. The increasing HTC with increasing solid circulation rate is reflected through a faster surface renewal by the downflow of the particle-gas suspension at the wall. The model predictions and experimental data are in very fair agreement, and the model expression can predict the influence of the dominant parameters of heat transfer geometry, solids circulation flow, and particle characteristics. Huili Zhang, Jan Degrève, Raf Dewil, and Jan Baeyens Copyright © 2015 Huili Zhang et al. All rights reserved. Investigation into the Flow Properties of Coarse Solid Fuels for Use in Industrial Feed Systems Wed, 27 May 2015 11:17:55 +0000 Material feeding and handling systems have been cited as one of the most common causes of process downtime where thermochemical conversion processes are concerned. New and emerging fuels come in a variety of forms, and if such fuels are to be deployed widely it is imperative that material feeding and handling systems are designed appropriately. This study proposes an approach for designing material feeding and handling systems for use with coarse solid fuels. The data obtained from this study indicates particle size to be one of the key issues affecting the flowability of bulk solids further to the uniformity in particle shape. Coarse bulk solid samples were shown to flow more freely than their milled and pulverised counterparts, generating higher degrees of flowability. The results from this study were also applied to a new feed system used for feeding solid fuels to high pressure processes named the Hydraulic Lock Hopper. In this study the Hydraulic Lock Hopper demonstrated the feeding of wood pellets, torrefied spruce pellets, and ground anthracite coal grains against a pressure of 25 barg in two modes of operation. Energy savings compared to conventional lock hopper systems were recorded in the region of 80%. James M. Craven, Jim Swithenbank, and Vida N. Sharifi Copyright © 2015 James M. Craven et al. All rights reserved. Measurement of Thermal Conductivity along the Radial Direction in a Vertical Cylindrical Packed Bed Tue, 03 Feb 2015 11:59:44 +0000 Heat transfer in packed beds and their thermal response have been of great interest for scientists and engineers for the last several years, since they play a crucial role in determining design and operation of reactors. Heat transfer of a packed bed is characterised through lumped parameter, namely, effective thermal conductivity. In the present studies, experiments were performed to investigate the thermal conductivity of a packed bed in radial direction. The packed bed was formed using iron ore particles. To determine the effective thermal conductivity a new transient methodology is proposed. The results obtained were compared with the models proposed by ZBS and Kunii and Smith. Swaren Bedarkar, Nurni Neelakantan Viswanathan, and Nidambur Bharatha Ballal Copyright © 2015 Swaren Bedarkar et al. All rights reserved. Recent Progress in Processing of Tungsten Heavy Alloys Mon, 29 Dec 2014 00:10:06 +0000 Tungsten heavy alloys (WHAs) belong to a group of two-phase composites, based on W-Ni-Cu and W-Ni-Fe alloys. Due to their combinations of high density, strength, and ductility, WHAs are used as radiation shields, vibration dampers, kinetic energy penetrators and heavy-duty electrical contacts. This paper presents recent progresses in processing, microstructure, and mechanical properties of WHAs. Various processing techniques for the fabrication of WHAs such as conventional powder metallurgy (PM), advent of powder injection molding (PIM), high-energy ball milling (MA), microwave sintering (MW), and spark-plasma sintering (SPS) are reviewed for alloys. This review reveals that key factors affecting the performance of WHAs are the microstructural factors such as tungsten and matrix composition, chemistry, shape, size and distributions of tungsten particles in matrix, and interface-bonding strength between the tungsten particle and matrix in addition to processing factors. SPS approach has a better performance than those of others, followed by extrusion process. Moreover, deformation behaviors of WHA penetrator and depleted uranium (DU) Ti alloy impacting at normal incidence both rigid and thick mild steel target are studied and modelled as elastic thermoviscoplastic. Height of the mushroomed region is smaller for and it forms sooner in each penetrator as compared to that for . Y. Şahin Copyright © 2014 Y. Şahin. All rights reserved. Wall-to-Bed Heat Transfer at Minimum Gas-Solid Fluidization Wed, 17 Sep 2014 10:52:09 +0000 The heat transfer from a fluidized bed to the cooling jacket of the vessel has been studied for various powders at minimum fluidization conditions, by both convection and conduction approaches. These heat transfer characteristics are important as the point of transition between packed and fluidized bed operations and are needed in designing heat transfer operations where bubble-flow is not permitted. The effective thermal conductivity of the emulsion moreover determines the contact resistance at the heating or cooling surface, as used in packet renewal models to predict the wall-to-bed heat transfer. In expressing the overall heat transfer phenomenon as a convective heat transfer coefficient, it was found that the results could be fitted by . Huili Zhang, Jan Degrève, Jan Baeyens, and Raf Dewil Copyright © 2014 Huili Zhang et al. All rights reserved. Synthesis, Characterization, and Crystal Structure Refinement of Lanthanum and Yttrium Substituted Polycrystalline 2M Type Zirconolite Phases: Ca1-xMxZrTi2O7 (M = Y, La and x = 0.2) Thu, 21 Aug 2014 08:27:32 +0000 Solid phases of zirconolite-2M with composition Ca0.8M0.2ZrTi2O7 (M = La, Y) have been synthesized through ceramic route and their structures refined to a satisfactory convergence using Rietveld analysis. Zirconolites crystallize in space group C2/c with Z = 8. The powder diffraction data of Ca0.8Y0.2ZrTi2O7 (CZTY) and Ca0.8La0.2ZrTi2O7 (CZTLa) have been subjected to General Structural Analysis System software to arrive at a satisfactory structure fit with Rp = 0.1128 and Rwp = 0.1805 for CZTY and Rp = 0.1178 and Rwp = 0.1874 for CZTLa, respectively. The unit cell parameters are a = 10.1708 (6) Ǻ, b = 6.2711 (4), and c = 11.2779 (6) Ǻ for CZTY and a = 11.2548 (6) Ǻ, b = 6.2601 (4), and c=11.2606 (7) Ǻ for CZTLa. Calculated interatomic distances and bond angles are in good agreement with their standard values. Particle size along prominent reflecting planes calculated by Scherrer’s formula ranges between 67 and 107 nm. The polyhedral (CaO8, ZrO7, and TiO6/TiO5) distortions and valence calculation based on bond strength analysis have been reported. The compositions of the zirconolites were determined using energy dispersive X-ray (EDAX) analysis. Cation site occupancies were determined by applied compositional constraints which were found consistent with the expected zirconolite-2M cation site occupancies. Ashish Bohre, Kalpana Avasthi, and O. P. Shrivastava Copyright © 2014 Ashish Bohre et al. All rights reserved. Workability Behaviour of Powder Metallurgy Aluminium Composites Tue, 01 Jul 2014 11:53:28 +0000 An efficient way to find the workability limit for powder metallurgy parts has been suggested. Compacts of Al-4%TiC, Al-4%WC, Al-4%Fe3C, and Al-4%Mo2C were produced to the relative density of 0.82 and 0.86 with three different geometries through primary operations of powder metallurgy routes. Each sintered compact was hot deformed to various strain levels till a visible crack appeared at the free surface. Oyane’s fracture principle was used to develop a theory to study powder metallurgy compacts. A least square technique was used to determine the constants in fracture criteria and these equations were finally used to find workability limit. It is found that the projected technique was well in agreement with the experimental values. S. Narayan and A. Rajeshkannan Copyright © 2014 S. Narayan and A. Rajeshkannan. All rights reserved. Cumulative Effect of Pressing and Drying on Stress Generation within a Green Ceramic Compact Tue, 08 Apr 2014 00:00:00 +0000 The internal stress field induced by uniaxial pressing and subsequent convective drying of a green ceramic powder was simulated by the finite element method. A density dependent elastoplastic constitutive law was used for the mechanical modeling of the compaction. A diffusive water transfer equation and a purely elastic behavior with imposed hydrostrain involving shrinkage were applied for the modeling of the drying process. The key material properties (hydrodiffusivity, hydrocontraction coefficient, Young’s modulus, Poisson’s ratio, and yield surface parameters) had been experimentally measured and introduced as functions of material density and water content. If residual stresses due to the compaction operation were taken into account, the maximum value of the tensile stress at the top external edge of the wheel and at the beginning of the drying process was two times higher than for a stress free green ceramic compact. Beyond the residual stress onset, the compaction operation induced density heterogeneities which had important consequences on the mechanical behavior of the compact. E. Vidal-Sallé, D. Falgon, R. Peczalski, and J-C. Boyer Copyright © 2014 E. Vidal-Sallé et al. All rights reserved. Choking Affects the Operation Diagram of a CFB Riser Tue, 04 Mar 2014 10:05:46 +0000 Experiments in 3 different CFB risers have confirmed that common riser operations can be hampered in a well-defined (U, G) range where choking occurs. Geldart A-type powders were investigated. Experimental results of the choking velocity were empirically correlated, being about 30% lower than predicted by the correlation of Bi and Fan, but largely exceeding other predictions. Introducing the findings into the operation diagram presented by Mahmoudi et al. adds a region where stable riser operation is impossible. The adapted diagram enables CFB designers to better delineate the operating characteristics. H. L. Zhang, J. Degrève, J. Baeyens, and R. Dewil Copyright © 2014 H. L. Zhang et al. All rights reserved. Self-Nanoemulsifying Powder of Isotretinoin: Preparation and Characterization Wed, 13 Nov 2013 17:19:22 +0000 In the present investigation an attempt was made to enhance the solubility and dissolution of poorly soluble drug, isotretinoin, by formulating self-nanoemulsifying drug delivery system (SNEDDS). Liquid SNEDDSs were prepared using Transcutol P as oil, Tween 80 as surfactant, and PEG 400 as cosurfactant. Pseudoternary phase diagrams were constructed to identify the efficient self-nanoemulsification region. The formulation with 40% oil (Transcutol P) and 60% surfactant: cosurfactant (Tween 80: PEG 400) ratio of 1 : 1 was optimized based on evaluation parameters for droplet size analysis, self-emulsification capacity, zeta potential, and in vitro drug release performance. The optimized system contains mean droplet size of 36.60 nm and zeta potential (ζ) −26.73 mV. The optimized formulation A1 was adsorbed onto Fujicalin to produce solid SNEDDS, which exhibited good flow properties and preserved the self-emulsification properties of liquid SNEDDS. The differential scanning calorimetry, FT-IR studies of solid SNEDDS revealed transformation of isotretinoin into molecularly dissolved state in the liquid SNEDDS. In vitro dissolution profiles showed that dissolution rate of ISN from solid SNEDDS was significantly greater as compared to pure drug. Hitesh Chavda, Jaimeen Patel, Gordhan Chavada, Shruti Dave, Ankini Patel, and Chhagan Patel Copyright © 2013 Hitesh Chavda et al. All rights reserved. The Effect of Hydrothermal Treatment on Silver Nanoparticles Stabilized by Chitosan and Its Possible Application to Produce Mesoporous Silver Powder Mon, 04 Nov 2013 08:29:07 +0000 Aggregation state of silver nanoparticles dispersed in an aqueous solution greatly varies with storage and treatment conditions. In this study, silver nanoparticles synthesized in chitosan solution by a chemical reduction method were hydrothermally treated at different temperatures. The variation in the aggregation state of silver nanoparticles in the solution was observed by UV-Vis spectroscopy and field emission transmission electron microscopy. Results indicated that a phase transition occurred while silver nanoparticles were hydrothermally treated for 5 h at 100 and ; however, they aggregated and completely precipitated at . Mesoporous silver powder obtained by hydrothermal treatment at was characterized by using X-ray diffraction technique, BET analyzer, and scanning electron spectroscope. Dang Viet Quang and Nguyen Hoai Chau Copyright © 2013 Dang Viet Quang and Nguyen Hoai Chau. All rights reserved. Sol-Gel Synthesis of Mullite Starting from Different Inorganic Precursors Mon, 28 Oct 2013 18:25:58 +0000 Using silicotetraetilortosilicate (TEOS) mixed with aluminum tri-sec-butoxide (TSBAI) or aluminum cloaures mullite ceramics were created by the sol-gel method. The quantities used of each substance were those that led to obtain stoichiometric mullite (3Al2O3·2SiO2). The experimental methodology used for obtaining mullite consisted in: sol-gel synthesis of precursor materials, isothermal treatment of those materials, and characterization of resulting materials. In order to determine the advance of reactions during mullite formation, isothermal treatments between 300°C and 1600°C were performed, keeping the samples at each temperature during 4 h. From XRD results, it may be said that precursor powders originally amorphous start to crystallize in Al2O3 and SiO2 at 1200°C, and the mullite formation starts at 1200°C, with being completed at 1600°C. The use of TSBAI favors the formation of mullite crystals at lower temperature. From SEM observations a microstructure that presents primary mullite with randomly oriented grains of secondary mullite with acicular shapes and sizes that range between 1.25 and 1.50 m long may be determined. Lucia Téllez Jurado, Rosa María Arévalo Hernández, and Enrique Rocha-Rangel Copyright © 2013 Lucia Téllez Jurado et al. All rights reserved. Investigations into Deformation Characteristics during Open-Die Forging of SiCp Reinforced Aluminium Metal Matrix Composites Thu, 10 Oct 2013 13:27:07 +0000 The deformation characteristics during open-die forging of silicon carbide particulate reinforced aluminium metal matrix composites (SiCp AMC) at cold conditions are investigated. The material was fabricated by liquid stir casting method in which preheated SiC particles were mixed with molten LM6 aluminium casting alloy and casted in the silicon mould. Finally, preforms obtained were machined in required dimensions. Two separate cases of deformation, that is, open-die forging of solid disc and solid rectangular preforms, were considered. Both upper bound theoretical analysis and experimental investigations were performed followed by finite element simulation using DEFORM, considering composite interfacial friction law, barreling of preform vertical sides, and inertia effects, that is, effect of die velocity on various deformation characteristics like effective stress, strain, strain rate, forging load, energy dissipations, and height reduction. Results have been presented graphically and critically investigated to evaluate the concurrence among theoretical, experimental, and finite element based computational findings. Deep Verma, P. Chandrasekhar, S. Singh, and S. Kar Copyright © 2013 Deep Verma et al. All rights reserved. New Technology for Increasing Through-Life Reliability of Ceramics Components Using Self-Crack-Healing Ability Thu, 13 Jun 2013 08:01:08 +0000 Structural ceramics are superior to metallic materials in terms of their high-temperature strengths and critical heat proof temperatures. However, compared to metallic materials, ceramics exhibit lower fracture toughness, so they are more sensitive to flaws such as pores and cracks. The shortness considerably decreases the component reliability. To overcome the shortness, in this study, special attention is paid to structural ceramics with self-crack-healing ability. There are several advantages for using a material with self-crack-healing ability. (1) After an efficient machine operation, the materials are able to self-heal the cracks introduced by the machining. (2) The materials are able to self-heal the cracks introduced during service and recover the strength completely at healing temperature. However, ways of organizing the available knowledge to increase the through-life reliability of ceramics components have not been extensively studied. The authors propose a new concept and the corresponding flowchart. This new concept is a promising technique for increasing the through-life reliability of ceramics components with excellent self-crack-healing ability. Kotoji Ando, Koji Takahashi, Wataru Nakao, Toshio Osada, and Kae Iwanaka Copyright © 2013 Kotoji Ando et al. All rights reserved. Improvement in Contact Strength of Si3N4/SiC Composite by Crack Healing Tue, 11 Jun 2013 11:14:56 +0000 Ceramics have been used as bearing and cutting tool components, which are subjected to contact loading during their operation. The presence of surface cracks on these components decreases their contact strength. Thus, the reliability of ceramic components can be increased by improving their contact strength through crack healing. In the present study, the effects of crack healing on the contact strength of a silicon carbide-(SiC-) reinforced silicon nitride (Si3N4) composite subjected to various machining processes were investigated. The contact strength of this composite was evaluated using a sphere indentation test in which acoustic emission was used. The results showed that the contact strength of the composite improved when it was subjected to crack healing in combination with rapping; this was true even when the composite had cracks due to a heavy machining process. Koji Takahashi, Keita Takahashi, and Kotoji Ando Copyright © 2013 Koji Takahashi et al. All rights reserved. Effect of Crack Healing of SiC according to Times of SiO2 Colloid Coating Sun, 02 Jun 2013 18:54:14 +0000 Crack healing behavior of SiC ceramics with large crack width has been studied as a function of coating and heat treatment. The SiO2 colloid coating was carried out on two types: hydrostatic pressure coating and roll coating. The crack healing was one hour at 1173 K in air. The crack part formed SiO2 oxides until the critical times by a hydrostatic pressure method. The crack does not anymore heal if it exceeds the critical times. The crack part and the base part have many O components and Si components regardless of the times of coating and heat treatment. The combined hydrostatic and rolling coating method did not have nearly an effect on crack-healing for large crack width over 1.4 m. The study for more effective healing of a large crack width must be carried out in the future. Ki Woo Nam Copyright © 2013 Ki Woo Nam. All rights reserved. Improvement of the Contact Strength of Al2O3/SiC by a Combination of Shot Peening and Crack-Healing Thu, 16 May 2013 10:08:52 +0000 Al2O3/SiC composite ceramics with high crack-healing ability were subjected to shot peening (SP) using zirconium oxide shots with several peening pressures and shot diameters. Specimens subjected to SP were heat-treated in air to heal the surface cracks induced by SP. The residual stress, the apparent fracture toughness, and the Weibull distribution of the contact strength were investigated, revealing that the combination of SP and crack-healing is effective for increasing the contact strength and decreasing the scatter of the contact strength of Al2O3/SiC. Tomoya Oki, Hiroki Yamamoto, Toshio Osada, and Koji Takahashi Copyright © 2013 Tomoya Oki et al. All rights reserved. The Solubility of Two Magnetite Powders in Oxalic Acid: Applicability of Empirical Modelling Thu, 03 Jan 2013 16:07:12 +0000 Phenomena-based models can be used in a predictive manner, but statistical modelling methods can also yield interesting findings and can serve as a tool for analysing the effects of different variables on the overall phenomenon. In addition, the generation of theoretical models can sometimes be limited due to the unideality of the studied system. Statistical modelling, in this case multiple-linear regression (MLR), was used to describe the effects of temperature and acid concentration on the dissolution of magnetite, Fe3O4 with oxalic acid. Whereas a linear model with an interaction term was sufficient in describing the dissolution of synthetic Fe3O4, a more complex full quadratic model had to be used to describe the dissolution of industrial Fe3O4 in the same conditions. Riina Salmimies, Mikko Huhtanen, Juha Kallas, and Antti Häkkinen Copyright © 2013 Riina Salmimies et al. All rights reserved. Mathematical Development and Comparison of a Hybrid PBM-DEM Description of a Continuous Powder Mixing Process Thu, 27 Dec 2012 17:47:58 +0000 This paper describes the development of a multidimensional population balance model (PBM) which can account for the dynamics of a continuous powder mixing/blending process. The PBM can incorporate the important design and process conditions and determine their effects on the various critical quality attributes (CQAs) accordingly. The important parameters considered in this study are blender dimensions and presence of noise in the inlet streams. The blender dynamics have been captured in terms of composition of the ingredients, (relative standard deviation) RSD, and (residence time distribution) RTD. PBM interacts with discrete element modeling (DEM) via one-way coupling which forms a basic framework for hybrid modeling. The results thus obtained have been compared against a full DEM simulation which is a more fundamental particle-level model that elucidates the dynamics of the mixing process. Results show good qualitative agreement which lends credence to the use of coupled PBM as an effective tool in control and optimization of mixing process due to its relatively fewer computational requirements compared to DEM. Maitraye Sen, Atul Dubey, Ravendra Singh, and Rohit Ramachandran Copyright © 2013 Maitraye Sen et al. All rights reserved. Correlation between Shear Wave Velocity and Porosity in Porous Solids and Rocks Tue, 20 Nov 2012 08:28:33 +0000 The shear wave velocity dependence on porosity was modelled using percolation theory model for the shear modulus porosity dependence. The obtained model is not a power law dependence (no simple scaling with porosity), but a more complex equation. Control parameters of this equation are shear wave velocity of bulk solid, percolation threshold of the material and the characteristic power law exponent for shear modulus porosity dependence. This model is suitable for all porous materials, mortars and porous rocks filled with liquid or gas. In the case of pores filled with gas the model can be further simplified: The term for the ratio of the gas density to the density of solid material can be omitted in the denominator (the ratio is usually in the range of (10−4, 10−3) for all solids). This simplified equation was then tested on the experimental data set for porous ZnO filled with air. Due to lack of reasonable data the scientists are encouraged to test the validity of proposed model using their experimental data. J. Kováčik and Š. Emmer Copyright © 2013 J. Kováčik and Š. Emmer. All rights reserved.