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Fine Powder (fine + powder)
Selected AbstractsPaste extrusion control and its influence on pore size properties of PTFE membranesADVANCES IN POLYMER TECHNOLOGY, Issue 3 2007Radium Huang Abstract Polytetrafluoroethylene (PTFE) is a remarkable membrane material. Owing to its high-melting point, PTFE fine powder cannot be processed using conventional melting processing methods. Instead, techniques such as paste extrusion, rolling, and sintering have to be employed. Each processing step has an important influence on the final pore size quality within the membrane. In this paper, a PID controller (proportional-integral-derivative controller) was used to improve the properties of PTFE paste during the extrusion process and the quality of the PTFE membrane. A range of lubricant content (18, 20, and 22 wt%) was used to monitor the pressure drop at different extrusion speeds (0.5, 1, and 2 mm/s) and reduction ratios (RR = 26.47, 47.06, 80.06). It was found that a higher lubricant content and a higher reduction ratio resulted in a lower pressure drop. It was also found that a higher stretching temperature tends to result in larger pore size and broader pore size distribution at the same stretching rate. At a monitored and controlled constant low-extrusion speed, the porosity of PTFE membrane was increased from 38% to 55% and the mean pore size was decreased from 0.22 to 0.15 ,m because of less migration and more uniform distribution of lubricant during extrusion. Properties and the associated property uniformity of the PTFE extrudate affect the subsequent membrane-forming process and the final pore size and size distribution significantly. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:163,172, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20099 [source] Growth and Mechanism of Network-Like Branched Si3N4 NanostructuresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Zhijian Peng The high-yield synthesis of network-like branched silicon nitride (Si3N4) nanostructures by a simple template catalyst-assisted pyrolysis of a polymer precursor, perhydropolysilazane, was reported. The templates were silicon wafers deposited with Fe films of 5,20 nm in thickness. The processes simply involved thermal cross-linking of the preceramic polymer, crushing of the solidified polymer chunks into fine powder, and thermal pyrolysis of the powder under flowing high-purity nitrogen. The collected white network-like branched nanostructures are ,-Si3N4 of hexagonal phase, and their microstructures, in which the diameters of each linear part of the network-like nanostructure varied in a very wide range from tens of nanometers to hundreds of nanometers, strongly depend on the applied growth parameters, where the key factors are the heating rate and catalyst thickness for change in the diameters. It was proposed that the Si3N4 nanonetworks were formed through "metal-absorption on the surface of nanostructures" model by vapor,liquid,solid mechanism. The reaction mechanism of Si3N4 nanonetworks was also discussed. [source] Sintering of AlN Using CaO-Al2O3 as a Sintering Additive: Chemistry and Microstructural DevelopmentJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2002Eirik Hagen The densification of aluminum nitride using Ca12Al14O33 as a sintering aid has been studied with emphasis on the effect of using coarse or fine powder, the amount of sintering aid, the sintering temperature, and embedding. Both crystalline and amorphous grain boundary phases were observed. Significant weight losses were observed for coarse-grained samples, and if suitable embedding was not used. Porous and coarse-grained ceramics with high contiguity and minor amounts of secondary phases were obtained by enhanced evaporation while dense ceramics were obtained limiting the evaporation. High weight losses in the graphite environment resulted in formation of a dense AlN surface layer. [source] Determination of Intrinsic Minimum Bubbling Velocity in Fine Powder Aerations Based on Experimentally Measured Elastic Deformation CoefficientsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2005Wiratni Wiratni Abstract It is found that the minimum bubbling velocity of aerated fine powder can be defined by experimentally measuring incremental elastic deformation coefficient (Y). The value of Y starts changing at a certain degree of powder expansion. The sudden change of Y indicates the initiation of the fractures in the homogeneously aerated expanded (HAE) emulsion phase. The intrinsic minimum gas velocity (Umb*), which causes this fracture initiation, can be significantly smaller than the so-called minimum bubbling velocity (Umb) defined by the classical concepts. On a trouvé que la vitesse d'ébullition minimum de fine poudre aérée peut se définir en mesurant expérimentalement le coefficient de déformation élastique incrémentiel (Y). La valeur de Y commence à changer à un certain degré d'expansion de la poudre. Le changement soudain de Y indique le départ de fractures dans la phase d'émulsion expansée et aérée de manière homogène (HAE). La vitesse de gaz minimum intrinsèque (Umb*), qui cause ce début de fractures, peut être significativement plus petite que la prétendue vitesse d'ébullition minimum (Umb) définie par les concepts traditionnels. [source] Optimization of Cr8O21 targets for Pulsed Laser DepositionCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2005L. Tortet Abstract This work describes the preparation of Cr8O21 pellets with optimised mass density to be used as targets for Pulsed Laser Deposition (PLD) of chromium dioxide thin films. Cr8O21 is synthesised by thermal decomposition of CrO3, at 270 °C. An attempt to reduce the grain size of the Cr8O21 powder to the nanometer scale has been made in order to increase the density of the pressed and sintered pellets serving as targets. The morphology of those starting fine powders as well as of targets (before and after laser ablation) and the corresponding thin films were characterized and studied using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Raman spectroscopy. The composition of the films is a mixture of crystallised Cr2O3 and amorphous CrO2. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pan-milling mixing , a novel approach to forming polymer blends and controlling their morphologyPOLYMER INTERNATIONAL, Issue 9 2001Zhe Chen Abstract A novel technique (pan-milling mixing) was developed to control the morphology and thus enhance the mechanical properties of polypropylene/polyamide 6 (PP/PA6) systems. Through pan-milling at ambient temperature, PP/PA6 pellets of particle size 2,4,mm can be effectively pulverized to well-mixed micrometre fine powders in the solid state. During pan-milling of mixtures of PP and PA6, the polymer molecules undergo chain scission and form copolymers that compatibilize the two polymers in situ. By press moulding the finely mixed PP/PA6 powder obtained at a temperature between the melting points of PA6 and PP (for example 200,°C), a blend can be obtained in which the PA6 powder, retained throughout the process in the solid state, is well dispersed in the PP matrix. The mechanical properties of the system are much better than that of PP/PA6 blends prepared by common twin screw extrusion mixing and injection moulding. Tensile strengths of the fine PA6 particle filled PP/PA6 (70/30) blend is 29.3,MPa, which is 6.1,MPa higher than that of a conventionally prepared PP/PA6 blend. The Izod notched impact strength of a fine PA6 particle-filled PP/PA6 (70/30) blend is 6.34,kJ,m,2, which is 1.72,kJ,m,2 higher than that of a conventionally prepared PP/PA6 blend. Morphological analysis shows that the domain size of PA6 in the system is much smaller than that of the PP/PA6 blend, and can be controlled by the processing conditions such as temperature. © 2001 Society of Chemical Industry [source] Synthesis of thermo-responsive microgels in supercritical carbon dioxide using ethylene glycol dimethacrylate as a cross-linkerPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2010Yaodong Hu Abstract Herein, we report the preparation of thermo-responsive polymers in a green medium. The white, dry, fine powders were obtained directly from the cross-linking polymerization of N -isopropylacrylamide (NIPA) in supercritical carbon dioxide (scCO2) at pressures ranging from 10 to 28,MPa utilizing ethylene glycol dimethacrylate (EGDMA) as a cross-linker. The effects of reaction pressure, cross-linker ratio, initiator concentration, and reaction time were investigated. In the presence of this cross-linker (26.4% w/w), much smaller poly(N -isopropylacrylamide) (PNIPA) microgels (<0.2,µm diameter) were formed, and it was shown that the particle size and the morphology of the polymer were strongly dependent on the cross-linker ratio in scCO2. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||