Inorganic membranes can be considered an alternative to organic membranes, due to their thermal, chemical and mechanical stability under harsh conditions. Ceramic membranes are used as support structures to increase permeability through composite inorganic membranes in separation processes. Tubular a-alumina membrane supports with smooth inner surfaces can be manufactured by means of the centrifugal casting technique.In this study, the effect of three different AKP powder sizes (0.25, 0.31 and 0.6lpm) and sintering temperatures (1000 to 1400°C) on the properties of the a-alumina supports were investigated in order to determine the optimum particle size and sintering temperature which would yield a porous support with an optimized permeability, while still retaining the smooth inner surface and adequate mechanical strength. A study concerning the possible replacement of the expensive AKP powder range with the less expensive Alcoa CT 3000 SG powder was also undertaken.The supports manufactured by centrifugal casting were characterized in terms of dimensions and by mercury porosimetry, water permeability and SEM. A novel strength testing apparatus was developed in order to determine the mechanical strength from the inside of the tubular structures.The effect of the polymer concentration, which is added to stabilize the colloidal suspension used in the centrifugal casting technique, as well as the influence of the sintering rate during polymer burn-off, was also investigated.A larger particle size resulted in an increased porosity, pore size and permeability, while a decrease in linear shrinkage and mechanical strength was observed. There was a decrease in porosity and permeability with increasing sintering temperature while the linear shrinkage and mechanical strength increased. The AKP-30 (0.31 pm) and AKP-1 S(O.61 pm) had a different particle packing than the AKP-50 (0.25pm) supports and consequently a decrease in pore size with increasing sintering temperature was observed for both the AKP-30 and AKP-15 supports, while the pore size remained constant for the AKP-50 supports. Increased polymer concentration Abstract resulted in an increase in permeability, pore size and porosity, while the mechanical strength of the support decreased. This was due to the evolution of "cracks" during sintering. The sintering rate had no profound influence on the properties of the membrane supports. The powder with the widest particle size distribution (AKP-15 powder) resulted in support structures with the widest pore size distribution. The aim of the study, i.e. the optimization of the supports, was attained when comparing the results in this study to our previous work as well as the available literature.Compared to our own previous study, the permeability increased from 28 to 41 ~.h.-'bar.-'m.-', the porosity from 36 to 37% and the pore radius from 99 to 167nm for the AKP-15 supports sintered at 1200°C.Structural cracking and warping during sintering of the powder compacts made from untreated Alcoa CT 3000 SG powder indicated tha...

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A chemical vapour deposition process using radio frequency induction heating operating at atmospheric pressure was developed for the deposition of ZrC coatings. The precursors utilised in this process were zirconium tetrachloride and methane as zirconium and carbon sources respectively, in an excess of hydrogen. Additionally, a stream of argon was used to, first, remove oxygen from the reactor and then to sweep the vapourised ZrCl 4 at 300 °C to the reaction chamber. The ZrC coatings were deposited on graphite substrates at substrate temperatures in the range of 1200 °C-1600 °C. The molar ratio of CH 4 /ZrCl 4 was varied from 6.04 to 24.44. Before the start of the deposition process, thermodynamic feasibility analysis for the growth of ZrC at atmospheric pressure was also carried out. Response surface methodology was applied to optimise the process parameters for the deposition of ZrC coatings. A central composite design was used to investigate the effects of temperature and molar ratio of CH 4 /ZrCl 4 on the growth rate, atomic ratio of C/Zr and crystallite size of ZrC 2 coatings. Quadratic statistical models for growth rate and crystallite size were established. The atomic ratio of C/Zr followed a linear trend. It was found that an increase in substrate temperature and CH 4 /ZrCl 4 ratio resulted in increased growth rate of ZrC coatings. The carbon content (and concomitantly the atomic ratio of C/Zr) in the deposited coatings increased with temperature and molar ratio of CH 4 /ZrCl 4. The substrate temperature of 1353.3°C and the CH 4 /ZrCl 4 molar ratio of 10.41 was determined as the optimal condition for growing near-stoichiometry ZrC coatings. The values were 1.03, 6.05 µm/h and 29.8 nm for C/Zr atomic percentage ratio, growth rate and average crystallite size respectively.

Abstract:This work was aimed at preparing polytetrafluoroethylene (PTFE) nanocomposites filled with graphene nanoplatelets and investigating how the graphene nanoplatelets and the preparation techniques influenced the physical properties. Graphene was incorporated up to 4 vol% of the total PTFE system by dry and solvent assisted blending. The powder compaction was evaluated using the Kawakita/Ludde model to describe the compressibility of the powder blends. The nanocomposite billets were prepared using cold compression moulding by applying preform pressures between 12.7 and 140 MPa and the preform billets were sintered at 380 °C using a specific sintering cycle. The changes in the physical dimensions, billet mass, density, and void content of the billets, pre and post sintering, were analysed with Experimental design software to evaluate the influence of the pre-compaction pressure and graphene loading. From the evaluation it was concluded that the ideal compaction pressure was at 12.7 MPa and the solvent assisted blending was superior to the mechanical blending method. Furthermore, the compression creep tests confirmed the ideal processing temperature and graphene loading range to improve the mechanical properties.2

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