Fully densified Al 2 O 3 ceramics with fine grain size were obtained by pulsed electric current sintering through a two-step heating profile (referred to as TS-PECS). Highly transparent Al 2 O 3 polycrystals with fine grain size (400 nm) were successfully fabricated by the TS-PECS process, namely, sintering at 1000uC for 1 h and followed at 1200uC for 20 min under uniaxial pressure of 100 MPa. Effects of the first step temperature and heating rate were discussed for bulk density, grain size and transparency. The temperature in the first step strongly affects densification and grain growth of Al 2 O 3 . On the other hand, heating rate, even of 100 K min 21 , in TS-PECS does not give significant influences on densification and grain growth of Al 2 O 3 . Inline transmittance at 640 nm in wavelength normalised to 1 mm in thickness is increased by decreasing heating rate even in TS-PECS.

Densification and sample temperature of alumina (Al2O3) powder during pulsed electric current sintering with different pulse power generators, inverter type and pulsed direct current type were investigated. The sample temperature for inverter generator was higher than that for pulsed direct current generator in same die temperature ranging form 800 to 1400oC. The relative density increased with increasing of the sample temperature.

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This paper reports the synthesis of a new printable ABS–MWCNT composite filament, for use in fused deposition modeling (FDM), using an extrusion technique. Acrylonitrile butadiene styrene (ABS) and multi-walled carbon nanotubes (MWCNTs) were the initial materials used for fabricating the filaments. The MWCNTs were dispersed in ABS resin, then extruded through a single-shaft extruder in filament form, with MWCNT contents of 0.5%, 1%, 1.5%, 2%, 3% or 4% by weight. After extrusion, the diameter of the filaments was about 1.75 mm, making them appropriate for FDM. The as-synthesized filaments were then used in FDM to print out samples, on which tensile tests and other analyses were carried out. The results demonstrate that the sample with 2% MWCNTs had the highest strength value, 44.57 MPa, comprising a 42% increase over that of the pure ABS sample. The morphology and dispersion of MWCNTs in the composite were observed by field emission scanning electron microscopy (FESEM), demonstrating the uniform distribution of MWCNTs in the ABS matrix. The thermal behavior results indicated no significant change in the ABS structure; however, the melt flow index of the filaments decreased with an increase in the MWCNT content.

Transparent MgAl₂O₄ceramic could be found in a wide range of applications for both military and civil sector due to its high melting point, good mechanical properties, small refractive index (1.71) and its ability to allow light in range from UV to mid-IR to pass through. In the present work, transparent MgAl₂O₄ was fabricated from metal nitrates via two steps. Firstly, the MgAl₂O₄ nanopowder was synthesized via solution combustion synthesis from the metal nitrates. Secondly, the powder was then consolidated by Pulsed Electric Current Sintering (PECS) technique to fabricate transparent ceramic. XRD patterns of the obtained powder showed the peaks of only MgAl₂O₄ phase. Besides, the atomic compositions of magnesium, aluminium and oxygen determined by EDX analysis were approximately corresponded to 1:2:4 of the molecular formula of MgAl₂O₄. After deagglomerating for 48 hours using soft ball-milling, the powder had the average particle of 27 nm. Transparent MgAl₂O₄ samples, which were sintered with two-step sintering mode of 1050^oC/60 minutes-1400^oC/20 minutes, permitted the transmission of visible and infrared light with the transmittance up to 80%, Vickers hardness of 14.2 GPa, and fracture toughness of 1.1 MPa.m^1/2. The results are a critical step toward fabrication of high-quality transparent ceramics from metal nitrates.

Aeration step, one of the major stages in the Becher process was carried out on reduced Hatinh (Vietnam) ilmenite in NH4Cl solution and the effect of several processing parameters were thoroughly investigated including the temperature, time, liquid/solid weight ratio (L/S), air flow rate and concentration of NH4Cl solution. The obtained results showed that longer rinsing time, higher liquid/solid ratio and air flow rate facilitated metallic iron rusting. The rusted iron amount increased when the temperature increased and reached the highest value at 70°C. Variation of NH4Cl concentration showed similar impact as that of temperature. The highest amount of rusted iron achieved at 0.5% NH4Cl. Chemical analysis and XRD results indicated that 98% of metallic iron in reduced ilmenite has been transformed to iron oxides at an aeration condition (70°C, 8 h, L/S=7/1, air flow rate = 4 l/min and 0.5% NH4Cl). Consequently, TiO2 content from approximately 60% in the reduced ilmenite increased up to approximately 80% in the aerated rutile.

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Micrometer-sized porosity, which cannot be recognized by typical density measurement method, was observed inside transparent polycrystalline alumina prepared by pulsed electric current sintering (PECS). The pores derive from hard agglomerates in starting powder and appear as black dots inside transparent bulk samples. In this study, porosity coming from the agglomeration was studied to degrade by chemical and mechanical treatments. Starting alumina powder was mixed with some surfactants as aqueous solutions. The slurries were ball-milled in 1 d, followed by drying and heat treatment to obtain treated alumina powders. Sintering of those alumina powders was carried out by two-step PECS technique. Transparent alumina specimens were evaluated by the density of black dots and the apparent transmittance. In summary, their treatments of alumina powder can break agglomerates and dramatically reduce the total density of black dots within transparent polycrystalline alumina. Consequently, the transmittance of polycrystalline alumina increased, from 68% for untreated sample to 7274% for treated samples.