Fault-Tolerant Single-Chip Vector Processor : architecture and performance analysis using Livermore loop benchmarks

Electrical Engineerin

Preparation and Characterization of Ni-Doped TiO2 Materials for Photocurrent and Photocatalytic Applications

Different amounts of Ni-doped TiO2 (Ni = 0.1 to 10%) powders and thin films were prepared by following a conventional coprecipitation and sol-gel dip coating techniques, respectively, at 400 to 800°C, and were thoroughly characterized by means of XRD, FT-IR, FT-Raman, DRS, UV-visible, BET surface area, zeta potential, flat band potential, and photocurrent measurement techniques. Photocatalytic abilities of Ni-doped TiO2 powders were evaluated by means of methylene blue (MB) degradation reaction under simulated solar light. Characterization results suggest that as a dopant, Ni stabilizes TiO2 in the form of anatase phase, reduces its bandgap energy, and adjusts its flat band potentials such that this material can be employed for photoelectrochemical (PEC) oxidation of water reaction. The photocatalytic activity and photocurrent ability of TiO2 have been enhanced by doping of Ni in TiO2. The kinetic studies revealed that the MB degradation reaction follows the Langmuir-Hinshelwood first-order reaction relationship

Preparation and characterization of Fe-doped TiO<SUB>2</SUB> powders for solar light response and photocatalytic applications

Different amounts of Fe-doped TiO2 (with 0.1 to 10 wt.% Fe) powders were prepared at temperatures in the range of 400 and 800 °C following a conventional co-precipitation technique and were thoroughly characterized by means of X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Fourier-transform Raman (FT-Raman), diffuse reflectance spectroscopy (DRS), BET surface area, zeta potential and flat band potential measurements. Photocatalytic ability of Fe-doped TiO2 powders was evaluated by means of methylene blue (MB) degradation experiments conducted under the irradiation of simulated solar light. Characterization results suggested that as a dopant Fe stabilized TiO2 in the form of anatase phase, reduced its band gap energy and adjusted its flat band potentials in such a way that these powders can be employed for photoelectrolysis of water into hydrogen and oxygen in photoelectrochemical (PEC) cells. The 0.1 wt.% Fe-doped TiO2 exhibited highest activity in the photocatalytic degradation of MB. The kinetic studies revealed that the MB degradation reaction follows the Langmuir-Hinshelwood first order reaction rate

Hydrolysis-induced aqueous gelcasting of &#946;-SiAlON-SiO<SUB>2</SUB> ceramic composites: the effect of AlN additive

Dense &#946;-SiAlON-SiO<SUB>2</SUB> (SiO<SUB>2</SUB>=20, 40, 50, 60, and 80 wt%) ceramic composites have been prepared from &#946;-Si<SUB>4</SUB>Al<SUB>2</SUB>O<SUB>2</SUB>N<SUB>6</SUB> and fused silica by sintering at 1500&#176;-1750&#176;C for 3-4 h. For comparison purposes, a powder mixture consisting 60 wt%&#946;-Si<SUB>4</SUB>Al<SUB>2</SUB>O<SUB>2</SUB>N<SUB>6</SUB> and 40 wt% fused silica has been consolidated following a new near-net shape technique based on hydrolysis-induced aqueous gelcasting (GCHAS) and sintered for 3 h at 1750&#176;C. In the GCHAS process, consolidation of suspensions containing 50 vol% solids was achieved by adding a polymerization initiator, a catalyst, and AlN powder equivalent to 1-5 wt% Al<SUB>2</SUB>O<SUB>3</SUB>. Thin-wall radomes consolidated by GCHAS (using AlN equivalent to 5 wt% Al<SUB>2</SUB>O<SUB>3</SUB> in the suspension) have exhibited green strengths &gt;20 MPa. The sintered materials were characterized for various properties including hardness, fracture toughness, mass loss, shrinkage, coefficient of thermal expansion, and dielectric constant. The Si<SUB>2</SUB>N<SUB>2</SUB>O formed from a powder mixture of 60 wt%&#946;-Si<SUB>4</SUB>Al<SUB>2</SUB>O<SUB>2</SUB>N<SUB>6</SUB> and 40 wt% fused silica at 1750&#176;C for 3 h exhibited a flexural strength of ~140 MPa, Young's modulus of 214 GPa, coefficient of thermal expansion of 3.5 &#215; 10<SUP>&#8722;6</SUP>&#176;C<SUP>&#8722;1</SUP>, hardness of 1390 kg/mm<SUP>2</SUP>, fracture toughness of 4.2 MPa&#183;m<SUP>1/2</SUP>, and a dielectric constant of 5.896 and tan &#948; of 0.002 at 17 GHz

Novel route to &#946;-SiAlON-SiO<SUB>2</SUB> ceramic composites

This paper reports a novel synthetic route to prepare dense &#946;-SiAlON-SiO<SUB>2</SUB> ceramic composites. The stoichiometric &#946;-Si<SUB>4</SUB>Al<SUB>2</SUB>O<SUB>2</SUB>N<SUB>6</SUB> extrudates prepared by the reaction sintering of &#945;-Si<SUB>3</SUB>N<SUB>4</SUB>, &#945;-Al<SUB>2</SUB>O<SUB>3</SUB>, AlN and Y<SUB>2</SUB>O<SUB>3</SUB> precursor mixture at 1675&#176;C for 4 h were fine ground and mixed with different amounts of commercial fused silica (20, 40, 50, 60 and 80 wt-%) powder, dry pressed and sintered for 3-4 h at 1500-1750&#176;C. These sintered materials were thoroughly characterised for bulk density, apparent porosity, water absorption capacity, phase composition, microstructure, hardness, dielectric constant and coefficient of thermal expansion. These characterisation results are presented and discussed in this paper

Formation and densification behavior of mullite aggregates from beach sand sillimanite

Dense mullite aggregates with 60% and 70% Al2O3 have been prepared from precursor mixtures consisting of beach sand sillimanite and a high-purity aluminum hydroxide following conventional single- and double-stage firing processes. The bulk density (BD), apparent porosity (AP), and water absorption (WA) capacity of sintered mullite aggregates were found to be strongly influenced by the premullitization step of this precursor mixture. Mullite aggregates formed in a double-stage firing process exhibited higher BD and mullite content and lower AP and WA capacity in comparison with those obtained by the single-stage firing process. The values of coefficient of thermal expansion of sintered mullite aggregates are close to those found in the literature reports for high-purity stoichiometric mullite

Aqueous slip casting and hydrolysis assisted solidification of MgAl<SUB>2</SUB>O<SUB>4</SUB> spinel ceramics

This paper reports on synthesis of MgAl<SUB>2</SUB>O<SUB>4</SUB> spinel (MAS) powders with six different chemical compositions and the consolidation of the synthesised MAS powders following an aqueous slip casting and hydrolysis assisted solidification (HAS) routes. The synthesised MAS powders were surface passivated against hydrolysis before being dispersed in distilled water to obtain suspensions with 41-45 vol.-% solid loading using suitable dispersing agents. In the case of the HAS process, the consolidation of suspensions was achieved in non-porous moulds under ambient conditions by the incorporation of AlN equivalent to 1-5 wt-%Al<SUB>2</SUB>O<SUB>3</SUB> into the suspension. The stoichiometric MAS powder consolidated by slip casting and dry pressing routes was sintered along with those consolidated by HAS route at 1550-1650&#176;C for 1 h. Various characterisation techniques were utilised to evaluate the effect of composition and consolidation technique on slurry characteristics and sintered properties of MAS ceramics

Effect of microarc oxidised layer thickness on plain fatigue and fretting fatigue behaviour of Al-Mg-Si alloy

The objective of this work was to investigate the performance of microarc oxide coatings of two different thicknesses (40 and 100 μm) on Al-Mg-Si alloy samples under plain fatigue and fretting fatigue loadings. Tensile residual stress present in the substrate of 40 μm thick coated samples induced early crack initiation in the substrate and so their plain fatigue lives were shorter than those of untreated specimens. Presence of more pores and tensile surface residual stress in 100 μm thick coated samples caused early crack initiation at the surface leading to their inferior plain fatigue lives compared with 40 μm thick coated samples. While the differences between the lives of coated and uncoated specimens were significant under plain fatigue loading, this was not the case under fretting fatigue loading. This may be attributed to relatively higher surface hardness of coated specimens. The performance of 40 μm thick coated samples was better than that of 100 μm thick coated specimens under both plain fatigue and fretting fatigue loadings

Effect of grinding on plain fatigue and fretting fatigue behaviour of detonation gun sprayed Cu-Ni-In coating on Al-Mg-Si alloy

Uniaxial plain fatigue and fretting fatigue tests were carried out on detonation gun sprayed Cu-Ni-In coating on Al-Mg-Si alloy samples. The samples in three conditions were considered: uncoated, as-coated and ground after coating. Ground coated specimens exhibited superior plain fatigue and fretting fatigue lives compared with uncoated and as-coated specimens. The life enhancement has been discussed in terms of surface finish and residual compressive stresses at the surface

Influence of detonation gun sprayed alumina coating on AA 6063 samples under cyclic loading with and without fretting

The influence of detonation gun sprayed alumina coating on Al-Mg-Si alloy (AA 6063) test samples subjected to cyclic loading with and without fretting was studied in the present work. Coated samples were grounded to have coatings of two different thickness values, 40 and 100 μm. Both 40- and 100-μm-thick coated specimens experienced almost the same but slightly higher friction force compared with uncoated samples. Under plain fatigue loading, 100 μm coated specimens exhibited inferior lives due to the presence of lower surface compressive residual stress compared with uncoated and 40-μm-thick coated samples. Under fretting fatigue loading, uncoated specimens exhibited inferior lives compared with coated samples owing to the very low hardness of the uncoated specimens (80 against 1020 HV0.2). The reason for the superior fretting fatigue lives of 40-μm-thick coated samples compared with 100-μm-thick coated samples was the presence of relatively higher surface compressive residual stress in 40-μm-thick coated specimens