Resistance of thermal barrier ceramic coatings to hot salt corrosion

Stabilized zirconia ceramics appear to have considerable potential as thermal barriers or corrosion-resistant coatings for application to gas turbine components. Salt corrosion tests have indicated however that under some conditions vanadium impurities in the fuel may cause accelerated failure of these coatings as a result of destabilization of the zirconia phase. The corrosion resistance, thermal stability and structure of the coatings depend to a large extent on the chemical composition of the ceramic phase. The results of a study of the behavior of plasma-sprayed Y₂O₃ZrO₂ coatings towards combustion gases and the typical salt deposits likely to be encountered in gas turbines which burn fuels containing sodium, sulfur, lead and vanadium impurities are described.     

A comparison of the mechanical properties and microstructures of intermetallic matrix composites fabricated by two different methods

The tensile properties of SCS-6 SiC fiber-reinforced Ti-24Al-11Nb (at. pct) have been measured over the past several years by a number of investigators. These composites have been fabricated by different techniques and tend to exhibit a large amount of scatter in the longitudinal tensile properties. To date, it is not known if one optimized fabrication method provides composites with improved mechanical properties over those produced by other optimized methods, since carefully controlled experiments have not been performed to determine this. Thus, the purpose of the present study was to compare the longitudinal tensile strengths of SCS-6 SiC/ Ti-24Al-11Nb composites that had been fabricated by the powder-cloth method and the lowpressure plasma spray (LPPS) method. In this study, the same lots of matrix powder and reinforcing fiber were used for fabricating the composites. It was determined that the powder-cloth and plasma spray methods produced composites having very similar tensile properties. Both fabrication methods induced damage in a small percentage of fibers, which manifested itself in the form of bimodal Weibull distributions of extracted fiber strengths. It appeared that the particular lot of SCS-6 fiber used in fabricating both types of composites was more susceptible to fabrication damage than those used in previous studies. This article also shows the dramatic effect that different handling and testing techniques can have on measured fiber strengths.     

Technical and economic assessment of charcoal and densified fuel from water hyacinths and cotton stalks

A study is presented on the production of charcoal and densified fuel using water hyacinths and cotton stalks as a feedstock. Both biomasses have no economic value and occur in fairly high concentrations. The circumstances of the town of Kosti in the Sudan are specifically investigated.The high water content of the water hyacinth has to be diminished by open-air drying. The high ash content of the air-dried plant material can be reduced to the cellular ash level of 12% by a combination of disintegration and screening. The air-dried water hyacinth is easily binderless-briquetted to a fuel wood substitute.The cotton stalks lend themselves to carbonization. 3.3 tons of chopped cotton stalks yield one ton of cotton-stalk charcoal and one MWh of electricity. The result of the study indicates that the process is technically feasible and economically viable. The cotton charcoal can be used in industry as a breeze or, after briquetting, as a lumpy smokeless fuel in households. A cotton-stalk carbonization plant should have a capacity of at least 15,000 t/a of charcoal.     

PET imaging of the pre-synaptic dopamine uptake sites in rapid-onset dystonia-parkinsonism (RDP)

BACKGROUND: Rapid-onset dystonia-parkinsonism (RDP) is a genetic movement disorder characterized by abrupt onset over hours to days of bradykinesia, postural instability, dysphagia, dysarthria, and severe dystonic spasms with decreased levels of the dopamine metabolite, homovanillic acid (HVA), in cerebrospinal fluid (CSF). METHODS: We imaged the dopamine re-uptake system with [O-methyl-11C]beta-CFT ([11C]beta-CFT) in three severely affected individuals with RDP and four patients with idiopathic Parkinson's disease (IPD). Results were compared with those of age-matched normal volunteers. RESULTS: Positron emission tomography images from those patients with IPD demonstrated a dramatic reduction in the volume of distribution of [11C]beta-CFT whereas patients with RDP showed slightly elevated values. CONCLUSIONS: The data suggest that patients with RDP do not have a decrease in the number of dopamine re-uptake sites. Our findings suggest that, unlike the situation in IPD, low CSF HVA concentrations seen in RDP patients are not the result of degeneration of striatal dopamine terminals or loss of dopamine re-uptake sites.     

Structure and anelasticity of Fe3Ge alloy

The structure and anelastic properties of Fe-27 at.%Ge alloy are studied. Long-term annealing of the as-cast alloy at 1273 K leads to homogenising and several transformations take place below 873 K. These low temperature transitions are studied by several methods: X-ray diffraction, calorimetry, vibrating-sample magnetometry and internal friction, and are related to magnetic transitions in the different phases. A high stability of the hexagonal (D0₁₉) phase at room temperature is recorded. The hexagonal β (B8₁) phase is also detected in the alloy at room temperature, while the presence of the ′ and phases is doubtful. A broad internal friction relaxation peak with the relaxation strength of Δ = 0.0036, the activation energy of about 1.78 eV and the preexponential relaxation time of τ₀ = 2 × 10⁻¹⁷ s was discovered and classified as the Zener peak in both the and β phases.     

Modelling of sputtering yield amplification effect in reactive deposition of oxides

Many reactive sputter deposition applications require high deposition rates. The primary limiting parameters in magnetron sputtering are the target power dissipation and sputtering yields of the target elements. In reactive deposition of oxides, the deposition rate is of particular interest due to the low sputtering yield of most commonly used oxides. Traditional high rate techniques rely on a feedback control of the oxygen partial pressure to prevent formation of oxide on the target and hence enable operation in the transition area. An alternative approach, based on target doping, is presented in this paper.By doping the sputtering target with heavy elements, it is possible to substantially enhance the sputtering yield and hence the deposition rate. Simulations of the partial sputtering yield values for aluminium from doped targets sputtered in reactive atmosphere have been carried out. The Monte Carlo based TRIDYN computer code has been used for simulations. The program has been used to find out optimum alloying conditions to obtain maximum partial sputtering yield for deposition of Al₂O₃. Our simulations indicate that the sputtering yield amplification in reactive sputtering may lead to much higher relative deposition rate increase than in a nonreactive case. The highest relative increase may be achieved in the transition region but substantial increase is predicted also in the oxide mode.