Effect of microstructure and temperature on the erosion rates and mechanisms of modified EB PVD TBCs

Thermal barrier coatings (TBCs) have now been used in gas turbine engines for a number of decades and are now considered to be an accepted technology. As there is a constant drive to increase the turbine entry temperature, in order to increase engine efficiency, the coatings operate in increasingly hostile environments. Thus there is a constant drive to both increase the temperature capabilities of TBCs while at the same time reducing their thermal conductivities. The thermal conductivity of standard 7 wt% yttria stabilized zirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can be reduced in two ways: the first by modification of the microstructure of the TBC and the second by addition of ternary oxides. By modifying the microstructure of the TBC such that there are more fine pores, more photon scattering centres are introduced into the coatings, which reduce the heat transfer by radiation. While ternary oxides will introduce lattice defects into the coating, which increases the phonon scattering, thus reducing the thermal conductivity via lattice vibrations. Unfortunately, both of these methods can have a negative effect on the erosion resistance of EB PVD TBCs.This paper compares the relative erosion rates of ten different EB PVD TBCs tested at 90° impact at room temperature and at high temperature and discusses the results in term of microstructural and temperature effects. It was found that by modifying the coating deposition, such that a low density coating with a highly ‘feathered’ microstructure formed, generally resulted in an increase in the erosion rate at room temperature. When there was a significant change between the room temperature and the high temperature erosion mechanism it was accompanied by a significant decrease in the erosion rate, while additions of dopents was found to significantly increase the erosion rate at room and high temperature. However, all the modified coatings still had a lower erosion rate than a plasma sprayed coatings. So, although, relative to a standard 7YSZ coating, the modified coatings have a lower erosion resistance, they still perform better than PS TBCs and their lower thermal conductivities could make them viable alternatives to 7YSZ for use in gas turbine engines.     

A systematic approach to choosing parameters for modelling fine structure in electron energy-loss spectroscopy

A potential methodology is presented for the systematic prediction of EELS edges using DFT, suitable for codes that calculate ELNES for a specific atom in a unit cell. The method begins with the selection of a unit cell, chosen as the smallest cell that still provides a physically valid representation of the bulk material. Within this small cell, a single electron core–hole is included in the atom for which the EELS ionisation edge is to be calculated. The basis-set size and k-point mesh of the DFT calculation are converged specifically against the predicted EELS result. Subsequently, the cell size is increased until the theoretical core–holes no longer interfere. At this point one can then modify the exact core–hole approximation. This methodology was applied to the new EELS module of the CASTEP pseudopotential DFT code, as well as the all-electron code Wien2k. Aluminium K edges were investigated for various aluminium metal systems. It was observed that as the cell size was increased the predicted EELS result became less sensitive to the exact core–hole approximation used. It was noted however that due to high screening in metals a ground state single cell calculation is often acceptable. The semiconductor aluminium nitride (wurtzite form) was also investigated. It was observed that for both Wien2k and CASTEP, with careful convergence of the key DFT code parameters, single cell ground state calculations gave a reasonable agreement with experiment, contrary to what might be expected for a semiconductor with a large band gap. This was particularly true of the Wien2k result. Given the greater computational effort required for supercell calculations, these results are likely to form the beginnings of a detailed investigation into accepted methods of ELNES predictions.     

The effect of furosemide on serum prolactin levels in the postpartum period

Furosemide, in combination with breast binding and milk fluid restriction, seems to inhibit postpartum lactation effectively, but has no effect in reducing serum prolactin levels. Inhibition of milk secretion must therefore be mediated by other mechanisms.     

Birth outcomes in the offspring of mentally disordered women

The course of pregnancy and birth were studied among schizophrenic, neurotic depressive, and personality-disordered women, compared to a normal control group. The lighter birthweight of schizophrenic women's offspring was found more strongly related to the severity and chronicity of their mental illness than to the diagnosis itself. Children of neurotic depressive women had lower APGAR scores and more fetal deaths.     

Defective platelet lipid peroxidation in myeloproliferative disorders: a possible defect of prostaglandin synthesis

The author discusses a number of genetically determined diseases, such as hemoglobinopathies, acute intermittent porphyria, familial Mediterranean fever and so-called acquired hypogammaglobulinemia from the geographical point of view. Possible factors explaining localized increases in incidence are discussed. The importance of isolates for the development of such foci is stressed.     

Fatal poisoning with propoxyphene: report from 100 consecutive cases

The first 100 deaths caused by propoxyphene and recorded by the Chief Medical Examiner of North Carolina were studied. Victims ranged evenly in age from the second to the seventh decade. Over 65% were suicides with a female to male ratio of 2:1. Blood propoxyphene concentrations of 0.2 mg/dl were fatal, representing rapid ingestion of approximately ten capsules. In North Carolina, deaths due to propoxyphene have increased from five in 1969 to 49 in 1975. Raising physician-awareness of propoxyphene's toxicity and placing the drug in Schedule II are two of the author's recommendations for reducing the number of propoxyphene deaths.     

Lymphocytes' cytotoxicity towards cells of human lymphoblastoid lines in patients with rheumatoid arthritis and systemic lupus erythematosus

A research study and discussion of antiinterferon immunoglobulin in the treatment of rheumatoid arthritis and systemic lupus erythematosus, and its possible value in the treatment of allergic diseases, autoimmune diseases and other diseases where it is presumed there may be an autoimmune genesis.     

The energetics of fat deposition during growth

Attention was paid to the levels of importance of maintenance, protein and fat deposition in growing monogastrics. Some information was presented on the composition of their daily gain. Theoretical efficiency values of fat synthesis were derived from biochemical information and compared with those found in balance trials. Factors determining maintenance needs including thermoregulation and physical activity were discussed. Some aspects of energy metabolism and regulation of body fat deposition and mobilization were described including the processes of hyperplasia and hypertrophy. Finally, the role of fat as a well-regulated, rapidly adaptable buffer within the monogastric's total metabolism was emphasized.