Library

Notes: The reaction-bonded aluminum oxide (RBAO) process is an attractive alternative to the conventional processing of Al2O3-based ceramics. The most attractive features of the process are the high strengths, densities, and easy machinability of the green powder compacts, and the low shrinkage and high strengths of the sintered ceramics. These advantages result from the presence of aluminum in the green bodies and are enhanced further with increasing aluminum contents. However, it is apparent that ZrO2-containing RBAO powders with higher aluminum contents (〉45 vol%) are increasingly more difficult to densify, as the start of densification is delayed (shifted to higher temperatures) and the densification rates are decreased. Ultimately, this results in a decrease in the limiting density to which the RBAO ceramic may be sintered. In this study, the cooperative effects of ZrO2 and aluminum contents on the sintering of RBAO ceramics are discussed in terms of densification behavior and microstructural analysis.

Notes: The microstructure evolution and densification of alumina containing 10 vol% calcium aluminosilicate glass and 0.5 wt% magnesium oxide sintered at 1600°C were quantified by measuring the evolution of pore-size distribution, the redistribution of liquid phase, and the fraction of closed and open pores. The densification stopped at a limiting relative density during the final stage of sintering, and the small and large pores were filled simultaneously by glass during sintering. In addition, the results indicate that the pressure build-up of the trapped gases in pores causes a significantly negative contribution to the driving force, and consequently the observed reduction in densification during the final stage of liquid phase sintering.

Notes: The microstructure evolution and densification kinetics of alumina containing 10 and 20 vol% calcium aluminosilicate glass were studied, for sintering under vacuum and air at 1600°C. Residual porosity was always present in the air-fired samples. The kinetic analysis lent strong support to the notion that trapped gases inhibited the densification and limited the attainment of full density. The samples containing 20 vol% glass were able to reach full density during vacuum sintering. However, the samples containing 10 vol% glass contained some residual porosity even after vacuum sintering, which was attributed to the preferential volatalization of liquid phase.

Notes: Alumina preforms containing artificial pores were sintered at 1630°C in air and vacuum. Glass penetration into the alumina preforms was conducted at 1600°C in air. It was found that the trapped gases in alumina preforms sintered in air caused the random and incomplete filling of the smaller and larger artificial pores. In contrast, the pores in the alumina preform sintered in vacuum were completely filled during glass penetration.

Notes: The reaction-bonded aluminum oxide (RBAO) process utilizes the oxidation of intensely milled aluminum/alumina powder compacts that are heat treated in air to make alumina-based ceramics. RBAO samples are typically oxidized in a furnace which is heated at 1°C/min to 1100°C. Heat-treating samples with a characteristic dimension 〉1 mm, without adjusting the furnace temperature program, usually results in a cracked ceramic. Cracking is caused by the excessive thermal and chemical stresses that result from steep temperature gradients (〉30°C/mm) and compositional gradients (〉5000 mol·(m3·mm)−1), which develop under the deleterious ignition and shrinking core reaction regimes. While adjustments to the furnace temperature program based on continuum models have had some success, the use of feedback-controlled firing is investigated as a means to avoid the furnace temperature program design step and to decrease the firing time. Feedback-controlled firing is shown to improve yields and significantly reduce the time required to completely oxidize the aluminum. For example, a 16 g sample with a characteristic dimension of 7.56 mm, which previously took 〉100 h to oxidize completely, was successfully oxidized crack free in 18.3 h using feedback control. Using the typical heat-treatment cycle, a 1 mm sample was fired in 18 h. With feedback-controlled firing, the same sized sample was fired in only 5 h.

Notes: Tantalum (V) oxide (Ta2O5) has potential applications as part of an environmental barrier coating system for Si3N4-based turbine components. However, at elevated temperatures, Ta2O5 undergoes a phase transformation from the orthorhombic (β) phase to the tetragonal phase (α), which is undesirable because of the associated volume change. The purpose of the present work was to study the effect of alumina additions (0–5 wt%) on the β to α transformation temperature, and associated modifications to the Ta2O5 microstructure. Sintered microstructures were characterized using SEM (scanning electron microscopy), and XRD (X-ray diffraction) was used to identify the phases present at room temperature. It was found that for undoped Ta2O5, transformation of the low-temperature β-phase begins at ∼1300°C, and leads to extensive microcracking of the sintered sample. For samples containing alumina, an increase in the transformation temperature was observed. The solubility limit of alumina in Ta2O5 was between 1 and 3 wt%; for samples in which this was exceeded, the AlTaO4 second and phase particles were seen to be highly effective at inhibiting grain growth.

Notes: The reaction-bonded aluminum oxide (RBAO) process relies upon the oxidation of Al/Al2O3 powder compacts, and many of its associated advantages stem from the presence of the aluminum in the green powder. Higher aluminum contents in the starting powders allow for higher green strengths, densities, and lower overall shrinkage, all while producing a fine-grained, high-strength sintered material. However, it is evident that the reaction and sintering of ZrO2-containing RBAO with higher aluminum contents are more challenging. Therefore, in this study, the effects of aluminum content on the processing, structure, and properties of RBAO ceramics were comprehensively characterized. It was found that RBAO samples with high aluminum contents were more prone to cracking during reaction and even when successfully fired were not able to be sintered to full density. Despite these characteristics, RBAO samples with increasing aluminum contents showed no significant degradation in mechanical properties.

Notes: The impact of hepatitis C virus on patient and graft survival after renal transplantation remains controversial. However, recent studies have given emphasis on the detrimental role of hepatitis C on long-term patient and graft survival after renal transplantation. Various mechanisms can promote the lower survival in hepatitis C virus-positive recipients, i.e. post-transplant diabetes mellitus, liver disease and infections.Novel evidence has been accumulated showing the inhibitory activity of ciclosporin on the hepatitis C virus replication rate in human hepatocytes; ciclosporin has been shown in vitro to suppress hepatitis C virus replication as effectively as interferon alpha. This effect has not been seen with tacrolimus and is separate from its immunosuppressive activity. Data from patients with normal kidney function or after bone marrow transplantation show that ciclosporin inhibits hepatitis C virus replication. It appears that the progression of liver fibrosis is slower in hepatitis C virus-positive liver transplant recipients treated with ciclosporin than tacrolimus. In contrast, the clinical outcome of hepatitis C in hepatitis C virus-positive patients after liver transplantation treated with ciclosporin vs. tacrolimus has given mixed results. No information after renal transplantation is available.Various parameters can promote the worsening of hepatitis C after renal transplantation but choice of calcineurin inhibition is one of the few risk factors that can potentially be modified by the physician. Prospective, comparative trials of ciclosporin and tacrolimus with large size and adequate follow-up after renal transplantation are in progress.

Notes: Background : Dialysis patients remain a high-risk group for hepatitis C virus infection. The current diagnosis of hepatitis C virus in dialysis patients includes serological measurement of anti-hepatitis C virus antibody; however, nucleic acid amplification technology for assessing hepatitis C virus viraemia is commonly used in other populations. An enzyme-linked immunosorbent assay test for detecting antibody to hepatitis C nucleocapsid core antigen (hepatitis C virus core antigen) in human serum has been recently developed (hepatitis C virus Core Antigen enzyme-linked immunosorbent assay test). It is conceived for screening of donor blood products to significantly reduce the ‘serologic window’ occurring before seroconversion during acute hepatitis C virus.Aim and methods : A cohort (n = 72) of patients on maintenance haemodialysis in a single unit in the years 2000–2003 was included. Study patients were tested monthly by hepatitis C virus Core Antigen enzyme-linked immunosorbent assay in a prospective, clinical trial. Routine results obtained by hepatitis C virus Core Antigen enzyme-linked immunosorbent assay test were confirmed by assessing hepatitis C virus viraemia by branched-chain DNA (bDNA) signal amplification assay.Results : De novo hepatitis C virus infection was identified in three patients during the study period; the hepatitis C virus incidence was 1.38% (95% confidence intervals, 1.31–4.09) per year. In each patient, hepatitis C virus core antigen testing allowed the serological identification of acute hepatitis C virus before anti-hepatitis C virus seroconversion. Hepatitis C virus RNA testing confirmed the results obtained by hepatitis C virus Core Antigen enzyme-linked immunosorbent assay in all cases. The time from initial hepatitis C virus detection by hepatitis C virus Core Antigen Assay and anti-hepatitis C virus seroconversion was not greater than four weeks. Two (67%) of three patients with de novo hepatitis C virus acquisition were HBsAg negative; both these patients underwent an initial phase of hepatitis C virus viraemia that was associated with an increase in alanine aminotransferase activity and preceded the seroconversion to anti-hepatitis C virus antibody. Nosocomial transmission of hepatitis C virus between haemodialysis patients was implicated in at least two (67%) of these three patients.Conclusions : Serological testing for hepatitis C virus core antigen can identify acute hepatitis C virus infection before anti-hepatitis C virus seroconversion. The time from initial hepatitis C virus detection by hepatitis C virus core antigen assay and anti-hepatitis C virus seroconversion was not 〉4 weeks. De novo acquisition of hepatitis C virus in haemodialysis was associated with a rise in alanine aminotransferase levels. Hepatitis C virus core antigen enzyme-linked immunosorbent assay test results can be obtained in routine laboratories without the need of special equipment or training. Hepatitis C virus core antigen testing among anti-hepatitis C virus negative patients on maintenance dialysis is suggested in order to early assess de novo hepatitis C virus within dialysis units.

Notes: A link between hepatitis C virus infection and development of diabetes mellitus has been suggested by many investigators; however, this remains controversial.The mechanisms underlying the association between hepatitis C virus and diabetes mellitus are unclear but a great majority of clinical surveys have found a significant and independent relationship between hepatitis C virus and diabetes mellitus after renal transplantation and orthotopic liver transplantation.We have systematically reviewed the scientific literature to explore the association between hepatitis C virus and diabetes mellitus in end-stage renal disease; in addition, data on patients undergoing orthotopic liver transplantation were also analysed. The unadjusted odds ratio for developing post-transplant diabetes mellitus in hepatitis C virus-infected renal transplant recipients ranged between 1.58 and 16.5 across the published studies. The rate of anti-hepatitis C virus antibody in serum was higher among dialysis patients having diabetes mellitus (odds ratio 9.9; 95% confidence interval 2.663–32.924). Patients with type-2 diabetes-related glomerulonephritis had the highest anti-hepatitis C virus prevalence [19.5% (24/123) vs. 3.2% (73/2247); P 〈 0.001] in a large cohort of Japanese patients who underwent renal biopsy. The link between hepatitis C virus and diabetes mellitus may explain, in part, the detrimental role of hepatitis C virus on patient and graft survival after orthotopic liver transplantation and/or renal transplantation.Preliminary evidence suggests that anti-viral therapies prior to renal transplantation and novel immunosuppressive regimens may lower the occurrence of diabetes mellitus in hepatitis C virus-infected patients after renal transplantation. Clinical trials are under way to assess if the hepatitis C virus-linked predisposition to new onset diabetes mellitus after renal transplantation may be reduced by newer immunosuppressive medications.