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The work herein verifies the changes of the elastic moduli, damping and modulus of rupture (MOR) of a high alumina refractory castable due to heating, cooling and heating-cooling thermal shock damage. Twelve prismatic specimens were prepared for the tests and divided into four groups. The thermal shocks were performed on three groups, each containing three specimens having abrupt temperature changes of 1100°C during heating in the first group, during cooling in the second and during heating followed by cooling in the third group. The fourth group, which was taken as a reference did not receive any thermal shock. The elastic moduli were measured after each thermal shock cycle. After 10 cycles, the MOR, the damping and the damping dependence on excitation amplitude were measured at room temperature for all specimens. The elastic moduli showed a similar decrease and the damping a similar increase due to the cooling and heating-cooling thermal shocks. The heating thermal shocks caused no significant changes on the elastic moduli and damping. However, the MOR appeared to be sensitive to the heating thermal shock. This work also shows that the damping for the studied refractory castable is non-linear (i.e., amplitude of excitation sensitive) and that this non-linearity increases when the damage level rises.En este trabajo se investigaron las alteraciones de los módulos elásticos dinámicos, del amortiguamiento y del módulo de rotura (MOR) de un material refractario moldeable de alta alúmina después de recibir choques térmicos de calentamiento, enfriamiento y calentamiento seguido de enfriamiento (calentamiento-enfriamiento). Para ello se prepararon doce cuerpos prismáticos dividiéndolos en cuatro grupos. Los choques térmicos se le aplicaron a sólo tres grupos, cada uno con tres muestras. Al primer grupo se le aplicó un cambio brusco de temperatura de 1100 °C en calentamiento, en enfriamiento al segundo grupo y calentamiento seguido de enfriamiento al tercer grupo. El cuarto grupo no recibió choque térmico. Los módulos elásticos se midieron después de cada ciclo de choque térmico. Después de 10 ciclos, el MOR, el amortiguamiento, y la dependencia de la amortiguación de la amplitud de la excitación fueron caracterizados a temperatura ambiente en todos los cuerpos de prueba. Como resultado se obtuvo que los cuerpos sometidos a cambios bruscos de temperatura por enfriamiento y calentamiento-enfriamiento presentaran una reducción similar en los módulos elásticos y aumento similar en la amortiguación mientras que el calentamiento no causó cambios significativos en estos parámetros. Sin embargo, el MOR pareció ser sensible a los cambios bruscos de temperatura por calentamiento. Este estudio también mostró que la amortiguación para el material refractario estudiado no es lineal y que este comportamiento no lineal se acentúa con el daño por choque térmico.

For the transformation to a CO2 neutral industry, fuel of traditionally fossil‐fired furnaces is substituted by the subsequently addition of hydrogen. In these studies, refractory components are identified for the corrosion of refractories in (highly) reducing atmospheres. A bauxite‐based refractory castable is set up in diluted, 9Ar 1H2, hydrogen atmosphere. Additionally, a focus is set on the behavior of a common matrix phase, anorthite. Corrosion experiments up to 1500°C using a tube furnace with the mentioned atmosphere have been scheduled. Amount and phase stability due to different time and temperature coordinates have been examined by XRD. Furthermore, the microstructure and in particular the bonding phase was observed by means of SEM and EDS. Microstructural components undergoing reaction or loss are identified and explained in regards of complete and incomplete hydrogen combustion. Reduction of impurities such as iron oxides, phosphorus oxides, and titanium oxides are considered in detail. [ABSTRACT FROM AUTHOR]

Al2O3‐ZrO2 composites exhibit excellent mechanical and high‐temperature properties. The solidification of various hypoeutectic compositions has been studied by means of aero‐acoustic levitation. A high‐speed camera recorded the crystallization, to the correlation of the video stills with the observed microstructures. Solidification takes place by formation of several nuclei and subsequent growth. Nuclei are formed in the supercooled melt, entailing to a fine‐grained, simultaneously solidified structure. The remaining melt between the growing nuclei is heated due to recalescence leading to primary precipitation of zirconia, followed by eutectic solidification. A consistent behavior is presented to explain the observed microstructures. Additionally, samples between 40 and 50 mol% ZrO2 exhibit lamellar areas, which exceed the initial zirconia composition. The observed microstructure strongly indicates the existence of a liquid miscibility gap. [ABSTRACT FROM AUTHOR]

For many years, the optimization of refractory castable formulations has been a key factor in improving the service life of unshaped materials during their application in the steel and iron industry as well as in the metallurgical industry. The incorporation of functional aggregates in common low cement castables based on tabular alumina raw materials was investigated within the framework of the study presented herein. Such an addition of eutectic aggregates aims to modify the elastic and mechanical properties of the castable leading to eventual thermal shock resistance amelioration. Different high alumina-based formulations were investigated. Starting with a reference tabular alumina-based castable, the largest grain fraction of this first formulation was replaced by three different aggregates. Andalusite was incorporated to favour microcrack formation due to in situ mullite and ensuing glass formation during the sintering process. Both mechanisms may explain the depletion of elastic and mechanical properties and furthermore the decrease of the stored elastic energy of the castable. Al2O3-ZrO2 addition may also result in crack formation because of expansion mismatch between the calcium aluminate matrix and the zirconia-containing aggregate. The martensitic transformation of zirconia at high temperature characterized by a considerable volume expansion is the second factor explaining the increase in mechanical stresses at the level of the grain boundaries between aggregates and matrix. An alternative to these materials was the examination of Al2O3-ZrO2-SiO2 eutectic aggregates in order to study the influence of zirconia in the presence of a silica glassy phase. This study will focus on the modification of the elastic and thermo-mechanical properties of the andalusitebased castable in comparison with the reference castable (without functional aggregate incorporation) to discuss the impact of such aggregates on thermal shock resistance. [ABSTRACT FROM AUTHOR]

The article focuses on the evaluation of damping change in high alumina refractory materials and estimation on its retained mechanical strength to quantify thermal shock damage. It notes that the result of the correlation was related to the Young's modulus test. It notes a proportional change in the damping, retained mechanical strength, and retained Young's modulus.

The article presents a study on the development of an equipment for non-destructive characterization of elastic moduli that is applicable to ceramics, concretes, and brittle materials based on American Society for Testing Materials (ASTM) standard. The study used the sonic resonance spectroscopy to measure the natural torsional and flexural vibration frequencies of the sample. The result shows that the equipment is more versatile than the current options to the measurement of the elastic moduli.

To describe important thermal properties of high temperature insulating wool (HTIW) materials, firing experiments have been performed at temperatures above their classification temperature and following shrinkage and resilience measurements for three HTIW material groups: AES (alkaline earth silicate wool), aluminium silicate wool (RCF) and polycrystalline wool. A temperature range of 1000–1600°C has been chosen. At industrial application temperatures the HTIW products should not reveal significant shrinkage behaviour, and their mechanical properties should be maintained after exposure to elevated temperatures. This is an important and critical aspect for these high temperature insulation materials. Microstructural examination after firing at different temperatures shows increasing crystallisation as a result of phase formation, leading to increased density and shrinkage. At classification temperature these processes enhance bending of fibres and fibre thickness in the length direction which also leads to higher shrinkage. These effects are supported by sintering processes of single fibres and diffusion at junction points. At high temperatures strong crystal growth takes place. The resulting crystals on the surface achieve dimensions larger than the fibre diameter. [ABSTRACT FROM AUTHOR]

Three sibs, a boy and two girls, born to Moroccan consanguineous parents, were affected with a syndrome characterized by brittle hair, mental retardation, short stature, ataxia, and gonadal dysfunction. The hair in these three patients displayed the morphological and biochemical hallmarks of trichothiodystrophy (TTD). Gonadal function tests showed abnormal gonadotropic responses to LHRH, consistent with delayed puberty in the male and ovarian failure in both females. Comparison with previously reported cases of TTD associated with mental retardation suggests genetic heterogeneity, although specific biochemical markers are needed in order to answer this question.

The amount and location of tRNA and 5-S rRNA genes in the macronucleus of Tetrahymena pyriformis GL was investigated by DNA-RNA hybridization. Hybridization of 32P-labelled tRNA in excess of unlabelled rRNA (25-S + 17-S + 5-S) showed that at saturation 0.021% of the macronuclear DNA was complementary to tRNA. Hybridization of 32P-labelled 5-S rRNA in excess of unlabelled 25-S + 17-S rRNA and tRNA showed a saturation value of 0.017%. In contrast to the 25-S + 17-S rRNA genes, which are found in DNA of high bouyant density, tRNA and 5-S rRNA genes were distributed evenly throughout the main peak observed when bulk macronuclear DNA was fractionated by density centrifugation in CsCl gradients. Sucrose gradient analyses of total macronuclear DNA showed that tRNA and 5-S rRNA genes were found in DNA of all size classes but a significant enrichment in the slowly sedimenting DNA fraction was observed. Saturation hybridization of 5-S rRNA to purified rDNA showed that rDNA did not contain any 5-S rRNA genes.

Daunomycin and ethidium bromide, two deoxyribonucleic acid-intercalating drugs, inhibit ribonucleic acid (RNA) and protein synthesis in Saccharomyces cerevisiae. Both agents rapidly curtail uptake of radioactive adenine, whereas the kinetics of radioactive leucine uptake after drug addition are consistent with translation of a pool of exponentially decaying messenger RNA. Messenger RNA half-life determinations from these experiments gave identical results over a range of drug concentrations; this value is 21 +/- 4 min at 30 C. In a temperature-sensitive mutant in which RNA synthesis is curtailed at the nonpermissive temperature, a similar half-life for messenger RNA decay is found both in the absence and in the presence of either drug. This indicates that at the concentrations used in this study, neither daunomycin nor ethidium bromide has an appreciable direct effect on translation and do not increase the lability of messenger RNA.