Ceramic properties of pugu kaolin clays. Part 2: Effect of phase composition on flexural strength

Whiteware compositions prepared using Pugu kaolin and industrial grade quartz and feldspar were studied with respect to varying sintering temperatures. The strength developed was correlated to mullite (3Al2O3.2SiO2) content and the microstructure. It was observed that within the vitrification temperature range, the strength mainly depended on the mullite content and the bulk density. Above the vitrification temperature range the deterioration of the strength is due to the coarsening of mullite needles and bloating. KEY WORDS: Ceremic properties, Kaolin clay, Flexural strength, Mullitisation, Bulk density, Modulus of Rupture, Microstructure  Bull. Chem. Soc. Ethiop. 2004, 18(1), 7-16.  

Ceramic properties of Pugu kaolin clays. Part I: Porosity and modulus of rupture

The utilisation of Pugu kaolin clay as a raw material in porcelain has been tested by laboratory scale experiments. Physical characteristics of the clay have shown it to be of satisfactory quality and comparable to commercial clays found elsewhere. The chemical analysis has indicated the presence of high levels of iron oxide (~ 1.43%) which could adversely affect the translucency of whitewares. The “as mined” material could be suitable for ceramics that do not require high brightness specifications, such as stoneware and sanitary ware. The level of this oxide can, however, be reduced by appropriate means to give a relatively cleaner product that could be excellent for other types of whiteware products.      Porcelain materials prepared using Pugu kaolin clay have shown to have similar properties as those prepared using other standard kaolin clays. The bulk density and flexural strength of the fired masses increase with firing temperature to a maximum at the soak temperature of 1200 oC. Beyond this soak temperature the flexural strength decreases. The decrease in strength is attributable to bloating which takes place as gasses are expelled from the matrix. Strictly firing procedures should be enforced in order to obtain a porcelain material of required strength. KEY WORDS: Kaolin clay, Ceramic properties, Porcelain materials, Bulk density, Sintering, Modulus of rupture, Bloating  Bull. Chem. Soc. Ethiop. 2003, 17(2), 147-154

High temperature X-ray diffraction and thermo-gravimetrical analysis of the cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ under different atmospheres

Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) with the cubic perovskite structure is known to be metastable at low temperature under an oxidizing atmosphere. Here, the thermal and chemical expansion of BSCF were studied by in situ high temperature powder X-ray diffraction and thermo-gravimetrical analysis (TGA) in partial pressure of oxygen ranging from an inert atmosphere (∼10−4 bar) to 10 bar O2. The BSCF powder, heat treated at 1000 °C and quenched to ambient temperature prior to the analysis, was shown to oxidize under an oxidizing atmosphere before thermal reduction took place. With decreasing partial pressure of oxygen the initial oxidation was suppressed and only reduction of Co/Fe and loss of oxygen were observed under an inert atmosphere. The thermal expansion of BSCF under different atmospheres was determined from the thermal evolution of the cubic unit cell parameter, demonstrating that the thermal expansion of BSCF depends on the atmosphere. Chemical expansion of BSCF was also estimated based on the diffraction data and thermo-gravimetrical analysis. A hexagonal perovskite phase, coexisting with the cubic BSCF polymorph, was observed to be formed above 600 °C during heating. The phase separation leading to the formation of the hexagonal polymorph was driven by oxidation, and the unit cell of the cubic BSCF was shown to decrease with increasing amounts of the hexagonal phase. The hexagonal phase disappeared upon further heating, accompanied with an expansion of the unit cell of the cubic BSCFAuthor preprin

Epidemiology of abdominal trauma: An age- and sex-adjusted incidence analysis with mortality patterns

Purpose Abdominal injuries may occur in up to one-third of all patients who suffer severe trauma, but little is known about epidemiological trends and characteristics in a Northern European setting. This study investigated injury demographics, and epidemiological trends in trauma patients admitted with abdominal injuries. Methods This was an observational cohort study of all consecutive patients admitted to Stavanger University Hospital (SUH) with a documented abdominal injury between January 2004 and December 2018. Injury demographics, age- and sex-adjusted incidence, and mortality patterns are analyzed across three time periods. Results Among 7202 admitted trauma patients, 449 (6.2%) suffered abdominal injuries. The median age was 31 years, and the age increased significantly over time (from a median of 25 years to a median of 38.5 years; p = 0.020). Patients with ASA 2 and 3 increased significantly over time. Men accounted for 70% (316/449). The injury mechanism was blunt in 91% (409/449). Transport-related accidents were the most frequent cause of injury in 57% (257/449). The median Injury Severity Score (ISS) was 21, and the median New Injury Severity Score (NISS) was 25. The annual adjusted incidence of all abdominal injuries was 7.2 per 100,000. Solid-organ injuries showed an annual adjusted incidence of 5.7 per 100,000. The most frequent organ injury was liver injury, found in 38% (169/449). Multiple abdominal injuries were recorded in 44% (197/449) and polytrauma in 51% (231/449) of the patients. Overall 30-day mortality was 12.5% (56/449) and 90-day mortality 13.6% (61/449). Conclusion The overall adjusted incidence rate of abdominal injuries remained stable. Age at presentation increased by over a decade, more often presenting with pre-existing comorbidities (ASA 2 and 3). The proportion of polytrauma patients was significantly reduced over time. Mortality rates were declining, although not statistically significant.publishedVersio

Removing fluoride-terminations from multilayered V2CTx MXene by gas hydrolyzation

Two-dimensional MXenes have shown great promise for many different applications, but in order to fully utilize their potential, control of their termination groups is essential. Here we demonstrate hydrolyzation with a continuous gas flow as a method to remove F-terminations from multilayered V2CTx particles, in order to prepare nearly F-free and partly bare vanadium carbide MXene. Density functional theory calculations demonstrate that the substitution of F-terminations is thermodynamically feasible and presents partly nonterminated V2CO as the dominating hydrolyzation product. Hydrolyzation at elevated temperatures reduced the F content but only subtly changed the O content, as inferred from spectroscopic data. The ideal hydrolyzation temperature was found to be 300 °C, as a degradation of the V2CTx phase and a transition to vanadium oxycarbides and V2O3 were observed at higher temperature. When tested as electrodes in Li-ion batteries, the hydrolyzed MXene demonstrated a reduced polarization compared with the pristine MXene, but no change in intercalation voltage was observed. Annealing in dry Ar did not result in the same F reduction, and the importance of water vapor was concluded, demonstrating hydrolyzation as a new and efficient method to control the surface terminations of multilayered V2CTx post etching. These results also provide new insights on the thermal stability of V2CTx MXene in hydrated atmospheres.publishedVersio

Impurity diffusion of 141 Pr in LaMnO 3 , LaCoO 3 and LaFeO 3 materials

The impurity diffusion of Pr 3+ in dense polycrystalline LaMnO 3 , LaCoO 3 and LaFeO 3 was studied at 1373-1673 K in air in order to investigate cation diffusion in these materials. Cation distribution profiles were measured by secondary-ion mass spectrometry and it was found that penetration profiles of Pr 3+ had two distinct regions with different slopes. The first, shallow region was used to evaluate the bulk diffusion coefficients

Performance Study of MXene/Carbon Nanotube Composites for Current Collector‐ and Binder‐Free Mg–S Batteries

The realization of sustainable and cheap Mg-S batteries depends on significant improvements in cycling stability. Building on the immense research on cathode optimization from Li-S batteries, for the first time a beneficial role of MXenes for Mg-S batteries is reported. Through a facile, low-temperature vacuum-filtration technique, several novel current collector- and binder-free cathode films were developed, with either dipenthamethylene thiuram tetrasulfide (PMTT) or $S_{8}$ nanoparticles as the source of redox-active sulfur. The importance of combining MXene with a high surface area co-host material, such as carbon nanotubes, was demonstrated. A positive effect of MXenes on the average voltage and reduced self-discharge was also discovered. Ascribed to the rich polar surface chemistry of $Ti_{3}C_{2}T_{x}$ MXene, an almost doubling of the discharge capacity (530 vs. 290 mA h $g^{−1}$) was achieved by using MXene as a polysulfide-confining interlayer, obtaining a capacity retention of 83 % after 25 cycles

Tuning the Thermoelectric Performance of CaMnO3-Based Ceramics by Controlled Exsolution and Microstructuring

The thermoelectric properties of CaMnO3-δ/CaMn2O4 composites were tuned via microstructuring and compositional adjustment. Single-phase rock-salt-structured CaO-MnO materials with Ca:Mn ratios larger than unity were produced in reducing atmosphere and subsequently densified by spark plasma sintering in vacuum. Annealing in air at 1340 °C between 1 and 24 h activated redox-driven exsolution and resulted in a variation in microstructure and CaMnO3-δ materials with 10 and 15 vol % CaMn2O4, respectively. The nature of the CaMnO3-δ/CaMn2O4 grain boundary was analyzed by transmission electron microscopy on short- and long-term annealed samples, and a sharp interface with no secondary phase formation was indicated in both cases. This was further complemented by density functional theory (DFT) calculations, which confirmed that the CaMnO3-δ indeed is a line compound. DFT calculations predict segregation of oxygen vacancies from the bulk of CaMnO3-δ to the interface between CaMnO3-δ and CaMn2O4, resulting in an enhanced electronic conductivity of the CaMnO3-δ phase. Samples with 15 vol % CaMn2O4 annealed for 24 h reached the highest electrical conductivity of 73 S·cm-1 at 900 °C. The lowest thermal conductivity was obtained for composites with 10 vol % CaMn2O4 annealed for 8 h, reaching 0.56 W·m-1K-1 at 700 °C. However, the highest thermoelectric figure-of-merit, zT, was obtained for samples with 15 vol % CaMn2O4 reaching 0.11 at temperatures between 800 and 900 °C, due to the enhanced power factor above 700 °C. This work represents an approach to boost the thermoelectric performance of CaMnO3-δ based composites

Effect of coating density on oxidation resistance and Cr vaporization from solid oxide fuel cell interconnects

Manganese cobalt spinel oxides are promising materials for protective coatings for solid oxide fuel cell (SOFC) interconnects. To achieve high density such coatings are often sintered in a two-step procedure, involving heat treatment first in reducing and then in oxidizing atmospheres. Sintering the coating inside the SOFC stack during heating would reduce production costs, but may result in a lower coating density. The importance of coating density is here assessed by characterization of the oxidation kinetics and Cr evaporation of Crofer 22 APU with MnCo1.7Fe0.3O4 spinel coatings of different density. The coating density is shown to have minor influence on the long-term oxidation behavior in air at 800 °C, evaluated over 5000 h. Sintering the spinel coating in air at 900 °C, equivalent to an in-situ heat treatment, leads to an 88% reduction of the Cr evaporation rate of Crofer 22 APU in air-3% H2O at 800 °C. The air sintered spinel coating is initially highly porous, however, densifies with time in interaction with the alloy. A two-step reduction and re-oxidation heat treatment results in a denser coating, which reduces Cr evaporation by 97%

Prospects for the future of pink salmon in three oceans: From the native Pacific to the novel Arctic and Atlantic

While populations of other migratory salmonids suffer in the Anthropocene, pink salmon (Oncorhynchus gorbusca Salmonidae) are thriving, and their distribution is expanding both within their natural range and in the Atlantic and Arctic following introduction of the species to the White Sea in the 1950s. Pink salmon are now rapidly spreading in Europe and even across the ocean to North America. Large numbers of pink salmon breed in Norwegian rivers and small numbers of individuals have been captured throughout the North Atlantic since 2017. Although little is known about the biology and ecology of the pink salmon in its novel distribution, the impacts of the species' introduction are potentially highly significant for native species and watershed productivity. Contrasts between pink salmon in the native and extended ranges will be key to navigating management strategies for Atlantic nations where the pink salmon is entrenching itself among the fish fauna, posing potential threats to native fish communities. One key conclusion of this paper is that the species' heritable traits are rapidly selected and drive local adaptation and evolution. Within the Atlantic region, this may facilitate further establishment and spread. The invasion of pink salmon in the Atlantic basin is ultimately a massive ecological experiment and one of the first examples of a major faunal change in the North Atlantic Ocean that is already undergoing rapid changes due to other anthropogenic stressors. New research is urgently needed to understand the role and potential future impacts of pink salmon in Atlantic ecosystems. Atlantification, biological invasions, climate adaptation, Pacific Ocean, regime shiftpublishedVersio