Ab Initio Study of Binary and Ternary Nb₃(X,Y) A15 Intermetallic Phases (X,Y = Al, Ge, Si, Sn)

Elastic and thermodynamic properties of binary and ternary A15 phases containing Al, Ge, Si, and Sn were studied using the first-principles pseudopotential plane-wave method based on density functional theory. The temperature dependence of the enthalpy of formation for the A15 intermetallics is reported using the quasiharmonic approximation. Elastic properties of the studied compounds were calculated at T = 0 K and were in agreement with the measured values reported in the literature. The elastic properties and thermodynamic data for the metastable A15-Nb₃Si are reported for the first time. The Nb₃Si has the highest bulk, shear, and Young’s modulus values and is predicted to be less ductile than the other three binary A15 intermetallics. The calculations suggest (i) that Al and Sn have a positive effect on the ductility of the A15 compounds of this study, (ii) that Ge as a ternary addition has a ductilizing effect only in the A15-Nb₃Si, and (iii) that Si as a ternary addition has a negative effect on the ductility of all the A15 compounds of the present study. The linear thermal expansion coefficients of the Nb, Al, the A15 Nb₃Al, Nb₃Ge, Nb₃Sn, and Nb₃Si (A15) phases are reported. The Sn and Al additions in the Nb₃Si stabilize the A15 structure, while the Ge addition has the opposite effect, stabilizing the tP32 Nb₃Si

Effect of synthesis conditions, Zn doping and Al/Fe ratio on calcium [alumino] ferrite structure

The use of steel waste for clinker production is a promising solution to reduce the environmental impact of Portland cement. While it is known that clinker produced from steel slag shows some advantageous properties e.g., lower burning temperature and reduced use of limestone, it is necessary to understand the formation and stability of iron-rich clinkers doped with the minor elements commonly found in steel wastes. In this study, pure ferrite phases were synthesized with varying Al/Fe ratios, burning temperature, cooling regimes, and in the presence of Zn as a minor element at various dosages. The phase assemblage and microstructure of the obtained ferrites were characterised by XRD/Rietveld and BSE-SEM/EDX. The results show that Zn is partially incorporated into the ferrite structure and partially replaces Al to form a Ca-Al-Zn phase. The Zn-incorporated ferrite leads to increased lattice parameter due to the bigger ionic radius of the dopant with respect to the substituted ions, and to increased crystallinity due to the increased ion mobility brought by ZnO which acts like a flux

Hydration of calcium [alumino] ferrite with limestone

Ferrite has the lowest embodied CO2 among the four major phases found in Portland cement, so increasing the ferrite content of the clinker would improve its CO2 footprint. Ferrite hydration is known to depend on the cooling regime during the production, Al/Fe ratio, and minor element uptake, and thus, their effects have to be fully understood to increase the composition of this phase in the Portland cement and assure their good hydration properties. Here, ferrites with different Al/Fe ratios (0, 0.5, 1, and 2), and minor elements (Zn) has been synthesized at two different burning temperatures, 1250 °C and 1350 °C and hydrated in presence of excess CaCO3 for 1 and 3 days. The ferrite with Al/Fe = 0 did not form any hydration product after 3 days of hydration, while Al-monocarbonate was the only hydration product in the other systems. The hydration kinetics increased with Al/Fe ratio, and when the burning temperature was increased. Comparing XRD and TGA data, the Al-monocarbonate formed from the ferrite with Al/Fe = 2 was found to be more amorphous than other ferrites. ZnO doping up to 2 wt.% had no prominent effect on hydration, implying that raw materials with Zn can be utilised in high-ferrite cement. These results indicate that high-ferrite limestone cement could be a promising solution to reduce cement the CO2 emission

Sustainable iron-rich cements: Raw material sources and binder types

The bulk of the cement industry's environmental burden is from the calcareous source. Calcium is mostly available naturally as limestone (CaCO3), where almost half of the mass is eventually released as CO2 during clinker manufacture. Iron (Fe) is the fourth most common element in the Earth's crust surpassed only by oxygen, silicon, and aluminium; therefore, potential raw materials for alternative cements can contain significant amounts of iron. This review paper discusses in detail the most abundantly available Fe-rich natural resources and industrial by-products and residues, establishing symbiotic supply chains from various sectors. The discussion then focusses on the impact of high iron content in clinker and on ferrite (thermo)chemistry, as well as the importance of iron speciation on its involvement in the reactions as supplementary cementitious material or alkali-activated materials, and the technical quality that can be achieved from sustainable Fe-rich cements

Corrosion of the International Simple Glass under acidic to hyperalkaline conditions

Assessment of glass dissolution kinetics, under disposal relevant temperature and pH environments, is required to credibly estimate radionuclide release rates from vitrified radioactive waste. Leaching of the International Simple Glass (ISG) under acidic to hyperalkaline conditions was examined. Forward rate measurements have been obtained using the dynamic leaching SPFT protocol and rate parameters for B, Na and Si in the basic regime; errors in rates predicted using these parameters at high pH and temperature are significant because the fitting uses logarithmic data. Longer term behaviour under hyperalkaline conditions, representative of some disposal environments, was investigated using the PCT and MCC-1 static leaching protocols with Ca(OH)2 solutions for up to 120 days (PCT) and 720 days (MCC-1). In hyperalkaline conditions dissolution was incongruent for all elements and the presence of alternating zirconia-rich and zirconia-poor alteration layers was observed on all leached monoliths, indicating the occurrence of a self-organisation phenomenon during leaching

Investigating the highest melting temperature materials : a laser melting study of the TaC-HfC system

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (\u3e4000 K) among other properties.  The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current  research, they were reassessed, for the first time in the last fifty years, using a laser heating technique.  They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest.  Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now

Kinesin Light Chain 1 Suppression Impairs Human Embryonic Stem Cell Neural Differentiation and Amyloid Precursor Protein Metabolism

The etiology of sporadic Alzheimer disease (AD) is largely unknown, although evidence implicates the pathological hallmark molecules amyloid beta (Aβ) and phosphorylated Tau. Work in animal models suggests that altered axonal transport caused by Kinesin-1 dysfunction perturbs levels of both Aβ and phosphorylated Tau in neural tissues, but the relevance of Kinesin-1 dependent functions to the human disease is unknown. To begin to address this issue, we generated human embryonic stem cells (hESC) expressing reduced levels of the kinesin light chain 1 (KLC1) Kinesin-1 subunit to use as a source of human neural cultures. Despite reduction of KLC1, undifferentiated hESC exhibited apparently normal colony morphology and pluripotency marker expression. Differentiated neural cultures derived from KLC1-suppressed hESC contained neural rosettes but further differentiation revealed obvious morphological changes along with reduced levels of microtubule-associated neural proteins, including Tau and less secreted Aβ, supporting the previously established connection between KLC1, Tau and Aβ. Intriguingly, KLC1-suppressed neural precursors (NPs), isolated using a cell surface marker signature known to identify cells that give rise to neurons and glia, unlike control cells, failed to proliferate. We suggest that KLC1 is required for normal human neural differentiation, ensuring proper metabolism of AD-associated molecules APP and Tau and for proliferation of NPs. Because impaired APP metabolism is linked to AD, this human cell culture model system will not only be a useful tool for understanding the role of KLC1 in regulating the production, transport and turnover of APP and Tau in neurons, but also in defining the essential function(s) of KLC1 in NPs and their progeny. This knowledge should have important implications for human neurodevelopmental and neurodegenerative diseases

Characterisation and disposability assessment of multi-waste stream in-container vitrified products for higher activity radioactive waste

Materials from GeoMelt® In-Container Vitrification (ICV)™ of simulant UK nuclear wastes were characterised to understand the partitioning of elements, including inactive surrogates for radionuclide species of interest, within the heterogeneous products. Aqueous durability analysis was performed to assess the potential disposability of the resulting wasteforms. The vitrification trial aimed to immobilise a variety of simulant legacy waste streams representative of decommissioning operations in the UK, including plutonium contaminated material, Magnox sludges and ion-exchange materials, which were vitrified upon the addition of glass forming additives. Two trials with different wastes were characterised, with the resultant vitreous wasteforms comprising olivine and pyroxene crystalline minerals within glassy matrices. Plutonium surrogate elements were immobilised within the glassy fraction rather than partitioning into crystalline phases. All vitrified products exhibited comparable or improved durability to existing UK high level waste vitrified nuclear wasteforms over a 28 day period

Changes in global groundwater organic carbon driven by climate change and urbanization

YesClimate change and urbanization can increase pressures on groundwater resources, but little is known about how groundwater quality will change. Here, we rely on a global synthesis (n = 9,404) to reveal the drivers of dissolved organic carbon (DOC), which is an important component of water chemistry and substrate for microorganisms which control many biogeochemical reactions. Groundwater ions, local climate and land use explained ~ 31% of observed variability in groundwater DOC, whilst aquifer age explained an additional 16%. We identify a 19% increase in DOC associated with urban land cover. We predict major groundwater DOC increases following changes in precipitation and temperature in key areas relying on groundwater. Climate change and conversion of natural or agricultural areas to urban areas will decrease groundwater quality and increase water treatment costs, compounding existing threats to groundwater resources