Electronic properties of SmxSr1−xMnO3 for solid oxide fuel cell application — a first-principles study

Electronic properties of orthorhombic SSM ([Formula: see text] and monoclinic SSM ([Formula: see text] are investigated using the first-principles calculation. The half-metallic behavior that leads to the mixed ionic and electronic conductivity (MIEC) property is identified in orthorhombic SSM. In addition, the strong covalent bonding between [Formula: see text]-p and [Formula: see text]-s orbitals of orthorhombic SSM is identified from the PDOS plot. The strong covalent bonding enhances the [Formula: see text] molecular adsorption on Mn atom. On the other hand, monoclinic SSM shows the pure conducting behavior and there is no covalent bonding between Mn and O atoms. Thus, the results suggest that the half-metal Sm[Formula: see text]Sr[Formula: see text]MnO3 might be a suitable cathode material for intermediate-temperature solid oxide fuel cells.

MECHANICAL PROPERTIES ENHANCEMENT OF BORON CARBIDE BASED ARMOUR MATERIALS

<p>Lightweight armor materials made from ceramics have become a great interest in the past decades. There have been many research efforts to develop the high-performance ceramics for this particular application. Boron carbide (B₄C) is one of the promised candidates due to its extraordinary hardness, wear resistance, chemical inertness, ultra-lightweight, and its high resistance to radiation. However, the strong covalent bonding nature of B₄C makes it hard to be sintered. Sintering at high temperatures and the presence of impurities can also result in grain coarsening. One of the methods being used to overcome the problems is to introduce Boron (B) as a sintering aid into raw materials of B₄C. To evaluate the effects of B addition on the sinterability of B₄C, B₄C powders were ball-milled with B powders in different ratios and the mixtures of B₄C and B were processed by spark plasma sintering technique. Density and toughness of the as-sintered materials were increased along with increasing B content in the range from 1 wt% to 7 wt% while hardness and strength of the samples were also increased when the percentage of B addition is up to 5 wt%.</p>

Efficient Cu catalyst for 5-hydroxymethylfurfural hydrogenolysis by forming Cu–O–Si bonds

Strong covalent bonding (Cu–O–Si) modulates the Cu status and boosts the C–O hydrogenolysis.

Use of CaO Loaded Mesoporous Alumina for Defluoridation of Potable Groundwater Containing Elevated Calcium Levels

Defluoridation in the presence of high calcium levels in potable groundwater is paramount, as the consumption of groundwater enriched with fluoride, and calcium has been implicated in causing chronic kidney disease of unknown etiology (CKDu) in Sri Lanka. CaO loaded mesoporous alumina (COMA) offers a great potential for defluoridation of potable water, but the effectiveness of COMA in the presence of calcium has not been investigated. This study, therefore, focuses on the investigation of the suitability of COMA for the defluoridation of potable water with high calcium levels. Mesoporous alumina was successfully functionalized with CaO to synthesize nano-level COMA with an optimum dosage for defluoridation being 2 g L−1. The amount of fluoride adsorbed increased (2.4–19.5 mg g−1) with the increase of the initial fluoride concentration (5–40 mg L−1), and the residual fluoride levels (0.8–1.47 mg L−1) were within the range specified by the WHO for drinking water. The amount of fluoride adsorbed by COMA varied between 6.50 and 7.97 mg g−1 with initial calcium levels between 0 and 1500 mg L−1, indicating that defluoridation was effective in the presence of high calcium levels. The fluoride adsorption was best fitted with the Langmuir model with a maximum monolayer capacity of COMA being 17.83 mg g−1, and adsorption kinetics fitted with the pseudo-2nd order model indicating strong covalent bonding by way of chemisorption. Thus, COMA can be effectively utilized as an adsorbent material in defluoridation efforts in areas prevalent with CKDu in the presence of high fluoride (15 mg L−1) and calcium (1500 mg L−1) levels.

Fabric Phase Sorptive Extraction: Current State of the Art and Future Perspectives

Fabric phase sorptive extraction (FPSE) is a novel and green sample preparation technique introduced in 2014. FPSE utilizes a natural or synthetic permeable and flexible fabric substrate chemically coated with a sol-gel organic-inorganic hybrid sorbent in the form of ultra-thin coating, which leads to a fast and sensitive micro-extraction device. The flexible FPSE requires no modification of samples and allows direct extraction of analytes. Sol-gel sorbent-coated FPSE media possesses high chemical, solvent, and thermal stability due to the strong covalent bonding between the substrate and the sol-gel sorbent. Therefore, any elution solvent can be used in a small volume, which achieves a high pre-concentration factor without requiring any solvent evaporation and sample reconstitution step. Taking into consideration the complexity of the samples and the need of further minimization and automation, some new, alternative modes of the FPSE have also been developed. Therefore, FPSE has attracted the interest of the scientific community that deals with sample pre-treatment and has been successfully applied for the extraction and determination of many analytes in environmental samples as well as in food and biological samples. The objective of the current review is to present and classify the applications of FPSE according to different sample categories and to briefly show the progress, advantages, and the main principles of the proposed technique.

Rare earth-rich cadmium compounds RE10TCd3 (RE=Y, Tb, Dy, Ho, Er, Tm, Lu; T=Rh, Pd, Ir, Pt) with an ordered Co2Al5-type structure

Eighteen new rare earth-rich intermetallic phasesRE10TCd3(RE=Y, Tb, Dy, Ho, Er, Tm, Lu;T=Rh, Pd, Ir, Pt) were obtained by induction melting of the elements in sealed niobium ampoules followed by annealing in muffle furnaces. All samples were characterized by X-ray powder diffraction. The structures of four representatives were refined from single-crystal X-ray diffractometer data: ordered Co2Al5type,P63/mmc,a=951.2(1),c=962.9(2) pm,wR=0.0460, 595F2values, 20 parameters for Er10RhCd3;a=945.17(4),c=943.33(4),wR=0.0395, 582F2values, 21 parameters for Lu9.89PdCd3.11;a=964.16(6),c=974.93(6) pm,wR=0.0463, 614F2values, 21 parameters for Y10Ir1.09Cd2.91;a=955.33(3),c=974.56(3) pm,wR=0.0508, 607F2values, 22 refined parameters for Dy9.92IrCd3.08. Refinements of the occupancy parameters revealed small homogeneity ranges resulting fromRE/Cd, respectivelyT/Cd mixing. The basic building units of theRE10TCd3phases are transition metal-centeredRE6trigonal prisms (TP) that are condensed with double-pairs of emptyRE6octahedra via common triangular faces. A second type of rods is formed by slightly distortedRE3@Cd6RE6icosahedra which are condensed via Cd3triangular faces. The shortest interatomic distances occur forRE–T, compatible with strong covalent bonding interactions. Temperature dependent magnetic susceptibility measurements were performed forRE10RhCd3(RE=Dy–Tm, Lu),RE10IrCd3(RE=Er, Tm, Lu) andRE10PtCd3(RE=Y, Lu). While Y10PtCd3and Lu10TCd3(T=Rh, Ir, Pt) show Pauli paramagnetic behavior, the compounds containing paramagnetic rare earth elements show Curie-Weiss behavior (the experimental magnetic moments indicate stable trivalentRE3+) and magnetic ordering at low temperatures:TC=80.5 K for Dy10RhCd3and Neél temperatures of 42.1, 23.3, 12.6, 5.9, 10.0 K for Ho10RhCd3, Er10RhCd3, Er10IrCd3, Tm10RhCd3, Tm10IrCd3, respectively.

First-principles Study of Vickers Hardness and Thermodynamic Properties of Ti3SnC2 Polymorphs

We have investigated Vickers hardness and the thermodynamic properties of the recently discovered nanolaminate carbide Ti3SnC2 polymorphs using the first-principles calculations. The chemical bonding shows a combination of covalent, ionic and metallic types. The strong covalent bonding is mainly responsible for high Vickers hardness of Ti3SnC2 polymorphs. Thermodynamic properties are studied using the quasi-harmonic Debye model. The variation of bulk modulus, thermal expansion coefficient, specific heats, and Debye temperature with applied pressure (P) and temperature (T) are investigated systematically within the ranges of 0 - 50 GPa and 0 - 1000 K. The calculated results have been compared with available experimental and theoretical data.

Intrinsic Brittlement of Mo3Si by First-Principle Calculations

First-principles method has been used to study the intrinsic brittlement of Mo3Si. The crystal constants, formation energy, cohesive energy, electronic structure, elastic constants of Mo3Si were calculated. The results were in good agreement with experiment data. Electronic structures showed that the strong covalent bonding between the nearest neighbour Mo atoms, which arrange perpendicularly each other, leads to embrittlement of Mo3Si.