New synthesis route of highly porous InxCo4Sb12 with strongly reduced thermal conductivity

Highly porous, In filled CoSb3 skutterudite materials with an attractive thermoelectric figure of merit ZT 1 and corresponding dense samples were fabricated through the cost effective method of reduction in oxides in dry hydrogen and the pulsed electric current sintering PECS method, respectively. The reduction process was described in detail using in situ thermogravimetric analysis of Co2O3, Sb2O3 and In NO3 3.5H2O separately and in a mixture. Two methods to synthesise the same material were examined a free sintering of an initially reduced powder and b PECS. The free sintered materials with higher porosities up to 40 exhibited lower values of electrical conductivity than the dense PECS samples porosity up to 5 , but the benefit of an even sixfold reduction in thermal conductivity resulted in higher ZT values. The theoretical values of thermal conductivity for various effective media models considering randomly oriented spheroid pores are in good agreement with the experimental thermal conductivity data. The assumed distribution and shape of the pores correlated well with the scanning electron microscope analysis of the microstructure. The lowest value of thermal conductivity, equal to 0.5 W m K, was measured at 523 K for In0.1Co4Sb12 with 41 porosity. The highest value of ZTmax 1.0 at 673 K was found for the In0.2Co4Sb12 sample in which the porosity was 3

Application of Artificial Neural Networks to Predict Insulation Properties of Lightweight Concrete

Predicting the properties of concrete before its design and application process allows for refining and optimizing its composition. However, the properties of lightweight concrete are much harder to predict than those of normal weight concrete, especially if the forecast concerns the insulating properties of concrete with artificial lightweight aggregate (LWA). It is possible to use porous aggregates and precisely modify the composition of lightweight concrete (LWC) with specific insulating properties. In this case, it is advisable to determine the parameters of the components and perform preliminary laboratory tests, and then use theoretical methods (e.g., artificial neural networks (ANNs) to predict not only the mechanical properties of lightweight concrete, but also its thermal insulation properties. Fifteen types of lightweight concrete, differing in light filler, were tested. Lightweight aggregates with different grain diameters and lightweight aggregate grains with different porosity were used. For the tests, expanded glass was applied as a filler with very good thermal insulation properties and granulated sintered fly ash, characterized by a relatively low density and high crushing strength in the group of LWAs. The aim of the work is to demonstrate the usefulness of an ANN for the determination of the relationship between the selection of the type and quantity of LWA and porosity, density, compressive strength, and thermal conductivity (TC) of the LWC

Properties of oxygen vacancy and hydrogen interstitial defects in strontium titanate: DFT + Ud,p calculations

This work presents extensive theoretical studies focused on the mixed ion-electron transport in cubic strontium titanate (STO). A new approach to the description of this difficult system was developed within the framework of linear-scaling Kohn-Sham density functional theory, as realized in the ONETEP program. The description we present is free of any empirical parameters and relies on the Hubbard U and Hund's J corrections applied to both Ti and O atoms. The proposed methodology was validated by considering perfect STO. Its calculated properties were found to be in close agreement with experiments and calculations at higher levels of theory. The validated approach was subsequently employed to study the oxygen vacancy (VO) and the hydrogen interstitial (IH), using very large supercells (625 ± 1 atoms). The relaxed configurations of defects were obtained through fastidious energy minimization and later analyzed from a number of perspectives. The calculated defect formation energies and charge transition levels (CTLs) were found to be in close agreement with the experiment. With the exception of the charge-neutral VO, all considered defects were found to introduce shallow states, located down to 0.2 eV below the conduction band. Our calculations revealed a large 1 eV difference in the thermodynamic and optical CTLs of the neutral VO, explaining the inconsistencies observed-till now-between conduction and spectroscopic measurements. The influence of defects on the bonding characteristics and the crystalline structure of STO was quantified, revealing that both VOand IHdefects lead to a significant polarization and strong tilting of the TiO6octahedra.</p

Changes on the Surface of the SiO2/C Composite, Leading to the Formation of Conductive Carbon Structures with Complex Nature of DC Conductivity

Sol–gel layers have been the subject of many studies in recent decades. However, very little information exists about layers in which carbon structures are developed in situ. Using the spin-coating method, we obtained thin iron-doped SiO2/C composite films. The results of Raman spectroscopy showed that our samples consisted of graphitic forms and polymers. The latter’s contribution decreases with rising temperature. FTIR and EDS studies show changes in carbon distribution on top of the layer, depending on the sintering temperature. The samples sintered at 800 °C showed a significant increase in the contribution of carbon forms to the layer’s surface. Therefore, high conductivity can be observed in this sample. The results of XPS spectroscopy showed that the contribution of sp3 hybridized carbon increases after etching. The total electrical conductivity, studied by a DC four-wire technique, increased with the temperature and showed almost linear characteristics with significant changes below 150 K. The reduced activation energy plot has a positive temperature coefficient, which is a characteristic property of the conductive polymers in a metallic regime of conductivity

Structural Properties and Water Uptake of SrTi1−xFexO3−x/2−δ

In this work, Fe-doped strontium titanate SrTi1&minus;xFexO3&minus;x/2&minus;&delta;, for x = 0&ndash;1 (STFx), has been fabricated and studied. The structure and microstructure analysis showed that the Fe amount in SrTi1&minus;xFexO3&minus;x/2&minus;&delta; has a great influence on the lattice parameter and microstructure, including the porosity and grain size. Oxygen nonstoichiometry studies performed by thermogravimetry at different atmospheres showed that the Fe-rich compositions (x &gt; 0.3) exhibit higher oxygen vacancies concentration of the order of magnitude 1022&ndash;1023 cm&minus;3. The proton uptake investigations have been done using thermogravimetry in wet conditions, and the results showed that the compositions with x &lt; 0.5 exhibit hydrogenation redox reactions. Proton concentration at 400 &deg;C depends on the Fe content and was estimated to be 1.0 &times; 10&minus;2 mol/mol for SrTi0.9Fe0.1O2.95 and 1.8 &times; 10&minus;5 mol/mol for SrTi0.5Fe0.5O2.75. Above 20 mol% of iron content, a significant drop of proton molar concentrations at 400 &deg;C was observed. This is related to the stronger overlapping of Fe and O orbitals after reaching the percolation level of approximately 30 mol% of the iron in SrTi1&minus;xFexO3&minus;x/2&minus;&delta;. The relation between the proton concentration and Fe dopant content has been discussed in relation to the B-site average electronegativity, oxygen nonstoichiometry, and electronic structure

Fully scalable one-pot method for the production of phosphonic graphene derivatives

Graphene oxide was functionalized with simultaneous reduction to produce phosphonated reduced graphene oxide in a novel, fully scalable, one-pot method. The phosphonic derivative of graphene was obtained through the reaction of graphene oxide with phosphorus trichloride in water. The newly synthesized reduced graphene oxide derivative was fully characterized by using spectroscopic methods along with thermal analysis. The morphology of the samples was examined by electron microscopy. The electrical studies revealed that the functionalized graphene derivative behaves in a way similar to chemically or thermally reduced graphene oxide, with an activation energy of 0.014 eV

Assessment of High-Temperature Oxidation Properties of 316L Stainless Steel Powder and Sintered Porous Supports for Potential Solid Oxide Cells Applications

In this work, the oxidation properties of austenitic 316L stainless steel powder and sintered porous support were investigated at the temperature range of ~600–750 °C for 100 hours in ambient air. Oxidation kinetics was deter-mined by continuous thermogravimetry and analyzed employing parabolic rate law. It was observed that oxidation leads to the formation of an oxide scale, with substantial oxidation occurring at ≥ 650 °C in the powder. The porous steel support was fabricated using the tape casting method with two distinct pore former concentrations. The micro-structural features of both the powder and support were investigated by X-ray diffractometry and scanning electron microscopy coupled with energy-dispersive X-ray analysis. The mechanical properties of the metal support were examined before and after oxidation via a microhardness test. The effect of porosity on the resulting properties of the metal support was also highlighted. In summary, 316L stainless steel support suits SOCs applications below 600 °C.</p

Electric and magnetic properties of Lanthanum Barium Cobaltite

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