Bulk p-CuInSe2 photo-electrochemical solar cells

Dense CuInSe₂ of high quality, prepared by the fusion technique in evacuated quartz ampoule from stoichiometric melt, crystallizes in the chalcopyrite structure. Compositional analysis carried out by secondary ion mass spectrometry (SIMS) and energy dispersive spectroscopy (EDS) indicates a uniform distribution of elements through the depth and a composition close to the stoichiometry. The diffuse reflectance spectrum gives a band gap at 0.94 eV. The electrical conductivity follows an Arrhenius-type law with activation energy of 23 meV in conformity with polarons hopping. Above 320 °C, CuInSe₂ undergoes an irreversible oxidation. The thermal variation of the thermopower indicates p-type behavior attributed to copper deficiency and a hole mobility μ_300 K of 0.133 cm² V⁻¹ s⁻¹, thermally activated. In KCl media, the compound exhibits an excellent chemical stability with a corrosion rate of 8 μmol cm⁻² month⁻¹. The photo-electrochemical properties, investigated for the first time on the ingots, confirm the p-type conductivity. From the capacitance measurements, the flat band potential (V_fb=−0.62V_SCE) and the holes density (N_A=4×10¹⁷ cm⁻³) were determined. The valence band, located at 4.43 eV below vacuum, is made up of mainly Se orbital with little admixture of Cu character. The change of the electrolyte causes a variation in the potential V_fb (dV_fb/dpH=−0.058 V pH⁻¹) indicating strong OH⁻ adsorption. The fill factor in S²⁻ media was found to be 0.54; such result was corroborated by semi-logarithmic plots.     

Factors Controlling Properties of Ca‐Mg,Ca‐Er,Ca‐Nd,or Ca‐Y‐Modified Aluminosilicate Glasses Containing Nitrogen and Fluorine

Glasses with composition (in eq.%) (30 ? x)Ca:xM:55Si:15Al:80O:15N:5F have been prepared with different levels of substitution of Ca²⁺ cations by Mg²⁺, Y³⁺, Er³⁺, or Nd³⁺. The properties of these glasses are examined in detail and changes observed in molar volume (MV), free volume, fractional glass compactness, Young's modulus, microhardness, glass transition temperature, and thermal expansion as a function of M content are presented. Using linear regression analysis, evidence is presented which clearly shows that these glass properties are either solely dependent on the effective cation field strength, if modifier cation valency is the same (e.g., Mg substitution for Ca), or dependent on the effective cation field strength and the number of (Si, Al) (O, N, F) tetrahedra associated with each modifier when Ca is replaced by the trivalent modifiers. Combining these correlations with those observed previously relating glass properties to N and F substitution for O, it becomes apparent that glass properties for Ca–M–Si–Al–O–N–F glasses can be described by correlations which involve independent, but additive contributions by N and F substitution levels, effective cation field strength, and the number of tetrahedra associated with each modifier ion.     

Performance of microtubular SOFCs with infiltrated electrodes under thermal cycling

In this research, tubes consisting of a co-extruded dense YSZ electrolyte (∼10 μm) and porous NiO–YSZ anode (∼200 μm) were modified with different cathodes and anode infiltration to investigate the effects on both power and thermal cycling tolerance. Type of cathode (produced by infiltration of LSM into a porous YSZ matrix or by hand-painting of an LSM–YSZ ink), the type of pore former used in the cathode (graphite or poly (methyl methacrylate), PMMA) and the infiltration of the anode (no infiltration, or with infiltration steps using a co-precipitated SDC (Samaria doped ceria) mixture, or Ni–SDC mixture) were investigated as variables. The overall aim of this work is to produce cells that are more tolerant to thermal cycling, without sacrificing power density.     

Thermal conductivity of limestone from Gaziantep (Turkey)

In this study, thermal conductivity (TC) of limestone from Gaziantep, Turkey, was investigated. The limestone samples were collected from different parts of the city representing Gaziantep and F?rat formation which are clay and chalky limestone. TC of the samples was measured for saturated, partially saturated and dried conditions. Water absorption, dry unit weight and apparent porosity of the samples were also measured to correlate with TC. Measurements showed that TC was increased with increasing the water content of samples. The TC of the samples decreased while the porosity increased. Relationships between TC and both dry unit weight and porosity were driven. There was a very good exponential relationship between TC and saturation degrees of sample, porosity and density. Moisture content increased TC up to 113%.     

Evaluation and characterization of nanostructure hydroxyapatite powder prepared by simple sol-gel method

Many attempts have been focused on preparing of synthetic hydroxyapatite (HA), which closely resembles bone apatite and exhibits excellent osteoconductivity. Low temperature formation and fusion of the apatite crystals have been the main contributions of the sol-gel process in comparison with conventional methods for HA powder synthesis. This paper describes the synthesis of nano-HA particles via a sol-gel method. Nanocrystalline powder of hydroxyapatite (HA) was prepared using Ca(NO₃)₂·4H₂O and P₂O₅ by a simple sol-gel approach. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for characterization and evaluation of the phase composition, morphology and particle size of products. The presence of amorphous and crystalline phases in the as-dried gel precursor was confirmed by the evaluating technique. Single phase of HA was also identified in the heat treated powder by XRD patterns. SEM and TEM evaluations showed that the obtained powder after heat treatment at 600 °C was agglomerated and composed of nanocrystalline (25-28 nm) HA particles. Increasing the sintering temperature and time could cause decomposition of HA into β-tricalcium phosphate and calcium oxide. The prepared nanocrystalline HA is able to improve the contact reaction and the stability at the artificial/natural bone interface for medical applications.     

Preparation and bioactivity evaluation of bone-like hydroxyapatite nanopowder

Calcium phosphate ceramic such as hydroxyapatite (HA) is good candidate for bone substitutes due to their chemical and structural similarity to bone minerals. The bone mineral consists of tiny hydroxyapatite crystals in the nanoregime. Nanostructured hydroxyapatite is also expected to have better bioactivity than coarser crystals. This paper reports on the preparation and in vitro evaluation of bone-like hydroxyapatite nanopowder. The sol–gel prepared hydroxyapatite nanopowder was characterized for its phase purity, chemical homogeneity and bioactivity. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups. X-ray diffraction (XRD) analysis was carried out to study the phase composition, crystallinity and the crystallite size of hydroxyapatite nanopowders that were sintered at different temperatures. The in vitro test was performed in a stimulated body fluid (SBF) medium. The changes of the pH of SBF medium were measured at pre-determined time intervals using a pH meter. The dissolution of calcium ions in SBF medium was determined by an atomic absorption spectrometer (AAS). FTIR result combined with the X-ray diffraction exhibited single phase of hydroxyapatite with carbonate peaks in the FTIR spectrum. The results indicate that increasing the sintering temperature increases the crystallinity and the crystallite size of hydroxyapatite nanopowders. Photomicrograph of transmission electron microscopy (TEM) showed that the obtained powder after sintering at 600 °C is composed of hydroxyapatite nanoparticles (20–30 nm). Dissolution rate of hydroxyapatite nanopowders was higher than conventional hydroxyapatite powders and closer to biological apatite due to its nanostructure dimensions. It was concluded that sol–gel prepared hydroxyapatite nanopowders had superior bioresorption and similar chemical and crystal structure to natural bone apatite.     

(Corn Starch and Montmorillonite Nanocomposite)‐Reinforced Polypropylene: Preparation,Properties, and Biodegradability

Blends of polypropylene and thermoplastic starch (TPS) containing different amounts of TPS were prepared with and without modified montmorillonite (C30B) in the presence of ethylene‐(vinyl acetate) copolymer. Mechanical properties, thermal stability, morphology, and biodegradation were investigated. The results of tensile tests showed that the tensile strength and Young's modulus increased but that elongation at break decreased in the presence of C30B. Small‐angle X‐ray scattering patterns and transmission electron microscopy confirmed that the prepared nanocomposites were exfoliated. Scanning electron microscopy (SEM) was used for the investigation of the phase morphology and particle distribution. Thermal gravimetric analysis indicated that the C30B caused an increase in thermal degradation temperature. Biodegradability tests of the specimens were conducted in a fungal culture medium. Biodegradation was assessed by SEM images, monitoring the changes in the FTIR spectra, and the weight loss of specimens after culturing. J. VINYL ADDIT. TECHNOL., 20:16–23, 2014. © 2014 Society of Plastics Engineers     

Bioactivity potential of calcium alumino-silicate glasses and glass–ceramics containing nitrogen and fluorine

Calcium alumino-silicate glasses of general composition (in eq.%) 28Ca:57Si:15Al:[100 ? (x + y)]O:xN:yF (x = 0 or 20 and y = 0, 3 or 5) and their glass–ceramic counterparts were immersed in simulated body fluid (SBF) at 37 ± 0.5 °C for 28 days to assess their potential bioactivity. The glasses showed no Ca release or surface calcium phosphate deposition due to their high network connectivities (>2.55). The glass–ceramics all showed potential bioactivity, as the SBF became enriched in Ca and calcium phosphate deposits formed on their surfaces. This was a result of Ca release from crystalline phases (predominantly wollastonite in the case of CaSiAlOF glass–ceramics and gehlenite in the case of CaSiAlONF glass–ceramics). No aluminium was leached from the glass–ceramics into the SBF, due to its pH always exceeding 7.0.     

Combined heat and mass transfer by natural convection at horizontal cylinder electrodes

Simultaneous heat and mass transfer in free convection at horizontal cylinder electrodes has been investigated experimentally using the electrochemical limiting diffusion current technique. The convective flow patterns occuring have been observed using Schlieren photography. The results confirmed the use of a combined Grashof number (GR_m) to account for thermal and concentration buoyancy effects. Various combinations of electroactive species concentration, cylinder diameter and cylinder surface temperature have been used. Results have been successfully correlated by the equations , 7×10⁷ < GR_mSc< 4×10⁹ and , 4×10⁹ mSc<10¹¹ The experiments cover the range of mass transfer and heat transfer Grashof numbers 3.64×10⁴ m <3.02×10⁶, 5.67×10⁴ h <6.55×10⁶