Hydrothermal gasification of Rosa Damascena residues: Gaseous and aqueous yields

The gasification of Rosa Damascena residues – by-products of the rose-oil industry – was investigated under hydrothermal conditions at 500 °C and 600 °C, 35–45 MPa pressure with a reaction time of 1 h. The experiments were performed in the absence and presence of catalysts of K₂CO₃ and trona in a batch type reactor. The composition of the gaseous and aqueous products was determined by gas chromatography and high performance liquid chromatography, respectively. H₂, CO₂ and CH₄ are the main gaseous products while carboxylic acids (formic acid, acetic acid, glycolic acid) are the main components found in the aqueous phase followed by furfurals, phenols, aldehyde and ketones. More gaseous products were obtained at the higher temperature of 600 °C. Adding catalyst was found to aid the conversion process but the effect was only slight. Rosa Damascena residues have the potential to be a useful source for H₂ production in the future.     

Antimicrobial activity of n-butyl lactate obtained via enzymatic esterification of lactic acid with n-butanol in supercritical trifluoromethane

The lipase-catalyzed synthesis of n-butyl lactate by esterification was performed in supercritical trifluoromethane. Immobilized lipase B from Candida antarctica (Novozym 435) was used as a biocatalyst. Process conditions (pressure and temperature) were optimized performing experiments in a high-pressure batch stirred-tank reactor. Experiments were carried out in the operative pressure ranges from 7.5 to 30 MPa and at temperatures 35 °C and 55 °C. For this purpose phase behavior for d,l-lactic acid/n-butanol/Novozym 435/supercritical fluid system at temperature 55 °C and different pressures was studied. The highest conversion of lactic acid after 26 h of reaction performance was obtained in supercritical trifluoromethane at 30 MPa and 55 °C.The n-butyl lactate (standard and enzymatically synthesized) and d,l-lactic acid were tested against four food-borne fungi: Saccharomyces cerevisiae, Aspergillus niger, Trichoderma viride and Penicillium cyclopium and three health-damaging bacteria: Escherichia coli, Pseudomonas fluorescens and Bacillus cereus by the agar well diffusion.     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

Creep behavior of a zirconium diboride–silicon carbide composite

Flexural creep studies of ZrB₂–20 vol% SiC ultra-high temperature ceramic were conducted over the range of 1400–1820 °C in an argon shielded testing apparatus. A two decade increase in creep rate, between 1500 and 1600 °C, suggests a clear transition between two distinct creep mechanisms. Low temperature deformation (1400–1500 °C) is dominated by ZrB₂ grain or ZrB₂–SiC interphase boundary and ZrB₂ lattice diffusion having an activation energy of 364 ± 93 kJ/mol and a stress exponent of unity. At high temperatures (>1600 °C) the rate-controlling processes include ZrB₂–ZrB₂ and/or ZrB₂–SiC boundary sliding with an activation energy of 639 ± 1 kJ/mol and stress exponents of 1.7 < n < 2.2. In addition, cavitation is found in all specimens above 1600 °C where strain-rate contributions agree with a stress exponent of n = 2.2. Microstructure observations show cavitation may partially accommodate grain boundary sliding, but of most significance, we find evidence of approximately 5% contribution to the accumulated creep strain.     

The effect of silica doping on neodymium diffusion in yttrium aluminum garnet ceramics: implications for sintering mechanisms

The Nd³⁺ cation diffusion into transparent polycrystalline YAG (Y₃Al₅O₁₂) was investigated as a function of temperature and silica content. Thin neodymium oxide layers were deposited on sintered YAG substrates prior to annealing under air at temperatures from 1400 to 1600 °C. Bulk and grain boundary neodymium diffusion coefficients were measured by secondary ion mass spectrometry. The experimental results show that silica addition increases the diffusivity of Nd³⁺ by a factor 10 whatever the diffusion path, probably as a result of extrinsic point defects formation, especially rare-earth vacancies.The experimental diffusion data were used to elucidate the sintering mechanism of Nd:YAG ceramics in the temperature range 1450–1550 °C. Firstly, it appeared that the intermediate stage of solid-state sintering should be controlled by the rare-earth diffusion along the grain boundary with an activation energy of about 600 kJ mol^?1. Secondly, grain growth mechanism at the final stage of liquid-phase sintering was investigated for silica-doped Nd:YAG samples. Thus, the grain growth should be limited by the reaction at interfaces at a temperature lower than 1500 °C, with an activation energy of about 880 kJ mol^?1. At higher temperature, it seems to be limited by the ionic diffusion through the intergranular liquid phase, with an activation energy of 250 kJ mol^?1.     

Structure and thermal expansion of (Crx,V1−x)n+1AlCn phases measured by X-ray diffraction

MAX phases in the (Cr_x,V_1−x)_n+1AlC_n system were synthesized by reactive sintering or hot isostatic pressing of elemental powders at temperatures between 1400 °C and 1600 °C. For n = 1, a complete range (0 ≤ x ≤ 1) of solid solutions was found; for n = 2 and 3 the solubility ranges were 0.25 ≤ x ≤ 0.75 and 0 ≤ x ≤ 0.5, respectively. Powder X-ray diffraction revealed that the lattice parameters of all (Cr_x,V_1−x)_n+1AlC_n solid solutions followed Vegard’s law. The thermal expansion coefficients of the various compounds were determined from Rietveld refinements of X-Ray patterns obtained at temperatures between ambient and 800 °C. For the n = 1 and 3 phases the thermal expansion coefficients were almost isotropic; those for the n = 2, however, were quite anisotropic with the expansion along the a-axis being significantly larger than along the c-axis. As a general trend, vanadium rich compounds have smaller thermal expansion coefficients than their Cr-rich counterparts.     

Linear thermal expansion coefficients of relaxor-ferroelectric 0.57Pb(Sc1/2Nb1/2)O3–0.43PbTiO3 ceramics in a wide temperature range

The objective of this work was to examine linear thermal expansion of virgin and poled 0.57Pb(Sc_1/2Nb_1/2)O₃–0.43PbTiO₃ ceramics between 30 °C and 600 °C by contact dilatometry. The thermal expansion dL/Lo of the virgin ceramic increases with increasing temperature until approximately 260 °C. The physical and technical thermal expansion coefficients were determined. At 260 °C the physical thermal coefficient is 2.08 × 10^?6 K^?1. Between 260.0 °C and 280.0 °C an anomaly in the thermal expansion vs. temperature and an endothermic peak in the differential scanning calorimetry curves correspond to the phase transition region from tetragonal to cubic phase. At temperatures from 280 °C to 600 °C the thermal expansion dL/Lo increases again.In the derivative of the dL/Lo heating curves of the poled ceramics, additionally to the anomaly at 270 °C, also the anomaly at 160 °C is observed, which is associated with the depolarization of the material during heating.     

Spark plasma sintering behavior of combustion-synthesized (Y,Ca)-α-SiAlON

This paper describes the sintering behavior of combustion-synthesized (Y, Ca)-α-SiAlON powders when using spark plasma sintering (SPS) technology. The effects of sintering temperature, heating rate, and holding time on the densification behavior, α→β phase transformation, and Vickers hardness were investigated in detail. Fully dense Y-α-Si_12−(m+n)Al_m+nO_nN_16−n (m=1.2, n=0.6, Y-α-SiAlON) and Ca-α-Si_12−(m+n)Al_m+nO_nN_16−n (m=1.0, n=0.5, Ca-α-SiAlON) were obtained during sintering for 10 min at final temperatures as low as 1400 °C and 1500 °C, respectively. X-ray diffraction results showed that more than 50 mass% of α-phase transformed to the β-phase for Y-α-SiAlON after SPS, whereas no obvious α→β phase transformation was observed for Ca-α-SiAlON, even after sintering at a high temperature of 1600 °C. A maximum Vickers hardness of 18.56 GPa and 19.95 GPa was reached for Y-α-SiAlON and Ca-α-SiAlON, respectively.     

Diffusion coefficients of C18 unsaturated fatty acid methyl esters in supercritical carbon dioxide containing 10% mole fraction ethanol as modifier

To determine the molecular diffusion coefficients of C18 unsaturated fatty acid methyl esters in supercritical carbon dioxide (scCO₂) containing 10 mol% ethanol as a modifier, four methyl esters of C18 fatty acids, i.e., methyl oleate, methyl ricinoleate, methyl linoleate and methyl linolenate were selected as the typical solutes. The diffusion coefficients were measured at temperatures from 313.15 to 333.15 K and pressures from 15 to 27 MPa using the Taylor–Aris chromatographic peak broadening (CPB) technique. The influences of temperature, pressure, density and viscosity of the solvent mixture on the diffusion coefficients were examined. The results show that methyl oleate always diffuses faster than methyl ricinoleate at the same operating condition. Moreover, the D₁₂ values in ethanol-modified scCO₂ decrease with the increase of the number of C-C double bonds in C18-methyl ester, which is consistent with the trend reported in pure scCO₂. The diffusivity data are compared with the estimation of eleven predictive models. The modified Wilke–Chang equation is the best purely predictive model and the free volume model of Dymond with two adjustable parameter gives the least errors with average absolute deviations lower than 2.5%.     

Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films

We modified the refractive index (n) of TiO₂ by annealing at various temperatures to obtain a high figure of merit (FOM) for TiO₂/Ag/TiO₂ (45 nm/17 nm/45 nm) multilayer films deposited on glass substrates. Unlike the as-deposited and 300 °C-annealed TiO₂ films, the 600 °C-annealed sample was crystallized in the anatase phase. The as-deposited TiO₂/Ag/as-deposited TiO₂ multilayer film exhibited a transmittance of 94.6% at 550 nm, whereas that of the as-deposited TiO₂/Ag/600 °C-annealed TiO₂ (lower) multilayer film was 96.6%. At 550 nm, n increased from 2.293 to 2.336 with increasing temperature. The carrier concentration, mobility, and sheet resistance varied with increasing annealing temperature. The samples exhibited smooth surfaces with a root-mean-square roughness of 0.37–1.09 nm. The 600 °C-annealed multilayer yielded the highest Haacke's FOM of 193.9×10⁻³ Ω⁻¹.     

Low-temperature microwave and THz dielectric response in novel microwave ceramics

Low-temperature dielectric properties of BaZn_1/3Nb_2/3O₃-based ceramics, CeO₂-based ceramics and Ruddlesden–Popper Sr_n+1Ti_nO_3n+1 (n = 1–4) ceramics has been studied in microwave, THz and infrared frequency range down to 10 K. Extrinsic dielectric losses originating probably from diffusion of charged defects are observed in two families of compounds by a minimum in the temperature dependence of microwave quality Q. The rise of microwave permittivity and dielectric losses at low temperatures in Sr_n+1Ti_nO_3n+1 (n = 2–4) ceramics was explained by softening of an optical polar mode in SrTiO₃, which is in the Sr_n+1Ti_nO_3n+1 (n = 3, 4) ceramics contained as a second phase.     

Densification of nanocrystalline Y2O3 ceramic powder by spark plasma sintering

Nanocrystalline Y₂O₃ powders with 18 nm crystallite size were sintered using spark plasma sintering (SPS) at different conditions between 1100 and 1600 °C. Dense specimens were fabricated at 100 MPa and 1400 °C for 5 min duration. A maximum in density was observed at 1400 °C. The grain size continuously increased with the SPS temperature into the micrometer size range. The maximum in density arises from competition between densification and grain growth. Retarded densification above 1400 °C is associated with enhanced grain growth that resulted in residual pores within the grains. Analysis of the grain growth kinetics resulted in activation energy of 150 kJ mol^?1 and associated diffusion coefficients higher by 10³ than expected for Y³⁺ grain boundary diffusion. The enhanced diffusion may be explained by combined surface diffusion and particle coarsening during the heating up with grain boundary diffusion at the SPS temperature.     

Piezoresistivity of n-type conductive ultrananocrystalline diamond

Recent developments of a piezoresistive sensor prototype based on n-type conductive ultrananocrystalline diamond (UNCD) are presented. Samples were deposited using hot filament chemical vapor deposition (HFCVD) technique, with a gas mixture of H₂, CH₄ and NH₃, and were structured using multiple photolithographic and etching processes. Under controlled deposition parameters, UNCD thin films with n-type electrical conductivity at room temperature (5 × 10^− 3 – 5 × 10¹ S/cm) could be grown. Respective piezoresistive response of such films was analyzed and the gauge factor was evaluated in both transverse and longitudinal arrangements, also as a function of temperature from 25 °C up to 300 °C. Moreover, the gauge factor of piezoresistors with various sheet resistance values and test structure geometries was evaluated. The highest measured gauge factor was 9.54 ± 0.32 at room temperature for a longitudinally arranged piezoresistor with a sheet resistance of about 30 kΩ/square. This gauge factor is well comparable to that of p-type boron doped diamond; however, with a much better temperature independency at elevated temperatures compared to the boron-doped diamond and silicon. To our best knowledge, this is the first report on piezoresistive characteristics of n-type UNCD films.     

The influence of crosslinking and fumed silica nanoparticles on mixed gas transport properties of poly[1-(trimethylsilyl)-1-propyne]

Crosslinking poly[1-(trimethylsilyl)-1-propyne] (PTMSP) films with 3,3′-diazidodiphenylsulfone, a bis(azide) crosslinker, rendered the films insoluble in common solvents for PTMSP such as toluene. At all temperatures, mixed gas CH₄ and n-C₄H₁₀ permeabilities of crosslinked PTMSP were less than those of uncrosslinked PTMSP, which correlates with lower free volume in the crosslinked material. The presence of fumed silica (FS) nanoparticles in both uncrosslinked PTMSP and crosslinked PTMSP increased mixed gas CH₄ and n-C₄H₁₀ permeabilities, consistent with the disruption of polymer chain packing by such nanoparticles. Mixed gas CH₄ permeabilities of all films were significantly less than their corresponding pure gas CH₄ permeabilities. For example, at 35 °C, the mixed gas CH₄ permeabilities were approximately 60–80% less than their pure gas values. The greatest decrease was observed for uncrosslinked PTMSP, while nanocomposite PTMSP films showed the least decrease. The mixed gas n-C₄H₁₀/CH₄ selectivities of crosslinked PTMSP and nanocomposite PTMSP films were less than those of uncrosslinked PTMSP at all temperatures. For example, at 35 °C, the mixed gas n-C₄H₁₀/CH₄ selectivities of uncrosslinked PTMSP, crosslinked PTMSP containing 10 wt% crosslinker, and uncrosslinked PTMSP containing 30 wt% FS were 33, 27, and 17, respectively, when the feed gas contained 2 mol% n-C₄H₁₀ and the total upstream mixture fugacity was 11 atm. For all films, as temperature decreased, mixed gas n-C₄H₁₀ permeabilities increased, and mixed gas CH₄ permeabilities decreased. Consequently, the mixed gas n-C₄H₁₀/CH₄ selectivities increased substantially as temperature decreased and the mixed gas selectivity of uncrosslinked PTMSP increased from 33 to 170 as temperature decreased from 35 °C to ?20 °C when the feed gas contained 2 mol% n-C₄H₁₀ and the total upstream mixture fugacity was 11 atm.     

Oxidation behavior of electrically conductive α/β SiAlON composites with segregated network of TiCN

The oxidation behavior of novel electrically conductive α/β SiAlON composites with a continuous network of 2.5–10 vol% TiCN particulates was investigated. Composites, produced by coating spray dried granules with nano TiCN particles by a simple blending method, were gas pressure sintered at 1990 °C for 1 h under 10 MPa N₂ pressure. Oxidation tests were carried out between 800 °C and 1200 °C in air for 2 and 48 h in atmosphere of dry air. Below 1000 °C, the formation of TiO₂ crystals on the surfaces of TiCN particles was observed. Before the glass transition temperature of intergranular phase (T_g < 1000 °C), it was revealed that oxidation is controlled by the diffusion of oxygen into pre-formed TiO₂ particles. Above T_g, liquid glass dissolves the intergranular phase elements such as Ti, Y, and Si at the interface between TiCN and SiAlON particles. Migration of Ti towards the (opening point of the TiCN network) surface was found to be the main reason for the formation of subsurface porosity that slows down Ti diffusion through the surface. Moreover, it was detected that at high temperatures surface porosity filled by the intergranular glassy phase. Consequently, the oxidation rate was found to be decreased due to the slower oxygen diffusion.     

X-ray single phase LSGM at 1350 °C

Synthesis of X-ray-phase-pure (La_1−xSr_xGa_1−yMg_yO_3−δ, LSGM, where x = 0.1, y = 0.15 and 0.17) powders were achieved at temperatures as low as 1350 °C via organic precursor method using tartaric acid as the carrier material. LSGM materials were characterized for their phase purity, crystallization and electrical properties. Pellets sintered at 1350 °C for 6 h were single phase and dense (>99%). Electron microscopy analysis of X-ray single-phase pellets revealed MgO precipitates with sizes ranging from 50–300 nm. Phase formation and distribution in this complicated multi-cation-oxide system as a function of temperature were reported and discussed. Amorphous LSGM first crystallizes at 625 °C. However, elimination of undesired phases require higher temperatures. Impedance measurements as a function of temperature up to 545 °C revealed that the X-ray phase pure pellets may have extrapolated ionic conductivity values as high as 0.14–0.16 S/cm at 800 °C. Possible implications of limited MgO solubility on the ionic conductivity are presented.     

Outstanding efficiency of indium in bimetallic catalysts for hydroconversion of bioacids to bioalcohols

Step by step reduction of acetic acid (AA) to ethanol was investigated over novel bimetallic catalysts (PtIn/Al₂O₃) for the processing of VFAs (volatile fatty acids) that can be produced simply by thermochemical or biological biomass degradation. A fixed bed flow-through reactor was applied with hydrogen stream at 21 bar total pressure in the temperature range of 220–380 °C. AA hydroconversion activity of the parent alumina supported Pt catalyst and the yield of selectively produced alcohol can be increased drastically by In₂O₃ addition. Appearance of metallic indium creating a bimetallic catalyst can direct the consecutive catalytic reduction to ethanol formation inhibiting hydrodecarbonylation. Comparing the In-containing bimetallic catalysts studied recently, NiIn-catalyst showing similar activity to that of the PtIn-catalyst can be a cheap substitute for the expensive Pt catalysts in the reduction carboxylic acids.     

Microstructure evolution and cation interdiffusion in thin Gd2O3 films on CeO2 substrates

Thin Gd₂O₃ films with a thickness of about 150 nm were deposited by pulsed layer deposition on polycrystalline CeO₂ substrates to study the structural evolution of the Ce_1−xGd_xO_2−x/2 system with respect to phase formation and cation interdiffusion in the temperature range between 986 °C and 1270 °C. Transmission electron microscopy combined with quantitative energy dispersive X-ray spectroscopy was applied to study the microstructure and to obtain composition profiles across the Gd₂O₃/CeO₂-interface. Gd₂O₃ was observed to occur in the bixbyite structure up to 1175 °C. The fluorite and the bixbyite phase are found at intermediate compositions without any indication for a miscibility gap. Interdiffusion coefficients were obtained from Gd₂O₃/CeO₂-concentration profiles on the basis of the diffusion-couple solution of the diffusion equation. The activation enthalpy and frequency factor of the diffusion coefficient were derived assuming an Arrhenius-type behavior in the investigated temperature range.     

Plastic deformation of dense nanocrystalline yttrium oxide at elevated temperatures

Nanocrystalline yttrium oxide, Y₂O₃ with 110 nm average grain size was plastically deformed between 800 °C and 1100 °C by compression at different strain rates and by creep at different stresses. The onset temperature for plasticity was at 1000 °C. Yield stress was strongly temperature dependent and the strain hardening disappeared at 1100 °C. The polyhedral and equiaxed grain morphology were preserved in the deformed specimens. The experimentally measured and theoretically calculated stress exponent n = 2 was consistent with the plastic deformation by grain boundary sliding. Decrease in the grain size was consistent with decrease in the brittle to ductile transition temperature.     

Oxidation reaction of high molecular weight dicarboxylic acids in sub- and supercritical water

Sebacic and azelaic acids, which are representative of high molecular weight dicarboxylic acids, were oxidized in a batch reactor with H₂O₂ oxidant in water from 300 °C to 400 °C at sub- and supercritical conditions. Intermediate products were identified based on GC–MS, HPLC, and ¹H NMR. The main oxidation products were dicarboxylic acids and the minor products were monocarboxylic acids. (ω − 1)-Keto acids, aldehyde-acids, and γ-lactones with carboxylic groups also were identified.On the basis of the products identified, the oxidation pathways of high molecular weight dicarboxylic acids were formulated. The oxidation of high molecular weight dicarboxylic acids proceed with the consecutive oxidation of higher to lower molecular weight dicarboxylic acids mainly through the oxidation at α-, β-, and γ-carbons to a –COOH group. The oxidation of dicarboxylic acids was also accompanied by oxidative decarboxylation, leading to the formation of monocarboxylic acids.