Spark plasma sintering of silicon nitride/barium aluminum silicate composite

Si₃N₄ based composites were successfully sintered by spark plasma sintering using low cost BaCO₃, SiO₂ and Al₂O₃ as additives. Powder mixtures were sintered at 1600–1800 °C for 5 and 10 min. Displacement-temperature-time (DTT) diagrams were used to evaluate the sintering behavior. Shrinkage curve revealed that densification was performed between 1100 and 1700 °C. The specimen sintered at 1700 °C showed the maximum relative density (99.8±0.1%), flexural strength (352±16 MPa), Vickers harness (11±0.1 GPa) and toughness (5.6±0.05 MPa m^1/2).     

Cosolvent-modified supercritical carbon dioxide extraction of phenolic compounds from bamboo leaves (Sasa palmata)

This study highlights the possibility of supercritical carbon dioxide for extracting phenolic compounds from bamboo leaves that have shown antioxidant and anticancer activities. The CO₂ extraction solvent was modified by adding ethanol–water mixture cosolvent of different concentrations to allow extraction of both polar and non-polar compounds. Conventional Soxhlet extraction was also done to investigate the advantages of supercritical extraction over the conventional extraction method. For addition of 5% (mol) of a 25:75 (mol:mol) ethanol–water mixture solvent to CO₂, the highest amount of polyphenols (7.31 ± 0.06 mg/g bamboo leaves in catechin equivalents) and radical scavenging activity (3.65 ± 0.05 mg/g bamboo leaves in BHA equivalents) at 20 MPa and 95 °C, could be obtained among the mixture cosolvents studied. For Soxhlet extraction with a 25:75 (mol:mol) ethanol–water mixture, 1.48 times the amount of phenolic compounds (10.85 ± 0.52 mg/g bamboo leaves in catechin equivalents), could be isolated compared with the supercritical extraction method, however, the radical scavenging activity (3.30 ± 0.05 mg/g bamboo leaves in BHA equivalents) was 0.90 times lower than the extract obtained from the supercritical extraction method. The seven major antioxidative compounds identified from the SC-CO₂ extraction method were: (1) dl-alanine, (2) gluconic acid, (3) phosphoric acid, (4) ß-siosterol, (5) β-amyrene, (6) α-amyrin acetate and (7) friedelin.     

Chemical characterisation of marine aerosol at Amsterdam Island during the austral summer of 2006–2007

Atmospheric aerosols were collected in separate fine (<2.5 μm) and coarse (>2.5 μm) size fractions in the period December 2006–March 2007 at Amsterdam Island in the southern Indian Ocean. A major objective of the study was to assess biogenic impact on the marine aerosol. The samples were analysed for organic carbon, water-soluble organic carbon, major inorganic ionic species, and organic species, including methanesulphonate (MSA), dicarboxylic acids, and organosulphates. The concentrations of sea salt, non-sea-salt sulphate, and water-soluble and water-insoluble organic matter (WSOM and WIOM) were estimated. Sea salt dominated the composition of the aerosol and accounted for 83% and 91% of the sum of the mass of the four aerosol types in the fine and coarse size fractions, respectively. WSOM, which can serve as a proxy for biogenic secondary organic aerosol (SOA), accounted for only 2.8% of the sum of the mass of the four aerosol types in the fine size fraction. MSA was the dominating organic compound with a median concentration of 47 ng m^?3. The organosulphates were characterised as sulphate esters of hydroxyl acids and a dihydroxylaldehyde, which may originate from the oxidation of algal/bacterial unsaturated fatty acid residues. No evidence was found for isoprene SOA.     

Sulfonated-polysulfone membrane surface modification by employing methacrylic acid through UV-grafting: Optimization through response surface methodology approach

Membrane surface modification through UV-grafting method was studied and optimized using response surface methodology (RSM) approach. Sulfonated-polysulfone (SPS) membrane was modified through grafting process by employing methacrylic acid (MAA) monomer solution under the exposure of UV light. The parameters used were the concentration of MAA in the range of 0–6 wt% and UV activation time of 0–50 min. The optimized parameters from RSM were 2.61 wt% of MAA and 21.10 min of UV activation time. The optimized water permeability obtained was 8.75 L m⁻² h⁻¹ bar⁻¹, while the rejection percentages for humic acid, NaCl and MgSO₄ solution were 95.0%, 65.7% and 48.3%, respectively.     

Shape forming alumina slurries via Colloidal IsoPressing

The relative density, deformation behavior, and dynamic rheology of bodies consolidated from aqueous alumina slurries, formulated at pH 4 and containing NH₄Cl, were studied as a function of the salt concentration (0.1–0.75 M). The smallest salt concentration produced the highest relative density (0.596), which was independent of consolidation pressure. Nearly identical relative densities were obtained for the other salt concentrations, ranging from 0.57 to 0.59 for consolidation pressures of 5–100 MPa, respectively. The consolidated bodies exhibited either a plastic or an elastic behavior when tested in compression. It was observed that the transition from a plastic to an elastic behavior occurred at a critical consolidation pressure. This critical consolidation pressure was directly dependent on the salt concentration. The storage (elastic) modulus for the fluidized, plastic bodies increased with salt concentration. The storage modulus was also observed to be dependent on the time the bodies were allowed to rest after they were subjected to a high shear rate. A pre-consolidated and fluidized slurry formulated to contain 0.5 NH₄Cl was extruded into a rubber mold cavity and further consolidated by isopressing at 200 MPa for 2 min. The body not only increased its relative density (0.58–0.62), but it also became elastic to enable its removal from the rubber cavity without shape distortion. No linear shrinkage was detected after the isopressed bodies were dried. Because of the lack of shrinkage, rapid drying was possible. For example, bar specimens (6.4 mm × 12.7 mm × 60 mm) would survive a 34 °C/min heating rate to 300 °C; the specimen was completely dried within 20 min. Because shrinkage does not occur during drying, bodies could be placed directly into a furnace and heated to 1500 °C for 0.5 h to achieve a relative density of >0.99 and an average grain size of 1.6 μm.     

Synthesis and physicochemical properties of new fatty (co)polyamides as potential UV powder coating

Partially or fully biosourced (co)polyamides have been prepared from commercial (11-aminoundecanoic acid, octadec-9-en-1,18-dioic acid, dodecan-1,12-diamine) and/or an original branched and unsaturated ((9Z)-octadecene-1,12-diamine) monomer. Undec-11-enoic acid was used as chain limiter in order to obtain controlled average number molecular weights around 7000 g mol⁻¹. By varying the relative composition of monomers and/or the amount of side chains and/or the amount of unsaturated repeating units, copolyamides exhibiting low glass transition temperatures ranging from −31 to 3 °C and low melting temperatures ranging from 60 to 143 °C have been obtained. The branched monomer was found to act as internal plasticizer. Coatings have been prepared from these polymer materials at their melting temperatures. The presence of carbon–carbon double bonds on the polymer backbone allowed their photocrosslinking in the presence of benzophenone. This UV curing enhanced the hardness of the obtained coatings. These polymers are therefore expected to be used as bio-based UV powder coatings for heat sensitive substrates.     

Kinetic study of atom transfer radical homo- and copolymerization of styrene and methyl methacrylate initiated with trichloromethyl-terminated poly(vinyl acetate) macroinitiator

Atom transfer radical bulk copolymerization of styrene (St) and methyl methacrylate (MMA) was performed in the presence of CuCl/PMDETA as a catalyst system and trichloromethyl-terminated poly(vinyl acetate) telomer as a macroinitiator at 90 °C. The overall monomer conversion was followed gravimetrically and the cumulative average copolymer composition at moderate to high conversion was determined by ¹H NMR spectroscopy. Reactivity ratios of St and MMA were calculated by the extended Kelen–Tudos (KT) and Mao–Huglin (MH) methods to be r_St = 0.605 ± 0.058, r_MMA = 0.429 ± 0.042 and r_St = 0.602 ± 0.043, r_MMA = 0.430 ± 0.032, respectively, which are in good agreement with those reported for the conventional free-radical copolymerization of St and MMA. The 95% joint confidence limit was used to evaluate accuracy of the estimated reactivity ratios. Results showed that in the controlled/living radical polymerization systems such as ATRP, more reliable reactivity ratios are obtained when copolymer composition at moderate to high conversion is used. Good agreement between the theoretical and experimental composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion was observed, indicating the accuracy of reactivity ratios calculated by copolymer composition at the moderate to high conversion. Instantaneous copolymer composition curve and number-average sequence length of comonomers in the copolymer indicated that the copolymerization system tends to produce a random copolymer.     

Increased high temperature strength and oxidation resistance of Al4SiC4 ceramics

Al₄SiC₄ bulk ceramics were synthesized by reaction hot-pressing using Al, graphite powders and polycarbosilane (PCS) as starting materials. The present work confirmed that this process was an effective method for the preparation of Al₄SiC₄ ceramics having high relative density and well-developed plate-like grains. The mechanical, thermal properties and oxidation behaviors of the Al₄SiC₄ ceramics were also investigated. The flexural strength, fracture toughness (K_IC) and Vickers hardness at room temperature were 297.1 ± 22 MPa, 3.98 ± 0.05 MPa m^1/2, 10.6 ± 1.8 GPa, respectively. The high-temperature bending strength showed an increasing trend with increasing test temperatures, with the value of 449.7 ± 26 MPa at 1300 °C. The thermal expansion coefficient was 6.2 × 10⁻⁶ °C⁻¹ in the temperature range from 200 °C to 1450 °C. The isothermal oxidation of Al₄SiC₄ ceramics at 1200–1600 °C for 10–20 h revealed that it had excellent oxidation resistance.     

Enthalpy of formation and dehydration of lithium and sodium zeolite beta

Zeolite Li-BEA and Na-BEA with Si/Al = 3–4 were synthesized by alumination and ion exchange, then characterized by XRD, TG–DSC and NMR. The enthalpies of formation and dehydration of Li and Na ion exchanged zeolite beta are investigated by high temperature oxide melt solution calorimetry. For Li-BEA, the formation enthalpies of formation from oxides at 25 °C are 25.6 ± 1.7 kJ/mol TO₂ for the dehydrated zeolite and −8.45 ± 0.94 kJ/mol TO₂ for the fully hydrated zeolite; for Na-BEA they are −2.4 ± 0.6 kJ/mol TO₂ for the dehydrated and −17.8 ± 1.0 kJ/mol TO₂ for the fully hydrated zeolite. The integral dehydration enthalpy at 25 °C is 33.2 ± 1.8 kJ/mol H₂O for Li-BEA and 16.5 ± 1.1 kJ/mol H₂O for Na-BEA. The partial molar dehydration enthalpies of both Li-BEA and Na-BEA are a linear function of water content. Molecular mechanics simulations explore the cation and water molecule positions in the framework at several water contents.     

Thermodynamically stable amorphous drug dispersions in amorphous hydrophilic polymers engineered by hot melt extrusion

In this study thermodynamically stable dispersions of amorphous quinine, a model BCS class 2 therapeutic agent, within an amorphous polymeric platform (HPC), termed a solid-in-solid dispersion, were produced using hot melt extrusion. Characterisation of the pre-extrudates and extrudates was performed using hyper-differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and Raman spectroscopy. Water uptake by the raw materials was determined using dynamic vapour sorption (DVS) analysis. Furthermore, the presence or absence of crystalline drug following storage at 25 °C/60% relative humidity and 40 °C/75% relative humidity in a sealed glass jar, and at 40 °C/75% relative humidity in an open glass jar for 3 months was determined using PXRD. Amorphous quinine was generated in situ during extrusion from both quinine base (5%, 10%, 20% w/w drug loading) and from quinine hydrochloride (5%, 10% w/w drug loading) and remained thermodynamically stable as a solid-in-solid dispersion within the HPC extrudates. When processed with HPC, quinine hydrochloride (20% w/w) was converted to amorphous quinine hydrochloride. Whilst stable for up to 3 months when stored under sealed conditions, this amorphous form was unstable, resulting in recrystallisation of the hydrochloride salt following storage for 1 month at 40 °C/75% relative humidity in an open glass jar. The behaviour of the amorphous quinine hydrochloride (20% w/w) HPC extrudate was related, at least in part, to the lower stability and the hygroscopic properties of this amorphous form.     

Aqueous gelcasting of ZrB2–SiC ultra high temperature ceramics

ZrB₂–SiC ultra high temperature ceramics containing B₄C and C as sintering additives were successfully prepared by aqueous gelcasting and pressureless sintering. Polyacrylic acid (PAA) was used as the dispersant throughout this research. The various effects of zeta potential, pH value, dispersant concentration, solid loading and ball-milling time on the rheology and fluidity behavior of ZrB₂–SiC suspension were investigated in detail. A well-dispersed suspension with 50 vol.% solid loading was prepared at pH 10 with 0.4 wt.% PAA after ball milling at 240 rpm for 24 h. Then crack-free green ZrB₂–SiC ceramics were obtained by gelcasting process and then pressureless sintered at 2100 °C to about 98% relative density. The microstructure and mechanical properties were examined, and the flexural strength and fracture toughness were 405 ± 27 MPa and 4.3 ± 0.3 MPa m^1/2, respectively.     

Study of the solubility of kerogen from oil shales (Puertollano,Spain) in supercritical toluene and methanol

In mixtures of bitumen–toluene and bitumen–methanol, supercritical equilibrium compositions were measured at 603.15, 613.15, 623.15 and 633.15 K (reduced temperatures 1.02, 1.04, 1.05 and 1.07) in a range of pressures of 4.5–14.5 MPa for toluene as solvent, and at 553.15; 583.15; 613.15 and 623.15 K (reduced temperatures 1.08, 1.14, 1.18 and 1.21) and pressures from 6.5 to 22.5 MPa for methanol as solvent. The solubility data were correlated by using Chrastil equation. At each temperature the number of molecules of solvent per molecule of solute was calculated for both toluene and methanol. Association numbers between 1.67 ± 0.02 and 2.47 ± 0.08 were obtained for toluene and 2.36 ± 0.10 and 2.60 ± 0.08 for methanol. In conclusion, association number was not independent of temperature. Also density data calculated with some equations of state (Peng-Robinson, Soave-Redlich-Kwong and Lee-Kesler) were compared to empirical density data in order to determine the effect of using any of them. Compounds obtained with each of solvents were analyzed using gas chromatography with a mass detector. Results obtained indicate that toluene extracts mainly aromatic compounds and little of paraffin and depletes the organic material in the oil shale. On the other hand with methanol lineal hydrocarbons insaturated and saturated with very little of aromatic compounds were obtained. This indicates that some reaction products are probably produced during the extraction process.     

High-temperature hot-pressing of titanium carbide–graphite hetero-modulus ceramics

Hetero-modulus ceramic–ceramic composite materials (HMC) present the combination of ceramic matrix with high Young's modulus and the inclusions of a dispersed phase with low Young's modulus. The densification of 60–100 vol% TiC–0–40 vol% C (graphite) HMC during hot-pressing of powder compositions at 2200–2400 °C and applied pressures of 8–16 MPa is studied. The general theory of bulk-viscous flow for porous body is developed to describe obtained experimental data. This relation as well as Kovalchenko's equation for the evolution of relative density for non-uniform deformation of porous body, incorporating different stages of creep, are used to determine the activation energy and the exponent constant of hot-pressing process, which values are 270 ± 30 kJ mol⁻¹ and 3 ± 0.3, respectively. The obtained experimental data are discussed on the basis of extensive and detailed analysis of the previous studies on diffusion and diffusion-related phenomena in the Ti–C system.     

Synthesis of tungsten oxide nanoparticles by acid precipitation method

Tungsten oxide (WO₃) nanoparticle having average size of 30 nm, and nanoplate having average dimension of 190 ± 15 nm wide and 50 ± 5 nm thick were prepared by controlling a precipitation of ammonium tungstate para pentahydrate with nitric acid. The two nanostructured microstructures were obtained by varying the stirring time during the precipitation reaction while the other synthesis parameters were identical. Phase transition of the WO₃ precipitate was investigated by means of thermal analysis and X-ray diffraction, while the microstructure was observed by using a scanning electron microscope and a transmission electron microscope. The effect of the concentrations of the tungstate salt and nitric acid on the rate of precipitation and the percent yield of the precipitating product is also described.     

Agglomerate strength and dispersion of pharmaceutical powders

This study aims to investigate quantitatively the direct correlation between the mechanical strength of powder agglomerates and their dispersion into aerosols by a dry powder inhaler. Agglomerates of mannitol as a model drug-only formulation were prepared by a rolling method followed by exposure to various relative humidity (RH: 55%, 82%, 86% and 90%). The agglomerate strength was obtained from the compression of single agglomerates at a selected speed rate using an Instron testing machine. The dispersion performance (FPF_Loaded) was determined at flow rates of 60 and 100 l min^?1 using an Aeroliser^® coupled to a multistage liquid impinger. Results showed an inverse linear relationship between the agglomerate strength and the dispersion performance. An increase in strength from 3 to 183 kPa resulted in a significant drop (P<0.05) of 18% in the FPF_Loaded. Agglomerates containing ‘solid bridges’ exhibited higher strength (three to eight times) and lower FPF (5–15%, corresponding to 86% and 90% RH) compared to those containing ‘liquid bridges’. These results have provided direct information on the agglomerate strength and its quantitative relationship with powder aerosol performance.     

Synthesis and characterization of positively charged interpenetrating double-network hydrogel matrices for biomedical applications

In this study, positively charged interpenetrating double-network (DN) hydrogels of polyvinyl alcohol/polyacrylamide (PVA/PAm) were prepared using bifunctional cationic salt as a crosslinker. The cationic salts were synthesized by the Michael-addition of piperazine (PZ) with butanediol diacrylate (BDDA)/hexanediol diacrylate (HDDA) separately followed by the methylation of the products. The chemical characterization of the quaternary salts was performed using ATR-FTIR and NMR (¹H, ¹³C, DEPT) spectroscopy. The zeta potential of the cationic salts was found to be in the range of 17.6 ± 8.03–20.3 ± 10.1 mV for various monomers. Chemical crosslinking (free radical polymerization) and physical crosslinking (freeze–thaw) techniques were employed to crosslink PAm and PVA, respectively. The quaternized salt of BDDA and PZ was used to crosslink the PAm hydrogel network. The thermal stability and the compression modulus of the hydrogel increased, while the displacement value and the water absorption capacity decreased when crosslinker concentration was increased from 1.0 to 4.0 mol%. The excellent cell viability (?94%) and gel content (?92%) suggest that these matrices can be utilized as future biomaterials for biomedical applications.     

Preliminary study on high temperature transport technology for molten salt in pyroprocessing

Pyroprocessing technology is one of the most promising technologies for an advanced fuel cycle with favorable economic potential and intrinsic proliferation-resistance. In pyroprocessing technology, the development of high-temperature transport technologies for molten salt is a crucial prerequisite and a key issue in the industrialization of pyro-reprocessing. However, there have been a few transport studies on high-temperature molten salt. Three different salt transport technologies (gravity, suction pump, and centrifugal pump) were investigated, a suction pump transport method was selected for molten salt transport owing to its flexibility. An apparatus for suction transport experiments was designed and installed for the development of high temperature molten salt transport technology. About 2 kg of LiCl–KCl eutectic salt was prepared by mixing 99.0%, LiCl and KCl and drying in a convection dry oven at 200 °C for 1 h. Predissolution tests of the prepared LiCl–KCl eutectic salt using the melting reactor of the experimental apparatus was carried out to investigate the dissolution behavior of the prepared LiCl–KCl eutectic salt. From the results of the pre-dissolution test, it was found that prepared LiCl–KCl eutectic salt was well dissolved at 500 °C. High temperature molten salt transport experiments by suction are currently being performed using the prepared LiC–KCl eutectic salt. The preliminary experimental results of lab-scale molten salt transport showed a 99.5% transport rate (ratio of transported salt to total salt) under a vacuum range of 100 m torr–10 torr at 500 °C.     

Photocatalytic degradation of humic acid in the presence of montmorillonite

Humic acids (HA) representing the major fraction of the naturally occurring humic substances (HS) are composed of highly functionalized carbon rich polydisperse organic fractions. Clay minerals which are responsible for the transport of inorganic and organic contaminants constitute the main component of the dispersed inorganic material in natural waters. The understanding of interactions between humic substances and clay minerals is an important task for the achievement of an effective water treatment performance. The aim of this research was to investigate the influence of montmorillonite as a representative clay mineral on the TiO₂ photocatalytic removal of humic acids as the model compound of natural organic matter. The interactions prevailing between humic acid, montmorillonite and TiO₂ surface were assessed prior to the application of photocatalysis in order to address the adsorptive and photolytic behavior of humic acids. The changes attained in humic acid were described by UV–vis spectroscopic i.e. color forming moieties (Color₄₃₆) and UV absorbing centers (UV₃₆₅ and UV₂₅₄), and dissolved organic carbon (DOC) contents. Application of the pseudo first order kinetic model revealed both an enhancement and retardation with respect to the applied montmorillonite dose. The overall effect of montmorillonite on the photocatalytic degradation of humic acid was also evaluated in terms of molecular size distribution profiles (0.45 μm filtered fraction, 100 kDa fraction, 30 kDa fraction and 3 kDa fraction) described by the specified and DOC normalized specific UV–vis parameters.     

Temperature induced gelation of non–aqueous alumina suspension using oleic acid as dispersant

A novel temperature induced gelation method for alumina suspension using oleic acid as dispersant is reported. Non–aqueous suspension with high solid loading and low viscosity is prepared using normal octane as solvent. Influence of oleic acid on the dispersion of suspension was investigated. There was a well disperse alumina suspension with 1.3 wt% oleic acid. Influence of gelation temperature on the coagulation process and properties of green body was investigated. The sufficiently high viscosity to coagulate the suspension was achieved at −20 °C. The gelation temperature was controlled between the melting point of dispersant and solvent. The gelation mechanism is proposed that alumina suspension is destabilized by dispersant separating out from the solvent and removing from the alumina particles surface. The alumina green body with wet compressive strength of 1.07 MPa can be demolded without deformation by treating 53 vol% alumina suspension at −20 °C for 12 h. After being sintered at 1550 °C for 3 h, dense alumina ceramics with relative density of 98.62% and flexural strength of 371±25 MPa have been obtained by this method.     

Pressurized liquid extraction and low-pressure solvent extraction of carotenoids from pressed palm fiber: Experimental and economical evaluation

In this work, a comparison of Soxhlet extraction (LPSE–SOX), percolation (LPSE–PE) and pressurized liquid extraction (PLE) for the recovery of carotenoid-rich extracts from pressed palm fiber (PPF) was carried out in terms of yield, carotenoid profile and economic viability to evaluate the methods’ industrial applicability. An optimization study was performed for each extraction technique with ethanol at a solvent/feed ratio of 20. The independent variables were temperature (35–55 °C), pressure (0.1–8 MPa) and flow rate (1.6, 2.4 g/min). The results showed that the global extraction yield obtained using LPSE–SOX (96 ± 4 mg extract/g PPF d.b.) after 6 h was higher than that obtained using LPSE–PE (74 ± 5 mg extract/g PPF d.b., 35 °C, 2.4 g/min) or PLE (44 ± 3 mg extract/g PPF d.b., 55 °C, 4 MPa, 2.4 g/min) after dynamic extraction time of 17 min under optimized conditions. On the other hand, the carotenoid yield obtained using PLE (305 ± 18 μg α-carotene/g extract and 713 ± 46 μg β-carotene/g extract) was higher than the obtained by LPSE–SOX (142 ± 13 μg α-carotene/g extract and 317 ± 46 μg β-carotene/g extract). PLE technique showed the highest selectivity for carotenoids than LPSE techniques. The lowest cost of manufacturing (COM) were obtained for LPSE–PE and PLE with values of US$13.4 and US$29.2/kg extract for a 0.5 m³ vessel capacity.