An apparatus for the measurement of surface tensions at high pressures and temperatures

An apparatus for the measurement of surface tensions of organic liquids in contact with a gas has been developed which is capable of operation to 400°C and to 14 MPa. It is based on the maximum bubble pressure technique, modified for hydrocarbon oils at high pressures and temperatures. Accuracy of measurement is of the order of ±3% for non‐aqueous systems for values down to 5 mN/m. Only a 20 to 30 mL liquid sample is required, and small gas volumes. In practice, it was found that measurements with most organic liquids could only be made to a maximum of about 350°C because of the thermal instability of most of these compounds, in particular, for hydrocarbon liquids. Any thermal decomposition or coke deposition leads to inaccurate results. Results obtained for known liquids are compared with values given in the literature.     

Geopolymer reinforced with E‐glass leno weaves

This study explores the viability of fiberglass‐geopolymer composites as an intermediate temperature structural ceramic composite. E‐glass fibers are cheap, readily available, resistant to heat, electricity and chemical attack. Geopolymers are refractory and can be processed at room temperature. However, pure geopolymers have low tensile strength and fracture toughness, as is typical of ceramics. In this work, tensile and flexure properties of metakaolin‐based sodium and potassium geopolymers reinforced with E‐glass leno weaves were measured and the data was analyzed by Weibull statistics. The average tensile and flexural strengths for sodium geopolymer reinforced with E‐glass leno weaves were 39.3 ± 7.2 MPa and 25.6 ± 4.8 MPa, respectively. For potassium geopolymer reinforced with E‐glass leno weaves, the average tensile and flexural strengths were 40.7 ± 9.9 MPa and 15.9 ± 4.0 MPa, respectively. The composites were heat treated for one hour at two temperatures, 300°C and 550°C and their flexure properties were studied at room temperatures. The average flexural strengths for sodium geopolymer reinforced with E‐glass leno weaves were reduced to 6.6 ± 1.0 MPa after heat treatment at 300°C, and 1.2 ± 0.3 MPa after heat treatment at 550°C, respectively. For potassium geopolymer reinforced with E‐glass leno weaves, the average flexural strengths were 6.1 ± 1.5 MPa and 1.3 ± 0.3 MPa after heat treatment at 300°C and 550°C, respectively. SEM and EDS were performed to observe the fiber‐matrix interface. XRD was done to check if the geopolymer was amorphous as expected.     

Vapour-liquid equilibrium study of methane and western shale oil

The bubble point pressures, saturated molar liquid volumes, and densities of a shale oil from the Green River formation in Utah, and a distillation fraction of the oil were experimentally determined as a function of temperature and methane mole fraction. These properties were measured in a static VLE apparatus capable of measuring pressures to 34,500 kPa and temperatures to 450 K. The phase change at the bubble point for the mixtures of oil and methane was determined using the statistical method of splines. The densities for the crude shale oil have been extrapolated to 288.7K (60 °F) using a standard API correlation.     

Wet oxidation of glucose

Wet oxidation is used to oxidize organic substances at a controlled rate in an aqueous medium at elevated temperatures and pressures. Aqueous glucose solutions were oxidized with pure oxygen at four different temperatures in the range 176.7°C to 260.0°C, and at an oxygen pressure of 2.3 MPa. Three distinct stages of wet oxidation were found — induction, rapid oxidation, and slow oxidation. During the rapid oxidation period the reaction was assumed to be confined to a thin liquid layer next to the gas-liquid interface. The activation energy for the rapid oxidation period was estimated to be 130 ± 20 kJ/mol. Acetic acid was found to accelerate the rate of wet oxidation of glucose only slightly.     

Mechanical and chemical properties of metakaolin-based geopolymer exposed to elevated temperature

A method is presented to fabricate metakaolin-based geopolymers that are structurally and mechanically stable up to 600°C. The chemical environment of the geopolymers is characterized using thermogravimetric analysis and Fourier-transform infrared spectroscopy. Residual free water turned into steam and caused damage to the geopolymer when exposed to elevated temperatures. The curing temperature was increased from 80 to 120°C to remove water during the curing process. A correlation was drawn between the amount of Si-O-Al linkage formed and the position of fingerprint peaks in infrared spectra, providing a tool to evaluate the level of geopolymerization. Flexural and tensile properties of geopolymers fabricated using the optimized method were measured for no heat treatment and for exposure to elevated temperatures of 200, 400, and 600°C. The flexural strength was measured to be 10.80 ± 2.99 MPa at room temperature, 10.36 ± 0.64 MPa at 400°C, and 8.04 ± 1.60 MPa at 600°C. The flexural modulus is reported to be 13.09 ± 3.40 GPa at room temperature and 11.03 ± 0.53 GPa at 600°C. The flexural toughness decreased with increasing temperature. The tensile properties of the geopolymer were measured with direct tensile tests paired with an extensometer. The tensile strength decreased from 4.16 ± 2.08 MPa at room temperature to 3.13 ± 0.97 MPa at 400°C, and 2.75 ± 0.86 MPa at 600°C. The Young's modulus decreased from 45.38 ± 30.30 GPa at room temperature to 26.88 ± 6.65 GPa at 600°C. Both flexural and tensile tests have shown that the metakaolin-based geopolymers cured at 120°C is mechanically stable at temperatures up to 600°C.     

Gamma-Ray method for measuring liquid expansion coefficient at high temperatures and pressures

Expandable vessels were designed to measure the density and thermal expansion coefficients of liquid at elevated temperatures and pressures by the gamma-ray attenuation method. Light Arabian vacuum bottoms was tested from 70°C to 300°C at 13.8 MPa. Results agree well with literature data.     

Low-temperature thermally modified fir-derived biomorphic C–SiC composites prepared by sol-gel infiltration

In order to solve the problems (i.e. low infiltration efficiency, cracks, interface separation and poor mechanical properties) in the process of wood-derived C–SiC composites, the thermal modification of fir at low temperatures (300 °C ～ 350 °C) combined with sol-gel infiltration was used to successfully produce biomorphic ceramics. The prepared materials were comprehensively characterized and exhibited improved interfacial bonding between C and SiC and mechanical properties. The weight gain per unit volume (0.123 g/cm³) of SiO₂ gel in the fir thermally modified at 300 °C is 167.4%, higher than that (0.046 g/cm³) of the unmodified fir. A well-bonded interface was formed between the SiO₂ gel and the pore wall of the fir thermally modified at 300 °C. With the increase of modification temperature from 300 °C to 350 °C, the distance between SiO₂ gel and the pore wall increases, and a gap (1–3 μm) is observed between SiO₂ gel and the pore wall of the fir carbonized at 600 °C. The C–SiC composites sintered at 1400 °C exhibited the highest compressive strength and bending strength of 40.8 ± 5.8 MPa and 11.7 ± 2.1 MPa, respectively, owing to the well-bonded interface between C of fir thermally modified at 300 °C and SiC. However, the composites sintered at 1600 °C for 120 min exhibited the lowest compressive strength and bending strength of 28.1 ± 13.4 MPa and 5.7 ± 1.6 MPa, respectively, which are 31.1% and 51.3% lower than those sintered at 1400 °C for 120 min, respectively. This might result from the porous structure formed by the excessive consumption of fir-derived carbon during the reaction between C and SiO₂ at 1600 °C for 120 min. Therefore, thermal modification in the preparation of biomorphic C–SiC composites can promote slurry infiltration and the formation of a well-bonded interface between C and SiC, thus improving the mechanical properties of the composites.     

Properties of Geopolymer Composites Reinforced with Basalt Chopped Strand Mat or Woven Fabric

Geopolymers or polysialates are inorganic polymeric, ceramic‐like materials composed of alumina, silica, and alkali metal oxides that can be made without any thermal treatment. Additions of reinforcing phases vastly improve the mechanical properties and high‐temperature stability of the geopolymer. The processing and mechanical properties of both chopped strand mat as well as 2‐D woven fabric‐reinforced potassium geopolymer composites have been evaluated. Hand lay‐up and hydraulic press processing methods were used to produce composite panels. The room‐temperature tensile and flexural strength of chopped strand mat composites was 21.0 ± 3.1 and 31.7 ± 4.4 MPa, respectively, while those of basalt weave‐reinforced geopolymer composites reached 40.0 ± 5.9 and 45.2 ± 9.3 MPa, respectively. Composite microstructures were examined using optical microscopy as well as scanning electron microscopy (SEM). Mass, volume, and porosity fractions were also determined. The effect of high‐temperature treatments at 25°C, 300°C, 600°C, and 800°C were analyzed. Finally, Weibull statistical analysis was performed, which showed an increase in reliability when a reinforcement phase was added to K‐geopolymer.     

PVT study of trifluoromethane by the burnett method

PVT data for trifluoromethane were obtained by means of a three-reservoir Burnett cell. Compressibility factors corresponding to seven isotherms (0, 25, 50, 75, 100, 150 and 200°C) were obtained experimentally, encompassing pressures up to 16.5 MPa (2,400 psia). Second and third virial coefficients were calculated for these seven temperatures, and parameters for the Stockmayer potential functions were obtained. The degree of molecular association for trifluoromethane was evaluated by the procedure proposed by Lambert and coworkers. Enthalpy and entropy of dimerization were also estimated.     

Additive-free low temperature sintering of amorphous SiBC powders derived from boron-modified polycarbosilanes: Toward the design of SiC with tunable mechanical,electrical and thermal properties

Additive-free SiC ceramics are prepared from polymer-derived powders with Si, C and B elements homogeneously distributed on the atomic level by rapid hot-pressing at 1750 °C and 1800 °C under argon and a load of 50 MPa. As-sintered samples display a Vickers hardness in the range of 9.6 ± 0.5 GPa–17.3 ± 1.9 GPa and an elastic modulus varying from 137 ± 3.4 GPa to 239 ± 6 GPa, both depending on the sample phase composition, crystallinity and porosity. Accordingly, the electrical conductivity changes from 340 to 3900 S/m whereas the thermal conductivity varies from 17.7 to 45.1 W/m⋅K as a function of these characteristics. Thus, we demonstrated that a polycarbosilane containing 0.7 wt.% of boron could produce boron-doped SiC powders that demonstrate tailored sinterability at temperatures as low as 1750 °C to form nearly dense SiC ceramics with adjusted hardness, Young’s modulus, electrical and thermal conductivities.     

Consolidation and high-temperature strength of monolithic lanthanum hexaboride

In this study we explored the densification, microstructure evolution, and high-temperature properties of bulk lanthanum hexaboride. LaB₆ bulks were consolidated using spark-plasma sintering only in the temperature range between 1400°C and 1700°C. We adopted flash spark plasma sintering (SPS) of LaB₆ using a direct current heating without a graphite die. We observed a peculiar grain-size gradient when coarse grains exceeding 300 μm were observed on the top side of the specimen, while the bottom side had a grain size of 15–20 μm. Such large grain was not observed using SPS at 2000°C, suggesting that these might originate from a local overheating. Based on the three-point flexural tests, it was observed that the toughness and strength of the LaB₆ were acceptable at room-temperature (3.1 ± 0.2 MPa m^1/2, 300 ± 20 MPa). However, at 1600°C, these parameters would decrease to 1.3 ± 0.1 MPa m^1/2 and 120 ± 40 MPa, respectively.     

An evaluation of the pressure‐dependent melt viscosity of polyphenylsulfone

A method for the determination of pressure‐affected viscosity from capillary rheometry and pressure–volume–temperature (PVT) data was tested on polyphenylsulfone melt. Shear viscosity data evaluated at selected temperatures (345–375°C) were interlinked to the PVT data at pressures ranging from 1 to 200 MPa. According to the recently proposed correlation approach, a pressure‐dependent shear viscosity is derived from the relationship (verified on several commodity polymers) between temperature‐dependent viscosity and a free volume parameter computed using the Simha–Somcynsky equation of state. Finally, the predicted pressure‐viscosity coefficient was compared with the value obtained experimentally on a modified single piston rheometer. POLYM. ENG. SCI., 54:711–715, 2014. © 2013 Society of Plastics Engineers     

Effect of interphase on mechanical properties and microstructures of 3D Cf/SiBCN composites at elevated temperatures

Interphase between the fibers and matrix plays a key role on the properties of fiber reinforced composites. In this work, the effect of interphase on mechanical properties and microstructures of 3D C_f/SiBCN composites at elevated temperatures was investigated. When PyC interphase is used, flexural strength and elastic modulus of the C_f/SiBCN composites decrease seriously at 1600°C (92 ± 15 MPa, 12 ± 2 GPa), compared with the properties at room temperature (371 ± 31 MPa, 31 ± 2 GPa). While, the flexural strength and elastic modulus of C_f/SiBCN composites with PyC/SiC multilayered interphase at 1600°C are as high as 330 ± 7 MPa and 30 ± 2 GPa, respectively, which are 97% and 73% of the values at room temperature (341 ± 20 MPa, 41 ± 2 GPa). To clarify the effect mechanism of the interphase on mechanical properties of the C_f/SiBCN composites at elevated temperature, interfacial bonding strength (IFBS) and microstructures of the composites were investigated in detail. It reveals that the PyC/SiC multilayered interphase can retard the SiBCN matrix degradation at elevated temperature, leading to the high strength retention of the composites at 1600°C.     

Phase behavior and reaction of nylon 6/6 in water at high temperatures and pressures

The phase behavior and reaction of nylon 6/6 in water were studied with a diamond anvil cell (DAC) technique and visual microscopy. Nylon 6/6 concentrations in water and cell temperatures were varied from 11 to 46% and from 264 to 425°C, respectively. The pressures studied ranged from 30 to 900 MPa. When an aqueous solution of 27% nylon 6/6 was rapidly heated (2.6°C/s) to 372°C at 30 MPa, the solution became homogeneous at 331°C. Upon cooling, the final pressure was 30 MPa and both particles and gas were observed. Analysis of the particles by Raman indicated decomposed nylon 6/6 solid. When an aqueous solution of 31% nylon 6/6 was rapidly heated (2.9°C/s) to 425°C at 58 MPa, the solution became homogeneous at 323°C. Upon cooling, the final pressure was 143 MPa, and, remarkably, only a second liquid precipitated and no gas or solids were observed. From the experiments, we concluded that the reaction pathways are completely different between the subcritical and supercritical water conditions. For the case of subcritical conditions, the final products were solid particles having a nylon character along with a considerable amount of gas. At supercritical water conditions, the final products were liquids having little nylon character and no gas. Experiments were performed at a constant temperature of 272°C at initial pressures ranging from 87 to 400 MPa. As the reaction proceeded, the pressure was measured at 30‐s intervals. At average pressures less than 300 MPa, the nylon 6/6 samples melted and appeared to become homogeneous. At average pressures higher than 520 MPa, the nylon 6/6 samples remained heterogeneous. From these results, the rate of hydrolysis was concluded to increase with pressure. The reaction volume was found to be −21.1 cm³/mol, which can be explained by the overall formation of water‐soluble products. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1062–1073, 2000     

Kinetics of cellobiose decomposition under subcritical and supercritical water in continuous flow system

The effects of reaction temperature, pressure and residence time were investigated with a flow apparatus. Cellobiose decomposition kinetics and products in suband supercritical water were examined at temperatures from 320 to 420 °C at pressures from 25 to 40 MPa, and at residence times within 3 sec. Cellobiose was found to decompose via hydrolysis and pyrolysis. The yield of desired hydrolysis product, glucose, was the maximum value of 36.8% at 320 °C, 35 MPa, but the amount of 5-(hydroxymethyl)furfural (HMF), fermentation inhibitor increased too because residence time increased in the subcritical region owing to decrease of reaction rate. Meanwhile, though the yield of glucose is low in the supercritical region, the yield of HMF decreased compared with the subcritical region; and at the minimum yield of HMF (380 °C, 25 MPa), the yield of glucose was 21.4%. The decomposition of cellobiose followed first-order kinetics and the activation energy for the decomposition of cellobiose was 51.05 kJ/mol at 40MPa.     

Gas holdup in a two-phase vertical tubular reactor at high pressure

Gas holdup in a tubular reactor was measured at pressures from 5 to 14 MPa at 300°C using a differential pressure cell. The effects on gas holdup of gas density, liquid superficial velocity and gas superficial velocity were studied using vacuum tower bottoms from a Venezuelan feedstock with 95.1 wt% +524°C material. Hydrogen was used at superficial gas velocities from 0.7 to 2.0 cm/s. The feed density at 15°C (0.1 MPa), 300°C (5.57 MPa) and 400°C (13.9 MPa) was measured and showed a linear decrease with temperature. Increased gas density at a constant temperature of 300°C increased the gas holdup at all superficial gas velocities. An increase in the liquid flow rate from about 0.04 to 0.1 cm/s did not affect the gas holdup.     

Solubility of red pepper (C<Emphasis Type="Italic">apsicum annum</Emphasis>) oil in near- and supercritical carbon dioxide and quantification of capsaicin

Red pepper oil was extracted using near- and supercritical carbon dioxide. Extraction was carried out at pressures ranging from 10 to 35 MPa and temperatures from 30 to 60 °C, with a CO₂ flow rate of 24.01 g/min using a semi-continuous high-pressure extraction apparatus. The duration for extraction was 2 h. The highest oil yield was found at high pressure and temperature. The highest solubility of oil (1.18 mg/g of CO₂) was found at 35 MPa and 60 °C. The solubility data of red pepper oil in near- and supercritical CO₂ were fitted in Chrastil model. The fatty acid composition of red pepper oil was analyzed by gas chromatography (GC). Linoleic acid was found to be the major fatty acid in the oil. Capsaicin was quantified in different extracts by high performance liquid chromatography (HPLC). The highest capsaicin yield was found at 35 MPa and 60 °C.     

Mechanical properties and microstructure evolution of 3D Cf/SiBCN composites at elevated temperatures

3D C_f/SiBCN composites were fabricated by an efficient polymer impregnation and pyrolysis (PIP) method using liquid poly(methylvinyl)borosilazanes as precursor. Mechanical properties and microstructure evolution of the prepared 3D C_f/SiBCN composites at elevated temperatures in the range of 1500‐1700°C were investigated. As temperature increased from room temperature (371 ± 31 MPa, 31 ± 2 GPa) to 1500°C (316 ± 29 MPa, 27 ± 3 GPa), strength and elastic modulus of the composite decreased slightly, which degraded seriously as temperature further increased to 1600°C (92 ± 15 MPa, 12 ± 2 GPa) and 1700°C (84 ± 12 MPa, 11 ± 2GPa). To clarify the conversion of failure mechanisms, interfacial shear strength (IFSS) and microstructure evolution of the 3D C_f/SiBCN composites at different temperatures were investigated in detail. It reveals that the declines of the strength and changes of the IFSS of the composites are strongly related to the defects and SiC nano‐crystals formed in the composites at elevated temperatures.     

An apparatus for phase equilibrium studies of carbon dioxide+heavy hydrocarbon systems

An apparatus for measuring the solubility of gas in liquid and that of liquid or solid in gas has been constructed. The apparatus can be used at system temperatures ranging from 20 to 70°C and at system pressures up to 15 MPa. The solubilities were determined by means of gravimetric measurements. The solubilities measured in this study for the carbon dioxide+n-decane and carbon dioxide + naphthalene systems agree very well with the literature values. The vapor-liquid equilibria of the carbon dioxide+Peace River bitumen system at 45 and 55 °C were studied. The new data indicate that the supercritical-fluid carbon dioxide can extract a fair amount of the light components from Peace River bitumen.     

Effect of high-pressure processing on moisture sorption properties of brown rice

The effect of high-pressure treatment (0.1 to 500 MPa for 10 min) on the moisture sorption properties of brown rice (Feng Liang You Xiang No. 1) was investigated. Air was maintained at selected conditions (temperature between 20°C and 40°C, equilibrium relative humidity between 11% and 75%) and equilibrium moisture content was measured. The control attained a higher equilibrium moisture content than treated samples, while the 300 MPa treated sample had the lowest. The area of hysteresis of the 300 MPa test sample was the largest and the BET model was applied to determine the monolayer moisture content.