Thermodynamic properties of the n-hexane and benzene system at elevated temperatures

The total vapour pressure and the composition of the liquid of the n-hexane and benzene mixtures have been measured under equilibrium conditions at 90, 110, 130, 150, 170 and 190°C. The corresponding vapour phase compositions were estimated using an expression of the liquid phase activity coefficient as a function of composition of the liquid phase. Several expressions were compared and the three-constant Redlich and Kister equation was found to give the best fit to the experimental vapour pressure data. The virial equation of state as well as a modified Redlich and Kwong equation were used to express the deviation of the vapour phase from the ideal. Results were compared and the discrepancy was found to be within the experimental tolerance. The low values of the liquid phase activity coefficients indicated that the behaviour of this particular system was not far from ideal. Also, it was found that the degree of deviation from the ideal decreased with the increase in temperature. The excess Gibbs free energy of mixing was calculated and it was found to be non-symmetrical with liquid composition. On increasing the temperature of the system, the liquid composition corresponding to the maximum G^E tended to shift to a lower n-hexane concentration, while at fixed liquid composition, G^E initially decreased and then remained stationary or increased again. This was thought to be due to differences in the molar volumes of the two components.     

Thermodynamic properties of the benzene and n-heptane system at elevated temperatures

The total vapour pressure and the composition of the liquid and vapour phases of the benzene and n-heptane system have been experimentally determined under equilibrium conditions at 110, 125, 140, 155, 170, 185, 200 and 215 °C. The corresponding composition of the vapour phase was also estimated using an expression for the liquid phase activity coefficient as a function of the composition of the liquid phase. Several expressions were compared and it has been found that the three-constant Redlich and Kister equation gave the best fit of the experimental vapour pressure data than the other equations. Comparison between the calculated and measured vapour compositions has shown a discrepancy of y_meas,—y_calc. of the order of 0.02 mol fraction or 10 times the experimental tolerance. Nevertheless, the experimental values were reasonably thermodynamically consistent. The low values of the liquid phase activity coefficients indicated that the behaviour of this particular system was not far from ideality. Also, it was found that the degree of non-ideality decreased with the increase in temperature. The behaviour of the vapour phase was shown also to be nearly ideal. The excess Gibbs free energy of mixing was calculated, and it was found to be non-symmetrical with mole fraction. On increasing the temperature of the system, the liquid composition corresponding to the maximum G^E tended to shift to a higher benzene concentration, whilst at a fixed liquid composition, G^E initially decreased and then remained stationary or increased again. This was thought to be due to differences in the molar volumes of the two components.     

Flow properties at elevated temperatures and clarity of HSPAN gel–water dispersions

Dispersions of hydrolyzed-starch–polyacrylonitrile (HSPAN) gel and distilled water underwent permanent diminuntion of room-temperature viscosity after maintenance above a threshold temperature of 75°C for periods of several weeks. Below the threshold temperature, viscosity measured at room temperature was unaffected. Above the threshold temperature, the final room-temperature viscosity exponentially varied as the inverse absolute temperature, and the viscosity decreased with increasing temperature. The HSPAN gel–distilled water dispersions exhibited both yield stress and velocity slip at a solid boundary, but the latter was not present at low shearing stresses. The former inhibited natural convection in a vertical slot with an imposed horizontal temperature difference. Clarity of the dispersions was demonstrated by a character-visibility test. Deaerating the distilled water by boiling before mixing with HSPAN gel improved the clarity of the resulting dispersion by eliminating the formation of bubbles at elevated temperature. © 1995 John Wiley & Sons, Inc.     

Thermodynamic properties of normal butane at refrigeration temperatures

Presented in both English and SI units are tables of the thermodynamic properties of normal butane over the temperature range -22 to +122°F (-30 to +50°C). Values are tabulated of the volume, enthalpy, and entropy for the subcooled liquid, the saturated liquid and vapor and the superheated vapor in both unit systems. The data used to calculate these properties have been carefully evaluated and include very recent values of the low temperature heat capacity of the vapor. Two enthalpy-entropy charts (Mollier diagrams), one in each of the unit systems are presented. These are suitable for the design of machinery used in thermo-mechanical energy cycles such as the freezing and eutectic processes for treating sea water and waste water. The calculated thermodynamic properties are the only ones available for n-butane which cover the above complete temperature range.     

Thermal properties of lightweight‐framed construction components at elevated temperatures

Fire resistance behaviour of lightweight‐framed assemblies is determined by defining the thermal and structural performances of the assembly when exposed to fire. To adequately model thermal behaviour in a lightweight wood‐framed assembly, thermal properties of the components of the assembly at elevated temperatures must be well defined. This paper presents results of measurements of thermal properties at elevated temperatures of construction materials commonly used to build lightweight wood‐framed assemblies that were conducted at the National Research Council of Canada since 1990. The test results, in graphical form, are given as a function of temperature for thermal conductivity, specific heat, mass loss and thermal expansion/contraction for wood, gypsum and insulation. In addition, the effects of temperature on the thermal conductivity, specific heat, mass loss and thermal expansion/contraction of these materials are discussed. Finally, in addition to providing a resource of information, this paper also identifies the additional thermal property tests required to complete the matrix of information. Copyright © 2005 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

Selective permeation and separation of steam from water–methanol–hydrogen gas mixtures through mordenite membrane

Separation properties of a mordenite membrane for water–methanol–hydrogen mixtures were studied in the temperature range from 423 to 523 K under pressurized conditions. The mordenite membrane was prepared on the outer surface of a porous alumina tubular support by a secondary-growth method. It was found that water was selectively permeated through the membrane. The separation factor of water/hydrogen and water/methanol were 49–156 and 73–101, respectively. Even when only hydrogen was fed at 0.5 MPa, its permeance was as low as 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ up to 493 K, possibly suggesting that water pre-adsorbed in the micropores of mordenite hindered the permeation of hydrogen. The hydrogen permeance dramatically increased to 6.5 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 503 K and reached to 1.4 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 523 K because of the formation of cracks in the membrane. However, the membrane was thermally stabilized in the presence of steam and/or methanol.     

Determining thermal properties of gypsum board at elevated temperatures

The National Institute of Standards and Technology (NIST) and the Center for Better Living have formed a collaboration to assess the performance and failure mechanisms of gypsum wall assemblies under real fires/furnace conditions. These measurements are being used to compile an experimental database necessary to validate models that could be used to predict their performance and ultimate failure under various design fires. A critical component of the database is thermal property data of gypsum board. The present paper describes the results of an effort to quantify thermal properties of gypsum board. The thermal conductivity specific heat mass loss and linear contraction for gypsum board types widely used in the U.S.A. and Japan were measured both at room temperature and at elevated temperatures. The gypsum board types tested include Type X and Type C from the U.S.A. and Type R and Type F from Japan. Results indicate that the difference in thermal properties of all gypsum board samples tested in the present study is not significant particularly at elevated temperatures. A large difference in linear contraction among gypsum board samples was observed at elevated temperatures, implying a significant difference in mechanical behavior at fire temperatures. The experimental data set provides valuable information that can be used to model the behavior of gypsum board at elevated temperatures. Copyright © 2009 John Wiley & Sons, Ltd.     

Observed changes in pitch properties aged at elevated temperatures

Several coal tar and petroleum-based binder and impregnating pitches have been aged in an inert atmosphere at 185°C for periods up to four weeks. The effect of the measured changes in the pitch properties with respect to the processing and properties of graphite artifacts is discussed.     

Tensile properties and stress relaxation of polypropylene at elevated temperatures

Samples of isotactic polypropylene(PP) were subjected to stress-relaxation experiments after simple tensile tests at four strain rates and at different levels of temperature. The relaxation moduli were determined in the range of temperature between 20 and 80°C with a relaxation period of 1200s duration. The activation energy value of the shift factor was determined using the time-temperature superposition principle. The calculated stress-strain curves and stress-relaxation curves were obtained from constitutive equations based on an overstress theory in which the temperature dependence of viscosity and the activation energy were considered. The temperature dependence of viscosity was amenable to an Arrhenius type equation. The quasi-equilibrium stress depends on both the current strain and the temperature. The calculated results were obtained by the proposed constitutive equation and compared with the data. The proposed constitutive equations based on the overstress model explain well the viscoelastic-plastic behavior of PP samples.     

Mechanical properties of borothermally synthesized zirconium diboride at elevated temperatures

The mechanical properties of a nominally phase pure ZrB₂ ceramic were measured up to 2300°C in an argon atmosphere. ZrB₂ was hot pressed at 2000°C utilizing borothermally synthesized powder from high purity ZrO₂ and B raw materials. The relative density of the ceramics was about 95% with an average ZrB₂ grain size of 8.8 µm. The room temperature flexural strength was 447 MPa, with strength decreasing to 196 MPa at 1800°C, and then increasing to 360 MPa at 2300°C. The strength up to 1800°C was likely controlled by a combination of effects: surface damage from oxidation of the specimens, stress relaxation, and decreases in the elastic modulus. The strength above 1800°C was controlled by flaws in the range consistent with sizes of the maximum ZrB₂ grain size and the largest pores. Fracture toughness was 2.3 MPa·m^1/2 at room temperature, increasing to 3.1 MPa·m^1/2 at 2200°C. The use of higher purity starting materials improved the mechanical behavior in the ultra-high temperature regime compared to previous studies.     

Several properties of mineral admixtured lightweight mortars at elevated temperatures

The improvement of thermal and mechanical properties of mortars including expanded perlite aggregate (EPA) containing either clinoptilolite, a type of natural zeolite (NZ), waste glass powder (GP) or blast furnace slag (BFS) cured at elevated temperature was analyzed using thermal conductivity, compressive strength, flexure strength and dry unit weight. EPA mortar specimens were prepared by replacing a varying part of the portland cement with the above minerals. All mortar samples were prepared and cured at 23±1°C lime saturated water for 28 days. The maximum thermal conductivity of 1.3511W/mK was determined with the control samples containing plain cement. GP has shown 1 and 4% decrease for both 10, 20% GP and 25% EPA, respectively. Both BFS and NZ have a decreasing effect on thermal conductivity. The experiments were carried out, in which the samples were subjected to temperature of 300, 500 and 800°C for 2 h, then cooled in air. The results indicated that all the mortars exposed to temperature of 500 and 800°C shown a significant decrease in thermal conductivity, compressive strength and flexure strength. However, compared with the mortars including 25% EPA, adding the other admixtures at all level replacement decreased thermal conductivity, compressive strength, flexure strength and dry unit weight as a function of replacement percent. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies in disperse dye transfer mechanism in polyester–viscose union at elevated temperatures

The thermofixation process of dyeing polyethylene terephthalate–viscose union fabric with disperse dyes has been experimentally studied with a view to understanding the phenomena of dyeing polyester blends. It is shown how the distribution of a disperse dyestuff changes on the terylene and viscose portions of a union during different stages of dyeing by the thermofixation process. Equilibrium adsorption isotherm and rate curves of adsorption of disperse dyes on the polyester portion of the union have been determined. The nature of staining of the viscose portion of the union with different disperse dyes has been investigated. From the presented typical data it is possible to deduce fairly simple semiempirical rules regarding the phenomena of the thermofixation process of dyeing polyester–viscose union. It is pointed out that it is not possible to derive an exact thermodynamic theory to explain the data and describe the molecular mechanisms in such systems.     

Development of methanol selective membranes for separation of methanol–methyl tertiary butyl ether mixtures by pervaporation

Several copolymers of acrylonitrile (AN) were synthesized. Methanol selective membranes were prepared from these copolymers of AN. The other monomers in the copolymers were selected on the basis of their solubility parameter values relative to those of methanol. These were hydroxyethyl methacrylate, methacrylic acid, and vinyl pyrrolidone. Thus, pervaporative separation of methanol from its mixture with methyl tertiary butyl ether over the entire concentration range of 0–100% methanol was studied using these copolymer membranes of AN. For each copolymer of AN three different membranes with different copolymer compositions were prepared. Copolymers of AN with hydroxyethyl methacrylate and methacrylic acid showed high selectivity and moderate flux for methanol (2561, 773, 0.057, and 0.045 kg/m² h, respectively, with a membrane of 50‐μm thickness for a feed mixture containing 5% methanol at 30°C). A copolymer of AN with vinyl pyrrolidone showed comparable flux, but methanol selectivity of this membrane was poor. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2645–2659, 1999     

Thermal properties of alkali‐activated aluminosilicate composite with lightweight aggregates at elevated temperatures

Thermal diffusivity, specific heat capacity and linear thermal expansion coefficient of a lightweight composite with alkali‐activated aluminosilicate binder and heat‐resistant aggregate mixture of expanded vermiculite and electrical porcelain are measured in a wide temperature range. Experimental results show that the studied material has good prerequisites for high‐temperature applications. The apparent thermal diffusivity at one‐sided heating is significantly lower than at room temperature, and decreases for temperatures higher than 400^°C. The effective specific heat capacity at elevated temperatures increases with temperature in almost the whole analyzed temperature range. The linear thermal expansion coefficient is substantially lower compared with common cement‐based composites. Copyright © 2010 John Wiley & Sons, Ltd.     

Crosslinked polyethylene at elevated temperatures

The behaviour of crosslinked polyethylene has been studied by differential thermal analysis (d.t.a.) up to 150°C, by stress relaxation up to 240°C and by thermogravimetry (t.g.) up to 350°C. No single technique is sufficient to characterize the polymer. D.t.a. gives a very rapid indication of the crystalline portion of the crosslinked polyethylene; t.g. shows the loss of degradation products some of which may be associated with crosslinking; stress relaxation gives information on crosslinking and degradation but is time consuming and does not provide absolute values. The results obtained agree with earlier work that showed marked differences between the properties obtained with low and high amounts of peroxide.     

Microstructural stability at elevated temperatures

The factors affecting the diffusion-controlled coarsening of microstructures at elevated temperatures are reviewed in this paper. Coarsening can occur in a variety of different ways. Perhaps the most familiar of these is Ostwald ripening of a dispersed phase, e.g. precipitates in a 2-phase alloy. However, there are other related Ostwald-ripening-types of processes, including coarsening of dispersed phases in 2-dimensions (e.g. precipitates in thin films, ‘fibers’ in directionally solidified eutectics) and coarsening of particles that grow in three dimensions in a 2-dimensional diffusion field (e.g. grain-boundary precipitates, particles on a substrate). Coarsening by fault migration, which is an important issue in the microstructural stability of directionally solidified rod and lamellar eutectics, and discontinuous coarsening, which affects the stability of cellular microstructures produced by discontinuous precipitation, eutectoid decomposition and eutectic solidification, are also discussed. The principal predictions of theories of these various types of coarsening mechanisms are described, and exemplified where possible by reference to published data. Emphasis is placed on ability of current theory to explain existing data obtained from real as well as computer simulation experiments. Possible reasons for the shortcomings of theory are discussed.     

Separation of methanol‐tetrahydrofuran mixtures by heteroazeotropic distillation and pervaporation

The experimental investigation of the separation of tetrahydrofuran‐methanol by heteroazeotropic‐batch‐distillation and methanol‐hexane by pervaporation is presented. In particular for this last task, four different specialty commercial membranes were tested (varying feed concentration and temperature). The “pore filling” PolyAn membranes show methanol permeance values higher than 5100 GPU (Typ M2^®); separation factor of 19; and a selectivity of about 119 (Typ M1^®). From the results, a coupling phenomenon was observed. An assessment of the temperature effect in the pervaporation process corroborates the hypothesis of the presence of a coupling phenomenon. Finally, a discussion is made on two industrial scale units for the separation of the same mixture: a system of a distillation column integrated with a decanter and stand‐alone pervaporation unit. The energetic comparison shows that when using pervaporation a large reduction of the energetic consumption compared to a conventional distillation system (up to 29%) can be obtained. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2584–2595, 2014     

Some properties of polyethylene–heptadecane mixtures

A mixture of high‐density polyethylene and its low‐molecular‐weight analogue heptadecane was studied. The mixture behaved as a compound, that is, differently from polyethylene. Heptadecane reduced the crystallinity of polyethylene, and it intricately changed the concentration of centers sorbing phenyl‐β‐naphthylamine, the antioxidant, and simultaneously changed the equilibrium constant of sorption. Heptadecane also prolonged the duration of the antioxidant action in polyethylene. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2597–2603, 2003     

Effect of polypropylene fibers on thermogravimetric properties of self‐compacting concrete at elevated temperatures

In this study, the effect of polypropylene (PP) fibers on thermogravimetric parameters of self‐compacting concrete (SCC) containing indigenous materials was investigated experimentally and statistically. The mixes containing cement, water, fly ash, fine aggregate, coarse aggregate, and super plasticizer, with the addition of PP fibers (0%, 0.05%, 0.1%, and 0.15%) by volume of the mixtures, were prepared. The physical properties of SCC were determined at elevated temperatures (200, 400, and 600 °C) after cooling in the laboratory. Regression models were developed to determine the responses, and the optimum amount of 0.05% PP fibers by volume was measured. Copyright © 2012 John Wiley & Sons, Ltd.