Isobaric thermal expansivities of binary mixtures ofn-Hexane with 1-hexanol at pressures from 0.1 to 350 MPa and at temperatures from 303 to 503 K

Isobaric thermal expansivities, α_p(p, T), of seven binary mixtures ofn-hexane with l-hexanol (0.0553, 0.1088, 0.2737, 0.2983, 0.4962, 0.6036, and 0.7455 mol fraction of l-hexanol) have been measured with a pressure-controlled scanning calorimeter over the pressure range from just above the saturation pressures to 350 MPa and at temperatures from 302.6 to 503.1 K. The low-temperature isotherms of α_p for particular mixtures observed with respect to the unique crossing point ofn-hexane isotherms reveal an association effect which is reduced when the temperature increases. The high-temperature isotherms of α_p are very similar to the isotherms of puren-hexane, especially for lower mole fractions ofn-hexanol. No known equation of state can reproduce these properties.     

Volumetric measurements under pressure for 2,2,4-trimethylpentane at temperatures up to 353.15 K and for benzene and three of their mixtures at temperatures up to 348.15 K

(p, V, T) data have been obtained in the form of volume ratios relative to 0.1 MPa for benzene (298.15 to 348.15 K), 2,2,4-trimethylpentane (TMP) (313.15 to 353.15 K), and their mixtures near 0.25, 0.5, and 0.75 mole fraction of benzene (313.15 to 348.15 K) for pressures up to near the freezing pressures for benzene and the mixtures, and up to 400 MPa for TMP. Isothermal compressibilitiesκ _T, isobaric expansivitie α, changes in heat capacity at constant pressureΔC _p, and excess molar volumesV ^E have been determined from the data. Literature data at atmospheric pressure have been used to convert theΔC _p toC _p at several temperatures. The isobars for α over the temperature range 278.15 to 353.15 K for TMP intersect near 47 MPa and reverse their order in temperature when plotted against pressure; normalization of the α's by dividing the values at each temperature by the α at 0.1 MPa prevents both the intersection and the reversal of the order. TheV ^E are positive and have an unusual dependence on pressure: they increase with temperature and pressure so that the order of the curves for 0.1, 50, and 100 MPa changes in going from 313.15 to 348.15 K.     

Thermophysical properties ofm-cresol as a function of temperture (303 to 503 K) and pressure (0.1 to 400 MPa)

Measured and derived thermophysical properties ofm-cresol are reported for pressures up to 400 MPa at temperatures from 303 to 503 K. Isobaric thermal expansivities were measured by pressure-scanning calorimetry from 303 to 503 K and 0.1 to 400 MPa. The specific volume at 353 K was determined by pycnometry at atmospheric pressure and calculated from isothermal compressibilities measured as a funtion of pressure up to 400 MPa. Specific volumes at other temperatures and pressures are calculated from isothermal compressibilities measured as a function of pressure up to 400 MPa. Specific volumes, isothermal compressibilities, thermal coefficients of pressure, and isobaric and isochoric heat capacities at pressures up to 400 MPa are derived at several temperatures. The effects of pressure on the isobaric heat capacities ofm-cresol,n-hexane, and water are compared. The effects of self-association ofm-cresol are apparent in both the thermal expansivity and the heat capacity data.     

Low temperature preparation ofβ-alumina by an alkoxide route

β-alumina has been prepared by the thermal decomposition of a mixture of sodium and aluminium isopropoxides followed by heating up to 1000°C. It has been found necessary to use sodium isopropoxide in excess (25–30%) for the complete formation ofβ-alumina at 1000°C. On the other hand one obtains a mixture ofβ-alumina andα-alumina when the starting materials are taken in the stoichiometric ratio Na₂O:11Al₂O₃. DTA, TG and DTG studies of a mixture of sodium and aluminium isopropoxide showedβ-alumina formation at 1000°C. NCL Communication No. 4446.     

Benzene-methanol association. The excess molar enthalpy and second virial cross coefficients of (benzene+methanol)(g) and (cyclohexane+methanol)(g)

New measurements of the excess molar enthalpyH _m ¹ of (yCH₃OH+(1−y)C₆H₆)(g) and (yCH₃OH+(1−y)C₆H₁₂)(g) measured at standard atmospheric pressure over the temperature range 363.2 to 433.2 K are reported. these measurements supplement earlier measurements made over the range 454.2 to 523.0 K at pressures up to 4.0 MPa. The nonideality of the methanol vapor is described using a quasi chemical model model in which only dimer and tetramer association equilibria are considered. The values ofH _m ¹ for the (methanol+cyclohexane)(g) mixture were found to agree well with values calculated using the association model. For (methanol+benzene)(g) the experimental values ofH _m ¹ were found to be approximately 20% smaller than values calculated from the model and this was attributed to weak association between the unlike molecules. A quasi-chemical model used to describe the association between the unlike molecules yielded a value of the equilibrium constantK ₁₂(298.15 K)=0.22 MPa⁻¹, and a value for the enthalpy of the methanol-benzene association of ΔH ₁₂=−13 kJ·mol⁻¹. Second virial crosscoefficientsB ₁₂ for methanol-cyclohexane and methanol-benzene have been derived from theH _m ¹ measurements.     

Thermophysical properties of quinoline as a function of temperature (303–503 K) and pressure (0.1–400 MPa)

Measured and derived thermophysical properties of quinoline are reported for pressures up to 400 MPa at temperatures from 303 to 503 K. The specific volume at 353 K was determined from the specific volume at atmospheric pressure measured b) pycnometry and from isothermal compressibilities measured as a function of pressure up to 400 M Pa. Specific volumes, isothermal compressibilities, thermal coellicients of pressure, and isobaric and isochoric heat capacities at pressures up to 4011 MPa are derived at several temperatures. The effects of pressure on the isobaric heat capacity of quinoline, a weakly self-associated liquid. are discussed and compared with the pressure effects on heat capacities ofn-hexane andm-cresol.     

Feasibility of <Emphasis Type="Italic">m</Emphasis>-cresol degradation using an indigenous mixed microbial culture with glucose as co-substrate

An indigenous mixed culture of microorganisms, isolated from the soil of a gasoline filling station, was used in degrading m-cresol in presence of glucose as an alternative carbon source. Initial glucose concentration was kept at either 250 or 500 mg l⁻¹, to initiate and support necessary culture growth, and that of m-cresol was varied between 50 and 400 mg l⁻¹. A maximum total biomass yield value of 0.925 g g⁻¹ was obtained at 100 mg l⁻¹ m-cresol and 500 mg l⁻¹ glucose initial concentrations in the media. Variation in the experimentally observed specific growth rate revealed that m-cresol initial concentrations, above 100 mg l⁻¹, inhibited the culture growth irrespective of the glucose concentrations used in the study. Complete degradation of m-cresol was observed within a time period of 18–26 h depending upon the initial concentrations of m-cresol and glucose in the media; on the other hand, glucose utilization was quick and preceded m-cresol degradation. A sum kinetics model was used to describe the variation in the culture specific growth rate, which gave a high coefficient of determination (R ²) value >0.98. From the interaction parameter values obtained by solving this model, the inhibitory effect of glucose on m-cresol degradation by the culture was found to be more pronounced compared to the effect of m-cresol on glucose utilization. This study showed good potential of the indigenous mixed culture in degrading m-cresol when it is provided with a simple alternative carbon source, such as glucose, for supporting its growth.     

An analytical equation of state for mercury

This paper presents a procedure for predicting the equation of state of mercury, by including mercury in the scope of a new statistical mechanical equation of state that is known for normal fluids. The scaling constants are the latent heat of vaporization and the density at the melting temperature, which are related to the cohesive energy density. Since experimental data for the second virial coefficient of mercury are scarce, a corresponding-states correlation of normal fluids is used to calculate theB(T) of mercury. The free parameter of the ISM equation, λ, compensates for the uncertainties inB(T). Also, we can predict the values of two temperature-dependent parameters, α(T) andb(T), with satisfactory accuracy from a knowledge of ΔH _vap andp _m, without knowing any details of the intermolecular potentials. While the values ofB(T) are scarce for mercury and the vapor pressure of this metal at low temperatures is very small, an equation of state for mercury from two scaling parameters (ΔH _vap,p _m) predicts the density of Hg from the melting point up to 100° above the boiling temperature to within 5%.     

Thermal conductivity of amorphous Teflon (AF 1600) at high pressure

The thermal conductivity, λ of amorphous Teflon AF 1600 [poly(1,3-dioxole-4,5-difluoro-2,2-bis(trifluoromethyl)-co-tetrafluoroethylene)] has been measured at pressures up to 2 GPa in the temperature range 93–392 K. At 295 K and atmospheric pressure, we obtained λ=0.116, W·m⁻¹·K⁻¹. The bulk modulus was measured up to 1.0 GPa in the temperature range 150–296 K and the combined data yielded the following values ofg=(∂ln λ ∂lnp) _r :2.8±0.2 at 296 K, 3.0±0.2 at 258 K, 3.0±0.2 at 236 K. 3.4±0.2 at 200 K. and 3.4±0.2 at 150 K.     

Energy spectrum of charge carriers in Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te

The electrical conductivity (σ), Hall coefficient (R _H, and thermopower (α) of Sm _x Pb_{1 − x} Te have been measured at temperatures from 80 to 800 K. The results demonstrate that the Sm _x Pb_{1 − x} Te solid solutions with x ≤ 0.04 are p-type semiconductors. We have determined the electron effective mass at the conduction band bottom (m _n = (0.031 ± 0.001)m ₀) and Fermi level (m* = (0.06 ± 0.001)m ₀) and the hole effective mass (m _p = (0.34 ± 0.001)m ₀). The temperature-dependent σ, R _H, and α data are interpreted in terms of a model with two carrier types.     

Tilted and crossing vortex chains in layered superconductors

In presence of the Josephson vortex lattice in layered superconductors, small c-axis magnetic field penetrates in the form of vortex chains. In general, structure of a single chain is determined by the ratio of the London [λ] and Josephson [λ _J ] lengths, α=λ/λ _J . The chain is composed of tilted vortices at large α's (tilted chain) and at small α's it consists of crossing array of Josephson vortices and pancake-vortex stacks (crossing chain). We study chain structures at the intermediate α's and found two types of phase transitions. For α≲0.6 the groud state is given by the crossing chain in a wide range of pancake separationsa≳[2−3]λ _J . However, due to attractive coupling between deformed pancake stacks, the equilibrium separation can not exceed some maximum value depending on the in-plane field and α. The first phase transition takes place with decreasing pancake-stack separation a ata≳[1−2]λ _J , and rather wide range of the ratio α, 0.4≲α≲0.65. With decreasing a, the crossing chain goes through intermediate strongly-deformed configurations and smoothly transforms into the tilted chain via the second-order phase transition. Another phase transition occurs at very small densities of pancake vortices,a ~ [20−30]λ _J , and only when α exceeds a certain critical value ∼0.5. In this case small c-axis field penetrates in the form of kinks. However, at very small concentration of kinks, the kinked chains are replaced with strongly deformed crossing chains via the first-order phase transition. This transition is accompanied by a very large jump in the pancake density.     

Thermal expansion of lead silicate glasses

The thermal expansion, when heated from 77 to 273 K, of two samples of lead silicate glass, containing 21 and 28.5 mol % PbO, has been measured. The temperature dependence of the thermal expansion coefficient,α, is in qualitative agreement with the expansion behaviour of sodium silicate glass. However, the addition of ∼ 21 mol % PbO to silica is required to produce an increase in the magnitude ofα comparable to the addition of only ∼ 10 mol % Na₂O. The differences in the magnitudes ofα for lead and soda glasses are considered in the right of previous proposals for their structures.     

Thermal sensor properties of PANI(EB)-CSA<Subscript>x</Subscript> (X = 0.4 ±0.1 mol) polymer thin films

Films of polyaniline(EB) doped with camphor sulfonic acid (CSA) fromm-cresol on glass substrates exhibit considerable metallic properties. Such polymer metallic films have thermal sensitivity superior to ceramic metal (Cermet) films, prepared by metallo organic deposition (MOD) technique on silicon substrates. These PANI(EB)-CSA_x (X = 0.5, 0.4, 0.3 mol) polymer films were developed through controlled temperature atmosphere 60 ±2°C for 60 min, and with the help of temperature dependence of resistivity (ρ) values, high temperature coefficient of resistance (TCR) i.e. a values, and figure of merit (ρα) values of these films, thermal sensitivity were compared from that we observed. Among the three doping ratios the PANI(EB)—CSA_{0.3 mol}i film (4.4 ⧎m thick) on glass substrate resistivity (ρ) values in the range of 838–1699 Ω.⧎m with high TCR i.e. a = 10,291 ppm/°C and figure of merit (ρα) value in range of 8.62-17.48 Ωm/dgC seems to be the best. This paper deals with these superior thermal-sensing properties together with optical studies and surface topography by atomic force microscopy (AFM). These polymer films offer design advantages in developing ‘thin film polymer thermal sensor’.     

Effect of titanium on the structure and mechanical properties of Cu-Al-Ti alloys

The structure and mechanical properties of Cu10 wt% Al base alloys with 0–2.5 wt% Ti additions were investigated using transmission electron microscopy, optical microscopy and tensile tests. Addition of titanium has a decreasing effect on the grain size after quenching fromα + β region and causes significant strengthening of alloys. Alloy containing 1 wt%Ti quenched from 900° C shows mixture ofα, retainedβ (DO₃), disorderedβ′ (3R) and orderedβ′ ₁ (18R) martensites. Alloy with 2.5 wt% Ti addition after quenching containsα, retainedβ (DO₃), ordered T₁ phase of L2₁ superlattice and orderedβ′ ₁ martensite with either R18 or L1₀ structure indicating different stacking of ordered planes as the effect of titanium addition.     

Speed-of-Sound Measurements in n-Nonane at Temperatures between 293.15 and 393.15 K and at Pressures up to 100 MPa

Speed-of-sound measurements in liquid phase n-nonane (C₉H₂₀) are reported along six isotherms between 293.15 and 393.15 K and at pressures up to 100 MPa. The experimental technique is based on a double reflector pulse-echo method. The acoustic path lengths were obtained by comparison with measurements carried out at atmospheric pressure and ambient temperature in pure water. The values of the speed of sound are characterized by an overall estimated uncertainty of less than 0.2 %. These results were compared with literature values and with predictions of a dedicated equation of state.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Photoluminescence and thermal stability of yellow-emitting Sr-α-SiAlON:Eu<Superscript>2+</Superscript> phosphor

Novel α-SiAlON:Eu²⁺-based yellow oxynitride phosphors with the formula Sr_0.375−x Eu _x ²⁺Si_12−m−n Al _m+n O _n N_16−n (m = 0.75, n = x = 0.004–0.04) have been prepared by firing the powder mixture of SrSi₂, α-Si₃N₄, AlN, and Eu₂O₃ at 2,000 °C for 2 h under 1 MPa nitrogen atmosphere. The luminescence properties, the dependence of the activator concentration of Eu²⁺ and the thermal stability of Sr-α-SiAlON:Eu²⁺ phosphor have been investigated in comparison with Ca-α-SiAlON:Eu²⁺ phosphor. Similar to Ca-α-SiAlON:Eu²⁺ phosphor, Sr-α-SiAlON:Eu²⁺ phosphor has the excitation wavelength ranging from the ultraviolet region to 500 nm, and exhibit intense yellow light. The strongest luminescence was achieved at about x = 0.02 with the emission peak at 578 nm, slightly shorter than that of Ca-α-SiAlON:Eu²⁺ phosphor at 581 nm. Temperature-dependent emission intensity of Sr-α-SiAlON:Eu²⁺ phosphor is comparable to that of Ca-α-SiAlON:Eu²⁺ phosphor. The results suggest that the different position of the emission peak for Sr- and Ca-α-SiAlON:Eu²⁺ depends on the composition and the Stokes shift, and the thermal stability is nearly independent of Sr and Ca or fixed by the network of (Si, Al)–(O, N) in α-SiAlON at the same Eu²⁺ concentration.     

Electrical properties of the system lanthanum lead cobalt titanium oxide

Measurements of DC electrical resistivity and Seebeck coefficient on the perovskite system La_1−x Pb _x−δ Co_1−x Ti _x O_3−δ for 0·2≤x≤0·9 have been made in the temperature range 300–800 K. AC conductivity,σ _a.c, of all the samples were measured as a function of temperature (300–573 K) and frequency (1 kHz-1 MHz). DC resistivity behaviour of all the samples is similar. However, the resistivity value, which varies over 5–6 orders of magnitude, depends on both the compositionx and the structure of the samples. All the samples exhibitp-type electronic conduction. The value of Seebeck coefficient,α, for samples withx≤0·5 initially increases with temperature up to a particular temperature. Above this temperature, the behaviour ofα for samples withx≤0·5 and for samples withx>0·5 over the entire temperature range is similar to that of La CoO₃. All the samples exhibit frequency-dependent a.c. conductivity at low temperatures.     

Hot-pressed β-Si3N4 containing small amounts of Be and O in solid solution

Single phase, hot-pressed Si₃N₄ ceramics with relative densities >95% and equiaxed grain structures have been prepared from high purity Si₃N₄ powders having specific surface areas of 8 to 20 m² g⁻¹ and oxygen contents ⩾2 wt % using a small amount of Be₃N₂ or BeSiN₂ as a densification aid. Densification depended sensitively on the concentration of Be and O in a given Si₃N₄ powder and on the usual hot-pressing parameters of pressure, temperature and time. A close association was found between densification and the conversion ofα- toβ-Si₃N₄ during hot-pressing. Based on the data presented, chemical reactions that occur during hot-pressing involve: (1) reaction of the densification aid with SiO₂ on the Si₃N₄ particle surfaces to form BeO and Si₂N₂O; (2) the further reaction of these two reaction products to give probable formation of a transient liquid phase (TLP); and (3) the reaction between TLP andα-Si₃N₄ particles to cause densification, probably by a solution-reprecipitation process, and conversion ofα-Si₃N₄ into aβ-Si₃N₄ solid solution. The chemical composition of a single phaseβ-Si₃N₄ solid solution prepared in this study by hot-pressing was approximately Si_2.9Be_0.1N_3.8O_0.2.     

Semiconductor quantum dots: Theory and phenomenology

Research in semiconductor quantum dots (q-dots) has burgeoned in the past decade. The size (R) of these q-dots ranges from 1 to 100 nm. Based on the theoretical calculations, we propose energy and length scales which help in clarifying the physics of this mesoscopic system. Some of these length scales are: the Bohr exciton radius (α_B*), the carrier de Broglie and diffusion length (λ_D andl _D), the polaron radius (α_p), and the reduction factor modulating the optical matrix element (M _x).R<α_B is an individual particle confinement regime, whereas the larger ones are exciton confinement regime wherein Coulomb interaction play an important role. Similarly a size-dependent dielectric constantε(R) should be used forR<α_p<α_B. An examination ofM _x reveals that an indirect gap material q-dot behaves as a direct gap material in the limit of very small dot size. We have carried out effective mass theory (EMT) calculations to estimate the charge density on the surface of the quantum dot. We present tight binding (TB) calculation to show that the energy upshift scales as 1/R ^x, wherex is less than 2 and the exponent depends on the orientation of the crystallite.     

Chemical vapour deposition of Si3N4 from a gas mixture of Si2Cl6, NH3 and H2

Si₃N₄ layers were obtained on a quartz substrate from a gas mixture of Si₂Cl₆, NH₃ and H₂ under a reduced pressure in a temperature range of 800 to 1300‡ C. Amorphous Si₃N₄ layers that were dense and adherent to the substrate were obtained in a temperature range of 800 to 1100‡ C. On the other hand,α-Si₃N₄ layers were obtained at 1200‡ C and a source-gas ratio (N/Si) of 1.33 to 1.77. The lowest deposition temperature of amorphous Si₃N₄ was considered to be about 700‡ C. The microhardness of amorphous Si₃N₄ obtained in a temperature range of 800 to 1100‡ C was 2400 to 2600 kg mm⁻² (load: 50 g), and that ofα-Si₃N₄ obtained at 1200‡ C was 3400 kg mm⁻². Chlorine contents in the Si₃N₄ layer decreased with increasing deposition temperature and source-gas ratio (N/Si), and with decreasing total pressure.