气相色谱法测定多溴联苯的蒸气压

采用气相色谱法,以二氯二苯三氯乙烷(DDT)为参考化合物,测定了6个多溴联苯(PBBs)在不同温度条件下的蒸气压, 然后使用Slide数理统计软件、以最小二乘法回归计算出Antoine方程的A,B,C参数,从而建立了6个PBBs的蒸气压与温度 的关联式。初步探讨了分子连接性指数与蒸气压的相关性,结果发现一阶拓扑指数与蒸气压表现出很好的线性关系,两者 的相关系数的平方大于0.99,标准偏差小于0.08。     

胍基硅前驱体的合成及应用

以胍基取代的二甲基二氯硅烷与胺基锂反应合成了3种硅基化合物,使用核磁共振、高分辨质谱、元素分析对化合物结构进行了表征,通过热重分析(TGA)研究了化合物的热稳定性、挥发性、蒸汽压等性能。 3种化合物均具有良好的热稳定性及挥发性,无明显热分解过程,固体残留小于1%,接近纯挥发过程,最高蒸汽压在3600~5300 Pa,满足前驱体使用要求。 以二甲基-胍基-甲乙胺基-硅烷为前驱体,采用螺旋波等离子体气相沉积(HWPCVD)工艺制备了硅基薄膜,使用X射线光电子能谱(XPS)和扫描电子显微镜(SEM)分析了薄膜的化学组成和膜表面结构,XPS分析结果证实该薄膜为Si、N、C组成,实验结果表明,该类胍基硅化合物可作为硅基化学气相沉积(CVD)前驱体材料应用于集成电路制造。     

Thermodynamic study on the sublimation of diphenyl and triphenyl substituted acetic and propanoic acids

Knudsen mass-loss effusion technique was used for measuring the vapor pressures at different temperatures of the following crystalline compounds: diphenylacetic acid, between 357.27 and 379.08 K; triphenylacetic acid, between 418.98 and 436.97 K; 2,2-diphenylpropanoic acid, between 366.08 and 386.00 K; 3,3-diphenylpropanoic acid, between 366.09 and 386.03 K; 3,3,3-triphenylpropanoic acid, between 402.17 and 420.10 K. From the temperature dependence of the vapor pressure of each crystalline compound, the standard (p ⁰ = 10⁵ Pa) molar enthalpies and Gibbs energies of sublimation, at T = 298.15 K, were derived. The measured thermodynamic properties are compared with literature results for phenylacetic and phenylpropanoic acids and correlations for estimation of the vapor pressures from the enthalpy of sublimation and the temperature of fusion of these and other compounds are presented.     

Phase diagram of the selenium–sulfur system in the pressure range 1 × 10<Superscript>–5</Superscript>–1 × 10<Superscript>–1</Superscript> MPa

The partial pressures of the components in the saturated vapor of the Se–S system were determined and presented as the temperature–concentration dependences. Based on these data, the boundaries of the melt–vapor phase transition at atmospheric pressure and in vacuum (1350, 100, and 10 Pa) were calculated. A complete phase diagram was constructed, which included the vapor–liquid equilibrium fields at atmospheric and low pressures, whose boundaries allowed us to determine the behavior of sulfur and selenium during distillation separation.     

Vapor pressure and density of thermotropic liquid crystals: MBBA, 5CB, and novel fluorinated mesogens

The vapor pressures and densities of six thermotropic liquid crystal-forming molecules (mesogens) have been determined experimentally as functions of temperature. The ubiquitous mesogenic compounds n-(4-methoxybenzylidene)-4-butylaniline (MBBA) and 4'-cyano-4-n-pentylbiphenyl (5CB), which both exhibit room-temperature nematic phases, are examined in this study, as are a number of trifluorinated bicyclohexyl and cyclohexylbiphenyl derivatives which find modern use in display applications. Although thermotropic mesogens are of prime importance in modern optoelectronic technologies, there is a scarcity of reliable saturation pressure data for such systems. An apparatus suitable for measurements of vapor pressures between 0.1 and 1333 Pa in the temperature range 298-523 K has been constructed. The adequacy of the apparatus has been verified by measurements on n-hexadecane at temperatures between 304 and 372 K, corresponding to vapor pressures between 0.4 and approximately 100 Pa. To our knowledge, our measurements represent the first reliable data for the saturation pressure of the fluid phase of these types of thermotropic compounds; we show that existing data for MBBA is thermodynamically inconsistent. The densities of the fluid phases of these compounds are also measured by means of a glass pycnometer at temperatures between 293 and 368 K.     

Adipic and malonic acid aqueous solutions: surface tensions and saturation vapor pressures

The surface tension of adipic aqueous solutions was measured as a function of temperature (T=278-313 K) and adipic acid mole fraction (X=0.000-0.003) using the Wilhelmy plate method. A parametrization fitted to these data is presented. The evaporation rates of binary water-malonic and water-adipic acid droplets were measured with a TDMA technique at different temperatures (T=293-300 K) and relative humidities (58-80%), and the saturation vapor pressures of subcooled liquid malonic and adipic acids were derived from the data using a binary evaporation model. The temperature dependence of the vapor pressures was obtained as least-squares fits to the derived vapor pressures: ln(Psat,l) (Pa)=220.2389-22634.96/T (K)-26.66767 ln T (K) for malonic acid and ln(Psat,l) (Pa)=140.6704-18230.97/T (K)-15.48011 ln T (K) for adipic acid.     

Micro conduction calorimeters to measure enthalpies of vaporization

Details of the construction of micro-conduction calorimeters for measuring enthalpies of vaporization (or sublimation) are described. Accuracy and precision of the calorimeters were tested by the use of a few standard reference compounds. Experimental results showed that the enthalpies of vaporization could be measured for compounds of vapor pressures of 10 Pa to 10 kPa at 298 K with uncertainty less than 0.2 per cent. Results of enthalpy of vaporization measurements for some compounds are also given. Since calorimetric cells of these calorimeters were composed of glass and PTFE, the calorimeters made it possible to measure the enthalpies of vaporization for metal corrosive compounds.     

Recommended sublimation pressure and enthalpy of benzene

Recommended vapor pressures of solid benzene (CAS Registry Number: 71-43-2) which are consistent with thermodynamically related crystalline and ideal-gas heat capacities as well as with properties of the liquid phase at the triple point temperature (vapor pressure, enthalpy of vaporization) were established. The recommended data were developed by a multi-property simultaneous correlation of vapor pressures and related thermal data. Vapor pressures measured in this work using the static method in the temperature range from 233 K to 260 K, covering pressure range from 99 Pa to 1230 Pa, were included in the simultaneous correlation. The enthalpy of sublimation was established with uncertainty significantly lower than the previously recommended values.     

Determination of cocaine and heroin vapor pressures using commercial and illicit samples

The establishment of drug vapor pressure reference values provides valuable information in the development of vapor sensing devices for drug detection. The purpose of this work was to determine equilibrium headspace vapor pressures for commercial and illicit drug samples for use in such applications. Samples of cocaine, both free base and hydrochloride forms, and heroin hydrochloride were evaluated. The procedure used to measure the vapor pressures was a modification of a previously published method. Vapor pressure values at 20 degrees C previously reported for cocaine free base range from 0.37 x 10(-7) to 1.20 x 10(-7) Torr. The vapor pressure value determined in this study was 2.96 x 10(-7) Torr. It is likely that the discrepancies are due to differences in experimental conditions, varying sources of samples, and uncertainty in the methodologies. When the values were compared for commercial (99% purity) and illicit (unknown purity) sources of cocaine free base, there were no statistical differences in the projected room temperature (20 degrees C) vapor pressure values. However, the commercial and illicit samples of cocaine hydrochloride did show statistical differences. Although no comparison was made with the vapor pressure values for a pure, commercial sample, the vapor pressures of heroin hydrochloride (81% purity) at various temperatures were determined using the method developed for cocaine and are reported in this paper.     

Halogenated methyl-phenyl ethers (anisoles) in the environment: Determination of vapor pressures, aqueous solubilities, Henry's law constants, and gas/water- (Kgw), n-octanol/water- (Kow) and gas/n-octanol (Kgo) partition coefficients

Halogenated methyl-phenyl ethers (methoxybenzenes, anisoles) are ubiquitous organics in the environment although they are not produced in industrial quantities. Modelling the fate of organic pollutants such as halogenated anisoles requires a knowledge of the fundamental physico-chemical properties of these compounds. The isomer-specific separation and detection of 60 of the 134 possible congeners allowing an environmental fingerprinting are reported in this study. The vapor pressure p0(L) of more than 60 and further physico-chemical properties of 26 available congeners are given. Vapor pressures p0(L), water solubilities S(L)W, and n-octanol/water partition coefficients Kow were determined by capillary HR-GC (High Resolution Gas Chromatography) on a non-polar phase and by RP-HPLC (Reversed Phase High Performance Liquid Chromatography) on a C18 phase with chlorobenzenes as reference standards. From these experimental data the Henry's law constants H, and the gas/water Kgw and gas/n-octanol Kgo partition coefficients were calculated. We found that vapor pressures, water solubilities, and n-octanol/water partition coefficients of the halogenated anisoles are close to those of the chlorobenzenes. A similar environmental fate of both groups can, therefore, be predicted.     

Application of correlation-gas chromatography to evaluate the vaporization enthalpy of a component in an equilibrium mixture

The vaporization enthalpies and vapor pressures of acetoin, ethyl 3-hydroxybutyrate and ethyl 3-hydroxyhexanoate, found in a variety of foods and flavors, are evaluated at T = 298.15 K using correlation-gas chromatography; values of (48.7 ± 0.4), (55.9 ± 0.6) and (61.9 ± 0.6) kJ mol⁻¹, respectively, were obtained. These values are in good agreement with estimated values. Vapor pressures of the standards as a function of temperature were also used to calculate vapor pressures of the target compounds and all resulting data were fit to second order polynomials. These polynomials were then used to predict boiling temperatures of both standards and target substances. Agreement with experimental boiling temperatures was generally within 10 K suggesting that vapor pressures are accurate to within a factor of two. Acetoin exists as an equilibrium mixture of monomer and dimer. This report provides an example of the utility of using correlation-gas chromatography to obtain thermochemical data on an impure material.     

Stability of Ca-montmorillonite hydrates: a computer simulation study

Classic simulations are used to study interlayer structure, swelling curves, and stability of Ca-montmorillonite hydrates. For this purpose, NP(zz)T and muP(zz)T ensembles are sampled for ground level and given burial conditions. For ground level conditions, a double layer hydrate having 15.0 A of basal spacing is the predominant state for relative vapor pressures (p/p0) ranging 0.6-1.0. A triple hydrate counting on 17.9 A of interlaminar distance was also found stable for p/p0 = 1.0. For low vapor pressures, the system may produce a less hydrated but still double layer state with 13.5 A or even a single layer hydrate with 12.2 A of interlaminar distance. This depends on the established initial conditions. On the other hand, the effect of burial conditions is two sided. It was found that it enhances dehydration for all vapor pressures except for saturation, where swelling is promoted.     

Estimation of solid vapor pressures of pure compounds at different temperatures using a multilayer network with particle swarm algorithm

Solid vapor pressures (P^S) of pure compounds have been estimated at several temperatures using a hybrid model that includes an artificial neural network with particle swarm optimization and a group contribution method. A total of 700 data points of solid vapor pressure versus temperature, corresponding to 70 substances, have been used to train the neural network developed using Matlab. The following properties were considered as input parameters: 36 structural groups, molecular mass, dipole moment, temperature and pressure in the triple point (upper limit of the sublimation curve), and the limiting value P^S → 0 as T → 0 (lower limit of the sublimation curve). Then, the solid vapor pressures of 28 other solids (280 data points) have been predicted and results compared to experimental data from the literature. The study shows that the proposed method represents an excellent alternative for the prediction of solid vapor pressures from the knowledge of some other available properties and from the structure of the molecule.     

Determination of Vapor Liquid Equilibrium from the Kovats Retention Index on Dimethylsilicone using the Wilson Mixing Model

Non-ideal mixing in a dimethylsilicone stationary phase is modeled according to the Wilson activity coefficient. Pure liquid vapor pressures of alkylated compound series are calculated from capillary GLC retention with the functional group heat of solution in a polymer solvent. The new method uses the Kovats index, molar mass, and functional group to determine the bubble line of a compound. Boiling points at reduced and normal pressure are compared to literature values of 194 gasoline components. An unlike molecular pair interaction parameter is derived, using only bubble line data of the pure liquids. Binary phase diagrams are constructed and compared to vapor liquid equilibrium data.     

Broad-Range Detection of Water Vapor using Cavity Ring-down Spectrometer

Quantitative measurement of water vapor is essential in many fields including semiconduc-tor industry, combustion diagnosis, meteorology, and atmospheric studies. We present an optical hygrometer based on cavity ring-down spectroscopy. The instrument is high-vacuum compatible, self-calibrated by using the free-spectral-range of the ring-down cavity made of low-thermal-expansion Invar. Using a single tunable diode laser working at 1.39 μm, detection of trace water vapor in vacuum and in high-purity helium gas, and also determination of humidity at ambient conditions, have been demonstrated. It indicates that the instrument can be used to detect the partial pressure of water vapor in a very broad range from 10^-7 Pa to 10³ Pa. Such an optical hygrometer can be potentially applied as a primary moisture standard to determine the vapor pressures of water (ice) at low temperatures.     

Chromatography with supercritical fluids

Molecular interactions in the gas phase may be utilized for enhancing the volatility of substances in gas chromatography. A study of the effect of pressure on equilibria in GLC revealed that at higher pressures these interactions are quite appreciable, especially near the critical point. Measurements of plate heights show that with suitable adaptation of columns to the specific properties of high-pressure, dense fluids, the separating efficiency can be high and the speed of analysis fast. Experiments conducted with n-pentane and isopropanol as mobile fluids under supercritical conditions demonstrate that the volatility of heavy compounds may be enhanced by a factor of as much as 10⁴. With either a liquid or a solid adsorbent as a stationary phase, chromatography with supercritical fluids proves to be very suitable for the rapid analysis of heavy compounds. The effect of various operational parameters on the separation is discussed. Certain features of the technique arc illustrated with several examples.bl]     

In Situ Direct Measurement of Vapor Pressures and Thermodynamic Parameters of Volatile Organic Materials in the Vapor Phase: Benzoic Acid,Ferrocene, and Naphthalene

We report the direct determination of vapor pressures and optical and thermodynamic parameters of powders of low‐volatile materials in their vapor phase using a commercial UV/Vis spectrometer. This methodology is based on the linear proportionality between the density of the saturated gas of the material and the absorbance of the gas at different temperatures. The vapor pressure values determined for benzoic acid and ferrocene are in good agreement with those reported in the literature with ～2–7 % uncertainty. Thermodynamic parameters of benzoic acid, ferrocene, and naphthalene are determined in situ at temperatures below their melting points. The sublimation enthalpies of the investigated organic molecules are in excellent agreement with the ICTAC recommended values (less than 1 % difference). This method has been used to measure vapor pressures and thermodynamic parameters of organic volatile materials with vapor pressures of ～0.5–355 Pa in the 50–100 °C temperature range.     

Some thermodynamic properties of benzocaine

The vaporization enthalpy of benzocaine, ethyl 4-aminobenzoate, has been evaluated using correlation gas chromatography at 298.15 K. The temperature dependence of retention time has also been used to evaluate the vapor pressure of the sub-cooled liquid from 298.15 K to the fusion temperature, 365.2 K, by correlation with the vapor pressures of the compounds used as standards. The vaporization enthalpy calculated from the vapor pressures of benzocaine at the melting point was combined with the experimental fusion enthalpy to evaluate the sublimation enthalpy at the fusion temperature. Application of the Clausius–Clapeyron equation together with the vapor pressure common to both phases permitted calculation of the vapor pressure of the solid at 298.15 K. Similar calculations were performed for two of the standards that were solids for comparisons with experimental data. Vaporization and sublimation enthalpies of (91.8 ± 4.2) and (112.9 ± 4.3) kJ mol^?1 are calculated for benzocaine at 298.15 K as are vapor pressures of 0.0083 and 0.0018 Pa for the sub-cooled liquid and crystalline material, respectively.     

Neutral and charged 1-butyl-3-methylimidazolium triflate clusters: equilibrium concentration in the vapor phase and thermal properties of nanometric droplets

Ground state energy, structure, and harmonic vibrational modes of 1-butyl-3-methylimidazolium triflate ([bmim][Tf]) clusters have been computed using an all-atom empirical potential model. Neutral and charged species have been considered up to a size (30 [bmim][Tf] pairs) well into the nanometric range. Free energy computations and thermodynamic modeling have been used to predict the equilibrium composition of the vapor phase as a function of temperature and density. The results point to a nonnegligible concentration of very small charged species at pressures (P approximately 0.01 Pa) and temperatures (T >or= 600 K) at the boundary of the stability range of [bmim][Tf]. Thermal properties of nanometric neutral droplets have been investigated in the 0 相似文献   

Melt–Vapor Phase Diagram of the Te–S System

The values of partial pressure of saturated vapor of the constituents of the Те–S system are determined from boiling points. The boundaries of the melt–vapor phase transition at atmospheric pressure and in vacuum of 2000 and 100 Pa are calculated on the basis of partial pressures. A phase diagram that includes vapor–liquid equilibrium fields whose boundaries allow us to assess the behavior of elements upon distillation fractioning is plotted. It is established that the separation of elements is possible at the first evaporation–condensation cycle. Complications can be caused by crystallization of a sulfur solid solution in tellurium.