Effusion Method Research Articles

Synthesis, crystal structure, and thermal behavior of dimethylgold(III) acetate

A dimethylgold(III) compound with an acetate fragment [(CH3)2AuOCOCH3]2 has been synthesized. The complex was identified from the melting point, IR, 1H NMR, and mass spectrometry data. The temperature dependence of saturated vapor pressure over crystals has been measured and the thermodynamic parameters of sublimation have been determined by Knudsen’s effusion method with mass spectrometric measurements of the composition of the gas phase: ΔH subl = 100.87 kJ·mol−1, ΔS subl = 216.67 J·mol−1·K−1. The thermal behavior of the solid compound was investigated by differential thermal analysis. The compound was studied by X-ray diffraction. Crystal data for C8H18Au2O4: a = 12.214(5) A, b = 14.307(3) A, c = 7.6635(15) A; β = 103.39(3)°, Z = 4, d calc = 2.917 g/cm3, space group P2(1)/c, R = 0.0261. The [(CH3)2AuOCOCH3]2 dimer complex with an Au...Au distance of 2.989 A is the structural unit. The gold atom has a square plane environment of two carbon and two oxygen atoms; the Au-O distances vary from 2.118 A to 2.139 A. The molecules are arranged in chains linked by van der Waals interactions.

Application of the effusion technique to water sorption on cellulose

Equilibrium vapor pressure of water over mechanically and chemically treated cellulose is determined by the effusion method at 298, 303, and 308 K. Thermodynamic characteristics of water desorption from cellulose are determined.

Thermodynamic properties of 2-adamantanone in the condensed and ideal gaseous states

The results of a comprehensive study of thermodynamic properties of 2-adamantanone in different phase states are reported. The heat capacity of the compound in the condensed state was measured from 5 to 310 K with an adiabatic calorimeter and between 290 and 610 K with a differential scanning calorimeter of the heat-bridge type. Adamantanone undergoes a solid-to-solid phase transition at 216.4 ± 0.1 K with Δ trs H m ° = 7.627 ± 0.014 kJ mo l − 1 and fusion at 557.5 ± 0.2 K with Δ fus H m ° = 11.77 ± 0.24 kJ mo l − 1 . The solid-phase transition is associated with formation of orientationally disordered (plastic) crystal. The thermodynamic functions of the compound in the crystalline and liquid states were obtained. The saturated vapour pressure for crystalline adamantanone between 280 and 333 K was determined by the Knudsen effusion method, the undersaturation of the vapours in the effusion cell being taken into account. The sublimation enthalpy of the compound was measured with a differential Calvet-type calorimeter. The weighted average value of the sublimation enthalpy was Δ sub H m ° ( 298.15 K ) = 66.38 ± 0.25 kJ mo l − 1 . The thermodynamic properties of the compound in the ideal gaseous state were calculated by statistical thermodynamics.

Thermodynamics of sublimation of aluminium triacetylacetonate

The equilibrium sublimation pressure Al(acac) 3(s) = Al(acac) 3(g) was measured in the range 376 ≤ T/K ≤ 467.5 by two procedures. One of them is mass spectrometric procedure “calibrated volume method” (CVM), which helped us to expand the possibilities of the effusion method toward the high pressure range. The second is the static method with quartz null Novikov–Suvorov manometers. Experimental data are in good agreement with each other. For this process, we obtained ln( P/Pa) = 35.67 − 13,207/ T, calculated according to the second law of thermodynamics, enthalpy Δ sub H ° (298.15) = 121.8 ± 1.5 kJ mol −1 and entropy Δ sub S ° (298.15) = 235.5 ± 4.3 J mol −1 K −1; according to the third law, 122 ± 1.5 kJ mol −1 and 235.0 ± 5 J mol −1 K −1.

Mass Spectrometric Measurements of the Gas Phase Composition over Mould Powder Samples in Vacuum Conditions at 50‐1550°C

Heating and melting of mould powders in a steel caster may lead to harmful gaseous emissions into the atmosphere. In the present work the volatility of commercial mould powders used in continuous casting processes was studied by the mass spectrometric Knudsen effusion method. Partial pressures of the vapour phase components were measured under vacuum conditions in the temperature range 50‐1550°C at a heating rate of 100°C/hour. In the temperature interval 50‐600°C gas phase is formed by H2O and CO2. At higher temperatures the principle vapour species are Na, NaF, Na2F2, KF, SiF4, SiF2, SiO, CaF2, and CO. Gaseous AIF3, MgF2 and AIOF were identified less reliably. A preliminary decarburised sample exhibited a noticeably different vaporisation pattern. HF was not detected. Under plant conditions SiF4 was pointed out as the most probable air polluting vapour component.

Studying thermodynamic properties of liquid alkali-metal mutual solutions with application of a new variant of the effusion method in the pressure range between Knudsen's and hydrodynamic efflux modes

A new variant of the effusion method for measuring the thermodynamic activity (Gibbs energy) in the alkali-metal binary and ternary systems (Cs–Na, K–Na, Cs–K, Cs–K–Na) is proposed. The activity is determined using the partial pressures of the components by the effusion method with measurement of atomic beam intensity. As oxygen inevitably reacts with a molten alkali metal, the effusion hole cannot be made in advance. Therefore, the effusive hole was machined directly in the vacuum chamber by the electron-ray pulse (the electron linear accelerator was located inside the chamber) after the cell acquired the working temperature. The pressure range was intermediate between Knudsen's mode and the hydrodynamic one. A detailed analysis shows that it is possible to operate outside the range where the Hertz–Knudsen equation applies.

Excess partial molar values of ibuprophene enantiomer and racemate in n-octanol

n-Octanol vapor pressures over solutions of (+)-and (±)-ibuprophene were measured at 25, 30, 35, 40, and 45°C by the effusion method. The excess partial molar values of ibuprophene in n-octanol at 25°C were calculated. The conclusion of n-octanol destructuring in solutions of (+)-ibuprophene was drawn. The suggestion was made that the pharmacological activity of (+)-ibuprophene was related to n-octanol destructuring caused by its solution.

Vapor pressure measurements and thermodynamics of some volatile phthalocyanines

Mass spectrometric studies of the composition of the gaseous phase for solid compounds of hexadecafluorinated phthalocyanines MPcF 16, M = Cu , Zn , VO and their unsubstituted MPc analogs were performed in a temperature range up to 600°C. It has been shown that phthalocyanines sublime into the form of monomers without thermal decomposition. The vapor pressure of these phthalocyanines was determined as a function of temperature by the Knudsen effusion method, in which the rate of effusion of the equilibrium vapor through a small orifice was measured. The thermodynamic parameters of the sublimation process for phthalocyanines were calculated.

Thermodynamic parameters of sublimation of calix[4]arenes

The temperature dependences of the vapor pressure of calix[4]arenes were determined by the Knudsen effusion method. Some calix[4]arenes can form congruently subliming intramolecular compounds with a solvent. The thermodynamic parameters of the sublimation of the compounds were calculated. Molecules of organic solvents incorporated in the cavity of calix[4]arenes stabilize the crystal lattice, increasing the enthalpy of sublimation. The electrostatic interactions presumably make a significant contribution to stabilization of the crystal lattice of stoichiometric complexes of calix[4]arenes with solvents.

The conditions of formation and stability of quasi-crystalline phases in aluminum-manganese alloys

The conditions of formation, stability, and thermodynamic properties of the icosahedral and decagonal quasi-crystalline phases in the Al-Mn system were studied experimentally. The thermodynamic properties of equilibrium crystalline Al-Mn compositions over the composition and temperature ranges 0–26 at % Mn and 628–1193 K, respectively, and of melts over wide temperature and composition ranges (1043–1670 K and 0–50.1 at % Mn) were determined. Measurements were made by the integral variant of the effusion method under the conditions of an ultrahigh oilless vacuum and Knudsen mass spectrometry. An original technique based on the initiation and study of equilibria in reactions of the alloys with special admixtures of sodium or magnesium fluorides with the formation of volatile products was used to extend the interval of measurements to low temperatures. Complete, reliable, and consistent data on the thermodynamic properties of icosahedral and decagonal quasi-crystalline and crystalline phases based on aluminum and Al-Mn melts were obtained for the first time. Al-Mn melts were shown to contain associates of three types, AlMn, Al2Mn, and Al5Mn. The contributions of covalent interactions to the Gibbs energy and enthalpy of mixing was found to be by far predominant. The thermodynamic properties of alloys of the same chemical composition in the quasi-crystalline and equilibrium crystalline states were compared. The decagonal phase was found to be more stable than icosahedral quasi-crystals. The difference of the Gibbs energies of quasi-crystals of the two types and crystalline compositions increased as the temperature lowered. Arguments in favor of the entropy nature of the stabilization of quasi-crystals were obtained. These phases, like metallic glasses, are only an intermediate state between liquids and crystals and cannot be ground stable alloy states. The conditions of obtaining quasi-crystalline phases from melts were found to be controlled by the appearance of a substantial fraction of icosahedral short-range order in liquids in the region of compositions where associates of a certain kind (Al5Mn) were formed in substantial amounts, x(Al5Mn) ≥ 0.11.

Chemical vapor infiltration method for deposition of gold nanoparticles on porous alumina supports

Knudsen’s effusion method with mass spectral analysis of the composition of the gas phase was used to measure the temperature dependence of the saturated vapor of several (CH3)2AuL chelate complexes and to determine the thermodynamic parameters of their sublimation. Based on the results of this study, conditions for chemical vapor deposition of gold using dimethylgold(III) chelates were chosen. Gold nanoparticles were synthesized by chemical vapor deposition (infiltration) of (CH3)2Au(acac) on porous granules of γ-Al2O3 with subsequent calcination in air at 325°C. Particle size and the chemical state of gold in Au/γ-Al2O3 systems were evaluated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A vapor infiltration procedure is suggested to prepare metallic gold particles ≤5 nm in diameter from Au/γ-Al2O3. It is shown that Au/γ-Al2O3 systems obtained by chemical vapor infiltration and containing small gold crystallites possess high catalytic activity in CO oxidation reactions at 40°C.

Thermodynamic properties and phase equilibria in the Nickel-Lanthanum system: Transition of melts into the amorphous state

The vapor composition and thermodynamic properties of liquid and crystalline Ni-La alloys were studied over a wide temperature range, 685–1854 K, and the whole range of compositions. Measurements were performed by the integral variant of the effusion method under superhigh oilless vacuum conditions and Knudsen mass-spectrometry. To extend the range of measurements toward lower temperatures, an approach based on initiating and studying equilibria in reactions with LiF and MgF2 admixtures, which caused the formation of volatile interaction products, was used. A representative array of data was obtained, including more than 1600 component activity values at various compositions and/or temperatures. For the first time, a complete and correct thermodynamic description of all intermediate phases in the Ni-La system was obtained. The accuracy and reliability of the thermodynamic functions found were proved by the coincidence of the results obtained using various calculation methods in studying samples of various compositions under various experimental conditions (various effusion cell and inner cavity coating materials) and agreement with independent experimental data on phase transitions. The thermodynamic functions of Ni-La melts were described with accuracy not inferior to the accuracy of measurements on the assumption of the formation of associates of two types, NiLa and Ni2La. Approaches to determining the contributions of various intercomponent chemical interaction types (covalent and metallic) to thermodynamic functions were developed. The thermodynamic data obtained and the model description of melts suggested were used to calculate phase equilibria in the Ni-La system and construct its phase diagram. The interval of the transition of Ni-La melts into the amorphous state was displaced from the compositions of maximum chemical short-range order close to Ni2La and coincided with the region of the predominance of much less stable NiLa groups characterized by a higher negative entropy of formation. It was this characteristic that determined the dynamics of changes in the structural state of melts, ΔC p and Δfus S, and could therefore be used for creating quantitative criteria of the propensity of liquid metals to form amorphous solids.

Interactions of water–DMSO mixtures with cellulose

The equilibrium in water–dimethylsulfoxide (DMSO) and cellulose–water–DMSO systems was studied in a wide range of solvent compositions by Knudsen's effusion method. It was shown that water sorption on cellulose dominates in the concentration range of 0 < x D < 0.28. At low DMSO concentrations ( x D ∼ 0.1) the water sorption on cellulose is higher than that for pure water. The hydrogen bonding between the hydroxyls of cellulose and the oxygen atom of DMSO is more favorable at x D > 0.6 when the formation of “large” DMSO clusters dominates over the formation of DMSO dimers with hydrophobic properties.

Vapor Pressure Characterization of Several Phenolics and Polyhydric Compounds by Knudsen Effusion Method

The vapor pressures of anthracene, catechol, hydroquinone, caffeic acid, ferulic acid, gentisic acid, and myoinositol have been measured by an isothermal Knudsen effusion method. The vapor pressure correlations fit to the following linear equations: anthracene, ln(p/Pa) = (31.886 ± 0.440) to (11496 ± 149) T/K (from 320 K to 354 K); catechol, ln(p/Pa) = (31.05 ± 0.18) to (9618 ± 56) T/K (from 295 K to 310 K); hydroquinone, ln(p/Pa) = (34.595 ± 0.455) to (12102 ± 150) T/K (from 327 K to 348 K); caffeic acid, ln(p/Pa) = (45.122 ± 1.320) to (20466 ± 550) T/K (from 409 K to 424 K); ferulic acid, ln(p/Pa) = (39.454 ± 0.402) to (15925 ± 153) T/K (from 369 K to 390 K); gentisic acid, ln(p/Pa) = (36.297 ± 0.454) to (14184 ± 168) T/K (from 362 K to 379 K); and myoinositol, ln(p/Pa) = (44.366 ± 0.702) to (20931 ± 315) T/K (from 438 K to 458 K). The sublimation enthalpies and entropies of these samples are calculated.

A simple experimental arrangement for measuring the vapour pressures and sublimation enthalpies by the Knudsen effusion method: Application to DNA and RNA bases

We measured the vapour pressure of several DNA and RNA bases—uracil, adenine, guanine, thymine and cytosine—in the 300–450 K range. In each case the sample mass loss rate was measured as function of temperature with a simple setup consisting of a commercial film deposition system and a homemade oven. Afterwards vapour pressure values were extracted from these data using the Knudsen effusion method. Sublimation enthalpy values, obtained from vapour pressure data by applying the Clausius–Clapeyron equation, are in very good agreement with literature values. The results suggest that crystal-based film thickness monitors may be useful in on-line cross-section measurements, monitoring the gas target thickness. They also show the viability of using this oven for producing a biomolecular gas target.

Measurement of temperature dependence for the vapor pressures of twenty‐six polychlorinated biphenyl congeners in commercial Kanechlor mixtures by the Knudsen effusion method

The vapor pressures of the major congeners in commercial polychlorinated biphenyl (PCB) mixtures (Kanechlors; Kanebuchi Chemical Industry, Tokyo, Japan) have been experimentally determined by Knudsen mass loss effusion. We obtained vapor pressures for the individual PCBs in the crystalline solid, liquid, and subcooled liquid forms as a function of temperature. We derived the thermodynamic parameters, such as the enthalpies of sublimation and vaporization, from the temperature dependence of the vapor pressure by the Clausius-Clapeyron equation. To decide whether the commercial PCB mixtures were ideal solutions, we obtained the activity coefficients by comparing our experimental vapor pressures for pure PCB congeners with those calculated from Kanechlor molar compositional data and vapor pressure values. In many cases, we found that, at 298 K, the values of the activity coefficients of major PCBs in Kanechlor 300 and 500 ranged from 1 to 2. Thus, we suggested that the commercial PCB mixtures show slight positive deviations from ideal solution (Raoult's Law) behavior at ambient temperatures.

Synthesis and thermal properties of some lithium β-diketonates

Five new volatile lithium complexes were synthesized by reactions of lithium hydroxide monohydrate (LiOH · H2O) with β-diketones, namely, dipivaloylmethane (HDpm), hexafluoroacetylacetone (HHfa), trifluoroacetylacetone (HTfa), benzoyltrifluoroacetone (HBtfa), pivaloyltrifluoroacetone (HPta), and valeryltrifluoroacetone (HVta). The complexes obtained were studied by IR and electronic absorption spectroscopy, mass spectrometry, and comprehensive thermal analysis. The temperature dependence of the vapor pressure, which was obtained by the Knudsen effusion method with mass-spectrometric analysis of the vapor phase composition in the 400–450 K range, was used to calculate the standard thermodynamic parameters of the Li(Dpm) sublimation: ΔH°subl = 45.7 ± 1.7 kcal mol−1 and ΔS°subl = 77.9 ± 4.0 cal mol−1 K−1.

Energetics of the Thermal Dimerization of Acenaphthylene to Heptacyclene

The energetics of the thermal dimerization of acenaphthylene to give Z- or E-heptacyclene was investigated. The standard molar enthalpy of the formation of monoclinic Z- and E-heptacyclene isomers at 298.15 K was determined as Delta(f)H(m)o (E-C24H16, cr) = 269.3 +/- 5.6 kJ x mol(-1) and Delta(f)H(m)o (Z-C24H16, cr) = 317.7 +/- 5.6 kJ x mol(-1), respectively, by microcombustion calorimetry. The corresponding enthalpies of sublimation, Delta(sub)H(m)o (E-C24H16) = (149.0 +/- 3.1) kJ x mol(-1) and Delta(sub)H(m)o (Z-C24H16) = (128.5 +/- 2.3) kJ x mol(-1) were also obtained by Knudsen effusion and Calvet-drop microcalorimetry methods, leading to Delta(f)H(m)o (E-C24H16, g) = (418.3 +/- 6.4) kJ x mol(-1) and Delta(f)H(m)o (Z-C24H16, g) = (446.2 +/- 6.1) kJ x mol(-1), respectively. These results, in conjunction with the reported enthalpies of formation of solid and gaseous acenaphthylene, and the entropies of acenaphthylene and both hepatcyclene isomers obtained by the B3LYP/6-31G(d,p) method led to the conclusion that at 298.15 K the thermal dimerization of acenaphthylene is considerably exothermic and exergonic in the solid and gaseous states (although more favorable when the E isomer is the product), suggesting that the nonobservation of the reaction under these conditions is of kinetic nature. A full determination of the molecular and crystal structure of the E dimer by X-ray diffraction is reported for the first time. Finally, molecular dynamics computer simulations on acenaphthylene and the heptacyclene solids were carried out and the results discussed in light of the corresponding structural and Delta(sub)H(m)o data experimentally obtained.

Vaporization Study of YbCl3, YbBr3, YbI2, LuCl3, LuBr3, and LuI3 and a New Assessment of Sublimation Enthalpies of Rare Earth Trichlorides.

The vapor pressures of YbCl3, YbBr3, YbI2, LuCl3, LuBr3, and LuI3 were measured by torsion and Knudsen effusion methods. Their temperature dependences may be reported as follows: YbCl3(s): log(p/...

Computed tomography-guided transpulmonary radiofrequency ablation for hepatocellular carcinoma located in hepatic dome

To determine the feasibility of performing computed tomography (CT)-guided transpulmonary radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC) located in the hepatic dome. A total of seven patients with HCC comprising seven nodules located in the hepatic dome were treated from April 2004 to December 2004. CT-guided transpulmonary RFA was performed using a cool-tip type electrode (Radionics Company) based on a standardized energy protocol. All tumors located in the hepatic dome were not detectable by the usual ultrasound (US) methods. The lesion diameters ranged from 15 to 27 mm. RFA was technically feasible in all the patients. The puncture procedure was performed twice or less and the total average performance time was 40.6 min. Local tumor control was achieved in all the patients. The necrosis diameter ranged from 25 to 35 mm. The mean follow-up period was 9.6 (7-14 mo) mo. There was no local recurrence at the follow-up points. Pneumothorax requiring pleural drainage was the main complication, which was observed in two of the seven patients (28.6%). However, it improved with chest drainage tube, and the tube could be removed within 2-3 d. No other major complications were observed. CT-guided puncture is useful for the treatment of tumors located in the hepatic dome which are hardly detectable by US, even though pneumothorax sometimes may occur as a complication. In the cases with adhesion in the pleura for which artificial pleural effusion methods are not appropriate, CT-guided RFA is thus considered to be an alternative treatment for HCC located in the hepatic dome.