Inert Gas Carrier Research Articles

Thermodynamic analysis of nifedipine sublimation, dissolution and solvation

The saturated vapour pressure of the cardiovascular drug nifedipine is measured within the temperature range (390.15–404.15) K by the inert gas-carrier method. The thermodynamic functions of sublimation of the compounds are calculated at a reference temperature. The standard molar enthalpy of nifedipine sublimation is found to be equal to 144.8 kJ∙mol−1. The drug solubility in solvents modeling various media of the human body is determined in the temperature range (293.15–313.15) K. In the ascending order of solubility values of the studied compound, the solvents can be arranged as follows: buffer pH 7.4, buffer pH 2.0, n-hexane, 1-octanol. The solute–solvent intermolecular interactions are discussed based on the thermodynamic functions of solubility, solvation and transfer.

Isavuconazole: Thermodynamic Evaluation of Processes Sublimation, Dissolution and Partition in Pharmaceutically Relevant Media.

A temperature dependence of saturated vapor pressure of isavuconazole (IVZ), an antimycotic drug, was found by using the method of inert gas-carrier transfer and the thermodynamic functions of sublimation were calculated at a temperature of 298.15 K. The value of the compound standard molar enthalpy of sublimation was found to be 138.1 ± 0.5 kJ·mol−1. The IVZ thermophysical properties—melting point and enthalpy—equaled 302.7 K and 29.9 kJ mol−1, respectively. The isothermal saturation method was used to determine the drug solubility in seven pharmaceutically relevant solvents within the temperature range from 293.15 to 313.15 K. The IVZ solubility in the studied solvents increased in the following order: buffer pH 7.4, buffer pH 2.0, buffer pH 1.2, hexane, 1-octanol, 1-propanol, ethanol. Depending on the solvent chemical nature, the compound solubility varied from 6.7 × 10−6 to 0.3 mol·L−1. The Hansen s approach was used for evaluating and analyzing the solubility data of drug. The results show that this model well-described intermolecular interactions in the solutions studied. It was established that in comparison with the van’t Hoff model, the modified Apelblat one ensured the best correlation with the experimental solubility data of the studied drug. The activity coefficients at infinite dilution and dissolution excess thermodynamic functions of IVZ were calculated in each of the solvents. Temperature dependences of the compound partition coefficients were obtained in a binary 1-octanol/buffer pH 7.4 system and the transfer thermodynamic functions were calculated. The drug distribution from the aqueous solution to the organic medium was found to be spontaneous and entropy-driven.

Sublimation thermodynamics of antifungal drugs: Tioconazole, miconazole and climbazole

The temperature dependence of the saturated vapour pressure of the antifungal drugs – tioconazole (TCZ), miconazole (MCZ) and climbazole (CLZ) – was determined by the inert gas carrier transfer method. The standard molar enthalpies of sublimation at T = 298.15 K calculated from these data were 117.2 ± 0.5 kJ·mol-1 for TCZ ± 0.9, 106.2 ± 1.0 kJ·mol-1 for MCZ and 113.3 kJ·mol-1for CLZ. The vaporization and sublimation enthalpies of the compounds were found by the Langmuir and Clausius-Clapeyron equations without determining the vapour pressures of the drugs. Sublimation enthalpies derived by both these methods were in good agreement. It was shown that it was possible to estimate the thermodynamic sublimation functions by applying the space clusterization approach to the studied and structurally related compounds. In addition, the temperature and enthalpy of fusion of the compounds were measured by differential scanning calorimetry.

Experiment and simulation on Zr2Fe bed for tritium capturing.

Zr based alloys are widely used in hydrogen storage and purification systems. For hydrogen isotope capturing and recycling, it is possible to design the tritium extraction system of the glove box taking into account the operating conditions and technical constraints. Zr2Fe alloy bed was adopted in the 2.5%H2/Ar capturing experiments as well as numerical simulation was also constructed. In this work, the breakthrough curve under conditions of 300 °C@200 sccm for the carrier gas penetration was obtained by establishing a single flowing bed. Then a new numerical model of the bed was established for simulating the penetration process, and a numerical solution to the mass conservation equation of carrier gas passing through the bed was obtained concerning the actual experimental parameters. Calculation results have shown the two-dimensional distribution of H2 concentration flowing through a one-dimensional reactor. It can be seen clearly that the H2 concentration distributed along the bed axial at different time. This distribution profiles can be used to globally illuminate the concentration variation of hydrogen in the reactor within the whole reaction time scale. Comparing the experimental result of 1.27 days in the breakthrough curve, the results of numerical simulation can predict the curve of about 1.5 days began to breakthrough, although there were certain deviation (∼18%). The results can provide a feasible numerical model support for optimizing the tritium capturing bed design.

Sublimation enthalpy of 1,3-thiazine structural analogues: Experimental determination and estimation based on structural clusterization

The saturated vapor pressures of 4 nonaromatic bicyclic 1,3-thiazine and 1,3-selenazine derivatives have been measured by the method of transpiration by inert gas-carrier in the temperature range of 308–392K. Based on the experimental data the thermodynamic functions of sublimation have been calculated. The sublimation enthalpies of the compounds vary from 104 to 150kJmol−1 depending on the chemical nature of the substituent in the aryl moiety and the heteroatom in the bicyclic fragment. The crystal lattice energy of thiazines decreases with the introduction of substituents in the following order: cyano>acetyl>isopropyl. New approach has been suggested to evaluating sublimation enthalpy of the studied and structurally related compounds by using clusterization of the space of experimental points.

Vapor pressures and thermodynamic sublimation of antitubercular drugs

The temperature dependencies of the saturated vapor pressure for antituberculous drug compounds: pyrazinecarboxamide and three isonicotinic acid hydrazides were obtained using the method of inert gas-carrier transfer. The standard sublimation molar enthalpies, entropies and Gibbs energies were derived at T = 298.15 K. The temperature and fusion molar enthalpy of the compounds were measured using the differential scanning calorimetry technique. The influence of the structure of the studied compounds on the crystal lattice energy and volatility was analyzed. It was estimated that the saturated vapor pressure of the studied substances decreases when the molecule polarizability and donor–acceptor ability increase.

Salicylamide cocrystals: screening, crystal structure, sublimation thermodynamics, dissolution, and solid-state DFT calculations.

A new cocrystal of 2-hydroxybenzamide (A) with 4-acetamidobenzoic acid (B) has been obtained by the DSC screening method. Thermophysical analysis of the aggregate [A:B] has been conducted and a fusion diagram has been plotted. Cocrystal formation from melts was studied by using thermomicroscopy. A cocrystal single-crystal was grown and its crystal structure was determined. The pattern of noncovalent interactions has been quantified using the solid-state DFT computations coupled with the Bader analysis of the periodic electron density. The sublimation processes of A-B cocrystal have been studied and its thermodynamic functions have been calculated. The classical method of substance transfer by inert gas-carrier was chosen to investigate sublimation processes experimentally. The lattice energy is found to be 143 ± 4 kJ/mol. It is lower than the sum of the corresponding values of the cocrystal pure components. The theoretical value of the lattice energy, 156 kJ/mol, is in reasonable agreement with the experimental one. A ternary phase diagram of solubility (A-B-ethanol) has been plotted and the areas with solutions for growing thermodynamically stable cocrystals have been determined.

Acetamidobenzoic acid isomers: Studying sublimation and fusion processes and their relation with crystal structures

Temperature dependencies of saturated vapor pressure for i-acetamidobenzoic acids (i = 2, 3 and 4) were obtained by flow inert gas-carrier transfer method. Thermodynamic parameters of sublimation were calculated for 2-acetamidobenzoic acid (2-AcAm-BA), 3-acetamidobenzoic acid (3-AcAm-BA) and 4-acetamidobenzoic acid (4-AcAm-BA) (2-AcAm-BA: ΔGsub298=54.4 kJ mol−1; ΔHsub298=116±1 kJ mol−1; ΔSsub298=205±4 J K−1 mol−1; 3-AcAm-BA: ΔGsub298=73.2 kJ mol−1; ΔHsub298=137±1 kJ mol−1; ΔSsub298=215±4 J K−1 mol−1; 4-AcAm-BA: ΔGsub298=72.3 kJ mol−1; ΔHsub298=138±1 kJ mol−1; ΔSsub298=221±8 J K−1 mol−1). Thermochemical parameters of fusion process for investigated substances were obtained, and vaporization enthalpies were estimated from fusion and sublimation enthalpies. The thermal data obtained in all experiments were used to find relationships between the thermal properties of these compounds and other benzoic acid derivatives and their structural properties. A correlation between enthalpy of sublimation and melting point was obtained. The influence of size and position of substituents on crystal lattice energy was discussed.

Vapor pressures and sublimation enthalpies of novel bicyclic heterocycle derivatives

The vapor pressures of five novel bicyclic heterocycle derivatives were measured over the temperature 341.15 to 396.15K using the transpiration method by means of an inert gas carrier. From these results the standard enthalpies and Gibbs free energies of sublimation at the temperature 298.15K were calculated. The effects of alkyl- and chloro-substitutions on changes in the thermodynamic functions have been investigated. Quantitative structure–property relationship on the basis HYBOT physico-chemical descriptors for biologically active compounds have been developed to predict the sublimation enthalpies and Gibbs free energies of the compounds studied.

Thermodynamics of sublimation and solvation for bicyclo-derivatives of 1,3-thiazine

Temperature dependencies of saturated vapor pressure of novel bicyclo-derivatives of 1,3-thiazine with methoxy- and carbonyl-substituents have been obtained by method of transference by means of an inert gas carrier. Thermodynamic functions of sublimation have been calculated. Correlations between thermodynamic functions of sublimation and thermophysical properties of the substances and molecular descriptors have been established. The enthalpies of solvation of compounds were calculated using the measured values of enthalpies of sublimation and of standard enthalpies of solution in hexane and buffer.

Vapor Pressures and Sublimation Thermodynamic Parameters for Novel Drug-Like Spiro-Derivatives

Temperature dependences of saturated vapor pressure for eight new molecular crystals of spiro-derivatives of 1,3-thiazine have been determined by transport method by means of an inert gas carrier. Thermodynamic functions of sublimation have been calculated. The processes of substances fusion have been examined by differential scanning calorimetry. The effect of alkyl substituents structure and introduction of halogen atoms on sublimation properties of spiro-compounds has been assessed. The correlation between thermodynamic parameters of sublimation processes and thermo-physical properties of the substances and molecular descriptors is established.

Thermodynamic and structural aspects of hydroxybenzamide molecular crystals study

Temperature dependencies of vapor pressure were obtained by flow inert gas-carrier transfer method for 2-, 3- and 4-hydroxybenzamide in the temperature interval (from 302.15 to 345.15)K, (from 367.65 to 396.15)K and (from 360.15 to 420.65)K, respectively. The thermodynamic functions of sublimation process were estimated on the basis of the experimental results. The fusion processes of the compounds under investigation were studied using the differential scanning calorimetry method. The comparative analysis of parameters describing packing density of molecules in crystal lattices was done and thermodynamic and thermophysical parameters of sublimation and fusion processes were analyzed. The influence of crystal density calculated based on the X-ray data on sublimation enthalpy under standard conditions was found. For some benzamide derivatives the sublimation enthalpy was observed to depend on the melting point temperature.

Validation of an effective oxidation pressure model for liquid binary alloys

Dynamic surface-tension measurements using the sessile drop method and acquisition times of a few seconds make it possible to study the evolution of the surface of molten metals and alloys and so reliably validate the predictive models of the interactions between pure liquid metals and an oxidizing atmosphere, in both an inert gas carrier and in a vacuum. The presence of active oxidation contributes to maintaining surface cleanness and then strongly affects the shape of the boundary separating oxidation and de-oxidation regimes. Recently the general physical–mathematical analysis we developed for pure liquid metals has been extended to liquid binary alloys and their oxides. In this work we present the experimental results of tests on some binary alloys chosen as test systems to try to obtain a preliminary validation of the extended model. The theoretical results obtained, indicating that the behaviour of the alloy towards oxidation tends to be similar to that of the less oxidizable component, have thus been confirmed experimentally.

The effective oxygen pressure of liquid binary alloys

In previous works a theoretical analysis was developed for the interactions of a pure liquid metal and an oxidizing atmosphere in both an inert gas carrier and a vacuum. In particular, the effects of oxidation reactions taking place in the gas phase and the evaporation of the condensed oxides were considered. In both cases the presence of oxidation phenomena contributed to maintaining interface cleanness and then strongly affected the shape of the boundary separating the oxidation and de-oxidation regimes. In this work we present a more general physico-mathematical analysis, which is extended to liquid binary alloys and their oxides. The theoretical results obtained indicate that the behaviour of the alloy towards oxygen tends to be similar to that of the less oxidizable component: so the existence of a volatile oxide can often prevent surface oxidation even if the corresponding metal is present in low percentages.

Development of Electrochemical Hydrogen Pump Under Vacuum Condition for a Compact Tritium Gas Recycling System

ABSTRACTJAERI has been developing an improved compact tritium gas enrichment/recycling system to handle relatively smaller amount of tritium for efficient researches on tritium processing and development work. An electrochemical hydrogen pump based on CaZr0.9In0.1O3− α proton conductor is investigated to separate hydrogen isotopes directly from inert gas carrier after the enrichment process of the system. The prototype hydrogen pump was developed for the first time to operate under vacuum condition at the cathode compartment, and the performance test was carried out.

Direct Deposition of Metal Film Patterns Using Nitrogen Laser

Rhenium, gold and platinum film micropatterns were obtained by the LCVD method on the surface of silicon and glass substrates from vapors of Re 2 (CO) 10 , (CH 3 ) 2 Au(dpm), Pt(hfa) 2 , respectively. The heated reaction chamber at atmospheric pressure with a flow of an inert gas-carrier was used. The high marginal sharpness and the thickness uniformity of deposited films was provided by the use of a powerful nanosecond pulse nitrogen laser (λ=337 nm), a projective system for delineation of the irradiation zone and by laser beam microscanning in the limits of the projective mask window. The metal pattern replicating the configuration of the projective mask window with a uniform 0.1-1 μm thickness was formed during 1-10 s. The writing rate of the straight metal lines was limited by the size of the irradiation zone and by the pulse repetition frequency and made of 150 μm/s. The smooth Re films were obtained with a good adhesion to the substrate and a surface resistivity of about 1 Ω/square. The films of Au and Pt were deposited as layers of microdrops whose coupling with one another and with the contact ground determined the film resistivity. The melting of Au and Pt films occurs during the laser-induced deposition process and influences the film growth dynamics and the film-to-substrate adhesion.

An exploratory study of vapor-phase lubrication of ceramics by monomers

Earlier studies on the use of the concept of tribopolymerization as an anti-wear mechanism for ceramics involved liquid carriers such as pure hydrocarbons (e.g. hexadecane) and mineral oils at temperatures ranging from ambient to 150°C. Recent studies have been carried out to determine the effects of potential tribopolymer-forming compounds on ceramic wear in the vapor phase using an inert gas carrier. Three addition-type monomers selected on the basis of the tribopolymerization concept were studied. The liquid additives were heated, vaporized and delivered to an enclosed alumina-on-alumina “pin-on-disk” contact region by a stream of dry nitrogen gas. The results of tests at bulk specimen temperatures up to 145°C showed that indeed significant reductions in ceramic wear were produced by the low vapor concentrations of these compounds in the nitrogen carrier gas. Alumina ball wear reductions of up to 99% were observed, and total wear reductions (ball and disk) of over 70% were also common. Colorful surface films visible to the naked eye were frequently observed. Higher compound delivery temperatures have a significant beneficial effect in reducing wear. Analysis of the worn surfaces using Fourier transform infrared micro-spectroscopy shows clear evidence of chemical reactions with the alumina surface to form soap-like compounds; in addition, evidence of surface polymerization with one of the monomers, diallyl phthalate, was obtained. It is believed that the surface films formed reduce adhesion and therefore decrease both wear and friction. These studies are continuing in an attempt to learn more about the detailed mechanisms involved.

Development of a Rapid Determination System for Phosphorus and Sulfur in Iron.

In order to determine the contents of phosphorus and sulfur rapidly in the iron-making process, a new determination system has been developed. This system is characterized by the rapid extraction of phosphorus and sulfur from a solid sample by the wet chemical reaction, and simple detection using a paper-tape detector. Hydrochloric acid is sprayed onto the surface of an iron sample, and about 5mg of the sample is dissolved. Phosphorus and sulfur in the sample are extracted as phosphine and hydrogen sulfide, respectively, during the supply of hydrochloric acid. These gases are transferred to a paper-tape detector with an inert-gas carrier. In the detector, phosphine and hydrogen sulfide are reacted with silver nitrate and lead acetate, respectively, on the paper tapes; the resulting stain is measured by reflectance photometry. As the result of analyzing pig iron, ranges of 0.01-0.1% phosphorus and 0.003-0.03% sulfur are determined simultaneously with relative standard deviations of 15% or less. The time required to analyze one sample is less than 2min. This system is expected to be used at production sites of the iron-making process.

Liquid metal surface tension measurements: a kinetic-fluodynamic model of surface oxygen availability

A kinetic and fluodynamic description of processes that may take place near the surface of some liquid metals in the presence of a gas flow containing definite oxygen amounts is given, with a particular regard to the thermodynamic properties of the metal-oxygen system and to the geometry of the experimental set-up. Diagrams have been obtained from which the following items of information are simultaneously available: (1) the range of P 02 and T in which the reaction considered is thermodynamically possible; (2) the accessibility of oxygen to the liquid metal surface, and the thermodynamic-kinetic conditions for which this surface can be considered oxygen free. Therefore, the treatment presented here and applied to many cases of technological interest allows us to define (a) the physical and chemical equilibrium conditions of a liquid metal surface in the presence of oxygen diluted in an inert gas carrier, under total pressures ranging from about 10 −4 to 0.1 MPa (10 −3−1 m), and (b) the kinetic and fluodynamic characteristics of the process through which the quilibrium conditions are reached, the geometry of the experimental set-up having been given.

Arsine Ambient Rapid Thermal Annealing

ABSTRACTWe have constructed a multiple wafer arsine ambient rapid thermal anneal (RTA) system and have applied it to the fabrication of high-performance refractory-gate self-aligned GaAs MESFETs. This has allowed us to take advantage of some of the features of rapid thermal annealing for these devices (reduced dopant movement and gate-channel interaction) without the difficulties of capped RTA (decapping problems, cap thermal mismatch stress driven dopant movement and gate-channel interaction) or the uncertain As loss characteristics of uncapped or proximity RTA. The anneal system uses a cylindrical furnace with a graphite boat heated by tungsten lamps with a 60 KW maximum power input. This allows heating rates in excess of 100°C/sec for up to four, two-inch wafers per run with a controlled arsine ambient of 0–20 Torr in an inert gas carrier. Closed loop temperature control is accomplished using a 5 μm wavelength optical pyrometer. The system has been designed to collect the As cracked from AsH, in a downstream trap and essentially no As is deposited in the wafer load area.Using arsine ambient RTA to anneal 15 KV 20Si+ self-aligning implants for GaAs MESFETs with MOCVD grown channels (30 nm, 1.7 × 1018/cm3), we have been able to fabricate enhancementmode self-aligned MESFETs with gm/gd > 20 and extrinsic k-factor as large as 765 mS/V-mm for 0.15 μm gate length.