Rapid solid-state synthesis of binary group 15 chalcogenides using microwave irradiation

Solid-state microwave synthesis was found to provide a simple, rapid and economical route to prepare Sb₂Se₃, Sb₂Te₃, Bi₂Se₃ and Bi₂Te₃. These technologically important materials were prepared via solid-state microwave synthesis in as little as 4 min. Through the process of finding the ideal synthetic conditions with which to produce each of these compounds, the effects that several synthetic variables have on the reaction outcomes were explored. Scanning electron microscopy, energy dispersive spectroscopy, powder X-ray diffraction, differential thermal analysis and diffuse reflectance measurements, when appropriate, were used to characterize the materials.     

Development of a group contribution method for the estimation of heat capacities of ionic liquids

In this communication, a new approach is presented which combines a group-contribution (GC) method approach with genetic function approximation (GFA) for the prediction of liquid heat capacities at constant pressure (C _pL) for ionic liquids at atmospheric pressure. The proposed method can be used instead of complicated nonlinear modeling approaches like artificial neural networks and support vector machine. The NIST standard reference database was used to prepare a dataset for C _pL data. The dataset comprised 82 ionic liquids and consisted of 3,726 experimental data points. The dataset was divided such that 80 % of the data were used as a training set, and 20 % as a validation and test set. GFA was used to select functional groups, from which the GC based model was developed. Statistical analysis of the model shows that it has an overall average absolute relative deviation of 1.68 %, coefficient of determination (R ²) of 0.990, and root mean square of error (RMSE) of 18.42 J mol^?1 K^?1.     

Non isothermal heat capacities and chemical reactions using a modulated DSC

An evaluation of measurements of heat capacities by modulated differential scanning calorimetry, MDSC is presented. Heat capacities were obtained from 130 to 550 K by a non isothermal technique in which a periodic modulation was added to the linear heating rate. Effects of amplitude and period of modulation, sample weight, sample type, pan type, and cell imbalance are described. Results are compared with those obtained using the isothermal technique. Heat capacity could be measured well into the decomposition region and separated from the non reversing signal due to chemical reaction (degradation), thus allowing a precise detection of onsets of the thermal degradation. This additional information will aid in the interpretation of the degradation chemistry, a field vital for the petroleum-industry.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayPart of this paper was presented at the 23rd Conference of the North American Thermal Analysis Society, Toronto, Canada, September 25–28, 1994.The author (MVN) acknowledges the experimental assistance provided by J. Balogh of Exxon Research and Engineering Company, Linden. Helpful discussions with A. Boller of the University of Tennessee at Knoxville, Dr. Y. Jin, General Electrical, and Dr. S. Sauerbrunn formerly of TA Instruments are also acknowledged.     

Borylation using group IV metallocene under mild conditions

A borylation reaction of aromatic diazonium salts has been optimized using titanocene and zirconocene derivatives as catalysts. The reaction employs diisopropylaminoborane as a borylating agent and proceeds smoothly at room temperature to provide arylboronates after methanolysis and transesterification with pinacol. The reaction mechanism has been found to proceed via a radical pathway.     

A group additivity approach for the estimation of heat capacities of organic liquids and solids at 298 K

A group additivity method is described which provides heat capacity estimates of the condensed phase. The data base consists of 810 liquids and 446 solids. Group values for carbon in various common substitution and hybridization states and for 47 functional groups are provided. The standard error of estimation using this approach on this data base is 19.5 (liquids) and 26.9 J/ (mole K) (solids). This can be compared to typical experimental uncertainties of 8.12 and 23,4 J/ (mole K) associated with these measurements, respectively. Experimental uncertainties were estimated from the numerical differences obtained for a given substance from multiple independent literature reports.     

Flow microcalorimeter for heat capacities of solutions

A new type of flow microcalorimeter for measuring heat capacities at constant pressure of liquids and solutions was constructed. This calorimeter is the similar in design to Picker's except for the flow system, which consists of two syringe type of pumps and two flowing paths in each flow cell. It was found that the magnitude of heat loss from cells depended on liquids themselves used and the flow rates of sample liquids. The molar heat capacities, C_p of benzene and ethanol were determined relative to those of cyclohexane and water, respectively. The excess molar heat capacities, C_p(E) for the systems of benzene + cyclohexane and water + ethanol were also determined at 298.15K by the direct mixing method. An inaccuracy for C_p(E) was estimated to be within ± 1%.     

Entropies and heat capacities of free radicals

Methods are presented for rapidly estimating the entropies and heat capacities of free radicals from the known S⁰ and C of structurally similar compounds. The methods consist of estimating the differences due to changes in mass, vibration frequencies, spin, symmetry, and changes in rotational barriers. Tables of contributions to S⁰ and C by different frequencies over the temperature range 300–1500°K are presented to facilitate the tabulation of the above differences. Conjugated radicals, such as benzyl and allyl, are included. It is shown that the greatest uncertainties in the estimates arise from uncertainties in the barriers to rotation in the radicals. The results are applied to kinetic data on the pyrolysis of branched hydrocarbons and the reverse reactions of radical recombination. Major discrepancies exist in these data which can be nearly reconciled by postulating improbably high rotational barriers of 8 kcal for CH₃ rotation in isopropyl and t-butyl radicals. It is shown that radical thermochemistry can be fitted into group schemes and tables of groups values are given for the rapid estimation of ΔH, S⁰, and C for different organic radicals, including those containing sulfur, oxygen, and nitrogen.     

Trends in the high-temperature heat capacities of ternary chalcopyrite semiconductors

The anharmonic contribution to the heat capacity of any chalcopyrite semiconductor A^IB^IIIC ₂ ^VI or A^IIB^IVC ₂ ^V is evaluated. It is shown that the degree of lattice anharmonicity decreases with increasing atomic weight of the constituent atoms of the compounds, and there is no essential difference in the degree of lattice anharmonicity of the two groups of compounds. Except for CdGeAs₂, the trend in the Grüneisen constants is the same.

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Zusammenfassung Der anharmonische Beitrag zur Wärmekapazität verschiedener Halbleiterverbindungen A^IB^IIIC ₂ ^VI und A^IIB^IVC ₂ ^V vom Chalkopyrit-Typ wird bestimmt. Es wird gezeigt, dass die Gitteranharmonizität mit steigender relativer Atommasse der Bestandteile der Verbindungen abnimmt und dass keine wesentlichen Unterschiede in der Gitteranharmonizität beider Gruppen von Verbindungen bestehen. Der Trend der Grüneisen-Konstanten ist der gleiche, ausgenommen bei CdGeAs₂.

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^IIII ₂ ^{VI IIIV} ₂ ^V . , , , . , CdGeAs₂.

     

Volumes and heat capacities of anionic-nonionic surfactant mixtures

Density, heat capacity and surface tension measurements of sodium decylsulfate (NaDeS)-dodecyldimethylamine oxide (DDAO)-water mixtures were carried out as functions of the surfactants total molality m_t at fixed stoichiometric mixture compositions X_NaDeS. From the surface tension data, the critical micelle concentration of NaDeS-DDAO mixtures as a function of X_NaDeS were obtained. From density and heat capacity data, the apparent molar volume V_,2 and heat capacity C_,2 of NaDeS-DDAO mixtures in water were calculated, respectively. At a given mole fraction, V_,2 and C_,2 monotonically increases and decreases, respectively, with increasing mt. However, anomalies were observed at X_NaDeS=0.1 and 0.3 for both V_,2 and C_,2 vs. mt curves. The nonideal contributions to the thermodynamic properties for the formation of surfactant-surfactant mixed micelles in water by mixing aqueous solutions of pure NaDeS and DDAO micelles were calculated at 0.3 mol-kg^–1 for the micellized surfactants mixture. The excess volume V^exc and heat capacity as functions of X_NaDeS are concave and S-shaped curves, respectively. All the properties are compared to those for sodium dodecylsulfate-DDAO mixture. In addition, to clarify the effect of the change in the hydrophobicity of the surfactants mixtures V^exc for the dodecyltrimethylammonium bromide-decyltrimethylammonium bromide mixture were calculated from literature data.     

Heat capacities of concentrated multicomponent aqueous electrolyte solutions at various temperatures

The specific heat capacities of the aqueous multicomponent system NaCl +KCl+MgCl₂+CaCl₂ with ionic strength between 8.3 and 9.6 (resembling Dead Sea waters) were measured between 15°C and 45°C. The obtained data were fitted to an empirical equation as a function of concentration and temperature. The thermodynamic functions of the studied multicomponent system were found to be strongly influenced by changes in MgCl₂ concentrations. The application of Young's rule to such concentrated systems was checked at 25°C. The calculated (by Young's rule) specific heat capacitiesC _p and apparent molar heat capacities C_p, of these multicomponent electrolyte solutions were in reasonable agreement with the measured values (–0.008 J-g^–1-K^–1 and –2.6 J-mol^–1-K^–1, respectively).     

An addition scheme of heat capacities of linear macromolecules

The prior developed addition scheme of heat capacities is expanded to macromolecules that contain non-C-bonds in the backbone. Tables for 31 groups are given. 713 data points which have been averaged for group contributions for which more than one measurement was available showed a deviation of 0.1±1.5% (internal consistency). Calculated heat capacities of homopolymers and copolymers for which independent measurements have been made showed average errors of 0.60% and a standard deviation of ±2.35% (177 data points).

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Zusammenfassung Das früher entwickelte Additionsschema für Wärmekapazitäten wird auf Makromoleküle erweitert, die Nicht-C-Bindungen im Stützgerüst enthalten. Tabellen für 31 Gruppen sind angegeben. Von 713 Meßdaten wurden für Gruppenbeiträge, für die mehr als ein Meßwert zur Verfügung stand, Mittelwerte berechnet, wobei sich eine Abweichung von 0.1±1.5% (interne Konsistenz) ergab. Berechnete Wärmekapazitäten von Homopolymeren und Kopolymeren, für die unabhängige Messungen ausgeführt wurden, weisen einen mittleren Fehler von 0.60% bei einer Standardabweichung von 2.35% auf (177 Meßwerte).

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, . 31 . 713 , , 0.1±1.58% ( ). , , 0,60% ±2,35% (177 ).

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This work was supported by the National Science Foundation of the US, Polymers Program, Grant # DMR 8317097.     

Catalytic ester-amide exchange using group (IV) metal alkoxide-activator complexes

A process for preparation of amides from unactivated esters and amines has been developed using a catalytic system comprised of group (IV) metal alkoxides in conjunction with additives including 1-hydroxy-7-azabenzotriazole (HOAt). In general, ester-amide exchange proceeds using a variety of structurally diverse esters and amines without azeotropic reflux to remove the alcohol byproduct. Initial mechanistic studies on the Zr(Ot-Bu)4-HOAt system revealed that the active catalyst is a novel, dimeric zirconium complex as determined by X-ray crystallography.     

Low-temperature heat capacities and thermodynamic properties of crystalline isoproturon

An incremental integral isoconversional method for the determination of activation energy as a function of the extent of conversion is presented. The method is based on the treatment of experimental data without their transformation so that the resulting values of activation parameters should not be biased. The method was tested for recovering the activation energies from simulated data and employed for the treatment of experimental data of the NiS recrystallisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

The heat capacities of selected inorganic alkali metal compounds

The heat capacities of selected inorganic binary and ternary alkali metal compounds are determined using differential scanning calorimetry (DSC). As part of an ongoing research program at Battelle Memorial Institute since 1983, the heat capacities of cesium and rubidium chalcogenides, aluminates, silicates and uranates in the temperature range 310 to 800 K have been added to the series of compounds. The measured data is to be combined with the standard enthalpies of formation and low temperature heat capacities to obtain reliable thermodynamic data on the alkali metal compounds to high temperatures.     

Volumes and heat capacities of some watersurfactant-alcohol ternary systems

The densities and volumetric heat capacities of urea and alcohols were measured in aqueous solutions of octylammonium bromide (OABr) and of OABr in aqueous urea and alcohol solutions. The alcohols studies were methanol, ethanol, 1-propanol, 2-propanol, n-butanol, t-butanol, n-pentanol, n-hexanol and 2-butoxyethanol (BE). In most experiments, the concentration of the reference solute was kept low, and volumes and heat capacities of transfer from water to the mixed solvent were calculated. A more complete study was made with the system BE-OABr-H₂O where both solutes were systematically changed. The observed trends in the thermodynamic functions can be explained through three effects: interactions between the reference solute and the cosolvent in the premiceller region of the surfactant or pre-aggregation region of the alcohol, a distribution of the reference solute between water and the micelle or microphase and an equilibrium displacement of the system, monomer-aggregate, in the vicinity of the reference solute.     

Low-temperature heat capacities and derived thermodynamic functions of cyclohexane

The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within ±0.3%, while the inaccuracy is within ±0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively. The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H_(T)-H _{298.15 K}} and {S _(T)-S_{298.15 K}}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric study was determined to be 99.9965% by fraction melting approach. This revised version was published online in July 2006 with corrections to the Cover Date.