Zum chemischen Transport von SiAs mit Iod — Experimente und Modellrechnungen

On the Chemical Transport of SiAs using Iodine — Experiments and Thermochemical Calculations Using iodine as transport agent siliconarsenide migrates in a temperature gradient. The direction of the migration depends on the chosen temperature and the concentration of the transport agent. The transport rates were measured for various transport agent concentrations (0.0002 ? C(I₂) ≥ 0,02 mmol/cm³) and for various mean transport temperatures (650 ? T? ? 1 000°C). For low temperatures (e.g. T₁ = 750°C→T₂ = 850°C), low iodine concentrations (e.g. C(I₂) = 0.001 mmol/cm³) and in the presence of H₂O (from wall of silica ampoule) the following exothermic reaction is responsible for the deposition of SiAs-crystals in the sink region:

• SiAs_s + 4HI_g = SiI_4,g + 2H_2,g + 1/4As_4,g

In case of higher temperatures (e.g. T₂ = 1 050°C→T₁ = 950°C) and higher iodine concentrations (e.g. C(I₂) = 0.02 mmol/cm³) SiI_4,g is the transport agent. According to model calculations the following endothermic reaction is responsible for the migration of SiAs to the region of the lower temperature:

• SiAs_s + SiI_4,g = 2SiI_2,g + 1/4As_4,g

The heterogeneous and homogenous equilibria will be discussed and an explanation of the non equilibrium transport behaviour of SiAs is given. Thermochemical data of SiAs are characterized by the quartzmembrane zero manometer technique and further verified by model calculations.     

Studies on the thermal decomposition of phosphides and arsenides of silicon and of germanium

The thermal decomposition in vacuum of phosphides and arsenides of silicon and germanium has been investigated using a simple set-up designed to resist the attack of the corrosive decomposition products. The phases GeP, GeAs, SiAs₂ and GeAs₂ disintegrate directly to the elements. X-ray amorphous intermediary products Si_≈5P and Si₆As are formed when SiP and SiAs are heated to 940 to 930°C, respectively. The electron diffraction pattern of Si₆As is reported.     

Elaboration,caracterisation et stabilite thermique des arseniures de germanium et de silicium

SiAs has been prepared by chemical transport using silicon, arsenic and iodine, and GeAs by reaction of gaseous arsenic on germanium in a temperature gradient.Chemical analysis and X-ray diffraction have been performed to characterize these compounds and especially to distinguish GeAs from GeAs₂ which also appears during the GeAs preparation. GeAs and SiAs have been shown to be quite stable up to 500°C and 700°C, respectively. The evaporation of GeAs becomes important above 650°C according to the three equilibria

In the same way the evaporation of SiAs becomes important above 900°C and can be written

     

Heat Dissipation of Flying Wax Moths (Galleria Mellonella) Measured by Means of Direct Calorimetry

Heat production rates and flight speed of adult wax moths (Galleria mellonella) were investigated by means of direct calorimetry at T_A=20 and 30°C. Specific heat production rates were not significantly different between males and females at T_A=20°C (p_TH=747±123.7 mW g^-1, n=5 for males and p_TH=791±169 mW g^-1, n=5 for females) even with females having a higher body mass (M_B=83.8±21.6 mg, n=9 for males and M_B=146.4±25.7 mg, n=11 for females) and wing load. In females, heat production rates were dependent on temperature with higher heat production rates at T_A=20°C (p_TH=791±169 mW g^-1, n=5) than at T_A=30°C (p_TH=441±74 mW g^-1, n=6). Flight speed was also clearly correlated with T_A. Both males and females flew more slowly at T_A=20 than at 30°C. This revised version was published online in August 2006 with corrections to the Cover Date.     

Zum chemischen Transport von Molybdän mit HgBr2 — Experimente und Modellrechnungen

On the Chemical Transport of Molybdenum using HgBr₂ ? Experiments and Thermochemical Calculations . Mo migrates under the influence of HgBr₂ in a temperature gradient (e.g. 1 000→900°C). Besides elementary Mo we observed in some experiments the occurence of MoBr₂ and MoO₂ (from oxygen containing impurities) respectively. The transport behaviour (deposition sequence; deposition rates of various phases) has been enlightened by continous measurement of the mass change during the transport experiments using a special “transport balance”. Thus obtained deposition rates m(Mo) for molybdenum reached in the temperature region 800 ≤ T ≤ 1 040°C a maximum at T = 980°C independend from the starting material (Mo or Mo/MoO₂ mixtures). For variable densities D of transport agent at a constant temperature (T = 950°C) increasing values for m(Mo) were observed (m(Mo) = 23 mg/h, D_max = 8.61 mg HgBr₂/cm³). Thermochemical calculation give strong evidence for the migration of Mo via the endothermal reaction . The experimental deposition rates are about half as large than the calculated values. Good agreement between calculations and experiments were obtained only assuming the presense of oxygen in the starting materials.     

Standard Chemical Thermodynamic Properties of Perfluoro N-Alkanes

The chemical thermodynamic properties C_p°, ΔH_f° S°, ΔG_r° and K_p of gaseous perfluoro n-alkanes, P(CF₂)n F(2≤n≤10), have been calculated from 298.15 to 1000 K using the Benson method with C_p° = a″;b/T + c/T², C_p°=a+bT+c+/T² and C_p°=a″ + bT +cT². Better results are obtained for C_p°=a+b/T+c/T². The calculated chemical thermodynamic properties of C₂ F₆ (g) are in excellent agreement with the literature data of Stull, Westrum, and Sinke under IBM/PC microcomputer with STEP data base management system.     

Zintlphasen mit isolierten SiAs4- bzw. GeAs4-Anionen: Darstellung und Struktur von Ba4SiAs4 und Ba4GeAs4 sowie Sr4SiAs4 und Sr4GeAs4

Die erstmals dargestellten isotypen Verbindungen Ba₄SiAs₄, Ba₄GeAs₄, Sr₄SiAs₄ und Sr₄GeAs₄ kristallisieren kubisch, Raumgruppe P4 3n, mit 8 Formeleinheiten in der Elementarzelle: In den Strukturen liegen isolierte, d.h. nur von Ba-Ionen umgebene SiAs - bzw. GeAs -Tetraeder vor. Die Verbindungen sind die bisher eindrucksvollsten Beispiele für Zintlphasen mit komplexen Anionen. Zintl Phases with Isolated SiAs₄ or GeAs₄ Anions: Preparation and Structure of Ba₄SiAs₄, Ba₄GeAs₄, Sr₄SiAs₄, and Sr₄GeAs₄ The new compounds Ba₄SiAs₄, Ba₄GeAs₄, Sr₄SiAs₄, and Sr₄GeAs₄ have been prepared and their structures determined. They crystallize in the cubic system, P4 3n, with axes: data see “Inhaltsübersicht”. There are isolated SiAs or GeAs tetrahedra in the structures. The compounds can be interpreted as Zintl phases with complex anions.     

INO thermodynamic properties and ultraviolet spectrum

The equilibrium I₂(g) + 2NO(g) = 2INO(g) has been studied at room temperature by ultraviolet absorption spectroscopy. The equilibrium constant has been measured as K_p = (2.7 ± 0.3) × 10^?6 atm^?1 at 298 K. Third-law calculations lead to ΔH°_f,298 (INO) = 120.0 ± 0.3 kJ/mol. The relative absorption spectrum of INO has been measured between 225 and 300 nm. Quantitative measurements gave ?(λ_max = 238 nm) = (1.79 ± 0.5) × 10⁴ L/mol·cm and ?(410 nm) = 234.7 ± 21 L/mol·cm.     

Dynamic Mechanical Analysis and Molecular Mobility of the R-BAPB Type Polyimide

Summary: Dynamic mechanical experiments are performed to study molecular mobility of the R-BAPB type polyimide based on 1,3-bis-(3,3′,4,4′-dicarboxyphenoxy)benzene (R) and 4,4′-bis-(4-aminophenoxy)biphenyl (BAPB) with a molecular weight M_w ∼ 80 000 g/mol. Frequency dependences of the storage and the loss tensile moduli are measured within the temperature domain 199°C ≤ T ≤ 211°C that includes the glass transition temperature of the compound, T_g = 206°C. It is shown that the time-temperature superposition principle holds for the R-BAPB type polyimide. A theoretical analysis of the master curves constructed at T_ref = 204°C is performed on the basis of the piecewise-power-type distribution function of the relaxation times. Relaxation times for typical scales of motion inside polyimide macromolecules are calculated and the molecular weights of the characteristic kinetic units (the Kuhn segment and the chain fragment between entanglements) are estimated.     

Chemischer Transport und Sublimationsverhalten von CrBr3 — Experimente und Modellrechnungen

On the Chemical Transport and Sublimation of CrBr₃ — Experiments and Model Calculations The migration of CrBr₃ in the presence of high concentrations of bromine (for example D(Br₂) = 0,05 mmol/ml; closed silica ampoules) in the investigated temperature range (T? = 625°C to 875°C; T? = 50°C) is a result from the endothermic reaction The chemical transport of CrBr₃ is superimposed with the sublimation. With low concentrations of D(Br₂) and high temperatures T? is the sublimation decisive participated. This is a result of the homogenous equilibrium between CrBr_3,g and CrBr_4,g (2a) The reaction (2a) in comparison with the chemical transport of CrCl₃ with Cl₂ (Gl. (2b)) is more shifted to CrBr_3,g.     

[PbAsSiiPr3]6 — the First Structurally Characterized Compound with Chemical Bonds between Lead and Arsenic

The compound [PbAsSiiPr₃]₆ ( 1 ) could be obtained by the reaction of PbCl₂ with iPr₃SiAs(SiMe₃)₂ in THF at 0 °C. Central structural motif is a hexagonal prism built by six lead and six arsenic atoms. The average Pb—As bond length is 281 pm. The cluster crystallizes in the monoclinic space group C2/c, the lattice constants are: a = 4460.8(9) b = 2296.6(5), c = 2734.4(6) pm, β = 117.57(3)°. The thermogravimetric analysis in vacuum shows the tendecy of 1 to decompose under formation of elementary lead and volatile arsenic compounds.     

Chemischer Transport von Cr2O3 mit CrI3/I2 – Experimente und Modellrechnungen zur Beteiligung von CrOI2,g

On the Chemical Transport of Cr₂O₃ with CrI₃/I₂ – Experiments and Model-Calculations for Participation of CrOI_2,g Gaseous chromium oxyiodides that were unknown up to now cause the migration of Cr₂O₃ in the temperature gradient 1 000°C→900°C when iodine (e. g. 0.1 mmol/ml) and CrI₃ is added (eq. (1)). Transport agent for Cr₂O₃ is gaseous CrI₄. With a smaller concentration of iodine (D(I₂) ? 0.016 mmol/ml) and lower temperatures (e.g. T? = 850°C) the influence of H₂O (from the wall of the silica ampoule) becomes more important. Under these conditions the transport of Cr₂O₃ is a result from the endothermic reactions (2), (3) and (4). H_2,g has on the basis of the decomposition of HI_g a positive difference of the solubility and H_2,g should not to be considered as a transport agent. Because of the range of equilibrium-values the reaction 4 has to be taken into consideration. Estimated value of the enthalpie for CrOI_2,g is fixed more precisely by thermodynamic model calculation to Δ_fH°₂₉₈(CrOI_2,g) = ?51.4 kcal/mol. The estimated limit of error for the enthalpie of formation is smaller than ± 5 kcal/mol. Without an addition of CrI₃ is in the system Cr₂O₃/I₂ a migration of Cr₂O₃ not observable.     

Polyimidothioether–polysulfide block polymers

The synthesis of a new class of block polymers that contain alternating polyimidothioether “hard” blocks and polysulfide elastomer “soft” blocks is described. Compositions with 70% and greater polysulfide component are solvent-resistant, thermoplastic elastomers exhibiting room temperature tensile strengths of up to 1500 psi and ultimate elongations of nearly 800%. The physical properties are a strong function of test temperature due to relatively short polyimidothioether blocks, 850 ≤ M?_n ≤ 3500 g/mole. These short polyimidothioether blocks were necessary to minimize degradation of the polysulfide elastomer blocks during thermal processing at temperatures ～100°C above the “hard” block domain T_g.     

Experimente und Modellrechnungen zum chemischen Transport von V2O5 mit NH4Cl

Experiments and Calculations for the Chemical Transport of V₂O₅ with NH₄Cl For the chemical transport of V₂O₅ in a temperature gradient (T₂ – T₁ = ΔT = 100 K) the influence of temperature (T₂ = 770 K to 970 K) on the transport rate n′(V₂O₅) using an admixture of 2 to 8 mg NH₄Cl (2,3 to 9,2 × 10^?3 mmol/cm³) has been investigated. Also the dependence of n′ on the admixture of the transport agent has been examined from 2 to 52 mg NH₄Cl (T₂ = 850 K, T₁ = 750 K). We observed that n′ increases with increasing temperature and increasing admixture of NH₄Cl. The model calculations show the opposite tendency of the dependence on temperature; for all experiments the value of n′ was lower by a factor of 10 to 320 than the calculated one. These deviations indicate, that our knowledge on the gas phase of this system is incomplete.     

Der chemische Transport von Platin mit Chlor. Experimentell bearbeitet mit Marita Trenkel

The Chemical Transport of Platinum with Chlorine Experiments show that the chemical transport of platinum by means of chlorine within a temperature gradient at temperatures below ≈ 1000°K goes into the hot temperature region, but at higher temperatures in the reverse direction. From the thermodynamic discussion it can be seen, that the platinum content of the gas phase at low temperatures is governed by the exothermic formation of Pt₆Cl_12,g, and at higher temperatures by the endothermic formation of PtCl_3,g and PtCl_2,g. The platinum content of the gas phase passes a minimum at ≈ 1000°K, if P(Cl₂) = 3.5 atm. This result is in agreement with the observed inversion of the transport direction.     

Variations of electrical properties and chemical composition of the FeCr2S4 spinel

In its stability domain (medium or high sulfur pressures) between 600 °C and 1000 °C, FeCr₂S₄(spinel type) is a weak p-type non-stoichiometric semiconductor. Its conductivity is an average one (2.3<logσ(Ωm)⁻¹<3.3). Its chemical composition (x in the formula FeCr₂S_x) extends from 4.00 to 4.12. At constant chemical composition, the conductivity versus temperature follows the law σ = σ₀ exp(−ε/kT) with ε = 0.69 eV. Under low pressure the formation of interstitial chromium (point defects n) destroys the lattice leading to complete decomposition.     

Kinetics of the reaction of cyclopentane with trichloroethylene

The kinetics of the thermally and radiation initiated chain reaction between trichloroethylene and cyclopentane to produce 1,1-dichlorovinylcyclopentane and hydrogen chloride have been investigated in the temperature range 250–360°C at high pressure in the gas phase. The rate governing step in the chain is (k₃ = 3.3 × 10⁹ exp ?(4800/RT) cc mole^?1 sec ^?1). The rate of the unimolecular decomposition of trichloroethylene is 1.4 × 10¹⁴ exp ?(61,200/RT) sec^?1.     

Untersuchungen zur Kristallisation von Rhodium(III)-Oxoverbindungen unter Beteiligung der Gasphase – Der chemische Transport von Rh2O3 mit Chlor

Investigations on the Crystallization of Rhodium(III) Oxo Compounds – Chemical Vapour Transport of Rh₂O₃ using Chlorine Rh₂O_3,s migrates in chemical transport experiments with chlorine as transport agent from the higher (T₂) to the lower (T₁) temperature of a gradient (Δ_T = 100°) due to endothermal reactions (900°C < T ≤ 1050°C; T = 0,5 · (T₂ + T₁)). Under the conditions of transport experiments RhCl_3,s is observed in most experiments as equilibrium solid besides the sesquioxide. The transport rates for Rh₂O_3,s and the sublimation rates for RhCl_3,s grow with increasing temperature T . The composition of the equilibrium solids, the rates of migration and the sequence of deposition (1. RhCl_3,s, 2. Rh₂O_3,s) is well reproduced by thermodynamic model calculations. As a result of this calculations the transport behaviour of the system Rh₂O_3,s/Cl₂ is determined by the two equilibria The influence of RhCl_2,g and RhCl_4,g on the transport behaviour of Rh₂O_3,s as well as the possible occurence of RhOCl_2,g in the equilibrium gas phase will be discussed. Predictions of the transport behaviour of ternary rhodium(III) oxo compounds will be made.     

Optimization of microwave‐assisted extraction for six inorganic and organic arsenic species in chicken tissues using response surface methodology

Response surface methodology was applied to optimize the parameters for microwave‐assisted extraction of six major inorganic and organic arsenic species (As(III), As(V), dimethyl arsenic acid, monomethyl arsenic acid, p‐arsanilic acid, and roxarsone) from chicken tissues, followed by detection using a high‐performance liquid chromatography with inductively coupled mass spectrometry detection method, which allows the simultaneous analysis of both inorganic and organic arsenic species in the extract in a single run. Effects of extraction medium, solution pH, liquid‐to‐solid ratio, and the temperature and time of microwave‐assisted extraction on the extraction of the targeted arsenic species were studied. The optimum microwave‐assisted extraction conditions were: 100 mg of chicken tissue, extracted by 5 mL of 22% v/v methanol, 90 mmol/L (NH₄)₂HPO₄, and 0.07% v/v trifluoroacetic acid (with pH adjusted to 10.0 by ammonium hydroxide solution), ramping for 10 min to 71°C, and holding for 11 min. The method has good extraction performance for total arsenic in the spiked and nonspiked chicken tissues (104.0 ± 13.8% and 91.6 ± 7.8%, respectively), except for the ones with arsenic contents close to the quantitation limits. Limits of quantitation (S/N = 10) for As(III), As(V), dimethyl arsenic acid, monomethyl arsenic acid, p‐arsanilic acid, and roxarsone in chicken tissues using this method were 0.012, 0.058, 0.039, 0.061, 0.102, and 0.240 mg/kg (dry weight), respectively.