Neue Beobachtungen zum chemischen Transport von GeO2. VI. Temperaturabhängigkeit mit dem Transportmittel Chlor

New Observations on the Chemical Transport of GeO₂. VI. Temperature Dependence with the Transport Agent Chlorine In a temperature gradient T₂ ? T₁ = 100 K the chemical transport of tetragonal GeO₂ is kinetically controlled at an average transport temperature T ≤ 1080 K. The same is true for the metastable hexagonal modification at T ≤ 1150 K. An Arrhenius equation describes the rate of deposition in a satisfactory way. The activation energy amounts to 21 kcal/Mol. At higher temperatures diffusion determines the rate of transport whereby GeCl₄, Cl₂, and O₂ are looked upon as prominent gaseous molecules and the formation of a solid solution of hexagonal GeO₂ with SiO₂ is taken into account. For a transport temperature T < 1100 K GeO₂ is deposited at T₁ only if seeds of the specific modification are present. The deposition of GeO₂(hex.) ceases at temperatures lower than T ≈ 1000 K. The formation of GeO₂(tetr.) requires not only seeds but also NaCl as mineralizer and the temperature should not be lower than T ≈ 900 K.     

Neue Beobachtungen zum chemischen Transport von GeO2 II. Transportmittel Wasserstoff

Novel Observations on the Chemical Transport of GeO₂. II. Transport Agent Hydrogen The endothermic reaction (1) (2) is the basis of the deposition of GeO₂ in the temperature gradient T₂ ? T₁ = 100 K at the low temperature T₁ = 1023 K. The quartz modification of GeO₂ is obtained as micro crystalline coating and acicular, colourless crystals adherent to it. The gaseous molecules H₂, H₂O and (GeO)_n (with n = 1, 2, 3) participate in the chemical transport. The chemical transport depends on the concentration of H₂. At low H₂-concentration GeO₂ is transported, with growing H₂-pressure at the beginning of the experiments Ge and GeO₂ are deposited simultaneously. A further increase of the H₂-pressure leads again to a chemical transport of GeO₂, followed by a range of Ge-deposition. After reaching a steady state in each experiment only one phase is transported. The sequence of deposition can be explained by model calculations. A comparison of experimentally determined rates of transport with calculated values shows that under the present conditions at a total pressure of ∑P = 1 atm (298 K) no kinetic inhibition of the phase transfer reactions exists.     

Neue Beobachtungen zum chemischen Transport von GeO2 IV. Temperaturabhängigkeit mit dem Transportmittel Wasserstoff

Novel Observations on the Chemical Transport of GeO₂. IV. Temperature Dependence with the Transport Agent Hydrogen The chemical transport of GeO₂ with H₂ proceeds on the basis of reaction (1) In the case of a filling pressure of 1 atm H₂ a micro crystalline coating of GeO₂(hex.) is obtained at T₁, using a temperature gradient T₂ ? T₁ = 100 K. In addition acicular, colourless crystals are growing. The shape depends on the mean transport temperatures T?. Besides GeO₂ a small amount of Ge is obtained at temperatures T? < 1023 K in the colder region of the ampoules. This additional Ge-Transport is not to be expected under equilibrium conditions. Model calculations show, that it is due to a kinetic inhibition of the deposition of GeO₂. In a wide range of temperature the experimentally determined rates of transport are in accordance with the expected values.     

Eine Methode zur kontinuierlichen Bestimmung von Transportraten Experimente im System GeO2/WO2/H2O und NiSO4/PbSO4/PbCl2

A Technique for the Continuous Determination of Rates of Transport.–Experiments on the Systems GeO₂/WO₂/H₂O and NiSO₄/PbSO₄/PbCl₂ We describe a computer controlled device for continuously measuring rates of transport in closed ampoules. The applicability and efficiency of the method is demonstrated by two examples. For the system GeO₂/WO₂/H₂O we could prove, that the non steady state transport is caused by the influence of the amount of the deposited solid phase in the sink. By means of the NiSO₄/PbSO₄/PbCl₂ system we could demonstrate, that the rates of transport of the successive deposition of PbSO₄ and NiSO₄ could be determined in a single experiment.     

Experimente und Modellrechnungen zum chemischen Transport von WO2 mit HgCl2 oder HgBr2

Experiments and Calculations on the Chemical Transport of WO₂ with HgCl₂ or HgBr₂ Transport experiments with WO₂ or WO₂ + W₁₈O₄₉ or W + WO₂ as starting phases show that HgCl₂ or HgBr₂ are suitable transport agents. When using HgBr₂ we observed (in customary silica ampoules) unusual high transport rates n′ > 1000 mg/h. Experimental and calculated results agree to a large extent if the presence of small amounts of H₂O from the quartz glass wall and the resulting gaseous particles (for example HCl or HBr) formed under equilibrium conditions as well as an influence of convection are taken into consideration.     

Chemischer Transport fester Lösungen. 8 [1] Zum Chemischen Transport von ternären und quaternären Cobalt(II)‐ und Nickel(II)‐germanaten

Chemical Vapor Transport of Solid Solutions. 8 The Chemical Vapor Transport of Ternary and Quarternary Cobalt and Nickel Germanates By means of chemical vapor transport methods using HCl as transport agent CoGeO₃, Co₂GeO₄, and Ni₂GeO₄ have been prepared (1000 → 900 °C and 900 → 700 °C). In this system the formation of a continuous crystalline solid solution of Co₂GeO₄ and Ni₂GeO₄ was found as well as the deposition of the compound NiGeO₃ which — although unknown as a pure solid — can be stabilized as a mixed crystal Ni_xCo_1—xGeO₃ (0 < x < 0, 6).     

Zum chemischen Transport von ZrO2 und HfO2 mit den Transportmitteln Cl2 und TeCl4

On the Chemical Transport of ZrO₂ and HfO₂ with the Transport Agents Cl₂ and TeCl₄ ZrO₂ und HfO₂ migrate in a temperature gradient (1100 → 1000°C) with the transport agent either Cl₂ or TeCl₄ by endothermic transport reaction. At experiments in silica glass tubes with TeCl₄ well developed crystals of ZrO₂ could be obtained. From HfO₂, as from both oxides using Cl₂, only powdery products are formed. The transport rates with TeCl₄ were higher than with Cl₂. The influence of different pressures was examined for the transport of ZrO₂ with TeCl₂ with thermochemical model calculations the expected transport rates could be investigated. The large correspondence between calculated and experimental received values speaks for a true interpretation of the transport observations.     

Neue Beobachtungen zum chemischen Transport von GeO2. III. Transportraten mit dem Transportmittel Wasserstoff

Novel Observations on the Chemical Transport of GeO₂. III. Rates of Transport with Hydrogen In the course of a chemical transport in the system GeO₂/H₂ the composition of the solid phases can change until a steady state is reached. In this case an iterative calculation of the equilibrium is now possible. The method takes into acount the mutual interaction of the processes in the source and in the zone of deposition and allows a general application. The participation of H₂ implies a large difference in the coefficients of diffusion which demands the estimation of the interaction of diffusion and laminar flow. The comparision of experimentally determined rates of transport with calculated values shows now that the increasing laminar flow is antagonistic to the deposition of GeO₂.     

Zur Thermochemie von gasförmigem GeWO4 und GeW2O7

Thermochemistry of Gaseous GeWO₄ and GeW₂O₇ Mass spectrometric investigations with a Knudsen cell arrangement at temperatures between 1258 and 1383 K proved the existence of GeWO₄ and GeW₂O₇ as component of the vaporphase over a mechanical mixture of GeO₂ and WO₂. Using the partial pressures heats of formation (2nd law calculation) and entropies (3rd law calculation) were computed; i. e. GeWO₄: δH°₁₃₃₀ = ?149.8 kcal · mole^?1, S°₁₃₃₀ = 129.9 cal K^?1 mole^?1, GeW₂O₇: δH°_f,₁₃₃₀ = ?310.6 kcal mole^?1, S°₁₃₃₀ = 190.0 cal K^?1 mole^?1. The standard heats of formation and entropies at 298 K, calculated with estimated Cp values are: GeWO₄: δH°_f,₂₉₈ = ?181.6 kcal mole^?1, S°₂₉₈ = 85.0 cal K^?1 mole^?1; GeW₂O₇: δH°_f,₂₉₈ = ?365.8 kcal mole^?1, S°₂₉₈ = 112.1 cal K^?1 mole^?1. The thermochemical data of the GeWO₄ and GeW₂O₇ molecules which also appear at chemical transport experiments [2] with GeO₂ + WO₂, are compared with known gaseous tungstates.     

Pulsed NMR study of proton mobility in a hydrogen tungsten bronze

Crystalline hydrogen tungsten bronze H_0.46WO₃ was prepared by reduction of WO₃ single crystals. NMR relaxation times T₂, T₁, and T_1? were measured for 80 K < T < 450 K at 16 MHz and second moments for 160 K < T < 450 K at 100 MHz. The relaxation data were analyzed in terms of proton diffusion to give an activation energy of about 16 kJ mole^?1 and a correlation time preexponential factor of about 70 nsec for the process.     

Zum chemischen Transport von Wolfram mit HgBr2 – Experimente und Modellrechnungen

On the Chemical Transport of Tungsten using HgBr₂ – Experiments and Thermochemical Calculations Using HgBr₂ as transport agent tungsten migrates in a temperature gradient from the region of higher temperature to the lower temperature (e.g. 1 000 → 900°C). The transport rates were measured for various transport agent concentrations (0.64 ? C(HgBr₂) ? 11.74 mg/cm³; T? = 950°C) and for various mean transport temperatures (800 ? T? ? 1 040°C). Under these conditions tungsten crystals were observed in the sink region. To observe the influence of tungsten dioxide (contamination of the tungsten powder) on the transport behaviour of tungsten, experiments with W/WO₂ as starting materials were performed. According to model calculations the following endothermic reactions are important for the migration of tungsten: In the presence of H₂O or WO₂ other equilibria play a role, too. Using a special “transport balance” we observed a delay of deposition of tungsten (e.g. T? = 800°C; 15 h delay of deposition) with W and W/WO₂ as starting materials. The heterogeneous and homogeneous equilibria will be discussed and an explanation for the non equilibrium transport behaviour of tungsten will be given.     

Zum chemischen Transport von Bismutoxidhalogeniden BiOX (X = Cl,Br, I) mit Halogen,Halogenwasserstoff sowie Wasser und Bestimmung der Molwärmen von BiOX

Chemical Transport of Bismuth Oxide Halides BiOX (X = Cl, Br, I) with X₂, HX and H₂O, and Determination of the Molar Enthalpies of BiOX By comparison of calculated and experimental chemical transport behaviour of BiOX (X = Cl, Br, I) with X₂, HX, and H₂O it was shown, that we understand the transport of BiOCl, BiOBr and BiOI with X₂ and HX in terms of the well known gaseous spezies in the systems. The existence of gaseous complexes Bi(OH)₂X is be concluded from high transport rates of BiOX with water, and their enthalpies and entropies were derived. The molar enthalpies and standard entropies of BiOX were determined by low temperature C_p measurements. (Data see Inhaltsübersicht)     

Beiträge zum Chemischen Transport oxidischer Metallverbindungen. II. Bemerkungen zum Transport von α-Fe2O3 über monomeres Eisen(III)-chlorid

Transport of α? Fe₂O₃ with HCl via monomeric iron(III) chloride according to Fe₂O_3(s) + 6 HCl_(g) = 2FeCl_3(g) + 3 H₂O_(g); T₂ → T₁ between T₂ = 1000°C and T₁ = 800°C in the region of diffusion produced crystals which contained, in dependence of total pressure, different amounts of divalent iron. By addition of oxygen to the transport gas stoichiometric crystals of hematite by otherwise unchanged conditions were obtained. The necessary amount of oxygen was calculated from the phase diagram Fe? O, and an explanation of the gas phase reactions is given. Dependence of the transport rate of hematite on total pressure in the region of diffusion (0.009 to 6 atm) is reported.     

Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram. IV. Der Transport von MoO2 mit J2 und die Existenz von MoO2J2

The possibility to transport MoO₂ with J₂ in a temperature gradient T₂/T₁ suggests the existence of MoO₂J₂. Starting from the reaction MoO₂ + J₂ ? MoO₂J₂ in the consideration of the function of temperature for the rates of chemical transport, the values ΔH^O_R ? 28.8 (±2) kcal/mole and ΔS^O_R ? 9.0 (±2) cl are deduced. From this the values ΔH^O(MoO₂J₂, g, 298) ? ?99.5 (±3.5) kcal/mole and S^O(MoO₂J₂, g, 298) ? 86 (±3) cl are derived. The comparison of the thermodynamic data for MoO₂X₂ and WO₂X₂ (X = Cl, Br, J) leads to the conclusion, that the existence of MoO₂J₂ in the vapour phase is very probable indeed.     

Übergangsmetallchalkogenverbindungen. Spectrophotometric evidence for the existence of MoO3Se2− and WO3Se2− in aqueous solution. Electronic Spectra of the Ions MeOxSe4−x2− (Me = Mo,W)

A spectrophotometric investigation of the reaction between MeO₄^2? (Me?Mo, W) and gaseous H₂Se leading to the identification of the unknown monoselenoanions of molybdenum(VI) and tungsten(VI) is reported. The electronic spectra agree well with the theoretically predicted ones. Further a comparative study of the spectra of different seleno- and thio-anions was made. The first band in the electronic spectra of MoO₃Se^2? and WO₃Se^2? is due to the Se → metal charge transfer transition.     

Chemischer Transport fester Lösungen. 10 [1] Zum Chemischen Transport von quaternären Cobalt(II)‐Zink‐ und Mangan(II)‐Zinkgermanaten

Chemical Vapor Transport of Solid Solutions 10 [1] The Chemical Vapor Transport of quarternary Cobalt(II)‐Zinc and Manganese(II)‐Zinc Germanates By means of chemical vapor transport methods using HCl or Cl₂ as transport agent the crystalline solid solutions (Zn_xCo_1—x)₂GeO₄ and (Mn_xZn_1—x)₂GeO₄ have been prepared (1050 → 900 °C, 850 → 700 °C, respectively). ZnGeO₃ — although unknown as a pure solid — can be stabilized as a mixed crystal (Mn_xZn_1—x)GeO₃ (x > 0, 5).     

An ab initio study of the geometry,energy, and selected force constants for the three planar conformers of carbonic acid,and the bicarbonate ion; and of the energy for the reaction H2O + CO2 → H2CO3

Ab initio calculations using the unscaled 4-31G basis set have been carried out on the cc, tc, and tt conformers of carbonic acid and the bicarbonate ion, with full geometry optimization assuming the structures to be planar. The complete harmonic force field is reported for the (most stable) tt conformer and for the bicarbonate ion, also selected quadratic force constants for the cc and tc conformers. The changes in certain bond lengths and stretching force constants in the cc → tc, tc → tt, and cc → tt conformer conversion reactions are indicative of intramolecular hydrogen bonding, C?O…H? O and H? O…H? O, which is examined in greater detail by partitioning the overall conformer conversion energy into distortion and bonding energy components. The fundamental vibration frequencies for the tt conformer and the bicarbonate ion are calculated from the force constant matrices, and hence, using a scaling factor based on a comparison of calculated and experimental values for the bicarbonate ion and trans-formic acid, a value is predicted for the zero-point energy of the tt conformer. A new estimate of ΔH? for the hydration reaction, H₂O + CO₂ → H₂CO₃, at 298 K in the gas phase; is made from thermochemical data, +20.2 ± 3.4 kJ mol^?1, which, together with estimates of (H₂₉₈? – H₀?) and the zero-point energy for H₂CO₃, gives +8.1 ± 7.0 kJ mol^?1 for ΔE_T(expt). ΔE_T calculated from the 4-31G basis set data is -29.1 kJ mol^?1. Comparison of the experimental value, the Hartree–Fock limit value, and values calculated with a variety of basis sets for the bond separation reaction, CO₂ + CH₄ → 2H₂CO, suggests that the differences, ΔE_T(expt) minus ΔE_T(SCF ), are due mainly to basis set limitations and not substantial correlation energy contributions.     

Neue Beobachtungen zum chemischen Transport von GeO2 I. Transportmittel Chlor

New Observations in the Chemical Transport of GeO₂. I. Transporting Agent Chlorine By using Chemical transport reactions with Cl₂ as transporting agent, the rutile modification of GeO₂ is obtainable with deposition temperature below 900°C. The shape of the crystals is columnar, and they show a colour which varies from yellow to amber. A comparison of calculated and observed rates of transport shows that an inhibition of the reaction exists. This inhibition is partially reduced if alkaline chlorides are added. In the presence of Mn(II) the calculated rates of transport are observed. In the presence of NaCl and KCl the crystals of GeO₂ (rutile) are needle shaped and colourless, in presence of Mn(II) the needles are brown.     

Thermodynamic properties of LiZr2(PO4)3 crystal phosphate

The temperature dependence of the heat capacity of LiZr₂(PO₄)₃ crystal phosphate is studied in an adiabatic vacuum calorimeter in the temperature range of 6 to 358 K. A phase transition caused by the transition of a low-temperature (triclinic) modification to a high-temperature (rhombohedral) modification is observed in the temperature range of 290–338 K and its standard thermodynamic characteristics are estimated and analyzed. Standard thermodynamic functions are calculated from experimental data: heat capacity, enthalpy, entropy, and Gibbs function in the range of T → 0 to 358 K. Fractal dimensionality D is calculated from the data on low-temperature (20 K ≤ T ≤ 50 K) heat capacity and the topology of the phosphate’s structure is estimated.     

Oberflächenverbindungen von Übergangsmetallen. XXX. Fischer-Tropsch-analoge Umsetzung von CO/H2 bzw. CO2/H2 an Oberflächen-Chrom(II)

Surface Compounds of Transition Metals. XXX. Fischer-Tropsch Analogous Reactions of CO/H₂ and CO₂/H₂ on Surface Chromium(II) Surface chromium(II)/silicagel catalyzes the reduction of CO and CO₂ by hydrogen to CH₄, C₂H₆ and C₃H₈. The catalyst is partially desactivated by this reaction, but a permanent activity of ca. 30% remains. – The reaction can be formulated via the sequence formaldehyde complex → <CH₂>-complex → alkane. If cycloalkenes or chlorobenzene are added simultaneously, these scavenger molecules are methylated by <CH₂>.