R. Gruehn

Zum absorptions- und desorptionsverhalten von quarzglas gegenüber wasser☆

Abstract By means of chemical transport of Ge the desorption of water from the wall of quartz glass ampoules is investigated. The experiments with various kinds of quartz glass and different amounts of ppm(OH) show that there is a linear dependence between the desorbed quantity of water n 0 (H 2 O) and log ppm(OH) for values greater than 25 ppm(OH). Ampoules with high ppm amounts can desorb up to 1.2×10 −5 moles H 2 O. The treatments of the quartz ampoules influences the desorbable H 2 O amounts as expected. Ampoules with lower ppm amounts absorb water during the preparation in the oxyhydrogen burner. In this case the desorbed H 2 O quantities amount to 4×10 −6 moles for the presented series of investigations.

New Results of Chemical Transport as a Method for the Preparation and Thermochemical Investigation of Solids.

Chemical transport experiments are a valuable aid of great potential in the synthesis and thermochemical characterization of solids. Compounds of interest can often only be crystallized by this method. The use of a transport balance allows very detailed observations, particularly of the course of the experiment over time (simultaneous or sequential deposition of multiple-phase solids). The computer program CVTRANS enables a quantitative thermochemical description of the experiment based on the cooperative transport model. A compilation of recent results illustrates the development and efficiency of the method. The transport of phosphides, anhydrous phosphates and sulfates, and rare-earth oxide and oxohalide compounds are treated in detail.

Beiträge zum thermischen Verhalten von Sulfaten XIV. Zum thermischen Verhalten von PdSO4 · 2H2O und PdSO4 · 0,75H2O sowie zur Struktur von M-PdSO4

Abstract Crystals of two modifications of PdSO4 (both red—brown, edge length up to 0.2 mm) could be prepared by treatment of Pd powder with an excess of nitrating acid at T ≈ 200–240 °C. The low temperature modification (N-PdSO4) which crystallizes with monoclinic symmetry is stable up to T ≈ 520 °C (from X-ray powder data and an electron microscopy investigation: a = 9.881(1) A , b = 9.888(1) A , c = 12.382(2) A , β = 92.81(1)°, Z = 16 , space group Pc or P2/c). According to single crystal data, the probably metastable modification (M-PdSO4) crystallizes with monoclinic symmetry (space group C2/c) and lattice constants a = 7.8447(8) A ; b = 5.1793(3) A , c = 7.9092(6) A , β = 95.606(7)° and Z = 4 (R 1 = 0.019 for 31 free parameters and 827 F o with F o > 4σ(F o )). The structure consists of tetrahedral SO4 groups. Four O atoms belonging to four different SO4 tetrahedra coordinate the Pd atoms in a plane. Applying the high temperature Guinier technique and using differential thermal analysis (DTA)—thermogravimetry (TG) equipment, the thermal behaviour of PdSO4·2H2O and its decomposition products (PdSO4 · 0.75H2O, PdSO4) was investigated. The thermodynamic data of PdSO4 (ΔFH298o = - 160.7 kcal mol−1 and S298o = 23.3 cal mol−1 K−1) could be determined by measurement of the pressure with respect to the temperature.

Zum chemischen transport von Ge MIT H2O

Abstract The chemical transport of Ge with H2O is based on the endothermic reaction Ges + H2Og = n-1 (GeO)n + H2 with n = 1, 2, 3. Investigations in a closed system show that in a temperature gradient Ge is deposited as a micro crystalline coating with acicular crystals adherent to it. The shape of the crystals depends on the H2O concentration and temperature. Under the present conditions no kinetic inhibition of the phase transfer reactions exists. The calculations of the steady state for both temperatures are carried out with an iterative method which takes into account the mutual interaction of the processes in source and sink.

Beiträge zum thermischen Verhalten von Sulfaten: IX. Einkristallstrukturverfeinerung der Metall(III)-sulfate Cr2(SO4)3 und Al2(SO4)3

Well shaped crystals of Cr 2 (S0 4 ) 3 and A12(S04)3 could be prepared by chemical transport reactions using HCl (Cr2(S04)3) or SOCl2 (A12(S04)3) as transport agent. Cr 2 (S0 4 ) 3 and A12(S04)3 are isostructural to the rhombohedral modification of Fe 2 (S0 4 ) 3 and crystallize in the trigonal space group R 3 with a = 8.1245(7) (8.0246(4)) Â and c = 21.944(3) (21.357(1 )) Â, Ζ = 6 (hexagonal setting). The crystal structures were refined to a residual R = 0.035 using 828 unique reflections with > 3 a\F\ for Cr 2(S0 4) 3 and to R = 0.026 (772 unique reflections with | F | > 3 a |F |) for A12(S04)3. Main building units of the two compounds are M06-octahedra and S04tetrahedra which are linked via common corners to a 3-dimensional network.

Beiträge zum thermischen Verhalten und zur Kristallchemie von wasserfreien Phosphaten XXXII [1] Neue Orthophosphate des zweiwertigen Chroms — Mg3Cr3(PO4)4, Mg3, 75Cr2, 25(PO4)4, Ca3Cr3(PO4)4 und Ca2, 00Cr4, 00(PO4)4†

Uber Festkorperreaktionen unter Beteiligung der Gasphase wurden in den Systemen A3(PO4)2 / Cr3(PO4)2 (A = Mg, Ca) die vier Verbindungen Mg3Cr3(PO4)4 (A), Mg3, 75Cr2, 25(PO4)4 (B), Ca3Cr3(PO4)4 (C) und Ca2, 00Cr4, 00(PO4)4 (D) erstmalig synthetisiert und mittels Einkristallstrukturanalyse charakterisiert [(A): P21/n, Z = 1, a = 4, 863(2) A, b = 9, 507(4) A, c = 6, 439(2) A, β = 91, 13(6)°, 1855 unabhangige Reflexe, 63 Variable, R1 = 0, 035, wR2 = 0, 083; (B): P21/a, Z = 2, a = 6, 427(2) A, b = 9, 363(2) A, c = 10, 051(3) A, β = 106, 16(3)°, 1687 unabh. Reflexe, 121 Variable, R1 = 0, 032, wR2 = 0, 085; (C): P-1, Z = 2, a = 8, 961(1) A, b = 8, 994(1) A, c = 9, 881(1) A, α = 104, 96(2)β, β = 106, 03(2)°, γ = 110, 19(2)°, 2908 unabh. Reflexe, 235 Variable, R1 = 0, 036, wR2 = 0, 111; (D): C2/c, Z = 4, a = 17, 511(2) A, b = 4, 9933(6) A, c = 16, 825(2) A, β = 117, 95(1)°, 1506 unabh. Reflexe, 121 Variable, R1 = 0, 034, wR2 = 0, 098]. Die Kristallstrukturen weisen mehrere kristallographisch unabhangige Lagen fur Chrom(II) auf, jeweils mit einer (4+n)-Koordination (n = 1, 2, 3). Bei den Magnesiumverbindungen und in Ca2, 00Cr4, 00(PO4)4 wird eine Fehlordnung der zweiwertigen Kationen Mg2+/Cr2+ bzw. Ca2+/Cr2+ beobachtet. Mg3, 75Cr2, 25(PO4)4 kristallisiert in einem neuen Strukturtyp, wahrend Mg3Cr3(PO4)4 isotyp zu Mg3(PO4)2 ist. Ca3Cr3(PO4)4 und Ca2, 00Cr4, 00(PO4)4 sind im Aufbau nahe verwandt und gehoren zur Ca3Cu3(PO4)4-Strukturfamilie. Das Orthophosphat Ca9Cr(PO4)7 mit dreiwertigem Chrom wurde als Nachbarphase zu C und D erhalten. Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXXII. New Orthophosphates of Divalent Chromium — Mg3Cr3(PO4)4, Mg3, 75Cr2, 25(PO4)4, Ca3Cr3(PO4)4 and Ca2, 00Cr4, 00(PO4)4 Solid state reactions via the gas phase led in the systems A3(PO4)2 / Cr3(PO4)2 (A = Mg, Ca) to the four new compounds Mg3Cr3(PO4)4 (A), Mg3.75Cr2.25(PO4)4 (B), Ca3Cr3(PO4)4 (C), and Ca2.00Cr4.00(PO4)4 (D). These were characterized by single crystal structure investigations [(A): P21/n, Z = 1, a = 4.863(2) A, b = 9.507(4) A, c = 6.439(2) A, β = 91.13(6)°, 1855 independend reflections, 63 parameters, R1 = 0.035, wR2 = 0.083; (B): P21/a, Z = 2, a = 6.427(2) A, b = 9.363(2) A, c = 10.051(3) A, β = 106.16(3)°, 1687 indep. refl., 121 param., R1 = 0.032, wR2 = 0.085; (C): P-1, Z = 2, a = 8.961(1) A, b = 8.994(1) A, c = 9.881(1) A, α = 104.96(2)°, β = 106.03(2)°, γ = 110.19(2)°, 2908 indep. refl., 235 param., R1 = 0.036, wR2 = 0.111; (D): C2/c, Z = 4, a = 17.511(2) A, b = 4.9933(6) A, c = 16.825(2) A, β = 117.95(1)°, 1506 indep. refl., 121 param., R1 = 0.034, wR2 = 0.098]. The crystal structures contain divalent chromium on various crystallographic sites, each showing a (4+n)-coordination (n = 1, 2, 3). For the magnesium compounds and Ca2.00Cr4.00(PO4)4 a disorder of the divalent cations Mg2+/Cr2+ or Ca2+/Cr2+ is observed. Mg3.75Cr2.25(PO4)4 adopts a new structure type, while Mg3Cr3(PO4)4 is isotypic to Mg3(PO4)2. Ca3Cr3(PO4)4 and Ca2.00Cr4.00(PO4) 4 are structurally very closely related and belong to the Ca3Cu3(PO4)4-structure family. The orthophosphate Ca9Cr(PO4)7, containing trivalent chromium, has been obtained besides C and D.

Neue Beobachtungen zum System TiO2Ta2O5

Zusammenfassung Im System TiO2Ta2O5 beobachtet man bei hoher Temperatur (1400–1500°C) und mit steigendem O σMe (mit σMe = Ti + Ta) eine Rutilmischphase, danach die Verbindung TiTa2O7 und schlieslich die mit HTa2O5 verwandten Phasen H2 und H1. Die Rutilmischphase enthalt z.B. nach Erhitzung an der Luft bei 1500°C 16–17 at.% Ta (Ti + Ta = 100%); unter diesen Bedingungen liegt ein Rutilgitter mit O σ Me = 2.05 vor. TiTa2O7 das mit TiNb2O7 wahrscheinlich isotyp ist, hat die Gitterkonstanten a = 11.847; b = 3.806; c = 20.39 A; β = 120.26°. In den Verbindungen Ti2Nb10O29 und TiNb24O62 ist eine partielle Substitution von Nb durch Ta moglich. Die Phase H2 tritt im Bereich 2.467 ⩽ O σ Me ⩽ 2.484 auf und besitzt die Gitterkonstanten (2.467 O Me ): a = 5.38; b = 5.35; c = 35.71 A; β = 91.66°. Die Phase H1 (2.489–2.492 O σ Me ) hat die Gitterkonstanten a = 3.79; b = 3.81; c = 35.73 A; β = 90.79°. Fur HTa2O5, das TiO2 bis zur Zusammensetzung 2.494 O σ Me aufnehmen kann, ist a = 3.78; b = 3.80; c = 35.74 A; α = 90.20°; β = 90.96°; γ = 89.97°.

Probing for Structural Features of Boron-rich Solids with EELS†

Crystal structures of boron-rich solids are characterized by boron atom arrangements that are quite diverse: chains, sheets, and a variety of polyhedra like octahedra, pentagonal bipyramids, cuboctahedra, and icosahedra are observed. Probing by electron energy-loss spectroscopy (EELS), these different structural features are mirrored by a pronounced variation of the energy loss near-edge fine structure (ELNES) of the BK ionization edges. For identification, characteristics of these fine structures can be used as so-called “coordination fingerprints”, which is shown for solids like MgB2, TaB2, ZrB2, CaB6, SrB6, BaB6, NaB5C, KB5C, Na3B20, Na2B29, UB12, ZrB12, LaB2C2, CeB2C2, and CaB2C2. In addition, theoretical calculations of ELNES based on the density functional theory (FLAPW method) are presented for an example of boron-rich solids. Bestimmung struktureller Charakteristika in borreichen Festkorpern durch Elektronenenergieverlustspektroskopie Die Kristallstrukturen von borreichen Festkorpern zeigen stark variierende Boratom-Anordnungen: Man findet Ketten, Schichten und eine Vielzahl verschiedener Polyeder wie Oktaeder, pentagonale Bipyramiden, Kuboktaeder und Ikosaeder. Mittels der Elektronenenergieverlustspektroskopie (EELS) konnen diese strukturellen Charakteristika abgebildet werden, denn die Nahkanten-Feinstruktur (ELNES) der BK-Ionisierungskanten variiert signifikant mit der Boratom-Anordnung. Fur Verbindungen wie MgB2, TaB2, ZrB2, CaB6, SrB6, BaB6, NaB5C, KB5C, Na3B20, Na2B29, UB12, ZrB12, LaB2C2, CeB2C2 und CaB2C2 wird gezeigt, das die unterschiedlichen Feinstrukturen als “Fingerabdruck” der Koordination der Boratome und damit der Identifizierung von Verbindungen dienen konnen. Zusatzlich werden fur ein Beispiel borreicher Festkorper theoretische Berechnungen der ELNES, die auf der Dichtefunktionaltheorie basieren (FLAPW-Methode), vorgestellt.

Nioboxidfluoride mit Blockstrukturen — Elektronenmikroskopische Durchstrahlungsaufnahmen und ihre Simulation

Niobiumoxidefluorides Nb59O147F, Nb31O77F, Nb65O161F3 and Nb34O84F2 were prepared by reaction of Nb2O5 and Nb3O7F at 1 270°C. These niobiumoxidefluorides have blockstructures which were examined by high resolution electron microscopy. The observed images of the crystal structures were compared with computer simulated images.

NaB15: a new structural description based on X-ray and neutron diffraction, electron microscopy, and solid-state NMR spectroscopy

A boron-rich sodium boride, formerly known as NaB15, has been subjected to a comprehensive structural reinvestigation using X-ray single-crystal and powder diffraction, low-temperature neutron and electron diffraction, high-resolution transmission electron microscopy, and 23Na solid-state NMR spectroscopy. The results indicate that the previously published orthorhombic space group is incorrect. Consistent with all of the experimental results a modified structural description is developed in the monoclinic space group Ilml (a = 585.92(3), b= 1039.92(6), c = 833.17(5) pin, beta = 90.373(5) from powder data). Because one of the interstitial boron atom positions remains unoccupied, the accurate compositional formula is NaB145 or Na2B29.