The oxalato complexes of titanium(IV)—I : Mononuclear Ti(OH)2(C2O4)22− in solution

Molecular weight, electrodialysis and anion exchange measurements between pH 1 and 4 showed that the titanyl oxalate anion is present in solution as mononuclear Ti(OH)2(C2O4)22 units. pH studies of solutions of (NH4)2TiO(C2O4)2·H2O in 0.5 M NaClO4 medium and computer evaluation and simulation by LETAGROP and HALTAFALL showed that the behaviour of such solutions can be simulated by applying stability constants of log β1 = 7.90 ± 0.02 and log β2 = 13.24 ± 0.07, when using hydrolysis constants given by Nazarenko et al.\ud \ud In an attempt to determine the stability constant β2 spectrophotometrically using an exchange method with pyrocatechol, a mixed ligand complex was found with a Ti:pyrocatechol:oxalate ratio of 1 : 1 : 1

The crystal and molecular structure of ammonium titanyl oxalate

Ammonium titanyl oxalate monohydrate, (NH4)2 TiO(C2O4)2·H2O, is monoclinic with cell parameters A = 13.473(2), B = 11.329(1), C = 17.646(2) Å, β = 126.66(1)°. The space group is P21/c with Z = 8, dc = 1.808 g cm−3 and dm = 1.80 g cm−3. The crystal structure was determined from single-crystal diffractometer data and refined by least-squares methods using isotropic thermal parameters. The conventional R factor was 7.0% for 2466 used reflections.\ud The anions consist of cyclic tetranuclear complexes [TiO O (C2O4)2]48− with symmetry. The titanium atoms are six-coordinated with two bridging oxygen atoms cis to one another and four oxygen atoms of bidentate oxalate groups, together forming a distorted octahedron. The titanium atoms of the tetramer are linked through oxygen atoms at two neighbouring apices of each octahedron. The actual name of the compound should therefore be: ammonium cyclotetra-di-μ-oxo-cis-dioxalatotitanate(IV)tetrahydrate.\ud The di-μ-oxo-tetratitanium unit is an eight-membered ---O---Ti---O--- ring with Ti-O distances of successively 1.840(7), 1.785(7) and 1.855(6), 1.788(8) Å, repeated by the centre of symmetry, and the orientation of the atoms suggests the presence of dπ---pπ 3-center 2-electron bonds in each Ti---O---Ti set.\ud The Ti---O distances trans to the bridging oxygen atoms are much longer: 2.060(7), 2.101(7), 2.081(7) and 2.116(7) Å respectively, as is to be expected from the charge displacement due to the dπ---pπ bonding. Most O---Ti---O angles in the distorted octahedra differ considerably from 90°.\ud As was found by difference Fourier synthesis and thermal analysis, half of the crystal water is held very loosely compared to the other half

A simple device in a horizontal TG analyzer to prevent mixing of corrosive and protective gases

A ceramic cylinder has been developed as an accessory to a standard DuPont 951 Thermogravimetric Analyzer to study weight changes of solid samples in corrosive atmospheres. This device has two purposes to be fulfilled at higher temperatures (≤ 9OO°C) and higher gas flow rates (≤ 14 cm s-l): (1) preventing mixing of reactant and purge gases at the location of the sample; and (2) keeping the corrosive reactant gas from the balance sections

Bismuth oxide based ceramics with improved electrical and mechanical properties: Part II. Structural and mechanical properties

Coprecipitation as a method of preparation for bismuth oxides based ceramics yields relatively strong and machineable materials in comparison with the solid state reaction. Compositions within the system (1−x)Bi2O3|xEr2O3 containing up to twenty five mole percent of erbium oxide show a slow transition on heating at 900 K from a cubic to a hexagonal (rhombohedral) phase. The resulting hexagonal phase is stable up to 1000 K where it transforms back to the cubic phase. Long term heating at 775 K causes formation of traces of ∝ - bismuth oxide in these samples, but the material itself remains cubic. Compositions containing thirty mole percent of erbium oxide do not show any such changes and hence are suitable for application purposes

Luminescent thin films by the chemical aerosol deposition technology (CADT)

Zinc sulphide thin films have been deposited with CART using zinc chlorideand zinc acetylacetonate as Zn compounds and thiourea and 1,1,3,3-tetramethylthiourea as S compounds soluted in methanol, ethanol, isopropanol and cellosolve. After optimalization of the deposition process homogeneous layers with a c-axis oriented hexagonal columnar structure with a high density (up to 96%) were obtained. Luminescence was observed with films grown above 500°C. The influence of the hot plate temperature, flow of carrier gas, nozzle geometry, distance nozzle substrate, and volatility of the solvent and reactants on the growth rate, homogenity and density of the film has been shown. Some rules for the selection of the starting compound are given. TG analyses of the reactant compounds was used to compare their volatility and stability

Structure and ionic conductivity of B_i2O₃ substituted with lanthanide oxides

A neutron diffraction study was performed on (Bi2O3)O.80(Er2O3)0.20 in the temperature region of 300–1100 K. There is no long-range ordering of vacancies. It is concluded from diffuse scattering that at low temperatures short-range ordering appears, leading to the occurrence of relatively short Ln-O distances. At temperatures above 870 K the oxygen lattice disorders.\ud \ud In the low temperature region of Bi2O3-Ln2O3 solid solutions with the δ-Bi2O3 structure the activation energy of the conductivity is determined by the strength of the Ln-O band. In the high temperature region the energy necessary for oxygen ions to migrate through the tetrahedron planes plays a role

Electrical and catalytic properties of some oxides with the fluorite or pyrochlore structure: Part 2: Catalytic oxidation of carbon monoxide

The catalytic properties of mixed oxides with the fluorite or pyrochlore structure were investigated using CO oxidation. The presence of ions with a variable valence state, the size of the ions and especially the extent of pyrochlore ordering affect kinetic behaviour and activity of the investigated materials

Electrical and catalytic properties of some oxides with the fluorite or pyrochlore structure: Part 1: Synthesis, characterization and conductivity

In view of their possible use as electrocatalysts, several oxides with the fluorite or pyrochlore structure were investigated. Part I of this paper deals with the synthesis, characterization and electrical conductivity of these materials. All lanthanide titanates investigated (partly doped with Bi) show the pyrochlore structure and are poor conductors, except for the compounds containing Tb. For Nd-zirconates, partly substituted with Ce, the degree of order depends on the amount of Ce and temperature treatment. Ionic and in some cases mixed conductivity was observed. Part II reports about the catalytic activity for CO oxidation