Die Synthese von Calciummetatitanat bei niedriger Temperatur. I.

Die Reaktionsfanigkeit des Gemenges Ca(OH)2 und Ca(N03h mit Ti02 wurde eingehend studiert. Fiir ein standardes Ti02 wurde die Abhangigkeit der Ausbeute von der Reaktionsdauer, Temperatur, Dispersitat der Agglomerate, Zusammensetzung und Uberschuss des Ca(OH)2 und Ca(N03)2 Gemenges untersucht. Verglichen wurde die Ausbeute wenn Ca(OH)2 im Gemenge mit Cao ersetzt wird, sowie die Ausbeute bei Reaktionen mit anderen Calciumverbindungen. Auf Grund dieser Untersuchungen kann auf den Einfluss der Schmelze, Atmosphare und Cao in statu nascendi auf den Verlauf dieser Synthese geschlossen werden. Mit geeignetem Ti02 Gel kann man bei 575oc mit einem Gemenge von 1,0 Ti02 + 0,7 Ca(OH)2 + 0,3 Ca(N03)2 bei 1-2 stiindiger Reaktionsdauer praktisch eine 100°/e Ausbeute von Cao . Ti02 erzielen

Vibrational Spectroscopy of Inorganic Coordination Compounds of Fluorine

Vibrational spectroscopy has been used many times in successfully elucidating the nature of chemical bonds and structures of molecules. This is fully valid for organic compounds, but in the case of some groups of inorganic compounds, like halide complexes, the results are sometimes necessarily limited by the insufficiently determined problems. This is conveniently illustrated by compounds of fluorine. The following examples are discussed here: correlations between fluorobasicity and chemical bonding with interaction force constants in AgF4~ and AuF4_ ions, the mixing modes in XeFs+ ion due to symmetry changes, high coordination number and asymmetry in UFio + ion, different linking of coordination polyhedra and different types of N2H62 + ions in the compounds or Zr and Hf, low temperature transformations like reversible hydration/dehydration of N2H6AIF5.H2O, reversible dimer-monomer transitions of (V202F6(0H2)22~, decomposition of (N2H6hTiF6.F2 through proton transfer from N2H62+ to F", and failure of simple correlations of spectra with H-bonds strength

Vibrational Spectroscopy of Inorganic Coordination Compounds of Fluorine

Vibrational spectroscopy has been used many times in successfully elucidating the nature of chemical bonds and structures of molecules. This is fully valid for organic compounds, but in the case of some groups of inorganic compounds, like halide complexes, the results are sometimes necessarily limited by the insufficiently determined problems. This is conveniently illustrated by compounds of fluorine. The following examples are discussed here: correlations between fluorobasicity and chemical bonding with interaction force constants in AgF4~ and AuF4_ ions, the mixing modes in XeFs+ ion due to symmetry changes, high coordination number and asymmetry in UFio + ion, different linking of coordination polyhedra and different types of N2H62 + ions in the compounds or Zr and Hf, low temperature transformations like reversible hydration/dehydration of N2H6AIF5.H2O, reversible dimer-monomer transitions of (V202F6(0H2)22~, decomposition of (N2H6hTiF6.F2 through proton transfer from N2H62+ to F", and failure of simple correlations of spectra with H-bonds strength

Navier-Stokes-Fourier analytic solutions for non-isothermal Couette slip gas flow

The explicit and reliable analytical solutions for steady plane compressible non-isothermal Couette gas flow are presented. These solutions for velocity and temperature are developed by macroscopic approach from Navier-Stokes-Fourier system of continuum equations and the velocity slip and the temperature jump first order boundary conditions. Variability of the viscosity and thermal conductivity with temperature is involved in the model. The known result for the gas flow with constant and equal temperatures of the walls (isothermal walls) is verified and a new solution for the case of different temperature of the walls is obtained. Evan though the solution for isothermal walls correspond to the gas flow of the Knudsen number Kn≤0.1, i.e. to the slip and continuum flow, it is shown that the gas velocity and related shear stress are also valid for the whole range of the Knudsen number. The deviation from numerical results for the same system is less than 1%. The reliability of the solution is confirmed by comparing with results of other authors which are obtained numerically by microscopic approach. The advantage of the presented solution compared to previous is in a very simple applicability along with high accuracy. [Projekat Ministarstva nauke Republike Srbije, br. 35046 i 174014

A microbearing gas flow with different walls´ temperatures

An analytical solution for the non-isothermal two-dimensional compressible gas flow in a slider microbearing with different temperatures of walls is presented in this paper. The slip flow is defined by the continuity, Navier-Stokes and energy continuum equations, along with the velocity slip and the temperature jump first order boundary conditions. Knudsen number is in the range of 10-3-10-1, which corresponds to the slip flow. The ratio between the exit microbearing height and the microbearing length is taken to be a small parameter. Moreover, it is assumed that the microbearing cross section varies slowly, which implies that all physical quantities vary slowly in x-direction. The model solution is treated by developing a perturbation scheme. The first approximation corresponds to the continuum flow conditions, while the second one involves the influence of rarefaction effect. The analytical solutions of the pressure, velocity and temperature for moderately high Reynolds numbers are presented here. For these flow conditions the inertia, convection, dissipation and rate at which work is done in compressing the element of fluid are also presented in the second approximation

Influence of Spike Shape at Supersonic Flow Past Blunt-Nosed Bodies

Abstract. In order to eliminate the appearance of a strong shock wave at a supersonic flight of a missile, which considerably increases the drag during its flight through the air, a spike is mounted on its nose. Presented paper offers the results of an experimental analysis of the influence of the spike's shape on the aerodynamic coefficients (drag, lift and pitching moment coefficient, as well as the location of th