New cobalt and rare earth metal tungstates CoRE<Subscript>2</Subscript>W<Subscript>2</Subscript>O<Subscript>10</Subscript>

A new family of cobalt and rare-earth metal tungstates (CoRE₂W₂O₁₀ where RE=Y, Dy, Ho and Er) were synthesized by heating in the solid-state equimolar CoWO₄/RE₂WO₆ mixtures. The obtained compounds are isostructural and crystallize in the monoclinic system. They melt incongruently in an inert atmosphere at 1494 K (CoY₂W₂O₁₀), 1523 K (CoDy₂W₂O₁₀), 1517 K (CoHo₂W₂O₁₀) and 1493 K (CoEr₂W₂O₁₀). For each CoRE₂W₂O₁₀ compound the solid product of melting is an adequate RE₂WO₆.     

A new phase in the Ag−O−S system

The investigations of reaction between Ag₂SO₄ and Ag₂S in air atmosphere have been carried. Results of DTA and X-ray phase powder diffraction of a reaction mixture have confirmed that in the Ag?O?S system exists a new phase. A formula of the phase is Ag₂SO₂.     

Statistical Analysis of Disordered Polytype Structures Observed by HREM Method

A statistical analysis of cp-layer distribution in ZnS:Al crystal was carried out. It was based on examinations of crystal structure by HREM (High Resolution Electron Microscopy). The analysis was carried out to compare the observed structures and structures expected from the Superlattice Model of Polytype Structure Formation (SMP). This comparison occurs acceptable to the Model.     

Kinetics of Reactions between Some Compounds from the Three-Component Silver -Oxygen -Sulfur System

Reaction between Ag₂O and SO₂ gives silver and Ag₂SO₄. Heating Ag₂O/Ag₂S mixtures comprising between 66.67 to 100.00 mol % of oxide, at forced flow of inert gas, gives only silver.     

Reactivity in The Solid State Between Ag2S and Ag2CrO4

Reactivity, in the solid state between Ag₂S and Ag₂CrO₄, was investigated by DTA, XRD and IR methods. It was found that, according to a composition of an initial Ag₂S/Ag₂CrO₄ mixture, the products of a reaction of Ag₂S with Ag₂ CrO₄ can be: solid solution with Ag₂CrO₄ structure (Ag₂Cr_1–xS_xO₄) and AgCrO₂; or solid solution Ag₂Cr_1–xS_xO₄, Ag₂SO₄, AgCrO₂ and metallic silver; or Ag₂S, β-Ag₈S₄O₄, Ag, AgCrO₂, Ag₂SO₄ and Ag₂Cr_1–xS_xO₄ solid solution. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Boudouard–Bell reaction analysis under high pressure conditions

A new method for the measurement of solid fuel reactivity towards carbon dioxide has been developed. This new method takes into account high-pressure and temperature effects. Three devolatilized carbonaceous materials have been used in experiments: chars derived from lignite, bituminous coal and blast furnace coke. Processes were carried out at temperatures of 800, 850 and 900?°C and pressures of 1.52, 2.5 and 3.4?MPa. Analysis of the product gas composition was carried out with the maximum degree of conversion of CO₂ (??_m) proposed as a representative reactivity parameter. Arrhenius and Eyring relationships have been analyzed, and values of the activation energy and activation volume have been calculated.     

Dielectric and magnetic permittivities of three new ceramic tungstates MPr2W2O10 (M = Cd,Co, Mn)

Broadband dielectric spectroscopy measurements revealed an anomalously large relative permittivity value (ε _r?=?884) for MnPr₂W₂O₁₀, a smaller value (ε _r?=?156) for CoPr₂W₂O₁₀ and the smallest value (ε _r?=?22) for CdPr₂W₂O₁₀ at low frequency (ν?=?0.1?Hz) and above room temperature in the insulating and paramagnetic state. Below 273?K, the relative permittivity (ε _r?～?24) did not depend significantly on frequency for all the tungstates under study. Electrical resistivity, thermoelectric power, electron paramagnetic resonance, magnetic susceptibility and magnetization provided experimental evidence that the studies tungstates were paramagnetic insulators with low n-type conduction. Only in the case of MnPr₂W₂O₁₀ was a ferrimagnetic order below 45?K observed. These effects are discussed within the framework of Maxwell–Wagner polarization, chemical covalent bonds and porosity mechanism.     

Sano-Tachiya-Noolandi-Hong versus Onsager modelling of charge photogeneration in organic solids

We have studied the electric field dependence of charge photogeneration efficiency in organic solids for various radial distribution functions (Dirac delta, Gaussian, exponential) of initial e-h pairs in the framework of Sano-Tachiya-Noolandi-Hong (STNH) theory assuming that the final recombination (capture reaction) proceeds on a sphere of finite radius (a) with a finite velocity (κ). We compare the STNH results with the conventional Onsager theory assuming a = 0. We show that charge photogeneration is more enhanced, especially in low-electric field range, for broader initial pair distributions and for smaller final recombination velocities. We compare theoretical results with experimental data taken from electromodulation of photoluminescence (EML) for two archetypical organic photoconductors, Alq₃ and Ir(ppy)₃, commonly used as emitters in organic LEDs. From analysis of our results we infer the lower limit of final recombination velocity, κ = 0.2-2 cm/s, in vacuum evaporated films of Alq₃ and Ir(ppy)₃ which compares favorably with an evaluation of this quantity in amorphous solids.     

Pressurized CO<Subscript>2</Subscript>-enhanced gasification of coal

Carbon dioxide was considered as a co-gasifying agent in a coal gasification reactor. The work presented herein describes the simulation results for the process and the experimental data on coal char gasification with CO₂ addition as the rate-controlling step for the entire process. To study the potentially beneficial effect of the introduction of CO₂ into the gasification system, several simulations were conducted using the commercial process simulation software ChemCAD 6.3^®. The results of a Gibbs equilibrium reactor were evaluated. The Boudouard reaction is a critical path for the development of this process, and the kinetics were studied experimentally. Four chars derived from the pyrolysis of Polish coals of different origins were selected for the experiments. The kinetic characteristics of this system were examined using a custom-designed pressurized fixed-bed reactor. To determine the effect of pressure on the gasification rate, several preliminary studies on the gasification of coal chars were performed isothermally at the temperature of 950 °C and pressures of 1, 10, and 20 bars. In contrast to the thermodynamic calculations, the experimental data revealed that increasing the CO₂ pressure leads to a higher reaction rate for medium-rank coal chars and low-rank lignite coal char, resulting in higher efficiency for carbon monoxide production. The pressure influences the reactivity more strongly when varied from 1 to 10 bars; a further increase in pressure affects the rate almost insignificantly. The observed behavior representing the changes in carbon conversion degree during gasification is satisfactorily described by the grain model.