- Synthesis and properties of tetracyanamidosilicates ARE[Si(CN 2)4]
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Tetracyanamidoslllcates of the type ARE[SI(CN2)4] with A=K, Rb, and Cs and RE=Y and La-Lu have been prepared by a solid-state metathesis reaction. The potassium compounds with RE = La-Gd crystallize orthorhombically in the space group P21212. Rubidium as well as cesium compounds crystallize tetragonally In the space group 14. The luminescent properties of ARE[Si(CN2)4]:Ln compounds with RE=Y, La, and Gd doped with 5 mol % Ln=Ce, Eu, or Tb were Investigated. Temperature-dependent magnetic susceptibilities were measured for KGd[Si(CN 2)4]. The value of the magnetic moment Is 7.3,μB/Gd3+ ion, which is In line with the expected value for the [Xe]4f7 configuration of Gd3+.
- Glaser, Jochen,Bettentrup, Helga,Justei, Thomas,Juergen Meyer, Land H.-
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- DISSOLUTION KINETICS OF CRYSTALLINE AND AMORPHOUS SILICA IN HYDROFLUORIC-HYDROCHLORIC ACID MIXTURES.
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The dissolution kinetics of crystalline and amorphous silica were studied as a function of time, temperature, concentration of HF, concentration of HCl, and crystallographic orientation. The results indicate that dissolution is a surface reaction-controlled process. The dissolution rate depends strongly on HF concentration and weakly on HCl concentration. The dissolution rates depend on crystallographic direction in alpha -quartz and are slower than for fused silica. The rate-controlling step is thought to be a ligand exchange process at the surface.
- Liang,Readey
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- Temperature dependence of photoluminescence spectra and dynamics of the red-emitting K2SiF6:Mn4+phosphor
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Investigating and understanding temperature-dependent photoluminescence (PL) properties of inorganic phosphors are of vital importance to optimize their performance and expand their application. Recently, K2SiF4:Mn4+phosphors have attracted intense attention as a red phosphor candidate for white LED applications because of their extremely narrow emission peaks in the red spectral region. Here, temperature-dependent (20–200?°C) diffuse reflection spectra and steady and transient PL spectra of K2SiF4:Mn4+were systematically investigated. Both the emission intensities and spectral characteristics of the phosphor showed excellent thermal stability at temperatures from 20 to 150?°C, ensuring its great potential for practical white LED applications. An abnormal PL enhancement was found at elevated temperatures that differed from the thermal quenching behavior of common phosphors and could be attributed to enhanced phonon-assisted radiative transitions at higher temperatures. We further successfully tested and verified that the intensity ratio of anti-Stokes and Stokes emission peaks of Mn4+ions was sensitive to temperature and followed a Boltzmann-type distribution function very well, making the K2SiF4:Mn4+phosphor a good candidate for temperature sensing, especially for investigating the thermal distribution of white LEDs.
- Shao, Qiyue,Wang, Lin,Song, Li,Dong, Yan,Liang, Chao,He, Jinhua,Jiang, Jianqing
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- Thermodynamic properties of silicalite SiO2
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Silicalite, a polymorph of SiO2, is a new and interesting molecular-sieve material.Low-temperature (5 to 350 K) heat-capacity, fluorine-combustion, high-temperature (350 to 1500 K) drop-calorimetric, and reaction-calorimetric with HF(aq) measurements have been performed on this material.At T' = 298.15 K, ΔfHm0(T') = -(905.20+/-0.84) kJ * mol-1; Cp,m0(T') = (46.34+/-0.23) J * K-1 * mol-1; 0T'Sm0(T')> = (46.29+/-0.23) J * K-1 * mol-1; and ΔfGm0(T') = -(852.23+/-0.84) kJ * mol-1.The enthalpies of reaction with 24.4 mass per cent hydrofluoric acid of silicalite at mass concentrations of 0.5, 1, 2, and 4 g * dm-3 were determined to be -(144.91+/-0.23), -(144.80+/-0.10), -(145.07+/-0.12), and -(145.06+/-0.14) kJ * mol-1, respectively.The enthalpies of reaction of silicalite with 20.1 and 15.0 mass per cent hydrofluoric acid at a silicalite mass concentration of 1 g * dm-3 were determined to be -(143.85+/-0.19) and -(142.68+/-0.08) kJ * mol-1, respectively.Because silicalite reacts rapidly with HF(aq) at 298.15 K, it has potential as a reference material for thermochemical measurements on inorganic silicates and silicate minerals.Silicalite is less stable than quartz, cristobalite, or tridymite, but more stable than SiO2(glass) or the high-pressure forms coesite or stishovite.
- Johnson, G. K.,Tasker, I. R.,Howell, D. A.,Smith, J. V.
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- Synthesis, properties, sintering and microstructure of sphene, CaTiSiO5: A comparative study of coprecipitation, sol-gel and combustion processes
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Sphene (CaTiSiO5), a titanosilicate ceramic considered as a host material for the immobilization of radioactive waste from nuclear power reactors, has been prepared using coprecipitation, sol-gel, and solution combustion methods. All these processes initially yielded amorphous powders, which on further calcination, crystallized to yield sphene along with perovskite, titania, and cristobalite. The coprecipitation-derived powder calcined at 1000 °C for 2 h showed the formation of single phase sphene; whereas, the sol-gel-derived and combustion-derived powders required higher temperature (1200 °C for 2 h) for single phase sphene to form. Coprecipitation-derived sphene powder achieved 96% theoretical density when sintered at 1300 °C for 2 h, and the microstructure of the sintered body showed a uniform grain size of ≈1 μm.
- Muthuraman,Patil
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- Sulfuric acid breakdown of fluorite in the presence of silica
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We study the reaction of CaF2 with concentrated sulfuric acid in the presence of silica at 120 and 140°C using fluorite mineral, fluorite concentrate, and mica-fluorite ore samples. When steam is fed to the reaction mixture, fluorosilicic acid
- Krysenko,Gordienko,Epov
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p. 1876 - 1879
(2010/05/01)
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- Effect of additives on copper outplating onto silicon surface from dilute HF solutions
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The effects of additives such as acids and surfactants on copper outplating onto silicon surfaces from dilute HF solution were studied. It was found that some additives could significantly reduce copper outplating. Results from potentiommetry, total-refle
- Chen, Zhan,Singh, Rajiv K.
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p. G360-G367
(2008/10/09)
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- REACTION OF ELECTROLYTIC POWDERY SILICON WITH SOLUTIONS OF ACIDS AND SODIUM HYDROXIDE.
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The reaction of electrolytic powdery silicon (ESP) with alkaline and acidic solutions was examined. EPS dissolves slowly in an hf medium with hydrogen formation. Treatment of EPS in concentrated H//2SO//4 leads to more complete passivation of the silicon particle surface. Monocrystalline silicon interacts with hydrofluoric acid in the presence of strong oxidizing agents (HNO//3, K//2Cr//2O//7, KMnO//4), during which significnt liberation of hydrogen occurs, together with formation of the reduced form of oxidizing agent.
- Boiko,Chernov
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