In-situ Observations on Cu-SiO2 and Stainless Steels

Specimens of Cu SiO₂ and of several high purity stainless steels have been observed during deformation in an HVEM. The behaviour of the Cu SiO₂ specimens is dominated by the free surfaces, even in the thickest regions which can be examined, but in the stainless steels it has been found that if the specimen is thicker than about 0.5 μm, bulk behaviour is observed. The formation of ϵ- and α-martensite has been directly observed and essentially identical observations of martensite formation have been made during cooling. It has been shown that ϵ-martensite is always formed in regions where appropriately, but usually irregularly spaced faults, are generated and detailed analyses of isolated and overlapping faults show that these faults contain close-packed planes of the appropriate eph spacing. α-martensite is formed in association with dislocation pile-ups.     

Infrared reflection spectra of selected modifications of SiO2 and Al2O3

Infrared reflection spectra were measured within the wave number range of 1400 – −400 cm⁻¹ for following SiO₂ and Al₂O₃ modifications: quartz, opal, quartz glass, cristobalite, tridymite, corundum, sapphire, ruby, gibbsite, boehmite, and diaspore. The spectral bands were attributed, according to literature quotations, to individual vibrations of bonds Si O, O Si O, Si O Si, Al O, O Al O, and Al O Al. The evaluation of infrared reflection spectra has shown that they are very sensitive to internal vibrations of Si O, Al O, which are affected by the symmetry of the surrounding crystal field. They are therefore selective for individual minerals and thus suitable for quick identifying purposes.     

The Precipitation of Alkaline-Earth Metal Polyacrylate Hydrate Powders from Aqueous Solution: Ionic Equilibria,Precipitate Compositions and Morphologies

The precipitation of barium, strontium, calcium and magnexium polyacryate hydrates was studied from equivalent aqueous solutions of initial concentrations 0.03 M to 0.30 M at ambient temperature: sodium polyacrylate (m. wt = 30,000 to 300,000) was added to metal chloride solution. The final yields of precipitate increased with decreasing solubility and/or peptisation (Ba > Sr > Ca > Mg) and increasing molecular weight of the polyacrylate; the precipitates had the compositions [BaA(COO)₂ · 1–2H₂O]_n, [SrA(COO)₂ · 1–2 H₂O]_n, [CaA(COO)₂ · 2 H₂O]_n and [MgA(COO)₂ · 2 H₂O]_n. The final yields of the precipitates from sodium polyacrylate solutions were far lower and these had the compositions [Na_2αM_1-αCA(COO)₂ · 2 H₂O]_n; A =  CH CH₂ CH . The metal polyacrylate hydrate powders consisted of microcrystalline ‘spherules’; their average diameters were from 0.03–0.05 μm (for lower m. wt products) to 0.01 to 0.02 μ,m (for higher m. wt products).     

Infrared fibers based on Te-As-Se glass system with low optical losses

Unclad optical fibers based on high-purity Te-As-Se glasses prepared by chemical and physical methods of purification have been drawn. The optical, thermal and mechanical properties of glasses and fibers were investigated. The minimum optical losses were 0.07 dB/m at 7.3 μm for Te₂₅As₄₀Se₃₅ glass fiber and 0.04 dB/m at 6.7 μm for Te₂₀As₃₀Se₅₀ glass fiber. Sixty five percent of input power of a tunable CO₂ laser emitting at 9.3 μm was transmitted through a 1 m long fiber with diameter of 900 μm.     

Dislocation Structure of Epitaxial Ferrite-Spinel Films

The dislocation structure of ferrite-spinel films obtained on the (001) plane of magnesium oxide has been studied. For the films of Mn and Mg Mn ferrites there has been found the formation of a cellular dislocation structure, complex dislocation clusters, for the Li ferrite the twinning. Experimental data are compared with the predictions of the theory of relaxation of internal stresses in heteroepitaxial structures. It has been shown that in the Li → Mn → Mg Mn ferrite the energy at the interface of magnesium ferrite and oxide ranges from 64 to 9 mJ · m⁻², the absolute magnitude of lattice mismatch at a synthesis temperature being 10.328 to 3.451 × 10⁻³ and the critical thickness of a continuous film 0.02–0.1 μm. The formation of three-dimensional islets-nuclei hinders the obtaining of pseudomorphous continuous films. The critical radius (R_cr) of a pseudomorphous islet in the same series of ferrites is 0.2–1.1 μm. For Li ferrite R_exp > R_er, for Mg Mn R_exp < R_er, that determines the prevailing types of defects. The process of relaxation of thermal stresses is associated with the overcoming of interaction barriers by dislocations and largely dependent on the film composition and temperature.     

High temperature ESR study of Fe(III) in various vitreous matrices

The Raman spectra of binary high-silica glasses have been studied. The main peaks at 808 cm^?1 and 710 cm^?1 in vitreous B₂O₃ and vitreous P₂O₅, respectively, are greatly reduced in binary high-silica glass, whereas a peak at 425 cm^?1 due to GeOGe vibration and a peak at 1320 cm^?1 due to P = O vibration remain strong, increasing in intensity with decreasing SiO₂ concentration. In the stimulated Raman spectra of a P₂O₅-SiO₂ glass fiber pumped by a mode-locked and Q-switched Nd:YAG laser at 1.064 μm, strong Stokes emissions due to the P = O vibration have been observed at 1.24 μm and 1.48 μm. In the spectra for a GeO₂-SiO₂ glass fiber, four narrow-width Stokes emissions due to the GeOGe vibration have been observed at 1.115, 1.172, 1.235 and 1.305 μm.     

The crystallization mechanism in high strength glass-ceramics

The addition of NiO to a MgO Al₂ Al₂O₃ SiO₂ basic glass has an influence on the phase separation and crystallization mechanism. The differentiation of the components already detectable in the amorphous state continues in the crystallization process of the nickel-rich glasses. The formation of Ni Al-spinel in the bulk restricts the precipitation of high quartz crystals to the skin. The result is a high strength glass-ceramic with clearly distinguishable bulk and surface regions.     

Melting and crystallization of silicon layers on insulator with millisecond lamp heating

Melting and crystallization of silicon layers in a SOI structure (Si SiO₂ Si) at millisecond lamp heating have been studied by model calculations using the solution of conduction equation. Pulse heating conditions that do not lead to silicon substrate melting under SiO₂ have been determined. For pulses of 1 and 4.4 ms duration the silicon melt lifetime on the SiO₂ surface has been estimated. The lengths of the crystal oriented growth from windows in the SiO₂ layer that open the single-crystalline silicon substrate have been measured (25 and 64 μm).     

Microstructure and spacings of directionally solidified metal-semiconductor eutectic alloys

Directionally solidified metal-semiconductor eutectic alloys, representing nonfacetted facetted eutectics, show a variety of microstructures caused by the great differences in semiconductor volume fraction (Zn Ge 7,8 %; Ge ZrGe₂ 98.6 %), the influence of growth rate and temperature gradient at the solid-liquid interface. The Al Si, Ag Si, Ag Ge, Zn Ge, Cu₃Si Si, NiGe Ge, CoGe₂ Ge, Mn₃Ge₂ Ge, FeGe₂ Ge, Mn₁₁Si₁₉ Si, Cu₃Ge Ge, Ge TiGe₂ and Ge ZrGe₂ eutectics habe been investigated. The following three models are applicable for the calculation of the spacings as a function of growth rate and temperature gradient at the solid-liquid interface to certain microstructures: diffusion-determined growth, branchinglimited growth and phase-lead-determined growth.     

Dielectric properties of fine-grained PbTiO3 crystals precipitated in a glass

The spontaneous deformation of PbTiO₃ crystals precipitated in a PbOTiO₂Al₂O₃SiO₂ glass was found to decrease with decreasing grain size. This trend remains even after the glass matrix surrounding PbTiO₃ crystals is removed completely by HNO₃ acid immersion. Consequently, a linear electro-optic effect cannot be expected from transparent glass-ceramics which necessarily comprise very-fine-grained crystals. The dielectric constant of PbTiO₃ crystals surrounded by a glassy matrix shows two maxima at grain sizes 0.15 μm and 250 Å, but is still fairly high even at a grain size as small as 160 Å. This suggests that a material with a large quadratic electro-optic effect may be produced from a transparent glass-ceramic. The maxima of the dielectric constant at grain sizes 0.15 μm and 250 Å were interpreted in terms of the internal stress and internal electric field, respectively.     

Analysis of spectral components in the 1.5 μm emission band of Er doped borosilicate glass

We measured the 1.5 μm emission spectra corresponding to ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ in borosilicate glass within the temperature range from 11 to 300 K. The spectral components emitting from the lowest and upper Stark levels of ⁴I_13/2 state were distinguished by analyzing the spectra with normalized area. The effect of optical properties of the spectral components on the 1.5 μm emission bandwidth is investigated. The results indicate that to search for a host with higher spontaneous emission probability of the upper Stark levels of ⁴I_13/2 state for Er³⁺ ions is very important to broadening of the 1.5 μm emission band. An equivalent model of four-level system is presented and applied to explain the spectral shape and temperature characteristics of the 1.5 μm emission band.     

Formation and optical properties of (R2O or R′O)Nb2O5Ga2O3 glasses

Glass-forming tendencies of melts in the systems (alkali oxide or alkaline earth oxide)-Nb₂O₅Ga₂O₃ were examined by an ordinary crucible-melting technique. The glass-forming tendency increased with increasing radius of alkali or alkaline earth ion in the respective groups. Clear glasses were obtained on a practically useful scale in the systems (K₂O or Cs₂O)Nb₂O₅Ga₂O₃ and (SrO or BaO)Nb₂O₅Ga₂O₃. The infrared absorption spectra indicated that the Ga³⁺ ions in the glasses are tetrahedrally coordinated with oxygen ions. The glasses showed high optical transmissions from the ultraviolet region of 0.3 μm in wavelength to the infrared region of 7 μm, except for a region near 3 μm. The absorption near 3 μm, which is attributed to OH vibration, could be eliminated by replacing part of the carbonate in the raw materials with a fluoride and melting the mixture of raw materials in a dry N₂ gas atmosphere. The glass-forming tendencies of the melts and the optical transmissions of the glasses were discussed in terms of the glass structure.     

Optical fibers and molded optics in infrared transparent glass-ceramic

Optical fibers and molded optics have been formed by using the Ga₅Sb₁₀Ge₂₅Se₆₀ base glass with appropriate thermal treatment to generate microcrystals. The crystal growth during the fiber drawing and molding process induces additional scattering losses in the short wavelength region, but does not have a significant effect beyond 6 μm. The molded optics have very good dimensional precision and the form defect is less than 0.5 μm peak-to-valley, which is excellent particularly for optics designed for operating at 8-12 μm.     

Electrical relaxation from hydrated surface layers in alkali silicate glasses

Complex impedance plots for a 25 Na₂O?75 SiO₂ glass exposed to the ambient atmosphere indicate the presence of a relaxation at frequencies well below those for the electrical relaxation of the bulk material, but above the frequencies where electrode polarization takes place. This low frequency relaxation is shown to occur in a high resistivity surface layer having a thickness a few times 0.1 μm and formed by the action of atmospheric water vapor. The rate of growth of the surface layer could be monitored by means of the impedance measurements and was found to decrease with the duration of exposure of the glass to the laboratory atmosphere. Complex impedance plots for a chemically durable lithium aluminosilicate glass indicate that the hydrated surface layer thickness is much smaller than in the 25 Na₂O?75 SiO₂ glass.     

Structure and mechanical properties of foils made of nanocrystalline beryllium

The phase composition and structural features of (45–90)-μm-thick foils obtained from nanocrystalline beryllium during multistep thermomechanical treatment have been established using electron microscopy, electron diffraction, electron backscattering diffraction, and energy-dispersive analysis. This treatment is shown to lead to the formation of a structure with micrometer- and submicrometer-sized grains. The minimum average size of beryllium grains is 352 nm. The inclusions of beryllium oxide (ВеО) of different modifications with tetragonal (sp. gr. P4₂/mnm) and hexagonal (sp. gr. P6₃/mmc) lattices are partly ground during deformation to a size smaller than 100 nm and are located along beryllium grain boundaries in their volume, significantly hindering migration during treatment. The revealed structural features of foils with submicrometer-sized crystallites provide the thermal stability of their structural state. Beryllium with this structure is a promising material for X-ray instrument engineering and for the production of ultrathin (less than 10 μm) vacuum-dense foils with very high physicomechanical characteristics.     

Glass formation and properties of chalcogenide systems (XXII) the phase diagram of the system PbSe?GeSe2 and on the compound Pb2GeSe4

The phase diagram of the system PbSe GeSe₂ is studied by X-ray analysis and DTA. Pb₂GeSe₄ is the only compound which is formed in the system. It melts incongruently at 590 ± 4°C. The formation of Pb₂GeSe₄ as a definite compound is supported by studying the phase relations in the corresponding area of the ternary system PbSe GeSe GeSe₂.     

Infrared transmitting chalcogenide glass ceramics

Infrared glass ceramics transmitting light from 2 to 15 μm have been produced from a Ga-Ge-Sb-Se glass. The glass composition is selected in the middle of the glass forming region and the annealing temperature must be close to T_g to avoid excessive crystal growth. A heating time of the order of two weeks is necessary to see evolution of the thermal expansion coefficient of the composite while keeping the optical transmission properties of the glass.     

Photobleaching in a g-Ge0.27Sn0.03Se0.7 thin film

Photobleaching was observed by optical transmission measurements performed using constant 655 nm (sub-band gap) illumination of a g-Ge_0.27Sn_0.03Se_0.7 thin (<2 μm) film sample deposited by thermal evaporation of bulk starting materials on silica. The threshold power density for destroying the film was 2.7 kW cm⁻² for a film thickness of 1.75 μm. The effective thermal conductivity was calculated and the temperature increase in the illuminated spots was estimated. A little below the destruction threshold photobleaching may be attributed to band gap increase with thermal annealing. But photobleaching is also observed at low power densities inducing spot temperatures well below the glass transition. No noticeable crystallization of the bleached film region was observed either optically or by X-ray diffraction.     

Bi2Te3 Crystals Heavily Doped with Germanium Atoms

Elemental Bi, Te, and Ge of 5N purity were used to prepare Bi₂Te₃(GeTe) single crystals with germanium content varying from 0 up to 2.3 × 10²¹ cm⁻³. The samples were characterized by reflectivity measurements in the plasma resonance frequency range and by measurements of the electrical conductivity. Germanium content in the samples was determined by means of energy dispersive analysis. The reflectivity spectra were interpreted on the basis of the Drude-Zener theory in the aim to obtain information on the concentration of the free carriers in the samples. It was found that Ge atoms in the Be₂Te₃ crystal lattice behave as acceptors. A comparison of the hole concentration with the amount of germanium built into the crystal lattice revealed that only about 1/100 of the total number of Ge atoms act as acceptors. This effect is explained by two different ways of incorporation of Ge atoms into the Bi₂Te₃ lattice, viz: the formation of substitutional Ge'_Bi defects acting as acceptors and the formation of seven-layer-lamellae of the Te Bi Te Ge Te Bi Te composition, which corresponds to the structure of GeBi₂Te₄.     

Crystallization kinetic of glass particles prepared from a mixture of coal ash and soda-lime cullet glass

The crystallization capability of a parent glass made from a mixture of coal ash (40 wt%) and soda-lime glass was investigated using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy. Different glass particle size distributions were considered in the range 20-500 μm. Two crystallization exotherms in DTA were attributed to the formation of both pyroxenes (diopside Ca(Mg,Al)(Si,Al)₂O₆ and augite Ca(Mg,Fe)Si₂O₆) and plagioclase (Na,Ca)(Si,Al)₄O₈. These phases were confirmed by XRD analyses. Analysis of non-isothermal DTA data yielded values of 545 kJ/mol and 1.8 for the activation energy of crystallization and the Avrami exponent, respectively. This value for the Avrami exponent was consistent with a decreasing nucleation rate and the observed dendritic morphology. The data on crystallization kinetics obtained in this study are relevant for the production of glass-ceramic materials by a sintering/crystallization method from powder compacts made of this parent glass.