Flame Fusion Research Articles

Assessment of shear zone-derived quartz from the Etam area, southwest Cameroon as potential high-purity quartz resource: petrography, geochemistry and technological studies

This study focuses on the evaluation of the high-purity quartz (HPQ) potential of a shear zone-hosted hydrothermal and metamorphic quartz deposit in Etam, southwest Cameroon. The shear zone quartz-rich rock is monomineralic and consists of both milky and translucent varieties. The combination of ICP-MS and LA-ICP-MS analytical techniques was used to assess the chemical purity of both quartz varieties. These compositional analyses show that all quartz samples have SiO2 content of 98.46–99.75 wt% with very low concentrations of all the other elements. Translucent quartz when compared to the milky quartz variety shows low concentration of most of the elements including the following principal impurities: Al (mean 107 µg g−1), Ca (mean 27.85 µg g−1) and Fe (mean 26.05 µg g−1). Bubble generation in the samples after flame fusion over a silica plate was assessed to test the suitability of the quartz in industrial uses. The results obtained from the chemical analyses and bubble formation tests indicate that all the samples investigated do not meet the HPQ requirement. However, the translucent quartz shows characteristics of medium-purity quartz and can produce silica glass for some industrial manufacturing even without further purification. In this study, the fluid inclusions in the samples were examined as this bears information on the economic viability of the deposit and provides clues on the genesis of the quartz vein. Also tiny mineral inclusions within individual quartz grains were identified by SEM–EDS. The results of these studies show that the deposit is probably of metamorphic origin marked by crystal-plastic deformation in quartz grains. The veins were later modified by hydrothermal fluid input. The results also indicate that the majority of impurities are likely hosted by fluid inclusions and thus the quartz can be upgraded to HPQ after purification by suitable methods.

The History of the German Association for Crystal Growth

The History of the German Association for Crystal Growth

Controlled-Atmosphere Flame Fusion Growth of Nickel Poly-oriented Spherical Single Crystals—Unraveling Decades of Impossibility

Experimental research using monocrystalline electrodes has been a hallmark of interfacial electrochemistry and electrocatalysis since 1980. However, it has been limited to mainly noble metals because of the challenges encountered when using non-noble metals. We report on the development of controlled-atmosphere flame fusion that enables the growth of spherical single crystals of non-noble metals in controlled gaseous atmosphere and without the formation of surface or bulk oxides. The set-up is used to grow nickel single crystals the structure of which is verified using Laue X-ray back-scattering and scanning electron microscopy (SEM). The equilibrium shape of the nickel single crystals calculated using Wulff construction agrees with the actual shape determined using SEM. Electrochemical measurements in aqueous NaOH solution using the monocrystalline Ni electrodes reveal cyclic voltammetry features unique to their surface structure. The methodology, transferrable to other metals, creates enormous research opportunities in interfacial electrochemistry, electrocatalysis, surface science, gas-phase catalysis, and corrosion science.

Effect of Beryllium Heat Treatment in Synthetic Ruby

We study the effect of Be atoms in the corundum structure by using UV-Vis–NIR spectroscopy as well as X-ray absorption spectroscopy on synthetic ruby samples obtained by the Verneuil process. From the X-ray absorption near edge structure (XANES) spectra, the Be atoms are shown not to be related to the Cr environment. Furthermore, the UV-Vis–NIR absorption spectra are similar for the unheated, traditionally heated, and Be-heated synthetic ruby samples. However, the Be atoms are able to produce a brown-colored center, and the mixing of the red and the brown colors yields the orange in the Be-heated synthetic ruby samples. We propose that the orange color in the Be-heated synthetic ruby samples is caused by the Be2+ donor state at 475 nm (2.61 eV) in multiple UV-Vis–NIR wavelength excitation spectra.

Growth of SrTiO3 Single Crystals with a Diameter of about 30 mm by the Verneuil Method

The work demonstrates growth by the Verneuil method of SrTiO3 single crystals of 30 mm in diameter. Experiments are performed under an industrial environment. Growth was for 4.75 h, i.e., within one production shift. The optimum growth conditions for which the length of the region with bubbles D is zero and the effective length EL (i.e., the crystal length of commercial value) is maximized are for the amount of SrCO3 additive of ∼3 wt % and for H2 outer flow rate of ∼35 L/min. These two parameters show the strongest influence on the bubble-free growth, but other growth parameters (H2 inner flow rate, O2 flow rate increase, rotation speed) were also optimized. Selected crystals are characterized from the structural, microstructural, optical, and THz spectroscopy viewpoints, and they are compared with a commercial substrate and with crystals reported in the literature. This work opens the possibility for the industrial growth of large SrTiO3 single crystals and commercialization of large area substrates.

МУЛЛИТ И ЕГО ИЗОМОРФНЫЕ ЗАМЕЩЕНИЯ ОБЗОР

Рассмотрена фазовая диаграмма системы SiO2-Al2O3. Представлен обзор методов синтеза муллита, в т. ч., обжигом природных алюмосиликатов, из расплава методом Чохральского, методом Вернейля из геля, и твердофазным методом из шихты стехиометрического состава. По литературным данным установлено, что параметры ромбической решетки и габитус кристаллов муллита напрямую зависят от величины соотношения алюминия и кремния в исходной шихте, содержания примесей, способа термической обработки и формы введения в шихту исходных компонентов. На размер кристаллов муллита влияет наличие фторида алюминия в шихте, что при определенных соотношениях позволяет получать конечный продукт в виде вискерсов. Рассмотрено воздействие минерализаторов на выход муллита: фториды щелочных металлов его уменьшают, а сульфаты и хлориды увеличивают, а также влияют на вязкость и структуру расплава. С этой целью рассмотрены различные добавки и их влияние на характер синтеза, структуру и свойства. Выявлены структурные особенности кристаллической решетки муллита, влияющие на изоморфные замещения. Рассмотрена возможность получения изоморфно замещенных разновидностей муллитов. В работе приведены оптические характеристики изоморфно замещенных муллитов, содержащих d-элементы.

Microstructure and wear behaviour of self-fluxing alloy coatings reinforced by WC-Co

The wear behaviour of Ni-base self-fluxing alloys, thermally sprayed as protective layers on martensitic stainless steel substrates, is affected by several factors, such as the microstructure of the coatings and their adhesion to the substrate, the porosity and the hardness of the surface. In this study, the mechanical wear properties of thermally sprayed self-fluxing alloys with different additions of Cermet powders (10, 20 and 30% WC-Co) were investigated using the pin-on-disk method. Moreover, it was highlighted that after the flame fusion process the morphology of the layers has been greatly improved. Based on scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis the evolution of the metallic matrix reinforced by ceramic phases consisting of carbides, borides and silicide’s was pointed out. Micro-hardness measurements were carried out as well, in order to evaluate the influence of flame fusion process on the coating hardness. The investigations revealed that the addition of up to 30% Cermet powder to self-fluxing alloys leads to the improvement of the wear resistance of the protective coatings, extending the range of practical applications of self-fluxing layers.

Feasibility Assessment for Leucosapphire Production from Aluminum Oxide Prepared Electrochemically

Technology was developed to produce high-purity Al2O3, the raw material for manufacturing leucosapphire, which is widely used in metallurgical processes, by electrochemical oxidation of aluminum. The optimum conditions and parameters for the electrochemical process; chemical, granulometric, and phase compositions; and size and shape of the obtained Al2O3 particles are reported. The high-purity Al2O3 could be used in principle to grow leucosapphire crystals by the Verneuil method, horizontal unidirectional crystallization (HUC), and zone refining.

Fabrication of ruby by flame fusion technique and their properties

In this work, ruby (Cr doped Al2O3 bulk crystal) with the size of ∅10×21 mm was grown by the flame fusion technique (FFT). Absorption spectrum was carried out in the range of 300–800 nm by spectrophotometer, It shows 2 absorption peaks of Cr3+ in ruby near 400 nm and 550 nm . The crystal structure and the lattice parameters were estimated using X-Ray diffraction studies. The density, refractive index and hardness of synthesis ruby were measured and shown the values in the range of natural ruby material.

Fabrication of sapphire crystal by flame fusion technique and their properties

In this work, bulk sapphire crystal has been growth by the flame fusion technique (FFT) and investigated their physical, structural and optical properties. The crystal structure of growth sapphire was studied by X-Rays Diffractometer (XRD) and found to be Al2O3 structure. The density, refractive index and hardness of growth sapphire were measured and show the values of these parameters are in the range of natural sapphire material. The optical spectrum was measured and optical bandgap was extrapolated and compared with natural sapphire material.

基于气炼法Yb2+/Yb3+共掺石英玻璃制备及光谱特性的研究

基于气炼法Yb²⁺/Yb³⁺共掺石英玻璃制备及光谱特性的研究

Design and Development of Instrumentations for the Preparation of Platinum Single Crystals for Electrochemistry and Electrocatalysis Research. Part 1: Semi-Automated Crystal Growth

In this contribution, we report on a novel design of semi-automated system for the growth of spherical platinum (Pt) single crystals. The system is based on the flame fusion methodology, where the crystal melting/solidification process is controlled by the vertical movement of a hydrogen–oxygen flame by using an actuator. The paper systematically examines the impact of several process variables on the crystal growth. First, the hydrogen–oxygen flame is optimized through control of the gas flow rate and the mixing ratio to ensure the formation of high-quality platinum single crystals. The procedure of crystal growth is documented in a step-by-step manner, starting with cleaning of the Pt wire, followed by the initial formation of metallic sphere, and ending with repetitive zone refining combined with chemical etching. The equilibrium shape of the platinum single crystals is discussed, and the individual low and high Miller index facets identified and visualized. The critical step in the single-crystal growth, the repetitive zone refining, is semi-automated in order to ensure the highest quality crystals and reproducibility, and to minimize any human error.

Experimental Study Regarding the Cavitation and Corrosion Resistance of Stellite 6 and Self-Fluxing Remelted Coatings

This paper aims to compare cobalt-based (type Stellite 6) and nickel-based self-fluxing alloys (type NiCrBSiMo) regarding both their cavitation erosion resistance and corrosion resistance. The two types of protective layers were thermally sprayed onto a substrate of martensitic stainless steel. In order to improve the layers’ characteristics and their metallurgical bonding to the substrate, the Stellite 6 coating was laser remelted, while the NiCrBSiMo coating was treated by flame fusion. The cavitation erosion resistance of the two materials was evaluated by measurements of the mean depth of erosion developed during a testing period of 165 minutes, using a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 50 μm. In addition, the corrosion resistance of the layers was assessed by potentiodynamic corrosion tests carried out in H2SO4 + NaCl solution at room temperature, using calomel as reference electrode. In order to highlight the differences regarding the behaviour of the two protective materials, the authors also carried out microstructural investigations of the layers before and after exposure to cavitation and corrosion. The investigations showed that both types of layers can provide improved protection of the martensitic stainless steel substrate against cavitation, whilst the NiCrBSiMo coating additionally confers significantly increased resistance to corrosion.

Structure and Phase Changes in Natural and Synthetic Magnesium Aluminum Spinel

Natural spinel crystals from Ural and Pamir deposits and synthetic magnesium aluminium spinel single crystals with different stoichiometry (MgO.nAl2O3 ) grown by Verneuil method were used. The photoluminescence (PL), its excitation (PLE) and optical absorption of stoichiometric and nonstoichiometric magnesium aluminium spinel crystals containing the chromium and manganese ions and defects produced by fast neutron irradiation( fluence up to 1020cm-2, E>0.1 MeV) are investigated. The broadening of R- and N-lines takes place in synthetic stoichiometric spinel. Structure of synthetic nonstoichiometric spinels (n>1) has to be more disordered, since in addition to the site exchange the so called stoichiometric vacancies are present in the structure. The R- and N-lines broadening takes place after spinel crystals irradiation by fast neutron too. The neutron irradiation causes increasing of the spinel inversion. Furthermore the great deviation from stoichiometry leads to the local structure of α-Al2O3 formation around Cr3+ ions. The orange emission band at 570 nm is belonging to complex center “Mn2+-F+ (or F centre)”.

Combustion Characteristic in Growth Chamber for Preparation of Single Crystal with Hydro-Oxygen Flame Fusion Method

Combustion characteristic in growth chamber for preparation of single crystal with hydrooxygen flame fusion method was investigated. The results show that along the centerline of growth chamber a peak temperature 3504.3 K could be reached when the flow rates of oxygen and hydrogen were 6 L/min and 20 L/min respectively. With the increasing hydrogen flow rate, the temperature of the center and the diameter of the central flame increased gradually in the chamber. With the increasing oxygen flow rate, the position of the peak temperature gradually moved down, which downward moved 5 mm when the central oxygen flow rate increased for 1 L/min, while the average temperature rose ca 230℃at a distance 110 mm to the nozzle. The diameter of hydrogen distribution circle had little effect on the center and radial temperature distributions, the central oxygen impact and the ignition position of the flame. As a result, the optimal position for single crystal growth could be easily acquired for the preset flow rates of the two gases and vice versa.

Quartz sand resources in the Santa Maria Eterna formation, Bahia, Brazil: A geochemical and morphological study

This study presents an evaluation of the quartz sand occurrences of the Santa Maria Eterna formation, in northeastern Brazil, as a potential source of raw material for silica glass manufacturing. Samples of quartz sand were analyzed by ICP-MS to determine a range of trace elements and establish its chemical purity. The technological potential of the sand was obtained by counting the quantity of bubbles formed during flame fusion over silica plate. Both chemistry and bubble formation indicate that the raw material is suitable for producing silica glass. The work also investigated the composition of fluid inclusions in the quartz grains and the surface micro-texture by scanning electron microscopy. With the results obtained by these procedures, we inferred that the quartz sand was probably formed in a marine environment, by the precipitation of silica in the form of quartz. The main impurities of the samples are probably present in the mineral inclusions implying that purification is possible and probably competitive.

Up-conversion and Photoluminescence in Er3+ Single Crystal MgAl-spinel

Traditional and up-conversion luminescence of MgAl2O4 single crystal doped with erbium ions obtained by the Verneuil method has been investigated. The time resolved spectral measurements of the green and red up-conversion luminescence bands show that a build-up part is present in the up-conversion luminescence kinetics. This means that energy transfer process is involved in the creation of the luminescence. Considering rather small concentration of Er3+ in the material (0.12 mass %), the expected up-conversion mechanism should be excited state absorption since the average distance between erbium ions is high. The above-mentioned considerations suggest that clustering of the activator ions is present in the material, which is supported by SEM analysis.

Study of Bubbles Elimination in Silica Glass Produced by Flame Fusion from Brazilian Natural Quartz Powder

Silica glass is a fundamental material for the high technology industry due to its physical properties. This material is widely used in the semiconductor, chemical and optical industry. For applications in the optical industry and special lamps, it is necessary that the silica has a reduced content of bubbles and high optical transmittance in the wavelength regions of visible and medium ultraviolet (200 nm – 300 nm). Silica glass samples were produced by the flame fusion Verneuil Method of Brazilian commercial natural quartz powder and imported high purity commercial powder. An acid leaching procedure of the national quartz powder was introduced before the fusion in order to decrease bubbles concentration. The results were compared with the silica glass produced with imported quartz powder and a commercial silica glass used for the fabrication of special lamps, showing an excellent feasibility of application of Brazilian natural quartz to produce high value added silica glass.

KrF- and ArF-excimer-laser-induced absorption in silica glasses produced by melting synthetic silica powder

KrF- and ArF-excimer-laser-induced absorption of silica glasses produced by electric melting and flame fusion of synthetic silica powder were investigated. The growth of KrF-laser-induced absorption was more gradual than that of ArF-laser-induced absorption. Induced absorption spectra exhibited a peak at about 5.8 eV, of which the position and width differed slightly among samples and laser species. Widths of ArF-laser-induced absorption spectra were wider than those of KrF-laser-induced spectra. KrF-laser-induced absorption is reproducible by two Gaussian absorption bands peaking at 5.80 eV with full width at half maximum (FWHM) of 0.62 eV and at 6.50 eV with FWHM of 0.74 eV. For reproduction of ArF-laser-induced absorption, Gaussian bands at 5.41 eV with FWHM of 0.62 eV was necessary in addition to components used for reproducing KrF-laser-induced absorption. Based on the discussion of the change of defect structures evaluated from change of absorption components, we proposed that the precursor of the 5.8-eV band ascribed to E′ center (≡Si·) is ≡Si−H HO−Si≡ structures formed by the reaction between strained Si−O−Si bonds and interstitial H2 molecules during the irradiation.

Ion channeling study of lattice distortions in chromium-doped SrTiO3 crystals

The results of ion channeling studies of lattice distortions in SrTiO3: Cr single crystals are presented. Two types of single crystals containing the same amount of Cr impurities but differing in stoichiometry have been investigated. The single crystals grown by the Verneuil method have the compositions of standard-grown SrTiO3: Cr (0.05 at % Cr), whereas the single crystals grown with a strontium deficiency and a chromium compensating amount have the composition Sr0.9995TiO3 (0.05 at % Cr). Analysis of the angular channeling spectra indicates that, in crystals of both types, the main defects are Cr impurities located in octahedral sites. In the SrTiO3: Cr crystals, impurity atoms manifest themselves as Cr4+ with tetragonal Jahn-Teller distortions of the surrounding lattice. In the Sr0.9995TiO3: Cr crystals grown with a Sr deficiency, the characteristic displacements of Ti ions in the third coordination sphere of the Jahn-Teller center Cr4+ exhibit the effect of interaction of the center with a neighboring vacancy in the Sr sublattice.