bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control over gas bubble distribution in shaped sapphire crystals
Authors: Borodin V. A. , Steriopolo T. A. , Tatarchenko V. A. , Yalovets T. N. 
Published: January 2007

AbstractBubble distribution in shaped sapphire crystals grown by Stepanov technique is found to depend on the field of velocities of the melt flows between the top surface of a die and the crystallization front. A die design defining the flows in the meniscus is a tool for control over the bubble distribution.
Composition and kinetic characteristics of vapour phase during mercuric iodide growing
Authors: Lyakh N. V. 
Published: January 2007

AbstractThe results of thermodynamical analysis of the vapour phase are presented for mostly often used growth conditions. It is shown that the vapour phase may contain: HgI2(g), Hg(g), I2(g), I(g). However, the degree of decomposition does not exceed one percent. Moverover, the following dependences are calculated and presented in a graphic form for HgI2 + I2 vapour mixture: the coefficient of dynamic viscosity from composition and temperature; the coefficient of diffusion with temperature and pressure; the coefficient of heat conductivity from composition and temperature.
Agglomeration of potash alum crystals
Authors: Karel Miloslav , Nývlt Jaroslav 
Published: January 2007

AbstractCrystals of potash alum, crystallized in suspension at higher supersaturations, are partially agglomerated. Two sets of experiments have been chosen: batch experiments with precipitation of potash alum from its components and continuous crystallization by cooling. Using three different ways described in the preceding paper the size distribution of potash alum crystals was analyzed and the effect of agglomeration on calculated kinetic data demonstrated.
Nonstoichiometric defects in YAG and YAP
Authors: Kvapil Jiří , Kvapil Jos. , Perner B. , Mánek B. , Blažek K. , Hendrich Z. 
Published: January 2007

AbstractSpectroscopic properties of undoped YAG and YAP grown under reducing protective atmosphere were compared. Blue (with F centre) or brown (with 0− centre) varieties both of the materials were prepared in the dependence of the Al2O3:Y2O3 ratio in the melt. Colour intensity depends on the H2O:H2 ratio in the protective atmosphere and on the sign of electrical potential above the melt level.The coloration may be easily removed by an annealing at > 1200–1400 °C. All the irregularities of the colourations or their remowing by annealing may be attributed to the presence of impurities.
The migration of gas‐filled brine inclusions in rock salt under a temperature gradient
Authors: Müller E. 
Published: January 2007

AbstractIn natural halite crystals two sorts of inclusions will move if there exists a temperature gradient. The direction of moving brine inclusions is orientated towards the heat source.Brine inclusions which additionally contain more than 10% gas move towards the cold end of a specimen. This model is well known but detailed information about the migration mechanism of these so‐called SORBY inclusions have been lacking in literature so far.In this paper it will be demonstrated that SORBY inclusions having a diameter of up to 20 micrometers can move undisturbed through the crystal. SORBY inclusions with a diameter of more than 20 micrometers are fixed and form droplets with their tips directed towards the cold side of the specimen. Later when the tips have grown the inclusions will emit a new daughter inclusion which can move through the crystal. The velocity of migration depends on the generation of daughters.Extended kinds of SORBY inclusions are stable for a long time. However, these can decay into many individuals which will move through the crystal like the others.
Reactor problems in modified chemical vapour deposition (i). the collapse of quartz glass tubes
Authors: Kirchhof J. 
Published: January 2007

AbstractIn the case of the so‐called “Modified Chemical Vapour Deposition” for the preparation of optical fiber preforms, the quartz glass reactor is identical with the substrate. Therefore, the knowledge of reactor properties such as the viscous flow of the tubes (collapse) and the heat transport through the wall are especially important for a successful control of the process. As a first step, an analysis is presented for the calculation of the viscous flow of the tubes under the real conditions of dynamic heating by a traversing flame. The experimental determination of the material parameters surface tension and viscosity by collapsing experiments yields an approach to the problem of the temperature distribution in the tube wall.
The coprecipitation of magnesium hydroxide aluminium hydroxide powders from aqueous solution with sodium hydroxide: Precipitate compositions and coprecipitation mechanisms
Authors: Packter A. , Panesar K. S. 
Published: January 2007

AbstractMagnesium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total CM = 0.1 M and Mg/Al2 ratios from 1 to 6 — with sodium hydroxide solution at ambient temperature, with different pre‐ageing conditions for the aluminium hydroxide pre‐precipitate. The coprecipitations were monitored by potentiometric (pH) titration and the final precipitate compositions were examined by chemical analysis, infrared spectrophotometry and thermal analysis.Magnesium hydroxide was coprecipitated onto completely recrystallised aluminium hydroxide as a simple mixture.Generally, with no to three days pre‐ageing, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then partially redissolved on further addition of sodium hydroxide (to form hydroxoaluminate anion) and magnesium aluminium hydroxide coprecipitates were formed continuously at pHs from 8.0–8.7 to 12.0–12.5. Their compositions were similar to the magnesium hydroxoaluminate hydrates formed by direct precipitation from high pH sodium hydroxoaluminate solutions.
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Interatomic force constants and localized effective charges in sphalerite‐structure compounds
Authors: Neumann H. 
Published: January 2007

AbstractThe Keating model with one bond‐stretching and one bond‐bending force constant and a localized effective charge to account for long‐range Coulomb forces and dipole‐dipole interactions is used to analyse the lattice vibrational properties of sphalerite‐structure binary compounds. It is shown that the trends in the model parameters can be readily explained in terms of the bond length and the bond ionicity.
A modified heater system for RF‐Czochralski equipments
Authors: Reiche P. , Hermoneit B. , Schultze D. 
Published: January 2007

AbstractThe temperature gradients in a Czochralski‐type crystal growth equipment with induction heating can be advantageously influenced by additionally heating the growing crystal and the crucible bottom during the pulling procedure. An experimental solution is presented for both afterheater and bottom heater coupled to the same induction coil as the crucible.
On the determination of kinetic data for the continuous crystallization of potassuim chloride
Authors: Kodura J. , Gramlich K. , Karwoth R. 
Published: January 2007

AbstractA method for the determination of the kinetic constants and the realization of experiments for the bulk crystallization from solutions with particular reference to potassium chloride have been described. A new relation has been used for determining the kinetic constant, i, affording the advantage of being less sensitive to experimental errors. It can be regarded as fitting quite well with the data reported in the literature. A marked trend in the decrease in magnitude of the superscript, i, with increasing companion salt contents is noted. The value of i varies from 3.8 for technical potassium chloride to 2.0 for a fourcomponent solution.
Surface topographical studies of prism faces of ammonium tartrate single crystals
Authors: Saraf A. G. , Saraf K. B. , Wani P. A. , Bhandari S. U. , Bhoraskar S. V. 
Published: January 2007

AbstractA study of surface structures of Prism faces (110) of ammonium tartrate single crystals grown by gel technique is described and illustrated. Vertical striations closly and widely spaced are observed. Isolated as well as densely populated rectangular elongated hillocks are reported and mechanism of the growth of these faces is assessed in the light of observed surface structure.
Mathematical modelling of the SSD‐process
Authors: Weinert B. , Buhrig E. , Hein K. 
Published: January 2007

AbstractIn order to achieve a better agreement between the calculated and experimental results of crystal production by the SSD‐process, it was essential to extend the application of the modell presented earlier (Weinert et al.).The thermal and geometrical conditions, which vary strongly during the course of the process and influence the GaP crystallisation, have never been taken into consideration. It has been attempted, in the present work, to consider these changes by dividing the total time of crystallisation into so small durations (Δt), that the evaluation model presented earlier for instant times can be successfully applied. The results of crystallisation for the total period can then be obtained through a mathematical analysis named as sequence correction of process parameters. It has been shown that an exact knowledge of the temperature distribution in the furnace will yield results which are in very good agreement with the experimental values. Moreover, the changes in the process parameters during the whole time of crystallisation have been represented graphically. — Application of this model to other systems, for example to GaAs, is also possible.
The precipitation of sparingly‐soluble metal chromates from aqueous solution in the presence of chelating organic anions: Induction periods and nucleation rates
Authors: Packter A. , Jakubowski J. 
Published: January 2007

AbstractThe precipitation of barium, zinc, lead, copper and silver chromates was studied in the presence of the chelating organic anions gluconate, tartrate, citrate, aspartate, glutamate and E.D.T. Aate. Generally, these chelators complex the metal cation and reduce the free metal cation and mean metal chromate concentrations in solution. The rates of nucleation with microcrystallite formation were then markedly reduced and the induction periods increased from below 1 sec to well above 100,000 sec with increasing chelator/cation concentration ratio; the experimental results were expressed by the relations;magnified image
The coefficients F at any metal chromate concentration were related in turn to the stability constants of the metal‐chelator complexes.
On the crystal structure stability of calcite‐type carbonates
Authors: Balarew Chr. , Markov L. , Petrov K. 
Published: January 2007

AbstractThe preparation of carbonates of the bivalent metals (Mg, Ca, Ba, Sr, Mn, Fe, Co, Ni, Cu and Zn) by two methods under ordinary conditions has been investigated. The stability of calcite type carbonates has been discussed. The shortest O—O distance (d*O—O) between two neighbouring octahedra has been proposed as a criterion for the formation of stable calcite type carbonates. The lower stereochemical boundary of the calcite carbonate stability has been found to be d*O−O ∼ 2.9 Å. The relative stability of carbonates with dO−O* < 2.9 Å (Zn, Co and Ni) has been studied with respect to their isomorphous incorporation into MnCO3.
Surface morphology of iron specimens boronized with BCl3—H—mixtures (I) influence of process parameters
Authors: Bochmann G. , Ritzel B. , Wagner W. , Marx G. 
Published: January 2007

AbstractSpecimens made of armco iron were boronized with 1.1 Vol.% BCl3 in H2 at 1023 K, 1123 K, and 1223 K during different periods. Afterwards, their surfaces were examined by scanning electron microscopy. As a result of variation of the process parameters the surface morphology of the boride layers formed was changed. The etch attack of the boronizing gas mixture on the substrate may be reduced by appropriate parameters.
The influence of water steam on the direct phase transformation of zeolite NaA to nepheline by thermal treatment
Authors: Lutz W. , Engelhardt G. , Fichtner‐Schmittler H. , Peuker Ch. , Löffler E. , Siegel H. 
Published: January 2007

AbstractHeating of zeolite NaA leads to the consecutive formation of amorphous phase, carnegieite and nepheline in the high temperature region. These phase transformations are influenced not only by temperature but also by the presence of water (inside of the crystals). Water causes destruction of zeolite framework by hydrolytic splitting of Si‐O‐Al‐bonds in addition to thermal effects. Thus, the amorphous phase as the first product of phase transformation occurs in the presence of water steam at a lower temperature. The formation of the crystalline phases carnegieite and nepheline was observed in a temperature range, 300 K lower than usually, and without occurrence of the amorphous phase.
High‐temperature specific heat of AgInS2 and AgGaSe2
Authors: Neumann H. , Kühn G. , Möller W. 
Published: January 2007

AbstractThe molar specific heat at constant pressure was measured for AgInS2 and AgGaSe2 in the temperature range from 300 to 500 K. An analysis of the experimental data showed that the contribution to the specific heat due to lattice anharmonicity can be described by a polynomial of third order in the temperature. This result is in agreement with the temperature dependence of the specific heat expected from thermal expansion data.
A fluctuation theory of normal crystal growth for the very dilute binary metallic solid solution's crystallization in the case of macroscopic systems
Authors: Chistyakov Yu. D. , Baikov Yu. A. 
Published: January 2007

AbstractA theory connected with spontaneous fluctuations of the limited spectrum solid state particle concentrations in the case of binary metallic macrosystems crystallizing from the binary melts is developed. Normal kinetics was found to be realized in the case of very dilute binary metallic solid solutions within the small ‘supercoolings’ region. A comparison between the theoretical and experimental data on the crystallization kinetics of very dilute binary metallic solid state solutions within the small ‘supercoolings’ region has been made. For some types of binary metallic macrosystems the quantitative restrictions of the supercooling regions within which a fluctuation mechanism and normal kinetics are assumed to act have been established. The restrictions are conditioned by some parameters of the binary macroscopic melt and two‐phase transitional zone considered.
Polarized MoLß2.15 X‐ray emission of MoS2 and density of the Mo d‐like valence states
Authors: Dräger G. , Czolbe W. , Šimůnek A. , Lévy F. 
Published: January 2007

AbstractDie polarisierten MoLβ2,15‐Röntgenemissionsbanden von MoS2 wurden gemessen und hinsichtlich lokaler partieller Zustandsdichten (DOS) mit Hilfe der Polarisationsabhängigkeit der Winkelanteile der Übergangswahrscheinlichkeit qualitativ analysiert. Die Ergebnisse werden im Zusammenhang mit den Bindungsverhältnissen im MoS2 abgeleitet und interpretiert. Ein Vergleich der Spektren und ihrer Anisotropie mit den entsprechenden DOS von einer kürzlich berechneten selbstkonsistenten Pseudopotentialbandstruktur bestätigt die theoretischen Ergebnisse experimentell.
Sattructural changes during post‐ageing of an AlZn (15 at.%) alloy at 100 °C studied by positron annihilation, small angele X‐ray scattering and microhardness measurements
Authors: Krause R. , Dlubek G. , Wendrock G. 
Published: January 2007

AbstractThe positron lifetime τ, the shape parameter of the Doppler‐broadened annihilation line S, the microhardness HV and the Guinier radii rG are studied in dependence on the ageing time during isothermal ageing of an AlZn (15 at.%) alloy at 100 °C following a pre‐ageing at R.T. for 1 h after the quench. Weak effects in HV and rG are interpreted by a transformation of spherical Guinier‐Preston zones into ellipsoidal ones. At an ageing time of 104s HV decreases strongly while rG starts to increase more rapidly. This behaviour is explained by the transformation of coherent GP zones into semicoherent α′R‐particles. Incoherent part of the α′R‐particle‐matrix interface are able to localize positrons resulting in a strong increase of τ and S. The characteristic parameters τ and S of the coherent defect‐free GP zones and of the semicoherent α′R‐particles are estimated. It is concluded that positrons can be used as a very sensitive tool in detecting the transformation of coherent particles into semicoherent or incoherent ones.
Dependence of the Kβ/Kα intensity ratio on the oxidation state
Authors: Möser B. 
Published: January 2007

AbstractThe Kβ/Kα line intensity ratio was measured using an energy dispersive X‐ray spectrometer for samples of Ti, TiO, Ti2O3, Ti3O5, and TiO2. A steady increase of the Kβ/Kα intensity ratio was observed with increasing oxidation. For metallic titanium a value Kβ/Kα = 0.131 was obtained whereas for TiO2 this ratio is 0.1365. A similar but weaker dependence was observed for Fe and some iron oxides, too. The origin of this dependence is discussed as well as consequences for quantitative X‐ray microanalysis. Furthermore, the width of Kβ‐lines was found to be about 5 eV higher than that of Kα‐lines of equal energy.
Growth flawing and strain in hydrothermal quartz
Authors: Nanev Chr. N. , Dimitrov V. 
Published: January 2007

AbstractWith the aid of optical methods (including interphako microscopy) combined with chemical analysis at selected microareas (X‐ray microprobe analyser) it is shown that some macro‐defects arise during the growth of quartz single crystals due to the incorporation of foreign particles which are gathered in groups. Frequently, the strain in such crystals is inherited from the seeds. Therefore, the emphasis is laid on the optical investigation of strain in quartz.
Organometallic Vapour Phase Epitaxy of Galliumnitride Using Ga(CH3)3 · N(CH3)3‐Adduct Pyrolysis
Authors: Seifert W. , Franzheld R. , Bönisch F. , Butter E. 
Published: January 2007

AbstractEpitaxial layers of GaN have been grown on {1102} sapphire in atmospheric OMCVD system using Ga(CH3)3 · N(CH3)3 adduct and NH3 as reactants. Optimum growth conditions for crystallographically perfect layers have been found at temperatures between 850 and 1000 °C. With increasing temperature the growth rate decreases whereas the concentration of free carriers increases. In photoluminescence spectra only the donor‐acceptor pair recombination could be found. It is concluded that the donor oxygen (ON) and the acceptor carbon (CN) are the dominant impurities.
Growth and Kinetic Studies of Spherulitic Gadolinium Tartrate Crystals from Silica Gel
Authors: Kotru P. N. , Gupta N. K. , Raina K. K. 
Published: January 2007

AbstractSpherulitic growth of gadolinium tartrate dihydrate crystals by controlled diffusion in silica gel is reported. The influence of growth parameters e.g., reactant concentration, gel pH and gel ageing, on the size, quality and nucleation density of the spherulites has been studied. It is observed that under varying experimental conditions involving change in reactant concentrations, gel pH and gel ageing, the material crystallizes in the form of spherulites. The results of growth kinetics are discussed. Scanning electron microscopy confirms spherulites to be aggregates of single crystallites, with each micro‐sized crystal exhibiting a cuboid morphology. Surface structures exhibited by the micro‐sized crystals indicate their growth by two‐dimensional nucleation mechanism.
CVD Processes with Direct and Indirect Incorporation
Authors: Arnold H. 
Published: January 2007

AbstractIndirect incorporation via adsorption, surface diffusion, and reaction at half crystal sites can be treated by the BCF theory of layer‐by‐layer growth in simple cases of CVD, even if there is strong surface coverage by adsorbed species. I that case, however, the parallel path by direct reactive incorporation of atoms into half crystal sites from the gas phase may play an important role. In any case, direct incorporation becomes the sole possibility for (normal) growth if the surface fraction yk of half crystal sites (kinks) becomes I. The continuous transition from singular faces (yk = 0) to half crystal faces (yk = l) is covered by a simplified analytical expression and can be included into an overall circuit representation of stationary CVD processes which holds for in‐situ doping, too. The model results in a good compromise between the conventional BCF treatment and Chernovs treatment of CVD surface processes.
The Coprecipitation of Basic Magnesium Nickel Carbonate Powders from Aqueous Solution: Precipitate Compositions and Precipitation Mechanisms
Authors: Packter A. , Uppaladinni S. C. 
Published: January 2007

AbstractMagnesium nickel carbonate hydrate catalyst precursors were coprecipitated from mixed metal cation solutions (Cmtot = 1 M) with different sodium hydrogen carbonate‐sodium carbonate solutions. The course of precipitation was monitored by potentiometric (pH) titration and the final coprecipitate compositions were determined by chemical analysis, infra‐red spectrophotometry and thermal analysis. Generally, the coprecipitates are solid solutions of basic nickel carbonate hydrate with magnesium carbonate, of composition mMgCO3. n[NiCO3. bNi(OH)2]. hH2O. m = 0.77 to 1.00, n = und 2.00, h = 2 to 4; the MgCO3 contents and the Ni(OH)2/NiCO3 ratios (b) increase with increasing pH of the carbonate solutions. The ionic equilibria involved in different coprecipitations are discussed.
On Peculiarities of Chemical Bond in the ZnP System from the Magnetic Susceptibility Data
Authors: Vitkina Ts. Z. 
Published: January 2007

AbstractThe measurements of magnetic susceptibility of the Zn‐P system compounds have been performed and their Langevin diamagnetic component has been calculated. The influence of the degree of covalency of bonding on the value of diamagnetic constituent of the compounds has been investigated. It is shown that the semiconductor compounds of the Zn‐P system have preferably covalent character of chemical bond.
Surface Roughening and Second Neighbour Interaction. A Monte Carlo Simulation
Authors: Tkayanov A. 
Published: January 2007

AbstractThe structure of (100) surface of simple cubic crystal is studied by means of Monte Carlo method, the first and the second neighbour interactions being considered. For different energies of second neighbour interaction the roughening temperatureTRis obtained. The ratiokTR/L(Lis the latent heat) remains constant and equal to 0.19. In order to calculate the roughening temperatureTRof a (100) crystal face with attractive interatomic forces it is not necessary to know separately the bond energies of first, second, etc. neighbour interactions. For this purpose it is sufficient to know only the latent heat.
Polytypism in CdI2: A Consequence of Restrictions in Close‐packed Arrangements
Authors: Wahab M. A. , Kant Rajni 
Published: January 2007

AbstractBased on theoretical and experimental observations, it has been established that the polytypes 2H and 4H act as basic structural units as regard to the formation of CdI2 polytypes. As a result of this, some general rules have been formulated which help understand (i) the nature of restrictions in the close‐packed arrangements and to deduce the genuine CdI2 polytypes, and (ii) the classification of CdI2 polytypes into various possible groups. This further helps to conclude that (i) the CdI2 polytypes are simply a consequence of restrictions in the close‐packed arrangements, (ii) the concept of stacking fault is superfluous as far as the formation of ordered polytypes are concerned, and (iii) the identification of CdI2 polytypes on the basis of intensity data has limited implications unless some practical use of polytypes are found.