Investigations of the process of crystal growth from a liquid zone by Seebeck measurements

An arrangement for measuring the thermoelectric voltage (Seebeck signal) during the crystal growth from a liquid zone is described. Using the example of growing PbTe single crystals by THM it is shown that different equilibrium temperatures at both phase boundaries provide a differential Seekeck voltage depending on the crystal growth rate. Relaxation times which are needed to reach steady-state conditions with respect to the concentration difference between the growing and solving interface in the case of a start or sudden stop of the heater motion can be obtained.     

Design of a sheet forming apparatus for overflow fusion process by numerical simulation

The overflow fusion process is an important method for the manufacture of glass sheets and is currently used for the production of TFT/LCD display devices. The design of the forming apparatus is critical for obtaining very high surface quality glass to allow the successful application of semiconductor type materials. However, there is only little work presented in the literatures, because of difficulties and expansions in experiments. In this study, a numerical model for simulation of molten glass flow through an isopipe during the overflow fusion process was carried out. An explicit finite difference algorithm with the surface tracking method has been proposed. The effect of the geometry of the forming apparatus, flow rate and viscosity of molten glass on the flow patterns during overflow was investigated. It was found that the stability and flatness of the sheet glass was influenced by the design of the forming apparatus, and the flow rate and viscosity of molten glass flow. The tilt angle at the bottom the of a trough should be high enough (5–7°) to avoid the accumulation of molten glass. The smaller root angle (<50°) was better for recombination of two stream of glass. High flow velocity will induce an unsteady flow profile along the wall of the isopipe. A precise control of the working temperature was needed for maintaining an equal thickness along the isopipe.     

Investigations on the nucleation kinetics of bis glycine sodium nitrate

The nucleation parameters such as, energy per unit volume, radius of critical nucleus, critical free energy barrier, number of molecules in the critical nucleus and nucleation rate have been evaluated for bis glycine sodium nitrate single crystals. The interfacial energy of the solution at various temperatures has been estimated from existing solubility data. The metastable zone width and induction period measurements have been carried out experimentally.     

Investigations on noncubic crystals with the divergent X-ray beam technique

The divergent X-ray beam technique is very useful for the study of small monocrystalline sample regions. The diffraction patterns are cone-shaped. The size of the cone angle and the direction of the cone axis depend form the lattice parameters and the orientation of the investigated crystal. An appropriate evaluation permits the simple determination of lattice parameters, even of those of noncubic crystals and the determination of crystal orientation. The comparison of X-ray divergent beam patterns of different regions of the sample makes it possible to discover changes in the imperfect crystal structure such as local lattice parameter variations, disorientations, and twinnings in regions up to 10 μm in diameter. Suitable methods for utilization will be shown here.     

Investigations on the structural perfection of bridgman-grown PbTe single crystals

It is reported on the possibility of improving the structural perfection by the Bridgman method, shown with the example of the influence on the low-angle grain boundary substructures in PbTe arranged in growth direction. In the employed crystal growth apparatus temperature gradients from 15 to 100°C/cm and solidification rates from 0.33 to 4.2 mm/hr could be achieved. The low-angle grain boundary substructure was characterized by X-ray-topographic and etch investigations on (100)-orientated ingots. The thermal conditions during the growth affect the structural perfection decisively. An axial spot dependence of etch pit density and substructure abundance was observed. By reducing the cooling rate during growth — expressed by the product of temperature gradient G and solidification rate V — it is possible to obtain more perfect PbTe-crystals. It seems that the diameter l of the substructure cells which was lying between 0.5 and 2 mm, is related to the cooling rate G · V by the functional coherency l ≈ 1/√G · V. The choice of different initial melt combinations up to 1 at.% Te-surplus exerted no influence on the abundance of the low-angle grain boundaries. The in literature suggested connection of low-angle grain boundary substructure with phenomena resulting from a constitutional supercooling could not be established.     

Investigations on the Nucleation Kinetics of L-Arginine Phosphate single crystals

The nucleation parameters, such as radius of the critical nucleus and critical free energy change have been evaluated for LAP single crystals. The interfacial tension determined by conducting the induction period measurements has been used for the evaluation of nucleation parameters. The determined interfacial tension is found to be comparable with theoretical literature values.     

Two routes of forming nanorods on the base of nanoparticles

With ZnS nanoparticles as raw materials, two kinds of nanorods were fabricated. When ZnS nanoparticles were dispersed in Zn(NO₃)₂ solution and were treated in a sealed autoclave at 150 °C for 24 h, ZnO nanorods formed. ZnS nanoparticles work as a source of monomers for the growth of ZnO nanorods. With increase of concentration of Zn(NO₃)₂ solution, the products present long nanorods, short nanorods, star structure and bulk particle sequentially. When ZnS nanoparticles were kept in a solution at room temperature, ZnS nanorods formed after 21 days. ZnS nanoparticles work as assembly parts. They fit together spontaneously and present ZnS nanorods with many parallel stripes along the lengthways surface. To check the generality of self-assembling, PdS and Y₂S₃ nanorods were also fabricated.     

单壁碳纳米管的稳定性研究

采用化学气相沉积法(CVD),以正己烷为碳源制备单壁碳纳米管(SWNTs),研究了纯化后的单壁碳纳米管在空气中的稳定性,分别对刚纯化后和在空气中放置5d、10d和15d后的样品进行了SEM、HRTEM和TG表征,结果发现单壁碳纳米管的氧化程度随在空气中放置时间的延长而增加,15d后几乎完全转化为无定形碳.表明单壁碳管在空气中不稳定,很容易氧化,需要密闭保存.     

Investigations on Flux Grown Cadmium Sulphide Crystals

Observations on surface microtopography of flux grown CdS crystals are reported. Crystals resulting with cooling rate above 30 °C/hr are reported to be dendritic crystals, while those with cooling rate below 30 °C/hr are reported to be normal crystals like mineral greenockite as reported in standard books on mineralogy. Reasoning for dendritic growth is briefly discussed. Growth patterns and etch pits formation on them are interpreted. It is established that these crystals grow by two-dimensional nucleation mechanism and by spreading and piling of growth layers.     

NMR Investigations on Di- and Tri-Azanaphthalenes Oriented in Liquid Crystals

Proton NMR spectra of 1,3-diazanaphthalene and 1,2,4-triazanaphthalene have been investigated in the nematic phase of three liquid crystals. The spectral analysis provided direct dipole-dipole couplings which have been used to derive the molecular structure. Geometry of the phenyl ring in both the molecules deviates from the regular hexagonal structure. Signs of the order parameter of the largest magnitude are opposite in liquid crystals with positive diamagetic anisotropies.     

常压混合碱液条件下ZnO单晶生长习性的研究

采用常压混合碱液法,以NaOH、LiOH和H2O的混合碱液作助熔剂,重复生长了无色透明的六方片状、六方柱状和带六方双锥的完整单晶.经X射线衍射确认所生长的晶体均为六方纤锌矿型ZnO.实验表明,生长体系中NaOH与LiOH的物质的量比及ZnO的物质的量分数都对晶体的形貌有明显影响.NaOH与LiOH物质的量比为10:1、ZnO物质的量分数为0.077时,获得ZnO晶体的尺寸、透明度为最佳.     

Investigations on the Synthesis of Zeolite ZSM-5 (III)

The effect of the chemical composition of the reacting mixture (RM) on the amount of zeolite ZSM-5 and other crystalline phases and the amorphous phase as well in the obtained preparations was investigated. Ethylenediamine (ED) served as a templating agent. The quantitative estimation of the phase composition was made on the ground of X-ray diffraction measurements. Zeolite ZSM-5 of maximum phase purity of 96%, contaminated mainly with quartz and mordenite, was obtained.     

Investigations on the crystallisation of potassium molybdenum bronzes from flux melts

Results are presented to identify the fields of primary crystallisation of red and blue potassium molybdenum oxide bronzes K_0.30MoO₃ and K_0.33MoO₃ in the ternary system K₂MoO₄–MoO₃–MoO₂. Starting from crystal growth experiments for the preparation of bronze crystals by electrolytic reduction the binary marginal systems K₂MoO₄–MoO₃ as well as MoO₃–MoO₂ and further pseudo‐binary sections have been investigated by differential thermo‐analysis, hot‐stage microscopy, and by quenching experiments under inert gas. We succeeded in determining phase transition temperatures in the binary section Mo₄O₁₁–K₂Mo₂O₇. Temperature and composition ranges have been found in this section to crystallise red and blue potassium molybdenum oxide bronzes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations of positron-annihilation rate in semimetals

The annihilation rates of thermalized positrons in the semimetals bismuth and antimony were measured. We found that the different rates were not based on the various conduction-electron densities. However, excellent agreement with experimental results was achieved by taking into consideration many-body effects in a random phase approximation.     

Autoradiographic Investigations on the Incorporation of Ca Ions in KCl Crystals during Kyropoulos Growth

Ca doped KCl crystals were grown by the Kyropoulos method. 10⁻⁵ to 10⁻³ mole fractions of Ca (as CaCl₂ with a small amount of Ca-45 (β-emitter)) were added to the melt. By autoradiography of suitable cleavage planes the incorporation of the Ca ions was found to take place preferentially in a periodic manner parallel to the solid liquid interface. In the case of a rotating seed there is a segregation process in which only one zone of maximum Ca content is built up like a helix throughout the whole crystal, the axis being identical with the growth axis of the crystal and the slope of the helix corresponding to the growth rate per seed rotation, this leading to striations of long range periodicity on vertical cleavage planes. In the case of a non-rotating seed there is a different segregation process including a periodical incorporation too, but in discrete layers of relatively small separation parallel to the solid liquid interface in short range periodicity. Explanations for the segregation phenomena are given in terms of periodically varying effective growth rates related to periodic temperature fluctuations in the neighbourhood of the solid liquid interface.     

RHEED Investigations on Low-temperature Thermal SiO2 Films

The structural changes in thermal SiO₂ films grown at 1123–1173 K in a double walled furnace tube with chlorine between the inner and the outer tube are studied. The layers have a higher degree of crystallinity in comparison with the layers grown by standard high temperature dry oxidation (1273 K). A difference between the crystalline type structures of SiO₂ films on p- and n-Si is observed. The increase of the growth temperature from 1123 to 1273 K increases the variety of crystalline structures in the layers but decreases strongly their quantity and makes the films predominantly amorphous.     

Ultrasonic Investigations in the Liquid Crystal p-Cyanophenyl-trans-4-Propylocyclohexane Carboxylate

The variation of ultrasonic velocity with temperature in the liquid crystal p-cyanophenyl-trans-4-propylcyclohexane carboxylate at four different fixed frequencies is studied. From the observed temperature variation of the ultrasonic velocities, relaxation parameters like adiabatic relaxation time, velocity at infinite frequency in the isotropic as well as in the nematic liquid crystalline phases are determined. The results are discussed.     

Investigations of the energy flow of X-ray wavefields in crystals

The energy flow of the X-ray wavefields in the Laue case of diffraction and its importance for X-ray topography and interferometry are discussed.     

Investigations on nitride layer formation at the iron surface during gas nitriding

The morphology of the nitride layer forming at gas nitriding can decisively be influenced by the pretreatment of the surface. At a temperature of about 550 °C an activated surface very swiftly covers with iron nitrides. After passivating of the surface the nitride formation and the geometrical order of the nitride layer are determined by the heating rate. At high heating rates the formation of iron nitrides is localized to a few spots and the extension of the nitride layer proceeds by the growth of these spots. At low heating rates the surface is reactivated by the reducing gas before reaching the nitriding temperature. By further investigations is shown that nitriding of the surface starts with the formation of γ′-nitrides. ϵ-Nitrides occur in the further process of nitriding as a second layer on the γ′-phase.     

Investigations of phase relations and eutectic directional solidification on the NiAl-V join

The NiAl-V join was investigated out to 45 at % vanaduim and the two-phase nature of the alloys formed indicates that a true binary exist with a eutectic at 40 ± 2% vanadium. The eutectic temperature was determined by optical methods to be 1350°C (1360°C was indicated by DTA). Directional solidification of the NiAl-V eutectic composition produced a structure which is lamellar, with interlamellar sapcing of λ = 4.2 μm at a solidification rate R = 1.5 cm/h.