Method Of Directed Crystallization Research Articles

An Analysis Approach to the Sapphire Crystals Growth by Horizontal Directed Crystallization Method

The model for sapphire crystals growth parameters estimation has been suggested. It can be served as a basis for the analysis of heat transfer processes during sapphire crystals obtaining. It allows to predict the bubbles, stresses and cracks appearing during sapphire crystals growth. We describe the results of the analysis and parameters estimation of sapphire crystals growth on all stages by horizontal directed crystallization method.

Optimization of the composition of the foundry heat-resistant nickel alloy for the manufacture of cast working blades using the method of (mono) crystallization for promising gas turbines

Purpose. Development of the composition of a heat-resistant nickel alloy not containing rhenium for the manufacture of cast working blades by the method of directional (mono) crystallization. The alloy should have increased structural stability, while maintaining the level of mechanical, anti-corrosion and heat-resistant properties and a significant reduction in cost.Research methods. To estimate the structural and phase stability of high-temperature nickel alloys, various calculation methods were used: « ΔE-method» for assessing the balance of the chemical composition of the alloys by the value of the unbalance parameter of the doping system; PHACOMP and New PHACOMP – on the chemical composition of γ- solid solutions; developed in ZNTU complex methodology that establishes the relationship between the various parameters of structural stability.Results. Computing-analytical methods have been used to develop the composition of an economically-alloyed heat-resistant nickel alloy for the manufacture of cast blades by the method of directional (mono) crystallization, which does not contain expensive imported rhenium.Scientific novelty. Using computational and analytical methods, a composition of a heat-resistant nickel alloy with increased structural stability, resistance to high-temperature corrosion, and heat-resistant properties necessary for cast single-crystal products has been developed.Improvement of structural stability and improvement of the complex of properties of the developed alloy is provided by balanced doping with tantalum and tungsten (8.5 % at an average level), at reducing the content of carbon, molybdenum and cobalt by almost 2 times, and absence of the most expensive component in the composition – rhenium.Practical value. The developed economically-alloyed heat-resistant nickel alloy, which does not contain expensive rhenium, provides all the necessary operational properties, with a significant reduction in cost, and can be recommended for use in the manufacture of single-crystal cast blades of land-based gas turbine units.

Optical and luminescence properties of Er,Yb:YAG crystals grown by horizontal directional crystallization method

Optical and luminescence properties of Er,Yb:YAG crystals grown by horizontal directional crystallization method

Behavior of Noble Metals during Fractional Crystallization of Cu–Fe–Ni–(Pt, Pd, Rh, Ir, Ru, Ag, Au, Te) Sulfide Melts

Abstract —The method of quasi-equilibrium directional crystallization was used for experimental modeling of the behavior of noble metals in the presence of Te during the fractional crystallization of Cu- and Ni-rich sulfide magma. The experimental melt contained (mol.%): Fe = 18.5, Ni = 19.1, Cu = 16.7, S = 44.1, and Pt = Pd = Rh = Ir = Ru = Ag = Au = Te = 0.2, i.e., is similar in composition to the massive pentlandite-bornite ores of platinum-copper-nickel deposits of the Noril’sk group. The crystallized sample consists of six primary zones differing in chemical and phase compositions. The main minerals crystallizing from the melt include the following sulfide phases: bornite solid solution (bnss), quaternary solid solution (tss), described earlier in the literature, and three phases (сfpn, cnpn, npn), which we attributed to pentlandite according to their chemical composition. The primary phases crystallized from the melt decay on cooling with the formation of secondary phases. The сfpn, cnpn, and tss phases decay completely, and the npn and bnss phases, partly. As a result, secondary zoning forms in the sample. Formation of drop-like inclusions of telluride melt was observed in the end zone of the ingot. The obtained data show that pentlandites and tss are the main high-temperature concentrators of PGE, with each of the macrophases showing specific PGE accumulation. Eight types of impurity phases have been detected. They form by different mechanisms: crystallization from sulfide melt of refractory compounds, deposition from telluride melt, and formation through complete or partial decay of primary macro- and microphases. A scheme of the zonal structure of the crystallized sample and the evolution of the phase composition during fractional crystallization has been constructed. It clearly demonstrates the intricate formation of primary and secondary major-component and impurity zonings and can be used to explain the nature of the zoned structure of massive PGE-bearing pentlandite–bornite orebodies.

Investigation of Influence of Sapphire Crystals Shape Factor on Its Growth by Horizontal Directed Crystallization

The value of shape factor allows to determine what processes (the surface or in crystal volume) define the dynamics of sapphire crystal growth by horizontal directed crystallization method and, as a result, estimate the influence of these processes on crystal quality. We receive the Stefan problem closed solution for sapphire crystals growth by horizontal directed crystallization method. It allows to investigate the growth process and the related factors (thermal stresses on different stages of growth process), melt hydrodynamics and its influence on defects formation. 1.

Spectral properties of Er-doped yttrium aluminum garnet crystals grown by modified horizontal directional crystallization method

Spectral properties of Er-doped yttrium aluminum garnet crystals grown by modified horizontal directional crystallization method

КРИСТАЛЛИЗАЦИЯ КВАЗИБИНАРНОЙ ЭВТЕКТИКИ bnss-tss В СИСТЕМЕ Cu-Fe-Ni-S

Исследование посвящено изучению процессов зональной кристаллизации в четырехкомпонентной системе Cu-Fe-Ni-S, являющейся базовой при формировании медно-никелевых сульфидных руд. Образец исходного состава (мол. %): Cu = 17.19, Fe = 19.05, Ni = 19.66, S = 44.10 синтезирован с применением метода квазиравновесной направленной кристаллизации. Результаты микроскопического исследования показали, что полученный слиток образован из 6 зон с разным фазовым и химическим составом. Основная часть слитка представлена зоной IV. Образцы, вырезанные из этой зоны, исследовались методами дифференциального термического анализа (ДТА), растровой электронной микроскопии (СЭМ) и рентгено-спектрального микроанализа (РСМА). Микроскопические исследования позволили предположить, что слиток состоит из твердых растворов tss и bnss, но при дальнейшем охлаждении tss разложился на дочерние фазы. Однако эти данные можно трактовать и как кристаллизацию четверной эвтектики. Результаты ДТА исследования образцов позволили измерить температуры фазовых эффектов и однозначно установить образование бинарной эвтектики bnss-tss. Температура бинарной эвтектики (L → tss + bnss) составляет 578±1 °С (851±1 K). Температуры ликвидуса незначительно повышаются от 857±2 °С до 862±2 °С (1130±2 K - 1135±2 K). Указанное изменение объясняется небольшими изменениями состава исследуемых образцов. Полученные результаты подтвердили адекватность и согласованной предложенной методики, сочетающей методы направленной кристаллизации, дифференциального термического анализа, растровой электронной микроскопии и рентгеноспектрального микроанализа при исследовании фазовых равновесий в многокомпонентных системах.
 
 Исследование выполнено в рамках госзадания (проект 0330-2016-0001) и при частичной финансовой поддержке комплексной программы фундаментальных научных исследований СО РАН II.1. № 303.

Development of casting Re-free nickel-lose superalloy for blade manufacturing using directional crystallization method

Development of casting Re-free nickel-lose superalloy for blade manufacturing using directional crystallization method

2D reentrant auxetic structures of graphene/CNT networks for omnidirectionally stretchable supercapacitors.

Stretchable energy storage systems are essential for the realization of implantable and epidermal electronics. However, high-performance stretchable supercapacitors have received less attention because currently available processing techniques and material structures are too limited to overcome the trade-off relationship among electrical conductivity, ion-accessible surface area, and stretchability of electrodes. Herein, we introduce novel 2D reentrant cellular structures of porous graphene/CNT networks for omnidirectionally stretchable supercapacitor electrodes. Reentrant structures, with inwardly protruded frameworks in porous networks, were fabricated by the radial compression of vertically aligned honeycomb-like rGO/CNT networks, which were prepared by a directional crystallization method. Unlike typical porous graphene structures, the reentrant structure provided structure-assisted stretchability, such as accordion and origami structures, to otherwise unstretchable materials. The 2D reentrant structures of graphene/CNT networks maintained excellent electrical conductivities under biaxial stretching conditions and showed a slightly negative or near-zero Poisson's ratio over a wide strain range because of their structural uniqueness. For practical applications, we fabricated all-solid-state supercapacitors based on 2D auxetic structures. A radial compression process up to 1/10th densified the electrode, significantly increasing the areal and volumetric capacitances of the electrodes. Additionally, vertically aligned graphene/CNT networks provided a plentiful surface area and induced sufficient ion transport pathways for the electrodes. Therefore, they exhibited high gravimetric and areal capacitance values of 152.4 F g-1 and 2.9 F cm-2, respectively, and had an excellent retention ratio of 88% under a biaxial strain of 100%. Auxetic cellular and vertically aligned structures provide a new strategy for the preparation of robust platforms for stretchable energy storage electrodes.

Methods of Fugitive Emission Reduction in Metallurgical Silicon Production at Kazsilicon Metallurgical Combine

KazSilicon Metallurgical Combine is the first enterprise in the Republic of Kazakhstan to produce highpurity metallurgical silicon. The silicon is produced in a 6.7 MW electric furnace from quartz, obtained from the Sarykul’skoe deposit, and charcoal by the method of vertical directional crystallization. As a result of large fugitive emissions of process gases, the operation of the open-type electric furnace creates very difficult conditions for maintenance work. The presence of leaks and a large number of access windows promotes atmospheric air indraft into the working region of the furnace, which causes the electrodes to break down. To solve these problens, we propose using the thermal pressure head of the process gases and extracting these gases through the furnace roof by means of three gas flues, each with capacity ~25000 m3/h. To extract the process gases fl owing from the furnace through the gasket of the electrode opening, we propose using a slotted hood covering the location of the electrode entry into the furnace. A number of recommendations are also made for improving the design of the electric furnace in order to reduce heat losses and fugitive atmospheric-air indraft into the furnace, eliminate the gas release into the atmosphere in the shop and residential zone, and simplify the operation of the electrode and current-cable holders.

Pure crystal orientation and anisotropic charge transport in large-area hybrid perovskite films.

Controlling crystal orientations and macroscopic morphology is vital to develop the electronic properties of hybrid perovskites. Here we show that a large-area, orientationally pure crystalline (OPC) methylammonium lead iodide (MAPbI3) hybrid perovskite film can be fabricated using a thermal-gradient-assisted directional crystallization method that relies on the sharp liquid-to-solid transition of MAPbI3 from ionic liquid solution. We find that the OPC films spontaneously form periodic microarrays that are distinguishable from general polycrystalline perovskite materials in terms of their crystal orientation, film morphology and electronic properties. X-ray diffraction patterns reveal that the film is strongly oriented in the (112) and (200) planes parallel to the substrate. This film is structurally confined by directional crystal growth, inducing intense anisotropy in charge transport. In addition, the low trap-state density (7.9 × 1013 cm−3) leads to strong amplified stimulated emission. This ability to control crystal orientation and morphology could be widely adopted in optoelectronic devices.

Investigation of cracks formation in sapphire crystals

The analysis of the possible reasons of cracks formation in the sapphire crystals received by the horizontally directed crystallization method on the basis of the received results of numerical simulation of thermoelastic tension in the sapphire crystal is carried out.

Optical properties of large germanium monocrystals

Optical characteristics of germanium monocrystals with a diameter of 150 and 200 mm grown by the Czochralski and directional crystallization methods were studied. We measured spectral transmittance of the monocrystals in the wavelength range of 2.3–25.0 μm, directional transmission and light scattering in the 2.4–3.0 μm range, and noninhomogeneity of the refractive index of monocrystals by the interference technique at 3.39 μm. The measurements were performed on antimony-doped germanium monocrystals with a diameter of 200 mm and thickness of 15 mm (grown by the directional crystallization method) and 18 mm thick (grown by the Czochralski method). Measurements were also performed on a germanium monocrystal with a diameter of 150 mm and thickness of 15 mm grown by the Czochralski method without adding a ligand. The measurement results revealed different optical quality of monocrystals, expressed in the nature and amount of refractive index inhomogeneity, which imposes restrictions on the use of blanks.

Phase equilibria in the quasiternary system Ag2S–Ga2S3–In2S3 and optical properties of (Ga55In45)2S300, (Ga54.59In44.66Er0.75)2S300 single crystals

The quasiternary system Ag2S–Ga2S3–In2S3 was investigated by differential thermal, X-ray diffraction analyses. The phase diagram of the Ga2S3–In2S3 system and nine polythermal sections, isothermal section at 820K and the liquidus surface projection were constructed. The existence of the large solid solutions ranges of binary and ternary compounds was established. The range of the existence of the quaternary phase AgGaxIn5−xS8 (2.25≤x≤2.85) at 820K was determined. The single crystals (Ga55In45)2S300 and (Ga54.59In44.66Er0.75)2S300 were grown by a directional crystallization method from solution-melt. Optical absorption spectra in the 500–1600nm range were recorded. The luminescence of the (Ga54.59In44.66Er0.75)2S300 single crystal shows a maximum at 1530nm for the excitation wavelengths of 532 and 980nm at 80 and 300K.

Formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet grown by horizontal directed crystallization method

It is shown that the formation of longitudinal aggregation of inclusions in bulk sapphire and yttrium‐aluminum garnet (YAG) grown by the method of HDC is caused by local accumulation of impurities, disturbance of morphological stability of the crystallization front and capture of inclusions and impurities in the nodal region of the melt two‐vortex convection. Studied is the influence of thermal and geometrical parameters of the melt and the shape of the crystallization front on the conditions of the formation of the capture of inclusions.

Treatment of textile wastewater under visible LED lamps using CuO/ZnO nanoparticles immobilized on scoria rocks

ZnO and CuO thin films were synthesized by a sol–gel and direct crystallization method on granular porous natural scoria respectively and CuO/ZnO/scoria was used for water treatment under visible light irradiation.

Directional Crystallization of Multicrystalline Silicon in a Weak Melt Convection and Gas Exchange

For the first time silicon was grown by means of directional crystallization and using the submerged into the melt heater multi−crystalline. To study interaction of the heater casing material with molten silicon we used the model of the heater in the form of a graphite plate coated with a protective layer of SiC of the special structure. During the crystallization, the plate was on the melt surface and almost completely overlaid the surface of the melt, thereby significantly reducing the intensity of gas exchange between the melt and the atmosphere in the furnace. The absence of a free surface of the melt resulted in the absence of Marangoni convection, and the crystal grew under the conditions of reduced melt convection, especially at the final stages of crystallization, when the thickness of the melt layer was much less than the cross size of the crucible. The crystal structure has a strongly pronounced columnar structure; measured data on resistivity varies over the ingot height from 1 to 1.3 Ω⋅cm, and the lifetime of minority carriers is about 3.7 µs. FTIR studies of a carbon content showed the longitudinal distribution to fundamentally differ from the linear dependence typical for the method of directional crystallization.

Effect of annealing and high-temperature heatings during soldering on structure and mechanical properties of alloy based on nickel aluminide

The article presents a study of the effect of various modes of annealing and process heatings on microstructure and properties of single-crystalline blanks of VKNA-1 intermetallic alloy on the basis of Ni3Al with crystallographic orientations of 〈001〉 and 〈111〉, obtained by the method of directional crystallization, and billets with polycrystalline structure from the VKNA-1VR alloy, made by the precision investment casting method.

Anomalous X-ray transmission through sapphire crystals

The triple-crystal X-ray diffractometry of anomalous X-Ray transmission is used to investigate sapphire single crystals grown in protective gaseous media with the help of the horizontal directional-crystallization method. The dependences between the integral intensities of anomalously transmitted and Bragg-Laue reflected X-ray beams (Ti and Ri, respectively) and the thickness of the samples under study, which enable us to determine regions of thin- and thick-crystal approximation, have been obtained at 2.52 ≤ μt ≤ 18.9. The integral coefficient μi of interference absorption and the integral characteristic yi are calculated in the dynamic thick-crystal approximation. It is demonstrated that dislocations are distributed mainly within the small-angle boundaries of a grown sapphire crystal. It is ascertained that the parameter μi is highly sensitive to the dislocation density and the pattern of the dislocation distribution in a crystal.

The section of the Fe–Ni–S phase diagram constructed by directional crystallization and thermal analysis

A nontrivial polythermal cross-section through the Fe–Ni–S phase diagram was plotted using a combination of directional crystallization and DTA methods. The crystallized sample was grown from the liquid (L) of the following composition Fe = 18, Ni = 35, and S = 47 at.%. It consisted of two single-phase sites formed from mss (Fe z Ni1−z )S1±δ and hzss (Ni z Fe1−z )3±δS2. The phase reaction L + mss = hzss proceeded on the boundary between these sites. The trajectories of melt and solid composition on the Gibbs triangle were calculated from the distribution of components along the sample. The tie-line transformation was determined from these data. Liquidus temperatures along the trajectory were measured by the DTA method and calculated with the help of a mathematical model. The nontrivial cross-section of the diagram constructed from these data shows the phase equilibrium conditions. The cross-section consists of two tie-line linear surfaces L–mss and L–hzss.