Cylindrical Ampoule Research Articles

Сравнение трех математических моделей процесса направленной кристаллизации многокомпонентного раствора

The paper provides the comparison of three mathematical models of directional crystallization. The one-dimensional models of crystal growth assuming complete mixing in the melt and no mixing in the melt are examined. The mathematical model of crystallization process in cylindrical ampoule, which accounts for crystallization interface movement, convective heat and mass transfer in the solution, diffusion heat and mass transfer in the crystal, is considered. The ranges of growth regime parameters, for which the simplified models are valid, are determined numerically.

Numerical simulation of solid-phase chemical transformations in thermite mixtures under shock-wave loading

Shock-wave loading of a steel cylindrical ampoule that contained an aluminum-copper oxide(Al/CuO) thermite mixture is simulated in three-dimensional space using the SPH method.The chemical reaction starts after the performance of the criterion on temperature or pressure.Thechemical reaction equations are integrated using the first-order Euler method.The elastic-plastic flow is calculated using the variational formulation.The numerical study of solid-phase chemical transformations in the Al/CuO thermite mixture under shock-wave loading shows that the initiation of reactions in the shock wave,further development,and completion depends significantly on the amplitude and duration of the shock wave.Sub-critical pressure pulse can lead to an incomplete reaction or incompletely compacted final product.

Formation of the structure and properties of polyvinylidene fluoride and composites based on it, prepared by explosive pressing

The possibility of forming PVDF composites with 20% Al2O3 content by explosive pressing in a cylindrical ampoule is shown. It has been established that a change in pressure when using this pressing method leads to the implementation of various compaction mechanisms for PVDF and its composites. A change in pressure affects almost all characteristics of the polymer and the composites being formed, up to their partial destruction.

Structure Formation in Nickel-Polytetrafluorethylene Composite Materials upon Explosive Pressing of Powders

In this paper, we study the features of structure formation in composite materials based on polytetrafluoroethylene containing from 50 to 90 vol % of nickel that results from the explosive pressing of powder mixtures in a cylindrical ampoule. It is revealed that, at an increase in parameters of explosive pressing, a change in the structure along the pressing radius that characterized by increased deformation of the components up to their grinding and remelting in the center of the pressing with a simultaneous increase in the physicochemical interaction of the components of the composite mixture is observed.

Initiation and development of exothermic reactions during solid-phase synthesis under explosive loading

The previous numerical and experimental studies of the solid-phase synthesis of porous reactive mixtures (Al-S and Al-Tf) placed into cylindrical ampoules subjected to explosive detonation revealed the sharp increase in temperatures and pressures. The results have shown that high heat release and high increase in pressure due to exothermic reactions in the mixture, on the one hand, promote the faster development of reactions and, on the other hand, contribute to the formation of a gas phase that, in turns, may lead to the damage or even fracture of ampoules. This problem is solved by adding an inert porous aluminum layer to the bottom part of the mixture. Computations are carried out using the model of a multicomponent medium and the finite element method. Numerical simulation has shown that in this case the fracture of cylindrical ampoules is not observed.

Explosive pressing of fluoroplastic composites

Abstract This work presents results of the research on morphology, thermal deformation properties of fluoroplast-4 based compositions with highly heat-resistant glassy PA polyarylate and phenylone C3 after explosive pressing of powder composite mixtures in a steel cylindrical ampoule with pressure of 0.8 GPa. It is shown that this type of high-energy exposure allows to obtain compacted materials with high adhesive interaction of the components of the composite mixture and high properties.

Determination of the crystallographic orientation of SrI2 crystals

Single crystals of strontium iodide (SrI2), an important material for nuclear detector applications, are grown commercially in cylindrical ampoules using the Bridgman self-seeding method. As a result, the axial orientation of Bridgman boules varies from run to run. Most crystal growth methods benefit from the use of oriented seeds, which can be helpful in maximizing growth rates and crystal quality. However, it is very difficult to orient SrI2 crystals because they are deliquescent and their surfaces damage easily during cutting and polishing. In this study, unpolished facets formed on an edge-defined film-fed growth (EFG) boule were used to generate the first Laue patterns. The principal boule used in this study had a square cross section and was grown using a seed cut from along the growth axis of a Bridgman boule. X-ray analysis showed that the EFG boule grown from this seed grew along the b-axis and the side facets were the (1 0 0) and (0 0 1) faces. This work made possible the fabrication of oriented SrI2 seeds for use in future EFG and Czochralski growth experiments and allowed for the determination of the optic axes using polarized light.

Study on structure formation in polyimide-polytetrafluoroethylene composites after explosive pressing

Features of structure formation in polyimide-polytetrafluoroethylene composites after explosive pressing of powder mixture in closed steel cylindrical ampoule have been researched. It is found that structure changes abruptly in the center of the compact with appearance of nanoscale phases, the change of the fine structure and the increase of microhardness which is implemented with certain parameters of explosives.

Fracture of cylindrical ampoules during solid phase synthesis under explosive loading

The paper presents the numerical and experimental study of the behavior of porous reactive mixtures (Al-S and Al-Tf) under explosive loading using a multicomponent medium model. The initial dispersion of the reactive mixture is varied to evaluate its contribution to the fracture of the cylindrical ampoule. The results have shown that the high rate of heat release during the chemical reaction in the bottom part of the ampoule and a sharp increase in pressure lead to the formation of the gas phase, which causes the ampoule fracture. It is found that the higher the initial dispersion of the mixture components is, the more intensive the ampoule failure is.

Modeling effects of solute concentration in Bridgman growth of cadmium zinc telluride

Numerical modeling is used to investigate the effect of solute concentration on the melt convection and interface shape in Bridgman growth of Cd1−xZnxTe (CZT). The numerical analysis is compared to experimental growth in cylindrical ampoules having a conical tip performed by Komar et al. (2001) [15]. In these experiments, the solidification process occurs at slow growth rate (V=2⋅10−7m/s) in a thermal field characterized by a vertical gradient GT=20K/cm at the growth interface. The computations performed by accounting the solutal effect show a progressive damping of the melt convection due to the depleted Zn at the growth interface. The computed shape of the crystallization front is in agreement with the experimental measurement showing a convex-concave shape for the growth through the conical part of the ampoule and a concave shape of the interface in the cylindrical region. The distribution of Zn is nearly uniform over the crystal length except for the end part of the ingots. The anomalous zinc segregation observed in some experiments is explained by introducing the hypothesis of incomplete charge mixing during the homogenization time which precedes the growth process. When the crystallization is started in ampoules having a very sharp conical tip, the heavy CdTe is accumulated at the bottom part of the melt, giving rise to anomalous segregation patterns, featuring very low zinc concentration in the ingots during the first stage of the solidification.

Problems of Solid-Phase Synthesis in Cylindrical Ampoules under Explosive Loading

The peculiarities of solid-phase synthesis are studied experimentally and numerically in the aluminum-fluoroplastic and aluminum-sulfur mixtures in cylindrical ampoules under explosive loading. The experimental results show that the use of a mixture capable of ultrafast exothermic reactions leads to the destruction of a cylindrical ampoule under explosive loading. When the transient shock wave is reflected from the bottom lid of the ampoule as a compression wave, there is a sharp increase in pressure in the lower part of the ampoule, which is accompanied by the increase in rate of the chemical reaction. The high rate of heat release during the chemical reaction in the lower part of the ampoule causes the formation of a gas phase, which leads to a further increase in pressure and destruction of the ampoule.

Explosive Compaction of Solid Inert Three-Component Mixtures Taking into Account a Different Thickness of the Explosive Axial Layer

We consider the axisymmetric problem of explosive compaction of a mixture from aluminum, sulfur and carbon placed into a cylindrical steel ampoule. The inert substance (graphite) is added to the mixture to avoid the reaction between aluminum and sulfur. We found the essential influence of the thickness of the explosive layer on the final result of explosive compaction. Insufficient thickness of explosives, as well as the excessive thickness may be a reason for an incompletely compacted final product or lead to the formation of cracks or damage.

Comparative study of phase transformations in carbon at different schemes of shock compression

A comparative study of phase transformations in carbon-base materials at shock compression has been carried out according to two different schemes: in cylindrical ampoules with a central rod at a direct contact of explosives with the ampoule and in ampoules without the central rod with throwable outer shells. It has been found that in the shock compression on the second scheme a higher absolute output of diamond is achieved, but as opposed to the first scheme, the shock compression products do not virtually contain lonsdaleite or dense amorphous phase. The analysis shows that in the second case the states with lower pressures but higher temperatures, which lead to a transformation of metastable phases into stable diamond, are realized.

Destruction of cylindrical ampoules containing solid phase reaction mixtures under explosive loading

Peculiarities of solid-phase synthesis are experimentally and numerically investigated in the aluminum-sulfur and aluminum-teflon mixtures placed in cylindrical ampoules under explosive loading. In the experiments, the parameters of explosive loading are chosen close to those that are commonly used for explosive compaction of inert porous fillers in cylindrical ampoules. The experimental results show that cylindrical ampoules are damaged when a mixture capable of ultrafast exothermic reactions is used as filler under explosive loading. To find the reasons of ampoule damage, the numerical computations are carried out by the finite element method based on the model of a multicomponent medium. The synthesis reaction in the mixture is described using the phenomenological model of irreversible chemical reactions based on zero-order kinetics. Simulation of porous mixture compaction is carried out using the kinetic model of the active type, which determines the growth or collapse of pores continually changing the material properties and causing stress relaxation. The sharp increase in pressure is found in the bottom part of the ampoule after reflection of the shock wave from the bottom lid of the ampoule in the form of a compression wave, which is accompanied by increasing the rate of chemical reactions. The high rate of heat release during chemical reactions in the bottom part of the ampoule leads to the formation of gas phase, which leads to further increase in pressure and fracture of the ampoule.

Experimental and Numerical Research in Explosive Loading of Two- and Three-Component Solid Mixtures

We have conducted experimental and numerical research in two- and three-component solid mixtures placed into a cylindrical recovery ampoule under explosive loading. Behavior of the mixture is described by a mathematical model of a multicomponent medium. In the model, every component of a mixture simultaneously occupies the same volume as the mixture. Components interact with each other, exchanging momentum, energy, and mass (if the chemical reaction between the components occurs). An equality of components’ pressure is chosen as a condition for joint deformation of components. Finite element method is used for solving the problems. We considered experimentally and numerically explosive loading of the<br />aluminum-sulfur mixture, and explosive compaction of the aluminum-sulfur-carbon mixture in a cylindrical steel ampoule. The inert substance (graphite) was added to the mixture to avoid the reaction between aluminum and sulfur. Most of the focus is on simulating the action of explosion products on the ampoule.<br />In the computations the actions of the detonation products surrounding the ampoule was simulated by the action of pressure on the upper part of the ampoule in a vertical (axial) direction and on the lateral surface of the ampoule in a horizontal (radial) direction. We varied the thickness of the explosive that acts on the upper part of the ampoule in the axial direction in order to study the influence of the parameter on a final shape and size of the ampoule. We founded the essential influence of the thickness of the explosive layer on the final result of explosive compaction. Insufficient thickness of explosives, as well as the excessive thickness may be a reason for an incompletely compacted final product or lead to the formation of cracks or damage.<br /><br />

The development of the aluminum sulfide synthesis reaction on explosive loading of a cylindrical ampoule

In the scientific literature, much attention is paid to investigation of phase transitions on explosive load� ing, in particular, solidphase chemical transforma� tions under the action of shock waves. However, such transformations are studied mostly experimentally (1, 2), and their mathematical models are virtually unavailable. It is natural because chemical transfor� mations are difficult to study in the course of explosive loading and reliable data on the dynamics of these phenomena are not always easy to obtain from experi� mental results. Meanwhile, novel promising materials are more and more often produced and used in fast processes at high strain rates, pressures, and temperatures. These processes are accompanied by structural changes and sometimes chemical reactions. The currently widely used explosive technologies in metal working are most developed in forming, welding, cutting, hardening, and sealing, and many of these technologies have already been commercialized. At the same time, the effect of shock waves on solidphase reactions is still insufficiently studied and, by the present time, has not yet reached a technology level because of the lack of experimental data and also mathematical models that could take into account both the coupling of mechan� ical and physicochemical processes, including their combined action, and the effect of each factor. The purpose of this work was to experimentally and numerically study the dynamics of development of aluminum sulfide synthesis on explosive loading of a cylindrical ampoule on the basis of a phenomenologi� cal model of chemical transformations. In this work, we proposed a new approach to numerical analysis of solidphase synthesis processes on explosive and shockwave loading on the basis of a developed mathematical model of a multicomponent medium. The time dependence of the pressure of the explosion products was described based on qualitative and quantitative agreement of the results of experi� mentally and theoretically determining the parame� ters of explosive loading of a cylindrical ampoule. The conditions were found for the transition from partial to complete conversion in the synthesis reaction in the shock front on reflection of the shock wave from the bottom cap of the ampoule. It was experimentally and theoretically established that, once the reaction in the shock wave is fully completed, the ampoule is broken down because of the formation of a gas phase and an increase in pressure, with the breakdown being initi� ated in the bottom part of the ampoule.

Growth of ZnSe1 − x S x solid solution crystals from vapor phase

Partially faceted ZnSe1 − xSx solid solution crystals have been grown from a vapor phase in a closed stationary horizontal system. The growth has been performed in cylindrical quartz ampoules—∼10 mm in diameter and evacuated to a residual pressure of less than ∼10−3 Pa-at a temperature of 1050°C and a temperature drop between the source and growth zones of 10–16°C. The crystal structure, optical absorption, and composition inhomogeneity along the ingot length have been investigated by X-ray diffractometry and optical spectroscopy in the wavelength range of 300–3000 nm. The solid-solution composition range corresponding to cubic polymorphs is determined. The concentration dependences of the lattice parameter and band gap are presented.

Shock compression of Ti–B–Cu powder mixtures: Microstructural aspects

Shock compression of Ti–B–Cu powder mixtures at a pressure of 3 GPa was investigated. The reaction between titanium and boron was initiated by the shock wave; however, it was not completed. Short high-energy mechanical milling of the powder mixtures before the shock compression ensured full conversion of titanium and boron to titanium diboride. Due to the geometrical issue of the interaction of the shock wave with the powder sample in a cylindrical ampoule, the outer part of the sample was denser but less uniform in the microstructure than the central part. The central part of the sample showed a nanocomposite structure with even distribution of 100–300 nm grains. The size of grain agglomerates of each of the two phases was not larger than 1 μm. In the outer part Cu and TiB 2-enriched areas up to 5–10 μm in size could be found. The observed difference is explained by intensive turbulization and mixing in the central part of the ampoule during shock compression.

In-situ measurements of mass transport rate in vapour growth of hexamethylenetetramine crystal layers

This paper refers to the implementation of a remote optical imaging system suitable for in-situ mass transport rate measurements in the growth of crystalline layers when grown in closed cylindrical ampoules by a physical vapour transport (PVT) technique. By means of this system, the measurements are carried out by taking photographs, at regular time intervals, of the source material volume as it reduces itself because of mass transfer. After storing the photographs, in real time, in a PC, a suitable software allows to estimate the mass transport rate during the growth process. The authors report here on the detailed setting up of such system when aimed at measuring the growth rate, as it varies with time, of hexamethylenetetramine (HMT, urotropine) crystal layers. A presentation and discussion of the results of these measurements have previously been reported. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of diamond-like BN phases under shock compression of graphite-like BN with different degree of structural ordering

The formation of diamond-like modifications of BN under high-temperature shock compression ( P = 33 GPa and T up to 3500 K) has been studied. The powders of graphite-like BN with different degree of three-dimensional ordering of structure ( D 3) were used as starting materials. To increase shock temperature and preserve dense phase formed, boron nitride powder mixed with alkali halide salt was compressed in cylindrical ampoule. The recovered samples were studied by X-ray diffraction and electron microscopy. It was revealed that the phase composition of shock compression products depends on the degree of three-dimensional ordering of initial graphite-like structure. Turbostratic BN with disordered structure ( D 3 = 0) transformed mainly into cubic cBN by diffusion mechanism, whereas highly ordered graphite-like BN ( D 3 = 0.95) transformed only into wurtzite wBN by martensitic mechanism. Both cubic and wurtzite dense modifications are formed from partly ordered initial structures (for which D 3 was 0.45 ÷ 0.7). The both diamond-like phases have nanocrystalline structure.