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High-temperature Synthesis (high-temperature + synthesis)
Kinds of High-temperature Synthesis Selected AbstractsA Heat-Integrated Reverse-Flow Reactor Concept for Endothermic High-Temperature Syntheses.CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2009Part II: Development of a Reformer Prototype for Hydrogen Production Abstract In the first part of the contribution, the asymmetric operation of a reverse-flow reactor for endothermic high-temperature syntheses has been introduced and front phenomena have been discussed. The current part presents the implementation of the concept to the production of hydrogen by methane steam reforming. A key element of the developed reformer is the integration of combustion chambers for in situ heat generation during reheating of the bed. To avoid local temperature peaks, the concept of flameless combustion is used. The concept was adapted to the requirements of the unsteady operation. A proper design of the combustion chamber was developed using computational fluid dynamics calculations, tracer experiments and tests in a single combustion chamber. The concept was further tested under periodic operation in a laboratory setup. The formation of the desired, axially extended high-temperature plateau in the center of the reactor could be shown experimentally. The results prove the adequacy of the reverse-flow reformer to attain a stable periodic operation without excess temperatures. [source] Enhanced Ductility of Dendrite-Ultrafine Eutectic Composite Fe3B Alloy Prepared by a Self-Propagating High-Temperature Synthesis,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Licai Fu The bulk dendrite-ultrafine eutectic composite Fe3B alloy was prepared by a self-propagating high-temperature synthesis. This technique is convenient, low cost, and capable of being scaled up for processing bulk nano/ultrafine-structured materials. The Fe3B alloy is composed of a micrometer-sized dendrite dispersed in an ultrafine laminar eutectic matrix and exhibits both high strength and large ductility in compressive tests. [source] Porous TiNi Biomaterial by Self-Propagating High-Temperature Synthesis,ADVANCED ENGINEERING MATERIALS, Issue 6 2004J.S. Kim Abstract Porous TiNi shape-memory alloy (TiNi SMA) bodies with controlled pore structure were produced from the (Ti+Ni) powder mixture by self-propagating high-temperature synthesis (SHS) method. The effect of processing variables such as the kind of starting powders, ignition temperature and preheating schedule on the behavior of combustion wave propagation, the formation of phases and pore structure was investigated. The relationship between pore structure and mechanical properties was also investigated. An in vivo test was performed to evaluate bone tissue response and histocompatibility of porous TiNi SMA using 15 New Zealand white rabbits. No apparent adverse reactions such as inflammation and foreign body reaction were noted on or around all implanted porous TiNi SMA blocks. Bone ingrowth was found in the pore space of all implanted blocks. [source] Self-Propagating High-Temperature Synthesis of Ti3SiC2: II.JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Kinetics of Ultra-High-Speed Reactions from In Situ Neutron Diffraction In situ neutron diffraction data at 0.9-s time resolution during the self-propagating high-temperature synthesis of Ti3SiC2 from stoichiometric 3Ti+SiC+C mixtures have been further analyzed to give the phase quantities during all five stages of the identified reaction [(i) preheating, (ii) ,,, phase transformation in Ti, (iii) preignition reactions, (iv) intermediate phase formation, and (v) rapid nucleation and growth of Ti3SiC2]. The phase quantities thus determined have been used, in conjunction with temperatures estimated from lattice parameters and thermal expansion data, to determine the kinetic parameters for the nucleation and growth stage using a nonisothermal form of the Avrami kinetic equation. The analysis gave an Avrami exponent, n, close to 3 in agreement with nucleation and the observed two-dimensional growth of Ti3SiC2 crystals. An activation energy of ,45 kJ/mol was also estimated. [source] Zirconia-Based Metastable Solid Solutions through Self-Propagating High-Temperature Synthesis: Synthesis, Characterization, and Mechanistic InvestigationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Filippo Maglia Cubic Zr1,xMexOy(Me = Fe, Co, Ni, Cu) metastable solid solutions with metal content significantly higher than equilibrium levels have been synthesized by the self-propagating high-temperature synthesis method based on a thermite reaction between metallic zirconium and the transition-metal oxides CoO, Fe2O3, CuO, and NiO. Through in situ XRD analysis, it was determined that when heated to 1100°C, the cubic solid solution transformed to the tetragonal phase with the concomitant formation of iron oxide. When cooled to lower temperatures, the tetragonal phase transformed to the monoclinic phase at or below 500°C. Results of auxiliary experiments strongly suggest that the formation of the solid solution takes place behind the combustion front by a reaction between zirconia and the metal. [source] High-Temperature Synthesis, Crystal Structure, and Properties of the New Sodium Rare-Earth Oxide Borates Na2Ln2(BO3)2O (Ln: Dy, Ho).CHEMINFORM, Issue 11 2005Gunter Heymann Abstract For Abstract see ChemInform Abstract in Full Text. [source] A Heat-Integrated Reverse-Flow Reactor Concept for Endothermic High-Temperature Syntheses.CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2009Part II: Development of a Reformer Prototype for Hydrogen Production Abstract In the first part of the contribution, the asymmetric operation of a reverse-flow reactor for endothermic high-temperature syntheses has been introduced and front phenomena have been discussed. The current part presents the implementation of the concept to the production of hydrogen by methane steam reforming. A key element of the developed reformer is the integration of combustion chambers for in situ heat generation during reheating of the bed. To avoid local temperature peaks, the concept of flameless combustion is used. The concept was adapted to the requirements of the unsteady operation. A proper design of the combustion chamber was developed using computational fluid dynamics calculations, tracer experiments and tests in a single combustion chamber. The concept was further tested under periodic operation in a laboratory setup. The formation of the desired, axially extended high-temperature plateau in the center of the reactor could be shown experimentally. The results prove the adequacy of the reverse-flow reformer to attain a stable periodic operation without excess temperatures. [source] Enhanced Ductility of Dendrite-Ultrafine Eutectic Composite Fe3B Alloy Prepared by a Self-Propagating High-Temperature Synthesis,ADVANCED ENGINEERING MATERIALS, Issue 3 2009Licai Fu The bulk dendrite-ultrafine eutectic composite Fe3B alloy was prepared by a self-propagating high-temperature synthesis. This technique is convenient, low cost, and capable of being scaled up for processing bulk nano/ultrafine-structured materials. The Fe3B alloy is composed of a micrometer-sized dendrite dispersed in an ultrafine laminar eutectic matrix and exhibits both high strength and large ductility in compressive tests. [source] Porous TiNi Biomaterial by Self-Propagating High-Temperature Synthesis,ADVANCED ENGINEERING MATERIALS, Issue 6 2004J.S. Kim Abstract Porous TiNi shape-memory alloy (TiNi SMA) bodies with controlled pore structure were produced from the (Ti+Ni) powder mixture by self-propagating high-temperature synthesis (SHS) method. The effect of processing variables such as the kind of starting powders, ignition temperature and preheating schedule on the behavior of combustion wave propagation, the formation of phases and pore structure was investigated. The relationship between pore structure and mechanical properties was also investigated. An in vivo test was performed to evaluate bone tissue response and histocompatibility of porous TiNi SMA using 15 New Zealand white rabbits. No apparent adverse reactions such as inflammation and foreign body reaction were noted on or around all implanted porous TiNi SMA blocks. Bone ingrowth was found in the pore space of all implanted blocks. [source] Microstructural analysis of iron aluminide formed by self-propagating high-temperature synthesis mechanism in aluminium matrix compositeJOURNAL OF MICROSCOPY, Issue 1 2006ANITA OLSZÓWKA-MYALSKA Summary An aluminium matrix composite with iron aluminide formed in situ as a result of self-propagated high-temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle-like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self-propagating high-temperature synthesis consisted only of the Al3Fe phase. [source] Thermochemistry and Crystallization of Glass-Forming Y-Substituted Sr-Analogues of Fresnoite (Sr2TiSi2O8)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Tae-Jin Park Strontium titanosilicate (Sr2TiSi2O8) is the Sr-analogue of fresnoite (Ba2TiSi2O8). It may provide useful properties due to the unusual five-coordinate titanium in its structure. Sr2TiSi2O8 is also a possible oxide form for the immobilization of short-lived fission products in radioactive waste. Through , decay, strontium decays to yttrium and then to zirconium. Therefore, not only the stability of Sr-loaded waste forms but also that of a potential decay product series with charge-balance in a naturally occurring mineral or ceramic is of fundamental importance. To incorporate the reaction 3Sr2+=2Y3++vacancy in the fresnoite composition, Y-substituted Sr-analogues of fresnoite, (Sr2,xY2/3x)TiSi2O8 (x=0, 0.5, 0.75, 1, 1.25, and 1.5) were prepared by a high-temperature synthesis and were found to form glass upon cooling. The Y-end-member (Y1.33TiSi2O8, x=2) crystallized to a mixture of Y2TiSiO7, TiO2, and SiO2 upon quenching in air. The enthalpies of formation of Y-substituted Sr-fresnoite glasses were obtained from drop solution calorimetry in a molten lead borate (2PbO·B2O3) solvent at 702°C. The enthalpies of formation from constituent oxides were exothermic but become less so with increasing Y content. The enthalpy of vitrification of Sr2TiSi2O8 composition was measured to be 68.5 ± 6.2 kJ/mol. The thermodynamic stability of the Y-substituted Sr-analogue of crystalline fresnoite may become marginal with increasing yttrium content. Their ready glass formation, even in the absence of radiation, suggests that amorphous phases may dominate as the Sr- and Cs-containing waste forms decay. [source] Self-Propagating High-Temperature Synthesis of Ti3SiC2: II.JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Kinetics of Ultra-High-Speed Reactions from In Situ Neutron Diffraction In situ neutron diffraction data at 0.9-s time resolution during the self-propagating high-temperature synthesis of Ti3SiC2 from stoichiometric 3Ti+SiC+C mixtures have been further analyzed to give the phase quantities during all five stages of the identified reaction [(i) preheating, (ii) ,,, phase transformation in Ti, (iii) preignition reactions, (iv) intermediate phase formation, and (v) rapid nucleation and growth of Ti3SiC2]. The phase quantities thus determined have been used, in conjunction with temperatures estimated from lattice parameters and thermal expansion data, to determine the kinetic parameters for the nucleation and growth stage using a nonisothermal form of the Avrami kinetic equation. The analysis gave an Avrami exponent, n, close to 3 in agreement with nucleation and the observed two-dimensional growth of Ti3SiC2 crystals. An activation energy of ,45 kJ/mol was also estimated. [source] Processing and Mechanical Behavior of CrN/ZrO2(2Y) CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Yoshihiko Takano CrN powder consisting of granular particles of ,3 ,m has been prepared by self-propagating high-temperature synthesis under a nitrogen pressure of 12 MPa using Cr metal. Dense pure CrN ceramics and CrN/ZrO2(2Y) composites in the CrN-rich region have been fabricated by hot isostatic pressing for 2 h at 1300°C and 196 MPa. The former ceramics have a fracture toughness (KIC) of 3.3 MPa ·m1/2 and a bending strength (,b) of 400 MPa. In the latter materials almost all of the ZrO2(2Y) grains (0.36,0.41 ,m) are located in the grain boundaries of CrN (,4.6 ,m). The values of KIC (6.1 MPa · m1/2) and ,b (1070 MPa) are obtained in the composites containing 50 vol% ZrO2(2Y). [source] Metastability of Corundum-Type In2O3CHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2008Aleksander Gurlo Dr. Abstract The description of structural relations between bixbyite- and corundum-type structures is of particular interest because of the common occurrence of both structures. One of the representative examples of the bixbyite to corundum transition is the high-pressure high-temperature synthesis of the corundum-type indium oxide. The wet chemistry synthesis and stabilisation of the corundum-type In2O3 under ambient pressure conditions calls for a re-interpretation of the InO phase diagram as well as for the clarification of the phase transitions in In2O3. One of the questions to be clarified is the stability of the corundum-type In2O3. In the present work we studied the stability of the corundum-type In2O3 both theoretically (by density-functional calculations) and experimentally. The synthesis of the corundum-type In2O3 was performed by the modified non-alkoxide sol,gel method based on the ammonia-induced hydrolysis of indium nitrate in methanol. The corundum-type In2O3 was subjected to thermal analysis (STA) as well as to structural studies, that is, it was examined using X-ray powder diffraction (XRPD) including in situ XRPD characterisation upon thermal treatment. For the first time we have undoubtedly demonstrated, both theoretically and experimentally, the metastability of the corundum-type In2O3 polymorph. The In2O3 polymorph appears to be metastable throughout the entire enthalpy,pressure phase diagram. Upon heating, corundum-type In2O3 transforms irreversibly into cubic bixbyite-type In2O3 as shown by STA as well as in situ heating XRPD experiments. Computations indicate the existence of another high-pressure modification of In2O3 with orthorhombic structure, iso-typic to Rh2O3 -II. We predict this new phase to form at pressures exceeding 15,GPa from both the cubic bixbyite-type and the corundum-type modification of In2O3. [source] The Stuffed Framework Structure of SrP2N4: Challenges to Synthesis and Crystal Structure DeterminationCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2007Friedrich Abstract SrP2N4 was obtained by high-pressure high-temperature synthesis utilizing the multianvil technique (5,GPa, 1400,°C) starting from mixtures of phosphorus(V) nitride and strontium azide. SrP2N4 turned out to be isotypic with BaGa2O4 and is closely related to KGeAlO4. The crystal structure (SrP2N4, a=17.1029(8), c=8.10318(5),Å, space group P63 (no. 173), V=2052.70(2),Å3, Z=24, R(F2)=0.0633) was solved from synchrotron powder diffraction data by applying a combination of direct methods, Patterson syntheses, and difference Fourier maps adding the unit cell information derived from electron diffraction and symmetry information obtained from 31P solid-state NMR spectroscopy. The structure of SrP2N4 was refined by the Rietveld method by utilizing both neutron and synchrotron X-ray powder diffraction data, and has been corroborated additionally by 31P solid-state NMR spectroscopy by employing through-bond connectivities and distance relations. [source] | |||||||||||||