V. Sh. Shekhtman’s research while affiliated with Russian Academy of Sciences and other places

Current technology requires that newly created materials have not only a set of functional properties but also be solid, lightweight, plastic, and easily machined. Intermetallic compounds based on the Nb–Al system occupy a prominent place among the advanced materials due to their unique properties. High-temperature intermetallides based on Nb and Al (Nb3Al, Nb2Al, NbAl3) are of great interest to aerospace engineering, power industry, etc. Therefore, the studies aimed at developing new methods for producing these materials performed in the present work are highly relevant. It is shown that the hydride cycle (HC) method for synthesizing refractory metal alloys developed in our laboratory can be successfully used to produce niobium aluminides. The main regularities and mechanism of the formation of niobium aluminide in the HC are investigated. All the phases known from the Nb–Al phase diagram are obtained. The advantages of the HC method compared to the conventional are demonstrated. In addition, the combustion of the produced niobium aluminide in a hydrogen atmosphere in the SHS mode is studied. The samples are analyzed using chemical methods, differential thermal analysis, and X-ray phase analysis.

The hydride cycle process was successfully applied to synthesize single-phase α2-Ti3Al, γ-TiAl, and TiAl3 aluminides. The formation of aluminides was found to proceed by solid-state reaction mechanism, without melting. The process takes advantage of its relatively low temperatures (600–1000°C), short duration (2–3 h) of a single-step synthetic procedure, and lower energy requirements.

In this work the results of investigation of mechanism of alloy formation in Ti–Nb system by “Hydride cycle” (HC) method are presented. The temperature regime of dehydrogenation-sintering is defined; the dependences of phase composition of the synthesized alloys on the dispersity and ratio of source reagents (TiH2 and NbHx powders) are studied. X-ray method is used for determination of structural characteristics of synthesized alloys and their hydrides. The results indicate that the crystal lattice and morphology of Ti–Nb alloys are sensitive to the content of Nb: at increasing of NbH portion in the charge, the β-phase becomes prevailing in the formed BCC alloy. The BCC alloys have been estimated as effective hydrogen storage materials. Therefore, we studied the interaction of synthesized alloys with hydrogen in combustion regime to obtain their hydrides.

In the present work, the possibility of formation of titanium and vanadium based alloys of BCC structure using hydride cycle was investigated. The mechanism of formation of alloys in Ti–V system from the powders of hydrides TiH2 and VH0.9 (or of V) by compaction followed by dehydrogenation was studied. Then, the interaction of the synthesized alloys with hydrogen in combustion regime (self-propagating high-temperature synthesis, SHS) resulting in hydrides of these alloys was investigated. DTA and DSC analyses of some alloys and their hydrides were performed and their thermal characteristics were measured.

Systematic X-ray diffraction studies of thermal expansion in CsHSO4, CsDSO4, RbHSO4 and Rb3H(SeO4)2 crystals have been carried out. An analysis of the results showed that the fast protonic conductivity is closely connected with the characteristic features of the structure, symmetry and orientation of hydrogens bonds in the crystals of MeXAO4 (Me=NI4, Rb, Cs; X= D,H; A= S,Se) family. How to Cite This Article Link to This Abstract Blog This Article Copy and paste this link Highlight all http://dx.doi.org/10.1557/PROC-293-453 Citation is provided in standard text and BibTeX formats below. Highlight all BibTeX Format @inproceedings{OPL:8154937,author = {Shekhtman,Veniamin Sh. and Dilanyan,Ruben A.},title = {In Situ X-Ray Investigation of Novel Protonic Conductors},booktitle = {Symposium U – Solid State Ionics III},series = {MRS Proceedings},volume = {293},year = {1992},doi = {10.1557/PROC-293-453},URL = {http://journals.cambridge.org/article_S1946427400467278},} Click here for full citation export options. Blog This Article Blog This Article : Highlight all In Situ X-Ray Investigation of Novel Protonic Conductors Veniamin Sh. Shekhtman and Ruben A. Dilanyan (1992). MRS Proceedings , Volume 293 , 1992, 453 http://journals.cambridge.org/action/displayAbstract?aid=8154937 The code will display like this In Situ X-Ray Investigation of Novel Protonic Conductors Veniamin Sh. Shekhtman and Ruben A. Dilanyan 1992 MRS Proceedings, ,Volume293, 1992, 453 http://journals.cambridge.org/abstract_S1946427400467278 Veniamin Sh. Shekhtman and Ruben A. Dilanyan (1992). In Situ X-Ray Investigation of Novel Protonic Conductors. MRS Proceedings, 293, 453 doi:10.1557/PROC-293-453. 0Comments

In the present work, an essentially new approach to production of quasicrystals in Ti-Zr-Ni system is described. It consists in co-compaction and dehydrogenation-sintering of mixture of powders of Ni with two and more hydrides of transition metals of IV group (Ti, Zr). The interaction of some of received quasicrystals with hydrogen in combustion mode is studied, the hydrides of these quasicrystals are synthesized and investigated. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

The symmetry conditions which rule the matching of a fulleren molecule's main axis in a translational lattice are considered. The full set of orientational states for the structure of fullerene are obtained. The different levels of correlations between symmetry axes of icosahedral molecule and cubic lattice are considered. This result used for analysis of orientational ordering models, including modulation structure and discrete orientational glass.

Briefly overviewed are the SHS-based processes developed at our lab for synthesis of metal hydrides and their alloys. More than 200 binary and complex hydrides have been synthesized by SHS reactions of metals in hydrogen. Radiation-induced synthesis of transition metal hydrides, termed Thermal-Radiation Synthesis (TRS), was suggested and used to prepare more than 50 different binary and complex hydrides. A phenomenon of Cold Synthesis (CS) of hydrides at room temperature from irradiated metal powders has been observed. Advance in these studies has led to elaboration of a new technique, termed hydride-cycle process, for fabrication of compact blocks of hydrides and refractory metal alloys. A wide range of binary and multicomponent alloys and their hydrides have been synthesized by this route. The developed processes are offered for industrial-scale implementation. Key wordsmetals hydrides-SHS-thermal-radiation synthesis-cold synthesis-hydride-cycle process-compact hydrides-dehydrogenation-alloys of refractory metals and compounds

We report the presence of large proportions of -phase in Ti-Hf-Zr alloys, prepared using the hydride cycle technique. We show that the -phase extends across the concentration triangle of Ti-Zr-Hf and report the partitioning of the three metals across the two sites in this structure from neutron and X-ray data. We examine the symmetry of the order parameter governing the phase transition and show that a two-step model for the phase transition involving site ordering followed by displacement is not likely to be correct. We suggest that an interstitial solid solution of oxygen and octahedral vacancies exists, and that the observation of any -phase diffraction pattern of alloys of these metals at ambient temperature and pressure should be viewed as a potential sign of the presence of oxygen in the octahedral interstitial sites.