ВОДОРОДНАЯ ЭКОНОМИКА
rJ
HYDROGEN ECONOMY
КОНСТРУКЦИОННЫЕ МАТЕРИАЛЫ
STRUCTURAL MATERIALS
PACS: 61.05.fm; 61.66.Fn
ФАЗОВЫЕ ПРЕВРАЩЕНИЯ В ПЕРЕСЫЩЕННОМ ТВЕРДОМ РАСТВОРЕ АЗОТА В a-Zr, ПОЛУЧЕННОМ ПУТЕМ ТЕРМОЭМИССИИ ВОДОРОДА
12 12 И. Хидиров , Т.Н. Везироглу , Н.Н. Мухтарова , А. Везироглу
1Институт ядерной физики НАН Узбекистана 100214, Ташкент, Узбекистан, e-mail: khidirov@inp.uz Исследовательский институт чистой энергии, Университет Майами 33124, США, Флорида, Корал Гейблс, e-mail: veziroglu@miami.edu
Методом дифракции нейтронов (к = 0,1085 нм) на примере твердого раствора азота и водорода в решетке a-Zr (ZrN0-43H0-38) показано, что синтез водородсодержащих фаз внедрения с последующим низкотемпературным удалением водорода в непрерывно откачиваемом высоком вакууме при температурах Тэв < Траспада позволяет инициировать ряд фазовых превращений, которые невозможно осуществить традиционными методами (длительным отжигом или закалкой). Таким способом получены три модификации пересыщенного твердого раствора ZrN0,43, не существующие на равновесной фазовой диаграмме. Между этими модификациями обнаружены энантиотропные и монотропные фазовые переходы. Изучены кристаллические структуры обнаруженных фаз. Предложена схема обратимых и необратимых фазовых превращений на основе индуцированной водородом фазы.
В индуцированной водородом фазе наблюдается изотропное сжатие гексагональной кристаллической решетки матрицы по сравнению с изоструктурной водородсодержащей фазой. Обнаружено, что смещение атомов металла относительно идеального положения в водородсодержащей и индуцированной водородом фазах происходит в разных направлениях. В водородсодержа-щей фазе атомы металла смещаются к плоскости, заполненной атомами азота, а в индуцированной водородом фазе - к плоскости, содержащей азотные вакансии. Это объясняется различным характером химической связи в водородсодержащем соединении и соединении без водорода.
PHASE TRANSITIONS IN OVERSATURATED SOLID SOLUTION OF NITROGEN IN THE a-Zr OBTAINED BY USING HYDROGEN TERMOEMISSION
I. Khidirov1, T.N. Veziroglu2, N.N. Mukhtarova1, A. Veziroglu2
'Institute of Nuclear Physics, Uzbekistan Academy of Sciences, 100214, Tashkent, Uzbekistan, e-mail: khidirov@inp.uz 2Clean Energy Research Institute, University of Miami, Coral Gables, Florida, 33124, USA, e-mail: veziroglu@miami.edu
By neutron diffraction (X = 0.1085 nm) it has been demonstrated with an example of the solid solution of nitrogen and hydrogen in a lattice of a-Zr (ZrN043H0 38) that the synthesis of hydrogenous interstitial phases, followed by low-temperature removal of hydrogen under continuous evacuating, makes possible to obtain metastable interstitial phases which cannot be obtained by traditional methods (long annealing or hardening). In this way three modifications of oversaturated solid solution ZrN043 which are absent in the equilibrium phase diagram has been obtained. Between these phases enantiotropic and monotropic phase transitions were found. The scheme of reversible and nonreversible phase transformations is offered on a basis of the hydrogen induced phase.
In the hydrogen induced phase the isotropic compression of HCP crystal lattice in comparison with the isostructural hydrogenous phase is observed. It is found that the displacement of metal atoms from their ideal position occurs in different directions in the hydrogenous and in the hydrogen-induced phases. In the hydrogenous phase the metal atoms shift toward a plane filled with nitrogen atoms, and in the hydrogen induced phase - toward a plane containing nitric vacancies. This may be explained by various characters of chemical bonding forces in the hydrogenous compound and in the hydrogen-free one.
Information about the author: Head of the laboratory of composite materials of the Institute of nuclear physics of Uzbekistan Academy of Sciences.
Education: Tashkent State Pedagogical University (1969 r.), doctor of sciences in physics and mathematics (1998), professor (2007).
Main range of scientific interest: structural phase transformations, interstitial alloys and solid solutions (carbides, nitrides, hydrides), intermetals and hydrides of intermetals, superconducting ceramics and other ceramics.
Publications: more 120 articles, 4 patents.
Irisali Khidirov
International Scientific Journal for Alternative Energy and Ecology № 2 (70) 2009
© Scientific Technical Centre «TATA», 2009
T. Nejat Veziroglu
Information about the author: President of International Association for Hydrogen Energy Association, Miami, USA; Director of Clean Energy Research Institute of University of Miami, USA. Education: A.C.G.I., Mechanical Engineering, 1946. B.Sc. Mechanical Engineering, 1946. D.I.C., Advanced Studies, London, 1947. Ph.D. - Heat Transfer, 1951. Professor, 1962.
Main range of scientific interest: hydrogen energy, interstitial heat transfer, environment, hydrogen storage and environmental impact of energy.
Publications: number of papers in refereed journals - 224; number of communications to scientific meetings - 155; number of books: 2 books, 84 proceedings.
Information about the author: Senior researcher of the laboratory of composite materials of the Institute of nuclear physics of Uzbekistan Academy of Sciences.
Education: Nizhni Novgorod State University (1958); PhD, 1982; the specialist in the field of X-ray structure analysis and crystal chemistry.
Main range of scientific interest: investigations into the effect of ionizing radiation (y-rays, neutrons) on the structure and properties of materials (solid solutions, HTS-ceramics, semiconductors, etc.). Publications: more 70 articles.
Nina Nikolaevna Mukhtarova
Information about the author: PhD student, The Instituto Superior Tecnico, Lisbon, Portugal. Education: University of Miami, Management of Technology, M.S., 2000-2004. University of Miami, Intensive English Program, 1999-2000. Marmara University, Marketing and International Enterprises, B.S., 1992-1999. Main range of scientific interest: hydrogen production from H2S; hydrogen transportation; hydrogen technology transfer. Publications: 10 articles.
Ayfer Veziroglu
Introduction
It is known that in the Zr-N-H system the ordered phase Zr2N1-xHy with structure of anti-CdI2 type (on nitrogen) is formed [1, 2]. Hydrogen has both small nuclear weight and binding energy and also high diffusion rate. These factors allow one to obtain oversaturated solid solution (sol. s.) ZrNx by evacuation of hydrogen out of three-component sol. s. ZrNxHy at rather low temperatures [3]. Dehydrogenation of the sol. s. under persistent evacuation at temperature 400° C results in full removal of hydrogen out of a lattice with conservation of the structure type [4]. However, with that, formation of the second, orthorhombic ordered phase with structure of anti-CaCl2 type (space group -sp. gr. Pnnm) on a basis of oversaturated sol. s. ZrNx is observed. It is of interest the vacuum evacuation of hydrogen out of a lattice of the ordered sol. s. ZrN0 43H038 (sp. gr. P3m1) at temperature lower than temperatures of orthorhombic ordering or formation of disordered hexagonal sol. s.: Tev <Tortho < Tdisord. It may be supposed that because of low temperature of hydrogen evacuation, in the Zr-N system the ordered
induced by hydrogen structure of sol. s. ZrNx (sp. gr. P3m1) will be "frozen" which is not observed under usual conditions. The analogous way of obtaining the phase induced by hydrogen in the Ti-N system has been offered in [5]. Besides, it is of interest to study mutual transformations in hydrogen-induced metastable and stable phases of the Zr-N system.
Thereby the aim of the present work was neutron diffraction investigation of hydrogen-induced phases (HIPh) and mutual transformations of metastable and stable phases in an example of the Zr-N system.
Experiment techniques
Neutron diffraction experiment was carried out using the neutron diffractometer mounted at a thermal column of atomic reactor WWR-SM of the Institute of Nuclear Physics of Uzbekistan AS (X = 0.1085 nm) [6]. Calculation of structural characteristics was carried out by Rietveld full-profile method [7, 8] using neutron diffraction data. X-ray diffraction patterns were obtained using the X-ray diffractometer (X = 0.15418 nm).
The sol. s. ZrN0 43H038 for studying was prepared by self-propagating high-temperature synthesis (SHS) [9]. SHS of inorganic compounds is based on exothermal reaction of initial reagents. As initial materials nitrogen of the "extra-pure" brand and Zr powder of the M-41 brand were taken. According to nameplate, the Zr powder contained 0.45 mas % of hydrogen. The pressure of nitrogen in a constant pressure bomb was 700 atm. After synthesis the sample was exposed to homogenizing annealing in evacuated and sealed-off quartz ampoule at temperature 1000° C during 12 h. Then for fixation of the high-temperature state samples were hardened in air. Powder samples with grain sizes no more than 60 ^m were studied.
Samples composition was determined by chemical analysis and was controlled by minimizing the R factors of structure determination using neutron diffraction patterns. Dehydrogenation of hydrogenous compounds was carried out under persistent evacuation (at vacuum not more than 5.3-10-3 Pa). After dehydrogenating at every temperature a neutron diffraction pattern was surveyed. Hydrogen quantity in samples was watched as decline of incoherent background caused by incoherent neutron scattering on H nuclei. Since hydrogen nucleus has the largest amplitude of incoherent neutron scattering, its background scattering falls away with the increase of Bragg angle [10]. The hydrogen content was also estimated by the analysis of reflection intensities and sometimes by chemical analysis.
Experiment results
As an initial sample the single-phase ordered solid solution ZrN0.43H0,38 was taken. According to X-ray structure analysis, the sample was single-phase and homogeneous and had hexagonal close-p
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