High pure zirconium

The results of investigations of zirconium refining processes by methods of electron-beam melting and zone recrystallization using high-vacuum technology are presented. It is shown that the applied methods of zirconium refin-ing allow to effectively reduce the content of impurities. Investigation of...

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Datum:	2018
1. Verfasser:	Pylypenko, M.M.
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Sprache:	English
Veröffentlicht:	Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2018
Schriftenreihe:	Вопросы атомной науки и техники
Schlagworte:	Чистые материалы и вакуумные технологии
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spelling	nasplib_isofts_kiev_ua-123456789-1373802025-02-09T20:20:59Z High pure zirconium Високочистий цирконій Высокочистый цирконий Pylypenko, M.M. Чистые материалы и вакуумные технологии The results of investigations of zirconium refining processes by methods of electron-beam melting and zone recrystallization using high-vacuum technology are presented. It is shown that the applied methods of zirconium refin-ing allow to effectively reduce the content of impurities. Investigation of the properties of the obtained samples of high-purity zirconium and the dependence of these properties on the content of impurities allowed to reveal new features of high-purity zirconium. Викладено результати досліджень процесів рафінування цирконію методами електронно-променевої плавки та зонної перекристалізації із застосуванням високовакуумної техніки. Показано, що ці методи рафі-нування цирконію дозволяють ефективно знизити вміст домішок. Дослідження властивостей отриманих зразків високочистого цирконію і залежності цих властивостей від вмісту домішок дозволили виявити нові особливості високочистого цирконію. Изложены результаты исследований процессов рафинирования циркония методами электронно-лучевой плавки и зонной перекристаллизации с применением высоковакуумной техники. Показано, что применяемые методы рафинирования циркония позволяют эффективно снизить содержание примесей. Исследования свойств полученных образцов высокочистого циркония и зависимости этих свойств от содержания примесей позволили выявить новые особенности высокочистого циркония. 2018 Article High pure zirconium / M.M. Pylypenko // Вопросы атомной науки и техники. — 2018. — № 1. — С. 3-8. — Бібліогр.: 16 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/137380 669.296 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection	DSpace DC
language	English
topic	Чистые материалы и вакуумные технологии Чистые материалы и вакуумные технологии
spellingShingle	Чистые материалы и вакуумные технологии Чистые материалы и вакуумные технологии Pylypenko, M.M. High pure zirconium Вопросы атомной науки и техники
description	The results of investigations of zirconium refining processes by methods of electron-beam melting and zone recrystallization using high-vacuum technology are presented. It is shown that the applied methods of zirconium refin-ing allow to effectively reduce the content of impurities. Investigation of the properties of the obtained samples of high-purity zirconium and the dependence of these properties on the content of impurities allowed to reveal new features of high-purity zirconium.
format	Article
author	Pylypenko, M.M.
author_facet	Pylypenko, M.M.
author_sort	Pylypenko, M.M.
title	High pure zirconium
title_short	High pure zirconium
title_full	High pure zirconium
title_fullStr	High pure zirconium
title_full_unstemmed	High pure zirconium
title_sort	high pure zirconium
publisher	Національний науковий центр «Харківський фізико-технічний інститут» НАН України
publishDate	2018
topic_facet	Чистые материалы и вакуумные технологии
url	https://nasplib.isofts.kiev.ua/handle/123456789/137380
citation_txt	High pure zirconium / M.M. Pylypenko // Вопросы атомной науки и техники. — 2018. — № 1. — С. 3-8. — Бібліогр.: 16 назв. — англ.
series	Вопросы атомной науки и техники
work_keys_str_mv	AT pylypenkomm highpurezirconium AT pylypenkomm visokočistiicirkoníi AT pylypenkomm vysokočistyicirkonii
first_indexed	2025-11-30T10:39:36Z
last_indexed	2025-11-30T10:39:36Z
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fulltext	ISSN 1562-6016. PASТ. 2018. №1(113), p. 3-8. SECTION 1 PURE MATERIALS AND THE VACUUM TECHNOLOGIES UDC 669.296 HIGH PURE ZIRCONIUM M.M. Pylypenko National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine The results of investigations of zirconium refining processes by methods of electron-beam melting and zone re- crystallization using high-vacuum technology are presented. It is shown that the applied methods of zirconium refin- ing allow to effectively reduce the content of impurities. Investigation of the properties of the obtained samples of high-purity zirconium and the dependence of these properties on the content of impurities allowed to reveal new features of high-purity zirconium. INTRODUCTION Pure metals are widely used in important areas of new technology and the national economy: nuclear power engineering, microelectronics, space technology, medicine, as well as fundamental research. The need for high-purity metals for science is determined by the need to establish their true properties. With an increase in the purity of metals, not only their known properties change, but also new, previously masked by the pres- ence of impurities. Optimum combination of nuclear, corrosion, me- chanical, thermal and other physical and chemical prop- erties [1–3] make zirconium one of the best materials for core of light water nuclear reactors with a working temperature of the coolant to 350…400 °C. However, impurities in zirconium alloys significantly affect their structure and properties. The presence in zirconium in C, Si, P, Mg, K, Ca, O, Na, Cl, F, Ni, H, especially in complex content, have a negative impact. Even very small additives effectively affect the physico- mechanical and physicochemical properties of zirconi- um, which may cause a change in the mechanical and corrosion properties of zirconium alloys, as well as changes in optimal modes of deformation and heat treatment [46]. In addition, the influence of the total content of impurities on the properties of zirconium alloys is also possible. It is also necessary to limit the content of materials with a high neutron absorption co- efficient, in particular hafnium (less than 0.01 wt.%) in zirconium, which is explained by the need to ensure the efficiency of the operation of the nuclear reactor. In order to meet the increasing requirements for zirconium alloys of nuclear reactors, it is necessary to reduce the concentration of these impurities to the minimum val- ues. High-purity zirconium is required both for the crea- tion of new structural materials with given properties, and for studies on the detection of new properties inher- ent in high-purity zirconium. Technical zirconium is mainly produced by the metal-thermal reduction of dioxide (ZrO2), the reduction of chloride (ZrCl4) by magnesium (sodium), or the elec- trolysis of halides in the melt of alkali metal chlorides. The content of the main component in technical zirconi- um is approximately 99.0…99.8%, with the main impu- rities are, %: О (5…30)·10 -2 ; С ~ 5·10 2 ; N (1…10)·10 -3 ; Hf, Fе, Ni ~ 10 -2 ; А1, Сr, Сu, Ti, Со ~10 -3 [1–3, 7]. The composition of such a metal does not meet the require- ments of modern technology and requires additional refinement. In particular, zirconium for nuclear reactors should contain a small amount of impurities with a large absorption of thermal neutrons, as well as impurities that reduce its technological plasticity and corrosion resistance (interstitial impurities and a number of metal- lic impurities) [7–10]. Usually methods of vacuum smelting, transport reac- tions, etc. are used for additional purification of tech- nical zirconium. Deep purification of this metal requires the use of a complex of methods, including chemical refining at the stage of obtaining zirconium salts and physical methods [3, 7, 9, 11]. Getting zirconium of high purity is very complicated by its high chemical activity in relation to interstitial impurities. The purity that is achieved is determined not only by the efficiency of the purification method, but also by the amount of impurities which absorbed by the metal during the refining process. The development of new and improved existing zir- conium alloys is impossible without a deep study of the processes of obtaining high purity zirconium. In this regard, it is necessary to study the patterns of behavior of impurities in the process of obtaining high-purity zirconium by physical methods and study the influence of the purity of the metal on its properties. The conducted research was aimed at physically substantiating and experimentally investigating the be- havior of impurities in the process of zirconium refining by physical methods and determining the effect of zir- conium purity on its properties. To achieve this goal the following tasks were solved: calculate and experimentally investigate the behavior of impurities in the process of zirconium refin- ing by electron-beam melting (EBM) and zone recrys- tallization in high vacuum; obtain high purity zirconium and investigate the effect of zirconium purity on its properties. MATERIALS AND METHODS For the refining of zirconium were used: melting and zone recrystallization in an ultra-high vacuum with the use of electronic heating and a combination of some methods. EBM of zirconium is performed on an ultra-high vacuum installation. For pumping of installation used two hetero-ion pumps with a pumping speed of 5000 l/s each, and a titanium sublimation pump. Application of such a system of vacuum pumping allows to get an ul- timate vacuum in the installation 1.7·10 -6 Pа [7]. In the spectrum of the residual gas in installation were absent heavy hydrocarbons. Refining of zirconium is carried out in vacuum (1…5)·10 -5 Pa. Refining is conducted in the regime: heating ⇒ melting ⇒ excerpt of metal in molten state ⇒ crystallization ⇒ pulling ingot. Zone recrystallization with an electron-beam heating is car- ried out in installations with combined pumping systems [7]. Diffusion pumps are equipped with sorption and condensation traps; sorption, cryogenic and ion-sorption pumps which are used to give “oil-free” ultrahigh vacu- um. Electron-beam zone recrystallization is carried out in vacuum 1·10 -6 …1·10 -5 Pa. Choice of pumping sys- tem for different methods of refining determined mainly by degree of interaction metals in refining conditions with residual gases of the vacuum environment. The initial materials used for research: zirconium obtained by calcium-thermal recovery of zirconium tetrafluoride (CTZ) and zirconium after iodide refining (IZr). RESULTS OF ZIRCONIUM REFINING ELECTRON-BEAM MELTING One of the main methods of zirconium refining is EBM, which allows to obtain pure metal. The process of EBM consists in the melting of the initial ingot in a vacuum and its further crystallization. The EBM process of zirconium is characterized by the presence of limiting degrees of purification of more volatile metallic impurities. Calculated minimum achievable concentrations of impurities in zirconium after EBM are given in Tabl. 1 [11]. The calculation of the minimum achievable concentration of impurity was carried out based on the fact that the distribution coeffi- cient is equal to 1, according to the formula: Zr Me MeMe ZrMe M M p p C 0 0 min    , (1) where 0 Zrp and 0 Mep – partial pressure of zirconium va- por and impurity; Me – coefficient of activity of the impurity; ZrM and MeM – the molecular masses of the components. It follows from Tabl. 1 that purification of zirconium from volatile impurities decreases in a series: Zn > Be > Mn > Al > Cr > Cu > V > Fe > Cо > Ni > Si. In the process of EBM, it may be difficult to purify zir- conium up to the required level from Co, Si, and Ni. The degree of metal purification can be related to the loss of the weight of the main component [7]:   0 0 lg1lg Zr Zr W W C C   , (2) where С0 and С are the initial and final concentrations of the impurity; 0 ZrW and ZrW – the initial and final weight of the main component; Me Zr Zr MeMe M M p p 0 0     – the purification factor. Effective purification is possible only when . For the study of the behavior of impurities in zirco- nium during its refining by the method of the EBM, the values included in equation (2) were determined. An estimation of efficiency of purification of zirconium from impurities was carried out by this method. Table 1 Minimum estimated concentrations of impurities in zirconium Impurity Coefficient of activity, Me Concentration, wt.% Aluminum 0.07 9.1·10 -4 Beryllium 0.38 3.9·10 -5 Vanadium 0.72 1.3·10 -2 Iron 0.052 4.4·10 -2 Cobalt 0.011 3.3·10 -1 Silicon 0.0006 1 Manganese 0.18 1.4·10 -4 Copper 0.088 4.8·10 -3 Nickel 0.004 0.9 Chrome 0.14 2.0·10 -3 Zinc 0.025 1.0·10 -5 Molybdenum, Niobium, Hafnium, Tungsten – No purification The content of impurities, which is expected after the EBM with weight loss of the main element (zirconi- um) from 1 to 5%, was determined. The analysis of the results of calculations made it possible to draw a con- clusion on the efficiency of purification of zirconium from metallic impurities when it was refined by the method of EBM. The generalized results of calculations of the efficiency of purification of zirconium by the method of EBM are given in Tabl. 2. It can be seen that when refining zirconium with this method, the metal impurities Al, Cu, Ti, Be, Fe, Mn, Cr have a purification factor  of more than 250 and are effectively removed from zirconium; impurities Si, Ni, B have  from 1 to 250 and will be removed only if the weight of the base is lost to 2%, and the impurities Hf, Nb, and Mo, having  < 1, will accumulate in zirconium, so they need to be removed at earlier stages of purification. Experimental studies have shown that electron-beam melting is a very effective process for refining of zirco- nium. Impurity contents in iodide zirconium after elec- tron-beam melting are shown in Tabl. 3. In the Table, in addition to the chemical purity of zirconium, which is characterized by the total content of impurities, the val- ue of the residual resistivity ratio RRR = R(300 K)/R(4.2 K) is given. From Tabl. 3 it can be seen that the use of EBM leads to a decrease in the content of impurities in Zr. The main elements that are not removed from zirconium during the EBM are Hf, C, and Mo. Comparison with the estimated concentrations of impurities carried out by the ratio (2) show that the concentration of Hf, Mo, and Ti in zirconium is well in line with the calculated val- ues. However, the content of other metal impurities ex- ceeds the calculated values, especially for Si, Fe, and Cr. Table 2 The efficiency of purification of zirconium by the method of EBM Coefficient  Efficiency Impurities <1 no purification even if the weight of the base is lost to 5% Hf, Mo, Nb 1…250 significant purification if the weight of the base is lost to 2% B, Si, Ni >250 significant purification if the weight of the base is lost <1% Al, Cu, Ti, Be, Fe, Mn, Cr The microhardness of the initial iodide zirconium was 1200 MPa, and after the EBM it dropped to 800 MPa. The dual remelting of iodide zirconium in an installation with an oil-free pumping system made it possible to get a zirconium ingot with a hardness of 640 MPa, a purity of 99.99 wt.%. Favorable refining conditions in combination with optimal technology allow to achieve a significant in- crease in metallurgical purity of zirconium at the EBM. The generalized results of systematic researches of the process of CTZ and iodide zirconium refining by the method of EBM, obtained by the author [12–14], are characterized by the following data: microhardness of zirconium decreases from 1200 to 800 MPa, there is a significant decrease in the concentration of metal and gas impurities in zirconium, as well as a decrease in the hardness of samples of zirconium. Moreover, the pa- rameters of the purity of the double refining of zirconi- um by the method of EBM are somewhat better. Changes in the content of metallic impurities in the CTZ after two EBM are shown in Fig. 1. The content of interstitial impurities in the CTZ varies from 0.18 to 0.12 wt.% after the first EBM and to 0.1 wt.% after the second EBM (Fig. 2,а). Brinell hardness of CTZ de- creases from 2250 to 1750 and 1370 MPa after the first and second EBM respectively (see Fig. 2,b). The given data testify to the efficiency of the EBM method when refining zirconium from impurities [12]. Тable 3 Impurity contents in iodide zirconium Impurity The content of impurities, wt.% Initial After EBM Oxygen 0.04 0.008…0.013 Nitrogen 0.006 0.004 Carbon 0.035…0.04 0.025 Hydrogen 0.0045 0.001 Iron 0.025 0.008 Aluminum 0.004 0.003 Copper 0.0065 0.0006 Nickel 0.0065 0.004 Chrome 0.005 0.002 Titanium 0.0023 0.0001 Silicon 0.006 0.005 Niobium <0.001 <0.001 Hafnium 0.018 0.018 Calcium 0.006 0.0001 Fluorine 0.003 0.0002 Molybdenum 0.005 <0.001 RRR 30 100 Fig. 1. Changes in the content of metallic impurities in zirconium after two EBM а b Fig. 2. Change in the oxygen content in CTZ and iodide metal (a) and the change in the hardness of Brinell of CTZ (b) depending on the number of melting Further purification of zirconium can be achieved by using a complex of chemical and physical refining tech- niques. In particular, in the previous stages, more com- plete removal of hafnium, nitrogen, carbon, etc. from zirconium is needed. The removal of volatile metallic impurities can be achieved by electron beam melting; it is advisable to add deoxidizing components for the re- fining of zirconium from oxygen. ZONE RECRYSTALLIZATION Of all the refractory metals, zirconium has the least pressure of the saturated vapor at the melting point, which allows it to be subjected to multiple zone recrys- tallization in a vacuum without noticeable evaporation. Perhaps for this reason, the method of zone melting (recrystallization) is most often used for deep purifica- tion of zirconium. The difficulty of zirconium refining by zone smelting is due to the fact that zirconium, un- like most other rare metals, has a hexagonal close- packed lattice (hcp) with large lattice periods and somewhat increased in comparison with the ideal ratio of с/а. The solubility of gas impurities in it, especially the oxygen admixture, is elevated; in addition, it does not form volatile oxides, which facilitate the removal of oxygen during the smelting of other refractory rare met- als. For this reason, the requirements for purity of the gas environment during refining of zirconium are in- creasing. Experimental results of the zone melting of metals showed the existence of two mechanisms of purification – zone recrystallization and evaporation. Therefore, it is possible to obtain higher purity of zirconium by using the zone melting. During the first passes of zone the refining occurs mainly by evaporation of volatile metal- lic impurities (Fе, Ni, А1, Ti, Cr, Si, etc.), removal of hydrogen and a certain amount of oxygen, carbon and nitrogen. After that, in zirconium, the main impurities are carbon, oxygen and hafnium. Next passes of the zone cause redistribution of impurities (mainly oxygen) along the sample length. Effective distribution coeffi- cient K for metal impurities is less than 1 (K < 1); for oxygen, nitrogen and carbon K > 1. Application of zone melting allowed to obtain high degree of purity zirconium. Studies have shown that zone melting in a higher vacuum ensures a more pure metal. With the increase in the number of passes of the zone there is a general increase in the purity of the me- tal, due to the evaporation of impurities and increase the distribution of impurities along the sample length. The holding of six passes of zone in vacuum 6·10 -6 Pa at a speed displacement of zone 1.2 cm/h it is possible to obtain a high-purity zirconium: residual resistivity ratio RRR = 250 and the value of microhardness of 590 MPa. Contents of oxygen, nitrogen and carbon equal 2.0·10 -3 , 1.7·10 -3 , and 9.0·10 -3 wt.%, respectively, the content of metallic impurities is less than 10 -5 wt.% [15]. INFLUENCE OF ZIRCONIUM PURITY ON ITS PROPERTIES The study of the effect of metal purity on the micro- structure and the mechanical properties of zirconium showed a significant effect of the purity of the metal on the properties. In the study of microstructure, it was found that the structure of pure zirconium (RRR ~100) consists of rela- tively large grains, the size of which is 5…10 mm. With a decrease in the purity of zirconium, the size of the grains decreases, and in the case of technical purity metal (RRR ~7) after annealing the grain size was 0.5…2.0 mm. The microstructure of zirconium with RRR = 30 is shown in Fig. 3. In all investigated sam- ples, irrespective of purity, two types of inclusion were found: needles, located mainly on the borders of the grains, and rounded inside the grains. With the increase of zirconium purity, the inclusions diminish from 0.5…1.0 to 0.2 μm, as well as their number decreases. Fig. 3. Microstructure of zirconium with RRR = 30 The mechanical properties of high purity zirconium and the effect of purity on the characteristics of strength and ductility of zirconium were investigated [15, 16]. Increasing the purity of zirconium leads to a decrease in the values of the ultimate strength and increase the plasticity (Tabl. 4). The microhardness (Н) of such samples is also reduced. The properties of metals, in particular the amount of microhardness, depend to a large extent on the content of impurities. The depend- ence of the change in the value of the microhardness of zirconium on the oxygen content is shown in Fig. 4. It is seen that the value of the value of microhardness of zirconium depends on the concentration of oxygen in the metal. Therefore, according to the value of micro- hardness, it is possible to determine the purity of the metal. Тable 4 Mechanical properties of zirconium of different purity Relative residual resistivity RRR Ultimate tensile strength В, МPа Yield strength 0.2, МPа Elongation , % 7 400…470 280…320 18.0 30 200 120 28.0 100 130 85 34.0 200 105 25 49.5 Fig. 4. Dependence of microhardness of zirconium on the oxygen content CONCLUSIONS The behavior of metallic impurities and interstitial impurities during electron beam melting and zone re- crystallization in high vacuum were investigated. Zirco- nium of high purity was obtained and the influence of zirconium purity on its properties was investigated. The peculiarities of zirconium properties are determined depending on the content of impurities. Thus, studies have shown that EBM and zone re- crystallization in high-vacuum allow to effectively re- duce the content of impurities in zirconium and to ob- tain high-purity zirconium. REFERENCES 1. А.С. Займовский, Е.В. Никулина, Н.Г. Решет- ников. Циркониевые сплавы в атомной энергетике. М.: «Энергоатомиздат», 1994, 453 с. 2. D.L. Douglass. The Metallurgy of Zirconium. Vienna: IAEA, 1971, 466 p. 3. . aseda, M. Isshiki. Purification Process and Characterization of Ultra High Purity Metals. Berlin: Springer-Verlag, 2002, 412 p. 4. S.A. Nikulin, A.B. Rozhnov, V.A. Belov, E.V. Li, V.S. Glazkina. Influence of Chemical Compo- sition of Zirconium Alloy E110 on Embrittlement Un- der LOCA Conditions – Part 1: Oxidation Kinetics and Macrocharacteristics of Structure and Fracture // Jour- nal of Nuclear Materials. 2011, v. 418, p. 1-7. 5. H.G. Kim, S.Y. Park, M.H. Lee, Y.H. Jeong, S.D. Kim. 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Thomazet, P.-B. Hoffmann, H.-J. Sell, G. Garner. Corrosion Be- havior of Alloy M5: Experience // 2008 Water Reactor Fuel Performance Meeting. Seoul. Korea, 2008, p. 126- 129. 11. М.Л. Коцарь, В.М. Ажажа, М.И. Борисов и др. Получение чистых циркония и гафния // Высоко- чистые вещества. 1992, №4, c. 85-92. 12. Н.Н. Пилипенко. Получение циркония ядерной чистоты // ВАНТ. Серия «Физика радиаци- онных повреждений и радиационное материалове- дение». 2008, №2, с. 66-72. 13. Н.Н. Пилипенко. Исследования и разработ- ки по получению ядерно-чистого циркония и сплава на его основе // ВАНТ. Серия «Вакуум, чистые ма- териалы, сверхпроводники». 2009, №6(64), с. 12-18. 14. В.М. Ажажа, С.Д. Лавриненко, Н.Н. Пили- пенко. Чистые и особо чистые металлы в атомной энергетике // ВАНТ. Серия «Вакуум, чистые мате- риалы, сверхпроводники». 2007, №4, с. 3-12. 15. С.Д. Лавриненко, Н.Н. Пилипенко, П.Н. Вьюгов. Чистые металлы для ядерной энерге- тики // ВАНТ. Серия «Физика радиационных повре- ждений и радиационное материаловедение». 2014, №4(92), с. 72-81. 16. S.D. Lavrynenko, M.M. Pylypenko. Pure Me- tals for Nuclear Power // SMC Bulletin. 2015, v. 6, N 1, p. 19-24. Article received 15.11.2017 ВЫСОКОЧИСТЫЙ ЦИРКОНИЙ Н.Н. Пилипенко Изложены результаты исследований процессов рафинирования циркония методами электронно-лучевой плавки и зонной перекристаллизации с применением высоковакуумной техники. Показано, что применяе- мые методы рафинирования циркония позволяют эффективно снизить содержание примесей. Исследования свойств полученных образцов высокочистого циркония и зависимости этих свойств от содержания приме- сей позволили выявить новые особенности высокочистого циркония. ВИСОКОЧИСТИЙ ЦИРКОНІЙ М.М. Пилипенко Викладено результати досліджень процесів рафінування цирконію методами електронно-променевої плавки та зонної перекристалізації із застосуванням високовакуумної техніки. Показано, що ці методи рафі- нування цирконію дозволяють ефективно знизити вміст домішок. Дослідження властивостей отриманих зразків високочистого цирконію і залежності цих властивостей від вмісту домішок дозволили виявити нові особливості високочистого цирконію.

High pure zirconium

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