Thermostimulated gas evolution from zirconium alloy saturated by hydrogen E_125 versus deformation degree has been studied. Samples of zirconium were subjected to straining with relative lengthening 2,5; 5,0 and 10,0 %, then they were saturated with hydrogen by electrolyte method at current density 0,5 A/sm2 during 4 hours. Or vice versa, they were first saturated with hydrogen being subjected to deformation afterwards. The deformation of alloy samples results in trap formation with different energies of hydrogen bond. In this case both bond energy and hydrogen quantity caught in traps depends on both deformation size and succession of «deformation-saturation» actions. The values of hydrogen bond energies in traps are estimated. Types of traps are defined

Cherdantsev, Y. P.

Chernov, Ivan Petrovich

Garanin, G. V.

Lider, A. M.

Nikitenkov, N. N.

Skirnevsky, A. V.

Tyrin, Y. I.

Electronic archive of Tomsk Polytechnic University

48IntroductionZirconium alloys are main constructional materialfor the elements of active zone and fuel systems of atomicreactors owing to small section of absorption of thermalneutron, high corrosion resistance, good mechanicalproperties and easy treatment [1]. One of the importantdemands of active zone materials is low hydrogen absorption. Saturation with hydrogen results in decrease of alloy plasticity and crack resistance, brittle hydrides in therange of stress concentration can become a cause of product destruction because of formation and growth ofhydride cracks according to mechanism of delayed destruction at the temperature of operation.Zirconium alloys absorb hydrogen actively even at300 °C forming solid solution and hydrides ZrH and ZrH2[2]. Therefore interdependence of elastic characteristicsof zirconium alloys and behavior of saturating hydrogenis of fundamental interest both from the point of view ofreactor facility safety and from the point of view of possibility to operate the mechanical properties of zirconium.The purpose of the given work is to examine regularities of hydrogen saturation depending on deformationdegree of binary zirconium alloy samples of E125 type(Zr–2,5 % Nb) used in some high technological APPunits.Methods of experimentBy means of thermostimulated gas evolutionmethod (ТSGE) 3 groups of binary zirconium alloysamples of E125 have been investigated:1. Initial and deformed (strained) samples with relative lengthening ΔA/A=2,5; 5,0 и 10,0 %.2. Initial and deformed at the beginning with the samerelative lengthening, but then saturated with hydrogen by electrolyte technique with current densityJ=0,5 А/см2 during 4 hours.3. First saturated with hydrogen, then deformed; theparameters of saturation and straining are the samein point 2.Initial samples of 30×3×3 mm size were polishedmechanically and annealed at pressure 10–4 Pa and temperature 550 °С during 60 min with subsequent coolingin furnace without vacuum deterioration. Hydrogen saturation was carried out in electrolytic cell using samplesas cathodes. Electrolyte – H2SO4 of molar concentrationat temperature 20 °С. To strain the samples experimental equipment ComTen DFM 5000 was used.The equipment to investigate ТSGE is described inthe works [3, 4]. Unit of programmed heating allows forlinear heating samples from 20 to 1100 °С with velocityfrom 0,1 to 5 degree/sec. Heating chamber is connectedwith single massspectrometer МХ7304 through sluice.Such a construction provides quick change of investigated samples as well as continuous recording of intensivities produced at gas heating of mass from 1 to 250 а.е.м.In the measuring cell of the massspectrometer vacuum isnot worse than 105 Pа. Final pumping out was made byion pumps. The relative error of intensivity measurementof the mass lines is not more than 5 %. Before the experiment repeated heating of vacuum cell without sampleshowed that intensivity of Н2 hydrogen evolution increases in comparison with vacuum level maximum 5...6 timesat temperature higher 800 °С. When heating vacuum cellwith the sample gas evolution intensivity increases incomparison with vacuum level up to fourfold (fig. 1–3).Technical sciencesUDC 539.16.04THE INVESTIGATION OF HYDROGEN ACCUMULATION IN ZIRCONIUM ALLOY BY THERMOSTIMULATED GAS EVOLUTION METHODN.N. Nikitenkov, Y.I. Tyrin, I.P. Chernov, A.V. Skirnevsky, G.V. Garanin, A.M. Lider, Y.P. CherdantsevTomsk Polytechnic UniversityEmail: nikitenkov@fnsm.tpu.edu.ruThermostimulated gas evolution from zirconium alloy saturated by hydrogen E125 versus deformation degree has been studied. Samples of zirconium were subjected to straining with relative lengthening 2,5; 5,0 and 10,0 %, then they were saturated with hydrogen byelectrolyte method at current density 0,5 A/sm2 during 4 hours. Or vice versa, they were first saturated with hydrogen being subjectedto deformation afterwards. The deformation of alloy samples results in trap formation with different energies of hydrogen bond. In thiscase both bond energy and hydrogen quantity caught in traps depends on both deformation size and succession of «deformationsaturation» actions. The values of hydrogen bond energies in traps are estimated. Types of traps are defined.Technical sciences49Therefore in the figures below one can see intensivity dependences of thermostimulated Н2 hydrogen evolutionfrom the samples of zirconium alloy E125 without subtraction of heater hum of the vacuum cell.To estimate hydrogen bond energy in the traps amethod based on calibrating lines of desorption activation energy dependency Ed on temperature Тmax,i was applied, at which imaximum of hydrogen evaluation ontemperature and velocity of heating was observed [5].Using the given dependences and taking into accountsmall differences between hydrogen atom bond energyin the sample Еb and desorption activation energy Еd onecan evidently use the dependences to estimate Еb. Tocompare hydrogen content in different samples thetemperature dependences of hydrogen evaluation onТSGE temperature (spectra) were integrated accordingto total time of heating. The spectra ТSGE presentedbelow were obtained at heating velocity 1 degree/sec.Results and discussionIn fig. 1–3 the intensivity dependences of thermostimulated hydrogen evolution from the samples ontemperature are shown.In fig. 4 the dependences of integrated hydrogenevolution on degree of deformation and hydrogen saturation are presented. Integration was made by means ofintegration module from applied program package OriginPro 7.0 (OriginLab Corporation).The comparison of the curves in fig. 1–3 shows thatdeformations and hydrogen saturation of zirconiumsamples E125 result in complication of type of ТSGEtemperature dependence, there appearing some peculiarities (peaks, steps, discontinuities). The temperaturemaximums Тmax,i corresponding the peculiarities areshown in fig. 1–3 by arrows. It should be noted that specific peculiarities are observed in all ТSGE spectra, buttheir Тmax are different, though some of them (for example, at Тmax=515 °С) are observed in all samples subjected to hydrogen saturation.Fig. 1. The temperature dependences of ТSGE intensivity fromzirconium alloy samples E125: 1) undistorted sample andthat subjected to straining with relative lengtheningΔA/A, %: 2) 2,5, 3) 5,0, 4) 10,0; 5) undistorted, hydrogen saturated sampleFig. 2. The temperature dependences of ТSGE intensivity fromzirconium alloy samples E125, first subjected to deformation and then hydrogen saturated by electrolyteΔA/A, %: 1) 2,5, 2) 5,0, 3) 10,0It should be pointed out that specific peculiaritiesare observed on all ТSGE curves, but their Тmax are different, though some of them (for example, atТmax=515 °С) are observed in all samples subjected tohydrogen saturation.It is known that peculiarities mentioned are connected with hydrogen evolution from traps with definitedesorption activation energy Ed, the Ed values beinguniquely connected with Тmax [5]. To analyze the peculiarities of ТSGE spectra let us take some abbreviationsand assumptions. Denote the type of sample «F+H» ifthe sequence of operations corresponds to first its straining, then hydrogen saturation, and, on the contrary,«H+F» denotes first hydrogen saturation then samplestraining, «F» denotes deformed, but not saturated samples. Let us point out the characteristic temperature regions where spectra peculiarities are situated. Evidently,each of the regions corresponds to definite type of hydrogen traps which are first numbered (hereinafter arguments in favour of concrete defects responsible foreach of the type of traps will be adduced)Fig. 3. The temperature dependences of ТSGE intensivity fromzirconium alloy samples E125, first hydrogen saturatedby electrolyte and then subjected to deformation,ΔA/A, %: 1) 2,5, 2) 5,0; 3) 10,0 %Bulletin of the Томsк Pоlyтеchnic University. 2006. V. 309. № 450Thus, the information on ТSGE peculiarities can bepresented in the tables 1 and 2.Таble 1. Types of traps (1–5), activation temperatures corresponding to them Тmax, desorption activation energy(Ed) and hydrogen atom bond energy in traps (Eb)From table. 1 it is obvious that in the set up temperature range the bond corresponding to energy vary inhundredth parts of eV, therefore it is supposed that wedeal with one of the types of trap in the given range.Таble 2. Classification of ТSGE spectra peculiarities fig. 1–3From table 2 it is obvious that the presence of eachtype of trap in samples depends on deformation size andsequence of deformation and saturation. Relative quantity of hydrogen caught in the traps is defined by the order of deformation and saturation operations. One cansee it both from comparison of intensivity of differentregions. It is seen both from the comparison of intensivity of different parts of ТSGE spectra (correspondingtraps 1–5) in fig. 1–3 and from that of total values of theabsorbed hydrogen (fig. 4).Fig. 4. The dependences of integral evolution of hydrogen onthe degree of deformation (The value of error alongboth axes is not more than linear point sizeThe most quantity of hydrogen is trapped at «F+H»sequence of operation.The comparison of the curves presented in fig. 4shows that integral evolution of heat:1. increases some times from deformed samples evenin the case if they are not saturated with hydrogenneither before nor after deformation;2. is significantly higher from samples first deformed,then saturated than in the other cases.3. in the case when samples first saturated with hydrogen the deformation value slightly influences the integral evolution.The maximum integral evolution of hydrogen is observed at 5 %deformation, at 10 %deformation theevolution in the given temperature range being lowerthan at that of 5 %. It does not mean, however, that relatively small deformations (≤5 %) provide hydrogenaccumulation, but at large deformations (≥10 %) hydrogen is distilled from sample. The point is that maximum heat evolution of hydrogen from zirconium alloyis higher 1000 °С and ТSGE spectra pattern behaviournear 1000 °С shows that this maximum at 10 % deformation is essentially higher than in any other cases. Infact, near 1000 °С intensivity of ТSGE spectrum fromsamples from ΔA/A=10 % (curve 3 in fig. 2, 3) increasesdistinctly quicker than the others, so that curve 3 crosses curve 2. I.e. at more degree of deformation hydrogenis captured and mostly accumulated by traps with largebond energy for which Тmax>1000 °С, а Еb≥3 eV. Let usname the traps as trap with strong bond, but traps of type 1–4 (table 1) that with weak bond.Obtain numerical evaluation of hydrogen redistribution between traps with weak and strong bonds at deformation. For this purpose in the case of 10 % deformation divide the spectrum intensivity 5 in fig. 1, as well asthat of spectra 3 in fig. 2 and 3 in the points corresponding maximum temperature (~1000 °C) by intensivity ofthe same spectra in the points corresponding the firstand third types of peculiarities (i.e. temperature 330 и515 °С). From the results of numerical evaluation presented in table 3 it is seen that relative evolution of hydrogen from the traps with strong bond at deformationincreases more than 2 times in comparison with thetraps of type 1 and more than 3 times in comparisonwith the traps of type 3.Table 3. Comparison of relative hydrogen evolution from thetraps with strong and weak bondsThe regularities described above permit to define thetraps of 1–4 types as dislocation (with their different modifications) and grain boundary, but the traps of type 5 andTypes oftrapsТmax °СTypes of samplesInitial, saturated with hydrogenF+H H+FY, rel. units5 880 943 4099 12101 330 57 130 353 515 473 562 164RelationsY980/Y430 15,5 31,5 34,5Y980/Y615 1,99 7,3 7,4Type of samples ΔA/A, %Presence of traps of the given type(«+» – present, «–» – absent)1 2 3 4 5Initial 0 + + + – +F+H 2,5 + – + – +F+H 5,0 + – + – –F+H 10,0 – + + – –H+F 2,5 + – + + +H+F 5,0 – + + + –H+F 10,0 – + + + –Type of trap Тmax, °С Ed, kkal/mole Eb, eV/atom1 320...345 39,0...40,7 1,70...1,772 390...420 43,7...45,7 1,90...1,983 515 52 2,254 610 58,2 2,535 860...880 74,6...76,1 3,24...3,30Technical sciences51more highly energetic ones (not observed in our experiment) are defined as microvoids and cracks. On the whole, such interpretation in the given experiment is obviousbecause when straining the samples it is just dislocationsand grain boundaries that give rise to pores and cracks.ConclusionIt was stated that deformations of zirconium alloyE125 result in trap formation with different hydrogenbond energies. The primary type of traps depends ondeformation degree. Bond energy and quantity of hydrogen captured in the traps depend on value of deformation as well as on sequence of deformation and saturation operations. The values of bond hydrogen energiesare estimated in the traps under study, the most probable identification of traps is given.The work is done at the International scientific technical centresupport, grant № 2864.Literature1. Duglas D. Material study of zirconium. – Moscow: Atomizdat,1975. – 360 p.2. Nikulin S.A., Rozhnov A.B., Babukin A.V. a. o. The structure andresistance to distruction of zirconium alloys for atomic power engineering // Material science and thermal treatment of metals. – 2005.– № 5. – P. 8–17.3. Turin Y.I., Chernov Y.I., Krening M., Baumbakh Ch. Radioactively stimulated evolution of hydrogen from metals. – Tomsk: TSU, 2000. – 263 p.4. Turin Y.I., Chernov Y.I., Krening M., Baumbakh Ch. Excitement of hydrogen subsystem in metals and alloys by ion radiation // Proceedings ofTomsk Polytechnic University. – 2000. – V. 303. – № 3. – P. 51–61.5. Woodraf D., Delchar T. Modern methods of surface investigation. –Moscow: Mir, 1989. – 564 p.IntroductionA unique ability of palladium to dissolve large quantity of hydrogen was discovered by T. Graham as early asin 1886. Hydrogen dissolution changes the physical properties of palladium considerably [1, 2]: increases lattice parameter, decreases conductivity and magnetizability, raises hardness and strength, decreases plasticity,results in embrittlement. PdHx system is diamagneticand possesses superconductivity; whereas pure Pd is paramagnetic and as it is known does not exhibit superconductivity [3]. It is evidently that these changes of palladium properties are connected with modification ofits atomic and electron structure when dissolving hydrogen in it.Dissolving hydrogen palladium retains its type ofcrystal lattice. At small concentration of hydrogen(x<0,03) the so called αphase PdHx is formed. At highconcentration of hydrogen (x>0,6) the solution is changed into βphase with peculiar for the phase change ofthe first type the uneven change of lattice constant. Dissolving in palladium hydrogen atoms occupy in interstitial spaces of its facecentred cubic (FCC) crystal lattice. FCC lattice is known to have two types of interstitialspaces: tetrahedral and octahedral. Based on the data ofneutron diffraction [4–6], it was inferred that hydrogenatoms occupy octahedral interstitial spaces in FCC lattice of palladium forming PdH monohydride with NaClstructure. However, there are someata on concentrationand temperature dependencies of electrical resistance ofPdH monohydride as well as neutron structure investigations [3, 6], indicating the transformation of hydrogen atoms from oct into tetrahedral type at temperature of order 50 К.During recent experiments information about hydrogen behavior in palladium lattice exposed to the action of ionized radiation has been obtained. So, the experimental data on radioactive stimulated hydrogenmigration and desorption from palladium includingUDC 537.9:539.12DIELECTRIC RESPONSE FUNCTION PdHx SYSTEMY.M. Koroteev*, O.V. Girmanova, I.P. Chernov*Resistance physics and material science institute of RAS, TomskTomsk polytechnic universityEmail: yury_koroteev@list.ruThe calculations of electron structure of pure Pd and PdHx (x=1,2,3) system have been made ab initio in the range of local density approximation. Total energy of PdHx system has been calculated for the cases of different coordination of hydrogen atom (octand tetrahedral), the conclusion on their most probable location in metal lattice has been made. In the approximation of constant matrix element the imaginary part of permittivity constant function ε2(ω) has been calculated. It was stated that dissolution of hydrogen inpalladium increases values of the function ε2(ω) in the investigated range of energies from 2 to 24 eV. Therefore in the case of radiation impact on PdHx system one can expect intensive excitement of the crystal electron subsystem, and, hence, decrease of potential barriers for hydrogen atom movement.

The investigation of hydrogen accumulation in zirconium alloy by thermostimulated gas evolution method

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