Journal of Alloys and Compounds 509 (2011) 128–133 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Hydrogen-sorption and thermodynamic characteristics of mechanically grinded TiH 1.9 as studied using thermal desorption spectroscopy O.G. Ershova, V.D. Dobrovolsky ∗ , Yu.M. Solonin, O.Yu. Khyzhun Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanovsky Street, UA-03142 Kyiv, Ukraine article info Article history: Received 21 July 2010 Received in revised form 31 August 2010 Accepted 2 September 2010 Available online 15 September 2010 Keywords: Titanium hydride TiH2 Thermal stability Mechanical milling Thermal desorption spectroscopy Scanning electron microscopy abstract Isobaric thermal desorption spectroscopy and X-ray diffraction analysis were used to study the inﬂuence of mechanical dispersion during high-energy milling -TiH 1.9 hydride upon its hydrogen-sorption char- acteristics, temperature and enthalpy of the  →  (TiH 1.9 → Ti[H]  ) phase transition at isobaric heating the sample under hydrogen atmosphere with speed 3 ◦ /min. Isobars of hydrogen thermal desorption in the regions of the  and  phases of the Ti–H 2 system at pressures of 0.1, 0.25, 0.315 and 0.45 MPa of hydrogen in the reactor have been derived. Experimental data obtained for initial titanium hydride and mechanically grinded for 20 min in a planetary ball mill have been used for construction of Van’t Hoff plots and for determination of enthalpy of formation of -hydride from solid solution of hydrogen in bcc titanium. Our experimental data reveal that 20 min high-energy inﬂuence on titanium hydride powder leads to increasing the speciﬁc surface of the samples from 0.13 to 8.58 m 2 /g and to signiﬁcant (more than 250 ◦ ) decreasing the temperature of the beginning of hydrogen release when heating the sample (i.e., to a decrease of thermal stability of mechanically activated TiH 1.9 ). However, mechanical dispersion does not change the temperature of the  →  phase transition. It has been established that high-energy milling TiH 1.9 powder causes the effect of a decrease of enthalpy of the formation of -hydride from 248 kJ/mole H 2 to 175 kJ/mole H 2 . © 2010 Elsevier B.V. All rights reserved. 1. Introduction Processes taking place during mechanical treatment (signiﬁcant dispersion and decreasing metallic powder particles, formation of new surfaces and accumulation of a great amount of different defects) can cause beginnings of excess energy and entropy and, as a consequent, a shift of phase equilibrium [1]. The inﬂuence of dispersion upon phase equilibrium has been studied in a great number of works; however studies of the inﬂuence of mechani- cal dispersion upon temperature of phase equilibrium in the Ti–H system, mainly upon temperature of decomposition and thermo- dynamic characteristics of TiH 2 hydride, in spite of wide practical applications of this hydride, are scarce. The necessity of studies of this inﬂuence is stressed in a number of works [2–8], where the mechanochemical method was adopted. In these works, it has been established that mechanical dispersion and alloying can change and increase hydrogen-sorption and kinetic characteristics of hydride phases, as well as can change and manage thermodynamic prop- erties of mechanical alloys [9,10] varying treatment conditions and a chemical content of components of a mixture treated. The ∗ Corresponding author. Tel.: +380 44 390 11 23; fax: +380 44 424 21 31. E-mail address: dobersh@ipms.kiev.ua (V.D. Dobrovolsky). mechanochemical method allows to change thermal stability of a hydride phase, to decrease/increase temperature of its decom- position or a phase transition, to expand signiﬁcantly a region of the -solid solution or to constrict a two-phase region, to change equilibrium pressure, etc. [11–15]. Zhang and Kisi [16] have adopted the gravimetric method to study a thermal decomposition of nanocrystalline titanium dihy- dride synthesized by reactive mechanical alloying (RMA) under hydrogen atmosphere and, for comparison, of commercial TiH 2 . The authors [16] have stressed different behavior of the above hydrides during their heating. Additionally, it has been established that nanocrystalline TiH 2 synthesized by the RMA method starts and completes to decompose at much more lower temperatures and dehydriding process occurs within signiﬁcantly narrower tem- perature region as compared with TiH 2 synthesized by traditional methods [16]. Extremely small sizes of particles, high speciﬁc sur- face as well as a great number of defects arising during the milling of TiH 2 powder synthesized by the RMA method are considered to be responsible for different dehydriding behaviors of the two titanium dihydrides studied in Ref. [16]. The inﬂuence of powder sizes upon dehydriding 40 m com- mercial TiH 2 undergone a high-energy mechanical treatment with different prolongation for obtaining titanium dihydride powder with different particle sizes has been studied in Ref. [17] employing 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.09.003