Decomposition Of Titanium Hydride Research Articles

The bioactivity of titanium-cuttlefish bone-derived hydroxyapatite composites sintered at low temperature

ABSTRACT The most limiting features of titanium as a bone substituent are lack of bioactivity and high Young’s modulus. We have prepared titanium-hydroxyapatite (Ti-HAp) composites using titanium hydride as sintering agent to provide titanium sintering at lower temperature and preserve the stability of apatite phase. After low temperature sintering, no hydroxyapatite decomposition was detected. Pure titanium samples sintered in the presence of hydride showed smooth surface indicating good densification at 800°C. Higher HAp content resulted in decreased density and higher porosity due to the formation of micro- and macro-pores caused by the integration of HAp particles into titanium matrix and titanium hydride decomposition. However, Vickers microhardness test showed increased hardness for Ti-HAp composite with 10% of HAp regarding pure Ti. The bioactivity of Ti-HAp composites evaluated in simulated body fluid significantly improved with HAp content. The presence of HAp has lowered the cytotoxic effect of Ti-based composites on Hek293 cells.

Beta Titanium Alloys Produced from Titanium Hydride: Effect of Alloying Elements on Titanium Hydride Decomposition

The use of titanium hydride as a raw material has been an attractive alternative for the production of titanium components produced by powder metallurgy, due to increased densification of Ti compacts, greater control of contamination and cost reduction of the raw materials. However, a significant amount of hydrogen that often remains on the samples could generate degradation of the mechanical properties. Therefore, understanding decomposition mechanisms is essential to promote the components’ long life. Several studies on titanium hydride (TiH2) decomposition have been developed; nevertheless, few studies focus on the effect of the alloying elements on the dehydrogenation process. In this work, the effects of the addition of different amounts of Fe (5 and 7 wt. %) and Nb (12, 25, and 40 wt. %) as alloying elements were evaluated in detail. Results suggest that α→β transformation of Ti occurs below 800 °C; β phase can be observed at lower temperature than the expected according to the phase diagram. It was found that β phase transformation could take place during the intermediate stage of dehydrogenation. A mechanism was proposed for the effect of allying elements on the dehydrogenation process.

The role of surface coarsening and sintering during thermal decomposition of titanium hydride

Temperature programmed desorption - mass spectrometry was utilized to study the non-isothermal hydrogen desorption from as-received and pre-oxidized TiH2 powder samples. Above the temperature of 750 °C, hydrogen desorption from the thermally decomposed as-received powder is kinetically delayed compared to that from the pre-oxidized samples. The scanning electron microscopy observations suggest that the delay stems from simultaneous surface coarsening and particles sintering that occur predominantly in the as-received powder at lower temperatures. It is also suggested that the difference in morphology evolution of the as-received and pre-oxidized powders originates from the dependence of Ti diffusion on the concentration of oxygen dissolved in Ti, since the oxide layer itself was found to dissociate at lower temperatures (∼500 °C).

Effect of hydrogen content on hydrogen desorption kinetics of titanium hydride

Abstract Thermal desorption behaviours of titanium hydride powders with different hydrogen contents were studied using simultaneous TG-TDS measurements at a heating rate of 10 °C/min. The as-received TiH 2 powders were pre-heated to different temperatures and subsequently cooled to room temperature in argon. The XPS depth profile analysis demonstrated that after heat treatments, the relative oxygen concentrations decreased slightly compared with that of as-received TiH 2 powder. The changes in the TDS spectra for the pre-heat treated TiH 2 powders were primarily associated with the residual hydrogen contents. The origins of the observed TDS peaks and shoulders were attributed to the equilibrium hydrogen pressures of the phase regions that the decomposition reaction passed through. The hydrogen content was demonstrated to be essential for the phase transformation sequence during titanium hydride decomposition.

Fabrication of Aluminum Foams with Small Pore Size by Melt Foaming Method

This article introduces an improvement to the fabrication of aluminum foams with small pore size by melt foaming method. Before added to the melt, the foaming agent (titanium hydride) was pretreated in two steps. It firstly went through the traditional pre-oxidation treatment, which delayed the decomposition of titanium hydride and made sure the dispersion stage was controllable. Then such pre-oxidized titanium hydride powder was mixed with copper powder in a planetary ball mill. This treatment can not only increase the number of foaming agent particles and make them easier to disperse in the melt, which helps to increase the number of pores, but also reduce the amount of hydrogen released in the foaming stage. Therefore, the pore size could be decreased. Using such a ball-milled foaming agent in melt foaming method, aluminum foams with small pore size (average size of 1.6 mm) were successfully fabricated.

Application of metal hydrides as pore-forming agents for obtaining metal foams

One of the well-known ways of metal foam production consists of adding powder which releases gaseous decomposition product at high temperatures into a melted metal. When producing aluminum foams, titanium hydride powder is most frequently used, while its main disadvantage is its insufficient thermal stability. This results in a premature gas loss in the process of the powder introduction into a melted metal matrix. The paper discloses approaches to suppression of the undesirable premature titanium hydride decomposition by means of its preliminary thermal treatment, as well as the external pressure elevation over that of the system being processed during the foam formation. A method of using the thermally treated powder is proposed, in order to obtain aluminum foam samples having a required geometry and sufficiently uniform porous structure.

Effect of Decomposition Kinetics of Titanium Hydride on the Al Alloy Melt Foaming Process

The gas released from the titanium hydride decomposition is one of the key factors to influence the Al alloy melt foaming process. In this study, a set of decomposition kinetic equations of titanium hydride was acquired by separating its temperature programmed decomposition (TPD) spectrum, which was acquired by a special designed TPD apparatus with argon used as carrier gas and thermal conductivity cell as the detector. According to these equations, the decomposition and hydrogen release characteristics of titanium hydride at a fixed/elevated temperature are described quantitatively, which can be applied to forecast the Al alloy melt foaming process and furnish the theoretical basis for fabrication of three-dimensional complex shaped Al alloy foam.

A model for the decomposition of titanium hydride and magnesium hydride

This work presents a theoretical model of metal hydride particle decomposition with particular relation to titanium hydride and magnesium hydride. The model is based on the shrinking core approach, revealing the variation of major parameters such as temperature and hydrogen fraction with time. An experimental effort aimed at examining the theoretical model includes TGA–DTA tests of hydride particle decomposition in argon atmosphere. The model predictions reveal good agreement with the experiments.

Dynamic Collapse Mechanisms in Metal Foam Expansion

The study provides insight into decomposition of titanium hydride as foaming agent for powder metallurgically produced aluminum foams. Decomposition is characterized using thermal and kinetic analysis, allowing prediction of decomposition reactions. Such predictions are made for various time-temperature cycles, which are experimentally evaluated in parallel foaming experiments. A new explanation of foam collapse is derived from the results, which interprets hints at a maximum gas release rate, limiting maximum expansion, in terms of the existence of a maximum cell wall stretching rate and expanding foam can sustain. Thus a dynamic collapse criterion is added to existing static ones.

Fabrication of lotus-type porous copper through thermal decomposition of titanium hydride

Lotus-type porous copper was fabricated by unidirectional solidification through thermal decomposition of titanium hydride. Effects of additive method and additive amount of titanium hydride on pore formation were investigated. The porosity of lotus copper depends on additive method and additive amount of titanium hydride. The pore formation effectively occurs in the method that titanium hydride decomposes in molten copper. For all the additive methods of titanium hydride, the porosity increases and pore diameter does not change with increasing additive amount of titanium hydride. While, for adding large amount of titanium hydride, the porosity became constant. This is because hydrogen solubility in liquid phase does not change owing to bubbling of hydrogen gas.

Fabrication of Porous Copper with Directional Pores through Thermal Decomposition of Compounds

Lotus-type porous copper with aligned long cylindrical pores was fabricated by unidirectional solidification in an argon atmosphere. The hydrogen dissolved in molten copper through thermal decomposition of titanium hydride contained in the mold, which then formed hydrogen gas that evolved into the gas pores in the solidified copper. On the other hand, titanium may form oxides in the melt that serve as nucleation sites for insoluble hydrogen. The porosity and pore size decreased with increasing atmospheric argon pressure during the solidification, which can be explained by the Boyle–Charles law and the possible suppression of the decomposition due to external pressure. The addition of titanium hydride was more effective when it was added just before the melt solidified than when it was added to the melt. Moreover, the thermal decomposition method (TDM) is superior to the conventional fabrication method, which requires high pressure hydrogen gas. Thus, TDM is a promising fabrication technique for various lotus metals.

Manufacturing challenges in obtaining tailor-made closed-cell structures in metallic foams

The evolution of closed-cell aluminum foam synthesized by titanium hydride decomposition is explained on the basis of foam stability and gravity-induced drainage of liquid. While the average pore size progressively increases due to TiH2 decomposition, the aspect ratio shows a sudden transition during the holding period. The sudden increase in aspect ratio with the major axis transverse to the growth direction is explained on the basis of the loss of elasticity of the cell wall due to drainage and subsequent cell wall collapse due to the weight of the overlying foam. Intermetallic particles with a high aspect ratio distributed in the cell wall matrix significantly improve the stability of the liquid foam. It is demonstrated that by varying a single process parameter, such as the holding time, foams with a wide range of structural parameters are accessed. The Gibson and Ashby model showed good correlation with the plateau stress and Young’s modulus results presented in this work.

The two steps thermal decomposition of titanium hydride and two steps foaming of Al alloy

Two steps foaming (TSF) technique was proposed to prepare shaped Al alloy foam. Based on the thermal decomposition kinetics equation of titanium hydride, the relationship between two steps thermal decomposition kinetics of titanium hydride and two steps foaming Al alloy melt was studied. Two steps thermal decomposition curve of titanium hydride under increasing and constant temperature was calculated respectively. The hydrogen mass needed in the second foaming step was also calculated. Results showed that the hydrogen mass of the second thermal decomposition of titanium hydride is enough for the second foaming step in the condition of as-received Al melt foaming. Experimental and theoretical results indicate that two steps foaming technique can be used to prepare Al alloy foam with high porosity, shaped components and sandwich with Al alloy foam core.

Tailoring Titanium Hydride Decomposition Kinetics by Annealing in Various Atmospheres

With series production of aluminium foams according to the Fraunhofer process a reality, further improvement of structural homogeneity has gained interest. Since this characteristic is strongly influenced by blowing agent decomposition, means to adapt the latter have been investigated: The paper concentrates on thermal treatment of TiH2, comparing effects induced by treatment time, temperature and atmosphere variation. Structural characteristics of AlSi7 foams using TiH2 variants as foaming agent are evaluated.

Synthesis of a low-density Ti–Mg–Si alloy

A low-density titanium alloy was synthesized from blended elemental powders of TiH 2 , Mg, and Si by mechanical alloying and/or heat treatment. The titanium hydride was used in place of titanium. Phase transformations occurring in the system during heating at a constant rate were studied with the use of DTA and XRD. During heating of the blended elemental powders decomposition of titanium hydride occurred in the temperature range 550–750°C and some silicon went into solid solution in titanium while the majority of the silicon reacted exothermically with magnesium at about 500°C producing an intermetallic phase Mg 2 Si. This phase was stable on heating up to 950°C, where a eutectic component of this phase began to melt leading to formation of a liquid solution of magnesium in silicon, followed by a reaction of the liquid silicon with titanium and formation of a Ti 5 Si 3 phase. A third reaction in the system was detected at about 1100°C due to formation of MgO, so that after annealing at 1150°C three stable phases, Ti(Si), Ti 5 Si 3 , and MgO, were present in the alloy. No decomposition of the Ti 5 Si 3 phase or formation of Mg 2 Si were detected either during subsequent cooling or a second heating of the alloy. Completely different kinetics of the phase reactions occurred in the mechanically alloyed powders. Magnesium and silicon dissolved in the titanium hydride during mechanical alloying. Decomposition of the titanium hydride occurred at 320–600°C, the Mg 2 Si phase was formed after heating to 450°C, and the Ti 5 Si 3 phase was detected after heating to 570°C. The Mg 2 Si decomposed completely at a temperature of 650°C with the formation of MgO and Ti 5 Si 3 . After heating to 1150°C, three stable phases, TiN 0.3 , Ti 5 Si 3 , and MgO, were present in the alloy. A discussion of the results is given.

Use of titanium hydride for the synthesis of titanium aluminides from powder materials

Titanium aluminides Ti3Al and TiAl were synthesized by the use of TiH2+Al powder mixtures. Phase transformations occurring upon the decomposition of titanium hydride in vacuum and inert gas and synthesis of titanium aluminides were studied. It was shown that the use of titanium hydride instead of titanium in powder mixtures with aluminum results in a significant activation of diffusion processes, and leads to an accelerated production of single-phase titanium aluminides upon isothermal heating. This is attributable to the small particle size of the charge, high density of defects (including those due to hydrogen-phase hardening) in the titanium and aluminum lattices, and possible reduction of Al2O3 films by atomic hydrogen. The type of atmosphere did not noticeably effect the rate of phase formation, however synthesis in vacuum appears to be more practical since hydrogen is completely removed with simultaneous formation of the aluminides. Due to the fact that aluminum reacted completely with titanium in the solid state, final products close to theoretical densities were obtained without the application of high pressure.

The Formation and Decomposition of Titanium Hydride

The Formation and Decomposition of Titanium Hydride

The Formation and Decomposition of Titanium Hydride

The Formation and Decomposition of Titanium Hydride

Hydrogen-induced phase separation in amorphous Cu0.5Ti0.5 alloys. II. Thermal evolution.

The thermal evolution of ${\mathrm{Cu}}_{0.5}$${\mathrm{Ti}}_{0.5}$ amorphous hydrides has been studied by both calorimetry and neutron-diffraction experiments for different hydrogen contents. At high hydrogen contents, real-time neutron experiments performed during heating at a constant rate show that long-range crystallization into copper and titanium hydride takes place at a well-defined temperature, as confirmed by the exothermic peak in calorimetry. The onset of desorption of hydrogen at high temperature leads to the formation of metastable Cu-rich and then stable \ensuremath{\gamma}-CuTi phases. At smaller hydrogen contents, the evolution is much more gradual. Cu and ${\mathrm{TiH}}_{\mathrm{x}}$ diffraction lines progressively appear in the diffraction pattern. In the meantime the small-angle maximum shifts towards the origin. Crystallization into \ensuremath{\gamma}-CuTi proceeds in two stages. In the first one, unusual variation of the lattice parameters is observed, whereas the size of the crystallites is constant. The second one coincides with the decomposition of titanium hydride upon desorption of hydrogen. Such variations are compared to those extracted from small-angle neutron scattering experiments.

Thermal decomposition of titanium hydride and its application to low pressure hydrogen control

Thermal decomposition behavior of titanium hydride (TiH2) powder at temperatures between 250 and 330 °C (523 and 603 K) has been studied from both thermodynamic and kinetic viewpoints. Equilibrium hydrogen pressure measured in a closed system was found to vary from the order of 10−3 to 10−2 Torr (10−1 to 1 Pa) and the enthalpy of formation of titanium hydride in the two phase (α+γ) region was evaluated to be 31 kcal/mol (130 kJ/mol). It has been found that steady state decomposition can be realized also in an open (continuously pumped) system as long as the two phases coexist. Hydrogen pressure at the steady state was in the order from 10−4 to 10−3 Torr (10−2 to 10−1 Pa) and the activation energy for the decomposition was determined to be 29 kcal/mol (122 kJ/mol). In addition, it has been demonstrated that hot titanium hydride can simply be applied to low pressure hydrogen control in vacuum systems.