Solubility of Hydrogen in Titanium Alloys. II. Blocking Models and Hole Size Considerations

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Assuming a geometrical model with mutual (H‐H) blocking, for hydrogen dissolved in titanium and titanium alloys experimental data are compared. It is found that interstitial sites with pure titanium coordination only host hydrogen atoms. In alloys with bcc crystal lattices only tetrahedral interstitial sites are occupied, whereas in hep alloys both tetrahedral and octahedral interstitials host hydrogen. A linear relation is found which connects the partial molar absorption enthalpy ΔHOH and the partial molar excess absorption entropy ΔSE, OH at infinite dilution of dissolved hydrogen. The enthalpy of absorption ΔHOH can be rationalized as a function of interstitial hole size and an optimum hole radius of 47 pm is found for titanium and titanium alloys.

Solubility of Hydrogen in Titanium Alloys. II. Blocking Models and Hole Size Considerations

Mrowietz

Weiß

1985

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¹H NMR studies of the system Ti₃SbH_x

Rajalakshmi

Rao

Weiß

1989

Proton magnetic resonance measurements were carried out on hydrogenated samples Ti3SbHx, at different hydrogen concentrations in the range 0.3 ≤ x ≤ 1.74. From a comparison of the experimental second moment of the 1H NMR line with the calculated one it was inferred that hydrogen occupies the tetrahedral interstitial sites surrounded by Ti atoms in the Ti3Sb lattice. The influence of temperature in the range 100 ≤ T/K ≤ 300 on the 1H NMR in some of the hydrides showed the occurrence of motional narrowing from which the correlation frequency (vc), activation energy (Ea) and diffusion coefficient (D) were evaluated as 104 Hz, 0.10 eV, and 10−12 cm2/s, respectively. It was found that the hydrogen diffusion is easier in the Ti3Sb lattice compared to other Ti based alloys.

A Comparative Study of the Solubility and Thermodynamics of Hydrogen in Pd_1‐xRE_x (RE = Dy, Gd, Sm, and Y; x = 0.05 and 0.08) Solid Solution Alloys

Ramaprabhu¹,

Rajalakshmi²,

Weiß³

1989

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Pressure‐composition‐temperature absorption isotherms have been determined for the Pd1‐xREx (RE = Dy, Gd, Sm, and Y; x = 0.05 and 0.08) solid solution face centered cubic alloys in the pressure and temperature ranges 2 ≦ P(H2)/mbar ≦ 1000 and 473 ≦ T/K ≦ 873 using the manometric method. The partial molar enthalpy of solution of hydrogen at infinite dilution (ΔH̄0H) becomes more exothermic with increasing content of RE. The partial molar excess entropy of hydrogen solution at infinite dilution (ΔS̄E.0H) decreases with xRE. A correlation of the atomic diameter (dRE) of the substituting rare‐earth metals when in solution in palladium with ΔH̄0H and with the metal‐hydrogen interaction shows that the increase in the exothermicity of the Pd1‐xREx solid solution alloys is due to the lattice expansion and an attractive metal‐hydrogen interaction. From the correlation of ΔH̄0H with dRE of Pd1‐xREx (x = 0.05 and 0.075), ΔH̄0H of Pd1‐xREx (RE = Yb, Ho, and Eu; x = 0.05 and 0.075) solid solution alloys have been predicted. The dependence of ΔH̄0H of the “expanded” and “contracted” Pd1‐xMx alloys on the size of the octahedral interstitial hole sites (rh) occupied by hydrogen atoms is discussed.