Calorimetrically measured enthalpies for the reaction of Hf with H(D){sub 2} (g)

Journal Article · Wed Dec 01 04:00:00 EST 1993 · Metallurgical Transactions, A

DOI:https://doi.org/10.1007/BF02659486· OSTI ID:142314

Luo, W ^[1]; Flanagan, T B; Clewley, J D ^[2]; Dantzer, P ^[3]

---

1. Univ. of Vermont, Burlington, VT (United States). Dept. of Chemistry
2. Univ. of Vermont, Burlington, VT (United States)
3. CNRS-URA, Orsay (France)

The enthalpy for the direct reaction of H{sub 2} (g) with Hf has been measured by calorimetry for the first time at both moderate, 334 K, and elevated, 919 K, temperatures. The enthalpy for the reaction: 1/2 H{sub 2} (g) + 1(b{minus}a)HfH{sub a}({alpha}) {r_arrow} 1/(b{minus}a)HfH{sub b}({delta}) is {minus}70 {+-} 2.0 kJ/mol H at 334 K over a range of H contents from (H/Hf) = 0.5 to 1.5 with similar values found for D. The quantities {alpha} and {delta} are the coexisting phases and a and b are the corresponding (H/Hf) ratios, respectively. The magnitude of the enthalpy decreases from (H/Hf) = 0 to 0.5 and is then stable from 0.5 to 1.7. The value of {Delta}H{degree}{sub f} (HfH{sub 1.5}) = {minus}107.5 kJ/mol and {Delta}H{degree}{sub f} (HfH{sub 2.0}) = {minus}142.0 kJ/mol. In the elevated temperature range, calorimetric and equilibrium hydrogen pressure were determined over the range of H contents from 0 to 1.6. The enthalpy for the plateau reaction is {minus}74.5 kJ/mol H and after the two-phase region, {vert_bar}{Delta}H{sub H}{vert_bar} increases with the increase of (H/Hf) passing through a maximum at about (H/Hf) = 1.3.

• Sponsoring Organization: USDOE
• OSTI ID: 142314
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 12 Vol. 24A; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
DEUTERIUM
HAFNIUM
HAFNIUM HYDRIDES
HYDRIDATION
HYDROGEN
PHASE TRANSFORMATIONS
REACTION HEAT