Hydride formation during cathodicpolarization of Ti—I. Effect of current density on kinetics of growth and composition of hydride

Hydrogen-induced cracking of drip shield

“…Ti + 2H 2 O à TiH 2 + 2OH Ð According to Phillips et al (1972) The composition of this hydride is in the range TiH 1.21 to TiH 1.48 . The amount of hydrogen absorbed could be expressed as a surface layer thickness, and considered as ÒlostÓ wall thickness as one would do for a general corrosion process.…”

Hydride Formation at Cathodic Charging of α-Ti

“…The maximum solubility of hydrogen occupying the tetrahedral holes in hcp α-Ti attains 0.2 wt % at 300 0 C [1 -3] and decreases to 0.001 -0.003 [1,2,4] wt. % at RT.…”

“…However, due to the difference in the lattice volume of both phases [7,9] the stresses have been introduced into the metals [10,11] and into the hydride [4]. Defects formed in Ti at the hydride precipitation provide the trapping sites for the hydrogen atoms [10].…”

“…At exposition of α-Ti to electrolytes, the formation of the continuous hydride layer [2,4,12], the hydride precipitates [2, 13 -15] or the hydrogen dissolution in the metal [10] may occur depending on the solution chemistry and pH, the applied potential, used temperature and time. The hydrogen absorption, and thus the amount of hydride phase increases at increased cathodic polarization [4,16] and time of charging [17].…”

“…The hydrogen absorption, and thus the amount of hydride phase increases at increased cathodic polarization [4,16] and time of charging [17]. In the case of acid solutions, the continuous surface layer of hydride is formed immediately [2,4] at application of cathodic current below 5 mA/cm 2 [4]. Cathodic charging in the near neutral or alkaline electrolytes causes the lower hydrogen absorption and the formation of the needle hydride precipitates [13].…”