Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: BTE-Dan on May 22, 2017, 10:10:52 PM
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I'm trying to derive what the max mass of hydrogen that a Nickel Hydride can hold.
Consider this link: https://en.wikipedia.org/wiki/Nickel_hydride
Wikipedia says: "Hydrogen's content in nickel hydride is up to 0.002% by weight."
But it also says: "Hydrogen to nickel atomic ratios are up to one, with hydrogen occupying an octahedral site."
So with an atomic ratio of one, you would expect:
Ni atomic mass = 58.6934
H atomic mass = 1.00794
Max % mass of H in NiH = 1.00794 / (1.00794+58.6934) x 100 = 1.69%.
But 1.69% is a long way from .002%. Anyone have an explanation?
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Welcome, BTE-Dan!
"Hydrogen to nickel atomic ratios are up to one"
occurs in the paragraph
"high pressure hydrogen gas at 600 MPa. Alternatively [a surface layer] can be produced electrolytically."
So under normal conditions, the answer is
"0.00005% at 25 °C"
which is the kind of figure expected from most normal materials. If 1 mol Ni could absorb 1 mol H, we would all have fuel cell cars already.
By the way, the Wiki article is written by a metallurgist, but he probably forgot to tell that hydrogen as a hardening agent is impractical because it outgasses too easily. At least steel (nickel should be similar) is freed from hydrogen (which embrittles it) by just 10min at 180°C in a kitchen oven.
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Thanks Enthalpy, that all makes sense. Nice analogy about the cars.
Can you say how you arrived at "0.00005% at 25 °C"?
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Wiki.