| http://www.w3.org/ns/prov#value | - M1 are identical or different and are a metal of the group IVb, Vb or VIb of the Periodic Table, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten, preferably zirconium, hafnium and titanium.
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