Molybdenum forms hard, refractory, and chemically inert interstitial compounds with boron, carbon, nitrogen, and silicon upon direct reaction with those elements at high temperatures.
The resulting nitride (TiN), carbide (TiC), and borides (TiB and TiB2) are interstitial compounds that are very stable, hard, and refractory.
Tungsten also forms hard, refractory, and chemically inert interstitial compounds with boron, nitrogen, and silicon upon direct reaction with those elements at high temperatures.
A number of examples of the application of XPS are given for various types of nitride coatings, including interstitial compounds, such as TiN, CrNx, etc., as well as compounds with predominantly covalent bonding, such as AlN, GaN, Si3N4 and CNx.
Chemically, the nonmetals have relatively high ionisation energy and high electronegativity; they usually exist as anions or oxyanions in aqueous solution; generally form ionic or interstitial compounds when mixed with metals, unlike metals which form alloys; and have acidic oxides whereas the common oxides of the metals are basic.
Unlike the interstitial intermetallic hydrides, these compounds release hydrogen through a series of decomposition/recombination reactions e.g.: NaAlH4⇔1/3Na3AlH6+2/3Al+H2⇔NaH+Al+3/2H2.
Metal ions can be implanted into TiN coatings to form ternary metal nitrides, displaced metal nitrides, or interstitial metal-atom inclusion compounds.
A blue emission band at approximately 468 nm was observed in the Zn-Fe-O compound that had interstitial zinc defects [23].
Of course, TM ions may also be at the interstitial site, but the matrix compound, TiO2, has a relatively close-packed structure, and this is not generally favorable for interstitial defects [32].
A number of "RX2" compounds have been reported in the literature for most of the lanthanides, but subsequent investigations have shown these phases were actually ternary compounds stabilized by interstitial impurities, such as hydrogen and carbon.
Adding to the value of identifying "new" substances in the interstitium, e.g., using proteomic approaches, it is also important to quantify known bioactive compounds in the interstitial fluid.
