BARIUM NITRIDE

Description

Barium nitride purportedly has the molecular formula of Ba3N2 and the molecular weight of 439.9944 g/mol. Its CAS number is 12047-79-9. It is offered for sale by several reputable manufacturers but the actual composition and identity may not coincide with the formula presented. Although Mg, Ca (and to some extent Sr) forms a number of compounds based upon the general formula M3N2, there is no report in the literature that or Ba forms such compositions. The literature is devoid of any data relating to Ba3N2 and the subnitride is mentioned only in the presence of Sr2N.
Barium nitride has been reported to be metastable and sublimes in the 915 to 1050 C temperature range. The reported equation for this behavior is: log P = 6.38 × 10⁴/T(K) and it decomposes when heated beyond this range to form the metal and nitrogen gas, i.e. it is metastable. Thus, the existence of barium nitride is doubtful and no report of its formation or properties exists to date.

Chemical Properties

yellowish brown; -20 mesh, 99.7% purity [CER91] [CIC73]

Physical properties

Barium–nitride–hydride is one of the fewdocumented H^--ionic conductors. It crystallizes in the a-NaFeO2 structure (space group R_m) with distorted Ba-octahedra centered alternately by H^- and N^3-. Neutron diffraction shows that the hydrogen ions are distributed independent of temperature over lattice sites: 85% on (3a) and 15% on (6c). At T > 525 K a sharp increase of the ionic conductivity can be observed. The diffusion process takes place by uncorrelated jumps of hydrogen ions between regular lattice sites. Using quasielastic neutron scattering techniques and a planar jump diffusion model, we were able to determine the mean residence time on a H^--site to be s = 20 ± 2d ps and the diffusion constant D to be 2.1×10^-5 cm²/s at T = 823 K.
Ba2Nhas been used to produce other subnitrides. Bulk thermal or filament-initiated reactions of mixed powders of transition metal chlorides and Ba3N2 produces transition metal nitrides (TiN, ZrN, HfN, VN, V2N) in good yield. The products were characterized by X-ray powder diffraction, SEM/EDAX, FT-IR, microelemental analysis and imaging XPS. The effect of diluting the reaction by the addition of LiCl was used to lower reaction temperatures and in the case of WCI4 and Li3N produced WN. Reaction propagation was investigated by using various mixtures of nitriding reagent (Li3N, Mg3N2, Ca3N2), this was correlated with T_ad(s), the maximum adiabatic combustion temperature for salt formation only.

Uses

Barium nitride is a ceramic that finds use as a dopant in optical materials such as white emitting LEDs. Ba₃N₂ is also used as a synthetic precursor for ternary metal nitrides and as a flux growth medium for GaN.

Safety Profile

A poison by ingestion. Flammableby spontaneous chemical reaction with water to liberateexplosive ammonia gas. Dangerous; explodes uponheating and by spontaneous chemical reaction, liberatingNH3 vapor which can form explosive mixtures with air.Violent

Synthesis

3 Ba + N2 = Ba3N2
The nitriding temperatures for Ba is and 560°C. To achieve complete conversion to the nitride, the heating must be continued for a long time or the temperature must be raised to 700-750°C on cessation of absorption of N2 .