ИСТИНА

Compressing a solid surrounded with hydrogen to high pressures (in order to increase the chemical potential of the hydrogen) at elevated temperatures (in order to overcome the kinetic barriers for chemical reactions) is an effective means to produce new hydrides (see, e.g., a monograph [1] and our recent paper [2] reporting on the first synthesis of a hydride of graphite). Using a Toroid-type high-pressure chamber with the high pressure cell shown in Fig. 1 makes it possible to produce hydride samples at pressures up to a few GPa and temperatures up to a few hundred degrees Celsius in quantities of dozens mm 3 [3]. Similar cells are used by some other research groups, e.g., by the Japanese group of Prof. Y. Fukai [1,4]. To produce hydrogen inside the cell, the Japanese group mostly use a reaction between NaBH4 and Ca(OH)2, but the products (yet unidentified) of this reaction are likely to be too chemically active, because the fcc high-pressure high-temperature phase produced in their experiments with molybdenum [4] was not a binary Mo-H hydride [3]. For many years, our group has used AlH3 proposed in Ref. [5]. Thermal decomposition of AlH3 produces only Al and pure H2, but the resulting Al particles start absorbing considerable amounts of the liberated hydrogen at P > 5 GPa and T > 350 °C and noticeably react with the Cu capsule at T > 500 °C.The present paper proposes NH3BH3 as the most appropriate material to produce hydrogen in the high pressure cells. If slightly cooled to 10 °C, aminoborane can be storied at ambient pressure for an indefinitely long time. It does not noticeably react with air that permits assembling the high pressure cells in air withou t any precautions. The only products of decomposition of NH3BH3 at low pressures and T≥200 °C are solid BN and H2 gas [6]. Our experiments have shown that it decomposes to BN and H2 gas, too, if heated to 300°C at any pressure from 0.6 to 9 GPa and does not absorb the liberated hydrogen in heating to 900 °C in this pressure interval. The coincidence of the isotherms of hydrogen solubility in rhodium measured using NH3BH3 or AlH3 as the internal hydrogen source (see Fig. 2) demonstrates that the gas evolved from NH3BH3 is practically pure H2 at 600°C. Taking into account that the high pressure cell is only filled with the chemically inert BN, one can expect that no considerable impurity will appear in the H2 gas at much higher temperatures as well.