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The binary phase diagram NaBO 2-H 2 O at ambient pressure, which defines the different phase equilibria that could be formed between borates, end-products of NaBH 4 hydrolysis, has been reviewed. Five different solid borates phases have been identified: NaBO 2 •4H 2 O (Na[B(OH) 4 ]•2H 2 O), NaBO 2 •2H 2 O (Na[B(OH) 4 ]), NaBO 2 •2/3H 2 O (Na 3 [B 3 O 4 (OH) 4 ]), NaBO 2 •1/3H 2 O (Na 3 [B 3 O 5 (OH) 2 ]) and NaBO 2 (Na 3 [B 3 O 6 ]), and their thermal stabilities have been studied. The boundaries of the different Liquid+Solid equilibria for the temperature range from-10 to 80 °C have been determined, confirming literature data at low temperature (20 °C ~ 50 °C). Moreover the following eutectic transformation, Liq. → Ice + NaBO 2 •4H 2 O, occurring at-7 °C, has been determined by DSC. The Liquid-Vapour domain has been studied by ebullioscopy. The invariant transformation Liq. → Vap. + NaBO 2 •2/3H 2 O has been estimated at 131.6 °C. This knowledge is paramount in the field of hydrogen storage through NaBH 4 hydrolysis, in which borate compounds were obtained as hydrolysis reaction products. As a consequence, the authors propose a comparison with previous NaBO 2-H 2 O binary phase diagrams and its consequence related to hydrogen storage through NaBH 4 hydrolysis.

Potassium borohydride KBH4 is an attractive chemical hydride for H2 generation and storage in portable fuel cell applications. Nevertheless, the control of the by-products, in terms of stability and solubility in aqueous solutions, is one of the limiting steps of the hydrolysis reaction of H2 release. We report here some physicochemical properties of concentrated KBO2 aqueous solutions: solubility and gravimetric density are measured as function of temperature between 10 to 80°C. The stability of hydrated metaborates KBO2.xH2O solid phases (with x = 4/3 and 4) in alkaline aqueous solutions is also evaluated at 20°C.

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The kinetics of the degradation of N-amino-3-azabicyclo[3,3, Oloctane by chloramine has been studied by GC and HPLC in stoichiometric conditions in a solution buffered with NaOH/KHaP04 and NaaB407.10 H2O between pH = 10.5 and 13.5. The second-order reaction exhibits specific acid catalysis which indicates competitive oxidation between the haloamine and the neutral and ionic forms of the bicyclic hydrazine. The enthalpy and entropy of activation were determined a t pH = 12.89.In a nonbuffered solution, the interaction is autocatalyzed due to acidification of the mixture by the ammonium ions. In basic medium, the reaction forms a n endocyclic hydrazone. A mathematical treatment based on an implicit equation allows a quantitative interpretation of all the phenomena observed over the above pH interval. This takes both the acid/base dissociation equilibria and the alkaline hydrolysis of the chloro-derivative into account. 0 1995 John Wiley & Sons, Ine.

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