A powder for sustained release of a gas including a hydrophilic core, a hydrophobic layer on an outer surface of the hydrophilic core, and particles in contact with the hydrophobic layer. The hydrophobic layer contains an acid releasing agent. The particles contain an anhydrous material capable of binding with water. The core, the particles, and the hydrophobic layer are substantially free of water, and the core is capable of generating and releasing a gas after hydrolysis of the acid releasing agent.
Stephen T. Wellinghoff;Sumner A. Barenberg;Hong Dixon;Joel J. Kampa;