The Effects of lithium hydroxide solution on alkali silica reaction gels created with opal

The reaction of Nevada opal with calcium hydroxide, potassium and lithium hydroxide solutions was investigated. In addition opal was exposed to a combined solution of these three hydroxides. The progress of the three reactions was followed using X-ray Diffraction (XRD), 29 Si Nuclear Magnetic Resonance (NMR) and Scanning Electron Microscopy (SEM). The XRD results indicated the presence of a low angle peak exclusive to the lithium-based reactions. The NMR results suggested a change in the silicate structure in the presence of lithium. These techniques indicated that the reaction of the alkali with the opal starting material is inhibited, and perhaps stopped in the presence of lithium hydroxides. SEM revealed that the morphology of the reaction products on the surface of the reacted opal grains is markedly different in all cases. It was concluded that evidence to support the theory of a protective layer exists and that the nature of the layer varies with ion type.