Dissolution retardation of solid silica during glass-batch melting

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t a r t i c l e i n f o During glass-batch melting, solid silica (quartz) usually dissolves last. The measured rate of dissolution, while the temperature was increasing at a constant rate, was compared with the hypothetical diffusion-controlled volume flux from regularly distributed particles through concentration layers of a uniform thickness. The actual rate was up to two orders of magnitude lower than that of the " ideal " case, revealing a progressive inhibition of silica dissolution. As a measure of this retarded dissolution, we introduced a retardation factor defined as a ratio of the actual and " ideal " dissolution rates measured as the volume flux at the melt-particle interface. The severe inhibition of silica dissolution has been attributed to the irregular spatial distribution of silica particles that is associated with the formation of nearly saturated melt on a portion of their surfaces. Irregular shapes and unequal sizes of particles also contribute to their extended lifetime. Reactions between quartz particles and the other glass-batch components have been studied by numerous researchers [1]. By definition, the batch-to-glass conversion process ends when the residual quartz particles (from quartz sand or crushed crystals) dissolve in the glass-forming melt via multicomponent diffusion of silica against the remaining glass components. The first steps toward understanding the diffusion-controlled dissolution of quartz particles were to solve the pertinent field equations for a single spherical particle in a quiescent melt while ignoring the effects of gravity [2–5]. Using a boundary-layer approach, Levich [6] obtained an analytical solution for a particle moving by buoyancy. The dissolution of multiple particles was described for stirred liquids [7,8] and later adapted to the case of sand grains in molten glass when the silica concentration in the melt was close to the solubility limit [9]. These developments assumed a constant temperature during the particle lifetime. In reality, the batch contains multiple particles randomly distributed in space that react and dissolve while the temperature is increasing. Moreover, the particle sizes are distributed within a certain range, the particle shapes are non-spherical, and their surfaces can be rough. Also, the melt is moving, driven …