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The influence of structural relaxation on crystal nucleation has been underexplored and remains elusive. This article discusses its possible effect on the nucleation process using a stoichiometric soda-lime-silica (2Na 2 O•CaO•3SiO 2 ) glass as a model system. We show that the relaxation effect is powerful at low temperatures, close and below the glass transition, T g , and leads to a continuous increase in the nucleation rate. At any given temperature, the nucleation rate eventually reaches its ultimate steadystate corresponding to the fully relaxed supercooled liquid (SCL). However, the time to reach the steady-state is two to three orders of magnitude longer than the average relaxation time estimated by the Maxwell relation (shear viscosity / shear modulus).The proposed nucleation mechanism and model, which take relaxation into account, and related experimental results also explain the alleged "breakdown" of CNT at low temperatures reported for various glasses. It confirms a few recent papers that this apparent flaw is merely because most researchers did not prolong nucleation treatments enough to complete the relaxation process to achieve a steady state. Another remarkable result is that the actual maximum nucleation temperature, T max , is significantly lower than the previously reported values. Finally, a comparative analysis of the kinetic coefficient using viscosity versus growth velocity favors the last. These results for this soda-lime-silica glass extend and validate recent findings for lithium disilicate on the significant (but often neglected) effect of relaxation on crystal nucleation.

We collected a plethora of new data to test the hypothesis that the failure of the Classical Nucleation Theory (CNT) below the glass transition range is just an experimental artifact. Since reaching the steady‐state nucleation regime takes a significant time for treatments below the glass transition temperature, data collected in this temperature range tend not to have reached a steady state. Because of this potential problem, we examined the CNT using new experimental data for three stoichiometric silicate glasses: Li2Si2O5, BaSi2O5, and Na4CaSi3O9. We also measured the equilibrium viscosity for the studied glass batches and used it as a proxy for the effective diffusion coefficient. The analysis was conducted by applying a steady‐state criterion and evaluating the error propagation throughout all calculations. Using this rigorous procedure, we have not observed the alleged CNT failure. Our comprehensive results support recent studies questioning this possible CNT failure helping solve a longstanding problem in glass science.

ResumoNeste trabalho foi avaliada a utilização de dregs, um resíduo sólido inorgânico proveniente do processo Kraft, como matéria-prima alternativa em cerâmica vermelha. As matérias-primas foram caracterizadas por fluorescência de raios X, difração de raios X, distribuição de tamanho de partículas, análise térmica diferencial e termogravimétrica. Os corpos de prova com adições de até 40% em massa do resíduo foram conformados por prensagem uniaxial e sinterizados a 850 e 950 °C, sendo então determinadas as seguintes propriedades físico-mecânicas: resistência à flexão, retração linear, absorção de água, porosidade aparente, massa específica aparente e perda ao fogo. Também foi feita análise das fases desenvolvidas durante a sinterização e da microestrutura final por difração de raios X e microscopia eletrônica de varredura, respectivamente. Os resultados mostraram que a incorporação de até 20% em massa de dregs não interferiu na resistência à flexão da massa, sendo possível sua utilização em substituição parcial da argila. Palavras-chave: cerâmica vermelha, resíduos industriais, dregs. AbstractIn this paper the use of dregs, an inorganic solid waste generated by Kraft process, as an alternative raw material in red ceramic was evaluated. The raw materials, dregs and clay, were characterized by X-ray fluorescence, X-ray diffraction, particle size distribution by laser diffraction, differential thermal analysis and thermogravimetry. Formulations with varying dregs content between 0 and 40 wt% were prepared. The plasticity of mixtures was evaluated by Atterberg method. Specimens were obtained by uniaxial pressing and fired at 850 and 950 °C, then the following physicalmechanical properties were determined: flexural strength, firing shrinkage, water absorption, open porosity, bulk density and loss on ignition. Crystalline phases developed during sintering and final microstructure were evaluated by X-ray diffraction and scanning electron microscopy, respectively. The results showed that incorporation of dregs until 20 wt% did not affect flexural strength, being possible its use in partial replacement of clay.

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