The Depolymerization of Silica in Sodium Hydroxide Solutions

Greenberg, S. A.

doi:10.1021/j150553a027

Cited by 70 publications

(37 citation statements)

References 2 publications

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“…This shows how the nature of the metal cation could have played a significant role in the diffusion of the hydroxide ions through the solution, which consequently had an effect on the dissolution rate of the glass fibres. Overall, the activation energies obtained from the reaction of glass fibre with KOH and NaOH solutions are similar to those reported in previous studies [22,28,31], although the value of 28 kJ/mol for the reaction of diatomite with NaOH is lower [29], and 159 kJ/mol, given by Molchanov and Prikhidko [18] for the dissolution of quartz glass in NaOH solution, is significantly high; this comes as no surprise given that quartz is a crystalline form of silica and is therefore more stable towards hydroxide attack.…”

Section: Determination Of Reaction Order and Activation Energysupporting

confidence: 88%

“…It is apparent that the activation energies are similar when rate constants are used from both models. The values are comparable with those in the literature concerning the reaction of bulk silicate glass or powder with alkaline solution [22,28,31]. Figure 12 Plot to determine activation energy for glass fibre reaction with KOH through curve fitting.…”

Section: Determination Of Reaction Order and Activation Energysupporting

confidence: 82%

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Kinetics of dissolution of glass fibre in hot alkaline solution

et al. 2017

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Kinetics of the dissolution of E-glass fibres in alkaline solutions was investigated. To allow an accurate determination of conversion, glass fibres were immersed individually in the corrosive medium and the diameter change was measured with the use of a scanning electron microscope. Few studies have been reported in the literature on the kinetics of E-glass fibre dissolution or the dissolution of individual fibres. Our experimental results fit well in the zeroorder and shrinking cylinder models, suggesting either the diffusion of hydroxide ions through the solution or the glass fibre etching itself was ratelimiting step. The rate constant for the reaction of glass fibre with alkaline solution at 95°C was found to be between 1.3 9 10 -4 and 4.3 9 10 -4 g/(m 2 s).The reaction order (n) was determined as 0.31-0.49 with respect to the alkaline solution, and the activation energy was 58-79 kJ/mol.

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Section: Determination Of Reaction Order and Activation Energysupporting

confidence: 88%

Section: Determination Of Reaction Order and Activation Energysupporting

confidence: 82%

Kinetics of dissolution of glass fibre in hot alkaline solution

et al. 2017

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“…XRD data has shown that a small amount of cristoballite is present in the sample 950°C which would confer greater resistance to attac k by alkaline solution. The effect of surface area and silica structure in this paper is in agreement with published literature using porous amorphous silicas [21].…”

Section: Silica Dissolutionsupporting

confidence: 91%

Valorisation of rice husks using a TORBED® combustion process

Blissett¹,

Sommerville

Rowson

et al. 2017

Fuel Processing Technology

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World production of rice exceeds 750 million tonnes per year of which a fifth is removed in the form of rice husk during the milling process. The use of rice husks as a source of sustainable and renewable energy is often hindered by lack of capital and a poor understanding of rice husk combustion characteristics. This results in the selection of poor quality technology which generates significant quantities of harmful crystalline silica waste. Despite previous work in the area, detailed characterisation of the combustion of rice husk ash in a TORBED reactor across a wide temperature range has not yet been attempted and little effort has been directed towards assessing the economic viability of generating quality rice husk ashes. The use of a TORBED reactor enables low residual carbon after combustion without the generation of harmful crystalline material. Rice husk was combusted in a 400mm reactor at temperatures between 700-950°C. In the subsequent characterisation studies the resulting materials were shown to be fully amorphous high purity silica (> 95%) and were readily digested in a series of alkaline digestion experiments. Complete silica conversion was only possible using uneconomic Na2O/SiO2 ratios and further optimisation of the combustion process to generate higher surface area material is necessary to increase the digestion rates further. Provisional economic analysis suggests that sales of the by-product enhance the returns from rice husk based power generation. TORBED reactors enable the combustion of rice husk with considerable operating flexibility and they generate products that could be used to displace resource intensive products and processes thus, added value from the by-products can be obtained by using TORBED reactor technology.

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“…At this time, no definitive explana- tions can be offered for these trends. However, it is not unreasonable to expect that, as in the case of silica formation in homogeneous alcohol-alkoxide systems (31,(41)(42)(43)(44)(45), the observed particle size dependence on ammonia concentration may be related to the ability of the OH Ϫ ion (generated by the hydrolysis of ammonia) to catalyze both hydrolysis and condensation reactions and the tendency for siloxane bonds to break in highly alkaline solutions (32,35,39).…”

Section: Amphiphilic Nature Of Partially Hydrolyzed Teosmentioning

confidence: 99%

“…The subsequent increase in the number of nuclei leads to smaller particles. The increase in particle size at relatively high ammonia concentrations may be due to the base-catalyzed depolymerization (32,35,39) which decreases the number of stable nuclei.…”

Section: Amphiphilic Nature Of Partially Hydrolyzed Teosmentioning

confidence: 99%