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Major Melt—Crucible Systems
Published in Nagaiyar Krishnamurthy, Metal–Crucible Interactions, 2023
One remedy suggested to diminish bath penetration through the cathode block to the refractory level is to limit average pore size in carbon cathode blocks to 5–15 μm. Bath penetration is facilitated if the pores in the carbon cathode blocks are above 25–30 μm. With bath components at the doorstep of the refractory layer, Siljan et al. (2002) singled out the silica content of the aluminosilicates as the major handle that can be used to stop the further progress of the reaction. By exposing samples of firebricks to a fluoride melt at 950°C (‘cup test') as well as to sodium vapour at 800°C, Siljan et al. (2002) found that materials high in silica deteriorated less than materials rich in alumina. The reason is that the silica-rich materials formed larger amounts of a viscous glass phase. A fluoride melt, which has penetrated through the carbon cathode, accumulates below the cathode carbon, while sodium aluminosilicate, which is denser than the fluoride, will settle below it and above the refractory lining. The continued contact and further reaction of the fluoride melt with the refractory is retarded by the dense viscous layer of the sodium aluminosilicate-based melt. This has been revealed in autopsies of shut-down cells as well as in laboratory-scale cup tests.
Applications of Nanomaterials in Agriculture and Their Safety Aspect
Published in Devarajan Thangadurai, Saher Islam, Jeyabalan Sangeetha, Natália Cruz-Martins, Biogenic Nanomaterials, 2023
Leo Bey Fen, Ahmad Hazri Abd. Rashid, Nurul Izza Nordin, M.A. Motalib Hossain, Syed Muhammad Kamal Uddin, Mohd. Rafie Johan, Devarajan Thangadurai
In the food sector, engineered nanomaterials (ENMs) are used as food additives to improve food stability during processing and storage, enhance characteristics of product, or increase the efficacy and bioavailability of nutrients in the food. Among ENMs-based food additives, synthetic amorphous silica (SAS) is the most common type. SAS is generally used as clarifying agent for beverages, while as an anti-caking and free-flow agent in several food products in powdered form (E551) (Dekkers et al., 2011). Besides SAS, several formulated anti-caking agents have been utilized in food items, including calcium silicate, dicalcium phosphate, sodium ferrocyanide, sodium aluminosilicate, and microcrystalline cellulose. However, there is a lack of concrete evidence whether such materials are (partly) available at the nanoscale (Peters et al., 2016).
Performance Criteria of Geopolymer as Repair Materials
Published in Ghasan Fahim Huseien, Abdul Rahman Mohd Sam, Mahmood Md. Tahir, Geopolymers as Sustainable Surface Concrete Repair Materials, 2023
Ghasan Fahim Huseien, Abdul Rahman Mohd Sam, Mahmood Md. Tahir
Figure 5.12 illustrates the effect of MK substituted by GBFS on the density of GPMs. The density of GMPs was found to increase with increasing percentage of MK replacement. The particle size and specific gravity of MK was found to influence the GPMs density. An increase in the content of Al2O3 and SiO2 led to produce sodium aluminosilicate hydrate (N-A-S-H) gel beside the calcium–silicate–hydrate (C-S-H) which in turn improved the microstructure of GPMs as evidenced earlier [25].
Iron Extraction from Red Mud using Roasting with Sodium Salt
Published in Mineral Processing and Extractive Metallurgy Review, 2021
Ding Wei, Xiao Jun-Hui, Peng Yang, Shen Si-Yue, Chen Tao
As shown in Figure 11, ΔGθ values of Reactions (2) and (3) are much more negative than those of Reaction (1) at temperature of 1200–1600 K. So, when the temperature was lower than 1200 K, the reaction occurring was mainly a reduction reaction, and the iron oxide was reduced in situ. When the temperature was higher than 1200 K, the reaction was converted into a chlorination reaction, and the ferric chloride diffuses to the carbon surface and was reduced to metallic iron. During the segregation roasting process, Na2SO4 reacts with SiO2 and Al2O3 to form sodium aluminosilicate via Reactions (6). By comparing Reaction (4) with Reactions (5), it can be seen that when Na2SO4 was added, Na2O produced by sodium sulfate in a reducing atmosphere can react with silicate minerals to form low-melting nepheline and exchange with ferrous oxide in silicate minerals. Sodium sulfate plays a catalytic effect on the chlorination-reduction of red mud in the novel process.
Optimization study of sodium hydroxide consumption in the coal demineralization process
Published in Mineral Processing and Extractive Metallurgy Review, 2018
A. Aditya, A. Suresh, S.K. Sriramoju, P.S. Dash, S. Pati, N.P.H. Padmanabhan
The major portion of alumino-silicates in feed coal reacts with NaOH during alkali leaching, which results in the formation of sodium aluminosilicate (sodalite). Subsequently during acid leaching, sodalite dissolves in HCl solution, which results in the reduction of mineral matter or ash content in coal. Dissolution of sodalite in acidic solution results in loss of sodium in the form of sodium chloride. This not only increases the operation cost of the coal demineralization process but also consumes more HCl and contaminates spent acid solution with NaCl. To minimize the loss of sodium (Na), it is required to minimize the formation of sodalite without affecting the percentage demineralization. In this context, the main challenge is to achieve the maximum demineralization with minimum sodalite formation by keeping the dissolved silicate and aluminate ions in the solution itself. These sodium silicate and aluminates can be readily regenerated to sodium hydroxide through an established process if they exist in the spent alkali solution in ionic form.