Comparison of MnO 2 and ZnO Additives on Zircon Decomposition and Formation of Solid Solution
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https://doi.org/10.1007/s11837-020-04331-0 Ó 2020 The Minerals, Metals & Materials Society
PROCESS DESIGN AND MATERIALS DEVELOPMENT FOR HIGH-TEMPERATURE APPLICATIONS
Comparison of MnO2 and ZnO Additives on Zircon Decomposition and Formation of Solid Solution HUDSA MAJIDIAN,1,2 LEILA NIKZAD,1 and MOHAMMAD FARVIZI1 1.—Ceramic Department, Materials 2.—e-mail: [email protected]
and
Energy
Research
Center,
Alborz,
Iran.
In this paper, the effects of MnO2 and ZnO additives on zircon decomposition were investigated. The substitution of Mn and Zn into zircon lattices and the formation of solid solutions are discussed. The additives were added at 0– 4 wt.% to zircon. The phase composition, physical properties, and microstructural changes for the sintered samples were characterized. Results of Rietveld refinement analysis showed that 1 wt.% of both additives retarded the decomposition of zircon. Further addition of additives slightly accelerated the zircon decomposition and improved sample densification. X-ray diffraction peaks of zircon were shifted to higher angles by the addition of MnO2, whereas ZnO did not alter zircon peaks. Energy dispersive spectroscopy analysis detected the presence of Mn and Zn in zircon grains. ZnO has a lower solubility than MnO2 in zircon, leading to the formation of a higher fraction of secondary phases, in turn leading to the suppression of grain growth.
INTRODUCTION Zircon (ZrSiO4) is an interesting ceramic material due to its high stability, good corrosion resistance, high melting point, good hardness, low thermal conductivity, and excellent thermal shock resistance. Zircon, as a common refractory material, is widely used for high-temperature applications and industries such as iron and steel production, energy technology, and protective coatings.1–3 The decomposition of zircon at elevated temperatures is one of the most challenging topics in the production of zircon refractories and composites. The decomposition temperature is important for the prediction of lifetimes of zircon and zirconia-based refractories.4 The decomposition temperature of zircon depends on several factors, such as purity and fineness of the zircon.1 This temperature is reported to be about 1673 ± 10°C, which is based on heat treatment experiments conducted on natural and synthetic zircon raw materials with known grain sizes and impurity levels, as well as zircon single crystals.2
(Received January 18, 2020; accepted August 17, 2020)
Zircon decomposition has been investigated to increase the working temperature of zircon refractories. Using zircon for high-temperature applications strongly depends on accurate knowledge about its thermal stability. There are some studies on the thermal stability of zircon without any additives.4–6 However, research is limited regarding the influence of oxides on the decomposition of zircon. Anseau et al.7 measured the degree of zircon decomposition and found that it starts between 1525°C and 1550°C and accelerates at 1650°C. Pavlik et al.8 studied the decomposition of pur
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