Effect of nickel nitrate on phase changes in mullite and mullite ? Corundum refractories when heated in oxidizing and reducing conditions

Pitak, N. V.; Ansimova, T. A.; Gavrish, A. M.; Zoz, E. I.; Karyakin, L. I.

doi:10.1007/bf01284841

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“…In the NiO-A1203 • 2SiO 2 system spinel is formed due to the decomposition of mul]ite under the effect of NiO, which begins at 1000°C [3]. A specimen heated to 1500°C with a 30-min hold is mainly represented by spinel; the amount of mullite and cristobalite is insignificant.…”

Section: Np--t692mentioning

confidence: 99%

Interaction between nickel nitrate and components of mullite-corundum refractories

Pitak

1996

Refractories

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Results of an investigation of the interaction between mullite-containing refractories and nickel nitrate additives under conditions of oxidizing-reducing gas media at 500-1500°C are presented. Mineral-forming processes in firing in a reducing medium and decomposition of newly formed compounds in firing in a medium of hydrogen and carbon oxide are described.Mullite-containing refractories are used in linings of reactors operating under conditions of oxidizing-reducing media. Conversion of natural gas is catalyzed by nickel nitrate Ni(NO3) 2 • 6H20, which reacts with components of the refractory operation. The processes occurring in the refractories under conditions of oxidizing-reducing gas media in contact with nickel nitrate were investigated at temperatures up to 1500°C. At a temperature exceeding 54°C nickel hexahydrate transforms into the tetrahydrate Ni(NO3) 2 -4H20, above 85°C it transforms into the dihydrate Ni(NO3) 2 • 2H20, and at higher temperatures Ni(-NO3): forms, which decomposes with possible formation ofNi304, Ni20 ~, NiO, and NiO2. A stable phase is NiO, which melts at 1960°C [1]. In a hydrogen medium, reduction occurs autocatalytically on the Ni-NiO phase boundary.We used silicic acid as the siliceous component, from which we pressed specimens K-l, K-10, K-25, and K-50 with additions of 1, 10, 25, and 50% nickel nitrate, respectively. The specimens were fired at 500, 900, 1100, 1300, and 1500°C with a 2-h hold in an oxidizing medium. Nickel orthosilicate Ni2SiO 4 is formed in the presence of SiO 2 and NiO. It crystallizes in a rhombic system with lattice parameters a= 0.4705 nm, b = 1.011nm, c=0.5914nm and has an olivine structure. The refractive indices are" Ng = 1.928,

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Section: Np--t692mentioning

confidence: 99%