Impact of Fly Ash as a Raw Material on the Properties of Refractory Forsterite–Spinel Ceramics

Abstract

This article examines the process for the synthesis of forsterite–spinel (2MgO·SiO2/MgO·Al2O3) refractory ceramics from fly ash and alumina as sources of aluminum oxide. Raw materials were milled, mixed in different ratios and sintered at 1500 °C for 2 h. Sintered samples were characterized by XRD, thermal analyses and SEM. Porosity, water absorption, bulk density, refractoriness, refractoriness under load and thermal shock resistance were also investigated. The impact of fly ash as a raw material was investigated in accordance with the resulting properties and microstructure of samples with fly ash and alumina as the raw materials. Due to the positive effect of flux oxides (iron oxides and alkalis) on sintering, the mullite contained in fly ash completely decomposed into silica and alumina, which, together with magnesium oxide, formed spinel. This led to improved microstructural and mechanical properties and thermal shock resistance. In particular, mixtures with 10 wt.% and 20 wt.% of fly ash had the most promising results compared to alumina mixtures. Both modulus of rupture and thermal shock resistance were improved, while the impact on refractory properties was minimal. The novelty of this research lies in the recycling of fly ash, a by-product from coal-burning power plants, into a raw material for the production of forsterite–spinel refractory ceramics.

Corrosion Resistance of Novel Fly Ash-Based Forsterite-Spinel Refractory Ceramics

“…Apparent porosity was higher in fly ash-based mixtures than alumina-based mixtures due to the expansion stage at 1250 • C, which was caused by the reaction of flux oxides and amorphous phase. This phenomenon is described in more detail in [15].…”

“…However, this adverse effect of forsterite ceramics can be reduced by the incorporation of magnesium alumina spinel (MgO•Al 2 O 3 ) directly into the raw material mixtures or indirectly by the addition of aluminum oxide as a raw material and its subsequent synthesis with magnesium oxide for the creation of spinel. Previous authors' studies have explored the feasibility of synthesis of spinel from the addition of raw materials containing aluminum oxide into forsterite mixtures [14,15]. Refractory spinel ceramics are also widely adopted in various fields, predominantly as linings of various industrial kilns and furnaces due to their numerous advantages, i.e., a very high melting point of 2135 • C, a low coefficient of thermal expansion compared to coefficient of forsterite, better thermal shock resistance, and chemical and corrosion resistance [16][17][18][19][20].…”

“…Previous studies have proven that spinel incorporation into forsterite ceramics has been shown to improve physico-mechanical properties such as microstructure, mechanical properties and thermal shock resistance due to the embedment of spinel crystals that are located predominantly near the grain boundaries of larger forsterite crystals or bound in the amorphous matrix and filling the empty sections of cavities and pores in between [14,15,21].…”

Žárovzdorné Vlastnosti a Korozní Odolnost Forsterit-Spinelové Keramiky S Využitím Vysokoteplotního Popílku

“…Předchozí výzkum také prokazuje úspěšné využití popílku jako zdroje oxidu hlinitého pro syntézu forsterit-spinelové keramiky. [11,12]…”

Thermal and Thermomechanical Properties of Refractory Forsterite-Spinel Ceramics

“…The latter was confirmed experimentally by previous research. [6,7] Refractory spinel ceramics are used together with magnesia ceramics as a lining of kilns and furnaces due to its high melting point of 2135°C, low thermal expansion coefficient in comparison with forsterite, good thermal shock resistance and chemical and corrosion resistance. [8][9][10] Addition of spinel into forsterite ceramics lead to improved microstructure, mechanical properties, and thermal shock resistance.…”