How does firing temperature affect the microstructure and properties of anorthite thermal insulation and refractory materials?

How does firing temperature affect the microstructure and properties of anorthite thermal insulation and refractory materials?

This paper aims to explore the influence mechanism of firing temperature on the microstructure and properties of anorthite insulating refractory materials. By analyzing the changes in the microstructure, such as crystal structure and pore characteristics, at different firing temperatures, as well as the corresponding changes in thermal insulation, mechanical, and chemical stability, this paper provides a theoretical basis for rationally controlling the firing temperature to optimize the material’s performance.

Introduction

Anorthite insulating refractory materials play a crucial role in many high-temperature industrial fields. However, their performance is affected by various factors, with firing temperature being one of the most important. Accurately understanding the influence of firing temperature on its microstructure and properties is of great significance for improving material quality and expanding its application range.

Experimental Section

(I) Experimental Materials High-purity anorthite raw materials were selected and pretreated to ensure that their particle size and purity met the experimental requirements.

(II) Experimental Methods Different firing temperature gradients were set, such as 800℃, 1000℃, 1200℃, and 1400℃. Firing was carried out under the same heating rate, holding time, and cooling method. Subsequently, various analytical testing methods were employed, including scanning electron microscopy (SEM) to observe the microstructure, thermal conductivity testing to determine thermal insulation performance, universal testing machine to test mechanical properties, and chemical immersion experiments to assess chemical stability.

Influence of Firing Temperature on Microstructure

(I) Crystal Structure Evolution At lower firing temperatures, anorthite crystal growth is limited, resulting in small and relatively uniform morphologies with relatively more lattice defects. For example, after firing at 800℃, the crystal grain size is often at the micrometer level. As the temperature increases, crystal growth accelerates, the grain size gradually increases, the shape becomes more regular, and lattice defects decrease. At 1400℃, clearly large, regular anorthite crystals can be observed.

(II) Changes in Pore Characteristics: At low temperatures, the porosity is high and the pore size is small, with a relatively diffuse distribution, mainly due to factors such as incomplete removal of volatiles from the raw materials. As the temperature increases, pores merge and grow, the porosity decreases, and the proportion of large-sized pores increases. This is related to the migration of substances within the material and sintering at high temperatures.

(III) Changes in Grain Boundary State: At low temperatures, the atomic arrangement at grain boundaries is disordered, with a large accumulation of impurities and insufficient bonding. At high temperatures, grain boundaries gradually become clearer, impurities diffuse and migrate, the atomic arrangement tends to be more ordered, and the grain boundary bonding strength increases.

Influence of Firing Temperature on Performance:

(I) Thermal Insulation Performance: Materials fired at lower temperatures have good thermal insulation performance and low thermal conductivity due to their high porosity, small pore size, and complex heat conduction paths. However, as the firing temperature increases, changes in the pore structure make the heat conduction path smoother, increasing thermal conductivity and decreasing thermal insulation performance.

(II) Mechanical Properties: Low-temperature firing results in small crystals and weak grain boundaries, leading to poor compressive and flexural mechanical properties. At high temperatures, the combined effect of large crystals and strong grain boundaries significantly enhances the material’s mechanical properties, enabling it to withstand greater external forces.

(III) Chemical Stability: At low temperatures, the material is susceptible to chemical corrosion due to microstructural defects, resulting in poor chemical stability. High-temperature firing improves the microstructure, enhancing its resistance to acids, alkalis, and other chemicals, thus increasing its chemical stability.

Conclusion

Firing temperature has a comprehensive and significant impact on the microstructure and properties of anorthite thermal insulation and refractory materials. Reasonable control of the firing temperature can optimize the material’s microstructure, thereby improving its thermal insulation, mechanical, and chemical stability properties, providing strong support for the efficient application of this material in various high-temperature industrial scenarios.