MECHANICAL AND THERMAL SHOCK BEHAVIOUR OF Al2O3-SiO2-ZrO2

NICOLAS RENDTORFF, ALBERTO SCIAN, ESTEBAN AGLIETTI.

Salvador - BRAZIL

Congreso; UNICTER 2009-Unified International Technical Conference of Refractories, 11th. Bienal Worldwide Congress; 2009

UNICTER

Aluminosilicate based refractories are commonly use in glass processing systems. Other compositions included zircon to improve corrosion resistance. [1, 2] These materials are widely used in the glass industry in distributors, and feeders, and as expendable materials as plungers, spouts, tubes, orifice rings, etc. Coarse alumina and mullite powders and grits are used in the construction of these materials, and during powder processing and sintering, any overall shrinkage occurs. Therefore in order to achieve maximum fired density, and high mechanical strength and resistance to corrosion by molten glass, a very efficient particle packing is required in the green state. Currently an alumina-mullite or alumina–zircon matrix is prefered. The starting materials are prepared by blending controlled proportions of components having particle sizes covering the range of multi-millimetre to submicrometer. Accessible porosity in the sintered product is normally in the region of 15–20%. The refractory can therefore be considered to be developed by the bonding of the finer fractions of particles to each other, and to the surfaces of the large grains. These materials are commonly subjected to thermal stresses during installation, they must have good thermal shock properties once installed, the service life is then determined mainly by its corrosion characteristics.. The testing of the thermal shock resistance (TSR) of refractories have being studied for over a century by many authors because many interactive factors, variables and parameters are involved [3, 4, 5]. A recent review on refractories TS testing provide some background regarding the basic materials properties and other factors that control TSR of refractory materials. The first approaches to determine the thermal stresses and to introduce the damage resistance parameters of ceramic material are a thermo-elastic theory, which is focused in the initiation of the fracture ( R σ (1 ν ) E.α f = − and R´ k.σ (1 ν ) E.α f = − [3] A second approach focuses on crack propagation for conditions of thermal shock more severe than those for crack initiation; ´´´= σ 2 (1−ν ) f R E [4,5]. A unified theory of the thermal shock resistance considering the initiation and crack propagation was proposed. For high strength refractories with short initial cracksR σ (1 ν ) E.α f = − and R´ k.σ (1 ν ) E.α f = − [3] A second approach focuses on crack propagation for conditions of thermal shock more severe than those for crack initiation; ´´´= σ 2 (1−ν ) f R E [4,5]. A unified theory of the thermal shock resistance considering the initiation and crack propagation was proposed. For high strength refractories with short initial cracks´´´= σ 2 (1−ν ) f R E [4,5]. A unified theory of the thermal shock resistance considering the initiation and crack propagation was proposed. For high strength refractories with short initial cracks ´´´´= ´´´γ. = γ σ 2 (1−ν ) WOF WOF f R R E and for lower strength refractories with larger initial cracks= ´´´γ. = γ σ 2 (1−ν ) WOF WOF f R R E and for lower strength refractories with larger initial cracks [ ]22 R 2.E 1 st WOF = γ α . According to Hasselman [6] the first model is applicable to brittle materials where the crack initiation is determining mechanism. And the second approximation is valid where the initiation of the cracks is inevitable. And the forth parameter can be used to predict the behaviour of materials with sufficiently long cracks under severe thermal stresses. Finally some authors also state that the TSR can be correlated with the characteristic length of Lc, commonly employed in concrete mechanical analysis. This parameter is proportional to R´´´´. Askel [7] studied the TS behaviour of aluminamullite- zirconia materials using the quenching technique; he concluded that zircon appears controlling the mechanical properties and the improvement of the TSR. In this work three kind of refractories were studied to observe and correlate mechanical properties with thermal shock behavior. The TS behavior was evaluated by measuring the decrease in E/E0 [8,9] ratio where E0 and E are the dynamic elastic modulus before and after one quenching respectively. Also the strength (σf; modulus of rupture, MOR) of the materials before and after the TS test was measured. The experiemntal behavior was correlated both the mechanical and fracture properties and other several theoretical parameter.2.E 1 st WOF = γ α . According to Hasselman [6] the first model is applicable to brittle materials where the crack initiation is determining mechanism. And the second approximation is valid where the initiation of the cracks is inevitable. And the forth parameter can be used to predict the behaviour of materials with sufficiently long cracks under severe thermal stresses. Finally some authors also state that the TSR can be correlated with the characteristic length of Lc, commonly employed in concrete mechanical analysis. This parameter is proportional to R´´´´. Askel [7] studied the TS behaviour of aluminamullite- zirconia materials using the quenching technique; he concluded that zircon appears controlling the mechanical properties and the improvement of the TSR. In this work three kind of refractories were studied to observe and correlate mechanical properties with thermal shock behavior. The TS behavior was evaluated by measuring the decrease in E/E0 [8,9] ratio where E0 and E are the dynamic elastic modulus before and after one quenching respectively. Also the strength (σf; modulus of rupture, MOR) of the materials before and after the TS test was measured. The experiemntal behavior was correlated both the mechanical and fracture properties and other several theoretical parameter.σf; modulus of rupture, MOR) of the materials before and after the TS test was measured. The experiemntal behavior was correlated both the mechanical and fracture properties and other several theoretical parameter.