Preparation and Mechanical Properties of Monolithic Refractories Containing In-Situ Calcium Hexaluminate

In-Situ Calcium Hexaluminateを含有する不定形耐火物の作製および機械的特性評価

2018-09-25

2018-09-25

Monolithic refractories are widely used in metal and steel industries. The important raw material as calcium aluminate cement (CAC) is used and calcium hexaluminate (CA6) phase is formed in hexagonal plate-like morphology. This microstructure helps to enhance toughening properties as resistance for fracture and thermal shock. In the present study, monolithic refractories containing in-situ CA6 was prepared under controlling CA6 content and microstructure. The results showed that CA6 could be prepared by using CAC and sintered Al2O3 in stoichiometric composition as 1:6 mol of CaO:Al2O3. The sintering condition had strong influence on controlling CA6 quantity and grain growth. The utilization of small Al2O3 grain (75 μm) accelerated the CA6 formation at lower temperature due to high surface area. The addition of SiO2 helped to enhance hexagonal plate-like microstructure but the presence of gehlenite (C2AS) obstructed CA6 formation. The mechanical properties as fracture toughness (KIC) and effective fracture energy (γeff) were measured. It was found that big grain Al2O3 (550 μm) samples with SiO2 addition enhanced high KIC and γeff because of toughening mechanisms as crack deflection and strong bond breaking. The results of high surface roughness at fractured surface were the evidences of high energy consumption from above mechanisms. However, plate-like microstructure was not only obtained from high in-situ CA6 content, but high apparent porosity was also gained which led to weakening of materials and decreasing both KIC and γeff. Finally, thermal shock damage resistance parameter R'''' was determined but the achieved values were lower than usual of commercial refractories. Thermal shock parameters as ?eff, modulus of rupture (σf) and Young’s modulus (E) were evaluated. High σf was the main reason of low R???? . Other thermal shock resistance as R and Rst was calculated to confirm R''''. The thermal shock behaviors were monitored by measuring the change of σf and E upon increase temperature difference. Samples with big grain Al2O3 showed high thermal shock damage resistance (R???? and Rst) due to high γeff. Nevertheless, samples with small Al2O3 grain and SiO2 addition expressed high thermal shock fracture resistance R led to catastrophic decrease of both σf and E.

博士（工学）

京都工芸繊維大学

14303甲第890号

http://hdl.handle.net/10212/2503

eng

none

4

Thesis or Dissertation

Thesis