Effects of corchorus olitorius derived binder on functional properties and thermal shock resistance of a Kaolinite refractory.
Abstract
The effect of corchorus olitorius derived binder on the functional properties (fracture
strength- modulus of rupture, thermal conductivity and Young's modulus or elasticity) of a
kaolinite-based refractory was investigated. The three-bend test was used to investigate
modulus of rupture; while scanning electron microscope (SEM) micrographs were used to
analyze the microstructure of the fractured surfaces. The flexure strengths of green samples
rose linearly from 18.39 MPa" (plain water plasticized samples) to 24.51 MPa (samples
plasticized with a formerly thickened binder), thus giving flexure strength improvement of
32.28% above binder free samples. Fired samples' strength reached a maximum of 106.61
MPa (at binder's concentration of 0.683) from strength of 37.5 MPa (for plain water
plasticized samples) corresponding to strength improvement of 184.29% compared to binder
free samples. SEM micrographs revealed an increase in pore closure (evident by the increased
coalescence of kaolinite plates) with increasing binder concentration. Fracture paths were also
observed to change from one dominated by intergranular fractures (in plain water plasticized
samples) to mainly intragranular fracture mode in samples plasticized with higher binder
concentrations.
Ultrasonic Nondestructive Technique (NOT) was used to investigate the elastic properties
namely: ultrasonic longitudinal velocity (VL) and Young's modulus of elasticity and the results
compared with some empirical models. A strong linear relationship was observed between the
samples' porosity and the measured ultrasonic longitudinal velocity (VL). Young's modulus
rose gradually from 17.39 GPa (plain water plasticized samples) to reach a plateau at a binder
concentration of 0.683 (after attaining a peak value of33.07GPa).
Transient hot wire method was used to measure the thermal conductivity in the temperature
range of 20 to 600De. Values of thermal conductivities were noted to be strongly dependent
on binder concentrations (at all temperatures). Samples plasticized with higher binder
concentrations had slightly higher values of thermal conductivity compared to those
plasticized with binders of lower concentration and binder free samples. Effective medium
IV
approximation was observed to agree well with the experimental data whereas geometric
mean model gave values, which were slightly higher.
Thermal shock test employing water quenching was done for temperature differences ranging
between 80 to 580°C; damage parameters (figures of merit) . were also evaluated. The results
showed that samples plasticized in the higher binder concentration, which initially had very
high strengths; experienced the largest strength loss (over 60% of their initial strengths) at
quench temperature difference ("..T, ) exceeding 345°C; the critical temperature difference
("..T, c) of the samples tested was noted to be lying between 270 - 345°C. SEM micrographs of
samples quenched at temperature difference of 580°C showed that samples plasticized with
the optimal binder concentration (0.683) experienced severest cracking of the matrix
compared to their counterparts plasticized with plain water, whose microstructures also
showed an inhibited crack propagation.
Citation
Master of Science(physics)Sponsorhip
University of NairobiPublisher
Department of Physics - University of Nairobi.