| الملخص | Different types of refractory bricks (magnesite, dolomite and alumina bricks) prepared from Iraqi local ores were studied. Ardhuma sand has a high percentage of silica and low quantities of impurities, used basically in glass industry. This study used Ardhuma sand to prepare silica bricks refractories. The influence of sand,s grain size, calcium oxide content and firing temperature on physical properties: bulk density, specific gravity, water absorption, porosity, compressive strength, mineral and chemical composition of the prepared silica bricks were studied.
Silica sand was milled and sieved into defined grain size between -1 and +0.075 mm (represents the coarse fraction), and -0.075mm (represents the fine fraction)). Three different percentages of coarse + fine fractions, were prepared (75%+ 25%, 60%+ 40% and 50%+ 50%) with 3% calcium oxide and 2% iron ore. Mixtures were molded by hydraulic pressing by 500 kg/ cm2, dried, fired at 1400, 1450 and 1500 ºC for two hours.
Mineral composition of prepared silica bricks composed of various modifications of SiO2 (cristobalite and tridymite). Furthermore, it is composed of an amount of unmodified quartz. Mineral composition at 1400 and 1500ºC consisted of quartz and cristobalite, while at 1450ºC tridymite phase appeared with cristobalite and quartz. Chemical composition of SiO2 ranges from 92.28% - 93.80%.
Linear and volume change of bricks were increased by increasing firing temperature and fine sand fraction. Specific gravity and true specific gravity were decreased by increasing firing temperature. Maximum compressive strength was reached at firing temperature 1450ºC with sand fractions 50% coarse sand +50% fine sand. Permanent linear change was increased by increasing coarse sand fraction. Porosity percent did not changed remarkably.
According to the physical, mineralogical and chemical properties of prepared silica brick the best parameters are: coarse sand 50%+ fine sand 50%, firing temperature 1450ºC.
The effect of increasing the amount of calcium oxide on the properties of silica bricks was tested in different percentages (4 and 4.5%) and fired at 1450ºC. Increasing the calcium content decreased the chemical composition of SiO2 from 93.8% to 91.48%. Specific gravity bulk density decreased. Linear change, volume change and compressive were increased. Therefore, the best calcium oxide content was 3%. | |
