Suitable sample preparation and measuring conditions are studied for BET specific surface area (BET SSA) evaluation by one-point nitrogen gas adsorption of the solid phase of early hydrated cement paste from just after mixing to 2 hours after mixing. Then, it is analyzed what phase of early hydrates is affected by pre-heating temperature for BET SSA measurement. It became clear that the suitable condition for BET SSA measurement is as follow : 1) Stopping the hydration of early hydrated cement paste by immersing into acetone, 2) Evaporating by exposing under ambient room environment for two hours, 3) Drying the sample under a relative humidity of 11% more than one day, 4) Pre-heating under a temperature of 60°C. Pre-heating temperature does not affect the BET SSA of unhydrated cement. Pre-heating over 80°C increases the BET SSA of early hydrates by four times because of the effects of ettringite decomposition.
Reactive evaporation method of injected silicon powders has been investigated to prepare SiO2 ultrafine particles. The method has good advantages such as effective evaporation resulted from exothermic reaction heat of the metal vapor with oxygen in radio frequency thermal plasmas. Tangential gas flow has been injected to the plasma tail flame to control the diameter and the yield of the SiO2 ultrafine particles. The purpose of this research is to investigate the effect of the injection gas flow on preparation mechanism of SiO2 ultrafine particles in thermal plasmas by experimental work as well as numerical analysis. An increase in the flow rate of the injection gas leads to an increase in the diameter as well as the yield of the prepared ultrafine particles. An increase in the silicon powder feed rate leads to an increase in the particle diameter. Numerical analysis provides the preparation mechanism of the SiO2 ultrafine particles, however more sophisticated model will be required.
Zeolites were synthesized by using aluminium sludge as a source of silica and alumina. The synthesis has been carried out for various aging time at 90°C in alkali solution. Characteristics of products were determined by means of X-ray diffraction (XRD) and scanning electron microscope (SEM), and cation exchange capacity (CEC) of them were measured. As a result of experiment, NaA, NaPl, KF and KG type zeolites were obtained by used aluminium sludge, and the type of them depended on reaction condition. Because aluminium sludge included silica less than chemical composition of zeolites, the yield was increased by the addition of sodium silicate to reaction solution as a source of silica. CEC of synthesized NaA type zeolite was approximately equal to that of the article on the market. It was suggested that aluminium sludge was able to recycle as a raw material of zeolites.
This study deals with the caking of granulated blast furnace slag sand and its suppressive technique. The above mechanism is also discussed. The caking rate was steeply increased with temperature during storing. The caking occurred by the reason that the hydration product, which is presumably noncrystallin C-S-H, filled the space among the slag grains. By adding sodium gluconate and mixing natural sand, respectively, the caking was depressed chemically and physically. However, when a crushed limestone sand was mixed, the caking was promoted because of its chemical reaction with slag. The effect of granulated blast furnace slag sand containing sodium gluconate on the concrete properties was actually negligible.