جستجوی مقالات مرتبط با کلیدواژه "silica fume" در نشریات گروه "علوم پایه"

Self-healing techniques are presented in three different ways: The first application is the use of bacteria to calcite in concrete cracks. In this way, relatively large cracks can be filled in reinforced concrete. This method does not improve the strength of the structure, but by filling the crack, the reinforcement path is blocked. This stops the entry of liquids and ions that start to corrode the reinforcement and thus increase the compressive strength but decrease the electrical resistivity of the structure. With this method, cracks can be filled and leakage can be prevented. In designs that use a self-healing additive such as Mix designation 7, the time interval obtained from the accelerated corrosion test between the cracked and intact specimens is reduced. Compressive strength in cracked and intact specimens in these designs is higher than in other designs. The use of more superplasticizers and more Silica fume are effective in these amounts. Its low electrical resistance can lead to increased corrosion intensity thus more superplasticizers in Plan 7 is not preferable to Plan 4. Low electrical resistance can lead to increased corrosion intensity thus Plan 4 is preferable to Plan 7.

Using mineral admixtures in cement composites as a way to improve their mechanical and durability properties is a common practice in concrete technology. Among them, silica fume and nano-silica effectively influence the composite's early and long-term properties. Due to the limited particle size distribution of nano and micro-silica, it is expected that the incorporation of some mineraladditives with a size greater than 500 nm may result in better mechanical and durability performance because of the filler effect. In this study, the effect of different percentages of TiO2 on the mechanical properties of cement composites containing nano-silica and silica fume was investigated. Six designs were tested for compressive strength with respect to zero, 2.5, and 5 percent replacementof cement with TiO2. The addition of TiO2 has led to an increase in compressive strength. The best results from the sample with 2.5% TiO2 are obtained. This could be due to the effect of TiO2 particles filling. Comparison of SF3, SF2, and SF1 at 28 days of age showed that SF2 increased the compressive strength. This shows that TiO2 has a great potential for improving the mechanical properties ofcomposite cement. The results showed that the addition of TiO2 had a positive effect on compressive strength. Increasing TiO2 nanoparticles content of more than 3 wt% is caused to reduce the compressive strength according to past studies. But in this study is shown that by adding 3% nanocillis or 20% silicified to increased TiO2 nanoparticles content of more than 3% wt, the results ofcompressive strength are not reduced. The use of 3% combined nano-silica or 20% silicafium will cover this defect of increased TiO2 nanoparticles content ofmore than 3% wt.

Silica fume, also known as micro silica, is a by-product of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys. This material and laccase-modified silica fume used as alternative low-cost adsorbent materials for dye removal from aqueous solutions. The silica fume was modified to maximize its adsorption capacity. For this purpose, the laccase enzyme was purified and immobilized on silica fume. Batch adsorption experiments have been performed as a function of pH, contact time, temperature, and adsorbent dosage. The equilibrium data were analyzed using Langmuir and Freundlich adsorption isotherms. The Langmuir adsorption model provided a better fit to the data. The kinetic data were evaluated with pseudo-first-order and pseudo-second-order kinetic models. The adsorption process undergoes pseudo-second-order kinetic as proved by the high value of R2. The thermodynamic parameters such as free energy, enthalpy, and entropy were also determined. These parameters indicated that the adsorption of Acid Fuchsin dye onto silica fume and laccase-modified silica fume was a spontaneous, endothermic, and entropy-driven process. The results show that both of them, especially laccase-modified silica fume, can be used as alternative low-cost adsorbents for dye removal from aqueous colored solutions or effluents.

Colloidal nanosilica is currently being produced by various methods which are mainly high energy intensive and/or not environmentally friendly. It is therefore essential to develop new energy efficient and environmentally friendly technologies. This paper introduces a new ultrasound assisted route based on alkali leaching of silica fume for synthesis of colloidal silica nanoparticles. The effects of sonication time on the particle size distribution of the colloidalnanosilica are studied via dynamic light scattering (DLS). The results show that the shape and size of nanoparticles are strongly depended on the ultrasonic time. DLS results show that average diameter of the produced colloidal nanosilicadecreases sharply from 337.10 nm to 93.27 nm during the first 5 minutes of sonication. Continued sonication up to 30 minutes, however, shows relatively slight decrease in average diameter of the colloidal nanosilica. Further, the produced colloidal nanosilica is characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD) and Fourier transform infrared (FTIR) spectroscopy.