Journal of Advanced Materials in Engineering (Esteghlal)

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Silica fume has been largely used in concrete in recent decades due to its effect on improvement of strength and durability of concrete. On the other hand, attention has been recently paid to the use of limestone powder as a substitute for part of cement in concrete, basically because of its low price and its positive effect on the durability of concrete. The aim of the current study is the investigation of the interactive effect of silica fume and limestone powder on the compressive strength of concrete and the optimization of the mix design. To do so, 27 mix designs including 3 water-to-cementitious materials ratios (W/CM=0.25, 0.3 and 0.4) 3 silica fume-to-cementitious materials ratios (SF/CM=%0, %5 and %10) and 3 limestone powder-to-cement ratios (LP/C=%0, %15 and %30) were used and 28-day compressive strength of the cubic concrete specimens were determined. Then, the interactive effect of silica fume and limestone powder on compressive strength of concrete was investigated using isoresponse curves. Furthermore, the optimization of the mix design for concretes containing silica fume and limestone powder was carried out using “cost effective factor” (CEF) which is defined compressive strength divided by cost of concrete.

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It is well known that the characteristics of concrete components greatly affect the durability of high strength/high performance (HS/HP) concrete against frost action. Undoubtedly, precise recognition of this relationship leads to appropriate selection of the type and proportions of concrete components in any particular project. In the current study, the aim is to investigate the possibility of developing some mathematical-experimental models to explain the frost resistance of high-performance concrete, regarding the role of some of its main components. To do so, the effects of four key elements, i.e. water, silica fume, coarse aggregate, and number of freeze-thawing cycles, were studied on the frost resistance of HS/HP concrete were studied. 24 concrete mix designs including 3 ratios of water to cementitious materials, i. e. 0.4, 0.3, and 0.25 4 ratios of silica fume to cementitious materials, i.e. 0, 5, 10, and 15 percent and 2 types of coarse aggregates, i. e. Limestone and Quartzite were utilized for HS/HP concrete. Overall, about 432 concrete cubes were cast, cured and tested under freeeze-thaw cycles. Finally, some models were proposed for describing the frost resistance of high strength concrete.

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In the present study phase transformation of silicon and silica during milling in different atmospheres was investigated. The silicon powder was subjected to high energy ball milling in ammonia (25%) atmosphere. The milled powder was subsequently annealed at 1200 ◦C for 1 hour. In another test a mixture of AlN and amorphous silica (micro silica) was subjected to high energy ball milling. The milled powder mixture was subsequently annealed at 1200 ◦C for 2 hours. Phase analysis of the as milled and annealed powders was performed by X-ray diffractometery (XRD). Powder morphology was also examined using a scanning electron microscope (SEM). Results showed that ball milling of silicon in ammonia formed an amorphous phase which transformed to quartz on further milling. After annealing quartz, cristobalite and another oxide phase called O phases were developed on XRD patterns. Ball milling of AlN and amorphous silica led to the transformation of amorphous silica to stishovite phase. This process was completed after annealing..

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The aim of this work was synthesis of MCM-41/HA nanocomposite and biodegradation behavior of pure silica-mesoporous in attendance of hydroxyapatite crystals. These materials were synthsized by sol-gel method and ageing at 100°C for 24hr. A surfactant was used as template. The pores were formed after removal of surfactant by calcination at 550°C. FTIR results demonstrated formation of silanol and siloxan groups of silica network and hydroxyl and phosphate groups of HA network. Also SEM, TEM and EDS results confirmed presence of HA crystals within MCM-41 structure. Finally biodegradation behavior was examined by ICP and FTIR analysis. The results indicated biodegradable HA phase in the nanocomposite (with release of Ca2+ inos in water and the increasing of the pH value) can increase non-bridging oxygens of the silica network and therefore, it improves biodegradation behavior of silica network.

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Polyethylene terephthalate (PET) based nanocomposites containing three differently modified silica particles were prepared by melt compounding. The influence of type and amount of nanosilica on various properties of nanocomposite was studied using atomic force microscope, thermal degradation, thermal-mechanical properties, scanning electron microscope, and reflectance spectra. AFM test was used to study the roughness of composites which indicated that the roughness is related to hydrophilicity degree of silica, increasing with an increase in hydrophilicity of particles. SEM images were studied on the surface, confirming that the surface roughness of nanocomposite depends on the type of nano-silica used. Results of thermal analysis showed that the interaction between nanosilica particle and polyethylene terephthalate chains is effective in thermal stability of composite. UV-vis spectra of polyester nanocomposites indicated that the refraction of hydrophilic silica nanocomposites is more than hydrophobic one, indicating agglomeration of hydrophilic particles at the surface of nanocomposite compared with hydrophobic one.

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In recent years, use of Sol-gel procedure for laboratory and industrial synthesis of Nanostructures and especially silica Nano-particles has increased. In this research, silica particles were synthesized by Sol-gel procedure and their physical properties were studied by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Thermal Gravimetric Analysis (TGA). Effect of structural modifiers on the morphology and diameter of Nano-particles was investigated. In addition, the reaction was carried out in the presence of ultrasonic waves in periods of 10, 30 and 60 minutes and the effect of these waves on different stages of reaction was studied by means of SEM. Finally, in this research, spherical particles of 50 to 80 nanometer sizes were synthesized and characterized. They can be very useful hosts for lanthanide complexes that can be used in drug delivery systems, radiotherapy, photoluminescence applications and manufacturing of special lasers. Also, different amounts of Lanthanum Nitrate hexahydrate were added to the mixture during the creation of Nano-particles. Then, Simulated Body Fluid (SBF) was produced for the study of ability of the Nanostructures in regulated delivery of drugs such as Lanthanides, and releasing of Lanthanides in 10 minute periods for 80 h was studied. Lanthanide concentration in SBF was also studied by means of Inductively Coupled Plasma (ICP). According to the results of ICP, loaded Lanthanide was not released from the silica network. Loaded Lanthanides in the mesopores can be used in radiation, especially in cases of liver cancer.

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In this research according to unique properties of fused silica and Its numerous applications fused silica parts with 77% by weight solid loading formed by gel casting. Rheological behavior of the slurry and sintering conditions were optimized. Sample sintered at optimum conditions has bulk density of 1.71 g/cm3, open porosity of 18.13%, water absorption of 10.60%, linear shrinkage after firing of 3.5%, closed porosity of 1.09% and relative density of 78.80%. Its thermal expansion coefficient in range of room temperature to 1000 ◦C has been measured 0.4432×10-6 1/ . Results showed that With increasing temperature and time In addition to the increased vscous flow, Crystallization also extend. Finally sintered at high temperature and short time for an instance with the lowest overall high crystallinity and density, were found suitable

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The aim of the present study is to study the effects of adding  diopside (CaMgSi₂O₆) as well as silica sulfuric acid nanoparticles to ceramic part of glass ionomer cement (GIC) in order to improve its mechanical properties. To do this, firstly, diopside (DIO) nanoparticles with chemical formula of CaMgSi₂O₆ were synthesized using sol-gel process and then, the structural and morphological properties of synthesized diopside nanoparticles were investigated. The results of scanning electron microscopy (SEM) and particle size analyzing (PSA) confirmed that synthesized diopside are nanoparticles and agglomerated. Besides, the result of X-ray diffraction (XRD) analyses approved the purity of diopside nanoparticles compounds. Silica sulfuric acid (SSA) nanoparticles are also prepared by chemical modification of silica nanoparticles by means of chlorosulfonic acid. Fourier transform infrared spectroscopy (FTIR) technique was used to find about the presence of the (SO₃H) groups on the surface of silica sulfuric acid nanoparticles. Furthermore, various amounts (0.1, 3 and 5 wt.%) of diopside and silica sulfuric acid nanoparticles were added to the ceramic part of GIC (Fuji II GIC commercial type) to produce glass ionomer cement nanocomposites. The mechanical properties of the produced nanocomposites were measured using the compressive strength, three-point flexural strength and diametral tensile strength methods. Fourier transform infrared spectroscopy technique confirmed the presence of the (SO₃H) groups on the surface of silica nanoparticles. The compressive strength, three-point flexural strength and diametral tensile strength were 42.5, 15.4 and 6 MPa, respectively, without addition. Although adding 1% silica solfonic acid improved nanocomposite mchanical properties by almost 122%, but maximum increase in nanocomposite mechanical properties was observed in the nanocomposites with 3% diposid, in which 160% increase was seen in the mechanical properties.

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In this study, iron powder (~45 μm) with the  minimum purity of 99% was insulated by the 1 to 4 wt% sodium silicate insulator (SiO₂.3Na₂O solution in 40 wt% water) and the 0.5 wt% zinc stearate. Insulated powders were pressed in a die with  a toroidal shape at the pressure of 320 MPa. The effects of insulator percentage and annealing temperature on the magnetic permeability, core loss tangent, and the total loss were investigated. The results indicated that the sodium silicate insulator could be suitable for insulating iron powders used in iron powder cores for high frequencies up to 1000 kHz. Also, this insulator could be stable against heat up to 450 °C.

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In this study, the synthesis of nano-porous calcium magnesium silicate was performed and studied to improve drug properties and drug release. This synthesis was carried out by using the tetraethyl ortho silicate precursor (TEOS) and the Cetyltrimethyl ammonium bromide surfactant (CTAB) in a sol-gel alkaline environment; and the product was heat treated at 600° C and 800° C temperatures. The purpose of this study is to investigate the effect of the calcination temperature on the potential for ibuprofen release by the production produced compound. The product was studied using X-ray diffraction patterns (XRD), Nitrogen adsorption / desorption, Fourier-transform infrared spectroscopy (FTIR), ultraviolet spectroscopy (UV) and Transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). The results of Nitrogen absorption-desorption assay showed a surface area of 42-140 m² /g The drug release after 240 hours showed that the calcite sample had a lower release at 600 ° C, temperature that which was is due to the smaller size of the cavities and the more surface area, as compared tothan the other specimens. Also, calcium and magnesium elements increased  the loading capacity, and createcreating a suitable substrate for for the slower drug release. Overall, This this study showed that nano-porous magnesium silicate calcium has had  the ability to load and release the ibuprofen and can could be, therefore, used as a modern drug delivery system in the bone tissue engineering field.
 

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In the present study, silica aerogel was evaluated by a two-step catalytic process at the ambient pressure drying, under different synthesis conditions. The effects of  the catalyst and water content in the hydrolysis step on the physical properties of silica aerogel, including density, porosity and shrinkage, were investigated. The results showed that increasing the water content in the hydrolysis step increased the shrinkage of gel network and density of obtained aerogel. Moreover, in the presence of insufficient water, NH₄OH as the condensation catalyst in the gel formation step was more effective on the physical properties of silica aerogel, as compared to HCl as  thehydrolysis catalyst; Moreover, the increase in the NH₄OH content led to lower density and higher porosity. On the other hand, NH₄OH effect on the physical properties of silica aerogel was not noticeable in the presence of enough water content. In the NH₄OH/HCl molar ratio of 6, the best silica aerogel sample was obtained with the density of 0.214 g/cm³, porosity of 90% and shrinkage of 23%

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