• Advances in nano research
• /
• v.4 no.3
• /
• pp.181-195
• /
• 2016

Addition of nano-$SiO_2$ (NS) to geopolymer composites has been studied through measurement of compressive strengths, FTIR and XRD analysis. Alumino-silicate materials are coarse aggregate included waste concrete and demolished walls with its cementing binder, cement kiln dust (CKD) used and can possess a pronouncing activation for the geopolymer reaction resulting from the high alkali contents within. Materials prepared at water/binder ratios in a range of 0.30: 0.40 under curing of $40^{\circ}C$ and 100% Relative Humidity (R.H.), while the used activator is sodium hydroxide in the ratio of 2 wt. %. First, CKD is added in the ratio from 10 up to 50 wt., %, and the demolished walls was varied depending on the used CKD content, while using constant ratio of waste concrete (40 wt., %). Second step, depending on the optimum CKD ratio resulted from the first one (40 wt. %), so the control geopolymer mix composed of cement kiln dust, demolished walls and waste concrete in the ratio (40:20:40, wt %). Nano-silica partially replaced waste concrete by 1 up to 8%. Results indicated that, compressive strengths of geopolymer mixes incorporating nano-silica were obviously higher than those control one, especially at early ages and specially with 3%NS.

• Journal of Powder Materials
• /
• v.19 no.3
• /
• pp.177-181
• /
• 2012

Copper composite materials have attracted wide attention for energy applications. Especially $CuInS_2$ has a desirable direct band gap of 1.5 eV, which is well matched with the solar spectrum. $CuInS_2$ nanoparticles could make it possible to develop color-tunable $CuInS_2$ nanoparticle emitter in the near-infrared region (NIR) for energy application and bio imaging sensors. In this paper, $CuInS_2$ nanoparticles were successfully synthesized by thermo-decomposition methods. Surface modification of $CuInS_2$ nanoparticles were carried out with various semiconductor materials (CdS, ZnS) for enhanced optical properties. Surface modification and silica coating of hydrophobic nanoparticles could be dispersed in polar solvent for potential applications. Their optical properties were characterized by UV-vis spectroscopy and photoluminescence spectroscopy (PL). The structures of silica coated $CuInS_2$ were observed by transmission electron microscopy (TEM).

• Advances in nano research
• /
• v.12 no.4
• /
• pp.387-403
• /
• 2022

Silica nanoparticles, which have a broad range of sizes and specific surface features, have been used in many industrial applications. This study was conducted to synthesize monodispersed silica nanoparticles directly from tetraethyl orthosilicate (TEOS) with an alkaline catalyst (NH₃) based on the sol-gel process and the Stöber method. A central composite design (CCD) is used to build a second-order (quadratic) model for the response variables without requiring a complete three-level factorial experiment. The process was then optimized to achieve the minimum particle size with the lowest concentration of TEOS. Dynamic light scattering and scanning electron microscopy were used to analyze the size, dispersity, and morphology of the synthesized nanoparticles. After optimization, a confirmation test was carried out to evaluate the confidence level of the software prediction. The results revealed that the predicted optimization is consistent with experimental procedures, and the model is significant at the 95% confidence level.

• Steel and Composite Structures
• /
• v.43 no.3
• /
• pp.389-401
• /
• 2022

This study investigated the flowability and mechanical properties of cost-effective steel fiber reinforced ultra-high performance concrete (UHPC) by using locally available materials for field-cast application. To examine the effect of mixture constituents, five mixtures with different fractions of silica fume, silica powder, ground granulated blast furnace slag (GGBS), silica sand, and crushed natural sand were proportionally prepared. Comprehensive experiments for different mixture designs were conducted to evaluate the fresh- and hardened-state properties of self-consolidating UHPC. The results showed that the proposed UHPC had similar mechanical properties compared with conventional UHPC while the flow retention over time was enhanced so that the field-cast application seemed appropriately cost-effective. The self-consolidating UHPC with high flowability and low viscosity takes less total mixing time than conventional UHPC up to 6.7 times. The X-ray computed tomographic imaging was performed to investigate the steel fiber distribution inside the UHPC by visualizing the spatial distribution of steel fibers well. Finally, the tensile stress-strain curve for the proposed UHPC was proposed for the implementation to the structural analysis and design.

• Steel and Composite Structures
• /
• v.47 no.5
• /
• pp.633-644
• /
• 2023

Taking a look at the previously published papers, it is revealed that there is a porosity index limitation (around 0.35) for the mechanical behavior analysis of the functionally graded porous (FGP) structures. Over mentioned magnitude of the porosity index, the elastic modulus falls below zero for some parts of the structure thickness. Therefore, the current paper is presented to analyze the vibrational behavior of the FGP Timoshenko beams (FGPTBs) using a novel refined formulation regardless of the porosity index magnitude. The silica aerogel foundation and various hydrothermal loadings are assumed as the source of external forces. To obtain the FGPTB's properties, the power law is hired, and employing Hamilton's principle in conjunction with Navier's solution method, the governing equations are extracted and solved. In the end, the impact of the various variables as different beam materials, elastic foundation parameters, and porosity index is captured and displayed. It is revealed that changing hygrothermal loading from non-linear toward uniform configuration results in non-dimensional frequency and stiffness pushing up. Also, Al - Al2O3 as the material composition of the beam and the porosity presence with the O pattern, provide more rigidity in comparison with using other materials and other types of porosity dispersion. The presented computational model in this paper hopes to help add more accuracy to the structures' analysis in high-tech industries.

• Journal of the Korean Wood Science and Technology
• /
• v.52 no.4
• /
• pp.331-342
• /
• 2024

Rubberwood (Hevea brasiliensis) has excellent physical and mechanical properties and is one of the most widely used species in Southeast Asia. However, it has poor resistance to subterranean termite attacks due to its high sugar and starch contents. The objective of this study was to evaluate the termite resistance of experimental wood-plastic composite (WPC) panels manufactured from rubberwood flour, polyethylene terephthalate, and silica in three different weight ratios (1/2/7, 1/3/6, and 1/4/5). The panels were exposed to Coptotermes curvignathus subterranean termites in a no-choice test under laboratory conditions based on Indonesian standards. Solid rubberwood used as control samples presented poor resistance, exhibiting 23.1% weight loss due to subterranean termite attack, as indicated by low termite mortality and high wood weight loss. In contrast, the WPC samples demonstrated extreme resistance, with weight loss ranging from 0.19% to 0.23%. Based on the findings of this study, the high termite mortality and overall low mass loss of the samples indicate that such manufactured panels could provide a high level of protection with regard to Indonesian standards.

• Computers and Concrete
• /
• v.19 no.6
• /
• pp.667-675
• /
• 2017

One of the main disadvantages of Ultra High Performance Concrete exists in the large suggested value of UHPC ingredients. The purpose of this study was to find the models mechanical properties which included a 7, 14 and 28-day compressive strength test, a 28-day splitting tensile and modulus of rupture test for Ultra High Performance Concrete, as well as, a study on the interaction and correlation of five variables that includes silica fume amount (SF), cement 42.5 amount, steel fiber amount, superplasticizer amount (SP), and w/c mechanical properties of UHPC. The response surface methodology was analyzed between the variables and responses. The relationships and mathematical models in terms of coded variables were established by ANOVA. The validity of models were checked by experimental values. The offered models are valid for mixes with the fraction proportion of fine aggregate as; 0.70-1.30 cement amount, 0.15-0.30 silica fume, 0.04-0.08 superplasticizer, 0.10-0.20 steel fiber, and 0.18-0.32 water binder ratio.

• The Journal of the Korean dental association
• /
• v.54 no.1
• /
• pp.21-26
• /
• 2016

The requirements for the successful treatment of all-ceramic restorations are not so different from the ones of conventional restorations. "The provisional restoration followed by an adequate tooth reduction" and "the accurately fitting prostheses with corresponding to final impression" can be the examples of them. Nevertheless, the one which all-ceramic restorations are distinguished from conventional restorations is the additional procedure of so called "bonding". In addition to the application of resin cement between "inner surface of restoration and outer surface of abutment", bonding technology can be also applied to the treatment process of "Post and Core" in particular if the abutments are non-vital teeth. Core build-up for all-ceramic crown is conducted with fiber post and tooth colored composite by considering the properties of the restorations transmitting light. I would like to share my clinical experience about "silica based ceramic and non silica based ceramic restoration.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.67 no.10
• /
• pp.1330-1337
• /
• 2018

In this study, 40, 50, 60, and 70 wt% filler dispersed samples were prepared for the current GIS Spacer or environmentally friendly GIS. In the AC electrical breakdown, EMSC and EMAC decreased with increasing filler content, and EMSC showed better breakdown strength than EMAC. The mechanical properties such as tensile strength and flexural strength of EMSC and EMAC were also increased with increasing filler content. In addition, EMSC results in better mechanical properties than EMAC. The reason for this is considered to be one in which the influence of the interface is important.

• Journal of the Korean Applied Science and Technology
• /
• v.22 no.2
• /
• pp.175-181
• /
• 2005

The spherical particles of $CeO_2/SiO_2$ composite powder with narrow-size distribution and pure phase particles were synthesized by ultrasonic spray pyrolysis method from aqueous cerium sulfate solution. The resulting composite powder was characterized by X-ray diffraction, scanning electron microscopy, transmittance electron microscopy, in-vitro sun protect factor, and BET surface area analysis. The concentration of cerium sulfate was tested to vary the particle size from $3.40{\times}10^{-3}$ to $1.02{\times}10^{-2}mol/cm^3$ to study concentration effect of starting material. The average particle size from the $3.40{\times}10^{-3}mol/cm^3$ concentration was found to be slightly smaller than that from the $1.02{\times}10^{-2}mol/cm^3$ concentration, because of the relation between the droplet size and the concentration of the starting material solution.