• Transactions on Electrical and Electronic Materials
• /
• v.11 no.6
• /
• pp.261-265
• /
• 2010

In this paper, we attempt to improve the electrical characteristics of epoxy resin at high temperature (above $80^{\circ}C$) by adding magnesium oxide (MgO), which has high thermal conductivity. Scanning electron microscopy (SEM) of the dispersion of specimens with added MgO reveals that they are evenly dispersed without concentration. The dielectric breakdown characteristics of $SiO_2$ and MgO nanocomposites are tested by measurements at different temperatures to investigate the filler's effect on the dielectric breakdown characteristics. The dielectric breakdown strength of specimens with added $SiO_2$ decreases slowly below $80^{\circ}C$ (low temperature) but decreases rapidly above $80^{\circ}C$ (high temperature). However, the gradient of the dielectric breakdown strength of specimens with added MgO is slow at both low and high temperatures. The dielectric breakdown strength of specimens with 0.4 wt% $SiO_2$ is the best among the specimens with added $SiO_2$, and that of specimens with 3.0 wt% and 5.0 wt% MgO is the best among those with added MgO. Moreover, the dielectric strength of specimens with 3.0 wt% MgO at high temperatures is approximately 53.3% higher than that of specimens with added $SiO_2$ at $100^{\circ}C$, and that of specimens with 5.0 wt% of MgO is approximately 59.34% higher under the same conditions. The dielectric strength of MgO is believed to be superior to that of $SiO_2$ owing to enhanced thermal radiation because the thermal conductivity rate of MgO (approximately 42 $W/m{\cdot}K$) is approximately 32 times higher than that of $SiO_2$ (approximately 1.3 $W/m{\cdot}K$). We also confirmed that the allowable breakdown strength of specimens with added MgO at $100^{\circ}C$ is within the error range when the breakdown probability of all specimens is 40%. A breakdown probability of up to 40% represents a stable dielectric strength in machinery and apparatus design.

• Journal of Korea Foundry Society
• /
• v.5 no.3
• /
• pp.19-26
• /
• 1985

This study has been carried out to examine into wettability of Cu-5%Sn alloy in $Al_2O_3$, MgO, $SiO_2$ and graphite, respectively and investigated into the change in macrostructure of Cu-5%Sn alloy according to kind and mixing rate of mold-coating. The results obtained from the experiment are summerized as follows; 1. Cu Cu-5%Sn alloy, wettabilities of $Al_2O_3$ and MgO were good, on the other hand, wettabilities of $SiO_2$ and graphite were bad. 2. The fine equiaxed zone was created because of the role of $Al_2O_3$ and MgO as preferential nucleation sites. 3. Notwithstanding change of mixing rate of $SiO_2$ in mold coating the equixed zone was not created. 4. The area of equiaxed zone was varied according to mixing rate in the case of using $Al_2O_3$ and MgO in mold-coating.

• Korean Journal of Agricultural Science
• /
• v.2 no.1
• /
• pp.61-100
• /
• 1975

This study has been made to find out the possibilty of successfully using the following $K_2O$ recommended equation $K_2O\;kg/10a=(Ko/\sqrt{Ca+Mg}-Ks/\sqrt{Ca+Mg})sqrt{Ca+Mg}.\;47.\;B\;D$. where $Ko/sqrt{Ca+Mg}=0.03518+0.0007658\;Sio_2/O.M$. $K_Ssqrt{Ca+Mg}$=Exchangeable K me/100g/$\sqrt{Total\;soluble(Ca+Mg)me/100g\;in\;Soil}$ B. D. =Bulk density of top soil, when the dose of Nitrogen for rice is estimated from the following equation: $N\;kg/10a=(4.2+0.096\;SiO_2/O.M).F$ where $F=0.907+0.263x-0.013x^2$ $SiO_2/O.M=(available\;SiO_2=ppm)/(organic\;matter\;%)$in soil For this. two field experiments. one in sandy and the other in clay paddy soil. have been conducted using 3 levels of wollastonite (0, 500, 100kg/10a) as main treatments; 3 levels of $K_2O$ application were used as sub-plots. These were as follows : (1) 8kg of $K_2O$/10a regardless of the K activity-$K/\sqrt{Ca+Mg}$; (2) kg of $K_2O$/10a estimated from the above equation. and (3) same as (2) above plus additional 30% of $K_2O$. The dose of N kg/ 10a was determined from the above equation based on the value of $SiO_2$/O.M. ratio in each treatment. There were three replications. The leading variety of rice in Chung Chong Nam Do area. Akibare (introduced from Japan) was used. The data obtained. through soil and plant analysis and growth and yield observations. have been throughly examined to attain the following summarized conclusions. 1. The nitrogen dose. estimated from the above equation. was in excess for optimum growth of the rice variety Akibare; indicating the necessity of modification onthe value of "F" or the constants in the equation. The concept of using $SiO_2$/O.M. in the equation was shown to be applicable. 2. The dose of potash. estimated from the respective equation given above. also was in excess of the rice requirements indicating the necessity of minor change in the estimation of $Ko/\sqrt{Ca+Mg}$ value and some great modification in the calculation of $Ks/\sqrt{Ca+Mg}$ value for the equation; however the concept of using $K/\sqrt{Ca+Mg}$ as a basis of $K_2O$ recommendation was shown to be quite reasonable. 3. It was found. from the correlation study using the data of paddy yield and amount of $K_2O$ absorbed by rice plants that the substitution of the value of $Ks/\sqrt{Ca+Mg}$ in the equation for the vaule $Ks/\sqrt{Ca+Mg}=0.037+0.78K\;me/100g$ soil was much more applicable than using the value calculated from the data of soil and wollastonite analysis.

• Resources Recycling
• /
• v.24 no.1
• /
• pp.35-42
• /
• 2015

To obtain the fundamental information on the dissolution of nickel into the slag in the pyrometallurgical processes for treatment of wasted PCB, the distribution ratios of nickel between CaO-$SiO_2-Al_2O_3$-MgO slag and copper-5 wt%Ni alloy were measured at 1623 K to 1823 K under a controlled $CO_2$-CO atmosphere. The distribution ratio of Ni increased linearly with increasing oxygen partial pressure. Therefore, the dissolution reaction of nickel into the slags could be described by the following equation; $$Ni(l)_{metal}+\frac{1}{2}O_2(g)NiO(l)_{slag}$$ The distribution ratio of Ni increased linearly with increasing content of basic oxides(CaO and MgO) in slag. However, the distribution ratio of Ni decreased linearly with increasing temperature. From these results, the empirical equation of distribution ratio of Ni was obtained by the following equation from the analysis of experimental conditions by multiple regression. $${\log}L_{Ni}=0.4000{\log}P_{O2}-5.1{\times}10^{-4}T+0.3375\(\frac{X_{CaO}+X_{MgO}}{X_{SiO2}}\)$$

• Applied Chemistry for Engineering
• /
• v.29 no.4
• /
• pp.461-467
• /
• 2018

In this study, $(n-BuCp)_2ZrCl_2$, was supported on $SiO_2/MgCl_2$ binary support. Before supporting the catalyst, the $SiO_2/MgCl_2$ binary support was surface treated with three different alkyl aluminum compound, namely trimethylaluminum, triethylaluminum, and ethylaluminum sesquichloride. The synthesized surface-treated $SiO_2/MgCl_2$ supported metallocene catalysts were used for the copolymerization of ethylene and 1-hexene. Their catalytic properties and performances were analyzed through BET, XPS analysis, ICP-AES analysis, and FE-SEM. While the resulting copolymers were analyzed through DSC analysis, GPC analysis, 13C-NMR analysis, and FE-SEM. The analysis of synthesized surface-treated $SiO_2/MgCl_2$ supported metallocene catalysts showed that the Zr content of these catalysts is relatively lower compared to that of the catalyst supported on $SiO_2$. This could be attributed to the reduction in the surface area of $SiO_2$ due to the presence of recrystallized $MgCl_2$ and alkyl aluminum. Furthermore, they exhibited a better copolymerization activity compared to that of $SiO_2$ supported catalyst, particularly the EASC-surface treated binary support, which has the highest activity of 1.9 kg PE/($mmol-Zr^*hr$) because EASC acts as a strong Lewis acid. It could also be observed that the larger the ligand of alkyl aluminum used, the rougher the particle surface of the resulting polymer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.2
• /
• pp.118-123
• /
• 2010

The eco-friendly technologies have been extended as matter of international concern due to various diseases and syndromes according to an environmental pollution. In this study, we have manufactured a ceramic cluster with thick film type for anion generation equipment which is maximized anion but minimized ozone contents generated. To develop the formulation of ceramic cluster, we conducted the $Mg_2SiO_4$ powders doped with 10 vol% glass frits as Na-Zn-B-O system and sintered at $1050^{\circ}C$ for 2 hours in air for starting materials and investigated the matching properties between the Ag-Pd electrode and the starting materials. The sintered sample for the composition of cluster has 6.7 of dielectric constant and 32 kV/mm of withstand voltage. The yield of anions was measured according to an electrode pattering, discharge gap between electrode, and thickness of electrode protective layer in the cluster of thick film type. We have manufactured the ceramic clusters with optimized thick film structure that have an anion over a hundred particles and the ozone of 0.6 ppb generated.

• Journal of Welding and Joining
• /
• v.21 no.1
• /
• pp.107-113
• /
• 2003

Joining of $Si_3N_4$ to $Si_3N_4$ with crystallized glass solder was studied. $SiO_2-Al_2O_3-MgO$ glass with $P_2O_5$ as a crystallizing reagent was used as a solder. To improve the hish temperature toughness of joined specimen, two stage heat treatment was applied to Joined sample for the crystallization of joined layer, Two factors, i.e. thickness of soldered layer and crystallization were taken and thier effects on joining strength were investigated by a SEM-EDX observation of joined interface and bending strength both at room and elevated temperatures. Obtained results are summarized as follows: (1) Nitrogen diffused from $Si_3N_4$ to solder during the Joining process. Average amount of nitrogen in soldered layer depended on the thickness of the soldered layer and increased with decrease of the thickness. (2) Joining strength of the specimen having a thinner soldered layer was stronger than that of thicker layer. This can be mainly attributed to the difference of the nitrogen content in the soldered layer. (3) Higher content of nitrogen in solder brought forth higher viscosity of the solder. Hence the crystallization of the solder become more difficult in thinner layer of the solder than thicker one. (4) Thus, the effect of crystallization was evaluated mostly by the thicker layer specimen. Crystallization of soldered layer improved markedly the fracure strength of joining at higher temperatures than the softening temperature of glass solder.

• Journal of the Korean Ceramic Society
• /
• v.33 no.7
• /
• pp.832-838
• /
• 1996

Thermite reaction products of MgO and Al were added to MgO-C refractory to improve the properties of corrosion against the attack of slag, oxidation and mechanical spalling. Corrosion rate of MgO-C-MgAl2O4 spinel refractory at the ratio of 3.3(CaO/SiO2) slag was smaller than that of MgO-C and MgO-C-Al refractory. The excellent corrosion resistance of the MgO-C-MgAl2O4 spinel refractory against the slag attack was appeared by Al and MgAl2O4 spinel with high melting point and corrosion resistance and the high thermal conductivity and low thermal expansion of AIN. Hot M.O.R at 140$0^{\circ}C$ and the resistance of oxidation weight loss at 90$0^{\circ}C$ were 210kg/cm2 and -12% respectively.

• Journal of Wetlands Research
• /
• v.25 no.4
• /
• pp.386-393
• /
• 2023

The domestic marine healing industry is undergoing significant revitalization efforts, with a focus on understanding the efficacy and effectiveness of marine healing resources. This study establishes utilization and management standards through a detailed analysis of the active components within well-recognized marine healing mud materials. Samples of mud materials were collected from domestic tidal flats. These samples exhibited an average composition of 7.87% sand, 74.95% silt, and 17.17% clay, with a combined mud content (silt+clay)(silt+clay) consistently exceeding 90%. Notably, SiO₂ emerged as the most prevalent effective ingredient at 68.4%, followed by Al₂O₃ (13.3%)>Fe₂O₃ (4.0%)>K₂O (2.9%)>Na₂O (2.3%)>MgO (1.6%)>CaO (1.0%)>TiO₂ (0.7%), in terms of average content. Subsequently, through an analysis of effective ingredients, Si, Al, Fe, K, Na, Mg, and Ca were identified as elements demonstrating significant functionality. Among these, key indicator ingredients were selected for quality control, all of which were found to possess efficacious properties. Notably, K, Mg, and Ca exhibited particularly high concentrations. Based on these findings and referencing existing literature, it is recommended that domestic tidal flat mud resources earmarked for utilization as marine healing resources should possess a raw material mud content of no less than 70.0%. Moreover, the cumulative index components K₂O+MgO+CaO should meet or exceed a threshold of 5.0% for optimal effectiveness.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2012.11a
• /
• pp.16-16
• /
• 2012

Mg and its alloys have been of great interest because of their low density of 1.7, 30% lighter than Al, but their wide applications have been limited because of their poor resistances against corrosion and/or abrasion. Corrosion resistance of Mg alloys can be improved by formation of anodic films using anodic oxidation method in aqueous electrolytes. Plasma electrolytic oxidation (PEO) is one of anodic oxidation methods by which hard anodic films can be formed as a result of micro-arc generation under high electric field. PEO method utilize not only substrate elements but also chemical components in electrolytes to form anodic films on Mg alloys. PEO films formed on AM50 magnesium alloy in an acidic fluozirconate electrolyte were observed to consist of mainly $ZrO_2$ and $MgF_2$. Liu et al reported that PEO coating on AM30 Mg alloy consists of $MgF_2$-rich outer porous layer and an MgO-rich dense inner layer. PEO films prepared on ACM522 Mg die-casting alloy in an aqueous phosphate solution were also reported to be composed of monoclinic $Mg_3(PO_4)_2$. $CeO_2$-incorporated PEO coatings were also reported to be formed on AZ31 Mg alloys in $CeO_2$ particle-containing $Na_2SiO_3$-based electrolytes. Magnesium tin hydroxide ($MgSn(OH)_6$) was also produced on AZ91D alloy by PEO process in stannate-containing electrolyte. Effects of $OH^-$, $F^-$, $PO{_4}^{3-}$ and $SiO{_3}^{2-}$ ions and alloying elements of Al and Sn on the formation of PEO films on pure Mg and Mg alloys and their protective properties against corrosion have been investigated in this work. $PO{_4}^{3-}$, $F^-$ and $SiO{_3}^{2-}$ ions were observed to contribute to the formation of PEO films but $OH^-$ ions were found to break down the surface films under high electric field. The effect of pulse current on the formation of PEO films will be also reported.