• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.23-27
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• 2017

This paper proposes an approach to predict the reliability of high temperature heaters by identifying their primary failure modes and mechanisms in the field. Test specimens were designed to have the equivalent stress conditions with the high temperature heaters in the field in order to examine the effect of stress conditions on the solder joint failures. There failures often result from cracking due to intermetallic compound (IMC) or void formation within a solder joint. Aging tests have been performed by exposing the test specimens to a temperature of $170^{\circ}C$ in order to reproduce solder joint failures in the field. During the test, changes in IMC formation were investigated by scanning electron microscopy (SEM) on the cross-sections of the test specimens, while changes in void formation were monitored both by resistance spectroscopy and by micro-computed tomography (microCT), alternately. The test results demonstrated the void volume within the solder increased as the time at the high temperature increased. Also, the phase shift of high frequency resistance was found to have high correlation with the void volume. These results implied the failure of high temperature heaters can be non-destructively predicted based on the correlation.

• Journal of the Korean Chemical Society
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• v.20 no.6
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• pp.469-478
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• 1976

Clinoptilolite zeolite samples were treated with hydrochloric acid, sulfuric acid and phosphoric acid of different strength and the adsorption characteristics and crystal structures of the original and acid-treated clinoptilolites were studied. By treating with hydrochloric acid, the adsorbed amount increased to 5-fold for nitrogen, to 3-fold for benzene, but for methanol no significant change was observed. As acid strength increased further, there were declines both in adsorption capacity and crystallinity. The results showed that the increase of adsorbed amount was caused by the rearrangement of the pore entrance and cation exchange. A method for determination of clinoptilolite content in natural mineral based on benzene adsorption on acid-treated sample is proposed. By this method, the original sample used in this study was found to contain approximately 40% of clinoptilolite. Using pulse technique in micro-catalytic reactor system, the catalytic activities of hydrochloric acid-treated clinoptilolites in cumene cracking and toluene disproportionation reactions were measured. For cumene cracking reaction, the maximum conversion was observed for the 0.5 N hydrochloric acid-treated sample. It is instructive to note that the maximum benzene adsorption was also observed for the sample treated with 0.5 N HCl. This suggest that the conversion rate was determined mainly by the rate of transport of reactants and the products through the pore structure. In the toluene disproportionation reaction, the same trend was observed. But the rate of deactivation was high for samples with strong acid sites. Since catalyst having higher activity was deactivated more easily, the conversion maximum was shifted to the sample treated with higher concentration of acid, -1N. The catalytic activity of $Ca^{2+} and La^{3+} ion exchanged samples for the toluene disproportion was much lower than that of acid-treated samples. Introduction of Ca^{2+} and La^{3+}$ into the pore structure apparently decreases the effective pore diameter of acid-treated clinoptilolite thus limiting the diffusion of reactants and products.

• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.332-336
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• 2009

When NCAs(non-conductive adhesives) are used for adhesion of micro-electronic devices, they often show problems such as delamination and cracking, due to the differences of CTE(coefficients of thermal expansion) between NCAs and substrates. Additions of inorganic particles or flexibilizers have been performed to solve those problems. The effects of silica addition on thermal/mechanical properties of amino modified siloxane(AMS)/silica/epoxy-nanocomposites were examined. The silica was treated by 3-glycidoxypropyltrimethoxysilane(GPTMS) for better compatibility between silica and epoxy matrix. AMS/silica/epoxy-nanocomposites filled with various amounts of AMS(1 and 3 phr) and various amounts of silica(3, 5 and 7 phr) were prepared. And Tg, moduli and CTE of nanocomposites were analyzed. Tg of AMS/Aerosil(non-modified silica)/epoxy-nanocomposites decreased from 125 to $118^{\circ}C$ with increasing Aerosil contents and moduli increased from 2,225 to 2,523 MPa with increasing Aerosil contents. Tg of AMS/M-silica (modified silica)/epoxy-nanocomposites decreased from 124 to $120^{\circ}C$ with increasing M-silica contents and moduli increased from 1,981 to 2,743 MPa with increasing M-silica contents. CTE of AMS/Aerosil/epoxy-nanocomposites and AMS/M-silica/epoxy-nanocomposites showed decreasing tendency regardless of the surface treatments.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.573-580
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• 2009

This paper presents the mix composition, production method, and curing condition applied to the extruded ECC(Engineered Cementitious Composite) panel which are able to exhibit multiple cracking and potential pseudo strain-hardening behavior. In addition to the production technique of extruded ECC panel, the effect of fiber distribution characteristics, which are uniquely created by applying extrusion process, on the flexural behavior of the panel is also focussed. In order to demonstrate fiber distribution, a series of experiments and analyses, including image processing/analysis and micro-mechanical analysis, was performed. The optimum mix composition of extruded ECC panel was determined in terms of water matrix ratio, the amount of cement, ECC powder, and silica powder. It was found that flexural behavior of extruded ECC panel was highly affected by the slight difference in mix composition of ECC panel. This is mainly because the difference in mix composition results in the change of micro-mechanical properties as well as fiber distribution characteristics, represented by fiber dispersion and orientation. In terms of the average fiber orientation, the fiber distribution was found to be similar to the assumption of two dimensional random distribution, irrespective of mix composition. In contrast, the probability density function for fiber orientation was measured to be quite different depending on the mix composition.

• Economic and Environmental Geology
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• v.36 no.5
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• pp.365-374
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• 2003

Various deleterious chemicals can be introduced to existing concrete structures from various external sources. The deterioration of concrete by seawater attack is involved in complex processes due to various elements contained in seawater. In the present study, attention was paid to the formation of secondary minerals and characteristics of mineralogical and micro-structural changes involved in concrete deterioration caused by the influence of major seawater composition. The characteristics of deterioration occurred in existing concrete structures was carefully observed and samples were collected at many locations of coastal areas in Busan-Kyungnam. The petrographic, XRD, SEM/EDAX analyses were conducted to determine chemical, mineralogical and micro-structural changes in the aggregate and cement paste of samples. The experimental concrete deteriorations were performed using various chloride solutions (NaCl, CaCl, $MgCl_2$ and $Na_2SO_4$ solution. The experimental results were compared with the observation results in order to determine the effect of major elements in seawater on the deterioration. The alkalies in seawater appear to accelerate alkali-silica reaction (ASR). The gel formed by ASR is alkali-calcium-silica gel which known to cause severe expansion and cracking in concrete. Carbonation causes the formation of abundant less-cementitious calcite and weaken the cement paste. Progressive carbonation significantly affects on the composition and stability of some secondary minerals. Abundant gypsum generally occurs in concretes subjected to significant carbonation, but thaumasite ({$Ca_6/[Si(OH)_6]_2{\cdot}24H_2O$}${\cdot}[(SO_4)_2]{\cdot}[(CO_3))2]$) occurs as ettringite-thaumasite solid solution in concretes subjected to less significant carbonation. Experimentally, ettringite can be transformed to trichloroaluminate or decomposed by chloride ingress under controlled pH conditions. Mg ions in seawater cause cement paste deterioration by forming non-cementitious brucite and magnesium silicate hydrate (MSH).

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.122-129
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• 2019

The movement of deterioration agents such as a chloride ion, etc. in concrete varies with loading conditions and micro-structure developed by age effect. In this paper, the carbonation behavior by accelerated carbonation test is evaluated considering curing periods(28 days, 91 days, and 365 days) and loading conditions. Carbonation velocity coefficients are obtained referred to KS F 2584. In the control case without loading condition, carbonation velocity coefficient of 91 days decreases to 50.0 % level and that of 365 days decreases to 44.8 % level than that of 28 days curing condition. In 28 curing days, carbonation velocity coefficients changed level of 103.9 ~ 108.8 % in tensile region and 91.9~104.6 % in compressive region by loading conditions. Carbonation velocity coefficients in the 30 % and 60 % tensile loading case at 28 days decreases to 47.3 % and 52.5 % level compared to control case after 1 year. Furthermore, 45.8 % and 44.9 % level of carbonation velocity coefficients are evaluated for 30 % and 60 % compressive loading conditions compared to control case after 1 year. Carbonation velocity coefficient decreases in the 30 % compressive loading level due to effective pore compaction and it increases afterwards due to micro-cracking. In the tensile loading condition, unlike the behavior of compressive region, it linearly increases with increasing loading level.

• Applied Chemistry for Engineering
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• v.22 no.1
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• pp.104-108
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• 2011

In the non-conductive adhesives (NCAs) for adhesion of micro electro mechanical system (MEMS), there are some problems such as delamination and cracking resulting from the large differences of coefficients of thermal expansion (CTE) between NCAs and substrates. So, the addition of inorganic particles such as silica and nano clay to the CTEs composit have been applied to reduce the CTEs of the adhesives. Additions of the flexibilizers such as siloxanes have also been performed to improve the flexibility of epoxy composite. Amino modified siloxane (AMSs) were used to improve compatibility between epoxy and siloxane. In this study, glass transition temperatures (Tg) and moduli of those composites were measured to confirm the effects of AMS with two different equivalents on thermal/mechanical properties of AMS/epoxy composites. Tg of KF-8010/epoxy composites decreased from 148 to $122^{\circ}C$ and those of X-22-161A/epoxy composites decreased from 148 to $121^{\circ}C$. Moduli of KF-8010/epoxy composites decreased from 2648 to 2143 MPa by adding KF-8010 and moduli of X-22-161A/epoxy composites decreased from 2648 to 2014 MPa. In short, using long Si-O chain AMS leads to a greater decrease in moduli. However, haven't showed significant differences in Tg's.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.3
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• pp.83-90
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• 2024

This study investigates the 3D printing characteristics of strain hardening cement composites (SHCC) reinforced by PVA fibers. Three SHCC mixtures with diverse fiber volume fractions (1.0% for F1.0 mixture, 1.5% for F1.5 mixture, and 1.8% for F1.8 mixture) were designed. Except for the F1.0 mixture, all mixtures met the necessary conditions for multiple micro-cracking, with higher fiber volume fractions more readily satisfying these conditions. The flow values of three SHCC mixtures were within the 3D printable range of 120~160 mm, exhibiting decreased flow values with increasing the fiber volume fractions. Observation of the printed SHCC surfaces indicated that the F1.0 mixture had a Level-3 (good) rating, while F1.5 and F1.8 were rated as Level-2 (average). Higher fiber volume fractions resulted in poorer surface quality, thus, further research needs to be performed for modulating SHCC mixture suitable for 3D printing. The uniaxial tension behavior showed that the F1.0 mixture failed at lower strain, whereas F1.5 and F1.8 exhibited higher strain performance with multiple micro-cracks occurring.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.751-756
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• 2016

Graphite was diffusion-bonded by hot-pressing to W-25Re alloy using a Ti interlayer. For the joining, a uniaxial pressure of 25 MPa was applied at $1600^{\circ}C$ for 2 hrs in an argon atmosphere with a heating rate of $10^{\circ}C\;min^{-1}$. The interfacial microstructure and elemental distribution of the W-25Re/Ti/Graphite joints were analyzed by scanning electron microscopy (SEM). Hot-pressed joints appeared to form a stable interlayer without any micro-cracking, pores, or defects. To investigate the high-temperature stability of the W-25Re/Ti/Graphite joint, an oxy-acetylene torch test was conducted for 30 seconds with oxygen and acetylene at a 1.3:1 ratio. Cross-sectional analysis of the joint was performed to compare the thickness of the oxide layer and its chemical composition. The thickness of W-25Re changed from 250 to $20{\mu}m$. In the elemental analysis, a high fraction of rhenium was detected at the surface oxidation layer of W-25Re, while the W-25Re matrix was found to maintain the initial weight ratio. Tungsten was first reacted with oxygen at a torch temperature over $2500^{\circ}C$ to form a tungsten oxide layer on the surface of W-25Re. Then, the remaining rhenium was subsequently reacted with oxygen to form rhenium oxide. The interfacial microstructure of the Ti-containing interlayer was stable after the torch test at a temperature over $2500^{\circ}C$.

• International Journal of Highway Engineering
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• v.16 no.5
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• pp.73-82
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• 2014

PURPOSES : The purpose of this study is to determine the optimum addition rate of SBR latex through the evaluation of durability and strength of SBR latex applied soil pavement. Formerly used materials such as fly ash and cement in soil pavement had resulted in decreased durability due to micro crack by heat of hydration and shrinkage crack in winter. However, that agglutinated polymers help adhesion to aggregate increased comes up with preventing the crack opening when the number of capillary tubes of SBR latex get decreased in the hydration process of cement. Therefore, in this study, it is suggested that the evaluation of the field applicability of soil pavement be conducted through the performance lab test in terms of strength increment, adhesion improvement, and crack resistance based on SBR latex addition rate. METHODS : In order to evaluate the field applicability of soil pavement, SBR latex was added 0 to 3% by 1% increment, with fixed cement contents of 3% and 5%. The resistance of shear failure and crack of soil pavement were evaluated by performing the uniaxial compressive strength test and indirect tensile strength test at -20 and $20^{\circ}C$, respectively. RESULTSCONCLUSIONS : It was found out that from both tests, resistance of shear failure and crack were improved with increment of curing time, and especially more than 2% of SBR latex addition rate and 5% cement content gave better results.