• Journal of the Korean Ceramic Society
• /
• v.39 no.11
• /
• pp.1097-1102
• /
• 2002

Hydroxyapatite(HAp) powders were synthesized by wet-precipitation precess using $Ca(NO_3)_2{\cdot}4H_2O$ and $(NH_4)_2HPO_4$ and homogeneous composites of four type were prepared by mixing of synthetic HAp and Polyacrylic Acid(PAA). Ca/P ratio of synthetic HAps was determined using ICP analysis and the thermal property of HAp/PAA composites were investigated by TGA. Good crystalline HAp was obtained at pH 11 and $60{\circ}C$. The ratio of Ca/P in synthetic HAps was quantified in a range of 1.35~1.49, from which Ca-deficient HAp was obtained. The specific surface area of HAp/PAA composite increased with increasing the content of PAA and the weight loss of HAp/PAA composite at $800{\circ}C$ decreased in a range of 3.5~9.6% due to the degradation of PAA binder. From FT-IR analysis of HAp/PAA composite, it was confirmed that the ionic bond between ion of HAp and carboxyl group of PAA was formed.

• Advances in concrete construction
• /
• v.10 no.5
• /
• pp.403-416
• /
• 2020

This study investigated the effect of alkaline activators - NaOH_aq (NH) (NH: 0-16 M) and Na₂SiO_3aq (NS) (NS/NH: 0-3.5) in the synthesis of silico-manganese fume (SMF) and ground blast furnace slag (BFS) blended alkali-activated mortar (AASB). The use of individual activator was ineffective in producing AASB of sufficient fresh and hardened properties, compared to the synergy of both activators. This may be attributed to incomplete dissolution and condensation of oligomers required for gelation of the binder. An inverse relationship was noted among the fresh properties and the NH concentration or NS/NH ratio. This was influenced by the dissolution and condensation of silicate monomers under polymerization process. The maximum 28-day strength of ~45 MPa, setting time of 60 min and flow of 182 mm was obtained with the use of combined activators (10M-NH and NS/NH=2.5). The combined activators at NS/10M-NH=2.5 constituted SiO₂/Na₂O, H₂O/Na₂O and H₂O/SiO₂ molar ratio of 1.61, 17.33 and 10.77, respectively. This facilitated the formation of C-S-H, C/K-A-S-H and C-Mn-S-H in the framework together with an increase in the crystallinity due to more silicate re-organization within the aluminosilicate chain. On comparison of the high concentrated with mild alkali synthesized product, it revealed that the concentration of OH^- and Si monomers together with alkali metals influenced the dissolution of precursors and embedment of the constituent elements in the polymeric matrix. These factors eventually contributed to the microstructural densification of the mortar prepared with NS/10M-NH=2.5 thereby enhancing the compressive strength.

• Polymer(Korea)
• /
• v.28 no.2
• /
• pp.135-142
• /
• 2004

Poly(vinyl acetate) (PVAc) prepared by emulsion polymerization has broad applications for additives such as paint binder, adhesive for wood and paper due to its low glass transition temperature which help to plasticize substrate resins. Since emulsion polymerization has a disadvantage that surfactant and ionic initiator degrade properties of the product polymer, poly(vinyl acetate-co-butyl acrylate) (VVc-BA) was synthesized using potassium persulfate as catalyst and poly(vinyl alcohol) (PVA) as protective colloid to prevent the degradation. The copolymer latex product was internally plasticized and has enhanced colloid stability, adhesion, tensile strength and elongation. During VAc-BA emulsion polymerization, no coagulation and complete conversion occur with the reactant mixture of 0.7wt% potassium persulfate, 15wt% poly(vinyl alcohol) (PVA-217), and the balanced monomer that the weight ratio of vinyl acetate to butyl acrylate is 19. As the concentrations of PVA increase, the copolymerization becomes faster and polymer particles are more stable, resulting in enhanced mechanical stability of the VAc-BA copolymer. However, the size of the polymer particles decreases with increasing PVA contents. Properties of the VAc-BA copolymer, such as minimum film formation temperature, glass transition temperature, surface morphology, molecular weight and molecular weight distribution, tensile strength and elongation, were characterized using differential scanning calorimeter, transmission electron microscope and other instruments.

• Journal of Sensor Science and Technology
• /
• v.10 no.2
• /
• pp.101-107
• /
• 2001

A highly selective, sensitive and reliable ozone sensing $In_2O_3$ thin film was fabricated by a sol-gel method. The fabricated film is operated at a relatively lower temperature than ever developed thin films and saved operating power. $In_2O_3$ films deposited by sol-gel technique has been recently attracted because it is an economical and energy saving method and precisely controlled microstructure. Indium alkoxide precursor was synthesized from the reaction between indium hydroxide and butanol. PVA binder was used to improve adhesion of the films. The $In_2O_3$ thin films were obtained by spin coating from 1 to 5 times followed by drying at $100^{\circ}C$ and calcining at $600^{\circ}C$ for 1h. The film thickness was controlled by the number of coating time. The morphology and the thickness of the $In_2O_3$ films were examined by a SEM and XRD. The $In_2O_3$ thin films show a high sensitive to ozone gas at operating temperature of $250^{\circ}C$. The $In_2O_3$ sensor has very good selectivity to $CH_4$, CO, $C_4H_{10}$ and ethanol.

• Journal of Adhesion and Interface
• /
• v.19 no.2
• /
• pp.74-82
• /
• 2018

Many methods for cross-linking acrylic PSAs have been discussed previously. For high cross-linking density, epoxy functionalized monomer and methyl aziridines as cross-linking agents were used in this study. Additionally, photopolymerization using different UV doses was investigated to synthesize a binder because of its rapid productivity. FT-IR analysis, curing behaviours and adhesion performance were examined for the relationship between UV doses and temperature as curing conditions. According to the results, the gel fraction was over 50% even at $120^{\circ}C$ after UV curing at a dose of $800mJ/cm^2$. On the other hand, while gel fractions of all samples reached approximately 80% only at $180^{\circ}C$ in thermal curing for 1 hour, gel fractions of the samples after thermal curing for 3 hours increased rapidly above $120^{\circ}C$ regardless of UV doses and reached approximately 100% at $180^{\circ}C$. This means that the second cross-linking reaction, esterification, is mainly dependent on the curing temperature.

• Journal of the Korean Electrochemical Society
• /
• v.22 no.4
• /
• pp.148-154
• /
• 2019

Vanadium oxide based materials have been studied as novel negative electrode materials in lithium-ion batteries (LIBs) because of their high specific capacity. In this study, potassium metavanadate ($KVO_3$) was synthesized and its electrochemical properties are evaluated as a negative electrode materials. The aqueous solution of $NH_4VO_3$ is mixed with a stoichiometric amount of KOH. The solution is boiled to remove $NH_3$ gas and dried to obtain a precipitate. The obtained $KVO_3$ powders are heat-treated at 300 and $500^{\circ}C$ for 8 h in air. As the heat treatment temperature increases, the initial reversible capacity decreases, but the cycle performance and Coulombic efficiency are improved slightly. On the contrary, the electrochemical performances of the $KVO_3$ electrodes are greatly improved when a polyacrylic acid (PAA) as binder was used instead of polyvinylidene fluoride (PVDF) and a fluoroethylene carbonate (FEC) was used as electrolyte additive. The initial reversible capacity of the $KVO_3$ is 1169 mAh/g and the Coulombic efficiency is improved to 76.3% with moderate cycle performance. The $KVO_3$ has the potential as a novel high-capacity negative electrode materials.

• Korean Chemical Engineering Research
• /
• v.60 no.2
• /
• pp.184-192
• /
• 2022

Porous NiO synthesized via hydrothermal synthesis was used in the electrodes of lithium-sulfur batteries to inhibit the elution of lithium polysulfide. The electrode of the lithium-sulfur battery was manufactured as a freestanding flexible electrode using an economical and simple vacuum filtration method without a current collector and a binder. The porous NiO-added S/CNT/NiO electrode exhibited a high initial discharge capacity of 877 mA h g^-1 (0.2 C), which was 125 mA h g^-1 higher than that of S/CNT, and also showed excellent retention of 84% (S/CNT: 66%). This is the result of suppressing the dissolution of lithium polysulfide into the electrolyte by the strong chemical bond between NiO and lithium polysulfide during the charging and discharging process. In addition, for the flexibility test of the S/CNT/NiO electrode, the 1.6 × 4 cm² pouch cell was prepared and exhibited stable cycle characteristics of 620 mA h g^-1 in both the unfolded and folded state.

• Journal of Soil and Groundwater Environment
• /
• v.27 no.4
• /
• pp.49-62
• /
• 2022

The magnesium and iron-based layered double hydroxide (Mg-Fe LDH) was synthesized by the co-precipitation process and the bead type LDH (BLDH, 5~6 mm in diameter) was manufactured by using the Mg-Fe LDH and the starch as a binder. To evaluate the feasibility of the BLDH as the As stabilizer in the soil, various experiments were performed and the As stabilization efficiency of the BLDH was compared to that of powdered type LDH (PLDH, <149 ㎛ in diameter). For the As sorption batch experiment, the As sorption efficiency of both of the PLDH and the BLDH showed higher than 99%. For the stabilization experiment with soil, the As extraction reducing efficiency of the PLDH was higher than 87%, and for the BLDH, it was higher than 80%, suggesting that the BLDH has similar the feasibility of As stabilization for the contaminated soil, compared to the PLDH. From the continuous column experiments, when more than 7% BLDH was added into the soil, the As stabilization efficiency of the column maintained at over 91% for 7 pore volume flushing (simulating about 21 months of rainfall) and slowly decreased down to 64% after that time (to 36 months) under the non-equilibrium conditions. Results suggested that more than 7% of BLDH added in As-contaminated soil could be enough to stabilize As in soil for a long time. The main As fixation mechanisms on the LDH were also identified through the X-ray fluorescence (XRF), the X-ray diffraction (XRD), and the Fourier transform infrared (FT-IR) analyses. Results showed that the LDH has enough of an external surface adsorption capacity and an anion exchange capability at the interlayer spaces. Results of SEM/EDS and BET analyses also supported that the Mg-Fe LDH used in this study has sufficient porous structures and outer surfaces to fix the As. The reduction of carbonate (CO₃^2-) and sulfate (SO₄^2-) anions in the LDH after the reaction between As and the LDH was observed through the FT-IR, the XRF, and the XRD analyses, suggesting that the exchange of some of these anions with the arsenate (H₂AsO₄^- or HAsO₄^2-) occurs at the LDH interlayers during the stabilization process in soil.

• Applied Chemistry for Engineering
• /
• v.21 no.4
• /
• pp.377-384
• /
• 2010

We perform a comparative study to investigate the properties of the new energetic chain extender (AzPD). A series of poly(glycidyl azide)/poly(tetramethylene oxide)-based energetic segmented polyurethane (GAP/PTMG ESPU) with different chain extender, which is 3-azidopropane-1,2-diol (AzPD), 1,4-butane diol (1,4-BD), or 1,5 pentane diol (1,5-PD), was synthesized by solution polymerization in dimethyl formamide (DMF) and their phase behaviors were investigated. The ESPUs were characterized with Fourier transform infrared-attenuated total reflection spectroscopy (ATR FT-IR), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results of the ATR FT-IR analysis of the urethane carbonyl group region showed that the 'free' C=O fraction was higher in GAP/PTMG AzESPU (0.5) than GAP/PTMG BDESPU (0.44) and GAP/PTMG PDESPU (0.41) for 7 days samples after preparation and that it was similar in the range of 0.26~0.29 for three 60 days ESPU samples. DMA curves of the GAP/PTMG AzESPU for 7 days samples showed amorphous polymers, but GAP/PTMG BDESPU and GAP/PTMG PDESPU showed viscoelastic behaviors with rubbery plateau and the flow region. However, DMA curves of the GAP/PTMG AzESPU for 60 days samples showed viscoelastic behaviors with rubbery plateau and the flow region like GAP/PTMG PDESPU, but GAP/PTMG BDESPU did not show the flow region. From phase behaviors with ATR FT-IR, DSC and DMA analysis, GAP/PTMG AzESPU showed good phase-mixing between components. However, it represented viscoelastic behavior of TPE similar to GAP/PTMG PDESPM according to phase equilibrium progress with aging time.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.5
• /
• pp.104-111
• /
• 2015

This study shows the mechanical properties of alkali-activated slag cement (AASC) synthesized using sulfate with NaOH solution. The used sulfates were calcium sulfate ($CaSO_4$, denoted CS) and sodium sulfate ($Na_2SO_4$, denoted SS). The replacement ratio of sulfates was 2.5, 5.0, 7.5 and 10.0% by weight of slag. NaOH solution of 2M and 4M concentration was used. A sample was activated with sulfate and activated with blended activator (blending NaOH solution with sulfate) respectively. 24 mix ratios were used and the water-binder weight ratio for the test was set 0.5. This research carried out the compressive strength, flexural strength, ultrasonic pulse velocity (UPV), absorption and X-ray diffraction (XRD). In the case of samples with CS, sample with 7.5% CS, sample with 2M NaOH+5.0% CS and sample with 4M NaOH+5.0% CS showed the good performance in the strength development. In the case of samples with SS, sample with 10.0% SS, sample with 2M NaOH+7.5% SS and sample with 4M NaOH+2.5% SS obtained good performance in strength. The results of UPV and water absorption showed a similar tendency to the strength properties. The XRD analysis of samples indicated that the hydration products formed in samples were ettringite, CSH and silicate phases. In this study, it is indicated that when compared to the use of sulfate only, the use of both sulfate and NaOH solution makes mechanical properties of AASC better.