• Journal of Pharmaceutical Investigation
• /
• v.12 no.4
• /
• pp.112-125
• /
• 1982

Sulfamethoxazole particles were microencapsulated using the gelatin-acacia complex coacervation method. Micromeritic properties and dissolution characteristics of the microcapsules were studied. The particle size distribution followed log-normal form. As the hardening time increased, the particle size and wall thickness increased ($45.3-52.0\;{\mu}m$, $2.02-5.12\;{\mu}m$, respectively). This is considered to be due to the cross-linked wall structure of formalized microcapsules which prevents shrinking of gelatin during the dehydration and drying processes. An increase of hardening time clearly delayed the release rate. The in vitro 50% dissolution time $(t_{50})$ for unencapsulated sulfamethoxazole powder was less than 3 min.; for microcapsules hardened for 30 min, the $t_{50}$ was 20.1 min.; for those hardened for 60 min. the $t_{50}$ was 25.0 min.; for those hardened for 120 min., the $t_{50}$ was 35.8 min. The surface of the unhardened microcapsules was smooth and had no cracking or pore penetration. However, the surface of the hardened microcapsules was folded and invaginated.

• Journal of the Korean Society for Heat Treatment
• /
• v.3 no.2
• /
• pp.10-19
• /
• 1990

The tempering behavoirs of 0.45% carbon steel treated by automatic progressive high frequency induction hardening equipment have been investigated. In order to examine the correlation of hardness with both tempering temperature and time, simple regression analysis has been made using the statistical quality control package. The maximum surface hardness value of induction hardened zone and its effective hardening depth have been determined to be Hv 810 and 0.76mm, respectively. The hardness obtained after tempering has been shown to vary lineary with tempering time at six different temperatures. The activation energies during tempering have been calculated to be 25.34kcal/mole, 32.73kcal/mole and 49.24kcal/mole for HRcs 60, 50 and 40, respectively, showing that tempering process occurs by a complex mechanism, The tempering hardness equation of $H=90.113{\sim}4.531{\times}10^{-3}$ [T(11.996+log t)] has proved to be in a reasonably good agreement with experimently determined data and it is also expected to be useful for the determination of tempering treatment conditions to obtain a required hardness value.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 2005.10a
• /
• pp.117-122
• /
• 2005

Prepacked polymer mortar that is mainly composed of MMA monomer and used for the patching and restoring materials of concrete structures was developed, and its hardening and strength properties were experimentally surveyed. Results of study show that the permeance of binder into the aggregate was excellent for the case of PMMA mixing ratio of below 10%, the surface hardening inferiority was not generated for the case of the ratio of over 5%. Working time of the prepacked polymer mortar and hardening shrinkage tended to decrease as the PMMA mixing ratio increased. On the other hand, the ratio turned out not to decisively affect on compressive and flexural strengths. Regardless of PMMA mixing content, the adhesive strength was about 2.5 MPa. Occurring the desquamation on the substrate of cement concrete showed the adhesive strength of MMA prepact polymer mortar was excellent.

• Journal of the Korean Society for Heat Treatment
• /
• v.24 no.4
• /
• pp.193-198
• /
• 2011

Effect of CaO addition on age hardening response has been studied by using optical microscopy, scanning electron microscopy and differential thermal analysis in AZ91 and CaO-containing ECO-AZ91 alloys. After solution treatment, the ${\beta}$($Mg_{17}Al_{12}$) phase formed during solidification mostly disappeared in the microstructure in the AZ91 alloy, whereas numerous ${\beta}$ precipitates containing Ca were still observed in the ECO-AZ91 alloy due to its enhanced thermal stability. The ECO-AZ91 alloy showed the delayed peak aging time and higher peak hardness compared with those of the AZ91 alloy. The activation energies for ${\beta}$ precipitation calculated by means of Kissinger method increased from 71.4 to 85.6 kJ/mole by the addition of CaO, which implies that CaO plays a role in reducing ${\beta}$ precipitation rate in the AZ91 alloy.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1998.10a
• /
• pp.92-98
• /
• 1998

Nonlinear finite element analyses of one dimensional consolidation problem were performed using an anisotropic hardening constitutive model. For the analyses, the anisotropic hardening elasto-plastic constitutive model based on the generalized isotropic hardening(GIH) rule was implemented into a nonlinear finite element analysis program, PLASTIC. In order to preserve the accuracy of the finite element solution for nonlinear problems, an implicit stress integration algorithm was employed. A consistent tangent moduli could also ensure the quadratic convergence of Newton's method. As a result, the nonlinear solution was accurately calculated and was converged to be asymptotically quadratic. In a consolidation problem, the relationship between load and settlement and between settlement and time vertical was analyzed comparing with results using the Cam-clay type model and the final consolidation settlement and the duration of primary consolidation could be evaluated rigorously using the GIH constitutive model.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.11 s.176
• /
• pp.51-58
• /
• 2005

Laser surface hardening technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for automotive parts. The objective of this research work is to investigate the influence of the process parameters, such as power of laser and defocused spot position, on the characteristics of laser heat treatment for the case of SM45C medium carbon steel. CW Nd:YAG laser is selected as the heat source. The optical lens with the elliptical profile is designed to obtain a wide heat treatment area with a uniform hardness. From the results of the experiments, it has been shown that the maximum hardness is approximatly 780 Hv when the power and the travel speed of laser are 1,095 W and 0.6 m/min, respectively. In addition, the hardening width using the elliptical lens was three time larger than that using the defocusing of laser beam.

• Korean Journal of Materials Research
• /
• v.23 no.3
• /
• pp.199-205
• /
• 2013

The mechanical properties and microstructures of aluminum-matrix composites fabricated by the dispersion of fine alumina particles less than $20{\mu}m$ in size into 6061 aluminum alloys are investigated in this study. In the as-quenched state, the yield stress of the composite is 40~85 MPa higher than that of the 6061 alloy. This difference is attributed to the high density of dislocations within the matrix introduced due to the difference in the thermal expansion coefficients between the matrix and the reinforcement. The difference in the yield stress between the composite and the 6061 alloy decreases with the aging time and the age-hardening curves of both materials show a similar trend. At room temperature, the strain-hardening rate of the composite is higher than that of the 6061 alloy, most likely because the distribution of reinforcements enhances the dislocation density during deformation. Both the yield stress and the strain-hardening rate of the T6-treated composite decrease as the testing temperature increases, and the rate of decrease is faster in the composite than in the 6061 alloy. Under creep conditions, the stress exponents of the T6-treated composite vary from 8.3 at 473 K to 4.8 at 623 K. These exponents are larger than those of the 6061 matrix alloy.

• Korean Journal of Metals and Materials
• /
• v.48 no.12
• /
• pp.1103-1108
• /
• 2010

We fabricated flanged outer races for wheel bearing units using 0.52%C clean steels, and then characterized and studied the transformation behavior. The outer races produced by hot forging and high frequency induction hardening in this study were analyzed through microstructural characterization using OM, SEM, TEM, and X-ray diffractometer and their microhardness depth profiles of the raceway contacted by balls were measured using MVH tester. The surface hardened layers with a uniform hardness profile in the raceway consisting of very fine martensite with sub-micron sized retained austenite could be formed for very short time during high frequency induction hardening after hot forging. The very fine martensite may be transformed on rapid cooling, from the inhomogeneous austenite nucleated on rapid heating in small particles of pearlitic cementite fragmentated by hot forging. On the other hand the sub-micron sized retained austenite may be chemically stabilized due to their extremely small size, from the small austenite nucleated at the grain boundaries.

• Restorative Dentistry and Endodontics
• /
• v.17 no.2
• /
• pp.331-341
• /
• 1992

The purpose of this study was to measure the polymerization contraction stress of two types of composite resins; chemical cured type(Cliarfil F II, Kuraray, Japan) and photo-cured type(Photo-Clearfil Bright, Kuraray, Japan). The stresses of composite resin by contraction measured with specially designed measuring device(Fig. 1). The stresses caused by shrinkage during hardening of specimens were measured according to the type of composite resins, thickness of specimen(0.65, 1.30 and 1.95mm), and ratio of catalyst to base in case of only chemical cured composite resin(0.5, 1.0 and 1.5). As the composite resin specimen shrank on hardening, the load cell recorded force vs time automatically on pen-recorder(Toa, Japan) with a cross-head speed 60mm/hr at 0~10 voltages up to 2 hours. The experiments were conducted in a room maintained at $23{\pm}2^{\circ}C$ and relative humidity $50{\pm}10%$. The results were as follows. 1. The contraction stress during hardening was higher in photo cured composite resin than in chemical cured composite resin. 2. The contraction stress during hardening was increased with thickness of composite resin specimen. 3. In chemical cured composite resin, the polymerization contraction stress was decreased with ratio of catalyst and base. 4. The contraction stress during polymerization was higher in early time after insertion of photo cured composite resin and chemical cured composite resin.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.39 no.3
• /
• pp.205-210
• /
• 1994

This experiment was conducted to investigate of soil hardening degree before sowing, furrow depth at sowing and flooding time after sowing at furrowing in flooded rice paddy field that many people have an interest in as direct sowing method most recently. As hardening period was increased, the percentage of seedling stand and seed floating at flooding were increased slightly, while buried depth of stem at maximum tillering stage and cone penetration depth were decreased, respectively. Therefore, optimum degree of soil hardening was about 3 days after draining, at this time, cone penetration degree was about 6~7cm. According to furrow depth was more and more deep, buried depth of stem was increased gradually, but percentage of seedling stand was decreased considerbly. Also, root distribution ratio on surpace horizon and lodging degree were increased gradually according to furrow depth become more and more shallow. As flooding time after sowing was late, percentage of seedling stand and panicle number per $m^2$ were decreased slightly. These results apparently indicated that sowing after 3 days hardening when cone penetration degree was 6~7cm, furrow depth 3~4cm degree and flooding time just after sowing the best method to good establish of seedling stand.