• Journal of the Korean Ceramic Society
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• v.44 no.10
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• pp.574-579
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• 2007

Porous $Al_2O_3$ ceramics were prepared by the gelcasting foams method (a slurry foaming process) with acrylamide monomer. The foaming and gelation behavior was investigated with the parameters such as the type and concentration of surfactant, solid loading of slurry, and the concentrations of initiator and catalyst. Density, porosity, microstructure, and strength of the green and sintered samples were characterized. Of the four kinds of surfactants tested, Triton X-114 showed the highest foaming ability for the solid loading of 55-30 vol%. The gelation condition giving the idle time off min was found to set the foamed structure without significant bubble enlargement and liquid lamella thinning. The green samples were fairly strong and machinable and showed maximum strength of 2.4 MPa in diametral compression. The sintered samples showed densities of 10-36% theoretical (i.e. porosity 90-64%) with a highly interconnected network of spherical pores with sizes ranging from 30 to $600{\mu}m$. The pore size and connectivity increased but the cell strut thickness decreased with decreasing the solid loading. Flexural strength of 37.8-1.7 MPa was obtained for the sintered samples.

• Journal of the Korean Applied Science and Technology
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• v.13 no.1
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• pp.11-19
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• 1996

The liposomes have been developed in many drugs and cosmetics fields. The liposomes prepared with main compounds of the intercellular lipids and lecithin. Amphiphile nonionic surfactants used for (PEG) n-sitosterol(n=5), diethanolamine cetylphosphate. The effect of gelation for liposomes have been on swelling reaction which have been mixed phospholipid with polyol-group at the high temperature. There were very good encapsulated properties of the active ingredients whether hydrophilic-group(magnesium ascorbyl phosphate, allantoin, sodium hyaluronate) and hydrophobic-group(vitamin-E acetate, vitamin-A palmitate). Optimum condition of liposomes were passed five times in the microfluidizer(700bar), wetting reaction temperature was at $95{\pm}5^{\circ}C$ for a hours. Particle size distribution of the vesicles should be within range 50-560nm(mean 200nm). The stability of liposomes for the course of time was stabilized for six months at $45^{\circ}C$. Application of the cosmetic was prepared moisturizing cream with liposomes of the phospholipid base.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.6
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• pp.732-746
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• 2003

Statement of problem. Soft lining materials, also referred to as tissue conditioning materials, tissue heating materials, relining materials, soft liners or tissue conditioners, were first introduced to dentistry by a plastic manufacturer in 1959. Since the introduction of the materials to the dental field, their material properties have been continually improved through the effort of many researchers. Soft lining materials have become widely accepted, particularly by prosthodontists, because of their numerous clinical advantages and ease of manipulation. Unfortunately, few reports have been issued upon the topic of increasing the bond strength between the base metal alloy used in cast denture bases and PMMA soft liner modified with 4-META, nor upon the pattern of debonding and material change in wet environment like a intra oral situation. Purpose. The purposes of this study were comparing the bond strength between base metal alloy used for the cast denture bases and PMMA soft liner modified with 4-META, and describing the pattern of debonding and material property change in wet environment like the intraoral situation. Material and Methods. This study consisted of four experiments: 1. The in vitro measurement of shear bond strength of the adhesive soft liner. 2. The in vitro measurement of shear bond strength of the adhesive soft liner after 2 weeks of aging. 3. A comparison of debonding patterns. 4. An evaluation the Relation time of modified soft liner. The soft liner used in this study was commercially available as Coe-soft (GC America.IL.,USA), which is provided in forms of powder and liquid. This is a PMMA soft liner commonly used in dental clinics. The metal primer used in this study was 4-META containing primer packed in Meta fast denture base resin (Sun Medical Co., Osaka, Japan). The specimens were formed in a single lap joint desist which is useful for evaluating the apparent shear bond strength of adhesively bonded metal plate by tensile loading. Using the $20{\times}20mm$ transparent grid, percent area of adhesive soft liner remaining on the shear area was calculated to classify the debonding patterns. To evaluate the change of the initial flow of the modified adhesive soft liner, the gelation time was measured with an oscillating rheometer (Haake RS150W/ TC50, Haake Co., Germany). It was a stress control and parallel plate type with the diameter of 35mm. Conclusion. Within the conditions and limitations of this study, the following conclusions were drawn as follows. 1. There was significant increase of bond strength in the 5% 4-META, 10% 4-META containing groups and in the primer coated groups versus the control group(P<0.05). 2. After 2 weeks of aging, no significant increase in bond strength was found except for the group containing 10% 4-META (P<0.05). 3. The gelation times of the modified soft liner were 9.3 minutes for the 5% 4-META containing liner and 11.5 minutes for the 10% 4-META liner. 4. The debonding patterns of the 4-META containing group after 2 weeks of aging were similar to those of immediaely after preparation, but the debonding pattern of the primer group showed more adhesive failure after 2 weeks of aging.

• Journal of Pharmaceutical Investigation
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• v.30 no.3
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• pp.167-172
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• 2000

The purpose of this study is to develop a transurethral liquid suppository containing prostaglandin $E_1\;(PGE_1)-loaded$ microemulsion, which undergoes a phase transition to gels at body temperature. The effects of oils, ethanol as solvent and HCl as pH-controlling agent on the physicochemical properties of liquid suppositories composed of poloxamer P 407, P 188 and carbopol was investigated. The stability of $PGE_1$ and release of $PGE_1$ from liquid suppository were evaluated. Oils such as Neobee and soybean oil significantly decreased the gelation temperature but increased the gel strength of liquid suppository due to their strongly binding with the components of liquid suppository base. However, ethanol slightly did the opposite. The pH of liquid suppositories hardly affected the gelation temperature and gel strength due to addition of very small HCl (0.005-0.01%). A liquid suppository [$PGE_1/P$ 407/P 188/carbopol/Neobee/ethanol/HCl (0.2/14/14/0.4/7/2/0.005%)], which had the gelation temperature $(34.2{\pm}0.6^{\circ}C)$ and gel strength $(31.35{\pm}4.37\;sec)$ suitable for liquid suppository system, was easily administered and not leak out from the body. About 60% of $PGE_1$ was released out within 2 h from this formulation. It was shown that the release of $PGE_1$ was proportional to the square root of time, indicating that $PGE_1$ might be released from the suppository by Fickian diffusion. It was stable at $4^{\circ}C$ for at least 2 months. The results suggest that transurethral liquid suppository containing prostaglandin $E_1-loaded$ microemulsion is thought to be a convenient, safe and effective dosage form for $PGE_1$. However, it should be further developed as a more convenient and stable dosage form for $PGE_1$.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.677-681
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• 1989

On the preparation of silica glass by sol-gel process, we used fine powder of silica gel to prevent cracking. In this case, the best condition of silica glass preparation is the contents of 10~40wt% seed and the gelation time of solution in contract. The dried gels conversed to silica glass by heat treatment up to 125$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.28 no.4
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• pp.324-328
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• 1991

Monolithic silica gel and glass were prepared from TMOS solution with high concentration of HCl. Appearance of the dried gels and gelation time varied with content of HCl and H2O were observed in the TMOS-CH3OH-HCl-H2O system. The conversion from gel to glass during heat treatment stage was investigated using TG-DTA, XRD, IR and SEM and characteristics of the gel were examined by measuring bulk density, linear shrinkage and Vicker's hardness. A transparent silica glass was prepared from the gel after heat treatment at 1050℃.

• Journal of the Korean Chemical Society
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• v.9 no.1
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• pp.16-22
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• 1965

The time-lag-effect of alkali salts on the gelation of sodium alginate-$CaSO_4{\cdot}$1/2 $H_2O$ is compared with Miyake's data, and then the formation rate of the elastics measured by the continuous method (an improved Schwedoff's method) and the change of rigidity with metallic oxides are studied as follows: (1) The gelation processes of sodium alginate and $CaSO_4{\cdot}$1/2 $H_2O$-aqueous sol are studied by measuring, continuously the increases of tensions ofsamples. (2) The time-lag-effect of $Na_3PO_4$ on the formation rate of the elastic gel is larger than that of $Na_2CO_3$, but the difference between the effects of the two alkali salts on the rate is found not so greater than predicted in Miyake's data. (3) Any regularities of the effect on the rate by metallic oxides are not observed. The increasing effects of the rates of $SiO_2$ and MgO are relatively large, and that of ZnO is relatively small. However, $Al_2O_3$, $Sb_2O_3$ and $TiO_2$show some decreasing effects. As a result it is noted that the regularities do not depend on the effect of oxide species and their amounts. (4) It is not found proportionality between the rigidity and the gelation rate. However, the increasing effect of the rigidity with the addition of metallic oxides can be observed. The rigidity increasing rate of MgO is the largest of them.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.216-224
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• 1997

Porous silica ceramics were prepared(with HCI catalyst) using H2O/TEOS molar ratios of 2.6~59.0, with the EtOH/TEOS ratio fixed. After preparing 9 kinds of sol, the followings were investigated; measurement of the gelation time, thermal analyses by TG/DTA, property analyses of the intermediates by FT-IR and X-ray diffractometry with dried samples, analyses of SiO2 polymer by FT-IR, the investigation of specific sur-face area and pore size distribution by N2-adsorption isotherm, and structural change of SiO2 polymer and pore morphology by TEM observation, with samples heat-treated to 50$0^{\circ}C$. In the concentrations of in-vestigated compositions and catalyst, gelation time showed a minimum at ca. 11 moles of water per one mole of TEOS, the highest degree of polymerization at ca. 8-18 moles, and the largest specific surface area at ca. 11 moles, which means that the polymerization proceeded fastest at ca. 11 moles of water. In con-clusion, the more water used, the faster the polymerization reaction up to ca. 11 moles, but more than ca. 11 moles of water caused retardation of gelation and resultant reduction of specific surface area.

• Polymer(Korea)
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• v.25 no.2
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• pp.168-176
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• 2001

The effect of novel N-crotyl-N,N-dimethyl-4-methylanilinium hexafluoroantimonate (CMH) curing agent as a thermal latent initiator on thermal behaviors, rheological properties, and thermal stability of diglycidylether of bisphenol A (DGEBA) epoxy cationic system was investigated. From DSC measurements of DGEBA/CMH system, it was shown that this system exhibits an excellent thermal latent characteristic at a given temperature. The conversion and conversion rate of DGEBA/CMH system increased with increasing the concentration of initiator, due to high activity of CMH. Rheological properties of the system were investigated under isothermal condition using a rheometer The gelation time was obtained from the analysis of storage modulus (G'), loss modulus (G"), and damping factor (tan $\delta$). As a result, the reduction of gelation time was affected by high curing temperature and concentration of CMH, resulting in high degree of network formation in cationic polymerization, due to difference of activity. The thermal stability of the cured epoxy resin was discussed in terms of the activation energy for decomposition and thermal factors determined from TGA measurements.ents.

• Analytical Science and Technology
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• v.26 no.3
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• pp.205-210
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• 2013

For the synthesis of crystalline LAS glass by sol-gel method, the effect of operation conditions including metal alkoxide ratio, nucleating agent composition and heat treatment on the crystalline properties was experimentally investigated. The gelation time and crystallization temperature were proportionally affected by the mole ratio of TEOS in metal alkoxides solution. The addition of $TiO_2$ had an influence on the increasing of the gelation time, but the crystallization temperature was rarely dependent on the adding of nucleating agent. The crystallinity of LAS glass was improved by the nucleating agent under same heat treatment conditions.