• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.107-115
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• 1999

Microstructural variation and strengthening effects with lamination methods of alumina fiber-reinforced ${\gamma}$-LiAlO2 matrixes for Molten Carbonate Fuel Cell(MCFC) were studied. The porosities of all matrix laminated by hot-pressing of two green sheets under 1 kg/$\textrm{cm}^2$ at 45$^{\circ}C$ for 1 min and by double-casting which the second layer cast on the first green sheet dried for 3.5h were more than 50%. The strength of the Al2O3 fiber-reinforced matrix prepared by lamination was enhanced by 70% in comparison with the non-laminated matrix (115 gf/$\textrm{mm}^2$) and the strength-directionality due to fiber-orientation also could be removed. The strength of matrixes laminated by triple-casting was higher than that of the double-cast matrix, but triple-cast matrix showed the directionality with the casting direction, and furthermore its porosity was less than 50%. Although the strength of matrixes laminated by double-casting (195 gf/$\textrm{mm}^2$) is slightly less than that of matrixes laminated by hot-pressing (212 gf/$\textrm{mm}^2$), the double-casting method was evaluated to be more efficient laminating process in MCFC matrix processing.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.3
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• pp.342-350
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• 2003

Statement of problem. Titanium-Nickel alloy might be used in various prosthetic restorations since it has a unique property such as super-elasticity and high fatigue resistance. However, little is known about the casting ability of this alloy. Purpose. This in vitro study compared the casting accuracy and the porosity made with different investments and various sprue designs to ascertain what casting condition would be better for the fabrication of Ti-Ni cast restorations. Material and methods. A total of 70 Ti-Ni alloy crowns were made and divided into 7 groups of 10 copings on a metal master die. For measuring the effect of the sprue numbers, two groups with one and two 8-gauge sprues were compared. Moreover, the results of the conventional sprue and the double thickness sprues were compared. Three investments were used; carbon free phosphate bonded investment, titanium investment and gypsum bonded investment. The cast restorations were evaluated at 48 points on the entire circumferential margin with a stereomicroscope measuring in micrometers. Each crown was radiographically examined for casting defects and porosity. Data on casting accuracy were analyzed using two-way and Post hoc Scheffe's comparison to determine whether significant differences existed at the 95% confidence level. Student-Newman-Keuls test were performed to identify significant differences in the number of voids. Results. The double sprueing group and double thickness group had significantly less marginal discrepancy than the single sprueing group (P<.05 and P<.01, respectively). The castings with phosphate bonded investment showed the least marginal discrepancy and the smoothest surface. The castings invested in the gypsum bonded investment had the greatest gaps in margin and the largest failure rate. The double sprueing group and phosphate bonded investment group had significantly smaller void numbers and smaller void size than the other groups. Conclusion. Within the limitations of this in vitro study, the casting accuracy of the groups using thicker, double sprue design and the phosphate bonded investment was significantly superior. Moreover, void number and size were less than other groups.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.6
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• pp.677-682
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• 2006

Statement of problem. Various double crown systems have been used with removable partial dentures in the clinical field. Although retentive force between inner and outer crown are affected by several factors, differences between the retentive forces of different double crown system types are expected. Purpose. The purpose of this study was to evaluate the initial retentive force of outer crowns fabricated by the conventional casting technique in conus and hybrid double crowns. Material and methods. Ten double crowns were fabricated. The groups were as follows. Group 1, double crowns of hybrid inner and outer crowns using the conventional casting method; Group 2, double crowns of conus inner and outer crowns using the conventional casting method. Tensile strengths of double crowns when the inner and outer crowns were separated on a universal testing machine were measured. These values of retentive force were then statistically analyzed using the Kruskal-Wallis test. Results. Retentive force in group 2 was significantly higher than that in group 1(p<.05). Conclusion. The initial retentive forces of double crowns were affected by the types of the double crown system.

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.4
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• pp.352-364
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• 2002

There has been a great interest in the use of titanium for fixed and removable prostheses in recent because of its excellent biocompatibility. However the high melting temperature and chemical reactivity of titanium necessitates casting systems different from those used in conventional casting. The current titanium casting systems are based on an electric-arc design for melting the metal in an argon atmosphere and its exclusive investment. Despite the new developments in Ti casting systems, inadequate mold filling and internal porosity are frequently observed casting defects. Therefore, the study on the fabrication technique including sprue design to solve these casting defects is still necessary. In this study to evaluate the effect of sprue design on the castability of simulated cast titanium crowns, 10 cylindrical cast crowns for each group with four different sprue design(Single group. Double group, Runner bar group. Reservoir group) were fabricated. An impression of the entire casting margin was made and cut at $90^{\circ}$ intervals, and the sections were photographed in a microscope at $100{\times}$ magnification to record marginal discrepancy. The internal porosities of the cast crowns were disclosed by radiographs. Within the limits of this study. the following conclusions were drawn. 1. The overall mean marginal discrepancies for each group were as follows: Double group, $43.65{\mu}m$; Reservoir group, $50.27{\mu}m$; Single group, $54.17{\mu}m$; Runner bar group, $58.90{\mu}m$ (p<0.05). 2. The mean of marginal discrepancies for wax patterns was $10.65{\mu}m$. 3 The numbers of internal porosity showed the most in Runner bar group followed by Single group, Reservoir group, and Double group.

• The Journal of Advanced Prosthodontics
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• v.9 no.4
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• pp.308-314
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• 2017

PURPOSE. The purpose of this study was to analyze the retention force changes and wear behaviours of double-crown systems over long-term use. MATERIALS AND METHODS. Ten groups, each consisting of six samples, were evaluated. Specifically, casting gold alloy primary crown - casting gold alloy secondary crown (AA), laser sintering primary crown - laser sintering secondary crown (LL), casting Cr alloy primary crown - casting Cr alloy secondary crown, (CC) zirconia primary crown - electroformed secondary crown (ZA), and CAD/CAM titanium alloy primary crown - CAD/CAM titanium alloy secondary crown (TT) groups were evaluated at cone angles of $4^{\circ}$ and $6^{\circ}$. The samples were subjected to 5,000 insertion-separation cycles in artificial saliva, and the retention forces were measured every 500 cycles. The wear levels were analyzed via SEM at the beginning and end of the 5,000 cycles. RESULTS. In all samples, the retention forces increased when the conus angle decreased. The highest initial and final retention force values were found in the $LL-4^{\circ}$ group (32.89 N-32.65 N), and the lowest retention force values were found in the $ZA6^{\circ}$ group (5.41 N-6.27 N). The ZA groups' samples showed the least change in the retention force, and no wear was observed. In the other groups, wear was observed mostly in the primary crowns. CONCLUSION. More predictable, clinically relevant, and less excursive retention forces can be observed in the ZA groups. The retention force values of the LL groups were statically similar to those of the other groups, except the ZA groups.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.04a
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• pp.111-114
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• 2009

Production of rolled steel has been growing partly supported by the advancement of rolls and rolling mills. Aiming at the further improvement in roll performance, various new techniques such as centrifugal casting, double poured casting cast steel, special build-up making, etc. have been introduced in the field of roll manufacture in these several years. The present paper describes the development of horizontal cast rolls(sleeve and indefinite chilled roll) made by Hyundai Steel and the results of mill tests. The developed roils are contributing the improvement of final products.

• Membrane Journal
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• v.33 no.4
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• pp.191-200
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• 2023

Polyethersulfone (PES) is a widely employed membrane material for water and industrial purification applications owing to its hydrophilicity and ease of phase separation. However, PES membranes and filters prepared using the nonsolvent induced phase separation method often encounter significant flux decline due to pore clogging and cake layer formation on the dense membrane surfaces. Our investigation revealed that tight microfiltration or loose ultrafiltration membranes can be subject to physical fouling due to the formation of a dense skin layer on the bottom side caused by water intrusion to the gap between the shrank membrane and the substrate. To investigate the effect of the bottom surface porosity on membrane fouling, two membranes with the same selective layers but different sub-layer structures were prepared using single and double layer casting methods, respectively. The double layered PES membrane with highly porous bottom surface showed high flux and physical fouling tolerance compared to the pristine single layer membrane. This study highlights the importance of physical optimization of the membrane structure to prevent membrane fouling.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.2
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• pp.147-156
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• 2006

Statement of problem: The high melting temperature and chemical reactivity of titanium necessitates casting machines different from those used in conventional casting. Despite the new developments in Ti casting systems , inadequate mold filling and internal porosity are frequently observed casting defects. Therefore, the study on the fabrication technique including sprue design to solve these casting defects is still necessary. Purpose: The purpose of this study was to evaluate the effect of sprue design and cross sectional area of sprue on the internal porosity. Materials and methods: 30 simulated cast three units titanium crowns were prepared. 5 cast crowns for each with different sprue design(sinlge sprue, double sprue and plate sprue) of two cross sectional areas (small and large cross sectional areas) were fabricated. The sections of titanium castings were photographed in a microscope at ${\times}100$ magnification to record internal porosities. Results and Conclusion: Within the limits of this study, the following conclusions were drawn: 1. There was a significantly lower in internal porosity of titanium castings for large cross sectional area of sprue group than the small group (P<.05) 2. There was no significant difference in internal porosity among sprue designs in similar cross sectional area of sprue (P>.05).

• Advances in Energy Research
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• v.5 no.3
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• pp.219-226
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• 2017

Electrochemical double layer capacitors (EDLCs) have received a tremendous interest due to their suitability for diverse applications. They have been fabricated using different carbon based electrodes including activated carbons, single walled/multi walled carbon nano tubes. But, graphite which is one of the natural resources in Sri Lanka has not been given a considerable attention towards using for EDLCs though it is a famous carbon material. On the other hand, EDLCs are well reported with various liquid electrolytes which are associated with numerous drawbacks. Gel polymer electrolytes (GPE) are well known alternative for liquid electrolytes. In this paper, it is reported about an EDLC fabricated with a nano composite polyethylene oxide based GPE and two Sri Lankan graphite based electrodes. The composition of the GPE was [{(10PEO: $NaClO_4$) molar ratio}: 75wt.% PC] : 5 wt.% $TiO_2$. GPE was prepared using the solvent casting method. Two graphite electrodes were prepared by mixing 85% graphite and 15% polyvinylidenefluoride (PVdF) in acetone and casting n fluorine doped tin oxide glass plates. GPE film was sandwiched in between the two graphite electrodes. A non faradaic charge discharge mechanism was observed from the Cyclic Voltammetry study. GPE was stable in the potential windows from (-0.8 V-0.8 V) to (-1.5 V-1.5 V). By increasing the width of the potential window, single electrode specific capacity increased. Impedance plots confirmed the capacitive behavior at low frequency region. Galvanostatic charge discharge test yielded an average discharge capacity of $0.60Fg^{-1}$.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1523-1526
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• 2012

In this work, we prepared activated multi-walled carbon nanotubes/polyacrylonitrile (A-MWCNTs/C) composites by film casting and activation method. Electrochemical properties of the composites were investigated in terms of serving as MWCNTs-based electrode materials for electric double layer capacitors (EDLCs). As a result, the A-MWCNTs/C composites had much higher BET specific surface area, and pore volume, and lower volume ratio of micropores than those of pristine MWCNTs/PAN ones. Furthermore, some functional groups were added on the surface of the A-MWCNTs/C composites. The specific capacitance of the A-MWCNTs/C composites was more than 4.5 times that of the pristine ones at 0.1 V discharging voltage owing to the changes of the structure and surface characteristics of the MWCNTs by activation process.