• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.1
• /
• pp.145-150
• /
• 1998

The electrical and mechanical properties of the 8 mol% yittria-stabilized zirconia and alumina composites have been examined as a function of the alumina content. The 3-point bending strength and fracture toughness of the composites increased with increasing alumina content up to 20 wt%. The average grain size of the composites decreased with increasing alumina content up to 20 wt%. The composite with 5 wt% $Al_2O_3$ showed a 3-point bending strength of 310 MPa and fracture toughness about $7.8MPa\cdot\textrm m^{1/2}$. The electrical conductivity of the composites at $1000^{\circ}C$ increased slightly with increasing alumina content up to 10 wt% and decreased monotonically with alumina content. The conductivity of the TZ-8YS with 5 wt% alumina was 0.4 S/cm at $1000^{\circ}C$.

• Composites Research
• /
• v.12 no.3
• /
• pp.8-16
• /
• 1999

Carbon woven fabric/C/SiC composites were fabricated by multiple impregnations of carbon woven fabric/carbon preform with the polymer precursor of SiC, i.e., polycarbosilane. In addition, two kinds of low density carbon/carbon preforms which had different fiber volume fraction and fiber orientation, i.e., a carbon woven fabric(${\thickapprox}$55 vol%)/carbon and a chopped carbon fiber${\thickapprox}$40 vol%)/carbon composites, were reaction-bonded with a silicon melt at 1$700^{\circ}C$ in a vacuum to fabricate dense carbon fiber/Si/SiC composites. The reaction-bonding process increased the density to ~2.1 g/$cm^3$ from 1.6 g/$cm^3$ and 1.15 g/$cm^3$ of a carbon woven and a chopped carbon preforms, respectively. All of the composites fractured with extensive fiber pull-out. The higher the density the higher the stiffness and proportional limit stress. The mechanical properties obtained from a three-point bend and tension tests were compared. The ratios of the peak tensile stresses to the bending strengths of a carbon woven and a chopped carbon composites were about one-third, respectively. The carbon woven fabric/Si/SiC composites with density of 2.06 g/$cm^3$ showed ~120 MPa of ultimate strength and ~80 MPa of proportional limit in bend testing.

• Journal of the Korean Wood Science and Technology
• /
• v.12 no.4
• /
• pp.12-18
• /
• 1984

Soaking treated in 20% aqueous solutions of $(NH_4)_2SO_4$, $NH_4H_2PO_4$, $(NH_4)_2HPO_4$, $Na_2B_4O_7-H_3BO_3$(60:40) and Minalith, the mixed salts for 9 hrs. the wet 3.5mm meranti (Parashorea spp.) plywoods were press-dried at 90, 120 and $150^{\circ}C$ and put to static bending test to examine the influence of redrying temperature on the strength of fire-retardant treated plywoods ill flexure. While water-soaking treatment (control) showed serious reduction in Stress at proportional limit, MOE, MOR, Work per unit volume at $150^{\circ}C$, all the fire-retardant treatments maintained bending strength even at $150^{\circ}C$ and showed rather increased values in case of some chemicals. In view of drying rate and maintenance of strength, the most pertinent platen temperature was $150^{\circ}C$ and Borax-Boric acid was the predominant fire-retardant in this study.

• Journal of the Korean Wood Science and Technology
• /
• v.4 no.1
• /
• pp.33-37
• /
• 1976

This experiment was carried out to study the effects affecting to particle board quality by the mixed use of sawdust abandoning as the sawmill residues. The obtained results at this study are summarized as follows: 1) There was no significance in bending strength between 5% sawdust addition and non mixed particleboard. 2) The water absorption was increased as accordance with adding more sawdust. When the boards were mixed with sawdust until 20% the differences were shown among the test boards. 3) There was no differences between the moisture contents and also specific gravities between the comparated boards. There was no difference between the boards mixed with 5% sawdust and non mixed boards.

• Korean Journal of Materials Research
• /
• v.7 no.3
• /
• pp.180-187
• /
• 1997

$La_{0.68}Ca_{0.32}Cr_{0.97}O_{3}$ interconnector films ior pimar rypn solid oxide fuel (,ells were prepared under various sinteririg conditions and their bending strength. relative ilerisit~. m t l c:lec ~ ~ - i i ; i l condl~cti\.lt\ were niexiureti in order to study their mechanical and electrical propertics Th' Irndirig sriength of $La_{0.68}Ca_{0.32}Cr_{0.97}O_{3}$ lt the room temperature \vas increased with increasing sinrering temperature dnfl tinic. The relative densit\- of more than 94% was ohtained 1)). sintering at $1400^{\circ}C$ for 5hrs. The present irlvestigiition rovcals thcit sirileririg of $La_{0.68}Ca_{0.32}Cr_{0.97}O_{3}$ at lorn. temperature xyvas greatly assisted by formation oi Ca,,,(CrO,),, Also the i,leitriczl conductivity at $1000^{\circ}C$ \vas more than 100S; cm d t e r heating at $1400^{\circ}C$ for 7hrs.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.10 no.4
• /
• pp.125-131
• /
• 2007

This paper considers the mechanical properties test results of the ceramic fiber reinforced plastic using hyper temperature. These materials were developed to make antenna cover which should not only protect antenna from high temperature and high pressure but also transmit and receive radio frequency for hypersonic missile. So the bending strength tests under the room temperature and the hyper temperature for new materials were done to evaluate of their performances. Also, the conductivity, specific heat, diffusivity and density were tested.

• Journal of the Korean Geographical Society
• /
• v.41 no.6 s.117
• /
• pp.670-681
• /
• 2006

The purpose of this study is to clarify the behavior of subsurface water flow during rainfall on the hillslope in the Dongguneung experimental basin. As a result of the study, the following conclusions were obtained. Under the total rainfall of 20mm, there were no groundwater level changes. However, it was found that total rainfall amount and rainfall intensity were important factors to change groundwater level in hilly slope. Also the rainfall duration and preexisted rainfall amount were important factors to change it on the head hollow. To analyze the modification of 'U-shaped Gol' landform, the pattern of return flow and through flow have to check during storm events. The microgeomorphic change of head hollow is based on the pattern of subsurface water flow.

• Journal of Korean Society of Forest Science
• /
• v.30 no.1
• /
• pp.19-29
• /
• 1976

The fiberboard and paper mills in this country are much affected by the price hikes and shortage of phenolic resins, since phenolic acid as a raw material depends on imported good. It is prerequisite to fiberboard industry to help replace with other sized and stabilize the prices and supply of them, improving the quality of boards. Thus, the present study was carried out to examine the effect of strength increasing sized such as urea formaldehyde resin (anion and cation type) and urea melamine copolymer resin, on the quality of the wet forming hardboard, and comparing them with two types of proprietary modified melamine resins, and ordinary size, phenol resin. The Asplund pulp was prepared from wood wastes mixed with 20 percent of lauan and 80 percent of pines as a fibrous material. After sizing agents were added at a pH of 4.5 for 10 minutes with alum in the beater, the stock was made in the form of wet sheet, prepared, and then performed by hot pressing cycle: $180^{\circ}C$, $50-6-5kg/cm^2$, 1-2-7 minutes. The properties of hardboard were examined after air conditioning. The results obtained are summarized as follows: 1. There is a significant difference in specific gravity among hardboards that were treated with strength increasing resins, but no difference is effected by the increase in the resin content. In the case of modified melamine resin, its specific gravity is highest. The middle group comprises cation type of urea resin, anion type of urea resin, and acid colloid of urea-melamine copolymer resin. The lowest is phenolic resin. 2. The difference of the moisture content of hardboard both by the resins and by the amount of each resin applied is significant. The moisture content of hardboard becomes lower along with the increase of each resin content, but there is no difference between 2 and 3 percent. 3. For water absorption, there is a significant difference both in the adhesives used and in the amount of paraffin wax emulsion. The water resistance becomes higher inn proportion to the content of the paraffin wax emulsion. To satisfy KS F standards of the water resistance, a proprietary modified melamine resin (p-6100) and modified cation type of urea resin (p-1500) do not require any paraffin wax emulsion, but in the case of anion type of urea resin, cation type of urea resin, and urea-melamine copolymer resin, 1 percent of paraffin wax emulsion is needed, and 2 percent of paraffin wax emulsion in the case of phenolic resin. 4. The difference of flexural strength of hardboard both by the resins and by the amount of each resin is significant. Modified melamine resin shows the highest degree of flexural strength. Among the middle group are urea-melamine copolymer resin, p-1500, anion type of urea resin, and cation type of urea resin. Phenolic resin is the lowest. The cause may be attributable to factors combined with the pressing temperature, sizing effect, and thermal efficiency of press platens heated electrically. 5. Considering the economic advantages and properties of hardboard, it is proposed that urea-melamine copolymer resin and cation type of urea resin be used for the development of the fiberboard industry. It is desirable to further develop the modified urea-melamine copolymer resin and cation type of urea resin through continuous study.

• Journal of dental hygiene science
• /
• v.9 no.1
• /
• pp.75-81
• /
• 2009

The effect of glass frit on the sintering behavior and mechanical properties of 3 mol% $Y_2O_3$-doped zirconia($3Y-ZrO_2$) have been studied. Up to 30 wt% of glass frit was added to $3Y-ZrO_2$. Sintering was performed in a box furnace up to $1300^{\circ}C$ for specimens with glass frit and $1600^{\circ}C$ for specimens without glass frit in air for 1h. Relative density and mechanical properties were measured to investigate the effect of glass frit. The addition of glass frit enhanced both sintered density and mechanical properties of $3Y-ZrO_2$ which is suitable for dental applications. Maximum sintered density 93.3% of theoretical density was obtained with the specimens containing 30 wt% frit sintered at $1300^{\circ}C$, whereas the optimum amount of frit addition for mechanical properties was determined as 10 wt%. Maximum value of strength, fracture toughness, and Vickers microhardness for specimens with glass frit were 206 MPa, $3.4\;MPa\;m^{1/2}$, and 5.3 GPa, respectively.

• Journal of Korean Society of Forest Science
• /
• v.16 no.1
• /
• pp.33-62
• /
• 1972

Pitch pine (Pinus rigida Miller) in Korea has become one of the major silvicultural species for many years since it was introduced from the United States of America in 1907. To attain the more rational wood utilization basical researches on wood properties are primarily needed, since large scale of timber production from Pitch Pine trees has now been accomplishing in the forested areast hroughout the country. Under the circumustances, this experiment was carried out to study the wood anatomical, physical and mechanical properties of Pitch Pine grown in the country. Materials used in this study had been prepared by cutting the selected pitch pine trees from the Seoul National University Forests located in Suwon. To obtain and compare the anatomical and physical properties of the different parts of tree such as stem, branch, top and rootwood, this study had been divided into two categories (anatomical and physical). For the anatomical study macroscopical and microscopical features such as annual ring, intercellular cannal, ray, tracheid, ray trachid, ray parenchyma cell and pit etc. were observed and measured by the different parts (stem, branch, root and topwood) of tree. For the physical and mechanical properties the moisture content of geen wood, wood specific gravity, shrinkage, compression parallel to the grain, tension parallel and perpendicular to the grain, radial and tangential shear, bending, cleavage and hardness wree tested. According to the results this study may be concluded as follows: 1. The most important comparable features in general properties of wood among the different parts of tree were distinctness and width of annual ring, transition from spring to summerwood, wood color, odor and grain etc. In microscopical features the sizes of structural elements of wood were comparable features among the parts of tree. Among their features, length, width and thickness of tracheids, resin ducts and ray structures were most important. 2. In microscopical features among the different parts of tree stem and topwood were shown simillar reults in tissues. However in rootwood compared with other parts on the tangential surface distinctly larger ray structures were observed and measured. The maximum size of unseriate ray was attained to 27 cell ($550{\mu}$) height in length and 35 microns in width. Fusiform rays were formed occasionally the connected ray which contain one or several horizontal cannals. Branchwood was shown the same features like stemwood but the measured values were very low in comparing with other parts of tree. 3. Trachid length measured among the different parts of tree were shown largest in stem and shortest in branchwood. In comparing the tracheid length among the parts the differences were not shown only between stem and rootwood, but shown between all other parts of tree. Trachid diameters were shown widest in rootwood and narrowest in branchwood, and the differences among the different parts were not realized. Wall thickness were shown largest value in rootwood and smallest in branchwood, and the differences were shown between root and top or branchwood, and between stem and branch or top wood, but not shown between other parts of tree. 4. Moisture contents of green wood were shown highest in topwood and lowest in heartwood of stem. The differences among the different parts were recognized between top or heartwood and other parts of tree, but not between root and branchwood or root and sapwood. 5. Wood specific gravities were shown highest in stem and next order root and branchwood, but lowest in topwood. The differences were shown clearly between stemwood and other parts of tree, but not root and branchwood. However the significant difference is realized as most lowest value in topwood. 6. In compression strength parallel to the grain compared among the different parts of tree at the 14 percent of moisture content, highest strength was appeared in stem, next order branch and rootwood, but lowest in topwood. 7. In bending strength compared among the different parts of tree at the 14 percent of moisture content clearly highest strength was shown in branchwood, next order stem and root, but lowest in topwood. Though the branchwood has lower specific gravity than stemwood it was shown clearly high bending strength.