• 한국결정성장학회지
• /
• 제3권2호
• /
• pp.176-184
• /
• 1993

$Li_2O-Al_2O_3-SiO_2$계 유리조성에서, 특히 주결정상으로 $\beta$-spodumene을 석출시킬 수 있는 조성영역에서 $P_2O_5, TiO_2, ZrO_2$ 등을 첨가하여 용융한 후 소결법을 이용하여 이론밀도에 가까운 결정화 유리를 만들기 위한 최적 열처리 조건, 유리 분말의 입도 변화에 따란 영향과 그 때의 물성을 시차열분석, X-선 회절분석, 비중 측정, 열팽창 측정, 전자현미경 관찰 등을 통하여 연구하였다. $P_2O_5$를 첨가하여 소결법으로 결정화할 때 소결을 증진시키는 효과가 있었으며 9wt% 첨가한 경우가 가장 치밀한 것으로 나타났다. 최적의 열처리 조건은 $740^{\circ}C$에서 소결하여 치밀화를 시키고$ 950^{\circ}C$에서 결정화를 시켰을 때로서 상대밀도는 90% 이상이었으며 열팽창계수는 $-1{\times}10^{-7}/^{\circ}C$ 정도로서 부팽창인 것으로 나타났다.

• 한국세라믹학회지
• /
• 제14권4호
• /
• pp.230-235
• /
• 1977

In this paper the conditions of surface crystallization of glass were studied. The basic glass which is apt to crystallize, with $SiO_2$ 72.50, $Al_2O_3$ 5, 00, $Na_2O$ 8.00 $K_2O$ 3.50, CaO 5.00, MgO 3.00, $B_2O_3$ 3.00 Wt% is chosen. The strain point and softening point of this glass is 4$25^{\circ}C$ and 778$^{\circ}C$ each, and between the two temperatures we could get grystal on its surface by immersion in salt baths during some controlled hours. The kind of crystal on the surface of glass was confirmed by X-ray diffraction analysis and the change of the thickness of crystalline layers depending on temperature and time, was surveyed by using optical microscope. The results are as follows; 1. The chloride group is more suitable than sulfate group for the treating salt. 2. In the condition with 50 LiCl.50NaCl at 62$0^{\circ}C$ for 2 hrs and with 50 LiCL.20-30 NaCl.30-20 $CaCl_2$ at 72$0^{\circ}C$ for 15-20 min. we could get the best crystalline layers. 3. The crystal was silica-O and petalite with a little tridymite and nepheline. 4. The thickness of crystalline layers increased with increasement of temperature and time.

• 공업화학
• /
• 제18권6호
• /
• pp.568-574
• /
• 2007

투명결정화 유리의 전구체로서 균열이 없는 $Li_2O1{\cdot}7Al_2O_3{\cdot}8.6SiO_2$ 조성인 다공성 괴상 겔을 formamide를 첨가한 알콕시드 용액으로부터 sol-gel방법으로 합성하였다. 겔 합성에서 겔화 활성화 에너지, 비표면적, 습윤겔의 완전 탈수에 필요한 온도, 기공의 부피 및 기공크기와 분포를 측정하였고, 겔의 결정화온도를 검토하고자 시차열분석을 실시하였다. 겔화의 활성화에너지는 가수분해에 필요한 물의 첨가량에 따라 13~14 kcal/mol 범위를 나타내고, 물의 첨가량이 가수분해시 필요한 이론량의 3배 이상일 경우, $70{\sim}75^{\circ}C$, 건조속도 0.1~0.3 %/h에서는 겔의 균열을 방지할 수 있어 안정한 괴상 겔을 제조할 수 있었다. $180^{\circ}C$에서 건조한 겔체는 비표면적, 기공부피 및 기공크기분포는 $239.40m^2/g$, 0.001~0.03 mL/g 그리고 1~122 nm 반지름의 미세구조로 된 투명 겔체로서 다공질 물질임이 확인되었고, 건조겔의 시차열분석 결과 $800^{\circ}C$ 부근에서 1차 발열피크, $980^{\circ}C$ 부근에서가 2차 발열피크가 확인되어 결정화가 일어남을 알 수 있었다.

• Carbon letters
• /
• 제6권2호
• /
• pp.71-78
• /
• 2005

Anti-oxidation coatings are the key technique for carbon/carbon (C/C) composites used as the thermal structural materials. The microstructure and oxidation behavior of several kinds of high-performance ceramic coatings for C/C composites prepared in Northwestern Polytechnical University were introduced in this paper. It showed that the ceramic coatings such as SiC, Si-$MoSi_2$, SiC-$MoSi_2$, $Al_2O_3$-mullite-SiC and SiC/yttrium silicate/glass coatings possessed excellent oxidation resistance at high temperatures, and some of these coatings were characterized with excellent thermal shock resistance. The SiC-$MoSi_2$ coating system has the best oxidation protective property, which can effectively protect C/C composites from oxidation up to 1973 K. In addition, the protection and failure reasons of some coatings at high temperature were also provided.

• 한국세라믹학회지
• /
• 제26권6호
• /
• pp.771-782
• /
• 1989

Synthesis of $\beta$-Sialon powder was attempted with carbothermal reduction of porous glass. The porous glass was prepared by heat and hydrothermal treatments of 9.32 Li2O.46.5B2O3.37.2SiO2.6.98Al2O3 glass. Carbon pyrolyzed from propane gas was deposited on the porous glass, thereafter activated carbon was added as reducing agents. The synthesized $\beta$-Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 1hr in N2 atmosphere. The characterization of the $\beta$-Sialon powder was performed with XRD, BET, SEM and particle size analysis. The sinterability and mechanical properties of the sintered bodies were investigated in terms of bulk density, M.O.R., fracture toughness, morphology of microstructure and etc. The reduction effect of deposited carbon was better than that of activated carbon mechanically added. The formation of SiC was precominant over that of Si2ON2 and $\beta$-Sialon owing to low partial pressure of N2 inside the pore, wehreas on the surface of porous glass the formation of Si2ON2 and $\beta$-Sialon were predominant. Thereafter, SiC reduced unreacted glass to be $\beta$-Sialon. Single phase of $\beta$-Sialon(Z=1.92) was obtained from PGA porous glass having the largest pore radius by the simultaneous reduction and nitridation method at 145$0^{\circ}C$ for 5hrs. The bulk density, M.O.R., and KIC of the sitered body are 3.17g/cc, 434.4MPa and 4.1MPa.m1/2, respectively.

• 한국결정성장학회지
• /
• 제2권2호
• /
• pp.20-32
• /
• 1992

$Na_2O-CaO-MgO-Al_2O_3-SiO_2$계를 기본조성으로 하여 $Na_2O$에 $Li_2O 0.05wt%, $K_2O$를, CaO에 MgO 12.0wt%, ZnO 6.0%를 각각 치환하여 조성을 선정하였다. 기본 유리조성의 결정상은 wollastonite이고, 치환된 조성들은 diopside, diopside.tremolite의 혼정이 나타났다. $Na_2O$를 $Li_2O$로 치환한 시편은 열팽창계수가 감소하였지만 CaO를 ZnO로 치환한 시편은 열팽창 계수가 증가하였다. 곡강도에 있어서는 치환에 따라 모두 증가시켰다. 핵행성제로 $ZrO_2와 $CaF_2$를 각각 1~2wt%의 변화를 시켜본 결과 핵형성제 $ZnO_2$와 $CaF_2$가 1:1, 1:2인 시편은 $1000~1050^{\circ}C$온도에서 급격한 결정성장을 보였으며 1:2시편이 가장 낮은 열팽창 계수값을 나타냈다. 곡강도는 모두 $1000~1050^{\circ}C$의 결정화 온도 범위에서 높은 강도를 나타내었다. 결정화에 필요한 활성화 에너지는 Ozawa와 Kissinger식으로 plot하여 각각 55.24kcal/mol과 53.05kcal/mol이다.

• 한국표면공학회지
• /
• 제27권2호
• /
• pp.99-108
• /
• 1994

Films of glass-ceramics $Li_2O-Al_2O_3-SiO_2$(LAS)system were prepared on substrate of an iron plate(SCP) by sol-gel technique using metal alkoxide such as Si$(OC_2H_5)_4$,Al$(OC_2H_9)_3$) and Ti$(OC_2H_6)_4$). Sol which was made by means of simple spray coating, on the substrate was hydrolyzed at 75~$80^{\circ}C$ in moisture cabinet (80~90 % humidity) to form the multicomponent gel. The films up to about 0.8~1.0$mu extrm{m}$ in thickness can be obtained by repeating operation, spraylongrightarrowhydrolysis and condensationlongrightarrowdryinglongrightarrowheating and crystallization at $700^{\circ}C$ for 3~5min. The far-infrared radiation spectra of the coated films on substrate were examined by FT-IR and of films was also observed by scanning electron micrograph technique. The thermal evaluation of the gel-film is followed by TG/DTA measurements. The structure evaluation is followedd X-ray diffraction. These results suggest that this process is applicable to far-infrared radiat at thin film technique.

• 한국세라믹학회지
• /
• 제27권2호
• /
• pp.288-296
• /
• 1990

Parent glasses for the experiments were prepared to be ratio of Li2O : Al2O3 : SiO2=4.5 : 25 : 70.5 as basic components, and TiO2 and ZrO2 in the mixing ratio of 1 : 1 were added as the nucleating agents, whose contents were increased in each sample. DTA, XRD, SEM, IR were observed, and thermal expansion and transmissivities were measured for the crystallized samples under the controlled heat-treatments. The transformation temperatures and the dilatometric softening temperatures in thermal expansion curves, and also the exothermic peaks in differential thermo-analytical curves were shifted to lower temperature. The crystal phase deposited through the heat-treatment was identified as ${\beta}$-quartz solid solution with XRD and IR analysis. The crystalline phases in oopactified samples were ${\beta}$-spodumene coexiting with ${\beta}$-quartz solid solution. The samples having more than 3% nucleating agents were transparent. The crystallized grain sizes were ranged 0.05 to 0.1$\mu\textrm{m}$. The crystallized transparent samples were exceeded 85% in the transmissivity.

• 한국세라믹학회지
• /
• 제25권3호
• /
• pp.251-260
• /
• 1988

$10Li_2O$.$(90-x)B_2O_3$.$xSiO_2$ 기초유리에 $Al_2O_3$ 또는 $MoO_3$를 첨가한 유리를 열처리한 후 열수 또는 산처리하여 이온교환성 다공질 유리를 제조하였다. 그리고 $Al_2O_3$ 또는 $MoO_3$ 첨가가 분상과 양이온교환능(CEC)에 미치는 영향을 조사하였다. 이들 유리의 분상최적조건은 48$0^{\circ}C$, 10시간 열처리하였다. 분상은 $Al_2O_3$ 10mol%까지는 급격히 억제되고 그 이후에는 분상억제 효과가 완화되었다. 양이온교환능의 최대값은 $1OLi_2O$.$45B_2O_3$.$45SiO_2＋7.5Al_2O_3$ 조성유리를 열수처리한 다공질유리에서 약 252meq/100g을 나타냈으며 이 유리의 세공평균반경은 약 16.3A이었다. $MoO_3$ 첨가는 분상과 용출속도를 증가시켰다. $MoO_3$첨가에 의해 다공질유리의 세공반경과 세공용적이 크게 증가하는 것으로 보아 $MoO_3$는 유리의 붕산염상중의 실리카 농도를 낮추고 용출처리중 실리카를 수용성 착체로 형성시키는 효과가 있다고 생각된다.

• 한국분말재료학회지
• /
• 제18권1호
• /
• pp.35-40
• /
• 2011

LAS-system ceramic powder, spodumene ($Li_2O{\cdot}Al_2O_3{\cdot}4SiO_2$), was successfully synthesized by a chemical solution technique employing PVA(polyvinyl alcohol) as an organic carrier. The PVA content affected the microstructure of porous precursor gels and the crystalline development. The optimum PVA content contributed to homogeneous distribution of metal ions in the precursor gel and it resulted in the synthesis of glass free $\beta$-spodumene powder having a specific surface area of $7.57\;m^2/g$. The agglomerated $\beta$-spodumene powders were also enough soft to grind to fine powders by a simple ball milling process. The microstructures of the densified powder compacts were strongly dependant on the minor phases of spodumene solid solution and amount of liquid phase, which were formed from the inhomogeneous precursors.