• The Korean Journal of Ceramics
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• 제5권4호
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• pp.414-418
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• 1999

The synthesis of polycrystalline $Al_2TiO_5$ ceramics with low thermal expansion by fusion in an electric arc furnance was investigated. The thermal expansion curves of $Al_2TiO_5$ ceramics were lowered because of microcracks caused by the strong thermal expansion anisotropy of the crystal axes and were accompanied by hysteresis curves. These phenomena are explained by the opening and closing of microcracks. The difference in microcracking temperatures of dilatometric cooling curves in the range of 400~$620^{\circ}C$ is caused by the difference in sintering temperature, grain size and stabilization status.

• The Korean Journal of Ceramics
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• 제2권4호
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• pp.246-250
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• 1996

The thermomechanical properties of materials from the system Al2O3-SiO2-TiO2(Tialite-Mullite) were investigated by correlating the thermal expansion anisotroypy, flexural strength and Young's modulus with grain size and atructural microcracking during cooling. Microcracking temperatures were determined by measuring the hysteresis of the thermal expansion anisotropy with dilatometry. Single phase Aluminium Titanate is a low strength material, while composites with more than 10 vol% mullite as second phase enhance the Young's modulus, thermal expansion coefficient and room temperature strength.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2001년도 춘계학술대회 발표논문집
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• pp.40-46
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• 2001

A1₂TiO/sub 5/ 세라믹스의 열적 안정성은 MgO와 고온 arc용융노에서 MgAl₂O₄ spinel과 같은 고용체를 이루고, SiO₂, ZrO₂와 α-Al₂O₃등의 첨가제로 입자크기와 미세 균열을 감소시킴으로서 증가시킨다. A1₂TiO/sub 5/ 세라믹스의 낮은 열팽창 특성은 상이한 열팽창으로 hysteresis 곡선을 나타내며 이 현상은 미세균열의 opening과 closing으로 설명된다. 이들의 열팽창 곡선, 소성온도에 EK른 관계를 dilatometer로 연구하였다.

• 한국세라믹학회지
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• 제35권10호
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• pp.1061-1069
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• 1998

The thermal instability of Al2TiO5 Ceramics was contrlled by solid solution with MgO SiO2 and ZrO2 through electrofusion in an arc furnace. The thermal expansion properties of Al2TiO5 composites show the hysteresis due to the strong anisotropy of The crystal axes of these material. These phenomena are ex-plained by the opening and closing of microcracks. The difference in microcracking temperatures e.g 587.6(ATG2), 405.9(ATG3) and 519.7$^{\circ}C$(ATG4) is caused by the difference in grain size and stabilizer type. The thermal shock behaviour under cyclic conditions between 750-1400-75$0^{\circ}C$ show no change in mi-crostructure and phase assemblage for all three stabilized specimens. After the thermal loading test at 110$0^{\circ}C$ for 100hrs. ATG1 and ATG2 materials decomposes completely to its components corundum and ru-tile in both cases. However with approximatelly 20% retention of the Al2TiO5 Thus in order to prevent decomposition of the stabilized material in the critical temperature range 800-130$0^{\circ}C$ it must be traversed within a short period of time.

• 한국세라믹학회지
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• 제37권2호
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• pp.122-127
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• 2000

The thermal expansion, thermal stability, mechanical strength and infrared radiative property of Al2TiO5-clay composites, prepared from synthesized Al2TiO5 and clay, were investigated to develop a material for far infrared radiators. The emittance of composites containing 10~50 wt% clay, heated at 1,20$0^{\circ}C$ for 3 h, increased with increasing clay content and emittance was about 0.3 and 0.92 in the ranges of 3,400~2,500 cm-1 and 2,500~400cm-1, respectively. The bulk density and bending strength of the Al2TiO5-clay composites increased with increasing clay content. 50 wt% Al2TiO5-50 wt% clay composite, heat-treated at 1,20$0^{\circ}C$, had an adequate strength for infrared radiators; 80 MPa. The degree of thermal expansion hysteresis decreased with increasing clay content and the mean thermal expansion coefficient increased with increasing clay content. The thermal expansion coefficient of 50 wt% Al2TiO5-50 wt% clay composite heated at 1,20$0^{\circ}C$ was 5.78$\times$10-6/$^{\circ}C$.

• 한국재료학회지
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• 제10권10호
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• pp.703-708
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• 2000

최근에 상용차용 디젤 엔진의 성능 향상을 목적으로 엔진 설계가 급격히 변화되면서 캠 팔로우어(cam follower)와 캠(cam) 사이에 작용하는 접동면 하중의 증가로 접동면에서의 마모가 중요한 문제가 되고 있다. 본 연구에서는 기존의 주절체 및 소결합금 캠 팔로우어에 비해 내마모성이 우수한 세라믹 캠 팔로우어를 개발하였다. 잔류 응력을 완화시켜주는 중간층을 사용하지 않고 질화규소($Si_3N_4$) 팁과 중탄소강을 활성납재를 사용하여 직접 접합후 냉각시키는 과정에서 두 모재의 열팽창계수차에 의한 크라우닝(crowning, R) 이 형성되도록 하였다. 접합에 사용한 중탄소강은 열팽창시 이력(hysteresis) 거동을 나타내었으며, $A_{c1}$ 변태점인 $723^{\circ}C$ 이하에서 접합할 경우 원하는 크라우닝이 형성되었다. 접합온도가 $723^{\circ}C$ 이상이 되면 크라우닝 (R) 값이 온도에 따라 지수함수적으로 증가하였으며 이는 중탄소강의 상변태에 의한 열팽창.수축의 이력 특성으로 설명되어질 수 있었다. 규격에 맞는 크라우닝이 형성되는 최적 접합 온도는 $700~720^{\circ}C$의 범위였다. 질화규소와 중탄소강의 직접 접합방법으로 접합과 동시에 크라우닝을 형성시키고 제어함으로써 난가공재인 세라믹을 곡면 가공하지 않고도 적당한 곡률을 갖는 저가의 세라믹 캠 팔로우어를 제조할 수 있었다.

• 한국세라믹학회지
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• 제40권2호
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• pp.109-112
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• 2003

The grain-boundary microcracking materials in the system $Al_2$TiO$_{5}$ -ZrTiO$_4$(ZAT) is influenced by the thermal expansion anisotropy. The range of ZAT compositions investigated had showed very low thermal expansions of 0.3~1.3$\times$10$^{-6}$ K loin compared to 8.29$\times$10$^{6}$ K of pure ZrTiO$_4$and 0.68$\times$10$^{6}$ K of polycrystalline $Al_2$TiO$_{5}$ , respectively, compared with the theoretical thermal expansion coefficient for a single crystal of $Al_2$TiO$_{5}$ , 9.70$\times$10$^{6}$ K. The low thermal expansion and microcraking temperature are apparently due to a combination of thermal contraction and expansion caused by the large thermal expansion anisotropy of the crystal a ies of the $Al_2$TiO$_{5}$ phase.

• 한국세라믹학회지
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• 제40권3호
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• pp.317-321
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• 2003

The grain-boundary microcracking materials in the system A1$_2$Ti $O_{5}$ -ZrTi $O_4$(ZAT) is influenced by the thermal expansion anisotropy. The range of ZAT compositions investigated had showed very low thermal expansions of 0.3~1.3$\times$10$^{-6}$K compared to 8.29$\times$10$^{-6}$K of pure ZrTi $O_4$and 0.68$\times$10$^{-6}$K of polycrystalline A1$_2$Ti $O_{5}$ , respectively, compared with the theoretical thermal expansion coefficient for a single crystal of A1$_2$Ti $O_{5}$ , 9.70$\times$10$^{-6}$K. The low thermal expansion and microcraking temperature are apparently due to a combination of thermal contraction and expansion caused by the large thermal expansion anisotropy of the crystal axes of the A1$_2$Ti $O_{5}$ phase.

• 한국세라믹학회지
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• 제27권3호
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• pp.345-354
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• 1990

The densification behaviro and resulting properties of cordierite-aluminium titanate composites containing 5 to 40wt.% aluminium titanate were investigated. Compared with cordierite monolithics a substantial increase of sintering temperature range for composites was observed, which was due to the formation of cordierite and glass phase at relatively low temperatures. The bending strength of composites showed its maximum at 30wt.% aluminium titanate content, which was about 50% increase relative to the cordierite monolithics, then decreased by a small amount at 40wt.% aluminium titanate content. The decrease was explained by the increase of microcracks whose presence was confirmed by the hysteresis of thermal expansion curve of composites. However, the microcracks formed was not severe enough to produce a significant decrease in strength, which was also evidenced by the continuous increase of thermal expansion coefficient up to 40wt.% aluminium titanate content.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.733-736
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• 2003

This paper presents two systems of two-stage electrohydraulic servovalve with a nozzle-flapper pilot stage, which is controlled by stack-type piezoelectric elements. Two flapper moving mechanisms proposed in this research can compensate for the hysteresis problem and thermal expansion of the piezoelectric elements. The experimental results show that the first flapper moving mechanism has the frequency response of over 500 Hz and the second one has the response of over 600 Hz. And the first simplified servovalve system rising the first flapper moving mechanism has the frequency response of about 150 Hz, and the second system has the response of about 300 Hz at the supply pressure of 210 bar