• 대한치과보철학회지
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• 제35권2호
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• pp.417-430
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• 1997

The purpose of this study was to compare the fracture resistance of copy-milled and conventional In-Ceram crown. Four groups of ten uniform sized all-ceramic crowns were fabricated. In-Ceram Spinell and In-Ceram Alumina crowns were fabricated as control group, Celay In-Ceram Spinell and Celay In-Ceram Alumina crowns were fabricated as test group. All specimen were cemented on stainless steel master die with resin cement, and stored in $37^{\circ}C$ water for 1 day prior to loading in Instron testing machine. Using a steel ball at a crosshead surfed of 0.5mm/min, the crowns were loaded at $30^{\circ}C$ angle until catastrophic failure occurred. The results obtained were as follows : 1. With the value of $984.8N{\pm}103.67N$, the strength of Celay In-Ceram Alumina crowns had a significantly higher fracture strength than conventional In-Ceram Alumina crowns ($876.2N{\pm}92.20N$) (P<0.05) 2. The fracture strength of Celay In-Ceram Spinell crowns($706.3{\pm}70.59N$) was greater than that of conventional In-Ceram Spinell crowns($687.4{\pm}90.26N$), but there was no significant difference(P>0.05). 3. The In-Ceram Alumina crowns had a significantly higher fracture strength than In-Ceram Spinell crowns in both methods(P<0.05). 4. Ther order of fracture strength was as followed : Celay In-Ceram Alumina, In-Ceram Alumina, Celay In-Ceram Spinell and In-Ceram Spinell crowns

• 폴리머
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• 제32권6호
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• pp.549-554
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• 2008

분산중합법에 의해 고분자 미립자를 합성하기 위해 스티렌과 n-butylmethacrylate가 알루미나와 함께 중합되었다. 스티렌과 n-butylmethacrylate의 비는 3 : 1이었고, 입자안정제는 poly (N-vinyl pyrrolidon), 중합 개시제로는 2,2'-azobis(isobutyronitrile)를 커플링제는 3-methacryloxypropyl trimethoxysilane을, 분산매로 이소프로판올과 이온교환수를 70 : 30의 비로 사용하였다. TEM 사진을 통해 알루미나가 고분자 미립자에 분산되어 있음을 확인하였고 알루미나의 농도가 증가함에 따라 평균 입자경이 증가하였으며 입자경 분포는 감소되는 경향을 보였다. XRD 측정에 의해 알루미나의 농도 증가는 피크 강도와 2$\theta$값의 증가를 보였으며 TGA 측정으로 알루미나의 농도의 증가는 고분자 미립자의 내열성을 증가시킴을 알 수 있었다. 사용한 개시제의 반감기가 길수록 입자경은 감소하였고 입자인정제의 농도가 증가할수록 반응초기의 핵생성이 증가하여 입자경이 또한 감소함을 알 수 있었다.

• 한국환경과학회지
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• 제5권5호
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• pp.561-567
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• 1996

31 종류의 유기 염소계 잔류 농약을 동시에 분석하는 기체 크로마토그래피 방법을 개발하기 위하여 본 연구를 수행하였다. 준비된 분석 시료를 ECD (electron capture detector)로 Ultra-2 column의 GC (gas chromatography)에 주입하였다. Column 충진 물질을 florisil과 alumina N으로 변화시키면서 잔류 용액을 column에 loading하고 용출 용매로는 ether . benzene(2 : 8) solution, hexane . benzene(1 . 1) solution, dichloromethane, acetone 및 methanol을 사용하였다. 분석 결과 column 충진 물질로 florisil을 사용하였을때 (첫째 조건) 6종류의 유기 염소(dichlorfluanid, captan, chlorofenvinfos, folpet, captafol과 dicofol)가 검출되지 않았다. 이 조건에서 dichloromethane과 methanol을 용출 용매로 첨가하였을때는 (둘째 조건) 첫째 분석 조건하에서 검출되지 않았던 6종류의 유기 염소가 검출되었고 thrin계 pesticides, 특히 captan과 captafol의 recovery가 증가하였다(첫째 조건에서와 마찬가지로 충진 물질로 florisil을 사용). 그러나 BHC(benzene hexachloride) 화합물의 recovery는 감 소하였다. 한편 alumina N을 column 충진 물질로 사용하였을 경우에는 dichlorfluanid, chlorofenvinfos, folpet 및 dicofol의 recovery가 증가하였으며 aldrin도 그러하였다. 하지만 captan과 captafol은 그렇지 못하였다. Thrin계 pesticides, captan 및 captafol을 동시에 검출하기 위하여 florisil과 alumina N을 충진 물질로 동시에 사용하고 n-hexane을 충진시켜 용출시킨 결과, captan과 captafol이 검출되지 않았는데 이는 column이 충분히 활성화되지 않았기 때문이라고 생각된다. Column(florisil과 alumina N을 충진 물질로 동시 사용)을 충분히 활성화시키고 여러가지 용출 용매를 사용하여 불순물을 제거하였을때 분석 결과가 가장 우수하였다(31 종류의 유기 염소계 잔류 농약이 sharp하게 검출되었고 높은 감도를 나타내었다).

• 한국세라믹학회지
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• 제32권12호
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• pp.1349-1356
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• 1995

The change of permeation mechanism from Knudsen diffusion to micropore diffusion was observed after CVD modification of an alumina-sol coated alumina support which was prepared by slip coating process. Permselectivities of He/N2, H2/N2, and CO2/N2 were 5.67, 5.02, and 1.44, respectively. These values were higher than those under Knudsen diffusion controlled region.

• 한국세라믹학회지
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• 제31권8호
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• pp.927-933
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• 1994

Alumina composite membranes were prepared by chemical vapor deposition (CVD) using aluminum-tri-isopropoxide as a precursor. Porous alumina supports were used in deposition, which were in disk shape with mean pore diameter of 0.1 ${\mu}{\textrm}{m}$ and prepared by slip-coasting process. film deposition morphology on porous support was simulated through depositing alumina film on polycrystalline silicon pattern, and its step coverage observed by SEM showed one deviated from uniform step coverage. N2 permeability through composite membranes and the pressure dependence decreased as the deposition time increased. Initially, the N2 permeability of the top layer was tend to decrease rapidly, and then the degree of decrease in N2 permeability was tend to diminish with deposition time. The N2 permeability increased with heat treatment temperature and the crack was generated in top layer at 100$0^{\circ}C$.

• 한국세라믹학회지
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• 제33권1호
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• pp.101-109
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• 1996

The mechanical propertieso f sintered AlN with the addition of alumina were investigated The flexural strength of the AlN dispersed ALON specimens was higher than that of ALON and fracture toughness showed similar tendency. The high-temperature flexural strength of specimens which 50 and 64.3 mol% alumina was added to AlN was constant up to 100$0^{\circ}C$ with about 290 and 420 MPa respectively but abruptly decreased at 120$0^{\circ}C$ In the specimens which contained 5 and 30mol% alumina the flexural strength increased to about 14% at 100$0^{\circ}C$ and did not decrease at 120$0^{\circ}C$ compared to at room temperature.

• 한국세라믹학회지
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• 제32권9호
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• pp.977-988
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• 1995

Several oxide (ZrO2, Al2TiO5, reactive Al2O3) and nonoxide (SiC, Si3N4, "ALON" (5AlN.9Al2O3)) additives were used as a microfiller for alumina based LCC (Low-Cement-Castable). High temperature prooperties (HMOR, softening under load) and the phase changes of developed LCC on various sintering temperatures were examined. In addition, thermal shock test and corrosion test were accomplished. Based on these data the effects of each microfiller on the properties of LCC were established comparing to those of the commercial LCC with amorphous silica as a microfiller. The castables, containing reactive alumina, ZrO2 and "ALON" (5AlN.9Al2O3) as a first portion, exhibited considerably higher HMOR-values over 100$0^{\circ}C$, better creep behavior, and thermal shock resistance than those of castables with amorphous silica. The LCC with 5% Al2TiO5 showed no corrosion against molten aluminum.nst molten aluminum.

• 한국세라믹학회지
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• 제29권5호
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• pp.347-356
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• 1992

Various kaolin samples with different alumina content were prepared from calcined admixture of kaolin and ammonium sulfate by varying the treatment time in sulfuric acid. Samples were nitridated under N2 or N2-H2 atmosphere with changing the amount of added carbon, the reaction time and temperature. As the alumina content lowered, the size of kaolin particles decreased and the specific surface area increased. XRD analysis indicated that ${\alpha}$-quartz remained by decomposition of halloysite and meta-halloysite. Experimental results of nitridation behavior are summerized as follows; 1) Nitridation under N2 atmosphere. With the increase of C/SiO2 ratio and with the decrease of Al2O3 content, disappearance of XRD pattern peaks of mullite, ${\alpha}$-quartz and ${\alpha}$-Al2O3 were accelerated at 1300$^{\circ}C$. SiC was the main phase in the reaction product of acid-treated kaolin samples nitridated at 1300$^{\circ}C$ for 10 hours regardless of C/SiO2 ratio. But the XRD peak intensities of ${\beta}$-Si3N4, ${\beta}$-sialon and SiC did not show much difference when untreated raw kaolin was fired at the same condition. When the ratio of C/SiO2 was 3.5, ${\beta}$-sialon and ${\beta}$-Si3N4 existed in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{\circ}C$ for 7 hours. Only ${\beta}$-sialon existed in the same sample fired at 1400$^{\circ}C$ for 10 hours. ${\beta}$-sialon was obtained from all of the acid-treated kaolin samples fired at 1400$^{\circ}C$ for 40 hours, but AlN and SiC remained in the untreated kaolin sample. Z value of the ${\beta}$-sialon obtained from the 22% alumina containing kaolin sample fired at 1400$^{\circ}C$ for 40 hours was about 1.3(XRD) and 1.5(EDS). 2) Nitridation under 80N2+2OH2 mixed gas atmosphere with the C/SiO2 ratio of 1 Mullite was not found, but ${\alpha}$-Si3N4, and ${\beta}$-sialon were present in the reaction product of about 22% alumina containing kaolin sample fired at 1300$^{\circ}C$ for 10 hours. When untreated kaolin sample was nitridated at the same condition, mullite remained. AlN and SiC were not found in the reaction product of about 22% alumina containing kaolin sample fired at 1350$^{\circ}C$ for 5 hours. On the other hand, AlN and SiC remained in the product of untreated kaolin fired at the same condition.

• 대한치과기공학회지
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• 제30권2호
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• pp.39-45
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• 2008

Titanium and its alloys are widely used as dental implants materials because of their excellent mechanical properties. However, the alumina and zirconia ceramics are preferred to use as the substitute of Ti implants because there is a problems in esthetics and biocompatibility in Ti implant. The the glass infiltrated alumina ceramics are studied to increase the toughness and biocompatibility. The 45S5 and soda-lime glass powder was mixed with ethanol at ratio of 1:1 and brushed on the surface of alumina. Then it was heat treated in the electric furnace at $1400^{\circ}C$ from 30 min. to 5 hours. The glass powder was controlled from 200 to $350{\mu}m$ using ball milling. After heat treatment, the glass infiltrated specimen was tested in universal testing machine to measure the bending strength. The surface microstructure of each specimen was observed with SEM. The biocompatibility of 45S5 and soda-lime glass coated alumina was investigated using PBS at $36.5^{\circ}C$ incubator. The specimen was immersed in PBS for 3, 5, 7, 10 days. After that, the surface morphology was investigated with SEM. As the results of experiment, the 45S5 bioglass infiltrated alumina show the increase of bending strength according to the increasing of heat treatment time from 30 min. to 5 hours at $1400^{\circ}C$ Finally the 1370N bending strength of alumina increased to 1958N at 5 hours heat treatment, which shows 1.4 times higher. In contrast to this, the soda lime glass infiltrated alumina ceramics shows the convex curve according to heat treatment time. Thus it shows maximum bending strength of 1820N at 1 hour heat treatment of $1400^{\circ}C$ It gives 1.3 times higher. However, the bending strength of soda lime glass infiltrated alumina is decreasing with increasing heat treatment time after 1 hour. The precipitation on the surface of 45S5 glass infiltrated alumina was revealed as a sodium phosphate ($Na_{6}P_{6}O_{24}6H_{2}O$) and the amount of precipitation is increasing with increasing of immersion time in PBS. In contrast to this, there is no precipitation are observed on the surface of soda lime glass infiltrated alumina. This implies that 45S5 glass infiltrated alumina brings more biocompatible when it is implanted in human body.

• 한국분말재료학회지
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• 제17권3호
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• pp.209-215
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• 2010

Mesoporous alumina particles were prepared by spray pyrolysis using cetyltrimethyl-ammonium bromide (CTAB) as a structure directing agent and the effect of Al precursor types on the texture properties was studied using $N_2$ adsorption isotherms, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The surface area and the microstructure of alumina particles were significantly influenced by the Al precursor type. The largest BET surface area was obtained when Al chloride was used, whereas alumina particles prepared from Al acetate had the largest pore volume. According to small-angle X-ray scattering (SAXS) analysis, the alumina powders prepared using nitrate and acetate precursors had a clear single SAXS peak around $2{\theta}=1.0{\sim}1.5^{\circ}$, indicating that regular mesopores with sponge-like structure were produced. On the basis of TEM, SAXS, and $N_2$ isotherm results, the chloride precursor was most profitable to obtain the largest surface area ($265\;m^2/g$), whereas, the nitrate precursor is useful for the preparation of non-hollow mesoporous alumina with regular pore size, maintaining high surface area (${\sim}233\;m^2/g$).