• 한국세라믹학회지
• /
• 제17권1호
• /
• pp.35-41
• /
• 1980

Alumina extraction from raw Hadong kaolin with sulfuric acid was studied to obtain relatively pure alumina. Factors as acid concentration, heating temperature and conditions of ammonium alum crystal formation from extracted solution are also surveyed and most of iron oxide in kaolin is eliminated in crystallization of ammonium alum. Pure crystal obtained from the extracted solution with ammonium sulfate is relatively free from iron containment in mother liquor. Alumina in ammonium alum crystal is converted to gibbsite form after complete hydrolysis in ammonia gas.

• 열처리공학회지
• /
• 제31권3호
• /
• pp.120-125
• /
• 2018

The PMMA composited material mixed with alumina studied to find the optimal condition, the adequate ratio of mixing, for the associated mechanical properties such as anti-corrosive, weatherproof performance. The 80% of hardness and 52% of scratch coefficient improved according to increasing ratio of alumina, which is mostly 3 times higher than that of pure PMMA, on other hand 16% of tensile strength and 35% of flexural strength has lost while alumina was adding in. The most proper ratio, having the best availability in substantial production, of composite between pure PMMA and alumina is determined as 93 wt. % vs 7 wt. %. Results of related five properties had estimated by using of a pentagram.

• 한국표면공학회지
• /
• 제25권3호
• /
• pp.150-157
• /
• 1992

A recovery process of pure alumina powder from the wasted aluminum etching solution of electrolytic condenser works was studied. The possibility of this process was considered in the basis of thermodynamic data nad physico-chemical properties for the recovered materials were tested. In order to obtain pure alumina, Fe3+ and Cu2+ in the solution as impurities were solvent-extracted, respectively, and then, Al3+ was precipitated by changing the pH of the solution. As the results, more than 99.9% of Al3+ in the solution was recovered by the precipitation method. The weight of the precipitate was reduced to about 65 wt.% of the original one by calcination and the sizes of the recovered powders were in order of 3-5$\mu\textrm{m}$. The precipitates were transformed to $\alpha$-Al2O3 at the calcination temperature about 120$0^{\circ}C$.

• 자원리싸이클링
• /
• 제28권1호
• /
• pp.15-22
• /
• 2019

습식법으로 고순도 알루미나를 제조할 수 있는 알콕사이드 가수분해법, 암모늄 명반의 열분해법, 암모늄 알루미늄탄산염(AACH) 열분해법을 소개하였다. 상기 세 공정으로 알루미나 제조시 용액의 pH, 온도와 불순물이 알루미나의 상전이와 고순도에 미치는 영향을 조사했다. 알콕사이드와 암모늄 명반의 열분해법으로는 ${\alpha}$와 ${\gamma}$알루미나의 제조가 가능하다. 그러나 AACH 열분해법으로는 ${\gamma}$알루미나 제조는 어렵다.

• 한국세라믹학회지
• /
• 제31권6호
• /
• pp.678-684
• /
• 1994

The surface of alumina is capable of acquiring a change when it is in an aqueous solution. This surface change will have a strong influence on the surrounding ions, particularly those of opposite change known as the counter ions. A site-binding model of the {{{{ gamma }}-alumina/KCl(aq) interface was used to calculated theoretical surface ionization constants and P.Z.C.(Point of zero change) of {{{{ gamma }}-alumina. This paper was carried out to investigate the effect of calcination temperature on the acidic and electrical properties of pure {{{{ gamma }}-alumina prepared by the precipitation method from the Al(NO3)3.9H2O and NH4OH. From the experimental data it was shown that {{{{ gamma }}-alumina have a mainly Br nsted acid site. However, the acidity of {{{{ gamma }}-alumina decreased with increasing calcination temperature at strength Ho +9.3. The surface charge density of {{{{ gamma }}-alumina was increased with electrolyte ionic strength and calcination temperature.

• 한국세라믹학회지
• /
• 제46권6호
• /
• pp.541-544
• /
• 2009

In Part III, the paper will show that an alumina-carbon nanotube-niobium nanocomposite produced fracture toughness values that are several times higher than that of pure nanocrystalline alumina. It was possible to take advantage of both fiber-toughening and ductile-metal toughening in this investigation.

• Membrane and Water Treatment
• /
• 제14권1호
• /
• pp.11-18
• /
• 2023

This work addresses the development of microfiltration ceramic membrane from alumina using extrusion method. The membranes were sintered at different temperatures ranging between 1000 and 1300℃. The alumina was characterized with thermogravimetric analysis, particle size distribution, X-ray diffraction, Fourier transform infrared spectrometer and scanning electron microscope analysis. Subsequently, the effect of sintering temperature on the membrane properties such as porosity, flexural strength, and pure water permeability was investigated and optimized for the sintering temperature. It is observed that with increasing sintering temperature, the porosity of the membranes decreases and the flexural strength, and pure water permeability of the membranes increase. The uncoated and coated membranes were compared at constant flux mode of filtration. Under the turbidity solution recirculation alone at 100 NTU, trans-membrane pressure (TMP) of uncoated membrane remained constant when the filtration flux was below 121 Lm^-2 h ^-1 , while the coated membrane was 111 Lm_-2 h ^-1 . Although suction pressure increased more rapidly at higher turbidity, coated membrane filtration showed better removal efficiency of the turbidity.

• 한국세라믹학회지
• /
• 제29권3호
• /
• pp.167-176
• /
• 1992

Zirconia-toughnened alumina(ZTA) powders that were uniformly coated with zirconia and yttria on the surface of alumina particles were prepared in order to inhibit the grain growth of alumina. Alumina particles were ultrasonically dispersed in the ethanol solution of Zr-n-propoxide, and then the Zr-alkoxide was hydrolyzed. Hydrated zironia as thin film was stabilized to tetragonal crystalline form by doping yttria as a stabilizer. The prepared ZTA powders had the good sinterability even at the lower temperature. As a result, the sintered bodies showed the enhanced fracture toughness compared with pure alumina. The relative density and fracture toughness(KIC) of the ZTA bodies sintered at 1550$^{\circ}C$ were 98% and 5 MPa$.$m1/2 respectively.

• The Korean Journal of Ceramics
• /
• 제6권1호
• /
• pp.78-82
• /
• 2000

Although alumina aggregates have been used as refractory aggregates due to the improved mechanical properties of refractories as a result of the low contraction of alumina aggregates, the aggregates have a difficulty in fabrication due to its low sinterability. Two types of alumina aggregates and a fused alumina aggregate containing transient liquid forming additives are prepared to investigate the sintering characteristics of aggregates. $Al_2O_3$rich composition in the $Al_2O_3$-MgO-$SiO_2$(-$TiO_2$) system is chosen for the transient liquid phase sintering and the final recrystallized bonding phase between grains inside the fused alumina aggregates is found to be a needle-like mullite phase. The flexural strength of alumina bars, reaction-bonded using the paste having a composition of $Al_2O_3$-MgO-$SiO_2$-$TiO_2$, is about 78 MPa, which is one half value of that of pure alumina.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.368-369
• /
• 2006

By means of magnetic pulsed compaction and sintering of weakly aggregated alumina based nanopowders the jet forming nozzle samples for the hydroabrasive cutting were fabricated. The ceramics was obtained from pure alumina, as well as from alumina, doped by $TiO_2$, MgO and AlMg. It was shown that the samples sintered from AlMg doped $Al_2O_3$ powder have the best mechanical properties and structural characteristics: relative density ${\sim}0.97$, channel microhardness. - 18-20 GPa, channel surface roughness ${\sim}0.7\;{\mu}m$, average crystallite size ${\sim}1\;{\mu}m$.