Alumina Nanosheets Research Articles

The influence of nanoparticles and functional metallic additions on the thermal shock resistance of carbon bonded alumina refractories

Modern steel casting plants require functional refractory components such as monobloc stoppers, submerged entry nozzles, and ladle shrouds. The functional flow control components in steel casting plants are often made of carbon bonded alumina refractories containing approximately 30% residual carbon after coking. This study investigated the mechanical and thermo-mechanical behavior of different functionalized Al2O3–C materials with additions based on alumina nanosheets, carbon nanotubes, semiconductive silicon, and a carbon content reduced to 20%. Furthermore, the curing temperature and the mixing order of the raw materials were altered. By optimizing the curing and mixing conditions of the samples that included all the additives, high residual strengths (with absolute values of up to 14.51MPa before thermal shock, after the first thermal shock, 12.11MPa, and after the fifth thermal shock, 13.87MPa, and a relative values of up to −19.81% and −4.29% respectively) could be recorded after thermal shock treatment.

Flexible and transparent polyimide films containing two-dimensional alumina nanosheets templated by graphene oxide for improved barrier property.

Unique two-dimensional alumina nanosheets (Alns) using graphene oxide (GO) as templates are fabricated and successfully incorporated with organo-soluble polyimide (PI) to obtain highly transparent PI nanocomposite films with improved moisture barrier property. The effects of filler types and contents on water vapor transmission rate (WVTR) and transparency of PI are systematically studied. The hydroxyl groups on GO react with aluminum isopropoxide via sol-gel process to obtain alumina coverd-GO (Al-GO), and then thermal decomposition is applied to obtain Alns. Alns are the most efficient fillers among others to restrict the diffusion of water vapor within PI matrix and simultaneously maintain the transparency of PI. XRD pattern, TEM, and AFM images confirm the sheet-like morphology of Alns with ultrahigh aspect ratio. With only 0.01 wt % of Alns, the PI nanocomposite film exhibits the most significant reduction of 95% in WVTR as compared to that of pure PI film. Most importantly, the resultant PI/Alns-0.01 film exhibits excellent optical transparency and high mechanical strength and great thermal stability.

Graphene oxide templated alumina nanosheet for the removal of As(V)

The current paper demonstrates a simple preparative method of alumina nanosheet through controlled hydrolysis and condensation on the surface of graphene oxide (GO). Taking into account the moisture sensitivity of the alumina precursor, its hydrolysis was carried out after introduction of interaction between the functional groups of GO and the alumina precursor in a non-aqueous solvent. On pyrolysis of the aluminum oxide-GO composite, a free-standing alumina nanosheet was obtained, which was further confirmed by XRD, TEM, STEM-EDX, FE-SEM, TGA, and N2 physisorption. Due to a favorable nanosheet structure, the alumina nanosheets showed a better performance in the removal of As (V) when compared to alumina prepared without GO template, even though the latter had a larger surface area than the alumina nanosheet.

Novel Al2O3‐C Refractories with Less Residual Carbon Due to Nanoscaled Additives for Continuous Steel Casting Applications

AbstractA new generation of thermal shock resistant Al2O3‐C refractories with approximately 30% less residual carbon and functionalized due to nanoscaled additives based on carbon nanotubes (CNTs) and alumina nanosheets (α‐Al2O3) were developed and investigated after coking at 1000 and 1400 °C. With the aid of electron backscatter diffraction analyses (EBSD) on fracture surfaces of the carbon bonded samples, Al3CON was identified on the nanosheet shapes already at 1000 °C coking temperature. The Al3CON new phase based on the reaction between alumina nanosheets and CNTs offers a chemical interconnecting phase for the carbon as well as for the oxide alumina filler. The new refractory composite structure presents excellent thermo‐mechanical properties in spite the lower carbon content. In addition, due to EDS and EBSD analyses amorphous whiskers and platelets within the system of SiO were observed in samples coked at 1000 °C, that were transformed to crystalline β‐SiC‐whiskers in samples coked at 1400 °C.

Improved thermal shock performance of Al 2O 3–C refractories due to nanoscaled additives

Carbon bonded alumina refractories with approximately 30 wt.-% residual carbon after coking are widely used as functional components such as submerged entry nozzles, monobloc stoppers and ladle shrouds in steel casting operations. Compositions with less residual carbon after coking based on nanoscaled magnesium aluminate spinel (MgAl 2O 4), alumina nanosheets (α-Al 2O 3) and carbon nanotubes (CNTs) either as single additives or combinations have been investigated according to their physical, mechanical and thermo-mechanical properties. The combination of nanoscaled powders based on carbon nanotubes and alumina nanosheets lead to superior thermal shock performance with approximately 30% less residual carbon in comparison to commercial available material compositions.

Hydrothermal Synthesis and Surface Characteristics of Novel Alpha Alumina Nanosheets with Controlled Chemical Composition

Novel alpha alumina (α-Al2O3) nanosheets with controlled chemical compositions were synthesized at 450 °C under 10.3 MPa pressure by the hydrothermal treatment of boehmite powder (γ-AlOOH) in the presence of soluble salts of metal dopants, α-Al2O3 seeds, and 5% SiO2 morphology modifier. Detailed XRD, SEM, HRTEM, STEM, and XEDS characterization was performed and it was found that the as-synthesized nanosheets were in most cases the phase-pure α-Al2O3 crystals exhibiting very strong (001) faceting, thicknesses of 10−50 nm, aspect ratios up to a few hundreds, and specific surface areas up to 35 m2/g. Metal dopants from nearly every group of the Periodic Table were present in these α-Al2O3 nanosheets in concentrations up to ∼0.5 atom % either as solid solutions or as nanosized inclusions. A thorough surface analyses using X-ray photoelectron spectroscopy (XPS), measurements of nitrogen adsorption isotherms at −196 °C, temperature-programmed desorption (TPD), and zeta potential measurements, revealed a very wi...