Alumina nanopowders

Bell, N. S. Rodriguez, M. A. Dispersion properties of an alumina nanopowder using molecular, polyelectrolyte, and steric stabilization. J. Nanosci. Nanotechnol, 2004, 4, 283-290. 

Y.Y. Funda, Y. Acar, E. Yurtsever and M. Akinc, Reduction of Viscosity of Alumina Nanopowder Aqueous Suspensions by the Addition of Polyalcohols and Saccharides, J. Am. Ceram. Soc., 93, 2630-2636 (2010). 

To provide a basis for comparison with PFA modified with CW and MMT, PFA resin without CW or MMT was prepared using 3phr y-alumina (nanopowder, Aldrich) as a catalyst. The resin obtained after reaction at 100 °C for 12 h (denoted y-Al-PFA) was stable during storage (at room temperature) for several months. 

Fig. 6. Shrinking and y, 6, a- AI2O3 concentration curves during alumina nanopowders sintering. Doping with (a) - titania, ATI, (b) - magnesia, AMI, (c) - AI2Q3 without dopants constant heating rate 10°C/ min.

Shrinkage peculiarities upon the sintering of the alumina nanopowders based ceramics doped with Zr02... 

In this context, the aims of this study are to clarify the effect of different fast sintering techniques such as microwaves field at 2.45 GHz and external pulsed electrical field (Spark Plasma Sintering-SPS) on densification behavior of zirconia dispersed alumina nanopowders, on the microstructure and mechanic properties and to enhance the mechanical properties of the sintered composites. 

The effect of the aluminum oxide layer is also known to reduce the propagation of thermite reactions since alumina is an effective absorber of thermal energy. A study by Weismiller et al. of a 49 % active aluminum nanopowder in a thermite... 

A typical jump test is shown in Fig. 9.44 of flow stress versus strain. The stress temperature is 1450 °C. The slopes of each line in Fig. 9.44b yield for m 0.5, meaning that the stress exponent of the strain rate is 2 this indicates the superplastic behavior of the zirconia-alumina-spinel composite under the test conditions of temperature and strain rate. In order to determine the activation energy, a plot of strain rate versus the inverse absolute temperature must be made (as in Fig. 9.44c). The average activation energy of PS-HEBM-SPS is 945 kJ/mol, which is much higher than that of the composite processed from nanopowder mixtures (622 kJ/mol). This should represent GBS, if the concept of superplasticity is the dominant mechanism of deformation. Table 9.1 summarizes the strain rates and various temperatures of two and/or three specimens. PS-SPS appears in the Table 9.1 as PS-SPS and is listed under column C. For the purpose of comparison, the flow-stress results for nanopowder mixtures are also listed in Table 9.1 and are smaller than those processed from PS powders with/without HEBM. 

The aim of the work is to fabricate alumina-based ceramics with high wear resistance. It is achieved by the usage of weakly aggregated nanopowders and by the apphcation of magnetic-pulsed compaction as well as by the addition of titania, magnesia and zirconia. 

Thus the form of the shrinkage curve of the compacts from the nanopowders of the metastable forms of alumina is determined by the processing of the polymorph transitions of alumina to stable a-AbOs. At the staring stage (t < Ta) the material consists of the y, 5, and 0 phases mixture. The polymorph transition (y + 8 + 0) a starts at Ta temperature and can... 

The usage of weakly aggregated nanopowders of imstable alumina phases, compacted by MFC method up to high density more than 0.65 (relative to theoretical one) allows obtaining dense ceramics with submicron structure at relatively low sintering temperatures in the 1400-1450°C range and up to 30 minutes dwell time. 

Bell NS et al (2005) Rheological properties of nanopowder alumina coated with adsorbed fatty acids. J CoUoid Interface Sci 287 94-106... 

Some phase separation is implied, although it is also possible that, because of the unique synthetic approach employed in forming the nanopowder, a metastable phase, m-alumina, related to P"-alumina was synthesized. No peaks are present that suggest the presence of the P phase, which has distinguishing diffraction peaks at 20,0 (4.45 A), 21.8 (4.07 A), and 33.5 20 (2.68 A). Because flame spray... 

Figure 4 XRD of the nanopowder after various heat treatments (a) as-prepared, (b) 800 °C for 1 h, (c) 1000 °C for 1 h, (d) 1200 C for 1 h, (e) 1400 C for 1 h, (f) 1600 °C followed immediately by cool down. Spectrum (g) is that of 100% p"-alumina crushed from a Ceramatec sample. The position of the characteristic peak from P (33.5 ) and p" (34.5°) are highlighted.

Nanopowder Stability. The question of nanopowder stability with respect to reproducible formation of p"-alumina is important. Many of the processing steps explored so far have not been executed with rigorous regard to purity, i.e. preparations are done in air with undistilled solvents. Still, the highly pure P" is consistently reproduced. Nanopowders have even been left exposed to the atmosphere for days at a time, prior to sintering, with no change in the results. 

Figure 7 DRIFTs-IR spectra of (a) p"-alumina precursor powder as received from Ceramatec, (b) as-prepared nanopowder, (c) Ceramatec powder heated to 1200 C, and (d) nanopowder heated to 1200 "C.

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