Isothermal and constant-grain-size sintering have been carried out to full density in Y 2 O 3 with and without dopants, at as low as 40% of the homologous temperature. The normalized densification rate follows Herring's scaling law with a universal geometric factor that depends only on density. The frozen grain structure, however, prevents pore relocation commonly assumed in the conventional sintering models, which fail to describe our data. Suppression of grain growth but not densification is consistent with a grain boundary network pinned by triple-point junctions, which have a higher activation energy for migration than grain boundaries. Long transients in sintering and grain growth have provided further evidence of relaxation and threshold processes at the grain boundary/triple point. Isothermal and constant-grain-size sintering have been carried out to full density in Y 2 O 3 with and without dopants, at as low as 40% of the homologous temperature. The normalized densification rate follows Herring's scaling law with a universal geometric factor that depends only on density. The frozen grain structure, however, prevents pore relocation commonly assumed in the conventional sintering models, which fail to describe our data. Suppression of grain growth but not densification is consistent with a grain boundary network pinned by triple-point junctions, which have a higher activation energy for migration than grain boundaries. Long transients in sintering and grain growth have provided further evidence of relaxation and threshold processes at the grain boundary/triple point.
Several biocompatible polymers are capable of large responses to small temperature changes around 37ºC. In water, their responses include shrinkage and swelling as well as transitions in wettability. These properties have been harnessed for biomedical applications such as tissue engineering scaffolds and drug delivery carriers. A soft material/hard material hybrid in which a magnetic metal or oxide is embedded in a temperatureresponsive polymer matrix can combine the thermal sensitivity with magnetic signatures. Importantly, nanosizing such construct brings about new desirable features of extremely fast thermal response time, small magnetic hysteresis and enhanced magnetic susceptibility. Remote magnetic maneuvering and heating of the hybrid nanocolloids makes possible such applications as high-throughput enzyme separation and cell screening. Robust drug release on demand may also be obtained using these colloids and nanoparticle-derived thin film devices of combined thermal magnetic sensitivity. • C. In water, their responses include shrinkage and swelling as well as transitions in wettability. These properties have been harnessed for biomedical applications such as tissue engineering scaffolds and drug delivery carriers. A soft material/hard material hybrid in which a magnetic metal or oxide is embedded in a temperature-responsive polymer matrix can combine the thermal sensitivity with magnetic signatures. Importantly, nanosizing such construct brings about new desirable features of extremely fast thermal response time, small magnetic hysteresis and enhanced magnetic susceptibility. Remote magnetic maneuvering and heating of the hybrid nanocolloids makes possible such applications as high-throughput enzyme separation and cell screening. Robust drug release on demand may also be obtained using these colloids and nanoparticle-derived thin film devices of combined thermal magnetic sensitivity. ARTICLE IN PRESS+Model NANTOD 7 1-14 Nano Today (2008) xxx, xxx-xxx 1 a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a
Conventional and new sintering mechanisms have beenporous compacts is well-known in the ceramic literature. [2][3][4][5][6] However, several reports have been presented recently that investigated using fine powders of CeO 2 and Y 2 O 3 of excellent sinterability. We have verified the validity of Herring's show that particle/grain size can remain essentially constant up to a density of ϳ92%, and such a resistance to coarsening has scaling law for 60%-84% relative density and found that it is consistent with grain-boundary-diffusion control. At been claimed to be essential for good sinterability because it signifies uniform packing. 7,8 These observations also have lower densities, we have found that pores larger than the critical size, in the sense of Kingery and Francois, can still reinforced the notion that sinterability reflects the competition between densification and coarsening and that coarsening is be sintered readily. This is rationalized by a new sintering mechanism based on particle repacking concurrent with detrimental to good sinterability. 9 However, in our study of fine CeO 2 and Y 2 O 3 powders, we have found good sinterability, particle coarsening, resulting in a higher packing factor. Very fine, surface-active powders that coarsen rapidly are regardless of coarsening behavior. 1 Specifically, CeO 2 coarsened more than Y 2 O 3 at comparable temperatures and densities; uniquely capable of taking advantage of this new sintering mechanism, which along with their propensity to homogeniyet, compacts of both oxides could be readily sintered to full density. Coarsening was further found to begin at very early zation, accounts for their remarkable sinterability even at stages, in all cases ϽϽ92%. These observations with fine powvery low green densities.ders clearly contradict the popular notion of an inverse correlation between sinterability and coarsening. Because this strong
Iron-oxide-containing double emulsion capsules carrying both hydrophilic and hydrophobic therapeutic molecules can deliver drugs and energy on demand in vivo. Magneto-chemotherapy/hyperthermia involves a burst-like release of hydrophilic doxorubicin and hydrophobic paclitaxel, remotely triggered by a high frequency magnetic field, which also releases energy via internalized iron oxide nanoparticles, all contributing to cell kill.
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