• PDF / 1,399,462 Bytes
• 2 Pages / 612 x 792 pts (letter) Page_size
• 91 Downloads / 197 Views

DOWNLOAD

REPORT

---

Figure 1. Bulk rare-earth aluminate glasses with the ALZ composition formed using the method described. No dopants were used for samples (a) and (b), while 5 wt% Nd2O3, Eu2O3, and Er2O3 were used for samples (c), (d), and e), respectively. Image (f) shows x-ray diffraction patterns, while (g) shows differential thermal analysis data for the microbead and bulk forms, revealing their amorphous nature and similar thermal behavior. Reprinted with permission from Nature 430 (August 12, 2004) p. 762. ©2004 Nature Publishing Group.

in the August 12 issue of Nature (p. 761), binary eutectic compositions of alumina and rare-earth oxide (Al2O3-RE2O3, RE = La, Gd, Y) as well as Al2O3:RE2O3:ZrO2 (ALZ) ternary compositions were investigated. In their flame-spraying technique, particulate precursors were fed into a high-temperature hydrogen–oxygen flame, producing molten particles that were then quenched in water. Glassy beads of the material with diameters of less than 140 µm were obtained. Beads with diameters in the range of 75–109 µm (selected by sieving) were consolidated into bulk glasses by sintering the beads at a temperature within the kinetic window—between Tg (the glass-transition temperature) and Tx (the crystallization temperature). X-ray diffraction, differential thermal analysis, optical microscopy, and scanning electron microscopy revealed that the bulk glass that formed remained amorphous and transparent (see Figure 1). The alumina-rich bulk glass was then heated above Tx for a short time to form a nanoscale glass–ceramic as a result of simultaneous crystallization and grain growth. The final microstructure contained ~100 nm crystalline grains, a finer and more homogeneous microstructure than that obtained using traditional methods. The glass–ceramics formed in this way also showed superior chemical, mechanical, and optical properties, as compared with silica-based glasses. This technique yielded alumina-based glass–ceramic composites with superior fracture toughness, important for potential structural applications. This discovery of glass-forming ability and glass-converted nanoscale ceramics can be extended to other nonconventional bulk oxide systems as well, so long as a sufficiently wide kinetic window ∆Tx = Tx – Tg is available. The method could pave the path to numerous bulk oxide glasses and nanocrystalline ceramics. GOPAL RAO

Composite Polymer–Carbon Nanotubes Function as Optoelectronic Memory Devices In the past few years, interest in making nanoscale electronic devices from carbon nanotubes has skyrocketed, with the hopes of making devices that are smaller and more versatile. In the September issue of Nano Letters (p. 1587), A. Star from Nanomix Inc., G. Grüner from the University of California, Los Angeles, and co-workers report the fabricaFor more information, see http://advertisers.mrs.org

688

MRS BULLETIN/OCTOBER 2004

RESEARCH/RESEARCHERS

where he began his independent career in 1982. Jagdish (Jay) Narayan (North Carolina State University) has received the 2004 Edward DeMille Campbell Memori