Polymer-derived SiCN composites with magnetic properties
- PDF / 136,132 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 13 Downloads / 247 Views
Stephen E. Russek National Institute of Standards and Technology, Boulder, Colorado 80305 (Received 1 May 2003; accepted 25 August 2003)
Composites consisting of particles of ␣-iron dispersed in silicon carbonitride (SiCN) were fabricated by a polymer route. The composites had iron inclusions with the same magnetization as bulk iron, but they resisted oxidation up to 500 °C and had a hardness of 5–7 GPa. The composites behaved as ferromagnets, albeit with a low susceptibility attributed to the pinning of the domains by imperfect interfaces and to the elastic resistance from the SiCN matrix. This low-cost, low-temperature processing method can be used to make different kinds of ceramic composites with multifunctional properties.
Polymer-derived amorphous silicon carbonitride (SiCN) exhibits excellent flexural strength and resistance to creep,1 oxidation,2 and thermal shock.3 It also possesses high chemical stability at elevated temperatures.4 In addition to the structural properties, polymer-derived ceramics also exhibit high-temperature semiconductivity. Their electrical conductivity can be changed from approximately 1 to 108 ⍀−1 cm−1 by doping.5 In this paper, we report a new direction for polymerderived ceramics: the design and processing of composites with an unusual set of attributes, incorporating the outstanding structural properties of SiCN as well as the functional property of the dispersed phase. The dispersed phase may be a metal or ceramic. Here we show how iron particles can be introduced by the polymer route, creating a “high-temperature” magnetic material for applications in harsh environments. The processing of the composite takes advantage of the polymer route for the fabrication of SiCN. In this process an organic liquid precursor is crosslinked and pyrolyzed to produce the SiCN ceramic material. We prepare the SiCN–Fe composites by incorporating Fe3O4 powder into the liquid precursor (Ceraset, KION Corporation) and then reducing the ferrite to ␣-iron during pyrolysis. The starting composition of Fe3O4 powder and Ceraset was designed to obtain 70 vol% Fe3O4 in pyrolyzed specimen, assuming a 25% weight loss in the Ceraset during pyrolysis. The powder was dispersed in Ceraset and the slurry was ultrasonicated to break up the agglomerates. The slurry was cross-linked at 400 °C in N2, and the resulting plastic material was pulverized to obtain fine, free flowing powders. The powders were pelletized in a graphite die by warm pressing at 400 °C in N2. Specimens were pyrolyzed up to different temperatures in N2 for 9 h, to study the influence of the pyrolysis J. Mater. Res., Vol. 18, No. 11, Nov 2003
http://journals.cambridge.org
Downloaded: 10 Sep 2014
temperature on phase evolution. The phases and crystal structure of Fe were identified by x-ray diffraction using an x-ray diffractometer with Ni filtered Cu K␣ radiation. The sintered density of the samples was measured by Archimedes’ method using water as the immersion liquid and a microbalance. For microstructural study, the samples were polished t
Data Loading...
