Mechanical–thermal synthesis of chromium carbides
Introduction
Chromium carbides may be synthesized from chromium–carbon mixtures via high energy milling or mechanical alloying [1], [2]. The present investigation, however, deals with the synthesis of chromium carbides (Cr3C2 and Cr7C3), starting from metallic chromium (obtained from the reduction of Cr2O3 with Al) and carbon (graphite). The synthesis was carried out via high energy milling, followed by heat-treating of pellets made of different milled mixtures at 800 °C, for 2 h, under an atmosphere of argon. Milling for relatively short periods of time before heat-treating the reactant mixtures appears to be an interesting route for synthesizing metallic carbides or other ceramic compounds, since the degree of contamination of the powders is minimized, as well as energy savings may occur due to this particular route [3], [4], [5], [6], [7], [8]. A SPEX CertPrep 8000 Mixer/Mill was used for milling under argon atmosphere. A tool steel vat and two 12.7 mm diameter chromium steel balls were used. The raw materials used and the products were characterized by differential thermal analysis, thermo gravimetric analysis, X-ray diffraction, electronic microscopy and X-ray fluorescence chemical analysis. The following variables were investigated: the quantity of carbon in the mixture, the milling time and the milling power.
Section snippets
Experimental
All the reactants used have a purity level higher than 99.5 pct. Table 1, Table 2 show, respectively, the chemical composition of chromium oxide and aluminium.
Fig. 1, Fig. 2, Fig. 3 present, respectively, the X-ray diffraction curves for chromium oxide, aluminium and graphite.
The graphite sample has been submitted to thermal analysis in order to determine the fixed carbon and ashes. In a differential thermal analyser/thermo gravimetric analyser (DTA/TG), a 20 mg sample of graphite was heated up
Results and discussion of the results
Fig. 6 shows the X-ray diffraction curves for the reactant mixture composed of Cr2O3 plus Al before milling and after milling for 1 h using the power of milling (ratio of mass of balls to mass of mixture) equal to 7.5:1.
It must be noted that after milling for 1 h with power of milling equal to 7.5:1, the peaks of the diffraction curve correspond to chromium oxide or aluminium, as to the peaks that appear on the curve related to the material before milling. The intensity of the peaks on the milled
Conclusions
The present investigation allows the following conclusions:
- (1)
Mechanical activation of the reactant mixture depends upon the milling power ratio used for processing. The energy liberated by the reduction of the chromium oxide with aluminium exhibits a maximum for milling power ratio between 5:1 and 7.5:1.
- (2)
Self-propagating reaction occurred for all heat-treated samples whatever the carbon content of the sample and the milling power ratio used.
- (3)
Bearing carbon samples exhibited hollow shell structures
Acknowledgements
The authors are grateful to the Foundation for the Support of the Research in the State of Sao Paulo (FAPESP), to the National Council for the Development of Science and Technology (CNPq) and to the Coordination for the Upgrading of the University Level Personnel (CAPES) for the support these organizations have provided to this particular research project.
References (11)
- et al.
J. Alloys Compd.
(1992) - et al.
J. Alloys Compd.
(1997) Mater. Sci. Eng.
(1998)- et al.
Intermetallics
(2002) - et al.
J. Eur. Ceram. Soc.
(2003)
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