Synthesis of Nanocrystalline Ni 3 Cu by Sol-Gel route
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nthesis of Nanocrystalline Ni3Cu by Sol-Gel Route S.K. PRADHAN, A. DATTA, M. PAL, and D. CHAKRAVORTY
Fig. 6—TEM image of 173 ks alloy powder after consolidation.
with a grain size of about 7 nm (Figure 3(e)). The HRTEM micrograph, which is oriented to the (001) plane direction (Figure 5), indicates the formation of a single phase of WC. The consolidation procedure of WC leads to a slight grain growth (Figure 3(f)) with an average grain size of about 40 nm in diameter (Figure 6). In contrast to the traditional sintering techniques,[7,8,9] the consolidated sample has maintained its unique nanocrystalline grain characteristics. In summary, we offer a powerful tool for the fabrication of nanocrystalline consolidated WC at room temperature using a simple process. The efficiency of preparation and low cost are the advantages of this method.
The authors are indebted to Professor Y. Minonishi for the fruitful discussions. We would like to thank Messrs. Y. Murakami and S. Ito for their kind technical support during the SEM and TEM observations. One of the authors (MSE) would like to thank Ms. Mitsuko El-Eskandarany for her kind assistance. This work was partially supported by a Grant-in-Aid for General Scientific Research (No. 06452323), given by the Ministry of Education, Science, Sports and Culture, Japan.
Nanocrystalline materials have been an active area of research in recent years.[1] The grains in these materials have a large surface-to-volume ratio. However, they show stability against spontaneous growth.[2,3] A local minimum in free energy has been cited as the reason for such metastability.[4] We have explored the possibility of synthesizing a metallic alloy phase in the nanocrystalline form so that the reaction temperature can be lowered significantly. A solgel technique has been used. We have chosen the Cu-Ni system in our work, because it has been studied extensively and the data are available in the literature.[5,6] The results are briefly reported in this article. For preparing the samples, first of all, two separate solutions were made—one containing Ni(NO3)2z6H2O and Si(OC2H5)4 and the other having Cu(NO3)2z3H2O and Si(OC2H5)4. The first of these comprised of 15 g of Ni(NO3)2z6H2O, 5 mL of Si(OC2H5)4, 96 mL of water, and 154 mL of ethyl alcohol (C2H5OH). The second solution was made of 15 g of Cu(NO3)2z3H2O, 5 mL of Si(OC2H5)4, 96 mL of water, and 154 mL of C2H5OH. The solutions were stirred for 30 minutes after adding nitric acid to them so that the pH was maintained to a value ;2.5 (the molarity of HNO3 ; 3.2 3 1023). The solutions were subjected to gelation for 72 hours. The alcogels so prepared were reduced in hydrogen at 550 7C for 40 minutes. The resultant powders were so mixed that the ratio of Ni:Cu in the final mixture would be 3:1. The mixture was ground by mortar and pestle for 1 hour with acetone and then evaporated to dryness. The resultant powder was divided into three parts. Each of these was packed in a graphite mold 1 cm in diameter and mounted onto a DSP 25 ATS sintering press (supplied b
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