Du Yanjun, Du Baoan, Zhao Lei, Lv Jiantong
(College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China)
AbstractNano-sized-Fe particles have been attracting great attentions due to its excellent physical and chemical properties in recent years. In this paper, nano-sized-Fe particles were prepared by solid phase method using Fe(NO·9HO and NaOH as raw materials. A series of experimental researches were carried out in order to obtain the nano-sized iron oxide powders with mono-phase and good dispersion.X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the products. The best preparation parameters were also obtained through these series of contrastive experiments. The results from XRD showed that the products were-Fe. It could be seen from TEM that their shapes were peanut-like, and the sizes of the particles were around 50 nm.
Nano-sized-Fe particles are widely used as functional materials because of its excellent physical and chemical properties. There are comprehensive applications in magnetic materials, gas-sensing materials, catalyst materials and so on . Generally, nanoparticles of-Fe can be prepared by sol-gel method [2,3], microemulsion method , hydrothermal method [1,5], microwave method [6, 7,8], solid phase method, and so on. In the present paper, nanoparticles of-Fe were prepared by solid-phase method using Fe(NO·9HO and NaOH as raw materials. Different experimental conditions were carried out in order to obtain the nano-sized iron oxide powders with mono-phase and good dispersion.Compared with other methods, the solid phase method applied for preparation of nano-sized-Fe particles has advantages of low cost of production, simple process and short period of production, which are suitable for industrial production. We hope that the method described in the paper is useful for production of nano-sized-Fe on industrial scale.
The nano-sized-Fe particles were prepared as follows: 10 g Fe(NO·9HO and 3 g NaOH were put into agate mortar, then were mixed and grinded thoroughly. With grinded, the mixture became glue gradually, and then solidified. The solidified materials were grinded to powders, and then washed three times with water and ethanol, respectively. The prepared materials were decompressing filtered, air dehydration naturally at ambient temperature, and then the precursors were obtained. Then the precursor was grinded, and calcined for different period at different temperature. Finally, the products were obtained. The phase compositions of the products were examined by XRD. The sizes and shapes of the products were testified by TEM.
3. RESULTS AND DISSCUSSION
3.1 XRD analysis of the nanoparticles of-Fe
The crystal structure of the five samples were analysed by X-ray diffraction using CuKradiation (CuKCu = 0.154178 nm). The conditions of calcinations were showed in Table 1. The XRD patterns of samples were illustrated in Fig. 1.
Table 1. The conditions for calcinations of the precursors
|Temperature and period||673K 2h||773K 2h||873K 2h||673K 2h , 873K 2h||573K 2h , 973K 2h|
Fig.1 XRD patterns of the samples
According to Fig.1, the sample #1 wasα-Fe and belongs to hexagonally, the shapes of peaks were in accordance with the other references [1,10]. However, the 3.66 characteristic peak was absent in the XRD pattern of sample #1, which indicated some impurity of-Fe was contained in sample #1. Thus, pure-Fe nano-sized particles could not be obtained by calcining the precursor for 2h at 673K. On the other hand, the reaction reagents could not be changed into-Fe completely due to the lower temperature and shorter period, some impurities and the residual precursor still remained in sample #1 . The sample #2 was better than the sample #1, although some impurities were still contained in the sample #2. According to Fig.1, the sample #3, #4 and #5 were pure-Fe
Seen from Fig. 1, with the temperature of calcinations ascending and the period extending, the X-ray diffraction peaks became higher and narrower. The average sizes of particles were calculated by the Scherrer formula:
D = k·/(·COS
where D (nm) is the primary diameter of the product, k equals 1.075,Cu (nm) is 0.154178,(arc) is integral peak width,(degree) is angle of diffraction. X-ray diffraction peaks with low angular degree (generally 2≤50°) were selected for calculation, and the average value was obtained. These results were showed in Table 2. From Table 2, it could be seen that the primary diameter of particles was in the range of 20-30 nm.
Table 2. Average primary diameter of samples by calculation according to XRD data
3.2 TEM analysis of nano-sized particles of-Fe
The TEM photograph of sample #3 was shown in Fig. 2. According to Fig. 2, the sizes of the particles were about 50 nm and their shapes were peanut-like. The TEM photographs of the other samples were similar to Fig. 2, so these photographs were not shown in the present paper. Commonly, the calculated primary diameter based on XRD was less than the primary diameter based on TEM, our result was accordant with this phenomenon in this study.
Fig. 2 The TEM photograph of sample #3
3.3 Optimization of temperature and period of calcinations
The temperature and period of calcinations were important factors for preparation of nano-sized-Fe particles. Pure and uniform Fe(OH) began to decompose at 575.1K,-Fe emerged at 573-673K, with the temperature ascending constantly, Fe(OH) decomposed completely at 873K 2h, then-Fe was obtained. With the temperature ascending and the period extending, the sizes of-Fe particles become larger. Finally, the temperature of 873K and the period of 2h were chosen for preparation of nano-sized-Fe particles.
3.4 Mechanism of preparation of nano-sized particles by solid-phase method
The mechanism can be described by the following two steps:
Fe(NO·9HO + 3 NaOH Fe(OH) + 3NaNO +9H
In the process of solid-phase reaction, the contact area of reagents becomes larger by grind; meanwhile the temperature of some area ascends, which can initiate reaction of the reagents. Crystal water was included by Fe(NO·9HO and the melting point of Fe(NO·9HO was low, therefore the trace crystal water can be used as space of accelerating the reaction. The particles collided with each other and nucleuses were formed rapidly, but particles were very difficult to cross every phase, therefore the nucleuses could not grow rapidly. According to the theories of crystal science, when the speed of forming nucleuses far exceeded the speed of growing of nucleuses, small particles can be formed easily. Therefore solid-phase method was a good way for preparation of nano-sized particles.
In this study, nano-sized-Fe particles were prepared by solid phase method using Fe(NO·9HO and NaOH as raw materials. The prepared production was characterized by X-ray diffraction and transmission electron microscopy. The experiment showed that the temperature and period of calcinations were important factors influencing preparation of nano-sized-Fe particles. The best preparation parameters were also obtained through contrastive experiments. The results from XRD showed that the products were-Fe. It could be seen from TEM that their shapes were peanut-like, and the sizes of the particles were around 50 nm. The technology for preparation of nano-sized-Fe particles by solid phase method had advantages of low cost of production, simple process and short period of production, which were suitable for industrial production.