Particle Size and Microstructure of Ni Nanopowders Prepared.ppt

1、Particle Size and Microstructure of Ni Nanopowders Preparedby Anodic Arc Plasma,Zhi-qiang Wei Lanzhou University of Science Lanzhou University,Outline,1. Introduction 2. Experimental 3.Results and discussions 4. Conclusions,Introduction,In recent years, metal nanopowders have attracted considerable

2、interest for scientific research and still is the subject of intense investigation due to their intriguing properties and their potential applications, which are determined by the particle size and structure. Consequently, they are important to a large variety of applications, including activator, l

3、ubricator, dope, activation and sintering materials, high-dense magnetic recording materials, etc. All these applications require the powders to be made of isolated particles. The particle size and the structure strongly depend on the method of the nanoparticle production. Accordingly, the preparati

4、on methods and characterization of these powders have been main topics in the field of metal materials.,Many techniques have been used to prepare nano metalpowders, such as vapor decomposition, mechanical crushing by ball milling, sol-gel processing, gas-phase chemical reaction, water-heating reacti

5、on, laser high temperature burning method, etc. However, such powders prepared by these methods usually cannot be isolated. In addition, the majority of the process cannot be fulfilled promptly and generally cannot be industrialized. Commercial exploitation of nanopowders is currently limited by hig

6、h synthesis costs. From a practical viewpoint, it is vital to develop a way to manufacture high quality nanopowders in large quantities at low costs.,For this reason, a special lucrative process has been developed in our laboratory to prepare high quality nano powders. Preliminary results showed tha

7、t this process as a very promising technique, there are three main advantages by anodic arc discharging plasma method: (1) this process is convenient, inexpensive and an effective preparation method, (2) The nanopowders by this process with uniform size, monodisperse and a narrow size distribution a

8、nd have low impurity contamination; (3) The properties can be easy improved by varying the technology Parameters in the process, especially capable of continuously productivity and suitable for bulk production in factory.,experimental equipment,The schematic diagram of the experimental equipment des

9、igned for obtaining metal nanopowders is shown in Fig.1. The experimental apparatus mainly consists of a stainless steel vacuum chamber, gas supply device, DC power supply current source plasma generator with high frequency initiator，vacuum pump, water-cooled collection cylinder; fixed water-cooled

10、copper anode crucible and plumb moveable tungsten cathode in a vacuum chamber and connected to a power supply. The raw material to be evaporated was placed on the anode.,Fig. 1schematic diagram of the experimental installation,experimental procedure,In the process of preparation, the vacuum chamber

11、was pumped to 10-3 Pa and then was backfilled with inert argon to near 103 Pa. Then the anodic arc plasma was fired, the metal Ni was heated, melted and evaporated into atom smoke of the metal by the high temperature of the plasma. The metal atoms diffused around and collided with gas atoms lose ene

12、rgy, and then the nano-Ni particles were formed by collision between the metal atoms. The formed nano-Ni particles were transferred to the wall of the cooled collection cylinder.,Schematic diagram illustrating the growth process of nanopowders,Characterization,The structures and particle size of the

13、 samples were characterized by X-ray powder diffraction (XRD) The morphology and particle size distribution were investigated by transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED) The specific surface area of the powders was determined by the Bruna

14、uerEmmettTeller (BET) method . The average pore diameter and cumulative pore volume of pores was estimated by Barrett-Joyner-Halenda (BJH) method. The main elements and their relative content were examined by X-ray energy dispersive spectrometry (XEDS) The nitrogen, hydrogen, oxygen and carbon conte

15、nt was analyzed by element analyze instrument,Fig.2 TEM micrograph of Ni nanopowders,Fig.2 Shows representative TEM image. We can see from these graphs that all of the particles are fairly homogeneous. Few large agglomerates of particles were seen because of their extremely small dimensions and high

16、 surface energy, most of the fine Particles with uniform size, smooth surface and spherical shape, particles assemble at random and link long chain, the spherical chainlike is the result of magnetic force and surface tension collaboration between the ultra-fine particles.,Results and discussions,Fig

17、.3 particle size distribution of Ni nanopowders,Fig.3 shows the particle size distribution of Ni nanopowders, the median diameter is about 47 nm, ranging from 20nm to70nm,Fig.2 the selected area electron diffraction pattern of Ni nanopowders,The selected-area electron diffraction (SAED) pattern can

18、be indexed to the reflection of fcc structure, particles tropism at random and small particles cause the widening of diffraction rings that made up of many diffraction spots.,Fig.4 XRD patterns of Ni nanopowder,Fig.4 shows the powder X-ray diffraction (XRD) pattern for the samples, All the peaks are

19、 corresponding to the bulk metallic Ni diffraction, no other phase components founded, it shows that the samples have FCC structure,The average particle size of the powder calculated from the XRD patterns according the Scherrer formula: d= 0.89/ Bcos, The average particle size in the perpendicular d

20、irection (111) Miller plane was calculated to be around 42nm, the results were consistent with TEM method.,Table 1 comparison of interplaner spacings (dhkl) and the lattice parameter (a) with standard ASTM data,According to electron diffraction formula Rdhkl= L and X-ray diffraction =2dhklcos . The

21、values of interplaner spacings dhkl calculated from the diameters of the diffraction rings, as well as obtained from XRD analysis. For FCC structure, the lattice parameter (a) of (111) Miller plane can be calculated respectively. Compared with standard ASTM data in Table 1, it can be seen that the r

22、esults were consistent with each other.,Fig.5 N2 adsorption-desorption isotherms of Ni nanopowders,Fig.5 shows the typical nitrogen adsorption isotherms of Ni nanopowders. It indicates that in the low-pressure region (P/P00.8), the isotherms relative flat, adsorption and desorption completely superp

23、osition because adsorption mostly occurs in the micropores. At the high relative pressure region(P/P00.8), it increase rapidly, and form a lag loop owing to capillary agglomeration phenomenon.,Fig.6 BET plots of Ni nanopowders,Fig.6 shows BET plots of Ni nanopowders, the specific surface area of Ni

24、nanopowder were calculated using the multi-point BET-equation is 14.23m2/g,Assuming the particles have solid, spherical shape with the same size,the surface area can be related to the average particle size by: DBET =6000/(p.Sw) (in nm), The average particle size is 46 nm.,Table 2 comparison of mean

25、particle size obtained by different methods,The average particle size of Ni nanopowders calculated from BET, TEM and XRD methods are listed in Table 2, we noticed that the particle size DTEM obtained from TEM about 47 nm, the particle size DXRD obtained from XRD is 42 nm, smaller than the values of

26、DTEM and DBET. This difference can be ascribed to the agglomerates to form larger particle,Fig.7 BJH pore size distribution curves of Ni nanopowders,Fig.7 shows the typical BJH pore size distribution curves of Ni nanopowder. The experimental fact indicates that most of the micropore with a size smal

27、ler than 40nm was observed,The average pore diameter estimated from the peak position is about 23 nm. assuming full saturation of the pores at the relative pressure of 0.95, the cumulative pore volume of pores is approximately 0.09 cm3/g.,Chemical compositions of the products were analyzed using thr

28、ee methods. XRD patterns of Ni nanopowder shows all the peaks are corresponding to the bulk metallic Ni diffraction, no other phase founded.,Fig.8 X-ray energy dispersive spectrometry of Ni nanopowders,fig.8 shows the X-ray energy dispersive spectrometry of Ni nanopowders. the XEDS spectrum shows ni

29、ckel, nitrogen, silicon and oxygen peaks. It is obvious that the silicon peak is caused by the glass substrate on which Ni nanopowders were mounted. XEDS quantitative microanalysis indicates a predominance of nickel (98.30 wt%), as the main nanopowders constituents, oxygen (0.58 wt%) and nitrogen (0.51 wt%) in the product.,Table3 chemical composition analyses of Ni nanopowders,Table