The material to be introduced is alumina (Al2O3) powder which is widely used in the ceramic material production. With the stable properties in both chemically and physically, alumina also has high heat resistance and high thermal conductivity, high strength and high hardness, etc.

Concerning the properties and the condition of the sample, we chose SEM, EDS and XRD for the characterization. SEM images provides the information of distributed patterns and the particle sizes. The EDS can quantitively test the components of the sample. And XRD can provide information of the phase identification of the crystalline material and the unit cell dimensions.

The scanning electron microscope (SEM) is a technique that uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. These signals obtained through SEM can reveal information about the sample including external morphology (texture), chemical composition, and crystalline structure and orientation of materials making up the sample. [1]

The principle is that the electron beam emitted by the electron gun will interact with the sample and produce secondary electrons. These secondary electrons will be collected by the secondary electron collector and then be translated to optical signal. Finally, the optical signals will be converted into electrical signals and present a secondary electron image.[2]

This technique can help us to identify the material well because SEM can help us to get the information of the morphology, structure and composition of the material. For example, we can easily identify different types of aluminium oxide such as Porous alumina, Lamellar alumina and Nano-Alumina. Compare to other types of microscope, SEM has a larger amplification factor(5~20000times), good resolution (Maximum value=0.8nm) and good depth of focus(100µm). It means we can identify the material precisely, accurately and comprehensively. This method is mainly applied to morphological characterization so that it gives qualitative information. In addition to the morphological information, SEM can also tell us the composition information of the material. Therefore, if we calibrate the image, quantitative information is also possible to be obtained.

Above are the SEM images of Lamellar alumina, it can be clearly seen the regular lamellar alumina structure and good dispersibility. The size and thickness are also very obvious.

Above are the SEM images of Porous alumina, it can be clearly seen the distribution of channels and the size of apertures.

X-Ray Energy Dispersive Spectroscopy (EDS) is used to determine the element content of Alumina Sample. Different element will emit different characteristic X rays so the qualitative analysis can be completed by detect the different frequency of photos which were ejected by different element in alumina sample.[4]

The principle of EDS: incident electrons beams interact with alumina sample to excite electrons in the inner layer of elements, while outer electrons transition to cavities to generate characteristic X rays and continuous X rays.[5]

Characteristic X rays are related to atomic number and element content is determined by counting the pulse of Si detector. It will generate a diagram in the EDS system [6] shown in figure1 different peaks can be identified by computer programs and show which elements it might be. In figure1 The X rays signal shows that there are three elements exist in the Alumina sample Carbon, Oxygen and Aluminum. Alumina is not electric conductive so Carbon spray layer was added on the sample so the electrons beams can interact with the sample.[7]

 The quantitative analysis of alumina can be completed in two conditions. First with reference material, under the same conditions, the X-ray intensity of each element in the standard sample and test sample was measured at the same time. Through the intensity ratio, the percentage content of each element could be calculated after modification it has higher accuracy. Secondly， without reference material it can analysis by data base or theoretical data. When using theoretical data， It can be calculated through this equation K=Iunk/Istd. When using data bases, the measured data of reference material has already put in the data base so it is similar to the first method. For Alumina, the modification method of quantitative analysis is ZAF. This method uses atomic number correction factor Z, X-ray absorption correction factor A and X-ray fluorescence correction factor F to modify the difference between sample and standard sample. The relative error for metal and oxide is generally 2.0% and the atomic number of sample must greater than 11.  [7]  

Figure1 EDS of Alumina particles [4]

X-ray powder diffraction (XRD) is an analytical technique which used for phase identification of a crystalline material and can provide information on unit cell dimensions. The analyzed material is finely round, homogenized, and average bulk composition is determined. X-ray diffraction is based on constructive interference of monochromatic X-rays and some crystalline samples. By scanning the sample through a range of 2θ angles, all possible diffraction directions of the lattice should be attained because of the random orientation of the powdered material.[8] XRD can be used for qualitative phase analysis, and it can also be used for quantitative analysis. The phase composition of the sample can be qualitatively analyzed by comparing the X-ray diffraction pattern of the sample to be tested with the X-ray diffraction pattern of the reference material; the quantitative analysis of the phase composition of the sample can be completed by analyzing and calculating the diffraction intensity data of the sample[9] Detection Limits: Quantitative multiphase analysis: ~0.5  to 1 .External standard quantitative analysis: ~0.1. The mean error of the measurement is about 3-5, indicating excellent agreement between the simulated weight fractions and those obtained with the Rietveld method.[10]

The typical characteristic peak d value is 0.2085, 0.2551,0.1601,0.3480,0.2379nm; 2θis 43.36,35.15 ,57. 50,25.58,37.78°. The X-ray with known wavelength is used to irradiate the crystal with unknown structure, and the distance d between the crystal faces is obtained by measuring the diffraction angle, so as to reveal the crystal structure.

α-Al2O3 is the most stable phase in the oxide of aluminum. It has high melting point, high hardness, good wear resistance, high mechanical strength, good electrical insulation and corrosion resistance. It is an ideal raw material for manufacturing pure aluminum series ceramics, abrasives, abrasives and refractories.[12]

[1] Scanning Electron Microscopy (SEM), Susan Swapp, Geochemical Instrumentation and Analysis. Retrieved from:

https://serc.carleton.edu/research_education/geochemsheets/techniques/SEM.html

[2] Jiang yuanru, Li zhao, Jia caixia, Zhao bing, Liu deyao(2011.10). Control synthesis and characterization of Lamellar alumina powder. Journal of Xi 'an University of Architecture and Technology,Vol 43,No.5

[3] Yang sirong, Liu shi, Cui yong(2010.08). Preparation and characterization of porous alumina. Atomic Energy Science and Technology,Vol 44,No.8

[4] Vijaya Pandurang Dhawale, Vaidei Balraj Khobragade, Satish Damodar Kulkarni. (2018) Synthesis and Characterization of Aluminium Oxide (Al2O3 ) Nanoparticles and its Application in Azodye Decolourisation. International Journal of Environmental Chemistry.

Vol. 2, No. 1, 2018, pp. 10-17. doi: 10.11648/j.ijec.20180201.13

[5] Wang qin Chen huifeng(2009) Principle and operation of EDAX energy spectrum Public platform of Ningbo Materials Institute, Chinese Academy of Sciences

[6] Element EDS System, Retrieved from:

https://www.edax.com/products/eds/element-eds-system

[7] Key questions about EDS analysis (2011) [online] Available at 22:53 2020/6/9

retrieved from：https://wenku.baidu.com/view/4190426277232f60dccca128.html?qq-pf-to=pcqq.c2c0

[8] Barbara L Dutrow, Christine M. Clark X-ray Powder Diffraction (XRD) , Retrieved from:

https://serc.carleton.edu/research_education/geochemsheets/techniques/XRD.html

[9] XRD analysis, Retrieved from:

https://www.antpedia.com/news/64/n-1482664.html

[10] Xingwen Lu,Kaimin Shih,Xiao-yan Li,Guoqiang Liu,Eddy Y. Zeng,Fei Wang. Accuracy and application of quantitative X-ray diffraction on the precipitation of struvite product[J]. Water Research,2016,90.

[11] Appraisal of alumina and aluminium hydroxide by XRD, Li Bo', Shao Lingling, (1. Zhengzhou Research Institute of Chalco , Zhengzhou 450041 ,China;2. Chalco , He 'nan Branch)

[12] Yang nanru. Test methods of inorganic nonmetallic materials: Wuhan University of Technology Press, 1990