1. Introduction to Silicon Carbide Ceramics

Silicon carbide ceramics are a high-performance ceramic material, usually made of silicon carbide (SiC) compounds, with excellent high-temperature mechanical strength, high hardness, high elastic modulus, high wear resistance, high thermal conductivity, corrosion resistance and other properties.

Silicon carbide ceramics are widely used in chemical, metallurgical, mechanical, energy, environmental protection, military and other industrial fields, as well as modern scientific and technological fields such as semiconductors and optoelectronics. They are often used to make high-temperature kiln tools, combustion nozzles, heat exchangers, sealing rings, sliding bearings, corrosion-resistant pipes, etc. In the third-generation power semiconductor devices, silicon carbide is also an important substrate material.

2.Silicon Carbide Properties

Silicon carbide is a man-made material with a molecular formula of SiC. Silicon carbide occasionally exists in meteorites and the earth's crust. The molecular weight of silicon carbide is 40.07 and the density is 3.16-3.2g/cm3. Pure silicon carbide is a colorless and transparent crystal. Industrial silicon carbide is colorless, light yellow, light green, dark green, light blue, dark blue and black. The degree of transparency decreases with the deepening of the color.

3. Silicon Carbide Crystal Structure 

Among them, the most widely used in industry is the α-SiC-6H crystal form, while the α-SiC-4H single crystal is mostly used as the substrate material of power semiconductor devices. The α-SiC-6H crystal form has excellent mechanical properties, while the α-SiC-4H crystal form has high insulation properties. When preparing silicon carbide powder, the product is mainly β-type below 2000°C, and the product is mainly α-type above 2200°C, and the 6H crystal form is the main one. The 15R crystal form is not very stable in terms of thermodynamics. It is an intermediate phase generated when β-SiC transforms to α-SiC-6H crystal form and does not exist at high temperatures.

3. Application of XRD in the analysis of silicon carbide ceramic materials

SiC ceramic materials have excellent mechanical properties, excellent oxidation resistance, extremely high wear resistance and low friction coefficient. The biggest advantage is that it can maintain high strength and hardness at a high temperature of 1400°C. Therefore, SiC ceramics are suitable for various harsh environments. However, when synthesizing SiC ceramic materials in industry, there is often unreacted free silicon. The presence of free silicon will lead to a decrease in the mechanical properties of SiC ceramic materials and a decrease in the use temperature. Therefore, it is very important to use X-ray diffractometer to identify the phase of SiC ceramic materials and determine the content of free silicon, which is very important for the research and development of SiC ceramics with excellent comprehensive performance. This is also the significance of phase analysis.

In addition, the grain size of SiC materials will also seriously affect the mechanical properties of sintered ceramics. The higher the sintering temperature and the longer the time, the larger the grain size. When the SiC grain size is about 40nm, the strength of SiC ceramics reaches the maximum. If it is greater than or less than this critical value, the strength will decrease. Therefore, it is of great significance to give the grain size of SiC ceramic materials by half-peak width calculation or Rietveld refinement.

4. Application of XRD in the analysis of silicon carbide ceramic materials

In this experiment, FRINGE CLASS benchtop X-ray diffractometer was used to perform phase analysis on SiC ceramic powder samples.

（1）Sample Display

（2）Test interface display

XRD spectrum of SiC ceramic powder

（3）Conclusion

The results of phase qualitative analysis show that the SiC ceramic sample contains 1.31% cristobalite low、9.11% quartz、  83.82% 6H-SiC and 5.76% 4H-SiC phase.   The free Si and trace amounts of O2 in the sample will produce SiO2, forming a dense protective layer on the surface of the SiC material. X-ray diffractometer can help determine the composition and content of SiC isomorphs (6H-SiC phase, 4H-SiC phase), thereby providing more accurate data support for the improvement of production processes and product quality research and development.