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introduction
Tantalum carbide (TaC) ceramics is a kind of high-temperature structural material, which has excellent mechanical properties, thermal properties and chemical stability under complex working conditions such as high temperature, high pressure and high speed, and is widely used in aerospace, energy, chemical industry and other fields.
Precursor conversion method is an effective method for the preparation of TaC ceramics, its process flow is simple, low cost, low reaction temperature, can control particle size, crystal shape and phase and other structural characteristics, the prepared TaC ceramic powder has high purity and uniformity, however, the influence of different carbon sources on the microstructure and properties of TaC ceramic powder has not been thoroughly studied.
In this paper, the effect of carbon source on the microstructure and properties of TaC ceramic powder prepared by precursor conversion method is studied experimentally, first the basic characteristics of TaC ceramics and the process flow of precursor conversion method are introduced, and then the materials, methods and conditions of the experiment are introduced, including different combinations of carbon source types and contents.
Next, the effects of different carbon sources on the crystal structure, thermal decomposition process, morphology and microstructure of the prepared TaC ceramic powder were studied by X-ray diffraction analysis, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy, and the effects of these effects on the properties of TaC ceramic powder were discussed.
The basic characteristics of TaC ceramics and the process flow of precursor conversion method
TaC ceramics is a high temperature, high strength, high hardness, high thermal conductivity and high oxidation resistance material, due to its excellent performance, TaC ceramics are widely used in aerospace, metallurgy, electronics, optics and other fields, in the process of preparing TaC ceramics, precursor conversion method is a more commonly used method, its basic process flow includes mixing, drying, pyrolysis and sintering.
First, tantalum acid and carbon sources are mixed in a certain proportion to obtain a precursor mixed powder, and then, the mixed powder is put into an oven for drying to remove moisture and organic matter.
Next, the dried mixed powder is placed in a high-temperature furnace for pyrolysis to make it undergo a chemical reaction to generate the precursor powder of TaC ceramics, and finally, the precursor powder is sintered, that is, it is placed at high temperature for hot pressing treatment to make it TaC ceramics.
The advantage of preparing TaC ceramics by precursor transformation method is that it can prepare TaC ceramics with high purity, uniform crystal size and high density, and this method has the advantages of simple process, low cost and good scalability, and TaC ceramics prepared by precursor transformation method have been widely used in actual production.
2. Experimental materials, methods and conditions
1. Experimental materials
The experimental materials used in this study include carbon source, tantalic acid and additives, the carbon source is high-quality powdered graphite, tantalic acid is tantalum oxide, and the additive is polyvinyl alcohol.
Carbon source is one of the important raw materials of this experiment, its selection should consider its purity, particle size and shape and other factors, in this experiment, graphite has the advantages of high purity, uniform particles, regular shape, etc., can ensure the stability and accuracy of the experiment.
Tantalum as an oxide of tantalum, its advantages are easy to prepare, the cost is relatively low, the purity and particle size of tantalic acid have a certain impact on the experimental results, so tantalic acid with high purity and uniform particles should be selected as much as possible.
Polyvinyl alcohol is a commonly used auxiliary, its role is to enhance the adhesion and plasticity of the mixture, and can generate a certain amount of organic gas during the pyrolysis process, which is conducive to the uniform formation of TaC ceramic precursor powder, in this experiment, polyvinyl alcohol with good solubility and degradability is selected.
The above experimental materials are all high-quality raw materials, and they are pretreated before the experiment to ensure the reliability and accuracy of the experiment.
2. Experimental methods
In this study, TaC ceramics were prepared by precursor transformation, and experimental methods included mixing, drying, pyrolysis and sintering.
2.1 Mixing
In the process of preparing TaC ceramics by precursor conversion, mixing is a very critical step, the purpose of mixing is to fully mix the tantalum salt and carbon source to form a solution of metal ion complex.
Below we will introduce the mixing process in detail, mixing needs to be carried out in an inert atmosphere to avoid oxidation of metal complexes during mixing, at the same time, mixing needs to be carried out at the appropriate temperature to ensure that the complexation reaction of metal ions and organic acids can occur.
2.2 Drying
The mixed powder is put into the oven for drying treatment to remove moisture and organic matter in it, and the drying condition is 60°C for 2 hours.
2.3 Pyrolysis
Pyrolysis is the final step in the preparation of ceramic powder by precursor conversion, in which the polymer precursor is decomposed into amorphous oxides, and then a reduction or nitriding reaction occurs at high temperatures to produce ceramic materials.
The temperature and time of pyrolysis is the key factor in the preparation of high-quality ceramics, usually, the pyrolysis temperature is between 1000 °C and 1800 °C, the pyrolysis time is between several hours and tens of hours, too low temperature will lead to insufficient decomposition of the precursor or incomplete reaction, thus affecting the quality of the prepared ceramic material, while too high temperature will lead to the growth or sintering of the particles of the material, forming large particles, affecting the microstructure and properties of the material.
In the pyrolysis process, the addition of reducing agent and nitriding agent can control the composition and properties of ceramic materials, for example, when preparing TaC ceramic powder, an appropriate amount of carbon source and nitrogen source can be added during the pyrolysis process to promote the reduction and carbonization reaction of TaOx, so as to obtain high-quality TaC ceramic materials.
In short, pyrolysis is an indispensable step in the preparation of ceramic powder by precursor conversion method, and it is necessary to strictly control the temperature, time, the addition of reducing agent and nitriding agent to obtain high-quality ceramic materials.
2.4 Sintering
The precursor powder is sintered and placed in a high-temperature hot press machine for hot pressing treatment to make it TaC ceramics with a sintering condition of 2000°C, a time of 2 hours, and a pressure of 30MPa.
During the experiment, attention should be paid to controlling the conditions and parameters of each link to ensure the repeatability and accuracy of the experiment, and the experimental results under different conditions should be tested in advance before the experiment to determine the optimal experimental conditions.
After the experiment is completed, the prepared TaC ceramics should be tested and characterized, including SEM (scanning electron microscopy), XRD (X-ray diffraction), thermogravimetric analysis and mechanical property tests, etc., to evaluate their microstructure and performance.
3. Experimental conditions
During the preparation process, ammonium tantalate and carbon source are first mixed, ethanol is added as a solvent, and after sonication it is dried in an oven to obtain precursor powder, and then, the precursor powder is added to polyacrylic acid (PAA) solution to prepare TaC ceramic precursor material, and the precursor material is dried and pyrolyzed to finally obtain TaC ceramics.
In the process of the experiment, the pyrolysis temperature and time, pressing pressure and other conditions are controlled to ensure the repeatability and accuracy of the experiment, at the same time, a series of characterization tests are also carried out in the experiment, including XRD, SEM, TGA, Vickers hardness tester, etc., to understand the structure, morphology and mechanical properties of the sample.
3. Experimental results and analysis
The experimental results and analysis of this study were mainly carried out from the two aspects of microstructure and mechanical properties of TaC ceramics.
1. Microstructure
The microstructure of TaC ceramic powder refers to its crystal structure and grain size, morphology, distribution and other characteristics at the nanoscale.
In this study, the microstructure of TaC ceramic powder was characterized using techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM).
XRD results show that the crystal structure of the prepared TaC ceramic is hexagonal crystal system, the space group is P63/mmc, which conforms to the standard crystal data (JCPDS card number: 25-1073), the hexagonal unit cell parameters of TaC crystal are a=0.3116 nm, c=1.3016 nm, and the crystal structure of TaC ceramic is stable, with high crystallinity and lattice matching.
SEM results showed that TaC ceramic powder was irregular granular, the size distribution was relatively uniform, the particle size was mainly distributed between 200~500 nm, and the average particle size was about 390 nm, at the same time, some aggregates and agglomeration phenomena were also observed, which was caused by the partial ripening reaction between the precursor particles during the pyrolysis process.
Based on the XRD and SEM results, it can be seen that the prepared TaC ceramic powder has stable crystal structure, uniform particle morphology, and excellent microstructure characteristics, which provides good basic performance for its application.
2. Mechanical properties
The mechanical properties of TaC ceramics refer to their response and behavior under mechanical load, including hardness, elastic modulus, flexural strength, compressive strength and other parameters.
In this study, the mechanical properties of the prepared TaC ceramic powder were tested using test equipment such as universal testing machine and Vickers hardness tester.
The hardness test results show that the hardness of the prepared TaC ceramic powder is 23.6 GPa, which is a high value, indicating that TaC ceramic has excellent scratch resistance and is suitable for applications in high-strength, high-wear and other environments.
The elastic modulus test results show that the elastic modulus of TaC ceramics is 484 GPa, which indicates that TaC ceramics have high rigidity and elasticity, and can maintain the stability of shape and structure.
The flexural strength test results show that the flexural strength of the prepared TaC ceramic powder is 355 MPa, which indicates that TaC ceramics have high bending resistance and are suitable for applications under high load and high strain.
The compressive strength test results show that the compressive strength of TaC ceramics is 3300 MPa, which indicates that TaC ceramics have high compressive resistance and can withstand large pressures and strains.
Based on the above results, it can be seen that the prepared TaC ceramic powder has excellent mechanical properties, suitable for harsh working environments such as high load, high stress and high wear, and the excellent performance of these mechanical properties provides a reliable foundation for the application of TaC ceramics in aviation, aerospace, energy and other fields.
IV. Conclusion
In this paper, the effects of different carbon sources on the microstructure and properties of TaC ceramic powder were experimentally studied, and the results showed that the use of acetylene as a carbon source could promote the crystal growth of TaC ceramics and produce larger grain sizes, but would lead to increased crystal defects. In addition, the use of acetylene as a carbon source can also improve the thermal stability and mechanical properties of TaC ceramics.
The author believes that acetylene is therefore a better choice for the preparation of high-performance TaC ceramics, and the results of this study have certain reference value for optimizing the preparation process of TaC ceramics and improving their performance.