The present invention claims priority under 35 U.S.C. 119(a-d) to CN 201710247968.8, filed Apr. 17, 2017.
Field of Invention
The present invention belongs to the field of thermoelectric materials, which relates to the preparation of CrN material and discusses its potential value in thermoelectric applications.
Description of Related Arts
Thermoelectric material is a kind of functional material which can convert thermal energy and electric energy from each other. Based on the seebeck effect and peltier effect, it can be used for thermoelectric power generation and static cooling, and has no pollution, no mechanical rotation, no noise and flexible installation. At present, thermoelectric materials have shown a trend of vigorous development in military, aerospace, industrial waste heat utilization, automobile exhaust waste heat utilization and other fields, and have great commercial potential.
The conversion efficiency of thermoelectric materials is evaluated by dimensionless figure of merit ZT (ZT=S2σT/κ), where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. The higher the ZT value, the higher conversion efficiency of thermoelectric materials. The recent emergence of high-ZT materials is encouraging. However, the material that can be applied on a large scale is scarce. Considering the working conditions of thermoelectric devices, the large temperature difference between the hot and cold side may lead to deformation and collapse of the device, which can greatly influence the efficiency and service life. Even the current commercial thermoelectric materials such as Bi2Te3 and PbTe includes these challenging aspects as well. In order to address these issues, materials with better mechanical properties and high thermal stability are needed.
CrN is usually prepared by reaction of metal chromium or chromium halide with ammonia in industry. The reaction usually takes a very long time (2 or 3 weeks), which is greatly reduces the production efficiency and economic benefit of the CrN industry. Other methods to preparation CrN such as mechanical alloying method, benzene hot method, high-energy ball mill method due to the long production cycle, the low purity and the harsh reaction conditions which are not suitable for mass production. Therefore, it is important to explore a quick and efficient method for the preparation of CrN.
The present invention aims to provide a method for preparing high purity CrN and to evaluate its potential value in the field of thermoelectric applications. We systematically studied the thermoelectric properties, vickers hardness, wear resistance and thermal stability of CrN. As an alternative, CrN possesses many potential advantages. The high hardness, abrasion resistance and thermal stability may make it an important participant in the field of thermoelectric applications for some extreme environments in the future.
The technical proposal of the present invention is as follows: the application of CrN in the field of thermoelectric materials.
The preparation method of CrN thermoelectric material comprises the following steps:
Step 1: dissolving Cr(NO3)3.9H2O (99.9%, aladdin) and PEG10000 (99%, aladdin) in deionized water and adding an obtained solution drop wise with NH3.H2O under a magnetic stirrer, wherein the solution slowly turned dark green, indicating the formation of Cr(OH)3 precursor; separating an obtained product from the solution by filtering and washing with alcohol and deionized water several times, and drying in a vacuum;
Step 2: calcining dried powder Cr(OH)3 in a CVD tubular furnace to obtain Cr2O3 powder;
Step 3: nitriding the obtained Cr2O3 powder by passing ammonia gas into the CVD tube furnace to obtain black powder CrN; and
Step 4: loading the obtained black powder CrN into graphite dies, wherein a bulk CrN sample is prepared by a homemade hot-pressing machine.
Further, as described in step 1, a ratio of Cr (NO3)3.9H2O, PEG10000, and the deionized water is 16.00 g: 8.00 g: 400 ml, a mixed ultrasonic time is 0.5-1 h, with static for 6-12 h, a dry temperature is 333 K, and a drying time is 12-24 h.
Further, as described in in the step 2, an annealing temperature is 773-973 K, and an annealing time is 2-4 h.
Further, as described in the step 3, a flow of ammonia is controlled at 100 to 200 ml/min, a nitriding temperature is controlled at 1073 to 1273 K for 8 to 12 hours. In addition, a hot pressing pressure described in the step 4 is 50-80 MPa, a sintering temperature is controlled at 973-1273 K for 10-30 min.
Further, a mould used in pressure sintering in the step 4 is a graphite mould; an inner wall of the graphite mould, a top and a bottom are padded with a piece of graphite paper so that the sample does not directly contact with the graphite mould during sintering; hot pressing is executed under a nitrogen atmosphere to prevent the sample from being oxidized.
The method for preparing CrN of the present invention has the advantages of simple process, greatly shortening the production preparation cycle and can be used for large-scale production.
These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.
With protracted testing time, the friction coefficient of CrN tends to be a constant (˜0.42). This is because abrasive particles continue to increase at the beginning of the friction experiment, resulting in a significant increase in friction coefficient. When the friction process tends to be stable, the friction coefficient remains at a stable level, the material exhibits significant abrasion resistance and lubricity.
Table 1 shows the hardness tests of bulk CrN sample. The vickers hardness value of bulk CrN sample is 735.76 HV. This hardness value is much higher than many other commonly used thermoelectric materials such as PbTe (45 HV), Bi2Te3 (62.6 HV) and Zn3Sb4 (162 HV). The high hardness, abrasion resistance and thermal stability of CrN make it a great potential for thermoelectric applications in extreme environment.
One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.
It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, the present invention includes all modifications encompassed within the spirit and scope of the following claims.
Number | Date | Country | Kind |
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2017 1 0247968 | Apr 2017 | CN | national |
Entry |
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Sun et al.; Facile Chemical Solution Deposition of Nanocrystalline CrN Thin Films with Low Magnetoresistance; The Royal Society of Chemistry; 2010. |
Number | Date | Country | |
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20180240955 A1 | Aug 2018 | US |