Chromium nitride thermoelectric material and preparation method thereof

Abstract

The present invention discloses CrN thermoelectric material and its preparation method, which belongs to the field of thermoelectric materials. Here, we provide a study for thermoelectric properties, hardness, wear-resisting performance and thermal stability of CrN. These results show that CrN possesses excellent mechanical properties and thermal stability. The hardness of the bulk CrN sample is as high as 735.76 HV, which is far superior to most of thermoelectric materials. The thermogravimetric analysis test indicates that CrN remain stable at 873 K. Friction and wear test results demonstrate that the low friction coefficient (0.42) and good wear resistance of CrN. The maximum ZT value of 0.104 is observed at 848 K. In this way, CrN may be a promising thermoelectric material in extreme environment application which requires both mechanical and thermoelectric properties. Such as collision avoidance systems and outerspace.

Claims

1. A method for preparing a CrN thermoelectric material, comprising steps of: Step 1: dissolving Cr(NO.sub.3).sub.3.9H.sub.2O and PEG10000 in deionized water and adding an obtained solution drop wise with NH.sub.3.H.sub.2O under a magnetic stirrer, wherein the solution slowly turned dark green, indicating the formation of Cr(OH).sub.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).sub.3 in a CVD tubular furnace to obtain Cr.sub.2O.sub.3 powder; Step 3: nitriding the obtained Cr.sub.2O.sub.3 powder by passing ammonia gas into the CVD tube furnace to obtain black powder CrN; and Step 4: padding an internal wall, a top and a bottom of graphite dies with a piece of graphite paper, and loading the obtained black powder CrN into the graphite dies; hot-pressing the black powder CrN in the graphite dies under a nitrogen atmosphere with a hot-pressing pressure of 50-80 MPa, and then sintering with a sintering temperature of 973-1273 K and a sintering time of 10-30 min, so as to form the CrN thermoelectric material.

2. The method for preparing the CrN thermoelectric material, as described in claim 1, wherein in the step 1, a proportion of Cr (NO.sub.3).sub.3.9 H.sub.2O, PEG10000, and the deionized water is: 16.00 g: 8.00g: 400 ml, a hybrid ultrasonic time is 0.5-1 h, with let stand for 6 to 12 h, a drying temperature is 333 K, and a drying time is 12-24 h.

3. The method for preparing the CrN thermoelectric material, as described in claim 1, wherein in the step 2, an annealing temperature is 773-973 K, and an annealing time is 2-4 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the preparation method of the bulk CrN thermoelectric materials provided by the present invention.

(2) FIG. 2 is the X-ray diffraction pattern of CrN thermoelectric material for the implementation example.

(3) FIG. 3 is Scanning electron microscopy (SEM) images with different magnifications of bulk CrN sample for the implementation example.

(4) FIG. 4 shows the temperature dependence of the measured Seebeck coefficient of CrN bulk sample.

(5) FIG. 5 reveals the temperature dependence of the measured thermal conductivity of CrN bulk sample.

(6) FIG. 6 demonstrates the temperature dependence of the measured electrical conductivity of CrN bulk sample.

(7) FIG. 7 demonstrates the temperature dependence of the ZT value of CrN bulk sample.

(8) FIG. 8 demonstrates the results of thermogravimetric analysis (TGA) of the CrN bulk sample.

(9) FIG. 9 demonstrates the change curve of friction coefficient with wear time of CrN sample.

(10) FIG. 10 demonstrates the wear resistance profile of the CrN sample substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(11) FIG. 1 is a schematic diagram of the preparation method of the bulk CrN thermoelectric materials provided by the present invention.

(12) FIG. 2 is the X-ray diffraction pattern of CrN thermoelectric material for the implementation example. The obtained samples are pure CrN material with the combination of CrN standard card PDF # 77-0047.

(13) FIG. 3 is Scanning electron microscopy (SEM) images with different magnifications of bulk CrN sample for the implementation example. (a) a scanning electron microscope that magnifies the sample by a factor of 5000, (b) a magnification of 200,000 times the sample, (c) a magnification of 500,000 times the sample, (d) a magnification of 80,000 times the sample. It can be seen that the sample comprises a large number of nanometer-sized grains with a diameter of about 300 to 400 nm.

(14) FIG. 4 shows the temperature dependence of the measured Seebeck coefficient of CrN bulk sample. The Seebeck coefficient increases with increasing temperature. At 848 K, the Seebeck coefficient reaches 67 uv/K.

(15) FIG. 5 reveals the temperature dependence of the measured thermal conductivity of CrN bulk sample.

(16) FIG. 6 demonstrates the temperature dependence of the measured electrical conductivity of CrN bulk sample. The electrical conductivity of the sample decreases with increasing temperature and has similar metal properties.

(17) FIG. 7 demonstrates the temperature dependence of the ZT value of CrN bulk sample. The max ZT value of 0.104 was obtained at 848 K.

(18) FIG. 8 demonstrates the results of thermogravimetric analysis (TGA) of the CrN bulk sample. The mass is essentially constant over the entire test temperature range, which indicates the high thermal stability of CrN sample.

(19) FIG. 9 demonstrates the change curve of friction coefficient with wear time of CrN sample. In the friction process, the friction coefficient fluctuates from 0.25 to 0.45.

(20) 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.

(21) FIG. 10 demonstrates the wear resistance profile of the CrN sample substrate. It is worth noting that, after the 1 hour friction test the minimum and maximum depths of the wear trajectories are 3.1 and 7.6 m, respectively, the wear marks are very smooth, and there is no sign of serious wear in the center of the wear track.

(22) 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), Bi.sub.2Te.sub.3 (62.6 HV) and Zn.sub.3Sb.sub.4 (162 HV). The high hardness, abrasion resistance and thermal stability of CrN make it a great potential for thermoelectric applications in extreme environment.

(23) TABLE-US-00001 TABLE 1 The hardness tests of bulk CrN sample Number of tests 1 2 3 4 Hardness (HV) 724.95 742.64 730.79 742.64 Average Hardness (HV) 735.76

(24) 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.

(25) 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.