Vanadium oxide powder with high phase-transition latent heat and preparation method thereof

Abstract

A preparation method of a vanadium oxide powder with high phase-transition latent heat includes steps of taking vanadium pentoxide, oxalic acid and PVP as raw materials, preparing a B-phase VO.sub.2 nano-powder modified by the PVP, and then annealing the B-phase VO.sub.2 nano-powder modified by the PVP at high temperature in an oxygen atmosphere, and obtaining the vanadium oxide powder with high phase-transition latent heat which includes M-phase VO.sub.2 with a mass percentage in a range of 96-99% and V.sub.6O.sub.13 with a mass percentage in a range of 1-4%, and has the phase-transition latent heat larger than 50 J/g. Compared with the vanadium oxide powder prepared by a traditional method without PVP modification and using a vacuum annealing process, the phase-transition latent heat of the vanadium oxide powder provided by the present invention is increased by at least 60%.

Claims

1. A vanadium oxide powder, which comprises M-phase VO.sub.2 with a mass percentage in a range of 96-99% and V.sub.6O.sub.13 with a mass percentage in a range of 1-4%.

2. A preparation method of a vanadium oxide powder, which comprises steps of: (S1) taking PVP (polyvinylpyrrolidone) as a surfactant and preparing a PVP-modified VO.sub.2(B) powder which is a B-phase VO.sub.2 nano-powder modified by the PVP; and (S2) annealing the PVP-modified VO.sub.2(B) powder in an oxygen atmosphere, and obtaining the vanadium oxide powder, which comprises M-phase VO.sub.2 with a mass percentage in a range of 96-99% and V.sub.6O.sub.13 with a mass percentage in a range of 1-4%.

3. The preparation method, as recited in claim 2, wherein: the step of (S1) comprises: (S11) preparing a uniform precursor dispersion which comprises adding deionized water to V.sub.2O.sub.5 (vanadium pentoxide) and H.sub.2C.sub.2O.sub.4 (oxalic acid), and then firstly stirring, and then adding the PVP, and then finally obtaining the uniform precursor dispersion after secondly stirring at room temperature, wherein: mass percentages of the PVP, the vanadium pentoxide and the oxalic acid are respectively in a range of 0.03-0.08%, 0.60-1.00% and 0.45-0.75% of a total weight of the precursor dispersion; (S12) preparing a suspension by a hydrothermal process which comprises adding the uniform precursor dispersion obtained by the step of (S11) to an autoclave liner, performing hydrothermal reaction at 220-240° C. for 4-8 h, cooling to room temperature and obtaining the suspension; and (S13) drying a precipitate after centrifugating the suspension obtained by the step of (S12), washing the precipitate, and obtaining the PVP-modified VO.sub.2(B) powder.

4. The preparation method, as recited in claim 3, wherein: in the step of (S11), the first stir is performed at room temperature for 1-3 h, and the second stir is performed at room temperature for 5-15 min.

5. The preparation method, as recited in claim 3, wherein: in the step of (S12), a filled ratio of the precursor dispersion in the autoclave liner is in a range of 35-45%.

6. The preparation method, as recited in claim 4, wherein: in the step of (S12), a filled ratio of the precursor dispersion in the autoclave liner is in a range of 35-45%.

7. The preparation method, as recited in claim 3, wherein: in the step of (S13), drying the precipitate at 50-80° C. for 12-24 h.

8. The preparation method, as recited in claim 4, wherein: in the step of (S13), drying at 50-80° C. for 12-24 h.

9. The preparation method, as recited in claim 2, wherein: the step of (S2) comprises: (S21) degassing the PVP-modified VO.sub.2(B) powder in a furnace at vacuum having a pressure of less than 20 Pa and at room temperature for 30-80 min; (S22) maintaining the vacuum, increasing the temperature at a rate in a range of 3-5° C./min from room temperature to T.sub.1, and maintaining the temperature at T.sub.1 for 30-60 min; (S23) introducing oxygen after increasing the temperature at a rate in a range of 12-15° C./min from T.sub.1 to T.sub.2, maintaining an oxygen flow, and maintaining the temperature at T.sub.2 for 45-90 min; and (S24) immediately stopping introducing oxygen, decreasing the temperature to be below 80° C., and obtaining the vanadium oxide powder.

10. The preparation method, as recited in claim 3, wherein: the step of (S2) comprises: (S21) degassing the PVP-modified VO.sub.2(B) powder in a furnace at vacuum having a pressure of less than 20 Pa and at room temperature for 30-80 min; (S22) maintaining the vacuum, increasing the temperature at a rate in a range of 3-5° C./min from room temperature to T.sub.1, and maintaining the temperature at T.sub.1 for 30-60 min; (S23) introducing oxygen after increasing the temperature at a rate in a range of 12-15° C./min from T.sub.1 to T.sub.2, maintaining an oxygen flow, and maintaining the temperature at T.sub.2 for 45-90 min; and (S24) immediately stopping introducing oxygen, decreasing the temperature to be below 80° C., and obtaining the vanadium oxide powder.

11. The preparation method, as recited in claim 4, wherein: the step of (S2) comprises: (S21) degassing the PVP-modified VO.sub.2(B) powder in a furnace at vacuum having a pressure of less than 20 Pa and at room temperature for 30-80 min; (S22) maintaining the vacuum, increasing the temperature at a rate in a range of 3-5° C./min from room temperature to T.sub.1, and maintaining the temperature at T.sub.1 for 30-60 min; (S23) introducing oxygen after increasing the temperature at a rate in a range of 12-15° C./min from T.sub.1 to T.sub.2, maintaining an oxygen flow, and maintaining the temperature at T.sub.2 for 45-90 min, and (S24) immediately stopping introducing oxygen, decreasing the temperature to be below 80° C., and obtaining the vanadium oxide powder.

12. The preparation method, as recited in claim 9, wherein: in the step of (S22), T.sub.1 is in a range of 100−150° C.

13. The preparation method, as recited in claim 10, wherein: in the step of (S22), T.sub.1 is in a range of 100−150° C.

14. The preparation method, as recited in claim 11, wherein: in the step of (S22), T.sub.1 is in a range of 100−150° C.

15. The preparation method, as recited in claim 12, wherein: in the step of (S23), T.sub.2 is in a range of 580−620° C.

16. The preparation method, as recited in claim 13, wherein: in the step of (S23), T.sub.2 is in a range of 580−620° C.

17. The preparation method, as recited in claim 14, wherein: in the step of (S23), T.sub.2 is in a range of 580−620° C.

18. The preparation method, as recited in claim 15, wherein: in the step of (S23), the oxygen flow is in a range of 1.5-2.0 sccm (standard cubic centimeter per minute).

19. The preparation method, as recited in claim 16, wherein: in the step of (S23), the oxygen flow is in a range of 1.5-2.0 sccm (standard cubic centimeter per minute).

20. The preparation method, as recited in claim 17, wherein: in the step of (S23), the oxygen flow is in a range of 1.5-2.0 sccm (standard cubic centimeter per minute).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1-1 is an XRD (X-ray diffraction) pattern of B-phase VO.sub.2 powders (VO.sub.2(B)-1) obtained by the preparation method according to the control example.

(2) FIG. 1-2 is an XRD pattern of vanadium oxide powders (VO—R) obtained by the preparation method according to the control example.

(3) FIG. 2-1 is an XRD pattern of B-phase VO.sub.2 powders modified by PVP (VO.sub.2(B)—PVP-1) obtained by the preparation method according to the first embodiment of the present invention.

(4) FIG. 2-2 is an XRD pattern of vanadium oxide powders (VO—PVP-1) obtained by the preparation method according to the first embodiment of the present invention.

(5) FIG. 3-1 is an XRD pattern of B-phase VO.sub.2 powders modified by PVP (VO.sub.2(B)—PVP-2) obtained by the preparation method according to the second embodiment of the present invention.

(6) FIG. 3-2 is an XRD pattern of vanadium oxide powders (VO—PVP-2) obtained by the preparation method according to the second embodiment of the present invention.

(7) FIG. 4-1 is an XRD pattern of B-phase VO.sub.2 powders modified by PVP (VO.sub.2(B)—PVP-3) obtained by the preparation method according to the third embodiment of the present invention.

(8) FIG. 4-2 is an XRD pattern of vanadium oxide powders (VO—PVP-3) obtained by the preparation method according to the third embodiment of the present invention.

(9) FIG. 5-1 is an XRD pattern of B-phase VO.sub.2 powders modified by PVP (VO.sub.2(B)—PVP-4) obtained by the preparation method according to the fourth embodiment of the present invention.

(10) FIG. 5-2 is an XRD pattern of vanadium oxide powders (VO—PVP-4) obtained by the preparation method according to the fourth embodiment of the present invention.

(11) FIG. 6-1 is an XRD pattern of B-phase VO.sub.2 powders modified by PVP (VO.sub.2(B)—PVP-5) obtained by the preparation method according to the fifth embodiment of the present invention.

(12) FIG. 6-2 is an XRD pattern of vanadium oxide powders (VO—PVP-5) obtained by the preparation method according to the fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(13) In order to better explain the present invention, the present invention is further verified by embodiments combined with accompanying drawings as follows.

Control Example

(14) Adding 40 ml of deionized water to 0.364 g of vanadium pentoxide and 0.378 g of oxalic acid dihydrate, stirring at room temperature for 2 h, obtaining a uniform precursor dispersion with a mass concentration of the vanadium pentoxide and the oxalic acid of 0.890/% and 0.66%, respectively, putting the precursor dispersion into a 100 ml of para-polyphenol (PPL) liner, putting the liner with the precursor dispersion into an autoclave, cooling to room temperature after performing hydrothermal reaction at 240° C. for 4 h, obtaining a suspension, centrifugating the suspension and washing the precipitate, drying the precipitate at 80° C. for 12 h in an oven, and finally obtaining a nano-VO.sub.2(B) powder without PVP addition (which is recorded as VO.sub.2(B)-1).

(15) Putting 0.2 g VO.sub.2(B)-1 into a furnace, vacuumizing for degassing it at vacuum having a pressure of less than 20 Pa and at room temperature for 30 min, increasing a temperature of the furnace from the room temperature to 120° C. at a rate of 3° C./min, keeping the temperature at 120° C. for 40 min, and then increasing the temperature from 120° C. to 600° C. at a rate of 13° C./min, keeping the temperature at 600° C. for 60 min under vacuum, and then naturally cooling to the room temperature, and finally obtaining a control vanadium oxide powder being annealed, which is recorded as VO—R. The control vanadium oxide powder acts as a control sample of the present invention for distinguishing the technical effects.

(16) An XRD (X-ray diffraction) analysis test is performed on the prepared VO.sub.2(B)-1 and VO—R, respectively, as shown in FIG. 1-1 and FIG. 1-2. Differential scanning calorimetry (DSC) analysis is performed on the sample VO—R at a temperature increase rate of 10° C./min to obtain the phase-transition latent heat of the VO—R. The relevant results are shown in Table 1.

(17) TABLE-US-00001 TABLE 1 DSC Test Results of VO-R Provided by the Control Example phase-transition Sample latent heat (J/g) VO-R 30.95

(18) It can be seen from FIG. 1-1 that VO.sub.2(B)-1 is a typical B-phase VO.sub.2.

(19) As shown in FIG. 1-2, the diffraction peak of the VO—R with the largest diffraction intensity is consistent with the diffraction peak of the monoclinic phase VO.sub.2, which shows that most of the VO.sub.2(B) powder after annealing treatment is converted into the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2), and the VO.sub.2(B) powder also contains A-phase VO.sub.2, V.sub.2O.sub.3 and V.sub.6O.sub.13.

First Embodiment

(20) Adding 35 ml of deionized water to 0.335 g of vanadium pentoxide and 0.249 g of anhydrous oxalic acid, stirring at room temperature for 1 h, adding 0.013 g of PVP (polyvinylpyrrolidone), stirring for 15 min, obtaining a uniform precursor dispersion with a mass concentration of the PVP, the vanadium pentoxide and the oxalic acid of 0.037%, 0.94% and 0.70%, respectively, putting the precursor dispersion into a 100 ml of para-polyphenol (PPL) liner, putting the liner with the precursor dispersion into an autoclave, cooling to room temperature after performing hydrothermal reaction at 220° C. for 8 h, obtaining a suspension, centrifugating the suspension and washing the precipitate, drying the precipitate at 50° C. for 20 h in an oven, and finally obtaining a nano-VO.sub.2(B) powder modified by the PVP (which is recorded as VO.sub.2(B)—PVP-1).

(21) Putting 0.2 g VO.sub.2(B)—PVP-1 into a furnace, vacuumizing it for degassing at vacuum having a pressure of less than 20 Pa and at room temperature for 80 min, increasing a temperature of the furnace from the room temperature to 100° C. at a rate of ° C./min, keeping the temperature at 100° C. for 60 min, and then immediately introducing oxygen with 99.9% concentration at a flow of 1.8 sccm after increasing the temperature from 100° C. to 580° C. at a rate of 15° C./min, keeping the temperature at 580° C. in the oxygen atmosphere for 70 min, and then stopping introducing oxygen, keeping vacuum, and then naturally cooling to the room temperature, and finally obtaining a vanadium oxide powder being annealed, which is recorded as VO—PVP-1.

(22) An XRD (X-ray diffraction) analysis test is performed on the prepared VO.sub.2(B)—PVP-1 and VO—PVP-1, respectively, as shown in FIG. 2-1 and FIG. 2-2. Differential scanning calorimetry (DSC) analysis is performed on the VO—PVP-1 at a temperature increase rate of 10° C./min to obtain the phase-transition latent heat of the VO—PVP-1. The relevant results are shown in Table 2.

(23) TABLE-US-00002 TABLE 2 DSC Test Results of VO-PVP-1 Provided by the First Embodiment phase-transition Sample latent heat (J/g) VO-PVP-1 51.72

(24) The result shows that compared with the control sample VO—R, most of the diffraction peaks of the VO—PVP-1 are consistent with the diffraction peaks of the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2), and there are also a small amount of diffraction peaks from V.sub.6O.sub.13, which means that the VO.sub.2(B)—PVP-1 powder modified by the PVP is converted into the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2) and a small amount of V.sub.6O.sub.13 after annealing treatment at high temperature in the oxygen atmosphere.

(25) According to the integral intensity A1 of the main diffraction peak from (011) plane of VO.sub.2(M) and the integral intensity A2 of the main diffraction peak from (110) plane of V.sub.6O.sub.13, a percentage of the V.sub.6O.sub.13 phase is calculated to be 3.3% based on a formula of X=A2×100%/(A1+A2). Meanwhile, the phase-transition latent heat of the VO—PVP-1 obtained by the first embodiment is 1.67 times that of VO—R.

Second Embodiment

(26) Adding 40 ml of deionized water to 0.364 g of vanadium pentoxide and 0.378 g of oxalic acid dihydrate, stirring at room temperature for 2 h, adding 0.017 g of PVP (polyvinylpyrrolidone), stirring for 10 min, obtaining a uniform precursor dispersion with a mass concentration of the PVP, the vanadium pentoxide and the oxalic acid of 0.042%, 0.89% and 0.66%, respectively, putting the precursor dispersion into a 100 ml of para-polyphenol (PPL) liner, putting the liner with the precursor dispersion into an autoclave, cooling to room temperature after performing hydrothermal reaction at 240° C. for 4 h, obtaining a suspension, centrifugating the suspension and washing the precipitate, drying the precipitate at 80° C. for 12 h in an oven, and finally obtaining a nano-VO.sub.2(B) powder modified by the PVP (which is recorded as VO.sub.2(B)—PVP-2).

(27) Putting 0.2 g VO.sub.2(B)—PVP-2 into a furnace, vacuumizing it for degassing at vacuum having a pressure of less than 20 Pa and at room temperature for 30 min, increasing a temperature of the furnace from the room temperature to 120° C. at a rate of 3° C./min, keeping the temperature at 120° C. for 40 min, and then immediately introducing oxygen with 99.9% concentration at a flow of 1.5 sccm after increasing the temperature from 120° C. to 600° C. at a rate of 13° C./min, keeping the temperature at 600° C. in the oxygen atmosphere for 60 min, and then stopping introducing oxygen, keeping vacuum, and then naturally cooling to the room temperature, and finally obtaining a vanadium oxide powder being annealed, which is recorded as VO—PVP-2.

(28) An XRD (X-ray diffraction) analysis test is performed on the prepared VO.sub.2(B)—PVP-2 and VO—PVP-2, respectively, as shown in FIG. 3-1 and FIG. 3-2. Differential scanning calorimetry (DSC) analysis is performed on the VO—PVP-2 at a temperature increase rate of 10° C./min to obtain the phase-transition latent heat of the VO—PVP-2. The relevant results are shown in Table 3.

(29) TABLE-US-00003 TABLE 3 DSC Test Results of VO-PVP-2 Provided by the Second Embodiment phase-transition Sample latent heat (J/g) VO-PVP-2 54.92

(30) The result shows that compared with the control sample VO—R, most of the diffraction peaks of the VO—PVP-2 are consistent with the diffraction peaks of the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2), and there are also a small amount of diffraction peaks from V.sub.6O.sub.13, which means that the VO.sub.2(B)—PVP-2 powder modified by the PVP is converted into the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2) and a small amount of V.sub.6O.sub.13 after annealing treatment at high temperature in the oxygen atmosphere. Referring to the method provided by the first embodiment, the percentage of V.sub.6O.sub.13 is calculated to be 2.4%. Meanwhile, the phase-transition latent heat of the VO—PVP-2 obtained by the second embodiment is 1.77 times that of VO—R.

Third Embodiment

(31) Adding 45 ml of deionized water to 0.345 g of vanadium pentoxide and 0.359 g of oxalic acid dihydrate, stirring at room temperature for 3 h, adding 0.022 g of PVP (polyvinylpyrrolidone), stirring for 15 min, obtaining a uniform precursor dispersion with a mass concentration of the PVP, the vanadium pentoxide and the oxalic acid of 0.048%, 0.75% and 0.56%, respectively, putting the precursor dispersion into a 100 ml of para-polyphenol (PPL) liner, putting the liner with the precursor dispersion into an autoclave, cooling to room temperature after performing hydrothermal reaction at 230° C. for 6 h, obtaining a suspension, centrifugating the suspension and washing the precipitate, drying the precipitate at 70° C. for 16 h in an oven, and finally obtaining a nano-VO.sub.2(B) powder modified by the PVP (which is recorded as VO.sub.2(B)—PVP-3).

(32) Putting 0.2 g VO.sub.2(B)—PVP-3 into a furnace, vacuumizing it for degassing at vacuum having a pressure of less than 20 Pa and at room temperature for 80 min, increasing a temperature of the furnace from the room temperature to 150° C. at a rate of 4° C./min, keeping the temperature at 150° C. for 30 min, and then immediately introducing oxygen with 99.9% concentration at a flow of 1.6 sccm after increasing the temperature from 150° C. to 620° C. at a rate of 12° C./min, keeping the temperature at 620° C. in the oxygen atmosphere for 50 min, and then stopping introducing oxygen, keeping vacuum, and then naturally cooling to the room temperature, and finally obtaining a vanadium oxide powder being annealed, which is recorded as VO—PVP-3.

(33) An XRD (X-ray diffraction) analysis test is performed on the prepared VO.sub.2(B)—PVP-3 and VO—PVP-3, respectively, as shown in FIG. 4-1 and FIG. 4-2. Differential scanning calorimetry (DSC) analysis is performed on the VO—PVP-3 at a temperature increase rate of 10° C./min to obtain the phase-transition latent heat of the VO—PVP-3. The relevant results are shown in Table 4.

(34) TABLE-US-00004 TABLE 4 DSC Test Results of VO-PVP-3 Provided by the Third Embodiment phase-transition Sample latent heat (J/g) VO-PVP-3 52.52

(35) The result shows that compared with the control sample VO—R, most of the diffraction peaks of the VO—PVP-3 are consistent with the diffraction peaks of the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2), and there are also a small amount of diffraction peaks from V.sub.6O.sub.13, which means that the VO.sub.2(B)—PVP-3 powder modified by the PVP is converted into the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2) and a small amount of V.sub.6O.sub.13 after annealing treatment at high temperature in the oxygen atmosphere. Referring to the method provided by the first embodiment, the percentage of V.sub.6O.sub.13 is calculated to 1.2%. Meanwhile, the phase-transition latent heat of the VO—PVP-3 obtained by the third embodiment is 1.70 times that of VO—R.

Fourth Embodiment

(36) Adding 35 ml of deionized water to 0.325 g of vanadium pentoxide and 0.241 g of anhydrous oxalic acid, stirring at room temperature for 1 h, adding 0.028 g of PVP (polyvinylpyrrolidone), stirring for 5 min, obtaining a uniform precursor dispersion with a mass concentration of the PVP, the vanadium pentoxide and the oxalic acid of 0.079%, 0.91% and 0.68%, respectively, putting the precursor dispersion into a 100 ml of para-polyphenol (PPL) liner, putting the liner with the precursor dispersion into an autoclave, cooling to room temperature after performing hydrothermal reaction at 220° C. for 8 h, obtaining a suspension, centrifugating the suspension and washing the precipitate, drying the precipitate at 60° C. for 20 h in an oven, and finally obtaining a nano-VO.sub.2(B) powder modified by the PVP (which is recorded as VO.sub.2(B)—PVP-4).

(37) Putting 0.2 g VO.sub.2(B)—PVP-4 into a furnace, vacuumizing it for degassing at vacuum having a pressure of less than 20 Pa and at room temperature for 60 min, increasing a temperature of the furnace from the room temperature to 100° C. at a rate of ° C./min, keeping the temperature at 100° C. for 60 min, and then immediately introducing oxygen with 99.9% concentration at a flow of 1.7 sccm after increasing the temperature from 100° C. to 580° C. at a rate of 15° C./min, keeping the temperature at 580° C. in the oxygen atmosphere for 80 min, and then stopping introducing oxygen, keeping vacuum, and then naturally cooling to the room temperature, and finally obtaining a vanadium oxide powder being annealed, which is recorded as VO—PVP-4.

(38) An XRD (X-ray diffraction) analysis test is performed on the prepared VO.sub.2(B)—PVP-4 and VO—PVP-4, respectively, as shown in FIG. 5-1 and FIG. 5-2. Differential scanning calorimetry (DSC) analysis is performed on the VO—PVP-3 at a temperature increase rate of 10° C./min to obtain the phase-transition latent heat of the VO—PVP-4. The relevant results are shown in Table 5.

(39) TABLE-US-00005 TABLE 5 DSC Test Results of VO-PVP-4 Provided by the Fourth Embodiment phase-transition Sample latent heat (J/g) VO-PVP-4 50.66

(40) The result shows that compared with the control sample VO—R, most of the diffraction peaks of the VO—PVP-4 are consistent with the diffraction peaks of the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2), and there are also a small amount of diffraction peaks from V.sub.6O.sub.13, which means that the VO.sub.2(B)—PVP-4 powder modified by the PVP is converted into the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2) and a small amount of V.sub.6O.sub.13 after annealing treatment at high temperature in the oxygen atmosphere. Referring to the method provided by the first embodiment, the percentage of V.sub.6O.sub.13 is calculated to 1.5%. Meanwhile, the phase-transition latent heat of the VO—PVP-4 obtained by the fourth embodiment is 1.64 times that of the reference VO—R.

Fifth Embodiment

(41) Adding 45 ml of deionized water to 0.355 g of vanadium pentoxide and 0.264 g of anhydrous oxalic acid, stirring at room temperature for 3 h, adding 0.033 g of PVP (polyvinylpyrrolidone), stirring for 15 min, obtaining a uniform precursor dispersion with a mass concentration of the PVP, the vanadium pentoxide and the oxalic acid of 0.072%, 0.78% and 0.58%, respectively, putting the precursor dispersion into a 100 ml of para-polyphenol (PPL) liner, putting the liner with the precursor dispersion into an autoclave, cooling to room temperature after performing hydrothermal reaction at 230° C. for 6 h, obtaining a suspension, centrifugating the suspension and washing the precipitate, drying the precipitate at 70° C. for 24 h in an oven, and finally obtaining a nano-VO.sub.2(B) powder modified by the PVP (which is recorded as VO.sub.2(B)—PVP-5).

(42) Putting 0.2 g VO.sub.2(B)—PVP-5 into a furnace, vacuumizing it for degassing at vacuum having a pressure of less than 20 Pa and at room temperature for 60 min, increasing a temperature of the furnace from the room temperature to 150° C. at a rate of 4° C./min, keeping the temperature at 150° C. for 30 min, and then immediately introducing oxygen with 99.9% concentration at a flow of 2.0 sccm after increasing the temperature from 150° C. to 620° C. at a rate of 12° C./min, keeping the temperature at 620° C. in the oxygen atmosphere for 90 min, and then stopping introducing oxygen, keeping vacuum, and then naturally cooling to the room temperature, and finally obtaining a vanadium oxide powder being annealed, which is recorded as VO—PVP-5.

(43) An XRD (X-ray diffraction) analysis test is performed on the prepared VO.sub.2(B)—PVP-5 and VO—PVP-5, respectively, as shown in FIG. 6-1 and FIG. 6-2. Differential scanning calorimetry (DSC) analysis is performed on the VO—PVP-3 at a temperature increase rate of 10° C./min to obtain the phase-transition latent heat of the VO—PVP-5. The relevant results are shown in Table 6.

(44) TABLE-US-00006 TABLE 6 DSC Test Results of VO-PVP-5 Provided by the Fifth Embodiment phase-transition Sample latent heat (J/g) VO-PVP-5 50.29

(45) The result shows that compared with the control sample VO—R, most of the diffraction peaks of the VO—PVP-5 are consistent with the diffraction peaks of the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2), and there are also a small amount of diffraction peaks from V.sub.6O.sub.3, which means that the VO.sub.2(B)—PVP-5 powder modified by the PVP is converted into the monoclinic phase VO.sub.2 (i.e., M-phase VO.sub.2) and a small amount of V.sub.6O.sub.13 after annealing treatment at high temperature in the oxygen atmosphere. Referring to the method provided by the first embodiment, the percentage of V.sub.6O.sub.13 is calculated to 1.7%. Meanwhile, the phase-transition latent heat of the VO—PVP-5 obtained by the fifth embodiment is 1.63 times that of VO—R.

(46) In summary, it can be known that:

(47) (1) The preparation method provided by the control example is to provide the vanadium oxide powder without being modified by PVP and using vacuum a vacuum annealing process, the obtained vanadium oxide powder contains A-phase VO.sub.2, V.sub.2O.sub.3 and V.sub.6O.sub.13 besides M-phase VO.sub.2, and has the phase-transition latent heat of only 30.95 J/g.

(48) (2) Compared with the preparation method provided by the control example, the preparation methods provided by the first, second, third, fourth and fifth embodiments are to fabricate the vanadium oxide powder with high phase-transition latent heat by preparing the B-phase VO.sub.2 powder modified by PVP and then annealing at high temperature in an oxygen atmosphere. From the compositions of the samples and data of the phase-transition latent heat provided by all the embodiments, within the preferred values of each process parameter, the phase-transition latent heat of the vanadium oxide powder prepared by the first, second, third, fourth and fifth embodiments reaches 50 J/g, which is increased by at least 60% compared with that of the vanadium oxide powder prepared by the control example. Moreover, the vanadium oxide powder products fabricated by the preparation methods provided by the first, second, third, fourth and fifth embodiments only contain M-phase VO.sub.2 and a small amount of V.sub.6O.sub.13 with a mass percentage in a range of 1 to 4%.

(49) The above are specific embodiments of the present invention, but are not intended to limit the present invention. Therefore, it should be noted that any modifications and improvements made by the present invention are intended to be within the protective scope of the present invention.