U.S. patent application number 13/980862 was filed with the patent office on 2013-12-26 for application and synthesis of doped vanadium dioxide powder and dispersing agent.
This patent application is currently assigned to SHANGHAI INSTITUTE OF CERAMICS, CHINESE ACADEMY OF SCIENCES. The applicant listed for this patent is Chuanxiang Cao, Lei Dai, Yanfeng Gao, Minoru Kanehira, Hongjie Luo. Invention is credited to Chuanxiang Cao, Lei Dai, Yanfeng Gao, Minoru Kanehira, Hongjie Luo.
Application Number | 20130344335 13/980862 |
Document ID | / |
Family ID | 46515144 |
Filed Date | 2013-12-26 |
United States Patent
Application |
20130344335 |
Kind Code |
A1 |
Gao; Yanfeng ; et
al. |
December 26, 2013 |
APPLICATION AND SYNTHESIS OF DOPED VANADIUM DIOXIDE POWDER AND
DISPERSING AGENT
Abstract
The present invention relates to a doped vanadium dioxide
powder, a dispersion, and preparation methods and applications
therefor. The chemical composition of the doped vanadium dioxide
powder is V1-xMxO2, 0<x.ltoreq.0.5, wherein M is a doping
element and said doping element is used to control the size and
morphology of the doped vanadium dioxide powder. The vanadium
dioxide powder of the present invention has evenly sized particles
and exhibits excellent dispersibility. The preparation methods for
the present invention are easy to implement, low in cost, provide
high yield, and are suitable for large scale production.
Inventors: |
Gao; Yanfeng; (Shanghai,
CN) ; Cao; Chuanxiang; (Shanghai, CN) ; Dai;
Lei; (Shanghai, CN) ; Luo; Hongjie; (Shanghai,
CN) ; Kanehira; Minoru; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gao; Yanfeng
Cao; Chuanxiang
Dai; Lei
Luo; Hongjie
Kanehira; Minoru |
Shanghai
Shanghai
Shanghai
Shanghai
Shanghai |
|
CN
CN
CN
CN
CN |
|
|
Assignee: |
SHANGHAI INSTITUTE OF CERAMICS,
CHINESE ACADEMY OF SCIENCES
Shanghai
CN
|
Family ID: |
46515144 |
Appl. No.: |
13/980862 |
Filed: |
January 4, 2012 |
PCT Filed: |
January 4, 2012 |
PCT NO: |
PCT/CN2012/070025 |
371 Date: |
July 19, 2013 |
Current U.S.
Class: |
428/402 ;
501/41 |
Current CPC
Class: |
B82Y 40/00 20130101;
C01P 2002/52 20130101; C01P 2004/64 20130101; C01G 31/02 20130101;
Y10T 428/2982 20150115; B82Y 30/00 20130101; C01G 49/0018 20130101;
C01P 2004/04 20130101; C03C 4/082 20130101; H01L 21/02565 20130101;
C03C 3/122 20130101; C01P 2002/54 20130101; C01P 2002/72 20130101;
C01G 39/00 20130101; C03C 3/127 20130101; C01P 2004/10 20130101;
C03C 2204/00 20130101 |
Class at
Publication: |
428/402 ;
501/41 |
International
Class: |
C03C 3/12 20060101
C03C003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2011 |
CN |
201110024215.3 |
Jan 21, 2011 |
CN |
201110024229.5 |
Claims
1. A kind of doped vanadium dioxide powder, the doped powder having
a chemical composition of V.sub.1-xM.sub.xO.sub.2,
0<X.ltoreq.0.5, and M is a doping element, which is introduced
to control a particle size and a morphology of the doped powder,
the doping element M is a transition element adjacent to vanadium
in a periodic table of elements, Tin and one of its adjacent
elements or their random combination, wherein the transition metal
element adjacent to vanadium in the periodic table of elements
includes titanium, chromium, manganese, iron, cobalt, nickel,
copper and zinc, tin and its adjacent elements include indium,
stibium, stannum, gallium, germanium, lead and bismuth, and wherein
the doped powder is in particle form of particles that have a
aspect ratio of 1:1-10:1, and wherein the particle size is no more
than 100 nm in at least one dimension.
2. (canceled)
3. The doped vanadium dioxide powder of claim 1, wherein 0.03
<X.ltoreq.0.3.
4. (canceled)
5. The doped vanadium dioxide powder of claim 1, wherein
0.005<X.ltoreq.0.025.
6. (canceled)
7. (canceled)
8. (canceled)
9. The doped vanadium dioxide powder of claim 1, wherein the
particle size is no more than 100 nm in all three dimensions.
10. (canceled)
11. The doped vanadium dioxide powder of claim 1, wherein a powder
component includes rutile vanadium dioxide.
12. A hydrothermal method for preparing the doped vanadium dioxide
powder of claim 1, the method comprising a step of a precursor
treatment of titrating a quadrivalent vanadium aqueous solution
with a basic reagent to obtain a precursor suspension, wherein the
precursor treatment involves titrating the quadrivalent vanadium
aqueous solution until the emergence of the precursor
suspension.
13. (canceled)
14. The method of claim 12, wherein a mole ratio of the basic
reagent to the quadrivalent vanadium aqueous solution is from 1:50
to 10:1.
15. The method of claim 14, wherein the mole ratio of the basic
reagent to the quadrivalent vanadium aqueous solution is 1:5 to
2:1.
16. (canceled)
17. The method of claim 12, further comprising a process of
introducing elements that can regulate a phase transition
temperature of vanadium dioxide, and/or elements that regulate
particle size and morphology of vanadium dioxide.
18. (canceled)
19. The method of claim 17, wherein a mole ratio of the doping
element to the quadrivalent vanadium aqueous solution is 1:1000 to
1:1.
20. (canceled)
21. (canceled)
22. The method of claim 12, further comprising a process of
preparing a quadrivalent vanadium aqueous solution.
23. The method of claim 22, further comprising a process of
dissolving a soluble raw material into water, the soluble raw
material including trivalent, quadrivalent, or pentavalent vanadic
salts.
24. The method of claim 22, further comprising a step of
oxidization, reduction or dissolving pretreatment of insoluble
vanadium raw material, the insoluble vanadium raw material
including metal vanadium, vanadium oxides or their mixture.
25. (canceled)
26. The method of claim 12, further comprising a step of
transferring the basic reagent treated quadrivalent vanadium
aqueous solution to a hydrothermal reactor to undergo a
hydrothermal reaction, for which a packing ratio of the reactor is
20%-90% , a reaction temperature is 200-400.degree. C. and a
holding time is 1-240 h.
27. The method of claim 26 wherein the holding time is 2-120 h.
28. (canceled)
29. The method of claim 26, wherein the packing ratio is
30-80%.
30. (canceled)
31. The method of claim 26, wherein the holding time is 4-60 h.
32. (canceled)
33. A vanadium dispersion, the dispersion including any kind of the
doped vanadium dioxide powder of claim 1.
34. The dispersion of claim 33, wherein a concentration of vanadium
dioxide is 0.1-100 g/L.
35. Application of any kind of the doped vanadium dioxide powder of
claim 1 in fabricating energy conservation and emission reduction
or energy information devices.
Description
TECHNICAL FIELD
[0001] This invention involves the synthesis of VO.sub.2 powder,
especially doped VO.sub.2 powder and its application.
BACKGROUND
[0002] Due to the worldwide growing energy crisis, energy
conservation and emission reduction are more important today than
ever before. In December of 2009, United Nations Environment
Programme reported that building energy consumption occupies about
one third of global greenhouse gas emissions. In China, building
energy consumption overall accounts for 30% of the total available
primary energy. In particular, energy exchange through windows
accounts for over 50% of energy consumed through a building's
envelope by means of conduction, convection and radiation. To
reduce energy consumption, it is necessary to develop smart windows
which are designed to intelligently control the amount of
transmitted light and heat (mainly in the near infrared region) in
response to an external stimulus.
[0003] At present low emissivity glass which has high visible
transmittance and high infrared reflection is prevalent in the
energy saving glass market and can greatly reduce heat transfer
from indoors to outdoors compared to the ordinary glass and
traditional building coating glass. However, low emissivity glass
is expensive and not intelligent enough. Therefore, there is
urgency to develop the next generation of smart windows with
independent intellectual property rights.
[0004] Vanadium dioxide (VO.sub.2) with a Mott-phase transition is
a key material for application to thermochromic smart windows
because it exhibits a reversible transformation from an
infrared-transparent semiconductive state at low temperatures to an
infrared-transparent semiconductive state at high temperatures,
while maintaining visible transmittance.
[0005] Various techniques including the sol-gel method, chemical
vapor deposition, sputtering deposition, pulsed-laser deposition,
and ion implantation have been utilized to deposit VO.sub.2 films,
however many problems exist, such as expensive equipment, complex
control processes, poor stability, low deposition rate and
unsuitable mass production. In addition, the application of smart
windows with VO.sub.2 films is restricted because it can only be
applied to new glass. Therefore, on the basis of energy saving
reconstruction, VO.sub.2 powders with intelligent energy-saving
effect are preferably coated on existing ordinary glass.
[0006] The vanadium-oxygen phase diagram shows nearly 15-20 other
stable vanadium oxide phases besides VO.sub.2, such as VO,
V.sub.6O.sub.13 and V.sub.7O.sub.13. The formation of VO.sub.2
occurs only over a very narrow range of oxygen partial pressures.
Additionally, more than ten kinds of crystalline phases of vanadium
dioxide have been reported, including tetragonal rutile-type
VO.sub.2 (R), monoclinic rutile-type VO.sub.2 (M), triclinic
VO.sub.2 (P*(2)), tetragonal VO.sub.2 (A), monoclinic VO.sub.2 (B),
VO.sub.2 (C), orthorhombic VO.sub.2.H.sub.2O, tetragonal
VO.sub.2.0.5H.sub.2O, monoclinic V.sub.2O.sub.4 and
V.sub.2O.sub.4.2H.sub.2O. Only the rutile-type VO.sub.2 (R/M)
undergoes a fully reversible metal-semiconductor phase transition
(MST) at approximately 68.degree. C. However, the preparation of
VO.sub.2 (M/R) powder has become a technical difficulty for the
application of smart windows.
[0007] High temperature sintering was usually used to fabricate
VO.sub.2 powder. A method to fabricate vanadium dioxide powder
doped with tungsten, in which VO.sub.2 (B) powder is first
synthesized and then heat treated at 350-800.degree. C. to attain
VO.sub.2 (R) powder is issued in patent (CN10164900). Moreover,
many methods including spray pyrolysis (U.S. Pat. No. 5,427,763),
thermal cracking (CN1321067C), sol-gel (U.S. Pat. No. 6,682,596)
and reverse microemulsion (WO2008/011198 A2) have been used to
synthesize VO.sub.2 powder. A patent (CN101391814) from our
research group describes one-step hydrothermal synthesis of
VO.sub.2 (M/R) powders.
SUMMARY
[0008] The preparation of composite film with VO.sub.2 powder and
other material was simple and beneficial for mass production, and
could be used not only for energy conservation reconstruction of
existing glass, but also for coating different substrates, thus
expanding the application of VO.sub.2. However, for preparation of
thin films and coatings of VO.sub.2, the morphology and particle
size of VO.sub.2 powder met special requirements that allowed
VO.sub.2 powder to possess excellent dispersibility.
[0009] However, the doped VO.sub.2 powder usually had a large size
(more than 100 nm) and rod shape (aspect ratio more than 10), and
furthermore doping elements couldn't control the crystalline phase,
and doped VO.sub.2 powder possessed poor dispersibility and were
unsuitable for preparation of VO.sub.2 thin films and coatings.
[0010] Although a patent (CN10164900A) demonstrated that the size
of VO.sub.2 powder doped with tungsten was smaller than 50 nm, it
was not involved in the microstructure of the powder, suggesting
that the doped tungsten element didn't modulate the aspect ratio of
VO.sub.2 powders. Moreover, it was difficult to control the
crystalline phase by means of high temperature sintering from
VO.sub.2(B) to VO.sub.2(R) powder. A patent (CN101391814A) from our
research group indicated the shape of VO.sub.2 powder was granular,
however it wasn't related to the size and aspect ratio of VO.sub.2
powder. According to FIG. 2, the grain was actually rod-shaped
rather than granular.
[0011] The doping of VO.sub.2 powder focused on the effect on the
phase transition temperature of VO.sub.2, and tungsten and
molybdenum are usually used as doping elements. But it pays no
attention to the influence on the grain size and morphology.
Furthermore, there is no discussion about regulation of the grain
size and morphology of VO.sub.2 by doping.
[0012] A patent illustrated the method to fabricate VO.sub.2 with
small size, however VO.sub.2(M) was synthesized through induction
on the surface of TiO.sub.2, meaning that VO.sub.2/TiO.sub.2
composite particles were attained, rather than doped VO.sub.2
particles with single chemical composition.
[0013] VO.sub.2 powder which could be controllable and have
excellent dispersibility was beneficial. On the one hand, the
present invention provides one approach to preparation of doped
V.sub.1-xM.sub.xO.sub.2 powder (M is a doping element and x lies
between 0 and 0.5. When 0.03<x.ltoreq.0.3, it is preferred. If
0.03<x<0.1 or 0.005<x<0.025, it is more preferred.), on
the other hand, this doping method can control the size and
morphology of VO.sub.2 powders.
[0014] In this invention, through doping with certain elements,
small and uniform VO.sub.2 powder was attained, and the doped
VO.sub.2 powder possessed stable crystalline phase and good
dispersibility in water and dispersing agent (such as polyvinyl
pyrrolidone) so that it was easily used to coat the glass substrate
and suitable for preparation of films and coatings of VO.sub.2.
[0015] Certain elements could be transition metal elements with
atomic number between 21 and 30, tin and its nearby elements such
as In, Sb, Sn, Ga, Ge, Pb and Bi. These transition metal elements
included Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu and Zn. The preferred
elements were Bi, Sn, Fe, Zn and Ti.
[0016] The above doping elements could not only change phase
transition temperature of VO.sub.2, but also regulate the size and
morphology of VO.sub.2 powder, and they were different from
previous doping elements which only adjust phase transition
temperature.
[0017] In this invention, the doped VO.sub.2 powder was granular
and possessed the aspect ratio between 1 and 10. The preferred
aspect ratio was 1.about.5 and the more preferred aspect ratio was
1.about.2. The particle size of VO.sub.2 in at least one dimension
was less than 1 .mu.m and if it was not more than 100 nm, it was an
preferred size. The more preferred particle size was not more than
100 nm in three dimensions and the most preferred size was less
than 70 nm in three dimensions. The particle could be various
shapes such as nearly sphere, ellipse, snowflakes, cube, tablet and
so on.
[0018] VO.sub.2 powder with the above size and morphology had
better dispersibility.
[0019] The doped VO.sub.2 powder contained rutile phase VO.sub.2
and the proportion of VO.sub.2(R) could be as high as 80%, even
100%. The doped VO.sub.2 powder had controllable size and
morphology and possessed a semiconductor-metal phase transition,
whose phase transition temperature was continuously adjusted
between -30 and 90.degree. C.
[0020] Due to extensive application of VO.sub.2 powder, it is
urgent to develop a simple and low-cost synthesis of VO.sub.2
powder. It was found that processing a reaction precursor lessened
the difficulty of hydrothermal reaction of VO.sub.2. This invention
provided a method to fabricate doped VO.sub.2 powder, in which the
V.sup.4+ ion aqueous solution was treated with a basic reagent and
then attained a suspension precursor.
[0021] Before doping certain elements, the V.sup.4+ ion aqueous
solution precursor was treated with basic reagent and we obtained
VO.sub.2 powder with controllable size and morphology. The particle
size was less than 1 .mu.m in at least one dimension and the
particle aspect ratio wasn't more than 10. Small and uniform
VO.sub.2 powder was attained, and the doped VO.sub.2 powder
possessed a stable crystalline phase and good dispersibility in
water and dispersing agent (such as polyvinyl pyrrolidone) so that
it was easy to coat in the glass substrate and suitable for
preparation of films and coatings of VO.sub.2.
[0022] In sum, this method had many advantages including simple
operation, low cost, easy control, excellent crystallinity and
suitable scale production.
[0023] In this invention, the molar ratio of the basic reagent and
V.sup.4.sup.+ ion aqueous solution was 0.02.about.10. The preferred
ratio was 0.1.about.5 and the more preferred ratio was 0.2.about.2.
The precursor was treated by means of a titration method in which
we used the basic reagent to titrate the V.sup.4+ ion aqueous
solution until the suspension precursor was attained. The pH at the
end of the titration was 2.about.12 and the preferred pH was
5.about.10. This method was easy to operate and control, and
performed without special equipment.
[0024] The concentration of V.sup.4+ ion aqueous solution was
between 0.005 and 0.5 mol/L, usually chosen to be 0.01 mol/L. The
V.sup.4+ ion aqueous solution was attained through dissolving
soluble vanadium raw material in deionized water. Commonly used
soluble vanadium raw material could be trivalent, quadrivalent or
pentavalent vanadium salts and their hydrates, and quadrivalent
vanadium salts and their hydrates such as VOSO.sub.4, VOCl.sub.2
and VOC.sub.2O.sub.4.5H.sub.2O are preferred. When trivalent and
pentavalent soluble vanadium salts and their hydrates were employed
as starting materials, V.sup.4+ ion aqueous solution was attained
through oxidation and reduction pretreatment respectively; at the
same time, the quadrivalent vanadium salts were obtained via
oxidation and reduction pretreatment respectively and then
dissolved in deionized water. Moreover, for insoluble vanadium raw
material such as metal vanadium, vanadium oxide or their
combination, V.sup.4+ ion aqueous solution was prepared via
oxidation, reduction or solvation pretreatment.
[0025] Alkaline reagents such as ammonia, sodium hydroxide,
potassium hydroxide, soda ash, sodium bicarbonate, potassium
carbonate solution, potassium bicarbonate and the arbitrary
combination could be used. Ammonia, sodium hydroxide and potassium
hydroxide were preferred choices and the more preferred choice was
sodium hydroxide. The basic reagent concentration could be
0.5.about.5 mol/L and the preferred concentration was 0.5.about.2
mol/L.
[0026] The attained suspension solution via alkali treatment could
be mixed with certain doping agents, and then doped VO.sub.2 powder
was fabricated through a hydrothermal reaction. The mole ratio of
doping elements and V.sup.4+ ion aqueous solution could be
0.001.about.1; preferred mole ratios were 0.03.about.0.43 mol/L and
0.005.about.0.026 and the more preferred mole ratio was
0.03.about.0.11. The temperature of the hydrothermal reaction could
be 200.about.400.degree. C.; preferred temperature was
200.about.350.degree. C. and the more preferred temperature was
250.about.300.degree. C. The time of the hydrothermal reaction was
1.about.240 h; preferred time was 2.about.120 h and the more
preferred time was 4.about.60 h. The filling ratio of the
hydrothermal reaction was 20.about.90%; preferred filling ratio was
30.about.80% and the more preferred filling ratio was
50.about.80%.
[0027] Before hydrothermal reaction, the V.sup.4+ ion aqueous
solution precursor was treated with basic reagent, and then the
reaction became one-step reaction with low reaction temperature and
high production. VO.sub.2 powder with controllable size and
morphology was attained. This method had many advantages including
simple operation, low cost, easy control and excellent
crystallinity.
[0028] The dispersing agent of VO.sub.2 powder was provided in this
invention and the concentration of VO.sub.2 powder could be 100
g/L; preferred concentration was 1.about.50 g/L and the more
preferred concentration was 5.about.30 g/L.
[0029] The above dispersing agent could be coated in suitable
matrix and used in the thermochromic film, energy-saving paint,
intelligent energy-saving glass curtain wall, temperature control
device(such as solar temperature control device) and energy-saving
coating. For example, this agent is suitable for direct
manufacturing energy-saving glass and could also be used to
transform existing common glass, and even used in surface
energy-saving reconstruction of buildings, and transportation.
What's more, this VO.sub.2 powder could be used in energy
information equipment including micro photoelectric switches,
thermistors, battery materials and optical information storage
devices.
[0030] Energy-saving film was prepared with doped VO.sub.2 powder
and possessed many advantages such as a simple process, low cost,
wide application and excellent spectral characteristics.
BRIEF DESCRIPTION OF THE FIGURES
[0031] FIG. 1 illustrates example XRD patterns of VO.sub.2
powders;
[0032] FIG. 2 illustrates example TEM images of VO.sub.2
powders;
[0033] FIG. 3 illustrates XRD patterns of VO.sub.2 powders from
example 1;
[0034] FIG. 4 illustrates TEM images of VO.sub.2 powders from
example 1;
[0035] FIG. 5 illustrates XRD patterns of VO.sub.2 powders from
example 2;
[0036] FIG. 6 illustrates TEM images of VO.sub.2 powders from
example 2;
[0037] FIG. 7 illustrates XRD patterns of VO.sub.2 powders from
example 8;
[0038] FIG. 8 illustrates TEM images of VO.sub.2 powders from
example 8;
[0039] FIG. 9 illustrates XRD patterns of VO.sub.2 powders from
example 12;
[0040] FIG. 10 illustrates TEM images of VO.sub.2 powders from
example 12;
[0041] FIG. 11 illustrates optical spectra of film fabricated with
VO.sub.2 powders before and after phase transition; and
[0042] FIG. 12 illustrates temperature dependence of the optical
transmittance of the film fabricated with VO.sub.2 powders at a
fixed wavelength of 2000 nm.
[0043] FIG. 13 illustrates XRD patterns of intermediate solid
vanadium dioxide powder suspension.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0044] According to the following figures, the implementation
method of this invention is explained in detail.
[0045] First, the hydrothermal reaction to fabricate doped
VO.sub.2(R) powder was taken for example. Furthermore, this method
could be used to prepare undoped VO.sub.2(R) powder and other
crystalline phase of VO.sub.2 powder such as VO.sub.2(A)
powder.
[0046] The V.sup.4+ ion aqueous solution acted as a reaction
precursor and was treated with a basic reagent.
[0047] The V.sup.4+ ion aqueous solution was prepared through
commonly used methods. The quadrivalent soluble vanadium salt and
its hydrate such as VOSO.sub.4, VOCl.sub.2 and
VOC.sub.2O.sub.4.5H.sub.2O was dissolved in a suitable amount of
deionized water and the proper concentration could be
0.005.about.0.5 mol/L, usually 0.01 mol/L. The V.sup.4+ ion aqueous
solution was prepared at room temperature, but slightly heating or
ultrasonic processing could help the dissolution.
[0048] When trivalent and pentavalent soluble vanadium salts and
their hydrates were employed as starting materials, they were
dissolved in deionized water, and then V.sup.4+ ion aqueous
solution was attained through oxidation and reduction pretreatment
respectively; at the same time, the quadrivalent vanadium salts
were obtained via oxidation and reduction pretreatment respectively
and then dissolved in deionized water. If insoluble precipitate
appeared in the redox process, it could be dissolved through
slightly heating or adding the right amount of deionized water.
[0049] V.sup.4+ ions aqueous solution can be prepared by using
insoluble vanadium material as raw materials, such as vanadium,
vanadium oxide or a combination of vanadium oxide. These materials
can be dissolved in water to form V.sup.4+ ions aqueous solution by
oxidation, reduction or other pretreatment.
[0050] The configured V.sup.4+ aqueous solution was titrated with
alkaline reagent until the suspension was generated. Ammonia,
sodium hydroxide aqueous solution, potassium hydroxide solution,
aqueous sodium carbonate, sodium bicarbonate aqueous solution,
aqueous potassium carbonate, potassium bicarbonate aqueous
solution, or any combination thereof may be used as the alkaline
reagent for titration. Aqueous ammonia, aqueous sodium hydroxide,
and aqueous potassium hydroxide solutions were preferable and
aqueous sodium hydroxide solution was more preferable. Through a
great deal of experiments, the inventor found that it was conducive
to the formation of the suspension to determine the titration end
point by controlling the concentration of the alkaline reagent and
V.sup.4+ ions in aqueous solution, wherein the favorable
concentration of alkaline agent was 0.5 to 2 mol/L. When the
titration was finished, the pH value of the suspension was usually
from 2 to 12, the molar ratio of alkaline reagent and V.sup.4+ ions
in the aqueous solution is usually from 1:50 to 10:1, and the
minimum amount of alkaline reagent should be capable of forming a
suspension. Therefore, the preferred molar ratio of alkaline
reagent and V.sup.4+ ions in aqueous solution was greater than
1:10, and more preferably from 1:5 to 2:1. However, it should be
understood that the alkaline agent was not excessive, and the molar
ratio of alkaline reagent and V.sup.4+ ions in aqueous also
preferably did not exceed 5:1. It was easy to observe and control,
without the need for additional equipment, when the suspension
appeared as the endpoint of the titration.
[0051] After titration with alkaline reagent, the suspension was
filtered to obtain a solid dry suspension, and was measured using
X-ray diffraction. As shown in FIG. 13, the suspension obtained
from the alkaline treatment had a chemical composition of
V.sub.4H.sub.6O.sub.10. The obtained suspension from above was
transferred to a hydrothermal reaction autoclave. The vanadium
dioxide powders can be prepared by hydrothermal reaction, drying,
and separating.
[0052] In the present invention, the doped vanadium dioxide powder
can be prepared through hydrothermal reaction of an aqueous
solution of vanadium ions and a dopant together. Predetermined
dopants were the oxide of the element M, and M can be near V in the
Periodic Table with an atomic number of 21-30, such as scandium,
titanium, chromium, manganese, iron, cobalt, nickel and copper. M
can be Zn and Sn or near them in the Periodic Table such as indium,
antimony, gallium, germanium, lead, and bismuth. The doping element
M can be a single element or any combination of the above elements.
Thus, it should be understood that the dopant M oxides may be a
single oxide, and also two or more than two of the oxides of the
doping elements, and also a mixture of different doping element
oxides. In the present invention, the size and morphology of the
resulting doped vanadium dioxide powders can be controlled by the
doping element. The molar ratio of the doping elements and V.sup.4+
ions in the aqueous solution can be determined according to the
amount of the dopant element. In the present invention, the ratio
ranged from 1:1000 to 1:1, preferably from 3:97 to 3:7, more
preferably from 3:97 to 1:9, in addition, the ratio ranging from
1:199 to 1:39 was preferred.
[0053] The hydrothermal reaction temperature can range from 200 to
400.degree. C., preferably from 200 to 350.degree. C., more
preferably from 250 to 300.degree. C. Within these temperature
ranges, the higher the temperature, the more easily the rutile
phase vanadium dioxide was prepared. The hydrothermal reaction time
could range from 1 to 240 h, preferably from 2 to 120 h, more
preferably from 4 to 60 h, and the reaction time can be adjusted
with the reaction temperature. Those skilled in the field can
select a suitable reaction vessel according to the packing ratio.
Usually the packing ratio of hydrothermal reaction may be from 20
to 90%, preferably from 30 to 80%, more preferably 50 to 80%.
[0054] Hydrothermal reaction products were separated and dried by
centrifugal drying, but it should be understood that the products
were also separated by freeze-drying, and other methods.
[0055] The powders prepared in the invention had a single chemical
composition with the expression of V.sub.1-xM.sub.xO.sub.2, and
wherein x satisfied 0<x.ltoreq.0.5, preferably
0.03<x.ltoreq.0.3, more preferably, 0.03<x.ltoreq.0.1 or
0.005.ltoreq.x.ltoreq.0.025. M was a doping element. The
crystalline phases of the nanoparticles were determined by X-ray
diffraction (XRD, Model D/Max 2550 V, Cu K.alpha., .lamda.=0.15406
nm, 4.degree. /min, Rigaku, Japan), and the patterns showed than
the powders belonged to VO.sub.2(M). The morphology was determined
by transmission electron micros-copy (TEM, JEM-2010F, JEOL, Tokyo,
Japan) and the results showed that the doped powders were comprised
of granulated particles with the size of 10-100 nm.
[0056] The method of the invention also can be used to prepare
undoped powders with the formula of VO.sub.2. The XRD pattern in
FIG. 3 (the horizontal ordinate is 20 degree, the vertical ordinate
is the intensity of the diffraction peak) showed that the undoped
powders belonged to VO.sub.2(A). The TEM photographs (FIG. 4)
showed the powders were comprised of long rod single crystals with
lengths of hundreds of nm to dozens of um and widths of hundreds of
nm.
[0057] The optical properties of the energy saving films prepared
with the doped VO.sub.2 powders were comparable to that prepared by
sputtering and chemical coating methods. The XRD pattern in FIG. 3
(the horizontal ordinate is 20 degree, the vertical ordinate is the
intensity of the diffraction peak) showed that the undoped powders
belonged to VO.sub.2(A). The TEM photographs (FIG. 4) showed the
powders were comprised of long rod single crystal with length of
hundreds of nm to dozens of um and width of hundreds of nm.
However, as was shown in FIG. 5 (the XRD pattern of one undoped
VO.sub.2 example) and FIG. 6 (the TEM photographs of one undoped
VO.sub.2 example), the undoped powders were comprised of uniform
particles of 50 nm, and the aspect ratio of the particles was 2:1.
The powder belonged to VO.sub.2(M). As a result, in comparison with
undoped VO.sub.2 powders , the morphology and size of the powders
were controlled through doping of unique element, and the prepared
powders had advantages of small grain size, uniform diameter, and
stable crystal structure. Furthermore, the powders can be dispersed
well in H.sub.2O and dispersant such as PVP. The concentration was
in the range of 0.1-100 g/L. The prepared suspension was easily
coated on the substrate of glass and applicable to preparing films
and coatings of VO.sub.2. The VO.sub.2 dispersion was prepared as
follows: the powders was added to distilled water with addition of
dispersant such as PVP to form a slurry, then the slurry was
stirred and ultrasonicated for 30-60 min. The powders disperse well
in H.sub.2O and dispersant. The prepared suspension was coated on
the substrate of glass and was dried to form VO.sub.2 films. FIG.
12 shows the VO.sub.2 films with uniform thickness. It is noted
that the dispersion can be coated on other substrates such as
plastic, silicon wafer and metal, and these coated substrates can
be used in construction and travel applications for energy
savings.
[0058] The VO.sub.2 spectral curve before and after the phase
transition were obtained through using a UV-vis-NIR
spectrophotometer, Hitachi Corp., Model UV-4100 with temperature
control unit at temperatures of 25 and 90.degree. C., respectively.
In FIG. 11, a great change in doped VO.sub.2 optical transmittance
occurred before and after the phase transition, for example, the
optical transmittance difference of 40.6% found at 2000 nm
wavelength. The hysteresis loops were obtained by measuring the
prepared film transmittance at 2000 nm with heating and cooling. In
FIG. 12, it is found that the doped VO.sub.2 films had phase change
properties and the transmittance after phase transition decreased
dramatically. The results showed that the optical properties of the
VO.sub.2 powders prepared by the invention were comparable to that
prepared by sputtering and chemical coating methods.
[0059] It is noted that the detailed method above in the invention
and the examples below were used to explained the invention but are
not limited the scope. The raw materials used, and the reagents can
be obtained through the purchase of commercially available starting
materials or synthesized by conventional chemical method. The
following examples, not including the detailed steps, were
implemented according to conventional conditions such as described
in Beilstein organic chemistry Manual(Chemical Industry Press,
1996) or the advice given by manufacturers. The ratios and
percentages, except where described otherwise, were based on the
molar mass. In addition, any methods and materials similar or
equivalent with the contents can be applied to the method of the
present invention. Other aspects of the present invention coming
from the disclosure of this article are easily understandable for
the skilled person.
[0060] The following examples give a detailed description of the
invention.
[0061] Comparative Example:
[0062] 0.225 g V.sub.2O.sub.5 powders were added to 50 mL, 0.015
mol/L H.sub.2C.sub.2O.sub.4 solution while stirring for 10 min and
transferred to an autoclave and added 26 mg tungstic acid followed
by hydrothermal treatment at 240.degree. C. for 7 days. Then the
VO.sub.2 powders were obtained through centrifugation and drying.
The yield of the powders with a formula of
V.sub.0.96W.sub.0.04O.sub.2 is 75%. As is shown in FIG. 1 and FIG.
2, the powders belonging to M phase is long rod-like.
[0063] Example One:
[0064] 1 g VOSO.sub.4 was dissolved in 50 mL deionized water and
titrated with 1 mol/L NaOH solution while stirring. After
titration, the suspension was transferred into a 50 mL autoclave
with 45 mL distilled H.sub.2O followed by hydrothermal treatment at
250.degree. C. for 12 h. Then the powders with a formula of
VO.sub.2 were obtained through centrifugation and drying and the
yield was 90%. As is shown in the XRD pattern (FIG. 3) and TEM
photographs (FIG. 4), the powders belonging to A phase are long and
rod-like, and the long rod products were single crystals with a
length ranging from several nm to a few micrometers and a width of
several nanometers.
[0065] Example Two:
[0066] 1 g VOSO.sub.4 was dissolved in 50 mL deionized water and
titrated with 1 mol/L NaOH solution while stirring. After
titration, the suspension and 25 mg Bi.sub.2O.sub.3 were
transferred into a 50 mL autoclave with 45 mL distilled H.sub.2O
followed by hydrothermal treatment at 250.degree. C. for 12 h. Then
the powders with a formula of V.sub.0.983Bi.sub.0.017O.sub.2were
obtained through centrifugation and drying and the yield was 90%.
As is shown in the XRD pattern (FIG. 5) and TEM photographs (FIG.
6), the powders belonging to A phase are granule-like, and the
particles with a main size of 40-50 nm and an aspect ratio of less
than 2:1 were single crystals.
[0067] Example Three:
[0068] The experiment was conducted according to the description of
Example Two with 1 g VOSO.sub.4 and 7.5 mg Bi.sub.2O.sub.3. The
powders with a formula of V.sub.0.995Bi.sub.0.005O.sub.2 were
obtained and the yield was 85%. The powders belonged to M phase and
the particles with main size of 40-70 nm and aspect ratio of
1:1-3:1 were single crystals.
[0069] Example Four:
[0070] The experiment was conducted according to the description of
Example Two with 1 g VOSO.sub.4 and 25 mg SnO in place of
Bi.sub.2O.sub.3. The powders with a formula of
V.sub.0.962Sn.sub.0.038O.sub.2 were obtained and the yield was 95%.
The powders belonged to M phase and the particles with main size of
30-40 nm and aspect ratio of 1:1-1.5:1 were single crystals.
[0071] Example Five:
[0072] The experiment was conducted according to the description of
Example Two with 1 g VOSO.sub.4 and 21 mg SnO in place of
Bi.sub.2O.sub.3. The powders with a formula of
V.sub.0.975Sn.sub.0.025O.sub.2 were obtained and the yield was 90%.
The powders belonged to M phase and the particles with main size of
40-50 nm and aspect ratio of 1:1-2:1 were single crystals.
[0073] Example Six:
[0074] The experiment was conducted according to the description of
Example Two with 1 g VOSO.sub.4 and 25mg Fe.sub.2O.sub.3 in place
of Bi.sub.2O.sub.3. The powders with a formula of
V.sub.0.953Fe.sub.0.047O.sub.2 were obtained and the yield was 90%.
The powders belonged to M phase and the particles with main size of
40-60 nm and aspect ratio of 1:1-3:1 were single crystal.
[0075] Example Seven:
[0076] The experiment was conducted according to the description of
Example Two with 1 g VOSO.sub.4 and 55 mg Fe.sub.2O.sub.3 in place
of Bi.sub.2O.sub.3. The powders with a formula of
V.sub.0.09Fe.sub.0.1O.sub.2 were obtained and the yield was 80%.
The powders belonged to M phase and the particles with main size of
30-40 nm and aspect ratio of 1:1-1.5:1 were single crystals.
[0077] Example Eight:
[0078] 5 g VOC.sub.2O.sub.4.5H.sub.2O was dissolved in 50 mL
deionized water and titrated with 0.5 mol/L NaOH solution while
stirring. After titration, the suspension and 50 mg ZnO were
transferred into 50 mL autoclave followed by hydrothermal treatment
at 260.degree. C. for 6 h. Then the powders with a formula of
V.sub.0.97Zn.sub.0.03O.sub.2 were obtained through centrifugation
and drying and the yield was 90%. As is shown in the XRD pattern
(FIG. 7) and TEM photographs (FIG. 8), the powders belonging to M
phase are granule-like and the particles with main size of 25-35 nm
and aspect ratio of 1:1-1.5:1 were single crystals.
[0079] Example Nine:
[0080] The experiment was conducted according to the description of
Example Eight with 5 g VOC.sub.2O.sub.4.5H.sub.2O and 550 mg ZnO in
place of 50 mg ZnO. The powders with a formula of
V.sub.0.7Zn.sub.0.3O.sub.2 were obtained and the yield was 85%. The
powders belonged to M phase and the particles with main size of
80-100 nm and aspect ratio of 1:1-3:1 were single crystals.
[0081] Example Ten:
[0082] The experiment was conducted according to the description of
Example Eight with 5 g VOC.sub.2O.sub.4.5H.sub.2O and 1.65 g ZnO in
place of 50 mg ZnO. The powders with a formula of
V.sub.0.5Zn.sub.0.5O.sub.2 were obtained and the yield was 80%. The
powders belonged to M phase and the particles with main size of
80-100 nm and aspect ratio of 1:1-5:1 were single crystals.
[0083] Example Eleven:
[0084] The experiment was conducted according to the description of
Example Eight with the reaction temperature of 300.degree. C. in
place of 260.degree. C. The powders with a formula of
V.sub.0.97Zn.sub.0.03O.sub.2 were obtained and the yield was 95%.
The powders belonged to M phase and the particles with main size of
80-100 nm and aspect ratio of 1:1-2:1 were single crystals.
[0085] Example Twelve:
[0086] 0.5 g VOCl.sub.2 was dissolved in 50 mL deionized water and
titrated with 2 mol/L NaOH solution while stirring. After
titration, the suspension and 50 mg Ti.sub.2O.sub.3 were
transferred into 50 mL autoclave with 35 mL distilled H2.sub.2O
followed by hydrothermal treatment at 260.degree. C. for 24 h. Then
the powders with a formula of V.sub.0.84Ti.sub.0.16O.sub.2 were
obtained through centrifugation and drying and the yield was 85%.
As is shown of the XRD pattern (FIG. 9) and TEM photographs (FIG.
10), the powders belonging to A phase are granule-like and the
particles with main size of 10 nm and aspect ratio of 1:1-1.5:1
were single crystals.
[0087] Example Thirteen:
[0088] The experiment was conducted according to the description of
Example Twelve with the reaction time of 36 h in place of 12 h. The
powders with a formula of V.sub.0.84Zn.sub.0.16O.sub.2 were
obtained and the yield was 95%. The powders belonged to M phase and
the particles with main size of 50 nm and aspect ratio of 1:1-3:1
were single crystals.
[0089] Example Fourteen:
[0090] The experiment was conducted according to the description of
Example Twelve with 50 mg molybdic acid in place of 50 mg
Ti.sub.2O.sub.3. The powders with a formula of
V.sub.0.93Mo.sub.0.07O.sub.2 were obtained and the yield was 85%.
The powders belonged to M phase and long rods with a size of
several nm and an aspect ratio of more than 10:1 were single
crystals.
[0091] Through detection, the dispersibilities of the Comparative
Example and Example One were poor, while that of Examples Two
through Thirteen were good, especially Examples Two, Four, Five,
Seven, Eight, Eleven, and Thirteen.
[0092] It is found from the examples above that the doping elements
had a vital impact on the size, morphology and crystal form of
VO.sub.2 powders. A transition accompanied by doping happened in
VO.sub.2 powders from the initial un-doped micro rod of A phase to
nano-granule, while the sizes can be controlled easily. In spite of
the description of doped elements of Bi, Sn, Fe, Zn, Ti, Mo, it is
noted that the elements near V in Periodic Table, such as the
atomic number ranges from 21 to 30, the elements near tin not
described in the examples, and even the element W can be used to
dope according to the detailed steps above.
[0093] 0.1 g VO.sub.2 powders after grinding prepared according to
Example Seven was added to a beaker with 5 mL distilled H.sub.2O
while stirring. Then 0.25 g PVP K-30 was added to the suspension.
The dispersed solution formed after stirring for 30 min and
ultrasonication of 60 min.
[0094] To obtain the VO.sub.2 thin films, the dispersion was coated
on a glass substrate by spin coating, then dried at room
temperature or in an oven.
[0095] As was shown in FIG. 11 and FIG. 12 the optical properties,
especially the properties of infrared solar control, of the
VO.sub.2 powders prepared by the invention were comparable to that
prepared by sputtering and chemical coating method.
[0096] Industrial applicability: the VO.sub.2 powders and
dispersion described in the invention can be applied to energy
saving and emission reduction equipment, such as energy saving
films, energy saving coatings and solar control equipment, or to
energy information devices such as micro-optical switching devices,
thermistors, battery materials, and optical information storage
devices. The method of preparation of VO.sub.2 powder of the
invention is simple, low cost, high yield, suitable for mass
production.
* * * * *