CN1186297C - Method for making vanadium dioxide and its adulterant nanoceramics - Google Patents

Abstract

The present invention relates to a preparation method of VO2 and adulterant nanometer ceramics thereof. In the method, V2O5 is reduced to prepare a VOCl2 solution, vanadyl (IV) alkali ammonium carbonate precursors are prepared from the VOCl2 solution, VO2 nanometer powder is prepared by the thermal decomposition of the precursors, and finally, VO2 nanometer ceramics are prepared through tabletting and sintering. The method has the advantages of simple process, low energy consumption, little investment, low cost and convenient scale production, and the prepared ceramics have the advantages of high strength and good thermoelectric performance.

Description

The preparation method of vanadium dioxide or its hotchpotch nano ceramics

Technical field

The invention relates to the preparation method of vanadium dioxide or its hotchpotch nano ceramics.

Background technology

As everyone knows, VO ₂The about 68 ℃ transformations that have a low temperature monocline (semi-conductor phase) to high temperature four directions (metallographic phase).During the phase transformation, some physical propertiess such as electric conductivity, magnetic moment and ir transmissivity generation hop; Particularly to VO ₂When mixing, transformation temperature (T _C) can regulate change, its variable quantity is relevant with kind of mixing impurity and quantity.For example mix Cr and increase Tc, V _0.976Cr _0.024O ₂T _CIt is 72 ℃.And whenever mix the 1%Mo atom, and Tc reduces 11 ℃, whenever mixes the 1%W atom, and Tc reduces 26 ℃.VO ₂These special propertys, can be used to contactless thermoelectric switch, thermorelay, hygrosensor and temperature equilibrator, photoswitch, optical storage material, inverting element and multiple sensors.And, for powder body material, except that being used for preparation pottery and thin layer, at critical temperature resistor (CTR), conductive polymer composite, electrode material of lithium battery, except that O ₂Agent, catalyzer, pigment and multiple space flight occasion have special application.Therefore for many years to VO ₂Research from uninterruptedly.Though in recent years to VO ₂The synthetic of fine powder body has considerable progress, but the high and economical and practical preparation nanometer VO of quality is not arranged as yet ₂The processing method of powder and nano ceramics.Use the induced with laser gas-phase reaction and decompose VOCl ₃Though, can obtain＜VO of 100nm ₂Powder, but the right cost of this Faxian is high, can not produce in enormous quantities.

Summary of the invention

The purpose of this invention is to provide a kind of manufacturing VO ₂Or the preparation method of its hotchpotch nano ceramics, its technological process is simple, and energy consumption is low, and it is big to make ceramics strength, and performance is good.

The present invention is with the compound V of vanadium ₂O ₅Reduction is mixed, and makes vanadyl (IV) the basic carbonate ammonium as presoma, after thermolysis gets VO ₂Nano-powder gets VO through the compressing tablet sintering ₂Nano ceramics, concrete preparation process is:

1. use H ₂C ₂O ₄2H ₂O and N ₂H ₂2HCl in hydrochloric acid medium with V ₂O ₅Reduction preparation VOCl ₂Solution: with prevailing vanadium compound V ₂O ₅Be starting raw material, in hydrochloric acid medium with oxalic acid or xitix prereduction V ₂O ₅, water hydrazine or hydrazine hydrochloride further reduce and prepare VOCl again ₂Solution.Also directly water hydrazine or hydrazine hydrochloride the reduction V ₂O ₅Preparation VOCl ₂Solution.For the preparation of hotchpotch, can be at VOCl ₂Add corresponding doped metal ion in the solution according to actual needs and obtain VOCl ₂Doped solution, the mol ratio of controlled doping ion and vanadium is regulated impurity at VO ₂In content ratio.When mixing Cr, can add CrCl ₃When mixing Mo, can add MoO ₂Cl ₂Or (NH ₄) ₂MoO ₄In hydrochloric acid medium by hydrazine hydrochloride reductive solution, also can be at NH in step 2 ₄HCO ₃Or (NH ₄) ₂CO ₃Middle (the NH that adds ₄) ₂MoO ₄When mixing w, can add WO ₂Cl ₂, also can be with (NH in step 2 ₄) ₂WO ₄Be added in NH ₄HCO ₃Or (NH ₄) ₂CO ₃In the solution.

2. the VOCl that step 1 is made ₂Solution is with (NH ₄) ₂CO ₃Or NH ₄HCO ₃Reaction, preparation vanadyl (IV) basic carbonate ammonium presoma (NH ₄) ₅[(VO) ₆(CO ₃) ₄(OH) ₉] 10H ₂O or doping presoma.Presoma or its dopant precursor in dehydrated alcohol with ultrasonic disruption to granularity≤2 μ m.

3. the presoma that step 2 is made or its dopant precursor obtain VO at inert atmosphere or contain thermolysis in the oxygen inert atmosphere ₂Or its hotchpotch nano-powder, 350～700 ℃ of Heating temperatures.The NH that emits in the presoma thermal decomposition process ₃Can be with part of V ⁴⁺Be reduced to V ³⁺One of characteristic of the present invention is to comprise O in the air-flow by the thermolysis system ₂Concentration, the logical O that contains ₂The time of air-flow and the selection of pyrolysis temperature, V in the control product ³⁺And V ⁵⁺Content, thereby obtain the whole high-quality powder of various differences than property.Adopt method of the present invention, can also control the granularity and the crystal form of powder.In 350～450 ℃ of scopes, can obtain amorphous or be main contain a small amount of B phase crystal, the powder of granularity＜10nm with amorphous.Between 450～560 ℃, can obtain accurate crystalline A phase powder, granularity＜20nm.Between 560～700 ℃, can obtain the A phase powder of better crystallinity degree, granularity＜30nm.

VO ₂The preparation method of nano ceramics: the nano-powder that makes with aforesaid method; the most handy crystal form or accurate crystalline powder; at 400～800MPa lower sheeting, then vacuumize or logical protection of inert gas under, the insulation 4～8 hours down in room temperature～800 ℃; slough adsorbed gas; 900～1100 ℃ of sintering 1 hour to 4 hours, can obtain grain fineness number＜150nm then, intensity is big; thermal circulation performance is good, has the nano ceramics of practical value.

VO ₂Material volume changes about 1% during phase transformation, consequent stress is huge to the body material, this causes in monocrystal material research, when carrying out resistance-temperature curve when measuring, even do not finish a thermal cycling and measure single crystal and just break, and to the polycrystalline micrometer ceramics, also just just break through several thermal cyclings.Therefore, this type of pottery commercialization of failing so far.For overcoming the transformation stress of material, main recently research mould material.But mould material is not suitable for the application scenario of high-voltage large current, and the cost height.Use the nano ceramics that method of the present invention is made, have high intensity, realized the practicability of this class pottery.In short, prepare VO with method of the present invention ₂And hotchpotch powder and pottery, have following outstanding advantage:

1. raw material obtains easily, presoma synthetic easy, and can carry out multiple metal doping.

2. the presoma heat decomposition temperature is low, can prepare amorphous state, accurate crystal form, and the nano-powder of crystal form, and can accurately control the whole of powder than property and non-stoichiometric.

3. ceramic sintering temperature is low, physical strength and temperature-sensitive good stability.

4. whole art production process is simple, low for equipment requirements, invests for a short time, and energy consumption is low, easily produces in enormous quantities, and the product cost is low, helps commercialization.

5. technological process is not introduced detrimental impurity and is produced hazard residue thing, product purity height.Production process is not discharged objectionable impurities, belongs to friendly process.

Embodiment

The invention will be further described by the following examples.

Embodiment 1

1. prepare VO ₂Nano-powder:

1) preparation VOCl ₂Solution

Take by weighing 91g V ₂O ₅, add 100～200mL distilled water and size mixing, add 38g H ₂C ₂O ₄2H ₂O, heating, gradation under agitation adds 140～160mL concentrated hydrochloric acid, and little several minutes that boils drips N then ₂H ₄H ₂O makes solution change mazarine into.Perhaps at above-mentioned V ₂O ₅In the suspension liquid, repeatedly alternately add 120～140mL concentrated hydrochloric acid and 26～29g N in heating with under stirring ₂H ₄2HCl, dissolving obtains blue solution.Use a small amount of V ₂O ₅Or N ₂H ₄2HCl (N ₂H ₄H ₂O) be adjusted to solution and can't check VO ₂ ⁺And V ³⁺Ion.Cross the elimination insolubles in case of necessity, rare again to 500mL.VO ₂ ⁺And V ³⁺Detect and use ferrous phenanthroline and potassium dichromate process.

2) preparation presoma

Take by weighing 14～16g NH ₄HCO ₃, or 8.5～10g (NH ₄) ₂CO ₃, add 40～60mL distilled water, feed CO ₂(at NH ₄HCO ₃Situation also can lead to Ar or N ₂Gas).Under agitation dropwise splash into the above-mentioned VOCl of 28～30mL then ₂Solution.Left standstill 0.5～2 hour, and also can under secluding air, place and spend the night.Suction filtration is used saturated NH ₄HCO ₃Solution washing is to there not being Cl ^-, use a small amount of absolute ethanol washing 2 times again, obtain 8.0～9.5g presoma, productive rate 80～95%.Add 20～40mL dehydrated alcohol to this presoma, use the ultrasonic grinding crusher machine, suction filtration washs 2 times with a small amount of ether, suction filtration, dry the presoma of granularity≤2 μ m.Ethanol in the process and ether can reclaim or recycle.

3) preparation VO ₂Nano-powder

At diameter is in the quartz boat of 35mm, long 280mm, the 3g presoma is paved into thin layer and places the silica tube of φ 42mm.The N of feeding 99.99% ₂The mixed airflow of the airflow of air-flow (3L/ minute) and required flow rate 15 minutes preferably vacuumizes and uses N ₂Air purge is washed system.Feed mixed airflow then and be heated to temperature required, the insulation certain hour.The time of bubbling air can optionally suitably be controlled between soak, also can reduce the flow velocity of air gradually.From tube furnace, extract silica tube then out and in nitrogen gas stream, be cooled to room temperature, take out powder.Table 1 is listed the powder of 4 kinds of different pyrolytical conditions and is formed and character.The granularity of powder is by transmissioning electric mirror determining, and crystalline state is by the x ray diffraction determination.Powder composition chemical analysis.Powder is dissolved in H under the noble gas protection ₃PO ₄-H ₂SO ₄In, use ferrous phenanthroline one potassium bichromate titrimetric method titration then.For VO _{X ± y}, y value error is less than 0.001, and methods and results conforms to the thermogravimetry of oxygen level in the measurement powder.

Composition, crystalline state and the granularity of different pyrolytical conditions of table 1 and powder

Pyrolysis temperature (℃)	Air flow quantity (mL/ minute)	The blowing air time (branch)	Pyrolysis time (branch)	Powder is formed	Crystalline state	Granularity (nm)
							400	3.5	15	30	VO 2.028	Amorphous	＜10
450	5.0	20	20	VO 2.021	Amorphous+the B phase	＜10
							500	10.0	15	30	VO 2.000	Accurate crystallization	＜20
600	8.0	10	20	VO 1.989	Crystallization	＜30

2. the preparation of nano ceramics and resistance measurement:

, place then in the quartz boat vacuumizing or feed under the protection of inert gas and heat at 500～700MPa lower sheeting with crystal form or accurate crystal form powder.Interval insulation is 4～8 hours in room temperature～800 ℃, at last 900～1100 ℃ of sintering 1 to 4 hour.Stop heating, furnace cooling promptly gets the high-strength ceramic of granularity＜150nm.Resistance one temperature curve of pottery is measured constant current 1mA with four terminal potential methods.The sintering condition and the thermoelectricity capability of 2 potteries that undope are shown in table 2.

The sintering condition of table 2 pottery and performance

Form	Sintering temperature (℃)	Sintering time (hour)	Transformation temperature (℃)	R Room temperature/R High temperature
					VO 1.902	1050	3	65	200
VO 2.000	1000	2	70	4000

Embodiment 2

When the Cr thing is mixed in preparation, at V _1-xCr _xO ₂The big I of x value is by VOCl in (0＜x≤0.06) ₂The change of the Cr/V mol ratio in the solution is regulated, the deviation of the repeated experiments of same x value＜3%.Be a specific examples below.At VOCl ₂Add CrCl in the solution ₃, making the Cr/V mol ratio is 0.065, then with the synthetic Cr presoma of mixing of the same method of embodiment 1, and powder and sinter pottery into.Obtain the V that consists of of powder and pottery _0.955Cr _0.045O ₂, 74 ℃ of transformation temperatures, R _{Room temperature}/ R _{High temperature}Be 500.

Embodiment 3

When the Mo thing is mixed in preparation, V _1-xMo _xO ₂The size of x value is regulated the deviation of the repeated experiments of same x value＜4% in (0＜x≤0.045) by the change of the Mo/V mol ratio in the presoma synthetic system.Lift an object lesson below.In hydrochloric acid medium, use N ₂H ₂2HCl is with (NH ₄) ₂MoO ₄Reduction.This reduzate adds VOCl ₂In the solution, making the Mo/V mol ratio is 0.11.Identical with embodiment 1 then method is synthetic mixes the Mo presoma, but NH ₄HCO ₃Consumption increase to 19～22g.Same preparation powder and pottery obtain V _0.985Mo _0.015O ₂Hotchpotch, 51 ℃ of transformation temperatures, R _{Room temperature}/ R _{High temperature}Be 240.

Embodiment 4

When the hotchpotch of preparation W, V _1-xW _xO ₂The size of x value is by the decision of the W/V mol ratio in the presoma synthetic system, the deviation of the repeated experiments of same x value＜4% in (0＜x≤0.028).Lift an example below.In embodiment 1, with (NH ₄) ₂WO ₄Be added in NH ₄HCO ₃In the solution, making the W/V mol ratio is 0.12, the synthetic W presoma of mixing of identical with embodiment 1 then method.Same preparation powder and pottery obtain V _0.981W _0.019O ₂Hotchpotch, 20 ℃ of transformation temperatures, R _{Room temperature}/ R _{High temperature}Be 130.

Claims (2)

1. the preparation method of a vanadium dioxide or its hotchpotch nano ceramics; it is characterized in that vanadium dioxide nano powder or vanadium dioxide hotchpotch nano-powder at 400～800MPa lower sheeting; vacuumize then or logical protection of inert gas; adsorbed gas is sloughed in insulation in ℃ scope of room temperature～800, again 900～1100 ℃ of sintering 1 hour to 4 hours.

2. the preparation method of a vanadium dioxide as claimed in claim 1 or its hotchpotch nano ceramics is characterized in that the nano-powder that the vanadium dioxide nano powder that adopted or vanadium dioxide hotchpotch nano-powder adopt crystal form or accurate crystal form.