CN101200282B - Vacuum heat-treating method for nano powder - Google Patents
Vacuum heat-treating method for nano powder Download PDFInfo
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- CN101200282B CN101200282B CN2007100507533A CN200710050753A CN101200282B CN 101200282 B CN101200282 B CN 101200282B CN 2007100507533 A CN2007100507533 A CN 2007100507533A CN 200710050753 A CN200710050753 A CN 200710050753A CN 101200282 B CN101200282 B CN 101200282B
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Abstract
The invention relates to a vacuum heat treatment method for nanometer powder, the nanometer powder is filled into a vacuum furnace, under the condition of not lower than 10E-2 Pa vacuum, the temperature of environment is raised to the 500-1300 DEG C at a rate of 5-20 DEG C/min and kept for 0.5-5h, and then cooled to room temperature. The vacuum heat treatment method of the invention can eliminatepowder agglomeration, remove gas absorbed on the surface of the powder, and improve nanometer sinter activity of powder, the treated powder shortens the sedimentation time greatly, thereby being advantageous for preparing massive non-cracked transparent nanometer ceramic.
Description
Technical field
The invention belongs to the nano-powder field, particularly the vacuum heat-treating method of nano-powder.
Background technology
Nano-powder is not only a kind of functional material, and for the compound of new functional material and exploitation have represented wide application prospect, has a wide range of applications in national economy and each field of national defence, plays crucial effect.
Nano-powder have very big specific area, very high surface can and surface-active, thereby have characteristic, surface and interfacial effect, quantum size effect and the small-size effects such as light, electricity, magnetic, thermodynamics of the not available excellence of many massive materials.Because the powder outer surface structure is different from the structure of inner surface, cause the i.e. generation of surface energy of excess energy.Along with powder attenuates, its specific area increases, the surface can increase, skin effect (as relaxation, segregation, absorption), quantum size effect (broaden as energy gap etc.) strengthen, fusing point reduces, make the surface nature of nano-powder become more active, many chemical reactions that just take place under heating condition or under the high temperature, very violent at normal temperatures.Part molecule in liquid phase or gas phase (or atom, ion) is when contacting with nano powder surface, because the factors such as high surface energy of powder, can produce between them and interact, consequently the part molecule in gas phase or the liquid phase (or atom, ion) is bound by the surface or make branch in bond give with the gas body mutually or the molecule of liquid bulk in mutually form certain dynamic equilibrium, make some molecules (or atom, ion) rest on powder surface, cause these molecules big in the concentration of the concentration ratio on the powder surface in gas phase or liquid phase, this phenomenon is called absorption.Nano-powder is exposed in the air, can adsorb a large amount of water from air, forms hydroxyl layer and multilayer physical absorption water on the surface, and hygroscopicity reducing and strengthen with apparent density, granularity.Along with reducing of particle size, more weak interaction forces such as the electrostatic attraction between the particle, Van der Waals force, capillary force seem more and more important, have formed soft-agglomerated between the particle.When particle size during less than 50 nanometers (nm), the Van der Waals force between the particle is very strong, at this moment forms stronger soft aggregate between the particle.On the other hand, along with reducing of granularity, the specific area of particle increases, and the trend that water vapour condenses between particle increases, and forms chemical bond between particle, has aggravated reunion.
In the preparation field of nano ceramics, the reunion of nano-powder will cause the biscuit bulk density low and big or small inhomogeneous, and will introduce a large amount of defectives and pore, have a strong impact on density, intensity, toughness, reliability and other performance of ceramic sintered bodies.In addition, aggregate also will speed up the secondary recrystallization of powder in sintering process, forms big crystal grain, does not reach the nano-scale requirement, thereby loses the distinctive performance of nano ceramics.Preparation does not have the prerequisite that the nano-powder of reuniting is the good nano ceramics of preparation.
In sum, be exposed to airborne nano powder and know from experience generation reunion and adsorption phenomena, suitably dry (heat treatment) is necessary before use.Drying means commonly used at present is for to heat in common drying box to about 200 ℃, to remove moisture.This kind method can guarantee the dispersion of nano-powder to a certain extent, but can not effectively solve agglomeration traits, and, after liquid phase moisture is heated and becomes gas phase steam, still can be adsorbed on nano powder surface.
Summary of the invention
The objective of the invention is to overcome the deficiencies in the prior art, a kind of heat treatment method of improved nano-powder is provided, to solve reunion and the absorption problem that nano-powder is exposed in the atmosphere to be produced.
Technical scheme of the present invention is to adopt vacuum heat-treating method that nano-powder is carried out surface modification.Vacuum heat is carried out according to the following steps.
Nano-powder is packed in the vacuum drying oven, be not less than 10 in vacuum
-2Be warming up to 500～1300 ℃ of insulations 0.5～5 hour under the vacuum environment of Pa, slowly cool to room temperature then.In above-mentioned holding temperature interval, lower holding temperature also can reach beneficial effect of the present invention, and can saves energy, so be mode more preferably 500～1000 ℃ of insulations 1～5 hour, being incubated 2～5 hours at 500～800 ℃ is optimal way.Heating rate and rate of temperature fall do not have obvious influence to the treatment effect of nano-powder, but according to the situation that has vacuum heat treatment equipment now, heating rate and rate of temperature fall are controlled between 5～20 ℃/minute and are advisable.
Vacuum heat-treating method of the present invention is applicable to the surface modification of various nano-powders.
Employed nano-powder post processing Evaluation on effect method is a sedimentation among the present invention, the specific practice of this method is that the nano-powder before and after the vacuum heat is put into solvent, absolute ethyl alcohol for example, fully mix the back and form suspension, the gained suspension is left standstill, observe the precipitation situation of this suspension.Chosen undressed MgAl among the present invention
2O
4The powder of nano-powder and process embodiment 1-3 vacuum heat utilizes sedimentation relatively, and the concrete processing step of this method is seen embodiment 13, and the result is shown in accompanying drawing 1-3.Powder after handling as can be seen is with respect to the easier sedimentation of undressed powder, its reason is, through after the application of vacuum, the powder reuniting phenomenon reduces on the one hand, the closed pore that causes of reuniting has not existed, the adsorbed gas of powder surface is effectively removed on the other hand, causes the suffered buoyancy of powder to reduce, so sinking speed is fast.
Employed nano-powder post processing Evaluation on effect method also has the Indirect evaluation method among the present invention, it is with the nano-powder through surface modification or other post processings, be directly used in the actual environment for use in downstream product or downstream, observe or detect its practical effect, estimate the post processing effect of nano-powder then with this.Adopt this method can be accurately, reflect, estimate the post processing effect of nano-powder truly.Nano-powder through overmolding and sintering, has been prepared block-shaped crackless transparent nano ceramic after handling through the vacuum heat-treating method described in the present invention again, has improved the success rate of preparation crystalline ceramics, makes high-pressure sinter transparent nano pottery become easy.The photo of the prepared crystalline ceramics that goes out as shown in Figure 4, concrete processing step is seen embodiment 14-15.
As follows for the mechanism discussion that nano-powder vacuum heat of the present invention can be improved sintering activity:
For nano-powder, high specific area and surface can be the very strong driving forces that nano-powder is reunited, foreign substance limit air, water etc.) at the chemisorbed and the chemical reaction on surface, surface texture and interactive property have been changed, generate new constructions such as hydroxyl at powder surface, make between powder attract each other (as the active force between hydrogen bond) and chemical reaction (as polymerisation between an OH base), this is to cause the serious basic reason of reuniting of most of nano-powders.And after the vacuum heat-treating method processing of the present invention of nano-powder process, the gas of powder surface physical absorption and the hydroxyl of chemisorbed etc. is effectively removed, and the particle of reunion is disperseed again, and the powder sintering activity is improved.
The present invention has following beneficial effect:
1, nano-powder can effectively be removed the gas of its surface physics absorption and the materials such as hydroxyl of chemisorbed through after the vacuum heat, and the particle of agglomerated disperses again.
2, nano-powder vacuum heat-treating method technology of the present invention is simple, easy operating control.
3, after nano-powder is handled through vacuum heat-treating method, not only can on belt type press, prepare block-shaped crackless transparent nano ceramic, and can on cubic hinge press, prepare block-shaped crackless transparent nano ceramic.The pottery that is arranged in Fig. 4 left side is formed by the nano raw material powder sintering without vacuum heat, can see ceramic cracked a lot of fritters that are; Be positioned in the middle of Fig. 4 and the pottery on the right forms for the nano-powder sintering through vacuum heat, gained pottery be a bulk integral body, and the contrast sintering effect of nano raw material powder handling front and back is fairly obvious.
4, can carry out separately as the method for nano powder surface modification, also can be used as nano ceramics preparation method's a step.
Description of drawings
Fig. 1-the 3rd, undressed MgAl
2O
4The MgAl of nano-powder and process vacuum heat
2O
4The sedimentation of nano-powder experiment photo, among each figure, it is MgAl without vacuum heat that first test tube played on a left side
2O
4Nano-powder, its excess-three prop up test tube and are the MgAl through vacuum heat
2O
4Nano-powder, the time that each test tube leaves standstill among Fig. 1 is 10 minutes, and the time that each test tube leaves standstill among Fig. 2 is 1 hour, and the time that each test tube leaves standstill among Fig. 3 is 7 hours.
Fig. 4 is the photo of magnesium aluminate spinel transparent nano pottery, and this photo is the grid substrate photographs that magnesium-aluminum spinel ceramic is placed on literal, showing the transparency of magnesium-aluminum spinel ceramic; The fragment pottery that is positioned at the left side in the photo is with without vacuum treated MgAl
2O
4Nano-powder is a raw material, and employing has low temperature now, the ultra-high pressure sintering method is prepared; In the middle of being positioned in the photo and the pottery on the right with through vacuum treated MgAl
2O
4Nano-powder is a raw material, is adopted as the described method preparation of embodiment of the invention 14-15.
The specific embodiment
Embodiment 1-12: the vacuum heat of nano-powder
Nano-powder is packed in the vacuum drying oven, be not less than 10 in vacuum
-2Be warming up to 500～1300 ℃ of insulations 0.5～5 hour with certain heating rate under the vacuum environment of Pa, be cooled to room temperature with certain rate of temperature fall then.
The concrete technological parameter of each embodiment is listed as follows:
| The embodiment sequence number | Raw material | Vacuum (Pa) | Temperature rate (℃/minute) | Holding temperature (℃) | Temperature retention time (hour) | Sedimentation experiment |
| Embodiment 1 | MgAl 2O 4 | 10 -2 | 5 | 500 | 5 | Fig. 1-3 |
| Embodiment 2 | MgAl 2O 4 | 10 -3 | 10 | 800 | 2 | Fig. 1-3 |
| Embodiment 3 | MgAl 2O 4 | 10 -3 | 20 | 1000 | 1 | Fig. 1-3 |
| Embodiment 4 | MgAl 2O 4 | 10 -3 | 20 | 1300 | 0.5 | - |
| Embodiment 5 | Al 2O 3 | 10 -2 | 5 | 500 | 5 | - |
| Embodiment 6 | Al 2O 3 | 10 -3 | 10 | 800 | 2 | - |
| Embodiment 7 | Al 2O 3 | 10 -3 | 20 | 1000 | 1 | - |
| Embodiment 8 | Al 2O 3 | 10 -3 | 20 | 1300 | 0.5 | - |
| Embodiment 9 | TiO 2 | 10 -2 | 5 | 500 | 5 | - |
| Embodiment 10 | TiO 2 | 10 -3 | 10 | 800 | 2 | - |
| Embodiment 11 | TiO 2 | 10 -3 | 20 | 1000 | 1 | - |
| Embodiment 12 | TiO 2 | 10 -3 | 20 | 1300 | 0.5 | - |
Embodiment 13: nano-powder post processing Evaluation on effect---sedimentation
With the MgAl before handling
2O
4MgAl after nano-powder and embodiment 1-3 gained are handled
2O
4Nano-powder utilizes sedimentation to compare.The 5 milliliters of absolute ethyl alcohols of at first respectively packing in four test tubes take by weighing above-mentioned four kinds of nano-powders, 0.1 gram then respectively, and load weighted powder is respectively charged in above-mentioned four test tubes, stir simultaneously, obtain the opaque suspension of powder and absolute ethyl alcohol.The photo of suspension in each test tube after leaving standstill ten minutes as shown in Figure 1, the photo of the suspension in each test tube after leaving standstill 1 hour as shown in Figure 2, the photo of the suspension in each test tube after leaving standstill 7 hours is as shown in Figure 3.Among each figure, the powder that is arranged in a left side the 1st test tube is the MgAl before the vacuum heat
2O
4Powder in the powder, the 2nd test tube is embodiment 1 a gained powder, and the powder in the 3rd test tube is embodiment 2 gained powders, and the powder in the 4th test tube is embodiment 3 gained powders.
Four kinds of suspensions do not have obvious difference as can be seen from Figure 1, and are all opaque.Through the suspension of the nano-powder after the application of vacuum and the ethanol state that is translucent, the difference of treatment process is not brought too big difference as can be seen from Figure 2, and the suspension of undressed powder formation then still is opaque state.Precipitate fully through the nano-powder suspension after the application of vacuum as can be seen from Figure 3, ethanol is pellucidity, and the suspension that undressed powder forms does not precipitate as yet fully, still is opaque state.
Embodiment 14-15: nano-powder post processing Evaluation on effect---nano-powder sintered ceramic experiment
Embodiment 14
The processing step of present embodiment is as follows:
(1) vacuum heat of powder
With magnesium aluminate spinel (MgAl
2O
4) nano-powder is packed in the vacuum drying oven, is 10 in vacuum
-3Under the vacuum environment of Pa, be warming up to 1000 ℃ of insulations 1 hour, be cooled to room temperature with 10 ℃/minute rate of temperature fall then with 10 ℃/minute heating rates;
(2) powder moulding
Magnesium aluminate spinel nano powder after 1 gram step (1) handled is packed in the steel die, and pressurize promptly was shaped to biscuit in 3 minutes under normal temperature, pressure 10MPa;
(3) high-pressure sinter
Biscuit is put into cubic hinge press, at 5 minutes pressure is risen to 4GPa, temperature slowly raises when keeping this pressure, at 5 minutes temperature is risen to 600 ℃, 600 ℃ of sintering 20 minutes, cooled the temperature to room temperature then at 5 minutes, 5 minutes with pressure drop to normal pressure, promptly make magnesium aluminate spinel transparent nano pottery, this pottery is the block pottery in the middle of being positioned in the described photo of Fig. 4.
Embodiment 15
The processing step of present embodiment is as follows:
(1) vacuum heat of powder
With magnesium aluminate spinel (MgAl
2O
4) nano-powder is packed in the vacuum drying oven, is 10 in vacuum
-3Under the vacuum environment of Pa, be warming up to 1300 ℃ of insulations 0.5 hour, be cooled to room temperature with 20 ℃/minute rate of temperature fall then with 20 ℃/minute heating rates;
(2) powder moulding
Magnesium aluminate spinel nano powder after 1 gram step (1) handled is packed in the steel die, and pressurize promptly was shaped to biscuit in 2 minutes under normal temperature, pressure 15MPa;
(3) high-pressure sinter
Biscuit is put into cubic hinge press, at 5 minutes pressure is risen to 6GPa, temperature slowly raises when keeping this pressure, at 5 minutes temperature is risen to 500 ℃, 500 ℃ of sintering 60 minutes, cooled the temperature to room temperature then at 5 minutes, 5 minutes with pressure drop to normal pressure, promptly make magnesium aluminate spinel transparent nano pottery, this pottery is for being positioned at the block pottery on the right in the described photo of Fig. 4.
The vacuum drying oven model of using in the foregoing description is WZD-20 high vacuum experimental furnace, and the cubic hinge press model is DS6 * 800 ton, is the commercial goods; The used pressue device of powder moulding is a jack.
Claims (3)
1. MgAl
2O
4The nano-powder vacuum heat-treating method is characterized in that described MgAl
2O
4Nano-powder is not less than 10 in vacuum
-2Be warming up to 500～1300 ℃ of insulations 0.5～5 hour under the vacuum environment of Pa, be cooled to room temperature then.
2. MgAl according to claim 1
2O
4The nano-powder vacuum heat-treating method is characterized in that described MgAl
2O
4Nano-powder is not less than 10 in vacuum
-3The vacuum environment of Pa is warming up to 500～1000 ℃ of insulations 1～5 hour, is cooled to room temperature then.
3. MgAl according to claim 1
2O
4The nano-powder vacuum heat-treating method is characterized in that described MgAl
2O
4Nano-powder is not less than 10 in vacuum
-3The vacuum environment of Pa is warming up to 500～800 ℃ of insulations 2～5 hours, is cooled to room temperature then.
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| CN103331129B (en) * | 2013-08-07 | 2015-09-16 | 四川大学 | Hinge type cubic hinge press is utilized to prepare the method for high-performance poly diamond |
| CN107523779A (en) * | 2016-06-21 | 2017-12-29 | 张家港市思杰五金工具有限公司 | Synthetic method for molybdenum base surface oxidation-resistant coating powder |
| CN106631008B (en) * | 2016-09-26 | 2019-11-08 | 四川大学 | A kind of bulk does not split high density nano crystalline substance gadolinium zirconate ceramics and preparation method thereof |
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| CN1733611A (en) * | 2005-08-12 | 2006-02-15 | 安泰科技股份有限公司 | Zirconium dioxide nano powder material preparation method |
| CN1927511A (en) * | 2006-09-22 | 2007-03-14 | 北京工业大学 | Preparation method of TiB2 nanometer micrometer structure feeding for hot spraying |
| CN101049956A (en) * | 2007-06-06 | 2007-10-10 | 上海大学 | Method for preparing monodisperse, non agglomerate Nano zinc oxide with high ultraviolet absorption |
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