CN103172346B - Method for preparing porous nano magnesium silicon based block body thermoelectric material by hot press method in electric field reaction - Google Patents
Method for preparing porous nano magnesium silicon based block body thermoelectric material by hot press method in electric field reaction Download PDFInfo
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Abstract
The invention relates to a method for preparing a porous nano magnesium silicon based block body thermoelectric material by a hot press method in an electric field reaction, and belongs to the technical field of thermoelectric materials and preparation methods. The method is characterized in that the method for preparing the porous nano Mg2Si-based block body thermoelectric material by the hot press method in the electric field reaction realizes reactive synthesis and compact sintering of Mg2Si in one step, so that the method is simple in step, low in cost, and high in purity of products. Various doping substances are convenient to add, and the products have porous nano-structures. Sustained pollution to the products in a multi-step preparation method can be effectively avoided. Meanwhile, reaction and compact sintering are performed at the same time, so that the temperature and time required by the preparation of products are reduced, and grain coarsening is effectively inhibited. Under the effect of protective gases, reaction byproducts are gathered in grain boundary in the form of nanoholes, so that grain growth is further inhibited and phonon scattering is enhanced. The generated products are completely reacted, the grain size is less than 70nm, the sectional hole ratio is about 5-15%, and holes and the nanocrystals coexist to the benefit of reducing the heat conductivity of the products.
Description
Technical field
Electric field reactive hot pressing of the present invention is prepared the method for the silica-based block thermoelectric material of porous nano magnesium, belongs to thermoelectric material and preparation method's technical field, is specifically related to a kind of electric field reactive hot pressing one step that adopts and prepares porous nano Mg
2the method of Si base block thermoelectric material, utilizes the method a step to realize Mg
2the reaction of Si is synthesized and densification sintering, and product is the Mg that granularity is less than the structure of 70nm and contains certain nanoporous
2si base thermoelectricity material.The Mg that utilizes the method to prepare
2si base block thermoelectric material has the feature of porous and nanometer, contributes to obtain higher thermo-electric conversion performance.
Background technology
Mg at present
2the preparation method that Si is traditional utilizes the Mg powder of simple substance and Si powder direct reaction to form, or utilizes other method to make Mg
2after Si powder, then in vacuum pressure stove or plasma agglomeration stove, carry out densification and obtain block Mg
2si thermoelectric material.The subject matter existing is: because the two fusing point differs larger, cause complicated process of preparation, and length consuming time, sintering later stage grain growth is serious.Utilize MgH
2powder replaces after pure Mg powder, can effectively fall the content that reduces MgO in product, reduces temperature of reaction to 350 ℃, after the replacement(metathesis)reaction of 15-20 hour, can obtain nano level Mg
2si powder, but inevitably again introduce impurity in the densification sintering process in later stage, and sintering temperature is 650-700 ℃, causes grain growth serious, seriously reduced Mg
2the thermoelectricity transmission performance of Si thermoelectric material.
Summary of the invention
Electric field reactive hot pressing of the present invention is prepared the method for the silica-based block thermoelectric material of porous nano magnesium, and object is: prepare Mg in order to overcome above-mentioned technique
2the deficiency of Si thermoelectric material, the present invention has designed a kind of electric field reactive hot pressing one step and has prepared porous nano Mg
2the method of Si block thermoelectric material, the method is conducive to overcome in traditional technology due to long reaction time, high product coarse grains and the high deficiency of MgO foreign matter content of causing of sintering temperature, a step makes nanometer Mg
2si base block materials, in addition, is conducive to determine bundle effect inhibiting grain growth by crystal boundary by introduce a small amount of nanoporous to crystal boundary, and strengthens phon scattering by quantum well effect, further reduces thermal conductivity and improves thermoelectricity capability.
Electric field reactive hot pressing of the present invention is prepared the method for the silica-based block thermoelectric material of porous nano magnesium, it is characterized in that one adopts electric field reactive hot pressing one step to prepare porous nano Mg
2the method of Si base block thermoelectric material, the method is to carry out in the auxiliary synthetic furnace of electric field-activate pressure, additional industrial frequency AC electric field and uniaxial pressure are by promoting MgH
2interface close contact and the transport of substances of powder, nanometer Si powder, a small amount of Y powder and Bi powder, synchronously complete the sintering densification of chemical reaction and product powder, prepares the starting material MgH of this material
2granularity≤45 μ the m of powder, purity>=99.5%, granularity≤the 50nm of nanometer Si powder, purity>=99.90%, the granularity≤45 μ m of rare earth metal y powder, purity>=99.5%, granularity≤45 μ the m of heavy metal Bi powder, purity>=99.5%, mole mixture ratio example is (2-x): (1-y): x:y(x≤0.01, y≤0.01), reactional equation is: (2-x) MgH
2+ xY+(1-y) Si+yBi=Mg
2-xy
xsi
1-ybi
y+ (2-x) H
2(1) (x≤0.01, y≤0.01), under the effect of additional inert protective gas, the by product H of generation
2slowly overflow, by reducing oxidation potential, prevent magnesian further formation, in later stage sintering process, remaining hydrogen is gathered in crystal boundary gradually simultaneously, crystal boundary is played to pinning effect, main manifestations is that the crystal boundary displacement producing in the time that diffusing atom flows to pore by crystal boundary has changed pore surface curvature radius, and the chemical potential gradient that this radius-of-curvature the causes motivating force of grain growing just, in the time that atom flows to crystal boundary by hole, in sub-macroscopic view, be just presented as that grain growing is obstructed, concrete grammar and processing step are:
1) first by the reactant MgH of granularity≤45 μ m and purity>=99.5%
2the heavy metal Bi powder of rare earth metal y powder, granularity≤45 μ m and purity>=99.5% of nanometer Si powder, granularity≤45 μ m and purity>=99.5% of powder, granularity≤50nm and purity>=99.90%, with (2-x): (1-y): the molar ratio of x:y mixes (x≤0.01, y≤0.01), assurance in ball milling 1-3 hour mixes, and forms mixed powder 9;
2) then mixed powder 9 is placed between the seaming chuck 6 and push-down head 7 of graphite jig 4; the graphite jig assembling is placed in to reaction cavity 3; contact with lower electrode 5 with top electrode 2; be evacuated to below 10Pa; then in cavity, pass into inert protective gas 11 by gas cylinder 12, until pressure reaches 10 in cavity
5pa also keeps;
3) connect power frequency AC 10 unidirectional pressurization 1, realize synchronous reaction and sintering densification, it is 30-40 ℃/min that powder heat-up rate is set, in the time that temperature reaches 350 ℃, insulation 10-15 minute, to guarantee that powder fully reacts and carries out sintering, in this process, apply the pressure of 30MPa, then continue to be warming up to after 450-550 ℃, apply the uniaxial pressure of 70-100MPa, insulation 5-10min, eventually sever power supply, sample furnace cooling after unloading.Preparation process technical process as shown in Figure 2.
The present invention is that a kind of beneficial effect of the method for preparing the silica-based block thermoelectric material of porous nano magnesium is: the method operation is simple, and cost is low, and resultant purity is high, the various dopants of convenient interpolation, and resultant has porous nanometer structure.The codope of transition metal Y and heavy metal Bi can improve the concentration of donor element, and then increases the quantity of current carrier, reaches the object of improving electrical property.Effectively avoid the chronic pollution to product in multistep preparation method.Meanwhile, reaction and sintering densification synchronously carry out, and have reduced product and have prepared needed temperature and time, effectively suppress grain coarsening.Under shielding gas effect, byproduct of reaction is gathered in crystal boundary with the form of nano aperture, and further inhibiting grain growth also strengthens phon scattering.The product generating reacts completely, and grain-size is about 40nm, and section hole ratio is about 5-15%, and co-existing in of hole and nanocrystal is conducive to reduce product thermal conductivity.
Accompanying drawing explanation
Fig. 1 reaction unit fundamental diagram
1-impressed pressure 2-top electrode 3-reaction cavity 4-graphite jig 5-lower electrode 6-seaming chuck 7-push-down head 8-thermopair 9-reaction powder 10-power frequency AC 11-inert protective gas 12-gas cylinder
Fig. 2 preparation process process flow sheet
embodiment:
embodiment 1
By reactant MgH
2powder (granularity≤45 μ m, purity>=99.5%), nanometer Si powder (granularity≤50nm, purity>=99.90%), rare earth metal y powder (granularity≤45 μ m, purity>=99.5%) and heavy metal Bi powder (granularity≤45 μ m, purity>=99.5%) mole mixture ratio example be 1.995:0.995:0.005:0.005 (x=0.005, y=0.005), assurance in ball milling 1-3 hour mixes, form mixed powder 9, then mixed powder 9 is placed between the seaming chuck 6 and push-down head 7 of graphite jig 4, the graphite jig assembling is placed in to reaction cavity 3, contact with lower electrode 5 with top electrode 2, be evacuated to below 10Pa, then in cavity, pass into Ar shielding gas 11 by gas cylinder 12, until pressure reaches 10 in cavity
5pa also keeps.Connect power frequency AC 10 unidirectional pressurization 1, realize synchronous reaction and sintering densification.It is 35 ℃/min that powder heat-up rate is set, and in the time that temperature reaches 350 ℃, is incubated 10 minutes, to guarantee that powder fully reacts and carries out sintering, in this process, apply the pressure of 30MPa, then continue to be warming up to after 450 ℃, apply the uniaxial pressure of 70MPa, insulation 15min.Eventually sever power supply, sample furnace cooling after unloading.The product generating reacts completely, and dense structure's degree is 75.3%, the about 40nm of grain-size.
By reactant MgH
2powder (granularity≤45 μ m, purity>=99.5%), nanometer Si powder (granularity≤50nm, purity>=99.90%), rare earth metal y powder (granularity≤45 μ m, purity>=99.5%) and heavy metal Bi powder (granularity≤45 μ m, purity>=99.5%) mole mixture ratio example be 1.995:0.099:0.005:0.01 (x=0.005, y=0.01), assurance in ball milling 1-3 hour mixes, form mixed powder 9, then mixed powder 9 is placed between the seaming chuck 6 and push-down head 7 of graphite jig 4, the graphite jig assembling is placed in to reaction cavity 3, contact with lower electrode 5 with top electrode 2, be evacuated to below 10Pa, then in cavity, pass into He shielding gas 11 by gas cylinder 12, until pressure reaches 10 in cavity
5pa also keeps.Connect power frequency AC 10 unidirectional pressurization 1, realize synchronous reaction and sintering densification.It is 40 ℃/min that powder heat-up rate is set, and in the time that temperature reaches 350 ℃, is incubated 15 minutes, to guarantee that powder fully reacts and carries out sintering, in this process, apply the pressure of 30MPa, then continue to be warming up to after 550 ℃, apply the uniaxial pressure of 70MPa, insulation 15min.Eventually sever power supply, sample furnace cooling after unloading.The product generating reacts completely, and dense structure's degree is 91.5%, the about 53nm of grain-size.
By reactant MgH
2powder (granularity≤45 μ m, purity>=99.5%), nanometer Si powder (granularity≤50nm, purity>=99.90%), rare earth metal y powder (granularity≤45 μ m, purity>=99.5%) and heavy metal Bi powder (granularity≤45 μ m, purity>=99.5%) mole mixture ratio example be 1.99:0.99:0.01:0.01 (x=0.01, y=0.01), assurance in ball milling 1-3 hour mixes, form mixed powder 9, then mixed powder 9 is placed between the seaming chuck 6 and push-down head 7 of graphite jig 4, the graphite jig assembling is placed in to reaction cavity 3, contact with lower electrode 5 with top electrode 2, be evacuated to below 10Pa, then in cavity, pass into 50%Ar+50%He shielding gas 11 by gas cylinder 12, until pressure reaches 10 in cavity
5pa also keeps.Connect power frequency AC 10 unidirectional pressurization 1, realize synchronous reaction and sintering densification.It is 40 ℃/min that powder heat-up rate is set, and in the time that temperature reaches 350 ℃, is incubated 15 minutes, to guarantee that powder fully reacts and carries out sintering, in this process, apply the pressure of 30MPa, then continue to be warming up to after 550 ℃, apply the uniaxial pressure of 100MPa, insulation 10min.Eventually sever power supply, sample furnace cooling after unloading.The product generating reacts completely, and dense structure's degree is 99.2%, the about 67nm of grain-size.
Claims (1)
1. electric field reactive hot pressing is prepared the method for the silica-based block thermoelectric material of porous nano magnesium, it is characterized in that one adopts electric field reactive hot pressing one step to prepare porous nano Mg
2the method of Si base block thermoelectric material, the method is to carry out in the auxiliary synthetic furnace of electric field-activate pressure, additional industrial frequency AC electric field and uniaxial pressure are by promoting MgH
2interface close contact and the transport of substances of powder, nanometer Si powder, a small amount of Y powder and Bi powder, synchronously complete the sintering densification of chemical reaction and product powder, prepares the starting material MgH of this material
2granularity≤45 μ the m of powder, purity>=99.5%, the granularity≤50nm of nanometer Si powder, purity>=99.90%, granularity≤45 μ the m of rare earth metal y powder, purity>=99.5%, the granularity≤45 μ m of heavy metal Bi powder, purity>=99.5%, mole mixture ratio example is (2-x): (1-y): x:y, and in formula, x=0-0.001, y=0-0.001, reactional equation is: (2-x) MgH
2+ xY+(1-y) Si+yBi=Mg
2-xy
xsi
1-ybi
y+ (2-x) H
2(1), in formula, x=0-0.001, y=0-0.001, under the effect of additional inert protective gas, the by product H of generation
2slowly overflow, by reducing oxidation potential, prevent magnesian further formation, in later stage sintering process, remaining hydrogen is gathered in crystal boundary gradually simultaneously, and crystal boundary is played to pinning effect, and the crystal boundary displacement producing in the time that diffusing atom flows to pore by crystal boundary has changed pore surface curvature radius, and the chemical potential gradient that this radius-of-curvature the causes motivating force of grain growing just, in the time that atom flows to crystal boundary by hole, in sub-macroscopic view, be just presented as that grain growing is obstructed, concrete grammar and processing step are:
1) first by the reactant MgH of granularity≤45 μ m and purity>=99.5%
2the heavy metal Bi powder of rare earth metal y powder, granularity≤45 μ m and purity>=99.5% of nanometer Si powder, granularity≤45 μ m and purity>=99.5% of powder, granularity≤50nm and purity>=99.90%, with (2-x): (1-y): the molar ratio of x:y mixes, in formula, x=0-0.001, y=0-0.001, assurance in ball milling 1-3 hour mixes, and forms reaction powder (9);
2) then will react powder (9) is placed between the seaming chuck (6) and push-down head (7) of graphite jig (4); the graphite jig assembling is placed in to reaction cavity (3); contact with lower electrode (5) with top electrode (2); be evacuated to below 10Pa; then in cavity, pass into inert protective gas (11) by gas cylinder (12), until pressure reaches 10 in cavity
5pa also keeps;
3) connect power frequency AC (10) unidirectional pressurization, realize synchronous reaction and sintering densification, it is 30-40 ℃/min that reaction powder (9) heat-up rate is set, in the time that temperature reaches 350 ℃, insulation 10-15 minute, to guarantee that powder reaction powder (9) fully reacts and carries out sintering, in this process, apply the pressure of 30MPa, then continue to be warming up to after 450-550 ℃, apply the uniaxial pressure of 70-100MPa, insulation 5-10min, eventually sever power supply, sample furnace cooling after unloading.
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| CN104109770B (en) * | 2014-07-18 | 2016-05-11 | 太原理工大学 | Microwave is assisted MgH2Solid reaction process is prepared Mg2SixSn1-xBiyThe method of base thermoelectricity material |
| CN106913582B (en) * | 2015-12-28 | 2020-04-17 | 中国科学院上海硅酸盐研究所 | Magnesium silicide nano material and preparation method and application thereof |
| CN106825585A (en) * | 2016-11-15 | 2017-06-13 | 上海电机学院 | Electric discharge quick consolidation method and device that a kind of titanium chip circulation is remanufactured |
| CN106694891A (en) * | 2016-11-15 | 2017-05-24 | 上海电机学院 | Ball milling electric field pressure-assisted sintering remanufacturing method and device of titanium chips |
| JP6536615B2 (en) * | 2017-03-31 | 2019-07-03 | トヨタ自動車株式会社 | Thermoelectric conversion material and method for manufacturing the same |
| JP6981094B2 (en) * | 2017-08-15 | 2021-12-15 | 三菱マテリアル株式会社 | Manufacture method of magnesium-based thermoelectric conversion material, magnesium-based thermoelectric conversion element, and magnesium-based thermoelectric conversion material |
| CN108963064B (en) * | 2017-12-28 | 2019-11-29 | 中国科学院物理研究所 | Hot pressed sintering device, the block thermoelectric material of micro-nano porous structure and its preparation method |
| CN109534385B (en) * | 2018-11-06 | 2020-11-06 | 武汉理工大学 | Nano-pore-rich silver sulfide and rapid preparation method thereof |
| CN110116206A (en) * | 2019-04-22 | 2019-08-13 | 武汉科技大学 | A kind of dedicated AC power frequency discharge sintering equipment of thermoelectric material and sintering method |
| CN112614929B (en) * | 2021-01-05 | 2021-08-13 | 哈尔滨工业大学 | Method for constructing grain boundary holes to improve SnTe thermoelectric performance |
| CN117645301B (en) * | 2024-01-30 | 2024-04-02 | 山东硅纳新材料科技有限公司 | High-purity submicron-order Mg 2 Si preparation method and continuous vacuum rotary kiln |
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