CN110777380A - Method for expanding melting point and solidifying point range of nano porous gold - Google Patents
Method for expanding melting point and solidifying point range of nano porous gold Download PDFInfo
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- CN110777380A CN110777380A CN201911079980.8A CN201911079980A CN110777380A CN 110777380 A CN110777380 A CN 110777380A CN 201911079980 A CN201911079980 A CN 201911079980A CN 110777380 A CN110777380 A CN 110777380A
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
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- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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- C01B32/182—Graphene
- C01B32/184—Preparation
- C01B32/186—Preparation by chemical vapour deposition [CVD]
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
- C23C16/26—Deposition of carbon only
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Abstract
The invention discloses a method for expanding the melting point and the solidifying point range of nano-porous gold, which comprises the steps of firstly preparing the nano-porous gold, namely NPG, by utilizing an alloy removing method; then the prepared NPG is used as a catalyst to catalyze CH
4The pyrolysis reaction is carried out by flushing the whole gas system with inert gas for 40 minutes under normal pressure and then introducing CH
4And heating the gas to 346 ℃, and generating obvious catalytic phenomenon to prepare the NPG under the constraint of the graphene. The temperature range of the NPG of the invention for complete melting and complete solidification is expanded to about 270 ℃, which is hopeful to expand the application range of graphene and NPG and also can be used for meltingThe study of the point and the overheating of the crystal plays a promoting role.
Description
Technical Field
The present invention relates to nanoporous gold (NPG), and more particularly, to a method for forming a graphene layer on the surface of NPG in the presence of gas phase catalysis, thereby enabling the melting point and freezing point range to be expanded.
Background
The overheating and overcooling of crystals has been of great interest to researchers due to the importance of the melting process. For crystals, it is quite difficult to heat the crystal above its normal melting point without melting, since the nucleation barrier for melting on the crystal surface is extremely small. If the surface (interface) structure of the metal particles can be altered such that the melt is difficult to nucleate at the interface, the melting behavior of the particles will be quite different, potentially overheating the crystal. At present, researches prove that Ag particles coated in Au are overheated for 1min at 24k above a melting point, but most of the obtained crystal overheating phenomena still belong to grain mosaic samples, and the stability is difficult to guarantee. The supercooling of the crystal means that the supercooled liquid can exist in a metastable state without solidification, the traditional melt is acknowledged to have the limit supercooling degree of 0.2Tm, the obtained solidification structure has larger segregation and lower alloying degree. If stable overheating and supercooling of crystals can be simultaneously realized, it is possible to prepare a novel material which still has reliable mechanical, optical, electrical and other properties under a super-normal environment (such as high temperature and high pressure), and the application temperature range of the material can be greatly increased. Therefore, it is necessary to find a preparation method which can realize the supercooling of the crystal and can greatly realize the stable overheating of the crystal.
NPG is a widely used porous metal, has double functions of function and structure, and is a multipurpose engineering material with excellent performance. We find that when methane catalyzes NPG, the melting point of the generated NPG in a graphene constraint state can be greatly improved, so that the conventional melting point of the crystal is heated to be close to 270 ℃ without melting, and a stable crystal overheating phenomenon is realized. Meanwhile, the temperature is reduced to be below the freezing point of the crystal without solidification, and the supercooling phenomenon of the crystal is realized. Based on the discovery, a preparation method which can realize crystal supercooling and can greatly realize the stable overheating range of the crystal to 270 ℃ is found, and the core idea of the patent application is provided.
Disclosure of Invention
The invention aims to overcome the defects of unstable crystal overheating and small supercooling and overheating temperature ranges of crystals in the prior art, and provides a simple and efficient method for expanding the melting point and the freezing point range of nano porous gold.
The invention is realized by the following technical scheme:
a method for expanding the melting point and the solidifying point range of nano porous gold comprises the following specific steps:
(1) preparing nano-porous gold (NPG) by using a dealloying method:
the Au-Ag alloy film is concentrated HNO in a constant temperature water bath at 25 DEG C
3Dealloying for 45 minutes, taking out the dealloying film, and then immersing the dealloying film into ultrapure water for 20 minutes to prepare an NPG (nitrogen phosphorus glass) sheet;
(2) subjecting the NPG flakes prepared in step (1) to catalytic CH
4And (3) pyrolysis reaction:
NPG flakes in ultrapure water were collected using a heater chip, which was assembled into an in-situ TEM gas phase system, the entire gas system first flushed with inert gas for 40 minutes at atmospheric pressure, then CH was introduced
4Gas, then at 20 ℃ for min
–1The heating rate of (a) is increased to 346 ℃, and obvious catalytic phenomenon occurs; and observing the growth of the graphene on the NPG surface, and stopping heating after the graphene layer on the NPG surface grows completely to prepare the NPG bound by the graphene.
The NPG prepared in the step (1) can also be obtained by an electrochemical method or a template method.
The ligament size of the NPG prepared by the dealloying method in the step (1) is not limited.
The carrier for putting the NPG slice in the step (2) can be a heating chip, a gas phase chip or a glass slide.
The acceleration voltage of the in-situ TEM gas phase system in the step (2) is 200 kv.
The inert gas of the step (2) is nitrogen, argon or other inert gases.
The graphene layer formed in the step (2) may be a single layer or a multilayer, and may exist in partial regions or in a large area.
The melting point and the solidifying point of the NPG constrained by the graphene are enlarged to about 270 ℃, so that the cognition of people on material melting and crystal overheating and supercooling is improved, and the application range of the graphene and the NPG is expected to be expanded.
Drawings
FIG. 1 is a transmission electron microscope photograph of NPG of example 1;
FIG. 2 is a high resolution picture of NPG under graphene constraints of example 1;
FIG. 3 is the NPG diffraction image of example 1 under graphene tethering at 1230 ℃;
FIG. 4 is the NPG diffraction image of example 1 under graphene tethering at 1210 deg.C;
FIG. 5 is the NPG diffraction image of example 1 under graphene tethering at 980 ℃;
figure 6 is the NPG diffraction image of example 1 under graphene tethering at 960 ℃.
Detailed Description
The invention is further illustrated by the following specific examples, which are intended to be illustrative only and not limiting.
Example 1
(1) Preparation of nanoporous gold using dealloying
The nano-porous gold is prepared by using a dealloying method. Dealloying a 12Ka Au-Ag alloy film with the thickness of 100nm in concentrated HNO3 at 25 ℃ in a constant-temperature water bath for 45 minutes, taking out the dealloying film, and then immersing the dealloying film in ultrapure water for 20 minutes. NPG with ligament width of 50nm was prepared. FIG. 1 is a transmission electron microscope image of NPG of example 1, and it can be seen that the width of the prepared nanoporous gold ligament is around 50 nm.
(2) Subjecting the NPG in the step (1) to CH catalysis
4Pyrolysis reaction
NPG pieces in ultrapure water were collected using a heating chip, NPG particles having a three-dimensional structure of 50nm were evenly distributed on the heating chip, and the chip was assembled into an in-situ TEM (acceleration voltage used here is 200kv) gas phase system. The whole gas system was flushed with argon at atmospheric pressure for 40 minutes and CH was then introduced
4A gas. Followed by a temperature of 20 ℃ for min
–1The heating rate of (a) was increased to 346 c (significant catalysis occurred). We observed that graphene began to grow on the surface of NPG by using in-situ electron microscopeThe heating was stopped when the graphene was found to be completely grown in NPG. NPG under graphene tethering, as shown in fig. 2.
(3) Subjecting the NPG under the constraint of the graphene obtained in the step (2) to 50 ℃ min
–1Heating was continued while observing the melting process by transmission electron microscopy, and electron diffraction spectroscopy was performed on the observed regions where melting was likely to occur. The diffraction pattern heated to 1210 ℃ indicated that there was still an incompletely melted NPG crystal structure, and the crystals were not completely melted on the surface and were in an overheated state, as shown in FIG. 3; when heated to 1230 ℃, the NPG electron diffraction pattern in the graphene-bound state becomes a distinct amorphous ring, indicating that the NPG crystals under graphene-bound have completely melted, as shown in fig. 4; the above situation illustrates the existence of a melting point between 1230 ℃ and 1210 ℃. After reaching the melting point, the heating chip is cooled for 30 min
–1Continuing to cool to 980 ℃, wherein the diffraction pattern at the moment is an amorphous ring, which indicates that the NPG crystal bound by the graphene is not completely solidified and is in a supercooled state, as shown in fig. 5; the temperature was further decreased to 960 deg.C, at which point the diffraction pattern showed crystalline and polycrystalline behavior, indicating that solidification had been completed, as shown in FIG. 6. From this, it is known that there is a freezing point between 980 ℃ and 960 ℃ and we can speculate that the temperature range for complete melting and complete freezing is around 270 ℃.
The electron microscope characterization means can also be characterized by DSC.
Claims (7)
1. A method for expanding the melting point and the solidifying point range of nano porous gold comprises the following specific steps:
(1) preparing nano-porous gold (NPG) by using a dealloying method:
the Au-Ag alloy film is concentrated HNO in a constant temperature water bath at 25 DEG C
3Dealloying for 45 minutes, taking out the dealloying film, and then immersing the dealloying film into ultrapure water for 20 minutes to prepare an NPG (nitrogen phosphorus glass) sheet;
(2) subjecting the NPG flakes prepared in step (1) to catalytic CH
4And (3) pyrolysis reaction:
collecting NPG flakes in ultrapure water using a heater chip, heating the chipThe plates were assembled into an in situ TEM gas phase system, the entire gas system was flushed with inert gas for 40 minutes at atmospheric pressure, and CH was then introduced
4Gas, then at 20 ℃ for min
–1The heating rate of (a) is increased to 346 ℃, and obvious catalytic phenomenon occurs; and observing the growth of the graphene on the NPG surface, and stopping heating after the graphene layer on the NPG surface grows completely to prepare the NPG bound by the graphene.
2. The method for extending the melting point and freezing point range of nanoporous gold according to claim 1, wherein the NPG prepared in step (1) can be obtained by electrochemical or templating method.
3. The method for expanding the melting point and freezing point range of nanoporous gold according to claim 1, wherein the ligament size of the NPG prepared by the dealloying method of step (1) is not limited.
4. The method for extending the melting point and freezing point range of nanoporous gold according to claim 1, wherein the NPG thin slice of step (2) is placed on a carrier such as a heating chip, a gas phase chip or a glass slide.
5. The method for extending the melting and freezing point ranges of nanoporous gold according to claim 1, wherein the acceleration voltage applied to the in-situ TEM gas phase system of step (2) is 200 kv.
6. The method for extending the melting and freezing point ranges of nanoporous gold according to claim 1, wherein the inert gas of step (2) is nitrogen, argon or other inert gas.
7. The method for expanding the melting point and the freezing point range of nanoporous gold according to claim 1, wherein the graphene layer formed in the step (2) can be a single layer or multiple layers, and can exist in partial areas or large areas.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111302331A (en) * | 2020-02-24 | 2020-06-19 | 天津理工大学 | Method for preparing graphene |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111302331A (en) * | 2020-02-24 | 2020-06-19 | 天津理工大学 | Method for preparing graphene |
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Application publication date: 20200211 |