CN112110731A

CN112110731A - Sc2SC (metal-ceramic) laminated material and preparation method thereof

Info

Publication number: CN112110731A
Application number: CN202010820088.7A
Authority: CN
Inventors: 胡前库; 周爱国; 王李波; 夏启勋; 吴庆华; 秦双红; 张斌; 李丹丹
Original assignee: Henan University of Technology
Current assignee: Henan University of Technology
Priority date: 2020-08-14
Filing date: 2020-08-14
Publication date: 2020-12-22
Anticipated expiration: 2040-08-14
Also published as: CN112110731B

Abstract

The invention provides Sc₂SC layered material and preparation method thereof, and Sc₂The SC layered material belongs to a hexagonal system, the space group is P63/mmc, the unit cell parameters are:

α is 90 °, β is 90 °, γ is 120 °; during preparation, scandium powder, sulfur powder and carbon powder are used as raw materials, and are synthesized at high temperature under two atmosphere conditions of a vacuum closed environment and an argon environment by adjusting experimental conditions such as raw material proportion, temperature, heat preservation time and the like to obtain Sc₂SC phase. Sc produced by the invention₂The SC material can stably exist in the air environment at the temperature of below 500 ℃, and in argonIn a gaseous environment, Sc₂The SC material may remain stable up to 1100 ℃.

Description

Sc2SC (metal-ceramic) laminated material and preparation method thereof

Technical Field

The invention belongs to the technical field of MAX phase layered materials, and particularly relates to Sc₂SC layered material and its preparation method.

Background

The MAX phase is a general term of a series of ternary layered compounds, and MAX phase materials have comprehensive excellent properties of ceramics and metals. The ceramic material has excellent performances of high hardness, high melting point, strong corrosion resistance, stable chemical performance and the like, and simultaneously has excellent performances of high Young modulus, strong thermal shock resistance, strong oxidation resistance, strong damage tolerance, strong thermal stability, high electric/heat conduction, good electric conductivity, machinability and the like of a metal material. The special properties of MAX phase materials are due to their special structural and bonding characteristics. MAX phase has a uniform chemical formula of M_n+1AX_nWhere M is an early transition metal (Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, etc.), A is primarily a group III, IV element (Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, etc.), and X is C or N.

Since the last 60 s, more than 30 ternary transition metal carbides or nitrides were first synthesized by the Nowotny team, the members of the MAX phase family are continuously growing and new members are continuously being explored.

The MAX phase series layered materials have excellent properties of ceramics and metals due to the special bonding type between M, A and X atoms, and the unique properties of the materials enable the materials to have wide application prospects. As more MAX phase materials have been successfully prepared, researchers have not just stayed exploring existing MAX phase materials. Therefore, the prediction and synthesis of new MAX phase materials are more and more attractive to researchers.

Disclosure of Invention

In order to obtain a new MAX phase material, the invention adopts a high-temperature synthesis method to carry out experimental synthesis of Sc₂SC。

In order to achieve the above purpose, the invention provides the following technical scheme:

sc (Sc)₂SC layered material, said Sc₂The SC layered material belongs to a hexagonal system, the space group is P63/mmc, the unit cell parameters are:

α＝90°、β＝90°、γ＝120°。

one kind of Sc as described above₂The preparation method of the SC layered material comprises the steps of weighing scandium powder, sulfur powder and carbon powder according to a molar ratio Sc: S: C: 2 (0.2-1) to (1-1.3) (such as 2:0.2:1, 2:0.3:1.3, 2:0.4:1.3, 2:0.5:1.3, 2:0.7:1.3 and 2:0.9:1.3), uniformly mixing, pressing to obtain a primary biscuit, wrapping with carbon paper, pressing again to obtain a secondary biscuit, and then placing the secondary biscuit in a vacuum sealed environment at the temperature of 1000-1300 ℃ (such as 1050 ℃, 1100 ℃, 1150, 1200, 1250 and 1280 ℃) for heat preservation for 1-5 hours (such as 2, 3 and 4 hours) to obtain the product.

As described above with respect to Sc₂In the preparation method of the SC layered material, preferably, the primary biscuit and the secondary biscuit are both pressed under the pressure of 8-15 MPa (such as 9, 10, 12, 13 and 14 MPa).

As described above with respect to Sc₂In the preparation method of the SC layered material, preferably, the heat preservation time is 2-3 h (for example, 2.5 h).

As described above with respect to Sc₂The preparation method of the SC layered material preferably comprises the following steps of (1-1.3) molar ratio of Sc to S to C to 2, wherein S is 0.2-0.4.

As described above with respect to Sc₂The preparation method of the SC layered material preferably has the temperature condition of 1100-1300 ℃ (such as 1150, 1200, 1250 and 1280 ℃).

As described above with respect to Sc₂Preferably, the SC layered material is prepared by adding the obtained product into a nitric acid solution for impurity removal.

As described above with respect to Sc₂Preferably, the impurity removal operation specifically comprises the following steps: and (3) placing the obtained product in a nitric acid solution with the mass fraction of 15% at 40 ℃, and corroding for 3-4 h (for example, 3.2, 3.3 and 3.5 h).

As described above with respect to Sc₂Preferably, the granularity of the scandium powder is 200 meshes, and the purity is more than or equal to 99.9%.

As described above with respect to Sc₂Preferably, the granularity of the carbon powder is 200 meshes, and the purity of the carbon powder is more than or equal to 99.9 percent.

Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:

the method takes scandium powder, sulfur powder and carbon powder as raw materials, and tries to synthesize Sc at high temperature under two atmosphere conditions of a vacuum closed environment and an argon environment by adjusting experimental conditions such as raw material proportion, temperature, heat preservation time and the like₂SC phase. Sc was determined by characterization and analysis of samples prepared under different conditions using laboratory instruments such as X-ray diffractometers (XRD) and Scanning Electron Microscopes (SEM)₂Optimal synthesis conditions for the SC phase. In a flowing argon environment, the synthesized sample contains a large amount of impure phase, Sc₂The SC phase content is less. Obtaining Sc by adjusting the conditions of heat preservation time, raw material ratio, temperature and the like in a vacuum closed environment₂The optimal synthesis conditions for the SC phase are: the raw materials have the molar ratio of Sc to S to C of 2 to 0.2 to 1, the temperature of 1300 ℃ and the heat preservation for 3 hours. Under these conditions, Sc in the synthesized sample₂The SC phase is already the main phase, but a certain amount of Sc is often present in the sample₂OC foreign phase, and possibly Sc₃C₄And (3) impurity phase.

The Sc of the nitric acid solution can be successfully removed by successfully selecting the nitric acid solution through adjusting the experimental conditions such as the type of acid (alkali), the reaction temperature, the reaction time, the concentration of the acid (alkali) and the like₃C₄Impurity phase, the best impurity removing condition is as follows: nitre of 15% concentrationAcid, at 40 deg.C for 3-4 hr.

For removing Sc₃C₄Later Sc₂As a result of XRD of the SC sample, refield refinement was performed. To give Sc₂The lattice parameters of the SC phase are:

α is 90 °, β is 90 °, and γ is 120 °. Sc of a target product in a sample₂SC content 92.4 wt%, hetero-phase Sc₂The OC content was 7.6 wt.%. SEM results show Sc in the samples₂The SC phase is a layered structure and has typical MAX phase morphology characteristics. STEM clearly gives Sc₂The atomic arrangement of the SC phase is consistent with the results of theoretical calculation.

For Sc₂The SC phase is subjected to heat stability research and found to be stably present at the temperature below 500 ℃ in an air environment, and basically not oxidized, and when the temperature reaches above 500 ℃, oxide Sc begins to appear in a sample₂O₃. When the temperature exceeds 700 ℃, Sc₂SC is totally oxidized to Sc₂O₃. Under the argon atmosphere, Sc₂The SC phase may remain stable up to 1100 ℃.

Drawings

FIG. 1 is a temperature profile set for synthesis in a vacuum sealed environment;

FIG. 2 is an XRD pattern of a synthesized product under a vacuum sealing environment at different temperatures;

FIG. 3 is an XRD (X-ray diffraction) diagram of a synthesized product of scandium powder, sulfur powder and carbon powder in different molar ratios at 1200 ℃ and after heat preservation for 3 hours in a vacuum sealing environment;

FIG. 4 is an XRD diagram of a product synthesized under vacuum sealing environment with Sc, S, C being 2:0.2:1 and different temperatures and heat preservation for 3 h;

FIG. 5 is an XRD diagram of a product synthesized under vacuum sealing environment with Sc, S and C being 3:0.5:2 and different temperatures and heat preservation for 3 h;

FIG. 6 is an XRD diagram of a product synthesized under vacuum sealed environment with Sc, S, C being 2:0.2:1, 1300 ℃ and different time holding conditions;

FIG. 7 is an XRD diagram of a product synthesized under vacuum sealed environment with Sc, S, C being 3:0.5:2, 1300 ℃ and different time holding conditions;

FIG. 8 shows Sc₂The XRD refinement result of the SC sample;

FIG. 9 shows the purified Sc₂Scanning electron microscope images (SEM) of SC samples;

FIG. 10 shows Sc after purification₂Transmission Electron Microscopy (TEM) images of SC samples (a) TEM images; (b) [100 ]]A high angle annular dark field image of direction; (c) [100 ]]A directional high angle annular bright field image;

FIG. 11 shows Sc₂DSC and TG curves of SC samples in air;

FIG. 12 is an XRD pattern of the sample after half an hour incubation at different temperatures in an air environment;

FIG. 13 shows Sc after treatment at different temperatures in air₂SEM image of SC sample: (a)200 ℃ (b)500 ℃ (c)600 ℃ (d)700 ℃ (e)900 ℃ (f)1100 ℃;

FIG. 14 shows Sc₂DSC and TG curves of SC under argon;

FIG. 15 shows Sc after treatment at different temperatures under argon₂XRD pattern of SC sample;

FIG. 16 shows Sc after treatment at different temperatures in argon₂SEM image of SC sample: (a)200 deg.C (b)500 deg.C (c)700 deg.C (d)900 deg.C (e)1100 deg.C.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments that can be derived by one of ordinary skill in the art from the embodiments given herein are intended to be within the scope of the present invention.

The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The experimental methods for preparing ternary layered MAX phase materials mastered by researchers at present mainly comprise a vacuum pressureless sintering method, a hot pressing sintering method (HP), and self-propagating high-temperature synthesisThe method (SHS), the spark plasma sintering method (SPS), and the solid phase synthesis method. The invention tries to synthesize Sc at high temperature under two atmosphere conditions of vacuum environment and argon environment₂SC phase, the most suitable Sc is selected by adjusting experimental conditions such as raw material proportion, temperature, heat preservation time and the like₂SC phase synthesis conditions.

Embodiments of the invention first provide a Sc₂SC layered material, said Sc₂The SC layered material belongs to a hexagonal system, the space group is P63/mmc, the unit cell parameters are:

α＝90°、β＝90°、γ＝120°。

the embodiment of the invention also provides the Sc₂The preparation method of the SC layered material is a vacuum pressureless sintering method (capable of avoiding loss of a sulfur source in the reaction process), and specifically comprises the steps of weighing scandium powder, sulfur powder and carbon powder according to the molar ratio of Sc to S to C to 2 (0.2-1) to (1-1.3), uniformly mixing, pressing to obtain a primary blank, wrapping with carbon paper, pressing again to obtain a secondary blank, and placing the secondary blank in a temperature condition of 1000-1300 ℃ (according to the invention, a quartz tube is used as a vacuum closed container, the highest temperature which can be borne by the quartz tube is considered when the temperature is set, the quartz tube is softened when the temperature is 1300 ℃, and if the temperature is higher, the set vacuum environment can be failed so as not to achieve the original purpose of an experiment, so that the invention sets the high-temperature synthesis of Sc in the range of 1000-1300 ℃ under the vacuum environment and tries to synthesize Sc at high temperature₂And SC), preserving the heat for 1-5 hours in a vacuum closed environment to obtain the product.

In the embodiment of the invention, the primary biscuit and the secondary biscuit are both pressed under the pressure of 8-15 MPa.

In the examples of the present invention, in order to determine whether or not a sample after synthesis is a synthesis target product Sc₂SC, XRD testing was performed by: firstly, taking out a sample wrapped by carbon paper, and then polishing off a layer of white substance on the sample by using sand paperThe sample was then ground to a powder and a portion of the powder was removed for X-ray diffraction analysis. Testing parameters: the scanning speed is 10 degrees/min, the scanning angle range is 10-90 degrees, the step length is 0.002, the voltage is 40kV, and the current is 200 mA.

In the embodiment of the invention, the heat preservation time is preferably 2-3 h.

In the embodiment of the invention, the molar ratio is preferably Sc to S to C to 2 (0.2-0.4) to (1-1.3).

In the embodiment of the invention, the temperature condition is preferably 1100-1300 ℃.

Although the product obtained is Sc₂The SC layered material has a high content, but some impurities still exist, and for this reason, in the embodiment of the present invention, after the product is obtained, the product is added to a nitric acid solution to perform an impurity removal operation.

In the embodiment of the invention, the impurity removal operation specifically comprises the following steps: and (3) placing the obtained product in a nitric acid solution with the mass fraction of 15% at 40 ℃, and corroding for 3-4 hours.

In the embodiment of the invention, the particle size of the scandium powder is 200 meshes, and the purity is more than or equal to 99.9%.

In the embodiment of the invention, the granularity of the carbon powder is 200 meshes, and the purity is more than or equal to 99.9%.

For Sc₂The invention relates to a preparation method of an SC layered material, which carries out synthesis exploration in an argon atmosphere according to the operation process completely same as that of a vacuum closed environment, firstly carries out synthesis experiments under different temperature conditions of 1000 ℃, 1100 ℃, 1200 ℃, 1300 and 1400 ℃, and only observes Sc in XRD spectrograms of products obtained at 1200 ℃ and 1300 DEG C₂The peak position of the crystal diffraction peak of SC, but the relative intensity is very different from that calculated theoretically. The present inventors have attempted to explore synthetic Sc by increasing the amount of sulfur, taking into account that the sintering process in an argon atmosphere may cause the loss of elemental sulfur as a raw material₂The optimal raw material ratio of the SC is that the Sc is synthesized according to the molar ratio of Sc to S to C of 2:1:1, 2:2:1 and 2:3:1₂SC, but not Sc₂The peak of SC crystals increased. The invention also tries to change the holding time to synthesize Sc with better purity₂SC, too, does not achieve the desired effect.

Therefore, Sc was synthesized under an argon atmosphere₂SC, whose intensity and purity are far from theoretical calculations. Thus determining suitable synthetic Sc₂The environment of the SC is a vacuum closed environment.

The following description will discuss Sc by way of specific examples₂And (3) preparation process of the SC layered material.

Example 1

In the examples, scandium powder (purity not less than 99.9%, Shanghai Bingmai Co., Ltd., the same below) of 200 mesh was used as a scandium source, and carbon powder (not less than 99.9%, Shanghai Jing Ming Sheng Co., Ltd., the same below) and sulfur powder (lump, Shanghai Bimai Co., Ltd., the same below) of 200 mesh were used as a carbon source and a sulfur source, respectively. According to Sc₂Molar ratio of three elements in SC crystal 2:1: and 1, weighing three raw materials according to the proportion by using an electronic balance, mixing the three raw materials, and manually grinding the mixture in an agate grinding body for 2-3 hours. Then the uniformly mixed powder is placed in a die with phi of 10mm, the powder is pressed into a biscuit under the pressure of 10MPa by using a powder tablet press, then the biscuit with phi of 10mm is wrapped by carbon paper with the length of 3cm and the thickness of 0.1mm, the biscuit wrapped by the carbon paper is placed in a die with phi of 13mm, and the biscuit with phi of 13mm is pressed by using the powder tablet press in the same way. The biscuit is placed in a glass quartz tube (quartz tube, phi 20mm L20 cm, Chinese Bailibo), vacuum-sealed by a vacuum tube sealing machine (MRVS-1002, Chinese Bailibo), finally the quartz tube is placed in a high-temperature box furnace (1600 ℃ rapid heating box furnace, DZF type, Tianjin middle-ring material technology limited company), the temperature is raised at the temperature raising rate of 2 ℃/min exceeding 1100 ℃ for protecting the high-temperature box furnace according to the temperature raising curve shown in figure 1, so that the current in the furnace is prevented from being too high due to too high temperature raising rate, the temperature is lowered according to the program set after the heat preservation stage is finished, the experiment error is caused because the time of the temperature lowering stage is longer than the program set, and the temperature is raised to 1200 ℃ for heat preservation 3 hours.

Example 2

Example 2 the same as example 1 except that the incubation temperature was slightly different from that of example 1, and in example 2, the incubation temperature was 1000 ℃.

Example 3

Example 3 the same as example 1 except that the incubation temperature was slightly different from that of example 1, and in example 3, the incubation temperature was 1100 ℃.

Example 4

Example 4 the same as example 1 except that the incubation temperature was slightly different from that of example 1, and in example 4, the incubation temperature was 1300 ℃.

In order to determine the phase of the sintered sample, firstly, the sintered quartz tube is smashed to take out the sample, then the sample wrapped by the carbon paper is taken out, then a layer of white substance on the sample is ground by sand paper, and then the sample is ground into powder and part of the powder is taken out for X-ray diffraction analysis. The XRD results are shown in FIG. 2. FIG. 2 is a theoretical simulation Sc₂And comparing the XRD pattern of the SC with the XRD result under different sintering temperatures in a vacuum environment. Analysis of this figure reveals that Sc increases from 1000 ℃ to 1200 ℃₂The intensity of the SC peak becomes stronger gradually with increasing temperature, and the intensity of the crystal peak is large at 1200 ℃, indicating that the phase has become the main phase. At the same time, Sc and S oxides can be found at this temperature₂O₂A very weak peak of S. However, when the temperature is 1300 ℃, Sc thereof₂The peak of the SC crystal was reduced and Sc was found₂O₂The S crystal is enhanced. The reason for this is that the temperature is too high, and the sulfur raw material in the quartz tube is already gaseous during the reaction process, so that the pressure in the quartz tube is increased, the thickness of the glass quartz tube is reduced, the softening process is accelerated, and a little oxygen enters the vacuum-sealed quartz tube to participate in the reaction. In addition, the figure also shows that Sc and S compounds ScS exist in the range of 1000-1300 ℃, which shows that the loss of sulfur is effectively controlled in a vacuum environment, and the participation amount of the sulfur raw material reaction is greatly improved. This is in agreement with the speculation before the experiment, and the new method is expected to synthesize Sc with purity and intensity close to the theoretical calculation₂SC。

In conclusion, Sc in a vacuum environment₂The optimum synthesis temperature range of SC is 1100-1300DEG C. Wherein when the raw materials are mixed according to the molar ratio of Sc to S to C of 2 to 1, the temperature is 1200 ℃, and the temperature is kept for 3 hours, the Sc₂SC crystals were present in the highest amount in the sample. However, a certain amount of ScS impurity is present, because sulfur changes from solid to gas at high temperature, which is equivalent to the sulfur gas reacting with the solid of Sc and C, and because the gas contact area is larger than that of the solid, an excessive amount of sulfur gas reacting with the solid of Sc to produce ScS compound, which indicates that the S content in the raw material ratio is higher. It was therefore possible to try to explore Sc by reducing the proportion of raw sulphur on the basis of this temperature₂Optimum conditions for the preparation of SC, the invention was therefore tested in the following examples.

Example 5

Example 5 the same as example 1 except that the molar ratio of the starting materials was slightly different from that in example 1, in example 5, the molar ratio of Sc: S: C was 2:0.2:1, and the starting materials were used as synthetic materials.

Example 6

Example 6 the same as example 1 except that the molar ratio of the starting materials was slightly different from that in example 1, in example 6, the molar ratio of Sc: S: C was 2:0.4:1, and the starting materials were used as synthetic materials.

Example 7

Example 7 the procedure of example 1 was repeated except that the molar ratio of the starting materials was slightly different from that of example 1, and in example 7, the molar ratio of Sc: S: C was 2:0.6: 1.

Example 8

Example 8 the procedure of example 1 was repeated except that the molar ratio of the starting materials was slightly different from that of example 1, and in example 8, the molar ratio of Sc: S: C was 3:0.5:2, which was used as the starting material for the synthesis.

The X-ray diffraction results of the samples obtained in examples 5 to 8 are shown in FIG. 3. FIG. 3 is an XRD spectrum of a synthesized sample under a vacuum closed environment and with different raw material molar ratios, the temperature of 1200 ℃ and the holding time of 3 h. From this figure, it can be observed that when the molar ratio of scandium powder, sulfur powder and carbon powder is reduced from 2:1:1 to 2:0.2:1, Sc in the product is reduced₂The purity of SC is gradually increasing. But when the molar ratio of the three raw materials is 2:0.2:1 and 2:0.4:1, two are usedUnder such conditions that the phase of the resultant product is substantially the same, in which case Sc₂The SC diffraction peak is strongest and the content is highest. However, it is also said that the effect is not changed by decreasing the S content.

It can be seen from the figure that when the molar ratio of the sulfur element is reduced, the impurity ScS in the product is also reduced, and when the molar ratio of the three elements is reduced to 2:0.6:1, it was found from the XRD result that the impurity ScS was not found in the product at all. This verifies that in a molar ratio of the three elements of 2:1:1, the ratio of sulfur is reduced, and Sc can be improved₂Estimation of the purity of SC also verified that excess sulfur reacted with SC solid to produce SCs compound. In this set of experiments, Sc₂The purity of the SC crystal peak can be judged when the molar ratio of the three raw materials is 2:0.2:1, its Sc₂The purity of the SC crystal peak works best. However, when the molar ratio of these three elements is 3:0.5:2, Sc thereof₂The crystallization effect of the SC peak is better. However, from the XRD results under these two conditions, it can be seen that both contain a small amount of Sc₃C₄And Sc₂OC impurities. The impurity Sc appears in the product₂The reason for OC is that the quartz tube is softened at high temperature, which causes a small amount of oxygen in the air to enter and react to form oxides. Sc in the product₃C₄The reason for analysis of the impurities is that the sulfur element in the raw material is completely consumed in the reaction process and cannot continuously participate in the reaction, and the residual scandium powder and the carbon powder react to generate compounds of Sc and C. Therefore, it can be tried to observe whether the impurity Sc in the product can be observed by changing the reaction temperature based on the two conditions₃C₄And Sc₂The OC is removed.

Example 9

Example 9 the same as example 5 except that the incubation temperature was slightly different from example 5, in example 9, the incubation temperature was 1100 ℃.

Example 10

Example 10 the same as example 5 was repeated, except that the incubation temperature in example 10 was slightly different from that in example 5, and the incubation temperature in example 10 was 1300 ℃.

XRD tests were carried out on the samples of examples 5, 9 and 10, and as shown in FIG. 4, XRD patterns of three raw materials of scandium powder, sulfur powder and carbon powder in a molar ratio of 2:0.2:1 were obtained at 1100, 1200 and 1300 ℃ under the condition of heat preservation for 3 hours. As can be seen from the analysis of FIG. 4, when the three elements are present in a molar ratio of 2:0.2:1, Sc is contained in the range of 1100 to 1200 deg.C₃C₄And Sc₂OC, two impurities. When the temperature is increased to 1300 ℃, only a small amount of Sc is contained in the product₂OC impurities, Sc₂The purity of the SC phase is highest.

Example 12

Example 12 the same as example 8 except that the incubation temperature was slightly different from that of example 8, in example 12, the incubation temperature was 1100 ℃.

Example 13

Example 13 the same as example 8 except that the incubation temperature was slightly different from example 8, in example 13, the incubation temperature was 1300 ℃.

XRD tests were performed on the samples of examples 8, 12 and 13, and FIG. 5 shows that scandium powder, sulfur powder and carbon powder were used in a molar ratio of 3:0.5: 2. XRD patterns of the samples were synthesized under the conditions of 1100, 1200 and 1300 ℃ for 3 h. As can be seen from the analysis of FIG. 5, when the sintering temperature was increased from 1100 ℃ to 1300 ℃, the Sc in the product was increased₃C₄The impurities decrease with increasing temperature, and the Sc in the product decreases when the temperature increases by 1300 DEG C₃C₄The impurities are relatively low, which also demonstrates that the feedstock at this molar ratio still has unreacted sulfur feedstock, and can continue to participate in the reaction as the temperature increases. In addition, Sc is always accompanied in the product₂OC impurities, and therefore it can be concluded that the vacuum-sealed quartz tube is softened at high temperature, which results in a small amount of oxygen entering to react with the raw material to form oxides.

Example 14

Example 14 the same as example 10 except that the heat-retaining time was slightly different from example 10, and in example 14, the heat-retaining time was 2 hours.

Example 15

Example 15 the same as example 10 except that the incubation time was slightly different from example 10, in example 15, the incubation time was 4 hours.

The samples obtained in examples 10, 14 and 15 were subjected to X-ray diffraction measurement, and the XRD results thereof are shown in FIG. 6. FIG. 6 shows that the molar ratio of scandium powder, sulfur powder and carbon powder is 2:0.2: 1. and synthesizing the XRD pattern of the sample at 1300 ℃ for 2, 3 and 4 hours. It can be seen from FIG. 6 that the product contained Sc when the temperature was 1300 ℃ and held for 2h₃C₄Impurities due to the reduction of the holding time, impurities Sc₃C₄Does not react fully with the raw material sulfur to generate the target product Sc₂And (4) SC. When the heat preservation time is increased to 4 hours, Sc reappears in the product₃C₄Impurities due to increased incubation time, Sc₂SC is decomposed, and thus Sc can be judged to be synthesized₂The SC process is not suitable for long-term incubation at high temperatures.

FIG. 7 shows that scandium powder, sulfur powder and carbon powder are respectively prepared from three raw materials according to a molar ratio of 3:0.5: 2. and synthesizing the XRD pattern of the sample at 1300 ℃ for 2, 3 and 4 hours. From the analysis in fig. 7, when the three elements are expressed in mol 3:0.5:2 heating to 1300 ℃ and containing impurities Sc whether the holding time is reduced or increased₃C₄It can be seen that when the three raw materials are in the molar ratio, the better effect is not achieved by changing the heat preservation time.

In conclusion, Sc was synthesized in a vacuum environment₂The optimal temperature range of the SC is 1100-1300 ℃, and a series of experimental exploration proves that the loss of a sulfur source can be effectively controlled in a vacuum environment, and the Sc synthesized in the environment₂The purity and intensity of the SC peak were significantly higher than those synthesized under argon atmosphere.

Example 16

The present invention is directed to synthesis of Sc₂SC sample contains Sc₃C₄And Sc₂The OC impurity phase is removed from the sample by an acid (base) reaction. Through systematic research on the types of acids, reaction temperature, time and acid concentration, hydrochloric acid and sulfuric acid are found to be ineffective on impure phases, and hydrofluoric acid is used for preparing a main phase Sc₂SC is removed, and the Sc in the sample can be removed by potassium hydroxide solution at high temperature₃C₄Impurities, but some unknown impurities are introduced. And nitric acid can successfully remove Sc₃C₄The best process conditions are as follows: nitric acid with concentration of 15 percent, temperature of 40 ℃ and reaction time of 3 to 4 hours.

Therefore, in example 16, the product obtained in example 8 was used as a sample for impurity removal, and the following impurity removal treatment was performed: using nitric acid solution with concentration of 15% (mass fraction, the same below) to react at 40 ℃ for 3-4 hours, and then removing Sc in the high-temperature synthesized sample₃C₄Impurities, only Sc remaining in the sample₂SC and Sc₂OC two phases, and the target product Sc₂SC is the main phase. To determine the target product Sc₂Lattice parameter of SC, and determining Sc in the product₂SC content, i.e. only Sc in the sample after acid treatment₂OC、Sc₂The XRD results of the samples of SC were refined using Rietveld method, and the refined results are shown in fig. 8.

After refinement by the Rietveld method, the residual error between the XRD pattern obtained by simulation using the crystal structure model and the experimental XRD data is 9.02%. The results show that Sc in the sample₂SC content 92.4 wt%, hetero-phase Sc₂The OC content was 7.6 wt.%. Table 1 shows Sc obtained by the refining₂Comparison of the SC lattice parameter with the theoretically predicted lattice parameter. Only the lattice parameter c differs the most from theory, but also only 0.48%.

TABLE 1 Sc₂Lattice parameter of SC

In conclusion, the present invention predicts Sc according to theory₂SC crystal, and the ternary phase is successfully prepared by using a high-temperature synthesis method.

Preferably, Sc is synthesized in a vacuum closed environment₂The optimum temperature range of SC is 1100-1300 ℃. By adjusting the conditions of heat preservation time, raw material proportion, temperature and the like, the optimal synthesis conditions are as follows: the raw materials are proportioned as followsSc, S, C and C are 2:0.2:1, the temperature is 1300 ℃, and the heat preservation time is 3 h.

Sc₂Microstructure and thermal stability studies of SC Compounds

Sc synthesized for more intuitive validation₂Whether the microstructure of the SC corresponds to the typical MAX phase was first analyzed for microstructure on the higher purity samples. Sc (Sc)₂SC is taken as MAX phase ceramic material, and the chemical formula can be expressed as M_n+ ₁AX_n. Because the material has a special crystal structure and bonding types, the material has special properties which are not possessed by other materials, such as excellent electric/thermal conductivity, high modulus, low density, damage tolerance, high-temperature oxidation resistance, thermal shock resistance and the like. Therefore, the series of excellent properties of the material can make the ceramic material have very wide prospect in the future use. Sc produced by the invention₂SC exists in powder form, and mainly Sc is explored₂Thermal stability properties of SC.

In an experiment for exploring thermal stability, Sc was removed in example 16₃C₄The samples thereafter were subjected to thermal stability tests in different environments. Study Sc₂The SC changes the crystal form of the sample along with the rise of the temperature in different environments, the sintered sample is characterized and analyzed through XRD and SEM, and then the thermal stability of the material is known and summarized, and the application prospect of the material is explored.

1.Sc₂Microstructure study of SC Compound

FIG. 9 shows Sc₂Scan Electron microscope image (SEM) of SC, Sc can be seen₂The microscopic morphology of the SC crystal presents a lamellar characteristic, which accords with the characteristic that the conventional MAX phase morphology has a lamellar structure.

To verify Sc₂Whether the SC was successfully prepared, the most efficient and intuitive method was to perform high resolution scanning transmission microscope (STEM) analysis on the samples, as shown in fig. 10. FIG. 10(a) shows Sc₂The SC crystal particles are of a lamellar structure. FIG. 10(b) is a high angle annular dark field image with bright spots ScAtoms and S atoms. It can be seen that the S atom is located between two layers of Sc atoms. FIG. 10(C) is a high angle annular bright field image for viewing the lighter mass atoms, where the heavier mass Sc atoms appear black, the lighter mass C atoms appear bright, and the same atoms appear well-layered, thus giving rise to Sc₂The SC structure conforms to a typical 211MAX phase atomic arrangement. Sc is known from the above₂The atomic arrangement of the SC is consistent with the predicted theoretical model. This also demonstrates that the sample we synthesized is indeed Sc₂(iii) a SC compound.

2.Sc₂Thermal stability study of SC Compounds

2.1 thermal stability Studies in air Environment

First, the prepared sample was dried in a vacuum oven at 100 ℃ for 24 hours in order to remove residual water from the sample to ensure the accuracy of the following experiment; secondly, the dried sample is placed in a thermal analyzer for differential thermal analysis experiments under different environments, and is heated from room temperature to 1100 ℃ at the heating rate of 5 ℃/min, and the change of the sample in the heating process is observed. And finally, placing the sample in a crucible and a tube furnace without introducing gas to ensure that the sample is heated and insulated at different temperatures in the air environment, and performing characterization analysis on the final sample.

FIG. 11 is a DSC and TG curve of a sample under an air atmosphere. We can see from it that in an air environment, the weight of the sample decreases by about 17% with increasing temperature. At 180, 500, 620, 730, 980 ℃, a distinct exothermic peak appeared on the DSC curve. The rate of weight loss observed in the TG curve was slow in the vicinity of the exothermic peaks corresponding to these temperatures, and the TG curve showed a substantially constant weight as the temperature continued to rise above 1000 ℃. In order to search the reason of the weight loss phenomenon of the TG curve and know the change of the sample under the five temperatures, critical temperatures are respectively set in the range of about the five temperatures, the sample is heated to the critical temperatures and then is cooled after being kept warm for a period of time, and XRD analysis is carried out on the sample.

FIG. 12 shows the sample being heated in an air environmentXRD patterns to different temperatures. From the differential thermal analysis curve and the XRD pattern, when the sample is heated to 200 ℃ and kept for 0.5 hour, the sample after reaction is not changed basically, so the weight loss of the sample before 200 ℃ is caused by the gas adsorbed on the surface and the evaporation of the water. When the temperature is raised to 500 ℃, oxide Sc appears in the XRD pattern₂O₃However, Sc₂SC remains the major phase in the sample. The main phase and content of the sample when the temperature is increased to 600 ℃ are basically consistent compared with the sample after 500 ℃ reaction. While as the temperature continues to rise to 700 c, it can be seen from the XRD results that the major component of the sample is Sc₂O₃，Sc₂The intensity of the SC peak sharply decreases very weakly. When the temperature continues to rise to 900 deg.C, 1000 deg.C and 1100 deg.C, the phase in the sample is now substantially all Sc₂O₃. We believe that Sc₂The oxidation behavior of SC in air is around 480 ℃, the preliminary oxidation is started, and the two emission peaks at 500-600 ℃ are caused by the preliminary oxidation. With surface oxidation of Sc₂O₃Preventing further oxidation of the interior. When the temperature is further raised to about 700 ℃, the interior of the sample begins to oxidize, and the surface oxide film prevents the further oxidation, and finally the Sc₂Total oxidation of SC to Sc₂O₃. The peak of the emission at about 700 ℃ in the DSC curve is the result of this oxidation. The S and C elements in the original sample react with O to generate SO₂And CO₂And becomes gas to be discharged. Sc (Sc)₂SC only generates one oxide Sc in the whole oxidation process₂O₃. One Sc, considered solely by its weight₂The SC molecule loses one S atom and one C atom in the oxidation process to obtain 3O atoms, so that the obvious weight gain phenomenon at the temperature of 700-800 ℃ can be seen from the TG curve.

Sc can also be found in scanning electron microscopy₂Oxidation behavior of SC with increasing temperature. FIG. 13 is a scanning electron microscope image of samples treated at different temperatures in air, with the temperatures increasing from (a) to (f) to 200 deg.C, 500 deg.C, 600 deg.C, 700 deg.C, 900 deg.C, and 1100 deg.C, respectively. We can see from the scanning electron microscope imageSc in the graph (a) at a temperature of 200 DEG C₂The structure of the SC remains a layered structure. While when the temperature is 500 ℃ and 600 ℃, it can be seen from the graphs (b) and (c) that Sc₂The surface of the SC layer crystals began to appear as small grains, indicating that there was a partial oxide of Sc₂O₃Is generated. When the temperature continues to rise to 700 ℃ Sc is seen in graph (d)₂O₃The number of crystal grains of (2) rapidly increases. When the temperature continues to rise to 900 ℃ and 1100 ℃, Sc at this time can be observed from graphs (e) and (f)₂O₃The crystal grains of (2) have become larger crystals, and the original layered structure completely disappears.

2.2 thermal stability study under argon atmosphere

Shown in FIG. 14 is Sc₂DSC and TG profile of SC under argon atmosphere. From the observation in fig. 14, it can be seen that the DSC curve of the sample in the argon atmosphere has no significant heat absorption and release peak during the temperature increase. However, the slope of the DSC curve in the figure was observed to be slightly changed at about 170 ℃, 420 ℃, 600 ℃ and 750 ℃. To observe Sc₂The SC changes at these temperatures, so a series of experiments can be set around these temperature ranges, namely, after the samples are heated to the temperatures of 200 ℃, 500 ℃, 700 ℃, 900 ℃ and 1100 ℃, the temperature is kept for 0.5 hour, and flowing argon is always introduced during the period to ensure the argon environment.

FIG. 15 is an XRD pattern of a sample heated to different temperatures in an argon atmosphere, and from an observation of FIG. 15, it can be seen that when the temperature is increased from 200 ℃ to 1100 ℃, the sample is substantially unchanged from the sample before heating, which indicates that Sc₂SC is stable under argon atmosphere and basically has no decomposition reaction. This explains why no significant heat absorption and release peaks appear on the DSC curve in FIG. 14, and more fully explains that the TG curve is finally decreased by 17% due to Sc₂The SC samples lost surface adsorbed gas during heating. In addition, in order to observe the change of the sample after the high temperature treatment, the sample after the heat treatment was subjected to SEM characterization, and the scanning result thereof is shown in fig. 16. The temperature is increased from (a) to (e) to 200 ℃, 500 ℃, 700 ℃, 900 ℃ and 1100 ℃. From the scanned images, we can clearly seeIt was observed that the Sc still appears in the graph when the temperature of the argon atmosphere was increased from 200 ℃ to 1100 ℃₂Crystalline layered structure of SC. This also effectively demonstrates that there is no Sc found in the XRD patterns of FIGS. 5-7₂Any decomposition reaction of SC.

According to the structural characterization and the thermal stability research results, the Sc is found through SEM microstructure characterization₂SC is a layered structure, which is a typical morphological feature of MAX phase. The results of the scanning transmission electron microscope show Sc₂The atomic arrangement of the SC is consistent with the results of theoretical calculations. Under the air environment, Sc₂SC is stable at a temperature below 500 ℃ and does not substantially oxidize, and when the temperature reaches above 500 ℃, oxide Sc begins to appear in a sample₂O₃. Sc with increasing temperature₂O₃The content of (A) is also increased when the temperature is increased>At 700 ℃ Sc₂All SCs are oxidized to Sc oxide₂O₃. Under the argon atmosphere, Sc₂The SC phase was stable up to 1100 ℃.

In conclusion, the invention successfully discovers and synthesizes a new MAX phase Sc₂SC compound, the following conclusions were drawn:

1. scandium powder, sulfur powder and carbon powder are used as raw materials, and the experiment conditions such as raw material proportion, temperature, heat preservation time and the like are adjusted to try to synthesize Sc at high temperature under two atmosphere conditions of a vacuum closed environment and an argon environment₂SC phase. Under flowing argon atmosphere, Sc₂The optimal synthesis conditions for SC are: the raw materials have the molar ratio of Sc to S to C of 2 to 1, the temperature is 1200 ℃, and the temperature is kept for 3 hours. However, the synthesized sample contains a large amount of a heterogeneous phase, Sc₂The SC phase content is less. In a vacuum closed environment, Sc₂The optimum temperature range of SC is 1100-1300 ℃. By adjusting the conditions of heat preservation time, raw material proportion, temperature and the like, the optimal synthesis conditions are as follows: the raw materials have the molar ratio of Sc to S to C of 2 to 0.2 to 1, the temperature of 1300 ℃ and the heat preservation for 3 hours. Sc in the synthesized sample₂Although the SC phase is already the main phase, a certain amount of Sc is often present in the sample₃C₄And Sc₂An OC heterogeneous phase.

2. Removing Sc by acid (alkali) reaction method₂Heterogeneous phase in SC samples.By adjusting the experimental conditions such as the type of acid (alkali), the reaction temperature, the reaction time, the concentration of the acid (alkali) and the like, the experimental result shows that hydrochloric acid and sulfuric acid cannot react with a heterogeneous phase and have no effect on impurity removal; although Sc can be removed by hydrofluoric acid₃C₄And Sc₂OC hetero phase, but may be simultaneously combined with the main phase Sc₂SC reacts to form a new impure phase Sc₃F; the potassium hydroxide solution can remove Sc in the sample at high temperature₃C₄A heterogeneous phase, but with some unknown other impurities introduced; whereas the nitric acid solution successfully removed Sc₃C₄Impurity phase, the best impurity removing condition is as follows: 15 wt% nitric acid, 40 deg.c and reaction time of 3-4 hr.

3. Sc removal by using a Retiveld method₃C₄Sc after heterofacies₂Refining the XRD pattern of the SC sample to accurately obtain Sc₂Lattice parameter of the SC phase is

Based on the refined result, the target product Sc in the sample can be known₂SC content 92.4 wt%, hetero-phase Sc₂The OC content was 7.6 wt.%. SEM results show Sc in the samples₂The SC phase is a layered structure and has typical MAX phase morphology characteristics. Sc given by STEM results₂The atomic arrangement of the SC phase is consistent with the result of theoretical calculation, and the reliability and the accuracy of the result of the theoretical calculation are effectively verified.

4. Sc by DSC and TG₂The thermal stability of the SC phase in air and argon environments was investigated. Combining XRD and SEM results, Sc is found in air environment₂The SC phase is stable at temperatures below 500 ℃ and substantially does not oxidize, and when the temperature reaches above 500 ℃, the oxide Sc begins to appear in the sample₂O₃. When the temperature exceeds 700 ℃, Sc₂SC is totally oxidized to Sc₂O₃. In an argon atmosphere at a temperature ranging from room temperature to 1100 ℃, Sc₂SC phase does not occurThe decomposition change is always kept stable, and the method is suitable for the fields of high-temperature ceramics and the like.

The above description is only exemplary of the invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the invention is intended to be covered by the appended claims.

Claims

1. Sc (Sc)₂SC layered material, characterized in that the Sc₂The SC layered material belongs to a hexagonal system, the space group is P63/mmc, the unit cell parameters are:

α＝90°、β＝90°、γ＝120°。

2. sc (Sc)₂The preparation method of the SC layered material is characterized by weighing scandium powder, sulfur powder and carbon powder according to a molar ratio of Sc to S to C to 2 (0.2-1) to (1-1.3), uniformly mixing, pressing to obtain a primary biscuit, wrapping with carbon paper, pressing again to obtain a secondary biscuit, and then placing the secondary biscuit at a temperature of 1000-1300 ℃ in a vacuum closed environment, and preserving heat for 1-5 hours to obtain a product.

3. The Sc as set forth in claim 2₂The preparation method of the SC layered material is characterized in that the primary biscuit and the secondary biscuit are both pressed under the pressure of 8-15 MPa.

4. The Sc as set forth in claim 2₂The preparation method of the SC layered material is characterized in that the heat preservation time is 2-3 h.

5. The Sc as set forth in claim 2₂The preparation method of the SC layered material is characterized in that the molar ratio of Sc to S to C is 2, (0.2-0.4) and 1-1.3.

6. The Sc as set forth in claim 2₂SC layer materialThe preparation method of the material is characterized in that the temperature condition is 1100-1300 ℃.

7. The Sc as set forth in claim 2₂The preparation method of the SC layered material is characterized in that the product is obtained and then added into nitric acid solution for impurity removal.

8. The Sc according to claim 7₂The preparation method of the SC layered material is characterized in that the impurity removal operation specifically comprises the following steps: and (3) placing the obtained product in a nitric acid solution with the mass fraction of 15% at 40 ℃, and corroding for 3-4 hours.

9. The Sc as set forth in claim 2₂The preparation method of the SC layered material is characterized in that the granularity of the scandium powder is 200 meshes, and the purity is more than or equal to 99.9%.

10. The Sc as set forth in claim 2₂The preparation method of the SC layered material is characterized in that the granularity of the carbon powder is 200 meshes, and the purity is more than or equal to 99.9%.