A high-purity Ti3SiC2 bulk ceramic and its preparation method

Abstract

The present invention relates to a high-purity Ti3SiC2 bulk ceramic and a preparation method thereof. To address the problem of low Ti3SiC2 phase content in the RMI Ti3SiC2 bulk ceramic currently prepared by the reactive melt infiltration (RMI) process (the highest volume fraction reported in existing literature is 85 vol.%), the generation of the Ti3SiC2 phase in the product is further promoted by "regulating the original powder ratio", "controlling the reaction temperature", and "introducing a mixed powder of Y2O3 and Al2O3 as a reaction aid", thereby increasing the Ti3SiC2 phase content in the RMI Ti3SiC2 bulk ceramic to 98 vol.%. This purity can reach and even exceed the Ti3SiC2 phase purity in the HP Ti3SiC2 bulk ceramic currently prepared commercially by the hot pressing process (HP).

Description

Technical Field

[0001] The invention belongs to a preparation method of Ti3SiC2 bulk ceramics, and relates to high-purity Ti3SiC2 bulk ceramics and a preparation method thereof. Background Art

[0002] Ti3SiC2 ceramics are a novel ceramic material with a nano-sized, two-dimensional layered structure, composed of periodically alternating layers of Ti3C2 and Si atoms. Due to its unique crystal structure, Ti3SiC2 ceramics combine the high-temperature and corrosion resistance of ceramics with the high toughness and thermal conductivity of metals. This unique performance among current ceramic materials earns it the nickname "cermet."

[0003] Ti3SiC2 ceramics are a type of MAX phase ceramic material and are the most typical MAX phase ceramic material. Ti3SiC2 ceramics are one of the easiest MAX phase materials to synthesize, making it one of the few MAX phase ceramic materials currently available for large-scale industrial production and the most widely used commercially.

[0004] The current mainstream preparation methods of Ti3SiC2 bulk ceramics are hot pressing sintering process and pressureless sintering process.

[0005] Commercially produced Ti3SiC2 dense bulk ceramics are mostly produced using hot pressing (HP). The hot pressing process involves high temperature and high pressure to ensure the high purity of the Ti3SiC2 phase in the produced bulk ceramics. However, the hot pressing sintering process places high demands on production equipment, and the production process requires maintaining a high temperature and high pressure environment. Therefore, the HP Ti3SiC2 ceramic process is very expensive. There are no published or authorized patents for the preparation of high-purity Ti3SiC2 bulk ceramics using the hot pressing process, but there are some rejected patents.

[0006] According to the results of literature research, the patents currently disclosed or authorized for the preparation of high-purity Ti3SiC2 ceramics mainly use a pressureless sintering process, that is, only heating without pressurization during the ceramic sintering process (CN110128145A A method for synthesizing high-purity Ti3SiC2; CN110156018A A method for preparing high-purity titanium silicon carbon materials). The pressureless sintering process is simple and the equipment cost is low, but the Ti3SiC2 block prepared by pressureless sintering is loose and porous and does not have mechanical bearing capacity. In addition, this method is mostly used to prepare high-purity Ti3SiC2 powder, and cannot prepare high-purity Ti3SiC2 dense ceramic blocks.

[0007] The most significant characteristic of ceramic materials produced by reactive melt infiltration (RMI) is their "denseness," which can achieve a porosity close to zero. Consequently, RMI-produced ceramics generally exhibit excellent mechanical properties, airtightness, and high thermal conductivity. However, a recognized industry challenge with the RMI process is the low purity of the target product in the resulting ceramic blocks, which often contain multiphase byproducts and incompletely reacted melt. This is an inherent problem with the RMI process.

[0008] The Ti3SiC2 phase content in the RMI Ti3SiC2 bulk ceramics currently prepared using the RMI process is generally low. Existing literature reports that the maximum volume fraction of the Ti3SiC2 phase in the product is 85 vol.%.

[0009] Patent No. 201810440245.4, entitled "A method for preparing an in-situ self-generated MAX phase modified composite material," uses the RMI process to prepare RMI Ti3SiC2 ceramics. The method includes selecting TiC powder as the precursor powder for preparing RMI Ti3SiC2 ceramics; f / SiC or SiC f / SiC porous ceramic composite material preforms are used to prepare RMI Ti3SiC2 ceramics; Al powder is mixed into the initial TiC powder as a reaction aid for the RMI process to prepare Ti3SiC2 ceramics; Si powder is used for the RMI process, while this patent selects AlSi alloy blocks as the reaction melt for the RMI process.

[0010] Patent application number 201310314549.3, entitled "Preparation Method for Ti3Si(Al)C2 Modified SiC-Based Composite Materials," also uses the RMI process to prepare Ti3Si(Al)C2 ceramics. The method follows the same principles as in Patent Application No. 201810440245.4, including the use of TiC powder as the raw material and AlSi alloy as the reaction melt in the RMI process. f / SiC or SiC f RMI Ti3SiC2 ceramics are prepared in the pores of a / SiC porous ceramic composite material preform; the target product prepared is Ti3Si(Al)C2 ceramics, compared with Ti3SiC2 ceramics, a portion of the Si atoms in the Ti3Si(Al)C2 ceramics are replaced by Al atoms in the molten alloy; no RMI process reaction additives are added during the original powder preparation stage.

[0011] In summary, while ceramic materials produced by the RMI process have high density and near-zero porosity, exhibiting excellent mechanical properties, airtightness, and high thermal conductivity, the process also produces ceramic materials doped with multiphase byproducts, resulting in a low content of the target product phase. This low phase purity has become a recognized inherent challenge of the RMI process for producing ceramic materials. For the target product, Ti3SiC2 ceramics, reported in existing literature, the highest Ti3SiC2 phase purity in RMI Ti3SiC2 ceramics is 85 vol.%.

[0012] Disadvantages of existing technology:

[0013] 1. The Ti3SiC2 phase purity in the Ti3SiC2 ceramics prepared by the RMI process is low, and there is no report on the preparation of high-purity Ti3SiC2 ceramics using the RMI process.

[0014] 2. Most of the existing patents on the preparation of high-purity Ti3SiC2 ceramics use a pressureless sintering process. The Ti3SiC2 ceramics prepared by this process are loose and porous and have poor bearing capacity.

[0015] 3. Currently, commercially available high-purity Ti3SiC2 ceramic blocks are generally produced using a hot-pressing sintering process. While hot-pressing sintering can produce high Ti3SiC2 content and dense materials, the production process requires continuous heating and pressure, placing stringent conditions and high demands on equipment, resulting in high production costs.

[0016] Therefore, the creative significance of the present invention lies in that not only RMI Ti3SiC2 dense ceramic blocks are prepared using the RMI process, but most importantly, the content of Ti3SiC2 phase therein is as high as 98 vol.%, and the remaining impurity phases are very small amounts of Y2O3 and Al2O3 reaction aids introduced, which avoid the formation of by-products such as TixSiy and SiC, and successfully solve the problem of low purity of Ti3SiC2 phase in RMI Ti3SiC2 ceramics. The present invention further promotes the formation of Ti3SiC2 phase in the product by "regulating the original powder ratio", "controlling the reaction temperature", and "introducing Y2O3 and Al2O3 mixed powder as reaction aids", thereby increasing the Ti3SiC2 phase content in RMI Ti3SiC2 bulk ceramics to 98 vol.%, which has reached or even exceeded the phase purity of Ti3SiC2 in HP Ti3SiC2 bulk ceramics currently prepared commercially using hot pressing technology (HP). Summary of the Invention

[0017] Technical problems to be solved

[0018] To address the shortcomings of the prior art, the present invention proposes a high-purity Ti3SiC2 bulk ceramic and a preparation method thereof. By regulating the Ti:C ratio in the raw materials, controlling the RMI process temperature, and introducing a mixed powder of Y2O3 and Al2O3 as a reaction aid, the formation of the Ti3SiC2 phase during the RMI process is promoted, while the formation of by-products such as TixSiy and SiC in the product is reduced, thereby solving the problem of low purity of the Ti3SiC2 phase in Ti3SiC2 ceramics prepared by the RMI process. The present invention regulates and improves the process for preparing Ti3SiC2 ceramics by the RMI process, so that the prepared Ti3SiC2 ceramics have the advantages of high density and high purity of the hot pressing process and the low cost of the pressureless sintering process.

[0019] Technical Solution

[0020] A method for preparing high-purity Ti3SiC2 bulk ceramics is characterized by the following steps:

[0021] Step 1: Add 0.1-0.5 wt.% of polyacrylic acid to distilled water and stir to form a uniform solution;

[0022] Step 2: Add the mixed powder of TiC and TiO2 as raw materials and the mixed powder of Y2O3 and Al2O3 as reaction aids to the solution, wherein the total mass of the powder added to the solution is 30-50 wt.% of the mass of the solution;

[0023] The mixture was placed in a ball mill for 36 to 48 hours to obtain a uniform slurry;

[0024] Step 3: Place the slurry in an oven at 120°C and dry for 24 hours to obtain a dry mixed powder;

[0025] Step 4: cold pressing the mixed powder to obtain a ceramic green body;

[0026] Step 5: placing the ceramic green body obtained by cold pressing in a vacuum furnace and keeping the temperature at 1200-1600° C. for 2 hours to obtain a porous ceramic preform;

[0027] Step 6: embed the porous ceramic preform in Si-containing alloy fragments, perform reactive infiltration in a vacuum furnace, and keep the temperature at 1250-1450°C for 30-60 minutes to obtain a high-purity Ti3SiC2 dense ceramic block.

[0028] The cold pressing in step 4 is to apply an axial pressure of 10 to 30 MPa to the mixed powder placed in the pressure mold and maintain the pressure for 10 minutes to obtain a ceramic green body.

[0029] The molar ratio of TiC to TiO2 is 3:1 to 1:1.

[0030] The molar ratio of Y2O3 to Al2O3 is 2:1 to 1:2.

[0031] The raw material TiC is replaced by a mixed powder of Ti powder and C powder.

[0032] The RMI process of infiltrating AlSi alloy in a vacuum furnace is replaced by infiltrating AlSi in a tube furnace or box furnace with good airtightness and in an inert atmosphere.

[0033] The Si-containing alloy is AlSi, ZrSi or YSi alloy.

[0034] The particle diameter of the TiC powder is 2-4 μm.

[0035] The particle diameter of the TiO2 powder is less than 5 μm.

[0036] A high-purity Ti3SiC2 bulk ceramic obtained by the preparation method is characterized in that: the Ti3SiC2 bulk ceramic is a Ti3SiC2 phase with a content increased to 98 vol.% obtained by the above RMI method.

[0037] Beneficial effects

[0038] The present invention proposes a high-purity Ti3SiC2 bulk ceramic and a preparation method thereof. Addressing the problem of low Ti3SiC2 phase content in the RMI Ti3SiC2 bulk ceramics currently prepared by the reactive melt infiltration (RMI) process (the highest volume fraction reported in the literature is 85 vol.%), the present invention further promotes the formation of Ti3SiC2 phase in the product by "regulating the original powder ratio", "controlling the reaction temperature", and "introducing Y2O3 and Al2O3 mixed powder as a reaction aid", thereby increasing the Ti3SiC2 phase content in the RMI Ti3SiC2 bulk ceramic to 98 vol.%. This purity can reach and exceed the Ti3SiC2 phase purity in the HP Ti3SiC2 bulk ceramics currently prepared commercially by the hot pressing process (HP).

[0039] The innovative features of the present invention are:

[0040] 1. In terms of the selection of reaction raw materials, the present invention selects to add TiO2 powder on the basis of the original TiC powder. On the one hand, TiO2 makes up for the lack of Ti in the Ti-Si-C reaction melt, moves the melt composition toward the Ti-rich direction in the Ti-Si-C ternary phase diagram, and avoids the formation of TixSiy by-products; on the other hand, the O element in TiO2 reacts with the excess Si and C elements in the Ti-Si-C reaction melt, causing the excess Si and C to escape in the form of SiO and CO, thereby reducing the formation of SiC by-products;

[0041] 2. In terms of reaction temperature control, the present invention provides a precise temperature control range according to the different proportions of the AlSi alloy components selected for the reaction. Combined with the phase diagram, the RMI process temperature is calculated to be above the eutectic temperature of the selected AlSi alloy, providing sufficient Si source for the Ti-Si-C reaction melt, promoting the formation of Ti3SiC2 phase, while preventing the thermal stability of the generated Ti3SiC2 phase from being affected by excessively high reaction temperature, leading to its decomposition.

[0042] 3. In terms of the selection of reaction aids, the present invention proposes to use mixed powders of Y2O3 and Al2O3 in different proportions as reaction aids, which greatly promotes the transformation of TiC raw materials into Ti3SiC2 phase.

[0043] The beneficial effects of the present invention compared with the prior art are:

[0044] 1. Compared with the Ti3SiC2 ceramics prepared by the RMI process, patent number 201810440245.4, entitled "A method for preparing an in-situ self-generated MAX phase modified composite material":

[0045] The same steps are: this patent also selects TiC powder as the precursor powder for preparing RMI Ti3SiC2 ceramics.

[0046] The different steps are:

[0047] 1. This invention is to use RMI technology to f / SiC or SiC f / SiC porous ceramic composite material preform to prepare RMI Ti3SiC2 ceramics, while this patent is to first prepare TiC ceramic preform and then perform RMI process to prepare high-purity Ti3SiC2 dense ceramic blocks;

[0048] 2. The invention uses Al powder mixed with the initial TiC powder as a reaction aid for the RMI process to prepare Ti3SiC2 ceramics, while this patent uses a mixed powder of Y2O3 and Al2O3 as a reaction aid for the RMI reaction;

[0049] 3. The invention uses Si powder for RMI process, while this patent selects AlSi alloy block for RMI process.

[0050] 2. Compared with the preparation method of Ti3SiC2 ceramics with patent number 201310314549.3, which is also prepared using the RMI process and is named Ti3Si(Al)C2 modified SiC-based composite materials:

[0051] The same steps are: TiC powder is selected as the raw material for preparation; AlSi alloy is selected as the reaction melt of the RMI process.

[0052] The different steps are:

[0053] 1. The existing technology is to use RMI process in C f / SiC or SiC f / SiC porous ceramic composite material preform pores to prepare RMI Ti3SiC2 ceramics, while the present invention is to first prepare the TiC ceramic preform and then perform the RMI process to prepare high-purity Ti3SiC2 dense ceramic blocks;

[0054] 2. The target product prepared by the prior art is Ti3Si(Al)C2 ceramic. Compared with Ti3SiC2 ceramic, Ti3Si(Al)C2 ceramic has some Si atoms replaced by Al atoms in the molten alloy, while the present invention prepares high-purity Ti3SiC2 ceramic;

[0055] 3. The prior art does not describe the addition of RMI reaction aids during the preparation of the original powder, while the present invention adds a mixed powder of Y2O3 and Al2O3 to the original powder as a reaction aid for the RMI reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 : Flow chart of the process of the present invention;

[0057] Figure 2 : Actual image of the high-purity Ti3SiC2 dense ceramic block prepared by the present invention;

[0058] Figure 3 :(a) XRD comparison of Ti3SiC2 ceramics prepared by the present invention and commercial hot pressing; (b) XRD refinement pattern of Ti3SiC2 ceramics prepared by the present invention;

[0059] Figure 4 :(a) Microscopic SEM image of Ti3SiC2 ceramics prepared by the present invention; (b) Microscopic SEM image of Ti3SiC2 ceramics prepared by commercial hot pressing; DETAILED DESCRIPTION

[0060] The present invention will now be further described with reference to the embodiments and accompanying drawings:

[0061] Glossary of relevant technical terms:

[0062] RMI Ti3SiC2 ceramic block refers to the Ti3SiC2 ceramic block obtained by RMI process, in which the main phase is Ti3SiC2 and also contains a small amount of impurity phase; similarly, HP Ti3SiC2 ceramic block refers to the Ti3SiC2 ceramic block obtained by HP process.

[0063] The preparation flow chart of the method of the present invention is as follows Figure 1As shown, it is characterized in that TiC powder with a particle diameter of 2 to 4 μm, TiO2 powder with a particle diameter of less than 5 μm, and a mixed powder of Y2O3 and Al2O3 with a molar ratio of 2:1 to 1:2 are used as reaction additives, TiC powder and TiO2 powder with a molar ratio of 3:1 to 1:1 are used as raw materials, and the mass ratio of the TiC and TiO2 mixed powder to the Y2O3 and Al2O3 mixed powder is 10:1, and is prepared according to the following steps:

[0064] Step 1: Add 0.1-0.5 wt.% of polyacrylic acid to distilled water and stir to form a uniform solution;

[0065] Step 2: Add TiC and TiO2 mixed powders and Y2O3 and Al2O3 mixed powders to the solution, with the mass of the mixed powder added to the solution being 30-50 wt.% of the mass of the solution, and place the above mixture in a ball mill for 36-48 hours to obtain a uniform slurry;

[0066] Step 3: Pour the slurry into a tray and dry it in an oven at 120°C for 24 hours to obtain a dry mixed powder;

[0067] Step 4: Place the mixed powder in a pressure mold and maintain the pressure for 10 minutes under an axial pressure of 10 to 30 MPa to obtain a ceramic green body;

[0068] Step 5: placing the ceramic green body obtained by cold pressing in a vacuum furnace and keeping the temperature at 1200-1600° C. for 2 hours to obtain a porous ceramic preform;

[0069] Step 6: embed the porous ceramic preform in AlSi alloy fragments and keep it in a vacuum furnace at 1250-1450℃ for 30-60 minutes to obtain a high-purity Ti3SiC2 dense ceramic block, such as Figure 2 shown.

[0070] In the above steps, by changing the following key invention points, selecting the raw materials and the molar ratio of the components, and selecting the RMI process temperature, the volume fractions of the various phases in the ceramic product are obtained as shown in the following table:

[0071]

[0072] From the above embodiments and comparative examples, it can be seen that:

[0073] 1. During the raw powder preparation stage, the present invention changes the Ti:C molar ratio in the reaction system by adding TiO2 powder, shifting the reactant components toward the Ti-rich direction in the Ti-Si-C ternary phase diagram, thereby ensuring the formation of high-purity Ti3SiC2 phase at the reaction raw material level and avoiding the large-scale formation of by-products such as SiC;

[0074] 2. In the raw powder preparation stage, the present invention greatly promotes the formation of Ti3SiC2 phase by adding a mixed powder of Al2O3 and Y2O3 as a reaction aid for precipitating Ti3SiC2 phase in the Ti-Si-C melt;

[0075] 3. During the reactive infiltration stage, the present invention controls the reactive infiltration temperature at 1250-1450°C based on the calculation results of the AlSi alloy phase diagram used, so as to promote the formation of the Ti3SiC2 phase while ensuring that the generated Ti3SiC2 phase does not decompose due to excessively high temperature, thereby achieving an almost single-phase Ti3SiC2 phase in the product.

[0076] It can be seen from the examples that the beneficial effects of the present invention are:

[0077] 1. The Ti3SiC2 phase content in the prepared RMI Ti3SiC2 ceramics exceeds 98 vol.%, with ultra-high purity, and does not contain TixSiy and SiC by-product impurity phases. The XRD characterization and refinement results of the product phase composition are as follows Figure 3 As shown;

[0078] 2. The prepared RMI Ti3SiC2 ceramic block is dense and compact, with a porosity of less than 1% and no obvious pores in the material. Figure 4 As shown;

[0079] 3. The RMI process temperature is lower than 1450°C, and no pressurization is required during the heating process. The preparation conditions are relaxed and the production cost is low.

[0080] 4. The RMI process does not involve pressure preparation, so it is suitable for the preparation of large-sized special-shaped ceramic components.

Claims

1. A method for preparing high-purity Ti3SiC2 bulk ceramics, characterized in that Here are the steps: Step 1: Add 0.1-0.5 wt.% of polyacrylic acid to distilled water and stir to form a uniform solution; Step 2: Add the mixed powder of TiC and TiO2 as raw materials and the mixed powder of Y2O3 and Al2O3 as reaction aids to the solution, place the mixture in a ball mill for 36 to 48 hours to obtain a uniform slurry; the mass of the mixed powder added to the solution is 30 to 50 wt.% of the mass of the solution; The molar ratio of TiC to TiO2 is 3:1 to 1:1; The molar ratio of Y2O3 to Al2O3 is 2:1 to 1:2; The mass ratio of TiC and TiO2 mixed powder to Y2O3 and Al2O3 mixed powder is 10:1; Step 3: Place the slurry in an oven at 120°C and dry for 24 hours to obtain a dry mixed powder; Step 4: cold pressing the mixed powder to obtain a ceramic green body; Step 5: placing the circular ceramic green body obtained by cold pressing in a vacuum furnace and keeping the temperature at 1200-1600° C. for 2 hours to obtain a porous ceramic preform; Step 6: The porous ceramic preform is embedded in Si-containing alloy fragments, and AlSi alloy is infiltrated by RMI process in a vacuum furnace, and the temperature is kept at 1250-1450°C for 30-60 minutes to obtain a high-purity Ti3SiC2 dense ceramic block.

2. The method for preparing high-purity Ti3SiC2 bulk ceramics according to claim 1, characterized in that: The cold pressing in step 4 is to apply an axial pressure of 10 to 30 MPa to the mixed powder placed in the pressure mold and maintain the pressure for 10 minutes to obtain a ceramic green body.

3. The method for preparing high-purity Ti3SiC2 bulk ceramics according to claim 1, characterized in that: The raw material TiC is replaced by a mixed powder of Ti powder and C powder.

4. The method for preparing high-purity Ti3SiC2 bulk ceramics according to claim 1, characterized in that: The RMI process of infiltrating AlSi alloy in a vacuum furnace is replaced by infiltrating AlSi in a tube furnace or box furnace used in an airtight and inert atmosphere.

5. The method for preparing high-purity Ti3SiC2 bulk ceramics according to claim 1, characterized in that: The Si-containing alloy is AlSi, ZrSi or YSi alloy.

6. The method for preparing high-purity Ti3SiC2 bulk ceramics according to claim 1, characterized in that: The particle diameter of the TiC is 2 to 4 μm.

7. The method for preparing high-purity Ti3SiC2 bulk ceramics according to claim 1, characterized in that: The particle diameter of the TiO2 is less than 5 μm.

8. A high-purity Ti3SiC2 bulk ceramic obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The Ti3SiC2 bulk ceramic is a Ti3SiC2 phase obtained by the RMI method described in any one of claims 1 to 7, with the content increased to 98 vol.%.

Images