Compositions and Preparation of Hafnium Carbide Ceramic Precursors

Abstract

Metal-containing polymer compositions useful for producing high-temperature metal carbide ceramics are described, including poly(carbohafnocene) compositions and related poly(carbometallocene) compositions, as well as compositions formed from the reaction of hafnium chloride and 2-butyne-1,4-diol. Methods for synthesizing such compositions are provided. In a preferred embodiment, the method for forming poly(carbohafnocene) polymers includes the steps of providing a bis(cyclopentadienyl)hafnium dihalide and reacting the bis(cyclopentadienyl)hafnium dihalide with a compound of the formula XMg(CH2). j MgX (wherein X is a halide and j is 4 or 5) with a di-Grignard reagent.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 107,615, filed October 30, 2020, the entire disclosure of which is incorporated herein by reference.

[0002] Technical Field The present invention relates to compositions and methods for synthesizing linear and branched polymers, including poly(carbohafnocene) polymers and hafnium-containing 2-butyne-1,4-diol polymers, useful for producing metal carbide ceramics, and more particularly to poly(carbohafnocene) polymers and hafnium-containing 2-butyne-1,4-diol polymers configured for synthesizing ultra-high temperature hafnium carbide (HfC) ceramics. [Background technology]

[0003] Background technology Hafnium carbide (HfC) has the highest melting point among ultra-high temperature ceramics (UHTCs), making it particularly useful for hypersonic aircraft components. As Ionescu and coworkers summarized in a recent review paper, an attractive approach to HfC fabrication involves the high-temperature conversion of polymeric HfC precursors (E. Ionescu et al., Polymer-Derived Ultra-High Temperature Ceramics (UHTCs) and Related Materials, Adv. Eng. Mat., 21, 1900269 (2019)). However, the preceramic polymers reported by Ionescu either had too much free carbon, were insoluble in solvents, or required lithium reagents for synthesis. Patent application China Patent Application Publication No. 104016679A reported a water-based HfC precursor using tartaric acid, oxalosuccinic acid, and citric acid. However, these polymers contained too much oxygen to be useful. With either approach, the resulting polymers have low ceramic yields, poor processability, or are simply too expensive. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Chinese Patent Application Publication No. 104016679A [Non-patent literature]

[0005] [Non-Patent Document 1] E. Ionescu et al., Polymer-Derived Ultra-High Temperature Ceramics (UHTCs) and Related Materials, Adv. Eng. Mat., 21, 1900269 (2019) Summary of the Invention [Means for solving the problem]

[0006] Overview of the embodiment According to one embodiment of the present invention, [ka] Disclosed is a ceramic precursor polymer composition comprising at least one poly(carbometallocene) selected from the formula: where C5H5 is a cyclopentadienyl ligand, n, x, and y are integers greater than zero, and M is a metal. In a preferred embodiment, M is a metal selected from Hf, Zr, Ti, V, Nb, Ta, and combinations thereof. In a preferred embodiment, the ceramic precursor composition comprises: [ka] Includes. In a preferred embodiment, the ceramic precursor composition comprises: [ka] Includes.

[0007] In some embodiments, the ratio x / y is greater than 2. In preferred embodiments, the ratio x / y is between 2 and 10.

[0008] In a preferred embodiment, the ceramic precursor polymer composition is prepared by the reaction: [ka] In the formula, C5H5 is a cyclopentadienyl ligand, and X 1 and X 2 is a halide and n is an integer greater than zero. In a preferred embodiment, X 1 and X 2 are independently selected from the group consisting of chloride and bromide. 1 and X 2 are both chlorides.

[0009] In a preferred embodiment, the ceramic precursor polymer composition is prepared by the reaction: [ka] In the formula, C5H5 is a cyclopentadienyl ligand, and X 1 , X 2 , and X 3 are halides independently selected from the group consisting of chloride and bromide, and x and y are integers greater than zero.

[0010] In a preferred embodiment, the method for forming a poly(carbohafnocene) polymer comprises the steps of providing a bis(cyclopentadienyl)hafnium dihalide and reacting the bis(cyclopentadienyl)hafnium dihalide with a compound of the formula XMg(CH2) j With a di-Grignard reagent of formula XMg(CH2), MgX, where X is a halide and j is 4 or 5. In another preferred embodiment, the method further comprises providing mono(cyclopentadienyl)hafnium trihalide and reacting the mixture of bis(cyclopentadienyl)hafnium dihalide and mono(cyclopentadienyl)hafnium trihalide with a di-Grignard reagent of formula XMg(CH2). j The method further comprises reacting MgX with a di-Grignard reagent. In a preferred embodiment of the method, the ratio of bis(cyclopentadienyl)hafnium dihalide to mono(cyclopentadienyl)hafnium trihalide is between 2 and 10.

[0011] In a preferred embodiment, the hafnium carbide ceramic is obtained by heating the above-described ceramic precursor polymer composition under an inert gas atmosphere to a temperature between about 850° C. and about 950° C. In a preferred embodiment, the ceramic precursor polymer is [ka] Includes.

[0012] In another preferred embodiment, the ceramic precursor polymer is [ka] Includes.

[0013] In a preferred embodiment, the x / y ratio is between 2 and 10.

[0014] In some embodiments, the ceramic precursor polymer composition comprises: [ka] wherein M is a metal selected from the group consisting of Hf, Zr, Ti, V, Nb, Ta, W, and combinations thereof, and x and y are integers greater than zero.

[0015] In a preferred embodiment, the metal in the ceramic precursor polymer composition is hafnium and the ceramic precursor polymer is: [ka] where x and y are integers greater than zero.

[0016] In some embodiments, the ratio of x / y in the ceramic precursor polymer is between 5:1 and 1:5. In preferred embodiments, the ratio of x / y is between 2:1 and 1:2.

[0017] In some embodiments, the ceramic precursor polymer is prepared by the following reaction: [ka] It is synthesized from hafnium chloride and 2-butyne-1,4-diol according to

[0018] In an embodiment, the hafnium oxycarbide ceramic is obtained by heating the ceramic precursor polymer to a temperature of about 850° C. to about 1000° C. under an inert gas atmosphere.

[0019] In embodiments, the hafnium carbide ceramic is obtained by heating the ceramic precursor polymer to a temperature of about 1000° C. to about 1600° C. under an inert atmosphere. DETAILED DESCRIPTION OF THE INVENTION

[0020] Detailed Description of Specific Embodiments Definition. As used in this description and the appended claims, the following terms shall have the meanings indicated below, unless the context otherwise requires.

[0021] A "cyclopentadienyl" ligand, represented herein as C5H5, or alternatively as Cp, is a planar, pentagonal, singly negatively charged aromatic moiety that can coordinate as a ligand to a metal atom by utilizing the overlap of the metal d orbitals and the cyclopentadienyl pi-electrons.

[0022] A "metallocene" is a metal coordination complex consisting of two cyclopentadienyl anions bonded to and "sandwiching" a metal center.

[0023] A "hafnocene" is a metallocene in which the metal coordinating two cyclopentadienyl anions is hafnium.

[0024] "Poly(carbometallocene)" polymers are polymers that have metallocene groups incorporated into the backbone.

[0025] "Poly(carbohafnocene)" polymers are polymers with hafnocene groups incorporated into the backbone. composition.

[0026] Embodiments of the present invention include compositions of metal-containing polymers useful as precursors for producing high temperature ceramics. In some embodiments, these metal-containing polymers are poly(carbometa- llocene) polymers. In some embodiments, these poly(carbometa- llocene) polymers have the linear structure: [ka] It has.

[0027] wherein C5H5 is a cyclopentadienyl ligand, n is an integer greater than zero, and M is a metal selected from the group consisting of Hf, Zr, Ti, V, Nb, Ta, and combinations thereof. In a preferred embodiment, the metal is selected from the group consisting of Hf, Zr, Ti, and combinations thereof.

[0028] In a preferred embodiment, the metal is hafnium: [ka] is.

[0029] In a preferred embodiment, the hydrocarbon chain is a butyl group (Structure I). In a preferred embodiment, the metal is hafnium and the hydrocarbon group is a butyl group (Structure III).

[0030] In some embodiments, the poly(carbometa- locene) polymer has a branched structure and can be depicted as follows: [ka]

[0031] In these structures, C5H5 is a cyclopentadienyl ligand, x and y are integers greater than zero, and M is a metal selected from the group consisting of Hf, Zr, Ti, V, Nb, Ta, and combinations thereof. In preferred embodiments, the metal is selected from the group consisting of Hf, Zr, Ti, and combinations thereof. Monomers enclosed by x brackets provide a linear poly(carbometallocene) along the polymer backbone, while monomers enclosed by y brackets are branched structures with repeating poly(carbometallocene) groups extending along and branching from the polymer backbone. In these structures, the x and y indices refer only to the number of unbranched and branched monomers, respectively, and do not provide an indication of the distribution of monomers along the backbone, thereby encompassing both random and block copolymers.

[0032] In a preferred embodiment, the metal is hafnium: [ka]

[0033] In a preferred embodiment, the hydrocarbon chain is a butyl group (Structure V). In a preferred embodiment, the metal is hafnium and the hydrocarbon group is a butyl group (Structure VII). In a preferred embodiment, the ratio x / y is between 2 and 20.

[0034] In embodiments, the metal carbide ceramic is obtained by heating a poly(carbometa- locene) polymer having any of structures (I) through (VII) under an inert gas atmosphere. In embodiments, the inert gas is argon. In preferred embodiments, the metal carbide ceramic is a hafnium carbide ceramic formed by heating a poly(carbohafnocene) polymer selected from the group consisting of polymers (III), (IV), (VII), and (VIII) to a temperature between about 850°C and about 950°C under an inert gas atmosphere.

[0035] In some embodiments, metal-containing polymer compositions useful as precursors in the production of high temperature ceramics include oxygen-containing hafnium polymers that can be used to form hafnium carbide having a 1:1 stoichiometric ratio of hafnium to carbon using a carbothermal reduction process. Preferred polymer compositions for such carbothermal reduction include: [ka] is.

[0036] In this composition, the ratio of x to y can vary between 5:1 and 1:5, with a preferred ratio being between 2:1 and 1:2, and a particularly preferred ratio being 1:1.

[0037] After thermal curing at temperatures below 200°C, which results in polymerization of the carbon-carbon triple bonds, hafnium oxycarbide can be formed in about 80% yield at temperatures between about 850°C and about 1000°C under argon. Excess carbon and oxygen can be removed by carbothermal reduction under argon at temperatures between 1000°C and 1600°C to form HfC with a 1:1 stoichiometry of Hf to C. Synthesis method.

[0038] In a preferred embodiment, the linear poly(carbohafnocene) polymer is prepared by the reaction of bis(cyclopentadienyl)hafnium dihalide (Cp2HfX2) with the di-Grignard reagent XMg(CH2) j MgX, where j is an integer equal to 4 or 5. In a preferred embodiment, the poly(carbohafnocene) polymer having butyl groups along the backbone is represented by the formula (1): [ka] It can be synthesized in an aprotic solvent according to

[0039] In a preferred embodiment, the reaction is carried out by combining ClMgCH2CH2CH2CH2MgCl in tetrahydrofuran (THF) and bis(cyclopentadienyl)hafnium dichloride (Cp2HfCl2) in toluene.

[0040] In another embodiment, poly(carbohafnocene) polymers with pentyl groups along the backbone are synthesized by the reaction of ClMgCH2CH2CH2CH2CH2MgCl with Cp2HfCl2.

[0041] In a preferred embodiment, the branched poly(carbohafnocene) polymer is prepared by reacting a mixture of bis(cyclopentadienyl)hafnium dihalide (Cp2HfX2) and mono(cyclopentadienyl)hafnium trihalide with the di-Grignard reagent XMg(CH2). j MgX, where j is an integer equal to 4 or 5. In a preferred embodiment, a poly(carbohafnocene) polymer having butyl groups along the main and side chains is synthesized by reaction with ... [ka] It can be synthesized in an aprotic solvent according to

[0042] In a preferred embodiment, the reaction is carried out by combining ClMgCH2CH2CH2CH2MgCl in tetrahydrofuran (THF) with bis(cyclopentadienyl)hafnium dichloride (Cp2HfCl2) and mono(cyclopentadienyl)hafnium trichloride (CpHfCl3) in toluene.

[0043] In another embodiment, poly(carbohafnocene) polymers bearing pentyl groups along the backbone and side chains are synthesized by the reaction of Cp2HfCl2 and CpHfCl3 with ClMgCH2CH2CH2CH2CH2MgCl.

[0044] In some embodiments, the polymer formed according to either of formulas (1) and (2) is heated to a temperature between about 850° C. and about 950° C. under an inert gas atmosphere to form a hafnium carbide ceramic.

[0045] In some embodiments, oxygen-containing hafnium polymers suitable for forming HfC in a 1:1 stoichiometry of hafnium to carbon are prepared by the reaction: [ka] It is synthesized from hafnium chloride and 2-butyne-1,4-diol according to

[0046] In some embodiments, the precursor is thermally cured at temperatures below 200° C. through polymerization of carbon-carbon triple bonds. In some embodiments, the thermally cured precursor is heated under argon at temperatures from about 350° C. to about 1000° C. to form hafnium oxycarbide. In some embodiments, the thermally cured precursor is heated to a temperature between 1000° C. and 1600° C., whereby excess carbon and oxygen are removed by carbothermal reduction to form HfC with a 1:1 stoichiometry of Hf to C. [Example]

[0047] Example 1 In a 500 mL three-necked round-bottom flask equipped with a water-cooled condenser, thermometer, and dropping funnel, 15.19 g (0.04 mol) of bis(cyclopentadienyl)hafnium dichloride was mixed with 80 g of toluene. The flask was kept under a nitrogen atmosphere to prevent moisture contamination and cooled externally with an ice / salt / water bath. The solution was stirred using magnetic stirring. When the solution temperature dropped below 0 °C, 0.04 mol of ClMgCH2CH2CH2CH2MgCl di-Grignard reagent in 30 mL of THF was added via the dropping funnel. The reaction temperature was maintained below 0 °C during the addition of the di-Grignard reagent. The di-Grignard reagent was added slowly over approximately 30 minutes. After the addition of the di-Grignard reagent, the reaction mixture was kept in the cooling bath for 2 hours, then removed from the cooling bath and stirred at room temperature overnight. A brown solution containing some solid precipitate was obtained. The liquid was filtered off under nitrogen, and the solid was washed with 20 ml of toluene. The washed toluene was also filtered and combined with the first filtrate. The combined solution was then distilled under reduced pressure to remove the THF and toluene solvents used. 13.3 g (91% of the theoretical yield) of a brown solid was obtained, corresponding to homopolymer (III). Thermogravimetric analysis (TGA) of the resulting solid under argon up to 900 °C provided a black ceramic residue in 69% yield.

[0048] Example 2 In a 500 mL three-necked round-bottom flask equipped with a water-cooled condenser, thermometer, and dropping funnel, 15.19 g (0.04 mol) of bis(cyclopentadienyl)hafnium dichloride and 3.5 g (0.01 mol) of (cyclopentadienyl)hafnium trichloride were mixed with 100 g of toluene. The flask was kept under a nitrogen atmosphere to prevent moisture contamination and cooled externally with an ice / salt / water bath. The solution was stirred using a magnetic stirrer. Once the solution temperature had dropped below 0°C, 0.055 mol of ClMgCH2CH2CH2CH2MgCl di-Grignard reagent in 40 mL of THF was added via the dropping funnel. The temperature of the reaction was maintained below 0°C during the addition of the di-Grignard reagent. The di-Grignard reagent was added slowly over approximately 30 minutes. After the addition of the di-Grignard reagent, the reaction mixture was kept in the cooling bath for 2 hours, then removed from the cooling bath and stirred overnight at room temperature. A brown solution containing some solid precipitate was obtained. The liquid was filtered under nitrogen, and the solid was washed with 25 ml of toluene. The washed toluene was also filtered and combined with the first filtrate. The combined solution was then distilled under reduced pressure to remove the used THF and toluene solvent, yielding 16.5 g (90% of the theoretical yield) of a dark brown solid corresponding to copolymer (VII). TGA of the resulting solid under argon up to 900 °C provided a black ceramic residue in 65% yield.

[0049] Example 3 To a 250 mL three-necked round-bottom flask equipped with a water-cooled condenser and thermometer, 70 grams of distilled water was added. The flask was magnetically stirred and externally cooled with ice / water, then 30 grams of hafnium chloride was added in several portions. After cooling to room temperature, 12.1 grams of 2-butyne-1,4-diol was added. At this point, the solution was saturated with both components without precipitation. The solution was then transferred to a 250 mL beaker and heated to 150-200 °C on a hot plate. Water and HCl evolved from the solution during heating. The solution turned brown and its viscosity gradually increased. Condensation of hydroxyl groups and partial polymerization of carbon-carbon triple bonds occurred during heating. After all the water had evaporated, 29 grams of a dark brown, dense solid was obtained. TGA of the resulting solid under argon up to 900 °C provided a black ceramic residue in 80% yield. Further heating to 1600 °C resulted in stoichiometric HfC.

[0050] The above-described embodiments of the present invention are intended to be illustrative only; numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. In one embodiment, for example, the following items are provided: (Item 1) [ka] (In the formula, C 5 H 5 is a cyclopentadienyl ligand, n, x, and y are integers greater than zero, and M is a metal selected from the group consisting of Hf, Zr, Ti, V, Nb, Ta, and combinations thereof. A ceramic precursor polymer composition comprising at least one poly(carbometallocene) selected from the group consisting of: (Item 2) 2. The ceramic precursor polymer composition of claim 1, wherein M is Hf. (Item 3) The composition comprises: [ka] 3. The ceramic precursor polymer composition of claim 2, comprising: (Item 4) The composition comprises:

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Claims

【Request Item 1】 【Chemistry 19】 (In the formula, C ５ H ５ is a cyclopentadienyl ligand, n, x, and y are integers greater than zero, and M is a metal selected from the group consisting of Hf, Zr, Ti, V, Nb, Ta, or a combination thereof.

1. A ceramic precursor polymer composition comprising at least one poly(carbometallocene) selected from the group consisting of:

2. 10. The ceramic precursor polymer composition of claim 1, wherein M is Hf.

3. The composition comprises: 【Chemistry 20】 3. The ceramic precursor polymer composition of claim 2, comprising:

4. The composition comprises: 【Chemistry 21】 3. The ceramic precursor polymer composition of claim 2, comprising:

5. A method of forming the ceramic precursor polymer composition of claim 4, comprising: The x / y ratio is between 2 and 10, and the reaction: 【Chemistry 28】 (In the formula, C ５ H ５ is a cyclopentadienyl ligand, and X １ , X ２ and X ３ is a halide, n, x, and y are integers greater than zero, and R is —CH ２ CH ２ CH ２ CH ２ -, -CH ２ CH ２ CH ２ CH ２ CH ２ - or a combination thereof) a Grignard coupling reaction according to A method comprising:

6. X １ , X ２ and X ３ 6. The method of forming a ceramic precursor polymer composition of claim 5, wherein is independently selected from the group consisting of chloride, bromide, or a combination thereof.

7. formula: 【Chemistry 23】 (In the formula, C ５ H ５ is a cyclopentadienyl ligand, and X １ , X ２ , and X ３ are halides independently selected from the group consisting of chloride, bromide, or a combination thereof, and x and y are integers greater than zero. using a Grignard coupling reaction of bis(cyclopentadienyl)hafnium dihalide and mono(cyclopentadienyl)hafnium trihalide according to 6. A method of forming the ceramic precursor polymer composition of claim 5, comprising:

8. 1. A method for forming a poly(carbohafnocene) polymer, comprising: providing a bis(cyclopentadienyl)hafnium dihalide; and The bis(cyclopentadienyl)hafnium dihalide is reacted with the compound of formula XMg(CH ２ ) ｊ reacting with a di-Grignard reagent of MgX, where X is a halide and j is 4 or 5; A method comprising:

9. providing mono(cyclopentadienyl)hafnium trihalide, wherein the reacting step comprises reacting the mixture of bis(cyclopentadienyl)hafnium dihalide and mono(cyclopentadienyl)hafnium trihalide with a compound of the formula XMg(CH ２ ) ｊ 9. The method for forming a poly(carbohafnocene) polymer of claim 8, further comprising reacting MgX with said di-Grignard reagent.

10. 10. The method for forming a poly(carbohafnocene) polymer of claim 9, wherein the ratio of bis(cyclopentadienyl)hafnium dihalide to mono(cyclopentadienyl)hafnium trihalide is between 2 and 10.

11. A hafnium carbide ceramic obtained by heating the preceramic polymer composition of claim 2 to a temperature between about 850°C and about 950°C under an inert gas atmosphere.

12. the ceramic precursor polymer composition 【Chemistry 24】 The hafnium carbide ceramic of claim 11 comprising:

13. the ceramic precursor polymer composition 【Chemistry 25】 The hafnium carbide ceramic of claim 11 comprising:

14. 14. The hafnium carbide ceramic of claim 13, wherein the x / y ratio is between 2 and 10. 【Request Item 15】 【Chemistry 26】 wherein M is a metal selected from the group consisting of Hf, Zr, Ti, Nb, Ta, W, or a combination thereof, and x and y are integers greater than zero.

1. A ceramic precursor polymer composition comprising:

16. 16. The ceramic precursor polymer composition of claim 15, wherein M is Hf.

17. 17. The ceramic precursor polymer composition of claim 16, wherein the ratio of x to y is between 5:1 and 1:

5.

18. formula: 【Chemistry 27】 16. A method of forming the ceramic precursor polymer composition of claim 15, comprising synthesizing the composition from hafnium chloride and 2-butyne-1,4-diol according to the formula:

19. 16. A hafnium oxycarbide ceramic obtained by heating the ceramic precursor polymer composition of claim 15 to a temperature between about 850°C and about 1000°C under an inert gas atmosphere.

20. 16. A hafnium carbide ceramic obtained by heating the ceramic precursor polymer composition of claim 15 to a temperature between about 1300°C and about 1600°C under an inert gas atmosphere.

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