KR102349498B1 - Hafnium Carbide Ceramic Precursor and Method for Preparing the Hafnium Carbide Ceramic - Google Patents

Abstract

The present invention relates to a hafnium carbide ceramic precursor and a method for manufacturing a hafnium carbide ceramic using the same. It relates to a manufacturing method.

Description

Hafnium Carbide Ceramic Precursor and Method for Preparing the Hafnium Carbide Ceramic Using the Same

The present invention relates to a hafnium carbide ceramic precursor and a method for manufacturing a hafnium carbide ceramic using the same. It relates to a manufacturing method.

In general, carbon compound materials based on carbon (C), for example, graphite materials formed by carbon-carbon (CC) bonds, or carbide-based ceramic materials such as silicon carbide-silicon carbide (SiC-SiC) composites are chemical and It has excellent physical properties. Such carbon-containing materials are particularly high-temperature materials having excellent heat-resistance properties, and are used as heat-resistant materials and the like in various industrial fields. However, most carbide-based ceramics have a disadvantage in that oxidation resistance (oxidation resistance) is low in a high temperature environment of 1,600 °C or higher.

On the other hand, recently, ultra high temperature ceramics (UHTC) having a high melting point are attracting attention as a heat-resistant material. Ultra-high temperature ceramic is an ultra-high temperature material having thermal and mechanical stability at high temperatures of 2,000 °C or higher, which can overcome carbon-containing materials having low oxidation resistance at 1,600 °C or higher. Such ultra-high-temperature ceramics include, for example, hafnium carbide (HfC) and tantalum carbide (TaC). and hardness. Such ultra-high temperature ceramics, for example, have high utility in supersonic vehicles, space launch vehicles, intercontinental ballistic missiles, rocket turbines, and power plant turbines.

In general, in order to be applied as a heat-resistant material such as a supersonic vehicle or a space launch vehicle, the ultra-high temperature ceramic must be molded and manufactured into a structural material of a predetermined shape. At this time, the ultra-high temperature ceramic is mainly manufactured through a sintering method, for example, as a structural material such as a block type.

In particular, when an ultra-high-temperature ceramic having a high melting point, such as hafnium carbide (HfC) as a representative ultra-high-temperature ceramic, is used as a sintering material, the strong covalent bonding of hafnium carbide (HfC), oxidizing impurities in the sintering process, and fast particles at high temperature Because densification is difficult for reasons such as growth, a lot of cost and resources are consumed to construct a high-density structural material (sintered body).

For this reason, in order to form and densify carbide-based ceramics, which are non-sintering materials, at low temperatures and to implement them in various shapes, inorganic polymer (pre-ceramic)-derived ceramics (PDC) manufacturing technology is sometimes applied. Polycarbosilane, the most well-known pre-ceramic, is used as a coating material for manufacturing fibers or molding composites by using the melting and dissolving properties of polymers. HfC has also been developed to manufacture pre-ceramic-derived fibers (US7,572,881). In order to design a carbide precursor, polymerization must be induced based on an organometallic compound. Organometallic compounds are generally treated in a non-oxidizing atmosphere because of their weak oxidative stability, but various ligands are used to stabilize the metal (M) element. is designed and applied to secure bonding stability. Among them, the stability of bonding between metals and various organic elements is the same as MO > MN > MC. In order to form carbides, MC bonding can be considered preferentially. There is a limit in that it can be easily converted into an oxide form. Although M-N bonding is more stable than M-C bonding, it is important to control the content of nitrogen remaining in the heat treatment process for converting into ceramics.

Korean Patent No. 0711140

The present invention is to solve the above problems, and an object of the present invention is to use a relatively stable amine-based hafnium carbide ceramic precursor, and to reduce the nitrogen content as much as possible when converting to a ceramic, and as an ultra-high temperature ceramic (UHTC), excellent physical properties and low To provide a hafnium carbide ceramic capable of exhibiting an oxide impurity content.

On the one hand, the present invention

To provide a hafnium carbide ceramic precursor, a monomer represented by a compound of the following formula (1) is presented:

[Formula 1]

In the above formula,

R and R` are each the same as or different from each other, hydrogen or a C ₁ to C ₆ alkyl group.

On the other hand, the present invention

(i) preparing a monomer of a hafnium carbide ceramic precursor represented by the compound of Formula 1 by reacting a hafnium (Hf) halide compound and an amine-containing compound;

(ii) preparing a hafnium carbide ceramic precursor by polymerization of a cage structure from the monomer;

(iii) thermally curing the hafnium carbide ceramic precursor; and

(iv) converting the thermosetting hafnium carbide ceramic precursor into hafnium carbide ceramic by heat treatment at 1,400 to 2,000 °C; provides a method of manufacturing hafnium carbide ceramic comprising a.

The hafnium carbide ceramic precursor according to the present invention exhibits excellent densification due to a high ceramic yield, and the hafnium carbide ceramic prepared using the same is an ultra-high-temperature ceramic (UHTC) and exhibits excellent physical properties and low oxide impurity content.

In addition, the hafnium carbide ceramic precursor according to the present invention can be dissolved/melted as an organic-inorganic composite polymer, so that it is possible to form a ceramic having a complex shape.

In addition, the hafnium carbide precursor according to the present invention has excellent thermal stability and a high ceramic yield compared to a polymer having a linear structure in a polymer state in which a complex network such as a cage structure is formed.

1 shows a hafnium carbide ceramic precursor (a) and a pellet-type thermoset hafnium carbide ceramic precursor (b) according to the present invention.
Figure 2 shows a hafnium carbide ceramic specimen pyrolyzed according to the present invention.
3 is a graph showing the results of FT-IR analysis of the hafnium carbide ceramic precursor according to the present invention.
4 is a graph showing the results of thermal analysis of the hafnium carbide ceramic precursor according to the present invention.
5 is a graph showing the results of XRD analysis of hafnium carbide for the heat treatment conditions according to the present invention.

Hereinafter, the present invention will be described in more detail.

A monomer for preparing a hafnium carbide ceramic precursor according to an embodiment of the present invention is,

It is characterized in that it is represented by the compound of Formula 1 below.

[Formula 1]

In the above formula,

R and R` are each the same as or different from each other, hydrogen or a C ₁ to C ₆ alkyl group.

As used herein, C ₁ to C ₆ Alkyl group refers to a linear or branched monovalent hydrocarbon having 1 to 6 carbon atoms, for example, methyl, ethyl, n-propyl, i-propyl, n-butyl , n-pentyl, n-hexyl, and the like, but are not limited thereto.

The hafnium carbide ceramic precursor (or hafnium composite polymer) according to the present invention is an amine-based hafnium precursor, which can secure stability from oxygen introduced during the process, and easily breaks the bond with nitrogen to be used as a carbide-based ceramic precursor. suitable for

The hafnium carbide ceramic precursor according to the present invention can be grown into a polymer having a complex network such as a cage structure by a condensation reaction. At this time, when the polymerization reaction proceeds, the metal element is considerably stabilized to ensure work stability, and melting/dissolution is possible, so it can be applied to forming hafnium carbide ceramics having a complex shape.

Specifically, the hafnium carbide ceramic precursor according to the present invention uses tetra(diisophenylamino)hafnium (TDiPS-Hf) having a relatively large number of carbon atoms, but is not limited thereto.

The molecular weight of the hafnium carbide ceramic precursor is not limited. In the hafnium carbide ceramic precursor, the number (n) of basic units containing metal (M) can be increased to 8 or more by a condensation reaction as shown in Figure 1 below. impossible However, when the molecular weight of the dark orange liquid monomer is increased by polymerization, the viscosity of the reactant increases and is converted to brown color.

[Figure 1]

A method of manufacturing a hafnium carbide ceramic according to an embodiment of the present invention,

(i) preparing a monomer of a hafnium carbide ceramic precursor represented by the compound of Formula 1 by reacting a hafnium (Hf) halide compound and an amine-containing compound;

(ii) preparing a hafnium carbide ceramic precursor by polymerization of a cage structure from the monomer;

(iii) thermally curing the hafnium carbide ceramic precursor; and

(iv) converting the heat-cured hafnium carbide ceramic precursor into hafnium carbide ceramic by heat treatment at 1,400 to 2,000 °C.

In one embodiment of the present invention, as the amine-containing compound in step (i), lithium diisopropylamide, lithium dimethylamide, lithium diethylamide, etc. may be used, It is not limited thereto.

The ceramic yield of the hafnium carbide ceramic precursor according to the present invention is 60 to 80 wt%, and the weight reduction due to solvent volatilization and thermal decomposition in the initial stage of heat treatment is minimized. Therefore, a ceramic manufactured using a hafnium carbide ceramic precursor having a high ceramic yield has little loss due to weight reduction in the heat treatment step, and thus is advantageous for high densification, and thus can exhibit excellent effects as an ultra-high temperature ceramic.

In one embodiment of the present invention, the heat treatment reaction is preferably carried out at 1,400 to 2,000 ° C., when the heat treatment is performed at a temperature lower than 1,200 ° C. The hafnium atomic state of hafnium carbide in an amorphous state that is not crystallized is unstable, so atmospheric It oxidizes when exposed to Accordingly, a heat treatment temperature of 1,200 °C or higher is required to start crystallization, and preferably a temperature of 1,400 °C or higher is required. When the heat treatment temperature exceeds 2,000 °C, crystal growth proceeds rapidly, and local coarse grains may be formed.

The heat treatment reaction may be performed by dividing it into thermal decomposition and crystallization. Specifically, the thermal decomposition process is preferably performed at 800 to 1,000 °C, and the crystallization process is preferably performed at 1,200 to 2,000 °C. The thermal decomposition process is a section in which the weight reduction occurs the most, and in order to stably maintain the molded article from shrinkage deformation due to the weight reduction, the temperature increase and the holding time in the pyrolysis process are important. The heat treatment reaction may be repeated one or more times.

The hafnium carbide ceramic precursor having a cage structure according to the present invention can be grown into a polymer represented by a three-dimensional structure as shown in the compounds of Chemical Formulas 2 to 4 below.

[Formula 2]

[Formula 3]

[Formula 4]

In the above formula,

M is Hf,

R and R` are each the same as or different from each other, hydrogen or a C ₁ to C ₆ alkyl group.

The bulk-type hafnium carbide ceramic precursor according to the present invention can be cured by a high-temperature pressurization reaction, and the bulk-type hafnium carbide ceramic cured by high-temperature pressure according to the present invention does not melt in the heat treatment step, so there is no fear that the molding may collapse. By minimizing oxidation, the inflow of oxygen can be blocked and the conversion rate to ceramic can be increased.

Hereinafter, the present invention will be described in more detail by way of Examples. These examples are only for illustrating the present invention, and it is apparent to those skilled in the art that the scope of the present invention is not limited to these examples.

Example 1: Preparation of Hafnium Carbide Ceramic Precursors

A solution was prepared by adding 25 ml of a 1M lithium diisopropylamide solution to 60 ml of diethylether. Then, _{2 g of HfCl 4} was slowly added dropwise to the solution in an ice bath, the mixed mixture was stirred, a reflux tube was installed, and the mixture was refluxed for 12 hours. LiCl, a by-product, is filtered from the reactant that has turned orange over the reaction time, and the reactant is separated from the solvent by distillation, which is a monomer of the hafnium carbide ceramic precursor. Tetra (diisophenylamino) hafnium (tetra (diisophenylamino) hafnium, TDiPS-Hf) was obtained (see Fig. 1 (a)).

Then, the reaction temperature of the liquid reactant was raised to 150° C. and further reacted to obtain a dark brown powdery hafnium carbide ceramic precursor in a polymer state.

Example 2: Preparation of hafnium carbide ceramic precursor moldings

1 g of the hafnium carbide ceramic precursor prepared in Example 1 was filled in a 10 mm diameter long-axis molding mold, a heating jacket was placed on the outside of the mold, and the reaction temperature was raised to 250 ° C., but the curing was completed by applying 1 torr pressure. A hafnium carbide ceramic precursor molding was obtained (see Fig. 1(b)).

Example 3: Preparation of hafnium carbide ceramic (HfC)

The hafnium carbide ceramic precursor powder prepared in Example 1 was mounted in an Ar atmosphere tube furnace. For the conversion of HfC, the heat treatment step was divided into thermal decomposition and crystallization. HfC was prepared by pyrolysis by holding at 1,000 ° C. for 1 hour, and crystallization by maintaining at 1,800 ° C. for 1 hour.

Example 4: Preparation of bulk type hafnium carbide ceramic (Bulk type HfC)

After the hafnium carbide ceramic precursor molded product prepared in Example 2 was mounted in an Ar atmosphere tube furnace, the temperature was raised at a rate of 1 C ℃/min, and pyrolyzed by maintaining at 400 °C and 1,000 °C for 1 hour, respectively, 2 °C/min After the temperature was raised to 1800 ° C. at a rate, crystallized and maintained for 1 hour to prepare bulk type HfC (see FIG. 2).

The prepared HfC did not show any deformation due to boiling even in the stage of thermal decomposition, and it was seen that the shape was maintained enough to handle movement, etc., so it appears that a curing step is not required after polymerization under pressure conditions.

Referring to FIG. 2 , some cracks were observed on the surface of the specimen, which is presumed to be caused by some volatile residues or shrinkage occurring during thermal decomposition.

Experimental Example 1: Confirmation of reactivity

FT-IR analysis was performed to confirm the reactivity of the hafnium carbide ceramic precursor prepared in Example 1, and Hf-NC bending vibration at the position of ^{wave number 1,263 cm -1 was confirmed.} It was confirmed that an Hf-amino complex polymer was formed (see FIG. 3 ).

Experimental Example 2: Evaluation of organic-inorganic conversion and ceramic yield

To evaluate the organic-inorganic conversion and ceramic yield of the hafnium carbide ceramic precursor, the hafnium carbide ceramic precursor pellets prepared in Example 2 were subjected to thermogravimetric analysis under _{N 2 conditions.}

During high-temperature heat treatment of pre-ceramic polymers, the back-bone structure made of Hf-C-N, etc. is converted to HfC through organic-inorganic conversion, which determines the high-temperature properties of the final ceramic.

Referring to FIG. 4 , according to the result of observing the weight change during temperature increase using TGA (Netzsh STA449 F3 Jupiter), it was confirmed that the weight loss occurred twice. First, (I) the weight loss (stage A) section that occurs under the condition of less than 100 °C generally corresponds to the solvent volatilization section, which is an amine-based by-product reproduced in polymerization and is not removed in the post-process and is estimated to remain in the sample. do. (II) 20% weight loss occurring in the 100 to 600 ℃ section (stage B) is due to thermal decomposition of organic matter.

Therefore, it was confirmed that the ceramic yield of the hafnium carbide ceramic precursor prepared in Example 2 was about 64 wt%.

Experimental Example 3: XRD measurement

As a result of XRD analysis of HfC prepared in Example 4, _{it was confirmed that HfO 2} was formed in addition to HfC crystals (see FIG. 5 ). This is a characteristic of organometallic compounds that are sensitive to oxidation, and it can be seen that oxides introduced during the process remain during the heat treatment process.

However, it was found that the amine-based compound was suitable for application as a carbide precursor as it did not form a nitrogen compound.

As the specific part of the present invention has been described in detail above, for those of ordinary skill in the art to which the present invention pertains, it is clear that these specific techniques are only preferred embodiments, and the scope of the present invention is not limited thereto. do. Those of ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (7)

delete (i) reacting a hafnium (Hf) halide compound and an amine-containing compound to prepare a monomer of a hafnium carbide ceramic precursor represented by the compound of Formula 1 below;
(ii) preparing a hafnium carbide ceramic precursor having the same three-dimensional structure as the compounds of Chemical Formulas 2 to 4 by polymerization of a cage structure from the monomer;
(iii) thermally curing the hafnium carbide ceramic precursor; and
(iv) converting the heat-cured hafnium carbide ceramic precursor into hafnium carbide ceramic by heat treatment at 1,400 to 2,000 ° C. Method for producing hafnium carbide ceramic comprising:
[Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

In the above formula,
M is Hf,
R and R` are each the same as or different from each other, hydrogen or a C ₁ to C ₆ alkyl group. delete The method of claim 2, wherein the amine-containing compound in step (i) is one selected from the group consisting of lithium diisopropylamide, lithium dimethylamide and lithium diethylamide. The method of claim 2, wherein the ceramic yield of the hafnium carbide ceramic precursor in step (ii) is 60 to 80 wt%. The method of claim 2, wherein the heat treatment reaction in step (iv) is performed by dividing the thermal decomposition and crystallization. The method of claim 2, wherein the heat treatment reaction in step (iv) is repeatedly performed one or more times.

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