METHOD FOR PREPARATION OF DENSE HfC(Si)-HfB2 COMPOSITE CERAMIC

Abstract

A method for the preparation of a dense HfC(Si)—HfB.sub.2 composite ceramic. hafnium oxide powders, nano-sized carbon black and silicon hexaboride powders are mixed in a molar ratio of (1-10):(1-20):(1-5) to obtain a powder mixture. The powder mixture is subjected to ball milling, dried and transferred to a graphite mold for spark plasma sintering. In this way, an in-situ carbon-boron reduction reaction and the sintering densification are completed in one step, and the obtained HfC(Si)—HfB.sub.2 composite ceramic has a density of 94.0%-100% and uniformly dispersed grains.

Claims

1. A method for the preparation a HfC(Si)—HfB.sub.2 composite ceramic, comprising: 1) mixing hafnium oxide powders, nano-sized carbon black and silicon hexaboride powders in a molar ratio of (1-10):(1-20):(1-5) to obtain a powder mixture; 2) subjecting the powder mixture obtained in step (1) to ball milling to obtain a ball-milled product; and drying the ball-milled product to obtain a dried product; 3) transferring the dried product to a graphite mold followed by spark plasma sintering to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 94.0%-100% and uniformly dispersed grains.

2. The method of claim 1, wherein in step (1), a particle size of the hafnium oxide powders is 50-500 nm; a particle size of the nano-sized carbon black is 50 nm; and a particle size of the silicon hexaboride powders is 1-5 μm.

3. The method of claim 1, wherein in step (2), the ball milling is performed in a planetary ball mill.

4. The method of claim 1, wherein in step (2), a medium used in the ball milling is isopropanol.

5. The method of claim 1, wherein in step (2), a weight ratio of the powder mixture to balls of the planetary ball mill is 1:(4-20).

6. The method of claim 3, wherein in step (2), the ball milling is performed at 200-500 r/min for 6-24 h.

7. The method of claim 1, wherein in step (2), the ball-milled product is dried in an electric blast drying oven at 50-80° C. for 4-10 h.

8. The method of claim 1, wherein in step (3), the graphite mold is covered with a graphite paper.

9. The method of claim 1, wherein in step (3), the spark plasma sintering is performed at a temperature of 1500-1850° C., a pressure of 20-60 MPa and a vacuum degree of 0-1.0 mbar for 5-30 min; and a heating rate is 50-200° C./min.

10. The method of claim 1, wherein in step (3), the spark plasma sintering is performed at 1500-1850° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is an X-ray diffraction (XRD) pattern of a HfC(Si)—HfB.sub.2 composite ceramic prepared in Example 3.

[0029] FIG. 2 is a scanning electron microscope (SEM) image of the HfC(Si)—HfB.sub.2 composite ceramic prepared in Example 3.

DETAILED DESCRIPTION OF EMBODIMENTS

[0030] This disclosure will be further described below with reference to the embodiments. The embodiments are merely illustrative of this disclosure, and are not intended to limit the disclosure. It should be noted that variations and modifications made by those skilled in the art without departing from the spirit of this disclosure should fall within the scope of the disclosure defined by the appended claims.

[0031] Provided herein is a method for the preparation of a HfC(Si)—HfB.sub.2 composite ceramic, which is specifically described as follows.

[0032] (1) Hafnium oxide (HfO.sub.2) powders having a particle size of 50-500 nm, nano-sized carbon black (50 nm) and silicon hexaboride (SiB.sub.6) powders having a particle size of 1-5 m are mixed in a molar ratio of (1-10):(1-20):(1-5) to obtain a powder mixture.

[0033] (2) The powder mixture obtained in step (1) is subjected to ball milling at 200-500 r/min in a planetary ball mill for 6-24 h to allow the HfO.sub.2 powders, the nano-sized carbon black and the SiB.sub.6 powders to be uniformly mixed, and then dried at 50-80° C. in an electric blast drying oven for 4-10 h, where a medium used in the ball milling is isopropanol; and a weight ratio of the powder mixture to balls is 1:(4-20).

[0034] (3) The reaction mixture obtained in step (2) is transferred to a graphite mold (diameter: 32 mm) covered with graphite paper and subjected to spark plasma sintering at a temperature of 1500-1850° C., a pressure of 20-60 MPa and a vacuum degree of 0-1.0 mbar for 5-30 min to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 94.0%-100% and uniformly dispersed grains, where a heating rate of the sintering is 50-200° C./min.

[0035] As used herein, the hafnium oxide powders used in the method have a purity ≥99.9%, and are produced by Chaowei-nano Co., Ltd (Shanghai, China); the isopropanol has a purity ≥99.8%; the nano-sized carbon black has a purity ≥99.9%, and is produced by Innochem Co., Ltd (Beijing, China); and the silicon hexaboride powders have a purity ≥98%, and are produced by Alfa Aesar (Shanghai, China).

[0036] The planetary ball mill is QM-3SP4 planetary ball mill manufactured by Nanjing University. The electric blast drying oven is DHG-9075A electric blast drying oven produced by Yiheng17 Co., Ltd (Shanghai, China). The spark plasma sintering is carried out in the HPD-25 spark plasma sintering system produced by FCT Systeme GmbH (Rauenstein, Germany).

[0037] The technical solutions and beneficial effects of this disclosure will be further described with reference to the embodiments.

Example 1

[0038] Provided herein was a method for the preparation of a dense HfC(Si)—HfB.sub.2 composite ceramic, which was specifically performed as follows.

[0039] (1) Hafnium oxide (HfO.sub.2) powders having a particle size of 50 nm, nano-sized carbon black (50 nm) and silicon hexaboride (SiB.sub.6) powders having a particle size of 5 μm were mixed in a molar ratio of 5:2:1 to obtain a powder mixture.

[0040] (2) The powder mixture obtained in step (1) was subjected to ball milling at 300 r/min in a planetary ball mill for 8 h to allow the HfO.sub.2 powders, the nano-sized carbon black and the SiB.sub.6 powders to be uniformly mixed, and then dried in an electric blast drying oven at 50° C. for 6 h, where a medium used in the ball milling was isopropanol; and a weight ratio of the powder mixture to balls of the planetary ball mill was 1:10.

[0041] (3) The reaction mixture obtained in step (2) was transferred to a graphite mold (diameter: 32 mm) covered with graphite paper, and subjected to spark plasma sintering at a temperature of 1600° C., a pressure of 45 MPa, and a vacuum degree of 0 mbar for 10 min to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 96% and uniformly dispersed grains, where a heating rate was 200° C./min.

Example 2

[0042] Provided herein was a method for the preparation of a dense HfC(Si)—HfB.sub.2 composite ceramic, which was specifically performed as follows.

[0043] (1) Hafnium oxide (HfO.sub.2) powders having a particle size of 100 nm, nano-sized carbon black (50 nm) and silicon hexaboride (SiB.sub.6) powders having a particle size of 4 μm were mixed in a molar ratio of 10:5:3 to obtain a powder mixture.

[0044] (2) The powder mixture obtained in step (1) was subjected to ball milling at 350 r/min in a planetary ball mill for 12 h to allow the HfO.sub.2 powders, the nano-sized carbon black and the SiB.sub.6 powders to be uniformly mixed, and then dried in an electric blast drying oven at 60° C. for 8 h, where a medium used in the ball milling was isopropanol; and a weight ratio of the powder mixture to balls of the planetary ball mill was 1:15.

[0045] (3) The reaction mixture obtained in step (2) was transferred to a graphite mold (diameter: 32 mm) covered with graphite paper, and subjected to spark plasma sintering at a temperature of 1700° C., a pressure of 35 MPa, and a vacuum degree of 0.5 mbar for 20 min to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 98% and uniformly dispersed grains, where a heating rate was 100° C./min.

Example 3

[0046] Provided herein was a method for the preparation of a dense HfC(Si)—HfB.sub.2 composite ceramic, which was specifically performed as follows.

[0047] (1) Hafnium oxide (HfO.sub.2) powders having a particle size of 200 nm, nano-sized carbon black (50 nm) and silicon hexaboride (SiB.sub.6) powders having a particle size of 1 μm were mixed in a molar ratio of 2:1:1 to obtain a powder mixture.

[0048] (2) The powder mixture obtained in step (1) was subjected to ball milling at 400 r/min in a planetary ball mill for 16 h to allow the HfO.sub.2 powders, the nano-sized carbon black and the SiB.sub.6 powders to be uniformly mixed, and then dried in an electric blast drying oven at 70° C. for 10 h, where a medium used in the ball milling was isopropanol; and a weight ratio of the powder mixture to balls of the planetary ball mill was 1:20.

[0049] (3) The reaction mixture obtained in step (2) was transferred to a graphite mold (diameter: 32 mm) covered with graphite paper, and subjected to spark plasma sintering at a temperature of 1850° C., a pressure of 60 MPa, and a vacuum degree of 0.2 mbar for 30 min to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 99% and uniformly dispersed grains, where a heating rate was 80° C./min.

[0050] An X-ray diffraction (XRD) pattern of the HfC(Si)—HfB.sub.2 composite ceramic prepared herein was presented in FIG. 1, from which it can be seen that the main crystal phases were HfC and HfB.sub.2 with good crystallinity, and there was a small amount of HfO.sub.2 doped in the main crystal phases. The HfC and HfB.sub.2 crystal phases were consistent with Powder Diffraction File (PDF) NO. 65-8747 and PDF NO. 65-8678, respectively. FIG. 2 was a scanning electron microscope (SEM) image of the HfC(Si)—HfB.sub.2 composite ceramic prepared herein, and it can be observed that the HfC and HfB.sub.2 grains with a size of about 600 nm were uniformly dispersed and the composite ceramic had relatively high density. There was a small amount of free carbon at the grain boundaries.

Example 4

[0051] Provided herein was a method for the preparation of a dense HfC(Si)—HfB.sub.2 composite ceramic, which was specifically performed as follows.

[0052] (1) Hafnium oxide (HfO.sub.2) powders having a particle size of 80 nm, nano-sized carbon black (50 nm) and silicon hexaboride (SiB.sub.6) powders having a particle size of 1 μm were mixed in a molar ratio of 1:1:1 to obtain a powder mixture.

[0053] (2) The powder mixture obtained in step (1) was subjected to ball milling at 200 r/min in a planetary ball mill for 24 h to allow the HfO.sub.2 powders, the nano-sized carbon black and the SiB.sub.6 powders to be uniformly mixed, and then dried in an electric blast drying oven at 50° C. for 10 h, where a medium used in the ball milling was isopropanol; and a weight ratio of the powder mixture to balls of the planetary ball mill was 1:4.

[0054] (3) The reaction mixture obtained in step (2) was transferred to a graphite mold (diameter: 32 mm) covered with graphite paper, and subjected to spark plasma sintering at a temperature of 1500° C., a pressure of 20 MPa, and a vacuum degree of 0 mbar for 30 min to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 94.0% and uniformly dispersed grains, where a heating rate was 50° C./min.

Example 5

[0055] Provided herein was a method for the preparation of a dense HfC(Si)—HfB.sub.2 composite ceramic, which was specifically performed as follows.

[0056] (1) Hafnium oxide (HfO.sub.2) powders having a particle size of 200 nm, nano-sized carbon black (50 nm) and silicon hexaboride (SiB.sub.6) powders having a particle size of 4 μm were mixed in a molar ratio of 10:15:3 to obtain a powder mixture.

[0057] (2) The powder mixture obtained in step (1) was subjected to ball milling at 450 r/min in a planetary ball mill for 12 h to allow the HfO.sub.2 powders, the nano-sized carbon black and the SiB.sub.6 powders to be uniformly mixed, and then dried in an electric blast drying oven at 60° C. for 6 h, where a medium used in the ball milling was isopropanol; and a weight ratio of the powder mixture to balls of the planetary ball mill was 1:12.

[0058] (3) The reaction mixture obtained in step (2) was transferred to a graphite mold (diameter: 32 mm) covered with graphite paper, and subjected to spark plasma sintering at a temperature of 1650° C., a pressure of 40 MPa, and a vacuum degree of 0.5 mbar for 20 min to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 98% and uniformly dispersed grains, where a heating rate was 100° C./min.

Example 6

[0059] Provided herein was a method for the preparation of a dense HfC(Si)—HfB.sub.2 composite ceramic, which was specifically performed as follows.

[0060] (1) Hafnium oxide (HfO.sub.2) powders having a particle size of 500 nm, nano-sized carbon black (50 nm) and silicon hexaboride (SiB.sub.6) powders having a particle size of 5 μm were mixed in a molar ratio of 8:20:5 to obtain a powder mixture.

[0061] (2) The powder mixture obtained in step (1) was subjected to ball milling at 500 r/min in a planetary ball mill for 6 h to allow the HfO.sub.2 powders, the nano-sized carbon black and the SiB.sub.6 powders to be uniformly mixed, and then dried in an electric blast drying oven at 80° C. for 4 h, where a medium used in the ball milling was isopropanol; and a weight ratio of the powder mixture to balls of the planetary ball mill was 1:20.

[0062] (3) The reaction mixture obtained in step (2) was transferred to a graphite mold (diameter: 32 mm) covered with graphite paper, and subjected to spark plasma sintering at a temperature of 1850° C., a pressure of 60 MPa, and a vacuum degree of 1.0 mbar for 5 min to obtain the HfC(Si)—HfB.sub.2 composite ceramic with a density of 100% and uniformly dispersed grains, where a heating rate was 200° C./min.

[0063] These embodiments are merely illustrative of the technical solutions of the disclosure, and are not intended to limit the disclosure. It should be understood that modifications, changes and improvements made by those skilled in the art without departing from the spirit of the disclosure should fall within the scope of the disclosure defined by the appended claims.