Effect of B Incorporation on the SiOC Precursor Fabrication and High-Temperature Oxidation Behavior of SiBOC Ceramics

Research Article

Ann Materials Sci Eng. 2021; 5(2): 1043.

Effect of B Incorporation on the SiOC Precursor Fabrication and High-Temperature Oxidation Behavior of SiBOC Ceramics

Sun Z1, Xu H2, Yuan F3, Zhou S4* and Zhou H5

1Yantai Vocational College, Yantai, PR China

2Shandong Industrial Ceramic Research & Design Institute Co., Ltd., Zibo, PR China

3Aerospace Research Institute of Materials & Processing Technology, Beijing, PR China

4National Key Laboratory of Science and Technology on Advanced Composites in Special Environments, and Center for Composite Materials and Structures, Harbin Institute of Technology, Harbin, PR China

5School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin, PR China

*Corresponding author: Shanbao Zhou, National Key Laboratory of Science and Technology on Advanced Composites in Special Environments and Center for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150040, PR China

Received: August 31, 2021; Accepted: September 29, 2021; Published: October 06, 2021


The SiBOC precursor ceramics were fabricated by polymer-derived method SiBOC pre-cursors with different B/Si molar ratios were synthesized by controlling monomer content. The effects of different process conditions on SiBOC ceramics and the oxidation resistance of SiBOC ceramics at the high temperature (1400OC) were studied. The SiBOC precursor’s bonds of Si-O-C, Si-O-Si, and Si-O-B were detected by FTIR. The precursor is converted to a rigid ceramic material that has an 85.3wt% ceramic yield of SiBOC ceramics with B/ Si=0.4 by TG-DSC. The results of SEM analysis show that the SiBOC ceramics surface bulges and folds increase with the increase of boric acid content. With the increase of pyrolysis temperature and pyrolysis time, the size and number of pores on the surface of SiBOC ceramics also increase. Static oxidation tests show that SiBOC ceramics with B/Si=0.4 have better oxidation resistance under other conditions being the same.

Keywords: Polymer-derived ceramics; SiBOC ceramics; Sol-gel method; Oxidation resistance


SiOC precursor ceramics have a wide range of raw materials, low price, large output, simple, preparation and designable molecular structure. However, its high-temperature resistance is still insufficient and carbothermal reduction begins at about 1300oC, which limits its wider application [1,2]. Besides, it was found that the content, pyrolysis atmosphere, particle size, and apparent morphology of the samples had a significant influence on the high temperature stability of SiOC ceramics [3]. The high-temperature stability of SiOC precursor ceramics can be improved by doping B, N, and Zr, and therein the improvement of element B is significant [4-7]. This kind of ceramic material prepared by using an organic polymer as a ceramic precursor is usually called polymer-derived ceramics (PDCs). The method of preparing ceramics by the polymer-derived method has been widely used in the preparation of silicon-based precursor ceramics. In the precursor of SiBOC, boron atoms are introduced into the SiOC gel network in the form of Si-O-B bonds, and the corresponding SiBOC ceramics are obtained through pyrolysis. SiBOC ceramics are composed of silicon carbide (SiCxO4-x) and boron carbide (BCyO3-y) mixed units [8]. The microstructure of SiBOC ceramics with different B/Si ratios has been studied by many researchers. In the temperature range of 1000-1500oC, the introduction of boron is conducive to the graphitization of free carbon, reducing the reaction activity of free carbon, thus inhibiting the carbothermal reduction reaction [9-12]. Also, the introduction of boron leads to a higher ceramic yield of 89% as well as the enhanced crystallization of both β-SiC and free carbon [13]. During crystallization, SiCxO4-x and BCyO3-y units were consumed and boron was mainly pre-sent in trigonal borosilicate BO3 sites at 1500oC [11,14,15].

To obtain SiBOC gel precursor, Schiavon et al add to Methyltriethoxysilane (MTES) a proper amount of boric acid with different B/Si molar ratios and gelation time. The weight loss showed that the addition of boron to the Si-O-C glass slightly increase the high-temperature stability of the ternary oxycarbide glass [14]. Riedel et al found that the polymer-to-ceramic transformation process which can avoid cristobalite formation and the degradation of oxidation resistance of the material [8].

In this paper, MTES and ethanol were alcoholized in the presence of Hydrochloric Acid (HCl) catalyst. Boric acid was used to provide B element to modify the SiOC precursor ceramic system to synthesize SiBOC precursor. A new structure of SiBOC ceramics was obtained by subsequent pyrolysis of the dry precursor at a high temperature. Then the synthesis mechanism of SiBOC precursor starting from gel to ceramic was investigated. The effect of different B/Si on the yield of SiBOC precursor ceramics, the influence of different pyrolysis temperatures and time on the morphology, and related properties of SiBOC ceramics at high temperatures were studied.


Materials synthesis and processing

The commercially available methyltriethoxysilane (MTES, CH3Si(OCH2CH3)3, Macklin Co. Ltd., Shanghai, China), boric acid (B(OH)3, Tianjin Zhiyuan Chemical Reagent Co., Ltd., Tianjin, China), anhydrous ethanol (CH3CH2OH, Harbin Chemical Reagent Factory Co. Ltd., Harbin, China) and hydrochloric acid (HCl, Harbin Chemical Reagent Factory Co. Ltd., Harbin, China) were used to synthesize SiBOC precursors. First, the appropriate mass of ethanol (4.0g) was added into MTES (50mmol), and then boric acid with a certain proportion corresponding to different B/Si (i.e., 0.4, 0.5, 0.6 and 0.7) was added into MTES, which was stirred evenly. Under magnetic stirring, an appropriate amount of hydrochloric acid catalyst was dropped until boric acid was completely dissolved to form a homogeneous solution. The SiBOC precursor sol was reacted at 40oC for 24h, and then at 50oC for 24h. The obtained SiBOC precursor xerogel was dried at 80oC for 12h. Finally, SiBOC xerogels were pyrolyzed in an argon-protected tubular furnace, so that SiBOC ceramics were pre-pared by controlling the pyrolysis temperature and the pyrolysis time under no pressure conditions.

Characterization and oxidation test

Fourier Transform Infrared Spectroscopy (FTIR) of EQUINOX-55 (produced by Brooke spectrometers, Germany) was used to qualitatively analyze the composition and bonding of precursor. The phase composition of the high-temperature pyrolyzed SiBOC ceramics was measured by the D/Max-2200 X-ray diffractometer (produced by Nippon Neoku Co. Ltd., Japan) at a scan speed of 5°/ min in the 2-theta range of 10-90°. To observe the uniformity, micro surface, and fracture morphology of SiBOC ceramics, and to study the oxidation resistance of SiBOC ceramics, Scanning Electron Microscopy (SEM) was performed on FEI Sirion200 (produced by Philip, Netherlands). Thermogravimetry differential thermal analysis (TG-DSC, Netzsch star 449c, Germany) was used to analyze the mass change and heat absorption, and release of the precursor. The test was carried out in an air atmosphere, and the temperature range was Rt- 1400oC. According to the DSC curve, it can be analyzed whether some components in the SiBOC ceramics are oxidized at high temperatures.

Results and Discussion

Synthesis mechanism of SiBOC polymer precursors

The infrared spectra of different B/Si in the process of synthesized SiBOC ceramic precursors are shown in Figure 1. The absorption bonds of pure MTES are mainly in the range of 1000-1200 cm-1, which is related to the Si-O-Si bond [16]. At the same time, the presence of the absorption peak at 890cm-1, related to Si-O-B= borosiloxane bridges [17] has been observed for all samples.