Influence of Carbon Powder on Crystallization Behavior of Fused Silica

doi:10.16552/j.cnki.issn1001-1625.2026.0222

Abstract

Abstract:

In this work， the effects of carbon powder， both individually and in combination with hexagonal boron nitride （h-BN）， on the crystallization behavior of fused silica were systematically investigated. Based on compositional variations， four experimental groups were designed： pure fused silica， fused silica with h-BN addition， fused silica with carbon powder addition， and fused silica with a co-addition of carbon powder and h-BN. Following heat treatment at 1 250 ℃ for 0.5 h， various characterization techniques were comprehensively employed to evaluate the effects of carbon powder on the degree of crystallization， microstructure， and thermal behavior of the fused silica. Experimental results demonstrate that the addition of carbon powder significantly accelerates the formation of the cristobalite phase. Notably， in the carbon/h-BN co-addition system， the carbon powder effectively overcomes and even completely negates the crystallization-inhibiting effect of h-BN. Consequently， the degree of crystallization approaches or even exceeds that of the pure fused silica samples without any added inhibitors. Furthermore， excessive carbon powder severely impedes the densification process of the samples， leading to the deterioration of mechanical properties and an increase in the coefficient of thermal expansion. This study highlights that the interaction mechanisms between carbon impurities and h-BN must be considered when evaluating the high-temperature service reliability of fused silica and controlling raw material purity in practical production. These findings provide a crucial theoretical basis for raw material management， process optimization， and lifespan prediction of high-purity silica-based materials under complex operating conditions.

Key words: fused silica, hexagonal boron nitride, carbon, crystallisation, inhibition effect

CLC Number:

O783

DENG Weijie, BAO Qifu, DONG Weixia, LIU Mingyuan, ZENG Shuai, LI Zhe, LI Yamin. Influence of Carbon Powder on Crystallization Behavior of Fused Silica[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(9): 3257-3266.

Figures/Tables 12

Fig.1 Particle size distribution of fused silica

Table 1 Main chemical composition of raw materials

Raw material	Mass fraction/%
Raw material	SiO₂	BN	C	Na₂O	K₂O	Li₂O	B₂O₃	Cl	Ignition loss
Fused silica	≥99.00	—	—	≤0.50	≤0.40	≤0.04	≤0.05	≤0.01	≤1.00
h-BN	—	≥99.99	—	—	—	—	≤0.01	—	—
Carbon powder	—	—	100	—	—	—	—	—	—

Fig.2 Temperature-time curve of heat treatment

Fig.3 TG-DTA curves of fused silica samples under different preparation conditions

Fig.4 Raman spectra of fused silica samples under different preparation conditions

Fig.5 XRD patterns of fused silica samples under different preparation conditions

Fig.6 Mechanisms of carbon powder and carbon powder/h-BN composite in fused silica

Fig.7 SEM images of fused silica samples under different preparation conditions

Fig.8 SEM images and corresponding EDS spectra （point 1） of fused silica samples after heat treatment at 1 250 ℃

Fig.9 Flexural strength， water absorption， porosity， and bulk density of fused silica samples after heat treatment at 1 250 ℃

Fig.10 SEM images of fused silica samples with 15% carbon powder before and after heat treatment at 1 250 ℃

Fig.11 CTE of fused silica samples under different preparation conditions

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