Research on Mechanism of CaO Enhancing Molybdenum Solubility in Borosilicate Glass

doi:10.16552/j.cnki.issn1001-1625.2025.1037

Abstract

Abstract:

The low solubility of molybdenum in borosilicate glass matrices presents a significant challenge in the vitrification of high-level liquid waste （HLLW）， as it often leads to the precipitation of the undesirable “yellow phase”， thereby compromising the safety and long-term stability of the vitrified waste form. In this study， the effect of CaO content on the molybdenum solubility and the structural evolution of borosilicate glass was investigated. A combination of analytical techniques， including SEM-EDS， XRD， and Raman spectroscopy， was employed to characterize the phase composition and microstructure of the samples. The results indicate that as the mass fraction of CaO increases， the macroscopic appearance of the glass transitions progressively from milky white and opaque （0%~4%） to transparent blue （6%）， when the mass fraction of CaO is 8%， the milky color disappears， and when the mass fraction of CaO is 10%， it is completely transparent. Microscopic analysis reveals that the milky white opacity originates from the crystallization of Na₂MoO₄， which is effectively suppressed by the addition of CaO. Correspondingly， the molybdenum solubility in the glass matrix increases consistently， reaching a maximum of 2.8% （mass fraction）. Raman spectroscopy further demonstrates that CaO modifies the glass structure by depolymerizing the silicate network and promoting the formation of Q³ units， thereby creating a more favorable chemical environment for accommodating ［MoO₄］^2- groups.

Key words: CaO, borosilicate glass, molybdenum, solubility, glass structure

CLC Number:

TQ171

JIAO Yunjie, ZHU Yongchang, YANG Debo, CUI Zhu, DONG Xuanjiang, WANG Dongyu, DU Zhanyuan, YANG Yanan. Research on Mechanism of CaO Enhancing Molybdenum Solubility in Borosilicate Glass[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(3): 806-812.

Figures/Tables 6

Table 1 Composition of glass samples

Sample No.	Mass fraction/%
Sample No.	SiO₂	B₂O₃	Al₂O₃	Na₂O	CaO	MoO₃
C0	61.1	8.9	3.3	26.7	0.0	4
C2	59.9	8.7	3.3	26.1	2.0	4
C4	58.7	8.5	3.2	25.6	4.0	4
C6	57.4	8.4	3.1	25.1	6.0	4
C8	56.2	8.2	3.1	24.5	8.0	4
C10	55.0	8.0	3.0	24.0	10.0	4

Fig.1 Macrograph images of samples with different CaO content

Fig.2 SEM images of samples with different CaO content

Fig.3 Molybdenum solubility in samples with different CaO content

Fig.4 XRD patterns of samples with different CaO content

Fig.5 Normalized Raman spectra of samples with different CaO content

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