The solubility of Mo in borosilicate glasses is relatively low. Therefore, molybdate is easy to separate from glass, forming Mo-yellow phase (alkali molybdates, such as Na2MoO4, CsLiMoO4, and Li2MoO4) or CaMoO4 crystals. The crystal CaMoO4 performs a superior water resistance ability, which can effectively reduce the Mo leaching rate of a high Mo content and high level waste (HLW) solidification glass. On the contrary, alkali-Mo-yellow phase is highly water-soluble, leading to a serious Mo-leaching, and thus decreases the chemical durability of the products. The duration of the chemical durability test of solidification glass is 7 or 28 days, thus retarding the whole cycle for the investigation of HLW solidification glass. Effective predicting Mo-yellow phase and the Mo leaching rate can accelerate the research via saving time on glass preparation and chemical durability test. Based on the glass structural gene modeling (GSgM), this paper proposed the Structure-Property (S-P) prediction models of chemical durability and the possibility of Mo-phase separation (PS, its value is xPS) for a simulated high Mo content (MoO3 2.6-3.3%) HLW borosilicate solidification glass. The key elements (i.e., Na, Li, B, and Mo) leaching rate rNa, rLi, rB, rMo as well as the Mo-phase separation xPS were predicted by the models. The reliability and practicability of the models were proved. In addition, combined with the Structure-Composition (S-C) modeling, the C-S-P analysis was also carried out for xPS and rMo.
Methods
Fifteen borosilicate glasses were designed by an one-component-at-a-time (OCAT) method. Glasses with different weights (130 g and 800 g) were prepared for each composition. Small samples with the mass of 130 g were melted and quenched. Large glass samples with the mass of 800 g were melted, and annealed. The properties of the samples were determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) with KBr, differential scanning calorimetry (DSC) and PCT-7 day chemical durability test, respectively. Mo-phase (xPS) was evaluated and scored for each sample by naked eyes (from 0-100%, high score means high probability of Mo-phase separation). The structural data used for modeling were derived from FTIR peak fitting area Ai. Each FTIR spectrum was decomposed into 10 Gaussian bands by a software named GRAMS AI 32 according to the same fitting rules. The S-P and S-C models were constructed by a software named JMP based on the Cornell first-order linear mixture formula. The sample (glass MV) for model validation was also prepared and measured by the same procedure.
Results and discussion
No Mo-phase appeats in the small samples (130 g), while a serious Mo-phase separation (i.e., yellow phase and white phase) occurs in some large samples (800 g), which can be attributed to the Mo-phase accumulation and the slow cooling rate of large size glasses. The XRD patterns indicate that the main components of Mo-phase are CsLiMoO4 (i.e., water-soluble yellow phase, yellow) and CaMoO4 (i.e., water-resistant crystal, white). The S-P models with satisfied statistical significance (i.e., P<0.0001) and model accuracy (i.e., Rsq≥0.87) are proposed based on the Ai and glass properties. The corresponding prediction formula of the target properties (i.e., Na, Li, B, Mo leaching rate ri, Tg, xPS) are
rB = 0.085 -0.036A3 +0.024A4 +0.002A5
rLi = 0.13 - 0.052A3 + 0.005A5 + 0.005A6
rNa = 0.38 - 0.086 A3 + 0.008A6 - 0.003(A6 + A7)
rMo = 3.16 -1.28A3
Tg = 456.1 + 0.57A7 + 1.51A8 + 1.31A10
xPS = 57.1 + 68.07 A2 - 42.37 A3
In order to test the reliability of the models, a validation glass (i.e., MV) is designed. The Ai values of MV (130 g, without Mo phase separation) are used to calculate the target properties by formulas (1) to (6), and the predicted values of each property are
rB =0.05 g·m-2·d-1,
rLi =0.06 g·m-2·d-1,
rNa =0.04 g·m-2·d-1,
rMo =1.49 g·m-2·d-1.
Tg=524.1℃,
xPS=83%.
The model prediction results show that MV glass can perform high Mo leaching rate, exceeding the EJ-1186 standard (ri<1 g·m-2·d-1). The Mo-phase possibility is 83%, indicating that MV glass has heavy Mo-phase separation. The rB, rLi, rNa meets the standard requirement. The large sample MV (800g) is prepared. Large area of MV glass is covered by Mo phase separation, which is scored by 70% by naked eyes, and the rB, rLi, rNa is qualified to EJ-1186. However, the rMo is as high as 0.91 g·m-2·d-1, which is close to the standard limit. Considering the test error, MV glass is not valuable for further investigation and measurement (such as viscosity, electrical resistance, liquidus temperature, etc.). The measured properties are
rB =0.06 g·m-2·d-1,
rLi =0.14 g·m-2·d-1,
rNa =0.15g·m-2·d-1,
rMo =0.91 g·m-2·d-1.
Tg=524.4 ℃,
xPS=70%.
The S-P models indicate that within the designed glass composition, the Mo phase separation can prevent effectively with the decrease of Si—O—Si vibrations at 518-528 cm-1, and the increase of B—O—B bending vibrations in [BO3] units. In order to figure out the components that affect the target structure as well as xPS and rMo, a detailed exploration of the components associated with the structure units that screen for PS and rMo from S-P models is simulated via S-C modeling. The results indicate that Li2O and CaO enhancement can increase the formation of Mo-phase, in which CaO can lead to the formation of the water resistance white crystal CaMoO4, while Li2O intensifies the precipitation of water-soluble Mo-yellow phase CsLiMoO4. SiO2 can affect the formation of CaMoO4 and CsLiMoO4. Certainly, Li2O can promote the Mo leaching rate.
Conclusions
A series of high Mo (MoO3 2.6%-3.3%), HLW borosilicate solidification glass was investigated by Glass Structural gene Modeling (GSgM) to establish the prediction models for the key elements (i.e., Na, Li, B, Mo) leaching rate rNa, rLi, rB, rMo and the Mo-phase separation. The rNa, rLi, rB, rMo and xPS with a satisfied accuracy were predicted. The results were summarized as bellow:
1) The main components of Mo-phase were water-soluble yellow phase CsLiMoO4 (yellow) and water-resistant white crystal CaMoO4.
2) The S-P models for all the target properties exhibited high accuracy (Rsq≥0.87) and satisfied statistical significance (P<0.000 1). The model validation proved the reliability of the models.
3) Composition-structure-property analysis showed that SiO2 variation could affect the concentration of Si—O—Si (at 518-528 cm-1) and B—O—B bending vibrations in [BO3] units, inducing two opposite effects on the Mo-phase separation, which could be evaluated via the simulated parameter calculation. Li2O enhancement increased the formation of water-soluble Mo yellow phase CsLiMoO4, and promoted the Mo leaching rate consequently. CaO could lead to the formation of the water resistance white crystal CaMoO4.
1.College of Materials Science and Engineering, Hunan University, Changsha 410082, China
2.Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
3.Nippon Electric Glass, North Carolina 28150, The United States
The solubility of Mo in borosilicate glasses is relatively low. Therefore, molybdate is easy to separate from glass, forming Mo-yellow phase (alkali molybdates, such as Na2MoO4, CsLiMoO4, and Li2MoO4) or CaMoO4 crystals. The crystal CaMoO4 performs a superior water resistance ability, which can effectively reduce the Mo leaching rate of a high Mo content and high level waste (HLW) solidification glass. On the contrary, alkali-Mo-yellow phase is highly water-soluble, leading to a serious Mo-leaching, and thus decreases the chemical durability of the products. The duration of the chemical durability test of solidification glass is 7 or 28 days, thus retarding the whole cycle for the investigation of HLW solidification glass. Effective predicting Mo-yellow phase and the Mo leaching rate can accelerate the research via saving time on glass preparation and chemical durability test. Based on the glass structural gene modeling (GSgM), this paper proposed the Structure-Property (S-P) prediction models of chemical durability and the possibility of Mo-phase separation (PS, its value is xPS) for a simulated high Mo content (MoO3 2.6-3.3%) HLW borosilicate solidification glass. The key elements (i.e., Na, Li, B, and Mo) leaching rate rNa, rLi, rB, rMo as well as the Mo-phase separation xPS were predicted by the models. The reliability and practicability of the models were proved. In addition, combined with the Structure-Composition (S-C) modeling, the C-S-P analysis was also carried out for xPS and rMo.
Methods
Fifteen borosilicate glasses were designed by an one-component-at-a-time (OCAT) method. Glasses with different weights (130 g and 800 g) were prepared for each composition. Small samples with the mass of 130 g were melted and quenched. Large glass samples with the mass of 800 g were melted, and annealed. The properties of the samples were determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) with KBr, differential scanning calorimetry (DSC) and PCT-7 day chemical durability test, respectively. Mo-phase (xPS) was evaluated and scored for each sample by naked eyes (from 0-100%, high score means high probability of Mo-phase separation). The structural data used for modeling were derived from FTIR peak fitting area Ai. Each FTIR spectrum was decomposed into 10 Gaussian bands by a software named GRAMS AI 32 according to the same fitting rules. The S-P and S-C models were constructed by a software named JMP based on the Cornell first-order linear mixture formula. The sample (glass MV) for model validation was also prepared and measured by the same procedure.
Results and discussion
No Mo-phase appeats in the small samples (130 g), while a serious Mo-phase separation (i.e., yellow phase and white phase) occurs in some large samples (800 g), which can be attributed to the Mo-phase accumulation and the slow cooling rate of large size glasses. The XRD patterns indicate that the main components of Mo-phase are CsLiMoO4 (i.e., water-soluble yellow phase, yellow) and CaMoO4 (i.e., water-resistant crystal, white). The S-P models with satisfied statistical significance (i.e., P<0.0001) and model accuracy (i.e., Rsq≥0.87) are proposed based on the Ai and glass properties. The corresponding prediction formula of the target properties (i.e., Na, Li, B, Mo leaching rate ri, Tg, xPS) are
rB = 0.085 -0.036A3 +0.024A4 +0.002A5
rLi = 0.13 - 0.052A3 + 0.005A5 + 0.005A6
rNa = 0.38 - 0.086 A3 + 0.008A6 - 0.003(A6 + A7)
rMo = 3.16 -1.28A3
Tg = 456.1 + 0.57A7 + 1.51A8 + 1.31A10
xPS = 57.1 + 68.07 A2 - 42.37 A3
In order to test the reliability of the models, a validation glass (i.e., MV) is designed. The Ai values of MV (130 g, without Mo phase separation) are used to calculate the target properties by formulas (1) to (6), and the predicted values of each property are
rB =0.05 g·m-2·d-1,
rLi =0.06 g·m-2·d-1,
rNa =0.04 g·m-2·d-1,
rMo =1.49 g·m-2·d-1.
Tg=524.1℃,
xPS=83%.
The model prediction results show that MV glass can perform high Mo leaching rate, exceeding the EJ-1186 standard (ri<1 g·m-2·d-1). The Mo-phase possibility is 83%, indicating that MV glass has heavy Mo-phase separation. The rB, rLi, rNa meets the standard requirement. The large sample MV (800g) is prepared. Large area of MV glass is covered by Mo phase separation, which is scored by 70% by naked eyes, and the rB, rLi, rNa is qualified to EJ-1186. However, the rMo is as high as 0.91 g·m-2·d-1, which is close to the standard limit. Considering the test error, MV glass is not valuable for further investigation and measurement (such as viscosity, electrical resistance, liquidus temperature, etc.). The measured properties are
rB =0.06 g·m-2·d-1,
rLi =0.14 g·m-2·d-1,
rNa =0.15g·m-2·d-1,
rMo =0.91 g·m-2·d-1.
Tg=524.4 ℃,
xPS=70%.
The S-P models indicate that within the designed glass composition, the Mo phase separation can prevent effectively with the decrease of Si—O—Si vibrations at 518-528 cm-1, and the increase of B—O—B bending vibrations in [BO3] units. In order to figure out the components that affect the target structure as well as xPS and rMo, a detailed exploration of the components associated with the structure units that screen for PS and rMo from S-P models is simulated via S-C modeling. The results indicate that Li2O and CaO enhancement can increase the formation of Mo-phase, in which CaO can lead to the formation of the water resistance white crystal CaMoO4, while Li2O intensifies the precipitation of water-soluble Mo-yellow phase CsLiMoO4. SiO2 can affect the formation of CaMoO4 and CsLiMoO4. Certainly, Li2O can promote the Mo leaching rate.
Conclusions
A series of high Mo (MoO3 2.6%-3.3%), HLW borosilicate solidification glass was investigated by Glass Structural gene Modeling (GSgM) to establish the prediction models for the key elements (i.e., Na, Li, B, Mo) leaching rate rNa, rLi, rB, rMo and the Mo-phase separation. The rNa, rLi, rB, rMo and xPS with a satisfied accuracy were predicted. The results were summarized as bellow:
1) The main components of Mo-phase were water-soluble yellow phase CsLiMoO4 (yellow) and water-resistant white crystal CaMoO4.
2) The S-P models for all the target properties exhibited high accuracy (Rsq≥0.87) and satisfied statistical significance (P<0.000 1). The model validation proved the reliability of the models.
3) Composition-structure-property analysis showed that SiO2 variation could affect the concentration of Si—O—Si (at 518-528 cm-1) and B—O—B bending vibrations in [BO3] units, inducing two opposite effects on the Mo-phase separation, which could be evaluated via the simulated parameter calculation. Li2O enhancement increased the formation of water-soluble Mo yellow phase CsLiMoO4, and promoted the Mo leaching rate consequently. CaO could lead to the formation of the water resistance white crystal CaMoO4.
Chen DAI, Hong LI, Liyan ZHANG, Lili HU, Xiaoli ZHU, Anlian PAN.
Structural Gene Modeling for Mo-Phase and Chemical Stability of Simulated High Level Waste Borosilicate Glass[J].
Journal of the Chinese Ceramic Society,
2024
, 52
(6)
: 2068
-2080
.
DOI: 10.14062/j.issn.0454-5648.20230947
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