Effect of borax on microstructure and viscosity of fluorine-free mold fluxes containing titanium-bearing blast furnace slag
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摘要: 为明晰硼砂作为氟替代物在含钛无氟保护渣中的作用机制，选用含钛高炉渣、石灰石、石英砂、纯碱、毒重石和硼砂等工业矿物原料配制含钛矿渣基无氟保护渣，采用分子动力学模拟和拉曼光谱技术研究了熔渣的偏径向分布函数、平均配位数、键角分布和结构单元Qn分布等结构特征，并从熔渣微观结构层面解析了宏观性能黏度随硼砂含量变化的内因。结果表明，随硼砂含量的增加（4%～12%），含钛矿渣基无氟保护渣的熔渣中Ca-O结构稳定性变差，低聚合度B-O结构大量形成，∠Si-O-Si键角有序度降低，结构单元Q0逐渐解聚转化为Q1和Q2，网络结构变得更加复杂且整体聚合度减小，即在宏观上表现为黏度性能下降；当硼砂含量增加至8%以上时，含钛矿渣基无氟保护渣降至低黏度水平并趋于稳定。Abstract: To clarify the role of borax as a fluoride substitute in fluoride-free and titanium-bearing mold fluxes, the test samples were prepared using industrial raw materials such as titanium-bearing blast furnace slag, limestone, quartz, soda ash, witherite, and borax. Molecular dynamics simulation and Raman spectroscopy were used to study structural characteristics of the samples, including radial distribution function, average coordination number, bond angle distribution, and structural unit Qn distribution. The intrinsic factors of the viscosity changing with borax content were analyzed from the perspective of slag structure. The results show that with the increase of borax content (from 4% to 12%), the stability of the Ca-O structure deteriorates, a large amount of low polymerization degree B-O structure forms, the order degree of Si-O-Si bond angle decreases, and the structural units Q0 gradually depolymerize into Q1 and Q2, making the slag structure more complex and the overall polymerization degree smaller. That is, the viscosity performance decreases macroscopically. Moreover, when the borax content increases to more than 8%, the fluoride-free and titanium-bearing mold fluxes reaches a low and steady viscosity level.
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图 1 B3渣样熔体中各原子对结构的偏径向分布函数
Figure 1. Partial radial distribution function of slag sample B3
图 2 硼砂含量对偏径向分布函数的影响
（a）Ca-O结构；（b）B-O结构
Figure 2. Effect of borax content on partial radial distribution function
图 4 硼砂含量对Si-O结构平均配位数的影响
Figure 4. Effect of borax content on mean coordination number of Si-O structure
图 5 硼砂含量对键角分布的影响
（a）∠O-Si-O；（b）∠Si-O-Si
Figure 5. Effect of borax content on bond angle distribution
图 6 硼砂含量对硅氧四面体Qn分布的影响
Figure 6. Effect of borax content on silicon-oxygen tetrahedron Qn distribution
图 7 不同硼砂含量试验渣的拉曼光谱分峰结果
（a）渣B1-硼砂4%；（b）渣B2-硼砂6%；（c）渣B3-硼砂8%；（d）渣B4-硼砂10%；（e）渣B5-硼砂12%
Figure 7. Raman spectrum peak separation of slags with different borax content
图 8 不同硼砂含量试验渣的黏度特征
（a）粘温曲线；（b） 1 300 ℃黏度值
Figure 8. Viscosity characteristics of slags with different borax content
图 9 硼砂对硅氧网络结构的分化机制
Figure 9. The differentiation mechanism of silicon-oxygen network structure by borax
表 1 配渣原料的化学成分
Table 1. Chemical compositions of raw materials
% 原料 SiO2 CaO TiO2 Al2O3 MgO Na2O B2O3 CaCO3 Na2CO3 BaCO3 含钛高
炉渣24.74 26.71 22.31 11.87 8.96 石英 98.32 石灰石 97.15 纯碱 >99 毒重石 >99 硼砂 30.49 68.51 
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表 2 试验渣的化学成分
Table 2. Chemical compositions of slags
% 渣号 CaO SiO2 Al2O3 MgO TiO2 BaO Na2O B2O3 B1 35.78 27.63 6.05 4.56 11.36 2.94 8.19 3.49 B2 34.88 26.22 6.01 4.54 11.30 2.93 8.91 5.20 B3 33.13 25.93 5.94 4.49 11.17 2.90 9.58 6.86 B4 32.27 24.56 5.91 4.46 11.11 2.88 10.28 8.53 B5 30.57 24.29 5.85 4.41 10.99 2.85 10.92 10.12
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表 3 分子动力学模型相关参数
Table 3. Molecular dynamics simulation related parameters
渣
号原子个数/个 总数/
个密度/
（g·cm−3）边长/
nmCa Si Al Mg Ti Ba Na B O B1 988 475 73 177 147 30 272 62 2776 5000 2.88 41.247 B2 967 452 73 176 146 30 298 92 2766 5000 2.81 41.488 B3 921 449 73 175 145 29 321 122 2765 5000 2.73 41.727 B4 900 426 72 174 145 29 345 152 2755 5000 2.67 41.946 B5 856 423 72 173 144 29 368 181 2755 5000 2.60 42.179
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