Study On The Structure And Property Of La-containing Borosilicate Glass And Glass-ceramic

The isolation treatment of radioactive waste has always been a problem that must be solved to ensure the development of nuclear energy industry.Borosilicate glass-ceramic immobilization product is the best matrix for curing radioactive waste due to its many advantages.It is known as the"third generation solidified material"and has a broad development prospect.As the most typical lanthanide element,lanthanide not only contains a large amount in radioactive waste,but also can simulate the curing behavior of radioactive actinide in radioactive waste in the curing study,so the curing study of lanthanide is very important for the treatment of radioactive waste.Based on Si O₂-B₂O₃-Na₂O-Ca O-La₂O₃,glass immobilization product was obtained by high-temperature melting cooling method.The influence of La₂O₃content on the structure and properties of borosilicate glass immobilization product was studied,and the ultimate solubility of La₂O₃in the glass was obtained.In addition,the glass-ceramic immobilization product was obtained by high temperature melting cooling and secondary heat treatment.The influence of component change（Si/Ca and Na/Ca）on the structure and properties of borosilicate glass-ceramic immobilization product was studied,and the optimum component formula of the preparation of lanthanum borosilicate glass-ceramic immobilization product was obtained.Finally,the optimum crystallization temperature and nucleation temperature of the glass-ceramic solidified body were investigated.Using XRD,DSC,FTIR,SEM,ICP and other analysis methods,analyzed the samples.The following conclusions were obtained:（1）The effect of La₂O₃content on the structure and properties of the borosilicate glass immobilization product:It was found that La₂O₃would destroy the structure of the glass network and play a depolymerization role,and the higher the content of La₂O₃,the stronger the depolymerization effect.With the increase of La₂O₃content,the volume density of glass immobilization product is increases,T_gis decreases,and T_pis firstly increases and then decreases.Borosilicate glass can cure Ca and La effectively and has excellent leaching resistance.The ultimate solubility of La₂O₃is 9 mol%.（2）The influence of Si/Ca on the structure and properties of the glass-ceramic immobilization product:The decrease of Si/Ca of samples can promote the precipitation of silicate oxyapatite,and inhibit the precipitation of other crystalline phases,and the decrease of Si/Ca can promote the transformation of silicate oxyapatite crystal from Na La₉（Si O₄）₆O₂to Ca La₄（Si O₄）₃O.With the decrease of Si/Ca,the volume density value is increases and the molar volume value is decreases.The change of Si/Ca will affect the crystal distribution,crystal shape,crystal type and grain size in ceramic phase.The smaller the Si/Ca of the sample,the lower the leaching rate of each element,the better the chemical stability,and silicate oxyapatite phase glass-ceramics have excellent curing ability for lanthanum.The optimum Si/Ca for preparing borosilicate glass-ceramics is 52/15.（3）The influence of Na/Ca on the structure and properties of the glass-ceramic immobilization product:It was found that increasing the Na/Ca of the sample can promote the precipitation of Ca La₄（Si O₄）₃O silicate oxyapatite crystal,and when the Na/Ca of the sample is a lower value,the increase of the Na/Ca will has a greater ability to promote the precipitation of Ca La₄（Si O₄）₃O.With the increase of Na/Ca,the volume density is decreases and the molar volume is increases.The change of Na/Ca will affect the crystal distribution,crystal shape,crystal type and grain size in ceramic phase.With the increase of Na/Ca,LR_Siincreases gradually,while LR_Caand LR_Ladecrease first and then remain unchanged.The optimum Na/Ca for preparing borosilicate glass-ceramics is 7/17.（4）The optimum crystallization temperature and nucleation temperature of preparing the glass-ceramic immobilization products were investigated:It was found that the intensity of Ca La₄（Si O₄）₃O diffraction peak of glass-ceramic immobilization product first increased and then decreased with the increase of crystallization temperature.With the increase of nucleation temperature,the intensity of Ca La₄（Si O₄）₃O phase diffraction peak also increases first and then decreases.Both crystallization temperature and nucleation temperature affect the distribution and grain size of the crystals formed in the glass-ceramic immobilization product.The optimum crystallization temperature and nucleation temperature of the allover silicate oxyapatite glass-ceramic immobilization product are900℃and 620℃,respectively.