| Superconducting materials have good applications in the fields of magnetic shielding,short distance large current transmission,electric power,and communication for information and new technology.REBCO series high temperature superconducting bluks(RE is rare earth element such as Y and Gd,Nd,Sm,Eu,Yb,etc.)have broad application prospects such as high field permanent magnets,superconducting maglev,superconducting magnetic bearing,and superconducting flywheel energy storage etc.GdBCO superconducting bulks with different number of seeds were successfully prepared by the Gd+011 new TSIG method in our laboratory.The large sized superconductors with a length of 60 mm,a width of 30 mm and a thickness of 20 mm which has large magnetic levitation force and strong trapped field.Mixed powder of Gd2O3 and BaCuO2,and 0.5wt%CeO2 were used as solid phase source.By adding a few Y2O3 pellet between the solid and liquid phase source pellet,it plays a supporting role after infiltration of the liquid phase to prevent the central depressed problem of large-size superconducting bulks and effectively improve the performance of GdBCO superconducting bulks.At the same time,this method can easily separate the residual liquid source pellet from the solid source pellet,and saves a lot of time.In order to solve the problem of multiple domain boundaries of superconducting bulks caused by the multi-seeded crystal method,we put seeds in a row and to be long strip,which can effectively reduce the domain boundary of the sample so as to improve the performance of the sample.The results are as follows:(1)The Gd+011 TSIG method was used to prepare the GdBCO superconducting bulk with a diameter of 20 mm and a thickness of 12 mm.The superconducting properties were not bad.(2)GdBCO superconducting bulks were fabricated by Gd+011 TSIG method,but cracks occurred at the interface between solid phase pellet and liquid phase pellet due to different thermal expansion coefficients of the two substances.In the process of assembling samples,several Y2O3 pillars were used to separate the solid phase pellet from the liquid phase pellet.It was found that the bottom of the solid phase pellet was no longer cracked,and the macroscopic morphology of the sample was perfect.Sample with a diameter of 30 mm,thickness of 12 mm was measured,and we found that the maximum magnetic levitation force of GdBCO superconducting bulk is 105 N,after magnetization with 1T magnetic field,it's maximum capture field is 0.79 T.(3)Discussed the method which is difficult to separate between the solid phase pellet and the residual liquid pellet of GdBCO superconducting bulks.Although we can fabricate single domain GdBCO superconducting material which has good performance by Gd+011 new TSIG method,we found that it is difficult to separate the residual liquid phase pellet from solid phase pelle in the process of practical experiments.The solution,which prevent crack of the solid phase at the bottom,has inspired us to remove residual liquid pellet.Because use pillars to isolate the solid phase pellet and liquid phase pellet,which has reduced the contact area of the two pellet.Repeated this method has obtained thick sample with the diameter of 30 mm,thickness of 16 mm,and the maximum magnetic levitation force close to 120 N.The sample was magnetized with 1T magnetic field,it's maximum capture magnetic field was 0.86 T.However,this method is difficult to control in the process of experiment,and the solid phase pellet is prone to tilt,so further study was made and got some improvements.After improving the process,thin samples with a diameter of 30 mm and a thickness of 10 mm were obtained,the maximum magnetic levitation force is 106 N.The sample was magnetized with 1 T magnetic field,and the maximum trapped magnetic field is 0.82 T,study have shown the sample has a strong magnetic field trapped ability.Therefore,this new assembly method is of great guiding significance for the preparation of large-sizeed superconducting bulks(4)Large sized GdBCO superconducting bulks are fabricated by the same method like small samples based on the experience of previous experiments.When several seeds crystals are arranged in a row to form long seed crystals,the grain boundary of the sample will be effectively reduced,and the sample performance get improved.In the fabricate process of large sized sample,sample is easy to happen center riding.And before the infiltration of oxygen,removed residual liquid pellet spent a lot of time,so we using method which be used to removed residual liquid phase pellet,and has solved the problem of big sample center sag,and solved the difficulty in separating the residual liquid phase pellet.At the same time it can prevent the crack of solid phase at the bottom because of the different heat coefficient between solid phase and liquid phase,and a choice serves three purposes.Finally,Large sized GdBCO superconducting bulks were obtained,which have good macro-structure.Through experiments,we fabricated large-sized superconducting samples with seeds of 1,2,3,4,5 and 6,respectively.Since the obtained samples happened unknown cracks after infiltrating oxygen gas process,further research is needed to be done.However,the performance of all samples is good.Some regular pattern have been established,which can be used for draw lessons from this way in future studies. |
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