| Summary: | 碩士 === 國立屏東科技大學 === 生物機電工程系所 === 98 === This study applied electrochemical machining (ECM) to an AISI 316 stainless steel tube, reducing inner-wall roughness and thus the probability of the formation of ice nuclei, and increasing the roughness of the outer-wall relatively thin pipe walls to increase the probability of the formation of ice nuclei. This method can not only improve the heat capacity and conduction of AISI 316 stainless steel, but also effectively raises the freezing rate and resolves a weakness conventional cryopreservation containers – the poor mechanical strength of quartz tubes. In experiments, conventional liquid nitrogen placement methods and placements of liquid nitrogen agents, combined with ECM techniques were used to produce four different types of AISI 316 stainless steel tube (unprocessed, outer-etched unprocessed, interior and exterior polished, and interior and exterior polished followed by electrochemical polishing of the outer surface and electrochemical etching), to compare the freezing rate of conventional quartz tubes.
The results showed that for traditional quartz tubes conventionally placed in liquid nitrogen and liquid nitrogen agents, the freezing rates were 956.11℃ / min and 1732.38℃/ min but, during the freezing process, the increase in
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volume of the de-ionized water as it transforms from liquid to solid causes the brittle quartz tube to fracture, resulting in loss of the preservation solution and the container. For the four different types of AISI 316 stainless steel pipe frozen in conventional liquid nitrogen in our experiment, the freezing rates were 971.26-1403.57℃ / min and 1470.07-2975.93℃ / min. With more conventional methods of placement into liquid nitrogen, the freezing rate of the AISI 316 stainless steel pipe was higher than that of the quartz tube, and the the AISI 316 stainless steel tube which had been internally and externally polished followed by electrochemical polishing of the outer surface and electrochemical etching pipe had a freezing rate 47% higher than that of the quartz tube. The method of using the liquid nitrogen agents significantly raised the freezing rate compared to conventional liquid nitrogen methods, and with this method the AISI 316 stainless steel tube which had been internally and externally polished followed by electrochemical polishing of the outer surface and electrochemical etching had a 72% higher freezing rate than the quartz tube. This was due to the fact that, when compared to the liquid nitrogen treatment of the quartz tube, the stability of the electrochemically etched AISI 316 stainless steel tube during freezing effectively raised the freezing rate, remedying the problem of mechanical weakness of conventional quartz tubes, and providing a useful container for cryopreservation.
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