液态氮 Liquid Nitrogen

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My best friend was working at a research institute in New Zealand as an engineer a while back. He was also an avid photographer, and even convinced the institute to make him the official photographer. For that, he got a big space inside the institute as his studio. One time I visited him while he was at work, so he showed me his studio. I asked for some test tubes, beakers and a dewar of liquid nitrogen, and started getting busy.

我的好朋友之前在新西兰的一家研究所当工程師。他也是个摄影爱好者，还兼职当了研究所的御用摄影师。研究所还给了他一个很大的工作室来搞摄影。有—次我放假去找他。他没有假，就把我带到他单位的摄影工作室。干什么好呢？於是我问他拿了些试管，量杯，和一罐液态氮，来一次摄影实验。

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To create the effects seen here, I used a piece of reflective black paper to line the table where the beakers were placed. I also turned off all the lights and solely use an infrared controlled flash to provide the lighting. The different flashes can also be used to provide lights of different colour using coloured cellophane. Since liquid nitrogen is very cold, it boils as soon as it is poured into the beaker. The mist generated from the condensing water vapour can be used to create different kinds of smoke art.

为了制造较果，在摄影过程中我把量杯放在反光的黑纸上，把摄影室的灯都关掉，只靠闪光灯在不同角度打光。闪光灯还可以打颜色: 用红色，橙色和蓝色的玻璃纸就可以做出七彩的较果。因为液态氮很冷，一倒进溶器就会沸腾起来，空气中水汽会遇冷变成白雾，给人一种烟霞的感觉。

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Nitrogen liquefies at -195°C, so one must be careful when handling liquid nitrogen to avoid burns and frost bites from the cold. But as a material scientist, I am very familiar with the handling of liquid nitrogen. That's because a lot of low temperature experiments, such as low temperature photoluminescence and low temperature Hall effect requires the use of liquid nitrogen. In semiconductor processing, liquid nitrogen is commonly used to control the etch rate of chemical etching. Liquid nitrogen is also very useful in generating high vacuum, due to its ability to condense vapour such as water and oxygen.

液态氮的温度是零下一百九十七度，所以玩的时候要很小心，免得冻伤。不过作为一个材料研究者，我对液态氮早已熟悉。因为很多低温实验，例如低温光激荧光，低温霍尔效应等都需要液态氮。在半导体加工中，液态氮广范用於控制化学蚀刻的速度。液态氮还可以凝固水汽，氧气等，对制造真空起重要的作用。

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When I was doing my PhD, we need to use liquid nitrogen everyday for our ultra high vacuum system. However, our department does not produce liquid nitrogen, so I would need to make a trip to the Physics department everyday, pulling a dewar the size of a LPG bottle, to collect our daily ration of liquid nitrogen. There was one time when I met my best friend (same guy) on my way back from my my daily LN2 run, and I just pour a little bit out from the dewar to show him how cool it was. Because liquid nitrogen is very cold, white fog immediately started to form as water start to condense. It so happens that someone walked past, and as soon as she saw it she covered her mouth and nose and looked as us frighteningly and exclaimed, “Oh my god is that poisonous?” And then she started running. We laughed！Of course it was not poisonous! We are PhD after all and we ain't stupid!

在大学读博的时候，我们的超真空仪器每天都需要液态氮。而在我们工程系则没有液态氮。于是每天都要拉着个煤气罐大小的真空保温瓶去物理系大楼取液态氮。有一次拉氮的时候碰到的好朋友（就是在研究所的那个，我们是大学同学），我就从瓶里倒了点出来给他看。因为液态氮很冷，比水要冷，所以一倒出来就冒起了一股白雾。刚好有个人走过，看到这白雾就捂着鼻子以惊恐的眼神看着我们， “天啊，这是有毒的吗?" 然后匆匆忙忙走了。我们狂笑！当然是没有毒啦，当我们傻子吗？

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