[sysyyang9184]

I'm a high school student in South Korea, and my school has this thing called 'Science Day' where you can do any experiment you want. I am planning to make pykrete, but apparently it takes a rather long time to freeze the mixture of sawdust and water, and the experiment has to last less than 2 hours. So, I thought about it, and I came up with the idea of using liquid nitrogen to freeze it, but i'm not sure if it will work. (http://en.wikipedia.org/wiki/Pykrete)

[curiouscat]

It could work. I see no theoretical reasons why not.

But often practical problems arise unanticipated. e.g. will the liq N2 cooling be so fast that the slab cracks?

If you try direct injection of liq  N2 then you face also the trapped gas bubble problem.

[sysyyang9184]

Is there any other way for me to freeze it within one and a half hours? I saw a site that mentioned using compressed ice, but it's never been tested before.
Also, I don't need a large amount, a block the size of a paper cup would be enough.