Make Crystals via Vacuum Distillation

by Jerry Liin Crystal Growthon Posted on

Table of content

  1. Introduction
  2. Metal Distillation Theory
  3. Experiment
  4. The End
  5. Reference

Introduction

Vacuum distillation is a widely applied in laboratories. Not only can vacuum environment prohibit most contaminations, but it also allows distillation to happen at lower temperature, which is both environment-friendly and time-saving. For most people, vacuum distillation is only a familiar process of collecting pure chemicals such as alcohols in a glass condenser, but here I will introduce you to metal distillation—a process gaining significance in the industry for producing pure metals cheaply and efficiently—that can be applied in home labs and use it to produce beautiful crystals for elemental collectors. This project is inspired by RGB(a element collection company in UK), who first provides the pretty mini metal domes and distilled crystals for us amateur crystal and element lovers.

Distilled Antimony Crystal Dome[1]
Industrially Produced Distilled Magnesium Crystal (Oxidized Due to Place in Air)

Metal distillation theory

I have posted part of my notes for a metallurgy college textbook.

Characters with ”*” is optional, not directly used in the experiments.

As an amateur, I only care about optimal furnace temperature, optimal pressure, and optimal diameter of my condenser. To make a crystal dome, I recommend you to use a finger-shaped condenser, though it is very inefficient.

The most useful content is in the ”Vacuum Evaporation Rate”. You should know how to calculate the critical pressure (optimum pressure) and the reaction rate.

For the optimum temperature, although I have posted some relative contents in the last chapter, please look at the book in my reference for more. I don’t want to post all of it because:

  1. Trust me, you will get satisfied results at a temperature a bit higher than the vaporization temperature, when your glass is quickly blocked by silver condensations.
  2. Too many equations make the post boring
  3. What do matter are the evaporated molecules’ temperature and the condenser temperature. Both are difficult to measure for amateurs (at least for me).

Basic definitions:

Molecular Interaction*:

Collision of Molecules with Container Walls*：

Vacuum Evaporation Rate：

Quantity of Condensation*:

Experiment

Here I use my first successful trial for zinc as an example. Zinc is cheap, non-toxic, relatively stable, and it can be distilled at a low temperature. Very friendly option for starters.

I haven’t yet gotten similar domes to the RGB ones. I feel like the diameter of my condenser is not correct. But I will update this after I deal with this problem and Covid.

Equipment

1. Vertical Pit Furnace

Buy one like mine will cost a lot, I won’t be able to afford it without my CVT project. But it is an easy DIY and you can find many cheaper options in the second-hand market.

Remember to test the thermometer’s performance at high temperatures. Let the producer to dig a suitable hole on the cap for the vacuum chamber before you purchase a furnace.

2. Vacuum Chamber

2D Blueprint
The Flange
The Quartz Body

Basic odules on your vacuum chamber (KF connector is recommended):

  1. Main port for the quartz or metal body
  2. One water-in port for the condenser
  3. One water-out port for the condenser
  4. One water-in port for the flange
  5. One water-out port for the flange
  6. One gas-in port
  7. One gas-out port
  8. One pressure detector port (here I have two—one for analogue meter and the other for digital meter
  9. One condenser port (either screw or weld the condenser on it)
  10. Weld something that can let you hang the heatproof blocks under the lid, which help to further cool the flange (mine has two hooks for the asbestos wire)
  11. (Optional) Two electrode ports for molten salt electrolysis or other detectors

It is better to use a metal body with a glass view port if you can solve the issue of heat conduction and fund. The quartz body is not very safe, so you need to make sure no cooling water leaks into the molten metal and causes explosion.

Test the gas leakage rate and make sure no cooling water leakage before experiments!!!

3. Vacuum Pump and Detector

An oil pump that can reach 50Pa is good enough for most works

You should have a suitable digital or analogue vacuum gauge. Accurate pressure control is the key.

My Inficon MPG400 is a full range digital gauge (to 10-9mbar), but here you only need cheaper ones that can go down to 10-2mbar (1pa). Make sure to buy second-hand digital gauges—new ones incredibly expensive but old ones incredibly cheap.

4. Cool Water Machine

I prefer to a cool water machine because otherwise you would waste much tab water and the condenser temperature would be hard to keep constant.

Again, there are many cheap ones on the second-hand market.

5. Other Items

For example: heatproof blocks, asbestos wires, crucibles…

Result

Material and Method

Material:

  1. Zinc metal 500g

Method:

  1. Temperature: 650ºC
  2. Distillation pressure: 130Pa
  3. Time: 45min

The End

For element collectors, we don’t care that much about the purity of the distillation product. So don’t go looking for dozens of research papers like I did, because scientists only care about purity and not about the beauty of the crystal. The relationship between variables and crystal shape has not been studied yet, so all we can do is experiment to find out (maybe I’m wrong because I’m not a professional in crystallography or I didn’t find the right article). In the end, I really enjoyed the process, finding out the effect of pressure changes on crystal shapes and using my hands to change natural reactions and create gifts never seen before.

Reference

[1] 戴. (2009). 有色金属真空冶金 (2nd ed.). 冶金工业出版社.