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I am new to chemistry, having gone down an electronics route in my career, so I decided to pick up where my 'O' levels ended (many years ago) and make a better understanding of the topic a sort of hobby.

As it seems it's almost impossible, at least as an individual, to obtain strong acids in this country. I am forced to create my own....

The research I've done so far pointed me to the Berkland-Eyde Process, being a means to directly synthesise Nitric Acid from air and being 'safer', with less also hard to obtain ingredients, than most other methods.

I built a Berkland-Eyde apparatus, and in about 8 hours managed to create a rather paltry yield of 250ml of 6% concentration HNO3. Which I could concentrate to ~60-70% through distillation, though that would be a very small yield for a rather large effort in time and equipment.

I notice that articles on this use significantly larger currents (I am limited to just 20mA at 10kV without spending a lot on a more powerful PSU)

I came here to search for answers and was surprised to find this question or anything like it does not exist - so here it is!

I could try to obtain an old style Neon sign transformer, but they are rare. Modern powerful ones are very expensive and I am looking for a cheap solution, i.e. This is just for self education and not worth investing in.

I have found a cheap 600W/50kV/DC (adjustable) PSU, huge compared to my current 200W (probably less) 20mA/10kV/400Hz/AC one (which is not happy about what I am asking of it, as it gets hot and is starting to arc internally).

Other options I have found:

Firstly, and the main purpose of this question:

  1. Would using DC rather than AC make a significant difference?

There are some other related questions (perhaps I should write more than one question?):

From a physics and chemistry perspective what attributes optimise the result, e.g. Any combinations of:

  • Geometry:
    • Area of air flow vs arc
    • Arc length
    • Electrode shape
  • PSU:
    • Current
    • Voltage
    • Power
    • Polarity
    • Frequency
    • Duty cycle (big regular pulses vs smaller contiguous arc)
  • Electrode temperature
  • Flow rate
  • Pressure
  • Additional attributes, e.g. Presence of magnetic field
  1. What is the best 'balance' between voltage and current? Is it the hot electrode or the gas plasma that does the work? I ask this as the PSU is adjustable so at a lower voltage I can have more current (within limits).

  2. A higher voltage means a longer (or hotter) arc. Would constraining the air path and forcing it past the electrodes be better than slowing the air down to have it spend longer in the reactor?

My current electrode are Tungsten TIG welding rods, which seem to work and I don't get any noticeable discolouration of the product, but:

  1. I have been advised that the red hot Tungsten reacts with the small quantity of acid present in the reactor due to water vapour being pulled in. This is true and what should be used instead. I first tried copper but it immediately melted.

  2. Is there any data on the rate of generation I should expect for a given air flow rate and voltage?

UPDATE: I read up on the current state of law and found that I was given incorrect information. Now a license for certain substances can be obtained by individuals rather than just corporate entities. In searching for this I also found a list of other controlled chemicals, to which I linked for completeness.

Substances on that list now require a license to possess (costing £40 and lasting 3 years) this is now to control (rather than prevent purchase as was the original intent from 2014) as a non-corporate entity - so actually an improvement!!

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  • $\begingroup$ I expect this is the topic of a PHD, any takers? $\endgroup$
    – Jay M
    Commented Nov 19, 2023 at 15:37
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    $\begingroup$ The process is so inefficient that you'd be paying far more for energy use than it would cost to buy ammonia water (or liquid NH3, if available) and convert it to $\ce{HNO3}$ by the Ostwald Process: en.wikipedia.org/wiki/Ostwald_process. $\endgroup$ Commented Nov 19, 2023 at 18:26
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    $\begingroup$ It is surprising to hear that you are able to find Tungsten TIG welding electrode, Neon signs PSU, CO2 laser PSU, and that you are unable to get ordinary nitric acid... $\endgroup$
    – Maurice
    Commented Nov 19, 2023 at 20:03
  • $\begingroup$ @Maurice: This UK legislation stems from the historic problems in Northern Ireland. I understood that unless a trading company, any strong acid (and for lots of other stuff) you need a government issued license to purchase any quantity and the seller has to keep records of the identity of the buyer - no company - no buy. I just read today that recent legislation (Oct'23) makes it illegal to possess certain items - which means I have to destroy my pathetic attempt :-| but it also opens things up as anybody can get a license if they pass a set of tests.... $\endgroup$
    – Jay M
    Commented Nov 20, 2023 at 15:33
  • $\begingroup$ As an electronics engineer I already have a PSU and I own a TIG welder (three in fact). $\endgroup$
    – Jay M
    Commented Nov 20, 2023 at 15:34

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