My first time mixing Kroll's reagent

[Jodo]

I am going to etch some titanium and need to mix up a 100ml batch of Kroll's reagent ( 92ml distilled water, 6ml nitric acid and 2ml hydrofluoric acid.
Do I add the nitric acid to the water first and then add the hydrofluoric or vice-versa?

 

[DrDu]

I don't think this matters. Be careful with the HF.

 

[Mayhem]

I feel like if you have to ask this question, you shouldn't be working with HF.

 

[Jodo]

I don't think this matters. Be careful with the HF.

Thanks DrDu. Chemist at the local research lab advised the same thing last night.

 

[DrJohn]

HF is definitely NOT for beginners.
IF HF lands on a finger, it goes through the skin with initially no pain, meets the bone, turns it into CaF₂ and the rest of the bone dies, and the fingertips will then be removed. Depends on the amount of course, but more than a couple of drops is highly risky.

A fellow researcher once told me about her accident with HF a few years earlier - a "simple" spill on all of one hand's fingertips. Just so I'd know how to react if she had a second incident as there were only ever two or three of us in our lab at any moment.

She had been rushed to hospital by the lab staff (who knew all about the possible outcome). And due to its location near the University, they too had a little bit of experience with this problem. They injected the antidote (calcium gluconate) under all five of her fingernails. To reduce the time and therefore the damage that would be done, they skipped using an anaesthetic! So I kept a few extra metres away when she had to use it in a couple of experiments she needed to do. And also decided I'd try to avoid ever using it.

To make that decision of mine clearer, I've worked with silanes and boranes (gases which explode on contact with air), Ni(CO)₄ (the joke we used was "so poisonous that if you can smell it, you're already dead) and fluorophosphines (related to nerve gases). But HF - no.

So are you sure you really need to do this?

PS HF eats glass for breakfast.

 

[Jodo]

HF is definitely NOT for beginners.
HF goes through the skin with initially no pain, meets the bone, turns it into CaF₂ and the rest of the bone dies, and the fingertips will then be removed. Depends on the amount of course, but more than a couple of drops is highly risky.

A fellow researcher told me about her accident with HF a few years earlier - a "simple" spill on all of one hand's fingertips. Just so I'd know how to react if she had a second incident as there were only ever two or three of us in our lab at any moment.

She had been rushed to hospital by the lab staff (who knew all about the possible outcome). And due to its location near the University, they too had a little bit of experience with this problem. They injected the antidote (calcium gluconate) under her fingernails. To reduce the time and therefore the damage that would be done, they skipped using an anaesthetic! So I kept a few extra metres away when she had to use it in a couple of experiments she needed to do. And also decided I'd try to avoid ever using it.

To make that decision of mine clearer, I've worked with silanes (gases which explode on contact with air), Ni(CO)₄ (the joke we used was "so poisonous that if you can smell it, you're already dead) and fluorophosphines (related to nerve gases). But HF - no.

So are you sure you really need to do this?

Thanks for the heads up DrJohn. I normally work with structural steels and I have been polishing/etching weld cross sections since the mid 90's ( nital etch ).
I can buy Kroll's online at a cost of 88 dollars for 250ml. Seeing as I already had the nitric I was trying to save a few bucks. Also 250ml is way more then I really need so I "mooched" 2ml of HF from a local lab . I actually had them mix it for me this morning ( I used to sell this same lab Silane on a regular basis. It's great to have contacts in high places )

 

[Borek]

Nota that even if technically the ready reagent is not a "HF solution" it contains exactly the same HF, which makes it similarly dangerous.

 

[DrDu]

Nota that even if technically the ready reagent is not a "HF solution" it contains exactly the same HF, which makes it similarly dangerous.

Ok, but it is very diluted. I know a guy who works in the production of some steel parts and they use these kind of HF baths in production. One of his colleagues fell into the bath and survived without damages.