Wet powders, ventilated oven and safety

[MinamotoKobayashi]

Hello forum.

I live in Italy, Po Valley, Padova city.

The Po Valley is a lowlands sorrounded by mountains, and here there is often the fog or the mist, in the seasons relation.

The humidity percentage is high, and this is a great problem for the powders!

Usually I buy potassium nitrate without anti-caking (I'm a purist ), but the powder is wet, and if not, it becomes!

So this is my procedure: the first step is to put the powder in an electric grinder to eliminate the lumps and to make it more fine, less granular.

Then I put a 1/2 cm thickness of powder on a rectangular metallic plate inside my ventilated electric oven at 100°C (212F) for 20 minutes.

After this I expect to cool it a little, and finally I put it inside my ball mill for 4 hours at 70RPM with my 100x1.5cm brass balls.

The powder become really fluffy, completely impalpable, a real wonder!

To keep it dry I put the powder in a near-vacuum vessel.

So far, so good .. BUT! Can I do the same procedure with other powders?

For example, with sulphur? Or barium nitrate?

Which ares the powders that cannot absolutely putted inside a ventilated electric ove?

At 212F for 20 minutes there is the risk of auto-ignition or exhalation of toxic fumes?

I need ABSOLUTELY to know those important informations before to create damages !!

Thanks for the help.

Richard.

 

 

[NeighborJ]

Richard, an electric oven will almost always create radiant heat. This radiant heat from the elements will heat the surface of the powder above and beyond the setpoint of the thermostat. It is almost impossible to determine how hot the surface becomes. As long as you are drying only individual chemicals there will be no danger of ignition because it will lack one of the three things required for ignition, heat, fuel, and oxygen.

 

It is common practice to dry chemicals in a dedicated oven and in a safe location but 20 minutes may not be long enough. Usually an hour or even two at the ovens lowest setting is required to dry most chemicals thoroughly.

 

Jason

Edited June 9, 2017 by NeighborJ

[MinamotoKobayashi]

Hi NeighborJ, and thanks a lot for the hints!

Do You think that the "ventilated" extra can help to keep the temperature of the powder surface lower (and also the capability to extract the humidity faster/better)?

My oven fans are really active, I can feel the moving air inside!

[NeighborJ]

I think the ventilated oven would remove moisture much quicker and would pose no problems. The only thing which could become a problem is if the chemicals you are drying are fine enough to become airborne. It could create deposits of various chemicals thruought the oven which may become a hazard.

If the ventilator fan can be turned off then it would be ideal for those airfloat chemicals. If it doesn't have a fan switch then you may be able to cover or shield the tray from the fan.

[Sulphurstan]

Richard. You were writing about Ba(NO3)2. Just be careful if you dry it with the fan, if it becomes airborne, it might be dangerous. This chemical is really nasty. For kno3, no problem.

[OldMarine]

Sulphur is almost hydrophobic so I don't dry it but my nitrates (potassium and sodium) and charcoal now get dried in my toaster oven for 2 hours before being placed in containers with silica gel packs. I was wrong. Barium nitrate is hygroscopic as well.

Edited June 10, 2017 by OldMarine

[Arthur]

Sulphur melts at 115C, If you have powder don't melt it, it's a pain to powder it again (it coats milling media).

[MinamotoKobayashi]

x NeighborJ: yes, I can turn off the fans. And also I can decide to use the 2 top, the 2 bottom, or all the 4 resistors.

Hovewer in my oven I use only rough granular powders.

The only powder that I buy in fluffy-state is the charcoal, but it is sealed already dried.

Whn the powders are dried and ballmilled, I put them in a near-vacuum anti-static plastic container

and put inside some silica gels bags like these:

 

 

x Sulphurstan: usually when I work with airfloat powders I wear this kind of mask:

 

 

 

This mask has two filters: one for the toxic steams and another for the toxic powders.

Sorry for the big images, there is no chance to reduce them directly from an URL

Edited June 10, 2017 by MinamotoKobayashi

[lloyd]

"The only powder that I buy in fluffy-state is the charcoal, but it is sealed already dried."

------------------

Don't you even begin to believe that! Charcoal is almost the worst absorber of atmospheric moisture! All the others 'tell the tale' when they get wet -- they become clumpy, hard to manage, and difficult to mill without clumping.

 

But charcoal can be wet to an ugly degree, and not manifest any of those symptoms.

 

Lloyd

[MinamotoKobayashi]

Hi Lloyd.

So You are telling me that the charcoal looks fluffy and vaporous also if it wet?

 

Recently I have done 200 gr of BP with my ball mill and the powder burn almost instantly like a flash, and I used airfloat charcoal without dry it.

This means that the charcoal was well dry?

[lloyd]

So You are telling me that the charcoal looks fluffy and vaporous also if it wet?

 

Yes. In fact, yes, indeed!

 

Recently I have done 200 gr of BP with my ball mill and the powder burn almost instantly like a flash, and I used airfloat charcoal without dry it.

 

Yes. It works in BP wet or dry.

 

This means that the charcoal was well dry?

 

No... not at all. Treat your charcoal as you would any other hygroscopic chemical, and dry it with heat. In 'plain BP', it seems not to matter. In other compositions, 'wet' charcoal will cause the powder to cake badly in mills.

 

IF you made the charcoal yourself, and packaged it as soon as it was cool, then I would feel comfortable calling it 'dry'. If you purchased it, always consider it 'wet' until properly dried.

 

Lloyd

[Sulphurstan]

Richard. Have you tried calcium chloride? I find it even better than silica gel...

 

Regarding the masks, I should wear these masks too when screening all my chems. In fact I only use masks when handling barium nitrate. Lloyd, is that wrong? (asking you, knowing you re on the professional side), but anybodys's answer is welcome..

[lloyd]

Sulfur,

I (during hobby activities) will "pick and choose" when to use breathing gear. I generally pick my days to mix so that a light breeze quarters off my left shoulder, and that keeps me from picking up much dust. But I always wear the lung gear when working with powdered dichromate or with barium nitrate.

 

For the professional side; ALL our employees are required to wear protective gear when mixing anything dry -- period.

 

Lloyd

[Mumbles]

I prefer wearing those half face respirators whenever mixing dry chemicals. The paper mask don't work all that well, but are better than nothing.

[Draco_Americanus]

One thing i do when drying things in my oven is to let it stabalise before putting anything in it and using a thermocuple type thermometer in the oven and even in the chemical I am trying to dry, an oven my fluctuate quite a bit before the temp is stable

 

I also use a half face respirators for just about every thing, even for charcoal, that way your not sneezing up charcoal for the next week, that and it is just a good habit to have, the more you wear one the less annoying they are to wear

I also like these

https://www.uline.com/Product/Detail/S-20752/Safety-Glasses/Flex-Seal-Safety-Goggles

 

they fit well with a half face respirators, at lest for the 3M model I use

[MinamotoKobayashi]

LOL Draco ... I use the same goggles:

 

 

I breathed a lot of airfloat charcoal the first time that I have make BP, and I was sneezing black for two days. Also I have found a fine black layer everything in my room ... it was distressing

It is a good idea to wait a bit until the temp is stable. I will do the same thing, thanks for the hint!

 

P.S. usually I do not wear anything when I'm handling fluffy potassium nitrate. It can cause issues?

[Mumbles]

All fine particulates can cause general irritation, and enough of any chemical will cause health issues. Very light or very high surface area materials like charcoal, lampblack, cab-o-sil, and flake aluminum powders are the worst culprits for getting airborne but anything can do it to some degree. I really try to avoid getting potassium nitrate in my air passages as I find it to be particularly irritating. It dries out you nose and throat if much is breathed in. In larger doses there are other complications, like with all nitrates, potentially causing issues with the oxygen carrying capacity of blood. This is an extreme case and would require very abnormal conditions and circumstances relating to pyrotechnics.

[lloyd]

I might add that some commercially-available nitrates have anti-cake agents in them. Although the nitrate (itself) isn't terribly prone to becoming airborne, the anti-cakes are.

 

PURE KNO3 doesn't seem to bother me. Charcoal is messy and can cause respiratory irritation. Barium nitrate requires breathing protection, as does potassium dichromate. If you use Cab-O-Sil or its equivalents in your milling (or have similar anti-cakes in your precursors), you should always wear protection, because it can cause silicosis.

 

Lloyd

[Mumbles]

If made correctly cab-o-sil, a fumed silica, actually wont/shouldn't cause silicosis. Fumed silica is amorphous. Crystalline silica is the one you avoid.

[lloyd]

I agree, Mumb, but many of the supposed Cab-O-Sil 'equivalents' are hardly-more than ground-up sand! Mostly, you find those in Chinese products, along with things like TCP (which isn't really great to breathe, either. 'Causes pneumoconiosis [if I spelled that right]).

 

Lloyd

[Sulphurstan]

Yes, wearING resp. protection when inside is a must for most chemicals, but i DO love the little breeze outside, as mentionned before. I do it this way also (and it keeps your working bench clean, double benefit!)

[Baldor]

About the different types of ovens...

 

Cheap toaster ovens are the worst for acheiving stable and precise temperatures, but are the easier to modify for some precision. Just buy a cheap electronic thermostat (Something like this, the cheaper you can find.) some K type thermocouple, and depending the power of the oven and the relay in the thermostat, a solid state relay. Make a hole in the oven so you can place the thermocouple in or over the composition you are drying, set the oven thermostat to max, and control the mains of the oven with the external thermostat. The difference is abysmal, you will be measuring at the point in space you need to know the temperature, and even the cheapest thermostats have a lot of parameters you can control, like hysteresis. Of course, you can go fancy and expensive, and use a PID controller. Toaster ovens are modified like this for soldering surface mount PCBs.

 

If you have a thermocouple thermometer, or a multimeter with a thermocouple you can easily check the difference between the set temp in a toaster oven and the real temp in the material you are drying.

 

Ventilated are much better at maintaining an stable temperature, but most difficult to tweak. There are two main types. With heating elements above and bellow, and a fan that circulates air, and the ones with the heating element around an axial fan. The second ones can be very precise, since no radiant heat is projected over what you are cooking, and all the heat is transmitted through the moving air. (convection ovens)

 

(Disclaimer: I'm in the hostelry equipment spare parts industry)