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sublination is going directly from a solid to vapor state, evaporation is going from a liquid to a vapor. to "evaporate" a solid, usualy the solid melts and evaporates. a liquid quickly evaporating we call boiling. slow sublination is called "freeze drying",,, unless your hobby is combining vocabulary and thermo-dynamics we are trying to split hairs here. i do not know what difference this makes??
The difference is that the idea of converting OA to Formic Acid discourages some from using it. The discussion is to determine if it can even happen with this sort of equipment.
 

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Is it fact or fiction that oxalic acid breaks down to formic acid, carbon monoxide and water when it undergoes sublimation? If it is false we can forget about that whole idea!

According to the above post sublimation will only occur at a higher temperature than vaporization. Not talking about adding more heat energy; heat and temperature are not even close to being synonymous!

OA has been used as a catch all term but as viesnest pointed out the two forms of it monohydrate and dihydrate have very different properties. Some of the arguments here seem to take for granted they are identical. In the form beekeeps will see the OA Dihydrate first has to be converted to the monohydrate which is a solid from whence the sublimation occurs. We see this as melting into a liquid as the water boils off. If you apply energy too quickly it will boil over or splatter. As the water boils off the percentage of solids will increase and some vaporization or sublimation will start to occur. As has been mentioned these processes will overlap and occur together.

I think everyone is familiar with how a drop of water will dance around on a hot stove top supported by the layer of steam escaping from it.

Now if you use drops of muddy water or containing dissolved solids you will see colored trails where the water droplet danced around. The water drop itself would not be above 212F, (its boiling point), but the temperature of the steam layer between it and the stove will be above this temperature otherwise no heat would be transferring into the droplet but we know it is getting smaller so have to assume a temperature differential. Note, the deposited mud or dissolved solids underneath the water ball or in its trail are quite free to rise to the temperature of the stove top.

The oxalic acid monohydrate that is left behind as the water of hydration is driven off would be in contact with the pan of the vaporizer in a similar situation as the dissolved solid in the dancing water ball is it evaporates.

What is the decomposition temperature? I think it is a fair bit higher than the vaporization or sublimation temperature and unless the pan is greatly over driven I doubt there would be more than a rather small percentage of the charge that experienced it. Somebody must have deemed it to be of some importance though as it used to be quite a precautionary advisory. Unless we ensure proper sizing of heat input by design or luck, we should not assume that portions of the pan are not at some higher temperatures than some of the contents and we also cannot assume that some solids cannot in that scenario, be overheating.

Incidentally many substances will sublimate from the solid to the vapor without going through the liquid stage and often at a much lower temperature than the melting point. Water is one such substance.
Steam is not greater than 212 degrees. I suppose I would have to look at ice and see if it can go directly from ice to steam. I also understand your point that if water or OA come into direct contact with a 1250 degree surface. it must be getting hotter than 212 degrees. not true. it reaches 212 and converts to steam. it just does so quickly. resulting in something more liken to an explosion rather than boiling. Would OA react the same? possibly, it might just result in a much faster vaporization.

I did go look up several temperatures because it seems like quite a few are getting tossed around. Specifically the melting, boiling and flash point of OA. This is what I found.
melting (sublimation/ vaporizes or boils) 216 to 217 degrees F dihydrate 214.7. (Note there is no boiling point listed for OA due to the sublimation. melting and boiling are basically the same temperature).
flash point is 331 degrees F.
Sublimation (decomposes) temperature is 372 degrees F.

So part of the issue is you have two sublimation temperatures. one where it sublimates to vapor while the other is a chemical decomposition. The vaporization happening just over the boiling point of water while the second happens well past the temperature that OA caught on fire. So as long as you don't catch your OA on fire I am not sure you have much to worry about.
 

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Steam is not greater than 212 degrees
Steam under pressure certainly is greater than 212 degrees.

The temperature difference regarding the drop of water supported by steam on a hot surface is fairly small, but that steam IS under pressure. That small amount of steam is pressurized by the weight of the water droplet above the steam.

This is in reference to this part of Frank's earlier post ...
I think everyone is familiar with how a drop of water will dance around on a hot stove top supported by the layer of steam escaping from it.

Now if you use drops of muddy water or containing dissolved solids you will see colored trails where the water droplet danced around. The water drop itself would not be above 212F, (its boiling point), but the temperature of the steam layer between it and the stove will be above this temperature otherwise no heat would be transferring into the droplet but we know it is getting smaller so have to assume a temperature differential.
 

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I suspect that the weight of water is already considered when it comes to the boiling point of water. maybe not. I would think that surface tension would also be a like factor. I know elevation changes atmospheric pressure and does effect the actual boiling point of water. Water will boil at a lower temperature here at 5000 feet than it does say in LA at near sea level. I don't think that indicates the steam gets any hotter. In fact by looking it up it does not. I looked up if you can burn water and so far came up with no you cannot. so the idea that water/steam ever increases above the 212 does not happen without an increase in pressure. Water placed directly on a burner not only transfers heat rapidly. possibly resulting in a violent or fast conversion to steam. but boiling itself is a metaphor for violent action. So it appearing violent is nothing new. Does OA react similarly? From what I can find OA does not boil. indicating it may not have a similar violent reaction. it simply converts from a solid to a gas. Consider the action of boiling to that of the steam rising from the pot. It would seem to me that OA may have the steam rising portion without the violent boiling portion. There is still the issue of other things in the OA and how they react. such as water. it will still act like water. How much would a fast heat transfer cause the water to erupt and disturb the OA?

I see three leading concerns with OAV.
1. does it even work?
2. even if it does work are you producing other nasties in the process?
3. it takes to much time, effort or both.

Faster treatment times seem to be getting hitched to issues of creating nasties. Seems to me an issue of seeing a ghost in all the places you cannot see.
 

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Daniel much of the stuff you are expecting to be accepted as fact you are just pulling out of your hat. I know you like to argue! Where did you get that OA catches on fire? Where did you get that the sublimation temperature is 372F.

The temperature of steam indeed can be increased far above its emanating temperature without the need to pressurize it further. You are confusing the elevated boiling point of pressurized water and subsequent steam temperature to indicate that steam could not ever be heated any hotter than the boiling point of the water that produced it. It most certainly can! Colloquially it used to be called dry steam ( steam at a temperature above its condensation temperature) Just add heat to it and it contains more energy at the same pressure. This is not advanced theory by any means.

Here is a link to some information on Oxalic acid and reactions.

http://www.uq.edu.au/_School_Science_Lessons/UNChem1.html#3.30.10
3.30.10 Decomposition of oxalic acid
Oxalic acid begins to sublime at 100oC, becomes anhydrous at 189oC and when heated rapidly decomposes into carbon dioxide,
carbon monoxide, formic acid and water.

It seems oxalic acid will start to sublime slowly at even lower temperatures. The rate of heat input will affect the amount that sublimes and the amount that could be forced into decomposition. A gentle heat input will result in sublimation while rapid input will result in some decomposition. I would think this would be near the end of the process where the volume of the solid OA dihydrate decreases and the pan temperature increases. I think any reasonable amount of heat input would not cause decompositiion.

What we as beekeepers are looking for is simply a change of state where oxalic acid is driven off in the form of a vapor which immediately reforms into the micro crystalline "smoke" that gets deposited on all hive contents.
It is not necessary or desirable to produce decomposition elements.
 

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Crofter, meet your own requirements and show your sources for information that you think you have about me.

This is one of my sources.

https://pubchem.ncbi.nlm.nih.gov/compound/oxalic_acid#section=Odor
scroll down to 4.2.4 Also note that this list gives it sources.

as for your source
189 degrees C is 372 degrees F. So I guess you don't need my source for that information you found your own.
100 C is 212 degrees F. Which your source says is the temperature OA begins to Sublime. it does not give the range my source did and claims a lower temperature. Mine says 215.
It says nothing about how heat it to 372 degrees. Only that if you do and now evidently rapidly. Information in a search on how to Produce Formic acid from Oxalic acid is extremely contradictory to the claim that the heating is quick. one method requiring the heating of OA to a specific temperature range for an hour while additional doses of OA are added to a distillation chamber. A second method is described also requiring a distillation chamber the use of glycerol and OA mixture that then produces a rapid production of Formic Acid. but it is hardly done on a hot plate with OA alone.

Actually every method of obtaining Formic Acid from OA requires an OA glycerol mixture so the claim that you can convert OA to Formic acid is a half truth or otherwise known as a lie. Formic acid can be produced from a mixture. and OA is just one part of that mixture. Kind of convenient to omit that detail.
 

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I see you are starting to get your head around the difference between sublimation and decomposition; good! I suppose the contradiction about temperatures required to achieve sublimation and avoid decomposition is the matter of degree. If your focus is to avoid the latter then slower application of heat is the takeaway. You are getting drawn off into the deliberate production of formic acid which is what is trying to be avoided here.

My source for steam theory goes back a lot of years to apprenticeship training. I just did a google now and if you want to get some steam theory search "dry steam, saturated steam" for starters. Lots of misconceptions about steam properties and in general change of state reactions of other gasses; Not much disagreement though amongst those who actually work with it.
 

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Regarding the formation of formic acid from (over)-heating of oxalic acid, this MSDS sheet for oxalic acid is interesting reading. :D
http://hillbrothers.com/pdf/downloads/msds/sds/n/oxalic-acid-sds.pdf

Under the "General Fire Hazards" section of that MSDS is this little gem ...
When involved in a fire, this material may decompose and produce irritating and toxic gasses (e.g. carbon dioxide, carbon monoxide and[HIGHLIGHT] formic acid[/HIGHLIGHT]).

http://hillbrothers.com/pdf/downloads/msds/sds/n/oxalic-acid-sds.pdf
That MSDS makes NO suggestion that the presence of glycerol is also required to produce formic acid from overheating oxalic acid. In fact, there is no mention of glycerol at all.



:gh:
 

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a couple of years ago back when oxalic acid vapor was an outlaw procedure in the usa, i talked to my son in law who has a phd. in chemical engineering, about oxalic and formic acids. only heat is required to change oxalic to formic as i recall. the acids act a lot alike and behave a lot alike and are very similar chemicaly. they have different melting and vaporization temperatures. super heating over vaporization temperature causes oxalic acid to change to formic plus more or less harmless by-products.
 

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What temperature does it get? Does yours turn to liquid first or vaporize from crystals as suggested?
who cares about the exact temperature.. we are talking about working out in a field with a half dead battery and doing the procedure in a box full of bugs.. we are not doing this in a clean room labratory.. oxalic acid vapor works, do not get it instantly too hot. heating up a bit less than a teaspoon full in 3 to 5 minutes will do the trick.
 

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who cares about the exact temperature.. we are talking about working out in a field with a half dead battery and doing the procedure in a box full of bugs.. we are not doing this in a clean room labratory.. oxalic acid vapor works, do not get it instantly too hot. heating up a bit less than a teaspoon full in 3 to 5 minutes will do the trick.
Yep and its fun watching the vapors coming out the cracks. Knowing the mites are in there going "oh no!" makes me smile.
 

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I was able to use 10A thermostatic disc in my design. I haven't tried treating any hive yet but "water boiling test" was a success!

2016-10-01 07.32.21.jpg 2016-10-01 07.32.33.jpg 2016-09-30 11.24.55.jpg
 

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Just about completed my new vaporizer, just waiting on the thermocouple. So far costs from Amazon are as follows mypin temperature controller $24.00 Band heater 300w 110v $8.20 and type J thermocouple $7.00. 2" of 1" copper pipe, a 1" copper pipe cap, 8" of 1"by 1/8" aluminum bar, about 12" of 1/2" by 1/2" aluminum angle a few screws and pop rivets so a total of about $50.00. I also have a 800w inverter from Harbor Freight I bought for about $40.00 some years ago. So the temperature controller will allow the band heater to heat the copper chamber to 350 degrees and when that temp is reached after about 5 minutes the 3/8" pipe is placed into a hole at the back of the hive and a quarter teaspoon of OA is dumped into the chamber and is closed off, this will vaporize in about 30 secs I think as I have not timed it yet. I know the band heater heats it up fine but have not used it yet as I am waiting for the thermocouple. IMG_1020.jpg
 

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Fantastic design like several European countries are producing.
So the heating element, and controller are both 110 powered?
I also like the idea of just a 3/8" hole for the OAV to enter the hive.
That unit is a guaranteed home run. So you will use 2 caps when vaporizing right? 1 to have filled and placed on the cup, turn it upside down to vaporize and then fill the 2nd with OA and when the 1st one is complete turn it back upside down and remove it and place the newly charged cup on and then flip it?
Be nice if you can use a silicone,teflon or HDPE cap that can withstand the 350degf and not have to burn a finger

I want to purchase your 1st manufactured unit here in the states when you start producing them.
 

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We still have to try the system out mgstei1, I have had my days in manufacturing and as I am rapidly approaching 73 I will not be starting again, however I am quite willing to help other beekeepers build their own.
Johno
 
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