Decaborane Handling Issues: Design Modifications for pB11 Fusion Research
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Discuss In ForumsLPPX is starting to plan for the modification of the chamber to use the decaborane gas. For this purpose, the chamber has to be heated and has to be maintained at 100-120oC to keep the decaborane gas from condensing. A separate chamber is needed to store the solid decaborane. Several other design modifications are required such as protection of the pumping system against fouling by boron particles.
Below is an email string that addresses issues related to decaborane handling.
Email Exchange
Hi Alex,
Nice to hear from you. I am Dr. S. Krupakar Murali (call me Murali) and am designing the chamber and heating system to handle decaborane. Since this material, as you know, is a solid at room temperature we intend to heat it up to fill the chamber with the gas. However, I am not sure how to handle this material. We need some special hoods, do you have any recommendations as to what we need to take into consideration before we order a hood for this application? I have shortlisted the following ductless hood, but am not sure if it would work http://www.air-science.com/portable.html what is your opinion?
Thanks,
MuraliPS: Do you have any references that speak specifically about decaborane and other gasesous forms of boron compounds
Hi Murali,
Greetings from Massachusetts. Wow! I’ve never seen one of these portable fume hoods. I’m impressed how compact it is. I think it’s fine for decaborane. As you may know decaborane needs to be in a fume hood both because of its toxicity and because it is hygroscopic. After opening the bottle we used to put tape around the bottle seal after closing it. Over time it starts to get clumpy and when heating a sample for the first time, it outgasses a fair amount of water. If you have an RGA on your system that would be very helpful. Before we had a fume hood we just minimized exposure time and avoided breathing directly next to it. As long as you’re careful there shouldn’t be much of a threat to anyone’s health. I don’t want to minimize its toxicity but any sort of air flow from a fume hood will be enough to protect people from breathing exposure when working with powder from a bottle. Some obvious points: wear gloves, wash hands after use, maybe even wear a simple face mask. Cleaning dirtied parts requires more protection.
If my memory is correct, decaborane at 100degC has a chamber pressure of about 10mtorr. One of the more aggravating aspects of working with the material was that any gas lines between your vaporizer and chamber must be at a temperature greater than the vaporizer temperature or else it will condense and clog up. Also very important: above ~300-350degC decaborane decomposes. Also important: at what ever temperature you operate, it’s messy stuff. It will coat everything up and maybe affect your plasma operating conditions. Anyone working with the material will get more decaborane exposure cleaning the chamber than handling material from the bottle. I believe we used hydrogen peroxide to clean it off chamber walls. That requires a mask. If you can put any parts that need cleaning under the fume hood your better off.
Hope this is helpful. Let me know if you have further questions.
Regards,
Alex
On different boron containing compounds:
Other boron compounds in solid form at room temp are octadecaborane and carborane. Octadecaborane has 18 boron atoms/molecule. It has a similar toxicity level and vapor pressure as compared with decaborane. Carborane is C2B10H12. If you can tolerate a little carbon, it’s easier to handle, less toxic, as compared with deca. It decomposes at a much higher temp, near ~700degC. In the semiconductor industry working with a gas is more reliable than a solid so we typically use boron trifluoride or diborane. Both are very toxic and require gas sniffing alarm systems.
I have a lot of references on decaborane but most are geared to using it for ion implantation. There are a some papers from M. Sosnowski of NJIT from the 80s and 90s and I. Yamada but I’m not sure they’re what you’re looking for.
Regards,
Alex
ICCD Camera
Decaborane and the Vacuum System
Comments
~300-350degC slightly less than 1 billion K, so I think we can predict the experimental outcome for the molecular structure of the decaborane in the plasmoid with confidence ;-D
decaborane does absorb into skin, so avoid contact.
what are its typical decomposition products when heated? it is likely they are also toxic? if you end up with some diborane in there, after a shot, will you need those gas alarms, anyway?
does the fume hood extract gas and vent directly to the outside air? or does it take it to scrubbers, first?
also, it seems that boron does react with metals. will it get embedded in the electrodes? if so, will that affect their conductivity?
Rather than a complex handling system, it might be possible to use a system similar to SIMS to form the required boron atmosphere. A sample of solid decaborane could be the target of an Ar+ ion beam.
$0.02
-yempski
There are lots of boranes. It will be chemical reactions making new unknown compounds at the walls. Take care.
if you insist on heating a solid to gas off decaborane tru using an extension for your viewing port with a regulated heated cup that could be replenished or vary the temperature. easily viewed and small. a thimble with a small 120 volt heater rtd or thermocouple with control, all in one flanged extension. this setup could also be used for other compounds. you might even screw it in from the bottom to make it easy to play with. cleaning condensate will become an issue. it may also foul your vacuum pump assembly.
Hi Everyone,
I am a professor specializing in boron chemistry research in areas such as synthesis and boron neutron capture therapy (BNCT). My group has a lot of experience working with decaborane, carboranes and polyhedral borate anions. Since I am also interested in alternative fusion research (outside of my own field) I wanted to add my two-cents worth to these discussions.
Please don’t consider my points as “preachy”, I just sincerely want to add my expertise as a boron chemist to your pursuits (if you find this helpful).
First, a couple of matters of safety. Decaborane is toxic, but not as much as one might think. It is so incredibly stinky that I doubt that anyone would breath in toxic quantities of the vapor without first becoming ill. Of course, ingestion of the material is another matter! (I’ve never heard of this happening). The inhalation of large doses have led to loss of consciousness, headaches and in some cases, short term amnesia. I know several chemists in the Czech Republic that use decaborane in large quantities without proper fume hoods. (while we also use huge quantities…we use great hoods!) They absolutely reek from the decaborane. It permeates their cloths, skin, hair, etc (imagine the smell of chain smokers x100). Diborane does not smell like chocolate. The closest I can describe it is really stinky napthalene, only much worse!
Decaborane will react with water to liberate hydrogen (explosion risk). However, it MUST NEVER be mixed with halogenated hydrocarbons (chloroform, carbon tetrachloride, etc.) as this will result in a massive spontaneous explosion. Back in the sixties, a pilot plant was being cleaned out using carbon-tet. In a fraction of a second, the entire plant any everyone present ceased to exist. It is stable in many dry solvents, just make sure of their identity before using.
Decaborane, as a fuel, contains much more energy than hydrocarbons. I’m certain that you are familiar with the 1950’s Navy and Air Force projects HEF and Zip where they investigated decaborane derivatives as jet and rocket fuels (read boron bomber, etc.) As such, an air-fuel mixture could easily result in a massive explosion! As it is proposed to use heated decaborane vapors here (under vacuum), extra precautions must be taken to ensure that there is no failure of the vacuum system or any other way for air to suddenly mix with the hot decaborane vapors.
I do have a suggestion that I want to throw out on the table. That is to propose using the gas diborane (B2H6), instead of decaborane. It is a gas at room temperature meaning that you will not need to heat the vacuum chamber. Like decaborane, it does undergo pyrolytic reactions at elevated temps. Of note, decaborane does readily decompose above 300 C, these polymerization reactions still occur at lower temps (only slower). While diborane is dirt cheap, decaborane costs near its weight in gold! Also, B-11 isotopically-enriched decaborane costs are astronomical! B-11 diborane would be much cheaper and easier to produce.
If you are interested in discussing the use of diborane…post a reply!
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