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Author: Subject: Silane and boranes as fuel for cars
Aurus
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[*] posted on 29-5-2010 at 15:44
Silane and boranes as fuel for cars


Just that. What do you think?



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[*] posted on 29-5-2010 at 16:54


Silane: Does it combust to SiO2 ? ==> Not too good for the engine, compared to CO2 & H2O from standard-fuel ...
==> ... and probably quite bad for any live-forms that breathe the air with that sort of dust ...

Are those silanes somehow easy to manufacture ? Some cycle, that uses some easily available energy with high enough efficiency ?

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[*] posted on 29-5-2010 at 17:01


Solid combustion products, not very good.

Many are pyrophoric, most have wide explosive and flammability limits; good for Hollywood scriptwriters, somewhat of a drag in the real world. There's nothing like a fairly minor accident turning into a 200 car inferno to ruin a day.

The energy you can get out is much less than the energy needed to make them. There are much more efficient synthetic fuels, ammonia with 10% hydrocarbon for example, and it's tough to beat the 85 to 95 percent power-in-to-power-out efficiency of batteries.

If you must have a solid combustion product, go with plain silicon. The FFC Cambridge process allows it to be produced using just electricity, many of its physical properties such as specific gravity and energy-density are similar to coal. You could burn powdered Si in an external combustion engine, fueling a Rankine, Stirling, or Brayton cycle.
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[*] posted on 30-5-2010 at 05:37


Boranes have actually been tested for rocket fuels in the 50s, but the trials came to nothing. Yes, it is a problem that the reactions are

SiH4 + 2O2 --> SiO2 + 2 H2O

and B2H6 + 3O2 --> B2O3 + 3H2O

resulting in solid boric oxide and silicon dioxide. I am aware that higher silanes are pyrophoric, and boranes are all pyrophoric. Furthermore, silane can be used as rocket fuel ,http://en.wikipedia.org/wiki/Silane, using carbon dioxide for combustion. But that is not relevant to the terrestrial situation. Silane would have a greater enthalpy of combustion and more energy given out per gram as two Si-O bonds are stronger than a C=O, and Si-H bonds weaker than C-H bonds.
Anyway, the suggestion of an external combustion engine seems to be quite good, though I suppose it will take a long time for silicon to reach a competitive price with hydrocarbons.




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[*] posted on 30-5-2010 at 07:11


At one time, in around the 1950s to 1970s, a boron-containing additive was added to Mobil gasoline. This has probably long since been removed, due to either the non-volatile B2O3 produced clogging up exhaust systems, else or increases in the cost of boron (extracted from raw borax and then usually reduced to Mg3B2 from which boranes and organo-boranes are obtained by hydrolysis), which is a fairly rare element and requiring a large amount of energy to reduce from borate.
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