New powerful Energetics based on Boron - Nitrogen reaction

Quote: Originally posted by Quadro

It is well known that boron easily reacts with nitrogen to produce solid boron nitride and a lot of energy, about 10 kJ/g. There was an idea, of mixing any borane (pentaborane for example) and any nitrogen hydride (ammonia, hydrazine etc.) forming a mix, solution or adduct. Several such addicts are known, such as Hydrazine Diborane (BH3•N2H4•BH3) which is excellent energetic material, although very low density one. Mixing pentaborane with hydrazine in milligram amounts resulted in violent explosion. Such energetic materials only produce hot gaseous hydrogen and solid boron nitride. So I've come up with an idea, of mixing or getting adduct/cocrystal of the most powerful and dense nitrogen hydride energetic material with the most dense boron hydride. It is mix/adduct/cocrystal of Hydrazinium Pentazolate (N2H5N5) and Decaborane (B10H14). Reaction is 10N2H5N5 + 7B10H14 = 70BN + 74H2. For 1 gram of N2H5N5 one needs 0,82993 grams of B10H14. Such materials can be made in a great variety, making ultra powerful gunpowders and explosives. Instead of Hydrazinium Pentazolate, one can use Hydrazinium Azide, which is much more easy to synthesise. I don't have anything to do such experiment, so I ask anyone with those compounds to try it. Results should be amazing.

Quote: Originally posted by j_sum1

TiH14 exists? I bet it does not like existing.

I'm sure you're correct! It does have a few things going for it though:

For one as you go down through the elements' Z HOMO-LUMO gaps decrease. Hydrogen being the first element helps keeping it kinetically stable by having a wide HOMO-LUMO gap.

The incredible atom number density should also give it an incredibly high heat capacity for a noble-gas-like molecule (it is a 18-electron complex).

The hydrogen should be arranged very symmetrically too at 14 in a rhombic dodecahedron.

Titanium is also the first transition metal with their characteristic electronegativity. Compare it with that of Hydrogen. Covalent bonding is favored.

Lastly internal hydrogen bonding bonding stabilizes molecules like these. When the hydrogen/electrons are there they stabilize each other but if you try to put them on one by one you will have a hard time forming it due to entropy barrier. That is why hydrides like these do not form spontaneously with brute force hydrogenation (literally; temp/pressure). Using non-standard physics I can say this effect is not linear. I.E greater valence electron density leads to much greater bond strength.

As for its analogs the most well known is NonahydridoperRhenate(VII) or ReH₉^-2 which can be made in, and is stable in, aqeous solution. Its second row analog of Nonahydridopertechnate(VII) apparently has been synthesized but I've not heard of it's properties. The first row Manganese analog has been predicted to exist. It is easy to surmise the analogous anions/species should exist for the transition metals to the right as well. In the case of Iron the starting point for the synthesis should probably be Ca₂FeH₆. Analogous salts exist for the other transition metals. I'm sure you can see then how I imagine TiH₁₄ could be produced. I.E gentle protonation of Th₂TiH₆

You are welcome to give it a try with one of the transition metals, it may be a long time til I can test these predictions myself .

PS: I left a lot out here in the explanation of why it should be stable but I'm sure you can fill in the blanks yourself.

A rhombus in a cube?? I do not like your description. But yes, I agree that a rhombic dodecahedron has 14 vertices. They are not identical and so it will not be perfect spherical symmetry. But close, and therefore not contributing greatly to strain.

Without doing any calculations based on the estimated radii of the H and Ti in this situation, I would still conject that there simply is not enough room around titanium to stack all of those hydrogens -- at least not without an exceptionally long bond length. And then, what form do you think it will be in? Surely not molecular? That puppy will blow apart. Equally though, you are not going to stuff than many hydrogens in the interstices of a metallic matrix.

It is an interesting thought experiment. I do not have the hubris to say it is impossible since I nearly always miss something in these kinds of situations. But I am picking that working fusion power will be easier.

And we should probably cease this off-topic conversation.
Back to boron and nitrogen...

The book Ignition! in the Sciencemadness library mentions these mixtures in the context of rocket propellants. Unfortunately, I think that the performance of these mixtures as rocket fuels may be better than their performance as explosives. In fact, in Ignition!, there was a fair amount of talk dedicated to these mixtures:

"One thing that might have kept pentaborane in the picture was the
advent of BN system, early in 1958. Callery Chemical was the originator of the idea, but within a year every propulsion contractor in the
country, plus JPL, NASA, and EAFB had got into the act.
This is the idea: Boron nitride, BN, is a white, crystalline solid, with
a hexagonal crystal structure like that of graphite.* It is a very stable
molecule, with an exothermic heat of formation of some sixty kilocalories per mole. Now, imagine the reaction of a borane with hydrazine.
B2H6 + N2H4 -» 2BN + 5H2
or
2B5H9 + 5N2H4 -» 10BN + 19H2
The heat of formation of the BN would be the energy source, and the
hydrogen would comprise the working fluid — dragging the solid BN
along with it, of course. Performance calculations indicated that the
pentaborane-hydrazine combination should have the astounding
performance of 326 seconds, and brought out the even more astounding fact that the chamber temperature should be only about 2000 K
—1500 K or so, cooler than anything else with that sort of performance. The thought of a storable combination with a performance above
300 seconds, and with such a manageable chamber temperature sent
every propulsion man in the country into orbit. "


The issue (as it appears to me) would be the very low molar mass of the gas formed, and potentially the low density of the explosives. Of course, it's impossible to know without testing, but what I recall from using the Kamlet-Jacobs equations and equations in the book Energetic Compounds - Methods for Prediction of their Performance was that a major component of detonation pressure (keep in mind that the equations given in the book are meant to be applied to CHNO explosives, or CHNO explosives that might contain Cl, F, or Al powder) was the density of the explosive and the molar mass of the gas formed. Moles of gas formed per gram and enthalpy of detonation are also components of the equations.

According to my calculations, the reaction of hydrazine and diborane should produce 9.977kJ/mol of energy, 0.084 moles of gas per gram, with an average molar mass of the gas of 2 g/mol, and a density somewhere between hydrazine's 1.021g/cc and diborane's 0.447 g/cc (as a liquid. This came from a very sketchy source but it was all I could find).

The comparable figures for a high performance explosive like HMX are 6.17kJ/gram enthalpy of detonation, 0.03378mol/g gas, average molar mass of gas 27.12 g/mol, and a density of 1.89g/cc. (figures taken from Keshavarz and Klapotke's book)

Using the Kamlet-Jacobs equation for detonation pressure yields (assuming a density of 1.0g/cc as a best-case scenario):

Det. Pressure = 240.86(0.084)(2*9.977)^0.5 (1.0)^2 = 90.38kbar

That is compared to a pressure of 376.9kbar calculated for HMX and an actual detonation pressure of 390kbar.

Of course, this is not a CHNO explosive and the Kamlet-Jacobs equations cannot be directly applied to it. Even so, I find it hard to imagine that this explosive could compete with HMX in terms of brisance given its very low density and the very low molar mass of the gas. The density may be improved by some of the mixtures mentioned below, like hydrazinium azide and decaborane.

However, decaborane's density is still below 1.0g/cc and none of the hydrazine derivatives are very dense either. Also, hydrogen gas is of course the least dense gas and a poor gas from an explosive perspective. Maybe some of the boron nitride would contribute to the brisance, like in tungsten-powder laden explosives.

So, even given the inapplicability of the K-J equations, it doesn't seem like it could be a more powerful explosive than current ones.

Perhaps these mixtures could be excellent gunpowders or artillery propellants, though, and it seems they can at least theoretically be excellent rocket fuels.

Of course, all the above calculations are very heavy speculation, and I would love to see an actual experiment, since experiments and reality can be quite different.

But it'll have to be performed by someone braver than me...