Lithium Borohydride as a Hydrogen source (Zack Iszard)

The following post was submitted by Zack Iszard

Much attention has been given to Lithium Aluminum Hydride (LAH) as a solid hydrogen source in LENR reactors. A chemical analogue of LAH, Lithium Borohydride (LiBH4, LB) deserves equal attention.

First, there are chemical advantages: the hydrogen density of LB is 26% higher (based on the ratio of molar volumes). LB is a milder reducing agent than LAH [1], and is thus safer to handle and likely less sensitive to moisture.  LB has a smaller and lighter anion, meaning that the anions can fill smaller interstitial spaces in the core material.

Second, there are nuclear advantages. Boron-10 absorbs fast neutrons to become lithium-7, and alpha particle, and a gamma ray [2], Boron-11 will fission to three alpha particles when struck by a fast proton [3]. The consequences of this nuclear reactivity in the LENR schema is unknown to me, but is likely consequential. If the neutron-absorbing properties of boron-10 are too troublesome, enriched boron-11 can be purchased, as it is a by-product of commercial light water fission reactors (used as a neutron absorbent in the coolant water).

The primary drawbacks to using LB are mostly cost. However, since LB can be prepared with a solid-phase metathesis reaction of sodium borohydride (NaBH4, much more common) and lithium bromide (LiBr) [4], the flexibility to the experimenter are immense. By using heavy-isotope-enriched LiBr and NaBH4 in a ball mill, Li(7)B(11)H4 can be prepared in good purity. This reaction must be carried out in a dry environment, as LiBr is hygroscopic and will ruin LB yields.

I do not understand enough of the nuclear physics to have any serious conjecture about the effect of borohydride anions in place of aluminohydride anions in an E-Cat-type core. It is important to note that at core operating temperatures, both LAH and LB decompose, likely to LiH, hydrogen gas, and metallic Al or B. My main motivator in posting this is to highlight the fact that alternative hydrogen-storing solids may be worth investigating in this application. I concede that LAH is a pretty good choice of material, but it’s hazardous nature is problematic to some experimenters. Alternately, any combination of solids containing lithium and a large hydrogen content could be applied: sodium borohydride and lithium hydride would be my choices for the sake of cost and safety.

-Zack Iszard

Citations (via wiki):
1. Ookawa, Atsuhiro; Soai, Kenso (1986). “Mixed solvents containing methanol as useful reaction media for unique chemoselective reductions within lithium borohydride”. The Journal of Organic Chemistry 51 (21): 4000–4005.
2. Duderstadt, James J.; Hamilton, Louis J. (1976).Nuclear Reactor Analysis. Wiley-Interscience. p. 245.
3. Nevins, W. M. (1998). “A Review of Confinement Requirements for Advanced Fuels”. Journal of Fusion Energy 17 (1): 25–32.
4. Peter Rittmeyer, Ulrich Wietelmann “Hydrides” in Ullmann’s Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim.