franklyn - 7-10-2009 at 08:42
Mercury forms alloys with metals at room temperature. This property enables mercury
to combine in the same way to form an alloy , or amalgam with some functional groups.
In the same way , interstitial Hydrides are formed by other metals such as Palladium.
There does not appear to be a rigorous molecular formula to these materials.
Sodium amalgam typically can be any empirical proportion from one percent on up.
25 % Sodium amalgam has the ratio of 1 part Sodium to 3 parts mercury by weight. This is
a molar proportion of 26 Na to 9 Hg , or nearly 3 Sodium atoms to every Mercury atom.
Ammonium amalgam has remained a curiosity since first made in 1808 , it has the
intriguing property of being seemingly comprised of free radical Ammonium NH3•H.
Subsequently amalgamations as with Tetramethyl Ammonium and even apparently
Hydrazinium have been isolated. Referenced here once before by Rosco Bodine
http://www.sciencemadness.org/talk/viewthread.php?tid=1128&a...
with a follow on comment from not_important
http://www.sciencemadness.org/talk/viewthread.php?tid=1128&a...
Immediately following is a compendium of available background information on
Ammonium amalgam. Discourse continues below that , after the double green line.
Ammonium amalgam , NH4 Hg , CAS number 26497-91-6
While the compound NH4, has never been isolated, its amalgam or compound with Mercury,
is readily prepared. When Sodium amalgam, a compound of Sodium and Mercury having the
composition Na.Hg, is treated with a concentrated solution of Ammonium Chloride, the
amalgam swells up, occupying a relatively large volume. The product has a metallic luster,
the reaction probably takes place in the sense of the following equation:
Na.Hg + NH4Cl -> NaCl + NH4.Hg
Ammonium amalgam preparation :
Introduce a few grams of Sodium amalgam into 20 to 30 c.c. of ice cold, concentrated
Ammonium Chloride solution; the amalgam at once begins to swell, and is changed to a grey
spongy mass of extremely voluminous Ammonium amalgam which floats on the surface.
Ammonium amalgam may also be prepared by electrolyzing a solution of Ammonium Hydroxide and
Ammonium Acetate at a low temperature ( - 30ºC ) with a Mercury cathode or by electrolysis of
Ammonium salts in liquid Ammonia with a Mercury cathode. Electrolysis of Ammonium Thiocyanate
in Acetone using a Mercury cathode also yields Ammonium amalgam.
The resulting Ammonium amalgam solution of Ammonium in Mercury decomposes completely
within a short time when allowed to come to room temperature, and Hydrogen and Ammonia
gas are slowly evolved, leaving eventually the pure Mercury. The partially decomposed amalgam
is larger in volume than the original Mercury, and has a stiff consistency, something like that
of butter. This stiffness is due to an emulsion of liquid Ammonia and some gas bubbles dispersed
through the Mercury.
In contrast to metal amalgams, Ammonium amalgam is a thermally unstable metallic system ;
it is stable only at temperatures below O°C. Ammonium amalgam , prepared and preserved
at 0ºC , does not swell up in the usual way ; the evolution of gas only takes place when it
is warmed. At higher temperatures, Ammonium amalgam will decompose to give Ammonia,
Hydrogen, and Mercury: 2NH4.Hg(x) -> 2NH3 + H2 + 2Hg(x) (1)
Because of reaction (1), Ammonium amalgam at temperatures above 10°C is a heterogeneous
system of a liquid homogeneous Ammonium amalgam and a pasty Ammonium amalgam
( gas emulsion containing Hydrogen and Ammonia bubbles ) at the electrode surface. A limiting
temperature at which Ammonium amalgams can be obtained in aqueous solutions is 45 to 50°C.
It would seem that Ammonium amalgam was a hopeful substance from which to obtain the
group Ammonium. It is, however, unstable, breaking down at ordinary temperatures into
Ammonia, Hydrogen. and Mercury. This is, apparently. the nearest that we have corne
thus far to obtaining the group Ammonium in the free condition.
From 1966 - http://www.dtic.mil/srch/doc?collection=t3&id=AD0373800
High Pressure Chemistry of Hydrogenous Fuels AD0373800
Abstract:
A research program was carried out to investigate the low temperature high pressure chemistry
of Ammonia, Hydrogen, and Ammonium amalgam. The thermodynamic data obtained and the calculations
performed are of importance for the synthesis of metallic Ammonium Hydride and metallic Ammonium,
which represent attractive high energy solid fuels for use in solid rocket propulsion systems.
A thermodynamic analysis was performed in which (1) H2 x NH3, a Hydrogen calthrate with Ammonia
as a guest, (2) NH4, metallic Ammonium, and (3) NH4H, Ammonium Hydride, were considered as plausible
products from reactions of Ammonia with Hydrogen. Enthalpies and free energies of formation for NH4
and NH4H were estimated by several methods. To obtain information regarding the physical and chemical
nature of Ammonium amalgam, a Bridgman opposed anvil high pressure apparatus was designed, constructed,
and used to pressurize Ammonium amalgam samples to 50 kilobars at low temperatures. To establish the
pressure scale and to test the Silver Chloride sample assembly, the resistance of several Bismuth samples
was determined as a function of pressure to 45 kilobars.
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The method outlined above whereby Sodium amalgam metathetically yields Ammonium amalgam
seems can just as easily be utilized to make a Hydrazinium amalgam from Hydrazine Dihydrochloride.
This is the point of this post and what I now relate here. This process whereby Sodium amalgam
with Mercury can be substituted by Amine free radicals. Enthalpy of their formation is undocumented
as is the extent to which the Mercury can assimilate these functional groups. Percent content of
each type in Mercury will determine overall energy density.
Disassociation of Ammonia is endothermic but recombination of atomic Hydrogen is exothermic.
What change in enthalpy there is from the formation of Ammonium amalgam is not studied as
is lattice energy and what exactly constitutes the bond if any , between Hydrogen and Ammonia
and Mercury.
Hydrazinium amalgam may likely exhibit exothermic disassociation , and if it can
substitute Sodium to an equivalent extent it will have meaningful energetic potential.
Na2.Hg(x) + HCl•H2N-NH2•HCl => 2 NaCl + H•H2N-NH2•H.Hg(x)
N2 + 2 H2 + 12 kcal , => H2N-NH2
H2 + 104 kcal , => 2 H
H•H2N-NH2•H => N2 + 3 H2 , - 116 kcal
∆He (Heat of explosion) = - 3412 kcal / kg
Chloramine is another candidate for metathetic substitution
This reference is old , 1949 , http://www.jstor.org/pss/98170
Value for N-N disassociation of Hydrazine is from Handbook of Bond Disassociation Energy
Na2.Hg(x) + 2 H2NCl => 2 NaCl + (NH2)2.Hg(x)
N2 + 2 H2 + 12 kcal , => H2N-NH2
H2N-NH2 + 66.5 kcal , => 2 NH2
2 NH2 => N2 + 2 H2 , - 78.5 kcal
∆He (Heat of explosion) = - 2453 kcal / kg
* Note CRC gives (NH2) Amidogen ∆Hf (Heat of formation) as + 44.2 kcal / mol
Related reference - http://fermi.uchicago.edu/publications/PDF/oka197.pdf
Metathetic substitution with Chlorine azide is another possibility
Na2.Hg(x) + 2 ClN3 => 2 NaCl + (N3)2.Hg(x)
2 HN3 => H2 + 2 (N3) + 126 kcal ∆Hf
(Heat of formation) of Azoimide (2 X)
2 (N3) => 3 N2 - 126 kcal
∆He (Heat of explosion) = - 1500 kcal / kg
Metathetic substitution with Nitrogen Trichloride may perhaps amalgamate atomic Nitrogen
Na6.Hg(x) + 2 NCl3 => 6 NaCl + N(2).Hg(x)
2 N => N2 , - 226 kcal
∆He (Heat of explosion) = - 8071 kcal / kg
As to whether this may result in some polynitrogen material is an open question.
Nitrogenous compounds of Mercury such as Azides are known. More interesting is
the Nitride , Hg6N2 Mercurous Nitride.
http://resources.metapress.com/pdf-preview.axd?code=g0865mt4...
http://www.springerlink.com/content/g0865mt481562109
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