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a gold-magnesium exothermic intermetallic

Gold-magnesium alloys. R. Vogel. Z. anorg. Chem., 1909, 63, 169-183. In: ? The Journal of the Society of Chemical Industry. 28 [10] 1041. October 15, 1909.

An extract.

In order to prepare the alloys, the magnesium was melted, and gold sheet added as necessary. The union was always accompanied by a very large evolution of heat, in some cases almost to explosiveness. The same characteristic occurs in the alloy of gold with zinc and cadmium, and indeed forms a series in accordance falling atomic weight. The miscibility of the gold with magnesium in the solid state, with the formation of mixed crystals, is up to 3 per cent., and with zinc and cadmium up to 5 per cent.

---- The late Alexander P. Hardt, Incendiary Potential of Exothermic Intermetallic Reactions, Lockheed Palo Alto Research Laboratory Report LMSC-D177523,

1971. Discusses a number of intermetallic reactions, none however, using Au.

Accepting carbon and silicon as metallic surprisingly high temperatures are possible:

TiB2 3770o C TiC 3600 ZrC 3800 NbSi2 3300 HfC 4200

I remain curious as to the source of the heat!

Reply to
donald j haarmann
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self-propagating high-temp synthesis

Reply to
Uncle Al

[hanson] In Al's reference:
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one reads: "Self-propagating high-temperature synthesis (SHS) means the synthesis of compounds (or materials) in a wave of chemical reaction (combustion) that propagates over starting reactive mixture owing to layer-by-layer heat transfer"

Well, in there one reads about the mechanism of this and related phenomena but not the source. All other posters so far only contributed additional well known examples of the phenomenon. But Haarmann's question still remains.

Some of these reactions are outright violent, like the production of HgNa (used in org. synthesis) Does a Na(+)Hg(-) product emerge? Do generally electron transfers provide the heat source, much like in classical redox reactions? Or is there another mechanism at hand?

There is a **related** phenomoneon that one can observe in some alloys. It is known in industry that the "golden" Bronze (CuSn), and the electro plated "platinumy" Nickel Tin (NiSn) alloys can acts as poor man's Gold resp. Platinum. Both of these alloys have similar visual, reflective and corrosion characteristics, analog to their real thing in the metallic noble element. Here comes the interesting part, which has not been generally looked at, the ***proton sum*** in the alloys equals that proton number in the respecive noble elements:

Cu = 29 + Sn = 50 :::: CuSn-Bronze = 79 ..... Au = 79 Ni = 28 + Sn = 50 :::: NiSn-NickelTin = 78 ..... Pt = 78

There are a number of other such binary or tertiary alloys whose proton sum of its constituents mimic the macro characteristics of the same proton number element. What or whether there are known theoretical reasons for his behavior similarity I do not know. hanson

BTW: I added a few other NG's in the hope for an elegant explanation

Reply to
hanson

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