[MSA-talk] wire iron

Anton Chakhmouradian Anton.Chakhmouradian at umanitoba.ca
Tue Dec 5 11:08:22 EST 2017


Jerry,


The subject of why such crystals form and how they grow is actually very well covered in the materials science literature (e.g., Journal of Crystal Growth, Crystal Growth & Design, etc.) because this type of crystals most closely approaches the "ideal crystal" models in their mechanical characteristics. A wide variety of alloys and compounds (from metals to organics) have been synthesized in that form, including iron - search under "whisker crystals". Keep in mind, though, that there are true synthetic whiskers, that grew that way because of some specific growth conditions (like the presence of a "catalytic impurity" in iron and copper whiskers), and long crystals obtained by pulling from a melt (i.e. not true whiskers comparable to natural crystals).


Anton Chakhmouradian

University of Manitoba

________________________________
From: msa-talk-bounces at minlists.org <msa-talk-bounces at minlists.org> on behalf of Silverstein, Joshua <silverj at miamioh.edu>
Sent: Tuesday, December 5, 2017 7:59 AM
To: Magloughlin,Jerry
Cc: msa-talk at minlists.org
Subject: Re: [MSA-talk] wire iron

Hi Jerry,

When gold precipitates from solution its crystal habit is dependent on the concentration of the gold. At low concentrations gold growth occurs as 2D growths where the growth is seen to preferentially deposit at steps, terraces and vacancies. With increasing concentration you move from 2D to dendritic (wire) growth. With higher concentrations gold hopper crystals are the dominate crystal form.

Why we do not see this in native iron I am not sure. Possible because golds outer electron shell is weaker and is more likely to exhibit dissolution/reprecipitation behaviors.

I recommend you contact my graduate adviser. Dr. John Rakovan (rakovajf at miamioh.edu<mailto:rakovajf at miamioh.edu>) is a professor at Miami University (http://www.cas.miamioh.edu/~rakovajf/). He is very knowledgeable about native metals and has done extensive work with Gold and Silver. He is currently looking at dendritic silver wires (synthetic and natural) to understand the crystal growth habits of silver.

Cheers,

Josh

On Mon, Dec 4, 2017 at 5:52 PM, Magloughlin,Jerry <Jerry.Magloughlin at colostate.edu<mailto:Jerry.Magloughlin at colostate.edu>> wrote:
Two related questions: Is anyone aware of papers describing native iron in a wire habit, akin to
what is sometimes present in native silver and native gold? I have a lot of papers on native iron
and nearly all seem to illustrate or describe a generally granular or blocky or irregular habit.

Second, why does a ‘wire’ habit develop in these isometric minerals? Any papers describing this
would be much appreciated.
Jerry

Jerry F. Magloughlin
Colorado State University





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Joshua Silverstein
Student Council Past-President, Microscopy Society of America
Editor, Micrograph of the Week, Microscopy Society of America
silverj at miamioh.edu<mailto:silverj at miamioh.edu>

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