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Dmitry Shintyakov
It takes twice the man to ride half the bike
It takes twice the man to ride half the bike

Dmitry Shintyakov's posts

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Transparent crystals under bright evening sunlight: ammonium alum and erythritol
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Crystals of sulfamic acid: H3NSO3

Sulfamic acid is a monoamide of sulfuric acid H2SO4; in other words, it is what one gets if one of OH groups in sulfuric acid is replaced with amino-group NH2.

Sulfamic acid is used as a descaling agent due to its ability to form well soluble salts with calcium and low toxicity. I extracted it from dishwasher descaler.

It crystallizes well, giving rectangular tablets with additional side facets. Crystal system is orthorhombic. My samples were grown using slow evaporation method, growth time was 4 weeks.

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These are crystals of potassium ferrioxalate: complex salt with formula K₃[Fe(C₂O₄)₃]·3H₂O

It is often prepared by students during inorganic chemistry practice, because it has unusual green color (most other compounds of trivalent iron are brown, like this ) and is easy to prepare and crystallize (thus easy to purify).

I grew them from aqueous solution, using the usual evaporation method, growth time was around two weeks. These crystals contain water of crystallization (see 3H₂O at the end), and are prone to slow deterioration if exposed to dry air. The process is very slow though, much slower than for sodium analog (see it here: )

They are also slightly light sensitive. I think that small cracks, visible as bright specks are caused by light. They appeared after a week spent on air.

If this salt is mixed with its sodium analog and crystallized together, mixed crystals of totally different shape grow:

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Gyroid made from a single shape of developable strip
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Here is my new crystal specimen: co-crystal of glucose and sodium bromide with formula 2C₆H₁₂O₆·NaBr·H₂O.

I have found a mention of this compound in some article, and immediately tried to grow it as far as got my hands to the sodium bromide. (by the way, the same article also mentioned that iodide analog exists).


The crystal has trigonal symmetry: it is essentially a cube, stretched along the main diagonal, with some additional facets. Its shape differs slightly from the shape of the chloride analog, being slightly more elongated.


Growth method was slow evaporation, growth time is around one month. This compound has big solubility (around 130g / 100cc of water, by my measurements), and does not grow well, being prone to spontaneous crystallization and parasite crystal formation, so I had to grow it really slowly in order to get good shape. Chloride analog grows easier.

To prepare solution, I took stoichiometric (i.e. 2:1 molar ratio) amounts of glucose and NaBr, dissolved them in warm water and let the solution evaporate slowly.

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I thought that I have solid grasp of basic mechanics, but let me confess: I could not predict the outcome of this simple experiment.

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New crystals of sugar alcohol mannitol.
They are hard and brittle, making glassy sound if hit.

All crystals grown in 2 weeks from slightly supersaturated solution (several grams of additional compound per 100ml of solution).

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A successful experiment: by crystallizing a mixture of sodium and potassium ferrioxalates. I unexpectedly produced a compound with different crystal shape and (apparently) structure. Its stability to dehydration suggests that it is an anhydrous compound.
Literature gives formula K2.5Na0.5[Fe(C2O4)3], while my experiment suggests that K:Na ratio is closer to 2:1.

This is a test crystal, grown in 5 days. Will try to make a bigger one indeed.

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New crystal: ammonium alum with 10% of chromium ammonium alum, formula is

NH4 Al0.9 Cr0.1 (SO4)2 · 12H2O

it was grown using slow evaporation method, growth time is 2 weeks. To protect the crystal from dehydration and as safety measure, I covered it with a transparent layer of a pure ammonium alum, without chromium.

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