In an article I am trying to understand, the following occurs: (summarized below)

Synthesis of octahedral $\ce{Cu_2O}$ seeds:In a typical synthesis, 2.9946 g of $\ce{Cu(CH_3COO)_2}$ was dissolved in deionized water (20 mL) using a beaker under a constant stirring at 70°C for 2 min. A dark precipitate was produced when a sodium hydroxide solution (9 M, 10 mL) was added dropwise to the above solution. After being stirred for 5 min, D-(+)-glucose powder (0.3 g) was added into the dark precursor with a constant stirring for another 60 min at 70°C,and then was allowed to cool to room temperature naturally. Afterward, the obtained products were centrifuged at 5000 rpm for 1min (XIANYI TG16-WS centrifuge). The precipitates were centrifuged twice more in deionized water and anhydrous ethanol, respectively. And finally were dried at 70°C for 12 hours in a vacuum oven.

My understanding of this paragraph is that copper acetate reacted with sodium hydroxide to form copper hydroxide and sodium acetate. A reducing sugar reduces the copper hydroxide to $\ce{Cu_2O}$. The ethanol dissolves the sodium acetate to leave only $\ce{Cu_2O}$ (octahedral) crystals.

The next morphology of $\ce{Cu_2O}$ crystals, "polyhedral M-pyramid $\ce{Cu_2O}$ architecture," was grown through essentially the same process, except using seed crystals from the first batch of octahedral crystals.

How do octahedral seed crystals give rise polyhedral ones?

  • 2
    $\begingroup$ It would seem that by very slight changes in conditions they can get the crystals to grow either at 8 corners, giving a cube, or 6 corners, giving an octahedron, or even somewhere in between, giving 14 facets. How they get 50 facets is beyond me. That would be 4x(8)+3x(6)=32+18=50 I guess. Iron pyrites is cubic and has several different growth habits, which can lead to stripy-faced crystals. This article explains that face-controlled and diffusion-controlled growth give different forms, but I'm having problems linking it correctly: www.researchgate.net/...pyrite.../0fcfd50b7c008b64e9000000 $\endgroup$ – Level River St Nov 8 '14 at 18:49

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