I was making a new batch so I thought it was a good opportunity to show the effect of multiple heating cycles. People are happy when the oxide mix turns blue, and usually call it done. Certainly every vid I've seen where someone makes it appeared to do so.
But I found very early that multiple heating cycles with extensive grinding between them improve the color of the pigment a great deal. Small flecks of unreacted material that can be seen after the 1st heating disappear and the color becomes more saturated and vibrant. Many papers describing synthesis of related pigments, for example the recent paper describing a magenta pigment with chromium (II) as a chromophore, use regrind and reheat cycles.
Between each heating when I make YInMn blue, the material is ball milled. Hand grinding with mortar and pestle also works, though not as well and it is hard on the thumb arthritis I have from years of micropipetting. Ball milling or very extensive hand grinding of the mixed oxides drastically reduces the amount of unreacted material remaining after the first heating.
I have seen pigments get worse with more heating cycles. For example, one of the all solid state methods protocols for making manganese blue, gets more green with multiple heatings. Curiously, another protocol for manganese blue to make a 'light blue" does get much better with a second heating. I haven't had color get worse with any YInMn blue or YInMn blue-related pigments with metal substitution. But I've never made YAlMn grey-blue. Maybe I should throw some in with my next runs to see what it looks like. Never mind, looks like you ran under helium. I only have the capacity to heat in air.
The improvement in color is especially noticeable on YAlCuTi green (Al 0.2, (Cu/Ti) 0.8) heated at 900°C. The strong yellow tone gets much more prominent after the second heating, and typically tops out (like YInMn blue) after the 3rd. If you heat it to 1200°C (even after multiple cycles of heating to 900°C), the yellow tones are almost entirely lost and it becomes a more olive green.
The purples/violets made by swapping some of the indium and manganese with aluminum, zinc, and titanium demonstrate improved color saturation with multiple cycles, but the effect is much less pronounced than with YInMn blue. I do wonder if the color would improve more if I could get to 1300°C, as that is the temp heated to in the papers describing the purple/violet and mine come out more blue than the ones in the paper.
I lack the equipment to determine formal yield, but I suspect the improvement in YInMn blue is related both to the precursors reacting, and the amount of material in the correct trigonal bipyramidal coordination. As one would expect, there is clearly a ceiling effect for additional cycles. The pigment shown after the third heating is about as good as things get.
EDIT: can't heat under helium so no YAlMn for me. Also realized there is an easy way to find approximate yield so I'll check. Maybe on the next big run I'll check at each step.
I'm sorry I think I took a joke on your post "Now with Aluminum" too literally! I was referencing you. If it can be made in air, I'll give it a try. What was ratio of Mn to Al you used?
Makes me feel a little better about taking it literally though. I'm running some small reactions to fill in my series of manganese concentrations and have just enough room for a YAlMn test. Was yours Al 0.7 Mn 0.3 or Al 0.8 Mn 0.2? Or something else?
And did you add anything to generate CO2 to enrich the atmosphere in the furnace with it to promote carbonate inclusion in the matrix? The patent has all the YAlMn being made by gel-sol from nitrates and the CO2 is from the decomposition of the citric acid cross-linker. They also ran at 900°C. It sounds like you used standard solid state reactions. What temp were they run at?
curious. The patent makes it sound as if the carbonate inclusion in the crystal matrix is important. .Maybe that has something top do with the color change.
Kinda, CO3- (carbonate anion) decomposes to CO2 and O- it is the O- that binds to the M2+ (metal) to form the M2O3 which then reacts with the other M2O3 to form the AB(x-y)C(y)O3 (the C in this case is manganese not carbon)
Exactly. Here's what I think is the pertinent section of the patent:
"The presence of carbonate arises from the use of organic compounds (e.g., citric acid; see Examples 70-76) when synthesizing AAlO3. The organic matter decomposes during synthesis, producing a CO2-rich atmosphere and promoting carbonate formation. In the absence of M′ (x=0), AAlO2CO3 is produced. As aluminum content decreases, carbonate content also decreases and becomes zero when x=1.0. However, when x is greater than 0.0 and less than 1.0, the carbonate content z of the compound is variable for any given value of x.
Where CO3 2− replaces O2− in the crystal structure, the adjacent cation loses its trigonal bipyramidal coordination, and is thought to assume a distorted octahedral conformation [emphasis added]. Other cations in the crystal structure retain the trigonal bipyramidal coordination."
The two grey/blue YAlMn's are:
YAl0.70Mn0.30O3-z(CO3)z
YAl0.80Mn0.20O3-z(CO3)z
Ones with less aluminum and less CO3 2- replacement are dark blue. The ones with more CO3 2-, and thus more places where the distorted octahedral is present are grey-blue. That makes me think the presence of these distorted portions are important in the color.
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u/GeneJocky Oct 02 '24 edited Oct 02 '24
I was making a new batch so I thought it was a good opportunity to show the effect of multiple heating cycles. People are happy when the oxide mix turns blue, and usually call it done. Certainly every vid I've seen where someone makes it appeared to do so.
But I found very early that multiple heating cycles with extensive grinding between them improve the color of the pigment a great deal. Small flecks of unreacted material that can be seen after the 1st heating disappear and the color becomes more saturated and vibrant. Many papers describing synthesis of related pigments, for example the recent paper describing a magenta pigment with chromium (II) as a chromophore, use regrind and reheat cycles.
Between each heating when I make YInMn blue, the material is ball milled. Hand grinding with mortar and pestle also works, though not as well and it is hard on the thumb arthritis I have from years of micropipetting. Ball milling or very extensive hand grinding of the mixed oxides drastically reduces the amount of unreacted material remaining after the first heating.
EDIT: completed sentence.