Let assume I understand you correctly, and you have pigments of a size smaller then 1µm and you want grind them. Theoretically this should be possible, the challenge is only the fixing of the particles during grinding. Here you need some special (high-fluid) epoxy and a preparation under vacuum so that all gas between the particles will be removed so that the particles are joint. But this sounds easier than in practically possible. One can do it but I guess it will not be perfect. Bigger crystals will improve it but also have the disadvantage that they can create bigger scratches if some of them  fall out.  

The problem is not so clearly described but I assume you try to mill pigment particles to a particle size below 1 micrometer but it changes its color. From our experience on luminescent powders, which are basically pretty hard ceramic materials, is that intensive milling contaminates your powder with the materials your milling balls (and milling jars) are made of, as well as with materials which were previously milled with them. I don't think you can say it destroys the crystal structure but some kind of mechanical alloying and let's call it "surface poisoning" may indeed happen. The common approach for obtaining particles in submicron range would be, as you say, some bottom-up sinthesis approach, be it sol-gel, precipitation or spray pyrolysis

In addition to "surface poisoning" or "surface contamination", there may be a mechanochemical reaction happening during the grinding process, causing change in particle size, phase transformation, etc. Did you check the phase after grinding? Depending on your material, you may reach less than 1 micrometer after long time grinding if there is no mechanochemical reaction as well as no contamination. For bottom-up approach, you may try hydrothermal/solvothermal synthesis. If you have a Teflon-lined autoclave, it is simple and straightforward.   

Dear Dr. Riva:

“Ceramics pigments: Is grinding under one micron possible?”

Yes. Downsizing of inorganic pigment is feasible.

“Grinding under micron ceramic pigments.

When using a pigment finely ground under one micron in most cases, is not obtained initial coloring (no grinding).”

This is common, it is due optical phenomenon and several times due chemical interactions.

“What does it depend ? the destruction of the crystal structure? (Wet grinding is done).”

In part, opacity degree of glaze. Really, dissolution (equivalent to “the destruction of the crystal”) of pigment-particle in the liquid at high temperature is common.

“How to avoid this?”

Seems that is a hard way, since involve the changing of chemical nature of pigment, without changing the color. In fact, it is possible to consider the development of a solid-solution that can be engineered, only that “color” be maintained.

“Better to change the type of synthesis? (Solid state reaction with So gels or other types?)”

Seems that no. Changing the synthesis (chemical route of the preparation) would result only in size effects, as example particles with distinct sizes, agglomeration level, etc… Solid state reaction gives typically great particles. If a new color went developed, some efforts can be spent in find a class of frit that new pigment is stable. Otherwise, reengineering the crystalline structure via solid-solution design for that new material cannot be solubilized in a frit.

As mentioned previously, there is a small number of information at a problem with multiple sources of problems. By hypothesis, it is possible to consider that the question involves an enameled ceramics, which can be a tile, ceramic floor, photo mug, beer mug, coffee mug…recipient to serve food etc. Also that technology applied in the fabrication is classic. In this sense, three parts can be further considered as follow support (body), engobe and glaze.

Inorganic pigments are added to the ceramic glaze (glassy surface on tile) composition. Both engobe and glaze are prepared from a specific frit. The frit composition depending on the abundance of raw-materials but in a gross manner two classes can be highlighted the first is based in boron compounds (agent decreasing of melting point) and another based in non-boron compounds. But is night that frits can exhibits an acid character or basic character that gives further reactivity characteristics to these materials. Here, the pigment selection begins to be relevant. After fusion, due the nature of liquid and its intrinsic properties, a very small part of inorganic pigment tend to be attach pigment surface of pigment particle. In this sense, nanometric particle tend to be dissolved. But coloring power, depending on the glaze composition was engineered to be exhibit transparence, transparence and slight opacity level or show high level of opacity. The fraction of inorganic pigment can provide some influence in the color development but this is non-conventional. Furthermore, if liquid dissolve pigment, cation of pigment tend to modify composition of liquid that after cooling tend to exhibits some defects to the glaze as an example: micro-bubbles, bubbles, micro-cracks, voids, pits, etc…etc.

Again, in above sense, changing the preparation or synthesis route is not change the chemical reactivity of pigment with melting glass. Unfortunately, almost ionic compounds with interesting colors are unusual as inorganic pigment at ceramic industry.

Best regards

Marcos Nobre

Many thanks to all for the answers. .

Dear Prof. Marcos Augusto Lima Nobre: 

 how to re-engineer the crystal structures? what parameters you mean?

my problem is precisely the presence of some elements in the glass that alters the composition of the pigment particles. (replacement of elements)

Dear Mirabbos Hojamberdiev :

I will check the phase with XRD.

Thanks in advance at all.

Dear Dr. Riva:

“ how to re-engineer the crystal structures? what parameters you mean?”

Well, all is complex with a great number of variables…but starting from idea that a ceramic/inorganic pigment is not a color in essence, but a material that is inert in a glass during specific time and under a temperature that a priori is very high, it is possible consider that some direct and another indirect properties of crystalline structure of pigment can be further considered. Also, frit (glass composition) should be considered, as mentioned previously.

The re-engineering of the crystalline structure can be carried out by modulation of amount of intrinsic and/or extrinsic defects concentration. In this sense, it is necessary the creation or annihilation of defects, sometimes increasing sometimes decreasing the concentration of a particular defect. As a whole, the objective is to attain further chemical stability of pigment without significant changing of chromatic coordinates (values) of the pigment.

If creation/modulation of extrinsic defects is further considered, this process can be reach via solid-solution development/optimization. Here, I believe that there are several strategies. I would like comment some few of strategies, see single phase characteristic of pigment should be maintained, only, as follow: isovalent substitution of a lattice atom, non-isovalent substitution of a lattice atom. Depending on the materials, a very slight excess of a specific type of cation can be result is some stability, in these cases the electrical neutrality law should be underestimated. Structural features can be monitored by X-ray diffraction, while color via chromatic coordinates deriving. If major color is maintained, an investigation of thermal stability in the glass can be conducted.

If creation/modulation of intrinsic defects is further considered, this process can be reach via engineering of the thermal cycle of synthesis of pigment and development/optimization of synthesis atmosphere. See, from this point some “hypothesis” can be highlighted as follow: some pigments can be stabilized from presence of a specific structural symmetry, another depending on the presence of chromophore cation in specific valence at two distinct sites, another chromophore cation can be occupy same site with two distinct valences, some pigments are non-stoichiometric depending on the oxygen concentration at lattice, another pigments have oxygen vacancy as an intrinsic defects but are only further stabilized at minor oxygen vacancy concentration. In this sense, it is possible prepare a pigment ceramic after calcination of precursors at high temperature, (new material is synthesized) furnace atmosphere exhibiting reducing character, and fast cooling-rate or quenching from high temperature...There is an infinity number of possibilities.

“my problem is precisely the presence of some elements in the glass that alters the composition of the pigment particles. (replacement of elements)”

Well, this phenomenon is a bit rare, but would be interesting. The phenomenon or process of  “replacement of elements” requires further investigation and analysis. This phenomenon is typically common at high temperature and high pressures.

In a gross manner, a most conventional phenomenon iwould be a partial or total dissolution of the pigment in the frit at high temperature. Again, all is complex with great number of variables…, the chromophore element of pigment when present in the pigment-lattice can gives a specific color, as an example green. As a function of dissolution, the chromophore is now free to occupy glass-matrix with new kind of lattice interaction and exhibiting new color, as an example blue. In particular, this event can occurs at chromophores elements belong to the transition metal series, while one or more cation belong to the pigment-lattice are network-formers and/or network-modifiers. In fact, based on general roles, involving coordination number and bond strength of oxide (MOx), M cations can be classified as glass-formers, intermediates and glass modifiers.

Best regards

Marcos Nobre

Dear Prof Marcos Augusto Lima Nombre:

For example, the system Perovskite  for so long time I was studying and then abandoned because chemically unstable (calcination).

I know this system is unstable beacouse:

-the Chemical stability especially When You change one uses glaze with hight content of ZnO, Al2O3, CaO at high temperatures (1200 ° C).

I changed the amount of chromophore, the cooking cycle, mineralizator etc ... but I dont Obtained good results.

I now read in the literature That if change the method of synthesis, solid state reaction with combustion synthesis is may be possible to Obtain major chemical stability.

Unfortunately for me I do not possess the necessary means for this type of synthesis.

What solutions do you have for these pigments chemically unstable?

I agree with you as far as written in Q & A before:

gross manner, in most conventional phenomenon iwould be in partial or total dissolution of the pigment in the frit at high temperatures. Again, all is complex with great number of variables ..., When the chromophore element of pigment present in the pigment-latex can gives a specific color, as an example green. As a function of dissolution, the chromophore is now free to occupy glass-matrix with new kind of lattice interaction and exhibiting new color, as an example blue.

It considers that the composition of the glass I can not change.

I do not understand what you mean by defects.

Thanks in advance

Riva V.