9 сентября, 2015 
Pokraskin Pseudobrookite, Fe2TiO5, is a stable structure that has even been observed as a decomposition product of overfired ZnFeTi spinel pigments. Despite this, it is difficult to make clean versions of this pigment.
The challenge in making high-quality pseudobrookite pigments (base formula Fe2TiO5) is obtaining complete reaction of the Fe2O3. This is a difficult reaction to force despite the availability of fine-sized pigmentary grades of Fe2O3 and TiO2 for use as raw materials. Unfortunately, Fe2O3 can be found in the XRD spectra of most commercial pigments, and is surely present in significant amounts even when it is undetectable in the XRD patterns.
There are at least two pseudobrookite pigment chemistries in products in the marketplace. The first uses a large excess of TiO2 to help force complete reaction of the Fe2O3. This results in a rutile secondary phase that is sometimes the dominant phase in the product. In fact, patents cover such composition with up to a 15 fold excess of TiO2 [25, 26].
The second chemistry is an (Fe, Al)2TiO5 formula that substitutes Al for some of the Fe. This partial substitution enhances reaction of the iron oxide and has less Fe2O3 in the formula that needs to react.
Fe(II) species such as FeTiO3 ilmenite and Fe2TiO4 spinel will not form under normal conditions. Of coarse, addition of low-valent metals could allow formation of some spinel structure, but they would be Fe(III)-containing spinels. A study that characterized one Pigment Black 12 source as mostly spinel did not convey the complete chemistry [41].
Опубликовано в рубрике 