Лако-красочные материалы — производство

X-ray diffraction (XRD) is a very useful characterization tool in today’s pigment industry. It is routinely used to verify RM quality and as a QC tool to control pro­duction. It can also be used to accurately measure lattice constants, study site — occupancies, measure crystallite size (when <100 nm), identify secondary phases, and quantify the concentrations of secondary phases.

A study of the effect of the various DR pigment chemistries on lattice constants in underway [48]. Surprisingly large variations of lattice constant changes have been observed that are dependent on both the low-valency cation (Cr, Mn, Ni) and the high-valency cation (Sb, Nb, W). The differences in the lattice constants affect the electronic states of the lattice, and have an impact upon the shade of the pig­ment. Some preliminary measurements are shown in Table 6.5.

It can be observed from Table 6.6 that the Mn-DR pigments have much greater lattice expansions than the Ni and Cr analogs. This is partially, but not entirely, because of the higher substitution levels used in the MnSbTi pigments. Second, Nb curiously causes an increase in the ‘a’ constant, but a decrease in the ‘c’ con­stant relative to the Sb addition. W causes the least expansion in the ‘c’ lattice con­stant. W often forms distorted WO6 octahedra [49] that can have a significant impact on the lattice and the color. It is observed that the W analogs are redder than the Sb or Nb analogs when they have similar particle sizes.

It has previously been reported that the Nb analogs give redder shades than the Sb analogs. However, it appears that this was mostly a particle size effect, and that an Nb analog of the same size as the Sb version will give approximately the same red­ness.