Comparative Study on the Defects of Kaolinite from America, Brazil and China Applied for Paper Coating: XRD and Refinement by Rietveld Method

Three kaolinite samples applied for paper coating were collected from America (KA), Brazil (KB), and China (KC), respectively. Parameters such as average bond length of Si-O and Al-O (l((Si-O)) and l ((Al-O))), tetrahedral rotation angles (alpha), changes of tetrahedral flattening angles (tau) and octahedral flattening angles (psi) comparative to ideal angle, particle layer thickness (T) and basal z corrugation (Delta z) were analyzed by XRD and Rietveld method. The experimental results indicated that Delta z(KA) > Delta z(KC) > Delta z(KB). KB has a regular structure and KA has a disorder structure, alpha(KA) > alpha(KC) > alpha(KB), Delta tau(KA) > Delta tau(KC) > Delta tau(KB), and Delta psi(KA) > Delta psi(KB) > Delta psi(KC). KA has unstable tetrahedron and octahedron. KB and KC have stable tetrahedron and octahedron, respectively. In the process of manufacture, kaolinite structure may be broken from places with unstable tetrahedron and octahedron. l(Si-O)(KA) > l(Si-O)(KB) > l(Si-O)(KC) and l(Al-O)(KA) > l(Al-O)(KC) > l(Al-O)(KB). What only considered is the effect of bond length, KA may be most easily broken in the manufacture. Compared with bond lengths of KA and KB, Si-O, and Al-O of KB and KC may be easily broken, respectively. T-KA < T-KC < T-KB. KB should be delaminated to finer particles, or it would hinder its dispersibility.