Inhomogeneous distribution, of elements

The maturity of GD-MS as a technique capable of routinely providing complete chemical analyses at the ultratrace level for insulating solid materials has clearly been demonstrated by quantification of a full range of elements (from Li to U) in coal and coal fly ash [643]. The samples were mixed with high-purity Ag powder as the binder and pressed into a pin shaped pellet by means of a polypropylene mold. Critical steps in the determination process were the inhomogeneous distribution of elements within and among the fly ash particles and the purity of the binder. The presence of highly volatile compounds hindered the application to bituminous coal. 

Lower conductivity values are reported for conventionally synthesized LST compositions and can be explained by hindered oxygen diffusion through the perov-skite crystal structure (Figure 4.4a). This observation is attributed to an inhomogeneous distribution of elements in crystallites along the conduction path, element gradients between the grains, or diffusion effects of impurities. 

---