Both the International Standards Organization (ISO) and Organization for Economic Co-operation and Development (OECD) subdivide nanomaterials into “nano-objects” and “nano-structured materials.” According to ISO TS 27687, nano-objects include nanoplates, nanofibers and nanoparticles, and are nano-scale at least in their exterior measure ments—in other words, they measure between one and 100 nanometers in length, width or height. Another ISO working group is currently working on the hierarchy and definitions of nanostructured materials, which include materials with a nanoscale structure within the material or on its surface. Prominent examples are nanocomposites, agglomerates and larger aggregates.
These kinds of aggregates and agglomerates are composed of primary particles (< 100 nm), which occur at an intermediate stage during the manufacturing process and react with each other under the relevant process conditions to form larger stable aggregates. In these aggregates, the primary particles are firmly connected by a chemical bond. For their part, the aggregates form micrometer-size agglomerates as a result of van der Waals forces.