9902.01.32 - Entirely spherical silicon dioxide micro-spheres, certified by the importer as having mean particle size of 3 to 18 micrometers (µm), linseed oil absorption 150 to 400 ml/g, microbial count less than 100 cfu/g, mold count less than 100 cfu/g, heavy metals less than 20 ppm, surface area 300 to 800 m²/g and pore volume of 0.8 to 2.5 ml/g (CAS No. 7631-86-9) (provided for in subheading 2811.22.10)

This HTS category, 9902.01.32, specifically classifies entirely spherical silicon dioxide micro-spheres meeting a stringent set of physical and chemical criteria. These micro-spheres are characterized by a defined mean particle size range of 3 to 18 micrometers, a specific linseed oil absorption capacity between 150 and 400 ml/g, and low microbial and mold counts (less than 100 cfu/g each). Furthermore, they must contain heavy metals below 20 ppm, exhibit a surface area of 300 to 800 m²/g, and possess a pore volume ranging from 0.8 to 2.5 ml/g. The importer's certification is a key requirement for classification under this provision.

As a temporary or special classification provision within Chapter 99, this entry is distinct from the permanent HTS classifications found in earlier chapters. For instance, while general silicon dioxide might be classified elsewhere, this code is reserved for these highly specific micro-spheres, often utilized in niche industrial or research applications. Its placement within Section XXII highlights its purpose as a temporary measure or a modification under trade agreements, rather than a standard commodity classification.

Since 9902.01.32 represents a leaf node within the HTS database, it has no further subcategories. Goods falling under this classification are considered fully defined by the descriptive criteria provided. The classification hinges entirely on the importer's confirmation that the imported silicon dioxide micro-spheres precisely match all specified physical and chemical parameters, including particle size, absorption, microbial load, heavy metal content, surface area, and pore volume, and are listed under CAS No. 7631-86-9, while also being provided for in subheading 2811.22.10 under the permanent tariff.