| hydrophobic | The property that defines a material as water repellent. Water exhibits an obtuse contact angle with hydrophobic materials. This property favours the use of such materials, for example sheets of ultra-high molecular density polyethylene, as contact surfaces for damp and wet bulk products, to minimise the wall cohesive effects of surface tension. |
| hydrostatic pressure | A state of stress in which all the principal stresses are equal, (there is no shear stress), as in a fluidised powder where the pressure in the voids is due to the head of product and acts in all directions. |
| milled powder | A powder produced by comminution in a mill. |
| natural powder | Material occurring naturally as a fine powder. |
| precipitated powder | A powder produced by chemical or electrostatic precipitation. |
| reference material | A material, the relevant properties of which are sufficiently established and consistent for it to be used for the calibration of a measuring instrument. (See also certified reference material, CRM116). |
Glossary of Terms in Powder & Bulk Technology
2. Types of Powder
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