| safety | See attributes, risk phases, MSDS, CMR substances, and Directives 99/45/EC, 67/548/EEC (in Appendix of standards). |
| scale of scrutiny | The amount, volume or mass, that is sufficient to ensure that specific determined qualities of interest in a bulk material sample will satisfy the requirement for purpose. A common use is to define the size of a mixture sample that must be taken, to ensure that the ratio of constituents falls within acceptable bounds for the application. In the case of a mix prepared for making pharmaceutical tablets, this should be no more than that required for an individual tablet to confirm that the amount of active ingredient per dose is within prescribed bounds. A larger sample may be appropriate for a detergent for use in domestic appliances and a different again scale for a solid fuel supply to a power station, where the average calorific value on a large scale is of interest. Some circumstances demand that more than one scale of scrutiny be considered, for each of which different levels of tolerances can apply. (See Scale of variation, intensity of variation, period of scrutiny). An analogy may be considered with colour differences in a fabric or sheet, where a small, intense spot is obvious, but a small shade difference at that scale would be un-noticed. However, a similar fine shade difference on a much large scale would be immediately apparent and un-acceptable. |
| scale of variation | The size of region over which a significant variation of an interesting physical property is detected. This may be from defined bounds or from the average in the universal sample. (See scale of scrutiny and Intensity of variation). Note that this term relates to the scale of causal occurrence of a variation, whereas the scale of scrutiny applies to the scale of significance relevant to an application, as with the suitability of the material to subsequent processing or for its ultimate use. |
| shear failure | The permanent disturbance of a particulate structure by the application of a shear stress. Interest may focus on incipient failure and/or sustained failure. |
| silo | A bulk storage container, usually of large volumetric capacity and tending to have a slender, cylindrical body section with a conical hopper section. May be built in banks and constructed of metal or concrete. Broadly synonymous with hopper and, to a limited extent, with bin and bunker. |
| solid | A state of matter in which the constituent molecules or ions possess no translational motion, but can only vibrate about fixed mean positions. A solid has definite shape and offers resistant to changes in shape and/or volume. |
| spot sample | A sample taken at random from a bulk mass. |
| state | (of a bulk material) The condition of dilatation of a bulk material, as characterised by the packing arrangement of the constituent particles. Material state is normally quantified by its condition of density, although strictly, this does not take account of any anisotropy in the system. |
| Stokes-Einstein equation | The equation relating the pace of Brownian motion to the diameter of the particle in motion, expressed as: D = kT/3π·η·d where: - D is the diffusion coefficient of the particle. - K is the Boltzmann’s constant. - T is the temperature. - η is the viscosity of the surrounding fluid - d is the particle diameter (diffusion diameter). and where D is determined in photo correlation spectroscopy using the equation: k = 4 π·n·sin (θ/2) / λ where - n is the refractive index of the suspending field - θ is the scattering angle - λ is the wavelength of incident light. |
| Stoke’s law | The equation which determines the free falling velocity, v, (terminal velocity), attained by a particle in viscous flow conditions and allows a calculation to be made of the particle size. v = d2·g ( ∂s - ∂f ) / 18 η in SI Units where: - v is the free-falling velocity. - d is the Stoke’s diameter of particle. - g is the gravitational acceleration. - ∂s is the density of particle. - ∂f is the density of fluid. - η is the viscosity. |
| strain ellipsoid | Representation of strain in the form of an ellipsoid into which a sphere of unit radius deforms and whose axis are the principal axis of strain. |
| stress | The value of an applied force divided by the area of its application. |
| stress ellipsoid | The representation of the state of stress in the form of an ellipsoid whose semi-axes are proportional to the magnitude of the principal stresses and lie in the principal directions. The coordinates of a point, P, on this ellipse are proportional to the magnitudes of the respective components of the stress along the planes normal to the direction, OP, where O is the centre of the ellipsoid. |
| stress history | The sequence of stress conditions that have brought a bulk material to the state in which it now resides. |
| stress relaxation | The reduction in stress due to creep or the reduction in confinement during flow. See Sigma Two relief. |
| surfactant | A substance which reduces surface tension. |
| suspension | A dispersion of particles in a fluid. |
| tangent modulus | The slope of the tangent to the stress-strain curve at a given stress value. (generally taken at a stress equal to half the compressive strength). |
| thixotropic suspension | A condition that requires an initiating stress to commence deformation, but then resistance decreases with increased strain. |
| turbitity | The light scattering properties of particles suspended in a fluid. |
Glossary of Terms in Powder & Bulk Technology
1.3 General Terms
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