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What is the proper name given to the particles in a suspension? Suspensae perhaps? When these particles are brought out of suspension, and precipitate down to the bottom of the mixture, what is that process called, and do they take on a different proper name when no longer in suspension?

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    $\begingroup$ I don't know if there is a general term for suspended particles, but solid and liquid particles suspended in the atmosphere are known as particulates: en.wikipedia.org/wiki/Particulates . The process of particulates coming out of a suspension is known as settling. That distinguishes suspensions from a colloids: Those in a suspension settle out with time (due to gravity), while those in a colloid do not. $\endgroup$
    – theorist
    Jan 21 at 3:40
  • $\begingroup$ Do generic precipitate or floc (en.wikipedia.org/wiki/Flocculation) apply? $\endgroup$ Jan 21 at 4:14
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    $\begingroup$ IUPAC's Gold Book states for suspension only «A liquid in which solid particles are dispersed.» $\endgroup$
    – Buttonwood
    Jan 21 at 8:37
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    $\begingroup$ +1 for "suspensae", quite ingenuitive. There is also obsolete "suspensoid", but it refers to the system, not just particles. $\endgroup$
    – andselisk
    Jan 21 at 13:43
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    $\begingroup$ @andselisk Even more so that there is the adjective (suspensus, suspensa, suspensum) and verb (suspendere) in Latin, though maybe no suspensa as noun in the a-declension. (Изучение латинского языка долго было фундамент всех изучений.) $\endgroup$
    – Buttonwood
    Jan 21 at 21:44

2 Answers 2

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Solid particles” is arguably the better term on its own, especially when size distribution is provided alongside with it. Alternatively, there is “dispersed phase” and its synonym “discontinuous phase” [1, p. 41]:

discontinuous phase In a dispersion or emulsion, the phase which is dispersed as particles or droplets in the continuous phase.

Note, however, that “dispersed phase” is a sloppy term as its applicability relies on properties match between bulk and dispersed phases and it doesn't necessarily refer to a suspension and may equally be used for particles or droplets [2, pp. 605–606]:

The name dispersed phase for the particles should be used only if they have essentially the properties of a bulk phase of the same composition.

[…]

In a suspension solid particles are dispersed in a liquid; a colloidal suspension is one in which the size of the particles lies in the colloidal range.

As for the case when “particles are brought out of suspension”, “precipitation” is not the proper term as it is applicable for solutions, not sols or suspensions [3, p. 260]:

precipitation
Formation of a solid material (a precipitate) from a liquid solution in which the material is present in amounts greater than its solubility in the liquid.

“Agglomeration” and “aggregation” are more correct, yet, strictly speaking, non-interchangeable terms [1, p. 5]:

agglomerate n A collection of primary particles or aggregates joined at their edges or corners, in such a way that the specific surface area is not markedly different from the sum of the areas of the constituent particles. —v the act of agglomeration.

aggregate n A collection of primary particles joined at their faces, with a specific surface area significantly less than the sum of the areas of the constituent particles. Aggregates are distinguished from agglomerates by the increased difficulty in separation. —v the act of aggregation.

Keep in mind that a colloidal particle itself could be an aggregate [2, p. 609], and there are several congregating processes for denoting particles that are “no longer in suspension”, such as flocculation/coagulation (for colloidal suspensions), sedimentation and sintering [2, p. 609–610]:

When a sol is colloidally unstable (i.e. the rate of aggregation is not negligible) the formation of aggregates is called coagulation or flocculation. These terms are often used interchangeably, but some authors prefer to introduce a distinction between coagulation, implying the formation of compact aggregates, leading to the macroscopic separation of a coagulum; and flocculation, implying the formation of a loose or open network which may or may not separate macroscopically. In many contexts the loose structure formed in this way is called a floc. While this distinction has certain advantages, in view of the more general (but not universal) acceptance of the equivalence of the words coagulation and flocculation, any author who wishes to make a distinction between them should state so clearly in his publication.

[…]

Sedimentation is the settling of suspended particles under the action of gravity or a centrifugal field. If the concentration of particles is high and interparticle forces are strong enough, the process of sedimentation may be better described as compaction of the particle structure with pressing out of the liquid. This particular kind of settling is also called subsidence.

Sediment is the highly concentrated suspension which may be formed by the sedimentation of a dilute suspension.

Coalescence is the disappearance of the boundary between two particles (usually droplets or bubbles) in contact, or between one of these and a bulk phase followed by changes of shape leading to a reduction of the total surface area.

[…]

Coalescence of solid particles is called sintering.

References

  1. Becher, P. F. Dictionary of Colloid and Surface Science, 2019 reprint by by CRC Press, Taylor&Francis Group.; M. Dekker: New York, 1990. ISBN 978-0-8247-8326-6.
  2. Everett, D. H. Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Pure and Applied Chemistry 1972, 31 (4), 577–638. DOI: 10.1351/pac197231040577.
  3. Gamsjäger, H.; Lorimer, J. W.; Scharlin, P.; Shaw, D. G. Glossary of Terms Related to Solubility (IUPAC Recommendations 2008). Pure and Applied Chemistry 2008, 80 (2), 233–276. DOI: 10.1351/pac200880020233.
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A colloidal suspension or a even a suspension consists of two phases: A dispersed phase and a dispersing medium. See this Table as an example:

Table 3.3. Combinations of two phases in colloidal systems.

Dispersed phase Dispersion medium Example
Solid Solid Alloys
Solid Liquid Starch in water
Solid Gas Dust in air
Liquid Solid Butter and cheese
Liquid Liquid Oil in water
Liquid Gas Clouds
Gas Solid Pumice stone
Gas Liquid Froth on beer

Ref: Biophysics, Principles and Techniques by M Subramanian, 2019

If the suspension settles, it is a floc or an agglomerate.

Please note that term dispersed phase is not sloppy usage. It is still widely used in high quality research journals. IUPAC recommends that

https://goldbook.iupac.org/terms/view/C01174

The name dispersed phase for the particles should be used only if they have essentially the properties of a bulk phase of the same composition.

Remember that definitions of chemical terms are human explanations, which are neither perfect nor rigid (to the extent of being "brittle").

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    $\begingroup$ I probably should've pointed out that "dispersed phase" is a sloppy term for what OP is asking about, not sloppy per se. Sorry if this wasn't evident from the context. I'm sure these high quality research journals are able to use IUPAC definitions correctly and precisely. Although I'm not ready to agree with "widely used" as a pro argument — this "billion flies can't be wrong" level of persuasion always puts me off. $\endgroup$
    – andselisk
    Jan 21 at 17:52

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