Preprint Evaluation of fluid-fluid and rock-fluid interfacial interac...

Ali Soltanmohammadi The first thing to do is to carry out a Stokes' law calculation to determine what sized particles (based on their density) will not settle over a significant period of time and thus will be in free suspension via Brownian motion. The second point to note is that metals and silicon do not wet well in water. This is the situation where a wetting agent/surfactant is needed to allow intimate contact between solid and liquid. The 3 stages in making a stable suspension (well-known to paint and ceramics chemists) from a powder are:

• Wetting - if the particles do not wet in the fluid, then a surfactant is needed
• Separation. The key step where energy is needed. Usually accomplished with ultrasound energy in the laboratory although high shear mixers (e.g. Silverson) are utilized in industry
• Stabilization. This is where, after separation, particles recombine (aggregate and agglomerate) due to attractive van der Waals forces. Here, either charge (sometime called electrostatic, but this is a deceptive term) stabilization (with an ionic additive in the optimum concentration) or steric stabilization (using a relatively low MW polymer such as 50kDa PEG or PEI) to keep particles apart on a geometric basis

One further point is that Mg metal reacts with water over a period of time. This is the basis of an amusing school experiment:

Mg + 2H2O → 2Mg(OH)2 + H2↑

For further detailed information on dispersion of small primary size powders please view this webinar (free registration required):

Dispersion and nanotechnology

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat

In this webinar both charge and steric stabilization (with zeta potential) are discussed. Note that the concept of zeta potential is best understood from a stability perspective in aqueous media.

Alan F Rawle ultrasonication would only dissolve the powder here?

Mustafa Iqbal Ultrasound disperses loose agglomerates (not tight aggregates) - dissolves nothing (other than perhaps by localized heating). See this webinar (free registration required):

Ultrasound, cavitation, and the singing kettle

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W130619UltrasoundCavitationSingingKettle.html