ISO 10076:1991 pdf download – Metallic powders – Determination of particlesize distribution by gravitational sedimentationin a liquid and attenuation measurement.
L2 Preparation of the suspension
L2.1 S.tectlon 01 the suspending liquid
The liquid used to make the suspension shall satisly the following requtremenlw
— the density of the liquid shall be lower than the density of the solid;
— the solid shall not dissolve in or react with the liquid;
the liquid shall wet the solid so that agglomerates are not formed;
— the viscosity of the liquid shall be such that the test does not take too long and the coarsest particles do not settle too rapidly (see 8 1).
Frequently, a pure liquid does not produce a good dispersion of the particles In such cases, a dispersing or welting agent shall be used, either dissolved in the liquid or added to the powder.
Annex C gives, as examples, a list of suspending liquids and dispersing agents. The suitability of a particular system shall be checked as Indicated in 622 below,
1.2.2 for dispersion
Several methods can be used to test whether a suspension Is free from agglomerates
L2.2t Microscopic eraminalion
A drop of the prepared suspension is placed on a microscope slide, and a cover glass Is lowered with extreme care over It, Examination of the preparation under a suitable magnification will show ii the partides are entirety separate and form a good dksper sion, or are assembled In chains or clusters.
62.2.2 QualitatIve sedimentation
The suspension Is loft to settle, A correctly dispersed suspension settles less rapidly than a flocculated suspension and shows no sharp boundary between the clear liquid and the turbid layer as settling proceeds. The sediment produced ii rigid and compact and has a minimum volume
L223 Quaniftath.. s.dimentation with pholomtrlc measurement
Attenuation rneasurenlenls are made immediately after agitation using different suspending liquids and the same powder concentration. A maximum value of optical density indicates an optimum dispersion
12.2.4 Quantitlve s.m.ntation with X-ray absorption
Quantitative tests are made with suspensions in diiferent liquids and having different concentrations, starting fur instance with a low concentration of 0.1 % (V/k) The best system is the one which gives the highest proportion ol fine fractions
62.3 Preparation of th. suspension The density end viscosity of the selected iiquid at the test temperature shell be known or measured The suspension may be prepared at the selected concentration, starling with a weighed test portion, or the suspending liquid may be added siowly and the powder worked to a paste, then diluted to a suspension A drop of wetting agent shall be added to the dry test portion or the suspending liquid if the liquid does not readily wet the powder. Make up to an appropriate volume The dispersion may be made by shaking Ihe suspension or stirring it In the sedimentation vessel If necessary, treat with ultrasonics or de-aerate under reduced pressure, either in a separate vessef or in the sedimentation vessel. The duration and intensity of dispersion Is selected so that unwanted agglomerates are destroyed bul any aggregates or desired particles are not damaged
6.3 SedImentation test
6.3.1 The general requirements For a satisfactory test are the following
— the sedimentation cell shall be installed rigidly in a vertical position and without vibration;
— the cell shall be fitted with a lherrnoslalic envelope, or the environment conditioned to maintain the cell at a known temperature, stable to within ± 1 C, with a rate of change 01 temperature or less than 0.01 C/min for prolonged analyses (longer than I h);
— care shalt be taken to avoid convection currents In the liquid (due to evaporation or to external heat sources, for Instance) and mass transFer currents (du. to density inversIon in the suspen. sion)
6.3.2 Stir the suspension using either a stirring rod or a magnetic bar until the analysis is started (i0).
6.3.3 In most instruments, the initial optical density or X-ray absorption of the suspension Is recorded.