Acoustic spectroscopy for particle size measurement

Citation

(2000), "Acoustic spectroscopy for particle size measurement", Pigment & Resin Technology, Vol. 29 No. 5. https://doi.org/10.1108/prt.2000.12929ead.008

Acoustic spectroscopy for particle size measurement

Acoustic spectroscopy for particle size measurementKeywords: Malvern Instruments, Spectroscopy, Particles, Sizing

The new Ultrasizer SV (small volume) from Malvern Instruments is described as a flexible ultrasonic spectrometer that uses Malvern's established acoustic spectroscopy technology for particle size measurement in concentrated systems.

Acoustic spectroscopy works by transmitting sound waves through a sample and measuring attenuation over a wide range of frequencies. Particle size is calculated from the measured spectra using software that models the physical basis of sound attenuation in concentrated systems. It claims the advantage over light based systems of being able to measure particle size in highly concentrated samples without requiring dilution.

The Ultrasizer SV (Plate 7) is reported to have many new features including an interchangeable measurement cell that can be swapped out in a matter of seconds. Fixed batch and flow cells are available with volumes starting at 450cm³. Thanks to the modular design of the measurement unit, customised cells can be designed for specific applications with no re-engineering of the system.

Malvern informs us that to ensure measurement integrity, the heater-chiller unit provides accurate temperature control, and also enables temperature profile studies to be undertaken.

Plate 7 Ultrasizer SV delivers advances in acoustic spectroscopy for particle measurement

The Ultrasizer SV is reported to offer size measurement from 10nm to 1,000mm, with operating concentrations of 0.5V per cent to 50V per cent and measurement of attenuation and velocity over the frequency range 1MHz to 150MHz. There is enhanced software for additional measurements, and the system is said to have the facility for change tracking through raw attenuation spectra or using particle size analysis and trend plots.

The Ultrasizer SV has applications in a wide range of industrial settings and Malvern Instruments remains committed to the continuing development of this technology for in-process as well as laboratory based applications.

Applications include:

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  Monitoring particle size reduction or growth in suspensions or emulsions

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  Examining the effects on emulsions of homogenisation time or shear rate

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  Determining the parameters affecting the rate of crystallisation, particle nucleation and growth kinetics

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  Measuring the effects of surfactants and other additives

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  Optimising process conditions and selecting raw materials for cost-effective formulation

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  Optimising and assessing the stability of disperse systems.

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  Aggregation studies are possible in suspensions and emulsions, as are studies of dissolution rates

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  Optimising polymerisation processes by controlling polymer growth and preventing coagulum formation.

Malvern Instruments has also launched the Sysmex SD-2000 ultra-high resolution particle counter and sizer at this year's Pittcon exhibition. This was the instrument's first showing outside Japan. Malvern Instruments has exclusive distribution rights in Europe, North America and the Middle East and will offer the Sysmex SD-2000 as part of its extensive range of particle size analysis systems.

The Sysmex SD-2000 (Plate 8) has a reported particle size measuring range from 1MHz to 120MHz. It is said to deliver high performance by combining electrozone sensing, which is a proven particle counting and sizing technology, with hydrodynamic focusing and sheath flow technology.

Hydrodynamic focusing with sheath flow directs particles through the centre of the measurement aperture to ensure that uniform electrical signals are produced for the generation of counting and sizing data. Combining the technologies is said to remove errors caused by coincidence counting, non-axial flow and particle re-circulation. With electrozone sensing the response is reported to be unaffected by the particle colour, shape, composition or refractive index, giving reliable, repeatable results whatever the sample.

Plate 8Sysmex SD-2000 ultra-high resolution particle converter and sizer Materials

The Sysmex SD-2000 is stated to be designed to be easy to use. It has a self-check and cleaning cycle that is triggered by switching the instrument on. Once measurement protocols have been defined, all measurement procedures, including output and cleaning, are automatic. Ideal measurement conditions are thought to be assured through systems diagnostics that deliver messages to the operator should there be any operation or measurement errors.

For convenience, factory calibration is standard, but users have the option to recalibrate for specific sample types. Apertures are available in diameters 50mm, 100mm and 200mm. For any given aperture, the particle sizing range is from 2 per cent to 60 per cent of the diameter.

Details available from: Malvern Instruments Ltd. Tel: +44 (0) 1684 892456; Fax: +44 (0) 1684 892789; E-mail: janr@malvern.co.uk; Web site: www.malvern.co.uk