Table of contents 1 Why is particle size important?
Particle size distribution is sufficient information for the majority of particle
tải về 7.54 Mb. Chế độ xem pdf
|
- Điều hướng trang này:
- Why am I making the measurement Must the new instrument match historic data Do I need only particle size distribu- tion
Particle size distribution is sufficient information for the majority of particle characterization applications. But some techniques are higher resolution than others. Ensemble technologies such as laser diffraction and dynamic light scattering are powerful techniques than are “resolution limited” compared to high resolution techniques which are based on particle counting (such as electro zone counting or image analysis). If the goal of the measurement is finding small populations of particles larger or smaller than the main distribution, then an investigation of the sensitivity to second distributions should be part of the selection process. Beginning the selection of a particle size analyzer should start with asking basic questions including: Why am I making the measurement? Must the new instrument match historic data? Do I need only particle size distribu- tion, or do I need additional information such as shape or surface charge? 29 Selecting a particle size analyzer Particle shape information may be either desirable or critical depending on the degree to which shape affects product performance. Particle shape influences bulk properties of powders including flow and compaction behavior and the viscosity of suspensions. For specific application such as glass beads used in highway paint, shape is a critical factor for reflectivity. When particle shape information is required, microscopy and image analysis are the only techniques that delivery the desired data. Manual microscopy provides basic qualitative size and shape information, but automated image analysis generates quantitative data that is statistically significant. For this reason, both dynamic and static image analysis are growing techniques replacing manual microscopy. Surface charge or zeta potential of suspensions is important information for formulators or chemists working on dispersion stability. For these applications a DLS system providing both particle size and zeta potential (along with other such as pH or conductivity) may be the best option. Consider the application of wanting to measure the particle size distribution of 50nm colloidal silica. Just considering the size range of the sample indicates that possible techniques include laser diffraction or DLS. One question worth asking would be will I need other capabilities in the future? If I might need zeta potential in the future, this removes laser diffraction from the list of possible techniques. If I might have particles > 1µm in the future, this would eliminate DLS. Be forewarned that future requirements can be difficult to ascertain and additional capabilities always carry incremental cost. tải về 7.54 Mb. Chia sẻ với bạn bè của bạn:
|