$laser diffraction particle size analysis ppt$

$laser diffraction particle size analysis ppt$

The single scattered light is thus separated from the multiple scattered light. By the cross correlation of both signals the single scattered light, used for the correct calculation of the particle size distribtion, is filtered out from the multiple scattered light part. PCCS acquires two separately induced scattered light intensities. The PCCS technology will help to eliminate the influence of multiple scattered light in principle. However, this conventional technology requires extremely diluted samples in order to deliver meaningful results. The principle of dynamic light scattering traditionally is realised with Photon Correlation Spectroscopy (PCS) which uses auto-correlation of scattered light intensities in order to determine particle size distribution. Unwanted sample dilution can be avoided and particle size measurements in the original concentration of the respective application are possible. The application of cross-correlation significantly enhances the concentration range for samples which can be measured with dynamic light scattering. PCCS opens possibilities for analysis of nanoparticles in suspensions and emulsions with hundreds of times higher solids concentrations than before. The particle size distribution can be calculated with the correlation function, which follows an exponential decay. The scattered signal is correlated with itself at different points in time (a comparison of the time lagged and the original function). With the help of a photodetector the scattered light intensity is monitored over time and then autocorrelated. Thus the intensity of the entire scattering wave fluctuates between a minimum (destructive interference) and a maximum value (constructive interference) over time. The random motion (Brownian motion) of the particles changes the distance to each other and therefore the spatial superposition (interference) of the individual scattering waves. Due to optical interference of all partial waves an overall scattered wave is generated. The particles interact with the laser light and generate single scattering waves. D 1 or D 99).The principle of DLS traditionally is realised with Photon Correlation Spectroscopy (PCS) where one laser beam is transmitted through the sample. The beginning and end of the distribution are commonly defined by D 10 and D 90, although other D values can be used to define the cumulative distribution as well (e.g. D 50 defines the point where 50 % of the particles are smaller and 50 % bigger than that certain diameter. In either direction, the cumulative curve always ranges from 0 % to 100 %, with the middle point D 50 being the most commonly reported result of particle sizing by laser diffraction. This is done either from the smallest to the biggest diameter (called the 'undersize curve') or in the opposite direction (called the 'oversize curve'). To get this distribution, values for all previous classes are added to the next. For this reason, usually the cumulative distribution is analyzed. spikey, flat, etc.), so peak values are rather unreliable.

$laser diffraction particle size analysis ppt$

However, there might be more peaks or the peak might be weakly defined (e.g. The D mode value defines the position of the highest peak. The basic particle size distribution might have one or more peaks for size classes, which indicate the most common particle sizes.

$laser diffraction particle size analysis ppt$

The sample de-agglomerates (breaks down into smaller sized particles) as particles collide with each other or with the wall of the dispersion unit.Ī typical result of a laser diffraction measurement is shown in Figure 11. In dry mode the powder is put into motion either by compressed air or by gravity, creating a dry flow which is positioned in front of the laser beam. The liquid dispersion unit is usually equipped with a mechanical stirrer with adjustable speed and with a sonicator with adjustable duration and power. The sample keeps circulating until the measurement is done. In liquid mode the particles are dispersed in a liquid and pumped into a glass measurement cell which is placed in front of the laser. it should be measured in liquid mode if the final product is a liquid dispersion and in dry mode if the final product is a powder. Usually a sample should be analyzed in a state relevant to its application, i.e. This means that each particle should be visible as a single particle in front of the laser, moving through either liquid medium or air. In order to get a clear diffraction, it is necessary to have a proper dispersion of the sample.

$laser diffraction particle size analysis ppt$

Laser diffraction particle size analysis ppt