What is Microscopic Technique and Disadvantages of microscopic technique

 Microscopic Technique

Optical microscopy is generally used for particle size measurement in the range of 0.2 um to about 100 um.At least 300 to 500 particles must be counted in order to obtain a good size distribution analysis of data.

A dilute suspension of the powder particles whose sizes are to be determined is prepared in liquid vehicle in which it is insoluble. If it is slightly soluble, a saturated solution of the powder can be used for the preparation of the suspension. A drop of the suspension is molinted on a slide or ruled cell and observed under the microscope. The eyepiece of the microscope is fitted with a micrometer by which an estimate of the particle size can be obtained. All the particles observed in a field are counted through the eye-piece. The data may be scientifically represented as size-frequency distribution curve. From the data, the average particle size as well as the size distribution is determined.

For ease in counting the particles, the field viewed through the microscope can be projected on a screen or photographed for latter measurement. Particles may also be counted with electronic scanners to avoid the strain of visual observation. For measuring very small particle size, an electron microscope or a scanning electron microscope may be used. The latter is also capable of proving an estimate of the particle depth.

  Disadvantages of microscopic technique

(i) The measured diameter of the particles represents two dimensions only. i., length and breadth and an estimate of the depth is not obtained.

(ii) The method tends to be slow and tedious since at least 300 to 500 particles should be counted to get a reliable data. Advantages: Agglomerates as well as particles of more than one component can be detected by this method.