MICROSCOPE TF

Practical 5

Analysis of Sizes and Shapes of Particles Using Microscope

Introduction:

            Particle size is one of the most important parameters in materials science and technology as well as many other branches of science and technology, from medicine, pharmacology and biology to ecology, energy technology and the geosciences. In this introduction we give an overview on the content of this lecture course and define the most important measures of size (equivalent diameters).Particle size influences many properties of particulate materials and is a valuable indicator of quality and performance. This is true for powders, suspensions, emulsions, and aerosols. The size and shape of powders influences flow and compaction properties. Larger, more spherical particles will typically flow more easily than smaller or high aspect ratio particles. Smaller particles dissolve more quickly and lead to higher suspension viscosities than larger ones. Smaller droplet sizes and higher surface charge (zeta potential) will typically improve suspension and emulsion stability. Powder or droplets in the range of 2-5µm aerosolize better and will penetrate into lungs deeper than larger sizes. For these and many other reasons it is important to measure and control the particle size distribution of many products.

The only techniques that can describe particle size using multiple values are microscopy or automated image analysis. There are many different methods which can be used to measure particle size which include size range of analysis, wet or dry methods, manual or automatic methods, and speed of analysis. The examples of the particle size analysis methods include sieve method, coulter counter, laser light scattering method, dynamic light scattering method, sedimentation method and also microscope method. In this experiment, the size and shape of different sand particles were observed and analysed using the microscope method.

Objective :

To observe and analyse the shape and size of different types of sand samplesby using microscope.

Procedure:

By using the microscope, 5 samples of different sizes of sand are observed in terms of their sizes and shapes. First and foremost, a small amount of sand is put on the microscope slide. Then the microscope is transferred to the stage on the microscope. Then it is observed under the microscope. The samples observed are drawn. The steps are repeated in the other four samples of sand.

Observation:

Discussion :

Particle shape is a complex geometric characteristic. It involves the form and habit of the particle as well as features like convexity and surface roughness. From the experiment, it was observed that sand particles have a characteristic, gravel-like shape. Like flakes,they have a lot of sharp edges. Hence, although there is difference in size for 355. 500 and 800 micrometer sand particles, but on the whole they have the similar shape as they has sharp edges. Various size of particles can be determined by observing using microscope. The spaces between the particles are relatively small as the smaller sand particles will occupied the gaps between two relatively larger particles. On the other hand, lactose which has different characteristic from sand has irregular rounded shape. They are relatively small and it is brittle. In the other words, they are easily broken into finer small fragment. Measurements for diameter of particles can be carried out based on the microscopic diagram obtain from this experiment. Projected area diameter, da; projected perimeter diameter, dp; Feret’s diameter, dF and Martin’s diameter, dM are some of the equivalent diameter which can be used to measure irregular shape particles.

Questions :

1.      Explain briefly on the various statistical methods that can be used to measure     the diameter of a particle.

There are various statistical method which can be used to measure the diameter of a particle such as sieve method, electrical stream sensing zone method, laser light-scattering method and sedimentation methods.

Sieve analysis always carried out using dry powders and it can be done within a short period of time and also enable a much wider variety of size and shape parameters to be processed. Sieve diameter  D_sieve= equivalent diameter corresponding to the diameter of a sphere passing through a sieve of defined mesh size with square or circular apertures.

Electrical stream sensing zone method can be carried out by dispersing particles in electrolyte and the voltage pulse passes through orifice tube wall was measured. Besides, laser light-scattering method can be used to measure diameter of particles also. Diffraction pattern of the particles when light is emitted on it is studied and being analyse. Laser diffraction equivalent diameter  DL= diameter of a sphere yielding on the same detector geometry the same electronic response from the optical signal.

For sedimentation method, particle size distribution can be determined by examining the powder as it sediments out. Since powders contain particles of a range of different equivalent diameters. To define a size distribution or compare the characteristics of two or more powders consisting of particles with different diameters such as the various size of sand in this experiment, the size distribution can be broken down into size ranges and presented in the form of histogram. A histogram allows different particle size distributions to be compared.

2. State the best scientific method for each sample that you used.

Since sand particles used in this experiment is relatively large, a lot of equipmenthave the suitable range of analysis for them. However, for 800 micrometer, 500 micrometerand 350 micrometer sand particles,sieve method is the best scientific method. The range of analysis for sieve method is within 45 to 1000 micrometer. Besides, sieve method is cheaper and readily usable for large particles. For other particle which is the lactose, microscopic method is preferred due to their small size range. Besides, microscope method can be used to detect the presence of agglomeration and their two-dimensional images are analyzed according to the desired equivalent diameter which is Feret’sdiameter,dF and Martin’s diameter,dm. For sand with various size, sedimentation method can be used.

Conclusion:

Microscope method was used in this experiment to observe lactose, various size, 355, 500, 850 micrometer sands particles. Sand particles has relatively sharp edges compared to lactose particles and it was found that the empty space in various size of sand particles is small as they are filled with smaller sand particles.