Practical 3: Particle Size and Shape Analysis Using Microscope

Date

17th November 2014

Objective

To analyse the size and shape of particles and to observe and compare the size of particles under microscope.

Introduction

The bulk properties such as particles size and shape of the powder are determined by using the size of particles. There are various method that can be used to determine particle sizes and shapes. Microscopic analysis is the most widely used method in this case. It can determine the diameter, shape, and surface area that cannot be determined with the bare eye.  In this experiment, different sizes and shapes of sands are used. . In this experiment, various type of sands ( 150µ, 355µ, 500µ, 850µ, mixed ) and two different powders ( MCC and lactose ) are given to be analyze. Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.  It exists in various different sizes rangingfrom 0.0625 mm (or 1⁄16 mm) to 2 mm.  Fine sand is defined as particles between 0.02 mm and 0.2 mm while course sand as those between 0.2 mm and 2.0 mm. It is used in this experiment as it is inert, easy to obtain and economical.

Materials

Sands( 150µ, 355µ, 500µ, 850µ, mixed )
Lactose powder
MCC powder

Apparatus

Microscope

100 ml beaker

Spatula

Glass slide and cover slip

Procedure

1. Sands with sizes of 150µ, 355µ, 500µ, 850µ, mixed, lactose and MCC are placed in the different beakers by using spatula. The beakers are labeled according to the content.
2. The microscope was set up and ready to be use.
3. 150µ sand scattered on the glass slide and covered with the cover slip.
4. The sand was observed under the microscope using 4x100 magnification.
5. The particles were observed microscopically and the shape was determined.
6. Steps 3 to 5 were repeated by using 355µ, 500µ, 850µ, mixedsands, lactose and MCC powder.


Observations

Size of sand 150 microns  (4 X 4 magnification)
(The particles are irregular in shape)

 Size of sand: 355 µm (4X4 magnification)
(All the particles are small, same size and irregular in shape.)

Size of sand: 500 µm
(All the particles are larger than 355 µm, the size is almost same and the shape is irregular.)

Size of sand: 850 µm (4x4 magnifications)
(The particles are larger compare to 500 µm, particles that present on the upper position look larger and can be seen clearly while particles at the lower position look smaller. The shape of the particles is irregular and without a defined shape.)

 Lactose (4x4 magnifications)
(All particles are small; some of them have round shape while others are irregular in shape.)

Sand of various sizes (4x4 magnification)
(All the particles have different size; most of them have irregular shape with different number of edges and sides.)

 MCC (4x4 magnification)
(the particles are irregular in shape)

Questions

1. Briefly describe the various statistical methods that can be used to measure the diameter of a certain particle.

     There are several method that can be used to measure the diameter of a certain particle.One of the methods is Feret’s  diameter.Feret diameters denoted as Dfh ( horizontal) and Dfv (vertical).Feret diameters are defined as the distance between parallel tangentsFeret diameters are easy to measure and relate intuitively to a characteristic dimensions (eg : length) that may be important in processes.In the early work,Feret diameters were measured using a projection of a photographic negative on a piece of graph paper.Horizontal and vertical Feret diameters were read directly from the graph paper by counting  the squares between parallel tangents.The techniques ensured that both tangents in the horizontal and verticalndirections were parallel to one another,and the horizontal and vertical directions were perpendicular.If significant error in measurement could be tolerated,Feret diameters were measured directly from photographs rather than projeciting a negative onto a piece of graph paper.
Martin;s diameter method also used to determine the diameter of certain particle.Martin’s diameter is the mean chord length of the projected particle perimeter, which can be considered as the boundary separating equal particle area.Martin;s diameter is determined by drawing successive diameters through the centroid of the profile and computing bisected areas.Where the bisected areas are equal,the Martin diameter is defined as the length of chord bisecting the two equal areas.

Another method is projected area diameter which is measured based on the equivalent area to that of projected image of that particle. Projected area is two-dimensional area measurement of a three-dimensional object by projecting its shape on to an arbitrary plane. Besides, another useful method is the projected perimeter diameter which is based on the circle having the same perimeter as the particle. Both of these methods are independent upon particle orientation. They only take into account of 2 dimensions of the particle, thus inaccurate for unsymmetrical particle.

        The other method is by using Fourier analysis to provide an accurate quantification of particle morphology and texture. Three lower order Fourier descriptors, denoted “Signature Descriptors” provide measures of Elongation, Triangularity and Squareness, whilst an additional descriptor, denoted “Asymmetry” provides a measure of particle irregularity. They describe the overall shape of soil particles (defined as “morphology”). A summary of higher order descriptors provides textural information which is related to local roughness features (defined as “texture”).
               


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

As such, the best statistical method is Feret’s and Martin’s diameter. It is because both of these are the statistical diameter which is the average over many different orientations to produce a mean value for each particle diameter. This will give an average value of diameter in more orientation and giving an average diameter value which is more accurate. Besides, since it is accessing the three-dimensional image of particle, we can use the electron microscope that considering the orientation and shape of the image.

Discussion

       At the most basic level, we can define a particle as being a discrete sub portion of a substance. For the purposes of this guide, we shall narrow the definition to include solid particles, liquid droplets or gas bubbles with physical dimensions ranging from sub-nanometer to several millimeters in size. The most common types of materials consisting of particles are powders and granules for example pigments, cement, pharmaceutical ingredients. Secondly suspensions, emulsions and slurries and example are. Vaccines, milk, mining muds. Thirdly aerosols and sprays with asthma inhalers, crop protection sprays as the example.

  We had conducted an experiment on particle size and shape analysis by using a microscope. From this experiment, we had determine a various size and shape of  150µ, 355µ, 500µ, 850µ, mixed, lactose and McCaw also least that particle size and shape play such an important rule. By far the most important physical property of particulate samples is particle size. Particle size measurement is routinely carried out across a wide range of industries and is often a critical parameter in the manufacture of many products. Particle size have direct influence on reactivity or dissolution rate, stability in suspension, efficacy of delivery, texture and feel appearance, flow ability and handling viscosity, packing density and porosity.


     As well as particle size, the shape of certain particles can also have a significant impact upon the performance or processing of the materials. Many industries are now also making particle shape measurements in addition to particle size in order to gain a better understanding of their products and processes. Some areas where particle shape can have an impact include reactivity and solubility ,powder flow and handling ,ceramic sinter properties ,abrasive efficiency, texture and feel Particle shape can also be used to determine the state of dispersion of particulate materials, specifically if agglomerates or primary particles are present.

The ability to analyze and characterize particle size and shape can significantly improve the manufacturing efficiency and product performance. Thus, we can use of microscopy and image analysis as the most reliable technique to characterize particle shape, size and volume distribution. From this practical, it is found that the overall shape of the sand is asymmetrical. One of the methods used to measure a particle is the projected area diameter which is measured based on the equivalent area to that of projected image of that particle. Another method is the projected perimeter diameter which is based on the circle having the same perimeter as the particle. Both of the methods do not account the 3 dimensional shape of particle (orientation). They only consider the 2 dimensions of the particle, thus it is inaccurate for unsymmetrical particle.

        During the experiment, we put different types of sand on slide to be directly observed them using a light microscope. The sand should be spread evenly and just thin layer to avoid agglomeration that will affect the observation. We observed that the particles are irregular in shape. The size analysis is carried out on two-dimensional image of particles which are generally assumed to be randomly oriented in 3-dimensional and they are viewed in their most stable orientation.


Conclusion

Different types of sands have different size and shape which can be analyzed by using  a light microscope. We are able to determine the overall distribution of shape and size of this particle which are asymmetrical and irregular.


References

1. http://golik.co.il/Data/ABasicGuidtoParticleCharacterization(2)_1962085150.pdf
2. http://www.surfaceanalysis.ru/surface/categors/1f/74/content_128015234686.pdf
3. http://www.nature.com/nature/journal/v162/n4113/abs/162329b0.html

Analyzing by using microscope: