Practical 5 : Particle Size Analysis & Analyze the size of particle using microscope

PURPOSE

To describe the general shape of various type of particles under a light microscope.

 
APPARATUS AND MATERIALS

Light microscope
Glass slide
Weighing boat
355, 500 and 850 micron sand

PROCEDURES

1. 355 micron sand was taken and put on a glass slide and it was made fairly flat on the surface of the glass slide.
2. The slide then was examined under a light microscope at 10x Magnification.
3. The experiment was repeated for another types of sands, which are 500 micron sand, 850 micron sand, and various size of sand.

RESULT

355 micron sand

500 micron sand

850 micron sand

Vary In Size of Sand

QUESTION

1. Discuss briefly the various statistical methods to measure the diameter of particles.

Diameter of a particle can be measured based on a circle having the same perimeter as the particle, which known as projected perimeter diameter. Meanwhile, projected area diameter can be measured from a circle of equivalent area to that of the projected image of a solid particle.

There are also methods called Feret's diameter and Martin's diameter. These two methods are dependent on both the orientation and the shape of the particles. The value of diameter is averaged over many different orientations produced for each particle. The only difference between these two is, Feret's diameter refers to the mean distance between two parallel tangents to the projected diameter. While Martin's diameter refers to the mean chord length of the projected particle perimeter which can be considered as the boundary separating the particle equally. 


 2. State the best statistical method for each sample used in this experiment.

355 micron sand : Martin's diameter
500 micron sand : Martin's diameter
800 micron sand : Martin's diameter
Vary in Size sand : Martin's diameter

CONCLUSION

By using microscope, we can analyses the shape of the particles and determine the best statistical method. Its dependent on the three-dimensional shape of the particles when using the Martin's diameter or Feret's diameter.
 

Practical 4 : Angle of Repose

Aim :

1) To measure the angle of repose of the sand.
2) To study the factor that can influence the angle of repose of the sand.
2) To study the effect of glidant on the angle of repose.

Introduction:


When bulk granular material is poured on a horizontal surface of conical pile, it will form the internal angle between the surface of the pile and the horizontal surface is known as angle of repose. Angle of repose or the critical angle of repose is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°.

In this experiment, we were measuring the angle of repose of the sand with 355 micron, 500 micron, 850 micron and various sizes without and with the addition of glidants. The experiment is done with a view to assessing the angle of repose of a substance and the factors that can influence the angle of repose.

Apparatus and Materials :

100g of 355, 500, 850 micron and various size of sand
Glidants
ruler

Procedure :

1. The 355 micron sand (without addition of the glidant yet) was poured in a level surface allowing it to build from the top.
2. The height of the pile from the peak to the ground eas measured by using the ruler
3. The horizontal distance from the middle of the pile to the edge was measured by using the ruler.
4. The equation tan-1 (height/width) had been used to find the angle of repose.
5. The procedure 1-5 was repeated with the addition of glidant.
6. The procedure 1-6 was repeated by using 500 micron, 850 micron and various size of sand

Result :

1.      Sand without Glidant

Size of particles of sand (micron)	Height (cm)	Width (cm)	Angle of repose
355	2.0	2.4	39.810
500	2.1	2.4	41.190
850	1.8	2.4	36.870
Various Size	2.0	2.4	39.810

2.      Sand is mixed with Glidant

Size of particles of sand (micron)	Height (cm)	Width (cm)	Angle of repose
355	2.0	2.4	39.810
500	1.9	2.4	38.370
850	1.7	2.4	35.310
Various Size	1.9	2.4	38.370

Calculation :

Tan  θ =        Height

               Width

                                                                            

Discussion:

What is the angle of repose for each materials?

Size of particles of sand (micron)	Angle of repose (Without Glidant)	Angle of repose (With Glidant)
355	39.810	39.810
500	41.190	38.370
850	36.870	35.310
Various Size	39.810	38.370

What other factor that will influence angle of repose for the materials?

Internal factor

• Particle size,coarser particles have high angles of repose than fine particles

• Particle shape

• Cohesiveness, fine particles may reveal cohesiveness owing to spherical particles having a greater tendency to roll

External Factors

• Methods of measurement,Ledge and erater method give higher angle of repose than from the heap formation methods

• Presence of other components example glidants

• Moisture, Angle of repose of loose dry powder increases by compacting as well as by introducing by moisture.Moist sand has a much higher angle of repose than dry sand.

•  The individual material will affect the angle of repose, a reflection of the different coefficients of friction between different substances.

What other method can be used to calculate the angle of repose for the materials?

Tilting box method

 

This method is appropriate for fine-grained, non-cohesive materials, with individual particle size less than 10 mm. The material is placed within a box with a transparent side to observe the granular test material. It should initially be level and parallel to the base of the box. The box is slowly tilted at a rate of approximately 0.3 degrees/second. Tilting is stopped when the material begins to slide in bulk, and the angle of the tilt is measured.

Fixed funnel method

The material is poured through a funnel to form a cone. The tip of the funnel should be held close to the growing cone and slowly raised as the pile grows, to minimize the impact of falling particles. Stop pouring the material when the pile reaches a predetermined height or the base a predetermined width. Rather than attempt to measure the angle of the resulting cone directly, divide the height by half the width of the base of the cone. The inverse tangent of this ratio is the angle of repose.

Revolving /Rotating cylinder method

Where a sealed hollow cylinder half full of powder surface is rotated until the powder surface shows its maximum angle with the horizontal.The material is placed within a cylinder with at least one transparent face. The cylinder is rotated at a fixed speed and the observer watches the material moving within the rotating cylinder. The effect is similar to watching clothes tumble over one another in a slowly rotating clothes dryer. The granular material will assume a certain angle as it flows within the rotating cylinder. This method is recommended for obtaining the dynamic angle of repose, and may vary from the static angle of repose measured by other methods. When describing the angle of repose for a substance, always specify the method used.

Crater Method /Discharge Method

Where circular tube is placed vertically on a plate with an orifice in the center.The height of the remaining powder against the wall of the tube is measured at eight equidistant points around the circumference to determine the angle of repose.

Dynamic Angle of Repose

Determine in the apparatus consisting of a drum with a roughened internal surface that is half filled with powder and slowly rotated around its horizontal axis.Within a certain range of rotation speeds (usually from 2.5 to 6 rpm) the surface of the powder in the drum comes to a sufficient steady condition.The maximum angle of bed inclination just before slump occurs is designated as the dynamic angle of repose.

Ledge Method

Where the powder is initially charged into a rectangular box.A slot at the base of one vertical wall is closed by a board.The closure board is then removed to allow the material to flow slowly through the narrow slot.The angle with the horizontal plane of the surface of the powder equilibrium when the flow stops is calculated as the angle of repose.

Conclusion:

A Glidant's effect is due to a counter-action to factors resulting in poor flowability of powders. For instance, correcting surface irregularity, reducing interparticular friction & decreasing surface charge. The result is a decrease in the angle of repose which is an indication of an enhanced powder's flowability.

References:

http://www.slideshare.net/visualbeeNetwork/angle-of-repose

http://en.wikipedia.org/wiki/Angle_of_repose

http://books.google.com.my/books?id=6aP3te2hGuQC&pg=PA40&lpg=PA40&dq=other+factors+influence+the+angle+of+repose&source=bl&ots=wP2LxPO4Uc&sig=TeOQ70O_DQE54n5bY2hHN9iMimg&hl=en&sa=X&ei=2g6OUvZtjcmtB6i1gcAF&ved=0CD8Q6A

Practical 3 : Powder Flow

Purpose

To determine the relationship between the types of powder (different size of the sand) and diameter of the opening of hopper.

Introduction

Powder flow is the ability of a particle to move by flow from a container. It is important in the process of making tablets and capsules as it can ensure uniform particle packing to produce uniform tablet/capsule weight and to have more consistent physicomechanical properties (tablet). Powder flow is important to ensure efficiency, either due to process design or intrinsic properties of the particles. For every powder of different size, the flowability is different. In this experiment, we are able to observe and evaluate the flowability of the sand of different diameter using different size of hoppers.

Apparatus

Hoppers with diameter of orifice of 8mm, 10mm, 11mm, 13mm and 16mm, stopwatch

Materials

Sand with size of 355µm, 500µm, 850µm and a mixture of sand containing various size.

Procedure

1.         Five hoppers with different diameter of orifice of 6mm, 8mm, 11mm, 13mm and 16mm were prepared.

2.         Four types of sand with different sizes and properties in which their particle sizes are

            355µm, 500µm, 800µm and a mixture of various size of sand were prepared, and each type of sand was weighed to be 100g.

3.         The orifice of the hopper with diameter of 8mm was covered with hand and 100g of

            355µm sand was poured into it .

4.         The orifice was opened so that the sand was allowed to flow out.

5.         The time taken for all the sand to flow out from the hopper was recorded.

6.         The test above (step 1 to 6) was repeated by using different sizes of sand and hoppers. 

Result and Calculation

Time Taken (s)
Sand Size Diameter of Hopper’s Orifice	355µm	500µm	850µm	Various
8mm	26.61	21.15	18.98	10.65
10mm	11.51	9.36	8.22	10.40
11mm	7.93	5.99	5.71	7.96
13mm	3.99	3.23	2.87	3.43
16mm	3.57	2.23	1.79	3.21

Questions

1. What are the factors that affect the powder flow?

            Flowability is affected by the physical properties of the powder, such as particle size and size distribution, particle shape and texture, surface properties and handling and processing condition.

2. According to the experiment, what size of sand and hopper size have the best powder flow?

            The biggest size of sand which is 850µm and the biggest size of orifice of hopper which is 16mm gives the shortest time and have the highest rate powder flow.

3. What are the methods that can be used to improve the powder flow?

           Methods to improve the powder flow are to alter the particle size and size distribution though granulation, alter of particle shape or texture to be more spherical and smooth,alter of surface forces such as electrostatic forces and moisture content, adding flow activators such as glidants and lter the process condition using vibration-assisted hoppers and force feeders.

Discussion

Flowability is the the capacity to move by flow that characterizes fluids and loose particulate solids. It can be determined by many ways, one of it is the by studying the rate of powder flow from a hopper. In this experiment, the rate of powder flow was dependent on the size of the sand and the diameter of the orifice of hopper, its rate was determined by comparing the time taken for the sand to flow completely from the hopper without interference such as shaking.

It is actually a direct method to measure the powder flow rate using a hopper. The result above in the table shows the hopper with orifice diameter of 16mm took the shortest time for the sand to flow out among the five different types of orifice size. For hopper with orifice diameter of 8mm, the sand took the longest time to flow out of the hopper. It is because when a larger orifice size used, there is more free space to allow more sand to be discharged from the orifice.

There is some of the sand left in the hopper if no shaking is applied to the hopper. The sand that discharges freely are said to be undergoing mass flow while the sand that don’t discharge freely due to high adhesion or cohesion forces and shallow hopper angles, are said to be undergoing funnel flow. For sand with a larger particle size, they can flow freely while the smaller ones are generally cohesive and difficult to flow freely. Based on the result, the bigger the particle size, the shorter the time taken for the sand to flow out indicates the higher the flow rate. For the various size of sand, some of it is very big and stuck at the orifice.

Conclusion :

In conclusion, flowability of the sand to flow out of the hopper is effected by the hopper orifice diameter and the particle size of it. The larger the orifice diameter (16mm) and the bigger the particle size (850µm) has higher flow rate. The time required for the sand to flow out of hopper is inversely proportional hopper flow rate.

References

1. Aulton, M.E. 2002. Pharmaceutics: The Science of Dosage form Design. Edinburgh Churchill

         Livingstone.

2. http://www.merriam-webster.com/dictionary/flowability