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SITI AMIRAH BINTI ABDUL WAHAB   A140181

PRACTICAL 1 : BALL MILLING

AIMS:

1. To grind the given material to a smaller size using a ball mill
2. To obtain the size distribution of the initial and the final mixture by sieving.
3. To analyze the results using the available theories.

INTRODUCTION:

Ball Mill is the equipment to be used for size reduction. It is a kind of grinder used for intermediate or fine grinding. Ball mill is a metal cylinder which rotates about its horizontal axis. The coarse sugar charged along with the metal balls breaks to fine powder by impact of metal balls. The size reduction is actually to make the too large to be used solid materials usable. It leads to an increase in surface area per unit volume that enhances the rate of the reaction by allowing more sites for the reaction to take place. Moreover handling of smaller size particles is much easier as compared to that of bigger particles. 

APPARATUS AND MATERIALS:

Metal balls (various sizes), coarse sugar, rotary milling, sieve nest.

PROCEDURE:

1. 300-500g of coarse sugar was weighed.
2. The various sizes of metal balls were put into the mill.
3. The coarse sugar was added into the mill.
4. The milling process was started for 15-20 minutes with the appropriate speed.
5. The product was weighed again.
6.The powder then was sieved using sieve nest.
7. A graph of distribution size particle was plotted.

RESULTS AND CALCULATION:

     Results and Calculation :

Group	Duration of ball Milling	Speed(ms-1)	Size Of (g)	Grinded	Salt
	(min)		150um	250um	300um
1 and 2	10	5	5.0079	3.6538	12.0589
3 and 4	20	5	2.8825	0.1794	20.2832
5 and 6	10	3	0.2967	1.3826	12.0507
7 and 8	20	3	0.4682	0.8602	11.1693

 Group 1 and 2: ( Set 1)

 Group 3 and 4: ( Set 2)

 Group 5 and 6: (Set 3)

  Group 7 and 8: (Set 4)

CALCULATION :

Weight of grinded salt that is in the range of  150um-300um

Set 1:

5.0079g+3.6583g+12.0589g=20.7206g

Set 2:

2.8825g+0.1794g+20.2832g=23.3451g

Set 3:

0.2967g+1.3862g+12.0507g=13.7336g

Set 4:

0.4682g+0.8602g+11.1693g=12.4977g

DISCUSSION:

            Based on the results we obtained, set 1 (10 min, speed 5), the amount of weight of grinded salt that is in the range of 150um-300um is 20.7206 g. Meanwhile, set 2  (20 min, speed 5) is 23.3451 g. This means that set 2 has higher amout of  weight of grinded salt that is in the range of  150um-300um. This is because set 2 has longer duration which is 10 minutes longer than set 1 while maintaining the same speed 5. This causes more smaller size salt to be produced.

After that, the amount of weight of grinded salt that is in the range of 150um-300um for set 3 (10 min, speed 3) is 13.7336 g. Meanwhile for set 4 (20 min, speed 3) is 12.4977 g. Based on the same reason, that is the set 4 has longer duration than set 3 with same speed 3, should be set 4 has higher amount of weight of grinded salt that is in the range of 150um-300um. However, in this experiment, set 3 has higher value than set 4. This is due to some errors that have occurred while carrying out the experiment. The error might be the spilling out of the powders during transmission to the sieving part.  And as well as the different strength of people used while sieving.

            Apart from comparing the duration of the sets, the comparison of the results can also be seen by comparing the speed of the sets. For example, set 1(10min, speed 5) is more (20.7206g) compared to set 3 (10min, speed 3) which is 13.7336g. The weight of the salt produced in the stated range from set 2 (20min, speed 5) is more (23.3451g) compared to set 4 (20min, speed 3) which is 12.4977g. This means that the faster the speed, the more product is produced in desired range.

QUESTIONS:

CONCLUSION:

As a conclusion, the higher the speed of the sets, the higher the products amount produced in desired size range. The high amount of products produced can also be because of the longer duration of the sets in ball milling process. However, the speed has more effects on products produced compared to duration of the sets in this experiment.

REFERENCES:

1. http://www.slideshare.net/eslam128/ball-mill-presentation
2. http://www.che.iitb.ac.in/online/system/files/92/course_details/FM+306.pdf
3. http://millengineering.com/enginnering_services.php?id=1002&sid=1010
4. http://wiredspace.wits.ac.za/bitstream/handle/10539/1506/Dissertation,%20Final%20Submission.pdf
5. http://www.mineraltech.com/MODSIM/ModsimTraining/Module10/BatchBallMillExperiment.htm

PRACTICAL 2 : SIEVING

OBJECTIVE

-determine the particle size distribution of a powder

-determine the size of a particle.

INTRODUCTION

A sieve analysis  is a practice or procedure used to assess the particle size distribution of a granular material. The size distribution is often of critical importance to the way the material performs in use. A sieve analysis can be performed on any type of non-organic or organic granular materials including sands, crushed rock, clays, granite, feldspars, coal, soil, a wide range of manufactured powders, grain and seeds, down to a minimum size depending on the exact method

APPARATUS AND MATERIAL

Lactose, microcrystalline cellulose (MCC), weighing machine, stack of sieves, mechanical sieve shaker

PROCEDURES

1. 100g of lactose was weighed

2. A 'sieve nest'  was prepared in ascending order and assigned appropriate sieve size

3. The lactose powder was put into the sieve.

4. Then, lactose powder was sieved for 20 minutes.

5. The results obtained was recorded and a graph on powder particle size distribution was built.

6. The process was repeated with MCC.

RESULT

GRAPH

DISCUSSION

From this experiment, there two materials that have been observed which are lactose and microcrystalline cellulose (MCC). The method used was sieving method,where we able to determine the particle size distribution. As a stack of sieves were prepared, the sieve that has larger opening size are placed above the ones that having smaller opening sizes . This means, the sieve that have diameter of aperture of 500 µm will be placed at the above followed by 425 µm, 300 µm, 150 µm, and 45 µm.

From the result obtained, the particle size of MCC falls in the range that less than 150 µm. At the same time, particle size for lactose also fall in the range of less than 150 µm. There are many factors that lead to this result. As the lactose and MCC are two different materials, so both of them have different physical properties. It seems that MCC has been affected more than lactose due to the physical vibration that applied on the particles since the hardness surface of particle is the one that contribute to the reduction of particle size. This experiment also cannot be considered accurate as the weight of lactose and MCC are not totally correct since there is still amount of powder left in the sieves after the process was carried out.  Besides that, some of powders are spilled out from the container since the machine is not closed correctly. This also affects to the result obtained.

So, before conducting this experiment, make sure the sieves are clean by using brush, because if many soil particles are stuck in the openings, this will affects the result of the experiments. The machine also must be set up correctly so that there is no problem occur during carrying out the process.

      

QUESTIONS

1)      What are the overall particles size of lactose and MCC?

The overall particle size range for MCC and lactose is 45µm, <45µm, between 45 and 150 µm , between 150 and 300 µm, between 300 and 425 µm, between 425 and 500 µm, and >500 µm.

2)      Are there any other methods that can be used to determine certain particle size?

The other methods that can be used to determine particle size are

a)      microscope methods

b)      coulter counter

c)      laser light scattering method

d)      dynamic light scattering method

e)      sedimentation method

3)      What are the importance of particle size in a certain formulation?

 Particle size in a certain formulation is important in achieving optimum production of efficacious medicines especially in pharmaceutical phase. It also can influence the bioavailability and activity of drug. For instance, it can influence segregation behaviour, the ease with which powder flows through the press and the compressibility of a formulation. This factor of formulation also can influence the disintegration and dissolution rate in the body cavity.

CONCLUSION

Based on the experiment, sieving process is one of the method to determine the size of particles.  The distribution of particles size are able to be analysed after conducting this experiment especially in achieving optimum production of efficacious medicines in pharmaceutical phase.

REFERRENCES

1. www.geog.ucl.ac.uk/about-the.../support...methods/.../sieving-method
2. http://www.pharma-excipients.com/micro-crystalline-cellulose.html
3. http://www.pharmaceutical-int.com/article/particle-size-is-important-particle-analysis-techniques.html
4. http://www.horiba.com/scientific/products/particle-characterization/applications/pharmaceuticals/

PRACTICAL 3 : POWDER FLOW

Objective:

To analysis the flow of sand of different sizes using hopper of different sizes and opening.

Introduction:

          Powders are a mass of solid particles or granules. In fact these particles are usually surrounded by air (or other fluid) and it is the solids plus fluid combination that largely determines the bulk properties of the powder. It is perhaps the most complicating characteristic because the amount of fluid can be so variable.
Powders are probably the least predictable of all materials in relation to flowability because of the large number of factors that can change their rheological properties. Physical characteristics of the particles, like size, shape, angularity, surface texture, porosity and hardness will all affect flow properties. External factors such as humidity, conveying environment, vibration and perhaps most importantly, aeration, will compound the problem. Another characteristic of powders is that they are often inherently unstable in relation to their flow performance. This instability is most obvious when a free flowing material ceases to flow. This transition may be initiated by the formation of a bridge in a bin, by adhesion to surfaces or by any event that may promote compaction of the powder. The tendency to switch in this way varies greatly from one powder to another, but can even be pronounced between batches of the same material.

          Powder behaviour will be very dependent upon particle size, the variation of size and the shape of the particles. In general powders with large particles (>100µm) will be non-cohesive, permeable and will probably fluidise and will have low compressibility and relatively low shear strength. Conversely, fine powders <10µm say, are likely to be cohesive, compressible, contain much entrained air and yet have poor aeration characteristics. Generally they have high shear strength, high flow energy, low permeability and are very affected by being consolidated when entrained air is excluded.

          There are many exceptions to the above – for example toner used in printers and copying machines are fine powders with an outstanding fluidisation characteristic. A small amount of aeration is sufficient to transform a consolidated powder into one with fluid like rheology. Another broad generalisation is that under forced flow conditions, where powders are made to move other than by gravity, fine powders can behave more like a fluid. They are able to extrude round corners or through holes, unlike coarse powders that are more likely to become solid like as particles realign and lock together and become very resistant to flow.
The nature of powders therefore is such that an adverse combination of environmental factors can cause an otherwise free flowing powder to block or flow with difficulty. Conversely, a very cohesive powder may be processed satisfactorily if the handling conditions are optimised.

          Ordinary sand is a granular mate¬rial with interesting properties. Individual sand grains are solids, yet sand as a whole can flow through a narrow opening as in the case of an hourglass. Unlike fluids, the average flow is almost constant through a hole and does not depend on the height of the sand column.


Apparatus and Materials:

5 hoppers (8mm, 10mm, 11mm, 13mm and 16mm),  4 types of sands (355μm, 500μm, 850μm and variable diameter), newspapers, electronic weighing balance, stopwatch


Procedures:

1. 5 hoppers with different opening sizes were prepared. (8mm, 10mm, 11mm, 13mm and 16mm)
2. 4 types of sands with different sizes and behaviour were prepared for this experiment. (355μm, 500μm, 850μm and variable diameter)
3. The opening of the hopper with 8mm diameter was closed and 100g of sands with 355μm diameter were put into the hopper.
4. The opening was let opened and the sands were released so they can flow out.
5. The duration needed for all the sands to flow out was recorded.
6. The experiment was repeated with sands of diameter 500μm, 850μm and various diameter and 10mm, 11mm, 13mm and 16mm openings of the hoppers.


Results:
Duration of sand flow

Discussion:

         The powder flow in this experiment is mass flow. Mass flow which is also known as mass transfer and bulk flow is the movement of material matter. Mass flow involves powder that discharged freely when first in first out. Mass flow also reduces the extent to which some types of segregation affect the powder. Although all of the material is moving, velocity profiles may still exist within the hopper.

          From this experiment, we can see that mass flow is influenced by both diameter of hopper orifice and also the particle size (diameter of sand). From the result obtained, the sands of different particle sizes flow through hopper with 16 mm orifice diameter with an average of 3.61 s, which is relatively fast compared to hopper with orifice diameter 13 mm (4.79 s), 11 mm (6.44 s), 10 mm (9.41 s) and 8 mm (11.03 s). Sand flows through the hopper with the smallest hopper orifice in this experiment (8 mm) with the highest average duration that is 11.03 s. This shows that hopper with larger orifice gives a better particle flow, in this case, sand flow while hopper with small orifice causes a slower flow. This can be explained as the larger the hopper orifice, the less the contact surface area of the particle (sand) to the wall of hopper. This causes reduction in friction and therefore the particle (sand) can move smoothly and faster.

          Another factor affecting powder flow in this experiment is size of particle, in this case, diameter of the sand. From the result obtained, sand of various diameters has a better flow than that of diameters 355 μm, 500 μm and 850 μm. This can be explained by strong cohesion between sand of different sizes as the sand with smaller size filling up the spaces in between sand with larger size, indicating larger contact surface area of and particle. This is followed by sand of diameter 850 μm, 500 μm and then 355μm. This shows that the larger the particle size, the faster the particle flow. This is due to larger particle has larger gravitational force which will pull down the particle faster towards the ground.

          There is some inconsistency of data obtained from the experiment where the duration of sand flow fluctuated. This might be caused by external forces accidentally applied by person holding the hopper, different shallow hopper angle and also hopper with different diameter. To overcome these problems, a distort stand can be used instead of using bare hand to hold the hopper when sand flow out from it. This can also ensure a constant height where the sand flows out of the hopper. Hoppers with same shallow hopper angles and also diameter should be used although the orifice diameter is difference. This can ensure more accurate results and prevent other factors affecting the experiment. There are many other factors that will influence flow property of powder such as shaking, presence of water and moisture, cohesion and adhesion force of particle, particle shape, particle density and particle packing geometry.


Questions:

1. What are the factors that affect powder flow?

Factors that influence the flow property of powder including shaking, presence of water and moisture, cohesion and adhesion force of particle, particle shape, particle density and particle packing geometry.

2. Based on the experiment above, what is the size of powder and hopper give the best powder flow?

Size of powder that gives the best powder flow is sand of various sizes. Hopper with orifice diameter 16 mm gives the best powder flow.

3. What are the methods that can be used to help the flow of certain powder?
Firstly, alteration of particle size and size distribution can be carried out by manipulating proportion of coarser and finer particles for example granulation. Alteration of particle shape or texture also can be carried out by making more spherical particles using spray drying. Surface forces also can be altered by reducing electrostatic forces through earthing and also reducing moisture content. Flow activators such as colloidal silicon dioxide and magnesium oxide help to reduce adhesion and cohesion thus improve powder flow. Process condition also can be altered for example using vibration-assisted hoppers and force feeders.


Conclusion:

Powder flow depends on the orifice diameter of the hopper and also particles size of powder a. Powder flow better and faster with larger hopper orifice diameter and larger particle size of powder while powder flows slower with smaller hopper orifice diameter and smaller particle size.

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

        Basically, the movement/slideness  of particle are due to  the angle of inclination that is more than frictional force between particles. In Addition, the object in motion will stop sliding when  angle of inclination is decrease to its limit, this due to the adhesion and cohesion 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 (0.5%,1%,2%,3%  of magnesium stearate). 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 MATERIAL

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


RESULTS

CALCULATION

QUESTIONS

1. What is the angle of repose for each of the materials?











2. What are the factors that influence the angle of repose of the materials?

a) Particle size - As particle size increases, the angle of repose decreases.
b) Particle shape- Spherical particles have a smaller angle of repose compared to irregular shape particle due to a greater tendency to roll.
c) Cohesiveness - Very fine particles may reveal cohesiveness owing to the electrostatic effect which increases the angle of repose.
d) The method by which the angle of repose is measured.
e) Coefficient of friction between particles.


3. What other methods that can be used to determine the angle of repose of the materials?

(a) Tilting box method – The material is placed within a box with a transparent side to observe the granular test material. The box is slowly tilted and stopped when the material begins to slide in bulk. The angle of the tilt is measured.

(b) 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. Pouring is stopped when the pile reaches a predetermined height or width.

(c) Revolving cylinder method – The material is placed within a cylinder with atleast one transparent face. The cylinder is rotated at a fixed speed. The granular material will assume a certain angle as it flows within the rotating cylinder.



DISCUSSION

         Angle of repose is one of the methods used to characterize the flow of a material. In this experiment, angle of repose for different sizes of sand and with the presence of a glidant is determined. The factors that affect the angle of repose are also studied.

         From the result obtained, in the absence of glidant, the angle of repose decreases as the size of particles increases. This is because smaller particles have dominant cohesive and adhesive forces as compared to particle weight, whereas in bigger particles gravity plays a dominant role thus giving a smaller angle of repose. Studies have shown that angle of repose is also gravity-dependant. Cohesiveness of finer particles due to electrostatic forces causes difficulties in flowing thus forming a steeper pile which shown by the 355 micron sand having the highest angle (36.3°) compared to 500 and 850 micron sand. On the other hand we can see that mixture of various sizes of sand give a high angle of repose also (39.2°). When particles of different sizes and irregular shape is mixed together, the mechanical interlocking of particles increases and thereby increase the rolling friction. As a result a steeper pile with bigger angle of repose is formed. Generally, a value of θ <30° indicates ‘excellent’ flow whereas θ >56° indicates ‘very poor’ flow. The intermediate scale indicates ‘good’ (θ between 31–35°), ‘fair’ (θ  between 36–40°), ‘passable which may hang up’ (θ  between 41–45°), and ‘poor which must be agitated or vibrated’ (θ  between 46–55°). In this experiment, sand of 355 micron size have a fair flow, 500 and 850 micron size have a good flow, and various sizes of sand have a fair flow.

          When 3% concentration of magnesium stearate is added, the angle of repose increases. Magnesium stearate is used as a glidant. It may also act as a lubricant in reducing friction. Glidant functions in improving the flow of a material. From the result, 500,850 micron sand and various sizes sand have a ‘passable which may hang up’ flow. On the other hand, 335 micron sand have a poor flow. The addition of a glidant should decreases the angle of repose and enhances the flow of the materials. But however the addition of 3% magnesium stearate in this experiment produces a product of viceversa. This is because the rate of flow is improved by the addition of magnesium stearate up to a limiting concentration of glidant. Above a certain concentration (in this case 3%), the glidant will in fact function to inhibit flowability. Thus, a glidant will only work at a certain range of concentrations. From the result of other groups, it is shown that addition of magnesium stearate is only effective at concentration of 0.5% and 1% where the angle of repose decreasing with the presence of a glidant. This proved it function in improving the flow of the material.

           For a better result, it is adviced to use a protractor instead of ruler as it reduces parallax error and it measures an accurate angle. The glidant and the sand should be mixed until an even distribution of mixture is obtained. This is to ensure that the glidant function effectively. Besides, the lifting velocity of the cylinder should just be moderate to avoid distraction to the material flow. For a clean and tidy working environment, a paper should be placed before starting the experiment so that the sand did not cluttered elsewhere. Experimenter must also wear goggle, mask and lab coat all the time to protect the eyes and nose from coming in contact with the sand.



CONCLUSION

From the experiment, the angle of repose for different materials is measured to describe the flow of each material. Smaller angle indicates a good flow property compared to bigger angle. Several factors that influence the angle of repose is also determined which are the particle size, particle shape, cohesiveness and the method by which the angle is measured. Smaller particles have a bigger angle of repose due to the cohesiveness. This cohesivity causes a poor flow. Mixture of particles with various sizes also gives a bigger angle of repose owing to the friction. Besides the angle of repose is also gravity-dependant. The flow of the materials is improved with the addition of a glidant at low concentration. The glidant only work at a certain range of concentration.


REFERENCES

1. Liu, Zhichao (2011) Measuring The Angle Of Repose Of Granular Systems Using Hollow Cylinders ; http://d-scholarship.pitt.edu/6401/
2. Rakhi B. Shah, Mobin A. Tawakkul, Mansoor A. Khan (2008 February 15) Comparative Evaluation of Flow for Pharmaceutical Powders and Granules ; http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2976911/
3. T. M. JONES (1969) The effect of glidant addition on the flowability of bulk particulate solids ; http://journal.scconline.org/pdf/cc1970/cc021n07/p00483-p00500.pdf
4. Aug 05, 2011 Angle of Repose ; http://www.slideshare.net/visualbeeNetwork/angle-of-repose