Particle Size and Shape

Title: Analyze particle shape and size using a microscope.

Objective : To analyze particle shapes and sizes of  5 various types of sand sample using a microscope.

Introduction:

Different types of particles have different sizes and shapes. In pharmaceutical field, particle size would determine the optimum efficacious of the medicine. The particle size of the drug would also influence the physical performance of the medicine such as flow ability in powder as well as it’s pharmacological performance such as increasing the absorption rate in smaller particle. Solid particle is often considered to approximate to a sphere which can then be characterized by determining its diameter.

Besides that, the particle size distributions for each material could be the same, but the two materials would behave differently during processing, or in final product form due to different particle shape. They may have different flow and abrasion characteristics.Therefore, the size, distribution and shape of the particles can affect bulk properties, product performance, stability and appearance of the end product.


In this experiment, a light microscope would be used to analyse the particle shape and sizes of various sizes of sand.

Methodology

Materials:

Mixture of various sizes of sand, 850 mic, 500 mic, 335 mic, 150 mic sand

Apparatus:

Light microscope, forceps, glass slide, cover slid. 

Procedures:

1. A small amount of mixture of various sizes of sand is placed on the middle of glass slide. The sand is spread evenly on the middle of glass slide.

2. A piece of cover slid is placed on top of the sand. The glass slide is placed into the microscope.

3. Observation is made on the sizes and shapes of the sand particle through the light microscope. The shapes of the sand particles are sketched.

4. The procedures above are repeated with 850mic, 500 mic, 335 mic and 150 mic sand.

Results:

Figure 1: Various Sizes of Sand Particles (magnification power: 0.25)

Figure 2: 850 mic Sand Particles (magnification power: 0.25)

Figure 3: 500 mic Sand Particles (magnification power: 0.25)

Figure 4: 335 mic Sand Particles (magnification power: 0.25)

Figure 4: 150 mic Sand Particles (magnification power: 0.25)

Discussion:

Different samples contains different sizes and shapes.

850 mic sands has the biggest size of particle, followed by 550 mic, 335mic and 150 mic as the smallest sand particle.

The shapes of the sand particle in the sand mixture with various sizes are more diverse compared to 500, 335 and 150 mic sand.

The overall shapes of particles in the sand mixture of various sizes is sub angular with medium sphericity.

For 850 mic sand, the overall shape is subrounded with low sphericity.

500 mic sand would be low sphericity and angular shape

335 mic have subround and sub-rounded and medium sphericity shape.

150 mic have medium sub rounded and medium sphericity.

Angular particles with low sphericity tend to mobilize more friction than rounded particles. On the other hand, particles which are more spherical tend to pack together more effectively to create denser sediments.

Questions:

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

One of the way to measure the diameter of a particle is via sieve method. It is applied by using a stack of sieves which have the smallest mesh above a collector tray followed by sieves which get coarser towards the top of the series. The sieve is then subjected to mechanical vibration. After a suitable time the particles are considered to be retained on the sieve mesh with an aperture corresponding to the sieve diameter.

Another method is microscope method where size analysis is carried out with a projection screen with screen distances related to particle dimensions by a preiously derived calibration factor using a graticule. Particles are compared with the circles and are sized according to the circle that corresponds most closely to the equivalent particle diameter being measured.

The third method is coulter counter which is to measure the size of particle suspended in the electrolyte. . The technique uses electrical impedance to measure the volume of particles as they individually pass through an aperture of defined size. electrodes are introduced on both sides of the aperture. Since electrical current is physically confined within the aperture, as particles are pulled via vacuum through the aperture, they displace a volume of conductive liquid equivalent to their size. This will cause a brief change to the electrical resistance of the liquid and detected by the counter. The higher the resistance, the bigger the particle volume.  The equivalent diameter of the particle is equal to the volume diameter.

Laser diffraction measures the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles. The angular scattering intensity data is then analysed to calculate the size of the using the Mie theory of light scattering. This method requires a laser and a suitable detector.

The fifth method is sedimentation methods, which is comparing the particles settling rate to a sphere settling at the same rate. This technique determines particle size as a function of settling velocity. However, the sample must be dispersed in a liquid medium. During a sedimentation analysis, particles of known density will settle through a liquid with a known density and viscosity. Evaluating the rate of the particles settle generates an equivalent spherical diameter. Different particles sizes settle at different rates. The larger particles settle more rapidly than the fines assuming a similar density and shape. Flat platy particles have different settling rate than spherical particles. There would be a potential area for bias under this particle sizing technique.

2. State the best statistical method for each sample you use
 Microscope method for all samples.

Conclusion:

Different samples of particles have various sizes and shapes. The different particle shapes and sizes would affect the particle’s own physical properties.

Reference

1. Aulton, M.E. 2002. Pharmaceutics: The Science of Dosage form Design. Edinburgh Churchill Livingstone. (pg 155,158)

2.http://www.particletechlabs.com/particle-size/sedimentation

3.https://www.beckmancoulter.com/wsrportal/wsrportal.portal?_nfpb=true&_windowLabel=UCM_RENDERER&_urlType=render&wlpUCM_RENDERER_path=%2Fwsr%2Findustrial%2Fproducts%2Fcoulter-counter-analyzers%2Findex.htm

4.http://www.analytica-world.com/en/whitepapers/61206/particle-shape-an-important-parameter-in-pharmaceutical-manufacturing.html

ANGLE OF REPOSE

TITLE: Experiment 4 (Angle of Repose)

OBJECTIVES:
1) To calculate the angle of repose for each type of sand with different particle size
2) To measure the change of angle of repose after addition of magnesium stearate

INTRODUCTION:
The angle of repose is one of the most important macroscopic parameters in characterising the behaviour of granular materials. It has been found that the angle of repose strongly depends on material properties such as sliding and rolling frictions and density of particles and particle characteristics such as size.  It is generally reported that the angle of repose increases with increasing sliding and rolling friction coefficients and deviation from spheres, and decreases with increasing particle size and container thickness. Angle of repose is the maximum angle to the horizontal at which rocks and soil will remain without sliding and the slope of a powder cone is formed by pouring a powder from a specific height. In general, the flowability of a powder is judged to be good when the angle of repose is less than 30 degrees and to be poor when the angle is larger than 40 degrees. The downhill movement of soil and loose unconsolidated sediments is due to the force of gravity and is resisted by friction. At angles steeper than the angle of repose friction is not sufficient to counter gravity and mass wasting occurs. At angles less than the angle of repose gravity cannot overcome friction and sediments may accumulate to form steeper slopes. Magnesium stearate was used in this experiment as glidants in which it will promote the flow of granulations or powder materials by reducing the friction between the particles.

METHODS:

APPARATUS
Plastic cylinder, stopper, 15% magnesium Stearate, 150 mm, 500 mm, 850 mm, 355 mm, various sand, funnel, newspaper, weighing boat, spatula, weighing balance

PROCEDURE
1) 100g of each type of sand (150 mm, 355 mm, 500 mm, 850 mm, and various sizes) was measured using weighing balance
2) For each type of sand, it was poured into plastic cylinder with the stopper at the bottom of it.
3) Plastic cylinder was pulled upwards and the substances was flowed to form a peak/heap.
4) The height of peak/heap was measured also the width of the stopper. This is to measure the angle of repose for the each type of sand.
5) Angle of repose for each type of sand was calculated.
6) 15% of magnesium stearate was measured and each type of sand was added to it until it reach 100g.
7) Step 2 until 5 was repeated

RESULTS AND CALCULATION:

Angle of repose : tan  θ = height/width

Angle of repose without glidant:
150 mm :  tan  θ = (2.20 cm)/(2.23 cm)
                                   = 43.11°
355 mm : tan  θ = (2.00 cm)/(2.23 cm)
                                 = 40.40°
500mm : tan  θ = (1.90 cm)/(2.23 cm)
          = 38.96°
850mm : tan  θ = (1.80 cm)/(2.23 cm)
                                 = 37.45°

Various size : tan  θ = (2.30 cm)/(2.23 cm)
                                       = 44.38°

Angle of repose with glidant:
150mm : tan  θ = (3.80 cm)/(2.23 cm)
                                = 58.27°

355mm : tan  θ = (2.30 cm)/(2.23 cm)
                                = 44.38°

500mm : tan  θ = (2.10 cm)/(2.23 cm)
                                = 41.78°

850mm : tan  θ = (2.10 cm)/(2.23 cm)
                                = 41.78°

Various sizes : tan  θ = (2.20 cm)/(2.23 cm)
                                        = 43.11°

Angle of repose without glidant
150 mm : tan  θ = (3.90 cm)/(2.50 cm)
                              θ = 57.34 °
355 mm :  tan θ = (2.20 cm)/(2.50 cm)
                              θ = 41.35 °
500 mm : tan θ = (1.90 cm)/(2.50 cm)
                             θ = 37.75 °
850 mm : tan  θ = (1.80 cm)/(2.50 cm)
                              θ = 35.75 °
Various sizes : tan θ = (2.40 cm)/(2.50 cm)
                                    θ = 43.83 °

Angle of repose with glidant
150 mm : tan  θ = (4.10 cm)/(2.50 cm)
                              θ = 58.63 °
355 mm :  tan θ = (3.50 cm)/(2.50 cm)
                              θ = 54.46 °
500 mm : tan θ = (2.40 cm)/(2.50 cm)
                             θ = 43.83 °
850 mm : tan  θ = (2.80 cm)/(2.50 cm)
                              θ = 48.23 °
Various sizes : tan θ = (3.00 cm)/(2.50 cm)
                                    θ = 50.19 °

Angle of repose without glidant
150 mm : tan  θ = (3.65 cm)/(2.40 cm)
                                 = 56.67 °
355 mm :  tan θ = (1.90 cm)/(2.40 cm)
                                 = 38.37 °
500 mm : tan θ = (1.75 cm)/(2.40 cm)
                                = 36.10 °
850 mm : tan  θ = (1.75 cm)/(2.40 cm)
                                = 36.10 °
Various sizes : tan θ = (2.00 cm)/(2.40 cm)
                                       = 39.81 °

Angle of repose with glidant
150 mm : tan  θ = (4.60 cm)/(2.40 cm)
                                 = 62.45 °
355 mm :  tan θ = (4.30 cm)/(2.40 cm)
                                 = 60.83 °
500 mm : tan θ = (3.50 cm)/(2.40 cm)
                                = 55.56 °
850 mm : tan  θ = (3.40 cm)/(2.40 cm)
                                 = 54.78 °
Various sizes : tan θ = (4.15 cm)/(2.40 cm)
                                       = 59.96 °

Angle of repose without glidant

150 mm : tan  θ = (2.20 cm)/(2.30 cm)

                                 = 43.73 °

355 mm :  tan θ = (2.00 cm)/(2.30 cm)

                                 = 41.00 °

500 mm : tan θ = (1.90 cm)/(2.30 cm)

                                 = 39.56 °

850 mm : tan  θ = (1.80 cm)/(2.30 cm)

                                = 38.05 °

  Various sizes : tan θ = (2.30 cm)/(2.30 cm)

                                       = 45.00 °

Angle of repose with glidant

150 mm : tan  θ = (3.80 cm )/(2.30 cm)

                                 = 58.82 °

355 mm :  tan θ = (3.70 cm)/(2.30 cm)

                                 = 58.13 °

500 mm : tan θ = (3.50 cm)/(2.30 cm)

                                 = 56.69 °

850 mm : tan  θ = (3.00 cm)/(2.30 cm)

                                 = 52.52 °

Various sizes : tan θ = (3.30 cm)/(2.30 cm)

                                       = 55.12 ° 

QUESTIONS:

1) What is the angle of repose for each of the substances?

2. What is the factors may influence the angle of repose for each of substances?

- 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.

- 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.

3. What other method can be used to calculate the angle of repose for each substances?

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 .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 cylinder method - 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

DISCUSSION:

One of the methods for testing powder flow is angle of repose. Angle of repose can be influenced by many different factors. Density, particle shape and size, moisture content, and texture of the particles all have a profound effect on an object’s ability to flow. If a material flows easily it has a low angle of repose and if it does not, it has a high angle of repose. As we can see from the section of results and calculation above, the smallest size of sand (150 mm) without glidant having high angle of repose. Meanwhile, for the largest size of sand which is 850 mm has low angle of repose. This is because the angle of repose is influenced by the particle size of material. From the result, it can be seen that the material of uniform size (150 mm, 355mm, 500 mm, 850 mm) have low angle of repose than the material of various sizes. This is because particles of uniform size will flow easily, hence low angle of repose. In addition, particles of irregular shape have showed high angle of repose because of the interlocking do not flow easily. Other factor that influences the angle of repose is the moisture content in the solids. 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. Solid materials of different structure like granular and fibres which show different flowabilty characteristics also influenced the angle of repose. It can be seen when we mix magnesium stearate (glidant) with the sand. The angle of repose become higher as we mix more magnesium stearate with the sand. The individual material will affect the angle of repose, a reflection of the different coefficients of friction between different substances. Each particulate material has its own unique angle of repose, and will interact with outside influences differently because of it. Every granulated or powder solid uses friction to “hold together” against the force of gravity. 

CONCLUSION:

Particles size and shape will influence the angle of repose of the material. Also affect the angle of repose is moisture and the density of material. All of this will give effect to the angle of repose and their flowability. A material which flows easily has a low angle of repose and it will has a high angle of repose when the flowability of the material is decrease.

REFERENCES:

http://diyattitude.com/2013/06/physics-of-everyday-life-angle-of-repose/

http://www.pharmacopeia.cn/v29240/usp29nf24s0_c1174.html

http://www.merriam-webster.com/dictionary/angle%20of%20repose

POWDER FLOW

Title of experiment: powder flow

Date of experiment: 19th September 2013

Objective: to study the powder flow ability using different size of hoppers

Introduction:
Powder flow ability is the ability of a powder to flow in a desired manner in a specific piece of equipment. Flow of powders can be free-flowing and non-flowing or cohesive. Manufacturing of tablets, capsules, filling of powder in container involves several powder handling steps, including blending, transfer, storage, and feeding to a press or a dosator. The inability to achieve reliable powder flow during these steps can have a significant adverse effect on the manufacture and release of a product to market.

Material and apparatus:
various size of sand, various size of hopper, weighing boat, spatula, newspaper, stopwatch, analytical balance

Procedure:
1) Five hopper that have different size are chosen
2) Five various size and properties of sand are chosen and weighed using analytical balance
3) The hole of hopper is closed and then, 100g of sand is poured into the hopper
4) The hole of hopper is opened and let the sand flow out
5) The time taken for the sand flow out from the hopper is recorded
6) The procedure above is repeated by using different size of hopper and also sand.

Result:

Questions
1) What are the factors that influenced the powder flow?
-The factors influencing the powder flow such as particle size, size distribution, container surface effects, flow rate and the diameter of the container hole.

2) Based on the experiment above, which one the powder and hopper that give the best flowing reading?
The powder that give the best flowing reading is 150cc (size of sand) and the hopper that give the best reading is 1.6 cm (the diameter of hopper).

3) What are the methods/ways that can be used to help flowing of powder?
-The methods/ways that can be applied to help powder flow such as increased the diameter of hopper, reduced filling height powder, reduced cohesive strength of powder and utilized agitation or mechanical assistance.

Discussion
The widespread use of powders in pharmaceutical industry has generated a variety of method for characterizing the powder flow. In this practical, we want to see what will happen to the rate of flow based on different size and properties of sand and also hopper. From the result that we have obtained, we can say that 150cc (size of sand) and 1.6 cm (diameter of hopper) give the best flowing reading. This is because the resistance between the sand and the surface of hopper is reduced, making it easier to flow out from the hopper. However, there are some precaution steps that need to be taken during conducting this practical such as make sure do not shake the container (hopper) as it will affect the reading of flow rate, make sure there is no any obstacles especially at the hole of hopper and the experiment should be conducted in proper manner to ensure we can get the best result.


Conclusion
The various size and properties of sand together with the different size of diameter’s hopper will influence the rate of powder flow. The smaller the size of particle and the bigger the diameter of container, will resulting the highest the rate of powder flow.

References

http://www.pharmacopeia.cn/v29240/usp29nf24s0_c1174.html

http://www.slideshare.net/nkp8490/powder-flow-testing-and-control-22531477

Title : Sieving

Objective

To determine the particle size distribution of the powder material with respect to the size of the solid particles.

Introduction

A sieve is a mesh strainer used to separate lumps and clumps from the fine material Or an instrument with a meshed or perforated bottom, used for separating coarse from fine parts of loose matter,

A sieve test is performed by first assembling a stack of interlocking sieves. In this stack the sieve with the largest openings is at the top each lower sieve will have a smaller opening than the one above it.. A pre-weighed sample of the material to be tested is placed in the top sieve. This sieve stack is the shaken until all all the material has either been retained on a sieve or passed through. The material retained in each sieve is weighed and compared to the weight on the other sieves. A sieve test analysis or distribution is calculated which shows the proportion of each particle size category in the sample

Test sieves usually have a round frame, in sizes that range from 3inches to 18 inches (and the metric equivalents) in diameter. Woven wire mesh with proscribed openings is the most common test sieve media, This is followed by perforated plate andelectroformed material. These are the most common media used for sieve analysis.

Material
glucose powder and micro crystalline cellulose (MCC)  powder

Apparatus
"sieve nest" machine

method

1. Consider 100g of lactose

2. Prepare a 'sieve nest' in ascending order and assigned appropriate sieve size

3. Put the powder into the sieve lactosa.

4. Sieve for 20 minutes.

5. After completing consider the results obtained and build a graph on powder particle size distribution.

6. Repeat the process with MCC

Result

sieve	Glucose (g)	MCC (g)
1	0.0162	3.5x10-3
2	0.0267	4.3x10-3
3	0.0160	0.0787
4	30.5684	4.9485
5	57.5150	51.8688
6	11.1436	42.1931

Discussion

A sieve test is performed by first assembling a stack of interlocking sieves. In this stack the sieve with the largest openings is at the top each lower sieve will have a smaller opening than the one above it.. A pre-weighed sample of the material to be tested is placed in the top sieve. This sieve stack is the shaken until all the material has either been retained on a sieve or passed through. The material retained in each sieve is weighed and compared to the weight on the other sieves.

The data can match sieve results for narrow and wide distributions, ranging from 30 micron to 30 mm. This is an essential point when replacing the traditional sieving technique with a faster and more precise method, but without changing the product specifications.

The ability to analyse the particle shape is important for the detection of aggregates. It is also required for the quality control of some types of particle which must consist of cubic or elongated particles. Figure shows a plot of particle shape as described by the aspect ratio calculation (x-axis) vs. % under on the y-axis.

It is also possible to display the particle size distribution as a histogram including the upper and lower specification ranges, as shown in    

          The graph show that the distribution of size particle is different. Size 2.5 mm is dominately for both powder which are glucose and lactose while size of 0.5 is the least. But in this experiment, there are some error due dust and other powder that effect of the weight.

Conclusions

 By the using of sieve nest, we can know that the distribution of particle size which is totally different that will effect the stability of the drug that we want to produce.

References

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

2)      Banker, G.S & Rhodes, C.T. 2000. Modern Pharmaceutics. Ed. Ke-2. New York. Marcel Dekker.

BALL MILLING

1. Title:
Experiment 1: Ball Milling

2. Objectives:
• To grind the coarse salt into small pieces by using ball milling method.
• Use the sieve method to determine the size of distribution of the small pieces of salt.

3. Introduction:
A ball mill, a type of grinder, is a cylindrical device used in grinding (or mixing) materials like ores, chemicals, ceramic raw materials and paints. Ball mills rotate around a horizontal axis, partially filled with the material to be ground plus the grinding medium. Different materials are used as media,  including ceramic balls, flint pebbles and stainless steel balls. An internal cascading effect reduces the material to a fine powder. In the experiment, ball milling method is used to grind 300g coarse salt to produce salt with smaller size. The size of distribution of the grinded salt was determined by the sieving method.

4. Methods:
• Apparatus and Materials:
Ball mill, 10 metal balls with various size, sieve, electronic balance, weighing boat, spatula, 300g coarse salt
• Procedures:
1. 300g of coarse salt was measured by using weighing balance.
2. Metal balls with various size were putted  into the mill.
3. 300g coarse was poured into the mill.
4. The process of milling was started with duration of 20 minutes with speed 3.
5. Once the milling process was done, the product was measured.
6. Sieve the product by using sieve nest method.
7. Histogram was plotted by using the data from the ball milling and sieving.

5. Results and Calculation :

Group 1 and 2: ( Set 1)

Group 3 and 4: ( Set 2)

Group 5 and 6: (Set 3)

Group 7 and 8: (Set 4)

6. Discussion:
First, when comparing the result from set1 (10min, speed 5) and set 2 ( 20 min, speed 5), the amount of grinded salt collected by sieving  that are in range of 150um-300um from set 2 is more (23.3451g) compared to set 1 ( 20.7206g).  This is because set 2 has longer duration for ball milling, therefore more smaller size salt can be produced.

Next, comparison is done between set 3(10min, speed 3) and set 4(20min, speed 3). The amount of grinded salt collected by sieving  that are in range of 150um-300um from set 4 is less (12.4977g) compared to set 3 (13.7336g). There is a little deviation since during the ball milling process both set use the same speed with the duration of set 4 is longer (20min) compared to set 3(10min), thus set 4 should produce more salt that is in the range of 150um-300um), however, in this experiment, the salt in the stated range produced by set 3 is more than set 4. This error may due to different people with different strength was used while using the sieving method.

Besides, comparison can also be done between sets with same duration during the ball milling but different speed. Weight of salt produced in the stated range from Set 1(10min, speed 5) is more (20.7206g) compared to set 3(10min, speed 3) which is 13.7336g. Furthermore, weight of 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 show ball milling process with faster speed can produce more product which is in the desired range. Moreover, from the experimental data it also indicate the speed influence more compared to the duration in the ball milling process.

7. Questions:

1. What are the factors that affect the milling process?
Speed and duration.

2. What are the equipments that can be used in milling?
Cutter mill, mortar and pestle, roller mills, hammer mill, fluid energy milling and others.
3. What are the factor that influence the selection of equipments that used in milling?
The desired size range of product and physical properties such as hardness of product will influence the selection of equipments that used in milling

8. Conclusion:

During ball milling process, set with longer duration and higher speed will produce more products that is in the desired size range. Variation in speed show greater effect compared to duration in ball milling process. 

9. References:

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

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