Milling

Question 1

What is milling?

Answer 1

Milling is a mechanical process to reduce the particle size of solids.

It includes terms like grinding, pulverization, crushing, and dispersion.

Question 2

How is the size of solid particles conventionally expressed?

Answer 2

The size of solid particles is conventionally expressed in mesh size, which indicates the number of pores per inch of screen.

Question 3

What is coarse milling characterized by?

Answer 3

Coarse milling produces particles longer than 20 mesh.

Question 4

What is intermediate milling characterized by?

Answer 4

Intermediate milling produces particles between 20-200 mesh.

Question 5

What is fine milling characterized by?

Answer 5

Fine milling produces particles greater than 200 mesh.

Question 6

What is the relationship between particle size and surface area in milling?

Answer 6

Smaller particle size leads to a larger surface area and faster dissolution.

Question 7

What is the formula for specific surface?

Answer 7

Specific surface = surface area / weight.

Question 8

What effect does size reduction have on specific surface?

Answer 8

Size reduction increases the specific surface area, resulting in increased contact between the solid and dissolving fluid.

Question 9

How does particle size affect extraction time?

Answer 9

Increased area contact due to size reduction reduces the time for extraction.

Question 10

What determines the position and retention of particles in inhalational aerosols?

Answer 10

Particle size in inhalational aerosols determines the position and retention of particles in bronchopulmonary systems.

Question 11

What can happen to the crystalline structure during milling?

Answer 11

Milling may alter the crystalline structure and cause chemical changes in some materials.

Question 12

What happens to starch and amylopectin during milling?

Answer 12

Starch and amylopectin structures are broken down to lower molecular weight polymers.

Question 13

What chemical change can occur to pure C12 and C16 fatty acids by ball mill?

Answer 13

They may be decarboxylated and converted to hydrocarbons containing one carbon less.

Question 14

What is one method to determine particle size?

Answer 14

Sieving method

Other methods include microscopy, sedimentation, electrical conductivity method, and light and X-ray scattering.

Question 15

Fill in the blank: The sieving method is one of the methods to determine _______.

Answer 15

particle size.

Question 16

True or False: Milling has no effect on the chemical structure of materials.

Answer 16

False.

Question 17

What is the mesh size for a particle size of 2000 microns?

Answer 17

10

The mesh size indicates how many openings there are in a screen per linear inch.

Question 18

What is the mesh size for a particle size of 850 microns?

Answer 18

20

Higher mesh sizes correspond to smaller particle sizes.

Question 19

What is the mesh size for a particle size of 600 microns?

Answer 19

30

Mesh size is inversely related to particle diameter.

Question 20

What is the mesh size for a particle size of 400 microns?

Answer 20

40

Mesh size can be used to classify particle sizes in various applications.

Question 21

What is the mesh size for a particle size of 300 microns?

Answer 21

50

The mesh size system is widely used in material processing.

Question 22

What is the mesh size for a particle size of 250 microns?

Answer 22

60

Mesh sizes continue to decrease as particle sizes decrease.

Question 23

What is the mesh size for a particle size of 200 microns?

Answer 23

70

Smaller particles tend to have higher mesh sizes.

Question 24

What is the mesh size for a particle size of 175 microns?

Answer 24

80

Accurate particle sizing is crucial for various industrial applications.

Question 25

What is the mesh size for a particle size of 150 microns?

Answer 25

100 ## Footnote The mesh size indicates the size of the openings in the sieve.

Question 26

What is the mesh size for a particle size of 75 microns?

Answer 26

200 ## Footnote This size is often critical for fine powders.

Question 27

What is the mesh size for a particle size of 37 microns?

Answer 27

400 ## Footnote Very fine particles require specific mesh sizes for accurate measurement.

Question 28

What is the range of particle size that can be measured by microscopy?

Answer 28

05 µm - 150 µm ## Footnote Microscopy allows for detailed observation of particles.

Question 29

How many particles are generally counted in the microscopy method?

Answer 29

625 ## Footnote This count helps in statistical analysis of particle size distribution.

Question 30

What is the range of particle size that can be measured by the sedimentation method?

Answer 30

1 µm - 200 µm ## Footnote Sedimentation methods are effective for analyzing suspended particles.

Question 31

What device is used in the sedimentation method?

Answer 31

Andreasen pipette ## Footnote This pipette is designed for precise measurement in sedimentation analysis.

Question 32

What is the formula used in the sedimentation method based on Stoke's law?

Answer 32

x/t = dp2 (ρp - ρo).g / 18η ## Footnote This formula relates sedimentation rate to particle properties and fluid characteristics.

Question 33

What does x/t represent in the sedimentation formula?

Answer 33

Rate of sedimentation or settling velocity ## Footnote This is the distance traveled over time by the sedimenting particle.

Question 34

What does dp represent in the sedimentation formula?

Answer 34

Particle diameter ## Footnote dp is a key variable affecting sedimentation rates.

Question 35

What does η represent in the sedimentation formula?

Answer 35

Viscosity of the medium ## Footnote The viscosity affects the movement of particles through the medium.

Question 36

What does (ρp - ρo) represent in the sedimentation formula?

Answer 36

Density gradient ## Footnote The difference in densities influences the settling behavior of particles.

Question 37

What does g represent in the sedimentation formula?

Answer 37

Acceleration due to gravity ## Footnote Gravity is a driving force in the sedimentation process.

Question 38

What is a common mill used for size reduction for almost all drugs?

Answer 38

Hammer mill ## Footnote Hammer mills are versatile and widely used in pharmaceutical processing.

Question 39

Which mill is suitable for soft material?

Answer 39

Roller attrition ## Footnote This mill applies pressure to reduce particle size in softer materials.

Question 40

Which mill is used for moderately hard and friable materials?

Answer 40

Fluid energy mill ## Footnote This mill utilizes high-velocity air to impact particles.

Question 41

Which mill is specifically used for fibrous materials?

Answer 41

Cutter mill ## Footnote Cutter mills are designed to chop and reduce fibrous materials effectively.

Question 42

Which mill is used for emulsions?

Answer 42

Colloid mill ## Footnote Colloid mills are essential for creating homogeneous emulsions.

Question 43

What type of mill is commonly used in grinding for fine powders?

Answer 43

Ball mill ## Footnote Ball mills are effective for achieving very fine particle sizes.

Question 44

What is the primary use of a hammer mill?

Answer 44

Wet granulation ## Footnote The material is fed at the top and thrown out centrifugally, with sieved material collected after passing through a perforated screen.

Question 45

How does a hammer mill discharge material?

Answer 45

Material is discharged with particle size smaller than the screen pore ## Footnote This is achieved by the centrifugal force acting on the material.

Question 46

What is the optimum volume of balls in a ball mill?

Answer 46

50% of the volume of the mill ## Footnote Balls of different sizes can be used for fine production of particles.

Question 47

What type of grinding does a ball mill use?

Answer 47

Impact and attrition ## Footnote The speed of the mill affects the grinding mechanism.

Question 48

What happens to the balls in a ball mill at slow speed?

Answer 48

Balls roll and cascade over one another ## Footnote This provides an attrition action.

Question 49

What is critical speed in a ball mill?

Answer 49

The speed at which balls begin to centrifuge ## Footnote At or above critical speed, there is no significant size reduction.

Question 50

At what percentage of critical speed are ball mills generally operated?

Answer 50

60-85% ## Footnote This range allows for effective size reduction.

Question 51

What does a fluid energy mill use for size reduction?

Answer 51

Impact and attrition ## Footnote Micronized material is carried with high velocity air in a cyclone separator.

Question 52

What is the particle size range produced by a fluid energy mill?

Answer 52

2-20µ ## Footnote Fine particles pass through a discharge outlet into a bag collector.

Question 53

What is the primary use of a colloid mill?

Answer 53

Production of emulsions ## Footnote It is not used for dry particles.

Question 54

What is the rotor speed range of a colloid mill?

Answer 54

2000-20000 rpm ## Footnote The space between the rotor and stator is adjusted to achieve the desired size of globules.