Milling Flashcards
What is milling?
Milling is a mechanical process to reduce the particle size of solids.
It includes terms like grinding, pulverization, crushing, and dispersion.
How is the size of solid particles conventionally expressed?
The size of solid particles is conventionally expressed in mesh size, which indicates the number of pores per inch of screen.
What is coarse milling characterized by?
Coarse milling produces particles longer than 20 mesh.
What is intermediate milling characterized by?
Intermediate milling produces particles between 20-200 mesh.
What is fine milling characterized by?
Fine milling produces particles greater than 200 mesh.
What is the relationship between particle size and surface area in milling?
Smaller particle size leads to a larger surface area and faster dissolution.
What is the formula for specific surface?
Specific surface = surface area / weight.
What effect does size reduction have on specific surface?
Size reduction increases the specific surface area, resulting in increased contact between the solid and dissolving fluid.
How does particle size affect extraction time?
Increased area contact due to size reduction reduces the time for extraction.
What determines the position and retention of particles in inhalational aerosols?
Particle size in inhalational aerosols determines the position and retention of particles in bronchopulmonary systems.
What can happen to the crystalline structure during milling?
Milling may alter the crystalline structure and cause chemical changes in some materials.
What happens to starch and amylopectin during milling?
Starch and amylopectin structures are broken down to lower molecular weight polymers.
What chemical change can occur to pure C12 and C16 fatty acids by ball mill?
They may be decarboxylated and converted to hydrocarbons containing one carbon less.
What is one method to determine particle size?
Sieving method
Other methods include microscopy, sedimentation, electrical conductivity method, and light and X-ray scattering.
Fill in the blank: The sieving method is one of the methods to determine _______.
particle size.
True or False: Milling has no effect on the chemical structure of materials.
False.
What is the mesh size for a particle size of 2000 microns?
10
The mesh size indicates how many openings there are in a screen per linear inch.
What is the mesh size for a particle size of 850 microns?
20
Higher mesh sizes correspond to smaller particle sizes.
What is the mesh size for a particle size of 600 microns?
30
Mesh size is inversely related to particle diameter.
What is the mesh size for a particle size of 400 microns?
40
Mesh size can be used to classify particle sizes in various applications.
What is the mesh size for a particle size of 300 microns?
50
The mesh size system is widely used in material processing.
What is the mesh size for a particle size of 250 microns?
60
Mesh sizes continue to decrease as particle sizes decrease.
What is the mesh size for a particle size of 200 microns?
70
Smaller particles tend to have higher mesh sizes.
What is the mesh size for a particle size of 175 microns?
80
Accurate particle sizing is crucial for various industrial applications.
What is the mesh size for a particle size of 150 microns?
100
The mesh size indicates the size of the openings in the sieve.
What is the mesh size for a particle size of 75 microns?
200
This size is often critical for fine powders.
What is the mesh size for a particle size of 37 microns?
400
Very fine particles require specific mesh sizes for accurate measurement.
What is the range of particle size that can be measured by microscopy?
05 µm - 150 µm
Microscopy allows for detailed observation of particles.
How many particles are generally counted in the microscopy method?
625
This count helps in statistical analysis of particle size distribution.
What is the range of particle size that can be measured by the sedimentation method?
1 µm - 200 µm
Sedimentation methods are effective for analyzing suspended particles.
What device is used in the sedimentation method?
Andreasen pipette
This pipette is designed for precise measurement in sedimentation analysis.
What is the formula used in the sedimentation method based on Stoke’s law?
x/t = dp2 (ρp - ρo).g / 18η
This formula relates sedimentation rate to particle properties and fluid characteristics.
What does x/t represent in the sedimentation formula?
Rate of sedimentation or settling velocity
This is the distance traveled over time by the sedimenting particle.
What does dp represent in the sedimentation formula?
Particle diameter
dp is a key variable affecting sedimentation rates.
What does η represent in the sedimentation formula?
Viscosity of the medium
The viscosity affects the movement of particles through the medium.
What does (ρp - ρo) represent in the sedimentation formula?
Density gradient
The difference in densities influences the settling behavior of particles.
What does g represent in the sedimentation formula?
Acceleration due to gravity
Gravity is a driving force in the sedimentation process.
What is a common mill used for size reduction for almost all drugs?
Hammer mill
Hammer mills are versatile and widely used in pharmaceutical processing.
Which mill is suitable for soft material?
Roller attrition
This mill applies pressure to reduce particle size in softer materials.
Which mill is used for moderately hard and friable materials?
Fluid energy mill
This mill utilizes high-velocity air to impact particles.
Which mill is specifically used for fibrous materials?
Cutter mill
Cutter mills are designed to chop and reduce fibrous materials effectively.
Which mill is used for emulsions?
Colloid mill
Colloid mills are essential for creating homogeneous emulsions.
What type of mill is commonly used in grinding for fine powders?
Ball mill
Ball mills are effective for achieving very fine particle sizes.
What is the primary use of a hammer mill?
Wet granulation
The material is fed at the top and thrown out centrifugally, with sieved material collected after passing through a perforated screen.
How does a hammer mill discharge material?
Material is discharged with particle size smaller than the screen pore
This is achieved by the centrifugal force acting on the material.
What is the optimum volume of balls in a ball mill?
50% of the volume of the mill
Balls of different sizes can be used for fine production of particles.
What type of grinding does a ball mill use?
Impact and attrition
The speed of the mill affects the grinding mechanism.
What happens to the balls in a ball mill at slow speed?
Balls roll and cascade over one another
This provides an attrition action.
What is critical speed in a ball mill?
The speed at which balls begin to centrifuge
At or above critical speed, there is no significant size reduction.
At what percentage of critical speed are ball mills generally operated?
60-85%
This range allows for effective size reduction.
What does a fluid energy mill use for size reduction?
Impact and attrition
Micronized material is carried with high velocity air in a cyclone separator.
What is the particle size range produced by a fluid energy mill?
2-20µ
Fine particles pass through a discharge outlet into a bag collector.
What is the primary use of a colloid mill?
Production of emulsions
It is not used for dry particles.
What is the rotor speed range of a colloid mill?
2000-20000 rpm
The space between the rotor and stator is adjusted to achieve the desired size of globules.
