30 Questions
What is the factor of greatest importance in the operation of the ball mill?
The rotation speed
At low rotating speeds, what happens to the balls in the ball mill?
The balls move with the drum until the force due to gravity exceeds the frictional force, and then slide back to the base
At high angular velocities, what happens in the ball mill?
The balls are thrown out onto the mill wall by centrifugal force
At about two-thirds of the critical angular velocity, what action is produced in the ball mill?
The balls produce a cascading action
Which of the following is a disadvantage of the ball mill?
It is difficult to clean and takes a long time for satisfactory milling
Which of the following is an advantage of the ball mill?
All of the above
What type of atmosphere is recommended for milling thermolabile, easily oxidizable, and combustible materials?
Inert atmosphere of carbon dioxide or nitrogen
Why does the milling chamber need to be cooled during the milling process?
To prevent the solid material from melting
What is the purpose of pretreatment for milling?
To ensure the feed is of proper size and enters uniformly
What can happen if the heat generated during milling is not removed?
The material will undergo a phase change
Which statement about milling in a closed system with dehumidified air is true?
It prevents explosive reactions in the mill
Why is it crucial to cool the milling chamber during the milling process?
To prevent excessive heat buildup in the material
What main method of size reduction involves the application of force over a very narrow area of material?
Cutting
Which milling method results in the creation of internal stresses in the particle?
Impact
What is the main factor that causes fracture or cracking of a particle during size reduction?
Energy exceeding the weakest flaw
Which part of a mill imparts energy to the material for size reduction?
Cutting device
In which method of size reduction are surfaces moving relative to each other, resulting in shear forces that break the particles?
Attrition
What is the typical pressure range for the air or steam used in a fluid-energy mill?
100 to 150 pounds per square inch (psi)
What is the role of residual strain energy in the process of fracture during size reduction?
Supply additional energy required for fracture
What is the primary mechanism by which particle size reduction occurs in a fluid-energy mill?
Interparticular attrition
Why is air typically used as the fluid in a fluid-energy mill rather than steam?
Most pharmaceuticals have a low melting point or are thermolabile.
Which of the following is NOT an important machine-related factor in a fluid-energy mill?
The material of construction of the mill.
What is a key disadvantage of using a fluid-energy mill?
High capital and running costs.
What is a key advantage of using a fluid-energy mill?
Ability to produce powders with all particles below a few micrometers.
What is the primary drawback associated with the type of mill described in the text?
The potential for the build-up of compressed product in the mill
Which type of materials cannot be effectively milled by pressure or impact?
Fibrous materials
Which statement best describes the effect of moisture content on the milling process?
Moisture content above 5% hinders comminution and may produce a sticky mass
What is the primary factor that determines the choice of equipment for milling?
The physical properties of the material to be milled
Which statement best describes the behavior of friable materials during milling?
Friable materials tend to fracture along well-defined planes and may be milled by attrition, impact, or compression
What is the primary advantage of using a wet milling process for materials with high moisture content?
It allows for the milling of materials that cannot be effectively milled dry
Learn about the process of milling in industrial pharmacy, where a particle absorbs strain energy and undergoes deformation until it fractures. Understand how the required strain energy for fracture is related to crack length and surrounding residual strain energy flow. This quiz is part of the College of Pharmacy Industrial Pharmacy I course, 4th stage, Second Semester.
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