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What is one of the main purposes of milling semi-solids?
What is one of the main purposes of milling semi-solids?
Which mechanism of milling is characterized by the crushing of material between two surfaces?
Which mechanism of milling is characterized by the crushing of material between two surfaces?
Which milling mechanism involves a material striking a stationary surface?
Which milling mechanism involves a material striking a stationary surface?
What particle size range does the Cutting method typically achieve?
What particle size range does the Cutting method typically achieve?
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Which of the following milling methods is specifically noted for its limited use in the pharmaceutical industry?
Which of the following milling methods is specifically noted for its limited use in the pharmaceutical industry?
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Which milling equipment is an example of both Impact and Attrition methods?
Which milling equipment is an example of both Impact and Attrition methods?
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What is the mechanism of Attrition in milling?
What is the mechanism of Attrition in milling?
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Which milling mechanism produces the finest particle size range?
Which milling mechanism produces the finest particle size range?
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What is the primary function of cutter mills?
What is the primary function of cutter mills?
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Which type of mill combines both compression and attrition methods?
Which type of mill combines both compression and attrition methods?
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What is one of the primary functions of size reduction in pharmaceutical processing?
What is one of the primary functions of size reduction in pharmaceutical processing?
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Which application of size reduction directly affects therapeutic efficacy?
Which application of size reduction directly affects therapeutic efficacy?
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What is the role of hammers in hammer mills?
What is the role of hammers in hammer mills?
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In terms of surface area, what changes when particle size is reduced from 10 µm to 0.1 µm?
In terms of surface area, what changes when particle size is reduced from 10 µm to 0.1 µm?
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Which mill type is specifically designed for tough, fibrous materials?
Which mill type is specifically designed for tough, fibrous materials?
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How does a three-roller mill achieve finer crushing of materials?
How does a three-roller mill achieve finer crushing of materials?
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What happens to the dissolution rate of a drug as its particle size decreases?
What happens to the dissolution rate of a drug as its particle size decreases?
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What distinguishes a ball mill from other impact mills?
What distinguishes a ball mill from other impact mills?
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What typical outcome characterizes particulate material that is 0.1 µm in size?
What typical outcome characterizes particulate material that is 0.1 µm in size?
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What mechanism do edge runner mills use to grind materials?
What mechanism do edge runner mills use to grind materials?
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What mechanism is used to ensure uniformly sized particles after milling?
What mechanism is used to ensure uniformly sized particles after milling?
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Which of the following mills is best suited for pre-milled or suspended materials?
Which of the following mills is best suited for pre-milled or suspended materials?
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How does size reduction affect the therapeutic dosing regimen of Griseofulvin?
How does size reduction affect the therapeutic dosing regimen of Griseofulvin?
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What characteristic of the particle size significantly influences its flowability?
What characteristic of the particle size significantly influences its flowability?
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What is the primary reason for having a cascade of balls in a ball mill?
What is the primary reason for having a cascade of balls in a ball mill?
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What can result from overfeeding a ball mill?
What can result from overfeeding a ball mill?
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What is the optimal speed for the operation of a ball mill?
What is the optimal speed for the operation of a ball mill?
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Which of the following is NOT a disadvantage of ball mills?
Which of the following is NOT a disadvantage of ball mills?
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What is one of the main advantages of using ball mills?
What is one of the main advantages of using ball mills?
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Which mechanism is primarily responsible for grinding in fluid energy mills?
Which mechanism is primarily responsible for grinding in fluid energy mills?
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What is a common requirement for grinding sensitive materials in fluid energy mills?
What is a common requirement for grinding sensitive materials in fluid energy mills?
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What can be a consequence of using soft and sticky materials in a ball mill?
What can be a consequence of using soft and sticky materials in a ball mill?
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What is the primary characteristic of a brittle material under stress?
What is the primary characteristic of a brittle material under stress?
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At what temperature does an amorphous material change from a hard state to a soft, rubbery state?
At what temperature does an amorphous material change from a hard state to a soft, rubbery state?
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Which of the following substances is likely to exhibit plastic behavior?
Which of the following substances is likely to exhibit plastic behavior?
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What effect does moisture content above 5% have on dry powders during milling?
What effect does moisture content above 5% have on dry powders during milling?
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What is one disadvantage of milling materials with low melting points at high temperatures?
What is one disadvantage of milling materials with low melting points at high temperatures?
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How can fibrous materials best be processed?
How can fibrous materials best be processed?
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Which method is NOT recommended for overcoming moisture issues in milling?
Which method is NOT recommended for overcoming moisture issues in milling?
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What happens to a material below its glass transition point?
What happens to a material below its glass transition point?
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What is the primary mechanism by which a pin mill reduces the size of materials?
What is the primary mechanism by which a pin mill reduces the size of materials?
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Which factor does NOT affect the size reduction process of materials?
Which factor does NOT affect the size reduction process of materials?
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What is the role of the classifier in the operation of a fluid energy mill?
What is the role of the classifier in the operation of a fluid energy mill?
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Which of the following statements about surface hardness is TRUE?
Which of the following statements about surface hardness is TRUE?
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What is a disadvantage of fluid energy mills?
What is a disadvantage of fluid energy mills?
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What does a higher position on Mohs' scale imply about a material?
What does a higher position on Mohs' scale imply about a material?
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Which of the following is a benefit of using fluid energy mills?
Which of the following is a benefit of using fluid energy mills?
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In the context of size reduction, how are materials with high moisture content likely to behave?
In the context of size reduction, how are materials with high moisture content likely to behave?
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Study Notes
Particle Size Reduction
- Comminution, pulverization, milling, and grinding are synonyms for size reduction
- Size reduction aids in further processing by facilitating powder mixing and increasing the dissolution rate of soluble ingredients.
- For suspensions, size reduction reduces sedimentation rate.
- Size reduction reduces bulk material volume, aiding transport.
Applications of Size Reduction in Pharmaceutical Industry
- Dissolution and therapeutic efficacy: Increased surface area per unit weight enhances drug dissolution in body fluids.
- Extraction: Smaller particles allow more thorough extraction with less solvent penetration depth.
- Drying: Size reduction increases surface area and shortens the moisture travel distance, speeding up drying.
- Flowability: Free-flowing powders and granules enhance product quality in equipment like high-speed filling.
- Mixing: Similar particle size makes mixing of ingredients easier and more uniform.
- Formulation: Fine particle size is crucial for lubricants to properly coat granules or powders, ensuring smooth texture and stability in ointments, creams, and pastes.
Mechanisms of Size Reduction
- Different milling equipment types produce an approximate size reduction range.
- The extent of size reduction is related to milling time.
- Mills apply energy for size reduction through different mechanisms such as:
- Cutting
- Compression
- Impact
- Attrition
Mechanisms of Milling
- Cutting: Applying force over a narrow area using a sharp edge slices material into smaller pieces (example: knife mills for fibrous materials).
- Compression: Material crushing between surfaces under pressure (example: roller or jaw crushers for brittle materials).
- Impact: Material contact with a fast-moving part, transferring kinetic energy, leading to internal stress and particle breakage (example: hammer mills for brittle and soft materials).
- Attrition: Material subjected to shear forces from relative motion of surfaces, leading to particle breakage (example: fluid energy mills for fine grinding).
Equipment
-
Cutter Mills: Use knives or cutters to reduce size for small and large-scale processes.
- Rotary knife cutters well-suited for tough, fibrous materials.
- Disc Mills suitable for pre-milled or suspended materials.
- Runner Mills (Mortar and Pestle): A mechanized form used for smaller-scale size reductions.
- Three-Roller Mill: Consist of multiple rollers of different speeds to crush and shear materials between rollers.
- Hammer Mills: Consist of hammers rotating rapidly to impact particles and fracture them. Used for sticky materials that clog other mills and for granulating damp masses.
- Vibration Mills: Cylindrical tanks filled with porcelain/steel balls that vibrate, creating impacts for size reduction.
- Ball Mills: Rotating cylinders with balls inside for impact and attrition size reduction.
- Fluid Energy Mills (Jet Mills or Micronizers): High-velocity fluids and high-pressure jets for size reduction and minimizing heat generation.
- Pin Mills (Kek Mills): Two discs with closely spaced pins, one rotating at speed for impact and attrition size reduction.
Factors Affecting Size Reduction
- Nature of the material: Material hardness, brittleness/plasticity, stickiness, and fibrous nature are influencing factors. Different materials require different techniques.
- Moisture Content: Dry powders (less than 5% water) are easily reduced - higher water levels or wet milling are required.
- Temperature: Heat generation can degrade heat-sensitive materials, melt materials with low melting points, or induce explosions in unstable compounds.
- Particle Shape: Size reduction methods may lead to irregular (tough) or regular/spherical (easy flow) particles.
- Product Specifications: Desired particle size, shape, moisture content, and physical/chemical properties.
- Sanitation Ease of cleaning, auxilary equipment compatability and operation mode are influencing factors.
- Economic considerations Equipment costs, power/labor and costs, and space requirements.
- Dust Control: Minimizing dust and reducing risks associated with contamination.
Applications
- Intermediate powders can come from almost any substance.
- Suitable for processing sticky materials, powdering barks, leaves, roots, filter cakes.
- Also used for granulating techniques.
Advantages
- Various materials.
- Controlled product size.
- Continuous operation.
- Little metal abrasion and little contamination.
Disadvantages
- Heat generation.
- Clogging during operation and machine damage.
- Wide size range of product.
- Increased wear of component materials.
- High energy consumption.
Wet vs. Dry Milling
- Dry milling (~100 µm) often involves higher power consumption and creates more dust, while wet milling (~10 µm, limited by flocculation) often eliminates dust and requires less power but may create a need for drying. Wet milling is favored when the product is moisture-sensitive.
Factors Affecting Size Reduction Choice
- Product specifications affect material properties and size reduction techniques.
- Equipment type and its processing capabilities affect production batch sizing, and materials handling.
- Sanitation, operational methods, dust control, and cost affect mill selection.
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Description
This quiz explores various milling mechanisms used in pharmaceutical processing, including the functions and characteristics of different milling methods. Test your knowledge on the role of size reduction, particle size ranges, and specific milling equipment utilized in the industry.
