Micromeretics and Powder Rheology One Shot Notes and MCQs

Micromeretics and Powder Rheology One Shot Notes

Micromeretics deals with the study of small particles, focusing on particle size, distribution, shape, and their effects on formulation behavior. Powder rheology examines the flow properties of powders, which are essential for pharmaceutical manufacturing.

1. Particle Size and Distribution

Particle size affects solubility, dissolution rate, bioavailability, and stability of drugs.
Particle size distribution describes the spread of particle sizes within a sample.

Number Distribution:
- Describes the proportion of particles within specific size ranges by count.
- Useful for microscopic particle size analysis.
Weight Distribution:
- Describes the mass fraction of particles in specific size ranges.
- Critical in formulations to ensure proper drug dosage and uniformity.

2. Average Particle Size

Mean particle size can be calculated using:
- Arithmetic mean diameter: Average size of all particles.
- Volume mean diameter (D4,3): Emphasizes larger particles more because it considers volume.
- Number mean diameter (D1,0): Gives equal importance to all particles, regardless of size.

3. Particle Number and Volume Determination

Particle number: Refers to the total count of particles in a sample.
Particle volume: Determined by measuring the individual volumes of particles, which is essential for estimating bulk and void spaces.

4. Methods for Determining Particle Size

Optical Microscopy:
- Particles are observed under a microscope and measured using a calibrated scale.
- Suitable for particles larger than 1 micron.
Sieving Method:
- Uses a series of sieves with decreasing mesh size to classify particles based on size.
- Commonly used for granules and coarse powders.
Sedimentation Method:
- Based on Stokes’ law, which states that particles settle at different rates depending on their size and density.
- Suitable for fine powders and suspensions.

5. Measurement of Particle Shape

Sphericity describes how close the shape of a particle is to a sphere.
Particle shape impacts flow properties and surface area:
- Spherical particles have better flow.
- Irregular particles increase surface area, enhancing solubility and reactivity.

6. Specific Surface Area

Specific surface area refers to the total surface area per unit mass or volume.
It affects dissolution rate, adsorption capacity, and reactivity.
Higher specific surface areas are desirable in drug formulations to enhance dissolution.

7. Methods for Determining Surface Area

Permeability Method:
- Measures the flow of gas or liquid through a packed powder bed.
- Used to estimate surface area based on the resistance to flow.
Adsorption Method (BET Method):
- Measures the adsorption of gas molecules on the surface of particles.
- Useful for determining external surface area and porosity.

8. Porosity and Packing Arrangements

Porosity:
- Refers to the ratio of void spaces to total volume in a powder sample.
- Important in determining the density and packing of powders.
- Formula:
  Porosity=Void VolumeTotal Volume×100\text{Porosity} = \frac{\text{Void Volume}}{\text{Total Volume}} \times 100Porosity=Total VolumeVoid Volume×100
Packing Arrangements:
- Cubic Packing: Particles are arranged loosely; higher porosity (~47%).
- Rhombohedral Packing: Particles are more tightly packed; lower porosity (~26%).

9. Densities and Bulk Properties

True Density:
- Excludes the void spaces between particles.
- Example: Density of a solid drug particle.
Bulk Density:
- Includes the volume of the particles and the void spaces between them.
- Formula:
  Bulk Density=Mass of PowderBulk Volume\text{Bulk Density} = \frac{\text{Mass of Powder}}{\text{Bulk Volume}}Bulk Density=Bulk VolumeMass of Powder
Tapped Density:
- Measured after tapping the powder container to reduce void spaces.
- Useful in determining the compressibility of powders.

10. Bulkiness and Flow Properties

Bulkiness:
- Inverse of bulk density.
- Formula:
  Bulkiness=1Bulk Density\text{Bulkiness} = \frac{1}{\text{Bulk Density}}Bulkiness=Bulk Density1
- Higher bulkiness indicates more space between particles and lower density.
Flow Properties:
- Essential for efficient tablet compression and capsule filling.
- Factors affecting flow:
  - Particle size and shape: Larger and spherical particles flow better.
  - Moisture content: Excess moisture can cause clumping.
  - Surface texture: Rough particles reduce flowability.
Flowability Tests:
- Angle of Repose: Measures the angle formed by a cone of powder when poured.
  - Smaller angles indicate better flow.
  - Formula:
    tan⁡(θ)=hr\tan(\theta) = \frac{h}{r}tan(θ)=rh
    where hhh = height, rrr = radius of the cone.
- Compressibility Index (Carr’s Index):
  - Determines the ability of a powder to compress.
  - Formula:
    Carr’s Index=Tapped Density−Bulk DensityTapped Density×100\text{Carr’s Index} = \frac{\text{Tapped Density} – \text{Bulk Density}}{\text{Tapped Density}} \times 100Carr’s Index=Tapped DensityTapped Density−Bulk Density×100
  - A value below 15% indicates good flow; above 25% indicates poor flow.
- Hausner Ratio:
  - Ratio of tapped density to bulk density.
  - Formula:
    Hausner Ratio=Tapped DensityBulk Density\text{Hausner Ratio} = \frac{\text{Tapped Density}}{\text{Bulk Density}}Hausner Ratio=Bulk DensityTapped Density
  - A value below 1.25 indicates good flow.

MCQs on Micromeretics and Powder Rheology

What is micromeretics?
a) Study of solubility
b) Study of small particles
c) Study of crystallization
d) Study of drug interactions
Answer: b) Study of small particles
Which factor primarily influences drug dissolution rate?
a) Particle size
b) Molecular weight
c) Temperature
d) Humidity
Answer: a) Particle size
In a sample with larger particles, which type of diameter is most significant?
a) Arithmetic mean diameter
b) Volume mean diameter
c) Number mean diameter
d) Median diameter
Answer: b) Volume mean diameter
Which type of distribution focuses on the mass fraction of particles?
a) Number distribution
b) Weight distribution
c) Particle number
d) Volume distribution
Answer: b) Weight distribution
Which method is suitable for measuring particles above 1 micron?
a) Sieving
b) Optical microscopy
c) Sedimentation
d) Electron microscopy
Answer: b) Optical microscopy
What does the sieving method measure?
a) Surface area
b) Particle size distribution
c) Particle shape
d) Flowability
Answer: b) Particle size distribution
Which method applies Stokes’ law for particle size measurement?
a) Microscopy
b) Sedimentation
c) Sieving
d) Permeability
Answer: b) Sedimentation
What is the principle of sedimentation used for particle size analysis?
a) Light scattering
b) Settling velocity
c) Bulk density
d) Adsorption
Answer: b) Settling velocity
Sphericity indicates how closely a particle resembles a:
a) Cube
b) Sphere
c) Cylinder
d) Polygon
Answer: b) Sphere
Which method is commonly used for surface area determination?
a) BET method
b) Sedimentation
c) Sieving
d) Light diffraction
Answer: a) BET method
Which property increases with a higher surface area?
a) Flowability
b) Dissolution rate
c) Particle density
d) Crystal stability
Answer: b) Dissolution rate
Which of the following methods measures surface area based on gas adsorption?
a) Optical microscopy
b) BET method
c) Sieving method
d) Permeability method
Answer: b) BET method
What is porosity?
a) Ratio of void volume to total volume
b) Ratio of bulk volume to true volume
c) Ratio of surface area to particle diameter
d) Ratio of density to particle size
Answer: a) Ratio of void volume to total volume
Which packing arrangement has the highest porosity?
a) Cubic packing
b) Rhombohedral packing
c) Hexagonal packing
d) Tetragonal packing
Answer: a) Cubic packing
Which density measurement excludes void spaces?
a) Bulk density
b) True density
c) Tapped density
d) Apparent density
Answer: b) True density
How does tapped density differ from bulk density?
a) Higher due to reduced void spaces
b) Lower due to increased void spaces
c) Equal to bulk density
d) Lower due to compression
Answer: a) Higher due to reduced void spaces
Which test measures the angle formed by a cone of powder?
a) Compressibility index
b) Hausner ratio
c) Angle of repose
d) BET surface area
Answer: c) Angle of repose
What does a Hausner ratio below 1.25 indicate?
a) Poor flowability
b) Good flowability
c) High porosity
d) Low porosity
Answer: b) Good flowability
Carr’s index indicates compressibility. What value suggests excellent flowability?
a) < 5%
b) 10–15%
c) 20–25%
d) > 30%
Answer: b) 10–15%
Which factor does not influence powder flow?
a) Particle shape
b) Temperature
c) Particle size
d) Moisture content
Answer: b) Temperature
What is the inverse of bulk density called?
a) Porosity
b) Bulkiness
c) Flow rate
d) Compressibility
Answer: b) Bulkiness
Which method measures surface area by gas flow through a powder bed?
a) BET method
b) Permeability method
c) Sedimentation method
d) Microscopy
Answer: b) Permeability method
What is adsorption in powders?
a) Binding of particles to moisture
b) Binding of gas or liquid on the surface
c) Formation of crystal structures
d) Release of gas from a surface
Answer: b) Binding of gas or liquid on the surface
What is the typical effect of irregular particle shapes on flowability?
a) Improves flowability
b) Reduces flowability
c) No effect on flowability
d) Increases surface tension
Answer: b) Reduces flowability
Which instrument measures gas adsorption for surface area analysis?
a) Permeameter
b) BET analyzer
c) Sedimentometer
d) Pycnometer
Answer: b) BET analyzer
Which formulation benefits from powders with low flowability?
a) Tablet compression
b) Capsule filling
c) Aerosol preparation
d) Ophthalmic solution
Answer: c) Aerosol preparation
Why is particle size reduction crucial in inhalers?
a) Reduces dosage frequency
b) Improves drug targeting
c) Increases bulk density
d) Enhances tablet hardness
Answer: b) Improves drug targeting
Which factor affects both dissolution rate and stability?
a) Porosity
b) Particle size
c) True density
d) Angle of repose
Answer: b) Particle size
Which device measures particle volume by displacement of a fluid?
a) Hydrometer
b) Pycnometer
c) Permeameter
d) BET analyzer
Answer: b) Pycnometer
Which method uses mercury to determine porosity and particle volume?
a) BET method
b) Sedimentation
c) Mercury intrusion porosimetry
d) Optical microscopy
Answer: c) Mercury intrusion porosimetry
Specific surface area is defined as:
a) Area per unit volume
b) Area per unit mass
c) Volume per unit surface area
d) Mass per unit length
Answer: b) Area per unit mass
Increased specific surface area in powders leads to:
a) Reduced dissolution
b) Increased adsorption
c) Decreased porosity
d) Higher density
Answer: b) Increased adsorption
Which packing arrangement yields the least porosity?
a) Hexagonal close packing
b) Simple cubic packing
c) Rhombohedral packing
d) Cubic close packing
Answer: a) Hexagonal close packing
How is porosity expressed mathematically?
a) (Bulk volume – True volume) / Bulk volume × 100
b) (True volume / Bulk volume) × 100
c) (Bulk density / True density) × 100
d) (True density / Bulk density) × 100
Answer: a) (Bulk volume – True volume) / Bulk volume × 100
Which factor increases when porosity is high?
a) Tapped density
b) Powder compressibility
c) True density
d) Powder stability
Answer: b) Powder compressibility
What happens to bulk density if particles are irregular and loosely packed?
a) Increases
b) Decreases
c) Remains constant
d) Varies with time
Answer: b) Decreases
What is the difference between bulk density and tapped density?
a) Bulk density excludes inter-particle voids
b) Tapped density is lower than bulk density
c) Tapped density accounts for settling after tapping
d) Bulk density measures true volume only
Answer: c) Tapped density accounts for settling after tapping
Which device measures tapped density?
a) Pycnometer
b) Tapped density tester
c) Permeameter
d) Sedimentometer
Answer: b) Tapped density tester
If a powder has poor flow, its Carr’s index will likely be:
a) < 5%
b) 10–15%
c) 20–25%
d) > 30%
Answer: d) > 30%
What is the significance of the angle of repose?
a) Measures powder stability
b) Indicates flowability of powders
c) Determines compressibility
d) Measures density variations
Answer: b) Indicates flowability of powders
Which powder property is inversely proportional to flowability?
a) Surface tension
b) Compressibility index
c) Bulk density
d) Porosity
Answer: b) Compressibility index
What is a typical angle of repose for powders with excellent flow properties?
a) < 25 degrees
b) 25–30 degrees
c) 30–35 degrees
d) > 40 degrees
Answer: a) < 25 degrees
How does particle size reduction affect powder flow?
a) Improves flowability
b) Reduces flowability
c) Has no effect
d) Increases porosity
Answer: b) Reduces flowability
What is bulkiness in terms of powder properties?
a) Inverse of true density
b) Ratio of porosity to bulk density
c) Inverse of bulk density
d) Ratio of surface area to volume
Answer: c) Inverse of bulk density
What is adsorption in powders primarily used for?
a) Determining flow rate
b) Measuring surface area
c) Increasing stability
d) Reducing moisture content
Answer: b) Measuring surface area
Which gas is commonly used in BET surface area measurements?
a) Carbon dioxide
b) Nitrogen
c) Oxygen
d) Argon
Answer: b) Nitrogen
Permeability methods measure:
a) Particle size
b) Gas flow through a powder bed
c) True density
d) Crystal formation
Answer: b) Gas flow through a powder bed
What is the impact of moisture on powder flow properties?
a) Increases flowability
b) Reduces flowability
c) Has no effect
d) Improves bulk density
Answer: b) Reduces flowability
In which formulation is powder stability critical?
a) Injectables
b) Aerosols
c) Tablets
d) Ophthalmic solutions
Answer: c) Tablets
Why is particle size control important in tablet manufacturing?
a) Prevents weight variation
b) Increases tablet hardness
c) Improves disintegration
d) Enhances dissolution rate
Answer: d) Enhances dissolution rate
What is the significance of polymorphism in pharmaceutical solids?
a) Affects drug solubility and bioavailability
b) Increases tablet hardness
c) Improves powder flow
d) Decreases porosity
Answer: a) Affects drug solubility and bioavailability
Which type of inhaler benefits from smaller particle sizes?
a) Dry powder inhaler
b) Metered-dose inhaler
c) Nebulizer
d) Nasal spray
Answer: a) Dry powder inhaler