**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.

- Describes the proportion of particles within specific size ranges by
**Weight Distribution:**- Describes the
**mass fraction**of particles in specific size ranges. - Critical in formulations to ensure proper drug dosage and uniformity.

- Describes the

**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

- Refers to the ratio of
**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.

- Essential for efficient
**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

**Also, Visit:**

B. Pharma Previous Year Question Paper