Micrometrics

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Author:
jcu1
ID:
199435
Filename:
Micrometrics
Updated:
2013-02-10 19:02:51
Tags:
DD3 exam
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Description:
Dr. Sant
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  1. coulter counter
    measures the conductivity change as particles move through a small orfice
  2. specific surface area
    • surface area/volume (Sv)
    • surface area/weight (Sw)

    density = Sv/Sw
  3. methods for measuring surface area
    • permeation method
    • adsorption method
  4. adsorption method to measure SA
    direct measure of particle SA

    measure the amt of gas that forms a layer around the particle. take the area of 1 mlcl of gas and multiply by the total number of gas particles (assumption that gas layer is one mlcl thick)
  5. BET equation
    used to measure the volume of gas adsorbed in the adsorption method
  6. surface activity is derived from:
    surface area, surface characteristics, energy storage capacity
  7. colloidal range
    range in which the electrical effects become dominant
  8. types of pores
    • micro
    • meso
    • marcro
  9. ways to measure pore size
    • gas adsorption - expansion of SA measurement method
    • mercury intrusion - 
  10. gas adsorption method for measuring pore size
    • inc pressure in increasing increments
    • as the pressure inc, more gas condenses into the pores
    • quantity of adsorbed gas is measured
    • saturation: all pores filled
    • desorption: measure as pressure is slowly decreased
  11. pore size measurement graph
    hysteresis where the desorption curve is above the adsorption curve
  12. air adsorption on poorly water soluble drugs...
    decreases dissolution rate
  13. crosslinking gelatin with formaldehyde...
    decreases hydration b/c of dec pore size
  14. water is adsorbed on excipients like:
    • methyl cellulose
    • povidone
  15. method of determining true density
    helium densitometer

    helium penetrates into the smallest pores (not adsorbed like in measuring pore size

    Vpowder = Vhelium - Vhelium+powder
  16. method of determining apparent density
    • liquid displacement
    • pycnometer
    • Wt of pyn+water - Wt of pyn+water+powder = volume of displacement
  17. method for measuring bulk density
    use graduated cylinder method

    defines how fibrous, granular, powdery materials pack

    low bulk density = large bulk volume
  18. flow properties important for:
    solid dosage forms
  19. factors that affect flow (what makes good flow)
    • particle size: too fine, doesn't flow well
    • particle size distribution: all same size is better
    • shape: spherical = good flow
    • porosity/density: high density and low porosity = good flow
    • surface roughness: use glidants to improve flow
    • cohesive forces: too small particles have more resistance to flow b/c cohesive force same as gravitational force
    • moisture content
    • humidity in environment
    • pressure on powder bed
    • equipment
  20. examples of glidants
    • talc
    • colloidal silicone dioxide
  21. ways to measure flow properties
    • angle of repose () - max angle possible between a pile of powder and a horizontal plane
    • measures frictional force btwn particles
    • tan = coefficient of friction ()
    • rougher, more irregular particles have higher 's (also smaller particles)

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