[PHA6113 lec] Micromeritics Flashcards
The science and technology of small particles
Micromeritics
Most accurate method of determining particle size
Optical Microscopy or Microscopic Method
T or F: The microscope eyepiece is fitted with a micrometer by which the size of particles may be estimated
True
Unit of particle size
Micrometer or micron (µm or µ)
1 µm or µ
10^-6 m, 10^-4 cm, 10^-3 mm
1 millimicron (mµ)
1 nanometer (nm) = 10^-9 m
Simplest method of determining particle size
Sieving (USP Method)
This method utilizes a series of standard sieves calibrated by the National Bureau of Standards
Sieving (USP Method)
This technique involves size classification followed by the determination of the weight of each fraction
Sieving (USP Method)
This method makes use of a coulter counter in determining the particle volume distribution of material suspended in an electrolyte-containing solution
Particle Volume Measurement
Makes use of the Andreasen apparatus
Sedimentation Method
This method employs the settling of particles in a liquid of a relatively low density under the influence of a gravitational or centrifugal field
Sedimentation Method
Law that expresses the rate of settling
Stoke’s Law
T or F: Stoke’s law is applicable for particles which aggregate or clump together
False, not applicable
Formula for Stoke’s Law
CHECK YOUR HANDOUT RIGHT NOW
[Derived Properties of Powders]
Formula for Porosity or Voids (Є)
CHECK YOUR HANDOUT RIGHT NOW
Most powders have a porosity between _______?
30-50%
Closest or rhombohedral packing arrangement
Low porosity - 26%
Open or cubic packing arrangement
Highest porosity - 48%
Density of the actual solid and is exclusive of the voids and interparticle pores
True Density
Formula of True Density
ρ = W/Vp
Determined from the bulk volume and the weight of a dry powder in a graduated cylinder
Bulk or apparent density
Formula of Apparent Density
ρ = W/Vb
Reciprocal of Apparent Density
Bulkiness
Determined by displacement of mercury which does not penetrate at ordinary pressure into pores smaller than about 10µm
Granule density
What is the relationship between true density and granule density when the solid is non-porous?
Equal
Based on bulk density, powder may be?
a. Light - low apparent or bulk density, large bulk volume and high porosity
b. Heavy - high apparent density, small bulk volume and low porosity
Powders may be free-flowing or cohesive depending on?
a. Particle size - as particle size increases, flow is facilitated
b. Shape
c. Porosity
d. Density
Loosely packed, high porosity, low density, does not flow freely
Elongated or Flat particles
Closely packed, low porosity, high density, free flowing
Nearly spherical particles
Dispersions in which the size of the dispersed particle is 0.5 µm – 10 µm
Coarse Dispersions
3 Types of Coarse Dispersions
- Suspensions
- Emulsions
- Semi-solids
Coarse dispersion in which insoluble solid particles are dispersed in a liquid medium
Suspension
Factors affecting sedimentation based on Stoke’s Law
- Particle size and density - larger particles sediment rapidly compared to smaller particles
- Viscosity of medium - inversely proportional to the sedimentation rate
Dispersed system of at least two immiscible liquid phases, one of which is dispersed as globules in other liquid phase
Emulsions
2 Types of Emulsions
O/W and W/O
Methods of Preparing Emulsions
- Continental or Dry Gum
- English or Wet Gum
- Bottle or Forbes
- In-situ Soap
Methods of detecting type of emulsion
- Dilution test - when oil is added to an o/w emulsion or water is added to a w/o emulsion = separation is apparent
- Conductivity test - o/w has high conductivity while w/o has no or low conductivity
- Dye-solubility test - water soluble dye is soluble in o/w while oil soluble dye is soluble in w/o
Forms of instability
- Creaming and sedimentation
- Aggregation and coalescence
- Inversion
[Forms of instability]
Upward movement of the dispersed droplets relative to the continuous phase
Creaming
[Forms of instability]
Downward movement of the particles
Sedimentation
[Forms of instability]
Dispersed droplets come together but do not fuse
Aggregation or flocculation
[Forms of instability]
Complete fusion of droplets leading to the ultimate separation of the 2 immiscible phases
Coalescence
[Forms of instability]
Change from w/o to o/w and vice-versa
Inversion
[Forms of instability]
Inversion is brought about by 2 things
- Addition of electrolyte
- Changing the phase volume ratio
A solid or semisolid system of at least 2 constituents, consisting of a condensed mass enclosing and interpenetrated by a liquid
Gels
Gel wherein the coherent matrix is liquid
Jelly (ex. table jellies)
Gel when the liquid is removed and only the framework remains
Xerogel (ex. gelatin sheets, tragacanth ribbon, and acacia tears)
3 Changes observed in gels
- Syneresis
- Swelling
- Imbibition
[Changes in Gels]
Natural shrinking of a gel after standing for some time with pressing out some of the liquid
Syneresis
[Changes in Gels]
Taking up of liquid by a gel with an increase in volume
Swelling
[Changes in Gels]
Taking up of liquid without increase in volume
Imbibition
Heterogeneous system in which the mean particle size of the dispersed phase is 1 nm to 0.5 µm
Colloidal Dispersion
Colloidal dispersion of solid in liquid
Sol
Colloidal dispersion of solid or liquid in gases
Aerosol
Types of Colloidal System
- Lyophilic colloids
- Lyophobic colloids
- Association of amphiphilic colloids
[Types of Colloidal System]
System containing colloidal particles that interact to an appreciable extent with the dispersion medium
Lyophilic colloids (ex. gelatin, acacia)
[Types of Colloidal System]
Materials which have very little attraction for the dispersion medium
Lyophobic colloids (ex. gold, silver, sulfur)
[Types of Colloidal System]
Small molecules in dilute solution tend to associate into aggregate (micelles) which are of colloidal dimensions
Association or amphiphilic colloids (ex. surface active agents)
Methods of Purifying Colloids
- Dialysis - diffusion through a membrane of parchment cellophane or collodion which removes molecules or ions which pass through
- Ultrafiltration - filtration through ultrafilters prepared from collodion impregnated with and dried for a long time, allowing passage of all substances EXCEPT colloidal particles
Properties of Colloids
- Optical Property
- Kinetic Property
- Electrical Property
Optical property of Colloids which refers to the scattering of light produced when a strong beam of light is passed through a colloidal solution
Tyndall Effect
Kinetic property of Colloids which refers to the random movement of the colloidal particles
Brownian Movement
Property of Colloids which refers to the presence of charge on the surface of particles
Electrical Property
