Powders Flashcards
What is a mono-disperesed powder ?
A powder in which EVERY particle is the same size. This means that the population can be identified by a SINGLE PARAMETER.
TRUE OR FALSE
The peak in a ‘positively skewed’ histogram lies on the lower value side.
TRUE
The tail in a negatively skewed histrogram faces the higher values.
FALSE - on a negatively skewed histrogram the tail faces the lower values.
What value is extractable from a histogram distribution ?
The mode
TRUE OR FALSE
A bimodal size distribution has two medians
FALSE - It has two local maxinums.
What data is extractable from a cumulative frequency graph ?
The median and the interquartile range.
The interquartile range describes how broad the distribution is within a dataset.
What does sieve analysis determine ?
Sieve analysis is used to determine the distribution of the particle diameters.
Every level has holes of different diameter and therefore the amount of particles in each level signify their diameter.
This data is best represented in a cumulative frequency graph.
What is the minimum particle diameter that a mechanical sieve can measure up to ?
45μm
What types of sieving are there ?
- Air jet sieving
- Mechanical sieving
What are the pros and cons of air jet sieving ?
Pros:
* More accurate
* More reproducable results
Cons:
* Takes longer time
* Air jet sieving requires a partial vacuum
TRUE OR FALSE
Optical microscopy is a three dimensional assessment method
FALSE
Light microscope max measure
10μm
Electron miscroscope maxinum measure
100μm
What are microscopes used for on particles ?
To measure their size (diameter).
What are the different types of diameters ?
- Projected perimeter diameter
- Projected area diameter
- Martins diameter
- Feret’s diameter
How is the projected area diameter measured ?
There is an equal amount of particle outside the diameter ring as there is inside.
How is the projected perimeter diameter measured?
The diameter ring encapsulates the WHOLE particle
How is Martins diameter measured?
Draw a line down the middle of the particle so that there is an EQUAL amount of particle on either side.
Disadvantage of wet granulation
Not suitable for moisture-sensetive drugs
Electrical stream sensing zone
The measuring of the particle volume diameter.
The particles are placed in an electrolyte solution. One-by-one they pass through between two electrodes. The electrodes pick up the increase in resistance from the particle.
ESSZ issues
Difficult to ensure that particles pass one-by-one.
* Electrode gap TOO LARGE = multiple particles fit through.
* Electrode gap TOO SMALL = particles are blocked from passing through.
The electrolyte solution should be SATURATED to avoid the particles dissolving.
IDEALLY you want single particle passage for the highest accuracy.
ESSZ benefits
- Quick and easy
- particle size aplication 0.1-1000μm
Laser light scattering
A laser is applied to a suspension of particles in which the level of diffraction correlates to a certain diameter range.
The smaller the particle = Higher level of diffraction.
Two types:
* Large-light particle analysers [1-1000μm]
* Photon correlation [10nm-1μm]
Laser light scattering issue
It has to be a helium-neon laser
TRUE OR FLASE
Large particle analysers can measure up to 10nm
FALSE - Photon correlation 10nm-1μm
large particle = 1-1000μm
LLS benefits
- Rapid
- Reliable results
- Can produce a particle size distribution graph.
TRUE OR FALSE
Adhesive powders DO NOT flow well
FALSE - Cohesive powders do not flow well.
Adhesion
The attraction between a material and a DIFFERENT material.
Cohesion
The attraction betweena material and an IDENTICAL material.
General rule of cohesion and powders
The less cohesive a powder is the better it will flow.
UNAVOIDABLE INTERPARTICULAR FORCE
van der Waals force
higher surface area = more van der waals
Interparticular forces
- Van der waal force
- Electrostatic charging
- Surface tension forces between absorbed liquid
TRUE OR FALSE
LARGE particles flow better than small particles
TRUE
TRUE OR FALSE
Round particles flow better than needles (or other complex shapes)
TRUE
Angle of repose
By pouring a powder onto a plate you can measure the angle between the flat surface and the peak of the heap.
HIGHER ANGLE = HIGHER LEVEL OF COHESION
>50 degrees = poor flow
Angle of inclination
Coefficient of internal friction
μ=tanθ
* μ= coefficient of internal friction
* θ = angle of repose
Bulk density measurement
- Measure the density of the initial powder.
- Pour powder into tube.
- Turn on machine and let it consolidate the tapping the tube.
- Measure density of the powder after tapping.
Use hausner ratio to measure flowability
Hausner ratio
An equation that allows you to determine the flowability of a powder.
Df/Do
* Df = Final bulk density
* Do = Initial powder density
TRUE OR FALSE
A hopper determines the singular flow rate of the bulk powder
FALSE - Different zones form in the hopper of which have different flow rates.
Hausner ratio standards
<1.2 = good flow
>1.6 = poor flow
Hopper issues
‘Ratholing’ or ‘bridging’ is very common
Hopper benefits
They display the efficiency of and reproducability of flow.
