Page 1 :
1
Page 2 :
What is Micromeritics?, The Science and Technology of small, particles is known as Micromeritics., , 3
Page 3 :
Properties of Powders, 1., , Fundamental properties :-These, properties relate to the individual particle., , 1., , Derived properties :- They are dependent, on fundamental properties & define the, factors relating to their measurement., , 3
Page 4 :
Fundamental properties:1., Particle size and size distribution, 2., Particle shape, 3., Particle surface area, 4., Particle weight, 5., Particle number, Derived properties:, 1., Density of powders (a) bulk density (b)tapped, density (c) granular density (d)true density, 2., Flow properties of powders, 3., Porosity, 4., Bulkiness, 4
Page 5 :
fundamental properties of, powders, , 10
Page 6 :
I. Particle size, Denoted in micrometers, , Particle size determination-Methods, Optical Microscopy, Sieving Method, Sedimentation Method, Conductivity Method(particle volume), , 6
Page 7 :
1.Optical Microscopy, Particle size in the range of 0.2 – 100 µm can be, measured.
Page 8 :
8
Page 9 :
Procedure:, 1. Eye piece of the microscope is fitted with a, micrometer., 2. This eye-piece micrometer is calibrated using a, standard stage micrometer., 3. The powder sample is dispersed in a suitable, vehicle in which it does not dissolve and its, properties are not altered. (eg. water, paraffin oil.), 4. This sample is mounted on a slide and placed on, the stage under the objective of microscope., 5. Around 625 particles are visualized. their, d14iameter is noted and mean is computed.
Page 10 :
Advantages, , One can view particles, Any aggregates detected, Contamination of particles detected, Easy and simple, Disadvantages, , Length and breadth can be detected but depth or, thickness of particles cannot be measured, Slow, time consuming , tedious, inaccurate, Number of particles to be measured is more
Page 11 :
2. Sieving Method, ⚫ Sieving, , method is an ordinary and simple, method., , ⚫, , 11
Page 12 :
12
Page 13 :
Method:, ⚫ A sieve stack usually comprises 6-8 sieves., ⚫ Powder is loaded on to the coarsest sieve of the, stack and then it is subjected to mechanical, vibration for specified time, eg 20 minutes., After this time, the powder retained on each, sieve is weighed, The particles are considered to be retained on, the sieve mesh with an aperture corresponding, to the sieve diameter., The size is estimated as per the standards, given in pharmacopoeia, 13
Page 14 :
14
Page 15 :
15
Page 16 :
Advantages- Inexpensive, Simple, Rapid,, , Disadvantages- lower limit is 50 microns, Powder if moist, can cause clogging of apertures, Attrition between particles during the process, may cause size reduction, giving inaccurate results.
Page 17 :
3. Sedimentation Method, ⚫ In, , this method particle size can be determined, by examining the powder as it sediments out., Sample preparation: Powder is dispersed in, a suitable solvent, , 17
Page 18 :
Andreasen pipette method:, , In this method , known volumes of, suspension are drawn off and the, concentration differences are measured, with respect to time., It involves measuring the % of solids that, settle with time in a graduated vessel., , 18
Page 19 :
36
Page 20 :
Construction:, ⚫ The Andreasen fixed-position pipette, consists of a graduated cylinder which can, hold about 500 ml of suspension fluid., ⚫ A pipette is located centrally in the cylinder, and is held in position by a ground glass, stopper so that its tip coincides with the, zero level., ⚫ A three way tap allows fluid to be drawn, into a 10 ml reservoir which can then be, emptied into a beaker or centrifuge tube.
Page 21 :
Method:, ⚫ A 1% suspension of the powder in a suitable, liquid medium is placed in the pipette., ⚫ At a given intervals of time, samples are, withdrawn from a specified depth without, disturbing the suspension., ⚫ The amount of powder can be determined by, weight following drying or centrifuging;, alternatively, chemical analysis of the, particles can be carried out., 21
Page 22 :
The particle size is determined in terms of stokes’, diameter (the diameter of a particle measured during, sedimentation at constant rate) using modified, Stokes' equation., , ⚫ dst: stokes’ diameter, ⚫ n:, , viscosity of medium, ⚫ h: sedimentation height, ⚫ ps- pf: difference in density of particle and fluid, ⚫ Fg: force of gravity, ⚫ t: sedimentation time, 22
Page 23 :
4.Conductivity methods, There are various subtypes. Two popular methods areElectrical stream sensing zone method (Coulter, counter), Laser light scattering methods, , 23
Page 24 :
Electrical stream sensing zone method(Coulter, counter), Sample Preparation:, ⚫ Powder samples are dispersed in an electrolyte, to form a very dilute suspension., ⚫, , 24
Page 25 :
Method, ⚫ The particle suspension is drawn through an, aperture accurately drilled through a sapphire, crystal set into the wall of a hollow glass tube., ⚫ Electrodes, situated on either side of the, aperture are surrounded by an electrolyte, solution., ⚫ These electrodes monitor the change in, electrical signal which occurs when a particle, momentarily occupies the orifice and displaces, itsown volume of electrolyte.
Page 26 :
The volume of electrolyte fluid which is, displaced in the orifice by the presence of, a particle causes a change in electrical, resistance between the electrodes which, is proportional to the volume of the, particle., , 26
Page 27 :
Advantage:, Particle size ranging from 0.5 – 500 microns, Gives number distribution, Particle volume measured, and can be converted to diameter., Accurate, sensitive, fast technique., 4000 particles per second can be counted., , Disadvantage, Expensive, , 27
Page 28 :
28
Page 29 :
29
Page 30 :
II., , Surface Area Determination, , 1. Adsorption method:, ▪ Surface area is most commonly determined based on, Brunauer-Emmett-Teller (BET) theory of adsorption., ▪ Most substances adsorb a monomolecular layer of gas, under certain conditions of partial pressure of gas and, temperature., ▪ The adsorption process is carried out at liquid nitrogen, temperatures -196˚C., ▪ Once surface adsorption has reached equilibrium, the, sample is heated at RT and Nitrogen gas is desorbed. Its, volume is measured., ▪ As each N2 mol. occupies fixed area, one can compute, surface area of pre-weighed sample., 30
Page 31 :
2. Air Permeability method:, , Powder is packed in sample holder, Packing appears as series of capillaries, Air is allowed to pass through the capillaries at, constant pressure, Resistance is created as air passes through, capillaries thus causing pressure drop., Greater the surface area greater the resistance, Air permeability is inversely proportional to the, surface area, 31
Page 33 :
Derived properties of, powders, , 51
Page 34 :
Derived properties of powders, ⚫ Volume,, , density,, porosity,, flow, properties etc. are the, properties, derived from fundamental properties., ⚫ e.g. Volume can be calculated from the, diameter of the particle., ⚫ However, derived properties can also, be calculated without the use of, Fundamental properties.
Page 35 :
DENSITY:, True density, bulk density/tapped density, granule density, True density-voids and pores not included, , 53
Page 36 :
Bulk Density Apparatus, Bulk density, , = Mass of the powder, Bulk volume, , Tapped bulk density, = Mass of the powder, , Tapped Bulk volume, , 36
Page 37 :
True density: volume occupied by voids (interparticle spaces) and intraparticle pores are not, included in this measurement., , Determined by helium displacement method, and liquid displacement method., , 37
Page 38 :
Powder flow properties, ▪, , P’ceutical powders may be broadly classified, as free-flowing or cohesive., , ▪, , Most flow properties are significantly affected, by changes in particle size, density,, electrostatic charges, adsorbed moisture., , ▪, , Good flow property is required for easy and, uniform flow from hopper to die cavity, ensuring accurate weight and dose., 66
Page 39 :
Angle of repose is calculated for estimating flow, properties., , It is defined as the maximum angle possible, between the surface of a pile of the powder, and the horizontal plane, , 39
Page 40 :
40
Page 41 :
Fixed funnel method (keeing height constant), Fixed cone method (keeping diameter constant), Tan Q=h/r, , Q=tan -1 h/r
Page 42 :
Powder flow properties estimation, ▪, , A, , volume, of, powder, is, filled, into, a, graduated glass cylinder and repeatedly tapped for a, known duration. The volume of powder after tapping is, measure., ▪, , % compressibility (Carr’s index), = (bulk volume- tapped volume) x 100, bulk volume, , Hausner’s ratio = tapped density/ Bulk density, Or, Bulk volume/ tapped volume, 69
Page 43 :
Flow description, , % Compressibility, , Excellent flow, , 5 – 15, , Good, , 16 – 18, , Fair, , 19 – 21, , Poor, , 22 – 35, , Very Poor, , 36 -40, , Extremely poor, , 40
Page 44 :
Compres, sibility, Flow, Index, Characte, (%), r, 10, , Excellent, , Hausner, Ratio, , Flow Property, Excellent, , Angle of, Repose, (degrees), 25–30, , 1.00–1.11, Good, , 31–35, , Fair—aid not, needed, , 36–40, , 11–15, , Good, , 1.12–, 1.18, , 16–20, , Fair, , 1.19–, 1.25, , 21–25, , Passable, , 1.26–, 1.34, , Passable—may, hang up, , 41–45, , 26–31, , Poor, , 1.35–, 1.45, , Poor—must agitate,, vibrate, , 46–55, , 32–37, , Very poor, , 1.46–, 1.59, , Very poor, , 56–65, , >38, , Very, very, poor, , >1.60, Very, very poor, 7, 0, , >66
Page 45 :
Packing properties (Porosity), Porosity definition:, It is the ratio of the, volume of voids between particles, plus the, volume of pores, to the total volume occupied, by, the powder, including voids and pores., A set of particles can be filled into a volume of space in, different ways., This is because by slight vibration, particles can be, mobilized and can occupy a different spatial volume, than before., This changes the bulk volume because of, rearrangement of the packing geometry of the, particles.
Page 46 :
Packing properties (Porosity), Example: :, A set of monosized spherical particles can, be arranged in many different geometric configurations., In Fig.a, when the spheres form a cubic arrangement, the, particles are most loosely packed and have a porosity of, 48%, In Fig.b, when the spheres form a rhombohedral, arrangement, they are most densely packed and have a, porosity of only 26%, The porosity used to characterize packing geometry is linked, to the bulk density of the powder., ., 72
Page 47 :
73
Page 48 :
Packing properties (Porosity), Thus bulk density, is a characteristic of a powder rather than, individual particles and can be variable., Thus,, powder can possess a single true, density but can have many different bulk, densities, depending on the way in which the, particles are packed and the bed porosity., , 74
Page 49 :
Factors affecting the flow properties, of powder, 1. Alteration of Particle’s size & Distribution, 2. Alteration of Particle shape & texture, , 3. Alteration of Surface Forces, 4. Formulation additives (Flow activators)
Page 50 :
Alteration of Particle’s size & Distribution, There is certain particle size at which powder’s flow, ability is optimum., Coarse particles are more preferred than fine ones as they, are less cohesive., The size distribution can also be altered to improve, flowability by removing a proportion of the fine particle, fraction or by increasing the proportion of coarser, particle’s such as occurs in granulation.
Page 51 :
Alteration of Particle shape & texture, Particle’s Shape, Generally, more spherical, particles, have, better flow properties than more irregular, particles., , Particle’s texture, Particles with very rough surfaces will be more, cohesive and have a greater tendency to, interlock than smooth surfaced particles.
Page 52 :
Alteration of Surface Forces, Reduction, of, electrostatic, flowability., Electrostatic chargescan, be, altering process, , chargescan, , improve, , reduced, , by, , onditions to reduce frictional contacts., Moisture content of particle greatly affects powder’s, flowability., Adsorbed, surface moisture, films tend to, increase, bulk density and reduce porosity., Drying the particles will reduce the cohesiveness and improve, the flow., Hygroscopic powder’s stored and processed under low, humidity conditions.
Page 53 :
Formulation additives (Flow activators), Flow activators are commonly referred, glidants., , as, , Flow activators improve the flowability of, powders by reducing adhesion and cohesion., e. g. Talc, maize starch and magnesium stearate., , a
Page 54 :
POWDER-DISTRIBUTION CURVES, 1. FREQUENCY DISTRIBUTION CURVE, No or weight of particles within a size range vs mean particle size, , Uneven size reduction in powders-unsymmetric curve
Page 56 :
2) Log-normal distribution curve, Y-axis: frequency, X axis: log mean particle size, , Advantage:- more symmetrical
Page 57 :
3) Cumulative frequency distribution curve, Cumulative % oversize/undersize against particle size
Page 58 :
4) Log probability plot, X axis: log particle size, Y axis: Cumulative % frequency
