# Chapter 18 Micromeritics

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Chapter 18 Micromeritics

Homework Chapter 22 (경구용 고형제) (pp. 563-577) 내용의 정리/요약 Hand writing할 것
Due date: Nov 11 (pm 5시)

Contents Particle Size and Size Distribution
Methods for Determining Particle Size Particle Shape and Surface Area Methods for Determining Surface Area Derived Properties of Powder

Micromeritics Science and technology of small particles

PARTICLE SIZE AND SIZE DISTRIBUTION

Particle Size Surface diameter(ds) Volume diameter(dv)
The diameter of a sphere having the same surface area as the particle Volume diameter(dv) The diameter of a sphere having the same volume as the particle

Particle Size Projected diameter(dp) Stokes’ diameter(dst)
The diameter of a sphere having the same observed area as the particle Stokes’ diameter(dst) An equivalent sphere undergoing sedimentation at the same rate as the asymmetric particle

Average Particle Size Fig. 18-1

Particle Size Distribution
Frequency distribution curve Fig. 18-2

Particle Size Distribution
Cumulative percent curve Fig. 18-3

Particle Size Distribution
Log-normal distribution curve Fig. 18-4

Particle Size Distribution
Log-probability curve Fig. 18-5

Particle Number (N) Number of particles per unit weight
e.g. if particle = sphere Example 18-2

METHODS FOR DETERMINING PARTICLE SIZE

Microscopic Method Based on number distribution of different particle size Range : m >200 counts ( counts)

Microscopic Method 장점 particle의 shape을 알 수 있다 단점 번거롭다
operater간 오차가 심하다 only two dimensions (길이, 폭)

Optical Microscopy 2 : Feret’s diameter 3 : Projected diameter
Fig. 18-7 1 : Martin diameter 2 : Feret’s diameter 3 : Projected diameter

Sieve Method This method uses a series of standard sieves
Range : m 20 mesh 100 mesh No opening

Sieve Mesh number number of openings per inch Sieve opening
actual size of openings between wires Sieve opening

Sedimentation The diameter is obtained by gravity sedimentation

Sedimentation Stoke’s law v : rate of settling h : distance of fall in
time t s : density of particle 0 : density of dispersion medium g : acceleration due to gravity 0 : viscosity of medium

Sedimentation Reynolds number Re Re > 0.2
 Stoke’s law cannot be used

PARTICLE SHAPE AND SURFACE AREA

Specific Surface The surface area per unit volume (Sv) or per unit weight (Sw) 단위용량당의 표면적 단위중량당의 표면적

METHODS FOR DETERMINING SURFACE AREA

Adsorption Method The volume in cubic centimeters of gas adsorbed per gram of adsorbent may be plotted against the pressure of the gas at constant temperature

Air Permeability Method
The principle resistance to the flow of a fluid, such as air, through a plug of compressed powder is the surface area of the powder The flow rate through the plug, or bed, is affected by the degree of compression of the particles the irregularity of the capillaries

DERIVED PROPERTIES OF POWDERS

Derived Properties of Powders
Porosity (공극률) Packing arrangement (충전배열) Densities of particles (입자밀도) Bulkiness (분말용적) Flow properties (유동성) Compaction (압축성)

Porosity (e) Void volume (v) : the volume of space
Bulk volume (Vb) : occupied volume True volume (Vp)

Packing Arrangements Fig e = 26% e = 48%

Densities of Particles
True density () Density of the actual solid material Granule density (g) (Particle density) The mass of particles devided by the volume as determined by the liquid(mercury) displace method Bulk density (b) (Apparent density) The mass of a powder divided by the bulk volume

Densities of Particles
Bulk density Tap density Granule density True density

Bulkiness Bulkiness(bulk) is specific bulk volume, the reciprocal of bulk density

Light vs. Heavy Powders Light(경질) : low bulk density or
large bulk volume Heavy(중질) : high bulk density or small bulk volume Light powders Heavy powders

Flow Properties A bulk powder is some what analogous to a non-Newtonian liquid(plastic flow, dilatancy) Flow property is affected by particle size, shape, porosity, density, surface texture Measurement : angle of repose() (= f(roughness)) tan  =   : coefficient of friction