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Chapter 18 Micromeritics

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Homework Chapter 22 ( 경구용 고형제 ) (pp ) 내용의 정리 / 요약 Hand writing 할 것 Due date: Nov 11 (pm 5 시 )

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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

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Micromeritics Science and technology of small particles

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PARTICLE SIZE AND SIZE DISTRIBUTION

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Particle Size Surface diameter(d s ) The diameter of a sphere having the same surface area as the particle Volume diameter(d v ) The diameter of a sphere having the same volume as the particle

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

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Average Particle Size Fig. 18-1

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Particle Size Distribution Frequency distribution curve Fig. 18-2

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Particle Size Distribution Cumulative percent curve Fig. 18-3

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

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

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

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METHODS FOR DETERMINING PARTICLE SIZE

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

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Microscopic Method 장점 particle 의 shape 을 알 수 있다 단점 번거롭다 operater 간 오차가 심하다 only two dimensions ( 길이, 폭 )

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

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

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

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Sedimentation The diameter is obtained by gravity sedimentation

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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

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Sedimentation Reynolds number R e R e > 0.2 Stoke’s law cannot be used

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PARTICLE SHAPE AND SURFACE AREA

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Specific Surface The surface area per unit volume (S v ) or per unit weight (S w ) 단위용량당의 표면적 단위중량당의 표면적

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METHODS FOR DETERMINING SURFACE AREA

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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

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Adsorption Method Fig

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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

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DERIVED PROPERTIES OF POWDERS

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

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Porosity ( Void volume (v) : the volume of space Bulk volume (V b ) : occupied volume True volume (V p )

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Packing Arrangements Fig

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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

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Densities of Particles Bulk densityTap density Granule densityTrue density

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

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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

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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

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