SAJJAD KHUDHUR ABBASCeo , Founder & Head of SHacademy

Chemical Engineering , Al-Muthanna University, IraqOil & Gas Safety and Health Professional – OSHACADEMY

Trainer of Trainers (TOT) - Canadian Center of Human Development

Episode 36 : What is Powder Technology?

What is Powder Technology?All the technology which concerns itself

with the handling or processing of powders, or materials in particulate form

- production, storage, transportation, mixing, dusting, characterization, packing, crushing and milling

Important role for medicines, food stuffs, plastics, metals, fertilizer, cement and etc.

A prominent academic discipline The roots of powder technology - in the areas of material handling and

processing.

What is Powder?What is Powder? We define powders as materials consisting of particles in the size

range 0-10 mm.

Like fluids and gas, powders can exhibit many complex physical and chemical characteristics, which play an important role in the selection of powder processing technologies.

grain

detergent

TABLE 1: The important powder characteristics required for the selection or TABLE 1: The important powder characteristics required for the selection or dimensioning of equipments (CEMA, 1971)dimensioning of equipments (CEMA, 1971)

Density/Bulk density AttritabilityDustiness Electrical propertiesSize distribution CorrosivityPlasticity Stability/ReactivityShape HygroscopicityAeratability Moisture contentFlow properties HardnessExplosivity CompressibilityErisivity CombustibilityStickiness Frictional propertiesCoating tendency Cohesiveness

Why is Powder Technology Why is Powder Technology important?important?

Proper design and handling of these fine particles often makes the difference between success and failure.

Failure to consider the particle science involved in a process can result in very expensive or unpleasant consequences.

Some 75% of chemical manufacturing processes involve small solid particles (fine particles) at some point.

Chapter 1: Particle Size Distribution

3.1: Selecting a Method and Sampling Regular shaped particles can be accurately described by giving the shape and a number of dimrnsions: e.g. Sphere-radius, Cube-side length etc. However, no single physical dimension can adequately describe the size of an irregularly shaped particle. Thus we need to make a selection.

a) Tepung pulut b) Tepung ubi c) Tepung beras

Rajah 1: Gambar daripada analisis imbasan mikroskop elekrtron bagi zarahan tepung.

Selecting the method for determining particle size (or size distribution)

i) Select a definition of particle size that is appropriate for the application.

E.g. for pneumatic conveying -- where the appropriate definition is the diameter of a sphere with the same settling velocity -- use a sedimentation method (Stoke’s diameter)

* For flow though packed or fluidised beds -- where the appropriate definition is the diameter of a sphere having the same surface to volume ratio as the particle -- measure the specific surface area.

ii) Select a method of measurement that is appropriate to the definition;

Some alternative definitions of particle size are: Diameter of a sphere which has the same property as the particle itself -- that is, the same volume, same settling velocity, etc.

Diameter of a circle which has the same property as the projected outline of the particle -- that is, the same projected area or same perimeter Linear dimension measured parallel to a particular direction

Equivalent circle diameter

Cirle with area equaled to projected area of particle.

Martin’s diameter

Line bisecting projected area

Feret’s diameter

Parallel tangents

Figure 3.1: Some diameters used in microscopy

Volume diameter, dv

Actual particle

Surface diameter, ds

Surface –volume diameter, dsv

Fig. 3.2: Comparison of equivalent sphere diameters.

Table 3.1: Comparison of equivalent sphere diameters

Shape 

Sphere passing the same sieve aperature, dA

CuboidCylinder 

33

Sphere having the same volume, dv

Sphere having the same surface to volume ratio, dsv

3.062.38

1.951.80

Shape 

CuboidCylinder 

Sphere having the same surface area, ds

3.832.74

Thus, in practice it is important to use the method of size measurement which is directly gives the particle size

which is relevant to the situation or process of interest.

Some definations and approximations.3/1

vV6

d

As = (dv2)/4

sAA

2/1

sAd

da = 1.40 dA

dst = 0.94 dA

dv 1.13dA

dsv 0.87dA

dv dsv dA Bagi zarah berbentuk sfera atau hampir sfera

For particles with, 0.8, where

(1/= )

A population of particles is described by a particle size distribution (PSD).PSD is often presented as a graph of the logarithm of the total number of

particles smaller than particle diameter d against the diameter itself, d (cumulative curves) or as frequency distribution curves.

This plot is based on counting particles in a series of adjacent size ranges often called channels.

The distributions can be by number, surface, mass or volume (where particle density does not vary with size the mass distr. = volume distr.)

Description of populations of particles

00.0050.01

0.0150.02

0.0250.03

0.035

0 20 40 60 80 100Particle size, d (m)

dF/d

d or

f(d)

(m

-1)

00.20.40.60.8

11.2

0 20 40 60 80 100Particle size, d (m)

F

Fig. 3.3 Differential frequency

distribution (dF/dd) or f(d)

Fig. 3.4 Cumulative frequency

distribution, F

0

0.1

0.2

0.3

0.4

0.5

0 5 10 15 20

Particle size d,m

fv(d) (by volume)fs(d) (by surface)

fN(d) (by number)

f(d) (m-1)

Fig. 3.5: Comparison between distributions

Common methods of displaying size distribution:

1. Arithmetic-normal distribution

2. Log-normal Distribution

Describing the population by a single number•In practice, we require to describe the particle size of a population of particles (millions of them) by a single number.

•The options available: the mode, the median and means.

00

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100g(d)

F

Area = g(d)

Definations of means

g(d) Means/notations

(d) Arithmetic, da

(d^2) Quadratic, dq

(d^3) Cubic, dc

(log d) Geometric, dg

1/d Harmonic, dh

Ai

iA

dx

1d

svi

iSV

dx

1d

From differential frequency distributions, the means can be calculated as:

T

iiln N

dNd

T

iilm M

dMd

2/1

T

2i

sn NdN

di

3/1

T

3i

vn NdN

di

3ii

4i

wn dN

dNd

i

Methods of particle size distribution:Laboratory sieving

•Commonly used for size analysis, using sieves up to 16 mm aperture, though usually in the range of 50 m to 3 mm. The size of coarser particles is determined by direct measurement.

•Based on a linear dimension, generally assuming spherical particles

•Mean particle diameter retained by a screen is the sum of the aperture of the screen on which the material is retained, plus the aperture of the next largest screen, divided by 2.

•Mean particle diameter of a sample is the sum of the mass fractions retained on each screen multiplied by the mean diameter of particles retained by that screen.

 

Fig. 3.6: Sieves BS 1377, 1975

3: Particle Size Distribution from sieving analysis --The results of a sieve analysis (using the example below) may be presented as a plot of:

•cumulative percent undersize (falling through) vs aperture size •cumulative percent oversize (retained on screen) vs aperture size

•weight or percent retained on each screen used in sequence versus aperture size (or average diameter) The horizontal axes (aperture size or average diameter) may be on an arithmetic or on a logarithmic scale.

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