LA-920 Instruction Manual Chapter 1 Overview 1.1 Overview The measurement of particle size distribution is used for fundamental studies and quality control in production process in a many diverse fields such as fine ceramics, cement, pharmaceuticals, metal powders, industrial minerals and ores, coatings and adhesives, pigments and dyes, carbon black and other mineral additives and fillers used in the rubber plastics and paper industries, explosives, solid fules, food, drugs and beauty care emulsions, micelles, polymers- and others. Particle sizes ranging from 0.02 to 2000 microns are divided into 85 sectors, and the full range is measured at one time with no adjustments. Measurement time is adjustable, but usually 20 seconds is used. Many options such as a batch type cell holder, an auto-sampler, and a dispersion diluter are available. Note: Any sample cell other than those for the LA-920 cannot be used. 1.2 Configuration The LA-920 is configured as shown below. The sample carrying liquid is circulated by the centrifugal circulation pump. The computer screen is used for displaying and setting the conditions for both measuring, retrieving, and displaying data. There are two light sources: a long-life 632.8-nm He-Ne laser expanded by a beam expander and a blue(405 nm) monochromed tungsten lamp. The light emitted from the laser and the tungsten lamp is radiated on the particles suspended in the liquid. After the laser beam has been dispersed and scattered by the particles in the flow cell, it passes through the condenser lens and is focused on the forward ring silicon diode array , comprised of 75 separate detection elements. The scattered light from the tungsten lamp is sensed by 6 wide-angle silicon diode detectors, ranging in angles up to 138° from the forward direction. The intensity of this scattered light from both the laser and tungsten lamp is converted into electrical signals, which are then used to calculate the size distribution of the particles.

Fig 1-1 Configuration of LA-920 System

Chapter 2 Installation 2.2 Unpacking 1. Unpack the packing case. The standard accessories are included in the upper section of the case. Check them with Table 1 below. Table 1 LA-920 Accessory kit

Name Q’ty Remark Power cable 1 RS-232C cable 1 For connecting PC Instruction Manual 1 Program Operation Manual

1

Fuse 2 3.15A Time Lag Phillips screwdriver 1 System program disk (software)

8 3.5” 2HD type

LA-920 software disk 3.5” 2HD type Drain hose 1 m φ13.5/9.5mm Drain hose 1 m φ9.5/6.5mm

Hose end and socket 1 ea. Small hose band 2 Large hose band 2 Cotton swabs 1 carton 100 pcs./carton Tungsten lamp 1 50W, for mounting to main unit Caution: The main unit weighs approximately 55 kg (129lb). Be sure to use more than one person to lift or carry it. 2. Be sure to raise the LA-920 with a minimum of two persons holding the slots on each side of the internal carton. The carton is made up as shown in Fig. 2-1. Use the vinyl cover wrapped over the unit as a dust-cover after installing the unit. Also remove the desiccant pack from the vinyl cover. 3. Be sure to place the unit on the installation mount with a minimum of two persons holding both sides of the unit. Fig. 2-1 Unpacking Chapter 3 Names and Functions 3.1 Front and Top Views of Main Unit

Fig. 3-1 Front view

Pre-treatment section lid

Power Indicator

Pre-treatment section lid Sample dispersion chamber lid of the centrifugal pump recirculation system. Power Indicator

Sample chamber lid

Pre-treatment section lid

Fig. 3-2 Top view Sample dispersion chamber lid Sample cell chamber lid Lid Lid for sample chamber 3.2 Right Side View of Main Unit

Drain outlet

Fig. 3-3 Right side view Drain outlets, used to connect to the drain hoses. Autofill pump inlet, used to connect to customer dispersion liquid supply line or reservoir. Auto-diluter inlet, used to connect to auto-diluter dispersion reservoir. 3.3 Rear Panel of Main Unit

Connectors for options

Reset switch RS-232C connector

Vents for fan

Fuses

AC connector

Power switch

Fig. 3-4 Rear panel

Power switch Used to turn on the LA-920. AC connector Used to connect the power cable to. Fuses Fuses for the LA-920. Their ratings are 3.15A Time lag. Vents for fan Vents for the fan which is used to cool the power source. Never block them. RS-232C connector Used to connect the RS-232C cable from the PC to. Reset switch Pressing this switch resets the unit.

Connectors for options These connectors are used for the optional auto-sampler and reservoir. 3.4 Sample Cell Chamber

Retaining screws

Tube for circulation Sample cell holder

Fig. 3-5 Sample Chamber Sample cell holder A unit to hold the sample cell. Tube for sample recirculation A tube used to recirculate the sample through the cell. Retaining screws Screws used to retain the cell holder to the mount on the main unit. Lid Lid for sample chamber Chapter 4 Maintenance 4.1 Daily Care

At start-up 1) While warming up the unit, circulate dispersant fluid for a minimum of 30 minutes. 2) When the analyzer has been warmed up, drain off the dispersant fluid, inject a fresh supply of dispersant fluid, and circulate it briefly (for about 30 seconds) and drain it off again. Do this once again with another fresh supply of dispersant fluid. At shutdown Drain off the fluid in the cell, rinse, inject fresh dispersant fluid again, circulate for 3 minutes and drain off. If a water soluble-solution is used as the dispersant fluid, the circulation system can be cleaned more easily by injecting in 1-2 drops of a natural or weak alkaline liquid detergent. (Do not inject excessive detergent as this will hinder the rinsing operation.) *If the outer surfaces of the analyzer are dirty, clean them with a dry cloth or wipe off with a gauze dampened with a neutral detergent. *Clean the sample cell. 4.2 Cleaning the Cell 1. After making sure that there is no dispersant in the cell, loosen the four retaining screws holding the top sample cell transition piece on the cell holder, and remove the top transition piece. 2. Clean the cell and the O-ring with the dispersant. Use a cotton applicator or soft cloth for this purpose. Caution: Since the outside cell surface is coated so as to prevent any reflection of light, take care that it is not exposed to detergent or chemical agent when cleaning the cell. 3. Use a cotton applicator to clean the O-ring slits in the holder, top and bottom. 4. Fit the O-ring and the cell to the cell holder. Place the top transition piece on the cell holder and then turn the retaining screws clockwise to retain the cell. Caution : *If samples that adhere to the cell were measured, clean the cell, and also make sure that the sample does not adhere to the wet part of the cell. *If there is too much sample adheres, remove it from each part using sponge or a plastic scraper.

*The outside surface of the cell should be cleaned with a cotton applicator or soft cloth. Never scrub it, nor touch it with anything hard.

4.3 Replacing the Fuses If the fuses are blown, replace them with those delivered with the LA-920. 1. Turn off the power switch. 2. Disconnect the power cable. 3. Replace the fuses. There are two fuses. The locations of the fuses are shown in

Fig. 3-4. Never use any fuse that is not specified. 4. Connect the power cable. 5. Turn on the power switch. 6. Check to see that the LA-920 operates normally. Caution: If the fuses are still blown after the replacement, immediately turn off the power switch, disconnect the power cable, and then contact a service center. Never use any fuse other than those specified. 4.8 Storage After carrying out the shut-down procedure described above, drain off all the dispersant fluid, dry thoroughly, place the dust cover over the unit and store

carefully. The analyzer must be stored where it will not be exposed to temperatures exceeding a range of 5°(40°F) - 40°C(104°F). If the unit has been stored for a long time, be sure to carry out all the appropriate steps described above before attempting to conduct measurements. Appendix A. Specifications Principles of measurement Based on Mie scattering theory Range of particle size displayed 0.02 to 2000µm Measurement time Approx. 20 seconds, normally from start of measurement to display of data (max. 3 min). Amount of sample liquid required for measurement 10 mg to 1 g per measurement, about 200 ml of dispersant fluid when using the flow cell - This figure depends on the sample. Optical system Light source: 632.8 mm He-Ne laser, 1 mW Tungsten halogen lamp, 50 W Photo-cell detector: ∗75-division, ring shaped silicon photo-diode array ∗Silicon photo-diode x 12 Sample recirculation system ∗Ultrasonic chamber 30 W, 22.5 kHz. ∗Circulation pump Centrifugal pump, discharge volume 8 l/min (in case of distilled water), 15-step selection, teflon-tubing

∗Sample flow cell Tempaxglass Power 100/110 to 200/220 to 240 VAC, selectable, 50/60 Hz approx. 300 VA Communications RS-232C Proper operation temperature and humidity 10°(50°F) to 35°C (95°F) less than 85% RH (no condensation) Dimensions 690 (W) x 525 (D) x 355 (H) mm 17.2(W) x 20.6 (D) x 14(H) inch Weight Approx. 55 kg, 121 lb. Options ∗Reservoir Unit (for automatic concentration adjustment and rinsing) ∗Auto Sampler (automatic injection and measurement of up to 24 samples) ∗Fraction cell holder with magnetic stirrer *Fraction cell ∗Dry Aerosol Feeder B. Principles of Measurement This analyzer measures the particle size distribution by angular light scattering technique. The light scattered intensity of particles at the photo-cell detector is shown below. When light goes into a spherical particle of radius r, the following three types of light will be emitted, as shown in Fig.B-1. 1. Light which reflects at the outer surface of the particle 2. Light which passes through the inside of the particle and then reflects at the

inner surface of the particle

3. Light which passes through the inside of the particle, and refracts and continues

to pass through the particle. General geometrical handling of scattering phenomenon

All of these phenomena can be handled as light scattering. Generally, light scattering can be often explained by the Mie scattering theory which was obtained by a strict application of Maxwell’s electromagnetic equation. The Mie scattering theory is precise, but difficult to use. Therefore, a simple approximation is generally used; i.e., relationships between the incident wavelength λ and the particle radius r can be stated as:

When the particle size is considerably less than λ, it is considered to be Rayleigh scattering. When the particle size is considerably greater than λ, it is considered as Fraunhofer diffraction. According to Fraunhofer diffraction theory, the scattered light intensity distribution of a particle, as shown in Fig. B-2, can be expressed by the following equation:

( )I I

J xx

=

0

12

2 ........... 5.1.1

I0: Intensity at the center of the diffractive pattern J1: Fist order spherical primary Bessel function

x rsf

=2πλ

........... 5.1.2

r: Radius of particle s: The radial distance as measured from the optical axis λ: Wavelength of incident light f: Focal length of the lens According to the Mie scattering theory, when monochrome light enters a single spherical particle, the intensity, Iθ, of scattered light in a certain direction from that particle is, as shown in Fig. B-3, determined by (A) the particle-size parameter, α (= 2πr/λ) which is defined by the ratio of the circumferential length of the sphere to the wavelength of the incident light, λ, and (B) the relative refractive index, m, ( = µ2/µ1) which is the ratio of the refractive index of the particle to that of the medium. See the diagram below.

(IR

i iθ

λπ

=2

2 2 1 28)+ ........... 5.1.3

where λ : Wavelength of incident light R: Distance from the particle to the observation position. i1 and i2 denote the polarized components in which the progressive vibration directions of the incident light are vertical and horizontal to the observed surface.

( ) { }i nn n

a bn n n nn

11

22 1

1=

++

+=

∞

∑ π τ ........... 5.1.4

( ) { }i nn n

b an n n nn

21

22 1

1=

++

+=

∞

∑ π τ

where

( ) ( ) ( ) ( )( ) ( ) ( ) ( )

aS S mS S

S mn

n n n n

n n n n

=′ − ′

′ − ′β α α β

β α α βΦ Φ S

( ) ( ) ( ) ( )( ) ( ) ( ) ( )

bmS S S S

mS Sn

n n n n

n n n n

=′ − ′

′ − ′β α α β

β α α βΦ Φ

( )S Jn nα

παα

=+

2 1

2

( ) ( ) ( ) ( )C Jnn

nαπα

α= − − +12 1

2

( ) ( ) ( )Φn n nS iCα α= + α

( )( )πθ

θn nP=1

1sin

cos

( )( )τ∂∂θ

θn nP= 1 cos

J is the Bessel function and Pn(1) the “associated function” of Legendre, i.e., i = −1

m =µµ2

1

µ1 : Refractive index of light in medium µ2: Refractive index of light in particle β = ma

απλ

=2 r

The scattering intensity, Iθ, varies depending on the direction in which light scatters from the particle, i.e., according to the scattering angle. As shown in Fig. B-4, the scattered light is classified according to the scattering angle as follows: 0 9≤ < °θ 0 :forward scattering θ = °90 :side scattering 90 180°< < °θ :back scattering

The intensity, , of the scattered light is in an infinite series, as shown in Equation

5.1.4. Therefore, calculations will take a very long time, especially when the particle size is large.

Iθ

If the incident wavelength is constant, when the particle size is larger than the incident wavelength, the scattered light focuses almost entirely in only the forward direction, ∠90°, and varies depending on the particle size. More specifically, the relation between the particle-size distribution and the light-intensity distribution is the ratio of 1:1. Therefore, if the light-intensity distribution of the particle to be measured is known, its particle size can be determined. On the other hand, when the particle size is smaller than the incident wavelength, the scattered light gradually shifts toward the side and rear, and finally spreads in all directions. When the particle size is smaller than 0.1 µm, the absolute value of the scattered-light intensity varies much more than before. In this situation, the intensity distribution of the front scattering does not depend on the particle size, becoming almost constant.

Therefore, even if the particle size is different in this region, there will be no difference in the intensity distribution of the forward scattered light. Accordingly, the size of a very small particle can be no longer determined by only the information from the forward scattered light. C. Principles of the optical system used in the Model LA-920 The optical system in an ordinary laser-diffraction type analyzer condenses the forward scattering from a laser beam with a condenser Fourier lens and forms an image on the ring-shaped detector located at the focal distance. Using only this method, however, it is difficult to measure the range of small particle sizes, in particular, particles under 0.1 µm. Very small particles cannot be measured merely by means of the forward scattering using the wavelength of a He-Ne laser beam, i.e., 632.8 nm. To measure such particles, it is necessary to have either information from the side and back scattering or that from the polarization scattering intensity. Therefore, as shown in Fig. C-1, the new optical system in the Model LA-920 uses three separate sets of detectors, one each for the wide angle and back scattering, and a third detector for the forward scattering. The light source used for detecting scattered light at wide angles and back scattering in the Model LA-920 is a tungsten lamp, filtered at 405 nm. This means: (1) the small angle forward scattered light is conventionally given by the He-Ne laser and detected by the ring detectora array, and (2) the wide angle and back scattered light is given by the tungsten lamp and detected by individual photo-diodes located at larger angles from the forward detector array.

Fig. C-1 Measuring the side and rear scattered light of blue-colored (405 nm) light Particle size distribution analysis Particles of various sizes exist in an actual sample solution, and their scattering light differs according to their size. Equation 5.2.1 shows the relationship between the intensity distribution of the scattering light and the particle size distribution.

( ) ( ) ( )g K D f Dθ θ=∞

∫ ,0

dD ........... 5.2.1

where g(θ) : the intensity distribution of the scatted light K(θ,D): response coefficient of scattered light f(D): particle size distribution coefficient D: particle diameter θ: scattering angle In reality, measurement is performed by n number of detectors. As the Mie scattering theory is used in combination for the response function, the equation corresponding to equation 5.2.1 becomes equation 5.2.2.

( ) ( ) ( )g N K N Di f Di Di

n

==∑ ,1

∆ ........... 5.2.2

where g(N) : output of N-th detector K(N,D): response coefficient of N-th detector f(Di): Particle size distribution Di: i-th representative radius ∆D: particle size segment number The particle size distribution f(Di) is calculated from the relationship between the output of the detector (expressed by equation 5.2.2) and the response function of the detector. f(Di) is calculated on the basis of volume. The particle size distribution by area, length and number basis are calculated by equation 5.2.3 to 5.2.5.

Distribution by area basis = ( )

( ){ }f Di Di

f Di Dii

m

=∑1

........... 5.2.3

Distribution by length basis = ( )( ){ }

f Di Di

f Di Dii

m

2

2

1=∑

........... 5.2.4

Distribution by number basis = ( )( ){ }

f Di Di

f Di Dii

m

3

3

1=∑

........... 5.2.5

The specific surface area is calculated by equation 5.2.6, on the assumption that the particles being measured are perfectly spherical.

Specific surface area = ( ){ }( )6 1041

2 3×=∑ f Di Di cm cmi

m

........... 5.2.6

Di : representative particle diameter D. Spare Parts and Options Spare Parts Part number Fraction cell U802030100 Flow cell U802030000 Options *LY-201 Reservoir *LY-202 Autosampler *LY-203 Fraction cell holder (Please use together with Fraction-type cell) E. LA-920 RS-232C Specification

Transmission format The transmittance format is as follows. If the setting need to be changed, please contact HORIBA for advice and assistance. HORIBA will reset the setting as necessary. Table RS-232C Transmission format Baud rate : 9600 bps Data length : 8 bits Parity check : NONE Parity : NONE Stop bit : 1 RS-232C cable The LA-920 should be connected to the Compaq PC by the supplied cable. Connection diagram for the RS-232C cable

RS-232C Connector terminal numbers Cable end as seen from terminal side.

G. List of the Refractive Index Values Table of Inorganic Substances Substance Composition Sp-gr Refractive

index, n1

of particle

Relative refractive index (RRI) m(n0=water)

Lead white Pb3(CO3)2(OH)2 6.8 2.02 1.51 Zink flower ZnO 5.6 2.00 1.50 Titanium oxide(rutile)

TiO2 4.2 2.75 2.06

Titanium oxide(anatase)

TiO2 3.9 2.50 1.88

Zinc sulfide ZnS 4.0 2.37 1.78 Lead titanate PbTiO2 7.3 2.70 2.03 Ziconium oxide ZrO 5.7 2.40 1.80 Barium sulfate BaSO4 4.4 1.62 1.22 Barium carbonate

BaCO3 4.3 1.60 1.20

Calcium carbonate

CaCO3 2.8 1.58 1.18

Gypsum CaSO4.2H2O 2.4 1.55 1.16 Alumina Al2O3 - 1.66 1.25 Iron oxide Fe2O3 4.8 2.90 2.17 Red lead Pb3O4 8.9 2.42 1.82

Mercuric sulfide

HgS 8.0 2.95 2.21

Lead chromate PbCrO4 6.0 2.40 1.80 Cadmium sulfide

CdS 4.4 2.42 1.81

Zinc yellow ZnCrP4 3.5 1.87 1.40 Strontium yellow

SrCrO4 - 1.96 1.47

Barium yellow BaCrO4 4.4 1.63 1.22 Chrome green - 4.1 2.40 1.80 Emerald green - 3.2 1.97 1.48 Chromium oxide

Cr2O3 5.1 2.50 1.88

Cobalt green CoO.nZnO - 1.97 1.48 Ultra marine Na7Al6Si6O24S3 2.4 1.57 1.18 Prussian blue Fe4[Fe(CH)6]3 1.8 1.56 1.17 Cobalt blue CoO.nAl2O3 3.8 1.74 1.31 Celuriene CoO.nSnO2 - 1.84 1.38 Cobalt violet Co3(PO4)2 - 1.72 1.29 Manganese violet

(NH4)2Mn2(P2O7)2

- 1.70 1.28

Silver chloride AgCl - 2.08 1.56 Fluorite CaF - 1.43 1.07 Germanium Ge - 4.10 3.07 Potassium bromide

KBr - 1.58 1.16*

Potassium chloride

KCl - 1.80 1.32*

Lithium fluoride

LiF - 1.39 1.04

Magnesium oxide

MgO - 1.76 1.32

Silicon Si - 3.50 2.63 Quartz SiO2 - 1.45 1.09 Rock crystal SiO2 - 1.54 1.16 Diamond - - 2.41 1.81 Sapphire Al2O3 - 1.76 1.32 Magnesium MgF2 - 1.37 1.03

fluoride Mica Kal2(AlSi3O10)(

OH)2 - 1.59 1.19

BaCa2(C3H5O2)6 - 1.45 1.09 Barium fluochloride

BaC12.BaF2 - 1.64 1.23

Barium fluoride

BaF2 - 1.47 1.10

Barium phosphate

BaHPO4 - 1.62 1.22

Barium sulfide BaS - 2.16 1.59 Calcium alminate

Ca3Al2O3 - 1.71 1.28

Calcium borate CaO.B2O3 - 1.60 1.20 Carbon C - 1.92-0.522 1.88 Chromium oxide

Cr2O3 - 2.50 2.03

Copper oxide Cu2O - 2.71 1.27 Copper sulfate CuSO4 - 1.73 1.24 Magnesium orthoborate

3MgO.B2O3 - 1.65 1.10

Potassium carbonate

K2CO3 - 1.50 1.09

Potassium hydrogencarbonate

KHCO3 - 1.48 1.04

Potassium cyanide

KCN - 1.41 1.22

Potassium chlorate

KClO3 - 1.62 1.20

Sodium bromide

NaBr - 1.64 1.06

Sodium cyanide

NaCN - 1.45 1.12

Sodium metasilicate

Na2SiO3 - 1.52 1.14

Sodium sulfate Na2SO4 - 1.55 1.28 Strontium SrCr2O7.3H2O - 1.71 1.08

dichromate Strontium fluoride

SrF2 - 1.44 1.58

Strontium sulfide

SrS - 2.11 1.22

Zinc metasilicate

ZnSiO3 - 1.62 -

Iron Fe - 2.4-1.4i - Zinc Zn - 2.4-5.5i - Gold Au - 0.34-3.2i - Silver Ag - 0.19-3.4i - Copper Cu - 0.6-3.6i - Aluminum Al - 1.6-5.4i - Antimony Sb - 3.2-5.0i - Magnesium Mg - 0.4-4.6i - Manganese Mn - 2.5-4.0i - Nickel Ni - 1.8-3.6i - Platinum Pt - 2.9-4.5i - Taken from 1) “Handbook of chemistry and physics”., C.R.C. Press, 2)”American Institute of Handbook”., MaGraw-Hill and 3) “The Merck Index”., MERCK & Co., Inc. ∗n0 of this value is methanol. Table of Organic Substances Substance Composition Sp-gr Refracti

ve index, n1

Relative index of refraction m(n0=water)

Asphalt -- - 1.63 1.22 Ebonite - - 1.66 1.25 Opal - - 1.44 1.08 Canadian balsam - - 1.52 1.14 Amber - - 1.54 1.16 Ivory - - 1.54 1.16 Vinyl chloride resin - - 1.54 1.16 Vinyliden chloride - - 1.61 1.21

resin Vinyl acetate resin - - 1.46 1.10 Silicon oil - - 1.40 1.05 Tetrafluoroethylene resin

- - 1.35 1.01

Nylon - - 1.53 1.15 Polyethylene - - 1.53 1.15 Polystyrene - - 1.60 1.20 Methylmethacrylic acid resin

- - 1.49 1.12

Melamine resin - - 1.60 1.20 Taken from 1)”Handbook of chemistry and physics” ., C.R.C. Press, 2) “American Institute of Handbook”, MaGraw-Hill and 3) “The Merck Index”., MERCK & Co., Inc. H. Sampling and Dispersion 1. Sampling Methods A representative sample is required in order to measure the particle size distribution of powders or particles suspended in a liquid. This measurement sample must, therefore, have the same particle size distribution as the overall sample. Obviously, when extracting measurement samples from a large reaction vessel, sample drawn from the top will have a different particle size distribution from samples drawn from the bottom. Small and heavy particles collect at the bottom of the vessel. This is called “segregation.” Taking samples from the upper and lower levels of the vessel is appropriate if the degree of particle settling is to be measured, but for particle size distribution measurements, meaningless, unreproducible data will be obtained unless suitable sampling techniques are employed. Sampling methods for powders 1. Take samples of equal weight from throughout the material. 2. Use a twin divider or rotary splitter. 3. Use the conical quartering or flow division method. (see Figs. H-1 and H-2.) 4. Disperse a large amount of the sample in a 215-315 ml dispersion medium.

5. Disperse evenly with ultrasonic energy or a stirrer. 6. Draw off a measurement sample while agitating and pour it into the cell. Particles suspended in a liquid 1. Do not dilute at once in a large amount of dispersion medium, but carry out the dilution over several smaller stages. 2. Agitate well while diluting. 3. Dilute in the same dispersion medium as the medium used in the original sample. 4. Disperse evenly with ultrasonic energy or a stirrer. 5. Draw off a measurement sample while agitating and pour it into the cell. Although the concept is rather difficult to explain, the sampling method must be chosen to suit the properties of the sample, as some particles (particularly fine particles) adhere or cluster together if they are made damp by humidity. Particles in solids 1. Dilute the solid containing the particles in an appropriate solution (a) Use the diluted samples as the measurement sample. (b) Remove only the particle and measure. Clean until the dissolved solid has completely been removed and extract the particles. All further operations are the same as in (a).

Fig. H-1

Fig. H-2

2. Dispersing Methods for Samples As the LA-920 carries out measurements with the particles in a diluted state, the dispersed state of the particles is an important factor in measurement accuracy. Even if the sampling of powders is carried out correctly, large particles that should not exist are measured and the distribution is unnatural if particles agglomerate. Alternatively, when a dispersant of the sort that dissolves the powder is used, particles are measured to be smaller than they are, and this error causes inaccurate results. In order to carry out accurate measurement without any of the above problems, the dispersant used and the dispersion method must be chosen carefully. Dispersion Methods Samples with Stable Particles The sample can be irradiated with ultrasonic energy from the internal ultrasonic

probe in the flow loop, and the agglomerated particles are thus dispersed. The ultrasonic time depends on the sample. However, 10 seconds to 1 minute is normally adequate. If vibration is carried out for too long, the particles may coagulate or be damaged. However, the ideal ultrasonic time must be experimentally determined for each sample in order to thoroughly disperse the solution. The LA-920 allows an ultrasonic time of up to 30 minutes to be set. The LA-920 allows the power to the ultrasonic probe to be adjusted also. The higher the power setting, the more ultrasonic vibration is employed and the more the particles are dispersed. The power setting can be varied from a low setting of 1 to a high of 7. Samples with Unstable (Fragile) Particles When measuring such particles using the flow cell, do not apply ultrasonic vibration. If even this damages the sample, conduct the measurement by placing a sample that has been dispersed manually in the small volume cell. Selecting the Dispersant It is important that the dispersant properly “wets” the sample powder. The dispersant must be one that does not cause coagulation, dissolving, swelling or chemical reaction. Water is used in most cases. However, in some cases, measurement may be carried out using organic solvents such as ethanol or ethylene glycol. Effect and Type of Dispersant Powder samples are generally charged, and may coagulate or may not be sufficiently dispersed due to the interaction with the solution. The role of the dispersant is to increase this interaction and to disperse each and every one of the particles. Widely used dispersants are sodium hexametaphosphate and sodium pyrophosphate. Surfactants are also used for hydrophobic (preferentially wet by oil or air) or lipophilic (preferentially wet by oil) particles. However, if there is an excessive amount of dispersant, the dispersant will coagulate. Therefore, care must be taken regarding the concentration and the type of dispersant

to be used. The concentration of the dispersant depends on the type of dispersant. A concentration of about 0.1-0.2% is widely used due to its stability.

Table H-1 shows typical examples of samples and dispersants. Table H-1 Sample Dispersant BaCO3 Ethanol CaCO3 0.2% NaHMP*, ethanol, isopropyl alcohol MgCO3 Ethanol Al2O3 0.2% NaHMP CeO2 0.2% NaHMP MgO Ethanol SiO2 0.2% NaHMP TiO2 0.2% NaHMP Fe2O3 Ethylene glycol Al(OH)3 0.2% NaHMP, ethanol Ca(OH)2 Ethanol Mg(OH)2 Ethanol SiC 0.2% NaHMP Si3N4 0.2% NaHMP

Cu Ethylene glycol Ceramics raw materials 0.2% NaHMP, ethylene glycol Clay De-ionized water, 0.2% NaHMP, 0.1%

surfactant Cement 0.2% NaHMP, ethanol Coal dust 0.1% surfactant Fly ash 0.2% NaHMP, 0.1% surfactant Toner 0.2% NaHMP, ethylene glycol Dyes O-xylene Carbon black 0.1% surfactant Gypsum Ethanol Wax De-ionized water, 0.1% surfactant Latex De-ionized water, 0.1% surfactant Coffee, cocoa De-ionized water Chocolate Food oil Powdered milk Octanol Pepper 0.1% surfactant Medicine Xylene ∗NaHMP stands for sodium hexametaphosphate.