Link points to Internet Archive / others. Not hosted by InfraLens. Details
IS 4961:1968 is the Indian Standard (BIS) for determination of particle size of powders by air elutriation methods. This standard specifies the method for determining the particle size distribution of fine powders using an air elutriator. The method involves separating particles based on their terminal settling velocity in a rising stream of air, making it suitable for materials too fine for standard sieving.
Determination of particle size of powders by air elutriation methods
Overview
Status
Current
Usage level
Specialized
Domain
Materials Science — Sieves, Sieving and Other Sizing Methods
Serves the same general purpose of particle sizing but uses a modern, fundamentally different technology (laser diffraction).
Key Differences
≠The Indian standard specifies the Gonell air elutriator, which separates particles into discrete fractions. Modern standards like ISO 13320 (laser diffraction) provide a continuous, high-resolution particle size distribution.
≠Air elutriation is a slow, manual process taking hours to complete. In contrast, methods like air-jet sieving (EN 196-6) or laser diffraction (ISO 13320) are significantly faster and often automated, providing results in minutes.
≠IS 4961 determines the aerodynamic equivalent diameter based on settling velocity. This is physically different from the sieving diameter (EN 196-6) or the equivalent spherical diameter from light scattering (ISO 13320), making direct numerical comparison difficult.
≠The reproducibility of air elutriation is generally lower than modern methods due to high sensitivity to operator technique, sample agglomeration, and electrostatic effects.
Key Similarities
≈The fundamental physical principle of separating particles based on their terminal velocity in an upward air stream is identical to that described in the historically equivalent BS 3406-3.
≈Both IS 4961 and its historical counterparts specify a similar apparatus: a vertical elutriation tube with controlled airflow, where finer particles are carried upwards and collected.
≈The primary result is expressed as the mass percentage of the powder in different size fractions, determined by gravimetric analysis (weighing) of the sample before and after separation.
≈All standards, including IS 4961 and modern alternatives, emphasize the critical importance of proper sample preparation, specifically ensuring the sample is dry and de-agglomerated for accurate analysis.
Parameter Comparison
Parameter
IS Value
International
Source
Primary Apparatus
Gonell's air elutriator with three tubes of specified dimensions.
Air-jet sieving apparatus with a rotating slotted nozzle and a specified sieve (e.g., 45 µm).
EN 196-6:2018
Separation Mechanism
Laminar upward air flow lifts particles with a terminal velocity less than the air velocity.
A jet of air from a rotating nozzle disperses particles and carries fines through a sieve mesh.
EN 196-6:2018
Typical Sample Mass
Approximately 10 g.
2.5 g ± 0.05 g (for 45 µm sieve).
EN 196-6:2018
Result Type
Mass percent of material in several discrete size fractions (e.g., <30 µm, 30-60 µm, >60 µm).
Mass percent of material retained on a single specified sieve (e.g., residue on a 45 µm sieve).
EN 196-6:2018
Test Endpoint Criteria
Elutriation is stopped when the rate of collection of fines becomes negligible (e.g., less than 0.01 g in 5 minutes).
Sieving is stopped when the mass passing through the sieve in 1 minute is less than a specified amount (e.g., 0.025 g).
EN 196-6:2018
Apparatus Description
Specifies Gonell's air elutriator.
Describes various elutriators, including the Gonell and the Roller analyser.
BS 3406-3:1963
Airflow Control
Controlled via a manometer and regulating valve to achieve specific air velocities for size cuts.
Controlled via manometers and valves to achieve desired separating velocities.
BS 3406-3:1963
⚠ Verify details from original standards before use
Key Values3
Quick Reference Values
Typical applicable particle size range5 to 75 microns
PrincipleSeparation based on terminal velocity in an upward air current
Air requirementsDry, clean, and at a constant measured flow rate
Key Formulas
V = k * D^2 — Relationship between terminal velocity (V) and particle diameter (D) based on Stokes' Law
Tables & Referenced Sections
Key Tables
No tables data
Key Clauses
Clause 3 - Principle
Clause 4 - Apparatus
Clause 5 - Preparation of Sample
Clause 6 - Procedure
Clause 7 - Calculation and Expression of Results
Frequently Asked Questions3
What is air elutriation?+
It is a laboratory process for separating particles by size or density using a vertically rising stream of gas, typically air.
Why use this method instead of sieving?+
It is used for particles that are too fine for practical analysis by sieving, generally those smaller than 75 microns (200 mesh).
What is the underlying principle of this test?+
The method is based on Stokes' Law. In a rising air current of a specific velocity, smaller/lighter particles are carried upwards while larger/heavier particles fall down, allowing for separation into different size fractions.