PARTICLE SIZE ANALYSIS WITH MICRO SIEVES USING ULTRASONIC VIBRATIONS

A SIMPLE AND RELIABLE TECHNIQUE IS DESCRIBED WHICH AVOIDS DAMAGE TO THE MICROMESHES INVOLVED IN SIEVING MATERIAL BELOW 20 MICROMETRES USING ULTRASONIC VIBRATIONS. THE SIEVE IS DRIED TO CONSTANT WEIGHT IN AN OVEN BELOW 70 DEGREES C AND COOLED IN A DESICCATOR. THE SIEVE AND ABOUT 1 GRAM OF THE SAMPLE ARE WEIGHED TO A PRECISION OF + OR - 0.2MG. THE SIEVE IS THEN FITTED LOOSELY INTO A METAL RETAINER PLATE CONTAINING AN 8 CM-DIAMETER HOLE PLACED ON TOP OF A 500ML BEAKER CONTAINING LIQUID TO A DEPTH OF ABOUT 1 CM ABOVE THE IMMERSED SIEVING SURFACE. AS AN ADDITIONAL PRECAUTION A PIECE OF WIRE GAUZE OF ABOUT 60 TO 100 MESH IS INSERTED IN THE BEAKER TO ATTENUATE THE VIBRATIONS. THE BEAKER AND SIEVE ARE PLACED IN A CONVENTIONAL ULTRASONIC CLEANING BATH CONTAINING WATER UP TO THE LEVEL IN THE BEAKER. ULTRASONIC VIBRATIONS ARE GENERATED FOR 2 TO 3 MINUTES, THE BEAKER AND SIEVE ARE TAKEN OUT OF THE BATH AND THE SIEVE IS PLACED IN ANOTHER SIMILAR BEAKER CONTAINING FRESH LIQUID. THE PROCEDURE IS REPEATED UNTIL THE PASSAGE OF PARTICLES THROUGH THE SIEVE IS NEGLIGIBLE. THE SIEVE IS REMOVED, DRIED AT 70C TO CONSTANT WEIGHT, AND THE QUANTITY OF MATERIAL PASSED THROUGH THE SIEVE IS THUS DETERMINED.