Ultrasonics 228, sieving

A new separation and analytical procedure for the a and P phases in K136 alloy using ultrasonic sieving apparatus has also been reported [65]. 

Heavy metals, boron (B(V)), arsenic and total phosphorus were determined in the fraction < 20 pm to improve the comparability of the results. This fraction was separated from the freeze-dried and non-milled samples by ultrasonic sieving (Ackermann 1980). Metals were analysed after microwave-assisted digestion with aqua regia at 180 °C in closed vessels by inductively coupled plasma optical emission spectroscopy, atomic fluorescence spectroscopy (mercury) and hydride atomic absorption spectroscopy (arsenic). 

Analyzed by ultrasonic sieving method Measured by nitrogen adsorption method... 

Ultrasonication was reported for the extraction of triazines from soil, previously sieved to 2 mm and stored at -18 °C, prior to analysis using CC/NPD and CC/lTD. A 5-g soil sample was placed in a polypropylene column and extracted for 15 min with 4 mL of ethyl acetate in an ultrasonic bath at room temperature. Subsequently, the solvent was filtered and collected in a graduated tube, and the extraction was repeated for another 15-min period using a second 4-mL portion of ethyl acetate. The two extracts... 

The three silicates obtained from Wards Scientific Establishment and employed in this study are obsidian from St. Helena, California, microline from Ontario, Canada and albite from South Dakota. The bulk of the samples were crushed and sieved to between 211 and 423 (im. Fines were removed by repeated ultrasonic cleaning and decantation. Measured BET... 

Sample dried, sieved and ground extraction with ultrasonication in acetonitrile containing internal standard dilution with aqueous CaCl2 filtration from reverse-phase column with methanol/water... 

Percent chrysotile asbestos in bulk samples may be measured by X-ray powder diffraction (NIOSH Method 9000, 1984) sample dust grinded under liquid N2 wet sieved through 10-mm sieve sieved material treated with 2-propanol agitated in an ultrasonic bath filtered on a silver filter measured by XRD, using a Cu target X-ray tube. 

Microcline, albite and labradorite were obtained from Ward s Canada Limited. Cleaved crystal fragments and 60 mesh-sized samples were ultrasonically cleaned prior to use. Powdered samples (particle size < 25 ym) were prepared by grinding in a tungsten carbide ball mill, wet-sieving and washing in water. 

Additionally, wet sieving down to a mesh size of 5 gm can be realized by applying special sieves of pure nickel membranes. The material is fluidized in an ultrasonic bath. 

The process is repeated with sieves of increasing fineness and the residue weights collated. Finally, the process is repeated with the finest sieve and the fines are added to the dust collected initially. Brushing is not recommended for sieves with aperture less than 200 pm due to the possibility of damage. Sieves should be washed and dried after use. Ultrasonics should be used to remove particles clogging the apertures or these may be leached out if this can be done without damage to the sieve. 

Vorti-siv manufacture gyratory and ultrasonic lab sieves that include a de-blinding kit for sieving powders as small as 5 pm. Units operate at 1,750 or 3,450 rpm and have an 8, 10 or 12 in diameter screen. Options include stainless steel or explosive proof construction and continuous discharge chutes. 

Several manual methods of wet sieving using micromesh sieves have been described. Mullion [84] uses an 80 kHz, 40 W ultrasonic bath in which the micromesh sieve rests on a support, which, in turn, rests on a beaker in the bath. Sieving intervals are 5 min. with an initial load of 1 g. and the operation is deemed complete when no further powder can be seen passing through the sieve. 

The Vibrosonic sieve employs ultrasonic vibration of the separator mesh for industrial separation at high rates down to 400-mesh. 

This automatic wet sieving machine determines a single point on the size distribution curve in a few minutes without the need to dry samples [1,16]. The sieving vessel is first filled with slurry and topped up with water to a precise level to allow accurate determination of the mass of solids added (W ) by application of Archimedes principle. The fine fraction is next removed from the vessel through a discharge valve. Screening is hastened by propeller agitation and with ultrasonics to maintain the sieve mesh free... 

One way to test an ordered mixture is to pass the blend through a nest of sieves and assay each particle size fraction. The lesser the variation in potency across the cuts, the better the ordered mix. Note that this test is highly dependent upon how much energy goes into the sieving process. Shaking the sieves by hand would be expected to produce different results than using an ultrasonic method. 

Ultrasonic extraction of sieved sample with acetonitrile filtration through teflon filter... 

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