Análise granulométrica por técnicas que se baseiam na sedimentação gravitacional: Lei de Stokes

Abstract

A caracterização tecnológica de materiais engloba, principalmente, a determinação de propriedades físicas. Entre estas está a determinação do tamanho das partículas e a distribuição e também a determinação das diferentes fases e dos constituintes químicos ali presentes. Como a grande maioria das partículas são de forma irregular, faz-se necessário utilizar técnicas de análise de tamanho que se baseiam em similaridades geométricas, como é o caso de diâmetro equivalente, determinado pelos métodos que utilizam a lei de Stokes, aplicada em regime laminar. Equipamentos mais modernos, como é o caso do sedigraph, possibilitam a determinação do tamanho de partículas até 0,1mim, devido à conjugação da velocidade terminal de sedimentação da partícula e à absorção dos raios X pela suspensão em análise. Porém há de se lembrar que essas técnicas devem ser aplicadas para materiais puros ou para materiais que contenham fases, cujas densidades são muito próximas.<br>Sizing and size particles distribution is very important in materials technological characterization. In general the particles have irregular shape, so the methods used to determine the particle size are based on geometrical similarity, like equivalent diameter that are determined by techniques that use the Stoke's law. This law is applied only in laminar flow. With nowadays technological development is possible to analyze sizes until 0.1 mum using the sedigraph analyzer that apply the Stoke's law plus the X-ray absorption by dispersion of particles in water environment. In order to use correctly these methods it is very important that the material have to be pure or if there are more than one phase the density of those should be very close. So the calculation of particles size present will be correct

Assessing the control exerted by soil mineralogy in the fixation of potentially harmful elements in the urban soils of Lisbon, Portugal

“…The percentage of sand fraction between 2 and 0.075 mm was obtained by wet sieving using ASTM 75 micron sieve. The sand fraction between 0.075 and 0.050 mm, silt and clay fractions were quantified by sedigraph, (Lima and Luz 2001).…”

Adsorption of lead (Pb) in strongly weathered tropical soil (Ribeira Valley region - Brazil)

“…The suspension was placed in Sedigraph and the sieved fractions were dried in an oven at 50 °C and weighed. The particle size and the granulometric fractions are estimated based on the Stokes law and the measurement was carried out by X-ray absorption (Lima and Luz, 2001). The determination was also carried out adding only distilled water to the sample.…”

A comparative study of particle size distribution using analysis of variance for sedimentation and laser diffraction methods

“…A particle falls due to the force of gravity in any fluid medium and during its movement is subject to a resistive force, whose magnitude depends on the fluid-dynamic regime and the morphological aspects of the particle. When the resistive forces (thrust and friction) equalize with the force of gravity, the particle reaches its terminal velocity, also known as sedimentation velocity, and falls at a constant rate [1,3]. As studies have advanced, methods based on Stokes' law were joined with laser diffraction.…”