The working zone in the interpolar area of the Faraday balance: an approach to testing the magnetic force factor stability criterion

Abstract

Abstract. Due to rapid development of the scientific and applied research in magnetic control and magnetophoresis of ferro-and ferromagnetic disperse fraction of various technological, natural and industry-specific media, the Faraday method is again in high demand as it is mainly aimed at defining magnetic susceptibility of solid and heterogeneous samples of small volumes. Based on the appearing (and then measured) ponderomotive force impacting the sample, the method allows accurate determining of single particles magnetic susceptibility by using the data of the sample represented by a conglomerate of the particles of such a fraction. In addition, it is mentioned that to date there is still a great gap in the methodology of the Faraday method as there are no exact recommendations on choosing both the form of the polar pieces of the Faraday balance and the positioning of the sample (the location of the working zone) in the interpolar area. Owing to these drawbacks, the well-known and long-time used Faraday method cannot be considered substantiated to a satisfactory degree. Thus, in our point of view, the treatment of the results obtained earlier with the help of the method should be cautious. In our work, we experimentally defined and substantiated an approach to identifying a working (local) zone, viz. the zone with stable values of the magnetic force factor -the product of the field intensity and induction by its gradient. The approach features the relative phenomenological analysis and is exemplified by polar pieces of non-traditional spherical form. It has been demonstrated that in order to state the fact of mere existence of this zone (and its location) in the interpolar area, the coordinate (usually nonlinear one) characteristic of intensity or induction, which is obligatorily obtained in an experiment, should have an inflexion, which guarantees a functionally extreme view of the following coordinate characteristics both of the gradient and that of the force factor. We also established the coordinates and the length of the working zone in a specific interpolar area.

Option of the Optical-mechanical Positioning of the Sensor and Sample in the Magnetometer. Determination of Magnetic Susceptibility of Powders and particles

“…Consequently, from the standpoint of the creation of a guaranteed working region, the using of spherically shaped pole pieces (Fig. 2) appears to be one of the most effective solutions to the problem of selecting the pole pieces for a Faraday balance [18][19][20]. (4), which is written for polynomial (3) of 5th and 4th degree correspondingly It should be used analytical (phenomenological) approximation at analysis of characteristic Bwith subsequent mathematical differentiation and obtaining gradBcharacteristic herewith obvious identifies an extremum's absciss.…”

“…(4), which is written for polynomial (3) of 5th and 4th degree correspondingly It should be used analytical (phenomenological) approximation at analysis of characteristic Bwith subsequent mathematical differentiation and obtaining gradBcharacteristic herewith obvious identifies an extremum's absciss. In this case it is appropriate using, for example, an approximation function of polynomial [18][19][20]:…”

Magnetic Susceptibility of Powders and Magnetic Particles (Modified Inclusions of Iron Oxides) Carbon Sorbents

“…In more frequent cases, when it is necessary to deal with dispersed samples of small volume, it is preferable to use the ponderomotive method. Based on the Faraday approach [5,6,[12][13][14][15], i.e. on the direct measurement of the ponderomotive (magnetic) force F, acting on a sample of small volume V, placed in a certain "point" of an inhomogeneous (gradH ≠ 0) magnetic field with an intensity H (averaged over the sample volume), the method makes it possible to calculate using the well-known expression [16][17][18][19][20][21][22][23][24][25][26] in the following form:…”

“…where μ0 = 4π 10 -7 H/m is the magnetic constant. The development of this method is the use of hemispherical poles in the corresponding magnetometer, which ensures the creation of the required working area (with a stable field inhomogeneity) for placing the studied sample [5,6,[12][13][14][15]. Secondly, after obtaining the experimental concentration (with argument γ) dependence of the data of χ , an assessment of the features of its trend should be given.…”

On the mutual consent of the coordinates of the interpolar zones of gradient stability and the force factor for the tip-hemispheres of different diameters

“…Первый -на основе использования электромагнитной системы (блока, состоящего из обмоток намагничивания, сердечников и полюсных наконечников) [1][2][3][4][5], второй -на основе коротких (в том числе сверхпроводящих) катушек [6][7][8], третий -на основе постоянных высокоэнергетичных магнитов (например, Nd-Fe-B) [9; 10]. В [11][12][13] обосновано оригинальное решение о целесообразности использования в магнетометрах первого типа (самых многочисленных) полюсных наконечников-полусфер. Оно аргументировано тем, что в этом случае в радиальном направлении плоскости симметрии межполюсной области специально получаемая координатная характеристика индукции B является извилистой.…”