RU2107279C1 - Method of determination of nuclear membrane porosity - Google Patents

Abstract

FIELD: membrane filters based on nuclear track membranes. SUBSTANCE: membrane is placed in irradiation chamber, and it is irradiated by beam of particles accelerated in cyclotron. Separation of signals associated with pores is performed by measuring the energetic spectrum of particles passed through pores and directly through membrane film. Then areas of energetic peaks of particles passed through pores and membrane film are determined, and porosity is ground by their relation processing from expression

, where N₀ is number of particles recorded in section of energetic spectrum near maximum energy E₀; N₁ is number of particles recorded in section of energetic spectrum near minimum energy E₁; N¹ is number of particles recorded in section of energetic spectrum in intermediate area between E₀ and E₁. EFFECT: more effective determination of nuclear membrane porosity. 2 dwg

Description

 The invention relates to the field of membrane filters based on nuclear track membranes used for the purification of drinking inlets and water for medications, for filtering blood plasma and biological fluids, for filtering air in extremely clean rooms (hospital operating rooms, industrial premises for the production of precision microelectronics, compact production drives).

 Known methods for determining the porosity of nuclear membranes [1,2].

где
ε - общая пористость; V_тв - объем твердой части образца; V_м- объем образца мембраны в целом. Однако прямой метод является деструктивным, т.е. связан с разрушением образца. Другим недостатком прямого метода является то, что он учитывает не только открытые, но и закрытые поры, что искажает информацию.1. The direct method. The sample is destroyed and the volume of the solid part of the porous sample is estimated [2]. The porosity is determined by the formula

Where
ε is the total porosity; V _TV is the volume of the solid part of the sample; V _m - the volume of the sample membrane as a whole. However, the direct method is destructive, i.e. associated with the destruction of the sample. Another disadvantage of the direct method is that it takes into account not only open, but also closed pores, which distorts information.

где
G_об - масса образца; a_i и ρ_i - соответственно процентное содержание и плотность i-й составной части мембраны.Weighting method [2]. Calculate the volume fraction by the formula

Where
G _about - the mass of the sample; a _i and ρ _i are the percentage and density of the i-th membrane component, respectively.

 However, this method can be applied in cases where the composition of the membrane is known, as well as the content and density of each component of the membrane. The weight method provides information about all pores (it simultaneously takes into account open and closed pores) and, accordingly, distorts information about the performance of membranes.

где
V₀ и

- объем сосуда с образцом и без образца соответственно: P₁ и P₂ - начальное и конечное давления в сосуде. Однако метод расширения газа является весьма грубым, он имеет невысокую точность.The method of gas expansion [2]. A membrane sample is placed in a vessel filled with gas, then this vessel is connected to another, from which the gas is evacuated. Knowing the initial P ₁ and final P ₂ pressure in the vessel, calculate the value

Where
V ₀ and

- the volume of the vessel with the sample and without the sample, respectively: P ₁ and P ₂ - the initial and final pressure in the vessel. However, the method of gas expansion is very crude, it has a low accuracy.

где
G_об-масса образца, насыщенного жидкостью, ρ_ж - плотность жидкости.Impregnation method [2]. A sample of the membrane, previously weighed, is saturated with a wetting liquid and weighing is repeated, after which ε _o

Where
G _{r is the} mass of the sample saturated with liquid, ρ _W is the density of the liquid.

 However, for thin membranes this method is also poorly suited due to a large error in the determination of porosity.

 An impregnation method is also known in combination with the optical method, when a membrane sample is brought into contact with the surface of an isosceles glass prism, which is a surface of total reflection. As filling under the liquid, the fraction of the base area of the prism, on which the total reflection is disturbed, increases. However, the impregnation method in combination with the optical method has low accuracy in determining the porosity of membranes.

 All considered known methods for determining the porosity of membranes have low accuracy.

 The essence of the proposed method is to conduct an energy analysis of particles, for example, helium ions (6-8 MeV) or nitrogen ions (16.2 MeV) that have passed through a nuclear track membrane oriented relative to the ion beam so that the pore axes (parallel to each other) are parallel to the ion trajectory of the collimated beam. The ratio of the areas of the energy peaks of the particles that passed directly through the film and through the pores in it determines the total area of pores per unit surface, i.e. determines the porosity of the nuclear membrane.

 An additional advantage of the proposed method for determining the porosity of nuclear membranes is the ability to determine the conicity of the holes of the nuclear membranes, since the ions that shot through the conical part of the holes (pores) have intermediate energy.

 An example implementation of the method.

To determine the porosity of the nuclear track membrane (5.3 μm thick), the latter is placed in the irradiation chamber with a cyclotron beam of nitrogen ions accelerated to an energy of E ₀ = 16.4 MeV. The energy analysis of particles passing through the film and the pores in it is carried out using a semiconductor detector and a pulse analyzer. Nitrogen ions passing directly through the pores in the nuclear membrane do not change their initial energy E ₀ , while ions passing through the film lose part of the energy in it and have a reduced energy E 'at the output.

In FIG. Figure 1 shows the characteristic energy spectrum of nitrogen ions that have passed through a track membrane. The spectral regions near E ₀ and E ₁ correspond to particles that flew through the membrane without collisions and through the main layer of the film, respectively. Ions, one way or another, shot through the cone-shaped part of the holes (pores), have an intermediate energy E ¹ .

где
N₀-число частиц, зарегистрированных в участке энергетического спектра вблизи максимальной энергии E₀;
N₁- число частиц, зарегистрированных в участке энергетического спектра вблизи минимальной энергии E₁;
N¹-число частиц, зарегистрированных в участке энергетического спектра в промежуточной области между E₀ и E₁.Membrane porosity is determined based on the expression

Where
N _{0 is the} number of particles recorded in the energy spectrum region near the maximum energy E ₀ ;
N ₁ is the number of particles recorded in the energy spectrum region near the minimum energy E ₁ ;
N ^{1 is the} number of particles recorded in the energy spectrum in the intermediate region between E ₀ and E ₁ .

 From the spectrum shown in FIG. 1, using the formula (5), the surface porosity ε ≈ 7% was obtained.

где
N₀ и N¹ то же, что и в формуле (5).The proposed method allows for a membrane of thickness t to evaluate the shape and size of the conical part of the pores (Fig. 2). The assessment of the ratio of pore diameters on the surface of the film d ₁ and in the cylindrical part d ₀ (Fig. 2) is carried out according to the formula

Where
N ₀ and N ^{1 is} the same as in formula (5).

 Thus, the proposed method allows us to determine the porosity of the membrane with sufficient accuracy for practical applications.

Claims (1)

A method for determining the porosity of nuclear membranes by isolating and processing signals associated with pores, characterized in that the membrane is placed in the irradiation chamber and irradiated with a beam of particles accelerated at the cyclotron, and the selection of signals associated with pores is carried out by measuring the energy spectrum of particles passing through the pores and directly through the membrane film, then the areas of energy peaks of the particles passing through the pores and the membrane film are determined, and their porosity is determined based on the expression

where N ₀ is the number of particles recorded in the energy spectrum region near the maximum energy E ₀ ;
N ₁ is the number of particles recorded in the energy spectrum region near the minimum energy E ₁ ;
N 'is the number of particles recorded in the energy spectrum in the intermediate region between E ₀ and E ₁ .

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