SU1260766A1 - Method of determining filter pore diameter - Google Patents

Abstract

The invention relates to the field of measurement technology and solves the problem of determining the diameter of pores with a size of one hundredth of a micrometer or less. The method consists in passing a control gas - benzene through a filter for a given pressure drop. Before measurements, select a reference filter with a known pore diameter d and with the material and pore length of the filter coinciding with the test one. Then calibration measurements are made on a filter of known geometry by measuring the dependence of benzene pressure over time from the low pressure side and determining from this dependence the diffusion delay time from the time a pressure drop is created until the steady-state flow of benzene through the filter is established. Similarly, the diffusion delay time for the filter under study is found to be 0, and the pore diameter is determined from the ratio d d 0 / c. 1 il. with (L with: ISD about About 05 about

Description

The invention relates to a measurement technique and can be used, in particular, to determine the geometrical characteristics of fine-porous membranes, namely, filters, having straight cylindrical channels, for example, nuclear filters. Regular geometrical filters and small dispersion of pore sizes of such membranes allows to achieve high selectivity in separating mixtures of gases and seats or cleaning them from mechanical impurities; less than 0.05 microns.

The purpose of the invention is to increase the accuracy of determining small values of pore diameters.

The drawing shows the dependence of the gas pressure in the chamber on time, the total view.

The method is carried out on a standard installation containing two chambers separated by a filter, in one of which a reduced pressure (vacuum) is created, with the possibility of recording the change in this pressure over time.

 The essence of the technique is as follows)

If one of the chambers of a volume divided into two parts permeable. filter, is filled to some pressure with gas, and the other is evacuated, then due to diffusion of this

gas through the filter, the pressure in the vacuum part will start to grow. However, this growth will not be observed. immediately, and with some time delay d (time of gas passing through the membrane). The drawing shows the dependence of the pressure P in the initially vacuumed up to 10 Torr of volumes on the time t. For sufficiently large t, the dependence (t) is becoming linear and intr-linear. The delay time of a diffu ae is defined as a segment of the time axis.

no, cut off by this straight line. The results of the experiments and the measurement of the delay time are well approximated by the following formula

:, iL

where 1 is the pore length;

A is a certain factor depending on the temperature, in the order of magnitude coinciding with the time of the sedentary life of gas molecules on the surface. The measurement wire on the reference filter FROM the same material with a known pore diameter d, is determined

0 d value A, where 9 - time

delays for the reference filter. From here

  : |.

0

five

0

five

o ° P values

 To ensure sufficient accuracy of measurements, the delay time should be in the range of 1–1000 s. Here, the lower limit is chosen from the condition of accurate recording of the time when the pressure differential is created, for which an error of less than 0.1 s cannot be achieved. The upper limit is associated with express measurement of the pressure at the filter outlet. The excess of this limit makes it impossible to record the change in pressure over time due to the limited sensitivity of the pressure sensor.

It was established experimentally that for pore diameters from 0.005 to 0.05 microns with a typical thickness of nuclear membranes of 10 microns, the delay time in the above range can be obtained for benzene at temperatures close to room temperature. Changing the room temperature to 40 K changes the delay time of benzene vapor by two

If pore size

unknown, then the temperature can be chosen experimentally. For this, experiments on determining the delay time are carried out successively for a series of temperatures through 40 K, starting for example from room temperature (this interval of temperature change provides for one of the values of T a delay time in the range of 1–1000 s).

° P values

Formula of invention

The method of determining the pore diameter φ 1ltra, which consists in passing a test gas through -1 ть-т tr when creating a pressure-gas differential across the filter, characterized in that, in order to improve the accuracy of determining small, diameters

then, benzene was used as a reference gas, the pressure drop across the filter was created by pre-evacuating the chamber separated by the test filter from the second chamber into which benzene was injected, the dependence of the benzene pressure in the evacuated chamber on the time after creating the pressure drop was recorded delay time from the moment of creating pressure drop to establishing steady flow

benzene through a filter, the same delay time is determined for a reference filter with a known pore diameter, and the pore diameter of the test filter is calculated by the ratio

1-70 f

where d, d - pore diameter of the test and reference filters, respectively

100 delay times for the test and reference filters, respectively.

Claims (1)

Claim A method for determining the pore diameter of the filter, which consists in passing the control gas through the filter when creating a differential pressure of gas on the filter, characterized in that, in order to increase the accuracy of determining small pore diameters, benzene is used as the control gas TG, the differential pressure on the filter is created by preliminary the evacuation of the chamber separated by the studied filter from 5 of the second chamber into which benzene is introduced, the dependence of the pressure of benzene in the evacuated chamber on time after anija pressure differential and is determined by ¹⁰ this dependence delay time from inception of the differential pressure before establishment of steady stream of benzene through the filter, similar to the delay time determined for the reference filter of known pore diameter, and pore diameter of the test, the filter was calculated from the ratio 1 1 О ^d = ^d o f> where d, d _o - pore diameter of the investigated and reference filters, respectively; - delay time for the studied and reference filters, respectively.