RU2124718C1 - Analyzer for selective determination of hydrogen in air - Google Patents

Abstract

FIELD: analytical technics. SUBSTANCE: application area: space, mining, and other industries, in particular, cryogenic engineering. Analyzer contains casing, gas-inlet and gas-outlet canals, and semiconductor sensor based on In₂O₃ modified with CuO additives. Sensor is placed in individual chamber separated from analysis chamber by polymer diffusion membrane selectively passing hydrogen and being blown with gas containing no hydrogen. EFFECT: increased selectivity with regard to hydrogen. 3 dwg

Description

The invention relates to the field of gas analysis and can be used to selectively determine the content of H ₂ in various gas mixtures in space, mining and other industries, in particular in cryogenic technology.

Known [1] is a sensor for determining the content of H ₂ in gases, containing a ceramic substrate on which a heater is applied, metal contacts for measuring conductivity and a sensitive layer based on In ₂ O ₃ . When H _{2 is} supplied, the conductivity of the sensor sensitive layer changes as a result of H ₂ chemisorption on the In ₂ O ₃ surface.

However, this sensor is not selective with respect to H ₂ and when other gases (CO, CH ₄ , C ₃ H ₈ , C ₄ H ₁₀ ) enter the mixture, it also changes its conductivity as a result of their chemisorption. In addition, since the sensor operates at a temperature of 100 ^o C, it requires periodic regeneration.

The closest in technical essence to the present invention is a gas composition analyzer [2], containing a housing, channels for input and output of gases, a flow interrupter and a semiconductor sensitive element containing a non-conductive substrate with a heater deposited on it, contacts for measuring conductivity and a sensitive layer on ZnO based, modified with metallic Zn. However, this analyzer does not allow selective determination of the concentration of H ₂ in the gas mixture, since the sensitive element based on modified ZnO reacts to the appearance of O ₂ and H ₂ O in the mixture, and the gas flow interrupter placed in the analyzer body passes both H ₂ and other gases .

The technical task of the present invention is to increase the selectivity, sensitivity and speed of the analyzer, as well as expanding the dynamic range when determining the concentration of H ₂ .

The technical result in the implementation of the claimed device is that the analyzer body is divided into two chambers: a measurement chamber and an analysis chamber, between which a polymer diffusion membrane is placed that selectively passes H ₂ and does not pass other gases (O ₂ , H ₂ O), this measurement chamber is purged with a gas not containing H ₂ , and the semiconductor sensor is made on the basis of In ₂ O ₃ , modified 1-10 wt.% CuO.

A comparative analysis with the prototype showed that the claimed device, characterized by features including the placement of a semiconductor sensor in a separate chamber, isolated from the analysis chamber by a polymer diffusion membrane, selectively transmitting H ₂ , and purged with a gas that does not contain it, and also including the implementation of the sensor based on In ₂ O ₃ modified with CuO additives meets the eligibility criteria of the “novelty” invention.

 Comparison with the prior art showed that in the claimed technical solution, the result is obtained due to distinctive features that do not explicitly follow from the known technical solutions, which meets the eligibility criteria of the invention "inventive step".

In FIG. 1 shows a diagram of the proposed analyzer. The analyzer case for selective determination of the concentration of H ₂ in gases contains: a measurement chamber (1), a selective H ₂ sensor (2) based on In ₂ O ₃ , modified CuO (1 - 10 wt.%), A polymer diffusion membrane (3), placed between the measurement chamber (1) and the analysis chamber (4), equipped with nozzles (5) for supplying gases.

The analyzer works as follows. A gas not containing H ₂ is supplied to the measurement chamber (1) at a speed of 20 cm ³ / min, and an analyzed mixture containing H ₂ is supplied to the analysis chamber (4), while the change in the relative conductivity of the sensor (σ / σ _o ) is measured, due to chemisorption of H ₂ .

In FIG. Figure 2 shows, for comparison, the calibration curves of the sensor based on In ₂ O ₃ / CuO when feeding H ₂ into an inert gas in the absence of a membrane (curve 1) and when it is placed between the measurement and analysis chambers (curve 2), as well as when feeding into this mixture 5.5 vol.% O ₂ and 55 rel.% H ₂ O (curve 3). The supply of O ₂ and H ₂ O to the analyzed mixture (curves 2 and 3) practically does not affect the sensor signals, which confirms the high selectivity of the analyzer.

In FIG. 2 also shows that in the absence of a membrane in the analyzer case (curve 1), the sensor signals are almost insoluble at a concentration of H ₂ in the mixture above 1 vol.%. In the presence of a membrane (curves 2 and 3), the dynamic range for measuring the concentration of H ₂ expands to 41.5 vol.%, I.e. to the limit of explosive concentrations. Thus, the placement of the membrane in the analyzer body allows you to significantly expand the dynamic range for determining the concentration of H ₂ in the mixture. From FIG. Figure 2 also shows that in the presence of a polymer diffusion membrane in the analyzer, the sensor signals from exposure to H ₂ decrease by more than 100 times (curves 1 and 2). In this regard, when choosing the material of the sensitive layer of the sensor, its sensitivity to H ₂ is essential. The use of a sensor based on In ₂ O ₃ modified with CuO additives (1–10 wt.%) Makes it possible to increase the sensitivity and speed of the analyzer, as well as the selectivity of the sensor itself.

In FIG. Figure 3 shows the kinetic curves of the sensor signals in an inert gas and when H ₂ and O _{2 are} supplied in the absence of a membrane in the analyzer case. Figure 3 shows that the modification of the material of the sensitive layer of the sensor with CuO additives (1 - 10 wt.%) Leads to an increase in its sensitivity by more than 10 times (curves 1 and 2). In addition, the relaxation of the sensor signal based on In ₂ O ₃ / CuO to the initial value of the relative conductivity when the H ₂ feed is switched off is much faster compared to the sensor based on pure In ₂ O ₃ (30 and 120 sec, respectively), i.e. modification of the In ₂ O ₃ sensor with CuO additives can significantly increase the analyzer performance.

From a comparison of curves 1 and 3 in FIG. 3 it is also seen that the proposed sensor modification significantly increases the selectivity of the sensor itself with respect to H ₂ compared to O ₂ . The values of the sensor signals for H ₂ and O ₂ in comparable conditions differ by almost 100 times.

Thus, the choice of the proposed analyzer design with a sensor placed in a separate chamber isolated from the analysis chamber by a polymer diffusion membrane selectively transmitting H ₂ , as well as the choice of the sensor material based on In ₂ O ₃ modified with CuO additives (1 - 10 wt.% ), allow to increase the selectivity, sensitivity and speed of the proposed analyzer and to expand its dynamic range in the determination of H ₂ and thereby solve the technical problem.

Sources of information
1. British patent N 1526751, 1978.

 2. USSR author's certificate N 596870, G 01 N 27/00, 1976.

Claims (1)

An analyzer for the selective determination of hydrogen in gases, comprising a housing, channels for inputting and outputting gases, and a semiconductor sensor, comprising a non-conductive ceramic substrate with a heater deposited thereon, conductivity measuring contacts and a sensitive layer, characterized in that the semiconductor sensor is placed in a separate chamber, insulated from the analysis chamber by a polymer diffusion membrane that selectively transmits hydrogen and is purged with a hydrogen-free analyte gas, and the sensor itself is made on ove In ₂ O _3, CuO-modified additives in an amount of 1 ^o C 10 wt.%.

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