RU2094795C1 - Sensitive element of electrochemical sensor of partial pressure of hydrogen in gas mixtures - Google Patents

Abstract

FIELD: analytical engineering. SUBSTANCE: element consists of solid composite electrolyte and two electrodes, one of them made of platinum or palladium and the other of silver and intermediate layer of silver-silver nitrate. Composite electrolyte is composed of mixture of an alkali metal bisulfate (20-70 mol.%) and superfine silicon oxide powder. EFFECT: improved sensitivity. 1 dwg , 1 tbl

Description

The invention relates to analytical instrumentation and can be used in chemical, electronic and other industries and energy, as well as safety services to determine the partial pressure of H ₂ in gas mixtures.

A known element of the electrochemical sensor H ₂ potentiometric type, operating in the temperature range of 20-200 ^o C, consisting of 2 electrodes, one of which is made of Pt, and the other of Ag, Tl, TiHx or ZrHx, between which a thin layer is placed electrolyte Zr (HPO ₄ ) • 2H ₂ O [1] The values of the EMF arising between the electrodes depend on the hydrogen pressure. Such a sensitive element allows to measure the partial pressure of hydrogen in the range of 10-10 ⁵ ppm.

 The disadvantage of this element is that measurements can only be carried out in the presence of water vapor, i.e. only in a humid atmosphere. Otherwise, there is a rapid dehydration of the electrolyte and, as a consequence, the degradation of the sensitive element.

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где в качестве электролита (ТЭ) используют композиты, представляющие собой смесь Sb₂O₅ и одной из солей цезия с общей формулой CsH_x(ЭО₄)₂, где Э s или P, x 3 или 5. Данный элемент работает стабильно при комнатной температуре в реальных газовых смесях с переменной влажностью.The closest technical solution is a sensitive element, which is a solid-state galvanic circuit [2]

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where composites are used as the electrolyte (TE), which are a mixture of Sb ₂ O ₅ and one of the cesium salts with the general formula CsH _x (EO ₄ ) ₂ , where E s or P, x 3 or 5. This element works stably at room temperature temperature in real gas mixtures with variable humidity.

The disadvantage of this element is the narrow range of operating temperatures. At T> 60 ^° C, the degradation of the cell begins, apparently due to a chemical reaction between the electrolyte components, resulting in the formation of a poorly conductive compound.

 The invention solves the problem of expanding the operating temperature range of the sensor element of the partial pressure of hydrogen in gas mixtures in conditions of different humidity.

в качестве твердого электролита используется композит, изготовленный из смеси MeHSO₄, Me Rb, Сs, K и мелкодисперсного порошка SiO₂, взятых в соотношении,мол.):
MeHSO₄ 20-70;
SiO₂ Остальное
Композит, используемый в чувствительном элементе, стабилен в диапазоне температур 20-200^oC, выдерживает многократное термоциклирование без изменения характеристик. Проводимость композита зависит от состава и составляет 10^-2 10^-6 Ом^-1см^-1 в рабочем интервале температур. При содержании MeHSO₄ менее 20 или более 70 мол. композит имеет значительно более низкую проводимость, вследствие чего резко снижается чувствительность и увеличивается время срабатывания датчика.The essence of the proposed technical solution lies in the fact that in the sensitive element type

as a solid electrolyte, a composite made of a mixture of MeHSO ₄ , Me Rb, Cs, K and finely divided SiO ₂ powder taken in the ratio, mol.) is used:
MeHSO ₄ 20-70;
SiO ₂ Else
The composite used in the sensitive element is stable in the temperature range of 20-200 ^o C, can withstand repeated thermal cycling without changing the characteristics. The conductivity of the composite depends on the composition and is 10 ^-2 10 ^-6 Ohm ^-1 cm ^-1 in the operating temperature range. When the MeHSO ₄ content is less than 20 or more than 70 mol. the composite has a significantly lower conductivity, as a result of which the sensitivity decreases sharply and the response time of the sensor increases.

 The invention is illustrated in the drawing.

The sensitive element is a tablet of solid electrolyte 1, two electrodes are pressed to the ends of the electrodes, one 2 of platinum or palladium, and the other 3 of silver with an intermediate layer 4 of a mixture of Aq -Aq ₂ SO ₄ .

Example 1. Take a fine powder of SiO ₂ and mix it thoroughly with RbHSO ₄ in a ratio of 70 to 30 mol. A tablet is pressed from the mixture, on one side of which an electrode is sprayed from an Ag-Ag ₂ SO ₄ mixture, which is coated with silver paste. The finished tablet is heated at 220 ^o C for 5 minutes Then, the sensing element thus obtained is placed in a thermostatically controlled volume with a known concentration of hydrogen, and the EMF values between the electrodes are measured.

Example 2-4. In the conditions of example 1 take other compositions of the composite RbHSO ₄ -SiO ₂ . The test results are shown in the table.

Example 5. In the conditions of example 1 take a composite containing CsHSO ₄ and SiO ₂ in a ratio of 50 to 50 mol.

Example 6. In the conditions of example 1 take a composite containing KHSO ₄ and SiO ₂ in the ratio of 40 to 60 mol.

Thus, the proposed sensitive element operates at temperatures of 20-200 ^o C while the prototype [2] only at room temperature.

 The EMF values (mv) of sensitive elements of various compositions at different temperatures (accepted abbreviations: n / s values are unstable in time) are given in the table.

 Literature.

 1. N. Miura, T. Harada, Y. Shimizu, N. Yamazoe / Cordless Solid State Hydrogen Sensor Using Proton Conductor Thick Film / Sensors and Actuators, B1 (1990) p. 125-129.

 2. RF patent N 2038592, cl. G 01 N 27/407, 1995.

Claims (1)

The sensitive element of the electrochemical partial pressure sensor of hydrogen in gas mixtures, consisting of a solid composite electrolyte and two electrodes, one of which is made of Pt or Pd, and the other of Ag and the intermediate layer of a mixture of Ag-Ag ₂ SO ₄ , characterized in that the solid the composite electrolyte consists of a mixture of one of the acid salts of the alkali metal sulfate MeHSO ₄ and finely divided SiO ₂ powder, taken in the ratio, mol. MeHSO ₄ 20 70
SiO _{2 the} rest

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