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Section 6. Chemistry
Abdurakhmanov Ilkhom Ergashevich, Applicant of the Department of analytical chemistry of the Samarkand state University Uzbekistan, Samarkand E-mail: ergash50@yandex.ru Kabulov Bahadir Jabborovich, Doctor. chem. sciences, Professor, Tashkent technical University, the head laboratories of State unitary enterprise "Science end progress" Uzbekistan, Tashkent, E-mail: kabulov@rambler.ru
Study of the dynamic and calibration characteristics of semiconductor sensors of Ammonia
Abstract: Revealed a linear territory of the signal of a semiconductor sensor of ammonia provides the definition of concentration in a wide interval. It is found that increasing the concentration of iron compounds in the gas sensing material leads to higher performance sensors. At the annealing temperature of 550 °C response time of the sensor reaches 14 s.
Keywords: Sensor, ammonia, performance, dynamic and calibration characteristics.
The most correct and correct solutions to the task rapid A test feature ofthe sensor ofammonia was accompanied
and accurate determination ofammonia in air and process by a continuous record of the transitional process diagram gases is the use of simple and available semiconductor sensors. In this regard, the development of highly effective semiconductor sensors for the determination of ammonia in the environment is an urgent issue. In [1; 2] studied a semiconductor sensor of ammonia.
The aim of this work is to study the dynamic characteristics and calibration of semiconductor sensors of ammonia.
Given the anticipated scope and high toxicity of ammonia, primary and satisfying conditions of use of the sensor should be time fast response. That is, the ammonia sensor should have good dynamic characteristics.
In environmental monitoring and control industrial emissions are usually measured the average concentrations ofgas impurities. For such measurements is acceptable time constant of the sensor in tens of seconds or a few minutes.
The performance of the obtained thin cover samples with respect to ammonia was measured on the example of standard gas mixtures of ammonia in air at 200 °C. In the experiments we used the gas mixture (GM) with ammonia concentrations of 50-500 mg/m 3.
tape recording device KSP-4. The value ofthe gas sensitivity (S) of the sensor was calculated by the formula
S= VRgaS (1)
Where: R — the electrical resistance of the cover in
air in the absence of gas, R is the electrical resistance
O ' gas
of the cover when exposed to a predetermined gas concentration.
Simultaneously, we measured the response time (tresp.) and recovery time (t ) sensors based on films of gas
' v recov/ O
sensitive material (gas sensitive material) ofthe composition SiO2/TiO2+5%Fe2O3, and Si02/Ti02+10% Fe2O3.
In experiments, each test point in the measurement range was characterized by six values: three for forward and three for reverse cycle measurement.
The analytical signal of the sensor was monitored with a digital voltmeter V7-35 after the establishment of a constant value (not less than 1 min after the filing of the instrument standard mixtures).
The results ofthe study. The results ofdetermining the dynamic characteristics of the SCS-NH3 are presented in table 1.
Study of the dynamic and calibration characteristics of semiconductor sensors of Ammonia
Table.1. - The dynamic characteristics of the sensor based on the films Si02/Ti02+I0% Fe2O3 при the effects of ammonia. (T= 600 °C)
The dynamic characteristics of the sensor *t 0,1 t0,65 t0.9 t p
the response time of the signal S. 1 S 1G 1S
the recovery time of the signal S. 2 7 14 2G
* t0i — the start time of the response; t0 65 — constant time, s; t09 — time us-development of testimony, with; Tp —full total measurement time, with
Research of gas sensitivity showed that the change in surface resistance of the cover in the direction of decreasing is observed within 10-15 seconds after receipt of ammonia in the measuring chamber.
Subsequent purging of the chamber with clean air
that does not contain ammonia, the resistance returns to the original value.
It is established that the value of the gas sensitivity and t and t depend on the content of the
response recovery L
catalyst in the gas sensitive material (GSM). (Table. 2.).
Table 2. - The dependence of response (sec.) sensor of ammonia from the content of the catalyst (Fe2O3) in the gas sensitive material annealed at 350 °C (the concentration of methane in the mixture 500 mg/m3)
№ Composition sensitivity material The response time of the sensor (t or t ), sec. v response 09' The recovery time of the sensor (t or t), sec. v recovery 01'
1 Si°2/Ti°2 63 83
2 Si02/Ti02+1%Fe203 55 61
3 Si02/Ti02+S%Fe203 22 27
4 Si02/Ti02+1G%Fe203 16 21
With increasing content of iron oxide in the cover there is a decrease in response time. Recovery time for purging the measuring cell with air ranges from 15 to 22 sec. and decreases with increase in the concentration of iron oxide in the cover. Therefore, increasing the concentration of iron compounds from 5 to 10% leads
to increase the performance of gas sensors in 1,21,4 times.
Based on the response time of a semiconductor sensor based on Si02/Ti02+10% Fe2O3 50 mg/m 3 of ammonia from the annealing temperature of gas sensitive material prividitsya in table.3.
Table 2. - The dependence of response (sec.) sensor of ammonia from the content of the catalyst (Fe2O3) in the gas sensitive material annealed at 350 °C (the concentration of methane in the mixture 500 mg/m3)
The composition of gas sensitive material Annealing temperature, °C
SiO2/TiO2+10%Fe2O3 3GG 3SG 4GG 4SG SGG SSG 6GG
The sensor response (тотк or т). sec.
34 24 19 16 1S 14 14
Cover Si02/Ti02+10%Fe203 annealed at a temperature of 300 °C are characterized by low gas sensitivity (S=0,06), compared with the samples annealed at temperatures 600 °C (S=0,17). Analysis of the dependence of the response (table.3.) samples of the cover annealed at temperatures 300-600 °C showed that the response time of the sensor depends on the annealing temperature of the cover and decreases with increasing annealing temperature in the temperature range from 300 to 550 °C. The minimum time constant (14 sec.) of the sensor based on Si02/Ti02+10%Fe203 is achieved at the annealing temperature of gas sensitive material 550 °C. Further improve-
ment ofthe performance of the sensors was not possible to the fact that at higher temperatures the stability is lost the heater and contacts the sensing layer and the heater. When checking concentrations of ammonia in the air by adjusting the amount of catalyst and increasing the temperature of annealing of a cover of gas sensitive material to the maximum possible managed to achieve the performance of the sensor based on titanium dioxide about 14 sec. It is established that the value of gas sensitivity, as well as t
O /' resp.
and t sensor of ammonia depend on the content of the
recov. -t
catalyst in the gas sensitive material. Increasing the concentration of iron compounds in the gas sensitive material
from 5 to 10% leads to increase the performance of gas sensors in 1,2-1,4 times.
At the annealing temperature of 550 °C response time of the sensor reaches a stable value (14 sec.) above which does not reduce the value of the indices of the sensor. The sensor response in the studied conditions, quite reproducible, and can be used to determine low concentrations of ammonia in air and
During the experiments, studied the calibration characteristics of the sensor of ammonia based on titanium oxide. To increase the sensitivity to ammonia on the titanium oxide was applied to the iron oxide, which is active and selective catalyst for the oxidation of ammonia by air oxygen.
Table.4. shows the dependence of the signal (S) of semiconductor sensors with different gas sensitive material on the concentration of ammonia.
process gases.
Table 4. - The dependence of the signal of the semiconductor sensor from the content of ammonia in the air (temperature experience — 350 °C)
The composition of gas sensitive material The content of ammonia in the air, mg/m 3
100 200 300 400 500 600 700 800 900 1000
sensor signal, ac/ct0
Si°2/TiO2 1,07 1,1 1,12 1,13 1,14 1,15 1,16 1,17 1,18 1,19
Si02/TiO2+1%Fe2O3 1,11 1,15 1,18 1,21 1,23 1,26 1,29 1,32 1,35 1,39
Si02/TiO2+5%Fe2O3 1,37 1,61 1,73 1,85 1,96 2,06 2,18 2,29 2,4 2,51
Si02/TiO2+10%Fe2O3 1,51 1,82 2,04 2,26 2,49 2,72 2,94 3,16 3,38 3,61
As shown, in a wide concentration range (20 to 1000 mg/m 3) the dependence of the signal of a semiconductor sensor of the concentration of ammonia in the calibration gas has a straightforward character.
The analysis presented in table.4. the data shows that the gas sensitive material based on SiO2/TiO2 and SiO2/TiO2-1% Fe2O3 is characterized by low sensitivity and selectivity to ammonia. The sensitivity threshold of sensors based on thin cover titanium dioxide is 20 mg/M 3 in the air. A sharp rise in the value of the gas sensitivity is observed for the sample with Fe content of 5-10%. Semiconductor sensors based on SiO2/TiO2-5% Fe2O3, and
SiO2/TiO2-10%Fe2O3 can detect NH3 gas impurities at the level of the TLV. 3
The conclusion. Thus, it was found that increasing the concentration of iron compounds in the gas sensitive material from 5 to 10% leads to increase the performance of gas sensors in 1,2-1,4 times. At the annealing temperature of 550 °C response time of the sensor reaches a stable value (14 sec.) above which does not reduce the value of the indices of the sensor. The results of the experiments revealed a linear territory of the signal, which determine the content of ammonia in a wide range of concentration.
References:
1.
Abdurakhmanov I. E., Murodova Z. B. Sattarova M. Dj. Highly sensitive automatic gas analyzer VG ammonia — NH3//The journal "Chemical industry". Russia. V. 92, No. 3, 2015. P. 138-141. 2. Abdurakhmanov I. E., Begmatov R. H., J. B. Kabulov. Study the influence of the amount of TEOS and acid (PH) on the properties of cover-forming solution.//Actual problems of humanitarian and natural sciences. No. 4, 2015. P. 12-17.
