M. V. Vinokurova

Chemisorption of hydrogen sulfide on lead sulfide

The hydrogen sulfide chemisorption on lead sulfide at 22–100°C is studied by static testing in a vacuum and by pulsed chromatography. It is established that H2S is sorbed in reversible and irreversible forms and that the process is accompanied by the sample charging. Irreversibly sorbed hydrogen sulfide is removed by heating the sample in a vacuum or in an inert-gas stream at temperatures exceeding the adsorption temperature by 30–50°C.

The effect of platinum on the SnO2 sorption properties

Chemisorption of SO2 and O2 at Pt-modified SnO2 is studied by using the vacuum static method, with simultaneous recording of electrical conductivity, over the 22 to 300°C temperature range. The SnO2 surface modification results in the increasing of SO2 adsorption and weakening of the gas-surface bonding. The chemisorption enhances the samples’ electrical conductivity. The surface pretreatment with oxygen leads to the decreasing of the successive SO2 chemisorption.

Effect of SO2 on chlorination of Bi2O3 + Fe2O3 mixtures

The reaction of Bi2O3 + Fe2O3 mixtures with chlorine and SO2 at 250–700°C is studied. At 300–500°C, the degree of bismuth chloride sublimation from the oxide mixture increases in the presence of SO2. Chemical sublimation of FeCl3 occurs after BiCl3 is virtually completely recovered from the solid phase.

Sorptive properties of antimony-doped In2O3

O2, Cl2, and SO2 chemisorption on the surface of nanocrystalline In2O3 doped with antimony (0.2 and 2.7 at %) has been studied at temperatures from 22 to 200°C. The results indicate that antimony prevents the formation of nonconducting indium chlorides on the surface of nanocrystalline In2O3 during Cl2 chemisorption. The logarithm of the conductivity of Sb-doped In2O3 is a nearly linear function of the surface coverage with chlorine, which makes it a candidate chlorine-sensing material. At the same time, antimony doping reduces the SO2 response of In2O3.

Investigation of chemisorption properties of the PbO surface

Chemisorption of O2, Cl2, and SO2on the orthorhombic and tetragonal PbO samples was studied in the 225—550 °C temperature range. The main features of chemisorption are independent of the crystal modification of the sample. The change in the type of conductivity of PbO during chemisorption of O2was found.

Effect of gallium oxide dopants on electrophysical and sorption properties of zinc oxide

The effects of lithium oxide dopants (0.5–0.8 at. % Li) on the electrophysical and sorption properties of ZnO were studied in the temperature range from 150 °C to 410 °C. The introduction of lithium increases the activation energy of the conductivity of ZnO, decreases its conductivity, and increases the amount of S02 sorbed. Two forms of chemisorbed SO2 (donor and acceptor) are observed on the surface.

Determination of chlorine in air using ZnO modified with gallium and indium oxides

We examine the possibility of detecting Cl2 in flowing air at temperatures from 150 to 350°C using polycrystalline ZnO containing additions of gallium and indium oxides. ZnO modified with gallium via impregnation has a fast, stable, well-reproducible response and a short relaxation time. Its response passes through a maximum at 250°C. The interaction is not complicated by formation of chlorination products. In the range 5−500 ppm, its resistance is a linear function of the square root of Cl2 concentration.

SO2 chemisorption on SnO2〈Sb〉

We have studied SO2 chemisorption on antimony-doped SnO2 samples annealed at 200 and 600°C. Increasing the annealing temperature from 200 to 600°C makes the sample surface more homogeneous. In the range 100–200°C, the electrical conductivity of the samples air-annealed at 600°C increases in proportion with the amount of absorbed SO2. Doping with 0.2 at % Sb ensures the largest increase in conductivity upon chemisorption.

Effect of antimony dopants on the sorption properties of SnO2

The effects of antimony modifying additive (0.15—0.50 at.% Sb) on the electrophysical and sorption properties of SnO2 powders with a well developed specific surface were studied in the temperature range of 25—250 °C. Small amounts of antimony (0.15 at.%) increase the conductivity of SnO2 containing SO2 and CO chemisorbed in the temperature range of 25—100 °C. This makes this composition promising as a sensitive element of gas sensors.

Chemisorption of SO2 and Cl2 on indium oxide

The mutual influence of SO2 and Cl2 during their consecutive chemisorption on the In2O3 surface has been investigated. It was found that SO2 is chemisorbed in the uncharged form, and the amount of chemisorption decreases as the temperature increases. The preliminary chemisorption of Cl2 results in a dramatic decrease in the amount of SO2 sorbed and in a change in the character of the bonding of SO2 with the oxide surface. When SO2 is sorbed first, the temperature of the formation of chlorides during subsequent chemisorption of Cl2 decreases.