Thermal Stability of Cadmium Telluride in Infrared Detectors for Monitoring Fire Conditions

Abstract

Introduction. Thermal effect of fire on technical means is a common and serious problem. In this regard, it seems an urgent task to study physicochemical and thermal transformations in devices based on cadmium telluride during man-made or natural fires. For a number of materials, such studies have not been conducted, and the available results are insufficient or narrowly focused. The proposed article presents new data on the defect resistance and applicability of the material depending on the thermal effect. The work objective is to study the features of degradation under the influence of extreme temperatures to create new materials with specified properties.Materials and Methods. Cadmium telluride (CdTe) samples used in solar panels and detectors were studied. In the practical part of the work, the thermal effect on the sample of normal and extreme temperatures was evaluated, followed by the study of the material by transmission electron microscopy methods. The experiments simulated a zone of thermal impact of a fire. The computational and theoretical work consisted in improving the mathematical model of physical and chemical transformations and the evolution of defects under thermal influence up to 1092 °C. The mathematical model took into account the heat dose characteristic of uncontrolled combustion. The Maple software package was used to solve the equations.Results. The formation of defects in a CdTe sample at significantly different levels of thermal exposure was visualized. The lower limit was about 20 °С, the upper one was more than 600 °С. Transformations in CdTe control samples under the influence of temperatures up to 1092 °С with a step of 15 °С were worked out in detail. Point defects caused by the influence of temperature were presented as a factor of destruction of the material, and consequently, failures in the operation of the device. A system of equations was solved that takes into account a set of parameters: the frequency of vibrations of atoms in the lattice, temperature, concentrations of CdTe nodes, interstitial atoms and vacancies, migration and attachment of interstitial atoms and vacancies. The concentrations of vacancies and interstitial atoms in CdTe samples depending on thickness and temperature were graphically presented. The results of scientific research allowed us to assert that CdTe-based detectors worked relatively correctly only at a heat dose of up to 400 °С. In the ranges of 400-600 °С, the defective network of the material actively evolved, preventing destruction. However, a further increase in thermal exposure led to complete degradation of the equipment, which did not allow the use of cadmium telluride in extreme conditions, even for a short time.Discussion and Conclusion. The proposed improved model of physical and chemical transformations in CdTe-based devices in heat-affected areas will allow a more selective approach to the use of equipment. In addition, it is necessary to improve materials and increase their resistance to extreme temperatures.