Traditionally, cadmium sulfide was used as a dye. It can be seen on the canvases of such great artists as Van Gogh, Claude Monet, Matisse. In recent years, interest in it is associated with the use of cadmium sulfide as a film coating for solar cells and in photosensitive devices. This compound is characterized by good ohmic contact with many materials. Its resistance does not depend on the magnitude and direction of the current. Due to this, the material is promising for use in optoelectronics, laser technology, and LEDs.
Cadmium sulfide is an inorganic compound that occurs naturally as the rare minerals zinc blende and howliite. They are of no interest to the industry. The main source of cadmium sulfide is artificial synthesis.
In appearance, this compound is a yellow powder. Shades can vary from lemon to orange-red. Due to its bright color and high resistance to external influences, cadmium sulfide has been used as a high qualitydye. The substance has been widely available since the 18th century.
The chemical formula of the compound is CdS. It has 2 structural forms of crystals: hexagonal (wurtzite) and cubic (zinc blende). Under the influence of high pressure, a third form is also formed, like rock s alt.
Cadmium sulfide properties
A material with a hexagonal lattice structure has the following physical and mechanical properties:
- melting point - 1475 °С;
- density - 4824 kg/m3;
- linear expansion coefficient – (4, 1-6, 5) µK-1;
- Mohs hardness - 3, 8;
- sublimation temperature - 980 °C.
This compound is a direct semiconductor. When irradiated with light, its conductivity increases, which makes it possible to use the material as a photoresistor. When alloyed with copper and aluminum, the effect of luminescence is observed. CdS crystals can be used in solid-state lasers.
The solubility of cadmium sulfide in water is absent, in dilute acids it is weak, in concentrated hydrochloric and sulfuric acid it is good. It also dissolves Cd well.
The following chemical properties are characteristic of a substance:
- precipitates when exposed to a solution of hydrogen sulfide or alkali metals;
- reacting with hydrochloric acid produces CdCl2 and hydrogen sulfide;
- when heated in an atmosphere with excess oxygen, it oxidizes to sulfateor oxide (this depends on the temperature in the kiln).
Cadmium sulfide is synthesized in several ways:
- when interacting with vapors of cadmium and sulfur;
- in the reaction of organosulfur and cadmium-containing compounds;
- precipitation from solution under the influence of H2S or Na2S.
Films based on this substance are made using special methods:
- by chemical precipitation using thiocarbamide as a source of sulfide anions;
- pulverization followed by pyrolysis;
- method of molecular beam epitaxy, in which crystals are grown under vacuum;
- as a result of the sol-gel process;
- by sputtering method;
- anodizing and electrophoresis;
- by screen printing method.
To make the pigment, the precipitated solid cadmium sulfide is washed, calcined to obtain a hexagonal crystal lattice, and then ground to a powder.
Dyes based on this compound have high thermal and light resistance. Additives of selenide, cadmium telluride and mercury sulfide make it possible to change the color of the powder to green-yellow and red-violet. Pigments are used in the production of polymer products.
There are other uses for cadmium sulfide:
- detectors (recorders) of elementary particles, including gammaradiation;
- thin-film transistors;
- piezoelectric transducers capable of operating in the GHz band;
- manufacture of nanowires and tubes that are used as luminescent labels in medicine and biology.
Cadmium sulfide solar cells
Thin-film solar panels are one of the latest inventions in alternative energy. The development of this industry is becoming more and more urgent, as the reserves of minerals used to generate electricity are rapidly depleted. The advantages of cadmium sulfide solar cells are as follows:
- lower material costs in their manufacture;
- increasing the efficiency of converting solar energy into electrical energy (from 8% for traditional types of batteries to 15% for CdS/CdTe);
- possibility of power generation in the absence of direct rays and the use of batteries in foggy areas, in places with high air pollution.
Films used to make solar cells are only 15-30 microns thick. They have a granular structure, the size of the elements of which is 1-5 microns. Scientists believe that thin-film batteries could become an alternative to polycrystalline batteries in the future due to their unpretentious operating conditions and long service life.