Traditionally, cadmium sulfide has been 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 has been associated with the use of cadmium sulfide as a film coating of solar cells and in photosensitive devices. This compound is characterized by good ohmic contact with many materials. Its resistance is independent of the magnitude and direction of the current. Due to this, the material is promising for use in optoelectronics, laser technology, LEDs.
general description
Cadmium sulfide is an inorganic compound that is found in nature in the form of rare minerals zinc blende and houliitis. They are not of interest to 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 was used as a high-quality dye. The substance has become 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, as in rock salt.
Cadmium Sulfide: Properties
A material with a hexagonal lattice structure has the following physical and mechanical properties:
- melting point - 1475 ° C;
- density - 4824 kg / m 3 ;
- coefficient of linear expansion - (4.1-6.5) µK -1 ;
- Mohs hardness - 3.8;
- sublimation temperature - 980 ° C.
This compound is a direct semiconductor. When exposed to light, its conductivity increases, which makes it possible to use the material as a photoresistor. When doped 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 - weak, in concentrated hydrochloric and sulfuric acid - good. Cd also dissolves well in it.
The following chemical properties are characteristic of a substance:
- precipitates when exposed to a solution of hydrogen sulfide or alkali metals;
- when reacting with hydrochloric acid, CdCl 2 and hydrogen sulfide are formed;
- when heated in an atmosphere with an excess oxygen content, it oxidizes to sulfate or oxide (this depends on the temperature in the kiln).
Getting
Cadmium sulfide is synthesized in several ways:
- in the interaction of cadmium vapor and sulfur;
- in the reaction of organosulfur and cadmium-containing compounds;
- precipitation from a solution under the influence of H 2 S or Na 2 S.
Films based on this substance are made using special methods:
- chemical precipitation using thiocarbamide as a source of sulfide anions;
- pulverization followed by pyrolysis;
- molecular beam epitaxy, in which crystals are grown under vacuum;
- as a result of the sol-gel process;
- ion spraying method;
- anodization and electrophoresis;
- screen printing method.
To prepare the pigment, the precipitated solid cadmium sulfide is washed, calcined to obtain a hexagonal crystal lattice, and then ground to a powder state.
Application
Dyes based on this compound have high thermal and light resistance. Additives from selenide, cadmium telluride and mercury sulfide can change the color of the powder to green-yellow and red-purple. Pigments are used in the manufacture of polymer products.
There are other uses for cadmium sulfide:
- detectors (registrars) of elementary particles, including gamma radiation;
- thin film transistors;
- piezoelectric transducers capable of operating in the GHz range;
- the manufacture of nanowires and tubes, which are used as fluorescent labels in medicine and biology.
Cadmium Sulfide Solar Panels
Thin-film solar panels are one of the latest inventions in alternative energy. The development of this industry is becoming increasingly important, as the mineral resources used to generate electricity are rapidly depleted. The advantages of cadmium sulfide solar panels 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);
- the possibility of generating energy in the absence of direct rays and the use of batteries in foggy areas, in places with high dustiness of air.
The films used for the manufacture of solar cells have a thickness of only 15-30 microns. They have a granular structure, the size of the elements of which is 1-5 microns. Scientists believe that in the future thin-film batteries will be able to become an alternative to polycrystalline ones due to their unpretentious operating conditions and long service life.