Gold is the most malleable of metals and it can be beaten into extremely thin sheets. A gram of gold can be worked into leaf covering near of six ft2 and only 0.0000033 inch thick. Although metallic gold can change its physical form easily, it is not attacked by nitric, hydrochloric, or sulphuric acid, but is dissolved by aqua regia, or by a solution of azoimide, and is attacked by sodium cyanide plus oxygen (cyanidation process basis). Also this latter aspect is used in order to prepare gold-plating solutions that contain 44 to 48% gold. Bromine, chlorine, iodine and fluorine tend to attack gold under specific conditions and for reason many researchers have been trying to develop an alternative leaching process without cyanide.
In geochemical terms, gold can be leached and transported by oxidizing hydrothermal fluids and will be precipitated when the fluid enters in reducing environment or the conditions can favored this environment.
The metal does not corrode in air, only a transparent oxide film forming on the surface. Its reflectivity of ultraviolet and visual light rays is low, but it has reflectivity of infrared and red rays and is thus valued for platting some types of reflectors.
For radiation control coatings for spacecraft, gold flake is used. Gold of 14-karat purity is used in the form of tiny, laminar platelets with overlap to form a film. Gold plated grid wires in electronic tubes give high conductivity and suppress secondary emission.
Gold-Gallium and Gold-Antimony alloys are used in electronic devices, they come in wires as fine as 0.005 inch in diameter and in sheet as thin as 0.001 inch. Gold powder and gold sheet for soldering semiconductors are 99.999% pure. The gold wets silicon easily at a temperature of 370 oC. Chemically reduced powder is amorphous and comes in particle sizes of 1 to 8 microns. Atomized gold powder has spherical form and is used in special synthetic coatings. Mercury reacts with the gold producing amalgams. This property is used in the extraction of gold from gravel and black sands.