Arsenical Bronze – a Natural Alloy of Tin

Arsenical bronze is a natural tin alloy with a trace of arsenic that is of a higher grade than pure copper. It is an alloy in which arsenic is added to copper instead of or in addition to tin or other constituent metals to form bronze. It is a form of arsenic-containing bronze. Bronze is a tin-and-pure-copper alloy. The employment of arsenic with copper, either as a secondary element or in conjunction with another component such as tin, results in a stronger end product with improved casting behavior. It has been utilized for a variety of purposes, including weapons and tools.

Because copper ore is frequently naturally contaminated with arsenic, the term “arsenical bronze” is normally applied exclusively to alloys with an arsenic level greater than 1% by weight, in order to differentiate it from possible accidental arsenic additions.

Properties

Copper and arsenic are combined to form arsenical bronze. It has been used for a variety of reasons in the past, including as a currency. Its key chemical feature is its extreme strength. As a result, it was well-suited for usage in weapons, decorative artifacts, building materials, and tools. It was also corrosion-resistant, making it ideal for ship construction.

Advantages of arsenical bronze

While arsenic was most likely originally blended with copper as a result of the ores already contained it, its use most likely continued for a variety of reasons. First, it serves as a deoxidizer, interacting with oxygen in the hot metal to generate arsenous oxides, which evaporate from the liquid metal. When a large amount of oxygen is dissolved in liquid copper, the copper oxide breaks out at grain boundaries and dramatically lowers the ductility of the final item. However, because of the solubility of hydrogen in the molten metal and subsequent loss as a bubble, its use can increase the danger of porosity castings.

Second, the alloy can withstand more work-hardening than pure copper, allowing it to function better when used for cutting or chopping. With increasing percentages of arsenic, the bronze’s work-hardening potential increases, and it may be work-hardened over a wide temperature range without risk of embrittlement. Its increased characteristics over pure copper can be demonstrated with as little as 0.5 to 2 wt% As resulting in a 10-to-30% increase in hardness and tensile strength.

Third, in the proper percentages, it can provide a silvery sheen to the product being created. There is evidence of arsenical bronze daggers from the Caucasus and other artifacts from various regions having an arsenic-rich surface layer that may have been intentionally manufactured by ancient craftsmen, and Mexican bells were made of copper with enough arsenic to color them silver.

Health effects of arsenical bronze use

Arsenic has a vaporization point of 615 °C, thus arsenical oxide will be lost from the melt before or during casting, and fumes from fire settings for mining and ore processing have long been recognized to affect the nervous system, eyes, lungs, and skin.

Modern uses of arsenical bronze

Arsenic bronze is strong and resilient, making it ideal for use in objects that must survive a lot of wear and tear. It is also corrosion-resistant, making it an excellent choice for things exposed to the outdoors.

In the present era, arsenical bronze has found minimal use. The closest counterpart appears to be arsenical copper, defined as copper with less than 0.5 wt percent As which is below the accepted percentage in archaeological artifacts. The addition of 0.5 wt percent arsenic in copper reduces its electrical conductivity to 34% of that of pure copper, while even 0.05 wt percent reduces it by 15%.