How Borates are used in Metallurgy
Borates are used in the production of steel and non-ferrous metals, amorphous metals, welding fluxes, alloys, rare earth magnets and plating compounds. Boron is generally used in Metallurgy (such as in abrasives, cutting tools, magnets and soldering) for the following purposes;
- to reduce melting temperature (thus to lower the energy consumed)
- to increase fluidity (as a fluxing agent)
- to increase strength (hardenability) of the steel
- to reduce the corrosion of the refractory material in the furnace
Boron is also used in the production of pure, strong metals to remove the oxygen and nitrogen that is either dissolved in the metal or chemically bound to it. In steel and non-ferrous metal production, borates act as a flux during the smelting operation helping to dissolve metallic oxide impurities which are then removed in the slag.
Borax Use in Gold Metallurgy
Boron in Powder Metallurgy
Boron Use in Slag
Boron Use in Slag - Intro
Boron Use in Slag Q&A
Boron, as a non-metallic solid element, can penetrate and form an alloy with steel under high temperatures. It forms a molecular bond with the metal. Unlike chrome, boron does not add a layer to the original surface. Rather, Boron treatment does the opposite; It removes carbon and other impurities from the steel, leaving a pure iron boride layer with boron.
Boron can significantly increase the hardenability of steel without loss of ductility. Its effectiveness is most noticeable at lower carbon levels. The addition of boron is usually in very small amounts ranging from 5-30 ppm.
Boron products can be added to the ladle furnace during steel production in order to transform the slag from a low density to powdery material to a compact form that is twice the density. This makes the slag easier and more environmentally friendly to handle. It helps reduce costs because the compressed slag can be reused in the steel production as a substitute for some of the lime used to remove impurities, or else sold to the construction industry for use as a filler. These opportunities further help to avoid disposal costs and fees.
Boron, bordering the transition between the metals and non-metals, is regarded as a semiconductor rather than a metallic conductor. Due to its ability to dissolve metal oxide films, as a flux, boron is used in soldering and welding. Most dry paste brazing and welding fluxes contain borates. More specifically, boron trichloride is used in the refining of aluminum, magnesium, zinc, and copper alloys to remove nitrides, carbides, and oxides from molten metal. It has been used successfully as a soldering flux for alloys of aluminum, iron, zinc, tungsten, and monel.
In view of borax and boric acid, they both break down (decompose) into boron trioxide (B2O3) at soldering temperatures of 575°C for boric acid and 765°C for borax (with borax there is also sodium metaborate produced as a part of the decomposition process). B2O3 is the active ingredient in the dissolving of metallic oxides. Copper oxides, for example, are converted into copper metaborate when they come in contact with the B2O3. These metaborates are water soluble and are dissolved away in the pickle after soldering.
Although neither boric acid nor borax is a soldering flux itself, as fire-retardants, they provide protection from oxidation on the rest of the piece while soldering. Many soldering fluxes have borax (or boric acid) as the main component but they also have other compounds like chlorides, fluorides and carbonates added to both reduce the temperature that the fluxing action takes place at and to help in dissolving the more difficult oxides, like the silicon dioxide.
In powder metallurgy (PM), the presence of Metal Borides, whether formed in-situ or added as a premix, provides multiple benefits to formed parts including high conductivity and mechanical strength. Boric Acid, Boron Nitride, and Boron Carbide each form intermetallic phases in-situ by forming metal borides.
In non-ferrous applications, both Anhydrous Boric Acid and Boric Acid are highly interactive with Mg, Al, and Cu. Boron is formed in-situ during sintering under either reducing or inert atmosphere, and further reacts to form metal borides. Boron-containing reaction products impart high conductivity, being present as a dopant in the metallic interstices or around grain boundaries. Even a small addition of Boric Acid can make a large difference in Mg. Boron is used in titanium PM for aviation to increase mechanical strength.
In Ferrous PM, the addition of boron has the following effects:
- Forms a liquid phase during sintering.
- Increases density and hardness with increasing sintering temperature.
- Significantly decreases wear rate and weight loss.
- Enhances corrosion resistance of steel
- Enables low temperature sintering.
Boron Carbide Powder is an important non-ferrous boron-based PM that has a wide range of industrial applications.
Amorphous Metals (Metallic Glasses) and Alloys
In the production of amorphous metal alloys by rapid cooling, boron-containing alloys used in soft magnetic cores help reduce energy losses by up to 85%. In alloys, borates readily associate with metallic oxide contaminants at a low temperature minimizing the loss of precious metals and reducing wear and tear on melting equipment.
Amorphous metals are used as transformer cores in the form of foils and provide increased efficiency by reducing power losses in conventional soft (non-permanent) magnets. Substantial reduction (70-85%) in the amount of energy loss can be achieved using soft magnetic cores made from amorphous metal alloys.
Amorphous metals or ‘Metallic Glasses’ are inorganic mixtures fused at high temperatures and rapidly cooled so they solidify and do not crystallize on cooling. These materials are rapidly cooled, molten alloys which do not have time to crystallize before solidifying. To achieve this, cooling rates of 1 million OC per second are required. These alloys can vary in composition and often contain up to 92% iron (Fe), 5% silicon (Si) and 3% Boron (B) by weight. In the preparation of such alloys the boron is mainly supplied as Ferroboron, which can be made using either boric acid or boric oxide (anhydrous boric acid).
Ferroboron is used in the production of rare earth magnets which show superior magnetic properties for bonded magnets and permanent magnet materials.