Boron is an essential micronutrient for growth and development of healthy plants. In small concentrations boron compounds are used as micronutrients in fertilizers,
in large concentrations they are used as herbicides, algaecides and other pesticides.
Function of boron in plants:
Essential for maintaining a balance between sugar and starch and functions in the translocation of sugar and carbohydrates.
Important in pollination and seed production.
Necessary for normal cell division, nitrogen metabolism and protein formation.
Boron is an essential element for plants’ development, growth, crop yielding and seed development by helping the transfer of water and nutrition in plants. Though plants’ boron requirement is very low in amount, their growth and crop yielding are severely affected when there is boron deficiency in the soil.
Borax decahydrate and borax pentahydrate are most widely used borates as boron fertilizer. Sodium borates can be used directly into the soil or by spraying onto plants successfully because of their good solubility. Colemanite which is a naturally occurring calcium borate is used especially in sandy soils because of its low solubility and it remains in soil longer than sodium borates.
Disodium octaborate tetrahydrate (Etidot-67) which is specially made for agricultural applications is the most preferable boron product in agriculture since it has much better solubility compared to theconventional boron products like borax decahydrate and borax pentahydrate.
Borates, in one method of application in fertilizing, are given to the soil directly in the solid form and dissolved in humid conditions then taken by plants’ roots. They are also applied by spraying over the leaves since some plants intakes better trough their leaves or in same cases spraying is a better way of fertilizing. The amount of boron to be given into soil as fertilizer varies according to plant type, method of application, the amount of rain, and soil’s lime and organic material contents.
Boron based herbicides are produced from borax and boric acid, and they are generally mixed with sodium chloride or other toxic chemicals.
Frit and Glaze:
Frit and glaze formulations can contain concentrations as high as 25% borates and the entire market accounts for more than 13% of the global borate demand. Borates improve glazes: facilitating the production process, ensuring a good fit between the glaze and the item it covers, and enhancing the chemical and mechanical strength.
Borates are used to initiate glass formation and reduce glass viscosity, helping to form a smooth surface; and to reduce thermal expansion; thus facilitating a good fit between the glaze and the clay. Borates also increase the refractive index, or lustre, of glazes and can enhance their resistance to chemicals.
Many glaze ingredients including borax are soluble in water. If these ingredients were applied wet to the surface of a clay body, they would be absorbed into the clay for which they are meant to provide a glassy outer surface. The process of fritting-or fusing the solubles with silica- renders these ingredients insoluble.
Fritting also starts the glass formation process well before the glaze is applied to the ware, significantly lowering the glaze firing temperature. Advanced ceramic components are increasingly being used in diesel and automotive engines where their light weight, high temperature and wear resistancy result in more efficient combustion and significant fuel savings.
Ceramics are also used to contain oil spills and encapsulate nuclear wastes. Despite established procedures and limits, industries and governments are under pressure to find alternative ingredients to Lead (Pb) in ceramic glazes, particularly those used to serve food. Two of the most viable alternatives to Lead (Pb)-based glazes are Bismuth and advanced Borosilicates (glass containing high levels of borates), or combinations of both. Therefore, Borates may serve as a viable alternative to enhancing safety while maintaining quality.
Boric oxide is a network former, but allows more fluxing oxides to be introduced without destroying the silicate lattice. The oxides of only four elements (boron , silicon, germanium and phosphorus) are able to form glasses alone.
Adding borates to tile bodies can make the tiles themselves stronger, and reduce energy used and waste in the process. Including borates in the batch also allows manufacturers to use a broader range of clays. Borates may also reduce furnace emissions at ceramic tile plants. These environmental benefits are associated with borates’ dual role in the bodies.
Borates act as a flux and as a powerful inorganic binder in ceramic tile body compositions: non more effectively than boric acid. A small amount of boric acid used in ceramic body can have a significant effect during the firing process by promoting the formation of a glassy phase with low viscosity. In the pressed body, the dry mechanical strength is increased, typically by about 40%.
For the porcelain floor tile composition, the main benefits of adding borates include:
Reducing the firing cycle typically by 10-20%, that translates the increased throughput in the furnace.
Reducing tile thickness due to a substantial increase (30-80%) in the dry mechanical strength of the unfired tiles. For example, an increase of 25% in dry mechanical strength allows the thickness to be reduced by around 10%.
Reducing the body formulation cost by substituting up to 20% feldspar and balancing with lower cost silica to
maintain the peak temperature and cycle length. Alternatively, the binding effect of the boric acid can be used to substitute some high quality clay with lower quality, less plastic clay to further increase cost savings. Reducing firing temperature by more than 25°C, keeping the same cycle length, and thereby producing energy savings.
Furthermore, addition of boric oxide to porcelain stoneware bodies raises the vitrification temperature and improves the densification properties, as well as increasing the modulus of rupture. Boric acid is added in the milling stage; mixing and distributing homogeneously in the composition. Its strong fluxing power-1% boric acid has the same fluxing power as 10-20% feldspar in the body composition- optimises the fluxing system wherever feldspar, talc, spodumene or other fluxing agents are used.
Glass in its various forms represents the largest single outlet for boron products. Boron is a powerful flux (reducing melting point, viscosity, thermal expanding coefficient; and increasing breakage index, transparency and brightness, and heat resistance), but also confers high chemical resistance for glasses in general.
In both insulation fibre glass (IFG) and reinforcement fibre glass (RFG), boron improves the fluxing capabilities of the batch, reduces glass batch melting temperatures and increases the fiberising efficiency by lowering the viscosity. It controls the relationship between temperature, viscosity and surface tension to create optimal glass fiberisation. Boron also reduces the tendency of crystallisation and increases the strength of the fibres and resistance against moisture.
For IFG, another important role of boron is to impart decompressibility. When the finished product is transported, it is firmly compacted into bales in order to minimize freight cost. When it is used for construction industry, main application area for IFG, it must be decompressed in order to provide the good air pockets/layers essential for insulation. Specifically in IFG, incorporation of boron reduces viscosity of the melt and thereby assists fiberisation as well as inhibiting the leaching of fluxes.
Constituents of fiberglass may vary with the type of production. ’’E-glass’’ which has the low alkaline property is the most widely consumed type. It accounts for about 90 percent of fiberglass consumption in the world since this type of fiber is less likely to brake during the application process. E-glass has boron oxide content up to 12 percent and is produced in a number of forms like filaments and copped strands as per the end uses.
Borosilicate glass is one of the primary consumption areas for borates in glass industry. The most significant properties borosilicate glass renders to the end products are resistance to thermal shocks and chemical attacks, withstanding scratches and high endurance to impacts. Thanks to these properties borosilicate glasses are used in many glass products like laboratory glasses, pharmaceuticals, cookware, solar energy systems and automotive lightings. Borosilicate glasses have boron oxide content between 5-30 percent.
Flat display panel glass, like LCD, production is one of the major boron consuming areas which have been growing recently. Flat panel glass production has increased dramatically since consumers’ preferences have shifted from cathode-ray tube (CRT) TVs to flat panel screens. Generally, 11-13 percent boron oxide is used in flat panel glass production. Alkaline materials, like sodium, are unwanted in flat panel glass production since alkaline ions degrade “the thin film transistor (TFT) property” of the glass by getting mixed with liquid crystal material. Therefore, alkaline-free boric acid is used as boron source in flat panel glass.
Boron is also used in fiber optic which enables luminary photons to be transferred effectively in communication systems. Fiber optics are formed of two different parts as inner core and outer sections. Inner core is made of glass with high index of refraction whereas outer section is made of glass with low index of refraction. Inner core is generally produced silicate molten with borosilicate glass.
In addition, borosilicate glass consumption in solar energy systems is gaining momentum since they are getting widely used in response to rising fossil energy cost and green energy policies.
Since boric acid and sodium borates are water soluble compounds which are absorbed by the wood surface and then penetrate by diffusion, they can be both used as wood preservatives. Moreover, these inorganic boron compounds are good fire retardants. Boric acid alone or in mixtures with sodium borates, is particularly effective in reducing the flammability of cellulose materials. Borax and Boric acid are therefore used as fire retardants in wood products and cellulose insulation.
It is the low electrical conductivity features that allowing the boron products to be used in the areas such as insulation, wire drawing and cables.
Although sodium borates have a good dissolution rate in water, in order to achieve highest concentration of boron, boric acid, as an extremely weak acid whose effect on pH is negligible, (which is also highly toxic to wood decay fungus yet is low in toxicity to mammals and fish) is used in most of the wood treatments.
The solubility of boric acid in water is influenced by the presence of certain other substances. Sodium chloride, lithium chloride and mineral acids decrease the solubility. Potassium nitrate, potassium sulphate, potassium chloride, sodium nitrate or sodium sulphate increase the solubility.
It is reported in literature that a ratio of 60% borax and 40% boric acid gives the maximum solubility of borates in water. A mixture of 65% water, 20% borax and 15% boric acid (by weight) will yield a solution containing 15.8% borates. To make this solution, mix required quantities and heat until dissolved. Boric acid in particular, dissolves slowly.
Flame retardants are used to reduce the degree of flammability of materials that support combustion.
Borates are used to impart or to contribute flame retardancy to a variety of materials. Borates suppress fire by melting and covering the flammable substance in a layer of char, excluding oxygen from the flame. Zinc borate is used in plastics, while soluble borates (such as boric acid and borax) are used in the treatment of cellulosic materials including wood, plywood, particle board, wood fibre, paper, neutral fibres such as cotton.
On the other hand, a reduction in the use of CCA (Chromated-Copper-Arsenate) owing to it being banned by the EPA assists borates to take more places in wood preservatives and zinc borates.
Detergents and soaps also take a considerable place in the application of borates. Boron is used as a cleaning and bleaching agent. It controls alkalinity of soaps and synthetic detergents, balances active oxygen, softens water, lowers the time and heat of the washing and prevents the corrosion of the metal/machine.
Borates are widely used in cleaning industry for various purposes like germicide and bleaching. Borax decahydrate is added to soaps and detergents because of its water softening and germicide properties. Sodium perborate is added to powder detergents for washing machines as bleaching agent since it is an active oxygen source.
Boron, in general, 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 dissolved in the metal or chemically bound to it.
In steel treatments: 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. 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.
In soldering: 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.
More specifically, boron trichloride is used in the refining of aluminium, 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 aluminium, 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.
The alkalinity and strong buffering action of boron compounds makes it useful as part of solutions for preventing corrosion of ferrous metals. The principal use of borates in this field is probably in anti-freeze formulations. The value of borax in this application is enhanced by its high solubility in ethylene glycol, the major constituent for commercial antifreeze. Break fluids and hydraulic systems in the motor industry also used boron compounds as a corrosion inhibitor, and it is also used as a corrosion inhibitor and a lubricant carrier in wire drawing.
Boron compounds are used as a peptizing agent in the manufacture of casein-based and dextrin based adhesives. The role of boron compounds in the production of adhesives is to control the viscosity. The major use of starch based adhesives is in the manufacture of corrugated cardboard.
Boron carbide is produced by the reduction of boric acid with finely divided carbon in electric furnaces at a temperature between 1400-2300°C. Alternatively boric oxide may be reduced with carbon and magnesium.
Due to its high hardness, B4C powder is used as an abrasive in polishing and lapping applications, and also as a loose abrasive in cutting applications such as water jet cutting. It can also be used for dressing diamond tools.
Preparation of fire retardant emulsion paints. Fire resistance in paper. Emulsifying agent in polishes. The preservation of rubber latex. Boron is used to control pH in a range of processing solutions. Boron is used in all dry powder fire extinguishers. Boron compounds are used in anodizing bath and in the electrolyte itself.
Boron is useful in the soaking of hides and skins, for stripping vegetable tans and for neutralizing chrome tans.
Boron is also used with salt in the control of red heat in sheep skins.
Use of boron based Fibre Glass to reinforce concrete as a substitute of steel and aggregates is growing.
Sodium Metaborate (NaBO2) is used in photography as a buffering agent.
Another application for boron compounds is the production of sodium borohydrate from boric acid which can be used as the hydrogen source in a new generation of fuel-cells. In this manner, borates fight global warming through clean fuel cell technologies that feature borates as a hydrogen carrier.
Boron compounds are used as stabilizers and bonding agents in refractory and refractory cements to increase insulation/refractory properties of the concretes, bricks and other construction materials.
Borates hold the key to controlling dust mites, the predominant cause of asthma attacks in children.
Borates help protect homes from insects and the elements in wood preservatives and insulation materials.
Borates hold premise in fighting cancer through boron neutron capture therapy.
Boron also is used in the production of foot powders, eye lotions, bath salts, hair creams, shampoos, and emulsification and buffering ointments.
The boron isotope is used for neutron screening and also for the control of nuclear reactions. All the known type of nuclear power stations use boron compounds.
Boron containing ceramics are also used to contain oil spills and encapsulate nuclear wastes.
Boron is used in radiation shielding to absorb fast neutrons in nuclear reactors. Boron-10, one of the naturally occurring isotopes of boron, is a good absorber of neutrons and is used in the control rods (steel and aluminium alloys consisting of 2% boron) of nuclear reactors, as a radiation shield and as a neutron detector.
In some Nuclear Power Stations, boric acid is added into the cooling water in order to prevent exceeding reactivity. To minimize radiation effects Borated concrete, with a high concentration of boron can also be used.
Finally and briefly; Boron is used in Nylon sizing, Paint, Paper, Plastics, Polishes, Refractory, Rubber, Catalysts, Cement and Concrete, Photography, Fire extinguishing, Electrolytic Capacitors, Leather and Skins, Pharmaceuticals, Cosmetics, Buffers in the manufacture of dyestuffs, Dying of nylon carpets, Absorbent to neutrons, Control of nuclear reactions