Tungsten carbide is a tungsten-carbon compound that contains an equal number of carbon and tungsten atoms. It is a fine, gray-black powder that is pressed into various shapes for use in applications. According to "Handbook of Chemical Vapor Deposition," tungsten carbide is prepared by the reaction of carbon with tungsten metal at temperatures between 1,400 Celsius to 2000 Celsius. Tungsten carbide powder comes in many shapes, particle sizes, microstructures and chemical compositions, including fine tungsten monocarbide powder and macrocrystalline tungsten.

Hardfacing
Tungsten carbide powder is commonly used for hardfacing metals. Hardfacing is the process in which a tougher, harder material is applied to a softer base metal. Tungsten carbide improves the wear-resistant properties of a base metal. It is applied to mining equipment parts (shovel teeth, heel plates, bucket wheel excavator teeth, wear parts, crushing hammers, cutter drums and longwall miners), mineral processing equipment (hammers, chutes, pulverizing and grinding parts), earth-moving and construction equipment (grader blades, cutting edges, augers, trencher teeth, ground engaging tools and tunneling equipment), drilling tools, processing equipment and agriculture equipment (subsoilers, discs and injectors).

Diamond Tools
Tungsten carbide powder is used to manufacture tools used in the diamond industry, such as segments, grinding wheels and scape. According to the book "Exploring Advanced Manufacturing Technologies," tungsten carbide diamond cutting tools are made by sintering diamond powder to a tungsten carbide base and then cutting them into various shapes. These shapes are inserted or brazed in tool bodies and then ground to finished shape and sizes. Diamond tools are used to cut hard materials, such as stone, glass and porcelain.

Consumer Goods and Sports
Tungsten carbide is used in common consumer goods, including razor blades. Tungsten carbide powder is used in men's wedding bands to give them a dark hue and to improve their scratch-resistance. Tungsten carbide powder is used to make sporting equipment and devices, such as trekking poles, cross-country skis, bicycle studs and drive tracks for snowmobiles. Hikers and trekkers use tungsten carbide-tipped poles and walking sticks to reduce pressure on leg joints and for balance. They are effective in providing traction on rock surfaces.

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Tungsten inert gas (TIG) welding, also known as gas tungsten arc welding (GTAW), is an arc welding process that uses a tungsten electrode to transmit the electric arc to the work piece. Unlike other arc welding methods, the tungsten electrode does not provide material to the weld, so a separate filler rod is needed for that purpose. Some tungsten electrodes are made with a small amount of thorium, which is a radioactive material and improves the welding qualities of the electrode.

Welding With Tungsten
Tungsten has the highest melting point of all metals, so the electrode material does not melt when exposed to the high temperatures of the arc. Tungsten can be used to weld metals and specific alloys designed to have a high melting point. Even though the tungsten electrode doesn’t melt during the welding process, the electrode can wear or chip over time. The electrode can be reshaped to a conical or rounded shape using a grinder.

Electrodes That Contain Thorium
Thoriated tungsten electrodes are made from tungsten combined with 1 to 2 percent thorium in the form of thorium dioxide. Thoriated tungsten electrodes result in improved welding properties over pure tungsten electrodes. By using thoriated tungsten electrodes, welders find it easier to start the arc and maintain the arc, reduce weld contamination, carry a higher level of current, and achieve a longer electrode life through reduction in wear.

Concerns
Thorium is a radioactive element, so thoriated tungsten electrodes do emit some radioactivity, but the amount is relatively low. Thorium mainly emits alpha particles, which can’t pass through a sheet of paper, but could potentially damage skin tissue with prolonged exposure. Thoriated tungsten electrodes should be stored in a steel container marked with the radiation trefoil as an identifier.

The Natural Council on Radiation Protection and Measurements (NCRP) estimates that the average annual effective dose welders are exposed to when working with thoriated tungsten electrodes regularly, is a maximum of 16 millirem. The amount of background and medical doses incurred by members of the U.S. population each year is about 250 to 1,000+ millirem, so the exposure due to the thoriated tungsten electrodes is small. However, common sense safety precautions should be taken to avoid excessive exposure, including not carrying electrodes close to the body, and wearing standard welding equipment while performing TIG welding. Welders should wear a mask while grinding thoriated tungsten electrodes to avoid breathing in particulates from the grinding process.

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An incredibly strong and dense metal, tungsten can be combined with ceramic to make rings and other fine jewelry. Tungsten ceramic rings are becoming a popular choice for many wedding bands due to their durability and beauty.

Identification
Tungsten is a steel-gray metal. When paired with tungsten, ceramic is often polished black for greater contrast.

Strength
When processed with carbon at high temperatures, tungsten forms tungsten carbide, the hardest metallic substance in the world. Tungsten ceramic rings have unmatched strength.

Benefits
Tungsten ceramic polishes to a mirror-like finish. It's also highly resistant to abrasions and scratches. It would take deliberate scratching from diamonds or corundum to inflict any damage whatsoever.

Considerations
Tungsten ceramic rings, while nearly impervious to scratching, are not indestructible. Tungsten ceramic's hardness makes it slightly more brittle than traditional jewelry metals, meaning it can be crushed under severe stress.

Warning
Once manufactured, tungsten ceramic rings can not be resized due to tungsten's remarkable hardness.

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According to the Centers for Disease Control and Prevention (CDC), tungsten "is a naturally occurring steel-gray to tin-white metal or fine powder that comes from more than 20 different tungsten-bearing minerals." Its atomic number is 74, and its atomic symbol is W. Normally used to toughen steel, the increase of industrial activity in the United States has heightened the chances of people being exposed to tungsten.

Means of Exposure
People can be exposed to tungsten by drinking water, eating food or breathing air that has been contaminated by tungsten. Although tungsten is naturally present in the environment in small amounts as minerals, industrial plants that manufacture tungsten can release large quantities of tungsten into the air.

Entering and Leaving the Body
Tungsten enters the body through eating, drinking, touching or breathing. Scientists are unsure about the metabolism of tungsten in the body, but it does enter the bloodstream and is spread to all parts of the body. Most of the tungsten is quickly processed in the digestive system, leaving your body either through urine or feces.

Health Effects
When exposed to high levels of tungsten, the immediate effects on the body can be irritation of the skin, eyes, throat or nose. Long-term effects can involve a myriad of lung problems, most likely coughing, wheezing and shortness of breath. Many of the long-term effects have been attributed to the use of cobalt in the tungsten-refining and compounding processes. It is important to understand that these side effects are the result of long-term heavy exposure to tungsten, not the minimal exposure to tungsten that most people experience.

Inconclusive Research
Currently, there is not enough scientific research to determine whether tungsten exposure leads to leukemia or other forms of cancer. The general rule of thumb is the more a person is exposed to tungsten, the higher the likelihood of that person experiencing some health effects

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Finding Tungsten
Tungsten is often found in conjunction with other metals such as wolframite (the element in which tungsten was first discovered whose name means "devourer of tin") and scheelite. Around the world, China is the most common place that tungsten is found and mined, though other locales such as Austria, Bolivia and Portugal also have mines that produce respectable amounts of this metal for use in light bulbs, rockets, and in the case of some first world countries, spacecraft.

Refining the Tungsten
Once the ores containing tungsten have been mined from the earth, a process developed by those who discovered tungsten (the Elhuyar brothers Juan and Fausto who were chemists in the late 1700s) is used to purify the metal. The ore that contains the tungsten is crushed, cleaned and then treated with various alkalis so that tungsten trioxide is formed. The tungsten trioxide is then heated using either carbon or hydrogen gas, which then separates the tungsten metal from either the water vapor or the carbon dioxide that forms, depending on which gas was used in the heating and refining process.

The Final Step
Pure tungsten, which is often a whitish or a gray color once it's separated from the ore it was mined in, is in a state referred to as powered tungsten. If necessary, powered tungsten can be used right away without any further modifications. However, if there is no pressing need for the tungsten right then, it will be shaped into bars to be stored or transported. Given that tungsten is a relatively malleable and ductile metal, this process isn't a very difficult one.

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The quality of a cutting tool can determine whether cuts will be smooth and clean or difficult and sloppy. A metal cutting tool's quality begins with the hardness and durability of its metal. According to the Society of Manufacturing Engineers, "carbide and carbide-coated tools cut about three to five times faster than high-speed steels" and "higher tungsten content increases wear resistance." There are tungsten carbide cutting tools for a wide variety of applications and, once you understand the breadth of their possible uses, you'll be able to choose one for professional, amateur or even industrial projects.

Circular Saw Blades
Circular blades surrounded by sharp, tungsten carbide-tipped teeth can be found in factories for manufacturing, carpenters' tool kits for milling---and in the home, because do-it-yourselfers can buy them at hardware stores. These circular saw blades are sized to fit not only in industrial machinery but also in standard table saws and hand-held circular saws. The most common tungsten carbide circular saw blades are not solid tungsten carbide; their body is typically tempered steel and only the cutting edges of the teeth are coated with tungsten carbide. A variation of the toothed saw blade is the grinding "wheel" or abrasive blade---still circular but without teeth. Their edge is coated with tungsten carbide and used to exert abrasive force as they grind through stone, ceramics and metal.

Reciprocating Saw Blades
Tungsten carbide coats the edges of blades for reciprocating saws, such as jigsaws and demolition reciprocal saws. The back-and-forth sawing motion of these types of saws is well-suited for abrasion, and their coating of tungsten carbide grit allows them to grind through metals, ceramics and masonry. Applications include removing cast iron pipes and metal fasteners during demolition or cutting access holes through stone and tile during remodeling.

Drill Bit Tools
Drill bits may be solid tungsten carbide or tipped with it to provide the speed, accuracy and wear resistance required by machine shops and high-precision manufacturing applications. Construction professionals and amateurs buy similar bits that attach to hand power drills, drill presses and hobbyist rotary tools. Precision drill bit and grinding tools with tungsten carbide tips might be used for milling or sculpting metal as well as decorative carving of stone and precious gemstones. As materials scientist Dale Wittmer stated in a Southern Illinois University publication, "Tungsten carbide tools have been the standard for over 50 years in the mining industry."

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Background

Osmium has the highest optical emission rate of all metals. Consequently, after Edison’s carbon filaments, it was used at the beginning of the lamp industry. Osmium’s big disadvantage is its high vapour pressure, resulting in a short lamp life. Tungsten withstands considerably higher temperatures than osmium and has a very low vapour pressure, resulting in more luminosity combined with a long lifetime.

Wire Properties

Tungsten wire possesses characteristics that have provided it with a unique place in the origin and growth of the lamp industry. The lamp industry represents the largest commercial application of tungsten wire. It is used in this application because it displays excellent creep resistance at elevated temperatures. Tungsten is an attractive lamp filament material because it has an extremely high melting temperature (~3680 K) and a low vapour pressure at high temperatures. Tungsten is also intrinsically brittle and, initially, this prevented the manufacture of tungsten wire. However, at the beginning of this century William Coolidge, working at the General Electric Company, pursued the idea of deforming tungsten at elevated temperatures in order to make small diameter tungsten wire. Two important findings of his work were, first, to develop a method to work a powder metallurgy ingot down to wire by using deformation at elevated temperatures; and, second, to produce a ductile material from this deformation. Today, the ability to handle tungsten wire and coil filaments without breakage is the backbone of the whole incandescent lamp industry.

Processing

The initial stages of thermomechanical processing of sintered tungsten ingot are usually performed by rolling and / or swaging. These operations allow large deformations at relatively high temperatures and during the initial stages of deformation the ingot reaches full density. By working the tungsten at elevated temperatures, the tungsten is maintained well above the ductile to brittle transition temperature but below the recrystallisation temperature. At various points during this deformation, anneals must be applied, or the tungsten will become overworked and begin to fracture. Finally, wire drawing is used to reduce the tungsten to its final desired diameter. At this point, the microstructure consists of fibres which have very high aspect ratios: they act like fibres in a rope and provide bend ductility.

It was not until the advent of transmission electron microscopy that potassium was located in small bubbles in the tungsten. It is these potassium bubbles which provide the wire with its unique high temperature creep resistance. Potassium is essentially insoluble in the tungsten. The bubbles are first formed from the doped powder in the ingot during sintering. During thermomechanical processing, these initial bubbles are drawn out into tubes. When the wire is annealed, these tubes break up to form the rows of bubbles.

Once wire drawing is complete, the tungsten can be coiled into a filament and recrystallised. When the wire is recrystallised, the grain boundaries interact with the potassium bubble rows as the boundaries migrate, giving rise to an interlocking grain structure.

‘Bamboo’ Structure

Recrystallized pure tungsten wire forms a bamboo structure: the grains occupy the entire wire diameter, and the boundaries are essentially perpendicular to the wire axis. At elevated temperatures, under the stress produced by gravity, these boundaries would slide past one another by diffusion and produce a rapid failure. However, when potassium is present in the wire, the interlocking grain structure reduces the rate of grain boundary sliding and extends the filament life. These bubbles continue to pin the grain boundaries at the temperatures of lamp operation, and thus maintain a stable microstructure during the life of the lamp.

Applications

Tungsten is used in many different types of incandescent lamps. The most common types are the general household lamps, automotive lamps, and reflector lamps for floodlight or projector applications. There are also many thousands of speciality lamps, which have a broad range of applications, such as audio-visual projectors, fibre-optical systems, video camera lights, airport runway markers, photocopiers, medical and scientific instruments, and stage or studio systems.

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Properties

Tungsten is practically the only material used for electron emitters. Although other, more electropositive, metals would yield higher emission rates, the advantage of tungsten is its extremely low vapour pressure even at high temperatures.

This property is also important for electrical contact materials. While more conductive metals like copper or silver evaporate (erode) under the conditions of an electric arc, tungsten withstands these.

Applications

The following list illustrates some of the resulting tungsten applications:

•         Directly heated cathodes or heater coils for indirectly heated cathodes in cathode ray tubes for TV sets or computer displays, X-ray tubes, electron tubes, klystrons, magnetrons for microwave ovens;

•         Thoria or rare earth oxide alloyed rod electrodes for inert gas welding (TIG welding electrodes), as well as High Intensity Discharge (HID) lamps;

•         Tungsten disks for substrate of high power semiconductor rectifying devices;

•         Sintered pure tungsten electrical contacts

•         Sintered tungsten-copper or tungsten-silver electrical contacts for high-voltage breakers

•         Infiltrated tungsten-copper or tungsten-silver contacts, made from very coarse (50-150 µm) tungsten metal powder

•         High temperature furnace parts such as tungsten heating coils, reflectors and structural material

•         Tungsten / tungsten-rhenium thermocouples for measuring the temperature in such furnaces

•         X-ray tubes for medical use are not only equipped with a tungsten emitter coil, but also with a rotary (or static) anode made of tungsten or tungsten/ tungsten-rhenium. Important here are not only the low vapour pressure, but also tungsten’s good heat conductivity and the wavelength of the resulting X-rays

•         Calcium and/or magnesium tungstate is the phosphor in intensifying screens used with the X-ray photo films. These phosphors convert X-rays into visible (blue) light, resulting in a smaller X-ray charge for the patient

•         Modern business machines, such as photocopiers, facsimile machines, laser printers and air cleaners are equipped with tungsten charger wires. Not only drawn tungsten wire, but also electro-polished, gold-plated or platinum clad tungsten wires are used for this application

•         Ceramic circuit boards are printed by means of a metal paste. After printing, the metallic layer is sintered to form the conductor, and tungsten is a commonly used metal for this purpose

•         Modern computer processors like the 586 series and higher, generate a heat output per square centimetre similar to that of a household cooker surface. Tungsten-copper heat sinks and the processor fan remove the heat

In modern microelectronics, the advantages of tungsten are its good electrical and thermal conductivity, and its thermal expansion coefficient is almost the same as that of silicon. Tungsten plays an essential role, as the following examples show:

•         Ultra high purity tungsten, tungsten silicide and tungsten-titanium PVD sputtering targets are used in VLSI and ULSI DRAM chip technology. A W-Ti layer on a wafer acts as a diffusion barrier, while W and WSi layers function as electrical conductor materials.

•         In liquid crystal display (LCD) technology, ultra high purity molybdenum-tungsten alloy targets are now used instead of molybdenum-tantalum, resulting in improved definition of LCD panels.

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The once ubiquitous 60W light bulb is about to plop off the production line for the last time across Europe. But while its light may be dimming, it is still illuminating many of our homes.

It is at once a thing of delicate beauty and robust science.

Encased in its own glass world, a miniature laboratory keeps a tiny thread of tungsten burning brightly. There is even a touch of romance in its soft flare, as it casts a painterly glow over the room and the faces of its occupants.

The 60W has long been the bulb of choice for the modestly-sized rooms in the typical British home. But this very domestic species will be put on the endangered list on Thursday 1 September, when an EU-wide ban on the manufacturing and importing of 60W incandescent clear light bulbs comes into force.

Customers will still be able to get hold of a 60W bulb but once stocks run out, it will go the same way as candlelight and gaslight before it.

People are being forced to use energy-saving light bulbs. And no matter how much fans of compact fluorescent lamps proclaim their virtues, there will be some who will see Thursday as the day which consigned their homes to eternal dimness.

Cultural historian Christopher Cook is not a fan of the new light bulbs. He says light creates an atmosphere in a room and the new bulbs give off a "different light".

"We are seeing a fundamental change in the way interiors are illuminated," he says.

"The light that the old bulbs cast through a lampshade is different. It's a softer, more natural light. The light is diffused through the shade."

Cook is not alone in preferring conventional light bulbs - the vast majority of the 600 million light bulbs in UK homes are tungsten filaments and people are still buying them.

The market share of incandescent bulbs was 56% in 2009, down from 85% in 2005, according to retail analysts Mintel. The compact fluorescent lamp accounted for 23% of the market in 2009 compared with only 3% in 2005.

But the 60W tungsten bulb means more than a warm glow, it is a beacon of modernity. The "perfect demonstration of a brilliant idea" is how cultural commentator Stephen Bayley describes it.

"Because it is such a very legible design, the tungsten light bulb became a symbol of switched-on genius. It's literally, as well as metaphorically, illuminating.

"Its one fault? Like many a genius, it gives off as much heat as light. So it now joins tallow and the gas mantle on technology's scrapheap."

He says one day the public might come to feel sentimental about its "charmless" replacement but if feels like a "poor trade" at the moment.

The 60W is the latest old-fashioned light bulb to be switched off in favour of the fluorescent lamps, energy-saving halogen bulbs and LED lights. Many of the major retailers stopped selling the bulbs well ahead of the European deadlines.

Bulbs of 100W and greater have already ceased production, as well as all pearl bulbs, and the same fate awaits all remaining clear incandescent lights next year.

But while the higher wattages may be missed by those with bigger homes, the loss of the ubiquitous 60W may be more keenly felt.

Critics continue to circle the substitutes although there is no doubt they have improved since they were first introduced.

However, the bulbs have still found it difficult to shake off that reputation for giving out a dim, cold, white light. Their critics say they are slow to warm up, the light flickers, and they are too big for some fittings. There also seem to be more types than there are shapes of pasta. The proponents say these problems have already been addressed.

But for the incandescent aficionados, fluorescent lights tend to be associated with morgues, prisons and tenement hallways. Cook says they give off a "cold creepiness" and make you feel like you're being interrogated.

The death warrant of the conventional bulb was signed by EU leaders in 2007 to help meet climate change targets, but other countries have been thinking about it too. In New Zealand, a new government scrapped the ban in 2008, saying it was an example of the "nanny state philosophy".

But the US will start banning the traditional bulbs from the start of next year and a very vocal opponent is Howard Brandston, one of the most respected lighting experts in the world who was asked to redesign the lighting of the Statue of Liberty as part of the 1986 restoration.

He is against the ban on many levels, including the unsatisfactory lighting quality, the cost of retrofitting homes to use the new light sources and the safety risk posed by the mercury.

Brandston has used compact fluorescent lamps in commercial projects but he says there is no place for them in people's homes.

"They are not bad products, just bad applications. Your home should be your castle and they are coming into your home and reducing the quality of light and life.

"It changes the colour of your appearance, your food, your furniture. They don't dim well and the colour of the light deteriorates."

But for Chris Oxlade, author of The Light Bulb: Tales of Invention, it is simply a matter of scientific progression and the new light bulbs should be embraced.

"I have no nostalgia for the old ones, which are knocking on 100 years," he says. "My parents will say that the new light bulbs are rubbish - they don't come on quickly enough or they are not bright enough but I have accepted them."

There will certainly be people who start hoarding bulbs in earnest on Thursday, but the 60W's days will soon be over.

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Background

Tungsten Carbide is often referred to as a Hard Metal due to it’s very high hardness in relation to other metals.

Typically a Tungsten Carbide Hard Metal can have a hardness value of 1600 HV, whereas mild steel would be in the region of 160 HV a factor of 10 lower.

Although called a hard metal, Tungsten Carbide is actually a composite material with hard particles of Tungsten Carbide embedded in a softer matrix of metallic Cobalt .

What is the Chemical Formula for Tungsten Carbide?

The chemical formula for Tungsten Carbide is WC.

What is the History of Hard Metals or Tungsten Carbide?

Tungsten Carbide was originally developed in Germany in the 1920’s as there was a requirement for die materials that were able to stand up to the high wear encountered in the drawing of tungsten filaments for light bulbs

How is Hard Metal or Tungsten Carbide Made?

Tungsten Carbide Hard Metals are primarily produced using a Powder Metallurgy process, whereby the powdered forms of tungsten carbide and cobalt are mixed using ball mills, a binder material is added to hold the powders together during the next stage of the process which is compaction or pressing.

During the compaction processes, hydraulic presses or isostatic presses are used to compact the powders into a shape which approximates the design of the finished product.

Whilst in this condition, the powder compact can be easily machined using conventional metal working tools. This process is often referred to as “Green Machining”. Care has to be taken with the removal of the fine powder particles as they can pose a health hazard so effective extraction methods are required.

Following “Green Machining” the powder compact is then ready to be Sintered. Typically this is done in a vacuum furnace at temperatures between 1300 and 1600°C.

The sintering process causes the tungsten carbide and cobalt matrix to fuse together to produce a dense “Hard Metal”.

After sintering the material is so hard that it can only be machined by diamond grinding, a specialised form of micro machining that is relatively expensive as it is not possible to remove large amounts of materials by this process.

Applications of Tungsten Carbide and Hard Metals

Tungsten Carbides have a wide range of application in many industry sectors such as metal machining, wear parts for mining and oil industries, metal forming tools, cutting tips for saw blades and have now expanded to include consumer items such as wedding rings, plus the ball that is in many ball point pens.

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