Tungsten is a chemical element with the chemical symbol W and atomic number 74. The word tungsten comes from the Swedish language tung sten directly translatable to heavy stone. Tungsten is a very hard, dense, silvery-white, lustrous metal that tarnishes in air, forming a protective oxide coating. In powder form tungsten is gray in color.

The metal has the highest melting point of all metals, and at temperatures over 1650 oC also has the highest tensile strength. Pure tungsten is ductile, and tungsten wires, even of a very small diameter, have a very high tensile strength.

In 1758, the Swedish chemist and mineralogist, Axel Fredrik Cronstedt, discovered and described an unusually heavy mineral that he called “tung-sten”, which is Swedish for heavy stone. He was convinced that this mineral contained a new and, as yet undiscovered, element.

It was not until 1781 that a fellow Swede, Carl Wilhelm Scheele,who worked as a pharmacist and private tutor in Uppsala and Köping, succeeded in isolating the oxide (tungsten trioxide). Independent of Scheele, two Spanish chemists, the brothers Elhuyar de Suvisa, first reduced the mineral wolframite to tungsten metal in 1783. Jöns Jacob Berzelius (1816) and later also Friedrich Wöhler (1824) described the oxides and bronzes of tungsten and gave the new metal the name “wolfram”. While this established itself in Germany and Scandinavia, the Anglo-Saxon countries preferred Cronstedt’s “tungsten”.

The first industrial application of tungsten was the alloying and hardening of steels late in the 19th century. Rapid growth and widespread application followed the invention, and the launch of high speed steels by Bethlehem Steel took place in 1900 at the Paris World Exhibition.

A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as a metal in 1783. Its important ores include wolframite and scheelite. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the non-alloyed metals and the second highest of all the elements after carbon. Also remarkable is its high density of 19.3 times that of water, comparable to that of uranium and gold, and much higher (about 1.7 times) than that of lead. Tungsten with minor amounts of impurities is often brittle and hard, making it difficult to work. However, very pure tungsten, though still hard, is more ductile, and can be cut with a hard-steel hacksaw.

The unalloyed elemental form is used mainly in electrical applications. Tungsten’s many alloys have numerous applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target), and superalloys. Tungsten’s hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are most often used industrially as catalysts.
Tungsten is the only metal from the third transition series that is known to occur in biomolecules, where it is used in a few species of bacteria. It is the heaviest element known to be used by any living organism. Tungsten interferes with molybdenum and copper metabolism, and is somewhat toxic to animal life.

Tungsten and its alloys are widely used for filaments in older style (not energy saving) electric bulbs and electronic tubes. It is used for making heavy metal alloys because of its hardness. Tungsten is used for high-temperature applications such as welding. High speed steel (which can cut material at higher speeds than carbon steel), contains up to 18% tungsten. Tungsten carbide (WC or W2C) is extremely hard and is used to make drills. It is also used for jewelry because of its hardness and wear resistance.

Most of the tungsten metal powder is converted to tungsten carbide (WC) by reaction with pure carbon powder, e.g. carbon black, at 900 – 2200°C in pusher or batch furnaces, a process called carburisation. Tungsten carbide is, quantitatively, the most important tungsten compound. Because of its hardness, it is the main constituent in cemented carbide. By melting tungsten metal and tungsten monocarbide (WC) together, a eutectic composition of WC and W2C is formed. This melt is cast and rapidly quenched to form extremely hard solid particles having a fine crystal structure. A tough, feather-like structure is preferred over the brittle, blocky structure obtained by insufficient quenching. The solids are crushed and classified to various mesh sizes.

References :

1. http://en.wikipedia.org/wiki/Tungsten
2. http://www.chemicool.com/elements/tungsten.html
3. http://www.azom.com/article.aspx?ArticleID=1201

Related Post

• Tungsten
  Tungsten was finally isolated by Fausto and Juan Jose de Elhuyar in 1783 by reduction acidified wolframite with charcoal...

Alumina Balls

What’s left is the white powder called alumina, which is transformed into aluminum metal in the smelting process. Aluminum originates as an oxide called alumina. Because aluminum itself does not occur in nature as a metal, the processing of aluminum took a giant leap forward with the advent of electricity. Deposits of bauxite ore are mined and refined into alumina—one of the feedstocks for aluminum metal. Then alumina and electricity are combined in a cell with molten electrolyte called cryolite. Direct-current electricity is passed from a consumable carbon anode into the cryolite, splitting the aluminum oxide into molten aluminum metal and carbon-dioxide.

Aluminium oxide is an amphoteric oxide with the chemical formula Al2O3. It is commonly referred to as alumina (alpha-alumina), or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry. Its most significant use is in the production of aluminium metal, although it is also used as an abrasive owing to its hardness and as a refractory material owing to its high melting point. There is also a cubic ?-alumina with important technical applications.

Alumina Production

Corundum is the most common naturally occurring crystalline form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colors to trace impurities. Rubies are given their characteristic deep red color and their laser qualities by traces of chromium. Sapphires come in different colors given by various other impurities, such as iron and titanium.

Alumina Powder

Aluminium oxide is an electrical insulator but has a relatively high thermal conductivity for a ceramic material. In its most commonly occurring crystalline form, called corundum or alpha-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools.

Aluminium oxide is responsible for the resistance of metallic aluminium to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin passivation layer of alumina (4 nm thickness) forms in about 100 picoseconds on any exposed aluminium surface. This layer protects the metal from further oxidation.

The thickness and properties of this oxide layer can be enhanced using a process called anodising. A number of alloys, such as aluminium bronzes, exploit this property by including a proportion of aluminium in the alloy to enhance corrosion resistance. The alumina generated by anodising is typically amorphous, but discharge assisted oxidation processes such as plasma electrolytic oxidation result in a significant proportion of crystalline alumina in the coating, enhancing its hardness.

References :

1. http://en.wikipedia.org/
2. http://www.aluminum.org/
3. http://www.alcoa.com/

Random Posts

• Metal Forming Processes
  Metal deformations are introduced through the application of external forces to the workpiece, these forces being in equ...
• Characterization of Materials
  Characterization, when used in materials science, refers to the use of external techniques to probe into the internal st...
• How to Weld Cast Iron ?
  Welding cast iron has proven to be a very difficult task to do...
• Austempered Ductile Iron (ADI)
  Austempered Ductile Iron, or ADI, is a type of ductile iron that is characterised by increased toughness, tensile streng...
• Nitriding – How it works?
  Nitriding is a case hardening process that depends on the absorption of nitrogen into the steel. All machining, stress r...

Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. It has a wide range of applications, from paint to sunscreen to food colouring. Titanium dioxide is a naturally occurring oxide of the element titanium.

Also referred to as titanium (IV) oxide or titania, this substance also occurs naturally as three mineral compounds known as anatase, brookite, and rutile. As a pigment, titanium dioxide is used to enhance the white color of certain foods, such as dairy products and candy. Titanium dioxide occurs in nature as well-known minerals rutile, anatase and brookite, and additionally as two high pressure forms, a monoclinic baddeleyite-like form and an orthorhombic ?-PbO2-like form, both found recently at the Ries crater in Bavaria. Rutile, anatase and brookite all contain six coordinated titanium.

TiO2 Powder

Crude titanium dioxide is purified via converting to titanium tetrachloride in the chloride process. This titanium tetrachloride is distilled, and re-oxidized in a pure oxygen flame or plasma at 1500–2000 K to give pure titanium dioxide while also regenerating chlorine. The by-product iron(II) sulfate is crystallized and filtered-off to yield only the titanium salt in the digestion solution, which is processed further to give pure titanium dioxide. One method for the production of titanium dioxide with relevance to nanotechnology is solvothermal Synthesis of titanium dioxide.

Since titanium dioxide reflects light so well, it is ideal for use as a protective coating for many products, such as automobile parts and optical mirrors. The plastic industry also makes use of titanium dioxide as a coating to absorb UV light and render increased durability. Titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index, in which it is surpassed only by a few other materials. Opacity is improved by optimal sizing of the titanium dioxide particles..

In cosmetic and skin care products, titanium dioxide is used as a pigment, sunscreen and a thickener. Titanium dioxide is produced in varying particle sizes, oil and water dispersible, and with varying coatings for the cosmetic industry. Titanium dioxide is found in almost every sunscreen with a physical blocker because of its high refractive index, its strong UV light absorbing capabilities and its resistance to discolouration under ultraviolet light. Sunscreens designed for infants or people with sensitive skin are often based on titanium dioxide and/or zinc oxide, as these mineral UV blockers are believed to cause less skin irritation than other UV absorbing chemicals.

The titanium dioxide particles used in sunscreens have to be coated with silica or alumina, because titanium dioxide creates radicals in the photocatalytic reaction. Titanium dioxide, particularly in the anatase form, is a photocatalyst under ultraviolet (UV) light. Titanium dioxide is thus added to paints, cements, windows, tiles, or other products for its sterilizing, deodorizing and anti-fouling properties and is used as a hydrolysis catalyst. The photocatalytic properties of titanium dioxide were discovered by Akira Fujishima in 1967  and published in 1972. The process on the surface of the titanium dioxide was called the Honda-Fujishima effect. Titanium dioxide has potential for use in energy production: as a photocatalyst, it can carry out hydrolysis; i.e., break water into hydrogen and oxygen.

References :

1. http://en.wikipedia.org/
2. http://www.wisegeek.com/
3. http://www.youtube.com/

Related Post

• What is Titanium Dioxide ?
  Titanium dioxide is a naturally occurring oxide of the element titanium...

Zirconia Knives

Pure zirconia exists in three crystal phases at different temperatures. At very high temperatures (>2370°C) the material has a cubic structure. At low temperatures (below 1170°C) the material transforms to the monoclinic structure. This behavior destroys the mechanical properties of fabricated components during cooling and makes pure zirconia useless for any structural or mechanical application.

Several oxides which dissolve in the zirconia crystal structure can slow down or eliminate these crystal structure changes. With sufficient amounts added, the high temperature cubic structure can be maintained to room temperature. Cubic stabilized zirconia is a useful refractory and technical ceramic material because it does not go through destructive phase transitions during heating and cooling.

Zirconia Bearing

Zirconium dioxide is one of the most studied ceramic materials. Pure ZrO2 has a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at increasing temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces very large stresses, and will cause pure ZrO2 to crack upon cooling from high temperatures. Several different oxides are added to zirconia to stabilize the tetragonal and/or cubic phases: magnesium oxide (MgO), yttrium oxide, (Y2O3), calcium oxide (CaO), and cerium(III) oxide (Ce2O3), amongst others.

Zirconia is often more useful in its phase ‘stabilized’ state. Pure Zirconia when heated goes through disruptive phase changes. In some cases, the tetragonal phase can be metastable. If sufficient quantities of the metastable tetragonal phase is present, then an applied stress, magnified by the stress concentration at a crack tip, can cause the tetragonal phase to convert to monoclinic, with the associated volume expansion.

The cubic phase of zirconia also has a very low thermal conductivity, which has led to its use as a thermal barrier coating or TBC in jet and diesel engines to allow operation at higher temperatures. Another low thermal conductivity use is a ceramic fiber insulation for crystal growth furnaces, fuel cell stack insulation and infrared heating systems. Thermodynamically the higher the operation temperature of an engine, the greater the possible efficiency (see Carnot heat engine). Stabilized zirconia is used in oxygen sensors and fuel cell membranes because it has the ability to allow oxygen ions to move freely through the crystal structure at high temperatures.

References :

1. http://en.wikipedia.org/
2. http://accuratus.com/

Related Post

• What is Zirconia?
  Zirconia is an extremely refractory material. It offers chemical and corrosion inertness to temperatures well above the ...

Graphite is very soft. It is used in the “lead” of pencils, which contain no lead at all, but are made of graphite and clay. Strangely enough, graphite has exactly the same chemical formula as diamond, the hardest substance known to mankind. They are both carbon. In diamond, the atoms of carbon lock together into an incredibly strong structure. In graphite, the atoms are arranged in a different way, in layers. This means that one layer can be rubbed off quite easily, which is what happens when you write with a pencil. If you tried to write with a diamond pencil, you would gouge holes in the paper, and the table underneath!

Graphite

The mineral graphite is an allotrope of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek “to draw/write”, for its use in pencils, where it is commonly called lead (not to be confused with the metallic element lead). Unlike diamond (another carbon allotrope), graphite is an electrical conductor, a semimetal.

It is, consequently, useful in such applications as arc lamp electrodes. Graphite is the most stable form of carbon under standard conditions. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is difficult to ignite.

Graphene from graphite: Graphene is one layer of carbon atoms linked chickenwire-like within graphite.

Graphite is a polymorph of the element carbon. diamond is another polymorph. The two share the same chemistry, carbon, but have very different structures and very different properties.

1. Diamond is the hardest mineral known to man, Graphite is one of the softest.
2. Diamond is an excellent electrical insulator, Graphite is a good conductor of electricity.
3. Diamond is the ultimate abrasive, Graphite is a very good lubricant.
4. Diamond is usually transparent, Graphite is opaque.
5. Diamond crystallizes in the Isometric system and graphite crystallizes in the hexagonal system.

Graphite has a layered, planar structure. In each layer, the carbon atoms are arranged in a hexagonal lattice with separation of 0.142 nm, and the distance between planes is 0.335 nm. The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral), have very similar physical properties (except that the graphene layers stack slightly differently). The hexagonal graphite may be either flat or buckled. The alpha form can be converted to the beta form through mechanical treatment and the beta form reverts to the alpha form when it is heated above 1300 °C. The layering contributes to its lower density.

Graphite occurs in metamorphic rocks as a result of the reduction of sedimentary carbon compounds during metamorphism. It also occurs in igneous rocks and in meteorites. Minerals associated with graphite include quartz, calcite, micas and tourmaline. In meteorites it occurs with troilite and silicate minerals.

According to the United States Geological Survey (USGS), world production of natural graphite in 2008 was 1,110 thousand tonnes (kt), of which the following major exporters are: China (800 kt), India (130 kt), Brazil (76 kt), North Korea (30 kt) and Canada (28 kt). Graphite is not mined in the US, but US production of synthetic graphite in 2007 was 198 kt valued at $1.18 billion. US graphite consumption was 42 kt and 200 kt for natural and synthetic graphite, respectively.

References :

1. http://en.wikipedia.org/
2. http://www.galleries.com/
3. http://gwydir.demon.co.uk

Random Posts

• What is Carbon Steel ?
  Carbon steel, also called plain-carbon steel, is a metal alloy, a combination of two elements, iron and carbon, where ot...
• What is Scrap Metal ?
  Scrap is a term used to describe recyclable and other materials left over from every manner of product consumption, such...
• Polymer Clay
  Polymer clay is a sculptable material based on the polymer polyvinyl chloride (PVC). ...
• White Cast Iron
  White Iron is unalloyed cast iron with low carbon and silicon content such that the structure is hard brittle iron carbi...
• Biomaterials
  A biomaterial is any matter, surface, or construct that interacts with biological systems. The development of biomateria...