Nanoparticles are particles between 1 and 100 nanometres in size with a surrounding interfacial layer. The interfacial layer is an integral part of nanoscale matter, fundamentally affecting all of its properties; the interfacial layer consists of ions and organic molecules. Organic molecules coating inorganic nanoparticles are known as stabilizers and surface ligands, or passivating agents. In nanotechnology, a particle is defined as a small object that behaves as a whole unit with respect to its transport and properties. Particles are further classified according to diameter; the term "nanoparticle" is not applied to individual molecules. Ultrafine particles are the same as nanoparticles and between 1 and 100 nm in size, as opposed to fine particles are sized between 100 and 2,500 nm, coarse particles cover a range between 2,500 and 10,000 nm; the reason for the synonymous definition of nanoparticles and ultrafine particles is that, during the 1970s and 80s, when the first thorough fundamental studies with "nanoparticles" were underway in the USA and Japan, they were called "ultrafine particles".
However, during the 1990s before the National Nanotechnology Initiative was launched in the USA, the new name, "nanoparticle," had become more common. Nanoparticles can exhibit size-related properties different from those of either fine particles or bulk materials. Nanoclusters have at least one dimension a narrow size distribution. Nanopowders nanoparticles, or nanoclusters. Nanometer-sized single crystals, or single-domain ultrafine particles, are referred to as nanocrystals. According to ISO Technical Specification 80004, a nanoparticle is defined as a nano-object with all three external dimensions in the nanoscale, whose longest and shortest axes do not differ with a significant difference being a factor of at least 3; the terms colloid and nanoparticle are not interchangeable. A colloid is a mixture; the term applies only if the particles are larger than atomic dimensions but small enough to exhibit Brownian motion, with the critical size range ranging from nanometers to micrometers. Colloids can contain particles too large to be nanoparticles, nanoparticles can exist in non-colloidal form, for examples as a powder or in a solid matrix.
Although nanoparticles are associated with modern science, they have a long history. Nanoparticles were used by artisans as far back as Rome in the fourth century in the famous Lycurgus cup made of dichroic glass as well as the ninth century in Mesopotamia for creating a glittering effect on the surface of pots. In modern times, pottery from the Middle Ages and Renaissance retains a distinct gold- or copper-colored metallic glitter; this luster is caused by a metallic film, applied to the transparent surface of a glazing. The luster can still be visible if the film has resisted other weathering; the luster originates within the film itself, which contains silver and copper nanoparticles dispersed homogeneously in the glassy matrix of the ceramic glaze. These nanoparticles are created by the artisans by adding copper and silver salts and oxides together with vinegar and clay on the surface of previously-glazed pottery; the object is placed into a kiln and heated to about 600 °C in a reducing atmosphere.
In heat the glaze softens, causing the copper and silver ions to migrate into the outer layers of the glaze. There the reducing atmosphere reduced the ions back to metals, which came together forming the nanoparticles that give the color and optical effects. Luster technique showed; the technique originated in the Muslim world. As Muslims were not allowed to use gold in artistic representations, they sought a way to create a similar effect without using real gold; the solution they found was using luster. Michael Faraday provided the first description, in scientific terms, of the optical properties of nanometer-scale metals in his classic 1857 paper. In a subsequent paper, the author points out that: "It is well known that when thin leaves of gold or silver are mounted upon glass and heated to a temperature, well below a red heat, a remarkable change of properties takes place, whereby the continuity of the metallic film is destroyed; the result is that white light is now transmitted, reflection is correspondingly diminished, while the electrical resistivity is enormously increased."
Nanoparticles are of great scientific interest as they are, in effect, a bridge between bulk materials and atomic or molecular structures. A bulk material should have constant physical properties regardless of its size, but at the nano-scale size-dependent properties are observed. Thus, the properties of materials change as their size approaches the nanoscale and as the percentage of the surface in relation to the percentage of the volume of a material becomes significant. For bulk materials larger than one micrometer, the percentage of the surface is insignificant in relation to the volume in the bulk of the material; the interesting and sometimes unexpected properties of nanoparticles are therefore due to the large surface area of the material, which dominates the contributions made by the small bulk of the material. Nanoparticles possess unexpected optical properties as they are small enough
Electrostatic discharge is the sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown. A buildup of static electricity can be caused by electrostatic induction; the ESD occurs when differently-charged objects are brought close together or when the dielectric between them breaks down creating a visible spark. ESD can create spectacular electric sparks, but less dramatic forms which may be neither seen nor heard, yet still be large enough to cause damage to sensitive electronic devices. Electric sparks require a field strength above 40 kV/cm in air, as notably occurs in lightning strikes. Other forms of ESD include corona discharge from sharp electrodes and brush discharge from blunt electrodes. ESD can cause harmful effects of importance in industry, including explosions in gas, fuel vapor and coal dust, as well as failure of solid state electronics components such as integrated circuits; these can suffer permanent damage.
Electronics manufacturers therefore establish electrostatic protective areas free of static, using measures to prevent charging, such as avoiding charging materials and measures to remove static such as grounding human workers, providing antistatic devices, controlling humidity. ESD simulators may be used to test electronic devices, for example with a human body model or a charged device model. One of the causes of ESD events is static electricity. Static electricity is generated through tribocharging, the separation of electric charges that occurs when two materials are brought into contact and separated. Examples of tribocharging include walking on a rug, rubbing a plastic comb against dry hair, rubbing a balloon against a sweater, ascending from a fabric car seat, or removing some types of plastic packaging. In all these cases, the breaking of contact between two materials results in tribocharging, thus creating a difference of electrical potential that can lead to an ESD event. Another cause of ESD damage is through electrostatic induction.
This occurs when an electrically charged object is placed near a conductive object isolated from the ground. The presence of the charged object creates an electrostatic field that causes electrical charges on the surface of the other object to redistribute. Though the net electrostatic charge of the object has not changed, it now has regions of excess positive and negative charges. An ESD event may occur. For example, charged regions on the surfaces of styrofoam cups or bags can induce potential on nearby ESD sensitive components via electrostatic induction and an ESD event may occur if the component is touched with a metallic tool. ESD can be caused by energetic charged particles impinging on an object; this causes deep charging. This is a known hazard for most spacecraft; the most spectacular form of ESD is the spark, which occurs when a heavy electric field creates an ionized conductive channel in air. This can cause minor discomfort to people, severe damage to electronic equipment, fires and explosions if the air contains combustible gases or particles.
However, many ESD events occur without a audible spark. A person carrying a small electric charge may not feel a discharge, sufficient to damage sensitive electronic components; some devices may be damaged by discharges as small as 30 V. These invisible forms of ESD can cause outright device failures, or less obvious forms of degradation that may affect the long term reliability and performance of electronic devices; the degradation in some devices may not become evident until well into their service life. A spark is triggered when the electric field strength exceeds 4–30 kV/cm — the dielectric field strength of air; this may cause a rapid increase in the number of free electrons and ions in the air, temporarily causing the air to abruptly become an electrical conductor in a process called dielectric breakdown. The best known example of a natural spark is lightning. In this case the electric potential between a cloud and ground, or between two clouds, is hundreds of millions of volts; the resulting current.
On a much smaller scale, sparks can form in air during electrostatic discharges from charged objects that are charged to as little as 380 V. Earth's atmosphere consists of 78 % nitrogen. During an electrostatic discharge, such as a lightning flash, the affected atmospheric molecules become electrically overstressed; the diatomic oxygen molecules are split, recombine to form ozone, unstable, or reacts with metals and organic matter. If the electrical stress is high enough, nitrogen oxides can form. Both products are toxic to animals, nitrogen oxides are essential for nitrogen fixation. Ozone is used in water purification. Sparks are an ignition source in combustible environments that may lead to catastrophic explosions in concentrated fuel environments. Most explosions can be traced back to a tiny electrostatic discharge, whether it was an unexpected combustible fuel leak invading a known open air sparking device, or an unexpected spark in a known fuel rich environment; the end result is the same if oxygen is present and the three criteria of the fire triangle have been combined.
Many electronic components microchips, can be damaged by ESD. Sensitive components need to be protected during and after manufacture, during shipping and device assembly
Potassium permanganate is an inorganic chemical compound and medication. As a medication it is used for cleaning dermatitis, it is a salt consisting of K + and MnO − 4 ions. It is a strong oxidizing agent, it dissolves in water to give intensely pink or purple solutions, the evaporation of which leaves prismatic purplish-black glistening crystals. In 2000, worldwide production was estimated at 30,000 tonnes. In this compound, manganese is in the +7 oxidation state; the wholesale cost in the developing world is about US$0.01 per gram of powder. In the United Kingdom a 400 milligram tablet costs the NHS £0.51. All applications of potassium permanganate exploit its oxidizing properties; as a strong oxidant that does not generate toxic byproducts, KMnO4 has many niche uses. Potassium permanganate is used for a number of skin conditions; this includes fungal infections of the foot, pemphigus, superficial wounds and tropical ulcers. It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system.
Potassium permanganate is used extensively in the water treatment industry. It is used as a regeneration chemical to remove iron and hydrogen sulfide from well water via a "Manganese Greensand" Filter. "Pot-Perm" is obtainable at pool supply stores and is used additionally to treat waste water. It was used to disinfect drinking water and can turn the water pink, it finds application in the control of nuisance organisms such as zebra mussels in fresh water collection and treatment systems. Aside from its use in water treatment, the other major application of KMnO4 is as a reagent for the synthesis of organic compounds. Significant amounts are required for the synthesis of ascorbic acid, saccharin, isonicotinic acid, pyrazinoic acid. Called Baeyer's reagent after the German organic chemist Adolf von Baeyer, KMnO4 is used in Qualitative organic analysis to test for the presence of unsaturation; the reagent is an alkaline solution of potassium permanganate. Reaction with double or triple bonds causes the color to fade from purplish-pink to brown.
Aldehydes and formic acid give a positive test. The test is antiquated. Potassium permanganate can be used to quantitatively determine the total oxidizable organic material in an aqueous sample; the value determined is known as the permanganate value. In analytical chemistry, a standardized aqueous solution of KMnO4 is sometimes used as an oxidizing titrant for redox titrations. In a related way, it is used as a reagent to determine the Kappa number of wood pulp. For the standardization of KMnO4 solutions, reduction by oxalic acid is used. Aqueous, acidic solutions of KMnO4 are used to collect gaseous mercury in flue gas during stationary source emissions testing. In histology, potassium permanganate was used as a bleaching agent. Ethylene absorbents extend storage time of bananas at high temperatures; this effect can be exploited by packing bananas in polyethylene together with potassium permanganate. By removing ethylene by oxidation, the permanganate delays the ripening, increasing the fruit's shelf life up to 4 weeks without the need for refrigeration.
Potassium permanganate is included in survival kits: as a fire starter, water sterilizer, for creating distress signals on snow. Potassium permanganate is added to "plastic sphere dispensers" to create backfires and controlled burns. Polymer spheres resembling ping-pong balls containing small amounts of permanganate are injected with ethylene glycol and projected towards the area where ignition is desired, where they spontaneously ignite seconds later. Both handheld and helicopter- or boat-mounted plastic sphere dispensers are used. Potassium permanganate is one of the principal chemicals used in the film and television industries to "age" props and set dressings, its ready conversion to brown MnO2 creates "hundred-year-old" or "ancient" looks on Hessian cloth, ropes and glass. In 1659, Johann Rudolf Glauber fused a mixture of the mineral pyrolusite and potassium carbonate to obtain a material that, when dissolved in water, gave a green solution which shifted to violet and finally red; this report represents the first description of the production of potassium permanganate.
Just under 200 years London chemist Henry Bollmann Condy had an interest in disinfectants. He patented this solution, marketed it as'Condy's Fluid'. Although effective, the solution was not stable; this was overcome by using potassium hydroxide rather than NaOH. This was more stable, had the advantage of easy conversion to the effective potassium permanganate crystals; this crystalline material was known as'Condy's crystals' or'Condy's powder'. Potassium permanganate was comparatively easy to manufacture, so Condy was subsequently forced to spend considerable time in litigation to stop competitors from marketing similar products. Early photographers used it as a component of flash powder, it is now replaced with other oxidizers, due to the instability of permanganate mixtures. Potassium permanganate is produced industrially from manganese dioxide, which occurs as the mineral pyrolusite; the MnO2 is fused with potassium hydroxide and heated in air or with another source of oxygen, like potassium nitrate or potassium chlorate.
This process gives potassium manganate: 2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O(With sodium hydroxide, the end produ
Incendiary weapons, incendiary devices, incendiary munitions, or incendiary bombs are weapons designed to start fires or destroy sensitive equipment using fire, that use materials such as napalm, magnesium powder, chlorine trifluoride, or white phosphorus. Though colloquially known as bombs, they are not explosives but in fact are designed to slow the process of chemical reactions and use ignition rather than detonation to start and or maintain the reaction. Napalm for example, is petroleum thickened with certain chemicals into a'gel' to slow, but not stop, releasing energy over a longer time than an explosive device. In the case of napalm, the gel adheres to resists suppression. A range of early thermal weapons were in use ancient and early armies using hot pitch, resin, animal fat and other similar compounds. Substances such as quicklime and sulfur could be blinding. Incendiary mixtures, such as the petroleum-based Greek fire, were launched by throwing machines or administered through a siphon.
Sulfur- and oil-soaked materials were sometimes ignited and thrown at the enemy, or attached to spears and bolts and fired by hand or machine. Some siege techniques—such as mining and boring—relied on combustibles and fire to complete the collapse of walls and structures. Towards the latter part of the period, gunpowder was invented, which increased the sophistication of the weapons, starting with fire lances; the first incendiary devices to be dropped during World War I fell on coastal towns in the south west of England on the night of 18–19 January 1915. The small number of German bombs known as firebombs, were finned containers filled with kerosene and oil and wrapped with tar-covered rope, they were dropped from Zeppelin airships. On 8 September 1915, Zeppelin L-13 dropped a large number of firebombs, but then the results were poor and they were ineffective in terms of the damage inflicted, they did have a considerable effect on the morale of the civilian population of the United Kingdom.
After further experiments with 5-litre barrels of benzol, in 1918, the B-1E Elektron fire bomb was developed by scientists and engineers at the Griesheim-Elektron chemical works. The bomb was ignited by a thermite charge, but the main incendiary effect was from the magnesium and aluminium alloy casing, which ignited at 650° Celsius, burned at 1,100 °C and emitted vapour that burned at 1,800 °C. A further advantage of the alloy casing was its lightness, being a quarter of the density of steel, which meant that each bomber could carry a considerable number; the German High Command devised an operation called "The Fire Plan", which involved the use of the whole German heavy bomber fleet, flying in waves over London and Paris and dropping all the incendiary bombs that they could carry, until they were either all shot down or the crews were too exhausted to fly. The hope was that the two capitals would be engulfed in an inextinguishable blaze, causing the Allies to sue for peace. Thousands of Elektron bombs were stockpiled at forward bomber bases and the operation was scheduled for August and again in early September 1918, but on both occasions, the order to take off was countermanded at the last moment because of the fear of Allied reprisals against German cities.
The Royal Air Force had used their own "Baby" Incendiary Bomb which contained a thermite charge. A plan to fire bomb New York with new long range Zeppelins of the L70 class was proposed by the naval airship fleet commander Peter Strasser in July 1918, but it was vetoed by Admiral Reinhard Scheer. Incendiary bombs were used extensively in World War II as an effective bombing weapon in a conjunction with high-explosive bombs; the most famous incendiary attacks are the bombing of Dresden and the bombing of Tokyo on 10 March 1945. Many different configurations of incendiary bombs and a wide range of filling materials such as isobutyl methacrylate polymer and similar jellied-petroleum formulas were used, many of them developed by the US Chemical Warfare Service. Different methods of delivery, e.g. small bombs, bomblet clusters and large bombs, were tested and implemented. For example, a large bomb casing was filled with small sticks of incendiary. An explosive charge would ignite the incendiary material starting a raging fire.
The fire would burn at extreme temperatures that could destroy most buildings made of wood or other combustible materials. The German Luftwaffe started the war using the 1918-designed one-kilogram magnesium alloy B-1E Elektronbrandbombe. Racks holding 36 of these bombs were developed, four of which could, in turn, be fitted to an electrically triggered dispenser so that a single He 111 bomber could carry 1,152 incendiary bombs, or more a mixed load. Less successful was the Flammenbombe, a 250 kg or 500 kg high explosive bomb case filled with an inflammable oil mixture, which failed to detonate and was withdrawn in January 1941. In World War II, incendiaries were principally developed in order to destroy the many small, decentralised war industries located throughout vast tracts of city land in an effort to escape destruction by conventionally aimed high-explosive bombs; the civilian destruction caused by such weapons earned them a reputation as terro
Copper oxide or cupric oxide is the inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of the other being Cu2O or cuprous oxide; as a mineral, it is known as tenorite. It is a product of copper mining and the precursor to many other copper-containing products and chemical compounds, it is produced on a large scale by pyrometallurgy used to extract copper from ores. The ores are treated with an aqueous mixture of ammonium carbonate and oxygen to give copper and copper ammine complexes, which are extracted from the solids; these complexes are decomposed with steam to give CuO. It can be formed by heating copper in air at around 300 – 800°C: 2 Cu + O2 → 2 CuOFor laboratory uses, pure copper oxide is better prepared by heating copper nitrate, copper hydroxide or basic copper carbonate: 2 Cu2 → 2 CuO + 4 NO2 + O2 Cu2 → CuO + H2O Cu2CO32 → 2CuO + CO2 + H2O Copper oxide dissolves in mineral acids such as hydrochloric acid, sulfuric acid or nitric acid to give the corresponding copper salts: CuO + 2 HNO3 → Cu2 + H2O CuO + 2 HCl → CuCl2 + H2O CuO + H2SO4 → CuSO4 + H2OIt reacts with concentrated alkali to form the corresponding cuprate salts: 2 MOH + CuO + H2O → M2It can be reduced to copper metal using hydrogen, carbon monoxide, or carbon: CuO + H2 → Cu + H2O CuO + CO → Cu + CO2 2CuO + C → 2Cu + CO2When cupric oxide is substituted for iron oxide in thermite the resulting mixture is a low explosive, not an incendiary.
Copper oxide belongs to the monoclinic crystal system. The copper atom is coordinated by 4 oxygen atoms in an square planar configuration; the work function of bulk CuO is 5.3eVCopper oxide is a p-type semiconductor, with a narrow band gap of 1.2 eV. Cupric oxide can be used to produce dry cell batteries; as a significant product of copper mining, copper oxide is the starting point for the production of other copper salts. For example, many wood preservatives are produced from copper oxide. Cupric oxide is used as a pigment in ceramics to produce blue and green, sometimes gray, pink, or black glazes, it is incorrectly used as a dietary supplement in animal feed. Due to low bioactivity, negligible copper is absorbed, it is used when welding with copper alloys. Cupric oxide can be used to safely dispose of hazardous materials such as cyanide, halogenated hydrocarbons and dioxins, through oxidation; the decomposition reactions of phenol and pentachlorophenol follow these pathways: C6H5OH + 14CuO → 6CO2 + 3H2O + 14Cu C6Cl5OH + 2H2O + 9CuO → 6CO2 + 5HCl + 9Cu Patina Copper oxide National Pollutant Inventory - Copper and compounds fact sheet Copper oxides project page CDC - NIOSH Pocket Guide to Chemical Hazards
RDX is an organic compound with the formula 3. It is a white solid without smell or taste used as an explosive. Chemically, it is classified as a nitramide, chemically similar to HMX. A more energetic explosive than TNT, it was used in World War II and remains common in military applications, it is used in mixtures with other explosives and plasticizers or phlegmatizers. RDX is stable in storage and is considered one of the most energetic and brisant of the military high explosives. RDX is known, but less as cyclonite, hexogen, T4, chemically, as cyclotrimethylenetrinitramine. In the 1930s, the Royal Arsenal, started investigating cyclonite to use against German U-boats that were being built with thicker hulls; the goal was to develop an explosive more energetic than TNT. For security reasons, Britain termed cyclonite as "Research Department Explosive"; the term RDX appeared in the United States in 1946. The first public reference in the United Kingdom to the name RDX, or R. D. X. to use the official title, appeared in 1948.
RDX was used during World War II in explosive mixtures with TNT such as Torpex, Composition B, H6. RDX was used in one of the first plastic explosives; the bouncing bomb depth charges used in the "Dambusters Raid" each contained 6,600 pounds of Torpex. RDX is believed to have been used in many bomb plots, including terrorist plots. RDX is the base for a number of common military explosives: Composition A: Granular explosive consisting of RDX and plasticizing wax, such as composition A-3 and composition A-5. Composition B: Castable mixtures of 59.5% RDX and 39.4% TNT with 1% wax as desensitizer. Composition C: The original composition C was used in World War II, but there have been subsequent variations including C-2, C-3, C-4. Composition CH-6: 97.5% RDX, 1.5% calcium stearate, 0.5% polyisobutylene, 0.5% graphite DBX: Castable mixture consisting of 21% RDX, 21% ammonium nitrate, 40% TNT, 18% powdered aluminium, developed during World War II, it was to be used in underwater munitions as a substitute for Torpex employing only half the amount of then-strategic RDX, as the supply of RDX became more adequate, the mixture was shelved Cyclotol: Castable mixture of RDX with TNT designated by the amount of RDX/TNT, such as Cyclotol 70/30 HBX: Castable mixtures of RDX, TNT, powdered aluminium, D-2 wax with calcium chloride H-6: Castable mixture of RDX, TNT, powdered aluminum, paraffin wax PBX: RDX is used as a major component of many polymer-bonded explosives.
Examples of RDX-based PBX formulations include, but are not limited to: PBX-9007, PBX-9010, PBX-9205, PBX-9407, PBX-9604, PBXN-106, PBXN-3, PBXN-6, PBXN-10, PBXN-201, PBX-0280, PBX Type I, PBXC-116, PBXAF-108, etc. Semtex: Plastic demolition explosive containing RDX and PETN as major energetic components Torpex: 42% RDX, 40% TNT, 18% powdered aluminium; the demolition of the Jamestown Bridge in the U. S. state of Rhode Island was one instance. RDX is classified by chemists as a hexahydro-1,3,5-triazine derivative, it is obtained by treating hexamine with white fuming nitric acid. This nitrolysis reaction produces dinitromethane, ammonium nitrate, water as byproducts; the overall reaction is: C6H12N4 + 10 HNO3 → C3H6N6O6 + 3 CH22 + NH4NO3 + 3 H2O RDX was used by both sides in World War II. The U. S. produced about 15,000 long tons per month during WWII and Germany about 7,000 long tons per month. RDX had the major advantages of possessing greater explosive force than TNT, used in World War I, requiring no additional raw materials for its manufacture.
RDX was reported in 1898 by Georg Friedrich Henning, who obtained a German patent for its manufacture by nitrolysis of hexamine with concentrated nitric acid. In this patent, the medical properties of RDX were mentioned; the German military started referring to it as hexogen. Research and development findings were not published further until Edmund von Herz, described as an Austrian and a German citizen, obtained a British patent in 1921 and a United States patent in 1922. Both patent claims were initiated in Austria; the British patent claims included the manufacture of RDX by nitration, its use with or without other explosives, its use as a bursting charge and as an initiator. The U. S. patent claim was for the use of a hollow explosive device containing RDX and a detonator cap containing RDX. In the 1930s, Germany developed improved production methods. During World War II, Germany used the code names
Titanium is a chemical element with symbol Ti and atomic number 22. It is a lustrous transition metal with a silver color, low density, high strength. Titanium is resistant to corrosion in sea water, aqua regia, chlorine. Titanium was discovered in Cornwall, Great Britain, by William Gregor in 1791, was named by Martin Heinrich Klaproth after the Titans of Greek mythology; the element occurs within a number of mineral deposits, principally rutile and ilmenite, which are distributed in the Earth's crust and lithosphere, it is found in all living things, water bodies and soils. The metal is extracted from its principal mineral ores by the Hunter processes; the most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments. Other compounds include a component of smoke screens and catalysts. Titanium can be alloyed with iron, aluminium and molybdenum, among other elements, to produce strong, lightweight alloys for aerospace, industrial processes, agri-food, medical prostheses, orthopedic implants and endodontic instruments and files, dental implants, sporting goods, mobile phones, other applications.
The two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element. In its unalloyed condition, titanium is less dense. There are two allotropic forms and five occurring isotopes of this element, 46Ti through 50Ti, with 48Ti being the most abundant. Although they have the same number of valence electrons and are in the same group in the periodic table and zirconium differ in many chemical and physical properties; as a metal, titanium is recognized for its high strength-to-weight ratio. It is a strong metal with low density, quite ductile and metallic-white in color; the high melting point makes it useful as a refractory metal. It is paramagnetic and has low electrical and thermal conductivity. Commercially pure grades of titanium have ultimate tensile strength of about 434 MPa, equal to that of common, low-grade steel alloys, but are less dense. Titanium is 60% denser than aluminium, but more than twice as strong as the most used 6061-T6 aluminium alloy.
Certain titanium alloys achieve tensile strengths of over 1,400 MPa. However, titanium loses strength when heated above 430 °C. Titanium is not as hard as some grades of heat-treated steel. Machining requires precautions, because the material can gall unless sharp tools and proper cooling methods are used. Like steel structures, those made from titanium have a fatigue limit that guarantees longevity in some applications; the metal is a dimorphic allotrope of an hexagonal α form that changes into a body-centered cubic β form at 882 °C. The specific heat of the α form increases as it is heated to this transition temperature but falls and remains constant for the β form regardless of temperature. Like aluminium and magnesium, titanium metal and its alloys oxidize upon exposure to air. Titanium reacts with oxygen at 1,200 °C in air, at 610 °C in pure oxygen, forming titanium dioxide, it is, slow to react with water and air at ambient temperatures because it forms a passive oxide coating that protects the bulk metal from further oxidation.
When it first forms, this protective layer continues to grow slowly. Atmospheric passivation gives titanium excellent resistance to corrosion equivalent to platinum. Titanium is capable of withstanding attack by dilute sulfuric and hydrochloric acids, chloride solutions, most organic acids. However, titanium is corroded by concentrated acids; as indicated by its negative redox potential, titanium is thermodynamically a reactive metal that burns in normal atmosphere at lower temperatures than the melting point. Melting is possible only in a vacuum. At 550 °C, it combines with chlorine, it reacts with the other halogens and absorbs hydrogen. Titanium is one of the few elements that burns in pure nitrogen gas, reacting at 800 °C to form titanium nitride, which causes embrittlement; because of its high reactivity with oxygen and some other gases, titanium filaments are applied in titanium sublimation pumps as scavengers for these gases. Such pumps inexpensively and reliably produce low pressures in ultra-high vacuum systems.
Titanium is the ninth-most abundant element in the seventh-most abundant metal. It is present as oxides in most igneous rocks, in sediments derived from them, in living things, natural bodies of water. Of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titanium, its proportion in soils is 0.5 to 1.5%. Common titanium-containing minerals are anatase, ilmenite, perovskite and titanite. Akaogiite is an rare mineral consisting of titanium dioxide. Of these minerals, only rutile and ilmenite have economic importance, yet they are difficult to find in high concentrations. About 6.0 and 0.7 million tonnes of those minerals were mined in 2011, respectively. Signi