An autoclave is a pressure chamber used to carry out industrial processes requiring elevated temperature and pressure different from ambient air pressure. Autoclaves are used in medical applications to perform sterilization and in the chemical industry to cure coatings and vulcanize rubber and for hydrothermal synthesis. Industrial autoclaves are used in industrial applications regarding composites. Many autoclaves are used to sterilize equipment and supplies by subjecting them to pressurized saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents; the autoclave was invented by Charles Chamberland in 1884, although a precursor known as the steam digester was created by Denis Papin in 1679. The name comes from Greek auto- meaning self, Latin clavis meaning key, thus a self-locking device. Sterilization autoclaves are used in microbiology, podiatry, body piercing, veterinary medicine, funerary practice and prosthetics fabrication, they vary in size and function depending on the media to be sterilized and are sometimes called retort in the chemical and food industries.
Typical loads include laboratory glassware, other equipment and waste, surgical instruments, medical waste. A notable recent and popular application of autoclaves is the pre-disposal treatment and sterilization of waste material, such as pathogenic hospital waste. Machines in this category operate under the same principles as conventional autoclaves in that they are able to neutralize infectious agents by using pressurized steam and superheated water. A new generation of waste converters is capable of achieving the same effect without a pressure vessel to sterilize culture media, rubber material, dressings, etc, it is useful for materials which cannot withstand the higher temperature of a hot air oven. Autoclaves are widely used to cure composites and in the vulcanization of rubber; the high heat and pressure that autoclaves generate help to ensure that the best possible physical properties are repeatable. The aerospace industry and sparmakers have autoclaves well over 50 feet long, some over 10 feet wide.
Other types of autoclaves are used to grow crystals under high pressures. Synthetic quartz crystals used in the electronics industry are grown in autoclaves. Packing of parachutes for specialist applications may be performed under vacuum in an autoclave, which allows the chutes to be warmed and inserted into their packs at the smallest volume, it is important to ensure that all of the trapped air is removed from the autoclave before activation, as trapped air is a poor medium for achieving sterility. Steam at 134 °C can achieve in three minutes the same sterility that hot air at 160 °C can take two hours to achieve. Methods of air removal include: Downward displacement: As steam enters the chamber, it fills the upper areas first as it is less dense than air; this process compresses the air to the bottom, forcing it out through a drain which contains a temperature sensor. Only when air evacuation is complete does the discharge stop. Flow is controlled by a steam trap or a solenoid valve, but bleed holes are sometimes used in conjunction with a solenoid valve.
As the steam and air mix, it is possible to force out the mixture from locations in the chamber other than the bottom. Steam pulsing: air dilution by using a series of steam pulses, in which the chamber is alternately pressurized and depressurized to near atmospheric pressure. Vacuum pumps: a vacuum pump sucks air or air/steam mixtures from the chamber. Superatmospheric cycles: achieved with a vacuum pump, it starts with a vacuum followed by a steam pulse followed by a vacuum followed by a steam pulse. The number of pulses depends on the particular cycle chosen. Subatmospheric cycles: similar to the superatmospheric cycles, but chamber pressure never exceeds atmospheric pressure until they pressurize up to the sterilizing temperature. A medical autoclave is a device; this means that all bacteria, viruses and spores are inactivated. However, such as those associated with Creutzfeldt–Jakob disease, some toxins released by certain bacteria, such as Cereulide, may not be destroyed by autoclaving at the typical 134 °C for three minutes or 121 °C for 15 minutes.
Although a wide range of archaea species, including Geogemma barosii, can survive and reproduce at temperatures above 121 °C, no archaea are known to be infectious or otherwise pose a health risk to humans. Autoclaves are found in many medical settings and other places that need to ensure the sterility of an object. Many procedures today employ single-use items rather than reusable items; this first happened with hypodermic needles, but today many surgical instruments are single-use rather than reusable items. Autoclaves are of particular importance in poorer countries due to the much greater amount of equipment, re-used. Providing stove-top or solar autoclaves to rural medical centers has been the subject of several proposed medical aid missions; because damp heat is used, heat-labile products cannot be sterilized this way or they will melt. Paper and other products that may be damaged by steam must be sterilized another way. In all autoclaves, items should always be separated to allow the ste
The IUPAC defines calcination as "heating to high temperatures in air or oxygen". However, calcination is used to mean a thermal treatment process in the absence or limited supply of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition. A calciner is a steel cylinder that rotates inside a heated furnace and performs indirect high-temperature processing within a controlled atmosphere; the process of calcination derives its name from the Latin calcinare due to its most common application, the decomposition of calcium carbonate to calcium oxide and carbon dioxide, in order to create cement. The product of calcination is referred to in general as "calcine", regardless of the actual minerals undergoing thermal treatment. Calcination is carried out in furnaces or reactors of various designs including shaft furnaces, rotary kilns, multiple hearth furnaces, fluidized bed reactors. Examples of calcination processes include the following: decomposition of carbonate ores, as in the calcination of limestone to drive off carbon dioxide.
Several reports on Microwave Assisted Calcination methods were made in 2011 years. Calcination reactions take place at or above the thermal decomposition temperature or the transition temperature; this temperature is defined as the temperature at which the standard Gibbs free energy for a particular calcination reaction is equal to zero. For example, in limestone calcination, a decomposition process, the chemical reaction is CaCO3 → CaO + CO2The standard Gibbs free energy of reaction is approximated as ΔG°r = 177,100 − 158 T; the standard free energy of reaction is 0 in this case when the temperature, T, is equal to 1121 K, or 848 °C. See calcination equilibrium of calcium carbonate Calcination can be used in carbon negative electricity generation. In some cases, calcination of a metal results in oxidation of the metal. Jean Rey noted that lead and tin when calcinated gained weight as they were being oxidized. In alchemy, calcination was believed to be one of the 12 vital processes required for the transformation of a substance.
Alchemists distinguished two kinds of calcination and potential. Actual calcination is that brought about by actual fire, from wood, coals, or other fuel, raised to a certain temperature. Potential calcination is that brought about by potential fire, such as corrosive chemicals. There was philosophical calcination, said to occur when horns, etc. were hung over boiling water, or other liquor, until they had lost their mucilage, were reducible into powder
Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
Bauxite tailings known as red mud, red sludge, bauxite residue, or alumina refinery residues, is a alkaline waste product composed of iron oxide, generated in the industrial production of alumina. Annually, about 77 million tons of the red special waste are produced, causing a serious disposal problem in the mining industry; the scale of production makes the waste product an important one, issues with its storage are reviewed and every opportunity is explored to find uses for it. Over 95% of the alumina produced globally is through the Bayer process. Annual production of alumina in 2015 was 115 million tonnes resulting in the generation of about 150 million tonnes of bauxite tailings/residue. Red mud is a side-product of the Bayer process, the principal means of refining bauxite en route to alumina; the resulting alumina is the raw material for producing aluminium by the Hall–Héroult process. A typical bauxite plant produces one to two times as much red mud as alumina; this ratio is dependent on the type of bauxite used in the refining process and the extraction conditions.
There are over 60 manufacturing operations across the world using the Bayer process to make alumina from bauxite ore. Bauxite ore is mined in open cast mines, transferred to an alumina refinery for processing; the alumina is extracted using sodium hydroxide under conditions of high pressure. The insoluble part of the bauxite is removed, giving rise to a solution of sodium aluminate, seeded with an aluminium hydroxide crystal and allowed to cool which causes the remaining aluminium hydroxide to precipitate from the solution; some of the aluminium hydroxide is used to seed the next batch, while the remainder is calcined at over 1000 °C in rotary kilns or fluid flash calciners to produce aluminium oxide. The alumina content of the bauxite used is about 50%, but ores with a wide range of alumina contents can be used; the aluminium compound may be present as boehmite or diaspore. The tailings/residue invariably has a high concentration of iron oxide which gives the product a characteristic red colour.
A small residual amount of the sodium hydroxide used in the process remains with the tailings, causing the material to have a high pH/alkalinity >12. Various stages in the solid/liquid separation process are introduced to recycle as much sodium hydroxide as possible from the residue back into the Bayer Process in order to make the process as efficient as possible and reduce production costs; this lowers the final alkalinity of the tailings making it easier and safer to handle and store. Red mud is composed of a mixture of metallic oxides; the red colour arises from iron oxides. The mud is basic with a pH ranging from 10 to 13. In addition to iron, the other dominant components include silica, unleached residual alumina, titanium oxide; the main constituents of the residue after the extraction of the aluminium component are insoluble metallic oxides. The percentage of these oxides produced by a particular alumina refinery will depend on the quality and nature of the bauxite ore and the extraction conditions.
The table below shows the composition ranges for common chemical constituents, but the values vary widely: Mineralogically expressed the components present are: In general, the composition of the residue reflects that of the non-aluminium components, with the exception of part of the silicon component: crystalline silica will not react but some of the silica present termed, reactive silica, will react under the extraction conditions and form sodium aluminium silicate. Discharge of red mud is hazardous environmentally because of its alkalinity. In 1972 there was a Red Mud discharge off the coast of Corsica by the Italian company Montedison; the case is important in international law governing the Mediterranean sea. In October 2010 one million cubic meters of red mud from an alumina plant near Kolontár in Hungary was accidentally released into the surrounding countryside in the Ajka alumina plant accident, killing ten people and contaminating a large area. All life in the Marcal river was said to have been "extinguished" by the red mud, within days the mud had reached the Danube.
However, the long-term environmental effects of the spill have been minor. Tailings storage methods have changed since the original plants were built; the practice in early years was to pump the tailings slurry, at a concentration of about 20% solids, into lagoons or ponds sometimes created in former bauxite mines or depleted quarries. In other cases, impoundments were constructed with dams or levees, while for some operations valleys were dammed and the tailings deposited in these holding areas, it was common practice for the tailings to be discharged into rivers, estuaries, or the sea via pipelines or barges. All disposal in the sea and rivers has now stopped; as residue storage space ran out and concern increased over wet storage, since the mid-1980s dry stacking has been adopted. In this method, tailings are thickened to a high density slurry, deposited in a way that it consolidates and dries. An popular storage method is filtration whereby a filter cake (typically <30%
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxyhydroxides. Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, are used by humans, e.g. as iron ores, catalysts, in thermite and hemoglobin. Common rust is a form of iron oxide. Iron oxides are used as inexpensive, durable pigments in paints and colored concretes. Colors available are in the "earthy" end of the yellow/orange/red/brown/black range; when used as a food coloring, it has E number E172. Oxide of FeIIFeO: iron oxide, wüstite FeO2: iron dioxide Mixed oxides of FeII and FeIIIFe3O4: Iron oxide, magnetite Fe4O5 Fe5O6 Fe5O7 Fe25O32 Fe13O19 Oxide of FeIIIFe2O3: iron oxide α-Fe2O3: alpha phase, hematite β-Fe2O3: beta phase γ-Fe2O3: gamma phase, maghemite ε-Fe2O3: epsilon phase iron hydroxide iron hydroxide, akaganéite, feroxyhyte, ferrihydrite, or 5 Fe 2 O 3 ⋅ 9 H 2 O, better recast as FeOOH ⋅ 0.4 H 2 O high-pressure FeOOH schwertmannite green rust Several species of bacteria, including Shewanella oneidensis, Geobacter sulfurreducens and Geobacter metallireducens, metabolically utilize solid iron oxides as a terminal electron acceptor, reducing Fe oxides to Fe containing oxides.
Under conditions favoring iron reduction, the process of iron oxide reduction can replace at least 80% of methane production occurring by methanogenesis. This phenomenon occurs in a nitrogen-containing environment with low sulfate concentrations. Methanogenesis, an Archaean driven process, is the predominate form of carbon mineralization in sediments at the bottom of the ocean. Methanogenesis completes the decomposition of organic matter to methane; the specific electron donor for iron oxide reduction in this situation is still under debate, but the two potential candidates include either Titanium or compounds present in yeast. The predicted reactions with Titanium serving as the electron donor and phenazine-1-carboxylate serving as an electron shuttle is as follows: Ti-cit + CO2 + 8H+ → CH4 + 2H2O + Ti + cit ΔE = –240 + 300 mV Ti-cit + PCA → PCA + Ti + cit ΔE = –116 + 300 mV PCA + Fe3 → Fe2+ + PCA ΔE = –50 + 116 mV Note: cit = citrate. Titanium is oxidized to Titanium; the reduced form of PCA can reduce the iron hydroxide.
On the other hand when airborne, iron oxides have been shown to harm the lung tissues of living organisms by the formation of hydroxyl radicals, leading to the creation of alkyl radicals. The following reactions occur when Fe2O3 and FeO, hereafter represented as Fe3+ and Fe2+ iron oxide particulates accumulate in the lungs. O2 + e− → O2• –The formation of the superoxide anion is catalyzed by a transmembrane enzyme called NADPH oxidase; the enzyme facilitates the transport of an electron across the plasma membrane from cytosolic NADPH to extracellular oxygen to produce O2• –. NADPH and FAD are bound to cytoplasmic binding sites on the enzyme. Two electrons from NADPH are transported to FAD which reduces it to FADH2. One electron moves to one of two heme groups in the enzyme within the plane of the membrane; the second electron pushes the first electron to the second heme group so that it can associate with the first heme group. For the transfer to occur, the second heme must be bound to extracellular oxygen, the acceptor of the electron.
This enzyme can be located within the membranes of intracellular organelles allowing the formation of O2• – to occur within organelles. 2O2• – + 2 H+ → H2O2 + O2 The formation of hydrogen peroxide can occur spontaneously when the environment has a lower pH at pH 7.4. The enzyme superoxide dismutase can catalyze this reaction. Once H2O2 has been synthesized, it can diffuse thro
Titanium dioxide known as titanium oxide or titania, is the occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891, it is sourced from ilmenite and anatase. It has a wide range of applications, including paint and food coloring; when used as a food coloring, it has E number E171. World production in 2014 exceeded 9 million metric tons, it has been estimated that titanium dioxide is used in two-thirds of all pigments, pigments based on the oxide has been valued at $13.2 billion. Titanium dioxide occurs in nature as the well-known minerals rutile and brookite, additionally as two high pressure forms, a monoclinic baddeleyite-like form and an orthorhombic α-PbO2-like form, both found at the Ries crater in Bavaria. One of these is known as akaogiite is an rare mineral, it is sourced from ilmenite ore. This is the most widespread form of titanium dioxide-bearing ore around the world. Rutile is the next contains around 98 % titanium dioxide in the ore.
The metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase upon heating above temperatures in the range 600–800 °C. Titanium dioxide has eight modifications – in addition to rutile and brookite, three metastable phases can be produced synthetically, five high-pressure forms exist: The cotunnite-type phase was claimed by L. Dubrovinsky and co-authors to be the hardest known oxide with the Vickers hardness of 38 GPa and the bulk modulus of 431 GPa at atmospheric pressure; however studies came to different conclusions with much lower values for both the hardness and bulk modulus. The oxides are commercially important ores of titanium; the metal can be mined from other minerals such as ilmenite or leucoxene ores, or one of the purest forms, rutile beach sand. Star sapphires and rubies get their asterism from rutile impurities present in them. Titanium dioxide is found as a mineral in magmatic rocks and hydrothermal veins, as well as weathering rims on perovskite.
TiO2 forms lamellae in other minerals. Molten titanium dioxide has a local structure in which each Ti is coordinated to, on average, about 5 oxygen atoms; this is distinct from the crystalline forms. Spectral lines from titanium oxide are prominent in class M stars, which are cool enough to allow molecules of this chemical to form; the production method depends on the feedstock. The most common mineral source is ilmenite; the abundant Rutile mineral sand can be purified with the chloride process or other processes. Ilmenite is converted into pigment grade titanium dioxide via either the sulfate process or the chloride process. Both Sulfate and Chloride Processes produce the titanium dioxide pigment in the rutile crystal form, but the Sulfate Process can be adjusted to produce the anatase form. Anatase, being softer, is used in paper applications; the Sulfate Process is run as a batch process. Plants using the Sulfate Process require ilmenite concentrate or pretreated feedstocks as suitable source of titanium.
In the sulfate process Ilmenite is treated with sulfuric acid to extract iron sulfate pentahydrate. The resulting synthetic rutile is further processed according to the specifications of the end user, i.e. pigment grade or otherwise. In another method for the production of synthetic rutile from ilmenite the Becher Process first oxidizes the ilmenite as a means to separate the iron component. An alternative process, known as the Chloride process converts ilmenite or other titanium sources to Titanium tetrachloride via reaction with elemental chlorine, purified by distillation, reacted with oxygen to regenerate chlorine and produce the Titanium dioxide. Titanium dioxide pigment can be produced from higher titanium content feedstocks such as upgraded slag and leucoxene via a chloride acid process; the five largest TiO2 pigment processors are in 2019 Chemours, Cristal Global, Venator-Huntsman and Tronox, the largest one. Major paint and coating company end users for pigment grade titanium dioxide include Akzo Nobel, PPG Industries, Sherwin Williams, BASF, Kansai Paints and Valspar.
Global TiO2 pigment demand for 2010 was 5.3 Mt with annual growth expected to be about 3-4%. For specialty applications, TiO2 films are prepared by various specialized chemistries. Sol-gel routes involve the hydrolysis of titanium alkoxides, such as titanium ethoxide: Ti4 + 2 H2O → TiO2 + 4 EtOHThis technology is suited for the preparation of films. A related approach that relies on molecular precursors involves chemical vapor deposition. In this application, the alkoxide is volatilized and decomposed on contact with a hot surface: Ti4 → TiO2 + 2 Et2O The most important application areas are paints and varnishes as well as paper and plastics, which account for about 80% of the world's titanium dioxide consumption. Other pigment applications such as printing inks, rubber, cosmetic products and food account for another 8%; the rest is used in other applications, for instance the production of technical pure titanium and glass ceramics, electrical ceramics, metal patinas, electric conductors and chemical intermediates.
Titanium dioxide is the most used white pigment because of its brightness and high refractive index, in whi
Diaspore known as diasporite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, α-AlO, crystallizing in the orthorhombic system and isomorphous with goethite. It occurs sometimes as flattened crystals, but as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the lustre is markedly pearly in character, it is colorless or greyish-white, sometimes violet in color, varies from translucent to transparent. It may be distinguished from other colorless transparent minerals with a perfect cleavage and pearly luster—like mica, talc and gypsum— by its greater hardness of 6.5 - 7. The specific gravity is 3.4. When heated before the blowpipe it decrepitates violently; the mineral occurs as an alteration product of corundum or emery and is found in granular limestone and other crystalline rocks. Well-developed crystals are found in the emery deposits of the Urals and at Chester, in kaolin at Schemnitz in Hungary. If obtainable in large quantity, it would be of economic importance as a source of aluminium.
Diaspore, along with gibbsite and boehmite, is a major component of the aluminium ore bauxite. It was first described in 1801 for an occurrence in Mramorsk Zavod, Sverdlovskaya Oblast, Middle Urals, Russia; the name, coined by René Just Haüy, is from the Greek for διασπείρειν, to scatter, in allusion to its decrepitation on heating. Csarite and zultanite are trade names for gem-quality diaspore from the İlbir Mountains of southwest Turkey