|#||Product||Value (in millions of USD)|
|12||Human and animal blood||4,129|
|22||Nitrogen heterocyclic compounds||3,201|
|26||Electric generating sets||2,457|
|34||Machinery having individual functions||2,087|
|37||Chemical analysis instruments||2,005|
|40||Low-voltage protection equipment||1,808|
|44||Precious metal scraps||1,653|
|45||Office machine parts||1,640|
|50||Raw plastic sheeting||2,458|
A centrifuge is a piece of equipment that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis of spin that can be strong. The centrifuge works using the sedimentation principle, where the centrifugal acceleration causes denser substances and particles to move outward in the radial direction. At the same time, objects that are less dense move to the center. In a laboratory centrifuge that uses sample tubes, the radial acceleration causes denser particles to settle to the bottom of the tube, while low-density substances rise to the top. There are three types of centrifuge designed for different applications. Industrial scale centrifuges are used in manufacturing and waste processing to sediment suspended solids, or to separate immiscible liquids. An example is the cream separator found in dairies. High speed centrifuges and ultracentrifuges able to provide high accelerations can separate fine particles down to the nano-scale, molecules of different masses.
Large centrifuges are used to simulate high acceleration environments. Medium-sized centrifuges are used in washing machines and at some swimming pools to wring water out of fabrics. Gas centrifuges are used for isotope separation, such as to enrich nuclear fuel for fissile isotopes. English military engineer Benjamin Robins invented a whirling arm apparatus to determine drag. In 1864, Antonin Prandtl proposed the idea of a dairy centrifuge to separate cream from milk; the idea was subsequently put into practice by his brother, Alexander Prandtl, who made improvements to his brother's design, exhibited a working butterfat extraction machine in 1875. A centrifuge machine can be described as a machine with a rotating container that applies centrifugal force to its contents. There are multiple types of centrifuge, which can be classified by intended use or by rotor design: Types by rotor design: Fixed-angle centrifuges are designed to hold the sample containers at a constant angle relative to the central axis.
Swinging head centrifuges, in contrast to fixed-angle centrifuges, have a hinge where the sample containers are attached to the central rotor. This allows all of the samples to swing outwards. Continuous tubular centrifuges do not have individual sample vessels and are used for high volume applications. Types by intended use: Laboratory centrifuges, are general-purpose instruments of several types with distinct, but overlapping, capabilities; these include superspeed centrifuges and preparative ultracentrifuges. Analytical ultracentrifuges are designed to perform sedimentation analysis of macromolecules using the principles devised by Theodor Svedberg. Haematocrit centrifuges are used to measure the volume percentage of red blood cells in whole blood. Gas centrifuges, including Zippe-type centrifuges, for isotopic separations in the gas phase. Industrial centrifuges may otherwise be classified according to the type of separation of the high density fraction from the low density one. There are two types of centrifuges: the filtration and sedimentation centrifuges.
For the filtration or the so-called screen centrifuge the drum is perforated and is inserted with a filter, for example a filter cloth, wire mesh or lot screen. The suspension flows through the filter and the drum with the perforated wall from the inside to the outside. In this way the solid material can be removed; the kind of removing depends on the type of centrifuge, for example manually or periodically. Common types are: Screen/scroll centrifuges Pusher centrifuges Peeler centrifuges Inverting filter centrifuges Sliding discharge centrifuges Pendulum centrifugesIn the sedimentation centrifuges the drum is a solid wall; this type of centrifuge is used for the purification of a suspension. For the acceleration of the natural deposition process of suspension the centrifuges use centrifugal force. With so-called overflow centrifuges the suspension is drained off and the liquid is added constantly. Common types are: Pendulum centrifuges. Though most modern centrifuges are electrically powered, a hand-powered variant inspired by the whirligig has been developed for medical applications in developing countries.
A wide variety of laboratory-scale centrifuges are used in chemistry, biology and clinical medicine for isolating and separating suspensions and immiscible liquids. They vary in speed, temperature control, other characteristics. Laboratory centrifuges can accept a range of different fixed-angle and swinging bucket rotors able to carry different numbers of centrifuge tubes and rated for specific maximum speeds. Controls vary from simple electrical timers to programmable models able to control acceleration and deceleration rates, running speeds, temperature regimes. Ultracentrifuges spin the rotors under vacuum, eliminating air resistance and enabling exact temperature control. Zonal rotors and continuous flow systems are capable of handing bulk and larger sample volumes in a laboratory-scale instrument. Another application in laboratories is blood separation. Blood separates into cells and proteins
In electricity generation, a generator is a device that converts motive power into electrical power for use in an external circuit. Sources of mechanical energy include steam turbines, gas turbines, water turbines, internal combustion engines and hand cranks; the first electromagnetic generator, the Faraday disk, was invented in 1831 by British scientist Michael Faraday. Generators provide nearly all of the power for electric power grids; the reverse conversion of electrical energy into mechanical energy is done by an electric motor, motors and generators have many similarities. Many motors can be mechanically driven to generate electricity and make acceptable manual generators. Electromagnetic generators fall into one of two broad categories and alternators. Dynamos generate pulsing direct current through the use of a commutator. Alternators generate alternating current. Mechanically a generator consists of a rotating part and a stationary part: Rotor The rotating part of an electrical machine.
Stator The stationary part of an electrical machine, which surrounds the rotor. One of these parts generates a magnetic field, the other has a wire winding in which the changing field induces an electric current: Field winding or field magnets The magnetic field producing component of an electrical machine; the magnetic field of the dynamo or alternator can be provided by either wire windings called field coils or permanent magnets. Electrically-excited generators include an excitation system to produce the field flux. A generator using permanent magnets is sometimes called a magneto, or permanent magnet synchronous generators. Armature The power-producing component of an electrical machine. In a generator, alternator, or dynamo, the armature windings generate the electric current, which provides power to an external circuit; the armature can be on either the rotor or the stator, depending on the design, with the field coil or magnet on the other part. Before the connection between magnetism and electricity was discovered, electrostatic generators were invented.
They operated on electrostatic principles, by using moving electrically charged belts and disks that carried charge to a high potential electrode. The charge was generated using either of two mechanisms: electrostatic induction or the triboelectric effect; such generators generated high voltage and low current. Because of their inefficiency and the difficulty of insulating machines that produced high voltages, electrostatic generators had low power ratings, were never used for generation of commercially significant quantities of electric power, their only practical applications were to power early X-ray tubes, in some atomic particle accelerators. The operating principle of electromagnetic generators was discovered in the years of 1831–1832 by Michael Faraday; the principle called Faraday's law, is that an electromotive force is generated in an electrical conductor which encircles a varying magnetic flux. He built the first electromagnetic generator, called the Faraday disk, it produced a small DC voltage.
This design was inefficient, due to self-cancelling counterflows of current in regions of the disk that were not under the influence of the magnetic field. While current was induced directly underneath the magnet, the current would circulate backwards in regions that were outside the influence of the magnetic field; this counterflow limited the power output to the pickup wires, induced waste heating of the copper disc. Homopolar generators would solve this problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in one current-flow direction. Another disadvantage was that the output voltage was low, due to the single current path through the magnetic flux. Experimenters found that using multiple turns of wire in a coil could produce higher, more useful voltages. Since the output voltage is proportional to the number of turns, generators could be designed to produce any desired voltage by varying the number of turns. Wire windings became a basic feature of all subsequent generator designs.
Independently of Faraday, the Hungarian Ányos Jedlik started experimenting in 1827 with the electromagnetic rotating devices which he called electromagnetic self-rotors. In the prototype of the single-pole electric starter both the stationary and the revolving parts were electromagnetic, it was the discovery of the principle of dynamo self-excitation, which replaced permanent magnet designs. He may have formulated the concept of the dynamo in 1861 but didn't patent it as he thought he wasn't the first to realize this. A coil of wire rotating in a magnetic field produces a current which changes direction with each 180° rotation, an alternating current; however many early uses of electricity required direct current. In the first practical electric generators, called dynamos, the AC was converted into DC with a commutator, a set of rotating switch contacts on the armature shaft; the commutator reversed the connection of the armature winding to the circuit every 180° rotation of the shaft, creating a pulsing DC current.
One of the first dynamos was built by Hippolyte Pixii in 1832. The dynamo was the first electrical generator capable of delivering power for industry; the Woolrich Electrical Generator of 1844, now in Thinktank, Birmingham Science Museum, is the earliest electrical generator used in an industrial process. It was used by the firm of Elkingtons for commercial electroplating; the modern dynamo, fit for use in industrial applications, was invented independently by Sir Charles
A pump is a device that moves fluids, or sometimes slurries, by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift and gravity pumps. Pumps operate by some mechanism, consume energy to perform mechanical work moving the fluid. Pumps operate via many energy sources, including manual operation, engines, or wind power, come in many sizes, from microscopic for use in medical applications to large industrial pumps. Mechanical pumps serve in a wide range of applications such as pumping water from wells, aquarium filtering, pond filtering and aeration, in the car industry for water-cooling and fuel injection, in the energy industry for pumping oil and natural gas or for operating cooling towers. In the medical industry, pumps are used for biochemical processes in developing and manufacturing medicine, as artificial replacements for body parts, in particular the artificial heart and penile prosthesis; when a casing contains only one revolving impeller, it is called a single-stage pump.
When a casing contains two or more revolving impellers, it is called a double- or multi-stage pump. In biology, many different types of chemical and biomechanical pumps have evolved. Mechanical pumps may be placed external to the fluid. Pumps can be classified by their method of displacement into positive displacement pumps, impulse pumps, velocity pumps, gravity pumps, steam pumps and valveless pumps. There are two basic types of pumps: centrifugal. Although axial-flow pumps are classified as a separate type, they have the same operating principles as centrifugal pumps. A positive displacement pump makes a fluid move by trapping a fixed amount and forcing that trapped volume into the discharge pipe; some positive displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses; the volume is constant through each cycle of operation.
Positive displacement pumps, unlike centrifugal or roto-dynamic pumps, theoretically can produce the same flow at a given speed no matter what the discharge pressure. Thus, positive displacement pumps are constant flow machines. However, a slight increase in internal leakage as the pressure increases prevents a constant flow rate. A positive displacement pump must not operate against a closed valve on the discharge side of the pump, because it has no shutoff head like centrifugal pumps. A positive displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is damaged, or both. A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary; the relief valve can be external. The pump manufacturer has the option to supply internal relief or safety valves; the internal valve is used only as a safety precaution. An external relief valve in the discharge line, with a return line back to the suction line or supply tank provides increased safety.
A positive displacement pump can be further classified according to the mechanism used to move the fluid: Rotary-type positive displacement: internal gear, shuttle block, flexible vane or sliding vane, circumferential piston, flexible impeller, helical twisted roots or liquid-ring pumps Reciprocating-type positive displacement: piston pumps, plunger pumps or diaphragm pumps Linear-type positive displacement: rope pumps and chain pumps These pumps move fluid using a rotating mechanism that creates a vacuum that captures and draws in the liquid. Advantages: Rotary pumps are efficient because they can handle viscous fluids with higher flow rates as viscosity increases. Drawbacks: The nature of the pump requires close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the fluids cause erosion, which causes enlarged clearances that liquid can pass through, which reduces efficiency. Rotary positive displacement pumps fall into three main types: Gear pumps – a simple type of rotary pump where the liquid is pushed between two gears Screw pumps – the shape of the internals of this pump is two screws turning against each other to pump the liquid Rotary vane pumps – similar to scroll compressors, these have a cylindrical rotor encased in a shaped housing.
As the rotor orbits, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump. Reciprocating pumps move the fluid using one or more oscillating pistons, plungers, or membranes, while valves restrict fluid motion to the desired direction. In order for suction to take place, the pump must first pull the plunger in an outward motion to decrease pressure in the chamber. Once the plunger pushes back, it will increase the pressure chamber and the inward pressure of the plunger will open the discharge valve and release the fluid into the delivery pipe at a high velocity. Pumps in this category range from simplex, with one cylinder, to in some cases quad cylinders, or more. Many reciprocating-type pumps are triplex cylinder, they can be either single-acting with suction during one direction of piston motion and discharge on the other, or double-acting with suction and discharge in both directions. The pumps can be powered manually, by air or steam
Natural gas is a occurring hydrocarbon gas mixture consisting of methane, but including varying amounts of other higher alkanes, sometimes a small percentage of carbon dioxide, hydrogen sulfide, or helium. It is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure under the surface of the Earth over millions of years; the energy that the plants obtained from the sun is stored in the form of chemical bonds in the gas. Natural gas is a occurring hydrocarbon used as a source of energy for heating and electricity generation, it is used as a fuel for vehicles and as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals. Natural gas is called a non-renewable resource. Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs in coal beds and as methane clathrates. Petroleum is another fossil fuel found in close proximity to and with natural gas. Most natural gas was created over time by two mechanisms: thermogenic.
Biogenic gas is created by methanogenic organisms in marshes, bogs and shallow sediments. Deeper in the earth, at greater temperature and pressure, thermogenic gas is created from buried organic material. In petroleum production gas is burnt as flare gas; the World Bank estimates that over 150 cubic kilometers of natural gas are flared or vented annually. Before natural gas can be used as a fuel, but not all, must be processed to remove impurities, including water, to meet the specifications of marketable natural gas; the by-products of this processing include: ethane, butanes and higher molecular weight hydrocarbons, hydrogen sulfide, carbon dioxide, water vapor, sometimes helium and nitrogen. Natural gas is informally referred to as "gas" when compared to other energy sources such as oil or coal. However, it is not to be confused with gasoline in North America, where the term gasoline is shortened in colloquial usage to gas. Natural gas was discovered accidentally in ancient China, as it resulted from the drilling for brines.
Natural gas was first used by the Chinese in about 500 BCE. They discovered a way to transport gas seeping from the ground in crude pipelines of bamboo to where it was used to boil salt water to extract the salt, in the Ziliujing District of Sichuan; the discovery and identification of natural gas in the Americas happened in 1626. In 1821, William Hart dug the first natural gas well at Fredonia, New York, United States, which led to the formation of the Fredonia Gas Light Company; the state of Philadelphia created the first municipally owned natural gas distribution venture in 1836. By 2009, 66 000 km³ had been used out of the total 850 000 km³ of estimated remaining recoverable reserves of natural gas. Based on an estimated 2015 world consumption rate of about 3400 km³ of gas per year, the total estimated remaining economically recoverable reserves of natural gas would last 250 years at current consumption rates. An annual increase in usage of 2–3% could result in recoverable reserves lasting less as few as 80 to 100 years.
In the 19th century, natural gas was obtained as a by-product of producing oil, since the small, light gas carbon chains came out of solution as the extracted fluids underwent pressure reduction from the reservoir to the surface, similar to uncapping a soft drink bottle where the carbon dioxide effervesces. Unwanted natural gas was a disposal problem in the active oil fields. If there was not a market for natural gas near the wellhead it was prohibitively expensive to pipe to the end user. In the 19th century and early 20th century, unwanted gas was burned off at oil fields. Today, unwanted gas associated with oil extraction is returned to the reservoir with'injection' wells while awaiting a possible future market or to repressurize the formation, which can enhance extraction rates from other wells. In regions with a high natural gas demand, pipelines are constructed when it is economically feasible to transport gas from a wellsite to an end consumer. In addition to transporting gas via pipelines for use in power generation, other end uses for natural gas include export as liquefied natural gas or conversion of natural gas into other liquid products via gas to liquids technologies.
GTL technologies can convert natural gas into liquids products such as diesel or jet fuel. A variety of GTL technologies have been developed, including Fischer–Tropsch, methanol to gasoline and syngas to gasoline plus. F–T produces a synthetic crude that can be further refined into finished products, while MTG can produce synthetic gasoline from natural gas. STG+ can produce drop-in gasoline, jet fuel and aromatic chemicals directly from natural gas via a single-loop process. In 2011, Royal Dutch Shell's 140,000 barrels per day F–T plant went into operation in Qatar. Natural gas can be "associated", or "non-associated", is found in coal beds, it sometimes contains a significant amount of ethane, propane and pentane—heavier hydrocarbons removed for commercial use prior to the methane being sold as a consumer fuel or chemical plant feedstock. Non-hydrocarbons such as carbon dioxide, nitrogen and hydrogen sulfide must be removed before the natural gas can be transported. Natural gas extracted from oil wells is called casinghead gas (whether or not produced up the a
Analytical chemistry studies and uses instruments and methods used to separate and quantify matter. In practice, identification or quantification may constitute the entire analysis or be combined with another method. Separation isolates analytes. Qualitative analysis identifies analytes, while quantitative analysis determines the numerical amount or concentration. Analytical chemistry consists of modern, instrumental methods. Classical qualitative methods use separations such as precipitation and distillation. Identification may be based on differences in color, melting point, boiling point, radioactivity or reactivity. Classical quantitative analysis uses volume changes to quantify amount. Instrumental methods may be used to separate samples using chromatography, electrophoresis or field flow fractionation. Qualitative and quantitative analysis can be performed with the same instrument and may use light interaction, heat interaction, electric fields or magnetic fields; the same instrument can separate and quantify an analyte.
Analytical chemistry is focused on improvements in experimental design and the creation of new measurement tools. Analytical chemistry has broad applications to forensics, medicine and engineering. Analytical chemistry has been important since the early days of chemistry, providing methods for determining which elements and chemicals are present in the object in question. During this period significant contributions to analytical chemistry include the development of systematic elemental analysis by Justus von Liebig and systematized organic analysis based on the specific reactions of functional groups; the first instrumental analysis was flame emissive spectrometry developed by Robert Bunsen and Gustav Kirchhoff who discovered rubidium and caesium in 1860. Most of the major developments in analytical chemistry take place after 1900. During this period instrumental analysis becomes progressively dominant in the field. In particular many of the basic spectroscopic and spectrometric techniques were discovered in the early 20th century and refined in the late 20th century.
The separation sciences follow a similar time line of development and become transformed into high performance instruments. In the 1970s many of these techniques began to be used together as hybrid techniques to achieve a complete characterization of samples. Starting in the 1970s into the present day analytical chemistry has progressively become more inclusive of biological questions, whereas it had been focused on inorganic or small organic molecules. Lasers have been used in chemistry as probes and to initiate and influence a wide variety of reactions; the late 20th century saw an expansion of the application of analytical chemistry from somewhat academic chemical questions to forensic, environmental and medical questions, such as in histology. Modern analytical chemistry is dominated by instrumental analysis. Many analytical chemists focus on a single type of instrument. Academics tend to either focus on new methods of analysis; the discovery of a chemical present in blood that increases the risk of cancer would be a discovery that an analytical chemist might be involved in.
An effort to develop a new method might involve the use of a tunable laser to increase the specificity and sensitivity of a spectrometric method. Many methods, once developed, are kept purposely static so that data can be compared over long periods of time; this is true in industrial quality assurance and environmental applications. Analytical chemistry plays an important role in the pharmaceutical industry where, aside from QA, it is used in discovery of new drug candidates and in clinical applications where understanding the interactions between the drug and the patient are critical. Although modern analytical chemistry is dominated by sophisticated instrumentation, the roots of analytical chemistry and some of the principles used in modern instruments are from traditional techniques, many of which are still used today; these techniques tend to form the backbone of most undergraduate analytical chemistry educational labs. A qualitative analysis determines the presence or absence of a particular compound, but not the mass or concentration.
By definition, qualitative analyses do not measure quantity. There are numerous qualitative chemical tests, for example, the acid test for gold and the Kastle-Meyer test for the presence of blood. Inorganic qualitative analysis refers to a systematic scheme to confirm the presence of certain aqueous, ions or elements by performing a series of reactions that eliminate ranges of possibilities and confirms suspected ions with a confirming test. Sometimes small carbon containing ions are included in such schemes. With modern instrumentation these tests are used but can be useful for educational purposes and in field work or other situations where access to state-of-the-art instruments are not available or expedient. Quantitative analysis is the measurement of the quantities of particular chemical constituents present in a substance. Gravimetric analysis involves determining the amount of material present by weighing the sample before and/or after some transformation. A common example used in undergraduate education is the determination of the amount of water in a hydrate by heating the sample to remove the water such that the difference in weight is due to the loss of water.
Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is water, contains proteins, mineral ions, carbon dioxide, blood cells themselves. Albumin is the main protein in plasma, it functions to regulate the colloidal osmotic pressure of blood; the blood cells are red blood cells, white blood cells and platelets. The most abundant cells in vertebrate blood are red blood cells; these contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and increasing its solubility in blood. In contrast, carbon dioxide is transported extracellularly as bicarbonate ion transported in plasma. Vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated.
Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin. Insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system. In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen. Jawed vertebrates have an adaptive immune system, based on white blood cells. White blood cells help to resist parasites. Platelets are important in the clotting of blood. Arthropods, using hemolymph, have hemocytes as part of their immune system. Blood is circulated around the body through blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled.
Medical terms related to blood begin with hemo- or hemato- from the Greek word αἷμα for "blood". In terms of anatomy and histology, blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen. Blood performs many important functions within the body, including: Supply of oxygen to tissues Supply of nutrients such as glucose, amino acids, fatty acids Removal of waste such as carbon dioxide and lactic acid Immunological functions, including circulation of white blood cells, detection of foreign material by antibodies Coagulation, the response to a broken blood vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding Messenger functions, including the transport of hormones and the signaling of tissue damage Regulation of core body temperature Hydraulic functions Blood accounts for 7% of the human body weight, with an average density around 1060 kg/m3 close to pure water's density of 1000 kg/m3.
The average adult has a blood volume of 5 litres, composed of plasma and several kinds of cells. These blood cells consist of erythrocytes and thrombocytes. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, white cells about 0.7%. Whole blood exhibits non-Newtonian fluid dynamics. If all human hemoglobin were free in the plasma rather than being contained in RBCs, the circulatory fluid would be too viscous for the cardiovascular system to function effectively. One microliter of blood contains: 4.7 to 6.1 million, 4.2 to 5.4 million erythrocytes: Red blood cells contain the blood's hemoglobin and distribute oxygen. Mature red blood cells lack a nucleus and organelles in mammals; the red blood cells are marked by glycoproteins that define the different blood types. The proportion of blood occupied by red blood cells is referred to as the hematocrit, is about 45%; the combined surface area of all red blood cells of the human body would be 2,000 times as great as the body's exterior surface.
4,000–11,000 leukocytes: White blood cells are part of the body's immune system. The cancer of leukocytes is called leukemia. 200,000 -- 500,000 thrombocytes: Also called platelets. Fibrin from the coagulation cascade creates a mesh over the platelet plug. About 55% of blood is blood plasma, a fluid, the blood's liquid medium, which by itself is straw-yellow in color; the blood plasma volume totals of 2.7–3.0 liters in an average human. It is an aqueous solution containing 92% water, 8% blood plasma proteins, trace amounts of other materials. Plasma circulates dissolved nutrients, such as glucose, amino acids, fatty acids, removes waste products, such as carbon dioxide and lactic acid. Other important components include: Serum albumin Blood-clotting factors Immunoglobulins lipoprotein particles Various
Iron is a chemical element with symbol Fe and atomic number 26. It is a metal, that belongs to group 8 of the periodic table, it is by mass the most common element on Earth, forming much of Earth's inner core. It is the fourth most common element in the Earth's crust. Pure iron is rare on the Earth's crust being limited to meteorites. Iron ores are quite abundant, but extracting usable metal from them requires kilns or furnaces capable of reaching 1500 °C or higher, about 500 °C higher than what is enough to smelt copper. Humans started to dominate that process in Eurasia only about 2000 BCE, iron began to displace copper alloys for tools and weapons, in some regions, only around 1200 BCE; that event is considered the transition from the Bronze Age to the Iron Age. Iron alloys, such as steel and special steels are now by far the most common industrial metals, because of their mechanical properties and their low cost. Pristine and smooth pure iron surfaces are mirror-like silvery-gray. However, iron reacts with oxygen and water to give brown to black hydrated iron oxides known as rust.
Unlike the oxides of some other metals, that form passivating layers, rust occupies more volume than the metal and thus flakes off, exposing fresh surfaces for corrosion. The body of an adult human contains about 3 to 5 grams of elemental iron in hemoglobin and myoglobin; these two proteins play essential roles in vertebrate metabolism oxygen transport by blood and oxygen storage in muscles. To maintain the necessary levels, human iron metabolism requires a minimum of iron in the diet. Iron is the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals. Chemically, the most common oxidation states of iron are +2 and +3. Iron shares many properties of other transition metals, including the other group 8 elements and osmium. Iron forms compounds in a wide range of oxidation states, −2 to +7. Iron forms many coordination compounds. At least four allotropes of iron are known, conventionally denoted α, γ, δ, ε; the first three forms are observed at ordinary pressures.
As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has a body-centered cubic crystal structure. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope; the physical properties of iron at high pressures and temperatures have been studied extensively, because of their relevance to theories about the cores of the Earth and other planets. Above 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into another hexagonal close-packed structure, known as ε-iron; the higher-temperature γ-phase changes into ε-iron, but does so at higher pressure. Some controversial experimental evidence exists for a stable β phase at pressures above 50 GPa and temperatures of at least 1500 K, it is supposed to have a double hcp structure. The inner core of the Earth is presumed to consist of an iron-nickel alloy with ε structure.
The melting and boiling points of iron, along with its enthalpy of atomization, are lower than those of the earlier 3d elements from scandium to chromium, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus. This same trend appears for ruthenium but not osmium; the melting point of iron is experimentally well defined for pressures less than 50 GPa. For greater pressures, published data still varies by tens of gigapascals and over a thousand kelvin. Below its Curie point of 770 °C, α-iron changes from paramagnetic to ferromagnetic: the spins of the two unpaired electrons in each atom align with the spins of its neighbors, creating an overall magnetic field; this happens because the orbitals of those two electrons do not point toward neighboring atoms in the lattice, therefore are not involved in metallic bonding. In the absence of an external source of magnetic field, the atoms get spontaneously partitioned into magnetic domains, about 10 micrometres across, such that the atoms in each domain have parallel spins, but different domains have other orientations.
Thus a macroscopic piece of iron will have a nearly zero overall magnetic field. Application of an external magnetic field causes the domains that are magnetized in the same general direction to grow at the expense of adjacent ones that point in other directions, reinforcing the external field; this effect is exploited in devices that needs to channel magnetic fields, such as electrical transformers, magnetic recording heads, electric motors. Impurities, lattice defects, or grain and particle boundaries can "pin" the domains in the new positions, so that the effect persists after the external field is removed -- thus turning the iron object into a magnet. Similar behavior is exhibited by some iron compounds, such as the fer