1.
Clock
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A clock is an instrument to measure, keep, and indicate time. The word clock is derived from the Celtic words clagan and clocca meaning bell, a silent instrument missing such a striking mechanism has traditionally been known as a timepiece. In general usage today a clock refers to any device for measuring and displaying the time, Watches and other timepieces that can be carried on ones person are often distinguished from clocks. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units, the day, the lunar month. Devices operating on several physical processes have been used over the millennia, a sundial shows the time by displaying the position of a shadow on a flat surface. There is a range of duration timers, an example being the hourglass. Water clocks, along with the sundials, are possibly the oldest time-measuring instruments, spring-driven clocks appeared during the 15th century. During the 15th and 16th centuries, clockmaking flourished, the next development in accuracy occurred after 1656 with the invention of the pendulum clock. A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation, the electric clock was patented in 1840. The development of electronics in the 20th century led to clocks with no clockwork parts at all, the timekeeping element in every modern clock is a harmonic oscillator, a physical object that vibrates or oscillates at a particular frequency. This object can be a pendulum, a fork, a quartz crystal. Analog clocks usually indicate time using angles, Digital clocks display a numeric representation of time. Two numeric display formats are used on digital clocks, 24-hour notation. Most digital clocks use electronic mechanisms and LCD, LED, or VFD displays, for convenience, distance, telephony or blindness, auditory clocks present the time as sounds. There are also clocks for the blind that have displays that can be read by using the sense of touch, some of these are similar to normal analog displays, but are constructed so the hands can be felt without damaging them. The evolution of the technology of clocks continues today, the study of timekeeping is known as horology. The apparent position of the Sun in the sky moves over the course of a day, shadows cast by stationary objects move correspondingly, so their positions can be used to indicate the time of day. A sundial shows the time by displaying the position of a shadow on a flat surface, sundials can be horizontal, vertical, or in other orientations
2.
Science Museum, London
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The Science Museum is a major museum on Exhibition Road in South Kensington, London. It was founded in 1857 and today is one of the major tourist attractions. Like other publicly funded museums in the United Kingdom, the Science Museum does not charge visitors for admission. Temporary exhibitions, however, may incur an admission fee and it is part of the Science Museum Group, having merged with the Museum of Science and Industry in Manchester in 2012. It included a collection of machinery which became the Museum of Patents in 1858, and this collection contained many of the most famous exhibits of what is now the Science Museum. In 1883, the contents of the Patent Office Museum were transferred to the South Kensington Museum, in 1885, the Science Collections were renamed the Science Museum and in 1893 a separate director was appointed. The Art Collections were renamed the Art Museum, which became the Victoria. When Queen Victoria laid the stone for the new building for the Art Museum, she stipulated that the museum be renamed after herself. On 26 June 1909 the Science Museum, as an independent entity, the Science Museums present quarters, designed by Sir Richard Allison, were opened to the public in stages over the period 1919–28. This building was known as the East Block, construction of which began in 1913, as the name suggests it was intended to be the first building of a much larger project, which was never realized. It also contains hundreds of interactive exhibits, a recent addition is the IMAX 3D Cinema showing science and nature documentaries, most of them in 3-D, and the Wellcome Wing which focuses on digital technology. Entrance has been free since 1 December 2001, the museum houses some of the many objects collected by Henry Wellcome around a medical theme. The fourth floor exhibit is called Glimpses of Medical History, with reconstructions, the fifth floor gallery is called Science and the Art of Medicine, with exhibits of medical instruments and practices from ancient days and from many countries. The collection is strong in clinical medicine, biosciences and public health, the museum is a member of the London Museums of Health & Medicine. The Science Museum has a library, and until the 1960s was Britains National Library for Science, Medicine. It holds runs of periodicals, early books and manuscripts, and is used by scholars worldwide and it was, for a number of years, run in conjunction with the Library of Imperial College, but in 2007 the Library was divided over two sites. The Imperial College library catalogue search system now informs searchers that volumes formerly held there are Available at Science Museum Library Swindon Currently unavailable, a new Research Centre with library facilities is promised for late 2015 but is unlikely to have book stacks nearby. The Science Museums medical collections have a scope and coverage
3.
Fort Mason
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Fort Mason served as an Army post for more than 100 years, initially as a coastal defense site and subsequently as a military port facility. During World War II, it was the port for the Pacific campaign. Today it is part of the Golden Gate National Recreation Area and it is a National Historic Landmark District with over 49 buildings of historic significance, spread over 1,200 acres. Fort Mason can be split into two distinct areas, the upper area, sometimes called Fort Mason, is situated on a headland and was the site of the original coastal fortifications. The lower area, Fort Mason Center, is situated close to level to the west of Upper Fort Mason. The Marina Green lies to the west of Fort Mason, while Aquatic Park is to the east, the nucleus of Fort Mason was a private property owned by John C. Frémont, the explorer of the US west, who also spearheaded the conquest of California from Mexico. Appointed a Major General in the Union army at the start of the Civil War, in 1863, the government seized the property without payment, by executive order of Lincoln, on the grounds it was needed for the war effort. Frémont would again contest the US presidency in 1864, running as the candidate of radical Republicans, the 1968 lawsuit was perhaps the last shot of a century-long legal struggle to obtain compensation for the seized realty. In 1870, the government returned property to 49 parties in the vicinity, but not to Frémont, but in 1968 the Frémont heirs complained it had failed to carry out this direction, with John Frémont then recently dead and his widow Jessie nearly 70 years old. The Civil War prompted the construction of coastal defense batteries located inside the Golden Gate. A breast-high wall of brick and mounts for six 10-inch Rodman cannons, excavation in the early 1980s uncovered the well-preserved remains of the western-half of the temporary battery, and it has now been restored to its condition during the Civil War. The fort was named Fort Mason in 1882, after Richard Barnes Mason, President Grover Cleveland established the Endicott Board in 1885 for the purpose of modernizing the nations coastal fortifications. Chaired by Secretary of War William Endicott, the board recommended new defenses at 22 U. S. seaports, as a result, an extensive series of forts, batteries, and guns were built on the harbor, including Fort Mason. The piers and sheds of Lower Fort Mason were originally built from 1912 to warehouse army supplies, by this time, the US Army began to build new bases in Hawaii, the Philippines, and various other Pacific islands. Most of the materiel for those bases was shipped through San Francisco, by 1915, the three piers together with their associated warehouse had been completed, and Fort Mason Tunnel driven under Upper Fort Mason to connect with the railroad network along the Embarcadero. With these new facilities, Fort Mason was transformed from a defense post into a logistical. The Army ferry USAT General Frank M. Coxe provided scheduled transportation from Fort Mason to the center at Fort McDowell on Angel Island up to eight times per day during the war
4.
Jeff Bezos
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The company began as an Internet merchant of books and expanded to a wide variety of products and services, most recently video streaming and audio streaming. Amazon. com is currently the worlds largest Internet sales company on the World Wide Web, Bezos’s other diversified business interests include aerospace and newspapers. He is the founder and manufacturer of Blue Origin with test flights to space beginning in 2015, in 2013, Bezos purchased The Washington Post newspaper. A number of other investments are managed through Bezos Expeditions. Bezos is currently the second-richest person in the world, with a net worth of US$77.1 billion as of March 2017. His rise to this occurred after Amazon registered a 67% jump in share price. Bezos was born Jeffrey Preston Jorgensen to Jacklyn and Ted Jorgensen in Albuquerque and his maternal ancestors were settlers who lived in Texas, and over the generations acquired a 25, 000-acre ranch near Cotulla. As of March 2015, Bezos was among the largest landholders in Texas, Bezos’s maternal grandfather was a regional director of the U. S. He retired early to the ranch, where Bezos spent many summers as a youth, at an early age, he displayed mechanical aptitude—as a toddler, he even dismantled his crib with a screwdriver. Bezos’s mother Jacklyn was a teenager at the time of his birth and her marriage to Jorgensen lasted a little more than a year. In April 1968 she married her husband, Miguel Bezos. His family was originally from Valladolid, Miguel Bezos worked his way through the University of Albuquerque, married Jacklyn, and legally adopted his stepson Jeff, who changed his surname from Jorgensen to Bezos. After the wedding the family moved to Houston and Miguel worked as an engineer for Exxon, the young Jeff attended River Oaks Elementary School in Houston from fourth to sixth grade. As a child, he spent summers working on his grandfathers ranch in southern Texas, Bezos often displayed scientific interests and technological proficiency, he once rigged an electric alarm to keep his younger siblings out of his room. The family moved to Miami, Florida, where he attended Miami Palmetto High School, while in high school, he attended the Student Science Training Program at the University of Florida, receiving a Silver Knight Award in 1982. He was high school valedictorian and was a National Merit Scholar, Bezos graduated summa cum laude and Phi Beta Kappa from Princeton University with bachelor of science degrees in electrical engineering and computer science. While at Princeton, he was elected to Tau Beta Pi. He served as the president of the Princeton chapter of the Students for the Exploration, in 2016 Bezos played a Starfleet official in the movie Star Trek Beyond, later joining the cast and crew at a San Diego Comic-Con screening
5.
Stewart Brand
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Stewart Brand is an American writer, best known as editor of the Whole Earth Catalog. He founded a number of organizations, including The WELL, the Global Business Network, and he is the author of several books, most recently Whole Earth Discipline, An Ecopragmatist Manifesto. He studied biology at Stanford University, graduating in 1960 and he was married to Lois Jennings, an Ottawa Native American and mathematician. As a soldier in the U. S. Army, he was a parachutist and taught infantry skills, Brand has lived in California since the 1960s. He and his wife live on Mirene, a 64-foot -long working tugboat. Built in 1912, the boat is moored in a shipyard in Sausalito. He works in Mary Heartline, a fishing boat about 100 yards away. A favorite item of his is a table on which Otis Redding is said to have written “ The Dock of the Bay”, through engaging in scholarship and by visiting numerous Indian reservations, Brand familiarized himself with the Native Americans of the West. Native Americans have continued to be an important cultural interest, one which has continually re-emerged in Brands work in various ways, by the mid-1960s, Brand became associated with author Ken Kesey and the Merry Pranksters. With his partner Zach Stewart, he produced the Trips Festival in San Francisco and this was one of the first venues at which the Grateful Dead performed in San Francisco. About 10,000 hippies attended, and Haight-Ashbury soon emerged as a community, tom Wolfe describes Brand in the beginning of his 1968 book, The Electric Kool-Aid Acid Test. In 1966, Brand campaigned to have NASA release the satellite image of the entire Earth as seen from space. He sold and distributed buttons for 25 cents each asking, Why havent we seen a photograph of the whole Earth yet, during this campaign, Brand met Richard Buckminster Fuller, who offered to help Brand with his projects. In 1967, a satellite, ATS-3, took the photo, Brand thought the image of our planet would be a powerful symbol. It adorned the first edition of the Whole Earth Catalog, later in 1968, a NASA astronaut took an Earth photo, Earthrise, from Moon orbit, which became the front image of the spring 1969 edition of the Catalog. 1970 saw the first celebration of Earth Day, during a 2003 interview, Brand explained that the image gave the sense that Earth’s an island, surrounded by a lot of inhospitable space. And it’s so graphic, this blue, white, green. During the late 1960s and early 1970s about 10 million Americans were involved in living communally, Brand and his wife Lois travelled to communes in a 1963 Dodge truck known as the Whole Earth Truck Store, which moved to a storefront in Menlo Park, California
6.
Gemstone
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A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks or organic materials that are not minerals are used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone, apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter, a worker is a diamantaire. The carvings of Carl Fabergé are significant works in this tradition, the traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious, similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire, other stones are classified by their color, translucency and hardness. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone, in modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition, for example, diamonds are made of carbon and rubies of aluminium oxide. Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic, another term used is habit, the form the gem is usually found in. For example, diamonds, which have a crystal system, are often found as octahedrons. Gemstones are classified into different groups, species, and varieties, for example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the Emerald, aquamarine, red beryl, goshenite, heliodor, and morganite, gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction and they may have luminescence and a distinctive absorption spectrum. Material or flaws within a stone may be present as inclusions, gemstones may also be classified in terms of their water. This is a grading of the gems luster, transparency. Very transparent gems are considered first water, while second or third water gems are those of a lesser transparency, there is no universally accepted grading system for gemstones. Diamonds are graded using a system developed by the Gemological Institute of America in the early 1950s, historically, all gemstones were graded using the naked eye
7.
Nuclear power
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Nuclear power is the use of nuclear reactions that release nuclear energy to generate heat, which most frequently is then used in steam turbines to produce electricity in a nuclear power plant. The term includes nuclear fission, nuclear decay and nuclear fusion, since all electricity supplying technologies use cement, etc. during construction, emissions are yet to be brought to zero. Each result is contrasted with coal and fossil gas at 820 and 490 g CO2 eq/kWh, there is a social debate about nuclear power. Proponents, such as the World Nuclear Association and Environmentalists for Nuclear Energy, contend that nuclear power is a safe, opponents, such as Greenpeace International and NIRS, contend that nuclear power poses many threats to people and the environment. These include the Chernobyl disaster which occurred in 1986, the Fukushima Daiichi nuclear disaster, there have also been some nuclear submarine accidents. Energy production from coal, petroleum, natural gas and hydroelectricity has caused a number of fatalities per unit of energy generated due to air pollution. In 2015, Ten new reactors were connected to the grid, seven reactors were permanently shut down. 441 reactors had a net capacity of 382,855 megawatts of electricity. 67 new nuclear reactors were under construction, Most of the new activity is in China where there is an urgent need to control pollution from coal plants. In October 2016, Watts Bar 2 became the first new United States reactor to enter commercial operation since 1996. The same year, his doctoral student James Chadwick discovered the neutron, further work by Enrico Fermi in the 1930s focused on using slow neutrons to increase the effectiveness of induced radioactivity. Experiments bombarding uranium with neutrons led Fermi to believe he had created a new, transuranic element and they determined that the relatively tiny neutron split the nucleus of the massive uranium atoms into two roughly equal pieces, contradicting Fermi. Numerous scientists, including Leó Szilárd, who was one of the first, recognized that if fission reactions released additional neutrons, a self-sustaining nuclear chain reaction could result. In the United States, where Fermi and Szilárd had both emigrated, this led to the creation of the first man-made reactor, known as Chicago Pile-1, which achieved criticality on December 2,1942. In 1945, the pocketbook The Atomic Age heralded the untapped atomic power in everyday objects and depicted a future where fossil fuels would go unused. One science writer, David Dietz, wrote that instead of filling the gas tank of a car two or three times a week, people travel for a year on a pellet of atomic energy the size of a vitamin pill. The United Kingdom, Canada, and the USSR proceeded over the course of the late 1940s, electricity was generated for the first time by a nuclear reactor on December 20,1951, at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW. Work was also researched in the US on nuclear marine propulsion
8.
Solar power
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Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics, or indirectly using concentrated solar power. Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam, Photovoltaic cells convert light into an electric current using the photovoltaic effect. Most solar installations would be in China and India, Solar PV is rapidly becoming an inexpensive, low-carbon technology to harness renewable energy from the Sun. The current largest photovoltaic power station in the world is the 850 MW Longyangxia Dam Solar Park, in Qinghai, commercial concentrated solar power plants were first developed in the 1980s. The 392 MW Ivanpah installation is the largest concentrating solar power plant in the world, long distance transmission allows remote renewable energy resources to displace fossil fuel consumption. Solar power plants use one of two technologies, Photovoltaic systems use solar panels, either on rooftops or in ground-mounted solar farms, concentrated solar power plants use solar thermal energy to make steam, that is thereafter converted into electricity by a turbine. A solar cell, or photovoltaic cell, is a device that converts light into electric current using the photovoltaic effect, the first solar cell was constructed by Charles Fritts in the 1880s. The German industrialist Ernst Werner von Siemens was among those who recognized the importance of this discovery, following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954. These early solar cells cost 286 USD/watt and reached efficiencies of 4. 5–6%, the array of a photovoltaic power system, or PV system, produces direct current power which fluctuates with the sunlights intensity. For practical use this usually requires conversion to certain desired voltages or alternating current, multiple solar cells are connected inside modules. Modules are wired together to form arrays, then tied to an inverter, which produces power at the voltage, and for AC. Many residential PV systems are connected to the grid wherever available, in these grid-connected PV systems, use of energy storage is optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups, such stand-alone power systems permit operations at night and at other times of limited sunlight. Concentrated solar power, also called concentrated solar thermal, uses lenses or mirrors, contrary to photovoltaics – which converts light directly into electricity – CSP uses the heat of the suns radiation to generate electricity from conventional steam-driven turbines. A wide range of concentrating technologies exists, among the best known are the trough, the compact linear Fresnel reflector, the Stirling dish. Various techniques are used to track the sun and focus light, in all of these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage. Thermal storage efficiently allows up to 24-hour electricity generation, a parabolic trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflectors focal line. The receiver is a tube positioned right above the middle of the mirror and is filled with a working fluid
9.
Pendulum
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A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, when released, the restoring force combined with the pendulums mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one cycle, a left swing and a right swing, is called the period. The period depends on the length of the pendulum and also to a degree on the amplitude. Pendulums are also used in instruments such as accelerometers and seismometers. Historically they were used as gravimeters to measure the acceleration of gravity in geophysical surveys, the word pendulum is new Latin, from the Latin pendulus, meaning hanging. The simple gravity pendulum is a mathematical model of a pendulum. This is a weight on the end of a massless cord suspended from a pivot, when given an initial push, it will swing back and forth at a constant amplitude. Real pendulums are subject to friction and air drag, so the amplitude of their swings declines and it is independent of the mass of the bob. For small swings the period of swing is approximately the same for different size swings, that is and this property, called isochronism, is the reason pendulums are so useful for timekeeping. Successive swings of the pendulum, even if changing in amplitude, for larger amplitudes, the period increases gradually with amplitude so it is longer than given by equation. For example, at an amplitude of θ0 = 23° it is 1% larger than given by, the period increases asymptotically as θ0 approaches 180°, because the value θ0 = 180° is an unstable equilibrium point for the pendulum. The length L used to calculate the period of the simple pendulum in eq. above is the distance from the pivot point to the center of mass of the bob. Any swinging rigid body free to rotate about a horizontal axis is called a compound pendulum or physical pendulum. The appropriate equivalent length L for calculating the period of any such pendulum is the distance from the pivot to the center of oscillation. This point is located under the center of mass at a distance from the pivot traditionally called the radius of oscillation, if most of the mass is concentrated in a relatively small bob compared to the pendulum length, the center of oscillation is close to the center of mass. Substituting this expression in above, the period T of a pendulum is given by T =2 π I m g R for sufficiently small oscillations. For example, a rigid rod of length L pivoted about one end has moment of inertia I = m L2 /3
10.
Balance wheel
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A balance wheel, or balance, is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock. It is a wheel that rotates back and forth, being returned toward its center position by a spiral torsion spring. It is driven by the escapement, which transforms the motion of the watch gear train into impulses delivered to the balance wheel. Each swing of the wheel allows the train to advance a set amount. From its invention in the 14th century until tuning fork and quartz movements became available in the 1960s, virtually every portable timekeeping device used some form of balance wheel. Modern watch balance wheels are made of Glucydur, a low thermal expansion alloy of beryllium, copper and iron. The two alloys are matched so their residual temperature responses cancel out, resulting in lower temperature error. The wheels are smooth, to air friction, and the pivots are supported on precision jewel bearings. Older balance wheels used weight screws around the rim to adjust the poise, Balance wheels rotate about 1½ turns with each swing, that is, about 270° to each side of their center equilibrium position. The rate of the wheel is adjusted with the regulator. This holds the part of the spring behind the slit stationary, moving the lever slides the slit up and down the balance spring, changing its effective length, and thus the resonant vibration rate of the balance. Since the regulator interferes with the action, chronometers and some precision watches have ‘free sprung’ balances with no regulator. Their rate is adjusted by weight screws on the balance rim, a balances vibration rate is traditionally measured in beats per hour, or BPH, although beats per second and Hz are also used. The length of a beat is one swing of the balance wheel, balances in precision watches are designed with faster beats, because they are less affected by motions of the wrist. Alarm clocks and kitchen timers often have a rate of 4 beats per second, Watches made prior to the 1970s usually had a rate of 5 beats per second. Current watches have rates of 6,8 and a few have 10 beats per second, during WWII, Elgin produced a very precise stopwatch that ran at 40 beats per second, earning it the nickname Jitterbug. Audemars Piguet currently produces a movement that allows for a high balance vibration of 12 beats/s. The precision of the best balance wheel watches on the wrist is around a few seconds per day, the most accurate balance wheel timepieces made were marine chronometers, which by WWII had achieved accuracies of 0.1 second per day
11.
Water clock
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A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into or out from a vessel where the amount is then measured. Water clocks, along with sundials and hourglasses, are likely to be the oldest time-measuring instruments, with the exceptions being the vertical gnomon. Where and when they were first invented is not known, the bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and in Egypt around the 16th century BCE. Other regions of the world, including India and China, also have evidence of water clocks. Some authors, however, claim that water clocks appeared in China as early as 4000 BCE, some modern timepieces are called water clocks but work differently from the ancient ones. Independently, the Chinese developed their own advanced water clocks, incorporating gears, escapement mechanisms, some water clock designs were developed independently and some knowledge was transferred through the spread of trade. These early water clocks were calibrated with a sundial, a water clock uses a flow of water to measure time. If viscosity is neglected, the physical principle required to study such clocks is Torricellis law, there are two types of water clocks, inflow and outflow. In an outflow water clock, a container is filled with water, and this container has markings that are used to show the passage of time. As the water leaves the container, an observer can see where the water is level with the lines, an inflow water clock works in basically the same way, except instead of flowing out of the container, the water is filling up the marked container. As the container fills, the observer can see where the water meets the lines, according to Callisthenes, the Persians were using water clocks in 328 BC to ensure a just and exact distribution of water from qanats to their shareholders for agricultural irrigation. The use of clocks in Iran, especially in Zibad. Later they were used to determine the exact holy days of pre-Islamic religions, such as the Nowruz, Chelah, or Yaldā - the shortest, longest. The water clocks used in Iran were one of the most practical ancient tools for timing the yearly calendar, -Persian water clocks were a practical and useful tool for the qanats shareholders to calculate the length of time they could divert water to their farm. The qanat was the water source for agriculture and irrigation so a just. The Fenjaan consisted of a pot full of water and a bowl with a small hole in the center. When the bowl became full of water, it would sink into the pot, and he would record the number of times the bowl sank by putting small stones into a jar. The place where the clock was situated, and its managers, were known as khaneh Fenjaan
12.
Corrosion
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Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfur, rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide or salt of the original metal, corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids, many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the surface, such as passivation and chromate conversion. However, some corrosion mechanisms are less visible and less predictable, in a galvanic couple, the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a slower rate. When immersed separately, each metal corrodes at its own rate, what type of metal to use is readily determined by following the galvanic series. For example, zinc is used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the industry and also anywhere water contacts pipes or metal structures. Factors such as size of anode, types of metal. The surface area ratio of the anode and cathode directly affects the corrosion rates of the materials, galvanic corrosion is often prevented by the use of sacrificial anodes. In any given environment, one metal will be more noble or more active than others. Two metals in electrical contact share the same electrons, so that the tug-of-war at each surface is analogous to competition for free electrons between the two materials. Using the electrolyte as a host for the flow of ions in the same direction, the resulting mass flow or electric current can be measured to establish a hierarchy of materials in the medium of interest. This hierarchy is called a series and is useful in predicting and understanding corrosion
