A chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical methods, i. e. without breaking chemical bonds. Chemical substances can be chemical elements, chemical compounds, ions or alloys, Chemical substances are often called pure to set them apart from mixtures. A common example of a substance is pure water, it has the same properties. Other chemical substances commonly encountered in pure form are diamond, table salt, however, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical. Chemical substances exist as solids, gases, or plasma, Chemical substances may be combined or converted to others by means of chemical reactions. Forms of energy, such as light and heat, are not matter, a chemical substance may well be defined as any material with a definite chemical composition in an introductory general chemistry textbook. According to this definition a chemical substance can either be a chemical element or a pure chemical compound.
But, there are exceptions to this definition, a substance can be defined as a form of matter that has both definite composition and distinct properties. The chemical substance index published by CAS includes several alloys of uncertain composition, in geology, substances of uniform composition are called minerals, while physical mixtures of several minerals are defined as rocks. Many minerals, mutually dissolve into solid solutions, such that a rock is a uniform substance despite being a mixture in stoichiometric terms. Feldspars are an example, anorthoclase is an alkali aluminium silicate. In law, chemical substances may include both pure substances and mixtures with a composition or manufacturing process. For example, the EU regulation REACH defines monoconstituent substances, multiconstituent substances and substances of unknown or variable composition, the latter two consist of multiple chemical substances, their identity can be established either by direct chemical analysis or reference to a single manufacturing process.
For example, charcoal is a complex, partially polymeric mixture that can be defined by its manufacturing process. Therefore, although the chemical identity is unknown, identification can be made to a sufficient accuracy. The CAS index includes mixtures, polymers almost always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance. However, the polymer may be defined by a precursor or reaction
A Taser or conducted electrical weapon is an electroshock weapon sold by Axon. It fires two small dart-like electrodes, which connected to the main unit by conductors, to deliver electric current to disrupt voluntary control of muscles causing neuromuscular incapacitation. Someone struck by a Taser experiences extreme pain and over-stimulation of sensory nerves and motor nerves, a 2009 Police Executive Research Forum study said that officer injuries drop by 76% when a Taser is used. However, while Taser CEO Rick Smith has stated that surveys show that the device has saved 75,000 lives. Although some other companies have produced similar devices, their significance as of 2014 is still marginal, Jack Cover, a NASA researcher, began developing the Taser in 1969. By 1974, Cover had completed the device, which he named after his childhood hero Tom Swift, the Taser Public Defender used gunpowder as its propellant, which led the Bureau of Alcohol and Firearms to classify it as a firearm in 1976. The backformed verb to tase is used sometimes, in 1993, Rick Smith and his brother Thomas began to investigate what they called safer use of force option for citizens and law enforcement.
At their Scottsdale, facilities, the worked with the. original Taser inventor. The U. S. firearms regulator, the ATF, stated that the Air Taser was not a firearm, in 1999, Taser International developed an. ergonomically handgun-shaped device called the Advanced Taser M-series systems, which used a. patented neuromuscular incapacitation technology. In May 2003, Taser International released a new weapon called the Taser X26, on July 27,2009 Taser International released a new type of Taser called the X3, which can fire three shots before reloading. It holds three new cartridges, which are much thinner than the previous model. The Taser fires two small dart-like electrodes, which connected to the main unit by conductive wire as they are propelled by small compressed nitrogen charges. The cartridge contains a pair of electrodes and propellant for a shot and is replaced after each use. There are a number of cartridges designated by range, with the maximum at 35 feet, cartridges available to non-law enforcement consumers are limited to 15 feet.
The electrodes are pointed to penetrate clothing and barbed to prevent removal once in place, earlier Taser models had difficulty in penetrating thick clothing, but newer versions use a shaped pulse that increases effectiveness in the presence of barriers. Tasers provide a safety benefit to police officers, Tasers have a greater deployment range than batons, pepper spray or empty hand techniques. This allows police to maintain a greater distance, the study found that only pepper spray was a safer intervention option. Use of the taser has been associated with deaths, the Guardian newspaper is running a database, The Counted, tracking US killings by police and other law enforcement agencies in 2015
Shielded metal arc welding
An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined. The workpiece and the electrode melts forming a pool of molten metal that cools to form a joint, because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the worlds first and most popular welding processes. The process is used primarily to iron and steels but aluminium, nickel. In 1885, Nikolay Benardos and Stanisław Olszewski developed carbon arc welding, obtaining American patents from 1887 showing a rudimentary electrode holder, in 1888, the consumable metal electrode was invented by Nikolay Slavyanov. Later in 1890, C. L. Coffin received U. S, patent 428,459 for his arc welding method that utilized a metal electrode. The process, like SMAW, deposited melted electrode metal into the weld as filler, around 1900, A. P. Strohmenger and Oscar Kjellberg released the first coated electrodes.
Strohmenger used clay and lime coating to stabilize the arc, while Kjellberg dipped iron wire into mixtures of carbonates and silicates to coat the electrode, in 1912, Strohmenger released a heavily coated electrode, but high cost and complex production methods prevented these early electrodes from gaining popularity. In 1927, the development of an extrusion process reduced the cost of coating electrodes while allowing manufacturers to produce more complex coating mixtures designed for specific applications, in the 1950s, manufacturers introduced iron powder into the flux coating, making it possible to increase the welding speed. In 1938 K. K. Madsen described a variation of SMAW. It briefly gained popularity in the 1960s after receiving publicity for its use in Japanese shipyards though today its applications are limited, another little used variation of the process, known as firecracker welding, was developed around the same time by George Hafergut in Austria. To strike the arc, the electrode is brought into contact with the workpiece by a very light touch with the electrode to the base metal is pulled back slightly.
This initiates the arc and thus the melting of the workpiece and the consumable electrode, striking an arc, which varies widely based upon electrode and workpiece composition, can be the hardest skill for beginners. The tip of the needs to be at a lower angle to the workpiece. As the electrode melts, the flux covering disintegrates, giving off shielding gases that protect the area from oxygen. In addition, the flux provides molten slag which covers the metal as it travels from the electrode to the weld pool. Once part of the pool, the slag floats to the surface. Once hardened, it must be chipped away to reveal the finished weld, as welding progresses and the electrode melts, the welder must periodically stop welding to remove the remaining electrode stub and insert a new electrode into the electrode holder. This activity, combined with chipping away the slag, reduces the amount of time that the welder can spend laying the weld, in general, the operator factor, or the percentage of operators time spent laying weld, is approximately 25%
William Whewell FRS FGS was an English polymath, Anglican priest, philosopher and historian of science. He was Master of Trinity College, Cambridge, in his time as a student there, he achieved distinction in both poetry and mathematics. What is most often remarked about Whewell is the breadth of his endeavours, in a time of increasing specialisation, Whewell appears as a vestige of an earlier era when natural philosophers dabbled in a bit of everything. In mathematics, Whewell introduced what is now called the Whewell equation, one of Whewells greatest gifts to science was his wordsmithing. He often corresponded with many in his field and helped come up with new terms for their discoveries. Whewell died in Cambridge in 1866 as a result of a fall from his horse and his father, a carpenter, wished him to follow his trade, but his success in mathematics at Lancaster and Heversham grammar schools won him an exhibition at Trinity College, Cambridge. In 1814 he was awarded the Chancellors Gold Medal for poetry and he was Second Wrangler in 1816, President of the Cambridge Union Society in 1817, became fellow and tutor of his college, and, in 1841, succeeded Dr Christopher Wordsworth as master.
He was professor of mineralogy from 1828 to 1832 and Knightbridge Professor of Philosophy from 1838 to 1855, Whewell died in Cambridge in 1866 as a result of a fall from his horse. He is buried in the Mill Road cemetery, together with his first and second wives, Cordelia Whewell and Everina Frances, in the Philosophy, Whewell attempted to follow Francis Bacons plan for discovery of an effectual art of discovery. He examined ideas and by the colligation of facts endeavoured to unite these ideas with the facts, but no art of discovery, such as Bacon anticipated, for invention, genius are needed at each step. In Philosophy of the Inductive Sciences Whewell was the first to use the term consilience to discuss the unification of knowledge between the different branches of learning, here, as in his ethical doctrine, Whewell was moved by opposition to contemporary English empiricism. As stated, one of Whewells greatest gifts to science was his wordsmithing and he often corresponded with many in his field and helped them come up with new terms for their discoveries.
Whewell was prominent not only in research and philosophy, but in university. His first work, An Elementary Treatise on Mechanics, cooperated with those of George Peacock and his work and publications helped influence the recognition of the moral and natural sciences as an integral part of the Cambridge curriculum. He opposed the appointment of the University Commission, and wrote two pamphlets against the reform of the university and he stood against the scheme of entrusting elections to the members of the senate and instead, advocated the use of college funds and the subvention of scientific and professorial work. The Whewell Professorship of International Law and the Whewell Scholarships were established through the provisions of his will, aside from Science, Whewell was interested in the history of architecture throughout his life. He is best known for his writings on Gothic architecture, specifically his book, in this work, Whewell established a strict nomenclature for German Gothic churches and came up with a theory of stylistic development.
His work is associated with the trend of architectural writers, along with Thomas Rickman
Gas tungsten arc welding
Gas tungsten arc welding, known as tungsten inert gas welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area is protected from contamination by an inert shielding gas. A constant-current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas, GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum and copper alloys. The process grants the operator control over the weld than competing processes such as shielded metal arc welding. However, GTAW is comparatively more complex and difficult to master, a related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated. After the discovery of the pulsed electric arc in 1800 by Humphry Davy and of the continuous electric arc in 1802 by Vasily Petrov. C. L. Processes using flux-covered electrodes did not satisfactorily protect the area from contamination.
To solve the problem, bottled inert gases were used in the beginning of the 1930s, a few years later, a direct current, gas-shielded welding process emerged in the aircraft industry for welding magnesium. Russell Meredith of Northrop Aircraft perfected the process in 1941, Meredith named the process Heliarc because it used a tungsten electrode arc and helium as a shielding gas, but it is often referred to as tungsten inert gas welding. The American Welding Societys official term is gas tungsten arc welding, linde Air Products developed a wide range of air-cooled and water-cooled torches, gas lenses to improve shielding, and other accessories that increased the use of the process. Initially, the electrode overheated quickly and, despite tungstens high melting temperature, to address this problem, the polarity of the electrode was changed from positive to negative, but the change made it unsuitable for welding many non-ferrous materials. Finally, the development of alternating current units made it possible to stabilize the arc, developments continued during the following decades.
Linde developed water-cooled torches that helped prevent overheating when welding with high currents, the use of any shielding gas containing an oxygen compound, such as carbon dioxide, quickly contaminates the tungsten electrode, making it unsuitable for the TIG process. In 1953, a new process based on GTAW was developed, called plasma arc welding, development within the GTAW process has continued as well, and today a number of variations exist. Among the most popular are the pulsed-current, manual programmed, hot-wire, manual gas tungsten arc welding is a relatively difficult welding method, due to the coordination required by the welder. Maintaining a short arc length, while preventing contact between the electrode and the workpiece, is important, to strike the welding arc, a high frequency generator provides an electric spark. Once the arc is struck, the moves the torch in a small circle to create a welding pool, the size of which depends on the size of the electrode. While maintaining a constant separation between the electrode and the workpiece, the operator moves the torch back slightly and tilts it backward about 10–15 degrees from vertical
In electronics, a diode is a two-terminal electronic component that conducts primarily in one direction, it has low resistance to the current in one direction, and high resistance in the other. A semiconductor diode, the most common today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. A vacuum tube diode has two electrodes, a plate and a heated cathode, semiconductor diodes were the first semiconductor electronic devices. The discovery of crystals rectifying abilities was made by German physicist Ferdinand Braun in 1874, the first semiconductor diodes, called cats whisker diodes, developed around 1906, were made of mineral crystals such as galena. Today, most diodes are made of silicon, but other such as selenium and germanium are sometimes used. The most common function of a diode is to allow a current to pass in one direction. Thus, the diode can be viewed as a version of a check valve. However, diodes can have complicated behavior than this simple on–off action.
Semiconductor diodes begin conducting electricity only if a threshold voltage or cut-in voltage is present in the forward direction. The voltage drop across a forward-biased diode varies only a little with the current, and is a function of temperature, a semiconductor diodes current–voltage characteristic can be tailored by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacture. These techniques are used to create special-purpose diodes that perform different functions. Tunnel, Gunn and IMPATT diodes exhibit negative resistance, which is useful in microwave, both vacuum and semiconductor, can be used as shot-noise generators. Thermionic diodes and solid state diodes were developed separately, at approximately the time, in the early 1900s. Until the 1950s vacuum tube diodes were used frequently in radios because the early point-contact type semiconductor diodes were less stable. In 1873, Frederick Guthrie discovered the principle of operation of thermionic diodes.
Guthrie discovered that a positively charged electroscope could be discharged by bringing a piece of white-hot metal close to it. The same did not apply to a negatively charged electroscope, indicating that the current flow was possible in one direction. Thomas Edison independently rediscovered the principle on February 13,1880, at the time, Edison was investigating why the filaments of his carbon-filament light bulbs nearly always burned out at the positive-connected end
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of an electrical current in one or more directions. Materials made of metal are common electrical conductors, Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases. In order for current to flow, it is not necessary for one charged particle to travel from the producing the current to that consuming it. Instead, the particle simply needs to nudge its neighbor a finite amount who will nudge its neighbor and on and on until a particle is nudged into the consumer. Essentially what is occurring here is a chain of momentum transfer between mobile charge carriers, the Drude model of conduction describes this process more rigorously. Insulators are non-conducting materials with few mobile charges that support only insignificant electric currents, the resistance of a given conductor depends on the material it is made of, and on its dimensions.
For a given material, the resistance is proportional to the cross-sectional area. For example, a copper wire has lower resistance than an otherwise-identical thin copper wire. Also, for a material, the resistance is proportional to the length, for example. The resistance R and conductance G of a conductor of uniform cross section, the resistivity and conductivity are proportionality constants, and therefore depend only on the material the wire is made of, not the geometry of the wire. Resistivity and conductivity are reciprocals, ρ =1 / σ, resistivity is a measure of the materials ability to oppose electric current. This formula is not exact, It assumes the current density is uniform in the conductor. However, this still provides a good approximation for long thin conductors such as wires. Another situation this formula is not exact for is with alternating current, the geometrical cross-section is different from the effective cross-section in which current actually flows, so the resistance is higher than expected.
Similarly, if two conductors are each other carrying AC current, their resistances increase due to the proximity effect. Aside from the geometry of the wire, temperature has a significant effect on the efficacy of conductors, temperature affects conductors in two main ways, the first is that materials may expand under the application of heat. The amount that the material will expand is governed by the expansion coefficient specific to the material. Such an expansion will change the geometry of the conductor and therefore its characteristic resistance, this effect is generally small, on the order of 10−6
Electricity is the set of physical phenomena associated with the presence of electric charge. Although initially considered a separate to magnetism, since the development of Maxwells Equations both are recognized as part of a single phenomenon, electromagnetism. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges, in addition, electricity is at the heart of many modern technologies. The presence of a charge, which can be either positive or negative. On the other hand, the movement of charges, which is known as electric current. When a charge is placed in a location with non-zero electric field, the magnitude of this force is given by Coulombs Law. Thus, if that charge were to move, the field would be doing work on the electric charge. Electrical phenomena have been studied since antiquity, though progress in theoretical understanding remained slow until the seventeenth and eighteenth centuries. Even then, practical applications for electricity were few, and it would not be until the nineteenth century that engineers were able to put it to industrial and residential use.
The rapid expansion in electrical technology at this time transformed industry, electricitys extraordinary versatility means it can be put to an almost limitless set of applications which include transport, lighting and computation. Electrical power is now the backbone of modern industrial society, long before any knowledge of electricity existed, people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BCE referred to these fish as the Thunderer of the Nile, Electric fish were again reported millennia by ancient Greek and Arabic naturalists and physicians. Patients suffering from such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them. Ancient cultures around the Mediterranean knew that certain objects, such as rods of amber, Thales was incorrect in believing the attraction was due to a magnetic effect, but science would prove a link between magnetism and electricity. He coined the New Latin word electricus to refer to the property of attracting small objects after being rubbed and this association gave rise to the English words electric and electricity, which made their first appearance in print in Thomas Brownes Pseudodoxia Epidemica of 1646.
Further work was conducted by Otto von Guericke, Robert Boyle, Stephen Gray, in the 18th century, Benjamin Franklin conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a key to the bottom of a dampened kite string. A succession of jumping from the key to the back of his hand showed that lightning was indeed electrical in nature
In an integrated circuit or IC, the components and interconnections are formed on the same substrate, typically a semiconductor such as silicon or gallium arsenide. An electronic circuit can usually be categorized as an analog circuit, breadboards and stripboards are common for testing new designs. They allow the designer to make changes to the circuit during development. Analog electronic circuits are those in current or voltage may vary continuously with time to correspond to the information being represented. Analog circuitry is constructed from two building blocks and parallel circuits. In a series circuit, the current passes through a series of components. A string of Christmas lights is an example of a series circuit, if one goes out. In a parallel circuit, all the components are connected to the voltage. The basic components of analog circuits are wires, capacitors, diodes, analog circuits are very commonly represented in schematic diagrams, in which wires are shown as lines, and each component has a unique symbol.
Analog circuit analysis employs Kirchhoffs circuit laws, all the currents at a node, wires are usually treated as ideal zero-voltage interconnections, any resistance or reactance is captured by explicitly adding a parasitic element, such as a discrete resistor or inductor. When the circuit size is comparable to a wavelength of the relevant signal frequency, wires are treated as transmission lines, with constant characteristic impedance, and the impedances at the start and end determine transmitted and reflected waves on the line. These values represent the information that is being processed, in the vast majority of cases, binary encoding is used, one voltage represents a binary 1 and another voltage represents a binary 0. Digital circuits make extensive use of transistors, interconnected to create gates that provide the functions of Boolean logic, AND, NAND, OR, NOR, XOR. Digital circuits therefore can provide both logic and memory, enabling them to perform arbitrary computational functions, the design process for digital circuits is fundamentally different from the process for analog circuits.
Each logic gate regenerates the binary signal, so the designer need not account for distortion, gain control, offset voltages, as a consequence, extremely complex digital circuits, with billions of logic elements integrated on a single silicon chip, can be fabricated at low cost. Such digital integrated circuits are ubiquitous in electronic devices, such as calculators, mobile phone handsets. Digital circuitry is used to general purpose computing chips, such as microprocessors. Field-programmable gate arrays, chips with logic circuitry whose configuration can be modified after fabrication, are widely used in prototyping
Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of a current or electrical discharge. Static electricity is named in contrast with current electricity, which flows through wires or other conductors, a static electric charge can be created whenever two surfaces contact and separate, and at least one of the surfaces has a high resistance to electric current. The familiar phenomenon of a static shock–more specifically, an electrostatic discharge–is caused by the neutralization of charge, materials are made of atoms that are normally electrically neutral because they contain equal numbers of positive charges and negative charges. The phenomenon of static electricity requires a separation of positive and negative charges, when two materials are in contact, electrons may move from one material to the other, which leaves an excess of positive charge on one material, and an equal negative charge on the other.
When the materials are separated they retain this charge imbalance and this is known as the triboelectric effect and results in one material becoming positively charged and the other negatively charged. The polarity and strength of the charge on a material once they are separated depends on their positions in the triboelectric series. The triboelectric effect is the cause of static electricity as observed in everyday life. Contact-induced charge separation causes your hair to stand up and causes static cling, pressure-induced charge separation Applied mechanical stress generates a separation of charge in certain types of crystals and ceramics molecules. Heat-induced charge separation Heating generates a separation of charge in the atoms or molecules of certain materials, all pyroelectric materials are piezoelectric. The atomic or molecular properties of heat and pressure response are closely related, charge-induced charge separation A charged object brought close to an electrically neutral object causes a separation of charge within the neutral object.
Charges of the same polarity are repelled and charges of the opposite polarity are attracted, as the force due to the interaction of electric charges falls off rapidly with increasing distance, the effect of the closer charges is greater and the two objects feel a force of attraction. The effect is most pronounced when the object is an electrical conductor as the charges are more free to move around. Careful grounding of part of an object with a charge separation can permanently add or remove electrons, leaving the object with a global. This process is integral to the workings of the Van de Graaff generator, removing or preventing a buildup of static charge can be as simple as opening a window or using a humidifier to increase the moisture content of the air, making the atmosphere more conductive. Air ionizers can perform the same task, fabric softeners and dryer sheets used in washing machines and clothes dryers are an example of an antistatic agent used to prevent and remove static cling.
Many semiconductor devices used in electronics are particularly sensitive to static discharge, conductive antistatic bags are commonly used to protect such components. People who work on circuits that contain these devices often ground themselves with an antistatic strap
Gas metal arc welding
Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from contaminants in the air. The process can be semi-automatic or automatic, a constant voltage, direct current power source is most commonly used with GMAW, but constant current systems, as well as alternating current, can be used. Originally developed for welding aluminium and other materials in the 1940s. The cost of inert gas limited its use in steels until several years later, further developments during the 1950s and 1960s gave the process more versatility and as a result, it became a highly used industrial process. Today, GMAW is the most common industrial welding process, preferred for its versatility, unlike welding processes that do not employ a shielding gas, such as shielded metal arc welding, it is rarely used outdoors or in other areas of air volatility. A related process, flux cored arc welding, often does not use a shielding gas, the principles of gas metal arc welding began to be understood in the early 19th century, after Humphry Davy discovered the short pulsed electric arcs in 1800.
Vasily Petrov independently produced the electric arc in 1802. It was not until the 1880s that the technology developed with the aim of industrial usage. At first, carbon electrodes were used in arc welding. By 1890, metal electrodes had been invented by Nikolay Slavyanov, in 1920, an early predecessor of GMAW was invented by P. O. Nobel of General Electric. It used an electrode wire and direct current, and used arc voltage to regulate the feed rate. It did not use a gas to protect the weld. In 1926 another forerunner of GMAW was released, but it was not suitable for practical use, in 1948, GMAW was developed by the Battelle Memorial Institute. It used a smaller diameter electrode and a constant voltage power source developed by H. E. Kennedy and it offered a high deposition rate, but the high cost of inert gases limited its use to non-ferrous materials and prevented cost savings. In 1953, the use of carbon dioxide as an atmosphere was developed. It quickly became the most popular GMAW variation, the spray-arc transfer variation was developed in the early 1960s, when experimenters added small amounts of oxygen to inert gases.
More recently, pulsed current has been applied, giving rise to a new method called the pulsed spray-arc variation, GMAW is one of the most popular welding methods, especially in industrial environments. It is used extensively by the metal industry and, by extension
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction of positively charged hydrogen ions with oxygen or another oxidizing agent. Fuel cells can produce electricity continuously for as long as these inputs are supplied, the first fuel cells were invented in 1838. The first commercial use of fuel cells came more than a in NASA space programs to generate power for satellites. Since then, fuel cells have been used in other applications. Fuel cells are used for primary and backup power for commercial and residential buildings and they are used to power fuel cell vehicles, including forklifts, buses, boats and submarines. There are many types of cells, but they all consist of an anode, a cathode. The anode and cathode contain catalysts that cause the fuel to undergo reactions that generate positively charged hydrogen ions and electrons. The hydrogen ions are drawn through the electrolyte after the reaction, at the same time, electrons are drawn from the anode to the cathode through an external circuit, producing direct current electricity.
At the cathode, hydrogen ions and oxygen react to form water, Individual fuel cells produce relatively small electrical potentials, about 0.7 volts, so cells are stacked, or placed in series, to create sufficient voltage to meet an applications requirements. In addition to electricity, fuel cells produce water, heat and, depending on the source, very small amounts of nitrogen dioxide. The energy efficiency of a cell is generally between 40–60%, or up to 85% efficient in cogeneration if waste heat is captured for use. The fuel cell market is growing, and in 2013 Pike Research estimated that the fuel cell market will reach 50 GW by 2020. The first references to hydrogen fuel cells appeared in 1838 and he used a combination of sheet iron and porcelain plates, and a solution of sulphate of copper and dilute acid. In a letter to the publication written in December 1838 but published in June 1839. His letter discussed current generated from hydrogen and oxygen dissolved in water, grove sketched his design, in 1842, in the same journal.
The fuel cell he used similar materials to todays phosphoric-acid fuel cell. In 1939, British engineer Francis Thomas Bacon successfully developed a 5 kW stationary fuel cell and this became known as the Grubb-Niedrach fuel cell. GE went on to develop this technology with NASA and McDonnell Aircraft and this was the first commercial use of a fuel cell