A furnace is a device used for high-temperature heating. The name derives from Latin word fornax; the heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces. In American English and Canadian English usage, the term furnace refers to the household heating systems based upon a central furnace, otherwise known either as a boiler, or a heater in British English. Furnace may be a synonym for kiln, a device used in the production of ceramics. In British English, a furnace is an industrial furnace used for many things, such as the extraction of metal from ore or in oil refineries and other chemical plants, for example as the heat source for fractional distillation columns; the term furnace can refer to a direct fired heater, used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking, is part of the standard English names for many metallurgical furnaces worldwide.
Furnaces can be classified based on efficiency and design. The first category of furnaces are natural draft, atmospheric burner furnaces; these furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel. The heat exchangers were vented through masonry chimneys. Air circulation depended on upwardly pitched pipes constructed of wood or metal; the pipes would channel the warm air into wall vents inside the home. This method of heating worked; the system was simple, had few controls, a single automatic gas valve, no blower. These furnaces could be made to work with any fuel by adapting the burner area, they have been operated with wood, coal, paper, natural gas, fuel oil as well as whale oil for a brief period at the turn of the century. Furnaces that used solid fuels required daily maintenance to remove ash and "clinkers" that accumulated in the bottom of the burner area. In years, these furnaces were adapted with electric blowers to aid air distribution and speed moving heat into the home.
Gas and oil-fired systems were controlled by a thermostat inside the home, while most wood and coal-fired furnaces had no electrical connection and were controlled by the amount of fuel in the burner and position of the fresh-air damper on the burner access door. The second category of furnace is the forced-air, atmospheric burner style with a cast-iron or sectional steel heat exchanger. Through the 1950s and 1960s, this style of furnace was used to replace the big, natural draft systems, was sometimes installed on the existing gravity duct work; the heated air was moved by blowers which were belt designed for a wide range of speeds. These furnaces were still big and bulky compared to modern furnaces, had heavy-steel exteriors with bolt-on removable panels. Energy efficiency would range anywhere from just over 50% to upward of 65% AFUE; this style furnace still used large, masonry or brick chimneys for flues and was designed to accommodate air-conditioning systems. The third category of furnace is the forced draft, mid-efficiency furnace with a steel heat exchanger and multi-speed blower.
These furnaces were physically much more compact than the previous styles. They were equipped with combustion air blowers that would pull air through the heat exchanger which increased fuel efficiency while allowing the heat exchangers to become smaller; these furnaces may have multi-speed blowers and were designed to work with central air-conditioning systems. The fourth category of furnace is condensing furnace. High-efficiency furnaces can achieve from 89% to 98% fuel efficiency; this style of furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. Because the heat exchanger removes most of the heat from the exhaust gas, it condenses water vapor and other chemicals as it operates; the vent pipes are installed with PVC pipe versus metal vent pipe to prevent corrosion. The draft inducer allows for the exhaust piping to be routed vertically or horizontally as it exits the structure; the most efficient arrangement for high-efficiency furnaces include PVC piping that brings fresh combustion air from the outside of the home directly to the furnace.
The combustion air PVC is routed alongside the exhaust PVC during installation and the pipes exit through a sidewall of the home in the same location. High efficiency furnaces deliver a 25% to 35% fuel savings over a 60% AFUE furnace. A single-stage furnace has only one stage of operation, it is either off; this means that it is noisy, always running at the highest speed, always pumping out the hottest air at the highest velocity. One of the benefits to a single-stage furnace is the cost for installation. Single-stage furnaces are inexpensive since the technology is rather simple. A two-stage furnace has to do two stage half speed. Depending on the demanded heat, they can run at a lower speed most of the time, they can be quieter, move the air at less velocity, will better keep the desired temperature in the house. A modulating furnace can modulate the heat output and air velocity nearly continuously, depending on the demanded heat and outside temperature; this means that it therefore saves energy.
The furnace transfers heat to the living space of the building through an intermediary distribution system. If the distribution is through hot water or through steam the furnace is more called a boiler. One adv
A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam. Superheated steam is used in steam turbines for electricity generation, steam engines, in processes such as steam reforming. There are three types of superheaters: radiant and separately fired. A superheater can vary in size from a few tens of feet to several hundred feet. A radiant superheater is placed directly in radiant zone of the combustion chamber near the water wall so as to absorb heat by radiation. A convection superheater is located in the convective zone of the furnace ahead of economizer; these are called primary superheaters. A separately fired superheater is a superheater, placed outside the main boiler, which has its own separate combustion system; this superheater design incorporates additional burners in the area of superheater pipes. This type of superheater is not popularly used, tends to be extinct due to efficiency of combustion ratio with steam quality, not better than other superheater types.
In a steam engine, the superheater re-heats the steam generated by the boiler, increasing its thermal energy and decreasing the likelihood that it will condense inside the engine. Superheaters increase the thermal efficiency of the steam engine, have been adopted. Steam, superheated is logically known as superheated steam. Superheaters were applied to steam locomotives in quantity from the early 20th century, to most steam vehicles, to stationary steam engines; this equipment is still used in conjunction with steam turbines in electrical power generating stations throughout the world. In steam locomotive use, by far the most common form of superheater is the fire-tube type; this takes the saturated steam supplied in the dry pipe into a superheater header mounted against the tube sheet in the smokebox. The steam is passed through a number of superheater elements—long pipes which are placed inside large diameter fire tubes, called flues. Hot combustion gases from the locomotive's fire pass through these flues just like they do the firetubes, as well as heating the water they heat the steam inside the superheater elements they flow over.
The superheater element doubles back on itself. The superheated steam, at the end of its journey through the elements, passes into a separate compartment of the superheater header and to the cylinders as normal; the steam passing through the superheater elements cools their metal and prevents them from melting, but when the throttle closes this cooling effect is absent, thus a damper closes in the smokebox to cut off the flow through the flues and prevent them being damaged. Some locomotives were fitted with snifting valves which admitted air to the superheater when the locomotive was coasting; this kept the cylinders warm. The snifting valve can be seen behind the chimney on many LNER locomotives. A superheater increases the distance between the throttle and the cylinders in the steam circuit and thus reduces the immediacy of throttle action. To counteract this, some steam locomotives were fitted with a front-end throttle—placed in the smokebox after the superheater; such locomotives can sometimes be identified by an external throttle rod that stretches the whole length of the boiler, with a crank on the outside of the smokebox.
This arrangement allows superheated steam to be used for auxiliary appliances, such as the dynamo and air pumps. Another benefit of the front end throttle is that superheated steam is available. With the dome throttle, it took quite some time before the super heater provided benefits in efficiency. One can think of it in this way: if one opens saturated steam from the boiler to the superheater it goes straight through the superheater units and to the cylinders which doesn't leave much time for the steam to be superheated. With the front-end throttle, steam is in the superheater units while the engine is sitting at the station and that steam is being superheated; when the throttle is opened, superheated steam goes to the cylinders immediately. Locomotives with superheaters are fitted with piston valves or poppet valves; this is. The first practical superheater was developed in Germany by Wilhelm Schmidt during the 1880s and 1890s; the first superheated locomotive Prussian S 4 series, with an early form of superheater, was built in 1898, produced in series from 1902.
The benefits of the invention were demonstrated in the U. K. by the Great Western Railway in 1906. The GWR Chief Mechanical Engineer, G. J. Churchward believed, that the Schmidt type could be bettered, design and testing of an indigenous Swindon type was undertaken, culminating in the Swindon No. 3 superheater in 1909. Douglas Earle Marsh carried out a series of comparative tests between members of his I3 class using saturated steam and those fitted with the Schmidt superheater between October 1907 and March 1910, proving the advantages of the latter in terms of performance and efficiency. Other improved superheaters were introduced by John G. Robinson of the Great Central Railway at Gorton locomotive works, by Robert Urie of the London and South Western Railway at Eastleigh railway works, Richard Maunsell of the Southern Railway a
National Institute of Standards and Technology
The National Institute of Standards and Technology is a physical sciences laboratory, a non-regulatory agency of the United States Department of Commerce. Its mission is to promote industrial competitiveness. NIST's activities are organized into laboratory programs that include nanoscale science and technology, information technology, neutron research, material measurement, physical measurement; the American AI initiative has called NIST to lead the development of appropriate technical standards for reliable, trustworthy, secure and interoperable AI systems. The Articles of Confederation, ratified by the colonies in 1781, contained the clause, "The United States in Congress assembled shall have the sole and exclusive right and power of regulating the alloy and value of coin struck by their own authority, or by that of the respective states—fixing the standards of weights and measures throughout the United States". Article 1, section 8, of the Constitution of the United States, transferred this power to Congress.
To coin money, regulate the value thereof, of foreign coin, fix the standard of weights and measures". In January 1790, President George Washington, in his first annual message to Congress stated that, "Uniformity in the currency and measures of the United States is an object of great importance, will, I am persuaded, be duly attended to", ordered Secretary of State Thomas Jefferson to prepare a plan for Establishing Uniformity in the Coinage and Measures of the United States, afterwards referred to as the Jefferson report. On October 25, 1791, Washington appealed a third time to Congress, "A uniformity of the weights and measures of the country is among the important objects submitted to you by the Constitution and if it can be derived from a standard at once invariable and universal, must be no less honorable to the public council than conducive to the public convenience", but it was not until 1838, that a uniform set of standards was worked out. In 1821, John Quincy Adams had declared "Weights and measures may be ranked among the necessities of life to every individual of human society".
From 1830 until 1901, the role of overseeing weights and measures was carried out by the Office of Standard Weights and Measures, part of the United States Department of the Treasury. In 1901, in response to a bill proposed by Congressman James H. Southard, the National Bureau of Standards was founded with the mandate to provide standard weights and measures, to serve as the national physical laboratory for the United States. President Theodore Roosevelt appointed Samuel W. Stratton as the first director; the budget for the first year of operation was $40,000. The Bureau took custody of the copies of the kilogram and meter bars that were the standards for US measures, set up a program to provide metrology services for United States scientific and commercial users. A laboratory site was constructed in Washington, DC, instruments were acquired from the national physical laboratories of Europe. In addition to weights and measures, the Bureau developed instruments for electrical units and for measurement of light.
In 1905 a meeting was called that would be the first "National Conference on Weights and Measures". Conceived as purely a metrology agency, the Bureau of Standards was directed by Herbert Hoover to set up divisions to develop commercial standards for materials and products.page 133 Some of these standards were for products intended for government use, but product standards affected private-sector consumption. Quality standards were developed for products including some types of clothing, automobile brake systems and headlamps and electrical safety. During World War I, the Bureau worked on multiple problems related to war production operating its own facility to produce optical glass when European supplies were cut off. Between the wars, Harry Diamond of the Bureau developed a blind approach radio aircraft landing system. During World War II, military research and development was carried out, including development of radio propagation forecast methods, the proximity fuze and the standardized airframe used for Project Pigeon, shortly afterwards the autonomously radar-guided Bat anti-ship guided bomb and the Kingfisher family of torpedo-carrying missiles.
In 1948, financed by the United States Air Force, the Bureau began design and construction of SEAC, the Standards Eastern Automatic Computer. The computer went into operation in May 1950 using a combination of vacuum tubes and solid-state diode logic. About the same time the Standards Western Automatic Computer, was built at the Los Angeles office of the NBS by Harry Huskey and used for research there. A mobile version, DYSEAC, was built for the Signal Corps in 1954. Due to a changing mission, the "National Bureau of Standards" became the "National Institute of Standards and Technology" in 1988. Following September 11, 2001, NIST conducted the official investigation into the collapse of the World Trade Center buildings. NIST, known between 1901 and 1988 as the National Bureau of Standards, is a measurement standards laboratory known as a National Metrological Institute, a non-regulatory agency of the United States Department of Commerce; the institute's official mission is to: Promote U. S. innovation and industrial competitiveness by advancing measurement science and technology in ways that enhance economic security and improve our quality of life.
NIST had an operating budget for fiscal year 2007 of about $843.3 million. NIST's 2009 budget was $992 million
A turbine blade is the individual component which makes up the turbine section of a gas turbine or steam turbine. The blades are responsible for extracting energy from the high temperature, high pressure gas produced by the combustor; the turbine blades are the limiting component of gas turbines. To survive in this difficult environment, turbine blades use exotic materials like superalloys and many different methods of cooling, such as internal air channels, boundary layer cooling, thermal barrier coatings. Blade fatigue is a major source of failure in steam turbines and gas turbines. Fatigue is caused by the stress induced by vibration and resonance within the operating range of machinery. To protect blades from these high dynamic stresses, friction dampers are used. Blades of wind turbines and water turbines are designed to operate in different conditions, which involve lower rotational speeds and temperatures. In a gas turbine engine, a single turbine section is made up of a disk or hub that holds many turbine blades.
That turbine section is connected to a compressor section via a shaft, that compressor section can either be axial or centrifugal. Air is compressed, raising the pressure and temperature, through the compressor stages of the engine; the temperature is greatly increased by combustion of fuel inside the combustor, which sits between the compressor stages and the turbine stages. The high-temperature and high-pressure exhaust gases pass through the turbine stages; the turbine stages extract energy from this flow, lowering the pressure and temperature of the air and transfer the kinetic energy to the compressor stages along the spool. This process is similar to how an axial compressor works, only in reverse; the number of turbine stages varies in different types of engines, with high-bypass-ratio engines tending to have the most turbine stages. The number of turbine stages can have a great effect on how the turbine blades are designed for each stage. Many gas turbine engines are twin-spool designs, meaning that there is a high-pressure spool and a low-pressure spool.
Other gas turbines use three spools, adding an intermediate-pressure spool between the high- and low-pressure spool. The high-pressure turbine is exposed to the hottest, highest-pressure air, the low-pressure turbine is subjected to cooler, lower-pressure air; the difference in conditions leads to the design of high-pressure and low-pressure turbine blades that are different in material and cooling choices though the aerodynamic and thermodynamic principles are the same. Under these severe operating conditions inside the gas and steam turbines, the blades face high temperature, high stresses, high vibrations. Steam turbine blades are critical components in power plants which convert the linear motion of high-temperature and high-pressure steam flowing down a pressure gradient into a rotary motion of the turbine shaft. Turbine blades are subjected to strenuous environments inside a gas turbine, they face high temperatures, high stresses, a potential environment of high vibration. All three of these factors can lead to blade failures destroying the engine, therefore turbine blades are designed to resist these conditions.
Turbine blades are subjected to stress from centrifugal force and fluid forces that can cause fracture, yielding, or creep failures. Additionally, the first stage of a modern turbine faces temperatures around 2,500 °F, up from temperatures around 1,500 °F in early gas turbines. Modern military jet engines, like the Snecma M88, can see turbine temperatures of 2,900 °F; those high temperatures make them more susceptible to creep failures. The high temperatures can make the blades susceptible to corrosion failures. Vibrations from the engine and the turbine itself can cause fatigue failures. A key limiting factor in early jet engines was the performance of the materials available for the hot section of the engine; the need for better materials spurred much research in the field of alloys and manufacturing techniques, that research resulted in a long list of new materials and methods that make modern gas turbines possible. One of the earliest of these was Nimonic, used in the British Whittle engines.
The development of superalloys in the 1940s and new processing methods such as vacuum induction melting in the 1950s increased the temperature capability of turbine blades. Further processing methods like hot isostatic pressing improved the alloys used for turbine blades and increased turbine blade performance. Modern turbine blades use nickel-based superalloys that incorporate chromium and rhenium. Aside from alloy improvements, a major breakthrough was the development of directional solidification and single crystal production methods; these methods help increase strength against fatigue and creep by aligning grain boundaries in one direction or by eliminating grain boundaries altogether. SC research took about 10 years to be implemented. One of the first implementations of DS was with the J58 engines of the SR-71. Another major improvement to turbine blade material technology was the development of thermal barrier coatings. Where DS and SC developments improved creep and fatigue resistance, TBCs improved corrosion and oxidation resistance, both of which became greater concerns as temperatures increased.
The first TBCs, applied in the 1970s, were aluminide coatings. Improved ceramic coatings became available in the 1980s; these coatings increased turbine blade te
Incandescence is the emission of electromagnetic radiation from a hot body as a result of its temperature. The term derives to glow white. Incandescence is a special case of thermal radiation. Incandescence refers to visible light, while thermal radiation refers to infrared or any other electromagnetic radiation. For information on the intensity and spectrum of incandescence, see thermal radiation. In practice all solid or liquid substances start to glow around 798 K, with a mildly dull red color, whether or not a chemical reaction takes place that produces light as a result of an exothermic process; this limit is called the Draper point. The incandescence does not vanish below that temperature, but it is too weak in the visible spectrum to be perceivable. At higher temperatures, the substance becomes brighter and its color changes from red towards white and blue. Incandescence is exploited in incandescent light bulbs, in which a filament is heated to a temperature at which a fraction of the radiation falls in the visible spectrum.
The majority of the radiation however, is emitted in the infrared part of the spectrum, rendering incandescent lights inefficient as a light source. If the filament could be made hotter, efficiency would increase. More efficient light sources, such as fluorescent lamps and LEDs, do not function by incandescence. Sunlight is the incandescence of the "white hot" surface of the sun; the word incandescent is used figuratively to describe a person, so angry that they are imagined to glow or burn red hot or white hot. Red heat List of light sources
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters are at Broadcasting House in Westminster, it is the world's oldest national broadcasting organisation and the largest broadcaster in the world by number of employees, it employs over 20,950 staff in total. The total number of staff is 35,402 when part-time and fixed-contract staff are included; the BBC is established under a Royal Charter and operates under its Agreement with the Secretary of State for Digital, Culture and Sport. Its work is funded principally by an annual television licence fee, charged to all British households and organisations using any type of equipment to receive or record live television broadcasts and iPlayer catch-up; the fee is set by the British Government, agreed by Parliament, used to fund the BBC's radio, TV, online services covering the nations and regions of the UK. Since 1 April 2014, it has funded the BBC World Service, which broadcasts in 28 languages and provides comprehensive TV, online services in Arabic and Persian.
Around a quarter of BBC revenues come from its commercial arm BBC Studios Ltd, which sells BBC programmes and services internationally and distributes the BBC's international 24-hour English-language news services BBC World News, from BBC.com, provided by BBC Global News Ltd. From its inception, through the Second World War, to the 21st century, the BBC has played a prominent role in British culture, it is known colloquially as "The Beeb", "Auntie", or a combination of both. Britain's first live public broadcast from the Marconi factory in Chelmsford took place in June 1920, it was sponsored by the Daily Mail's Lord Northcliffe and featured the famous Australian soprano Dame Nellie Melba. The Melba broadcast caught the people's imagination and marked a turning point in the British public's attitude to radio. However, this public enthusiasm was not shared in official circles where such broadcasts were held to interfere with important military and civil communications. By late 1920, pressure from these quarters and uneasiness among the staff of the licensing authority, the General Post Office, was sufficient to lead to a ban on further Chelmsford broadcasts.
But by 1922, the GPO had received nearly 100 broadcast licence requests and moved to rescind its ban in the wake of a petition by 63 wireless societies with over 3,000 members. Anxious to avoid the same chaotic expansion experienced in the United States, the GPO proposed that it would issue a single broadcasting licence to a company jointly owned by a consortium of leading wireless receiver manufactures, to be known as the British Broadcasting Company Ltd. John Reith, a Scottish Calvinist, was appointed its General Manager in December 1922 a few weeks after the company made its first official broadcast; the company was to be financed by a royalty on the sale of BBC wireless receiving sets from approved domestic manufacturers. To this day, the BBC aims to follow the Reithian directive to "inform and entertain"; the financial arrangements soon proved inadequate. Set sales were disappointing as amateurs made their own receivers and listeners bought rival unlicensed sets. By mid-1923, discussions between the GPO and the BBC had become deadlocked and the Postmaster-General commissioned a review of broadcasting by the Sykes Committee.
The Committee recommended a short term reorganisation of licence fees with improved enforcement in order to address the BBC's immediate financial distress, an increased share of the licence revenue split between it and the GPO. This was to be followed by a simple 10 shillings licence fee with no royalty once the wireless manufactures protection expired; the BBC's broadcasting monopoly was made explicit for the duration of its current broadcast licence, as was the prohibition on advertising. The BBC was banned from presenting news bulletins before 19.00 and was required to source all news from external wire services. Mid-1925 found the future of broadcasting under further consideration, this time by the Crawford committee. By now, the BBC, under Reith's leadership, had forged a consensus favouring a continuation of the unified broadcasting service, but more money was still required to finance rapid expansion. Wireless manufacturers were anxious to exit the loss making consortium with Reith keen that the BBC be seen as a public service rather than a commercial enterprise.
The recommendations of the Crawford Committee were published in March the following year and were still under consideration by the GPO when the 1926 general strike broke out in May. The strike temporarily interrupted newspaper production, with restrictions on news bulletins waived, the BBC became the primary source of news for the duration of the crisis; the crisis placed the BBC in a delicate position. On one hand Reith was acutely aware that the Government might exercise its right to commandeer the BBC at any time as a mouthpiece of the Government if the BBC were to step out of line, but on the other he was anxious to maintain public trust by appearing to be acting independently; the Government was divided on how to handle the BBC but ended up trusting Reith, whose opposition to the strike mirrored the PM's own. Thus the BBC was granted sufficient leeway to pursue the Government's objectives in a manner of its own choosing; the resulting coverage of both striker and government viewpoints impressed millions of listeners who were unaware that the PM had broadcast to the nation from Reith's home, using one of Reith's sound bites inserted at the last moment
The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors, metals and synthetic gemstones. The process is named after Polish scientist Jan Czochralski, who invented the method in 1915 while investigating the crystallization rates of metals, he made this discovery by accident, while studying the crystallization rate of metals: instead of dipping his pen into his inkwell, he dipped it in molten tin, drew a tin filament, which proved to be a single crystal. The most important application may be the growth of large cylindrical ingots, or boules, of single crystal silicon used in the electronics industry to make semiconductor devices like integrated circuits. Other semiconductors, such as gallium arsenide, can be grown by this method, although lower defect densities in this case can be obtained using variants of the Bridgman-Stockbarger technique. Monocrystalline silicon grown by the Czochralski process is referred to as monocrystalline Czochralski silicon.
It is the basic material in the production of integrated circuits used in computers, TVs, mobile phones and all types of electronic equipment and semiconductor devices. Monocrystalline silicon is used in large quantities by the photovoltaic industry for the production of conventional mono-Si solar cells; the perfect crystal structure yields the highest light-to-electricity conversion efficiency for silicon. High-purity, semiconductor-grade silicon is melted in a crucible at 1,425 °C made of quartz. Dopant impurity atoms such as boron or phosphorus can be added to the molten silicon in precise amounts to dope the silicon, thus changing it into p-type or n-type silicon, with different electronic properties. A oriented rod-mounted seed crystal is dipped into the molten silicon; the seed crystal's rod is pulled upwards and rotated simultaneously. By controlling the temperature gradients, rate of pulling and speed of rotation, it is possible to extract a large, single-crystal, cylindrical ingot from the melt.
Occurrence of unwanted instabilities in the melt can be avoided by investigating and visualizing the temperature and velocity fields during the crystal growth process. This process is performed in an inert atmosphere, such as argon, in an inert chamber, such as quartz. Due to the efficiencies of common wafer specifications, the more after the other semiconductor industry has used wafers with standardized dimensions. In the early days, the boules were only a few inches wide. With advanced technology, high-end device manufacturers use 300 mm diameter wafers; the width is controlled by precise control of the temperature, the speeds of rotation and the speed the seed holder is withdrawn. The crystal ingots from which these wafers are sliced can be up to 2 metres in length, weighing several hundred kilograms. Larger wafers allow improvements in manufacturing efficiency, as more chips can be fabricated on each wafer, so there has been a steady drive to increase silicon wafer sizes; the next step up, 450 mm, is scheduled for introduction in 2018.
Silicon wafers are about 0.2–0.75 mm thick, can be polished to great flatness for making integrated circuits or textured for making solar cells. The process begins when the chamber is heated to 1500 degrees Celsius, melting the silicon; when the silicon is melted, a small seed crystal mounted on the end of a rotating shaft is lowered until it just dips below the surface of the molten silicon. The shaft rotates counterclockwise and the crucible rotates clockwise; the rotating rod is drawn upwards slowly—about 25 mm per hour when making a crystal of ruby—allowing a cylindrical boule to be formed. The boule can be depending on the amount of silicon in the crucible; the electrical characteristics of the silicon are controlled by adding material like phosphorus or boron to the silicon before it is melted. The added material is called dopant and the process is called doping; this method is used with semiconductor materials other than silicon, such as gallium arsenide. When silicon is grown by the Czochralski method, the melt is contained in a silica crucible.
During growth, the walls of the crucible dissolve into the melt and Czochralski silicon therefore contains oxygen at a typical concentration of 1018 cm−3. Oxygen impurities can have detrimental effects. Chosen annealing conditions can give rise to the formation of oxygen precipitates; these have the effect of trapping unwanted transition metal impurities in a process known as gettering, improving the purity of surrounding silicon. However, formation of oxygen precipitates at unintended locations can destroy electrical structures. Additionally, oxygen impurities can improve the mechanical strength of silicon wafers by immobilising any dislocations which may be introduced during device processing, it was experimentally shown in the 1990s that the high oxygen concentration is beneficial for the radiation hardness of silicon particle detectors used in harsh radiation environment. Therefore, radiation detectors made of Czochralski- and Magnetic Czochralski-silicon are considered to be promising candidates for many future high-energy physics experiments.
It has been shown that the presence of oxygen in silicon increases impurity trapping during post-implantation annealing processes. However, oxygen impurities can react with boron in an illuminated environment, such as that experienced by solar cells; this results in the formation of an electrically active boron–oxygen