Silicones known as polysiloxanes, are polymers that include any synthetic compound made up of repeating units of siloxane, a chain of alternating silicon atoms and oxygen atoms, combined with carbon and sometimes other elements. They are heat-resistant and either liquid or rubber-like, are used in sealants, lubricants, cooking utensils, thermal and electrical insulation; some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, silicone caulk. More called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon-oxygen backbone chain with organic side groups attached to the silicon atoms; these silicon atoms are tetravalent. So, silicones are polymers constructed from inorganic-organic monomers. Silicones have in general the chemical formula n, where R is an organic group such as an alkyl or phenyl group. In some cases, organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, crosslinking, silicones can be synthesized with a wide variety of properties and compositions.
They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is a silicone oil; the second largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes. F. S. Kipping coined the word silicone in 1901 to describe polydiphenylsiloxane by analogy of its formula, Ph2SiO, with the formula of the ketone benzophenone, Ph2CO. Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted that Ph2SiO and Ph2CO had different chemistry; the discovery of the structural differences between Kipping's molecules and the ketones means that silicone is no longer the correct term and that the term siloxanes is correct according to the nomenclature of modern chemistry. Silicone is confused with silicon, but they are distinct substances. Silicon is a chemical element, a hard dark-grey semiconducting metalloid which in its crystalline form is used to make integrated circuits and solar cells.
Silicones are compounds that contain silicon, hydrogen and other kinds of atoms as well, have different physical and chemical properties. Compounds containing silicon-oxygen double bonds, now called silanones but which could deserve the name "silicone", have long been identified as intermediates in gas-phase processes such as chemical vapor deposition in microelectronics production, in the formation of ceramics by combustion; however they have a strong tendency to polymerize into siloxanes. The first stable silanone was obtained in 2014 by others. Most common are materials based on polydimethylsiloxane, derived by hydrolysis of dimethyldichlorosilane; this dichloride reacts with water as follows: n Si2Cl2 + n H2O → n + 2n HClThe polymerization produces linear chains capped with Si-Cl or Si-OH groups. Under different conditions the polymer is a cyclic, not a chain. For consumer applications such as caulks silyl acetates are used instead of silyl chlorides; the hydrolysis of the acetates produce the less dangerous acetic acid as the reaction product of a much slower curing process.
This chemistry is used in many consumer applications, such as adhesives. Branches or cross-links in the polymer chain can be introduced by using organosilicone precursors with fewer alkyl groups, such as methyltrichlorosilane and methyltrimethoxysilane. Ideally, each molecule of such a compound becomes a branch point; this process can be used to produce hard silicone resins. Precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain; when silicone is burned in air or oxygen, it forms solid silica as a white powder and various gases. The dispersed powder is sometimes called silica fume. Silicones exhibit many useful characteristics, including: Low thermal conductivity Low chemical reactivity Low toxicity Thermal stability; the ability to repel water and form watertight seals. Does not stick to many substrates, but adheres well to others, e.g. glass. Does not support microbiological growth.
Resistance to oxygen and ultraviolet light. This property has led to widespread use of silicones in the construction industry and the automotive industry. Electrical insulation properties; because silicone can be formulated to be electrically insulative or conductive, it is suitable for a wide range of electrical applications. High gas permeability: at room temperature, the permeability of silicone rubber for such gases as oxygen is 400 times that of butyl rubber, making silicone useful for medical applications in which increased aeration is desired. Conversely, silicone rubbers can not be used. Silicone can be developed into rubber sheeting, where it has other properties, such as being FDA compliant; this extends the uses of silicone sheeting to industries that demand hygiene, for example and beverage and pharmaceutical. Silicones are used in many products. Ullmann's Encyclopedia of Industrial Chemistry lists the following major categories of application: Electrical, elec
Thermal grease is a thermally conductive compound, used as an interface between heat sinks and heat sources. The main role of thermal grease is to eliminate air gaps or spaces from the interface area in order to maximize heat transfer. Thermal grease is an example of a thermal interface material; as opposed to thermal adhesive, thermal grease does not add mechanical strength to the bond between heat source and heat sink. It will have to be coupled with a mechanical fixation mechanism such as screws, applying pressure between the two, spreading the thermal grease onto the heat source. Thermal grease consists of a polymerizable liquid matrix and large volume fractions of electrically insulating, but thermally conductive filler. Typical matrix materials are epoxies, silicones and acrylates. Aluminum oxide, boron nitride, zinc oxide, aluminum nitride are used as fillers for these types of adhesives; the filler loading can be as high as 70–80% by mass, raises the thermal conductivity of the base matrix from 0.17–0.3 W/ up to about 2 W/.
Silver thermal compounds may have a conductivity of 3 to 8 W/ or more, consist of micronized silver particles suspended in a silicone/ceramic medium. However, metal-based thermal grease can be electrically capacitive; the most effective pastes consist entirely of liquid metal a variation of the alloy galinstan, have thermal conductivities in excess of 13 W/. These are difficult to apply evenly and have the greatest risk of causing malfunction due to spillage; these pastes contain gallium, corrosive to aluminium and cannot be used on aluminium heat sinks. In PCs and laptops, thermal paste is invariably used in between the top of the CPU and a heat sink, but may or may not be used in between the CPU die and its integrated heat spreader. In many CPUs, the die is attached to the heat spreader by solder. However, in others the die is not directly attached to the heat spreader, but maintains contact via a layer of thermal paste. In the latter case, performance enthusiasts sometimes pry the heat spreader from the die, replace the thermal paste, of low quality, with a thermal paste which has a greater thermal conductivity - a process known as "delidding".
Liquid metal thermal pastes are used in such instances. Computer cooling Hot-melt adhesive Phase-change material Thermally conductive pad Thermal adhesive List of thermal conductivities
National Renewable Energy Laboratory
The National Renewable Energy Laboratory, located in Golden, specializes in renewable energy and energy efficiency research and development. NREL is a government-owned, contractor-operated facility, is funded through the United States Department of Energy; this arrangement allows a private entity to operate the lab on behalf of the federal government. NREL receives funding from Congress to be applied toward development projects. NREL performs research on photovoltaics under the National Center for Photovoltaics. NREL has a number of PV research capabilities including research and development and deployment. NREL's campus houses several facilities dedicated to PV research. NREL's areas of research and development are renewable electricity, energy productivity, energy storage, systems integration, sustainable transportation. Established in 1974, NREL began operating in 1977 as the Solar Energy Research Institute. Under the Jimmy Carter administration, its activities went beyond research and development in solar energy as it tried to popularize knowledge about existing technologies, like passive solar.
During the Ronald Reagan administration the institute's budget was cut by nearly 90%. In years, renewed interest in the energy problem improved the institute's position, but funding has fluctuated. In 2011, anticipated congressional budget shortfalls led to a voluntary buyout program for 100 to 150 staff reductions; the budget for fiscal 2016 was $427.4 million, down from a peak of $536.5 million five years earlier. Changes in the budget have sometimes forced NREL to cut staffing. Since its inception in 1977 as the Solar Energy Research Institute, it has been operated under contract by MRIGlobal. In September 1991, the NREL was designated a national laboratory of the U. S. Department of Energy by President George H. W. Bush and its name was changed to NREL. NREL is managed for the DOE by the Alliance for Sustainable Energy, LLC; the Alliance was formed in 2008 as a joint venture between Battelle. Dr. Martin Keller became NREL's ninth director in November 2015, serves as both the director of the lab and the president of the Alliance.
He succeeded Dan Arvizu. The FY 2016 Congressional Appropriations for renewable energy items were: Solar Energy $55.5 million Wind Energy $17.7 million Biomass and Biorefinery Systems R&D $56.3 million Hydrogen Technology $17.8 million Geothermal Technology $3.8 million Water Power $4.1 million NREL works with a number of private partners to transfer technological developments in renewable energy and energy efficiency technologies to the marketplace and social arena. NREL's technologies have been recognized with 61 R&D 100 Awards; the engineering and science behind these technology transfer successes and awards demonstrates NREL's commitment to a sustainable energy future. The idea of technology transfer was added to the mission of NREL as a means of enhancing commercial impact and societal benefit justifying the use of tax dollars to in part fund the projects in the lab; as many of these technologies are young and just emerging, NREL aims to reduce the risk of private sector investment and adoption of their developments.
Three key pieces of federal legislation laid the policy framework to enact technology transfer: The Stevenson-Wydler Technology Innovation Act of 1980, The Bayh-Dole Act or The University and Small Business Patent Procedures Act of 1980, The Federal Technology Transfer Act of 1986. Many of the deployed technologies help mitigate the oil dependence of the United States, reduce carbon emissions from fossil fuel use, maintain U. S. industry competitiveness. Deployment of technologies is accomplished by developing technology partnerships with private industry. NREL serves as a reduced-risk platform for research, through partnerships those advances can be translated into serving the interest of both the private sector and the public sector; the energy goals set by the DOE are at the forefront of the research done in the laboratory, the research reflects the energy goals, which are designed with the interest of "U. S. industry competitiveness" in mind. The challenge to achieving these goals is investment security.
Part of the technology transfer process is to form partnerships that not only focus on financial security, but to consider partners who have demonstrated core values that reflect the integrity to manage the introduction and assimilation of the technological developments. NREL focuses on the core values of the partnering entity, the willingness to set and meet timely goals, dedication to transparency, a reciprocating intent to further development. Under these partnership agreements, NREL does not fund projects conducted by their private partners. NREL does provide funding opportunities through their competitively placed contracts. In order to form a Technology Partnership Agreement with NREL, there are seven steps: Discuss the project proposal with the appropriate NREL technical contact Determine if the project meets qualifications Develop statement of work Review and/or negotiate Sign agreement Send funds and start work Manage commitmentThe process is estimated to require 45 business days, subject to negotiations.
Technology Partnership Agreements provide only the technical services of NREL. NREL has a user access program that allows outside researchers to use the Energy Systems Integration Facility and rely on its staff of scientists and engineers to develop and evaluate energy technologies. Several other ways exist for universities and industry to work with NREL, including a Cooperative Research
A heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature at optimal levels. In computers, heat sinks are used to cool central graphics processors. Heat sinks are used with high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light emitting diodes, where the heat dissipation ability of the component itself is insufficient to moderate its temperature. A heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it, such as the air. Air velocity, choice of material, protrusion design and surface treatment are factors that affect the performance of a heat sink. Heat sink attachment methods and thermal interface materials affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease improve the heat sink's performance by filling air gaps between the heat sink and the heat spreader on the device.
A heat sink is made out of copper or aluminium. Copper is used because it has many desirable properties for thermally efficient and durable heat exchangers. First and foremost, copper is an excellent conductor of heat; this means. Aluminium heat sinks are used as a low-cost, lightweight alternative to copper heat sinks, have a lower thermal conductivity than copper. A heat sink transfers thermal energy from a higher temperature device to a lower temperature fluid medium; the fluid medium is air, but can be water, refrigerants or oil. If the fluid medium is water, the heat sink is called a cold plate. In thermodynamics a heat sink is a heat reservoir that can absorb an arbitrary amount of heat without changing temperature. Practical heat sinks for electronic devices must have a temperature higher than the surroundings to transfer heat by convection and conduction; the power supplies of electronics are not 100% efficient, so extra heat is produced that may be detrimental to the function of the device.
As such, a heat sink is included in the design to disperse heat. To understand the principle of a heat sink, consider Fourier's law of heat conduction. Fourier's law of heat conduction, simplified to a one-dimensional form in the x-direction, shows that when there is a temperature gradient in a body, heat will be transferred from the higher temperature region to the lower temperature region; the rate at which heat is transferred by conduction, q k, is proportional to the product of the temperature gradient and the cross-sectional area through which heat is transferred. Q k = − k A d T d x Consider a heat sink in a duct, it is assumed. Applying the conservation of energy, for steady-state conditions, Newton’s law of cooling to the temperature nodes shown in the diagram gives the following set of equations: Q ˙ = m ˙ c p, i n Q ˙ = T h s − T a i r, a v R h s where T a i r, a v = T a i r, i n + T a i r, o u t 2 Using the mean air temperature is an assumption, valid for short heat sinks; when compact heat exchangers are calculated, the logarithmic mean air temperature is used.
M ˙ is the air mass flow rate in kg/s. The above equations show that When the air flow through the heat sink decreases, this results in an increase in the average air temperature; this in turn increases the heat sink base temperature. And additionally, the thermal resistance of the heat sink will increase; the net result is a higher heat sink base temperature. The increase in heat sink thermal resistance with decrease in flow rate will be shown in this article; the inlet air temperature relates with the heat sink base temperature. For example, if there is recirculation of air in a product, the inlet air temperature is not the ambient air temperature; the inlet air temperature of the heat sink is therefore higher, which results in a higher heat sink base temperature. If there is no air flow around the heat sink, energy cannot be transferred. A heat sink is not a device with the "magical ability
Zalman Tech Co. is a South Korean company that develops and provides aftermarket desktop computer products with primary focus on cooling enhancement. Zalman has done considerable product development since its founding in January 1999, now holds several patents focusing on both cooling and fan noise-reduction. Personal computer systems can generate significant heat and noise, the management of, important for those modifying or assembling computer systems. Zalman's product range includes specialized heat sink and fan solutions for CPUs, as well as quiet power supplies, computer water cooling systems, motherboard chipset coolers, graphics card heat sink and fan combos, laptop coolers and hard disk cases that lower temperature and reduce noise. Zalman's primary competitors include Vantec, Spire, Cooler Master and Arctic. Zalman has developed a fanless case, it uses a fin based design to dissipate heat with heat generating components like the graphics card and motherboard transferring heat to the case body via a system of heat pipes and radiators.
Zalman introduced the CNPS9500AM2, a heatsink was meant for socket AM2 compatibility on May 23, 2006. The company broke into the headphone market with its 5.1 headphone system, ZM-RS6F/M. Zalman is a pioneer in stereoscopic LCD monitors, which utilize +45°/+45° polarized 3D glasses; these products allow the user to play other 3D media in full 3D stereoscopy. Its 3D driver requires the native vertical resolution. M190 M215W M220W M240W M320W-F Mxxx ≙ xxx÷10 inch SG100G SG100C On 30 October 2014, it was reported that Zalman had defaulted on a large loan amounting to over 3 billion won. Following this, the company applied for "initiation of corporate turnaround process"; this means. Antec Arctic Computer cooling Cooler Master FSP Group Lian Li PCCooler Quiet PC SilverStone Technology Thermalright Thermaltake Vantec Zalman Korea Zalman USA
A ceramic is a solid material comprising an inorganic compound of metal, non-metal or metalloid atoms held in ionic and covalent bonds. Common examples are earthenware and brick; the crystallinity of ceramic materials ranges from oriented to semi-crystalline and completely amorphous. Most fired ceramics are either vitrified or semi-vitrified as is the case with earthenware and porcelain. Varying crystallinity and electron composition in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators. With such a large range of possible options for the composition/structure of a ceramic, the breadth of the subject is vast, identifiable attributes are difficult to specify for the group as a whole. General properties such as high melting temperature, high hardness, poor conductivity, high moduli of elasticity, chemical resistance and low ductility are the norm, with known exceptions to each of these rules. Many composites, such as fiberglass and carbon fiber, while containing ceramic materials, are not considered to be part of the ceramic family.
The earliest ceramics made by humans were pottery objects or figurines made from clay, either by itself or mixed with other materials like silica and sintered in fire. Ceramics were glazed and fired to create smooth, colored surfaces, decreasing porosity through the use of glassy, amorphous ceramic coatings on top of the crystalline ceramic substrates. Ceramics now include domestic and building products, as well as a wide range of ceramic art. In the 20th century, new ceramic materials were developed for use in advanced ceramic engineering, such as in semiconductors; the word "ceramic" comes from the Greek word κεραμικός, "of pottery" or "for pottery", from κέραμος, "potter's clay, pottery". The earliest known mention of the root "ceram-" is the Mycenaean Greek ke-ra-me-we, "workers of ceramics", written in Linear B syllabic script; the word "ceramic" may be used as an adjective to describe a material, product or process, or it may be used as a noun, either singular, or, more as the plural noun "ceramics".
A ceramic material is an inorganic, non-metallic crystalline oxide, nitride or carbide material. Some elements, such as carbon or silicon, may be considered ceramics. Ceramic materials are brittle, strong in compression, weak in shearing and tension, they withstand chemical erosion that occurs in other materials subjected to acidic or caustic environments. Ceramics can withstand high temperatures, ranging from 1,000 °C to 1,600 °C. Glass is not considered a ceramic because of its amorphous character. However, glassmaking involves several steps of the ceramic process, its mechanical properties are similar to ceramic materials. Traditional ceramic raw materials include clay minerals such as kaolinite, whereas more recent materials include aluminium oxide, more known as alumina; the modern ceramic materials, which are classified as advanced ceramics, include silicon carbide and tungsten carbide. Both are valued for their abrasion resistance and hence find use in applications such as the wear plates of crushing equipment in mining operations.
Advanced ceramics are used in the medicine, electronics industries and body armor. Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with them tend to fall into one of two categories – either make the ceramic in the desired shape, by reaction in situ, or by "forming" powders into the desired shape, sintering to form a solid body. Ceramic forming techniques include shaping by hand, slip casting, tape casting, injection molding, dry pressing, other variations. Noncrystalline ceramics, being glass, tend to be formed from melts; the glass is shaped when either molten, by casting, or when in a state of toffee-like viscosity, by methods such as blowing into a mold. If heat treatments cause this glass to become crystalline, the resulting material is known as a glass-ceramic used as cook-tops and as a glass composite material for nuclear waste disposal; the physical properties of any ceramic substance are a direct result of its crystalline structure and chemical composition.
Solid-state chemistry reveals the fundamental connection between microstructure and properties such as localized density variations, grain size distribution, type of porosity and second-phase content, which can all be correlated with ceramic properties such as mechanical strength σ by the Hall-Petch equation, toughness, dielectric constant, the optical properties exhibited by transparent materials. Ceramography is the art and science of preparation and evaluation of ceramic microstructures. Evaluation and characterization of ceramic microstructures is implemented on similar spatial scales to that used in the emerging field of nanotechnology: from tens of angstroms to tens of micrometers; this is somewhere between the minimum wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, micro-