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Depolymerizable Polymers
Depolymerizable polymers or Low-Ceiling Temperature Polymers refer to polymeric materials that can undergo depolymerization to revert the materials to their monomers at relatively low temperatures, such as room temperature. For example, the ceiling temperature Tc for formaldehyde is 119 °C, and that for acetaldehyde is -39 °C. Introduction Unlike stable polymers such as PVCs that have high thermal stability, depolymerizable polymers and closely related self-immolative polymers can be triggered by stimuli to break fast under moderate to low temperatures. The first type of polymers, poly ( olefin sulfone), was reported by Snow and Frey in 1943. It was further confirmed and explained in terms of the thermodynamics of a reversible propagation step by Dainton and Ivin. Closely related to depolymerizable polymers, self-immolative polymers can also irreversibly disassemble into their constituent parts in response to stimuli such as temperature, biological inputs or pH. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymeric Material
Polymer engineering is generally an engineering field that designs, analyses, and modifies polymer materials. Polymer engineering covers aspects of the petrochemical industry, polymerization, structure and characterization of polymers, properties of polymers, compounding and processing of polymers and description of major polymers, structure property relations and applications. History The word “polymer” was introduced by the Swedish chemist J. J. Berzelius. He considered, for example, benzene (C6H6) to be a polymer of ethyne (C2H2). Later, this definition underwent a subtle modification. The history of human use of polymers has been long since the mid-19th century, when it entered the chemical modification of natural polymers. In 1839, C. Goodyear has found a critical advance in the research of rubber vulcanization, which has turned natural rubber into a practical engineering material. In 1870, J. W. Hyatt uses camphor to plasticize nitrocellulose to make nitrocellulose plas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain Propagation
Chain propagation (sometimes referred to as propagation) is a process in which a reactive intermediate is continuously regenerated during the course of a chemical chain reaction. For example, in the chlorination of methane, there is a two-step propagation cycle involving as chain carriers a chlorine atom and a methyl radical IUPAC Gold Book which are regenerated alternately: :•Cl + CH4 → HCl + •CH3 :•CH3 + Cl2 → CH3Cl + •Cl The two steps add to give the equation for the overall chain reaction: :CH4 + Cl2 → CH3Cl + HCl. Polymerization In a chain-growth polymerization ...[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymer Substrate
Polymers and plastics known as polymer substrates are used for banknotes and other everyday products. The banknote is more durable than paper, won't become soaked in liquids and is harder to counterfeit, though not impossible. Countries whose whole banknote production is in polymer are: Australia, Romania, Vietnam and New Zealand. Other countries that have partial polymer and paper issue include Papua New Guinea, Samoa, Solomon Islands, Mexico, Zambia, Brunei, Malaysia, Singapore, Nigeria, Chile, England and Nepal.CBN Issues New 5,10 and 50 Naira Polymer Notes PDF Format. The material is also used in commemorative notes in some other countries. The process of polymer substrate creation was developed by the Australia |
Circuit (electronics)
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electrical circuit and to be referred to as ''electronic'', rather than ''electrical'', generally at least one active component must be present. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another. Circuits can be constructed of discrete components connected by individual pieces of wire, but today it is much more common to create interconnections by photolithographic techniques on a laminated substrate (a printed circuit board or PCB) and solder the components to these interconnections to create a finished circuit. In an integrated circuit or IC, the components and interconnections are formed on t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Substrate (electronics)
In electronics, a wafer (also called a slice or substrate) is a thin slice of semiconductor, such as a crystalline silicon (c-Si), used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The wafer serves as the substrate for microelectronic devices built in and upon the wafer. It undergoes many microfabrication processes, such as doping, ion implantation, etching, thin-film deposition of various materials, and photolithographic patterning. Finally, the individual microcircuits are separated by wafer dicing and packaged as an integrated circuit. History In the semiconductor or silicon wafer industry, the term wafer appeared in the 1950s to describe a thin round slice of semiconductor material, typically germanium or silicon. Round shape comes from single-crystal ingots usually produced using the Czochralski method. Silicon wafers were first introduced in the 1940s. By 1960, silicon wafers were being manufactured in the U.S. by c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phthalaldehyde
Phthalaldehyde (sometimes also ''o''-phthalaldehyde or ''ortho''-phthalaldehyde, OPA) is the chemical compound with the formula C6H4(CHO)2. It is one of three isomers of benzene dicarbaldehyde, related to phthalic acid. This pale yellow solid is a building block in the synthesis of heterocyclic compounds and a reagent in the analysis of amino acids. OPA dissolves in water solution at pH < 11.5. Its solutions degrade upon UV illumination and exposure to air. Synthesis and reactions The compound was first described in 1887 when it was prepared from α,α,α’,α’-tetrachloro- ortho-xylene. A more modern synthesis is similar: the hydrolysis of the related tetrabromo-o-xylene using potassium |
Electronic Waste
Electronic waste or e-waste describes discarded electrical or electronic devices. Used electronics which are destined for refurbishment, reuse, resale, salvage recycling through material recovery, or disposal are also considered e-waste. Informal processing of e-waste in developing countries can lead to adverse human health effects and environmental pollution. Electronic scrap components, such as CPUs, contain potentially harmful materials such as lead, cadmium, beryllium, or brominated flame retardants. Recycling and disposal of e-waste may involve significant risk to the health of workers and their communities. Definition E-waste or electronic waste is created when an electronic product is discarded after the end of its useful life. The rapid expansion of technology and the consumption driven society results in the creation of a very large amount of e-waste. In the US, the United States Environmental Protection Agency (EPA) classifies waste into ten categories: # Large ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Consumer Electronics
Consumer electronics or home electronics are electronic (analog or digital) equipment intended for everyday use, typically in private homes. Consumer electronics include devices used for entertainment, communications and recreation. Usually referred to as black goods due to many products being housed in black or dark casings. This term is used to distinguish them from "white goods" which are meant for housekeeping tasks, such as washing machines and refrigerators, although nowadays, these would be considered black goods, some of these being connected to the Internet. In British English, they are often called brown goods by producers and sellers. In the 2010s, this distinction is absent in large big box consumer electronics stores, which sell entertainment, communication and home office devices, light fixtures and appliances, including the bathroom type. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver. Later produc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronics Industry
The electronics industry is the economic sector that produces electronic devices. It emerged in the 20th century and is today one of the largest global industries. Contemporary society uses a vast array of electronic devices built-in automated or semi-automated factories operated by the industry. Products are primarily assembled from metal-oxide-semiconductor (MOS) transistors and integrated circuits, the latter principally by photolithography and often on printed circuit boards. The industry's size, the use of toxic materials, and the difficulty of recycling have led to a series of problems with electronic waste. International regulation and environmental legislation have been developed to address the issues. The electronics industry consists of various sectors. The central driving force behind the entire electronics industry is the semiconductor industry sector, which has annual sales of over as of 2018. The largest industry sector is e-commerce, which generated over in 2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transient (electricity)
In electrical engineering and mechanical engineering, a transient response is the response of a system to a change from an equilibrium or a steady state. The transient response is not necessarily tied to abrupt events but to any event that affects the equilibrium of the system. The impulse response and step response are transient responses to a specific input (an impulse and a step, respectively). In electrical engineering specifically, the transient response is the circuit’s temporary response that will die out with time. It is followed by the steady state response, which is the behavior of the circuit a long time after an external excitation is applied. Damping The response can be classified as one of three types of damping that describes the output in relation to the steady-state response. ;Underdamped :An underdamped response is one that oscillates within a decaying envelope. The more underdamped the system, the more oscillations and longer it takes to reach steady-state ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frederick Dainton
Frederick Sydney Dainton, Baron Dainton, Kt, FRS, FRSE (11 November 1914 – 5 December 1997) was a British academic chemist and university administrator. A graduate of Oxford and Cambridge, he was successively Professor of Physical Chemistry at the University of Leeds, Vice-Chancellor of the University of Nottingham, Dr Lee's Professor of Chemistry at Oxford and Chancellor of the University of Sheffield. Early life and education Dainton was born in Sheffield on 11 November 1914, the son of George Whalley Dainton (born 1857), a Clerk of Works to a building contractor, and his second wife Mary Jane Bottrill, as the youngest of nine children. He obtained a scholarship to the Central Secondary School in Sheffield, but it was in the public library that he became enthused of chemistry by reading the books of Sidgwick and Hinshelwood. Dainton won an Exhibition at St John's College, Oxford with a supplementary grant and loan from the City of Sheffield, which enabled him to st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermodynamics
Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology. Historically, thermodynamics developed out of a desire to increase the efficiency of early steam engines, particularly through the work of French physicist Sadi Carnot (1824) who believed that engine efficiency was the key that could help France win the Napoleonic Wars. Scots-Irish physicist Lord Kelvin was the first to formulate a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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