Passivation, in physical chemistry and engineering, refers to a material becoming "passive," that is, less affected or corroded by the environment of future use. Passivation involves creation of an outer layer of shield material, applied as a microcoating, created by chemical reaction with the base material, or allowed to build from spontaneous oxidation in the air; as a technique, passivation is the use of a light coat of a protective material, such as metal oxide, to create a shell against corrosion. Passivation can occur only in certain conditions, is used in microelectronics to enhance silicon; the technique of passivation preserves the appearance of metallics. In electrochemical treatment of water, passivation reduces the effectiveness of the treatment by increasing the circuit resistance, active measures are used to overcome this effect, the most common being polarity reversal, which results in limited rejection of the fouling layer. Other proprietary systems to avoid electrode passivation, several discussed below, are the subject of ongoing research and development.
When exposed to air, many metals form a hard inert surface, as in the tarnish of silver. In the case of other metals, such as iron, a somewhat rough porous coating is formed from loosely adherent corrosion products. In this case, a substantial amount of metal is removed, either deposited or dissolved in the environment. Corrosion coating reduces the rate of corrosion by varying degrees, depending on the kind of base metal and its environment, is notably slower in room-temperature air for aluminium, zinc and silicon; the inert surface layer, termed the "native oxide layer", is an oxide or a nitride, with a thickness of a monolayer of 0.1-0.3 nm for a noble metal such as platinum, about 1.5 nm for silicon, nearer to 5 nm for aluminium after several years. Surface passivation refers to a common semiconductor device fabrication process critical to modern electronics, it is the process by which a semiconductor surface is rendered inert, does not change semiconductor properties as a result of interaction with air or other materials in contact with the surface or edge of the crystal.
This is achieved using a form of thermal oxidation. In a silicon semiconductor, this process allows electricity to reliably penetrate to the conducting silicon below the surface, to overcome the surface states that prevent electricity from reaching the semiconducting layer. Surface passivation by thermal oxidation is one of the key features of silicon technology, is dominant in microelectronics. Known as the Atalla passivation technique, the surface passivation process was developed by Mohamed M. Atalla at Bell Labs in the late 1950s, it is used to manufacture MOSFETs and silicon integrated circuit chips, is critical to the semiconductor industry. Surface passivation is critical to solar cell and carbon quantum dot technologies. There has been much interest in determining the mechanisms that govern the increase of thickness of the oxide layer over time; some of the important factors are the volume of oxide relative to the volume of the parent metal, the mechanism of oxygen diffusion through the metal oxide to the parent metal, the relative chemical potential of the oxide.
Boundaries between micro grains, if the oxide layer is crystalline, form an important pathway for oxygen to reach the unoxidized metal below. For this reason, vitreous oxide coatings – which lack grain boundaries – can retard oxidation; the conditions necessary for passivation are recorded in Pourbaix diagrams. Some corrosion inhibitors help the formation of a passivation layer on the surface of the metals to which they are applied; some compounds, dissolving in solutions form non-reactive and low solubility films on metal surfaces. In the mid 1800s, Christian Friedrich Schönbein discovered that when a piece of iron is placed in dilute nitric acid, it will dissolve and produce hydrogen, but if the iron is placed in concentrated nitric acid and returned to the dilute nitric acid, little or no reaction will take place. Schönbein named the first state the second the passive condition. If passive iron is touched by active iron, it becomes active again. In 1920, Ralph S. Lillie measured the effect of an active piece of iron touching a passive iron wire and found that "a wave of activation sweeps over its whole length".
The surface passivation process known as the "Atalla passivation" technique, was first developed by Mohamed M. Atalla at Bell Telephone Laboratories in the late 1950s, he discovered that the formation of a thermally grown silicon dioxide layer reduced the concentration of electronic states at the silicon surface, discovered the important quality of SiO2 films to preserve the electrical characteristics of p–n junctions and prevent these electrical characteristics from deteriorating by the gaseous ambient environment. He found, he developed the surface passivation process, a new method of semiconductor device fabrication that involves coating a silicon wafer with an insulating layer of silicon oxide so that electricity could reliably penetrate to the conducting silicon below. By growing a layer of silicon dioxide on top of a silicon wafer, Atalla was able to overcome the surface states that prevented electricity from reaching the semiconducting layer. For the surface pass
Henry Cow were an English experimental rock group, founded at Cambridge University in 1968 by multi-instrumentalists Fred Frith and Tim Hodgkinson. Henry Cow's personnel fluctuated over their decade together, but drummer Chris Cutler, bassist John Greaves, bassoonist/oboist Lindsay Cooper were important long-term members alongside Frith and Hodgkinson. An inherent anti-commercial attitude kept them at arm's length from the mainstream music business, enabling them to experiment at will. Critic Myles Boisen writes, " was so mercurial and daring that they had few imitators though they inspired many on both sides of the Atlantic with a blend of spontaneity, intricate structures and humor that has endured and transcended the'progressive' tag."While it was thought that Henry Cow took their name from 20th-century American composer Henry Cowell, this has been denied by band members. According to Hodgkinson, the name "Henry Cow" was "in the air" in 1968, it seemed like a good name for the band, it had no connection to anything.
In a 1974 interview, Cutler said. What could be sillier than Henry Cow?" Fred Frith met Tim Hodgkinson, a fellow student, in a blues club at Cambridge University in May 1968. Recognising their mutual open-minded approach to music, the two began performing together, playing a variety of musical styles including "dada blues" and "neo-Hiroshima". One of Henry Cow's first concerts was supporting Pink Floyd at the Architects' Ball at Homerton College, Cambridge on 12 June 1968. In October 1968 Henry Cow expanded when they were joined by Andy Powell, David Attwooll and Rob Brooks, they performed with this line-up until December that year, when Frith and Powell split off from the rest of the group and became a trio. Powell at the time was studying music at King's College under the resident composer. Smalley was influential in Henry Cow's early development, he exposed them to a variety of new music from bands and musicians like Soft Machine, Captain Beefheart and Frank Zappa. Smalley introduced them to the idea of writing long and complex musical pieces for rock groups.
It was at this time that Henry Cow began writing music to challenge their collective ability to play using it to improve on themselves. As a trio, with Frith on bass guitar, Powell on drums and Hodgkinson playing an organ that Frith and Powell had persuaded him to learn, Henry Cow performed a number of gigs on the university calendar, including the annual Architects' Ball and the Midsummer Common Festival, as well as a performance on the roof of a 14-storey building in Cambridge. In April 1969, Powell left and the band reverted to a duo, with Frith playing violin and Hodgkinson on keyboards and reeds. In October 1969 philosopher Galen Strawson auditioned for the band. Frith and Hodgkinson persuaded bassist John Greaves to join the band, with the services of a couple of temporary drummers and Sean Jenkins, Henry Cow performed as a quartet for the next eight months. In May 1971, Martin Ditcham replaced Jenkins on drums, with this line-up they played at several events, including the Glastonbury Festival alongside Gong in June 1971.
Ditcham left in July 1971, it was not until September that year that the drummer's seat was filled again, this time by Chris Cutler. Responding to one of Cutler's adverts in Melody Maker, the band invited him to a rehearsal, it was only when Cutler joined that Henry Cow settled into a permanent core of Frith, Hodgkinson and Greaves; the band relocated to London, where they began an aggressive rehearsal schedule. After having entered John Peel's "Rockortunity Knocks" contest in 1971, Henry Cow recorded a John Peel session for BBC Radio 1 in February 1972, they went on to record another session in October that year and a further three sessions between 1973 and 1975. In April 1972, Henry Cow wrote and performed the music for Robert Walker's production of Euripides' The Bacchae; this involved an intense and demanding three-week period of concentrated work that changed the band completely. It was during this time that Henry Cow became a quintet. In July 1972, the band performed at the Edinburgh Festival, wrote and performed music for a ballet with artist Ray Smith and the Cambridge Contemporary Dance Group at the Edinburgh Festival Fringe.
Smith appeared with Henry Cow at several of their early 1970s performances, to "add a dimension to the whole experience". Smith's acts included "set up an ironing board stage left and spen the whole evening... ironing" at the Rainbow Theatre, "read out short passages of discontinuous text between each piece of music" at the Hammersmith Palais, miming with a glove puppet at the New London Theatre. Smith went on to do the "paint sock" art work for three of Henry Cow's LP covers. Back in London, they started to organise a series of concerts and events under the names Cabaret Voltaire and Explorers' Club at the Kensington Town Hall and the London School of Economics respectively. Invited guests included Derek Bailey, Lol Coxhill, Ivor Cutler, Ron Geesin, David Toop, Lady June and Smith. Improvisers Bailey and Coxhill became "enthusiastic supporters" of Henry Cow and attended many of their concerts. For the first time the band started getting some attention from the national music press. Reviewing the first Cabaret Voltaire event with Kevin Ayers in October 1972 in New Musical Express, Ian MacDonald described Henry Cow as "one of the most resilient and obstinate of that range of groups ignored by the popular music press".
This exposure, a John Peel recording se
Encasement is the coating over, covering or "encasing" of all building components and exterior. This includes all roofing and toxic hazards materials, such as asbestos, lead-based paint, mold/mildew and other harmful substances, found in buildings; the technique of encasing all building components, including unsafe ones, with green coatings is by far the most efficient way to reduce the harmful effects on people and the environment while lengthening the life of buildings. It is an economical alternative to other abatement methods such as removal and replacement. Encasement with green coatings is a long-term and renewable solution compared to typical paints or coatings which only last a few years. In place management and restoration with encasement green coatings is the best and most practical way to extend a buildings life along with safely dealing with most of its components. Encasement is less disruptive of ongoing services, it does not require shutting down buildings or having to relocate occupants, costly and time-consuming.
Most work can be completed with no building disruption at all. Encasement with green coatings can result in savings of 25% to 75% over removal and replacement, extend the life of most building surfaces. Green coatings have no environmental downside to using them, they are non-toxic, water based, low VOCs, no ODS, Class A fire rated. The products are backed up with toxicological reports proving that they are so clean, that pregnant women and children can be present when applying them. Green coatings used for encasement should be durable, long lasting and able to take a lot of abuse, they must be flexible. Since the early 1980s, four major methods have been used for the abatement of Asbestos-Containing Materials and Lead-Based Paint. Enclosures – Dust-tight barriers such as sheetrock or plywood are erected to protect against the release of the hazardous material into the environment; when the enclosure is removed, the hazardous material is once again exposed and it has become more friable and prone to being released into the atmosphere.
Care must be taken to insure that untrained or uninformed workers do not re-expose the hazardous surfaces unknowingly and endanger themselves and/or the inhabitants by causing a release into the environment. Encapsulation – A coating material that passes U. S. Environmental Protection Agency-specified ASTM tests is applied over a surface to prevent the release of hazardous materials into the atmosphere. A problem experienced with encapsulants in some cases is that the added weight of the encapsulant can cause ACM fireproofing on ceilings or walls to delaminate. A second potential problem with encapsulants is that if the coating is compromised (e.g. by a forklift truck running into a column, encapsulated, the potential for release of the hazardous material into the environment is once again present. With LBP, a significant amount of scraping of loose, flaking paint is required to provide a stable surface before the encapsulant, applied can be expected to achieve adequate adhesion. Encasement – A 2-coat system which passes EPA-specified ASTM testing wherein the first coat stabilizes the substrate by penetrating into the friable ACM and through the loose flaking paint and cures into a flexible film that mitigates these hazardous properties.
The second coat bonds to the topcoat providing a tough, long-lasting, composite coating system that prevents the release of any hazardous material into the environment. Because of the penetration of the primer, the adhesion of the overall system is increased. A necessity as the weight of the system increases. Additionally if the outer coat is compromised in any manner, there is little or no risk of the hazardous material being released because the surface-stabilizing primer has mitigated the brittle and friable properties of the hazardous surface. In a real sense, encasement can be viewed as "stabilization + encapsulation". Removal and Replacement- removal of ACM or LBP causes the release of asbestos fibers and lead dust that can become airborne subjecting installers and/or occupants to the risk of inhaling the particulate matter. Based on industry trends, the increased risk associated with this method has led building owners and contractors to select this as the least preferred method and a last resort unless the ACM is in a friable condition.
Due to its high cost and risk factors, only certified and insured abatement professionals should perform this method. If a party is exposed to these risks and are affected, symptoms of various diseases such as asbestosis, a scarring of lung tissue that leads to difficulty in breathing and mesothelioma may not appear for 15 years. In addition and replacement is time-consuming, carries high insurance costs, causes building use downtime and requires relocation of occupants, it requires the disposal of the hazardous materials, which alone can amount to 30% of total abatement costs. An ever-increasing number of building owners choose alternative in place management methods. Encasement has significant benefits in every application, can be applied to fireproofing, asbestos-containing paint, block etc. If the building has a 5-10yr life span remaining, or more, encasement offers major benefits, and for due diligence purposes encased areas should be inspected as one would inspect other building components as part of a regular inspection cycle.