Zinc is a chemical element with symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: both elements exhibit only one normal oxidation state, the Zn2+ and Mg2+ ions are of similar size. Zinc has five stable isotopes; the most common zinc ore is sphalerite, a zinc sulfide mineral. The largest workable lodes are in Australia and the United States. Zinc is refined by froth flotation of the ore and final extraction using electricity. Brass, an alloy of copper and zinc in various proportions, was used as early as the third millennium BC in the Aegean, the United Arab Emirates, Kalmykia and Georgia, the second millennium BC in West India, Iran, Syria and Israel/Palestine. Zinc metal was not produced on a large scale until the 12th century in India, though it was known to the ancient Romans and Greeks; the mines of Rajasthan have given definite evidence of zinc production going back to the 6th century BC. To date, the oldest evidence of pure zinc comes from Zawar, in Rajasthan, as early as the 9th century AD when a distillation process was employed to make pure zinc.
Alchemists burned zinc in air to form what they called "philosopher's wool" or "white snow". The element was named by the alchemist Paracelsus after the German word Zinke. German chemist Andreas Sigismund Marggraf is credited with discovering pure metallic zinc in 1746. Work by Luigi Galvani and Alessandro Volta uncovered the electrochemical properties of zinc by 1800. Corrosion-resistant zinc plating of iron is the major application for zinc. Other applications are in electrical batteries, small non-structural castings, alloys such as brass. A variety of zinc compounds are used, such as zinc carbonate and zinc gluconate, zinc chloride, zinc pyrithione, zinc sulfide, dimethylzinc or diethylzinc in the organic laboratory. Zinc is an essential mineral, including to postnatal development. Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children, deficiency causes growth retardation, delayed sexual maturation, infection susceptibility, diarrhea.
Enzymes with a zinc atom in the reactive center are widespread in biochemistry, such as alcohol dehydrogenase in humans. Consumption of excess zinc may cause ataxia and copper deficiency. Zinc is a bluish-white, diamagnetic metal, though most common commercial grades of the metal have a dull finish, it is somewhat less dense than iron and has a hexagonal crystal structure, with a distorted form of hexagonal close packing, in which each atom has six nearest neighbors in its own plane and six others at a greater distance of 290.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C. Above 210 °C, the metal can be pulverized by beating. Zinc is a fair conductor of electricity. For a metal, zinc has low melting and boiling points; the melting point is the lowest of all the d-block metals aside from cadmium. Many alloys contain zinc, including brass. Other metals long known to form binary alloys with zinc are aluminium, bismuth, iron, mercury, tin, cobalt, nickel and sodium.
Although neither zinc nor zirconium are ferromagnetic, their alloy ZrZn2 exhibits ferromagnetism below 35 K. A bar of zinc generates a characteristic sound when bent, similar to tin cry. Zinc makes up about 75 ppm of Earth's crust. Soil contains zinc in 5–770 ppm with an average 64 ppm. Seawater has only 30 ppb and the atmosphere, 0.1–4 µg/m3. The element is found in association with other base metals such as copper and lead in ores. Zinc is a chalcophile, meaning the element is more to be found in minerals together with sulfur and other heavy chalcogens, rather than with the light chalcogen oxygen or with non-chalcogen electronegative elements such as the halogens. Sulfides formed as the crust solidified under the reducing conditions of the early Earth's atmosphere. Sphalerite, a form of zinc sulfide, is the most mined zinc-containing ore because its concentrate contains 60–62% zinc. Other source minerals for zinc include smithsonite, hemimorphite and sometimes hydrozincite. With the exception of wurtzite, all these other minerals were formed by weathering of the primordial zinc sulfides.
Identified world zinc resources total about 1.9–2.8 billion tonnes. Large deposits are in Australia and the United States, with the largest reserves in Iran; the most recent estimate of reserve base for zinc was made in 2009 and calculated to be 480 Mt. Zinc reserves, on the other hand, are geologically identified ore bodies whose suitability for recovery is economically based at the time of determination. Since exploration and mine development is an ongoing process, the amount of zinc reserves is not a fixed number and sustainability of zinc ore supplies cannot be judged by extrapolating the combined mine life of today's zinc mines; this concept is well supported by data from the United States Geol
Gilberto Kassab is a Brazilian politician, former mayor of São Paulo. His term ended in 2013. A civil engineer and economist, one of the most famous Brazilians of Syrian descent, Kassab took over from José Serra, after Serra decided to run for governor of São Paulo, he belongs to the Syrian community of São Paulo, is a member of the Partido Social Democrático. He is mentioned in 2017 among the beneficiaries of bribes from the multinational JBS. 1993–1994: Alderman of São Paulo 1995–1999: State Deputy of São Paulo 1999–2004: Federal Deputy 2005–2006: Vice Mayor of São Paulo 2006–2013: Mayor of São Paulo The advertising industry criticized the city of São Paulo administration for the Cidade Limpa law, which prohibits all forms of external media and visual pollution such as billboards. Ad companies tried to keep the billboards in the streets with injunctions, but the supreme court determined the law to be constitutional. At any rate, support for the initiative from the public continues to be widespread.
Mayor Kassab appeared at length in the Morgan Spurlock 2011 documentary The Greatest Movie Ever Sold talking about the decision of the City Council to ban advertising in the city. Official page BBC News article about Cidade Limpa Folha de S. Paulo first page with a before-after picture CityMayors profile
Polyurethane is a polymer composed of organic units joined by carbamate links. While most polyurethanes are thermosetting polymers that do not melt when heated, thermoplastic polyurethanes are available. Polyurethane polymers are traditionally and most formed by reacting a di- or tri poly-isocyanate with a polyol. Since polyurethanes contain two types of monomers, which polymerise one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make polyurethanes contain, on average, two or more functional groups per molecule. Polyurethanes are used in the manufacture of high-resilience foam seating, rigid foam insulation panels, microcellular foam seals and gaskets, durable elastomeric wheels and tires, automotive suspension bushings, electrical potting compounds, high performance adhesives, surface coatings and surface sealants, synthetic fibers, carpet underlay, hard-plastic parts and hoses. Otto Bayer and his coworkers at IG Farben in Leverkusen, first made polyurethanes in 1937.
The new polymers had some advantages over existing plastics that were made by polymerizing olefins or by polycondensation, were not covered by patents obtained by Wallace Carothers on polyesters. Early work focused on the production of fibres and flexible foams and PUs were applied on a limited scale as aircraft coating during World War II. Polyisocyanates became commercially available in 1952, production of flexible polyurethane foam began in 1954 using toluene diisocyanate and polyester polyols; these materials were used to produce rigid foams, gum rubber, elastomers. Linear fibers were produced from hexamethylene 1,4-Butanediol. In 1956 DuPont introduced polyether polyols poly glycol, BASF and Dow Chemical started selling polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols, became more popular. Union Carbide and Mobay, a U. S. Monsanto/Bayer joint venture began making polyurethane chemicals. In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced.
The availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, methylene diphenyl diisocyanate allowed polyurethane rigid foams to be used as high-performance insulation materials. In 1967, urethane-modified polyisocyanurate rigid foams were introduced, offering better thermal stability and flammability resistance. During the 1960s, automotive interior safety components, such as instrument and door panels, were produced by back-filling thermoplastic skins with semi-rigid foam. In 1969, Bayer exhibited an all-plastic car in Germany. Parts of this car, such as the fascia and body panels, were manufactured using a new process called reaction injection molding, in which the reactants were mixed and injected into a mold; the addition of fillers, such as milled glass and processed mineral fibres, gave rise to reinforced RIM, which provided improvements in flexural modulus, reduction in coefficient of thermal expansion and better thermal stability. This technology was used to make the first plastic-body automobile in the United States, the Pontiac Fiero, in 1983.
Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity known broadly as resin injection molding, or structural RIM. Starting in the early 1980s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air-filter seals, replacing PVC polymers. Polyurethane foams have gained popularity in the automotive realm, are now used in high-temperature oil-filter applications. Polyurethane foam is sometimes made using small amounts of blowing agents to give less dense foam, better cushioning/energy absorption or thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol restricted the use of many chlorine-containing blowing agents, such as trichlorofluoromethane. By the late 1990s, blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane and 1,1,1,3,3-pentafluoropropane were used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries.
Polyurethane products are called "urethanes", but should not be confused with ethyl carbamate, called urethane. Polyurethanes neither are produced from ethyl carbamate. Non-isocyanate based polyurethanes have been developed to mitigate health and environmental concerns associated with the use of isocyanates to synthesize polyurethanes. Polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, phenolics. Polyurethanes are produced by reacting an isocyanate containing two or more isocyanate groups per molecule with a polyol containing on average two or more hydroxyl groups per molecule in the presence of a catalyst or by activation with ultraviolet light; the properties of a polyurethane are influenced by the types of isocyanates and polyols used to make it. Long, flexible segments, contributed by the polyol, give elastic polymer. High amounts of crosslinking give rigid polymers. Long chains and low crosslinking give a polymer, stretchy, short chains with lots of crosslinks produce a hard polymer while long chains and intermediate crosslinking give a polymer useful for making foam.
The crosslinking present in polyurethanes means that t
Marco Zero (São Paulo)
Marco Zero is a geographic monument in downtown São Paulo. In 1934, the marble milestone was installed in front of the São Paulo Cathedral on the Praça da Sé to symbolize the center of the city; the sculpture is a both a tourist attraction and a central point of reference for street numbers in the city. Marco Zero has been registered for historic preservation since 2007. Proposed by journalist Américo Netto in 1921, the project to mark an official center of the city with a monument was not adopted until 1932 by mayor Antônio Carlos de Assumpção. Prior to this period and highways were numbered based on at least three different marcos zero scattered around São Paulo. Netto wrote his ideas in the Estado de São Paulo newspaper and Boas Estradas magazine complaining of the confusion that this decentralized approach caused. Four months prior to the inauguration of Marco Zero, Netto compared this new monument to both the Zero Milestone in Washington, DC and to the Milliarium Aureum in Ancient Rome. Since it was installed in 1934, Marco Zero on the Praça da Sé has remained the official spot from which roads, rail lines, telephone lines are marked.
Marco Zero was designed based on ideas from Américo Netto. It is a carved hexagonal marble structure on a granite pedestal with a bronze plate on the top; each side of the monument is decorated with the name of the state which it faces. For example, the side facing northeast has the words "Rio de Janeiro" along with an outline of the Pão de Açucar; the other sides are marked with Goiás, Minas Gerais, Paraná, Mato Grosso, along with iconic images for each. On the bronze top, the names are repeated along the sides and in the center is a map of the city of São Paulo with important landmarks and roads leading out of the city; these engravings include: Avenida Paulista, Tietê River, Luz Station. In 2007 Marco Zero was registered as a protected monument by the Municipal Council for the Preservation of Historical and Environmental Patrimony of the City of São Paulo. Three similar stone monuments, marking the outer edges of the city, all dating to 1916, were registered by Conpresp in June 2013; these markers are located in the districts of Butantã, Vila Mariana, Ipiranga
Steel is an alloy of iron and carbon, sometimes other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, tools, automobiles, machines and weapons. Iron is the base metal of steel. Iron is able to take on two crystalline forms, body centered cubic and face centered cubic, depending on its temperature. In the body-centered cubic arrangement, there is an iron atom in the center and eight atoms at the vertices of each cubic unit cell, it is the interaction of the allotropes of iron with the alloying elements carbon, that gives steel and cast iron their range of unique properties. In pure iron, the crystal structure has little resistance to the iron atoms slipping past one another, so pure iron is quite ductile, or soft and formed. In steel, small amounts of carbon, other elements, inclusions within the iron act as hardening agents that prevent the movement of dislocations that are common in the crystal lattices of iron atoms; the carbon in typical steel alloys may contribute up to 2.14% of its weight.
Varying the amount of carbon and many other alloying elements, as well as controlling their chemical and physical makeup in the final steel, slows the movement of those dislocations that make pure iron ductile, thus controls and enhances its qualities. These qualities include such things as the hardness, quenching behavior, need for annealing, tempering behavior, yield strength, tensile strength of the resulting steel; the increase in steel's strength compared to pure iron is possible only by reducing iron's ductility. Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in the 17th century, with the production of blister steel and crucible steel. With the invention of the Bessemer process in the mid-19th century, a new era of mass-produced steel began; this was followed by the Siemens–Martin process and the Gilchrist–Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron.
Further refinements in the process, such as basic oxygen steelmaking replaced earlier methods by further lowering the cost of production and increasing the quality of the final product. Today, steel is one of the most common manmade materials in the world, with more than 1.6 billion tons produced annually. Modern steel is identified by various grades defined by assorted standards organizations; the noun steel originates from the Proto-Germanic adjective stahliją or stakhlijan, related to stahlaz or stahliją. The carbon content of steel is between 0.002% and 2.14% by weight for plain iron–carbon alloys. These values vary depending on alloying elements such as manganese, nickel, so on. Steel is an iron-carbon alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction. Too little carbon content leaves iron quite soft and weak. Carbon contents higher than those of steel make a brittle alloy called pig iron. While iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel.
Common alloying elements include: manganese, chromium, boron, vanadium, tungsten and niobium. Additional elements, most considered undesirable, are important in steel: phosphorus, sulfur and traces of oxygen and copper. Plain carbon-iron alloys with a higher than 2.1% carbon content are known as cast iron. With modern steelmaking techniques such as powder metal forming, it is possible to make high-carbon steels, but such are not common. Cast iron is not malleable when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties. Certain compositions of cast iron, while retaining the economies of melting and casting, can be heat treated after casting to make malleable iron or ductile iron objects. Steel is distinguishable from wrought iron, which may contain a small amount of carbon but large amounts of slag. Iron is found in the Earth's crust in the form of an ore an iron oxide, such as magnetite or hematite. Iron is extracted from iron ore by removing the oxygen through its combination with a preferred chemical partner such as carbon, lost to the atmosphere as carbon dioxide.
This process, known as smelting, was first applied to metals with lower melting points, such as tin, which melts at about 250 °C, copper, which melts at about 1,100 °C, the combination, which has a melting point lower than 1,083 °C. In comparison, cast iron melts at about 1,375 °C. Small quantities of iron were smelted in ancient times, in the solid state, by heating the ore in a charcoal fire and welding the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily. All of these temperatures could be reached with ancient methods used since the Bronze Age. Since the oxidation rate of iron increases beyond 800 °C, it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iro
Bronze is an alloy consisting of copper with about 12–12.5% tin and with the addition of other metals and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon. These additions produce a range of alloys that may be harder than copper alone, or have other useful properties, such as stiffness, ductility, or machinability; the archeological period in which bronze was the hardest metal in widespread use is known as the Bronze Age. The beginning of the Bronze Age in India and western Eurasia is conventionally dated to the mid-4th millennium BC, to the early 2nd millennium BC in China; the Bronze Age was followed by the Iron Age starting from about 1300 BC and reaching most of Eurasia by about 500 BC, although bronze continued to be much more used than it is in modern times. Because historical pieces were made of brasses and bronzes with different compositions, modern museum and scholarly descriptions of older objects use the more inclusive term "copper alloy" instead. There are two basic theories as to the origin of the word.
Romance theoryThe Romance theory holds that the word bronze was borrowed from French bronze, itself borrowed from Italian bronzo "bell metal, brass" from either, bróntion, back-formation from Byzantine Greek brontēsíon from Brentḗsion ‘Brindisi’, reputed for its bronze. Proto-Slavic theoryThe Proto-Slavic theory reflects the philological issue that in the most of Slavonic languages word "bronza" corresponds to "war metal" while at the early stages of the Bronze working it was used exclusively for military purposes; the discovery of bronze enabled people to create metal objects which were harder and more durable than possible. Bronze tools, weapons and building materials such as decorative tiles were harder and more durable than their stone and copper predecessors. Bronze was made out of copper and arsenic, forming arsenic bronze, or from or artificially mixed ores of copper and arsenic, with the earliest artifacts so far known coming from the Iranian plateau in the 5th millennium BC, it was only that tin was used, becoming the major non-copper ingredient of bronze in the late 3rd millennium BC.
Tin bronze was superior to arsenic bronze in that the alloying process could be more controlled, the resulting alloy was stronger and easier to cast. Unlike arsenic, metallic tin and fumes from tin refining are not toxic; the earliest tin-alloy bronze dates to 4500 BC in a Vinča culture site in Pločnik. Other early examples date to the late 4th millennium BC in Egypt and some ancient sites in China and Mesopotamia. Ores of copper and the far rarer tin are not found together, so serious bronze work has always involved trade. Tin sources and trade in ancient times had a major influence on the development of cultures. In Europe, a major source of tin was the British deposits of ore in Cornwall, which were traded as far as Phoenicia in the eastern Mediterranean. In many parts of the world, large hoards of bronze artifacts are found, suggesting that bronze represented a store of value and an indicator of social status. In Europe, large hoards of bronze tools socketed axes, are found, which show no signs of wear.
With Chinese ritual bronzes, which are documented in the inscriptions they carry and from other sources, the case is clear. These were made in enormous quantities for elite burials, used by the living for ritual offerings. Though bronze is harder than wrought iron, with Vickers hardness of 60–258 vs. 30–80, the Bronze Age gave way to the Iron Age after a serious disruption of the tin trade: the population migrations of around 1200–1100 BC reduced the shipping of tin around the Mediterranean and from Britain, limiting supplies and raising prices. As the art of working in iron improved, iron improved in quality; as cultures advanced from hand-wrought iron to machine-forged iron, blacksmiths learned how to make steel. Steel holds a sharper edge longer. Bronze was still used during the Iron Age, has continued in use for many purposes to the modern day. There are many different bronze alloys, but modern bronze is 88% copper and 12% tin. Alpha bronze consists of the alpha solid solution of tin in copper.
Alpha bronze alloys of 4–5% tin are used to make coins, springs and blades. Historical "bronzes" are variable in composition, as most metalworkers used whatever scrap was on hand; the proportions of this mixture suggests. The Benin Bronzes are in fact brass, the Romanesque Baptismal font at St Bartholomew's Church, Liège is described as both bronze and brass. In the Bronze Age, two forms of bronze were used: "classic bronze", about 10% tin, was used in
Urban planning is a technical and political process concerned with the development and design of land use and the built environment, including air and the infrastructure passing into and out of urban areas, such as transportation and distribution networks. Urban planning deals with physical layout of human settlements; the primary concern is the public welfare, which includes considerations of efficiency, sanitation and use of the environment, as well as effects on social and economic activities. Urban planning is considered an interdisciplinary field that includes social and design sciences, it is related to the field of urban design and some urban planners provide designs for streets, parks and other urban areas. Urban planning is referred to as urban and regional planning, regional planning, town planning, city planning, rural planning, urban development or some combination in various areas worldwide. Urban planning guides orderly development in urban and rural areas. Although predominantly concerned with the planning of settlements and communities, urban planning is responsible for the planning and development of water use and resources and agricultural land and conserving areas of natural environmental significance.
Practitioners of urban planning are concerned with research and analysis, strategic thinking, urban design, public consultation, policy recommendations and management. Enforcement methodologies include governmental zoning, planning permissions, building codes, as well as private easements and restrictive covenants. Urban planners work with the cognate fields of architecture, landscape architecture, civil engineering, public administration to achieve strategic and sustainability goals. Early urban planners were members of these cognate fields. Today urban planning is a independent professional discipline; the discipline is the broader category that includes different sub-fields such as land-use planning, economic development, environmental planning, transportation planning. There is evidence of urban planning and designed communities dating back to the Mesopotamian, Indus Valley and Egyptian civilizations in the third millennium BCE. Archeologists studying the ruins of cities in these areas find paved streets that were laid out at right angles in a grid pattern.
The idea of a planned out urban area evolved. Beginning in the 8th century BCE, Greek city states were centered on orthogonal plans; the ancient Romans, inspired by the Greeks used orthogonal plans for their cities. City planning in the Roman world was developed for public convenience; the spread of the Roman Empire subsequently spread the ideas of urban planning. As the Roman Empire declined, these ideas disappeared. However, many cities in Europe still held onto the planned Roman city center. Cities in Europe from the 9th to 14th centuries grew organically and sometimes chaotically, but in the following centuries some newly created towns were built according to preconceived plans, many others were enlarged with newly planned extensions. From the 15th century on, much more is recorded of the people that were involved. In this period, theoretical treatises on architecture and urban planning start to appear in which theoretical questions are addressed and designs of towns and cities are described and depicted.
During the Enlightenment period, several European rulers ambitiously attempted to redesign capital cities. During the Second French Republic, Baron Georges-Eugène Haussmann, under the direction of Napoleon III, redesigned the city of Paris into a more modern capital, with long, wide boulevards. Planning and architecture went through a paradigm shift at the turn of the 20th century; the industrialized cities of the 19th century grew at a tremendous rate. The pace and style of this industrial construction was dictated by the concerns of private business; the evils of urban life for the working poor were becoming evident as a matter for public concern. The laissez-faire style of government management of the economy, in fashion for most of the Victorian era, was starting to give way to a New Liberalism that championed intervention on the part of the poor and disadvantaged. Around 1900, theorists began developing urban planning models to mitigate the consequences of the industrial age, by providing citizens factory workers, with healthier environments.
At the beginning of the 20th century, urban planning began to be recognized as a profession. The Town and Country Planning Association was founded in 1899 and the first academic course in Great Britain on urban planning was offered by the University of Liverpool in 1909. In the 1920s, the ideas of modernism and uniformity began to surface in urban planning, lasted until the 1970s. Many planners started to believe that the ideas of modernism in urban planning led to higher crime rates and social problems. Urban planners now focus more on diversity in urban centers. Planning theory is the body of scientific concepts, behavioral relationships, assumptions that define the body of knowledge of urban planning. There are eight procedural theories of planning that remain the principal theories of planning procedure today: the rational-comprehensive approach, the incremental approach, the transactive approach, the communicative approach, the advocacy approach, the equity approach, the radical approach, the humanist or phenomenological approach.
Technical aspects of urban planning involve the applying scientific, technical processes and features that are involved