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#151 2018-06-09 12:40:35

Monox D. I-Fly
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From: Indonesia
Registered: 2015-12-02
Posts: 1,204

Re: Miscellany

ganesh wrote:

(The name may be somewhat of a misnomer - game theory generally does not share the fun or frivolity associated with games.)

So that's why I never enjoy learning about game theory.


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away. May his adventurous soul rest in peace at heaven.

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#152 2018-06-09 17:32:45

ganesh
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Registered: 2005-06-28
Posts: 25,096

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

(The name may be somewhat of a misnomer - game theory generally does not share the fun or frivolity associated with games.)

So that's why I never enjoy learning about game theory.

smile smile

135) Chromium

Chromium (Cr), chemical element of Group 6 (VIb) of the periodic table, a hard, steel-gray metal that takes a high polish and is used in alloys to increase strength and corrosion resistance. Chromium was discovered (1797) by the French chemist Nicolas-Louis Vauquelin and isolated as the metal a year later; it was named for its multicoloured compounds. The green colour of emerald, serpentine, and chrome mica and the red colour of ruby are due to small amounts of chromium. The name of the element chromium (from Greek chrōmos, “colour”) connotes the pronounced and varied colorations of chromium compounds.

Occurrence, Uses, And Properties

Chromium is a relatively abundant element in Earth’s crust; the free metal is never found in nature. Most ores consist of the mineral chromite, the ideal formula of which is FeCr2O4. It is widely dispersed in natural deposits, which are usually contaminated with oxygen, magnesium, aluminum, and silica; their chromium content varies from 42 to 56 percent. One of the chief uses of chromium is in ferrous alloys, for which the pure metal is not required. Accordingly, chromite is often reduced with carbon in a furnace, producing the alloy ferrochromium, which contains iron and chromium in an atom ratio of approximately 1 to 2.

To obtain pure chromium, chromite is first treated with molten alkali and oxygen, converting all of the chromium to the alkali chromate, and the latter is dissolved in water and eventually precipitated as sodium dichromate, Na2Cr2O7. The dichromate is then reduced with carbon to chromium sesquioxide, Cr2O3, and that oxide in turn is reduced with aluminum to give the chromium metal.

Chromium is added to iron and nickel in the form of ferrochromium to produce alloys specially characterized by their high resistance to corrosion and oxidation. Used in small amounts, chromium hardens steel. Stainless steels are alloys of chromium and iron in which the chromium content varies from 10 to 26 percent. Chromium alloys are used to fabricate such products as oil tubing, automobile trim, and cutlery. Chromite is used as a refractory and as a raw material for the production of chromium chemicals.

The metal is white, hard, lustrous, and brittle and is extremely resistant to ordinary corrosive reagents; this resistance accounts for its extensive use as an electroplated protective coating. At elevated temperatures chromium unites directly with the halogens or with sulfur, silicon, boron, nitrogen, carbon, or oxygen. (For additional treatment of chromium metal and its production, see chromium processing.)

Natural chromium consists of a mixture of four stable isotopes: chromium-52 (83.76 percent), chromium-53 (9.55 percent), chromium-50 (4.31 percent), and chromium-54 (2.38 percent). The metal is paramagnetic (weakly attracted to a magnet). It exists in two forms: body-centred cubic (alpha) and hexagonal close-packed (beta). At room temperature, chromium slowly dissolves in hydrochloric and dilute sulfuric acids. Certain oxidizing agents produce a thin unreactive oxide layer on the metal, rendering it passive also to dilute mineral acids, such as sulfuric, nitric, or cold aqua regia. At ordinary temperatures the metal shows no reaction to seawater or to wet or dry air.

Top producers of chromium include South Africa, India, Kazakhstan, and Turkey.

Principal Compounds

The most common oxidation states of chromium are +6, +3, and +2. A few stable compounds of the +5, +4, and +1 states, however, are known.

In the +6 oxidation state, the most important species formed by chromium are the chromate, and dichromate,  ions. These ions form the basis for a series of industrially important salts. Among them are sodium chromate, Na2CrO4, and sodium dichromate, Na2Cr2O7, which are used in leather tanning, in metal surface treatment, and as catalysts in various industrial processes.

Chromium forms several commercially valuable oxygen compounds, the most important of which is chromium oxide, commonly called chromium trioxide or chromic acid, CrO3, in which chromium is in the +6 oxidation state. An orange-red crystalline solid, chromic acid liquefies gradually when exposed to moist air. It is usually produced by treatment of sodium dichromate with sulfuric acid. Chromic acid is used chiefly for chromium plating but is also employed as a colorant in ceramics. It is a powerful oxidant and may react violently with some organic materials, but such solutions are often utilized by controlled oxidations in organic synthesis.

Another significant oxygen compound is chromium oxide, also known as chromium sesquioxide or chromic oxide, Cr2O3, in which chromium is in the +3 oxidation state. It is prepared by calcining sodium dichromate in the presence of carbon or sulfur. Chromium oxide is a green powder and is employed extensively as a pigment; its hydrate form, known as Guignet’s green, is used when chemical and heat resistance are required.

chromium-metal-chips-250x250.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#153 2018-06-11 01:14:57

ganesh
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Registered: 2005-06-28
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Re: Miscellany

136) Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE), a strong, tough, waxy, nonflammable synthetic resin produced by the polymerization of tetrafluoroethylene. Known by such trademarks as Teflon, Fluon, Hostaflon, and Polyflon, PTFE is distinguished by its slippery surface, high melting point, and resistance to attack by almost all chemicals. These properties have made it familiar to consumers as the coating on nonstick cookware; it is also fabricated into industrial products, including bearings, pipe liners, and parts for valves and pumps.

PTFE was discovered serendipitously in 1938 by Roy Plunkett, an American chemist for E.I. du Pont de Nemours & Company (now DuPont Company), who found that a tank of gaseous tetrafluoroethylene refrigerant had polymerized to a white powder. During World War II it was applied as a corrosion-resistant coating to protect metal equipment used in the handling of radioactive material for the Manhattan Project. For more than a decade after the war, PTFE saw little commercial use, owing to difficulties encountered in devising methods for processing the slippery, high-melting material. DuPont released its trademarked Teflon-coated nonstick cookware in 1960.

Tetrafluoroethylene (C2F4), a colourless, odourless gas, is made by heating chlorodifluoromethane (CHClF2) in the range of 600–700 °C (1,100–1,300 °F). Chlorodifluoromethane in turn is obtained by reacting hydrogen fluoride (HF) with chloroform (CHCl3). Tetrafluoroethylene monomers (small, single-unit molecules) are suspended or emulsified in water and then polymerized (linked into giant, multiple-unit molecules) under high pressure in the presence of free-radical initiators. The polymer consists of a chain of carbon atoms with two fluorine atoms bonded to each carbon.

The fluorine atoms surround the carbon chain like a protective sheath, creating a chemically inert and relatively dense molecule with very strong carbon-fluorine bonds. The polymer is inert to most chemicals, does not melt below 327 °C (620 °F), and has the lowest coefficient of friction of any known solid. These properties allow it to be used for bushings and bearings that require no lubricant, as liners for equipment used in the storage and transportation of strong acids and organic solvents, as electrical insulation under high-temperature conditions, and in its familiar application as a cooking surface that does not require the use of fats or oils.

Fabrication of PTFE products is difficult because the material does not flow readily even above its melting point. Molded parts can be made by compressing and heating fine powders mixed with volatile lubricants. Metallic surfaces can be sprayed or dipped with aqueous dispersions of PTFE particles to form a permanent coating. Dispersions of PTFE can also be spun into fibres.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#154 2018-06-12 22:32:13

ganesh
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Re: Miscellany

137) Bulldozer

Bulldozer, also called Dozer, powerful machine for pushing earth or rocks, used in road building, farming, construction, and wrecking; it consists of a heavy, broad steel blade or plate mounted on the front of a tractor. Sometimes it uses a four-wheel-drive tractor, but usually a track or crawler type, mounted on continuous metal treads, is employed. The blade may be lifted and forced down by hydraulic rams. For digging, the blade is held below surface level; for transporting, it is held at the surface level; and for spreading, it is held above the surface level, as the tractor moves forward.

Bulldozers are used for shallow digging and ditching; short-range transportation of material; spreading soil dumped from trucks; rough grading; removing trees, stumps, and boulders; and cleaning and leveling around loading equipment. A bulldozer alone can do many types of excavation, and it is useful in combination with other machinery in most excavation work.

dozer_D5.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#155 2018-06-15 01:13:27

ganesh
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Registered: 2005-06-28
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Re: Miscellany

138) Kaleidoscope

Kaleidoscope, optical device consisting of mirrors that reflect images of bits of coloured glass in a symmetrical geometric design through a viewer. The design may be changed endlessly by rotating the section containing the loose fragments. The name is derived from the Greek words kalos (“beautiful”), eïdos (“form”), and skopeïn (“to view”).Kaleidoscope, optical device consisting of mirrors that reflect images of bits of coloured glass in a symmetrical geometric design through a viewer. The design may be changed endlessly by rotating the section containing the loose fragments. The name is derived from the Greek words kalos (“beautiful”), eïdos (“form”), and skopeïn (“to view”).

The kaleidoscope was invented by Sir David Brewster about 1816 and patented in 1817. Sold usually as a toy, the kaleidoscope also has value for the pattern designer.

The kaleidoscope illustrates the image-forming properties of combined, inclined mirrors. If an object is placed between two mirrors inclined at right angles, an image is formed in each mirror. Each of these mirror images is in turn reflected in the other mirror, forming the appearance of four symmetrically placed objects. If the mirrors are inclined at 60°, a hexagonally symmetrical pattern results from one object producing six regularly placed images.

A simple kaleidoscope consists of two thin, wedge-shaped mirror strips touching along a common edge or of a single sheet of bright aluminum bent to an angle of 60° or 45°. The mirrors are enclosed in a tube with a viewing eyehole at one end. At the other end is a thin, flat box that can be rotated; it is made from two glass disks, the outer one ground to act as a diffusing screen. In this box are pieces of coloured glass, tinsel, or beads. When the box is turned or tapped, the objects inside tumble into an arbitrary grouping, and when the diffusing screen is illuminated, the sixfold or eightfold multiplication creates a striking symmetrical pattern. The number of combinations and patterns is effectively without limit.

Some kaleidoscopes dispense with the object box and use a lens to throw images of distant objects on the mirrors, an eyepiece at the viewing eyehole then being an advantage.

Kaleidoscope.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#156 2018-06-17 00:11:17

ganesh
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Re: Miscellany

139) Dead Sea

Dead Sea, Arabic Al-Baḥr Al-Mayyit (“Sea of Death”), Hebrew Yam HaMelaẖ (“Salt Sea”), also called Salt Sea, landlocked salt lake between Israel and Jordan in southwestern Asia. Its eastern shore belongs to Jordan, and the southern half of its western shore belongs to Israel. The northern half of the western shore lies within the Palestinian West Bank and has been under Israeli occupation since the 1967 Arab-Israeli war. The Jordan River, from which the Dead Sea receives nearly all its water, flows from the north into the lake.

The Dead Sea has the lowest elevation and is the lowest body of water on the surface of Earth. For several decades in the mid-20th century the standard value given for the surface level of the lake was some 1,300 feet (400 metres) below sea level. Beginning in the 1960s, however, Israel and Jordan began diverting much of the Jordan River’s flow and increased the use of the lake’s water itself for commercial purposes. The result of those activities was a precipitous drop in the Dead Sea’s water level. By the mid-2010s measurement of the lake level was more than 100 feet (some 30 metres) below the mid-20th-century figure—i.e., about 1,410 feet (430 metres) below sea level—but the lake continued to drop by about 3 feet (1 metre) annually.

Physical Features

Physiography and geology

The Dead Sea is situated between the hills of Judaea to the west and the Transjordanian plateaus to the east. Before the water level began dropping, the lake was some 50 miles (80 km) long, attained a maximum width of 11 miles (18 km), and had a surface area of about 394 square miles (1,020 square km). The peninsula of Al-Lisān (Arabic: “The Tongue”) divided the lake on its eastern side into two unequal basins: the northern basin encompassed about three-fourths of the lake’s total surface area and reached a depth of 1,300 feet (400 metres), and the southern basin was smaller and considerably shallower, less than 10 feet (3 metres) deep on average. During biblical times and until the 8th century CE, only the area around the northern basin was inhabited, and the lake was slightly lower than its present-day level. It rose to its highest level, 1,275 feet (389 metres) below sea level, in 1896 but receded again after 1935, stabilizing at about 1,300 feet (400 metres) below sea level for several decades.

The drop in the lake level in the late 20th and early 21st centuries changed the physical appearance of the Dead Sea. Most noticeably, the peninsula of Al-Lisān gradually extended eastward, until the lake’s northern and southern basins became separated by a strip of dry land. In addition, the southern basin was eventually subdivided into dozens of large evaporation pools (for the extraction of salt), so by the 21st century it had essentially ceased to be a natural body of water. The northern basin—effectively now the actual Dead Sea—largely retained its overall dimensions despite its great loss of water, mainly because its shoreline plunged downward so steeply from the surrounding landscape.

The Dead Sea region occupies part of a graben (a downfaulted block of Earth’s crust) between transform faults along a tectonic plate boundary that runs northward from the Red Sea–Gulf of Suez spreading centre to a convergent plate boundary in the Taurus Mountains of southern Turkey. The eastern fault, along the edge of the Moab Plateau, is more readily visible from the lake than is the western fault, which marks the gentler Judaean upfold.

In the Jurassic and Cretaceous periods (about 201 million to 66 million years ago), before the creation of the graben, an extended Mediterranean Sea covered Syria and Palestine. During the Miocene Epoch (23 million to 5.3 million years ago), as the Arabian Plate collided with the Eurasian Plate to the north, upheaval of the seabed produced the upfolded structures of the Transjordanian highlands and the central range of Palestine, causing the fractures that allowed the Dead Sea graben to drop. At that time the Dead Sea was probably about the size that it is today. During the Pleistocene Epoch (2,588,000 to 11,700 years ago), it rose to an elevation of about 700 feet (200 metres) above its modern level, forming a vast inland sea that stretched some 200 miles (320 km) from the H̱ula Valley area in the north to 40 miles (64 km) beyond its present southern limits. The Dead Sea did not spill over into the Gulf of Aqaba because it was blocked by a 100-foot (30-metre) rise in the highest part of Wadi Al-ʿArabah, a seasonal watercourse that flows in a valley to the east of the central Negev highlands.

Beginning about 2.5 million years ago, heavy streamflow into the lake deposited thick sediments of shale, clay, sandstone, rock salt, and gypsum. Later, strata of clay, marl, soft chalk, and gypsum were dropped onto layers of sand and gravel. Because the water in the lake evaporated faster than it was replenished by precipitation during the past 10,000 years, the lake gradually shrank to its present form. In so doing, it exposed deposits that now cover the Dead Sea valley to thicknesses of between about 1 and 4 miles (1.6 and 6.4 km).

The Al-Lisān region and Mount Sedom (historically Mount Sodom) resulted from movements of Earth’s crust. Mount Sedom’s steep cliffs rise up from the southwestern shore. Al-Lisān is formed of strata of clay, marl, soft chalk, and gypsum interbedded with sand and gravel. Both Al-Lisān and beds made of similar material on the western side of the Dead Sea valley dip to the east. It is assumed that the uplifting of Mount Sedom and Al-Lisān formed a southern escarpment for the Dead Sea. Later the sea broke through the western half of that escarpment to flood what is now the shallow southern remnant of the Dead Sea.

Another consequence resulting from the Dead Sea’s lower water level has been the appearance of sinkholes, especially in the southwestern part of the region. As the water in the lake dropped, it became possible for groundwater to rise up and dissolve large subterranean caverns in the overlying salt layer until the surface finally collapses. Several hundred sinkholes have formed, some of them in areas popular with tourists.

Climate and hydrology

The Dead Sea lies in a desert. Rainfall is scanty and irregular. Al-Lisān averages about 2.5 inches (65 mm) of rain a year, the industrial site of Sedom (near historical Sodom) only about 2 inches (50 mm). Because of the lake’s extremely low elevation and sheltered location, winter temperatures are mild, averaging 63 °F (17 °C) in January at the southern end at Sedom and 58 °F (14 °C) at the northern end; freezing temperatures do not occur. Summer is oppressively hot, averaging 93 °F (34 °C) in August at Sedom, with a recorded maximum of 124 °F (51 °C). Evaporation of the lake’s waters—estimated at about 55 inches (1,400 mm) per year—often creates a thick mist above the lake. On the rivers the atmospheric humidity varies from 45 percent in May to 62 percent in October. Lake and land breezes, which are relatively common, blow off the lake in all directions in the daytime and then reverse direction to blow toward the centre of the lake at night.

The inflow from the Jordan River, whose high waters occur in winter and spring, once averaged some 45.5 billion cubic feet (1.3 billion cubic metres) per year. However, the subsequent diversions of the Jordan’s waters reduced the river’s flow to a small fraction of the previous amount and became the principal cause for the drop in the Dead Sea’s water level. Four modest streams descend to the lake from Jordan to the east through deep gorges: the wadis (intermittent streams) Al-ʿUẓaymī, Zarqāʾ Māʿīn, Al-Mawjib, and Al-Ḥasā. Down numerous other wadis, streams flow spasmodically and briefly from the neighbouring heights as well as from the depression of Wadi Al-ʿArabah. Thermal sulfur springs also feed the rivers. Evaporation in summer and the inflow of water, especially in winter and spring, once caused noticeable seasonal variations of 12 to 24 inches (30 to 60 cm) in the level of the lake, but those fluctuations have been overshadowed by the more-dramatic annual drops in the Dead Sea’s surface level.

Salinity

The waters of the Dead Sea are extremely saline, and, generally, the concentration of salt increases toward the lake’s bottom. That phenomenon can create two different masses of water in the lake for extended periods of time. Such a situation existed for some three centuries, lasting until the late 1970s. Down to a depth of about 130 feet (40 metres), the temperature varied from 66 to 98 °F (19 to 37 °C), the salinity was slightly less than 300 parts per thousand, and the water was especially rich in sulfates and bicarbonates. Beneath a zone of transition located at depths between 130 and 330 feet (40 and 100 metres), the water had a uniform temperature of about 72 °F (22 °C) and a higher degree of salinity (approximately 332 parts per thousand); it contained hydrogen sulfide and strong concentrations of magnesium, potassium, chlorine, and bromine. The deep water was saturated with sodium chloride, which precipitated to the bottom. The deep water thus became fossilized (i.e., because it was highly salty and dense, it remained permanently on the bottom).

The dramatic reduction in inflow from the Jordan River that began in the 1960s gradually increased the salinity of the upper-layer waters of the Dead Sea. By the late 1970s that water mass had become more saline (and denser) than the lower layers, but, because it remained warmer than the layers beneath it, it did not sink. By the winter of 1978–79, however, the upper-level layer had become cool and saturated enough to sink, setting off an event known as an overturn (a mixing of the water layers). Since then the trend has been toward restoring the formerly stratified water layers, but with more instances of overturning.

The saline water has a high density that keeps bathers buoyant. The fresh water of the Jordan stays on the surface, and in the spring its muddy colour can be traced as it spreads southward from the point where the river empties into the Dead Sea. The lake’s extreme salinity excludes all forms of life except bacteria. Fish carried in by the Jordan or by smaller streams when in flood die quickly. Apart from the vegetation along the rivers, plant life along the shores is discontinuous and consists mainly of halophytes (plants that grow in salty or alkaline soil).

Human Imprint

The name Dead Sea can be traced at least to the Hellenistic Age (323 to 30 BCE). The Dead Sea figures in biblical accounts dating to the time of Abraham (first of the Hebrew patriarchs) and the destruction of Sodom and Gomorrah (the two cities along the lake, according to the Hebrew Bible, that were destroyed by fire from heaven because of their wickedness). The desolate wilderness beside the lake offered refuge to David (king of ancient Israel) and later to Herod I (the Great; king of Judaea), who at the time of the siege of Jerusalem by the Parthians in 40 BCE barricaded himself in a fortress at Masada, Israel, just west of Al-Lisān. Masada was the scene of a two-year siege that culminated in the mass suicide of its Jewish Zealot defenders and the occupation of the fortress by the Romans in 73 CE. The Jewish sect that left the biblical manuscripts known as the Dead Sea Scrolls took shelter in caves at Qumrān, just northwest of the lake.

The Dead Sea constitutes an enormous salt reserve. Rock salt deposits also occur in Mount Sedom along the southwestern shore. The salt has been exploited on a small scale since antiquity. In 1929 a potash factory was opened near the mouth of the Jordan. Subsidiary installations were later built in the south at Sedom, but the original factory was destroyed during the 1948–49 Arab-Israeli war. A factory producing potash, magnesium, and calcium chloride was opened in Sedom in 1955. Another plant produces bromine and other chemical products. There are also chemical-processing facilities on the Jordanian side of the southern basin. Water for the extensive array of evaporation pools in the south, from which those minerals are extracted, is supplied by artificial canals from the northern basin.

Because of its location on the contested Jordanian-Israeli frontier, navigation on the Dead Sea is negligible. Its shores are nearly deserted, and permanent establishments are rare. Exceptions are the factory at Sedom, a few hotels and spas in the north, and, in the west, a kibbutz (an Israeli agricultural community) in the region of the ʿEn Gedi oasis. Small cultivated plots are also occasionally found on the lakeshore.

Concern mounted quickly over the continued drop in the Dead Sea’s water level, prompting studies and calls for greater conservation of the Jordan River’s water resources. In addition to proposals for reducing the amount of river water diverted by Israel and Jordan, those two countries discussed proposals for canals that would bring additional water to the Dead Sea. One such project, which received approval from both sides in 2015, would involve constructing a canal northward from the Red Sea. The plan, which would include desalinization and hydroelectric plants along the course of the canal, would deliver large quantities of brine (a by-product of the desalinization process) to the lake. However, the project met with skepticism and opposition from environmentalists and others who questioned the potentially harmful effects of mixing water from the two sources.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#157 2018-06-18 23:04:07

ganesh
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Re: Miscellany

140) Liquid Oxygen

What Is Liquid Oxygen?

Liquid oxygen is oxygen that’s cooled to -183° C (-297°F) at which point it becomes a pale blue liquid. It is one of the physical forms of the element and serves as an efficient means of supplying home oxygen to a variety of patients.

Liquid Oxygen Supply Systems

The liquid oxygen supply system usually consists of a bulk storage unit or reservoir that’s housed in a permanent place in the home and a refillable, portable unit that you can carry around. The reservoir and portable units have a design similar to that of a thermos bottle, consisting of a container inside a container separated by a vacuum. To remain in liquid form, the oxygen must be stored at very cold temperatures inside the thermos-like container. When you’re ready to use the oxygen and you turn it ON, the liquid warms as it leaves the container, changes to gas, and is supplied at room temperature for you to breathe. Depending upon the manufacturer, there are a wide variety of styles and sizes of liquid oxygen systems, each operating under the same principle.

Understanding the Bulk Stationary Storage Unit

Oxygen is often stored as a liquid – although it’s used primarily as a gas – because it’s less bulky and less expensive than storing the equivalent capacity of high-pressure gas. One liter of liquid oxygen is equivalent to approximately 860 liters of gaseous oxygen. A typical bulk storage unit is filled with approximately 40 liters of liquid oxygen. This may last up to 10 days at a flow rate of 2 liters per minute. When you’re at home, you can use the stationary unit as your primary oxygen source. Depending upon your flow rate, your oxygen supply company will routinely refill the stationary storage unit every 1 to 2 weeks.

Understanding the Portable Container

The portable carrying container can be refilled from the large storage unit whenever necessary. When full, the portable unit typically weighs between 6 and 11 pounds and provides approximately 1,025 liters of gaseous oxygen. When you’re at home and out of reach of your stationary unit, you exercise or perform activities outside the home, you can fill the portable system and be free to go wherever you choose.  Because oxygen in its liquid state takes up less space and can be stored at much lower pressures than when in its gaseous state, the portable unit carries more oxygen and is much lighter than a standard oxygen gas cylinder.

Is a Liquid Oxygen Supply System for Me?

Choosing an oxygen supply system is one of the most important decisions you will ever make. If you’re having trouble deciding whether a liquid oxygen system is right for you, it’s a good idea to compare the advantages and disadvantages of different systems.

One of the biggest advantages of using liquid oxygen is that it consumes no electricity. This may be ideal for people on fixed incomes who are unable to afford the higher electricity bills that come with using an oxygen concentrator. Portable liquid oxygen tanks are also lighter and take up less space than compressed gas cylinders making them easier to transport. But oxygen in its liquid form can be more expensive than compressed gas. It can’t be stored for long periods of time because it tends to evaporate. Because the main system needs to be refilled on a regular basis by a service technician, you’re subject to scheduling deliveries, which may be inconvenient. Lastly, refilling the portable tank is said to require dexterity and strength which some folks find difficult.

The Bottom Line

The right oxygen supply system is one that meets your needs and suits your lifestyle. Before you make that choice, talk to your primary health care provider about each system’s pros and cons.

liquid-oxygen-252x300.png


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#158 2018-06-19 23:12:33

ganesh
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Re: Miscellany

141) Phenol

Phenol, any of a family of organic compounds characterized by a hydroxyl (−OH) group attached to a carbon atom that is part of an aromatic ring. Besides serving as the generic name for the entire family, the term phenol is also the specific name for its simplest member, monohydroxybenzene (C6H5OH), also known as benzenol, or carbolic acid.

Phenols are similar to alcohols but form stronger hydrogen bonds. Thus, they are more soluble in water than are alcohols and have higher boiling points. Phenols occur either as colourless liquids or white solids at room temperature and may be highly toxic and caustic.

Phenols are widely used in household products and as intermediates for industrial synthesis. For example, phenol itself is used (in low concentrations) as a disinfectant in household cleaners and in mouthwash. Phenol may have been the first surgical antiseptic. In 1865 the British surgeon Joseph Lister used phenol as an antiseptic to sterilize his operating field. With phenol used in this manner, the mortality rate from surgical amputations fell from 45 to 15 percent in Lister’s ward. Phenol is quite toxic, however, and concentrated solutions cause severe but painless burns of the skin and mucous membranes. Less-toxic phenols, such as n-hexylresorcinol, have supplanted phenol itself in cough drops and other antiseptic applications. Butylated hydroxytoluene (BHT) has a much lower toxicity and is a common antioxidant in foods.

In industry, phenol is used as a starting material to make plastics, explosives such as picric acid, and drugs such as aspirin. The common phenol hydroquinone is the component of photographic developer that reduces exposed silver bromide crystals to black metallic silver. Other substituted phenols are used in the dye industry to make intensely coloured azo dyes. Mixtures of phenols (especially the cresols) are used as components in wood preservatives such as creosote.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#159 2018-06-21 22:09:28

ganesh
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Re: Miscellany

142) Electroplating

Electroplating, process of coating with metal by means of an electric current. Plating metal may be transferred to conductive surfaces (metals) or to nonconductive surfaces (plastics, wood, leather) after the latter have been rendered conductive by such processes as coating with graphite, conductive lacquer, electroless plate, or a vaporized coating.

Figure 1 shows a typical plating tank containing copper sulfate (CuSO4) solution. A dynamo supplies electric current, which is controlled by a rheostat. When the switch is closed, the cathode bar, which holds the work to be plated, is charged negatively. Some of the electrons from the cathode bar transfer to the positively charged copper ions (Cu2+), setting them free as atoms of copper metal. These copper atoms take their place on the cathode surface, copperplating it. Concurrently, as shown in the drawing, the same number of sulfate ions are discharged on the copper anodes, thereby completing the electrical circuit. In so doing, they form a new quantity of copper sulfate that dissolves in the solution and restores it to its original composition. This procedure is typical of nearly all ordinary electroplating processes; the current deposits a given amount of metal on the cathode and the anode dissolves to the same extent, maintaining the solution more or less uniformly. If this balance is perfect and there are no side reactions or losses, a 100 percent cathode efficiency and 100 percent anode efficiency could possibly be realized.

If the metal surface of the cathode is chemically and physically clean, the discharged atoms of copper are deposited within normal interatomic spacing of the atoms of the basis metal and attempt to become an integral part of it. In fact, if the basis metal is copper, the new copper atoms will frequently arrange themselves to continue the crystal structure of the basis metal, the plate becoming more or less indistinguishable from and inseparable from the basis metal.

If suitable solutions of different metals are mixed, it is possible to plate a wide variety of alloys of metals. By this means plated brass can be made more or less indistinguishable from cast brass. It is also possible, however, to deposit alloys or compounds of metals that cannot be produced by melting and casting them together. For example, tin-nickel alloy plate has been used commercially for its hardness and corrosion resistance, which are superior to that of either metal alone. The deposit consists of a tin-nickel compound (Sn-Ni) that cannot be produced in any other way.

Other common alloy plates include bronze and gold, with varying properties, such as different colours or hardnesses. Magnetic alloy plates of such metals as iron, cobalt, and nickel are used for memory drums in computers. Solder plate (Sn-Pb) is used in printed circuit work.

Development Of Electroplating

While some metal coating procedures date back to ancient times, modern electroplating started in 1800 with Alessandro Volta’s discovery of the voltaic pile, or battery, which made noteworthy quantities of direct current electricity available. At about the same time, the battery was employed to deposit lead, copper, and silver. After a nodule of copper had been deposited on a silver cathode, the copper could not be removed. In the same year, zinc, copper, and silver were deposited on themselves and on a variety of basis metals (the metals on which the plating is applied), such as gold and iron.

Electroplating on a commercial scale was begun about 1840–41 and was accelerated by the discovery of cyanide solutions for plating silver, gold, copper, and brass. A cyanide-copper solution, for example, gave adherent deposits of copper directly on iron and steel. A cyanide-copper solution is still used for this purpose and also for the initial plating on zinc die castings. The copper sulfate solution described above corrodes these metals, giving nonadherent deposits.

Electroplating has become a large and growing industry with sophisticated engineering and equipment requirements. The metals that can be readily plated from aqueous solutions at high-current efficiencies near 100 percent can best be surveyed from Figure 2. It shows these metals in a single rectangle in their proper relationship to each other. The only metal shown outside the rectangle that is in common use is chromium, which is usually plated at low-current efficiencies of about 10–20 percent. Iron, cobalt, nickel, copper, zinc, ruthenium, rhodium, palladium, silver, cadmium, tin, iridium, platinum, gold, and lead are more or less commonly used for plating. The others can be deposited easily but have not found much use in this way either owing to cost or availability or lack of useful properties.

The introduction of chromium plating in 1925 stimulated repercussions all through the plating industry. Chromium was essentially a bright plate and retained its brightness indefinitely. Chromium plate found a ready market in the automotive and appliance fields, in which the merits of the combination plate nickel-chromium or copper-nickel-chromium were soon proven. The requirements for closer control procedures in bath composition, temperature, and current density were reflected in better control and development of other processes.

So-called hard-chromium plating likewise created a new way of improving the wear resistance of machine parts and improving their operation owing to good frictional and heat resistance properties. Worn or undersized parts were built up with chromium plate.

While nonmetallic materials have been plated since the mid-19th century, a period of rapid growth in the utilization of electroplated plastics began in 1963 with the introduction of ABS plastic (acrylonitrile-butadiene-styrene), which was readily plated. The plastic part is first etched chemically by a suitable process, such as dipping in a hot chromic acid–sulfuric acid mixture. It is next sensitized and activated by first dipping in stannous chloride solution and then in palladium chloride solution. It is then coated with electroless copper or nickel before further plating. A useful degree of adhesion is obtained (about 1 to 6 kg per cm [5 to 30 pounds per inch]) but is in no way comparable to the adhesion of metals to metals.

Principal Applications

Copperplating is used extensively to prevent case hardening of steel on specified parts. The entire article may be copperplated and the plate ground off on the areas to be hardened. Silver plating is used on tableware and electrical contacts; it has also been used on engine bearings. The most extensive use of gold plating is on jewelry and watch cases. Zinc coatings prevent the corrosion of steel articles, while nickel and chromium plate are used on automobiles and household appliances.

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#160 Today 00:59:33

ganesh
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Registered: 2005-06-28
Posts: 25,096

Re: Miscellany

143) Aerosol container

Aerosol container, any package, usually a metal can or plastic bottle, designed to dispense its liquid contents as a mist or foam. This type of container was developed in 1941 by the American chemist Lyle D. Goodhue and others for dispensing insecticides. Since that time a wide variety of products ranging from disinfectants to whipping cream have been packaged in aerosol containers.

The most common type of aerosol container consists of a shell, a valve, a “dip tube” that extends from the valve to the liquid product, and a liquefied-gas propellant under pressure. The liquid product is generally mixed with the propellant. When the valve is opened, this solution moves up the dip tube and out the valve. The propellant vaporizes as it is released into the atmosphere, dispersing the product in the form of fine particles. In foam packs, such as shaving cream, the propellant and product are present together as an emulsion. On release, the liquid vaporizes, whipping the whole into a foam.

Chlorofluorocarbons, often called Freons, were used extensively as propellants in aerosol-spray products manufactured in the United States until 1978, when the federal government banned most uses of those compounds because of their potentially harmful environmental effect. Scientific studies indicated that chlorofluorocarbons released into the air rise up to the stratosphere, where they catalyze the decomposition of ozone molecules. The stratospheric ozone helps shield animal life from the Sun’s intense ultraviolet radiation, and it was feared that a significant reduction of atmospheric ozone by chlorofluorocarbons could lead to higher rates of radiation-induced skin cancer in humans.

In compliance with the federal ban, American and European manufacturers have substituted hydrocarbons and carbon dioxide for chlorofluorocarbons in most aerosol products. They also have developed aerosol containers that use air pressure produced by hand-operated pumps instead of a propellant.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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