CALCIUM Chemische Eigenschaften,Einsatz,Produktion Methoden
Beschreibung
Calcium is the chemical element with the symbol Ca
and atomic number 20. It has an atomic weight of
40.078 g/mol. Calcium is the fifth most abundant dissolved
ion in seawater by both molarity and mass, after
Na
+, Cl
-, Mg
2+ and SO4
2-. Calcium metal is quite
reactive. It readily forms a white coating of calcium
nitride (Ca3N2) in air at room temperature. It reacts
with water and the metal burns in air with an orangered
flame, forming largely the nitride, but some oxide.
In the visible portion of the spectrum of many stars,
including the Sun, strong absorption lines of singly
ionized calcium ions are evident. Prominent among
these are the H line at 3968.5 A ° and the K line at
3933.7 A°of singly ionized calcium, or Ca II. For the
Sun, and stars with low temperatures, the prominence
of the H and K lines is an indication of strong magnetic
activity in the chromosphere. Measurement of periodic
variations of these active regions can also be used to
deduce the rotational periods of these stars.
Physikalische Eigenschaften
Before the nineteenth century, calcium and some other alkali earth metals were consideredminerals rather than metals because they readily formed hydroxides and, thus, were classedas alkaline substances (bases). Calcium and other alkali earth metals were mined as ores.Therefore, early chemists considered them earth elements.Calcium metal is moderately hard and has a lustrous, silvery color when freshly cut, but itsoon oxidizes to a dull gray. It is a good conductor of heat and electricity, but has few uses inthe electronics industries. Calcium is an important element for the nutrition of living organisms, particularly vertebrates. Vitamin D from foods, sunlight, and milk aids in the depositionof calcium in bones and teeth. The elemental metal is very reactive in water as it releases hydrogen from the water. It is somewhat less reactive in air. Its melting point is 839°C, its boilingpoint is 1484°C, its density is 1.54 g/cm
3, and it has a cubic crystal structure.
Isotopes
There are 20 isotopes of calcium, ranging from Ca-35 to Ca-54. Of the sixstable isotopes, Ca-40 makes up 96.941% of the calcium found in the Earth’s crust, andCa-42 = 0.647%, Ca-43 = 0.135%, Ca-44 = 2.086%, Ca-46 = 0.004%, and Ca-48 =0.187% found on Earth. All the other isotopes of calcium are radioactive and are artificially produced with half-lives ranging from a few microseconds to 1×10
5 years.Radioactive Ca-45 emits beta particles (high-speed electrons) and has a half-life ofabout 163 days. It is used to determine the calcium levels in bones and in soils.
Origin of Name
Its modern name was derived from the word calcis or calx, which is
Latin for “l(fā)ime.
Occurrence
Calcium is the fifth most abundant element found in the Earth’s crust. It is not found asa free element, but as calcium compounds (mostly salts and oxides), which are found on alllandmasses of the world as limestone, marble, and chalk. Calcium, particularly as the compound calcium chloride (CaCl
2), is found in the oceans to the extent of 0.15%.Calcium is produced by two methods. One method is the electrolysis of calcium chloride(Ca++ + 2Cl- → CaCl
2) as the electrolyte at a temperature of ?800°C, during which processmetallic calcium cations (Ca++) are deposited at the cathode as elemental calcium metal.Calcium can also be produced through a thermal process under very low pressure (vacuum)in which lime is reduced by using aluminum.In addition to limestone, calcium is also found in other rocks, coral, shells, eggshells, bones,teeth, and stalactites and stalagmites.
Charakteristisch
Finely powdered calcium metal is flammable in air because it liberates hydrogen from themoisture. It can be extremely reactive in water but can be dissolved in acids. Calcium is harderthan sodium metal, but softer than aluminum. In its elemental form it can be machined (cuton a lathe), extruded (pushed through a die), and drawn (stretched into rods or wires).Calcium is present in a number of products used in our everyday lives. It is found inclassroom chalk, teeth, and bones. About 2% of the human body consists of various forms ofcalcium compounds. Calcium is an essential inorganic element (usually in compound form)for plant and animal life.
History
Calcium (Latin word calcis meaning “l(fā)ime”) was
known as early as the first century when the Ancient
Romans prepared lime as calcium oxide from limestone
and used “slaked lime” as a “whitewash” on various
homes and buildings. Literature dating back to 975 AD
notes that “Plaster-of-Paris” (calcium sulfate), is useful
for setting broken bones. The metal was not isolated
until 1808 when Sir Humphrey Davy of England electrolyzed
a mixture of lime and mercuric oxide, using then
the new “Voltaic Cell” as an energy source. Davy was
trying to isolate calcium. When he heard that Swedish
chemist J?ns Berzelius and his colleague, Pontin, had
prepared calcium amalgam by electrolyzing lime in
mercury, he set up a similar system and was successful.
He worked with electrolysis throughout his life and also discovered/isolated boron, sodium, potassium, magnesium,
calcium, strontium and barium. Calcium metal
was not available on a large scale until the beginning
of the twentieth century.
Verwenden
Calcium is an alkaline earth element that contributes toward bone
and teeth formation, muscle contraction, and blood clotting. it
occurs in milk, vegetables, and egg yolk.
Indications
Calcium is the principal extracellular electrolyte regulated
by PTH, calcitonin, and D3. Extracellular calcium
is a critical component of signal transduction across the
plasma membrane, which regulates a wide spectrum of
physiological events including muscle contraction, secretion
of neurotransmitters and hormones, and the action
of growth factors, cytokines, and protein hormones.
Intracellular calcium is an important cofactor in many
enzymatic reactions.
Definition
calcium: Symbol Ca. A soft greymetallic element belonging togroup 2 (formerly IIA) of the periodictable; a.n. 20; r.a.m. 40.08; r.d.1.54; m.p. 839°C; b.p. 1484°C. Calciumcompounds are common in theearth’s crust; e.g. limestone and marble(CaCO
3), gypsum (CaSO
4.2H
2O),and fluorite (CaF
2). The element is extractedby electrolysis of fused calciumchloride and is used as a getterin vacuum systems and a deoxidizerin producing nonferrous alloys. It isalso used as a reducing agent in theextraction of such metals as thorium,zirconium, and uranium.
Calcium is an essential element forliving organisms, being required fornormal growth and development. Inanimals it is an important constituentof bones and teeth and ispresent in the blood, being requiredfor muscle contraction and othermetabolic processes. In plants it is aconstituent (in the form of calciumpectate) of the middle lamella.
Hazard
The metallic form of calcium, particularly the powdered form, combines with water oroxidizing agents to release hydrogen that may explode, as do the other alkali metals. There aremany useful calcium compounds; some are excellent reducing agents, some are explosive, andothers are essential for life.
The radioactive isotope calcium-45 is deposited in bones and teeth as well as other plantand animal tissues. Because our bodies cannot distinguish between Ca-45 and the stable Ca-40, the radioactive isotope Ca-45 is used as a tracer to study diseased bone and tissue. At thesame time, a massive overexposure to Ca-45 can displace the stable form of Ca-40 in animalsand can cause radiation sickness or even death.
A few calcium compounds, when in powder or vapor form, are toxic when ingested orinhaled.
Pharmazeutische Anwendungen
Calcium is mostly found in limestone and its related forms, such as chalk, and marble and lime (CaO). Calcium is the most abundant inorganic element in the human body and is an essential key for many physiological
processes. Calcium ions are a critical
factor in several life-defining biochemical processes as well as in the endocrine, neural and renal aspects of
blood pressure homeostasis.
Calcium has the symbol Ca and atomic number 20 and is a soft grey alkaline earth metal. Calcium has
four stable isotopes (
40Ca and
42Ca–
44Ca) and the metal reacts with water with the formation of calcium
hydroxide and hydrogen.
Industrielle Verwendung
Calcium (symbol Ca) is a metallic elementbelonging to the group of alkaline earths. It isone of the most abundant materials, occurringin combination in limestones and calcareousclays. The metal is obtained 98.6% pure byelectrolysis of the fused anhydrous chloride. Byfurther subliming, it is obtained 99.5% pure.Calcium metal is yellowish white in color. Itoxidizes easily and, when heated in air, burnswith a brilliant white light. It has a density of1.55 g/cm3, a melting point of 838°C, and aboiling point of 1440°C. Its strong affinity for O2 and sulfur is utilized as a cleanser for nonferrous alloys. As a deoxidizer and desulfurizerit is employed in the form of lumps or sticks ofcalcium metal or in ferroalloys and Ca–Cu.
Many compounds of calcium are employedindustrially, in fertilizers, foodstuffs, and medicine.It is an essential element in the formationof bones, teeth, shells, and plants. Oyster shellsform an important commercial source of calciumfor animal feeds. They are crushed, andthe fine flour is marketed for stock feeds andthe coarse for poultry feeds. The shell is calciumcarbonate.
CALCIUM Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
