Didymium
Encyclopedia
Didymium is a mixture of the elements praseodymium
and neodymium
. It is used in safety glasses
for glassblowing
and blacksmithing, especially when a gas (propane
) powered forge
is used, where it provides a filter
which selectively blocks the yellowish light at 589 nm emitted by the hot sodium
in the glass, without having a detrimental effect on general vision, unlike dark welder's glasses. Blocked also is the strong ultraviolet
light emitted by the superheated forge gases and insulation lining the forge walls thereby saving the crafters' eyes from serious cumulative damage. (See also arc eye, also known as welder's flash or photokeratitis.)
Didymium photographic filter
s are often used to enhance fall scenery by making leaves appear more vibrant. This is accomplished via the special properties of the substance which causes the removal of part of the orange region of the color spectrum. When present, this group of colors tends to make certain elements of a picture appear "muddy". The "Sodium Vapor Process" used in motion picture matte
work included a didymium filtering prism
in the camera.
Didymium is also used in calibration materials.
, with which it was found. Mosander wrongly believed didymium to be an element
, under the impression that "ceria" (sometimes called cerite) isolated by Jöns Jakob Berzelius
in 1803 was really a mixture of cerium
, lanthanum
and didymium. He was right about lanthanum's being an element, but not about didymium. Mosander did as well as could be expected at the time, since spectroscopy
had not yet been invented. His three "elements" accounted for at least 95% of the rare earths in the original cerite from Bastnäs
, Sweden
. Didymium had not been difficult to find, since it was providing the pinkish tinge to the salts of ceria when in trivalent form. During the period when didymium was believed to be an element, the symbol Di was used for it. At the illustration of Mendeleev's first attempt at a peiodic table, shown on the right, it will be noted that the atomic weights assigned to the various lanthanides, including didymium, reflect the original belief that they were divalent. Their actual trivalency meant that his atomic weights for them were only about 67% of their true values.
In 1874, Per Teodor Cleve
deduced that didymium was made up of at least two elements. Then in 1885, Carl Auer von Welsbach
succeeded in separating salts of these elements, which were soon named praseodymium
and neodymium
. He used a fractional crystallization
of the double ammonium nitrates from a solution of nitric acid
. Welsbach decided to name his two new elements "praseodidymium" and "neodidymium" ("green didymium" and "new didymium"), but one syllable was soon dropped from each name. The name of "didymium" lived on in untruncated version, partly due to the use in glassblower's goggles. The name "didymium" also lived on in mineralogical texts.
During World War I, didymium glass was reportedly used to transmit Morse Code
across battlefields. Didymium does not absorb enough light to make the variation in lamp's light output obvious, but someone with binoculars attached to a prism in the right way could see the absorption bands flash on and off.
The name "didymium" also continued to be used in the rare earth metal industry. In the United States, commercial "didymium" salts were what remained after cerium had been removed from the natural products obtained from monazite
, and thus it contained lanthanum
, as well as Mosander's "didymium". A typical composition might have been 46% lanthanum, 34% neodymium, and 11% praseodymium, with the remainder mostly being samarium and gadolinium for material extracted from South African "rock monazite". (from Steenkampskraal).
The European usage was closer to Mosander's concept. Such cerium-depleted light lanthanide mixtures have been widely used to make petroleum-cracking catalysts. The actual ratio of praseodymium to neodymium varies somewhat depending on the source of the mineral, but it is often around 1:3. Neodymium always dominates, which is why it got the "neo" appellation, being responsible for most of the color of the old didymium in its salts.
Typically, in ores, neodymium is higher in relative abundance in monazite, as compared to the bastnäsite compositions, and the difference is noticeable when unseparated mixtures derived from each are examined side-by-side: the monazite-derived products are more pinkish, and the bastnäsite-derived products are more brownish in tinge, due to the latter's increased relative praseodymium content. (The original cerite from Bastnäs has a rare earth composition highly similar to that of monazite sand.)
In the late 1920s, Leo Moser (Moser glass-works Director General, 1916 to 1932) recombined praseodymium and neodymium in a 1:1 ratio to create his "Heliolite" glass ("Heliolit" in Čeština
), which has color-changing properties between amber, reddish, and green depending on the light source. This was one of a number of decorative glasses using rare earth colorants, with "Heliolit" and "Alexandrit" being the first two, introduced by Moser in 1925. [One can only hope that an appropriate intermediate fraction of the Pr-Nd separation might have been used, to save some expense, since at the time, separated praseodymium and neodymium oxides were the most costly glass colorants in use.]
Praseodymium
Praseodymium is a chemical element that has the symbol Pr and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating.The element...
and neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
. It is used in safety glasses
Eye protection
Eye protection is protective gear for the eyes, which comes in many types depending upon the threat that is to be reduced. The threats can be particles, light, wind blast, heat, sea spray or some type of ball or puck used in sports...
for glassblowing
Glassblowing
Glassblowing is a glassforming technique that involves inflating molten glass into a bubble, or parison, with the aid of a blowpipe, or blow tube...
and blacksmithing, especially when a gas (propane
Propane
Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...
) powered forge
Forge
A forge is a hearth used for forging. The term "forge" can also refer to the workplace of a smith or a blacksmith, although the term smithy is then more commonly used.The basic smithy contains a forge, also known as a hearth, for heating metals...
is used, where it provides a filter
Filter (optics)
Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....
which selectively blocks the yellowish light at 589 nm emitted by the hot sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
in the glass, without having a detrimental effect on general vision, unlike dark welder's glasses. Blocked also is the strong ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light emitted by the superheated forge gases and insulation lining the forge walls thereby saving the crafters' eyes from serious cumulative damage. (See also arc eye, also known as welder's flash or photokeratitis.)
Didymium photographic filter
Photographic filter
In photography and videography, a filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. The filter can be a square or oblong shape mounted in a holder accessory, or, more commonly, a glass or plastic disk with a metal or plastic ring frame, which...
s are often used to enhance fall scenery by making leaves appear more vibrant. This is accomplished via the special properties of the substance which causes the removal of part of the orange region of the color spectrum. When present, this group of colors tends to make certain elements of a picture appear "muddy". The "Sodium Vapor Process" used in motion picture matte
Matte (filmmaking)
Mattes are used in photography and special effects filmmaking to combine two or more image elements into a single, final image. Usually, mattes are used to combine a foreground image with a background image . In this case, the matte is the background painting...
work included a didymium filtering prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
in the camera.
Didymium is also used in calibration materials.
History
Didymium was discovered by Carl Mosander in 1841 and was so named because it is very similar to lanthanumLanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
, with which it was found. Mosander wrongly believed didymium to be an element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
, under the impression that "ceria" (sometimes called cerite) isolated by Jöns Jakob Berzelius
Jöns Jakob Berzelius
Jöns Jacob Berzelius was a Swedish chemist. He worked out the modern technique of chemical formula notation, and is together with John Dalton, Antoine Lavoisier, and Robert Boyle considered a father of modern chemistry...
in 1803 was really a mixture of cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
, lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
and didymium. He was right about lanthanum's being an element, but not about didymium. Mosander did as well as could be expected at the time, since spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
had not yet been invented. His three "elements" accounted for at least 95% of the rare earths in the original cerite from Bastnäs
Bastnäs
Bastnäs is an ore field near Riddarhyttan, Västmanland, Sweden. The mines in Bastnäs were earliest mentioned in 1692. Iron, copper and rare earth elements was extracted from the mines and 4,500 tons of cerium was produced between 1875 and 1888....
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
. Didymium had not been difficult to find, since it was providing the pinkish tinge to the salts of ceria when in trivalent form. During the period when didymium was believed to be an element, the symbol Di was used for it. At the illustration of Mendeleev's first attempt at a peiodic table, shown on the right, it will be noted that the atomic weights assigned to the various lanthanides, including didymium, reflect the original belief that they were divalent. Their actual trivalency meant that his atomic weights for them were only about 67% of their true values.
In 1874, Per Teodor Cleve
Per Teodor Cleve
Per Teodor Cleve was a Swedish chemist and geologist.After graduating from the Stockholm Gymnasium in 1858, Cleve matriculated at Uppsala University in May 1858, where he received his PhD in 1863...
deduced that didymium was made up of at least two elements. Then in 1885, Carl Auer von Welsbach
Carl Auer von Welsbach
Carl Auer Freiherr von Welsbach was an Austrian scientist and inventor who had a talent for not only discovering advances, but turning them into commercially successful products...
succeeded in separating salts of these elements, which were soon named praseodymium
Praseodymium
Praseodymium is a chemical element that has the symbol Pr and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating.The element...
and neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
. He used a fractional crystallization
Fractional crystallization (chemistry)
In chemistry, fractional crystallization is a method of refining substances based on differences in solubility. If a mixture of two or more substances in solution is allowed to crystallize, for example by allowing the temperature of the solution to decrease, the precipitate will contain more of...
of the double ammonium nitrates from a solution of nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
. Welsbach decided to name his two new elements "praseodidymium" and "neodidymium" ("green didymium" and "new didymium"), but one syllable was soon dropped from each name. The name of "didymium" lived on in untruncated version, partly due to the use in glassblower's goggles. The name "didymium" also lived on in mineralogical texts.
During World War I, didymium glass was reportedly used to transmit Morse Code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
across battlefields. Didymium does not absorb enough light to make the variation in lamp's light output obvious, but someone with binoculars attached to a prism in the right way could see the absorption bands flash on and off.
The name "didymium" also continued to be used in the rare earth metal industry. In the United States, commercial "didymium" salts were what remained after cerium had been removed from the natural products obtained from monazite
Monazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...
, and thus it contained lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
, as well as Mosander's "didymium". A typical composition might have been 46% lanthanum, 34% neodymium, and 11% praseodymium, with the remainder mostly being samarium and gadolinium for material extracted from South African "rock monazite". (from Steenkampskraal).
The European usage was closer to Mosander's concept. Such cerium-depleted light lanthanide mixtures have been widely used to make petroleum-cracking catalysts. The actual ratio of praseodymium to neodymium varies somewhat depending on the source of the mineral, but it is often around 1:3. Neodymium always dominates, which is why it got the "neo" appellation, being responsible for most of the color of the old didymium in its salts.
Typically, in ores, neodymium is higher in relative abundance in monazite, as compared to the bastnäsite compositions, and the difference is noticeable when unseparated mixtures derived from each are examined side-by-side: the monazite-derived products are more pinkish, and the bastnäsite-derived products are more brownish in tinge, due to the latter's increased relative praseodymium content. (The original cerite from Bastnäs has a rare earth composition highly similar to that of monazite sand.)
In the late 1920s, Leo Moser (Moser glass-works Director General, 1916 to 1932) recombined praseodymium and neodymium in a 1:1 ratio to create his "Heliolite" glass ("Heliolit" in Čeština
Czech language
Czech is a West Slavic language with about 12 million native speakers; it is the majority language in the Czech Republic and spoken by Czechs worldwide. The language was known as Bohemian in English until the late 19th century...
), which has color-changing properties between amber, reddish, and green depending on the light source. This was one of a number of decorative glasses using rare earth colorants, with "Heliolit" and "Alexandrit" being the first two, introduced by Moser in 1925. [One can only hope that an appropriate intermediate fraction of the Pr-Nd separation might have been used, to save some expense, since at the time, separated praseodymium and neodymium oxides were the most costly glass colorants in use.]