Praseodymium is a metal element with atomic number 59,Atomic weight 140.908[7], ofRare earth metal。The element name comes from Greek, which originally means "green".The crystal structure is hexagonal cell.Praseodymium corrosion resistance ratio in airlanthanum、cerium、neodymiumandeuropiumBoth must be strong, but exposure to air will produce a layer of fragile green oxide, and pure praseodymium must be stored in mineral oil or sealed plastic.One of the uses of praseodymium is for petroleumcatalytic cracking 。The activity, selectivity and stability of petroleum cracking catalyst can be improved by adding praseodymium neodymium concentrate into Y zeolite molecular sieve.Praseodymium like othersrare earth elementSimilarly, it has chronic low toxicity and is not an essential element of biology.
Chinese name
praseodymium
Foreign name
Praseodymium
Element symbol
Pr
Atomic weight
one hundred and forty point nine zero seven six five
In 1841, C · G · Mosander obtained a mixture of praseodymium and neodymium from cerium soil, named didymia.[1]
In 1885, the Austrian chemist Wiesbach separated samarium oxide from oxidation and then separated the oxide of a new element. He named this new element Praseodidymium, which is composed of Praseo (green) and Didymium (mixture of neodymium and praseodymium), namely "green", because its salt is green.The name of this element is reduced to Praseodymium.Translated into praseodymium, the element symbol is Pr.The English name of praseodymium derives from the Greek prasios, which originally means "green twin brothers".[1]This is because praseodymium and neodymium coexist, and praseodymium oxide PrtwoOthreeIt is light green.
the distribution of mineral deposits
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The content of praseodymium in the crust is about 5.53 × 10-4%It mainly exists in monazite and bastnasite, and praseodymium is also contained in nuclear fission products.Praseodymium in nature is a stable isotope praseodymium - 141.[1]
physical property
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silvery whiteColored metal, soft and ductile.Praseodymium is bcc structure at room temperature.[1]
There is only one stable isotope of praseodymium in nature,one hundred and forty-onePr。But there are 38 kinds of radioisotopes, among which the more stable ones areone hundred and forty-threePr，The half-life is 13.57 days;one hundred and forty-twoPr，The half-life is 19.12 hours.The half-life of other radioisotopes is less than 5.985 hours, and most of them are less than 33 seconds.Praseodymium has 6 metastable states, and the more stable one isone hundred and thirty-eightPr，one hundred and forty-twoPr andone hundred and thirty-fourPr。The isotope atomic weight of praseodymium ranges from 120.955u（one hundred and twenty-onePr) to 158.955u（one hundred and fifty-ninePr）。stable isotope one hundred and forty-onePr will capture electrons if it emits beta rays.The main radioactive products are cerium isotopes and neodymium isotopes.
melting point
931℃[1]
boiling point
3520℃[1]
density
6.773g/cmthree[1]
Natural content:
Element content in the sun (ppm)
zero point zero zero one
Element content in seawater (ppm) Pacific surface
zero point zero zero zero zero zero zero four four
Content in crust (ppm)
nine point five
chemical property
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Metal praseodymium appearance
Element symbol Pr, belongs to periodic system Ⅲ B group, rare earth element, lanthanide element.[1]
The corrosion resistance in air is better than that of lanthanum, cerium, neodymium andeuropiumBoth should be strong, but exposure to air will produce a layer of fragile green oxide, and praseodymium will slowly form a green fragile oxide layer in the air;Praseodymium usually exists in the+3 oxidation state and also in the+4 valence form.It darkens in humid air and forms a layer of oxide film.The praseodymium ion solution is green.[7]
In industry, solvent extraction and ion exchange are used to treatBastnasiteorMonaziteSeparation and purification of praseodymium from the obtained mixed rare earth solution.Praseodymium metal is prepared by reducing praseodymium fluoride or chloride with calcium.[1]
Lanthanum, cerium, praseodymium, neodymium and other light rare earth metals can be separated on the cathode in a molten state during electrolysis due to their low melting points, so they are generally prepared by electrolysis.
Usually composed of praseodymium chloride hydrate PrClthree·xHtwoO is prepared by dehydration, reduction with metallic calcium, or melting and electrolysis of anhydrous praseodymium chloride.
Specific methods:
1. Take 70gPrClthreeAnd 18.5gCaMix thoroughly in inert atmosphere, shake well and loadtantalumCrucible or use a power driven press to press it into a cylinder and put it into a tantalum crucible. The crucible is equipped with a perforated tantalum cover for ventilation and placed in a closed positionMgOCrucible (d=0.0508m, h=0.1778m).Then put it into a quartz tube (d=0.05715m), one end of the tube is fused, and the other end is polished and embedded into a 55/50 tapered joint.The quartz tube is sealed in a vacuum system with paraffin.Fill in Ar (pass the overheated metal firsturaniumPurified) to P=101.325kPa, and heated to 550~600 ℃ with a 6kW induction furnace, so that the reaction takes place (based on the sudden rise of the temperature of the tantalum crucible).After 5min, it reaches 1000 ℃ and maintains for 13min to make the produced rare earth metal completely agglomerate.Cool to room temperature, soak the tantalum crucible with water to remove CaCltwo, Ca, rare earth metal melt remains at the bottom (containing 1% ～ 3% Ca).[7]
2. 25gKOH+10gNaOH+2.5gH electrofused in 100mL nickel crucibletwoO + 4gPrtwoOthree+ 2gKClOthreeA mixture of.The nickel crucible is placed in a 300 watt electric furnace, and the temperature is measured with a glass thermometer with a metal hoopplatinumThe wire as anode is slightly immersed in the molten liquid level, and the crucible as cathode, with a voltage of 4V.The temperature shall be controlled at 320~335 ℃ until clear molten substance is obtained, and then a layer of shiny black shell like substance is formed, which shall be taken out gently.The second and third electrolysis is carried out at 350 ℃ and 380 ℃ to obtain the product.[7]
application area
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Praseodymium can be used as a catalyst in petrochemical industry.[1]
Praseodymium, as a large amount of rare earth element, is mostly used in the form of mixed rare earth, such as as purification modifier for metal materials, chemical catalyst, agricultural rare earth, etc.Addition of Y type in the form of praseodymium neodymium concentrateZeolite molecular sieveThe activity, selectivity and stability of petroleum cracking catalyst can be improved by preparing petroleum cracking catalyst in.As a plastic modification additive, adding praseodymium neodymium concentrate in polytetrafluoroethylene (PTFE) can significantly improve thePTFEWear resistance.
Rare earth permanent magnetic materialsIt is the hottest application field of rare earth nowadays.Praseodymium alone as a permanent magnetic material is not outstanding, but it is an excellent synergistic element that can improve the magnetic properties.Whether it is the first generation rare earth permanent magnetic materialsamarium cobaltPermanent magnet alloy, or the third generation rare earth permanent magnet materialNdFeB The properties of permanent magnetic materials can be effectively improved by adding appropriate amount of praseodymium.As in SmCofiveAdding some Pr instead of Sm can improve the magnetic energy product of permanent magnetic materials. The ratio of the two is generally 80% Sm-20% Pr. If praseodymium is added too much, the coercivity and stability of the materials will be reduced.In the third generation of rare earth permanent magnet Nd-Fe-B, the addition of praseodymium can improve the coercivity of the material. Germany, Japan and other countries all add part of praseodymium in the production of high coercivity Nd-Fe-B magnets.Praseodymium can replace 1/3 neodymium with the addition amount of 5%~8%, up to 10%.Magnetic materials have high requirements for praseodymium quality, which should at least reach the same quality as neodymium.The addition of praseodymium can also improve the oxidation resistance (air corrosion resistance) and mechanical properties of magnets, which have been widely used in various electronic devices and motors.
Praseodymium can also be used for grinding and polishing materials.pureceriumThe base polishing powder is usually light yellow, which is a high-quality polishing material for optical glass and has replaced the one with low polishing efficiency and polluting production environmentIron oxide redPowder.Neodymium oxideIt has little effect on polishing, but praseodymium has good polishing performance.The rare earth polishing powder containing praseodymium will be reddish brown, also known as red powder, but this red is not iron oxide red, but because it contains praseodymium oxide, the color of rare earth polishing powder will become darker.Praseodymium is also used as a new grinding material to make praseodymium containing corundum grinding wheel.Compared with white corundum, the efficiency and durability of grinding carbon structural steel, stainless steel and superalloy can be improved by more than 30%.In order to reduce costs, praseodymium neodymium concentrates were used as raw materials in the past, so they were called praseodymium neodymium corundum grinding wheels.
Praseodymium is also used more and more widely in the field of optical fibers. Praseodymium doped fiber amplifiers (PDFAs) have been developed to amplify the 1300~1360nm spectrum, and the technology is becoming more mature.With its excellent performance price ratio, PDFA is of great practical significance to the construction, transformation and system upgrade of the 1550nm CATV system optical cable television currently widely laid in China.PDFA will fundamentally change the existing network pattern of 1550nm CATV, making 1310nm CATV system an ideal alternative to 1550nm system in HFC system transformation.
Calculate chemical data
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data[7]：
1. Reference value for drainage parameter calculation (XlogP): None
2. Number of hydrogen bond donors: 0
3. Number of hydrogen bond receptors: 0
4. Number of rotatable chemical bonds: 0
5. Number of tautomers: none
6. Topological molecular polar surface area 0
7. Number of heavy atoms: 1
8. Surface charge: 0
9. Complexity: 0
10. Number of isotope atoms: 0
11. Determine the number of atomic structure centers: 0
12. Number of uncertain atomic structure centers: 0
13. Determine the number of chemical bond structural centers: 0
14. Number of indeterminate chemical bond structure centers: 0
15. Number of covalent bond units: 1
Biological function
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The chloride of praseodymium inhibited the activities of lactate dehydrogenase, glutamate dehydrogenase, 6-phosphate glucose dehydrogenase and aldolase.In turn, it interferes with the metabolism of sugars, lipids and proteins.[3]Praseodymium is a trace element whose biological effect has yet to be confirmed. It has been found in animal tissues, but its biological effect is unknown and yet to be confirmed.This situation indicates that the research on the function of trace elements in animals and the relationship between trace elements and health needs further development.[4]
Analytical method
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The detection technologies of rare earth alloys mainly include titrationInductively coupled plasma atomic emission spectrometry（ICP—AES）、X-ray fluorescence spectrometry(XRF), etc.XRF method has many analytical elements and wide concentration range (10-6~100%), high analysis accuracy, and widely used in the detection of various metal alloys.[6]
Photometric analysis
Photometric analysis of praseodymium mainly adopts conventional photometric method, direct photometric method and fluorescence photometric method.Conventional photometry is divided intoArsenazoIII, PBA, TBA, DBCA, CPA III, DBC-CPA, PAN, etc.The color reagents used in the photometric analysis of praseodymium are basically arsenazo and chlorophosphonazo.[5]
XRF
Main methods: The metal alloy was transformed into oxide form through the steps of "acid decomposition precipitation filtration ignition", and the content of La, Ce, Pr, Nd in the rare earth alloy was determined by X-ray fluorescence spectrometry after melting and sample preparation.
Specific steps: dissolve the lanthanum cerium praseodymium neodymium rare earth alloy sample with nitric acid, add ammonia to precipitate the substance to be measured, filter it with ashless filter paper, and the filter residue will be converted into oxide after burning.A method for the determination of La, Ce, Pr, Nd in La Ce Pr Nd rare earth alloys by wavelength dispersive X-ray fluorescence spectrometry was established by melting the burning residue with a mixed flux of lithium tetraborate and lithium metaborate.
Test results: The precision and accuracy of the method can meet the requirements of quality inspection.[6]
safety protection
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praseodymium[2]
Praseodymium has low toxicity, and safety protection shall be paid attention to when contacting it.[1]Pure praseodymium must be stored in mineral oil or sealed plastic.
matters needing attention
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Like other rare earth elements, praseodymium has chronic low toxicity and is not a necessary biological element.
