Yttrium elements

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions.  [c.441]

Lanthanides is the name given collectively to the fifteen elements, also called the elements, ranging from lanthanum. La, atomic number 57, to lutetium, Lu, atomic number 71. The rare earths comprise lanthanides, yttrium, Y, atomic number 39, and scandium. Sc, atomic number 21. The most abundant member of the rare earths is cerium, Ce, atomic number 58 (see Ceriumand cerium compounds).  [c.539]

High Temperature Corrosion. The rate of oxidation of magnesium adoys increases with time and temperature. Additions of berydium, cerium [7440-45-17, lanthanum [7439-91-0] or yttrium as adoying elements reduce the oxidation rate at elevated temperatures. Sulfur dioxide, ammonium fluoroborate [13826-83-0] as wed as sulfur hexafluoride inhibit oxidation at elevated temperatures.  [c.334]

Pressureless sintering of a- and P-SiC powders can also be achieved by the addition of aluminum and/or aluminum compounds together with carbon or rare-earth elements (95—105). Boron-free, aluminum-containing sintering aids inhibit grain growth (95,104). Aluminum oxide together with yttrium oxide as additives yield a fine and unique microstmcture (104). A Hquid-phase sintering mechanism has been reported in this aluminum oxide and rare-earth oxide-doped SiC system (104,106). Fine microstmcture, good chipping resistance, and over 800 MPa (116,000 psi) room temperature strength have been reported (97,104). Creep resistance and other high temperature related properties are not as good as the boron- and carbon-doped SiC, in general.  [c.466]

Yttrium and lanthanum are both obtained from lanthanide minerals and the method of extraction depends on the particular mineral involved. Digestions with hydrochloric acid, sulfuric acid, or caustic soda are all used to extract the mixture of metal salts. Prior to the Second World War the separation of these mixtures was effected by fractional crystallizations, sometimes numbered in their thousands. However, during the period 1940-45 the main interest in separating these elements was in order to purify and characterize them more fully. The realization that they are also major constituents of the products of nuclear fission effected a dramatic sharpening of interest in the USA. As a result, ion-exchange techniques were developed and, together with selective complexation and solvent extraction, these have now completely supplanted the older methods of separation (p. 1228). In cases where the free metals are required, reduction of the trifluorides with metallic calcium can be used.  [c.945]

Compared to later elements in their respective transition series, scandium, yttrium and lanthanum have rather poorly developed coordination chemistries and form weaker coordinate bonds, lanthanum generally being even less inclined to form strong coordinate bonds than scandium. This is reflected in the stability constants of a number of relevant 1 1 metal-edta complexes  [c.950]

The only on-line detector for TEM with moderate-to-high spatial resolution is the slow-scan CCD camera. A light-sensitive CCD chip is coupled to a scintillator screen consisting of plastic, an yttrium-aluminium garnet (Y AG) crystal, or phosphor powder. This scintillator layer deteriorates the original resolution of the CCD chip elements by scattermg light into neighbouring pixels. Typical sizes of chips at present are 1024 x 1024 or 2048 X 2048 pixels of (19-24 uu) the achievable dynamic range is about 10 grey levels.  [c.1632]

Ytterby, a village in Sweden near Vauxholm) Yttria, which is an earth containing yttrium, was discovered by Gadolin in 1794. Ytterby is the site of a quarry which yielded many unusual minerals containing rare earths and other elements. This small town, near Stockholm, bears the honor of giving names to erbium, terbium, and ytterbium as well as yttrium.  [c.73]

For organometailic compounds, the situation becomes even more complicated because the presence of elements such as platinum, iron, and copper introduces more complex isotopic patterns. In a very general sense, for inorganic chemistry, as atomic number increases, the number of isotopes occurring naturally for any one element can increase considerably. An element of small atomic number, lithium, has only two natural isotopes, but tin has ten, xenon has nine, and mercury has seven isotopes. This general phenomenon should be approached with caution because, for example, yttrium of atomic mass 89 is monoisotopic, and iridium has just two natural isotopes at masses 191 and 193. Nevertheless, the occurrence and variation in patterns of multi-isotopic elements often make their mass spectrometric identification easy, as depicted for the cases of dimethylmercury and dimethylplatinum in Figure 47.4.  [c.349]

Applications of rare-earth luminescence developed in the early 1960s, as these elements became available in industrial quantities at a high level of purity. Intense and quasi monochromatic emissions obtained from rare-earth activators diluted in appropriate matrices have been used in many applications since that time. Color television was among the first to use rare-earth-based phosphors (see Luminescent materials, phosphors). The use of europium-activated yttrium oxysulfide, Y202S Eu ", as the red component allowed a twofold increase in brightness compared to ZnS Ag. Although more expensive, Y202S Eu " has totally superseded ZnS Ag in commercial television sets (29). The outstanding performance of rare-earth-based phosphors is also utilized Hi a wide number of professional apphcations for cathode ray tubes, like monitors for computers, instmment panels in airplanes, or TV projection (30).  [c.547]

Structural Applications. Primary magnesium, like most metals, lacks sufficient strength in its elemental state to be used as a stmctural metal. Therefore, it must be alloyed with various other metals, such as aluminum, manganese, rare-earth metals, lithium, tin [7440-31 -5] 2inc, 2irconium, silver, and yttrium [7440-65-5] (90—94). The combined market for stmctural appHcations accounted for 17% of reported shipments in 1992 and includes die cast, gravity, and wrought products. The primary reason for selecting magnesium for stmctural components is its light weight. Having a specific gravity of 1.74, it is the world s lightest stmctural metal. Aluminum weighs 1.5 times mote 2inc weighs 4 times more and iron and steel weigh more than 4.5 times more on an equivalent volume basis.  [c.324]

Alloy Designations. Magnesium alloys ate most commonly designated by a system estabHshed by ASTM which covers both chemical compositions and tempers (97,98). Tempers are treatments which usually improve toughness. The designations are based on the chemical composition, and consist of two letters representing the two alloying elements specified in the greatest amount, arranged in decreasing percentages, or alphabetically if of equal percentage. The letters are foUowed by the respective percentages rounded off to whole numbers, with a serial letter at the end. The serial letter indicates some variation in composition. Experimental alloys have the letter X between the alloy and a serial number. The foUowing letters designate various alloying elements A, aluminum C, copper D, cadmium E, rare earths H, thorium K, 2irconium L, Hthium M, manganese Q, silver S, siHcon T, tin W, yttrium and Z, 2inc.  [c.324]

Two types of coatings have been used for superaHoys diffusion coatings, in which a layer of nickel, cobalt, platinum, or paHadium aluminide, ie, NiAl, CoAl, PtAl, or PdAl, is formed on the surface by diffusion and overlay coatings, in which a complex coating material such as nickel—cobalt—cbromium—aluminum —yttrium, NiCoCrAlY, is appHed to the surface. Pack cementation is the most widely used process for applying diffusion coatings to superaHoys, but bmshing, dipping into, or spraying a prepared mixture of the coating elements foHowed by high temperature heating is also used. Physical and vapor deposition, plasma spraying, and sputtering are often used for applying the overlay coatings. Pack cementation, fluidized-bed deposition, and spray or dip-and-sinter processes are used for the appHcation of sHicide and aluminide diffusion coatings to refractory metals (40,41).  [c.136]

Nickel—Chromium. Nickel and chromium form a soHd solution up to 30 wt % chromium. Chromium is added to nickel to enhance strength, corrosion resistance, oxidation, hot corrosion resistance, and electrical resistivity. In combination, these properties result in the nichrome-type alloys used as electrical furnace heating elements. The same alloys also provide the base for alloys and castings which can withstand hot corrosion in sulfur and oxidative environments, including those containing vanadium pentoxides which are by-products of petroleum combustion in fossil-fuel electric power plants and in aircraft jet engines. AHoy additions to nickel—chrome usually are ca 4 wt % aluminum and ca <1 wt% yttrium. Without these additions, the nichrome-type alloys provide hot oxidation or hot corrosion resistance through the formation of surface nickel—chromium oxides. Aluminum provides for surface AI2O2  [c.6]

Some nut trees accumulate mineral elements. Hickory nut is notable as an accumulator of aluminum compounds (30) the ash of its leaves contains up to 37.5% of AI2O2, compared with only 0.032% of aluminum oxide in the ash of the Fnglish walnut s autumn leaves. As an accumulator of rare-earth elements, hickory greatly exceeds all other plants their leaves show up to 2296 ppm of rare earths (scandium, yttrium, lanthanum, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). The amounts of rare-earth elements found in parts of the hickory nut are kernels, at 5 ppm shells, at 7 ppm and shucks, at 17 ppm. The kernel of the Bra2d nut contains large amounts of barium in an insoluble form when the nut is eaten, barium dissolves in the hydrochloric acid of the stomach.  [c.272]

Emulsions have been employed to produce spherical powders of mixed cation oxides, such as yttrium aluminum garnets (YAG), and many other systems (15). Sol—gel powder processes have also been appHed to fissile elements (16). Spray-formed sols of UO2 and UO2—PUO2 were formed as rigid gel spheres during passage through a column of heated Hquid. Abrasive grains based on sol—gel-derived mixed alumina are important commercial products (1). Powders for superconductors, eg, the YBaCuO system, and magnetic ceramics were also developed using the sol—gel technology (see Magnetic materials).  [c.249]

Allochromatic (other-colored) transition-metal compounds, iavolve small amounts of these same transition elements but ia the ligand field of the host lattice. Examples ia addition to the above discussed chromium-containing mby, emerald, and alexandrite ate red beryl containing manganese the iron-containing green or blue beryl aquamarine [1327-51 -1] and many brown and red iron-containing minerals such as sandstone and red iron ore the intense blue cobalt glass a green vanadium-containing form of emerald and purple neodymium-containing yttrium aluminum garnet YAG [12005-21 -9], Y2A1 022- Some of these, such as mby and Nd YAG, serve as the active media of optically pumped crystal lasers. The absorptions and fluorescence emissions from ligand field energy levels tend to be relatively narrow in crystals in glasses, where the disorder leads to a range of ligand fields, these absorptions and emissions ate much broader, as in the Nd glass used in lasers such as the NOVA thermonuclear fusion lasers. In the decolorizing of glass, the greenish color caused by iron impurities is removed by a dding MA 02 [1313-13-9]. This acts in two ways it reduces some of the green-producing Ee(II) to the yeUow-producing but weaker colorant Ee(III) while forming some Mn (III). This latter also produces a purple color since this is complementary to the green of Ee(II), it results in an inconspicuous very pale grey.  [c.419]

In accordance with spin-orbit coupling [4.93], higher energy levels are split, enabling additional transition processes. Thus, for the Ka radiation two individual Kaj and Kaz lines can be differentiated which are attributed to transitions from 2p3/z and 2pi/2 levels to the lsi/2 state, because A1 = 1 and Aj = 0, 1. In practice, because of an average energy resolution of approximately 130 eV of EDXS detectors this splitting of energy levels is only measurable for heavier elements, whereas WDXS can usually be used to resolve the individual sub-lines (Fig. 4.22). The Kai/Kaz line splitting amounts to approximately 2 eV for potassium (Z = 19), 75 eV for yttrium (2 = 39), and 1.815 keV for gold (2 = 79).  [c.195]

Scandium is very widely but thinly distributed and its only rich mineral is the rare thortveitite, Sc2Si20v (p. 348), found in Norway, but since scandium has only small-scale commercial use, and can be obtained as a byproduct in the extraction of other materials, this is not a critical problem. Yttrium and lanthanum are invariably associated with lanthanide elements, the former (Y) with the heavier or Yttrium group lanthanides in minerals such as xenotime, M "P04 and gadolinite, M M SijOio (M = Fe, Be), and the latter (La) with the lighter or cerium group lanthanides in minerals such as monazite, M P04 and bastnaesite, M C03F. This association of similar metals is a reflection of their ionic radii. While La is similar in size to the early lanthanides which immediately follow it in the periodic table, Y , because of the steady fall in ionic radius along the lanthanide series (p. 1234), is more akin to the later lanthanides.  [c.945]

Not least of the confusions associated with this group of elements is that of terminology. The name rare earth was originally used to describe almost any naturally occurring but unfamiliar oxide and even until about 1920 generally included both Th02 and Zr02. About that time the name began to be applied to the elements themselves rather than their oxides, and also to be restricted to that group of elements which could only be separated from each other with great difficulty. On the basis of their separability it was convenient to divide these elements into the cerium group or light earths (La to about Eu) and the yttrium group or heavy earths (Gd to Lu plus Y which, though much lighter than the others, has a comparable ionic radius and is  [c.1227]

To avoid this confusion, and because many of the elements are actually far from rare, the terms lanthanide , lanthanon and lanthanoid have been introduced. Even now, however, there is no general agreement about the position of La, i.e, whether the group is made up of the elements La to Lu or Ce to Lu. Throughout this chapter the term lanthanide and the general symbol, Ln, will be used to refer to the fourteen elements cerium to lutetium inclusive, the Group 3 elements, scandium, yttrium and lanthanum having already been dealt with in Chapter 20.  [c.1227]

The bulk of both monazite and bastnaesite is made up of Ce, La, Nd and Pr (in that order) but, whereas monazite typically contains around 5-10% Th02 and 3% yttrium earths, these and the heavy lanthanides are virtually absent in bastnaesite. Although thorium is only weakly radioactive it is contaminated with daughter elements such as Ra which are more active and therefore require careful handling during the processing of monazite. This is a complication not encountered in the processing of bastnaesite.  [c.1229]

See pages that mention the term Yttrium elements : [c.198]    [c.228]    [c.375]    [c.949]    [c.949]    [c.951]   
Chemistry of the elements (1998) -- [ c.0 ]