Cerium physical properties, 1003

In bulk form cerium is a reactive metal that has a high affinity for oxygen and sulfur. It has a face centered cubic crystal stmcture, mp 798°C, bp 3443°C, density 6.77 g/mL, and a metallic radius of 182 pm. Detailed chemical and physical property information can be found in the Hterature (1,2). 

These same researchers also explored the efficacy of the individual rare earths as nodulizers (17). They concluded, by their ability to produce nodular iron having adequate physical properties without excessive iron carbides present, that cerium was the most effective of the four rare earth elements (lanthanum-neodymium) evaluated as nodulizers. They reported that it required 1.5 times as much neodymiun or praseodymium and three times as much lanthanum as cerium to yield equivalent results. 

Further, it was demonstrated that the introduction of cerium, as mischmetal, in proper amounts was effective in eliminating iron carbides which cause deterioration in physical properties (21). The elimination of iron carbides in thin sections by proper use of the rare earths represents a major contribution to the industry. Different researchers have agreed that there is an optimum percentage for this rare earths addition, which they reported as cerium only, from 0.01% to 0.02% cerium (from about 0.02% to 0.04% total rare earths) that provides this increase in nodule count and control of iron carbides when used in conjunction with magnesium nodulizers (see Figure 9). 

Designing a catalyst for effective removal of SOx (S02 + S03) in a fluid catalyst cracking unit regenerator is a challenging problem. One must come up with a particle having physical properties similar to FCC catalysts which will 1) oxidize S02 to S03, 2) chemisorb the S03/ and 3) be able to release it as H2S as it enters the reactor side of the unit. A cerium containing magnesium aluminate spinel was found to be very effective for this purpose (1). The preparation methods and characterization techniques utilized for this spinel catalyst and how the SOx abatement activity of this catalyst is related to the preparative route used are discussed in this paper. 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

The high affinity of cerium for oxygen and sulfur underlies the use of cerium-containing ferro-alloys to improve the physical properties of highstrength low-alloy (HSLA) steels [34]. 

The characteristic valency of the elements is 3, but a few of them can function in other capacities they then show marked differences in the physical properties of their derivatives and can often be separated very completely from their congeners in this way. For example, oxidation of cerous (trivalent) compounds to ceric (tetravalent) enables cerium to be separated. It yields, for example, beautiful orange crystals of ceric ammonium nitrate,... 

Kubsch, J.E., J.S. Rieck and N.D. Spencer, 1991, Cerium oxide stabilization physical property and three-way activity considerations, in Catalysis and Automotive Pollution Control II, ed. A. Crucg (Elsevier, Amsterdam) pp. 125-138. 

Due to the recent discoveries of the rare-earth elements, most of their chemical and physical properties were stUl shrouded in mist at the beginning of 1869, and Mendeleev had to manage with the limited information he had at his disposal. At the time, Mendeleev stUl adhered to the old Berzelian atomic weights for the rare-earth elements. Not one of these values corresponded to the real atomic weights however, as they were based on the erroneous assumption that most rare-earth elements were bivalent instead of trivalent Their oxides were thus represented by the formula RO (with the higher oxide of cerium denoted as R2O3). 

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