Cobalt-rare earth compounds

As has been alluded to above, the catalysts are extensively transformed when exposed to a mixture of CO and H2 at T > / 225°C. This transformation was first noted by Takeshita, Wallace, and Craig (14) in the use of these materials as synthetic ammonia catalysts. RCo. and RFca, intermetallics were converted into iron or cobalt rare earth nitride. This was established by conventional x-ray diffraction measurements. Coon (16) observed that the RNis compounds were transformed by the CO/H2 mixture into R2O3 and Ni, and a similar transformation also was observed by Elattar et al. (17) for ThNis, UNis, and ZrNis. SEM and EDAX results on ThNis show the formation of nickel nodules 0.5 /un in diameter situated on a Th02 substrate. 

In addition to the Kirchmayr-Poldy review, additional information concerning the magnetic behaviors of rare earth compounds are found in the reviews by Buschow (1977, 1979), Nesbitt and Wernick (1973), Taylor and Darby (1972) and Wallace (1973). The review by Nesbitt and Wernick is exclusively on rare-earth-cobalt permanent magnets, while the others generally cover a wide range of compounds. 

Thermodynamics and Kinetics of Hydrogen Absorption in Rare Earth-Cobalt (R2C07 and RC03) and Rare Earth-Iron (RFes) Compounds... 

GOUDY ET al. Rare Earth-Cobalt and -Iron Compounds... 

The intermetallic compounds were prepared from the best grade of metals commercially obtainable. The rare earth metals, obtained from Research Chemicals, Inc., were 99.9% pure, and cobalt and nickel, obtained from the United Mineral Corp., were 99.999% pure. After each element was weighed to obtain the correct stoichiometric amounts, the compounds were formed by induction melting in a water-cooled copper boat under an argon atmosphere, purified by passage through a titanium-gettering furnace. 

Assay of beryllium metal and beryllium compounds is usually accomplished by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryllium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryllium content of the sample is calculated from the titration volume. Standards containing known beryllium concentrations must be analyzed along with the samples, as complexation of beryllium by fluoride is not quantitative. Titration rate and hold times are critical therefore use of an automatic titrator is recommended. Other fluoride-complexing elements such as aluminum, silicon, zirconium, hafnium, uranium, thorium, and rare earth elements must be absent, or must be corrected for if present in small amounts. Copper—beryllium and nickel—beryllium alloys can be analyzed by titration if the beryllium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

Among the rare-earths, samarium is the most commonly used because it provides the best permanent-magnet property. Other rare-earth elements are sometimes employed in combination with samarium to meet special requirements. The compounds SmCos and Sm2Coi7 are the most important magnetic materials among the cobalt-lanthanide alloys. 

C. The Rare Earth-Cobalt Compounds 1. TheRCo2 Series... 

---