Similarity to hafnium

Rutherfordium is chemically similar to hafnium, the element above it in the same subgroup. The element has no commercial application. 

Element 103, lawrencium, completes the actinides. Following this series, the transition elements should continue with the filling of the 6d orbitals. There is evidence for an element 104 (eka-hafnium) it is believed to form a chloride MCl4, similar to that of hafnium. Less positive evidence exists for elements 105 and 106 attempts (so far unsuccessful) have been made to synthesise element 114 (eka-lead). because on theoretical grounds the nucleus of this elemeni may be stable to decay by spontaneous fusion (as indeed is lead). Super-... 

Element 104, the first transactinide element, is expected to have chemical properties similar to those of hafnium. It would, for example, form a relatively volatile compound with chlorine (a tetrachloride). 

Study of the chemical properties of element 104 has confirmed that it is indeed homologous to hafnium as demanded by its position in the Periodic Table (20). Chemical studies have been made for element 105, showing some similarity to tantalum (25) no chemical studies have been made for elements 106—109. Such studies are very difficult because the longest-Hved isotope of 104 ( 104) has a half-Hfe of only about 1 min, of 105 ( 105) a half-Hfe of about 40 s, of 106 ( 106) a half-Hfe of about 1 s, and of elements 107—109 half-Hves in the range of milliseconds. 

Hafnium tetrabromide [13777-22-5], HfBr, is very similar to the tetrachloride in both its physical and chemical properties. Hafnium tetraiodide [13777-23-6], Hfl, is produced by reaction of iodine with hafnium metal at 300°C or higher. At temperatures above 1200°C, the iodide dissociates to hafnium metal and iodine. These two reactions are the basis for the iodide-bar refining process. Hafnium iodide is reported to have three stable crystalline forms at 263—405°C (60). 

Thenoyltrifluoroacetone(TTA), C4H3S,CO,CH2,COCF3. This is a crystalline solid, m.p. 43 °C it is, of course, a /1-diketone, and the trifluoromethyl group increases the acidity of the enol form so that extractions at low pH values are feasible. The reactivity of TTA is similar to that of acetylacetone it is generally used as a 0.1-0.5 M solution in benzene or toluene. The difference in extraction behaviour of hafnium and zirconium, and also among lanthanides and actinides, is especially noteworthy. 

In view of Thompson s results on the carrying of Pu+I by bismuth phosphate, Cunningham and Werner made an immediate test today to see whether it is carried at a ratio of Bi+3 Pu+1 of about 100 1. Their results indicate that under conditions similar to those of Thompson s experiment, the Pu+I> is carried to the extent of 98%. This was fast work and illustrates the pace at which our group is now working. They also made a test of the carrying of Pu+I> by hafnium phosphate at a ratio of Hf Pu of 100 1 and they find that about 90% of the Pu is carried. 

Chemical Resistance. Hafnium carbide oxidizes in air at 500°C. It is not as chemically resistant as TiC and is similar to ZrC in that respect. 

This belongs to the second series of the transition metals. So far as reactivity is concerned, this series is very similar to the first and especially the third. Thus, zirconium and hafnium are so similar that it is very difficult to separate them (except for nuclear purposes where the presence of the second is harmful). The same goes for tantalum and niobium. There are two main differences between the three series within each group. 

The volatilities of both zirconium tetrachloride and hafnium tetrachloride are very similar to each other at normal operating temperatures, and their separation by a simple distillation or fractional distillation operation is not viable. However, when the mixed chloride vapor is contacted with an eutectic molten salt mixture of aluminum chloride and potassium chloride, zirconium chloride is preferentially absorbed. The vapor pressure difference between zirconium and hafnium tetrachlorides is greatly enhanced over the molten... 

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

Hafnium-centered Lewis acid usage is limited in organic chemistry, because of its lower availability and its similarity to zirconium. There are some reactions, however, for which HfIV compounds are used as effective activators. Glycosylation of glycosyl fluorides using a combination... 

Hafnium is a ductile metal that looks and feels much hke stainless steel, but it is significantly heavier than steel. When freshly cut, metallic hafnium has a bright silvery shine. When the fresh surface is exposed to air, it rapidly forms a protective oxidized coating on its surface. Therefore, once oxidized, hafnium resists corrosion, as do most transition metals, when exposed to the air. Chemically and physically, hafnium is very similar to zirconium, which is located just above it in group 4 on the periodic table. In fact, they are so similar that it is almost impossible to secure a pure sample of either one without a small percentage of the other. Each will contain a small amount of the other metal after final refining. 

Bohr s theory received a striking confirmation when the element hafnium was discovered at his institute in 1923. During the early 1920s most chemists believed that element 72 would turn out to be a rare earth. But Bohr s theory implied that this element should have four electrons in its outermost shell, not three as the rare earths did. It should therefore have properties similar to those of the element zirconium. 

The chemical properties of hafnium are very much similar to those of zirconium. In aqueous solutions, the metal exists in tetravalent state. The elec-... 

Hafnium had lain hidden for untold centuries, not because of its rarity but because of its dose similarity to zirconium (16), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, C. F. Rammelsberg, A. E. Nordenskjold, J.-C. G. de Marignac, and other experts on the chemistry of zirconium, he found that they contained from 1 to 5 per cent of the new element (26, 27). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (24, 28). Some of the minerals were of nepheline syenitic and some of granitic origin (20). Hafnium and zirconium are so closely related chemically and so closely associated in the mineral realm that their separation is even more difficult than that of niobium (columbium) and tantalum (29). The ratio of hafnium to zirconium is not the same in all minerals. 

As with the Sm- Nd and Re- Os systems, careful chemistry is required to cleanly separate the parent and daughter elements because mass spectrometry cannot resolve 176Lu from 176Hf. The ion-exchange chemistry is similar to that for samarium-neodymium. In fact, fractions of samarium, neodymium, lutetium and hafnium are often produced in a single procedure. Mass spectrometry is done by ICPMS because this is the only method that effectively ionizes hafnium. 

In the lower oxidation states the chemistry of titanium has little or no counterpart in the chemistries of the group IVB elements. The only lower oxidation state of these elements is two, for which the stability order is Ge < Sn < Pb. However,, both zirconium(III) and hafnium(III) are similar to if less stable (towards oxidation) than titanium(III) and have comparable although less extensively investigated chemistries. 

Zirconium and hafnium are two refractory elements which are closely, related to titanium (see Encycl Vol 9, T227-R) but which in addition to having desirable corrosion resistance and mechanical properties, have many significant ordnance applications. Hf free Zr moreover is possessed of a low neutron capture crossection, and is therefore of value as a reactor material. In as much as Hf is chemically similar to Zr and as in nature it is always found in association with Zr, it will be discussed as part of the Zr technology, except where its special properties... 

The typical display of the inner transition metals. The count of elements in the sixth period goes from lanthanum (La, 57) to cerium (Ce, 58) on through to lutetium (Lu, 71) and then back to hafnium (Hf, 72). A similar jump is made in the seventh period. 

In view of the fact that no hafnium is present in the unhydrolyzed form under any of the conditions given in Table II, the ion exchange mechanism of adsorption by glass may be disregarded. This is substantiated by the fact that a different treatment of the glass had no effect upon its adsorption capacity for hafnium. This is similar to the results of Starik and Rozovskaya who found small effects upon the adsorptivity of hydrolyzed ions caused by glass modification even when drastic treatment... 

Table IV lists specific examples of compounds related through this form of dimensional reduction, By far, the majority of these are zirconium chloride and iodide phases, in which case lower main group and even transition metals have been found to incorporate as interstitial atoms. A few analogues are known with hafnium (135), and very recently it has been shown that nitrogen can be substituted for carbon in tungsten chloride clusters adopting the centered trigonal-prismatic geometry (see Fig. 2) (32). It is hoped that a variability similar to that exposed for the octahedral zirconium clusters will be attainable for such trigonal-prismatic cluster phases.

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