Thulium, abundance

The silver gray metal can be cut with a knife, although it only melts at 1545 °C (for comparison, iron 1538 °C). It is the rarest of the "rare earths", but is nevertheless more abundant than iodine, mercury, and silver. Thulium has few applications, especially because it is relatively expensive. The element occurs naturally as a single isotope, namely 169Tm (compare bismuth). The artificial, radioactive 170Tm is a transportable source of X-rays for testing materials. Occasionally used in laser optics and microwave technology. 

Thulium was discovered in 1879 by Cleve and named after Thule, the earliest name for Scandinavia. Its oxide thulia was isolated by James in 1911. Thulium is one of the least abundant lanthanide elements and is found in very small amounts with other rare earths. It occurs in the yttrium-rich minerals xenotime, euxenite, samarskite, gadolinite, loparite, fergusonite, and yttroparisite. Also, it occurs in trace quantities in minerals monazite and... 

Of the remaining elements such as holmium, erbium, thulium ytterbium and lutetium it is unfortunately true that their relatively low abundance coupled with high cost has tended to preclude their use in applications outside of the laboratory. 

Even more striking in the old tooth is the abundance of rare earths (dysprosium, holmium, erbium, thulium, ytterbium, and lutetium) and the elements tantalum, tungsten, gold, thorium, and uranium. Rare earth minerals are found in Scandinavia (in fact, many rare earth elements were discovered there), but what were they used for Did people prepare food with them Did they somehow get into the food chain ... 

Comparing the relative abundance of the rare earths and the other elements listed in Table 1, the rare earths are not so rare. Cerium, the most abundant of the rare-earth elements is roughly as abundant as tin thulium, the least abundant, is more common than cadmium or silver. Over 200... 

In general, Y and the heavier lanthanides, Gd to Lu, are less abundant than the lighter lanthanides. La to Eu. However, there are two further complicating factors one is that the elements with even atomic number are more abundant than those of odd atomic number, reflecting the greater stability of such nuclei. Secondly, some ores (e.g. bastnasite, monazite) are richer in the lighter metals while others (e.g. xenotime) have more of the heavier metals. The abundance of yttrium in the Earth s crust is 31 ppm while the total abundance of the lanthanides is some 180 ppm cerium is the most abundant (66 ppm), while thulium and lutetium are the rarest (0.5 and 0.8 ppm, respectively). 

Samarium is regarded as a relatively abundant lanthanoid. It occurs to the extent of about 4.5 to 7 parts per million in Earth s crust. That makes it about as common as boron and two other lanthanoids, thulium and gadolinium. 

Thulium is probably the rarest of the lanthanoid elements. Its abundance is estimated at about 0.2 to 1 part per million in Earth s crust. This still makes it more abundant than silver, platinum, mercury, and gold. 

Thulium is the least abundant of the naturally occurring rare earth elements, although it is believed to have a natural abundance similar to gold. 

The most common isotope of thulium is Tm, which has a natural abundance of 100 percent and is the only stable isotope. Other isotopes range from Tm to Tm and have half-lives ranging from 0.36 milliseconds ( Tm) to 1.92 years ( Tm). Examples of thuhum compounds include thulium iodide (Tmlj), thulium fluoride (TmFj), and thulium oxide (Tm203). 

Many elements such as tin, copper, zinc, lead, mercury, silver, platinum, antimony, arsenic, and gold, which are so essential to our needs and civilization, are among some of the rarest elements in the earth s crust. These are made available to us only by the processes of concentration in ore bodies. Some of the so-called rare-earth elements have been found to be much more plentiful than originally thought and are about as abundant as uranium, mercury, lead, or bismuth. The least abundant rare-earth or lanthanide element, thulium, is now believed to be more plentiful on earth than silver, cadmium, gold, or iodine, for example. Rubidium, the 16th most abundant element, is more plentiful than chlorine while its compounds are little known in chemistry and commerce. 

It would be a preferable situation if the demand for elements that are very abundant would control the REE market. Unfortunately, this is not the case. The most wanted elements at this time are neod3unium and dysprosium (Binnemans et al. 2013). Cerium, praseodymium, and the heavy REEs holmium, gadohnium, thulium, ytterbium and lutetium are produced in excess, and are stockpiled. 

Although these elements are some times referred to as the rare earth elements, they are, with the exception of man-made promethium (element 61), far from rare cerium is five times more abundant than lead, whereas thulium, the rarest stable lanthanide, is more abundant than iodine. 

The rare earth elements (lanthanum and the ensuing fourteen elements) proved very troublesome to isolate. The difficulties stemmed partly from the fact that these elements are so similar in properties (and occur together) that their separation was extraordinarily difficult. Tlie metals are also fairly reactive, and most were known for many years as the oxide (or earth) before they were successfully reduced to the metal. The term rare earth element is something of a misnomer, as the least abundant of the group, thulium, is as abundant as bismuth in the earth s crust and more common than arsenic, cadmium and mercury. 

Thus La and Ce are the most abundant rare earths while Lu and Tm are the most scarce. This leads us finally to the issue of the inappropriate nature of the term rare earth to describe these elements. In fact, the most abundant rare earth, Ce, has about the same abundance in the earth s crust as Cu (copper) and is more abundant than B (boron— a major constituent of all glass), Co (cobalt—a commonly used alloying agent in steelmaking). Ge (germanium— used to make the first transistor), Pb (lead—automobile batteries and gasoline), Sn (tin—as in cans), or U (uranium). Even Tm (thulium), the rarest of the rare earths, is more abundant than Cd (cadmium—a battery component), I (iodine—from the medicine chest), Hg (mercury—as in barometers and thermometers), and certainly Ag (silver), Au (gold), and Pt (platinum). 

The rare earth minerals are composed of scandium, yttrium, and the lanthanides. The lanthanides comprise a group of 15 elements that include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Cerium is the most abundant element in the rare earth group at 60 ppm, followed by yttrium at 33 ppm, lanthanum at 30 ppm, and neodymium at 28 ppm. Thulium and lutetium are the least abundant at 0.5 ppm. 

Besides triplet-triplet annihilation, a further process for achieving upconversion luminescence emission under continuous wave low-energy irradiation is based oti the use of lanthanide ions, most often erbium, holmium, and thulium (III) cations. In particular, a large variety of phosphors based on an inorganic host doped by lanthanide cations have been developed. The abundance of available states in these cations opens a large variety of paths for upconversion. As an example (Scheme 7.6), upconversion nanoparticles codoped with ytterbium and erbium cations exhibit a green emission due to the transitions from Hn/2 and respectively " Sn/2 excited states to the ground state as well as a red emission from the F9/2 state [10]. 

It surprises most people to learn that several of the so-called rare earth elements are not actually that rare compared to much more familiar elements. Neodymium, praseodymium, samarium, gadolinium, dysprosium, erbium, and ytterbium are all more abundant than more familiar elements like bromine, uranium, or tin. Europium, holmium, terbium, lutetium, and thulium are more abundant than iodine, silver, or mercury. Yet few people have even heard of most of the rare earths. The reason is that rare earths tend not to concentrate in large ore deposits in the way that better known metals do. Historically there have been fewer profits to be made from mining rare earth elements, and there have been fewer applications developed for them in industry. 

On the other hand, two presumptions are responsible for the late development of organometallic chemistry with lanthanoids and actinoids. One is that rare-earth metals implies sparsity and high expenses as impediments for the use of these metals. However, the element concentrations in the continental crust (Figure 6.1) show that these elements are certainly very seldom compared to iron (abundance 43 200 ppm) yet the rarest, uranium and thulium, are far more common than the precious metals, e.g. silver, platinum, or frequently used transition metals such as palladium, rhodium or iridium. 

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