Other Useful Elements

Although only 17 elements are considered to be essential for plant nutrition at this time, many other elements are known to occur in plant tissues. Positive effects of some of these elements have been reported by numerous researchers. Whether any of these elements eventually will be discovered to be essential for plant grovTth remains to be seen. Current criteria for an ele- 

Another term, beneficial elements, has been proposed to describe some elements that appear to have specific functions in plant nutrition but do not meet all of the three criteria required for essentiality as described above. Two such elements (cobalt and silicon) will be discussed here. 

Cobalt is essential for animal nutrition, but it has not been established as essential for plant growth. Ruminant animals require cobalt for the synthesis of vitamin Bi2 by their rumen microflora. This was established about 1935, but an essential role of cobalt in plants was not demonstrated until 1960 [33]. Cobalt has been found to be essential for the growth of legumes which rely on symbiotic nitrogen fixation. 

Field responses to cobalt applications by subterranean clover were reported on sandy soils of South Australia and Western Australia. Later, it was shown that narrow-leafed lupins were even more sensitive to cobalt deficiency. Concentrations of cobalt are less than 1 ppmw in many plant tissues, which is even lower than those of molybdaium, a micronutrient. Cobalt application rates -alsG-arfrqtHte40WrIesS than-l-4f g/ha.-Although it is possible to prevent cobalt deficiency of livestock by applying cobalt-containing fertilizers to pastures, it may be more practical to supply the cobalt directly to animals in the form of a cobalt bullet given orally to youi animals in cobalt-deficdent areas 133]. 

Highly weathered soils in the tropics and volcanic soils generally contain the least silicon. Growth reductions 

---

So only the two-electron integrals with p > v, and X > a and [pv] > [Xa] need to be computed and stored. Dpv,Xa only appears in Gpv, and Gvp, whereas the original two-electron integrals contribute to other matrix elements as well. So it is much easier to form the Fock matrix by using the supermatrix D and modified density matrix P than the regular format of the two-electron integrals and standard density matrix. 

Plain Carbon and Low Alloy Steels. For the purposes herein plain carbon and low alloy steels include those containing up to 10% chromium and 1.5% molybdenum, plus small amounts of other alloying elements. These steels are generally cheaper and easier to fabricate than the more highly alloyed steels, and are the most widely used class of alloys within their serviceable temperature range. Figure 7 shows relaxation strengths of these steels and some nickel-base alloys at elevated temperatures (34). 

Other uses of oxyacetylene flames in mill operations are in building up or hardfacing metal, lancing (piercing a hole in a metal mass), and a variety of metal cleaning procedures. A minor but interesting fuel use of acetylene is in flame spectrophotometry where oxygen and nitrous oxide are used as oxidants in procedures for a wide variety of the elements. 

Niobium is important as an alloy addition in steels (see Steel). This use consumes over 90% of the niobium produced. Niobium is also vital as an alloying element in superalloys for aircraft turbine engines. Other uses, mainly in aerospace appHcations, take advantage of its heat resistance when alloyed singly or with groups of elements such as titanium, tirconium, hafnium, or tungsten. Niobium alloyed with titanium or with tin is also important in the superconductor industry (see High temperature alloys Refractories). 

Other Uses. Other uses include intermediate chemical products. Overall, these uses account for 15—20% of sulfur consumption, largely in the form of sulfuric acid but also some elemental sulfur that is used directly, as in mbber vulcanization. Sulfur is also converted to sulfur trioxide and thiosulfate for use in improving the efficiency of electrostatic precipitators and limestone/lime wet flue-gas desulfurization systems at power stations (68). These miscellaneous uses, especially those involving sulfuric acid, are intimately associated with practically all elements of the industrial and chemical complexes worldwide. 

In the tributyl phosphate extraction process developed at the Ames Laboratory, Iowa State University (46—48), a solution of tributyl phosphate (TBP) in heptane is used to extract zirconium preferentially from an acid solution (mixed hydrochloric—nitric or nitric acid) of zirconium and hafnium (45). Most other impurity elements remain with the hafnium in the aqueous acid layer. Zirconium recovered from the organic phase can be precipitated by neutralization without need for further purification. 

BeryUium aUoys ate usuaUy analyzed by optical emission or atomic absorption spectrophotometry. Low voltage spark emission spectrometry is used for the analysis of most copper-beryUium aUoys. Spectral interferences, other inter-element effects, metaUurgical effects, and sample inhomogeneity can degrade accuracy and precision and must be considered when constmcting a method (17). 

Limit Switches and Stem-Position Transmitters Travel-limit switches, position switches, and valve-position transmitters are devices that, when mounted on the valve, actuator, damper, louver, or other throtthng element, detect the component s relative position. The switches are used to operate alarms, signal hghts, relays, solenoid valves, or discrete inputs into the control system. The valve-position transmitter generates a 4-20-mA output that is proportional to the position of the valve. 

Processing and Recovery The functional element of processing and recoveiy includes all the techniques, equipment, and facilities used both to improve the efficiency of the other functional elements and to recover usable materials, conversion products, or energy from solid wastes. Materials that can be recycled are exported to facilities equipped to do so. Residues go to disposal. 

These eoatings are usually 75-500 pm thiek and sometimes have other minor element additions used to improve environmental resistanee sueh as Pt, Hf, Ta, and Zr. Carefully ehosen, these eoatings ean give very good performanee. 

Air monitoring will be required, e.g., when volatiles are handled in quantity, where use of radioaetive isotopes has led to unaeeeptable workplaee eontaiuination, when proeessing plutonium or other transuranie elements, when handling unsealed sourees in hospitals in therapeutie amounts, and in the use of hot eells/reaetors and eritieal faeilities. Routine monitoring of skin, notably the hands, may be required. 

Nitrogen makes up 78 % of the atmosphere, hence, it is readily available. Ammonia is produced by fixing of atmospheric nitrogen with hydrogen. Mineral sources of phosphorus and potassium are converted to a suitable form for fertilizer. These three elements have other use than fertilizer they are used and interact with other facets of the chemical industry, making a highly complex picture. A schematic of the interactions is presented in Figure 7.2-1. 

Other electropositive elements have been used (e.g. Li, Na, K, Be, Ca, Al, Fe), but the product is generally amorphous and contaminated with refractory impurities such as metal borides. Massive crystalline boron (96%) has been prepared by reacting BCI3 with zinc in a flow system at 900°C. 

As with other transition elements, the lanthanides can be induced to form complexes with exceptionally low coordination numbers by use of the very bulky ligand, N(SiMe3)2 ... 

---