Tungsten determination

OPTIMIZATION OF THE METHOD FOR TUNGSTEN DETERMINATION IN STEELS AND ALLOYS BY INDUCTIVELY... 

The simple analytieal proeedure of tungsten determination in high alloy steel and niekel base alloys by atomie emission speetrometry with induetively eoupled plasma (AES-ICP) was developed. Proposed teehnique ineludes the dissolution of 0.1-0.5 g of material in mixed aeids (25 ml HCl, 3 ml HNO, 5 ml HF), eomplexation of tungsten by 9 % solution of oxalie aeid and measurement of tungsten emission intensity (k = 207.911 nm). 

A simple ealibration eurve based on distilled water is suitable for tungsten determination (linearity range is 1-50 mg/dm of W), no interferenee from Fe, Co, Cr, Ni was found. The aeeuraey of the method is eonfirmedby analysis of eertified referenee materials of high alloy steels and niekel based alloys (in range of 0.3 to 15 % W). The analyzed values are agreeing well with the eertified values. 

Results of the tungsten determination in Russian referenee materials of steels and alloys by the proposed AES-ICP proeedure n = 16)... 

Melting temperatures for gold clusters supported on tungsten determined in this way are plotted in Figure 4 as a function of cluster size. The melting temperatures are... 

The electron sources used in most sems are thermionic sources in which electrons are emitted from very hot filaments made of either tungsten (W) or lanthanum boride (LaB ). W sources are typically heated to ca 2500—3000 K in order to achieve an adequate electron brightness. LaB sources require lower temperatures to achieve the same brightness, although they need a better vacuum than W sources. Once created, these primary electrons are accelerated to some desired energy with an energy spread (which ultimately determines lateral resolution) on the order of ca 1.5 eV. 

Permissible Exposure Limits in Air. Occupational exposure to insoluble tungsten needs to be controlled so that employees are not exposed to insoluble tungsten at a concentration greater than 5 mg tungsten/m air, determined as a TWA concentration for up to a 10-h workshift in a 40-h workweek. An STEL value of 10 mg/m has been set by ACGIH in 1983. 

The hardness of carbides can only be deterrnined by micro methods because of britdeness, the usual macro tests caimot be used. Neither can the extremely high melting points of the carbides be readily deterrnined by the usual methods. In the so-called Priani hole method, a small hoUow rod is placed between two electrodes and heated by direct current until a Hquid drop appears in the cavity. The temperature is determined pyrometricaHy. When high temperature tungsten tube furnaces are used, the melting point can readily be estimated by the Seger-type cone method. The sample may also be fused in a KroU arc furnace and the solidification temperature determined. 

In order to determine the concentration of molybdenum (VI), tungsten (VI) and vanadium (V) the reagents of triphenylmethane series, in particular brompyrogallolic red (BPR) and pyrogallolic red (PR) are widely used. 

The molybdenum, tungsten and tantalum concentration influence on LCD nickel-ferrous HRS resistance, used for gas turbine installations parts is investigated. The tests were carried out on modeling compositions. Samples were molded on the basis of an alloy of the ZMI-3C. The concentration of tantalum varied from 0 up to 5% with a step of 0,5%. The contents of elements were determined by a spectral method. 

Determination of tungsten as the trioxide (tannic acid-phenazone method) Discussion. Tungstic acid is incompletely precipitated from solutions of tungstates by tannic acid. If, however, phenazone (2,3-dimethyl-l-phenyl-5-pyrazolone) is added to the cold solution after treatment with excess of tannic acid, precipitation is quantitative. This process effects a separation from aluminium, and also from iron, chromium, manganese, zinc, cobalt, and nickel if a double precipitation is used. 

There are ways of coping with these interferences. Pulse-height selection (2.13) is a direct method. As we shall see in Chapter 7, a particularly bad case, the determination of tungsten in aqueous solution with scattered target line and the identical line from the sample superimposed, could be handled successfully by properly correcting the background. 

The following experimental details apply both to the determination of tungsten with bromine as internal standard, and to the experiments of Table 7-2. The solutions filled a 3-ml container made by sectioning a 10-ml beaker. To prevent" evaporation and to maintain a fixed distance between x-ray tube window and sample surface, the beaker-section was covered with Mylar film, 0.0025 cm thick, placed in a plastic sample holder and pressed firmly against the sample drawer. The Mylar film attenuated the x-rays uniformly enough so as not to affect the precision of the results. 

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