Tungsten blue

Tungsten alloy machine chips, 25 371 Tungsten blues, 25 381 Tungsten borides, 25 386 Tungsten bromide... 

For a number of years, phenolic substances were dosed by colorimetric techniques, based on redox reactions usually known as Folin Ciocalteau methods, even if a number of adjustments were developed to fit different matrix characteristics. The Folin Cioalteau reagent is a mixture of phosphomolybdic and phosphotingstic acids, with molybdenum in the 6+ oxidation state and, when the reaction takes place, it is reduced to form a complex called molybdenum blue and tungsten blue. In this complex, the mean oxidation state is between 5 and 6 and the formed complex is blue so it can be read spectrophotometrically at 750 nm. 

Zinc and hydrochloric acid If a solution of a tungstate is treated with hydrochloric acid and then a little zinc added, a blue colouration or precipitate is produced. The product is called tungsten blue and has a composition near to the formula W205. 

The spot-test technique is as follows. Mix 1-2 drops of the test solution with 3-5 drops of the tin(II) chloride reagent on a spot plate. A blue precipitate or colouration of tungsten blue W2Os. 

SYNS C.I. 77901 TUNGSTEN BLUE TUNGSTEN TRIOXIDE TUNGSTIC ANHYDRIDE TUNGSTIC OXIDE WOLFRAMITE... 

A comprehensive review of spectrophotometric methods for the determination of ascorbic acid (1) was presented. Most of the methods are based on the reducing action of ascorbic acid, making use of an Fe(III)-Fe(II) redox system, and to a lesser extent Cu(II)-Cu(I), V(V)-V(IV) and phosphomolybdate/phosphotungstate-molybdenum/tungsten blue redox systems. A kinetic spectrophotometric method for the determination of L-ascorbic acid and thiols (RSH) was developed, whereby the absorbance of the Fe(II)-phen complex formed during the reaction of 1 or RSH with Fe(III)-phen was continuously measured at 510 nm by a double beam spectrophotometer equipped with a flow cell. The linearity range for 1 was 4-40 p,M and for RSH 8-80 xM. The method was validated for pharmaceutical dosage forms . 

These methods are based on the development of a blue reaction (tungsten blue) as PTA is reduced by urate in an... 

Hornung D. and Krivan V. (1999) Solid sampling electrothermal atomic absorption spectrometry for analysis of high-purity tungsten trioxide and high-purity tungsten blue oxide, Spectrochim Acta, Part B 54 1177— 1191. 

The effect of the addition of 0.1 mol of alkali metal to tungsten blue oxide is shown in Table 3.1. It can be seen that the influence in grain growth is considerable. Moreover, there are differences between the different metals which are mainly based on the properties of the metal. At the end of the reduction process the respective alkali tungstate is reduced and at 1000 °C the metal is evaporated. The vapor piessiue of Li is the lowest of the three metals and therefore the amount remaining is the highest. 

CS structures have the ability to build-in foreign metal ions, especially in the reduced form. This seems to play an important role in the dopant uptake of tungsten blue oxide in non-sag tungsten production (for more information see Section 5.4.5). 

With the exception of the lowest x and y. (NH4)q,06WO3-(H20)o.n> which is tetragonal, they belong to the hexagonal system. The dominance of the hexagonal symmetry can be understood as a consequence of the large size of the ammonium ion. They are partially contained in the industrial tungsten blue oxide, especially at low APT decomposition temperatures or short exposure times. 

In hydrogen tungsten bronzes x values between 0.03 and 0.53 and y values from 0.015 to 0.3 can be found. They have quite different structures (tetragonal, orthorhombic, monocline, hexagonal, and cubic) and can also be detected in tungsten blue oxides. 

As precursor for the W and WC powder production, WO3 lost its importance mainly to tungsten blue oxide. WO3 is also used as a yellow pigment. 

The common starting materials are tungsten trioxide (WO3) and tungsten blue oxide (W03 t), the latter being the most widely used material. Tungstic acid (H2WO4) is used only for selected metal grades. 

TUngsten blue oxide is treated with aqueous solutions of the respective element compounds. 

Production. The classical method is to mix Re and W powders in the desired ratio prior to compaction and sintering. In order to achieve a more even W-Re distribution, restricting the danger of local a-phase formation, mixtures of tungstic acid or tungsten trioxide or tungsten blue oxide with ammonium perrhenate can be used as raw materials. These mixtures are co-reduced by hydrogen to metal powder. 

FIGURE 6.4. From tungsten blue oxide to non-sag wire (schematic presentation). 

---