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general information

 

The ever-increasing awareness in the chemicals industry of the importance of environmental issues has resulted in an overall steady increase in the use of sodium polytungstate over recent years. We are absolutely sure that sodium polytungstate will completely replace the highly toxic, carcinogenic, chlorinated brominate hydrocarbons in the field of sink/swim analysis in future.

Sodium polytungstate – also known as sodium metatungstate – belongs to the group of so-called "non-phase-in" substances, which means that was sodium polytungstate has already been registered under the requirements of the German Law on Chemical Substances and in accordance with the EC Directive 67/548/EC.

Sodium polytungstate has therefore been subjected to all the necessary statutory test procedures, a summary of the certificates for which is contained under the ELINGS No. 412-770-9.

Sodium polytungstate has been registred under the EU's REACH regulations with following number 01-2120061128-61-0000.

Sodium polytungstate has already been tested using all the currently available methods for toxicity and eco-toxicity. The present state of knowledge about the effects of sodium polytungstate on humans, animals and the environment is sufficiently high for us to be able exclude the possibility of any risks to health arising from the proper use of this new type of heavy liquid.

This extensive series of tests has also demonstrated that sodium polytungstate may be classified as being non-toxic, which means that the use of the use of aqueous sodium polytungstate solution is set to increase even further across the whole world.

Furthermore, we should like to point out that another important benefit of aqueous sodium polytungstate is the fact that it may be reused. We will collect free of charge and for reuse any used sodium polytungstate solutions which are no longer required by customers, even if they have been diluted or contaminated.

On the following pages we shall describe the most important properties of sodium polytungstate and its aqueous solutions. We should also like to draw your attention to some interesting publications which describe its possible uses.

 

SODIUM POLYTUNGSTATE (CAS 12141-67-2, CAS 12333-13-0) is a compound, which has been successfully used in the manufacture of heavy liquids for a relatively short period. It has significant advantages when compared to the use of zinc chloride solution or the highly toxic halogenated carbons for sink/swim analysis.
     

formula:

 

formel1 or formel2

     

appearance:

 

White crystals or light yellow-green transparent solution

     

properties:

 

Very easily soluble in water, pH-neutral solution, maximum possible density of solution: 3,1 g/cm3 at 25° C

     

features:

 

non-toxic
non-flammable
odourless
reusable
density may be adjusted by dilution from ρ = 1,1 - 3,1 g/cm3
low viscosity
easy-to-use
sinks and floats may be easily cleaned with water after use
environmentally friendly

     

application:

 

The heavy liquid solution is prepared by dissolving sodium polytungstate in de-ionized water. Te resulting compound is a salt which is easily soluble in water. The maximum attainable density of the solution in water at room temperature is 3.1 g/cm3. Further chemical properties of the solution may be ascertained by studying the diagrams. These show density as a function of the sodium polytungstate content (Fig. 1) and viscosity as a function of density (Fig. 2). As may be seen from Fig. 2, viscosity increases only slightly with densities up to 2.5 g/cm3. This process also allows the fine granules to be separated. The use of a laboratory centrifuge will speed up the separation process.

     
    Dichte_Diagramm Fig. 1:
density of aqueous
sodium polytungstate
as a function of mass
concentration
     
    Visko_Diagramm Fig. 2:
viscosity of
aqueous sodium
polytungstate
solutions as a
function of density
     

structure:

 

This is a 12-fold aggregated isopolytungstate with a molar mass of 2986.12 g/Mol. The structure of polytungstate is modelled using octahedrons in which the oxygen ions are located in the corners and the tungsten ions in the middle of the octahedrons. When represented as a spherical model, the oxygen ions form a dense spherical shell while the tungstate ions fill the open spaces in the octahedra.
Because of this structure this substance may be considered a “true” metatungstate, represented structurally as formel1. It is known that in “true” metatungstates both of the oxygen ions are located in the central empty space of the polyanion and that they are unable to penetrate the external shell of the spherical casing.
Solid crystalline sodium polytungstate is not hygroscopic and may be stored for an unlimited period at room temperature.

     

notes:

 

The following points should be observed when using aqueous polytungstate solutions:

  1. Only distilled or de-ionized water should be used.
  2. All containers must be sealed properly after use.
  3. Only containers made from glass, synthetic materials or stainless steel should be used.
  4. Do not bring the solution into contact with reduced substances.
    The resultant blue colouring will not, however, affect the achievement of the required
    density in any way. Colour may be removed from the solution and a blue colouration
    prevented by the addition of a few drops of hydrogen peroxide.
  5. The Sinks and floats used should not contain any water soluble ions.
    Pb2+-, Ag+-, Sn2+- and Ba2+ - ions in particular form deposits which are difficult to dissolve.
    If these ions should be present in the samples these must be washed with hot water prior
    to the – sink/swim analysis.
     

analysis:

 

Solid sodium polytungstate contains at least 86 % ± 1 % WO₃.

The quantity of bound water in sodium polytungstate may vary slightly.

Typical analysis values (not guaranteed values) are:
Al ≤ 0.0015 %; As ≤ 0.012 %; Cu ≤ 0.001 %; Fe ≤ 0.005 %; Mo ≤ 0.005 %; Si ≤ 0.005 %; Ti ≤ 0.001 %.

     

form of supply:

 

A standard delivery of sodium polytungstate will be of a ready-to-use aqueous solution with a density of 2.82 ± 0.02 g/cm3 or with densities of ≥ 3.0 g/cm3 in 1 kg, 5 kg, 10 kg and 25 kg.

Sodium polytungstate may also, however, be supplied in crystalline form or as granules batches in batches of 1 kg, 5 kg, 10 kg and 25 kg.

relevant information:

Reagenzglas2

 

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