General information: Solid, crystalline sodium polytungstate is not hygroscopic and has an unlimited shelf life at room temperature.
Please note the following when using aqueous polytungstate solutions:
More information regarding the composition, properties, production and use of sodium polytungstate can be found below in our FAQ:
Product: SPT-0, SPT-1, SPT-2, SPT-3, SPT-5, SPT-R
|Substance type/trade name||Hexasodium tungstate hydrate|
|Main ingredient of the substance||Hexasodium tungstate hydrate|
|Physical state||Solid or liquid (aqueous solution)|
|Colour||White greenish solid or slightly yellow-greenish solution|
|Relevant identifiable uses||Aqueous solution acts as a heavy liquid (sink-float analysis)|
|Synonyms||Sodium metatungstate hydrate, sodium metatungstate, sodium polytungstate, SPT|
|CAS No.||12141-67-2, 12333-13-0|
|REACH registration no.||01-2120061128-61-0000|
|ph value||approx.. 3 at 20°C|
|Melting point/freezing point||cannot be determined (decomposition)|
|Initial boiling point and boiling range||not applicable (solid)|
|Flash point||not applicable|
|Flammability (solid, gas)||not applicable|
|Explosive limits||not relevant|
|Vapour pressure||not relevant|
|Relative density||5,47 g/cm³ at 20°C|
|Viscosity||approx. 60 mPa•s (solution with density 3.1 g/cm³)|
|Bulk density||approx. 1570 kg/m³|
|Solubility in water||> 1000 g/l at 20°C|
|Surface tension||73,4 mN/m at 20°C and 1254 mg/l|
|Partition coefficient n-Octanol/H2O||< -5,2 at 20°C|
|Auto-ignition temperature||not applicable|
The benefits of this heavy liquid solution are clear to see when sodium polytungstate is compared with organic heavy liquids and aqueous LST:
|Properties||Sodium polytungstate (SPT)||LST||Halogenated hydrocarbons|
|PropertiesBase||Sodium polytungstate (SPT)aqueous||LSTaqueous||Halogenated hydrocarbonsorganic|
|PropertiesSupply form||Sodium polytungstate (SPT)liquid & crystal||LSTliquid||Halogenated hydrocarbons–|
|PropertiesReusability||Sodium polytungstate (SPT)yes||LSTyes||Halogenated hydrocarbons–|
|PropertiesThermal stability (see also question below)||Sodium polytungstate (SPT)>100°C (liquid and solid)||LST>100°C||Halogenated hydrocarbons–|
|PropertiesToxicity||Sodium polytungstate (SPT)non-toxic||LSTnon-toxic||Halogenated hydrocarbonshighly toxic|
|PropertiesSolubility >20°C||Sodium polytungstate (SPT)very good||LSTvery good||Halogenated hydrocarbons–|
|PropertiesSolubility <15°C||Sodium polytungstate (SPT)very good||LSTcrystallisation||Halogenated hydrocarbons–|
|PropertiesCrystallisation temperature at density of 2,8g/cm³||Sodium polytungstate (SPT)< 0°C||LST< 16-18°C||Halogenated hydrocarbons–|
|PropertiesMaximum density at 25°C||Sodium polytungstate (SPT)3,08g/cm³||LST2,95g/cm³||Halogenated hydrocarbons–|
|PropertiesViscosity at density of 2.4 g/cm³||Sodium polytungstate (SPT)4cP||LST4cP||Halogenated hydrocarbons–|
|PropertiesViscosity at density of 2.8g/cm³||Sodium polytungstate (SPT)19cP solution prepared in minutes||LST10cP adjustment of high densities is time-consuming||Halogenated hydrocarbons–|
|PropertiesIn combination with tungsten carbide for high densities||Sodium polytungstate (SPT)very suitable||LSTless suitable||Halogenated hydrocarbons–|
|PropertiesIn combination with organic matters or humic-acid soils||Sodium polytungstate (SPT)partly inert||LSTsome reaction||Halogenated hydrocarbons–|
In order to produce a heavy liquid solution, the SPT (SPT-0, -1, -2) must be dissolved in de-ionised water (ultrasound bath optional). The higher the concentration, the higher the density (checked e.g. with a hydrometer). The maximum achievable density of an aqueous solution is 3.1 g/cm³ at room temperature. The density can be lowered by adding water, or increased by evaporating the solution in a beaker (preferably with a large surface) at 70°C in a drying chamber. The liquid must not be boiled! You can also add solid SPT to increase the density again.
Producing the solution in this way allows fine granules, particles or solids to be separated by density (sink-float process). A laboratory centrifuge accelerates the separation process.
Overview for production of an SPT solution (50 ml)
|Density p in g/cm³||SPT mass in g||H2O mass in g|
|Density p in g/cm³1,08||SPT mass in g5,00||H2O mass in g48,80|
|Density p in g/cm³1,15||SPT mass in g10,00||H2O mass in g47,66|
|Density p in g/cm³1,23||SPT mass in g15,08||H2O mass in g46,63|
|Density p in g/cm³1,32||SPT mass in g20,00||H2O mass in g45,87|
|Density p in g/cm³1,40||SPT mass in g25,02||H2O mass in g44,98|
|Density p in g/cm³1,56||SPT mass in g35,01||H2O mass in g42,94|
|Density p in g/cm³1,73||SPT mass in g45,15||H2O mass in g41,10|
|Density p in g/cm³1,88||SPT mass in g55,01||H2O mass in g38,93|
|Density p in g/cm³2,04||SPT mass in g65,17||H2O mass in g36,99|
|Density p in g/cm³2,19||SPT mass in g75,00||H2O mass in g34,68|
|Density p in g/cm³2,35||SPT mass in g85,00||H2O mass in g32,54|
|Density p in g/cm³2,50||SPT mass in g95,00||H2O mass in g30,10|
|Density p in g/cm³2,67||SPT mass in g105,01||H2O mass in g28,42|
|Density p in g/cm³2,82||SPT mass in g115,17||H2O mass in g25,92|
|Density p in g/cm³2,98||SPT mass in g125,12||H2O mass in g23,72|
|Density p in g/cm³3,10||SPT mass in g133,00||H2O mass in g22,00|
Density of aqueous sodium polytungstate solutions as a function of mass concentration
You can reduce the density of an SPT solution as required by adding de-ionised water.
This reduces the density as follows:
Initial solution: 500 ml solution SPT-3 with density of 3.00 g/cm³
|Addition of H2O in mL||Density ACTUAL|
|Addition of H2O in mL0||Density ACTUAL3,00|
|Addition of H2O in mL10||Density ACTUAL2,95|
|Addition of H2O in mL20||Density ACTUAL2,91|
|Addition of H2O in mL35||Density ACTUAL2,86|
|Addition of H2O in mL52||Density ACTUAL2,81|
|Addition of H2O in mL71||Density ACTUAL2,75|
|Addition of H2O in mL91||Density ACTUAL2,69|
|Addition of H2O in mL112||Density ACTUAL2,63|
|Addition of H2O in mL132||Density ACTUAL2,58|
|Addition of H2O in mL151||Density ACTUAL2,54|
|Addition of H2O in mL168||Density ACTUAL2,49|
|Addition of H2O in mL182||Density ACTUAL2,46|
|Addition of H2O in mL200||Density ACTUAL2,42|
|Addition of H2O in mL225||Density ACTUAL2,37|
|Addition of H2O in mL252||Density ACTUAL2,32|
|Addition of H2O in mL283||Density ACTUAL2,26|
|Addition of H2O in mL314||Density ACTUAL2,22|
|Addition of H2O in mL347||Density ACTUAL2,17|
|Addition of H2O in mL383||Density ACTUAL2,12|
|Addition of H2O in mL427||Density ACTUAL2,07|
|Addition of H2O in mL476||Density ACTUAL2,01|
|Addition of H2O in mL586||Density ACTUAL1,91|
|Addition of H2O in mL726||Density ACTUAL1,81|
|Addition of H2O in mL886||Density ACTUAL1,71|
|Addition of H2O in mL1096||Density ACTUAL1,62|
|Addition of H2O in mL1396||Density ACTUAL1,52|
Please notice that this table or better each cell is only valid for initial solution of 500 ml with density 3.0 g/cm³ because of an exponential dependence.
If you have reduced the density of the solution too much, you can increase it again by evaporating the solution in a beaker at 70°C in a drying chamber. The liquid must not be boiled!
Yes, a diluted SPT solution can be brought to boiling to drive out excess water and thus increase the density. The boiling point of SPT solutions is, as water, about 100°C. However, it is important to note that crystallization should be avoided when concentrating (initial skin formation on the boiling surface). This leads to a slight turbidity of the solution, which has no influence on the quality of the solution (except the optical properties). To avoid this we recommend not to exceed 70°C. At this temperature a SPT solution can also be completely and reversibly converted to a solid.
In general we recommend the use of a rotary evaporator at moderate temperatures.
Viscosity is shown in the following table and diagram as a function of density at 25°C. As seen in the figure, the viscosity only increases very slightly to a density of 2.5 g/cm³. This also allows separation within the fine grain range. The use of laboratory centrifuges can also accelerate the separation process here. If you need a very low viscosity please ask for LVP-3.
|Density ρ in g/cm³||Viscosity η in mPa•s|
|Density ρ in g/cm³1,08||Viscosity η in mPa•s0,99|
|Density ρ in g/cm³1,15||Viscosity η in mPa•s1,05|
|Density ρ in g/cm³1,23||Viscosity η in mPa•s1,13|
|Density ρ in g/cm³1,32||Viscosity η in mPa•s1,19|
|Density ρ in g/cm³1,40||Viscosity η in mPa•s1,29|
|Density ρ in g/cm³1,56||Viscosity η in mPa•s1,51|
|Density ρ in g/cm³1,73||Viscosity η in mPa•s1,83|
|Density ρ in g/cm³1,88||Viscosity η in mPa•s2,27|
|Density ρ in g/cm³2,04||Viscosity η in mPa•s2,90|
|Density ρ in g/cm³2,19||Viscosity η in mPa•s3,93|
|Density ρ in g/cm³2,35||Viscosity η in mPa•s5,15|
|Density ρ in g/cm³2,50||Viscosity η in mPa•s8,19|
|Density ρ in g/cm³2,67||Viscosity η in mPa•s12,18|
|Density ρ in g/cm³2,82||Viscosity η in mPa•s20,55|
|Density ρ in g/cm³2,98||Viscosity η in mPa•s36,65|
|Density ρ in g/cm³3,10||Viscosity η in mPa•s59,52|
Viscosity of aqueous sodium polytungstate solutions as a function of density at 25°C
The pH value of the solution depends on the density. A solution with a density of 3.0 g/cm³ typically has a pH between 2 and 3. The solution has long-term stability at this pH value (several years). Each SPT solution must therefore be stored at a pH between 2 and 3.
The pH value can short term (several hours) be changed e.g. to a pH of 7 by adding e.g. NaOH. After completion of the test at the increased pH value, the solution should generally be reduced again to a pH of 2 to 3 using e.g. a few drops of HCl. Please recheck next day.
It is a 12-fold aggregated isopolytungstate with a molar mass of 2986.12 g/Mol.
According to the models, polytungstate has a octahedral structure, in which oxygen ions are found in the corners and tungsten ions in the centre of the octahedra. As the spherical model shows, the oxygen ions form a very dense spherical shell, in which the tungsten ions are found in the open spaces of the octahedra.
The structure indicates that this compound is a “true” metatungstate with the formula
In a true metatungstate, the two hydrogen atoms are present in the central cavity of the polyanion, and cannot penetrate the spherical shell.
Solid sodium polytungstate contains at least 86% ± 1 % WO₃.
Bound water in the sodium polytungstate may vary very slightly.
Typical analysis results (no guaranteed values):
|RegulationDSL / NDSL||CountryCanada||Statusin process|
|RegulationKEIC / KECL||CountryKorea||Statusin process|
Our product SPT-3R is a recycled sodium polytungstate solution that we have reprocessed in a complex cleaning process. Ideally, customers collect their used SPT solutions and return them to us free of charge. We produce reusable solutions using multi-stage purification steps and offer these solutions at a lower price. SPT-3R solutions are ideally suited for simple sink-float analyses or for preparing suspensions and do not differ physically from original solutions, e.g. SPT-3. You can work with the recycled version as usual. As we depend on the return of used SPT solutions, availability is always limited. We also recommend not to dry SPT-3R solutions until they are solid. Likewise, SPT-3R is not suitable for elemental analyses or e.g. radiocarbon dating.
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