Oxide content description

From time to time, I come by to see what people do with my mhchem package. [Here](https://chemistry.stackexchange.com/a/83499/24052), I came across a notation that I did not know yet: $\ce{K2O-nSiO2-xH2O}$ and $\ce{K2O - 3.2SiO2 - 2.7H2O}$


What is this? Is this really a bond? Is this a short form for writing $\ce{K2O-Si\_nO\_{2n}-H\_{2x}O\_x}$ and $\ce{K2O - Si\_{3.2}O\_{6.4} - H\_{5.4}O\_{2.7}}$? Is this an established notation that mhchem should support? (It doesn't yet with the numbers.) Do you have authoritative References?




The notation, upon replacing potassium with sodium, can refer to a water glass composition. The unique notation, in my opinion, is warranted based on the following comment from a paper1:



> 
> Despite of years of investigations, there are still questions about
> the molecular species configuration of these solutions that need to be
> answered to gain clarity over the best conditions for the various
> applications
> 
> 
> When adding sodium hydroxide ($\ce{NaOH}$) to a water glass, the ratio (molar
> or weight) $\ce{SiO2/Na2O}$ is decreased. This ratio is called water glass
> modulus (n) and determines various physical and chemical properties
> such as the pH and the viscosity of the solution.
> 
> 
> [...]
> 
> 
> the viscosity is extremely dependent on the modulus and increases as
> the solution becomes either more siliceous or more alkaline, i.e. at
> both higher and lower $\ce{SiO2/Na2O}$ molar ratios (n). Since the viscosity
> of such disperse systems like this is given by the silicate
> conformation i.e. extended chain conformation and the degree of
> polymerization
> 
> 
> [...]
> 
> 
> the degree of polymerization of the predominant silicate species in
> the alkali-solution [...]
> 
> 
> 


So we have apparently a weakly specified structure characterized by extended chain conformation and degrees of polymerization with its rather unique notation (seems right to me).


**Reference**


1. Helén Jansson, Diana Bernin, and Kerstin Ramser , "Silicate species of water glass and insights for alkali-activated green cement", AIP Advances 5, 067167 (**2015**), DOI: [10.1063/1.4923371](https://aip.scitation.org/doi/full/10.1063/1.4923371)


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