XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
186
T1: P–53
Stabilization of kaolin suspensions with different sodium silicates
Piotr Izak
1
, Longin Ogłaza
2
, Włodzimierz Mozgawa
1
,
Joanna Mastalska-Popławska
1
, and Agata Stempkowska
3
1
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, 30-059
Krakow, Poland, e-mail: izak@agh.edu.pl
2
Rudniki S.A. Chemical Plant, 42-240 Rudniki by Częstochowa, Poland
3
AGH University of Science and Technology, Faculty of Mining and Geoengineering, 30-059
Krakow, Poland
Main purpose of the work was to explain the phenomena occurring during the stabilization of
ceramic slurries based on kaolin using aqueous sodium silicates (received with the same technology)
with the silicate moduli in the range of 1.74–3.25. Analysis of MIR (Fig. 1) and NMR spectroscopic
studies enabled to link stabilization mechanisms with the silicate structures occurring in different
aqueous sodium silicates. Based on rheological measurements, it was also determined which aqueous
sodium silicate possessed the best fluidization properties.
Fig.1. Comparison of ATR spectra of the selected aqueous sodium silicates.
Aqueous sodium silicates, depending on the silicate modulus, can form various structures that
have different fluidization properties of the ceramic slurries. Moreover, these properties depend on
the type of the alkali metal and the alkali concentration. The best stabilization results of the kaolin
slurries can be obtained by using aqueous sodium silicates of silicate moduli 2–2.5. Aqueous sodium
silicates of the moduli smaller than 2 precipitate free silica in the suspension and increase the
alkalinity of ceramic slurry while those larger than 2.5 create independent silicate micelles, co-
existing with the dispersed clay grains, what results in deterioration in the fluidization of the ceramic
suspension.
To test the effect of medium (water) on the formation of silicate structures in aqueous sodium
silicates, samples of sodium silicates with D
2
O were prepared (Mk=2.05–2.08). Rheological
calculation, i.a. work of the thixotropic structure destruction, confirmed that D
2
O, due to its structure,
produces stronger hydrogen bonds and reduces ion exchange than normal water. This leads to an
increase in the amount of silicate micelles with polymeric structures that form a separate dispersed
fraction (thixotropy index determined in the suspension in D
2
O for Mk= 2.08 was 1.05 and for
identical composition in H
2
O, 0.87).
These studies should be helpful in the design of new casting slurries used in the ceramic industry,
as well as in the understanding of the silicate fluidizers structure and the mechanisms of stabilization
of the ceramic slurries.
Keywords: aqueous sodium silicates; silicate modulus; kaolin clay
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
187
T1: P–54
Chemically bonded phosphate ceramics based on sodium silicates and
its derivatives
Joanna Mastalska-Popławska
1
, Matteo Pernechele
2
, Tom Troczynski
2
,
Piotr Izak
1
, and Zuzanna Góral
1
1
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, al.
Mickiewicza 30, 30-059 Krakow, Poland; e-mail: jmast@agh.edu.pl
2
University of British Columbia, Faculty of Applied Science, 309-6350 Stores Road, Vancouver V6T
1Z4, BC, Canada
The chemically bonded phosphate ceramic (CBPC) technology chemistry is based on acid-
base reaction between a supersaturated solution of sparsely soluble oxide or an oxide mineral,
for example calcined magnesium oxide (MgO) at a pH=10.4, and a solution of phosphoric acid
or an acid phosphate at a very low pH:
H
3
PO
4
+ MgO + 2 H
2
O → MgHPO
4
·3H
2
O
(1)
During formation of chemically bonded phosphate ceramics, in first step, acid phosphate is
dissolved or phosphoric acid is dissociated. Released hydrogen ions (H
+
) facilitates dissociation
of the oxide, for example:
MgO → Mg(aq)
2+
+ O
2–
(2)
The cations and anions in solution neutralize each other and new compound, for example
magnesium hydrogen phosphate (MgHPO
4
) is produced. Water ends up as the crystallization
water (bound water) and the reaction products form insoluble phosphate ceramic products [1, 2].
Based on the literature data, we chose one formulation in which silicate mineral, i.e. pure silica,
was replaced by sodium water glass with silicate modulus in the range of 1.74–3.25 or silica
obtained from filters residues enriched i.e. with iron oxide (Fe
2
O
3
) and silicon carbide (SiC).
Additionally, some fire retardants, such as aluminum hydroxide (Al(OH)
3
·nH
2
O), and sodium
phosphate dibasic (Na
2
HPO
4
), were added to the samples.
Morphology analysis of the SEM microphotographs (Fig. 1) for the sample with aluminum
hydroxide and sodium water glass with the silicate modulus Mk=2.5 revealed the presence of
glassy phase with white inclusions which in this case may be aluminates derivatives or
aluminum phosphates [3, 4]. MIR and XRD studies confirmed these suppositions.
Fig. 1. SEM microphotographs of the sample containing aluminum hydroxide
and sodium water glass with the silicate modulus Mk=2.5.
Keywords: CBPC; silicate modulus; sodium water glass.
References
[1] A.S. Wagh, Recent Progress in Chemically Bonded Phosphate Ceramics, ISRN Ceramics 1 (2013) 1.
[2] A. J. Rao. K. R. Pagilla, A. S. Wagh, J. Air Waste Manage. 50 (2000) 1623.
[3] D. dos Santos Tavares, L. de Oliveira Castro, G. D. de Almeida Soares, G. Gomes Alves, G. M.
Granjeiro, J. Appl. Oral Sci. 21 (2013) 37.
[4] J. Płaska, Synthesis and properties of the selected titanium phosphates and titanates, PhD Thesis ZUT
Szczecin (2010) (in Polish).
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