The effect of SiO2 Al2O3 ratio on the structure and microstructure of the glazes from glaze system

The effect of SiO 2/Al 2O 3ratio on the structure and microstructure of the glazes from SiO

–Al O –CaO–MgO–Na O–K O system q

Janusz Partyka a AGH University of Science b

AGH University of Science Poland

leads to dominance of Si A O A Al and Si A O A Si bands.

With the lowest molar ratio crystals of gahnite occurs –other glazes are amorphous.

a r t i c l e i n f o Article history:

Received 30December 2013

Received in revised form 15May 2014Accepted 9June 2014

Available online 3July 2014Keywords:Ceramic glaze Structure

Phase composition FTIR analysis

a b s t r a c t

Ceramic glazes are commonly used to covering of the facing surface of ceramics ware.A well-chosen oxide composition and ?ring conditions of glazes causes signi?cant improvement of technical parameters of ceramic products.Modern glazes are classi?ed as glass–ceramic composites with different crystalline phases arising during ?ring.The presence of crystals in the glass matrix is in?uenced by many factors,especially by oxides molar composition.A crucial role is played by the molar ratio of SiO 2/Al 2O 3.In this work the six composition of glazes from SiO 2–Al 2O 3–CaO–MgO–Na 2O–K 2O system were examined.The only variable is the ratio of the silicon oxideto alumina at a constant content of other components:MgO,CaO,K 2O,Na 2O,ZnO.In order to determine the real phase composition of the obtained glazes research

on ?uorescence spectrometer (XRF)were done.For structural studies X-ray diffraction (XRD)and spectroscopic in the middle infrared (MIR)were performed.In order to determine the state of the surface (microstructure)research on the scanning electron microscope (SEM)

with EDX.The research allowed to determine the in?uence of SiO 2/Al 2O 3ratio on the structure and phase composition of glazes and the nature,and type of formed crystalline phases.

ó2014Elsevier B.V.All rights reserved.

Introduction

Glazes are complex mixtures of various oxides systems,each of which affects the resulting properties of the vitreous coating on the surface of ceramic.Adequate selection determines compliance of the ?nal properties with expected ones due to the destiny of prod-ucts.Oxides included in the glaze can be divided into three groups:

https://www.360docs.net/doc/733919074.html,/10.1016/j.saa.2014.06.068

1386-1425/ó2014Elsevier B.V.All rights reserved.

q

Selected paper presented at XIIth International Conference on Molecular

spectroscopy Kraków –Bia?ka Tatrzan

′ska,Poland,September 8–12,2013.?Corresponding author.Address:Faculty of Material Science and Ceramics,Department of Ceramics and Refractories,AGH University of Science and Technol-ogy,Krakow,Poland.Tel.:+48126173654;fax:+48126331593.

E-mail address:partyka@https://www.360docs.net/doc/733919074.html,.pl (J.Partyka).

Glass-forming oxides–forming a glass framework,having a similar importance as the crystal lattice.The most commonly used glass-forming oxide in the ceramic industry is SiO2[1–5], although it can include a whole variety of acidic metal oxides tri-and tetra-value[1–3].

Modi?er oxides–not forming the glazes themselves but which may to some extent replace silicon cations within the glass framework of silica glazes.Their role consists in breaking bridge bonds and depolymerization of glass framework or loosening it. This group consists of alkali metal oxides(Na2O,K2O,Li2O),and alkaline earth metals(CaO,MgO,ZnO,BaO,etc.)[1–3].

Amphoteric oxides–can contribute to tetrahedral glass framework.Of these,the most common used oxide in conven-

tional ceramic glazes is Al2O3[1–6].

Studies on the effect of SiO2to Al2O3ratio on the properties of ceramic glazes were conducted at the beginning of the twentieth century by Stull[4]and Seger[5].This work focused mainly on simple oxide systems where alkali oxides most frequently are represented by K2O and alkali earth metal oxides,mainly by CaO. The results showed that the change in the silicon oxide to aluminum oxide ratio has an evident effect on the characteristic temperatures of glazes.The research was continued by a number of other researchers as Parmeele[3]Eppler and Eppler[1],Taylor and Bull[2]and Carty et al.[6].The results of their work show that in more complex oxide systems,which are used in modern glazes, there is no simple relationship between the molar composition and and controlled crystallization[10–19].The in?uence of grain size distribution on selected surface parameters was discussed by Partyka and Lis[20].Presented experimental results concern the in?uence of SiO2to Al2O3ratio on the phase composition and structure of porcelain glazes of the SiO2–Al2O3–CaO–MgO–Na2O–K2O.

Experimental

Six sets of porcelain glazes designed for?ring temperature of 1220–1240°C were selected for the study.The oxide composition of glazes marked from SANK-1to SANK-5and SANK-17were based on multiple system of SiO–Al O–CaO–MgO–Na O–K O.Modi?er Table1

Oxides molar composition of glazes SANK1–5and17.

Oxides Na2O K2O CaO MgO ZnO SiO2 Molar fraction0.220.300.210.27 3.37

Table2

Molar ratio of SiO2to Al2O3SANK glazes.

SiO2/Al2O3SANK-1SANK-2SANK-3SANK-4SANK-5SANK-17

8.14 6.48 4.87 4.19 3.56 3.01

Fig.1.XRD patterns of SANK-1to SANK-5and SANK-17glazes.

622J.Partyka et al./Spectrochimica Acta Part A:Molecular and Biomolecular Spectroscopy134(2015)621–630

temperature of1230°C for a total time of12h.Glazes from cruci-bles were used to prepare samples for electron microscopy studies. Reduced to a grain size of less than40l m glazes were allocated for determining the chemical and phase composition and structural studies in the mid-infrared.The chemical composition was deter-mined using a WD-XRF Axios Max spectrometer with Rh4kW PAN-alytical lamp and the phase composition by using PANalytical X-ray Diffractometer X’Pert Pro in range of9–90°with Cu lamp.Structural studies were carried out in the mid-infrared using BrukerVertex 70v Fourier spectrometer.Spectra were collected in the middle infrared regions(MIR)4000–400cmà1after128scans at4cmà1 resolution.Samples were prepared by the standard KBr pellets methods.The SEM microscopic images of the?red glazes were obtained using a NOVA NANO SEM200scanning electron micro-scope with EDS microanalyser by EDAX Company.Observations and analysis were performed in a low vacuum by using a detector LVD and at an accelerating voltage in the range of10–18kV.Results and discussion

The basic premise of the presented research was to obtain such mole composition in which there is constant molar fraction of modi?er oxides with varying SiO2/Al2O3ratio.The results of chem-ical analysis con?rmed these assumptions,the molar shares of oxide modi?ers is shown in Table1(the deviation of the individual glazes does not exceed±1%).The only variable is the mole ratio of SiO2/Al2O3which is shown in Table2.

X-ray phase analysis allows to specify the type of crystalline phases occurring in the studied glazes.Depending on the destina-tion,glazes may contain crystalline phases introduced in the set of raw materials and non-solvent in the melt and/or whose crystalli-zation is induced intentionally,planning oxide composition. Furthermore,the crystals of materials that have not melted in the?ring process may occur or those which crystallized in an unplanned manner.Because the crystalline phases

can Fig.2.Phase analysis of SANK-1glaze(A–summary of diffraction patterns,B–diopsyde,C–alumina oxide).

signi?cantly affect the mechanical and chemical properties of glazes information on this topic is extremely important.

The results of analyzes of phase composition showed consider-able diversity.The studied samples revealed the presence of crystalline phases in glazes SANK-1,SANK-2and SANK-17(Fig.1). In SANK-1glaze(Fig.2A)there is diopside(CaMg[Si2O6]),PDF01-078-1391,(Fig.2B)and alumina(Al2O3)(Fig.2C).The presence of alumina in the crystalline form is due to the high content of silicon oxide in the liquid phase which decreases the solubility of the Al2O3.On the other hand,the silica supersaturation in the alloy and the presence of calcium and magnesium are the cause of diopside crystallization.In the SANK-2glaze only diopside(CaMg[Si2O6]), PDF01-078-1391,was detected(Fig.3).In comparison to SANK-1glaze there is a bit lower content of SiO2and higher of Al2O3.This change results in a complete,dissolution of alumina,but still main-tain favorable conditions for crystallization of diopside.The phase composition of the SANK-17glaze is completely different,only one crystalline phase was found–gahnite(ZnAl2O4)of spinels,PDF01-082-1043,(Fig.4).Crystallization is induced by high concentration of aluminum oxide in the liquid phase in the presence of zinc oxide. Other glazes are completely amorphous as shown in Fig.1.In sum-mary,the presence of crystalline phases listed above is associated only with changes within silicon oxide to aluminum oxide ratio. Crystallization phenomenon concerns only extreme oxide composi-tions where there is an excess of silicon oxide(SANK-1,SANK-2), or at the highest proportions of aluminum oxide(SANK-17).

Fig.2(continued)

Fig.3.Phase analysis of SANK-2glaze.

Fig.4.Phase analysis of SANK-17glaze.

Fig.5.SEM images of cross-section of SANK1glaze(A–EDAX analysis point1,B–EDAX analysis point2).

Fig.6.SEM images of cross-section of SANK2glaze(A–EDAX analysis point1,B–EDAX analysis point2,C–EDAX analysis point3).

Fig.8.SEM images of cross-section of SANK4. Fig.7.SEM images of cross-section of SANK3.

Scanning electron microscopy allows identi?cation and deter-mination of the texture of the crystalline phases present in the glazes.The shape of the crystalline phases and the grain size and distribution thereof have a signi?cant effect on the properties of the glaze.EDAX microprobe coupled with a microscope for X-ray analysis of elements allows to pinpoint the chemical composition. In the case of studied SANK glazes SEM–EDAX observations were carried out on the polished cross-section of the samples prepared from?red glazes.Photos of cross-sectional views of glazes and spot chemical analysis of crystalline phases are shown in Figs.5–10.

Observations made by electron microscopy coincide with SANK-2,SANK-3,SANK-4and SANK-17glazes phase compositions results.Differences were found in two glazes:SANK-1and SANK-5. In the SEM microscopy of SANK-1glaze Al2O3grains were not encountered,which may be due to their small amount and dispersion in the entire volume of the glaze.In the case of SANK-5glaze phase analysis did not detect the presence of crystalline phases,while the scanning electron microscopy studies detected the presence of crystals(Fig.9).EDAX analysis does not state clearly the type of crystals,but comparing the habit of crystals present in the SANK-5glaze(Fig.8)with crystals occurring and as indicated in the test phase composition for SANK-17glaze (Fig.10)it can be stated that these are also crystals of https://www.360docs.net/doc/733919074.html,ck of gahnite in XRD of SANK-5glaze comes from a small amount of these crystals–below the detection threshold.

Most data on the structure of glazes provide infrared FTIR analysis.Depending on the chemical composition of glazes and the?ring conditions,glazes form a bond that signi?cantly affect their performance parameters.Porcelain glazes on the?ring tem-perature above1200°C are based on Si A O bonds forming the

basic Fig.9.SEM images of cross-section of SANK5glaze(A–EDAX analysis point1,B–EDAX analysis point2).

silico-oxygen framework.There are several bands speci?c to bonds between silicon(CN=4)and oxygen:band at about1200cmà1 associated with the stretching vibration of Si@O,defects of silicon oxide tetrahedron connected by edges.Then,the band at approxi-mately1090cmà1associated with stretching vibration of O A Si A(Si)and at about1000cmà1associated with the stretching vibration of Si A Oà.The last two bands represent the previously mentioned so-called bridging oxygens(bridging silicon–oxygen) and non-bridging oxygens(broken silico-oxygen bridges).At about 790cmà1appear bands that are associated with bending vibration of Si A O A Si,and at about470cmà1bands associated with a bend-ing vibration of O A Si A O.In MIR spectra of silicate glasses bands also appear in the range of750–550cmà1related to the vibration of silico-oxygen rings and/or alumino-silico-oxygen rings of differ-ent number of rings members.

Fig.11shows the FTIR spectra for all the studied SANK glazes.In the spectra there are three broad bands.The most intense bands occur in the ranges of1300–850cmà1,500–400cmà1and450–400cmà1.Absorption band at1300–850cmà1is assigned to the asymmetric stretching vibration of Si A O A Si bridges and Si A O A Al bonds linked with[SiO4]4àand[AlO4]5àtetrahedra.Band at800–650cmà1is assigned to the symmetric stretching vibration of Si A O A(Si,Al)between the tetrahedra.In turn,the band in the range of500–400cmà1is due to bending vibrations Si A O A Si and Si A O A Al.A large half-width of the bands makes it dif?cult to accu-rately make the assignments of all the bands and hinges to the respective types of vibration and assess the impact of aluminum ions on the structure of the investigated materials.Analyzing the spectrum in Fig.11can only be concluded that the increase of alu-minum ions at the expense of silicon ions leads to a

substantial Fig.10.SEM images of cross-section of SANK17glaze(A–EDAX analysis point1,B–EDAX analysis point2).

shift in the main band towards lower wavenumbers(1060cmà1–SANK-1to1030cmà1–SANK-17).This is a result of the difference is associated with the existence of densely packed areas in the glass structure(between domains)[13,14].The most intensive

Fig.11.Summary of FTIR spectra in the mid infrared range for all studied glazes.

Fig.12.Decomposition of selected MIR spectra:(A)SANK-1;(B)SANK-17.

J.Partyka et al./Spectrochimica Acta Part A:Molecular and Biomolecular Spectroscopy134(2015)621–630629

(4)In turn,at higher content of alumina,SiO2/Al2O3ratios in the

range of about3.6–3.0(SANK-5,SANK-17),sharp decline in the intensity of band associated with the vibrations of Si A O A Al with a simultaneous increase of intensity of the band associated with the vibrations of Si A O A Si is due to crystallization gahnite.

(5)At the SiO2/Al2O3ratios in the range of about4–5glaze are

amorphous.

(6)The results of the XRD and SEM–EDAX studies con?rm the

conclusions regarding the FTIR analysis.

Acknowledgment

This work was carried out thanks to support from NCBiR grant number PBS1/B5/17/2012.

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