Eva Kuzielová - Academia.edu (original) (raw)

Papers by Eva Kuzielová

Journal of Thermal Analysis and Calorimetry

Accelerated carbonation of cement mixtures consisting of class G cement, silica fume, metakaolin,... more Accelerated carbonation of cement mixtures consisting of class G cement, silica fume, metakaolin, or blast furnace slag was studied by thermogravimetric, X-ray diffraction and Fourier transform infrared analyses for 1 year. Surface parts were fully carbonated during the first 7 days. Polymerization of amorphous hydrates due to their decalcification was observed together with the rising amount of calcium carbonates and reformation of gypsum from ettringite and monosulfate. Decalcification of clinker phases took place fast after the depletion of portlandite. Although portlandite was still present in unblended pastes, because of slower carbonation rate in the surface parts and higher C/S ratio of amorphous hydrates, the carbonation front moved inward during 3 months. Pozzolanic reactions in the samples with 30 mass% of additives depleted portlandite, however, higher amounts of C–(A)–S–H phases with lower C/S ratio, denser microstructure and faster carbonation of surface parts ensured t...

Journal of Thermal Analysis and Calorimetry

In this paper, the composition and properties of two different activated calcinated clays were in... more In this paper, the composition and properties of two different activated calcinated clays were investigated under selected curing conditions. The tendency of metabentonite and metakaoline to form geopolymers and zeolites was investigated by FTIR spectroscopy, TGA and DSC techniques, PXRD, HT-PXRD, SEM, and BET-N2 adsorption analyses. The selection of the optimal sample compositions was done on a basis of preliminary results obtained from bentonite and kaolin clays activated at calcination temperatures (700, 750, 800 °C) with a holding time of 3 h in a combination with different NaOH concentrations (5, 10, 20 mass%). In a more detailed examination, the samples calcined at a temperature of 800 °C with different NaOH concentrations were studied. For metakaolin-based samples, dominant geopolymer formation was achieved using 5 mass% NaOH. The zeolite amount increased concomitantly with the concentration of the alkali activator, whereas zeolite A and zeolite P were determined as the predo...

<jats:title>Abstract</jats:title> <jats:p>The present work investigates the inf... more <jats:title>Abstract</jats:title> <jats:p>The present work investigates the influence of curing conditions on the mechanical and physical properties of heavyweight concrete. The prismatic bars of 40 mm × 40 mm × 160 mm dimension were cured in a climatic chamber (relative humidity 30%, average temperature 26°C), wet (100% of humidity, average room temperature 26°C) and CO<jats:sub>2</jats:sub> chamber-wet (relative humidity 90%, average temperature 50°C and average CO<jats:sub>2</jats:sub> concentration 20 %) conditions for 2, 7, 28 and 90 days. Density, compressive strength, dynamic modulus of elasticity, and longitudinal shrinkage were determined at different ages of curing. Mercury Intrusion Porosimetry was used to analyze and determine the influence of carbonation on pore structure evolution. Samples cured under CO<jats:sub>2</jats:sub>-wet conditions showed a higher compressive strength (54.05, 66.83, 84.98, 96.35 MPa) compared to that of the samples exposed to wet (45.49, 65.87, 78.91, 93.80 MPa) and dry (39.62, 46.52, 48.45, 45.28 MPa) conditions at all ages. The dynamic modulus of elasticity of CO<jats:sub>2</jats:sub>-wet cured samples (53.02, 51.48, 59.24, 67.60 GPa) was lower than that of samples cured in wet conditions (59.82, 66.76, 78.84, 80.27, GPa), but higher than that of dry-cured samples (45.74, 45.73, 43.91, 44.62 GPa). The density of the samples exposed to all curing conditions was higher than 3800 kg/m<jats:sup>3</jats:sup>. Carbonation led to a decrease in total porosity (from 10% to 20%) and an increase in density (from 320 to 390 kg/m<jats:sup>3</jats:sup>). Also, the time and curing conditions have strongly influenced the pore structure. The precipitation of calcium carbonate in the matrix of concrete and the acceleration of hydration reaction under wet conditions has led to a decrease in porosity.</jats:p>

Journal of Thermal Analysis and Calorimetry

Journal of Thermal Analysis and Calorimetry

Materials, 2020

Increasing utilization of secondary raw materials and alternative fuels results in increasing con... more Increasing utilization of secondary raw materials and alternative fuels results in increasing contents of metals in cements. Zinc is one of these elements. It comes to cement with secondary raw materials such as slag or fly ash or by the utilization of used tires as an alternative fuel. Zinc ions significantly prolong the hydration process in cement. This work deals with the influence of zinc ions in the form of very poorly soluble ZnO salt and easily soluble ZnCl2 and Zn(NO3)2 on the hydration of cement blended with fly ash. Zinc was dosed in the range of 0.05%, 0.1%, 0.5% and 1% of cement weight. The effect of zinc on hydration was monitored by isothermal and isoperibolic calorimetry. A 15% addition of fly ash to cement mainly causes further retardation of hydration reactions due to the reactions of fly ash particles with Ca2+ ions from cement. The strongest effect on the hydration retardation from all investigated compounds showed in ZnO as it dissolves very slowly. On the contra...

Increasing utilization of secondary raw materials and alternative fuels results in increasing con... more Increasing utilization of secondary raw materials and alternative fuels results in increasing contents of metals in cements. One of elements, the content of which keeps rising in cement is zinc. It comes to cement with secondary raw materials such as slag or fly ash or by the utilization of used tires as an alternative fuel. Zinc ions significantly prolong the hydration process in cement. This work deals with the influence of zinc ions in the form of very poorly soluble ZnO salt and easily soluble ZnCl2 and Zn(NO)3 on the hydration of cement blended with fly ash. Zinc was dosed in the range of 0.05, 0.1, 0.5 a 1% of cement weight. Final products were next analyzed using X-Ray Diffraction.

Ceramics, 2007

The present investigation reports the results of P 2 O 5 , CaO and CaF 2 (in stechiometric ratio ... more The present investigation reports the results of P 2 O 5 , CaO and CaF 2 (in stechiometric ratio corresponding to fluoroapatite) effect upon the controlled crystallization of grain-sized particles of lithium disilicate (LS 2 ) glass and upon the bioactivity of given glasses, that have been investigated by means of DTA and by in vitro testing after 4 weeks, respectively. The crystallization of pure lithium disilicate glass as well as that of glass containing the above components proceeds by surface and internal mechanism as function of particle size. The onset of internal crystallization, which substitutes the surface one is found at about 0.3 mm for pure lithium disilicate glass, while this change occurred at size of 0.9 mm approximately in glass containing CaO, P 2 O 5 and CaF 2 . The addition of different amount of "apparent fluoroapatite" enhances the bioactivity of bio-glasses as confirmed by SEM and EPMA.

The bioactivity of glass ceramics from Li 2 O–SiO 2 –CaO–P 2 O 5 –CaF 2 system, with different am... more The bioactivity of glass ceramics from Li 2 O–SiO 2 –CaO–P 2 O 5 –CaF 2 system, with different amount of fluorapatite expressed as P 2 O 5 content, has been tested in vitro under static and dynamic regime. The paper reports the results of bioactivity test of glass ceramics in static and dynamic regime. XRD, SEM and EPMA analysis were used to characterise the sample as well as to detect the presence of new phase onto the surface of glass ceramics. The bioactivity, as demonstrated by the formation of new apatite layer, depends on P 2 O 5 content and testing regime. In static regime, one can observe a fine microstructure of hydroxyapatite layer on the surface on glass ceramics samples. In dynamic regime, the formation rate of this layer seems to be retarded in comparison with that of static regime.

2009 2nd International Symposium on Applied Sciences in Biomedical and Communication Technologies, 2009

The bioactivity of glass ceramics from Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system, with different amou... more The bioactivity of glass ceramics from Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system, with different amount of fluorapatite expressed as P 2 O 5 content, has been tested in vitro under static and dynamic regime. The paper reports the results of bioactivity test of glass ceramics in static and dynamic regime. XRD, SEM and EPMA analysis were used to characterise the sample as well as to detect the presence of new phase onto the surface of glass ceramics. The bioactivity, as demonstrated by the formation of new apatite layer, depends on P 2 O 5 content and testing regime. In static regime, one can observe a fine microstructure of hydroxyapatite layer on the surface on glass ceramics samples. In dynamic regime, the formation rate of this layer seems to be retarded in comparison with that of static regime.

Key Engineering Materials, 2007

Lithium disilicate glass and glass with addition of P2O5, CaO and CaF2 (in relative ratios corres... more Lithium disilicate glass and glass with addition of P2O5, CaO and CaF2 (in relative ratios corresponding to 10 wt. % of „apparent fluoroapatite”) were prepared by quenching their melts obtained at 1400 °C. Then, the parent glasses were thermally treated at 550°C and 750°C to obtain glass ceramics. The bioactivity test in vitro and the Wicker hardness in relation to „apparent fluoroapatite“ presence and heat treatment were investigated. The presence of fluoroapatite in samples promotes mineralization of new phase apatite-like on the surface of glass and glass ceramics after 6-week immersion in SBF as proved by SEM and EPMA. The bioactivity decreases with thermal treatment of parent glass. However, whole surface of glass-ceramics was covered with apatite phase after long-term immersion in SBF. The Vickers hardness of samples increases with increasing temperature treatment and with the presence of fluoroapatite.

Journal of Thermal Analysis and Calorimetry, 2008

Two glasses, the first one with the composition of Li 2 O•2SiO 2 and the second one with the addi... more Two glasses, the first one with the composition of Li 2 O•2SiO 2 and the second one with the addition of CaO, P 2 O 5 and CaF 2 in the stoichiometric ratio corresponding to fluoroapatite were prepared and their tendency to crystallize has been studied by non-isothermal DTA analysis. The values of kinetic parameters calculated using the isoconversional integral method have been used to determine the temperature dependencies of both the length of isothermal induction period and the length of overall isothermal crystallization for both glasses. The estimated dependencies indicate that the glass containing CaO, P 2 O 5 and CaF 2 has a lower thermal stability.

Central European Journal of Chemistry, 2009

Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesis... more Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesised in the Li2O-SiO2-CaO-P2O5-CaF2 system with P2O5: CaO: CaF2 ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle sizes. Inclusion of FA in the LS2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (299 ± 1 kJ mol-1 for pure LS2 glass and 288 ± 7 kJ mol−1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS2 glass and 303 ± 8 kJ mol-1 fo...

Advances in Applied Ceramics, 2008

Glass samples in Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system with different contents of P 2 O 5 , CaO a... more Glass samples in Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system with different contents of P 2 O 5 , CaO and CaF 2 in relative ratios responded to fluoroapatite (FA) composition (referred to P 2 O 5 addition) have been prepared and heat treated at 550 and 750uC to obtain glass ceramics. Bioactivity of all samples has been proved in vitro by the presence of new layer of apatite-like phases formed after soaking in simulated body fluid (SBF). The development and the apatitic character of created layers have been demonstrated by Fourier transform infrared analysis. Scanning electron microscopy and electron probe microanalysis have demonstrated that the density and the thickness of new layer depend on P 2 O 5 content, crystallisation temperature and immersion time. The bioactivity has been enhanced by P 2 O 5 addition as well in the case of the base glasses as in the case of glass ceramics. The additional heat treatment appeared to inhibit the bioactive behaviour, though the longer SBF acting leads to the additional formation of apatite-like layer. The mechanical properties, expressed as Vicker hardness, have been found higher and increasing with P 2 O 5 in glass ceramics treated at 750uC comparatively with base glass samples and the highest value of 7?37 GPa has been achieved by 14 wt-%P 2 O 5 addition. The same content of P 2 O 5 in glass ceramics heat treated at 550uC resulted in a decrease in hardness to a minimum value from all samples. The increase and decrease in hardness responded to development and suppression of crystallisation respectively. The inhibition of crystallisation has been affected by the presence of 'amorphous' FA according to X-ray diffraction and differential thermal analysis results.

Referred work is a preliminary investigation of the lithium disilicate (LS 2 ) and the fluoroapat... more Referred work is a preliminary investigation of the lithium disilicate (LS 2 ) and the fluoroapatite (FA) crystallization in bio-glass ceramics. Composite glass-ceramics with various content of P 2 O 5 in oxide system SiO 2 -Li 2 O-CaO-CaF 2 -P 2 O 5 were prepared by heat treatment of glass at different temperatures. Two crystalline phases lithium disilicate (LS 2 ) ana fluorapatite (FA) were developed in the samples depending on P 2 O 5 content and temperature. The increase of temperature as well as the content of P 2 O 5 promote the crystallization ofFA. XRD measurements supplemented by DTA results showed that LS 2 crystallization at lower temperature is inhibited because of the present of amorphous FA. On the contrary, crystalline phase ofFA promoted the crystallization of LS 2 . Phase separation of the samples is well observed in scanning electronic micrograph. The Vickers hardness values of prepared bio-glass ceramics are higher than the average hardness of biological tooth and...

Possible preferential formation of ettringite instead of required calcium silicate hydrate (CSH) ... more Possible preferential formation of ettringite instead of required calcium silicate hydrate (CSH) and calcium aluminosilicate hydrate (CASH) phases when aluminosilicates were added to the blended cements was investigated on the model systems comprising of metakaolin, lime and gypsum. Compressive strength, microstructure and phase composition of the samples were evaluated after 7 days of curing at 50°C, using thermal analysis, X-ray diffraction techniques and scanning electronic microscopy. Samples prepared from equal amounts of metakaolin, lime and with more than 8 wt. % of gypsum, displayed the highest compressive strength values. Development of compressive strength was correlated with the formation of ettringite. Further rising of gypsum content resulted in the decrease of compressive strength, which is notable in the samples with a different metakaolin/lime ratio. Lower content of gypsum led to the preferential formation of portlandite, CSH and CASH. Calcite was detected in all th...

Journal of Thermal Analysis and Calorimetry

Accelerated carbonation of cement mixtures consisting of class G cement, silica fume, metakaolin,... more Accelerated carbonation of cement mixtures consisting of class G cement, silica fume, metakaolin, or blast furnace slag was studied by thermogravimetric, X-ray diffraction and Fourier transform infrared analyses for 1 year. Surface parts were fully carbonated during the first 7 days. Polymerization of amorphous hydrates due to their decalcification was observed together with the rising amount of calcium carbonates and reformation of gypsum from ettringite and monosulfate. Decalcification of clinker phases took place fast after the depletion of portlandite. Although portlandite was still present in unblended pastes, because of slower carbonation rate in the surface parts and higher C/S ratio of amorphous hydrates, the carbonation front moved inward during 3 months. Pozzolanic reactions in the samples with 30 mass% of additives depleted portlandite, however, higher amounts of C–(A)–S–H phases with lower C/S ratio, denser microstructure and faster carbonation of surface parts ensured t...

Journal of Thermal Analysis and Calorimetry

In this paper, the composition and properties of two different activated calcinated clays were in... more In this paper, the composition and properties of two different activated calcinated clays were investigated under selected curing conditions. The tendency of metabentonite and metakaoline to form geopolymers and zeolites was investigated by FTIR spectroscopy, TGA and DSC techniques, PXRD, HT-PXRD, SEM, and BET-N2 adsorption analyses. The selection of the optimal sample compositions was done on a basis of preliminary results obtained from bentonite and kaolin clays activated at calcination temperatures (700, 750, 800 °C) with a holding time of 3 h in a combination with different NaOH concentrations (5, 10, 20 mass%). In a more detailed examination, the samples calcined at a temperature of 800 °C with different NaOH concentrations were studied. For metakaolin-based samples, dominant geopolymer formation was achieved using 5 mass% NaOH. The zeolite amount increased concomitantly with the concentration of the alkali activator, whereas zeolite A and zeolite P were determined as the predo...

<jats:title>Abstract</jats:title> <jats:p>The present work investigates the inf... more <jats:title>Abstract</jats:title> <jats:p>The present work investigates the influence of curing conditions on the mechanical and physical properties of heavyweight concrete. The prismatic bars of 40 mm × 40 mm × 160 mm dimension were cured in a climatic chamber (relative humidity 30%, average temperature 26°C), wet (100% of humidity, average room temperature 26°C) and CO<jats:sub>2</jats:sub> chamber-wet (relative humidity 90%, average temperature 50°C and average CO<jats:sub>2</jats:sub> concentration 20 %) conditions for 2, 7, 28 and 90 days. Density, compressive strength, dynamic modulus of elasticity, and longitudinal shrinkage were determined at different ages of curing. Mercury Intrusion Porosimetry was used to analyze and determine the influence of carbonation on pore structure evolution. Samples cured under CO<jats:sub>2</jats:sub>-wet conditions showed a higher compressive strength (54.05, 66.83, 84.98, 96.35 MPa) compared to that of the samples exposed to wet (45.49, 65.87, 78.91, 93.80 MPa) and dry (39.62, 46.52, 48.45, 45.28 MPa) conditions at all ages. The dynamic modulus of elasticity of CO<jats:sub>2</jats:sub>-wet cured samples (53.02, 51.48, 59.24, 67.60 GPa) was lower than that of samples cured in wet conditions (59.82, 66.76, 78.84, 80.27, GPa), but higher than that of dry-cured samples (45.74, 45.73, 43.91, 44.62 GPa). The density of the samples exposed to all curing conditions was higher than 3800 kg/m<jats:sup>3</jats:sup>. Carbonation led to a decrease in total porosity (from 10% to 20%) and an increase in density (from 320 to 390 kg/m<jats:sup>3</jats:sup>). Also, the time and curing conditions have strongly influenced the pore structure. The precipitation of calcium carbonate in the matrix of concrete and the acceleration of hydration reaction under wet conditions has led to a decrease in porosity.</jats:p>

Journal of Thermal Analysis and Calorimetry

Journal of Thermal Analysis and Calorimetry

Materials, 2020

Increasing utilization of secondary raw materials and alternative fuels results in increasing con... more Increasing utilization of secondary raw materials and alternative fuels results in increasing contents of metals in cements. Zinc is one of these elements. It comes to cement with secondary raw materials such as slag or fly ash or by the utilization of used tires as an alternative fuel. Zinc ions significantly prolong the hydration process in cement. This work deals with the influence of zinc ions in the form of very poorly soluble ZnO salt and easily soluble ZnCl2 and Zn(NO3)2 on the hydration of cement blended with fly ash. Zinc was dosed in the range of 0.05%, 0.1%, 0.5% and 1% of cement weight. The effect of zinc on hydration was monitored by isothermal and isoperibolic calorimetry. A 15% addition of fly ash to cement mainly causes further retardation of hydration reactions due to the reactions of fly ash particles with Ca2+ ions from cement. The strongest effect on the hydration retardation from all investigated compounds showed in ZnO as it dissolves very slowly. On the contra...

Increasing utilization of secondary raw materials and alternative fuels results in increasing con... more Increasing utilization of secondary raw materials and alternative fuels results in increasing contents of metals in cements. One of elements, the content of which keeps rising in cement is zinc. It comes to cement with secondary raw materials such as slag or fly ash or by the utilization of used tires as an alternative fuel. Zinc ions significantly prolong the hydration process in cement. This work deals with the influence of zinc ions in the form of very poorly soluble ZnO salt and easily soluble ZnCl2 and Zn(NO)3 on the hydration of cement blended with fly ash. Zinc was dosed in the range of 0.05, 0.1, 0.5 a 1% of cement weight. Final products were next analyzed using X-Ray Diffraction.

Ceramics, 2007

The present investigation reports the results of P 2 O 5 , CaO and CaF 2 (in stechiometric ratio ... more The present investigation reports the results of P 2 O 5 , CaO and CaF 2 (in stechiometric ratio corresponding to fluoroapatite) effect upon the controlled crystallization of grain-sized particles of lithium disilicate (LS 2 ) glass and upon the bioactivity of given glasses, that have been investigated by means of DTA and by in vitro testing after 4 weeks, respectively. The crystallization of pure lithium disilicate glass as well as that of glass containing the above components proceeds by surface and internal mechanism as function of particle size. The onset of internal crystallization, which substitutes the surface one is found at about 0.3 mm for pure lithium disilicate glass, while this change occurred at size of 0.9 mm approximately in glass containing CaO, P 2 O 5 and CaF 2 . The addition of different amount of "apparent fluoroapatite" enhances the bioactivity of bio-glasses as confirmed by SEM and EPMA.

The bioactivity of glass ceramics from Li 2 O–SiO 2 –CaO–P 2 O 5 –CaF 2 system, with different am... more The bioactivity of glass ceramics from Li 2 O–SiO 2 –CaO–P 2 O 5 –CaF 2 system, with different amount of fluorapatite expressed as P 2 O 5 content, has been tested in vitro under static and dynamic regime. The paper reports the results of bioactivity test of glass ceramics in static and dynamic regime. XRD, SEM and EPMA analysis were used to characterise the sample as well as to detect the presence of new phase onto the surface of glass ceramics. The bioactivity, as demonstrated by the formation of new apatite layer, depends on P 2 O 5 content and testing regime. In static regime, one can observe a fine microstructure of hydroxyapatite layer on the surface on glass ceramics samples. In dynamic regime, the formation rate of this layer seems to be retarded in comparison with that of static regime.

2009 2nd International Symposium on Applied Sciences in Biomedical and Communication Technologies, 2009

The bioactivity of glass ceramics from Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system, with different amou... more The bioactivity of glass ceramics from Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system, with different amount of fluorapatite expressed as P 2 O 5 content, has been tested in vitro under static and dynamic regime. The paper reports the results of bioactivity test of glass ceramics in static and dynamic regime. XRD, SEM and EPMA analysis were used to characterise the sample as well as to detect the presence of new phase onto the surface of glass ceramics. The bioactivity, as demonstrated by the formation of new apatite layer, depends on P 2 O 5 content and testing regime. In static regime, one can observe a fine microstructure of hydroxyapatite layer on the surface on glass ceramics samples. In dynamic regime, the formation rate of this layer seems to be retarded in comparison with that of static regime.

Key Engineering Materials, 2007

Lithium disilicate glass and glass with addition of P2O5, CaO and CaF2 (in relative ratios corres... more Lithium disilicate glass and glass with addition of P2O5, CaO and CaF2 (in relative ratios corresponding to 10 wt. % of „apparent fluoroapatite”) were prepared by quenching their melts obtained at 1400 °C. Then, the parent glasses were thermally treated at 550°C and 750°C to obtain glass ceramics. The bioactivity test in vitro and the Wicker hardness in relation to „apparent fluoroapatite“ presence and heat treatment were investigated. The presence of fluoroapatite in samples promotes mineralization of new phase apatite-like on the surface of glass and glass ceramics after 6-week immersion in SBF as proved by SEM and EPMA. The bioactivity decreases with thermal treatment of parent glass. However, whole surface of glass-ceramics was covered with apatite phase after long-term immersion in SBF. The Vickers hardness of samples increases with increasing temperature treatment and with the presence of fluoroapatite.

Journal of Thermal Analysis and Calorimetry, 2008

Two glasses, the first one with the composition of Li 2 O•2SiO 2 and the second one with the addi... more Two glasses, the first one with the composition of Li 2 O•2SiO 2 and the second one with the addition of CaO, P 2 O 5 and CaF 2 in the stoichiometric ratio corresponding to fluoroapatite were prepared and their tendency to crystallize has been studied by non-isothermal DTA analysis. The values of kinetic parameters calculated using the isoconversional integral method have been used to determine the temperature dependencies of both the length of isothermal induction period and the length of overall isothermal crystallization for both glasses. The estimated dependencies indicate that the glass containing CaO, P 2 O 5 and CaF 2 has a lower thermal stability.

Central European Journal of Chemistry, 2009

Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesis... more Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesised in the Li2O-SiO2-CaO-P2O5-CaF2 system with P2O5: CaO: CaF2 ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle sizes. Inclusion of FA in the LS2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (299 ± 1 kJ mol-1 for pure LS2 glass and 288 ± 7 kJ mol−1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS2 glass and 303 ± 8 kJ mol-1 fo...

Advances in Applied Ceramics, 2008

Glass samples in Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system with different contents of P 2 O 5 , CaO a... more Glass samples in Li 2 O-SiO 2-CaO-P 2 O 5-CaF 2 system with different contents of P 2 O 5 , CaO and CaF 2 in relative ratios responded to fluoroapatite (FA) composition (referred to P 2 O 5 addition) have been prepared and heat treated at 550 and 750uC to obtain glass ceramics. Bioactivity of all samples has been proved in vitro by the presence of new layer of apatite-like phases formed after soaking in simulated body fluid (SBF). The development and the apatitic character of created layers have been demonstrated by Fourier transform infrared analysis. Scanning electron microscopy and electron probe microanalysis have demonstrated that the density and the thickness of new layer depend on P 2 O 5 content, crystallisation temperature and immersion time. The bioactivity has been enhanced by P 2 O 5 addition as well in the case of the base glasses as in the case of glass ceramics. The additional heat treatment appeared to inhibit the bioactive behaviour, though the longer SBF acting leads to the additional formation of apatite-like layer. The mechanical properties, expressed as Vicker hardness, have been found higher and increasing with P 2 O 5 in glass ceramics treated at 750uC comparatively with base glass samples and the highest value of 7?37 GPa has been achieved by 14 wt-%P 2 O 5 addition. The same content of P 2 O 5 in glass ceramics heat treated at 550uC resulted in a decrease in hardness to a minimum value from all samples. The increase and decrease in hardness responded to development and suppression of crystallisation respectively. The inhibition of crystallisation has been affected by the presence of 'amorphous' FA according to X-ray diffraction and differential thermal analysis results.

Referred work is a preliminary investigation of the lithium disilicate (LS 2 ) and the fluoroapat... more Referred work is a preliminary investigation of the lithium disilicate (LS 2 ) and the fluoroapatite (FA) crystallization in bio-glass ceramics. Composite glass-ceramics with various content of P 2 O 5 in oxide system SiO 2 -Li 2 O-CaO-CaF 2 -P 2 O 5 were prepared by heat treatment of glass at different temperatures. Two crystalline phases lithium disilicate (LS 2 ) ana fluorapatite (FA) were developed in the samples depending on P 2 O 5 content and temperature. The increase of temperature as well as the content of P 2 O 5 promote the crystallization ofFA. XRD measurements supplemented by DTA results showed that LS 2 crystallization at lower temperature is inhibited because of the present of amorphous FA. On the contrary, crystalline phase ofFA promoted the crystallization of LS 2 . Phase separation of the samples is well observed in scanning electronic micrograph. The Vickers hardness values of prepared bio-glass ceramics are higher than the average hardness of biological tooth and...

Possible preferential formation of ettringite instead of required calcium silicate hydrate (CSH) ... more Possible preferential formation of ettringite instead of required calcium silicate hydrate (CSH) and calcium aluminosilicate hydrate (CASH) phases when aluminosilicates were added to the blended cements was investigated on the model systems comprising of metakaolin, lime and gypsum. Compressive strength, microstructure and phase composition of the samples were evaluated after 7 days of curing at 50°C, using thermal analysis, X-ray diffraction techniques and scanning electronic microscopy. Samples prepared from equal amounts of metakaolin, lime and with more than 8 wt. % of gypsum, displayed the highest compressive strength values. Development of compressive strength was correlated with the formation of ettringite. Further rising of gypsum content resulted in the decrease of compressive strength, which is notable in the samples with a different metakaolin/lime ratio. Lower content of gypsum led to the preferential formation of portlandite, CSH and CASH. Calcite was detected in all th...