The results of this work indicate that rapid firing is not a special condition in porcelain manufacturing from the point of view of the kinetics and thermodynamics of the process and the findings of previous works have been confirmed and demonstrated to be valid for a wide range porcelain chemistry. 2. quartz amount) in the body can be directly predicted from the burning conditions and initial chemistry of the body.
Reactions occurring during firing of triaxial porcelain bodies
As the temperature is further increased, the feldspar grains melt completely but retain the original shape due to the high viscosity of the glass. Under the influence of gravity, the flow is plastic due to the shearing of the glass phase.
Factors influencing the maturing behavior of triaxial porcelains
It has been found that the potash/soda ratio has no significant influence on the firing properties of the porcelain bodies. Baking conditions, especially temperature and time, are important because they are related to the thermodynamics and kinetics of the chemical reactions that take place during the baking process.
Arrhenius model and activation energy of densification
The log-time dependence of the baking temperature during soaking is measurable and this behavior is determined by the quartz dissolution kinetics. The activation energy is a measure of the amount of energy required to complete different processes occurring at the same time interval.
Fast Firing
The amount of mullite was found to be independent of alkali levels and firing conditions.6. The firing temperature can be calculated for any composition of porcelain, since the kinetics of the chemical reactions involved in the sintering process are known to follow the Arrhenius model.7,23,24.
Raw materials selection and chemical composition
Green sample preparation
The three slurries were then mixed in slurry form in the specified ratio before mixing the rest of the bodies. The final porcelain masses were prepared by dispersing the nepheline syenite and quartz in the clay mixture slurry at a density of 1758 g/l (± 4 g/l) and the viscosity was adjusted with Darvan C prior to casting. The rods were cut and ground into 7 mm (± 0.1 mm) pellets and dried overnight at 110°C before firing.
Since the amount of RO oxides is significant (>0.1 on a UMF basis), this was taken into account in the models.
Firing
The thermocouple for temperature control is located in the center of the stage below the samples. For all compositions, three samples were fired at temperatures from 1175°C to 1300°C with increments of 25K and residence times of and 1.00 hours (equally spaced time intervals on a log time scale); the heating rate was constant at 30K/min because previous work showed that the heating rate affects compaction but not mineralogy.8 A total of 1080 samples were fired.
Characterization of the fired samples
The aim of this characterization scheme was to verify the influence of heat treatment on mineralogy and as a function of body chemistry. Depending on the size of the mullite needles, the sharpness of the peaks in the diffraction pattern changes.8 To avoid quantification errors using peak intensities, three non-overlapping peaks were selected for quartz, mullite and fluorite, the combined area of the three chosen peaks for quartz and mullite was divided by the combined area of the fluorite peaks and then a previously developed calibration curve was used to quantify the volume concentration of each phase based on its relative area. The samples were ground and pulverized in a mechanical mortar, and then the density was measured with a helium pycnometer at room temperature (AccuPyc 1330, Micromeritics Instruments Corp, Norcross, GA, USA).
True density measurement is needed to calculate the density of the glass phase through the rule of mixtures. Using the true density, the mineralogy can be calculated on a weight basis from the volumetric concentrations obtained via quantitative X-ray diffraction data. The mineralogy is then used to calculate the glass phase chemistry by subtracting the mineral components from the measured body chemistry.
Mullite formation
Relationship between Al2O3 in glass phase (UMF) and the alkali level in the body as (R2O+RO) (mol. Comparison between measured mullite content (from quantitative X-ray diffraction and a glass density of 2.39 g/cm3) and calculated mullite level which is a alumina saturation level of 1.16 mol Al2O3 per mol flux in the glass phase is assumed.
Quartz dissolution and glass chemistry
Quartz dissolution and undissolved quartz
Contour plot of fraction of residual quartz (QUD=QF/Q0) as a function of firing parameters, temperature (°C) and residence time (hours). As can be seen from the surface contour plot (Figure 7), dissolution of quartz begins in such a short residence time of 0.1 hour (6 minutes) at temperatures above 1250 °C. When the temperature is reduced to 1200 °C, dissolution can be measured if the residence times are at least 0.35 hours (20 minutes).
Comparison between calculated and measured undissolved quartz (Ratio QF/Q0) for different annealing conditions (Dashed lines represent 99% confidence interval).
Chemistry of the glass phase
Comparison between calculated and measured undissolved quartz (QF/Q0 ratio) for different firing conditions (dashed lines represent the 99% confidence interval). The silica content in the glass phase is a function of the amount of silica available in the original body13,32,34 and the data in this thesis support this suggestion, as shown in Figure 9. The problem is that the number of moles of SiO2 in the original body and the silica in the glass phase are both normalized to the same amount: the total amount of fluxes of the porcelain composition. As the alkali level increases, the SiO2 in the native body and in the glass phase both decrease on a UMF basis.
As already noted, the dissolution rate of quartz and thus the amount of SiO2 in the glass phase is controlled by temperature and residence time (reaction rate). Quartz UMF in the glassy phase as a function of the amount available in the starting body. The difference between the 1:1 line and the amount of SiO2 in the glass phase is a combination of the amount of silica in the crystalline phases of mullite and undissolved quartz.
Densification
Vitrification temperature
To avoid overignition and the uncertainty associated with measuring 0% water absorption on small samples, densification was defined as having a water absorption level of ≤0.2%. From this cutoff, ripening temperature temperature gradient curves were obtained at 0.2% water absorption, which corresponds to 0.995 apparent bulk density/specific gravity ratio. The increase of the flux level by one (mole) percent also allows a reduction of the firing temperature by 26.9K.
Ripening temperature for different retention times as a function of body alkali level (Data were obtained from temperature gradient curves at 0.2% water absorption value). For example, if a body containing 6.0% R2O+RO (mole%) is intended to be fired on a firing schedule with a residence time of 0.2 hours, the temperature required for 0.2% water absorption would be 1275 °C . The results showed that the hypothetical water absorption value of 0.20% was within the confidence interval of the sample mean (0.18% to 0.22%).
Activation Energy for densification
Therefore, the measured experimental values and the values predicted by the model are statistically the same. An average activation energy of 872 (±75 kJ/mol) was obtained, which is in agreement with the data reported by Dannert of 870 (±35) kJ/mol,26 as shown in Figure 2. This value is higher than the , calculated by other authors (200-600 kJ/mol) and assumed to be the case because their studies focused on an intermediate degree of densification. At temperatures above 1200 °C, the glass phase is enriched with silica from the dissolution of quartz and therefore the viscosity of the glass gradually increases as the level of silica increases.
This increase in viscosity is proposed to cause a decrease in the rate of densification, which would cause an increase in the activation energy.25. From the Arrhenius plots it can be seen that the curves are roughly parallel to each other and the effect of the flux content is to shift the curve to lower temperatures without changing the activation energy. Regression analysis data for Arrhenius plots are reported in Table VI (and shown in Figure 18) for all ten compounds and remain constant, regardless of flux level, at 872 (±75) kJ/mol.
Glass phase
Glass density
The density of the porcelain glass phase is required to accurately calculate the composition of the mineral phase from QXRD data and to correctly convert to a mass basis. Previous works have shown the validity of the rule of mixture on a volume basis for calculating the properties of a dense porcelain body.8,13 The density of the glass can be obtained by knowing the density of the crystalline phases and the true density of the body. (measured value). The density of the glass phase is inversely proportional to the total amount of [SiO2.
These results are consistent with data obtained by Skovira.13 Accordingly, flux density increases with flux concentration, as shown in Figure 20, which is consistent with previous work.13. It has been proposed that in aluminosilicate glasses, most of the aluminum (Al3+) enters the silicate glass network as a network former in fourfold coordination, replacing Si4+, resulting in a negative tetrahedron [Al(O2)]1- (with each of the four apical oxygens sharing with adjacent tetrahedrons). The density of the glass phase as a function of the total amount of silica and aluminum in the glass.
Amount of Glass required for vitrification
Sintering Mechanisms of Porcelain Stoneware Tiles,” Proceedings of the VIII World Congress on Ceramic Tile Quality, Qualicer. Correlation matrix for the amount of mullite with the firing parameters and initial composition of the porcelain body. With a confidence level of 95%, it is possible to conclude that there is no correlation between the amount of Al2O3 in the glass phase with the composition of the porcelain body and the firing parameters (The P-values for all parameters are greater than 0.05).
93% of the observed variation in the amount of undissolved quartz can be explained by the empirical model (R-sqr adjusted=93.0%). 95.3% of the observed variation in the SiO2 level of the glass phase can be explained by the empirical model (R-sqr adjusted=95.3%). 90.9% of the observed variation in the SiO2 level of the glass phase can be explained by the empirical model (R-sqr adjusted=90.9%).
97.5% of the observed variation in the SiO2 level of the glass phase can be explained through the empirical model (adjusted R-sqr=97.5%). The histogram for the data along with the confidence interval of the sample mean and the hypothetical mean is shown in the figure.
