IV. RESULTS AND DISCUSSION
4.3 Densification
4.3.3 Measured Apparent Bulk Density by Immersion
42
43
Dwell time (hour)
0.1 1 10 100
Apparent Bulk Density (g/cm3 )
2.0 2.1 2.2 2.3 2.4 2.5 2.6
Figure 26. Apparent bulk density as a function of dwell time showing a strong dependence on dwell temperature and a minor but measureable dependence on heating rate.
1300 ˚C1250 ˚C1200 ˚C
Calculated density (1300°C)
1200 ˚C 1250 ˚C 1300 ˚C
5 ˚C/min 20 ˚C/min 60 ˚C/min Measured apparent bulk density Open porosity Closed porosity
44
Temperature (oC)
1180 1200 1220 1240 1260 1280 1300 1320
Apparent bulk density (g/cm3 )
1.8 2.0 2.2 2.4 2.6
Figure 27. Densification is strongly dependent on temperature which exhibits a non-linear dependence. The plot shows samples fired at 5 K·min-
1. The same trend, however, can be observed in others heating rate. The inset presents drop off density results in bloating of samples fired in 1300°C with 10 and 32 hours of dwell time.
0.1-hour 0.32-hour 1.0-hour 3.2-hour 10-hour 32-hour
Temperature (oC)
1240 1250 1260 1270 1280 1290 1300 1310
Apparent bulk density (g/cm3)
2.30 2.35 2.40 2.45 2.50
32-hour 10-hour
45
Heating rate (oC/min)
1 10 100
Apparent bulk density (g/cm3 )
2.0 2.1 2.2 2.3 2.4 2.5
Heating rate (oC/min)
1 10 100
Apparent bulk density (g/cm3 )
2.25 2.30 2.35 2.40 2.45 2.50
Figure 28. Apparent bulk density as a function of heating rate for dwell times of (A) 0.1 hours and (B) 3.2 hours. The effect of heating rate becomes less pronounced at longer dwell times.
0.1 hours
3.2 hours
1200 ˚C 1250 ˚C 1300 ˚C
1200 ˚C 1250 ˚C 1300 ˚C
46
Dwell time (hour)
0.1 1 10 100
Apparent Bulk Density/True density (%)
80 85 90 95 100
Figure 29. The ratio of Apparent Bulk Density/True density represents to the constant closed porosity. (Samples were fired in different temperature with 5 K·min-1, the same trend was observed in other heating rate).
4.3.4 Glass Content on Porcelain Body Densification
The dense porcelain is identified as its water absorption is less than 0.5%.**
Consequently, the result shows a unique relationship between the amounts of glass required to reach the peak apparent bulk density (via the water absorption <
0.5%). It is proposed that increasing in temperature and dwell time results in an increasing of the glass content within the porcelain matrix (Figure 30a). In other words, increasing of the glass content is a function of quartz dissolution (i.e., increasing in the silica level in the glass phase) but with no added densification.
** Porcelain is identified as a hard, translucent ceramic ware. Porcelain is biscuit fired at a low temperature, and glost fired at a high temperature, or it may be once fired. The body is non-porous and translucent. There are many products in porcelain group such as tableware, artware, chemical ware, electrical insulator, spark plug cores, valve seats, cutting tools, substrates and abrasion-resisting ware. The extremely low water absorption is a highlight of this product type: about 0-0.5%.2, 3, 70
95.3±0.8%
1200 ˚C 1250 ˚C 1300 ˚C
47
Figure 30b shows that the % WA decreased as a function of amount of glass content. According to the Figure 30a and 30b the glass level of 53.3± (0.9) % is necessary to achieve the proper densification with < 0.5% of WA and 95.8(±0.5)
% of the apparent bulk density and true density ratio. Even though the glass content increased, but the apparent bulk density/true density ratio remained constant indicating a constant level of closed porosity (Figure 29 and 30a).
This result is consistent to the previous study that showed the glass content needed to achieve maximum apparent bulk density is 52± (1.5) %.71
Glass content (%)
40 45 50 55 60 65
Apparent Bulk Density/True density (%)
75 80 85 90 95 100
Figure 30a. The amount of glass content as a function of temperature and dwell time (regardless of heating rate). The standard deviation of the glass content needed is calculated from samples which present full densification.
The vertical dash lines represent the standard deviation.
95.3±(0.8)%
53.3±0.9
%
Porous samples [< 95.3% (±0.8)]
Dense samples [(95.3% (±0.8)]
Samples with bloating
48
Water Absorption (%)
0 2 4 6 8 10 12
Glass content (%)
40 45 50 55 60 65 70
W ater Absorption (%)
-0.5 0.0 0.5 1.0 1.5 2.0
Glass content (%)
40 45 50 55 60 65 70
Figure 30b. The amount of glass content needed to achieve the dense porcelain body. The dense and porous bodies are presented by the fill of the symbol: no fill, porous porcelain body (%WA >0.5), and solid fill, dense (%WA < 0.5). The solid line is the regression line and the dash lines represent 95 % confident interval. The vertical solid line represents the 0.5
% WA.
53.3±(0.9) %
49 4.4 Microstructural Analysis
The SEM micrographs in Figure 31 show porcelain samples fired in different firing conditions but exhibit a same quartz dissolution level. It is clear that the quartz dissolution rim thicknesses of the three samples are very similar. The distribution and shape of pores, moreover, are also indistinguishable from the three microstructures.
Figure 32 presents a schematic diagram—how a quartz dissolution rim thickness was measured. The four directions were measured to present the average size of quartz particles as presented by L1-L4. The R1-R8 presents the dissolution rim thickness by different positions. The particle size and dissolution rim thickness are presented in average value and standard deviation as presented in the appendix.
The three sets of samples were selected to evaluate the dissolution rim. Set 1 and Set 2 represent the samples which have the same quartz dissolution levels (presented in the appendix) and Set 3 represents the samples isothermally fired at 1300°C, and at a given dwell time, to present the effect of heating rate as presented in Figure 33. It was observed from Figure 33 that the dissolution rim thickness is independent of initial particles. The scatter of the final quartz particle size data results from the irregular shape of quartz particles as graphically presented in Figure 32. Figure 34 demonstrates that the quartz dissolution rim thickness increases linearly with temperature but with a log-time dependence and it is consistent to the quartz dissolution. It is also statistically independent of the heating rate.
The porcelain samples fired at 1300 °C for 3.2 hours with different heating rates were used to demonstrate the effect of heating rate on the dissolution rim as presented in Figure 35. It is clear that the dissolution thickness is independent of the heating rate. (The result was consistent to the undissolved quartz level that it is independent of the heating rate.) Figure 36 presents the plot of undissolved quartz level as a function of log-dissolution rim thickness. A linear relationship can be plotted with excellent correlation. Therefore, the quartz dissolution level can be predicted by examining the dissolution rim thickness.
50
Figure 31. SEM micrographs of porcelain samples fired at different heating rates, dwell times and temperatures to demonstrate the similarity of quartz dissolution rim thickness.
1,200 ˚C, 60 min.
Porcelain sample fired at 1300 °C with 5 K·min-1 and 0.1 hours of dwell.
time.
Porcelain sample fired at 1250 °C with 5 K·min-1 and 0.32 hours of dwell. time.
Porcelain sample fired at 1200 °C with 5 K·min-1 and 1.0 hour of dwell time.
51
Figure 32. Schematic presentation of quartz dissolution rim measurement.
Final Quartz Particle Size ( m)
0.1 1 10 100
Thickness of quartz dissolution rim (m)
0.0 0.2 0.4 0.6 0.8 1.0
Figure 33. The plot of dissolution rim thickness against the final particle size of quartz.
R2
R1
1200 ˚C 1250 ˚C 1300 ˚C
52
Dwell time (hour)
0.1 1 10
Thickness of quartz dissolution rim (m)
0.1 1 10
Figure 34. The plot of dissolution rim thickness as a function of temperature and dwell time.
Heating rate (oC/min)
1 10 100
Thickness of quartz dissolution rim (m)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Figure 35. The plot of dissolution rim thickness as a function of heating rate (Samples fired at 1300 °C, 3.2-hour dwell). It appears to be independent of heating rate.
1200 ˚C 1250 ˚C 1300 ˚C
53
Quartz dissolution rim ( m)
0.1 1 10
Undissolved quartz (wt. %)
14 16 18 20 22 24 26 28
Figure 36. The plot of undissolved quartz presented as a function of quartz dissolution rim thickness.
r² = 0.9804
54
V. CONCLUSIONS
This experiment was meant to determine the effect of fast firing process on densification and mineralogy in commercial porcelain. The 43 experiments were studied with varying levels of temperature, dwell time, and heating rate. The results are:
1. The results from the Quantitative XRD analysis shows that peak temperature, dwell time, and heating rate had no effect on mullite levels above 1200 ˚C;
2. Mullite crystallite size increased as a function of peak temperature, dwell time, and heating rate but the heating rate plays a minor role if compared to the other two;
3. The plot of wt. % of undissolved quartz linearly scales against log-dwell time and it represent that the quartz dissolution is affected solely by temperature and dwell time;
4. Quartz dissolution is the particle size independent presented by the microstructural analysis;
5. Densification is affected by temperature, dwell time and heating rate based the measured apparent bulk density result and that fast firing cycles are on the same continuum as conventional firing cycles;
6. True density is dictated by the mineralogical phase composition and lineally related to calculated density;
7. The ratio of the maximum measured apparent bulk density to the true density, both measured and calculated from mineralogy, shows that these samples maintained a constant closed porosity of 4.2 (±0.5)%; and
8. The amount of glass needed to achieve full densification is about 53.3(±0.9) % and the glass density is constant at 2.36 (±0.02) g•cm-3.
55
Fast firing has been proposed to be limited by heating rate due to heat transfer but this was not observed in this study as both mullite formation and quartz dissolution are independent of heating rate. In other words, quartz dissolution and mullite formation are “diffusion limited process”. In contrast, densification shows a heating rate dependent phenomenon consistent with a viscous deformation model for densification. It can therefore be concluded in this study that fast firing processes are not limited by heat transfer because of the disagreement of three results.
These results provide a new matrix for the design of porcelain bodies that would allow prediction of the mullite, glass, and residual quartz levels to potentially tailor the fired porcelain properties. A porcelain body could be fired over a wide range of temperatures and dwell times and the firing cycle optimized to obtain the desired mineralogy and the level of glass necessary for densification.
56
VI. FUTURE WORK
The parameters such as heating rate (r), dwell time (t), and temperature (T) could be used to predict the densification behavior of a porcelain body. It has been extensively reported that the theory of Master Sintering Curve (MSC) is a powerful tool to predict the densification under the different thermal conditions for a particular porcelain body.
For a given green body, the relationship between activation energy of densification, (Q) and bulk density, (ρ) could be established through the construction of an MSC. The MSC can be constructed by the equation as given by:
𝜌 = 𝜌
0+
1−𝜌01+𝑒𝑥𝑝[𝑙𝑛∅−𝑎
𝑏 ] (12)
Where, ρ0 is the green density, Ф is defined as work of densification as presented elsewhere72. The a and b are constants that can be obtained by the experiment. The particular equation is a typical sigmoid function and its shape representing the densification behavior that is determined by both constants.
Figure 37. An expected Master Sintering Curve (MSC) of commercial porcelain as a function of temperature and log-dwell time.
Green density, ρ0
ρmaximum
T2 T3
Density, ρ
Log time, t
T1
57
The model of MSC, moreover, has been successfully applied to many of the ceramic oxides such as ZnO,73, 74 Al2O3,73 and Al2O3+5% ZrO2.73 However, little attention has been paid to the studies on the formulation of MSC for porcelain.
58
VII. REFERENCES
1. F. H. Norton and F. B. Hodgdon, " The Influence of Time on the Maturing Temperature of Whiteware Bodies I," J. Am. Ceram. Soc., 14 [3], 177-91 (1931).
2. F. H. Norton, Fine Ceramics: Technology and Applications, R. E. Krieger., Huntington, NY, pp 258-280, 1978.
3. W. M. Carty and U. Senapati, "Porcelain—Raw Materials, Processing, Phase Evolution, and Mechanical Behavior," J. Am. Ceram. Soc., 81 [1], 3- 20 (1998).
4. J. Juthapakdeprasert, Translucency of Porcelain, M.S. Thesis, Alfred University, Alfred, NY, 2011.
5. J. M. Amigó, F. J. Serrano, M. A. Kojdecki, J. Bastida, V. Esteve, M. M.
Reventós, and F. Martí, "X-ray Diffraction Microstructure Analysis of Mullite, Quartz and Corundum in Porcelain Insulators," J. Eur. Ceram. Soc., 25 [9], 1479-86 (2005).
6. O. I. Ece and Z.-e. Nakagawa, "Bending Strength of Porcelains," Ceram.
Int., 28 [2], 131-40 (2002).
7. Y. Iqbal and W. E. Lee, "Microstructural Evolution in Triaxial Porcelain," J.
Am. Ceram. Soc., 83 [12], 3121-7 (2000).
8. W. M. Carty, "Observations on the Glass Phase Composition in Porcelains,"
Ceram. Eng. Sci. Proc., 23 [2], 79-94 (2002).
9. W. M. Carty and B. M. Pinto, "Effect of Filler Size on the Strength of Porcelain Bodies," Ceram. Eng. Sci. Proc., 23 [2], 95-105 (2002).
10. O. Castelein, B. Soulestin, J. Bonnet, and P. Blanchart, "The Influence of Heating Rate on the Thermal Behaviour and Mullite Formation from a Kaolin Raw Material," Ceram. Int., 27 [5], 517-22 (2001).
59
11. C. Zanelli, M. Raimondo, M. Dondi, G. Guarini, and P. Tenorio Cavalcante,
"Sintering Mechanisms of Porcelain Stoneware Tiles," Qualicer 2004, GI.- 247-59 (2004).
12. C. Dannert, B. Durschang, F. Raether, and F. Becker, "Optimization of Sintering Processes for Porcelain Using In-Situ Measuring Methods," Glass Sci. Technol., 76, 71-7 (2003).
13. M. Romero, J. Martín-Márquez, and J. M. Rincón, "Kinetic of Mullite Formation from a Porcelain Stoneware Body for Tiles Production," J. Eur.
Ceram. Soc., 26 [9], 1647-52 (2006).
14. D. I. Seymour, Phase Evolution of Electrical Porcelains during Firing; M.S.
Thesis, Alfred University, Alfred, NY, 2000.
15. J. Martín-Márquez, A. G. De la Torre, M. A. G. Aranda, J. M. Rincón, and M. Romero, "Evolution with Temperature of Crystalline and Amorphous Phases in Porcelain Stoneware," J. Am. Ceram. Soc., 92 [1], 229-34 (2009).
16. H. Lee and W. M. Carty, "Glass Phase Composition in Porcelains and Correlation with Firing Temperature", in Proceedings of the 106th Annual Meeting and Exposition of the American Ceramic Society, April 18–21 2004, Indianapolis, Indiana, USA, 2004.
17. M. D. Sacks, Sintering Behavior of Mullite-Containing Materials; Ph.D.
Thesis, University of California, Berkeley, CA,1979.
18. S. M. Johnson, Mullitization of Kaolinite and Al2O3-SiO2 Mixtures, M.S.
Thesis, University of California, Berkeley, CA,1979.
19. F. J. Serrano, J. Bastida, J. M. Amigó, and A. Sanz, "XRD Line Broadening Studies on Mullite," Cryst. Res. Technol., 31 [8], 1085-93 (1996).
20. B. Pinto, W. M Carty, and S. T. Misture, “Measurement of Residual Strain in Quartz Particles in Porcelain”; Science of Whiteware III, Alfred University, Alfred, NY, 2000 (presentation).
60
21. E. Rambaldi, W. Carty, A. Tucci, and L. Esposito, "Using Waste Glass as a Partial Flux Substitution and Pyroplastic Deformation of a Porcelain Stoneware Tile Body," Ceram. Int., 33 [5], 727-33 (2007).
22. A. Shah, The Glass Formation Boundary in Porcelains, M.S. Thesis, Alfred University, Alfred, NY, 2007.
23. W. Jander, "Reaktionen im festen Zustande bei temperaturen.
reaktionsgeschwindigkeiten umsetzungen," Z. Anorg. Allg. Chem., 163 [1], 1-30 (1927).
24. P. Krause and E. Keetman, "Zur kenntnis der keramischen brennvorgange (On Combustion Processes in Ceramics)," Sprechsaal, 69, 45-7 (1936).
25. L. Mattyasovszky-Zsolnay, "Mechanical Strength of Porcelain," J. Am.
Ceram. Soc., 40 [9], 299-306 (1957).
26. Y. Iqbal and W. E. Lee, "Fired Porcelain Microstructures Revisited," J. Am.
Ceram. Soc., 82 [12], 3584-90 (1999).
27. Y. Iqbal, "On the Glassy Phase in Tri-axial Porcelain Bodies," J. Pak. Mater.
Soc., 2 [2], 62-71 (2008).
28. C. J. McConville, A. Shah, and W. M. Carty, "Quartz Dissolution into Porcelain Glasses," Ceram. Eng. Sci. Proc., 25 [2], 51-58 (2009).
29. A. Monshi, "A Kinetic Equation for Diffusion-Controlled Dissolution of Quartz Spherical Particles in Glassy Matrix of Whitewares during Firing,"
Interceram, 47 [3], 155-63 (1998).
30. M. Jackson and B. Mills, "Dissolution of Quartz in Vitrified Ceramic Materials," J. Mater. Sci., 32 [20], 5295-304 (1997).
31. S. T. Lundin, Studies on Triaxial Whiteware Bodies. Almqvist & Wiksell:
Stockholm, 1959.
61
32. E. Rambaldi, W. Carty, A. Tucci, and L. Esposito, "Using Waste Glass as a Partial Flux Substitution and Pyroplastic Deformation of a Porcelain Stoneware Tile Body," Ceram. Int., 33 [5], 727-33 (2007).
33. W. M. Carty, M. Katz, and J. Gill, "The Unity Molecular Formula Approach to Glaze Development," Ceram. Eng. Sci. Proc., 21 [2], 95-107 (2000).
34. L. Hermansson and R. Carlsson, "Crystallization of the Glassy Phase in Whitewares," Trans. J. Br. Ceram. Soc., 77 [2], 32-5 (1978).
35. S. Chaudhuri, "Influence of Mineralizers on the Constitution of Hard Porcelain: II, Microstructures," Am. Ceram. Soc. Bull., 53 [3], 251-4 (1974).
36. I. K. Moroz and A. F. Mironova, "Establishing the Composition of Glass Phase in an Electrical-Engineering Porcelain," Glass Ceram., 43 [5], 209- 12 (1986).
37. J.L.Reid, "The Bullers' Ring," Interceram, 35 [4], 44 (1986).
38. N. G. Holmström, "Fast Firing of Triaxial Porcelain," Am. Ceram. Soc. Bull., 60 [4], 470–43 (1981)
39. H. Mörtel, "Influencing of the Processing Parameters on the Properties of Rapid Fired Porcelain," Materials Science Research, Vol. 11, Processing of Crystalline Ceramics, Eds. H. Palmour III, R. F. Davis, T. M. Hare, 253-62, Springer, New York, 1978.
40. G. C. Robinson, "Designing Firing Schedules with Thermal Analysis."
Science of Whitewares, Eds: G. Y. Onoda, Victoria E. Henkes, William M.
Carty, pp. 249-63, Amer. Cer. Soc., Westerville, OH, 1995.
41. G. T. Saleiro and J. N. F. Holanda, "Processing of Red Ceramic Using a Fast-Firing Cycle," Cerâmica, 58 [347], 393-9 (2012).
42. M. N. Rahaman, Sintering of Ceramics. CRC Press, Boca Raton, FL, (2008).
62
43. D. Garcia, J. Seidel, R. Janssen, and N. Claussen, "Fast Firing of Alumina,"
J. Eur. Ceram. Soc.,15 [10], 935-38 (1995).
44. L. Amorós, M. J. Orts, J. García-Ten, A. Gozalbo, and E. Sánchez, "Effect of the Green Porous Texture on Porcelain Tile Properties," J. Eur. Ceram.
Soc., 27 [5], 2295-301 (2007).
45. E. Sanchez, M. Orts, J. Garcia-Ten, and V. Cantavella, "Porcelain Tile Composition Effect on Phase Formation and End Products," Am. Ceram.
Soc. Bull., 80 [6], 43-9 (2001).
46. V. Biasini, M. Dondi, G. Guarini, M. Raimondo, A. Argnani, and S. Di Primio,
"Effect of Talc and Chlorite on Sintering and Technological Behaviour of Porcelain Stoneware Tiles," Silic. Ind., 68 [5-6], 67-73 (2003).
47. J. Martín-Márquez, J. M. Rincón, and M. Romero, "Effect of Firing Temperature on Sintering of Porcelain Stoneware Tiles," Ceram. Int., 34 [8], 1867-73 (2008).
48. E. Sánchez, J. García-Ten, V. Sanz, and A. Moreno, "Porcelain Tile: Almost 30 Years of Steady Scientific-Technological Evolution," Ceram. Int., 36 [3], 831-45 (2010).
49. S. Shiva and S. Amin, "Mechanisms of Momentum Transport in Viscous Flow Sintering"; Sintering Applications. Ed. B. Ertug, pp. 287-318, Intech Rijeka, Croatia, 2013.
50. F. Matteucci, M. Dondi, and G. Guarini, "Effect of Soda-Lime Glass on Sintering and Technological Properties of Porcelain Stoneware Tiles,"
Ceram. Int., 28 [8], 873-80 (2002).
51. A. Salem, S. Jazayeri, E. Rastelli, and C. Timellini, "Effect of Nepheline Syenite on the Colorant Behavior of Porcelain Stoneware Body," J. Ceram.
Process. Res., 10 [5], 621-7 (2009).
63
52. R. Sladek, "The Fast Firing Process in the Ceramic Industry," Interceram, 35 [4], 5 (1986).
53. T. S. Possamai, R. Oba, V. P. Nicolau, D. Hotza, and D. E. García,
"Numerical Simulation of the Fast Firing of Alumina in a Box Furnace," J.
Am. Ceram. Soc., 95 [12], 3750-7 (2012).
54. C. E. Baumgartner, "Fast Firing and Conventional Sintering of Lead Zirconate Titanate Ceramic," J. Am. Ceram. Soc., 71 [7], C-350-3 (1988).
55. A. Seal, R. Mazumder, A. Sen, and H. S. Maiti, "Fast Firing of Lead Zirconate Titanate Ceramics at Low Temperature," Mater. Chem. Phys., 97 [1], 14-8 (2006).
56. C. Miclea, C. Tanasoiu, C. Miclea, L. Amarande, R. Iorgulescu, V. Tanasoiu, and S. Moscu, "Advanced Technology for Making PZT Type Ceramics by Fast Firing," J. Opt. Adv. Mater., 3 [1], 83-8 (2001).
57. M. Dondi, M. Marsigli, and I. Venturi, "Microstructure and Mechanical Properties of Clay Bricks: Comparison Between Fast Firing and Traditional Firing," Br. Ceram. Trans., 98 [1], 12-8 (1999).
58. G. T. Saleiro and J. N. F. Holanda, "Processing of Red Ceramic Using a Fast-Firing Cycle," Cerâmica, 58, 393-9 (2012).
59. T. Manfredini and L. Pennisi, "Recent Innovations in the Fast Firing Process," Science of Whitewares, Eds: G. Y. Onoda, Victoria E. Henkes, William M. Carty, pp. 213-23, Amer. Cer. Soc., Westerville, OH, 1995.
60. W. Schulle, "Trends and Problems in the Development of the Porcelain Firing Process," Interceram, 52 [4], 192-6 (2003).
61. M. Huckabee, T. Hare, H. Palmour, "Rate-Controlled Sintering as a Processing Method,” Processing of Crystalline Ceramics, Eds: H. Palmour, R. Davis, T. Hare, Plenum Press, New York, 203-15 (1978).
64
62. J. Funk, "Designing the Optimum Firing Curve for Porcelain," Am.
Ceram.Soc. Bull., 61 [6], 632-5 (1982).
63. A. Klein and D. Hotza, "Advanced Ceramics with Dense and Fine-Grained Microstructures Through Fast Firing," Rev. Adv. Mater. Sci, 30, 273-81 (2012).
64. M. M. Gauthier, Engineered Materials Handbook, pp.784-822, ASM International, Materials Park, OH, 1995.
65. K. R. Venkatachari, D. Huang, S. P. Ostrander, W. A. Schulze, and G. C.
Stangle, "Preparation of Nanocrystalline Yttria-stabilized Zirconia," J. Mater.
Res., 10 [3], 756-61 (1995).
66. “Standard Test Methods for Apparent Porosity, Water Absorption, Apparent Specific Gravity, and Bulk Density of Burned Refractory Brick and Shapes by Boiling Water," ASTM Designation C20-00. American Society for Testing and Materials, West Conshohocken, PA, 2010.
67. W. D. Kingery, H. K. Bowen, and D. R. Uhlmann, Introduction to ceramics, 2nd ed.; Wiley-Interscience, New York, 1976.
68. W. W. Meyer, "Computational of Heat Treatments for Whiteware Bodies,"
J. Am. Ceram. Soc., 21 [3], 75-9 (1938).
69. W. Lerdprom and W. M. Carty, "Mullite Formation Kinetic in Porcelain on Fast and Conventional Firing Schedules." (in process)
70. W. Eitel, Silicate Science, V.III, pp.13-4. Academic Press, New York,1976.
71. E. Skovira, Properties of the Porcelain Glass Phase, M.S. Thesis, Alfred Univerity, Alfred, NY, 2006.
72. B. Griese, “Porcelain in The Ceramic Tile Industry-Definition differs: water absorption of 0.5 percent or less is key” (2007). Accessed on: Febuary 2014. Available at <http://www.tileusa.com.>
65
73. D. C. Blaine, S.-J. Park, and R. M. German, "Linearization of Master Sintering Curve," J. Am. Ceram. Soc., 92 [7], 1403-9 (2009).
74. H. Su and D. L. Johnson, "Master Sintering Curve: A Practical Approach to Sintering," J. Am. Ceram. Soc.,79 [12], 3211-7 (1996).
75. K. G. Ewsuk, D. T. Ellerby, and C. B. DiAntonio, "Analysis of Nanocrystalline and Microcrystalline ZnO Sintering Using Master Sintering Curves," J. Am.
Ceram. Soc., 89 [6], 2003-9 (2006).
76. W. M. Carty and H.Lee, Alfred University, Alfred, NY, February 2014, Private Communication.
77. Minitab 16. {CD-ROM]. Minitab Inc., State College, PA, 2010.
66 APPENDIX
8.1 Preliminarily study of the thermal equilibration
This experiment was performed to determine how uniform the phase development is in a sample during fast firing process. If the same amount of heat work was provided through the sample body, it would be expected that the quantities for each phase would be equal throughout the sample. Due to the samples needing to be fired at fast heating rate, it would be different of heat work absorbed in the sample body by the effect of temperature gradient that is associated with heat transfer phenomenon. This assumption is easily illustrated by the densification of work-piece after heat treatment and it is simple to examine by
“ink test” that is suggested by Carty and Lee. 75
Moreover, the extrusion process might cause an inhomogeneity to develop into an extruded piece due to possibility of particle migration. If the composition varies throughout the sample, then different phase formation would be expected.
If different phase formation occurred in the body, it would be difficult to say whether it was the fast firing process or the extrusion process that was responsible.
However, in this experiment, the extrusion die of 15 mm diameter was used so that varying in composition could be minimized by suggestion of Seymour’s study. 14 He reported that there was no composition gradient in the extruded samples due to the extrusion process; even the 16 cm diameter die was used.
Therefore, the three different sizes of extruded porcelain pellets were made from particular porcelain body with 7 mm, 14 mm, and 21 mm of thicknesses while the sample’s diameter was equal. The different firing conditions were selected to study of thermal equilibration including peak temperatures of 1,200 and 1250 ˚C, 0.1-hour of dwell time and 5, 20 and 60 K·min-1 of heating rate. These firing conditions represent to the most critical conditions that could lead to thermal gradient in the samples. Once the samples were fired, a diamond saw blade was used to cross section the pieces for ink test. After cross section cutting, the samples were examined for the densification behavior by “ink test” then the densification gradient could be observed.