本研究透過三階段燒結法，在燒結體相對密度超過99.5 %、微結構完整無孔洞且晶界平直的條件下，針對以往研究中較少探討的晶粒區間1-20 μm的氧化鋁陶瓷，觀察晶粒大小連續變化與全穿透率的關係，確認晶粒尺寸需要長到多大，能使全穿透率達50 %。因長時間的燒結容易產生異常晶粒成長現象，本實驗在生坯中加入0 ppm、500 ppm與1000 ppm添加量的Mg2+作為修飾劑，希望改善異常晶粒成長現象，因添加量不同造成試片在第三階段的燒結過程中，晶粒成長速率有所改變，間接影響最終的全穿透率表現，探討上述添加量與晶粒成長的關係也是本研究的一大主軸。
為製備出目標中最小的1 μm試片，需要利用起始晶粒100 nm的生坯進行燒結，配合三階段的燒結製程，使燒結過程更省時與減少耗能，才能輕鬆製備出晶粒最大20 μm的氧化鋁陶瓷，於燒結的第一階段使晶粒成長至相對密度90 %後進入第二階段燒結，降低燒結收縮的速度，避免晶粒生長過快產生封閉性孔洞，進而提升試片的相對密度達99.5 %、幫助晶界平直化，第二階段燒結完成後試片晶粒約為1 μm，借助第三階段燒結，使晶粒二次快速成長，最終製備出各種不同晶粒大小且晶界平直無孔洞的高緻密透光氧化鋁。
經實驗得知晶粒尺寸在1-20 μm連續變化的條件下，全穿透率隨燒結體晶粒增大而升高，19 μm透光氧化鋁全穿透率可達50 %。藉由晶粒成長前後的體積差除以原本的表面積，得到晶粒實際增加量以此作為本研究中成長速率的值，而Mg2+添加量越多會使MgAl2O4越早析出，發生異常晶粒成長的時間反而延後，但兩者的產生都會使成長速率提升，不僅如此，比較相同晶粒大小的試片，當添加量提升時，穿透率也會提高，因此只要適量調控Mg2+的添加量，在未產生MgAl2O4的前提下，就能讓小晶粒的氧化鋁具備與未添加Mg2+的氧化鋁有相同的透光表現，有助於未來高強度微晶透光氧化鋁的開發。

This study chooses three-stage sintering techniques to observe the relationship between the continuous change of the grain interval 1-20 μm and the total-forward transmission (TFT) of translucent alumina with their relative densities all exceeding 99.5 %, meanwhile, confirming the grain size that achieves TFT of 50%. Due to abnormal grain growth (AGG) caused by three-stage sintering, in this experiment, 0 ppm, 500 ppm and 1000 ppm Mg2+ was added into alumina to inhibit AGG and at the same time affect alumina’s grain growth and transmittance performance. To prepare the specimen with grain size of 1-20 μm, a green body with a starting size of 100 nm and three-stage sintering techniques are indispensable. As the second stage of sintering is completed, grain size of specimen is about 1 μm and the density has reached more than 99.5%. On next step, with the help of the third stage of sintering, the grains grow rapidly again, and finally high-density translucent alumina with various grain sizes and straight grain boundaries without holes are prepared.
Experiments show that TFT will increase with the increase of grain size with continuously changes from 1 to 20 μm, and TFT of the sample with grain size of 19 μm under the condition of none Mg2+ addition can reach 50 %. Besides, the more Mg2+ added before sintering, the sooner MgAl2O4 will precipitate, but occurrence of abnormal grain growth will be delayed. As the addition amount increases, TFT will also increase, which compares to different specimens with the same grain size; If the amount of Mg2+ is appropriately controlled, avoiding that MgAl2O4 is not produced, small-grained alumina can have better mechanical strength but maintain the same transmittance performance as large-grain.

[1] M. A. Meyers, A. Mishra, and D. J. Benson, "Mechanical properties of nanocrystalline materials," progress in materials science, vol. 51, no. 4, pp. 427-556, (2006).
[2] G. Wei, "Transparent ceramic lamp envelope materials," journal of physics D: applied physics, vol. 38, no. 17, p. 3057, (2005).
[3] W. W. Mullins, "Two‐dimensional motion of idealized grain boundaries," journal of applied physics, vol. 27, no. 8, pp. 900-904, (1956).
[4] 孫梓萱，以 θ-Al2O3與PEG混合模式製備50 nm晶粒α-Al2O3生坯及其燒結行為觀察。國立成功大學資源工程研究所碩士論文，(2021)。
[5] 黃姵文，模擬 θ-Al2O3@ PEG核殼技術製作細晶粒α-Al2O3生坯之特性觀察。國立成功大學資源工程研究所碩士論文，(2020)。
[6] M. Demuynck, J.-P. Erauw, O. Van der Biest, F. Delannay, and F. Cambier, "Densification of alumina by SPS and HP: A comparative study," journal of the European ceramic society, vol. 32, no. 9, pp. 1957-1964, (2012).
[7] B.-N. Kim, K. Hiraga, K. Morita, and H. Yoshida, "Spark plasma sintering of transparent alumina," scripta materialia, vol. 57, no. 7, pp. 607-610, (2007).
[8] B.-N. Kim, K. Hiraga, K. Morita, H. Yoshida, T. Miyazaki, and Y. Kagawa, "Microstructure and optical properties of transparent alumina," acta materialia, vol. 57, no. 5, pp. 1319-1326, (2009).
[9] G. Mata-Osoro, J. S. Moya, and C. Pecharroman, "Transparent alumina by vacuum sintering," journal of the European ceramic society, vol. 32, no. 11, pp. 2925-2933, (2012).
[10] J. Petit , "Sintering of α-alumina for highly transparent ceramic applications," journal of the European ceramic society, vol. 31, no. 11, pp. 1957-1963, (2011).
[11] T. W. Hansen, A. T. DeLaRiva, S. R. Challa, and A. K. Datye, "Sintering of catalytic nanoparticles: particle migration or Ostwald ripening ?," accounts of chemical research, vol. 46, no. 8, pp. 1720-1730, (2013).

[12] F. S. Yen, H. S. Lo, H. L. Wen, and R. J. Yang, "θ-to α-phase transformation subsystem induced by α-Al2O3-seeding in boehmite-derived nano-sized alumina powders," journal of crystal growth, vol. 249, no. 1-2, pp. 283-293, (2003).
[13] 黃雯巧、黃姵文、向性一、黃啓原、顏富士，奈米級晶粒 α-Al2O3的生坯製作。鑛冶：中國鑛冶工程學會會刊，(2021)。
[14] 楊榮澤，奈米 α-Al2O3 晶粒之成長熱力學。國立成功大學資源工程研究所博士論文，(2009)。
[15] I. J. Bae and S. Baik, "Abnormal grain growth of alumina," journal of the American ceramic society, vol. 80, no. 5, pp. 1149-1156, (1997).
[16] P. Jorgensen and J. Westbrook, "Role of solute segregation at grain boundaries during final–stage sintering of alumina," journal of the American ceramic society, vol. 47, no. 7, pp. 332-338, (1964).
[17] P. Franken and A. Gehring, "Grain boundary analysis of MgO-doped Al2O3," journal of materials science, vol. 16, pp. 384-388, (1981).
[18] P. Jorgensen, "Modification of sintering kinetics by solute segregation in Al2O3," journal of the American ceramic society, vol. 48, no. 4, pp. 207-210, (1965).
[19] R. L. Coble, "Sintering crystalline solids. II. Experimental test of diffusion models in powder compacts," journal of applied physics, vol. 32, no. 5, pp. 793-799, (1961).
[20] L. Miller, A. Avishai, and W. D. Kaplan, "Solubility limit of MgO in Al2O3 at 1600 °C," journal of the American ceramic society, vol. 89, no. 1, pp. 350-353, (2006).
[21] W. Johnson and D. Stein, "Additive and impurity distributions at grain boundaries in sintered alumina," journal of the American ceramic society, vol. 58, no. 11‐12, pp. 485-489, (1975).
[22] J. Mollá, R. Moreno, and A. Ibarra, "Effect of Mg doping on dielectric properties of alumina," journal of applied physics, vol. 80, no. 2, pp. 1028-1032, (1996).
[23] R. Apetz and M. P. Van Bruggen, "Transparent alumina: a light‐scattering model," journal of the American ceramic society, vol. 86, no. 3, pp. 480-486, (2003).
[24] M. Stuer, Z. Zhao, U. Aschauer, and P. Bowen, "Transparent polycrystalline alumina using spark plasma sintering: effect of Mg, Y and La doping," journal of the European ceramic society, vol. 30, no. 6, pp. 1335-1343, (2010).
[25] J. Schroeder and J. H. Rosolowski, "Light scattering in polycrystalline materials," imerging optical materials, vol. 29, pp. 156-168, (1982).
[26] R. M. German, "Sintering theory and practice," (1996).
[27] M. Barsoum, "Fundamentals of ceramics. CRC press," (2019).
[28] R. L. Coble, "Sintering crystalline solids. I. Intermediate and final state diffusion models," journal of applied physics, vol. 32, no. 5, pp. 787-792, (1961).
[29] U. Sutharsini, M. Thanihaichelvan, and R. Singh, "Two-step sintering of ceramics," sintering of functional materials, pp. 3-22, (2018).
[30] F. J. Lin, L. C. De Jonghe, and M. N. Rahaman, "Microstructure refinement of sintered alumina by a two‐step sintering technique," journal of the American ceramic society, vol. 80, no. 9, pp. 2269-2277, (1997).
[31] N. Lóh, L. Simão, C. Faller, A. De Noni Jr, and O. Montedo, "A review of two-step sintering for ceramics," ceramics international, vol. 42, no. 11, pp. 12556-12572, (2016).
[32] P. Streitenberger and D. Zöllner, "Von Neumann–Mullins-type evolution equations for triple and quadruple junction controlled grain growth," scripta materialia, vol. 109, pp. 52-55, (2015).
[33] M. Hillert, "On the theory of normal and abnormal grain growth," acta metallurgica, vol. 13, no. 3, pp. 227-238, (1965).
[34] W. D. Kingery, H. K. Bowen, and D. R. Uhlmann, "introduction to ceramics. John wiley & sons," (1976).
[35] G. Nichols, "A review of the terms agglomerate and aggregate with a recommendation for nomenclature used in powder and particle characterization," journal of pharmaceutical sciences, vol. 91, no. 10, pp. 2103-2109, (2002).
[36] 張恩碩，以 100 nm 原料粉末製備之高純度氧化鋁在無異常晶粒成長前的機械性質。國立成功大學資源工程研究所碩士論文，(2022)。
[37] B. R. Marple and D. J. Green, "Mullite/alumina particulate composites by infiltration processing," journal of the American ceramic society, vol. 72, no. 11, pp. 2043-2048, (1989).
[38] 劉冠偉、謝志鵬、吳音，液相前驅體浸滲技術調控陶瓷材料組成和特性的研究進展。無機材料學報，(2011)。
[39] S. W. Hughes, "Archimedes revisited: a faster, better, cheaper method of accurately measuring the volume of small objects," physics education, vol. 40, no. 5, p. 468, (2005).
[40] W. Walton, "Feret‘s statistical diameter as a measure of particle size," nature, vol. 162, no. 4113, pp. 329-330, (1948).