現今製備二矽酸鋰材料之傳統製程主要可分為熔融、淬火與結晶化熱處理等部份。對於生產成本而言，無論是白金容器、高溫熔融與多次結晶化熱處理甚至於淬火設備皆造成生產成本大幅增加。故如以較有經濟效益之精密陶瓷製程，以固相反應法進行起始粉末之合成，再經壓製成型後進行緻密化燒結熱處理以得緻密之二矽酸鋰陶瓷材料，對此材料在牙體復形與重建之應用有相當大的助益。
本研究以目前二矽酸鋰玻璃陶瓷材料常使用之SiO2 - K2O - P2O5 - Li2O系統為主要組成，並藉由添加Al2O3成份細化其微觀結構以得到更佳之機械強度表現。此材料中，SiO2與Li2O之莫耳比為2.39：1之共晶組成。Li2Si2O5/SiO2將形成高強度之共晶板層組織，而Li2Si2O5結晶傾向朝(010)之優選方向成長而形成針狀晶粒，此針狀晶粒間則因互相交錯形成聯鎖(interlocking)效應而使此材料具有良好的韌性表現。
在固相反應製程中，Li2O將首先與SiO2以莫耳比1比1之比例反應形成偏矽酸鋰(Li2SiO3)結晶相。而Li2Si2O5結晶相則於750℃開始由Li2SiO3與過量之SiO2反應轉化而成，但直到850℃之煅燒溫度才開始快速反應，在850℃煅燒3小時後Li2SiO3幾乎以完全轉為二矽酸鋰結晶相。
氧化鋁成份的添加確實可有效細化二矽酸鋰晶粒結構及其共晶板層間距而提升其抗彎強度高達27%。但氧化鋁的存在亦同時抑制二矽酸鋰結晶相的晶粒成長，過量添加之氧化鋁則將嚴重阻礙其結晶在(010)優選方向上的發展而使針狀晶粒長度大為縮短，造成二矽酸鋰材料針狀晶粒間無法有效形成特殊的聯鎖效應而使二矽酸鋰陶瓷在材料韌性上的表現不佳。
二矽酸鋰粉末經乾壓成胚體後燒結，加熱至920℃以上之溫度可快速於1小時內完成燒結緻密化。然而在緻密化階段完成的同時，試片內部殘留之封閉氣孔(primary pores)形成體積明顯膨脹之Secondary pores，而使材料密度隨著持溫時間增加而下降。
由粉末粒徑細化至400 nm以下的二矽酸鋰粉末壓製成型之胚體經920℃燒結1小時後，其相對密度可達95%以上，試片之四點抗彎強度達192.1MPa，維氏硬度則為600HV以上。而為了進一步提升二矽酸鋰陶瓷材料之緻密性以得較佳之機械強度表現，本研究利用2 kg/cm2之外加壓力進行920℃熱壓燒結可有效提升其相對密度至97%以上。但由於封閉氣孔內氣體壓力的抵消，欲達更佳之緻密性表現則需輔以更大之外加壓力。

The conventional process for the lithium disilicate glass ceramics includes melting, quenching and crystallization with heat treatment. For the fabrication of lithium disilicate glass ceramics, the high temperature melting, Pt crucible, quenching equipment and repeated crystallization process and high production cost. Therefore, a cost-effective process such as advanced ceramic process, including the synthesis of the precursor powder by a solid state reaction, die-pressing process and sintering to obtain dense silicate lithium ceramic materials is beneficial for this material to be used for dental restoration and reconstruction.

In this study, the SiO2-K2O-P2O5-Li2O system was selected to form lithium disilicate. The microstructure was refined by adding a small amount of Al2O3 to improve the performance of mechanical strength. In the lithium disilicate glass ceramic, the molar ratio of SiO2 and Li2O is 2.39:1 which the eutectic composition of Li2O-SiO2 system. The lithium disilicate phase and quartz phase tend to form a high strength lamellar eutectic structure. The (010) orientation is the preferred growth direction for Li2Si2O5 crystal that result in needle-like grains. The interlocking network formed by needle-like grains provides better toughness performance.

In the solid state reaction process, lithium carbonate and quartz reacted into Li2SiO3 with the molar ratio of 1:1. When the Li2CO3 was exhausted, the Li2SiO3 reacted with excess SiO2 to form Li2Si2O5 as the temperature reached 750℃. The reaction rate of lithium disilicate was slow until the temperature reaches to 850℃. While calcination occurs at 850℃, almost all of the Li2SiO3 phase turns into Li2Si2O5 phase within 3 hours.

For better mechanical strength, the addition of Al2O3 in lithium disilicate effectively enhanced the bending strength of lithium disilicate ceramic as much as 27%. But the presence of Al2O3 also inhibited Li2Si2O5 grain growth along the preferred (010) orientation. As a result, the length of needle-like grain is shortened and the interlocking behavior was not as effective.
The densification of the lithium disilicate green body may complete within one hour at 920℃ by conventional sintering process. However, at the same time, the residual closed pores (so-called primary pores) may develop to abnormal huge pores (so-called secondary pores) which result in the decreasing of density with extended sintering time.

Relative density of lithium disilicate bulk could reach over 95% after sintering at 920℃ for one hour by using the fine powder with particle size below 400 nm. The 4-points bending strength test and Vickers-hardness for above-mentioned sample were 192.1 MPa and 628.8HV, respectively. In order to enhance the mechanical strength of lithium disilicate, we used hot-pressing process with 2 kg/cm2 pressure to obtain a higher relative density of >97%. However, due to the counteraction of the vapor pressure in the closed pores, higher heat-pressing pressure may be needed to obtain higher density.

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