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A glass is defined in ASTM (American Society for Testing and Materials) as ”an inorganic product of fusion which has been cooled to a rigid condition without crystallization ”. According to this definition, a glass is a noncrystalline material obtained by a melt-quenching
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A glass is defined in ASTM (American Society for Testing and Materials) as ”an inorganic product of fusion which has been cooled to a rigid condition without crystallization”. According to this definition, a glass is a noncrystalline material obtained by a melt-quenching process. Nowadays, noncrystalline materials that can not be distinguished from melt-quenched glasses of the same composition are obtainable by using various techniques such as chemical vapor deposition, sol-gel process, etc. Therefore, most glass scientists regard the term `glass' as covering all noncrystalline solids that show a glass transition regardless of their preparation method.
SiO2晶體結構 Quartz Tridymite
玻璃與晶體的結構比較 晶體結構稱為長程有序。玻璃結構成為短程有序，長程無序。
玻璃與晶體徑向原子分布的比較 Schematic diagram of radial atomic distribution function of gas, liquid, amorphous and crystal
Schematic representation of the temperature dependence of system volume for a liquid that can both crystallize and form a glass.
Kauzmann temperature ： 玻璃與晶體間熵的差值為零。 一階相變： 有吸熱或放熱反應， 比熱有不連續的變化，例如水變冰、水變水蒸氣。 二階相變： 沒有吸熱或放熱反應， 比熱連續的變化，例如超導的變化、磁性物質的變化，玻璃轉換可視為二階的變化(但不是完全的二階相變化)。 Measurement of Tg by DSC Determination of Tg by dilatometry
熵(Entropy) 熱力學第零定律引入狀態函數溫度；熱力學第一定律引入狀態函數內能； 熱力學第二定律將引入狀態函數熵(S)。 與路徑無關，僅與最初與最後狀態有關 物質常見的三態為氣態、液態以及固態，但是物質在某些狀態下，有時可能有多種不同的相。冰、水共存的系統有兩個相，兩物態相之間為液－固界面。 不同相之間的轉變稱為相變(phase transition)，一些物理性質會有不連續變化，例如： (1) 氣－液相變：密度發生不連續變化 (2) 超導體的超導態－正常態相變：導電度發生不連續變化。 (3) 液態氦氦Ⅰ(正常態)－氦Ⅱ(超流態)相變：黏滯係數發生不連續變化。 (5) 鐵磁體－順磁體相變：磁化率(magnetic susceptibility)發生不連續變化 。 一階相變之熵不連續，有潛熱 L=T(Sf-Si) 。二階相變的過程不會出現潛熱。
不同類型玻璃的玻璃轉換溫度 PC PP PVAc PET PVC PS
1P = 1g/(cm．s) 常溫下，水的黏度約 1cP， 空氣的黏度約 0.02cP Viscosity of some silicate glasses strain point h=1014.6P the thermal expansion curve begins to deviate from linearity strain point annealing point h=1013.4P glass becomes strain-free in 15min when anneals at this Tg h=1013P softening point h=107.6P glass will elongate under its own weight work point h=104P glass can be formed or sealed
Measurement of viscosity At low viscosity (up to 108P), the rotating cylinder method is used. r0, r1 are radii of inner and outer cylinders, h is the height of the liquid, F is the force applied for keeping a constant angular velocity w. At high viscosity (high than 108P), rod elongation method is used. L is the length of the glass rod, r is the its radius, m is the mass hanging on it, v is the velocity of elongation, f is a calibration factor of the instrument.
1. SiO2 2. GeO2 3. 0.045mol%Na2O in GeO2 4. 20mol%Na2O in SiO2 5.24.5mol% K2O in SiO2 Four types of glasses 1. Strong network liquid show linear behavior: SiO2, GeO2, BeF2. 2. Partially broken three-dimensional network: alkali silicate, soda-lime silicate, As2S3. 3. Liquids have a more severely distorted structure: CaAl2SiO8, alkali phosphate, ZnCl2. 4. Completely ionic and molecular glasses: 0.4KNO3-0.6Ca(NO3)2.
The viscosity fits an Arrhenius-type equation over some temperature range E is activation energy, R is gas constant (8.31 J/(K-mol)). GeO2 E=75kcal/mol(540~1500 ℃), P2O5 E=41.5kcal/mol(545~655 ℃) The empirical equation h0 and B are temperature-independent .
Metal oxide (mol%) Effects of metal oxide on the viscosity of binary liquid silicates Energy of activation for viscous flow (Eh) in binary liquid silicates.
玻璃形成子(glass-former):SiO2、B2O3、GeO2、P2O5可單獨形成玻璃。玻璃形成子(glass-former):SiO2、B2O3、GeO2、P2O5可單獨形成玻璃。 玻璃修飾子(glass modifier):Na2O、CaO、La2O3… 無法單獨形成玻璃者。 中間子(conditional glass-former):Al2O3、V2O5無法單獨形成玻璃， 但與形成子混合，可以變成形成子
氧化物如SiO2、P2O5和B2O3本身可快速冷卻形成玻璃的網狀結構稱玻璃形成子。這些氧化物滿足所提玻璃生成條件。這些條件是：氧化物如SiO2、P2O5和B2O3本身可快速冷卻形成玻璃的網狀結構稱玻璃形成子。這些氧化物滿足所提玻璃生成條件。這些條件是： Zachariasen criteria (a)氧離子和陽離子數相接不超過2， (b) 以陽離子為中心於四周的氧離子的配位數為4或更小， (c) 於陽離子為中心的多面體間為共點結合，非共邊或共面結合， (d) 每個氧至少有 3個鍵角跟其他四面體連結。 滿足Zachariasen criteria:B2O3, SiO2, P2O5, GeO2, P2O3, As2O5, As2O3, Sb2O3, Nb2O5, GeO2, Ta2O5, As2O5, Stanworth criteria (a)陽離子的價位數必須大於3， (b)形成玻璃的容易程度隨著陽離子的半徑減小而增加， (c) 陽離子的Pauling’s electronegativity介於1.5~2.1之間 滿足Stanworth criteria : Si, Ge, As, P, B, Sb, V, W, Mo, Te
Fictive temperature (假想溫度) glass at temperature T2 has the same structure as a super cooled liquid at temperature Tf. Tf is an artificial temperature used to describe the glassy state. Super cooled liquid glass
Change of refractive index, density and viscosity versus equilibrium time
Refractive index versus time at constant T Two relaxation time, one fast 7.77mins, one slow 64.4mins. The fast relaxation processes corresponds to the more mobile structure with higher fictive temperature. The slow relaxation processes corresponds to the denser and therefore less mobile structure with lower fictive temperature.
In the literature, there are three main ways that the Fictive Temperature is defined. Structure: The fictive temperature is where the structure freezes. The fictive temperature distribution serves as a map from equilibrium to nonequilibrium phase space distributions. Property values: May have practical value. Different properties would have different fictive temperatures. No connection to microscopic physics. Relaxation processes: Here a new fictive temperature is defined as each relaxation mode freezes. Does not try to map equilibrium to nonequilibrium states. Glass transition temperature actually is a glass transition region. The region broadens with increasing of cooling rate.
