Glass V.M. Sglavo GlassEng - UNITN 2017

Transcription

1 Glass Definition material with no long range order matarial characterized by the glass transition phenomenon amorphous solid without long range order and ordered atomic structure, which shows the glass transition effect

2 Glass structure silica glass short range order, ONLY O Si quartz / crystobalite long and short range order - crystal Glass science, R. H. Doremus, J. Wiley & Sons, 1994

3 Glass formation T g = glass transition or glass transformation temperature T f = fictive temperature (temperature characterizing the structure of the liquid in equilibrium with the glass obtained from it) Introduction to ceramics, W. D. Kingery, H. K. Bowen and D. R. Uhlmann, J. Wiley & Sons, 1975 Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

4 speci&ic volume liquid undercooled liquid kinetic crossroad glass crystal temperature

5 Thermal histories of glass Heating and cooling with different rates structural relaxation time (movement of atoms / molecules) heating /cooling rate Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

6 Isotherms within the transition interval Introduction to glass science and technology, J. E. Shelby, The Royal Society of Chemistry, 1997

7 Experimental data Soda-lime silicate glass (7loat) - common glass , cooling#rate#( C/min)# 565 Tg#( C)# 2,500 2,490 2,480 2,470 2,460 2,450 2,440 2,430 2,420 density (g/cm3) 2,410 2,400 0, cooling rate ( C/min)

8 Genesis of glass: structural features Radial distribution (SiO 2 ) r oxide glasses m = ρ 0 4π r 3 3 radial density m r = ρ 04π r 2 gas or liquid crystal radius (Å) Vetri, G. Scarinci, T. Toninato e B. Locardi, Casa Editrice Ambrosiana, 1977

9 X-ray diffraction spectra Glass = frozen liquid difficulty in the crystallization from melt Suggested reading: X-ray determination of the structure of glass, B.E. Warren, J. Am. Ceram. Soc., 1935 Introduction to ceramics, W. D. Kingery, H. K. Bowen and D. R. Uhlmann, J. Wiley & Sons, 1975

10 Zachariasen observations: glass forms a random network instead of an ordered structure (energy differences are minimal) Rules for the formation of glass 1. Each oxygen can bond two cations or less 2. The coordination number of cation must be small (< 4) 3. The polyhedra share only the vertices 4. At least 3 vertices must be shared SiO 2, B 2 O 3, P 2 O 5

11 Basic structures Th 4+ in ThO 2 r C /r A > 1 coordination = 12 Ba 2+ in BaZrO 3 Mg 2+ in MgO, Al 3+ in Al 2 O 3 Si 4+ in SiO 2 B 3+ in B 2 O 3 H + in H 2 O Introduction to ceramics, W. D. Kingery, H. K. Bowen and D. R. Uhlmann, J. Wiley & Sons, 1975

12 bonds between polyhedra tetrahedra octahedra

13 Zachariasen: random network theory Porai-Koshits: paracrystalline domans theory triangles or tetrahedra short range order Introduction to ceramics, W. D. Kingery, H. K. Bowen and D. R. Uhlmann, J. Wiley & Sons, 1975

14 TEM micrograph 1 nm Suggested reading: Imaging atomic rearrangements in two-dimensional silica glass: watching silica s dance, P.Y. Huang et al., Science, 2013 P.Y. Huang et al., Science, 342, 224 (2013)

15 Computer simulations molecular dynamics analyses (minimization of the potential energy) Boria-alumina-soda silicate glass Courtesy of M. Montorsi, Università di Modena, 2005

16 Former and modifier oxides silica glass bridging oxygen non-bridging oxygen soda silicate glass Introduction to ceramics, W. D. Kingery, H. K. Bowen and D. R. Uhlmann, J. Wiley & Sons, 1975