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1、B10010605刘钟霞,The glass sciences,The world of glass Preparation of glass Structure and properties of Glasses Applications of glass Recent Topics Of Optoelectronics materials (光电材料),Contents：,We are live in the world of glasses,Can you count how many things in our around that are made from glass ?,4.1
2、 The World of Glasses,Glass wall,Glass art,reagent bottle,Glass kettle,4.1.1 Natural Glasses,The volcanic outflow (火山喷发) of the molten magma (岩浆) get cooled and form glasses.,Natural glass (1),Natural glass (2),Impactites (击变岩) are natural glasses formed from crystalline materials rendered amorphous
3、 by the shock of meteoric (陨石) impact. Glasses formed from impacted melts are known as tektites (玻陨石).,4.1.2 Glasses in Modern Time,Sheet glass : a few mm in thickness,Glass fibers : by extruding melts through metal orifices and rolled on to large diameter spindles or are gathered as (fibrous) glass
4、-wool.,Use of glass fibers :,As insulating materials For information transmission,Plate glass : by a float process where melts are made to settle and freeze on molten tin pools , which provide optically smooth and parallel surfaces. Color glass :by adding oxides or halides and made to change their c
5、olor .,Tempered glass (钢化玻璃) Heated on both sides and cooled rapidly with a stream of air. This causes the outside to compress rapidly and place tension on the inside of the glass. Approximately four times stronger than untempered glass. Breaks in small pieces. Used for car windows, shower doors, wi
6、ndows in public buildings. Laminated glass (夹层玻璃) Made by placing a piece of plastic between two layers of glass. Main use is for windshields and bulletproof glass. Container glass Blown at 600 800 celsius. Contain very little iron Refractive index can vary from top to bottom of bottle. Annealing wi
7、ll raise the refractive index,Other glasses,Oxide glasses Chalcogenide Glasses Thioborate glasses (B2S3) Halide glasses (BeF2, ZnCl2 etc.) Heavy metal fluoride glasses (ZrF4) Oxy-halide glasses Oxynitride glasses Metallic glasses Glass-like Carbon,4.1.3 Different Types Of Glasses,Oxide glass,Silica
8、and Silicate glasses,B2O3 and borate glasses,GeO2 and Germanate glasses,P2O5 And phosphate glasses,Complex oxide glasses,More than 90% of the glass in use is based on oxides and in particular silica.,4.2 Preparation Technologies of Glasses,Speaker : 吕金建B10010624,Preparation Technologies of Glasses,T
9、he first question we need to address is “what is glass?“The traditional view is that glass is a solid obtained by supercooling a liquid and that it is X-ray amorphous.,Tg: Glass transition temperature at Tg,Second derivative thermodynamic properties, namely heat capacity, thermal expansivity and com
10、pressibility undergo more or less sudden changes,Tm: Melting temperature Crystalline product: When a liquid is cooled to its Tm, it generally solidifies to a crystalline product. Not crystallize:It is only rarely that melts do not crystallize when they are cooled slowly. Supercooling process:Therefo
11、re in order to obtain a glass the rate of Supercooling has to be such that crystallization is bypassed,Dependence of rate of crystallization of an undercooled liquid on temperature,4.2.1 Preparation of Glasses,In the case of good glass forming materials like SiO2 ,GeO2 or B2O3, the required rate of
12、cooling of the melts is remarkably low because the maximum crystallization velocities in these materials are themselves very low. It appears that any liquid can be quenched into a glass provided the required high degree of quenching rate is achieved.,4.2.2 Microwave Heating in Glass Preparation,Adva
13、ntage: Extremely rapid Disadvantage: Once the melt is formed ,the temperature of melt appears to remain nearly constant,4.2.3 Sol-gel Process,Sol-gel process is another important method of preparation of Glasses Sol-gel procedure provides a convenient route to make siticophosphate glasses which are
14、otherwise difficult to make,4.2.4 Chemical Nature of Glass Forming Materials,In material of all chemical types:covalent,ionic,molecular,metallic and hydrogen bonded materials.Been made from elements ,simple chemical compounds,complex organic molecules,salt mixtures and alloys.,The key factor is just
15、 how fast the melt can be quenched. Other factors is structural aspects,4.2.5 Structural Approach to Glass Formation,The requirement that the structures shoud be disordered in glasses suggests that open structures are more likely to give rise to such disorder,Rules as follows:,Oxygen atom may be lin
16、ked to no more than two A atoms The number of oxygen atoms surrounding A atoms must be small The oxygen polyhedra share only comers with each other,neither edges nor faces At least three comers in each polyhedron must be shared,4.3 Structures And Properties Of Glasses,匡宇鹏 B10010625,Definition of glasses,A more transparent solid material, and in the molten formed when continuous network structure, cooling process viscosity increase gradually and hardening and not crystalline silicate kind of nonmetallic material.,
