Introduction: Phosphate glasses and glass ceramics are useful for applications such as bone transplantation, glass to metal seals, containment of radioactive wastes, fast ion conductors, laser host materials etc. They have a comparatively high transmission in the ultraviolet region compared to silicate and borate glasses. They also have low glass transition and melting temperatures compared to silicate glasses. The network structure of simple phosphate glass consists of P tetrahedra linked to neighboring tetrahedral through bridging oxygen (BOs). Addition of Al +3 B Bi etc has been found to improve the chemical durability because of the formation and relative stability of M +3 O P bond. These ions modify various physical properties including thermo mechanical and optical behaviour basically due to change in glass structural network through formation of cross linked bonds. Borophosphate glasses having improved durability are among the multi component glasses studied for various interesting applications. Alkali and silver borophosphate glasses have been developed for fast ion conducting applications. Zinc calcium borophosphate glasses were studied as candidates for applications as low-melting glass solders glass to metal seals. The structure of borophosphate glasses was studied by NMR spectroscopy and it was found that both BO 3 and BO 4 structural units were present in the glass structure. The fraction of BO 4 units in the glasses was also found out in this study, which is an important parameter in the context of improvement of durability of these glasses. The presence of BO 3 and BO 4 structural units affects the chemical bonding with the phosphate tetrahedra, which becomes important in determining the chemical durability of these glasses. The corrosion studies on alkali alkaline earth phosphate glasses revealed that corrosion resistance of these glasses to water attack was improved by small addition of Al 2 O 3 and glasses with thermal expansion coefficients (TEC) greater than 200 10 7 0 C and glass transition temperatures Tg below 400 C and melting points below 600 C which could be thermetically sealed to aluminium alloys. Sodium borophosphate glass studies show an increase in Tg and decrease in TEC for y = B / (B + P) = 0 0 5 (B = B 2 O 3 content in mol% P = P 2 O 5 content in mol %) where BO 4 units dominate over BO 3 units. The maximum TEC reported for sodium borophosphate glasses is 199 10 7 for y < 0 5. Therefore it seems interesting to study the effect of B 2 O 3 addition in sodium barium phosphate glass since the addition of boron oxide tends to improve the durability of sodium phosphate glass without any major change in the TEC of these glasses. In this work we report the degradation behavior of sodium barium borophosphate glasses in water acid and
alkali media at room temperature and at 60 C. To the best of our knowledge this data is new for phosphate glasses and the structural and physico-mechanical properties for these glasses are reported elsewhere. We have prepared a vacuum seal using glass composition x = 10 mol% with Al metal withstanding 10 6 Torr pressure and also carried out glass to metal interface study. (1) The relation between the resulting structure and property is outmost importance in the design of the desired glass. In view of this, currently research has been focused on low melting glasses. In the present work we have selected a binary,ternary borophosphate glass containing alkali and alkaline earth metal oxides to investigate the chemical durability optical and electrical studies. Now a day attention is being drowned to investigate glasses as useful solid materials, especially those containing alkali oxide, alkaline earth oxide, and transition metal cations. Early on boron was identified as an important glass former which can be used in the preparation of glasses for both scientific and technological applications. The presence of glasses in our everyday environment is so common that we rarely notice their existence. Our current casual attitude toward the family of materials known as glasses has not always existed. The earliest glasses used by man were found in nature. The ease of formation of sharp edges on obsidians, for example, allowed the production of knives, arrow heads, and other cutting tools. These naturally occurring glasses, which result from the cooling of molten rock, or lava, contain a wide variety of components, including alkali, alkaline earths and transition metal oxides. In every case however silica is found to be the major constituent of these materials. (2) Types of Glasses : Depending on the network former used, glasses can be classified as silicate, borosilicate, alumina silicate, borate, phosphate glasses, chalcogenide glasses etc. and depending on its end used as optical glasses, sealing glasses, special application glasses etc. Large varieties of glass are obtained by varying the composition of the batch. Based on the composition the different types of glasses have been discussed as follows. 1. Soda lime Glass: (Soda glass or Normal Glass or Soft Glass)
Soda lime or lime glasses are made by fusing together appropriate quantities of sand, lime or lime stone and soda ash 2 Phosphate Glasses: There is relatively poor chemical durability, which often limits their usefulness in various applications (3). Durability can be improved by the addition of Bi 2 O 3,Al 2 O 3, Fe 2 O 3 etc. (4) These types of glasses have considerable potential applications. (5) These glasses have wide technological interest due to their unique physical properties such as low glass transition temperature (T g ), lower melting temperature, high thermal expansion coefficient high ionic conductivity & bio compatibility. (6) 3 Borosilicate Glasses: The glass is used in the manufacture of kitchenware, glass pipelines in factories, high tension insulators; it is mainly used as heat resisting ware like oven ware and laboratory glass ware. (7) The special types of glass called Pyrex, Jena, corning etc. are manufactured from borosilicate glass. It is widely used in laser technology. (8) 4 Alumino silicate glasses: When part of the silica in glass composition is replaced by Alumina (Al 2 O 3 ), Aluminosilicate glass gets formed (9) Aluminosilicate glasses are used commercially because they are chemically stable and withstand at high temperatures. Thus applications include combustion tubes, gauge glasses for high-pressure steam boilers and in halogentungsten lamps capable of operating at temperature as high as 750 o C. (10) Tungsten ions are well known due to their unusual influence on the optical and electro chemical properties of the glasses for the simple reason that the oxides of tungsten participate in the glass network. (11) 5 Telluride Glasses: Telluride glasses were first prepared and studied by Starwort in 1952 (12). The important properties of these glasses are refractive index up to 2.3 and high thermal
expansion coefficient ~25.0 10-6 0 C, TeO 2 based glasses have also been used in preparation of transparent glass ceramics. Most of the telluride glasses have got good stability under ambient conditions. 6 Van date Glasses: Pure V 2 O 5 melts at around 660 0 C and forms glass only when it is cooled rapidly. Glass formation between V 2 O 5 and a number of oxides like P 2 O 5, TeO 2, B 2 O 3, GeO 2, BaO, ZnO, CdO, MgO etc. has been investigated by various authors and the regions of glass formation and the quenching rate required for the glass formation have been reported. (13) 7. Chalcogenide glasses: Amorphous chalcogenide materials can be prepared by a variety of methods. Some methods for forming glasses are Slow cooling (melt quenching), moderate quenching, rapid quenching or splat cooling, roller quenching or melt spinning, laser glazing, condensation from the gas phase, sol-gel method. (14) Melt quench technique is used to make this type of glasses. (15) B 2 O 3 is also used as a glass former. The effects of B 2 O 3 addition in the properties and structures of two series of Sn (II)-borophosphate glasses were determined. (16) The refractive index of the series I glasses decreases slightly, from 1.784 to 1.725, and increases for series II, to 1.834, at 632.8 nm. Raman spectroscopy reveals that borate additions to both series reduce the number of P-O-P linkages by converting pyrophosphate anions to orthophosphate anions. 11B NMR spectra indicate that tetrahedra Phosphate glass is a class of optical glasses composed of metaphosphate of various metals. Instead of Sio 2 in the slicate glass, the glass forming substrate is P 2 O 5 borophosphate units, B(OP) 4, are initially formed when B 2 O 3 is added to the Sn-pyrophosphate base glass. More complex tetrahedral and trigonal borate sites form when B 2 O 3 contents exceed about 10 mol %. ( 17) P 2 O 5 crystallizes in at least four forms. The most familiar polymorph (see fig.no.1) comprises molecules of P 4 O 10. The other polymorphs are polymeric, but in each case the phosphorus atoms are bound by a tetrahedron of oxygen atoms, one of which forms a
terminal P=O bond. The O-form adopts a layered structure consisting of interconnected P 6 O 6 rings, not unlike the structure adopted by certain polysilicates. (18) Fig.no.1 glass formers. The P 4 O 10 cage like structure which provides the basic building block for phosphate Phosphate glasses are highly resistant to hydrofluoric acid. With addition of iron oxide, they act as efficient heat absorbers. Iron phosphate and lead iron phosphate glass are alternatives to borosilicate glass for immobilization of radioactive waste. (19) Phosphate glasses can be advantageous over silica glasses for optical fibers with high concentration of doping rare earth ions (20-21) a mix of fluoride glass and phosphate glass is glass. Silver-containing phosphate glass is used in phosphate glass dosimeter. It emits fluorescent light when irradiated by ultraviolet light, when previously exposed to ionizing a radiation in an amount proportional to the close. Some phosphate glasses are bio-compatible and water-soluble and are suited for use as degradable tissue and bone scaffolds within the human body. (22) As B 2 O 3 content in the glass increases, the Meta phosphate chains are converted into orthophosphate structural units with the formation of P OH and Na + -OH bonds, which are relatively weak in nature, resulting in increase in the dissolution rate. B 2 O 3
reacts with water and forms boric acid, which readily dissolves in water. It is also observed that with increase in B 2 O 3 content, BO 4 units are increased. BO 4 structural units exist as BO 4 Na + units, which readily react with aqueous medium to form sodium borate, which is soluble in water or acidic medium. There by it increases the dissolution rate. Now our aim is to enhance the hardness of borophosphate glass by using different addiditives.