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Laboratory works require apparatus made in a Borosilicate 3.3 expansion glass which offers maximum inertness to widest range of chemical substances, withstand thermal shock, high temperature without deforming and resilient enough to withstand the normal laboratory handling, washing and sterilizing processes.
Borosilicate glass represents unmatched standardized glass for construction of Laboratory Glasswares. Its steadily growing use is due to many advantages over conventional materials.
* Outstanding corrosion resistance
* Smooth pore and surface.
* Catalytic, inertness
* No effect on taste and odour
* Physiological inertness
Borosilicate glass is chosen for its unique chemical and physical properties. Borosilicate glass can be considered as being composed of Oxides. Silica (SiO ), Boron oxide (B O ) and Phosphorous Pentaoxide (P O ) are chief glass form Oxides. Soda (Na O), Lime ( CaO ), Alumina (Al O ) Potash (K O) Magnesia (MgO) and Lead Oxide (PbO) are the principle modifiers/fluxes.
The composition of borosilicate glass used has following approximate composition.
SiO - 80.6 % B O - 12.5% 2 2 3 Na O - 4.5 % Al O - 2.2 % 2 2 3
RESISTANCE TO CHEMICALS
Borosilicate glass is inert to almost all materials except hydrofluoric acid (HF) phosphoric acid (H PO ) and hot 3 4 strong caustic solutions. Of these, Hydrofluoric acid has the most serious effect, even when it is present in PPM (parts per million) in solutions, Whereas phosphoric acid and caustic solutions cause no problems when cold but at elevated temperature corrosion occurs. In case of caustic solutions upto 30% concentration can be handled safely at ambient temperature.
Under actual operating conditions, the effect of turbulance, and traces of other chemicals in the solution may increase or decrease the rate of attack.Thus, corrosion by caustic solutions can not be predefine.
Linear coefficient of thermal expansion of borosilicate glass over the temperature 0-300 C is 3.3 x 10 / C. This is very low when compared with other glasses and metals. That is why borosilicate glass is often called low expansion borosilicate glass.
Specific heat between 25 C and 300 C is average to be 0.233 Kcal/Kg C.
Thermal conductivity is 1.0 Kcal/hr. m C over the permissible operating temperature range.
Annealing of glass is the process where the glass is heated and kept for a defined period of time to relieve internal stresses. Careful cooling under controlled conditions is essential to ensure that no stresses are reintroduced by chilling/cooling.
The lack of ductility of glass prevents the equalization of stresses at local irregularities or flaws and the breakage strength varies considerably about a mean value. This latter is found to occur at a tensile strength of about 2700 kg/cm .
In order to allow for the spread of breaking stress, a large factor of safety is applied when determining the wall thickness requirement to allow operation up to specified limit of working pressure.
Borosilicate glass shows no appreciable absorption in the visible region of spectrum and therefore appears clear and colorless. In photo chemical process the transparency of ultra violet is of particular importance. It follows from the transmittance of material in UV region that photochemical reactions such as chlorination & sulphochlorination can be performed in it.