Saturday, 27 July 2013

Goel's TECHNICAL INFORMATION

Posted by Hemant Goel On 07:11

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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 steadly growing use is due to many advantages over conventional materials.

  • Outstanding corrosion resistance
  • Smooth pore and surface.
  • Transparency
  • 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 (SiO2 ), boric oxide (B2O3 ) and phosphorous
pentaoxide (P2O5 ) are chief glass form oxides. Soda (Na2O), Lime ( CaO ), Alumina (Al2O3 ) Potash
(K2O) Magnesia (MgO) and lead oxide (PbO) are the principle modifiers/fluxes.

CHEMICAL COMPOSITION
The composition of borosilicate glass used has following approximate composition.
SiO2 - 80.6 %B2 O3 - 12.5%
Na2O - 4.5 %Al2 O3 - 2.2 %

RESISTANCE TO CHEMICALS

Borosilicate glass is inert to almost all materials except hydrofluoric acid (HF) phosphoric acid (H3PO4)
and hot 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. So it is not possible to give exact figures for
corrosion by caustic solutions.

THERMAL PROPERTIES

Linear coefficient of thermal expansion the coefficient of thermal expansion of borosilicate glass over
the temperature 0-300 OC is 33 x 10-7 / OC. 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
Specific heat between 25OC and 300 C is average to be 0.233Kcal/Kg C.


THERMAL CONDUCTIVITY


Thermal conductivity is 1.0 Kcal/hr. m C over the permissible operating temperature range.









ANNEALING
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.




MECHANICAL PROPERTIES
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 700kgs/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.


OPTICAL PROPERTIES
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 & sulpho -chlorination can be performed in it. 

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