Borosilicate Glass 3.3 is resistant to chemical attack by almost all products/ chemicals. It is highly resistant to saline solutions, organic substances, halogens such as chlorine & bromine and also to almost all acids. There are only few chemicals which can cause noticeable corrosion on the glass surface such as hydrofluoric acid, concentrated phosphoric acid and strong caustic solutions at elevated temperatures. However at ambient temperature, caustic solution up to 30% concentration can be handled safely by borosilicate glass. The given diagram (Fig-1) gives some information about the attack by acid and alkali on Borosilicate glass. The corrosion curves in the following figure shows a maximum for different acids in concentration range between 4 N and 7N. Above that the reaction speed decreases considerably so that the eroded layer amounts to only a few thousand of millimetres after some years. Therefore, there is justification for referring to borosilicate glass 3.3 as an acid resistant material.

Fig1

Fig 2

It can be seen from the corrosion curves in fig-2 that the attack on the glass surface initially increases as the concentration of the caustic solution increases but after exceeding a maximum it assumes a virtually constant value. Raise in temperature increases the corrosion, while at low temperature the reaction speed is so low that the reduction of the wall thickness is hardly detectable over a number of years.

The most important physical properties are listed below,    

Optical Properties
Borosilicate glass 3.3 shows no appreciable light absorption in the visible area of the spectrum and consequently it is clear and colourless.

With borosilicate glass 3.3, the transmission of UV light, which is of great importance for photo chemical reactions, is somewhat greater in the middle spectrum than with normal window glass. The chlorine molecule absorbs in the 280 to 400 nm range and thus from the levels of transmission shows in the following fig, it can be seen that plant made from this material is therefore ideal for Chlorination and Sulfo-Chlorination process.

If photosensitive materials are being processed, it is recommended that amber coated borosilicate glass 3.3 to be used. This coating reduces UV light transmission to a minimum, since absorption limit, as can also be seen from figure below, is changed to approximately 500nm.  

Mechanical Properties
Borosilicate Glass cannot withstand much tensile force. But it can withstand high compressive force.

Permissible operating conditions
The permissible values for operating temperature & pressure must always be seen in combination. This is because the thermal stresses those results from temperature differences between inner and outer surfaces of the glass component. These stresses are superimposed on the stresses resulting from working pressure. Higher thermal stresses results in a reduction of permissible working pressure.

Permissible operating temperature
Borosilicate glass only deforms at temperatures which approach its transformation temperature (approx 525^oC). Upto this point it retains its mechanical strength. The permissible operating temperature is however considerably lower at about 200^oC

At subzero temperature tensile strength tends to increase. Therefore Borosilicate glass 3.3 can be used safely at temperature as low as -80^oC

The above mentioned temperature limits should be regarded only as guide lines and must always be modified in accordance with the actual operating conditions of a given application.

Thermal shock
Rapid changes in temperature across the walls of glass component results in increased thermal stresses in the glass which has an adverse effect on the permissible operating pressure of the components. Although it is not possible to give a definite figure applicable to all the operating conditions likely to be encountered in the practice, a maximum permissible thermal shock of 120^oC can be taken as general guide.

Permissible operating pressure
Borosilicate Glass in all nominal sizes that are basically cylindrical, domed and spherical in shape can withstand full vacuum.
The maximum permissible operating pressure is shown in the below given table

 cGMP Complaint installations
Special care is required for the selection of components & equipment for the construction of installation complying with cGMP guidelines as regards their design & material of construction used. Because of its special properties which are highly valued in the pharmaceutical industry, and when used in conjunction with the material on the FDA approved list such as glass lined steel and PTFE , borosilicate glass guarantee that the build up of deposits is avoided in the areas in contact with the product. Minimum dead space is to be ensured for complete draining and simple and effective in-situ cleaning are achieved by design of the components, their layout and selection of valves. Stainless steel coupling and support material is available for the design of complete unit complying with clean room conditions from external aspect.

Electrostatic earthing
If the glass plant is operated in areas where there is a risk of flammable atmosphere occurring, then precautions must be taken against spark generation by the discharge of electrostatic charges.

Precautions are of special importance with the glass plant due to the joint coupling, each of which can include a combination of conductive and non conductive materials. It is necessary to earth all metal flanges.

All the mechanical connection used for earthing must be so resistant to match the demand occurring in operation. Only welds, soldered joints or protected bolts coupling may be used. They should not be interrupted at any point by non conductive intermediate items. Also they may not be disconnected for repair work while the glass plant is in operation.