Sintered Ware

TECHNICAL DATA Borosil Brand sintered glassware is used for the filtration of liquids and gases in the laboratory. It incorporates a porous glass disc as a filter media, which is non corrosive and reusable. It is also used for gas washing, dispersion and absorption. Sintered disc is manufactured by crushing Borosil brand glass, powdering, cleaning, separating into various mesh sizes and then fusing together in the form of a disc. The sintered disc is graded into 5 grades -G1, G2, G3, G4 and G5. The grades are classified by maximum pore size, which is obtained by measuring pressure at which the first air bubble breaks away from filter under certain conditions. The pressure differential is then used to calculate the equivalent capillary diameters in microns. The desired pore size is obtained by suitably controlling the grain size, firing time, temperature and the thickness of the disc. Each disc is tested and graded individually. The pore diameters are reasonably uniform, which ensures required flow rate through the filter. The flow rate further depends on pressure differential between the two sides of the disc, free area of the disc, viscosity of the fluid being filtered, etc. Between different discs of same size and grade, there is a fair amount of uniformity in pore size and hence the results from two or more discs of the same size and grade will be uniform. This ensures reproducible analytical results. The discs have maximum surface hardness and hence glass powder does not get scraped off during cleaning or with chemicals. Filters do not shed particles during usage. The discs are sealed to tubing without blocking the pores. Then they are annealed properly in automatically controlled lehrs.

POROSITY GRADES AND THEIR GENERAL USE

Porosity Grade	Pore Size (Microns)	General use
1	90-150	Filtration of coarse materials / precipitates, gas dispersion, gas washing, extractor bed, support for other filter materials.
2	40-90	Filtration of medium precipitates gas disperation, gas washing.
3	15-40	Filtration of fine grain precipitates. Anayical work with medium precipitates. Mercury filtration
4	5-15	Analytical work with fine and very fine precipitates. Non return mercury valves.
5	1-2	Bacteriological filtration.

CHEMICAL DURABILITY

Borosil Sintered ware is produced from the same high quality material from which all Borosil brand borosilicate laboratory glassware are manufactured and thus have excellent resistance to chemical attack.

OPERATING PRESSURE

The sintered discs and the glassware are incorporating them are mainly designed for the application of vacuum or for passage of gases at a relatively low pressure. In all cases the differential pressure must not exceed 100 KN / m2 (15 psi)

THERMAL LIMITATIONS

The resistance to thermal shock of sintered ware is comparatively less than that of standard Borosil glassware. Therefore, articles of sintered ware should not be subjected to excessive temperature changes nor to direct flames.

Borosil Sintered crucibles are particularly suited for drying to constant weight. Dry sintered crucibles at room temperature can be placed directly into a drying oven at 1500C, although customary practice is to dry at 1100C. Sintered ware may safely be heated in furnace to 5000C without ill effect, provided that the cycle of heating and cooling is gradual. It is advisable that rate of heating should not be more that 20C / min. This prevents internal strains caused by excessive temperature differences between the surrounding glass vessel and the sintered disc, which can lead to fracture of apparatus.

Sintered ware of porosity grades 4 and 5 when cold and damp should never be subjected to a sudden temperature change since the evolution of steam may set up sufficient pressure within the filter, to crack it.

Filtration Apparatus should be kept on its rim (stem upwards) in oven or sterilizer. A perforated support base is advantageous for air convection in case of pipeline filters. Care should be taken by use of heat insulating material such as asbestos to avoid premature heating near filter seal. Apparatus should remain in the oven or sterilizer during cooling to avoid too fast cooling rate.

CLEANING OF SINTERED WARE

1>.New sintered filters should be washed carefully with hot hydrochloric acid and then rinsed with distilled
water before they are used. This treatment will ensure that all loose particles are removed from the filter.
2>.It is recommended that all sintered filters are thoroughly cleaned “immediately” after use. This is the most favorable time for ease of cleaning and will ensure less risk of contamination in subsequent use.
3>.Many precipitates can be removed from the filter by backflushing with water. However, great care must be taken with large diameters and fine filters, as positive pressures on the reverse side may break the filter.
4>.Under no circumstances, should sintered apparatus be subjected to mains water pressure when back flushing as in most instances this will lead to fractured filters.
5>.Drawing water through the filter from the reverse side with a vacuum pump is also effective.
6>.Filters clogged by dust and dirt during gas filtration can be restored by treatment with a warm detergent solution followed by blowing through clean air from the clean side of the filter. Dirt particles are brought to the surface by the foam and removed by rinsing with water.
7>.Some precipitates may clog the filter which may be removed by chemical cleaning as given below :

Fats and grease :

Carbon tetrachloride or suitable organic solvent.

Albumen, Glucose :

Hot ammonia or hydrochloric acid, mixture of hot concentrated sulphuric and nitric acids.

Organic substances :

‘Chromic’ acid cleaning solution* or concentrated sulphuric acid containing a little potassium nitrate or Perchlorate (0.5%) (possibly need to soak overnight)

Copper or iron oxide :

Hot concentrated hydrochloric acid with potassium chlorate.

Barium sulphate :

Hot concentrated sulphuric acid

Mercury Residues :

Hot concentrate nitric acid

Mercury Sulphide :

Hot aqua regia

Silver chloride :

Ammonia or sodium hyposulphite
Stannic oxide : Boiling sulphuric acid**
Alumina or silica residues :

2% hydrofluoric acid followed by concentrated sulphuric acid. Rinse immediately with distilled water and then with acetone. Continue rinsing until no trace of acid remains.

High concentrations of hydrofluoric acid, hot phosphoric acid or caustic alkali solutions should never be used for cleaning. Their use will cause a rapid deterioration in the filter and an increase in pore size.

* For bacteriological, pharmaceutical and biological work, “chromic” acid cleaning solution should be avoided because of the biological effect of chromium ions.

** Undue thermal strain may be introduced with boiling sulphric acid.It is therefore adviseable to leave the item in the acid to cool.

Please ensure prolonged rinsing with water after chemical cleaning.