Buchner Funnels, Glass, With Sintered Disc

Quick Answer: A sintered glass Buchner funnel is a glass filter funnel with a porous disc of fused glass particles sealed in place of the usual perforated plate and filter paper. It is used for suction filtration of precipitates, crystals and liquids that would attack paper, seated on a filtering flask connected to a vacuum source.

A Filter Built into the Funnel

In a conventional Buchner funnel the solid is caught on a circle of filter paper laid over a perforated plate. Here the filtering layer is part of the funnel itself: a disc made by heating graded glass grains until they fuse at their points of contact, leaving a network of fine channels. Liquid drawn through by suction passes along those channels, while particles larger than the pores stay on top as a cake that can be washed and sucked dry on the disc.

Doing without paper matters in several situations. Strong acids, oxidising solutions such as potassium permanganate and hot concentrated reagents can weaken or char cellulose, while glass is unaffected by most of them. No paper fibres enter the filtrate or the product, and the same funnel can be cleaned and reused many times. Fritted discs are made in a series of porosity grades, from coarse ones that pass liquid quickly to fine ones that hold back very small crystals; the listing does not state which grade is supplied, so choose it by the particle size of your precipitate.

Seat the funnel in a filtering flask using a bored bung or conical rubber adapter, then connect the side arm to a water filter pump or vacuum line. The porcelain Buchner funnel with sintered disc is the opaque ceramic alternative; glass has the advantage that the disc can be inspected for clogging or for colour left by earlier samples.

Specifications

Applications

• Collecting recrystallised organic products, such as aspirin or acetanilide, and washing them with cold solvent on the disc
• Filtering solutions of potassium permanganate, chromic acid or other oxidising reagents that damage filter paper
• Removing fine solids from reagents or solvents before use, without adding paper fibres
• Isolating precipitates in teaching labs where the funnel is reused by successive groups

Care & Handling

• Wet the disc with the solvent before pouring in the mixture, and apply suction gently at first so fine particles do not pack deep into the pores.
• Clean straight after use by drawing through a solvent that dissolves the residue, then plenty of water; flushing from below clears pores better than rinsing from above.
• Dry in an oven with gradual heating and cooling, never by putting a wet frit into a hot oven or over a flame, as uneven heating can crack the seal between disc and wall.
• Do not scrape the disc with a metal spatula; lift the cake with a plastic or rubber-tipped tool.

Why Choose LabEquip

University organic labs, pharmacy colleges and quality control rooms that filter corrosive or oxidising mixtures tend to prefer a sintered glass Buchner funnel to paper. LabEquip supplies it within the chemistry lab equipment range; state the disc porosity and funnel size you need on the contact page.

Frequently Asked Questions

Do I still need filter paper with a sintered disc?

No. The fused glass disc is the filter medium. Some users lay a paper circle on top when a precipitate is very fine or gelatinous, simply to protect the pores from clogging, but it is not required for normal work.

Which porosity grade should I choose?

Match the grade to the particle size. Coarse grades filter quickly and suit large crystals, medium grades suit most recrystallised products, and fine grades hold back small precipitates but filter slowly. Grading systems differ, so compare the stated pore-size range rather than only the grade name.

How do I clean a clogged sintered disc?

Pull a solvent that dissolves the deposit through the disc, then water. Inorganic residues often respond to warm dilute hydrochloric acid, organic residues to a suitable solvent. Back-flushing from the stem side helps. Avoid hot strong alkali, which etches glass and enlarges the pores.

Can the funnel be heated or dried in an oven?

Yes, glass frits are routinely oven-dried, but raise and lower the temperature gradually. A sudden temperature change, or a wet frit placed straight into a hot oven, can crack the disc or its seal to the funnel wall.

Which chemicals should not be filtered through sintered glass?

Hydrofluoric acid, hot concentrated phosphoric acid and hot concentrated alkali solutions attack glass. For those, use a filter made of a resistant plastic. Most acids, oxidising agents and organic solvents are compatible at room temperature.

Why is filtration through the disc so slow?

Usually because fine particles have been drawn into the pores, or the grade is finer than the solid requires. Start with gentle suction, let a thin layer of solid build up before applying full vacuum, and clean the frit fully between uses so it does not gradually block.

Last Updated: September 2026