A Guide to Types of Whatman Filter Paper Grades

A device that transmits part of a received signal and rejects the rest. The signal

may be in the form of a beam of light or other radiation or may be an electrical

signal. Optical, ultraviolet, and infrared filters are dyed plastic or gelatin, glass

or glasslike substances, or confined liquids, all of which absorb incident radiation

except for a relatively narrow band of wavelengths. Such filters are used in

astronomical photometry, especially in measurements of magnitudes; transmitting bands

typically 100 nanometers wide, they are termed broadband filters. Much narrower

wavelength bands, of maybe 1 nm, can be obtained with interference and birefringent

filters.
Electrical filters are devices whose attenuation varies with frequency. Filters

that allow low or high frequencies to pass without serious attenuation are called

low-pass and high-pass filters, respectively. A filter that allows only a limited

range of frequencies through is a band-pass

filter while its converse is a band-stop filter. See also bandwidth.

The term “filter” is also applied to a number of other devices, which are not

discussed in the present article. For example, devices that pass or reject acoustic or

electromagnetic waves of certain frequencies are called filters, and the term is

sometimes applied to devices that separate polymer ions into fractions or remove salts

from solutions by means of ion exchangers.

According to the nature of the heterogeneous system, a distinction is made between

liquid filters, which are used to LTE

filter suspensions, and gas filters, which are used to separate out aerosols and

to purify gases. The simplest filter is a vessel that is divided into two parts by a

filter medium. A pressure difference is established across the filter to force the

liquid or gas through the filter medium, which holds back the solid particles.

Liquid filters. Liquid filters are divided according to their method of operation

into two groups: filters that operate intermittently, that is, on a batch basis, and

filters that operate continuously. Within each group, filters are classified according

to the way the pressure difference is created (application of vacuum or pressure), the

geometry of the filtering surface (plane or curvilinear), and the type of filter

medium used. In an intermittent filter the entire surface of the filter medium is

subjected by turns to the following operations: influx of a slurry and formation of a

cake (filtration), dewatering, washing and discharge of the cake, and regeneration of

the filter medium. In a continuous filter these operations occur simultaneously and

independently of one another in an appropriate filter zone.

The intermittent group includes filter presses and capacity, leaf, and cartridge

filters.

Leaf filters are used to clarify solutions and to separate slurries that contain

no more than 5 percent (by volume) of a solid phase. The

bands filter elements, or

leaves, are circular or rectangular in shape and are usually covered with a cloth

filter medium. Each leaf has an outlet through which the filtrate is discharged. The

slurry is fed into the filter tank. The layer of cake is washed after all the slurry

has been removed from the tank.

Filter presses are used chiefly for fine slurries. They include plate-and-frame

presses, chamber presses, and automatic filter presses.

A plate-and-frame filter press consists of an assembly of alternating vertical

plates and frames. Compression of the assembly is accomplished by a hand screw or a

hydraulic or electromechanical closing device. The frames form hollow chambers, into

which the slurry is fed when the filter is in operation. The filter medium is laid

over each plate, whose faces are ribbed to provide drainage. Under pressure, the

filtrate passes through the filter media, runs down the ribbed surface of the plates,

and passes through the filtrate outlets to an open launder or a closed channel. The

cake formed in the chambers is removed by separating the plates.

The chamber filter press operates in a manner similar to that of the plate-and-

frame filter press but permits higher pressures.

In automatic chamber filter presses the filter plates are located between two

supporting plates and are positioned horizontally at a certain distance from one

another. The top of each filter plate is covered with a perforated sheet, over which

an endless-belt filter medium is located. When the plates are compressed, chambers are

formed between them. The slurry, wash liquid, and compressed air (for drying) are

successively fed into the chambers from the corresponding channels. The filtrate

passes through the filter medium, and the solid phase remains on it in the form of a

cake. Upon completion of the filtration cycle, the plates are separated, a gap opens

up between them, and the filter medium is set in motion. The cake is carried out from

between the plates and is removed with scrapers. The filter operates automatically and

is four to ten times more efficient than the plate-and-frame filter press.

The principal application of the rotating-pan filter (Figure 4) is the dewatering

of coarse slurries in, for example, the production of potassium and the preparation of

hard coal and ores. The device is a vacuum filter. The filter surface is annular in

shape and is divided into trapezoidal segments, each of which constitutes a filter

cell. The upper part of each cell is open, and the bottom is inclined toward the

center to facilitate the flow of liquid. The cell is covered by a perforated sheet, on

which the filter medium is placed. The interior of each segment is connected by pipes

to the channels of a distribution system, which is rigidly fastened to the housing.

The 5G LTE filter

is rotated by an electric motor. During one rotation a filter cell is

successively connected to vacuum and compressed-air lines. The slurry is fed into the

cell from above. The cake is removed with a scraper or a screw conveyor.

Tilting-pan filters are used for coarse slurries. They are operated by vacuum and

consist of trapezoidally shaped pans held in an annular frame. The pans are connected

by pipes to a distributor, through which the filtrate and wash liquid are removed. The

pans revolve as a unit around a vertical axis. Each pan consists of a shell, which,

together with the drainage plates and filter medium, constitutes the working element

of the filter. The slurry and wash liquid are fed into the pan from above. For

discharge of the cake, the pan is automatically rotated by 180° when it is above the

discharge site.

Gas filters. Gas filters are continuously operating devices. They may be divided

according to their structure into two groups: filters having a plane filtering surface

and bag, or fabric, filters.

The filters of the first group consist of a chamber that is divided by one or two

perforated plates. In the case of one plate, the filter medium—which may be, for

example, sand or quartz—is placed on the plate. In the case of two plates, a

compressed fibrous material—such as asbestos fiber, glass fiber, or glass wool—is

clamped between the plates, which are attached to each other. When the gas flows

through the filter medium, the particles suspended in the gas are removed. At certain

time intervals the filter medium is cleaned or replaced.

Superhydrophobic and superoleophilic filter paper was successfully prepared by

treating commercially available filter paper with a mixture of hydrophobic silica

nanoparticles and polystyrene solution in toluene. Applications of the filter paper in

separating liquids with low surface tensions such as oil and ethanol from water were

investigated in detail. The oil uptake ability of the superhydrophobic filter paper

was evaluated and the results show that the filter paper can selectively adsorb oil

floating on a water surface or in aqueous emulsions. Furthermore, filtration of

mixtures of oil and water through the paper can reduce the water content in the oil.

Additionally, the filter paper can also extract ethanol from homogeneous aqueous

solution.

For the knowledge search results, you can configure standard and custom fields as

filters to help your agents find the content and improve their productivity.

You can set up the customization of knowledge article search filters by first

enabling the feature, and then setting the 4G LTE filter configurations. 

Any filter configurations that you set will be available wherever the knowledge

search experience is configured, such as, the form-based knowledge control, knowledge

search page, productivity pane-based knowledge search control, embedded search control

in Unified Service Desk, and the application tab search experience in Customer Service

workspace.

If you enable the customization of the knowledge search filters, the web client

and maker experience knowledge management filter experience are deactivated. In full

text search, the archived and discarded status filters are not supported.

Qualitative filter papers are what most users would consider general purpose

filter papers. There are a vast range of applications in and out of the laboratory.

Composed of cellulose fiber, these filters are manufactured from high-quality cotton

linters treated to maximize alpha cellulose.

Alpha cellulose is the most stable form of cellulose, with the highest degree of

polymerization. Cellulose paper made from a high percentage of alpha cellulose, such

as Whatman paper, is a sign of high quality and consistency.

Qualitative filter paper grades are based on various properties including particle

retention, thickness, and weight. Unlike quantitative filter papers, of which ashless

grades can be burned off for analytical applications, qualitative papers are more

suited for general purpose use.