POROUS CERAMICS
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HISTORY
CHOOSING A POROUS MATERIAL - ADVANTAGES
OF SOILMOISTURE
UNDERSTANDING
POROUS CERAMICS
PHYSICAL PROPERTIES
OF POROUS CERAMICS - TABLE1
APPLICATIONS &
USES
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viewing of our Ceramics Catalog.
0600 Series Porous Ceramic Plates
0630 Series Porous Ceramic
Rods
0640 Series Porous Ceramic Cylinders
0651 Flat Bottom, Straight Wall
Porous Ceramic Cups
0652 Round Bottom, Straight Wall
Porous Ceramic Cups
0653 Round Bottom, Neck Top Porous
CeramicCups
0655 Round Bottom, Tapered
Neck Porous Ceramic Cups
0660 Series Custom Shape Porous
Ceramics
0675 Series Pressure Plate Cells
0676 Soil Retainer Assemblies
0685 Porous Cup Assemblies
Ceramics Accessories
FORMULAS
HINTS:GLAZING
AND ACID WASH
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CERAMICS CATALOG (.PDF Format)
HISTORY
Since the earliest of times, ceramics have made the transition from
simple utilitarian products, graduating into the first mass storage
containers for wines and grains, to highly sought after ornamental treasures
like service sets from Roman, Chinese and English artisans. Today's
ceramics have moved from the dinner table and storage cabinet to the
forefront of technology providing advanced superconducting wires, specialized
space shuttle tiles that protect astronauts from the heat of reentry,
to the turbine blades that will lift your next jet flight into the air.
For the most part, ceramics are thought of as dense, hard, extremely
strong, functional shapes that fit the needs of man. These generic ceramic
types are found in everything from cabinet pull knobs and electric wire
insulators to optical glass fibers, fine china and keepsakes such as
dolls and figurines. There are other ceramics, however, that are developed
for their porous natures, that are "hydrophilic" (water loving)
and provide capillary wicking and transport of polar substances like
water. This unique class of ceramics has become extremely important
in finding and measuring the fundamental relationships of liquid/gas/material
interactions found in many naturally occurring environments. A porous
ceramic is akin to many natural substances you are familiar with. .
. plants, soils, rocks, outcrops, even bone. Such natural materials
have crevices and pathways (pores) that allow liquids and gases to mix,
migrate and flow. It is this unique porous structure of our ceramics
that makes them ideal for instruments, processes or procedures that
can replicate, measure or monitor these complex, long term interactions
and relationships in our natural world.
Early porous ceramics were developed from high temperature
porcelain "bisqueware" the ("fired" but unglazed)
ceramic used in fine china. Other common recipes called for lower firing
temperatures associated with talc/clay mixtures to produce a similar
porous structure. Today, most porous ceramics are fabricated from either
porcelain or Alumina bodies. Porous ceramics manufactured and sold by
Soilmoisture are engineered for an "open cell/pathway" ceramic,
which means that the pores and pathways are interconnected and interlinked
to provide a complete flow pathway throughout the material for migrating
liquids and/or gases. Since 1955, Soilmoisture has provided the world's
largest selection of porous ceramics in a broad variety of shapes and
sizes with a wide assortment of air entry values to meet your specific
needs. Our advanced ceramics continue to find evolving applications
in science and industry where they make a significant impact on how
we measure, monitor, and control our global environment.
You will find some of the world's best porous ceramics
in numerous shapes and sizes within this section. Soilmoisture manufactures
the widest choice of air entry values and flow characteristics combined
with a large selection of material types. Each porous ceramic part is
produced with the utmost attention paid to detail and quality. These
careful production procedures assure consistently close, uniform tolerances
from purchase to purchase.
Perhaps your interests peak at incorporating a porous
ceramic plate to filter or interface with a slurry or soil or finding
a porous cup housing for a sensor. In any case, Soilmoisture most likely
has a standard porous product to match your needs. For those with interests
and needs a bit more unusual, let us provide you with a reasonable quote
for a special ceramic in a size and shape that will specifically meet
your needs.
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CHOOSING
A POROUS MATERIAL - ADVANTAGES OF SOILMOISTURE PRECISION POROUS CERAMICS
These materials, generally available in small rod or sheet form, are
fabricated from one of several plastic materials. The most common are
products formed by beads of Polyethylene or Polypropylene joined together
or, in other cases, an expanded Teflon product. Generally the pores
created are rather large, having discontinuities and bubbling pressures
in the 1-5 psi range. To achieve a wetted surface takes special etchants
to chemically etch the surface (usually hydrofluoric acids) and surface
additives to achieve a reasonable capillary capacity. The life of these
artificial hydrophilic coatings can substantially vary with use and
are not generally guaranteed for extended use. Newer PVC extrusions
or injected products that employ naturally porous additives result in
a product with a wettable surface but rather moderate flow rates and,
again, limited selection of low bubbling pressures. One might question
these types of materials in any long term applications or projects requiring
pressures or extraction differentials exceeding 5 psi, where the capillarity
and flow characteristics must remain constant.
POROUS PLASTIC FILMS
Special porous films can be purchased in a wide range of thicknesses
and pore sizes. Some are naturally wettable, while others require special
coatings to assure wettability. The films themselves are, unfortunately,
quite flimsy and almost always require supportive backing materials
and mechanical support to assure stability. The thinness of these materials
also leaves them vulnerable to tearing and scratching. In the lab these
film materials and devices work well in the filtering of solutions.
Applying this technology, however, to in-situ work associated with soils,
agricultural, and earth sciences applications would cause one to question
their practicality. For instance, real hazards exist at the time of
installation into soils for tearing, scratching, or pitting of the thin
films or subsequent adequate and uniform surface by a contact highly
flexible film. Then there are the other long term problems of loss or
disassociation of the backing materials and supporting structures from
the films that cause significant concerns.
POROUS METALS
Generally found in disk form and occasionally in tubes, porous metals
are comprised of small particles (soot size) pressed under high pressures
and temperatures into a finished product. Most porous metal products
are naturally wettable having a high ratio of pores, some of very large
size. The result is that the products often have small amounts of leakage
at bubbling pressures under 3 psi making them unsuitable for high pressures
or extended extraction work. If the porous metals are fabricated from
ferric metals, the product will quickly oxidize, "rusting"
closed all possible pore pathways.
PRECISION POROUS CERAMICS
Unlike porous materials developed from plastics that are hydrophobic
(water hating), ceramics are naturally wettable and hydrophilic (water
loving). The tough durable nature of a fired porous ceramic makes it
the preferential material of choice in the field of in-situ measurements,
sampling or processing. Unlike porous metals that may oxidize or leak,
porous ceramics are generally inert and can be produced with very consistent
and uniform pore structures. Structures and devices fabricated from
thick-walled porous ceramics can take the punishment of mechanical installation.
With a wide selection of pore sizes, our precision porous ceramics can
meet the most demanding pressure differential or suction values without
leaks. The porous ceramic products we have available today have been
proven for more than 40 years in all types of real world use. Each ceramic
production batch and many individual ceramic products are individually
tested for hydraulic properties and bubbling pressures. Our specialized
knowledge of ceramics, glazing, assembly, or slip casting techniques
allow us to meet your needs with creativity and value.
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UNDERSTANDING
POROUS CERAMICS
POROUS MATERIALS
Materials containing a passage or channel,
a small opening for absorbing or discharging fluids.
THE CLOSED PORE STRUCTURES
As the name would imply, this is a material in which the pathways or
channels are blocked and do not provide the fluid a continuous and interconnected
network of channels to connect one surface of the material to an opposing
surface.
THE OPEN PORE STRUCTURES
An open pore structure denotes a material that permits a fluid to move
from one surface to an opposing surface in the material through a convoluted
pathway of interconnecting networked channels. Soilmoisture ceramics
are an example of an open pore structured material.
HYDROPHOBIC MATERIAL - WATER
REPELLING
This term refers to materials such as porous plastics that have no affinity
to wetting by water. These substances may have pores and channels but
have no surface ability to wick water into the pores by the action of
capillarity. Such materials are generally made from long chain organic
molecules which have no substantial surface charges. Without a charged
surface, there is no attractive or bonding effects on the polar molecules
of water, and such substances must be specially treated.
HYDROPHILIC MATERIAL - WATER
ACCEPTING
This term refers to those materials, such as porous ceramics and metals,
that have a natural ability to fill pores by capillary action. This
means the pores and channels of a ceramic have a highly charged pore
surface that attracts and bonds the polar molecules of water and other
polar fluids. The net effect is called "wicking" the ability
to pull fluids into the material and transport that fluid by capillary
forces. Soilmoisture ceramics are all hydrophilic.
THE PORE SIZE
The pore size of a porous ceramic is of critical importance because
it directly affects the ceramic's air entry value or "bubbling
pressure" and hydraulic conductivity. The air entry value is the
pressure at which air will break through a wetted pore channel. The
hydraulic (liquid) conductivity of a porous ceramic is a measure of
the rate at which a ceramic material of known thickness may conduct
liquid from one surface to an opposing surface under a known pressure.
The hydraulic conductivity will vary with the type of pore fluid used
which is generally water, but can be oils or other natural and artificial
liquids. The effective pore size is determined by the minimum orifice
within a channel or pore. These properties that are determined by pore
size are intrinsic to ceramics and to all other porous materials.
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|
Air
Entry
Value
|
BUBBLING
PRESSURE
(PSI)
|
APPROXIMATE
POROSITY
( % vol.)
|
SATURATED
HYDRAULIC
CONDUCTIVITY
(cm/sec)
|
MAXIMUM
PORE
SIZE
(µm)
|
FLOW
THROUGH 1/4-INCH PLATE
(ml/hr/cm2/14.7 psi)
|
.5 BAR
(-B0.5M2)*
HIGH FLOW |
7 to 9 |
50% |
3.11 x 10-5 |
6.0 |
180 |
1BAR
(-B01M3)*
HIGH FLOW |
19 to 28 |
45% |
8.6 x 10-6 |
2.5 |
50 |
1 BAR
(-B01M1)*
STANDARD
FLOW |
20 to 30 |
34% |
7.56 x 10-7 |
1.7 |
5.0 |
2 BAR
(-B02M1)*
STANDARD
FLOW |
38 to 45 |
32% |
6.30 x 10-7 |
1.1 |
4.2 |
2 BAR
(-B02M2)*
HIGH FLOW
|
32
to 42 |
38% |
6.93
x 10-7 |
1.3 |
4.6 |
3 BAR
(-B03M1)*
STANDARD
FLOW |
46 to 70 |
34% |
2.5 x 10-7 |
.7 |
1.6 |
5 BAR
(-B05M1)*
STANDARD
FLOW |
80 |
31% |
1.21 x 10-7 |
.5 |
.7 |
15 BAR
(-B15M1)*
STANDARD
FLOW |
220 |
32% |
2.59 X 10 -9 |
.16 |
.15 |
*Part number suffix corresponding to the appropriate air entry value and
mix number. See addendum page for more details. Table 1. Physical properties
of porous ceramics
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POROUS
CERAMICS - APPLICATIONS AND USES
COLUMN WORK
Laboratory soil columns or boxes are easily constructed and are a common
way to simulatecomplex field conditions of interest. It's an easy way
to monitor and see what's happening in real time. Whether the problem
is field drainage, creating the proper matrix suction values for growth,
or measuring changes in hydraulic potentials, Soilmoisture's porous
ceramic products can help provide the answers.
MOISTURE RETENTION CURVES
A basic of any soils study is the relationship between its water holding
capability and the release of any held water. The universally recognized
method for gaining this vital information is by using Soilmoisture Pressure
Extractors, soil samples, and our porous ceramic plate or cup assemblies.
The result of such testing, commonly known as a "moisture retention
curve", is the relationship between volumetric or gravimetric water
content and the extraction pressures necessary for a plant to remove
that water. Soilmoisture has both the extractors and porous ceramic
products you will need to run your own moisture retention curves.
SOLUTION EXTRACTION OR TENSION
MEASUREMENTS
Simply attaching a porous ceramic cup to the end of a piece of connecting
tubing and sealing the end makes a simple device that will provide significant
scientific information. If a vacuum measuring device is tied into the
connecting tube while water is withdrawn through the porous cup, water
tension is measured (a tensiometer). On the other hand, if a vacuum
is induced within a closed connecting tube, it is now possible to pull
in water from the surrounding soil or material (a suction lysimeter
or "soil water sampler").
PORE WATER INTERFACE
The unique characteristics of a wetted (pores filled with water) porous
ceramic is its ability to join with wetted surfaces of materials nearby,
therein creating a pore/water interface. With a wide variety of pore
sizes, air entry values, shapes and sizes you are able to interface
and measure hydraulic conductivity and flow rate properties without
impedance from ceramic materials that are too fine or coarse for your
work. The ability to monitor the interactive effects of water and 2
or 3 party systems having one or more immiscible liquids such as oils,
etc., and their effects within natural pore structures are of great
interest to oil and gas industries.
FILTERS/DRAINS
Porous ceramics are a natural for a wide variety of filtering applications
using liquids and pastes. Porous ceramics provide the tough and rigid
capability suited to those filtering requirements that will not work
with softer pliable paper or membrane filters. Because of their naturally
hydrophilic surfaces, variety of fine pores sizes, and ability to be
used under pressure or suction conditions, they assure that only the
liquid portion of any phase mixture comes through.
AERATORS
The infusion of gases into liquids and pastes are important to process
industries. Control of the size and volume of those bubbles is very
important and Soilmoisture's porous ceramics provide a rich selection
of aeration materials. Whether it's air sparging to accelerate bacterial
digestion deep in underground remediation wells or the foaming of a
liquid in an infusion process, there is probably a porous ceramic to
fit the need.
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