POROUS CERAMICS

CERAMICS - CATALOG 2008 (.pdf 8.23mb)

HISTORY

CHOOSING A POROUS MATERIAL - ADVANTAGES OF SOILMOISTURE

UNDERSTANDING POROUS CERAMICS

PHYSICAL PROPERTIES OF POROUS CERAMICS - TABLE1

APPLICATIONS & USES

Click on any of the sections below for immediate 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

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

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*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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HINTS

GLAZING
All glazing used in conjunction with the fabrication of standard or special products is of highest quality and contains no lead How to specify or heavy metals that could leach into solution samples. Glazes come in several firing temperatures and can be applied in one or two step processes to meet the most demanding requirements. Glazing can also be applied to one or more surfaces to create the wicking or capillary pathways of desired width and direction.

ACID WASH
There are some who believe that all ceramics need to be washed with a strong acid to “clean” pores of possible ionic exchange sites prior to use in liquid sampling. This misconception is based upon older ceramic mix formulas (1960’s) of moderately fired ceramics such as our B01M1 which has a talc component with potential ion exchange sites. In those early cases, some ionic exchange did occur during the first sampling periods as weak mineralogical lattice sites exchanged larger ions for more highly charged smaller ions. In reality, however, after several weeks in situ the transfer of ions was completed and the saturated lattice sites within the ceramic were at equilibrium with local soil waters. Acid washing cleaned most of the susceptible lattice sites in pore areas of these moderately fired ceramics leaving new holes within the ceramic lattice. As before, the first samples lacked uniformity with pore water content as the highly charged ions found these preferential “cleaned” mineralogical sites within the ceramic. After several weeks of installation and use, the cleaned sampler ionic sites were saturated and at equilibrium with the surrounding soil waters.

For solution sampling we recommend only the use of high fired, very stable and clean porous ceramics like the B0.5M2, B01M3, B02M2 that provide not only the hydraulic properties and air entry values that far exceed older formulas, but also possess the levels of cleanliness and stability designed for liquid content sampling. Even these extremely clean ceramics may, upon first use, attract some cations that have an affinity for the generally negative surfaces within the ceramic. All naturally hydrophilic materials will have these tendencies to affect initial ionic content in some slight manner no matter how pure and inert the hydrophilic material. The rule of thumb is “pore structure and pore liquids reach an equilibrium state after 5 to 8 pore volumes have traveled the pore spaces”. This is the reason why the first several samples should be ignored as the samples will probably not precisely represent the actual pore fluids.

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