Ceramic foam

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Ceramic foam is a tough foam made from ceramics. Manufacturing techniques include impregnating open-cell polymer foams internally with ceramic slurry and then firing in a kiln, leaving only ceramic material. The foams may consist of several ceramic materials such as aluminium oxide, a common high-temperature ceramic, and gets insulating properties from the many tiny air-filled voids within the material.

Contents

The foam can be used not only for thermal insulation, [1] but for a variety of other applications such as acoustic insulation, [1] absorption of environmental pollutants, [1] filtration of molten metal alloys, [2] and as substrate for catalysts requiring large internal surface area.

It has been used as stiff lightweight structural material, specifically for support of reflecting telescope mirrors.

Properties

Ceramic foams are hardened ceramics with pockets of air or another gas trapped in pores throughout the body of the material. With its ability to create a large specific surface area, these materials can be fabricated as high as 94 to 96% air by volume with temperature resistances as high as 1700 °C. [1] Because many ceramics are already oxides or other inert compounds, there is little danger of oxidation or reduction of the material. [3]

Previously, pores had been avoided in ceramic components due to their brittle properties. [4] However, in practice ceramic foams have somewhat advantageous mechanical properties, showing high strength and plastic toughness, compared to bulk ceramics. One example is crack propagation, given by:

where σt is the stress at the tip of the crack, σ is the applied stress, a is the crack size and r is the radius of curvature. For certain stress applications, this means ceramic foams actually outperform bulk ceramics because the porous pockets of air act to blunt the crack tip radius, leading to a disruption of its propagation and a decrease in the likelihood of failure. [5]

Preparation Methods

Organic Foam Impregnating Method

The organic foam impregnating method is one of the more widely used in industry, creating the ceramic foam with a 3D mesh skeleton structure and coat a ceramic slurry on a polyurethane organic foam mesh body. The ceramic foam is obtained by allowing the body to dry at room temperature and burn the mesh body to retrieve the ceramic foam. This method is best used to prepare silicon carbide foam ceramics. [6]

Foaming Method

The foaming method uses a chemical reaction of a foaming agent. The foaming agent generates volatile gas that foams the slurry. The slurry is dried and sintered to obtain the ceramic foam. The product’s shape and density can be controlled and manipulated with the foaming method. This method can be used in the preparation of small pore size closed cell ceramics. [6]

Manufacturing

Much like metal foams, there are a number of accepted methods for creating ceramic foams. One of the earliest and still most common is the polymeric sponge method. [7] A polymeric sponge is covered with a ceramic in suspension, and after rolling to ensure all pores have been filled, the ceramic-coated sponge is dried and pyrolysed to decompose the polymer, leaving only the porous ceramic structure. The foam must then be sintered for final densification. This method is widely used because it is effective with any ceramic able to be suspended; however, large amounts of gaseous byproducts are released and cracking due to differences in thermal expansion coefficients is common. [4]

While the above are both based on the use of a sacrificial template, there are also direct foaming methods that can be used. These methods involve pumping air into a suspended ceramic before setting and sintering. This is difficult because wet foams are thermodynamically unstable and can end up with very large pores after setting. [4]

A recent method of creating aluminum oxide foams has also been developed. [1] This technique involves heating crystals with the metal and forming compounds until a solution is created. At this point, polymer chains form and grow, causing the entire mixture to separate into a solvent and polymer. As the mixture begins to boil, air bubbles are trapped in solution and locked in to place as the material is heated and polymer is burned off.

Use

Insulation

Due to ceramics' extremely low thermal conductivity, the most obvious use of a ceramic is as an insulation material. [1] Ceramic foams are notable in this regard because their composition by very common compounds, such as aluminum oxide, makes them completely harmless, unlike asbestos and other ceramic fibers. Their high strength and hardness also allows them to be used as structural materials for low stress applications.

Electronics

With easily controlled porosities and microstructures, ceramic foams have seen growing use in evolving electronics applications. These applications include electrodes, and scaffolds for solid oxide fuel cells and batteries. Foams can also be used as cooling components for electronics by separating a pumped coolant from the circuits themselves. [8] For this application, silica, aluminum oxide, and aluminum borosilicate fibers can be used.

Pollution Control

Ceramic foams have been proposed as a means of pollutant control, particularly for particulate matter from engines. [9] They are effective because the voids can capture particulates as well as support a catalyst that can induce oxidation of the captured particulates. Due to the easy means of deposition of other materials within ceramic foams, these oxidation-inducing catalysts can easily be distributed through the entire foam, increasing effectiveness.

Filtering

Ceramic foam filters (CFF) are used for the filtration of liquid metal. Passing liquid metal through the ceramic foam filter reduces impurities, including nonmetallic inclusions, in the liquid metal and the corresponding finished product (casting, sheet, billet, etc). It has found success in its application and use in continuous casting (sheet), semi-continuous casting (billet and slab), and casting gating systems in metal foundries. [6] [10]

Wastewater Treatment

Due to the foam’s unique pore structure and large specific surface area, it sees a use as a filter for wastewater. The filtration process is a combination of adsorption, surface filtration, and deep filtration with deep filtration providing a majority of the filtration process. [6]

Construction

Close-cell ceramic foam serves as a good insulation material for walls and roofs. The large number of closed cells allow the material to be resistant to corrosion and absorb sound internally and externally. Buildings in China have utilized ceramic foam as a thermal insulation material. [6]

Noise Reduction

Foam ceramics has its use in sound absorption in wet and oily environments. The sound waves vibrate in the pores of the foam and transform the energy into heat through friction and air resistance, thus reducing echos in the environment. [6]

Automobile

Due to the three-dimensional connected mesh structure, high temperature resistance, and thermal stability of ceramic foam, its use in catalytic converters in exhaust systems help remove oxides and other particulate matter from exhaust gasses. [6]

Biomaterial

Current research sees ceramic foams often formulated with Bioglass to create tissue scaffolds for bone repair Their porous characteristic shows promise in load-bearing bone tissue engineering applications. [11] The bioglass allows the material to be bioactive and form hyaluronic acid on the surface of the material as biological fluid contacts with glass-ceramic foam. Glass-ceramic shows promise as its properties of having adequate porosity to allow cells to migrate through the scaffold, high mechanical strength to bear load, and good bioactivity to allow cells to flourish. [12]

Related Research Articles

<span class="mw-page-title-main">Ceramic</span> Inorganic, nonmetallic solid prepared by the action of heat

A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, and brick.

<span class="mw-page-title-main">Sintering</span> Process of forming and bonding material by heat or pressure

Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plastics, and other materials. The nanoparticles in the sintered material diffuse across the boundaries of the particles, fusing the particles together and creating a solid piece.

<span class="mw-page-title-main">Refractory</span> Materials resistant to decomposition under high temperatures

In materials science, a refractory is a material that is resistant to decomposition by heat or chemical attack that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compounds that may be porous or non-porous, and their crystallinity varies widely: they may be crystalline, polycrystalline, amorphous, or composite. They are typically composed of oxides, carbides or nitrides of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium. Many refractories are ceramics, but some such as graphite are not, and some ceramics such as clay pottery are not considered refractory. Refractories are distinguished from the refractory metals, which are elemental metals and their alloys that have high melting temperatures.

An artificial membrane, or synthetic membrane, is a synthetically created membrane which is usually intended for separation purposes in laboratory or in industry. Synthetic membranes have been successfully used for small and large-scale industrial processes since the middle of the twentieth century. A wide variety of synthetic membranes is known. They can be produced from organic materials such as polymers and liquids, as well as inorganic materials. Most commercially utilized synthetic membranes in industry are made of polymeric structures. They can be classified based on their surface chemistry, bulk structure, morphology, and production method. The chemical and physical properties of synthetic membranes and separated particles as well as separation driving force define a particular membrane separation process. The most commonly used driving forces of a membrane process in industry are pressure and concentration gradient. The respective membrane process is therefore known as filtration. Synthetic membranes utilized in a separation process can be of different geometry and flow configurations. They can also be categorized based on their application and separation regime. The best known synthetic membrane separation processes include water purification, reverse osmosis, dehydrogenation of natural gas, removal of cell particles by microfiltration and ultrafiltration, removal of microorganisms from dairy products, and dialysis.

In materials science, the sol–gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides, especially the oxides of silicon (Si) and titanium (Ti). The process involves conversion of monomers into a colloidal solution (sol) that acts as the precursor for an integrated network of either discrete particles or network polymers. Typical precursors are metal alkoxides. Sol–gel process is used to produce ceramic nanoparticles.

<span class="mw-page-title-main">Bioactive glass</span>

Bioactive glasses are a group of surface reactive glass-ceramic biomaterials and include the original bioactive glass, Bioglass. The biocompatibility and bioactivity of these glasses has led them to be used as implant devices in the human body to repair and replace diseased or damaged bones. Most bioactive glasses are silicate-based glasses that are degradable in body fluids and can act as a vehicle for delivering ions beneficial for healing. Bioactive glass is differentiated from other synthetic bone grafting biomaterials, in that it is the only one with anti-infective and angiogenic properties.

<span class="mw-page-title-main">Metal foam</span> Porous material made from a metal

In materials science, a metal foam is a material or structure consisting of a solid metal with gas-filled pores comprising a large portion of the volume. The pores can be sealed or interconnected. The defining characteristic of metal foams is a high porosity: typically only 5–25% of the volume is the base metal. The strength of the material is due to the square–cube law.

<span class="mw-page-title-main">Ceramic engineering</span> Science and technology of creating objects from inorganic, non-metallic materials

Ceramic engineering is the science and technology of creating objects from inorganic, non-metallic materials. This is done either by the action of heat, or at lower temperatures using precipitation reactions from high-purity chemical solutions. The term includes the purification of raw materials, the study and production of the chemical compounds concerned, their formation into components and the study of their structure, composition and properties.

<span class="mw-page-title-main">Nanofoam</span>

Nanofoams are a class of nanostructured, porous materials (foams) containing a significant population of pores with diameters less than 100 nm. Aerogels are one example of nanofoam.

Ceramic membranes are a type of artificial membranes made from inorganic materials. They are used in membrane operations for liquid filtration.

A vacuum ceramic filter is designed to separate liquids from solids for dewatering of ore concentrates purposes. The device consists of a rotator, slurry tank, ceramic filter plate, distributor, discharge scraper, cleaning device, frame, agitating device, pipe system, vacuum system, automatic acid dosing system, automatic lubricating system, valve and discharge chute. The operation and construction principle of vacuum ceramic filter resemble those of a conventional disc filter, but the filter medium is replaced by a finely porous ceramic disc. The disc material is inert, has a long operational life and is resistant to almost all chemicals. Performance can be optimized by taking into account all those factors which affect the overall efficiency of the separation process. Some of the variables affecting the performance of a vacuum ceramic filter include the solid concentration, speed rotation of the disc, slurry level in the feed basin, temperature of the feed slurry, and the pressure during dewatering stages and filter cake formation.

<span class="mw-page-title-main">Bioceramic</span> Type of ceramic materials that are biocompatible

Bioceramics and bioglasses are ceramic materials that are biocompatible. Bioceramics are an important subset of biomaterials. Bioceramics range in biocompatibility from the ceramic oxides, which are inert in the body, to the other extreme of resorbable materials, which are eventually replaced by the body after they have assisted repair. Bioceramics are used in many types of medical procedures. Bioceramics are typically used as rigid materials in surgical implants, though some bioceramics are flexible. The ceramic materials used are not the same as porcelain type ceramic materials. Rather, bioceramics are closely related to either the body's own materials or are extremely durable metal oxides.

<span class="mw-page-title-main">Ceramic matrix composite</span> Composite material consisting of ceramic fibers in a ceramic matrix

In materials science ceramic matrix composites (CMCs) are a subgroup of composite materials and a subgroup of ceramics. They consist of ceramic fibers embedded in a ceramic matrix. The fibers and the matrix both can consist of any ceramic material, including carbon and carbon fibers.

Membrane technology encompasses the scientific processes used in the construction and application of membranes. Membranes are used to facilitate the transport or rejection of substances between mediums, and the mechanical separation of gas and liquid streams. In the simplest case, filtration is achieved when the pores of the membrane are smaller than the diameter of the undesired substance, such as a harmful microorganism. Membrane technology is commonly used in industries such as water treatment, chemical and metal processing, pharmaceuticals, biotechnology, the food industry, as well as the removal of environmental pollutants.

<span class="mw-page-title-main">Freeze-casting</span>

Freeze-casting, also frequently referred to as ice-templating, or freeze alignment, is a technique that exploits the highly anisotropic solidification behavior of a solvent in a well-dispersed slurry to controllably template a directionally porous ceramic. By subjecting an aqueous slurry to a directional temperature gradient, ice crystals will nucleate on one side of the slurry and grow along the temperature gradient. The ice crystals will redistribute the suspended ceramic particles as they grow within the slurry, effectively templating the ceramic.

Robocasting is an additive manufacturing technique analogous to Direct Ink Writing and other extrusion-based 3D-printing techniques in which a filament of a paste-like material is extruded from a small nozzle while the nozzle is moved across a platform. The object is thus built by printing the required shape layer by layer. The technique was first developed in the United States in 1996 as a method to allow geometrically complex ceramic green bodies to be produced by additive manufacturing. In robocasting, a 3D CAD model is divided up into layers in a similar manner to other additive manufacturing techniques. The material is then extruded through a small nozzle as the nozzle's position is controlled, drawing out the shape of each layer of the CAD model. The material exits the nozzle in a liquid-like state but retains its shape immediately, exploiting the rheological property of shear thinning. It is distinct from fused deposition modelling as it does not rely on the solidification or drying to retain its shape after extrusion.

<span class="mw-page-title-main">Foam glass</span> Porous glass foam material used as a building material

Foam glass is a porous glass foam material. Its advantages as a building material include its light weight, high strength, and thermal and acoustic insulating properties. It is made by heating a mixture of crushed or granulated glass and a blowing agent such as carbon or limestone. Near the melting point of the glass, the blowing agent releases a gas, producing a foaming effect in the glass. After cooling the mixture hardens into a rigid material with gas-filled closed-cell pores comprising a large portion of its volume.

Titanium foams exhibit high specific strength, high energy absorption, excellent corrosion resistance and biocompatibility. These materials are ideally suited for applications within the aerospace industry. An inherent resistance to corrosion allows the foam to be a desirable candidate for various filtering applications. Further, titanium's physiological inertness makes its porous form a promising candidate for biomedical implantation devices. The largest advantage in fabricating titanium foams is that the mechanical and functional properties can be adjusted through manufacturing manipulations that vary porosity and cell morphology. The high appeal of titanium foams is directly correlated to a multi-industry demand for advancement in this technology.

<span class="mw-page-title-main">Polymer derived ceramics</span>

Polymer derived ceramics (PDCs) are ceramic materials formed by the pyrolysis of preceramic polymers, usually under inert atmosphere.

<span class="mw-page-title-main">Engineered cellular magmatic</span>

Engineered cellular magmatics (ECMs) are synthetic stone of glass and ceramic. ECMs replicate rare, naturally occurring volcanic materials, and exhibit useful structural and chemical properties of those materials. The US Department of Energy has recognized ECMs as an advanced material, funding further research into the manufacture and application of ECMs through ARPA-E and Savannah River National Laboratory.

References

  1. 1 2 3 4 5 6 "Novel Ceramic Foam Is Safe And Effective Insulation". Science Daily . May 18, 2001. Retrieved November 11, 2011.
  2. ↑ "Ceramic Foam". ERG Aerospace. Retrieved 2022-02-17.
  3. ↑ "Ceramic Foam Insulation - Industrial Ceramics". www.induceramic.com. Retrieved 2016-03-04.
  4. 1 2 3 Studart, André R.; Gonzenbach, Urs T.; Tervoort, Elena; Gauckler, Ludwig J. (2006). "Processing routes to macroporous ceramics: a review". J Am Ceram Soc. 89 (6): 1771–1789. CiteSeerX   10.1.1.583.9985 . doi:10.1111/j.1551-2916.2006.01044.x.
  5. ↑ Tallon, Carolina; Chuanuwatanakul, Chayuda; Dunstan, David E.; Franks, George V. (2016). "Mechanical strength and damage tolerance of highly porous alumina ceramics produced from sintered particle stabilized foams". Ceramics International. 42 (7): 8478–8487. doi:10.1016/j.ceramint.2016.02.069.
  6. 1 2 3 4 5 6 7 Mengqi Wang and Shuqiong Xu 2018 IOP Conf. Ser.: Earth Environ. Sci. 186 012066
  7. ↑ K. Schwartzwalder and A. V. Somers, Method of Making Porous Ceramic Articles, US Pat. No. 3090094, May 21, 1963
  8. ↑ W. Behrens, A. Tucker. Ceramic foam electronic component cooling. US Pat No 20070247808 A1. October 25, 2007.
  9. ↑ P. Ciambelli, G. Matarazzo, V. Palma, P. Russo, E. Merlone Borla, and M. F. Pidria. Reduction of soot pollution from automotive diesel engine by ceramic foam catalytic filter. Topics in Ceramics, 42-43. May 2007.
  10. ↑ Aubrey, L.S.; Schmahl, J.R.; Cummings, M.A. (1993). "Application of Advanced Reticulated Ceramic Foam Filter Technology to Produce Clean Steel Castings". AFS Transactions. 101: 56–69.
  11. ↑ Francesco Baino and Chiara Vitale-Brovarone. Mechanical properties and reliability of glass–ceramic foam scaffolds for bone repair. “Materials Letters,” 27-30. March 2004
  12. ↑ Fiorilli, S., Baino, F., Cauda, V. et al. Electrophoretic deposition of mesoporous bioactive glass on glass–ceramic foam scaffolds for bone tissue engineering. J Mater Sci: Mater Med 26, 21 (2015). https://doi.org/10.1007/s10856-014-5346-6
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