Foam ceramic holds a special place in the regime of material science and its advancements. The minimal density, porosity and excellent insulation properties of the material makes them useful in variety of applications. The below written article covers the different aspects and delineates different possible methods of foam Ceramic manufacturing.
What makes ceramic and metal foams famous?
Foams be it ceramic or metal foams are made from filling gas in pores of a base material. The pores can be either sealed or closed in nature or interconnected and left open. The main entity that defines the characteristic of a foam is the extend of pores it possesses. Generally, the pores or void spaces ranges from 75 – 90 % of the base material.
Aluminium foams Vs Ceramic foams: A comparison
Aluminium foams
Metal foam in simple terms is a metal filled with porous gas spaces that comprises large portion of their volume. The high-grade metal foams are generally manufactured keeping aluminium as the base metal. Aluminium metal foam made up of aluminium where pores are created by gas into the hot metal. A gas or a dispersant can be used to create pores in the molten aluminium.
The structure of the aluminium metal foam has interconnected aluminium fibers that are basically of two types. The two types of Aluminium metal foam are open celled type of aluminium foam or closed cell type. The major use of the foams are these aluminium foams remain alterable with respect to the favorable properties one requires. The huge surface area, different morphology and the light weight are the attractive features of Aluminium foams.
Properties of Aluminium foams
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Aluminium foams generally stay inert to flames
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The aluminium foam has size in the range of 2- 11 mm in each cell and has porosity around 70 – 90%
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The dimensions of the foam can be varied with regard to applications and they offer strength of 44 MPa
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The aluminium metal foam has resistance larger than normal aluminium metal which is around 100 time or more.
Application of Aluminium Foams
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Automobile safety is becoming popular day by day relying on lightweight materials so as aluminium foam.
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The sound absorption of aluminium foam makes a best additive material in automobile manufacturing
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Aluminium foams are lightweight in nature and finds application in aerospace sector.
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Aluminium foams are best fitting in designer industry as it functions as good setting material when combines with wood.
How is metal foam made?
The popular method of producing Aluminum foam or metal foams is the method of air injection. The initial step involves the preparation of a metal matrix composite using oxides of aluminium and magnesium or silicon carbide. Once the melt is formed air, nitrogen or argon is injected though nozzle or impellers to ensure uniform distribution in the mix.
The other way of manufacturing metal foams is using a blowing agent. The heat induced decomposition causes the blowing agent to release gases and create voids. Industries also use other method of solid gas eutectic formation to induce foaming in the presence of hydrogen. In such manufacture the pores ranges from 10 micrometer to 10 mm.
Ceramic foams
Ceramic foams due to its cellular structure has been an integral part in material manufacturing. The simple manufacturing incorporates usage of polymers with ceramic slurry. The body will retain ceramic in its structure where the high temperature and insulating property has added benefit. The ceramic foam has various application such as thermal insulation, acoustic insulation and various applications that are energy intensive.
Properties of Ceramic foams
Ceramics foams are generally composed of cellular structures that are porous in nature. The three-dimensional network structure is on the other hand brittle with visible spaces or voids in the material. The voids in the cells are linear in dimension and is usually measured in millimeters to micrometers. Although porous ceramic foams are hard with voids being occupied by air or gas up to 95 – 96%.
There are different types of ceramic foams made of Silicon Carbide, Alumina, Zirconia, Titania and Silica. Ceramic foams are known for its lightweight. They have good permeability towards selected entities. The compressive strength of ceramic foams is superior.
The very property of these ceramic foams makes them good choice for machining applications.
Application of Ceramic foams
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The microstructures of ceramic industry have been useful in electronic industry. They are useful in producing entities of batteries, electrodes etc.
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The insulation properties of ceramic are used to provide good heat resistance. They can be used as structural materials in insulation to provide the dual role of insulation and strength.
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Ceramic foams can be used for pollution control. The permeability makes them an effective entity to deal with pollution control. The ceramic foams provide surface area for catalysts to oxidize the captured particles.
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Ceramic foams are also used to aid supportive structures in human body due to their biocompatibility.
Ceramic manufacturing methods
Some of the popular methods of manufacturing ceramic foams are given for reference below:
Direct foaming Process
The process is initiated by making a suspension of ceramic slurry followed by foaming. Once the polymerization is done, the mold is removed and the foam formed is dried and later sintered. This process creates stronger voids which could withstand higher machining.
The process is aided by a foaming agent that initiates the foam when mixed in ceramic slurry is later stabilized followed by solidification. The direct foaming based ceramic manufacturing is known to be simple and reliable and is beneficial to control porosity. The stabilization is generally done once the additives are well scrutinized.
Application and Advantages
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It is generally employed in metallurgical industry where porosity plays a crucial role
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Such foams are used for insulation
Gel Casting Method
When homogeneity and higher strength is preferred gel casting is the best method for ceramic manufacturing. The process is simple and is initiated with the mixing of a colloidal suspension with a monomer that is water soluble and a foaming agent. Post the polymerization the foam gets gelled. The gel casting produces strong and rigid ceramic foams.
Application and Advantages
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It is used to produces filters or durable membranes in chemical industries
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Biomedical fields for implants and supportive super structures
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The process ensures porosity control and high degree of uniformity.
Replication Technique
Replication method involves the method of ceramic manufacturing in which a ceramic slurry is coated over a foam. The polymeric foam is later burnt off through Sintering. This will duplicate a ceramic foam which is originally lookalike of a polymeric foam. The ceramic foams that are produced by the replication technology possesses higher permeability and lesser strength.
Application and Advantages
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It is used to produces complex geometries such as bone implants in biomedical field
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Automotive and Aerospace industries generally use ceramics manufactured by replica method due to its light weight
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The careful considerations in the process ensures there are no void defects prevailing in the essential geometry of the material.
The process of starch consolidation
The starch consolidation method of ceramic manufacturing is generally cheap and doesn’t impart any toxicity. It is environment friendly and employs a temperature of around 300 – 600 degc for burning. The temperature ensures that there form no defects during the formation of the ceramic foam.
The gelling agent such as food grade starch is added into the ceramic powder and then mixed in distilled water. The mixture then undergoes processes such as stirring, casting, coagulation and finally drying. Once dried the entity formed is sintered at higher temperature ensuing the formation of ceramic foam.
Application and Advantages
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Ensures no void defects
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Ecofriendly method of ceramic manufacturing
Emulsion Method
In emulsion method as the name suggests emulsions are used to do ceramic manufacturing to create foams. The ceramic particles are made to suspend in a mixture made of two immiscible liquids. Once the emulsion is formed and stabilized the other liquid phase is removed by either evaporation or combustion.
Application and Advantages
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The emulsion technique ensures to provide good filter efficiency hence is widely acknowledged in filtration systems
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They are used for the manufacture of porous insulating materials and offers lightweight.
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Although the technique ensures good pore size and uniform distribution, the cruciality of the manufacturing method makes the technique tougher to use.
Sol gel Method
Sol gel method as the name suggests is the conversion of a solution into a ceramic structure while the chemical conditions are being controlled in the step. In sol gel method of ceramic manufacturing the porosity is intricately controlled without compromising the essential strength of the material.
Application and Advantages
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The method is generally employed in manufacture of films, coatings, sensors etc.
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High purity foam is produced
Conclusion
The write up covered the detailing of the foams, different types of foams and the global techniques of ceramic foam manufacturing. For ceramic foams the property control plays a crucial role. The different manufacturing method ensures that the favourable property is brought on table to aid the application subjected to.