Name: Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity (Video) | JoVE Journal
Uploaded: 2014-12-11T13:00:00.000+00:00
Duration: 9 min 22 s
Description: Learn the infiltration method to produce open-celled aluminum foam using sodium chloride preforms and argon gas pressure. This protocol enables precise control of porosity for materials science applications.

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5 minutes

The corresponding author would like to acknowledge the Mexican Government&#8217;s National Council of Science and Technology CONACYT for provision of a scholarship.

NOTE: The instructions below are for Protocol A (Figure 1). Modifications for Protocol B, C, and D are listed as well.
1. Aluminum Bar Preparation
<ol>
	<li>Place a large piece (500 g &#8211; 1 kg) of commercial purity aluminum ingot into a crucible.</li>
	<li>Place the crucible in a furnace at 800 &#176;C for about 1 hr, until molten.</li>
	<li>Take the crucible out of the furnace and pour the molten aluminum into a cylindrical mold that is 50 mm in diameter, slightly smaller than the final diameter of the chamber to be used for infiltration (51 mm) giving a gap of about &#189; mm.</li>
	<li>Wait 1 hr for the bar to cool down.</li>
	<li>Remove the bar from the mold.</li>
	<li>Using a band saw, cut it into 4 same-size pieces.</li>
	<li>Sand the edges of each piece to ensure a good fit in the infiltration mold.</li>
</ol>
2. Furnace Preparation
<ol>
	<li>Program the furnace to reach a 740 &#176;C plateau for at least 2 hr.</li>
	<li>Set the heating rate of the furnace to 20 &#176;C/min.</li>
</ol>
3. Preform Preparation
NOTE: Depending on the height of the foam aimed for, vary the amount of NaCl to use for infiltration between 100 g and 300 g.
<ol>
	<li>Choose the infiltration NaCl to use, with a diameter corresponding to the pore size range required (for example a range between 1.4 mm and 1.7 mm). The material can be obtained from chemical suppliers in high purity, or supermarket bought table salt can be used (such material will have additives such as iodine and anti-caking agents, but these do not in practice influence the process to a significant extent).</li>
	<li>Select sieves of an appropriate size range and stack on a base container with the smaller opening size at the bottom.</li>
	<li>From the suppliers&#8217; bag of NaCl, take approximately 500 g and pour it in the stacked sieves.</li>
	<li>Agitate the sieves, either manually or using a sieve shaker, for 1 min.</li>
	<li>Discard the NaCl left in the larger aperture size sieve and the bottom container, the NaCl left in the smaller aperture sieve is used for infiltration.</li>
	<li>Weigh the amount of infiltration NaCl obtained.</li>
	<li>If the amount is insufficient, repeat steps 3.4 to 3.7. 
	NOTE: For Protocols B, C or D, obtain 100 g of fine NaCl (&#60; 500 &#181;m). This creates an extra space in the mold for air trapped in the preform during infiltration in case the air in the preform does not escape the chamber adequately.</li>
</ol>
4. Mold Preparation
<ol>
	<li>Using sandpaper and laboratory paper roll, clean the mold cylinder (Figure 2), taking special consideration for both the top and bottom edges, and keeping the mold free of any noticeable impurities from previous use.</li>
	<li>Spray the inside of the mold cylinder with boron nitride aerosol spray, creating a thin coat covering the inside of the mold. 
	NOTE: This is achieved when the original color of the mold is replaced by a white layer of the spray; it is not necessary to measure its specific concentration.</li>
	<li>Let the mold cylinder dry for at least 5 min at RT (heating to around 100 &#176;C for up to 1 hr may be applied for further drying if desired).</li>
	<li>Using fine sandpaper, remove any residue of boron nitride from the edges of the mold cylinder, to improve the seal between the mold cylinder and the mold base. 
	NOTE: The next 3 steps are for Protocols A and B; for Protocols C and D cut only one gasket ring for the lid.</li>
	<li>Cut 2 gasket rings from 1 mm thick graphite sheet (OD = 60 mm, ID = 51 mm), one for the union between the top edge of the mold cylinder and the mold lid leading up to the valve system, the other for the union between the bottom edge of the mold cylinder and the mold base.</li>
	<li>Place one of the gaskets in the mold base groove.</li>
	<li>Place the bottom of the mold cylinder into the groove with the gasket.</li>
	<li>Tap lightly with a mallet on the top of the mold cylinder to secure the bottom to the base groove. 
	NOTE: For Protocol B, C, or D, add the following step.
	<ol>
		<li>Pour the 100 g of fine NaCl (&#60; 500 &#181;m) into the mold cylinder and flatten the top with an uncut aluminum bar tapping the top of it lightly with the mallet to ensure the fine NaCl is packed to a high density. 
		NOTE: For Protocol D add the following step.</li>
		<li>Cut 2 circles of soft 2 mm thick ceramic Kaowool blanket the size of the mold diameter (51 mm) and place them on top of the fine NaCl, use the uncut aluminum bar and the mallet to press them against the fine NaCl.</li>
	</ol>
	</li>
	<li>Pour the NaCl to be infiltrated into the mold cylinder. 
	NOTE: For Protocol D add the following step.
	<ol>
		<li>Attach the mold and base to a vibrating table, making sure the mold cylinder does not move from the base groove. Vibrate for 1 min at 50 Hz with a 0.01 m amplitude.</li>
	</ol>
	</li>
	<li>Holding the top of the cylinder in place, pick up the base and shake lightly until the NaCl inside the mold forms a flat surface at the top.</li>
	<li>Place the prepared aluminum bar on top of the NaCl preform.</li>
	<li>Place a graphite gasket in the groove of the mold lid.</li>
	<li>By hand screw the 4 stainless steel studs to the base and secure them with 4 sets of stainless steel nuts and washers on the top of the base using a wrench and place the mold lid on top of the mold cylinder through the studs.</li>
	<li>With a torque wrench set at 16 N&#183;m, screw the 4 sets of steel nuts and washers on the 4 threaded rods screwed into the base and extending up through the lid, where the nuts are tightened to lock the mold lid in place.</li>
	<li>Attach the top of the lid to the valve system with the gasket, clamp, bolt and butterfly nut.</li>
	<li>Close all the valves of the system.</li>
	<li>Open the valve leading to the vacuum pump and the mold (valve 3).</li>
	<li>Turn on the vacuum pump until the dial gauge of the valve system indicates the lowest pressure possible.</li>
	<li>Turn off the vacuum pump.</li>
	<li>If the loss of vacuum in the system is lower than a rate of 50 Torr/sec for the first 10 sec after shutting down the vacuum pump the seal is sufficiently good for infiltration.</li>
	<li>Leave the lid valve open (valve 3) to keep the system at ambient pressure and close the vacuum pump valve (valve 1).</li>
	<li>Without detaching the valve system, place the mold in the preheated furnace and wait for 1 hr.</li>
</ol>
5. Infiltration
<ol>
	<li>Close all the valves of the system (Figure 3).</li>
	<li>Open the valve leading to the argon gas cylinder (valve 2).</li>
	<li>Open the main valve on the argon gas tank and set the infiltration pressure with the regulator valve (for a range of 1.4 mm to 1.7 mm of NaCl particle size, use a pressure of 3.5 bars). 
	NOTE: For Protocol B, an infiltration pressure of 3 bar is used. Use a pressure of 1 bar for Protocols C and D.</li>
	<li>In a swift manner, open the lid valve (valve 3).</li>
	<li>After 1 min, remove the mold from the furnace and place it on top of a cooling surface (in this case a copper block). 
	NOTE: While cooling, the pressure in the system will change. For the first 5 min of this process, pay close attention to the pressure indicated by the regulator and adjust back to the infiltration pressure if necessary.</li>
</ol>
6. Sample Extraction
<ol>
	<li>After 30 min, when the mold is cool enough to handle with light heat resistant gloves, detach the valve system and place the mold base on a workbench vise. Unscrew the lid from the top of the cylinder.</li>
	<li>With the lid off, lightly tap the top of the mold cylinder with a mallet in a perpendicular direction to the vise&#8217;s grip to loosen the mold cylinder from the base groove.</li>
	<li>Remove the mold base from the vise and place the mold cylinder in the vise grip.</li>
	<li>With the mallet tap the remaining aluminum on top of the sample to push it out of the mold cylinder.</li>
	<li>Using a band saw, cut the bottom part of the foam sample, removing the surplus aluminum.</li>
	<li>Depending on the height of foam required, cut where desired, close to the top of the sample.</li>
	<li>Place the infiltrated foam in a beaker with water and a magnetic stirring bar on a stirring hot plate to dissolve the NaCl preform.</li>
	<li>Set the temperature of the hot plate to 60 &#176;C. Change the water every 10 min until there is no NaCl left in the foam. 
	NOTE: To ensure there is no NaCl left in the foam, change the water approximately 10 times. It is also possible to make periodic checks of the sample weight after a brief drying stage. When this ceases to change significantly with further immersion, the NaCl must be completely removed.</li>
	<li>Finally using an electric air drier remove all the water left in the foam. The foam sample is ready.</li>
</ol>

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<li>Conde, Y., Despois, J. -F., Goodall, R., Marmottant, A., Salvo, L., San Marchi, C., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Replication+processing+of+highly+porous+materials%5BTitle%5D)+AND+%22Advanced+Engineering+Materials%22%5BJournal%5D)">Replication processing of highly porous materials.</a> Advanced Engineering Materials. 8 (9), 795-803 (2006).</li>
<li>Goodall, R., Mortensen, A. Chapter 24. Porous Metals. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aGoodall%2C+R+%22Physical+Metallurgy%22">Physical Metallurgy</a>. Laughlin, D. E., Hono, K. , 5th Ed, 2399-2595 (2014).</li>
<li>Polonsky, L., Lipson, S., Markus, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Lightweight+Cellular+Metal%5BTitle%5D)+AND+%22Modern+Castings%22%5BJournal%5D)">Lightweight Cellular Metal.</a> Modern Castings. 39, 57-71 (1961).</li>
<li>San Marchi, C., Mortensen, A. Chapter 2.06. Infiltration and the Replication Process for Producing Metal Sponges. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aSan+Marchi%2C+C+%22Handbook+of+Cellular+Metals%22">Handbook of Cellular Metals</a>. Degischer, H. P., Kriszt, B. , Wiley-VCH. 44-56 (2002).</li>
<li>Galliard, C., Despois, J. F., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Processing+of+NaCl+powders+of+controlled+size+and+shape+for+the+microstructural+tailoring+of+aluminium+foams%5BTitle%5D)+AND+%22Materials+Science+and+Engineering+A%22%5BJournal%5D)">Processing of NaCl powders of controlled size and shape for the microstructural tailoring of aluminium foams.</a> Materials Science and Engineering A. 374 (1-2), 250-262 (2004).</li>
<li>Despois, J. F., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Permeability+of+open-pore+microcellular+materials%5BTitle%5D)+AND+%22Acta+Materialia%22%5BJournal%5D)">Permeability of open-pore microcellular materials.</a> Acta Materialia. 53 (5), 1381-1388 (2005).</li>
<li>Goodall, R., Despois, J. F., Marmottant, A., Salvo, L., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+effect+of+preform+processing+on+replicated+aluminium+foam+structure+and+mechanical+properties%5BTitle%5D)+AND+%22Scripta+Materialia%22%5BJournal%5D)">The effect of preform processing on replicated aluminium foam structure and mechanical properties.</a> Scripta Materialia. 54, 2069-2073 (2006).</li>
<li>Goodall, R., Marmottant, A., Salvo, L., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Spherical+pore+replicated+microcellular+aluminium%3A+Processing+and+influence+on+properties%5BTitle%5D)+AND+%22Materials+Science+and+Engineering+A%22%5BJournal%5D)">Spherical pore replicated microcellular aluminium: Processing and influence on properties.</a> Materials Science and Engineering A. 465 (1-2), 124-135 (2007).</li>
<li>Despois, J. F., Marmottant, A., Salvo, L., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Influence+of+the+infiltration+pressure+on+the+structure+and+properties+of+replicated+aluminium+foams%5BTitle%5D)+AND+%22Materials+Science+and+Engineering+A%22%5BJournal%5D)">Influence of the infiltration pressure on the structure and properties of replicated aluminium foams.</a> Materials Science and Engineering A. 462, 68-75 (2007).</li>
<li>San Marchi,, Despois, C., F, J., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Uniaxial+deformation+of+open-cell+aluminium+foam%3A+the+role+of+internal+damage%5BTitle%5D)+AND+%22Acta+Materialia%22%5BJournal%5D)">Uniaxial deformation of open-cell aluminium foam: the role of internal damage.</a> Acta Materialia. 52 (10), 2895-2902 (2004).</li>
<li>Goodall, R., Weber, L., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+electrical+conductivity+of+microcellular+metals%5BTitle%5D)+AND+%22Journal+of+Applied+Physics%22%5BJournal%5D)">The electrical conductivity of microcellular metals.</a> Journal of Applied Physics. 100, 044912(2006).</li>
<li>Kadar, C., Chmelik, F., Kendvai, J., Voros, G., Rajkovits, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Acoustic+emission+of+metal+foams+during+tension%5BTitle%5D)+AND+%22Materials+Science+and+Engineering+A%22%5BJournal%5D)">Acoustic emission of metal foams during tension.</a> Materials Science and Engineering A. 462, 316-319 (2007).</li>
<li>Goodall, R., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microcellular+aluminium%5BTitle%5D)+AND+%22Child%E2%80%99s+Play%21+Advanced+Engineering+Materials%22%5BJournal%5D)">Microcellular aluminium.</a> Child’s Play! Advanced Engineering Materials. 9 (11), 951-954 (2007).</li>
<li>Wada, T., Inoue, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fabrication%2C+Thermal+Stability+and+Mechanical+Properties+of+Porous+Bulk+Glassy+Pd-Cu-Ni-P+Alloy%5BTitle%5D)+AND+%22Materials+Transactions%22%5BJournal%5D)">Fabrication, Thermal Stability and Mechanical Properties of Porous Bulk Glassy Pd-Cu-Ni-P Alloy.</a> Materials Transactions. 44 (10), 2228-2231 (2003).</li>
<li>DeFouw, J. D., Dunand, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Processing+and+compressive+creep+of+cast+replicated+IN792+Ni-base+superalloy+foams%5BTitle%5D)+AND+%22Materials+Science+%26+Engineering+A%22%5BJournal%5D)">Processing and compressive creep of cast replicated IN792 Ni-base superalloy foams.</a> Materials Science & Engineering A. 558, 129-133 (2012).</li>
<li>Berchem, K., Mohr, U., Bleck, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Controlling+the+Degree+of+Pore+Opening+of+Metal+Sponges%2C+Prepared+by+the+Infiltration+Preparation+Method%5BTitle%5D)+AND+%22Materials+Science+and+Engineering+A%22%5BJournal%5D)">Controlling the Degree of Pore Opening of Metal Sponges, Prepared by the Infiltration Preparation Method.</a> Materials Science and Engineering A. 323 (1-2), 52-57 (2002).</li>
<li>Lu, T. J., Ong, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Characterization+of+closed-celled+cellular+aluminum+alloys%5BTitle%5D)+AND+%22J.+Mater.+Sci%22%5BJournal%5D)">Characterization of closed-celled cellular aluminum alloys.</a> J. Mater. Sci. 36, 2773-2786 (2001).</li>
<li>Chou, K. S., Song, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+Novel+Method+for+Making+Open-cell+Aluminum+Foams+with+Soft+Ceramic+Balls%5BTitle%5D)+AND+%22Scripta+Materialia%22%5BJournal%5D)">A Novel Method for Making Open-cell Aluminum Foams with Soft Ceramic Balls.</a> Scripta Materialia. 46 (5), 379-382 (2002).</li>
<li>Dairon, J., Gaillard, Y., Tissier, J. C., Balloy, D., Degallaix, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Parts+Containing+Open-Celled+Metal+Foam+Manufactured+by+the+Foundry+Route%3A+Processes%2C+Performances+and+Applications%5BTitle%5D)+AND+%22Advanced+Engineering+Materials%22%5BJournal%5D)">Parts Containing Open-Celled Metal Foam Manufactured by the Foundry Route: Processes, Performances and Applications.</a> Advanced Engineering Materials. 13 (11), 1066-1071 (2011).</li>
<li>LeMay, J. D., Hopper, R. W., Hrubesh, L. W., Pekala, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Low-Density+Microcellular+Materials%5BTitle%5D)+AND+%22Materials+Research+Society+Bulletin%22%5BJournal%5D)">Low-Density Microcellular Materials.</a> Materials Research Society Bulletin. 15 (12), 19-20 (1990).</li>
<li>Seliger, H., Deuther, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Die+Herstellung+von+Schaum-+und+Zellaluminium%5BTitle%5D)+AND+%22Feiburger+Forschungshefte%22%5BJournal%5D)">Die Herstellung von Schaum- und Zellaluminium.</a> Feiburger Forschungshefte. , 103-129 (1965).</li>
<li>Kuchek, H. A. Method of Making Porous Metallic Article. US patent. , 3,236,706 (1966).</li>
<li>Han, F., Cheng, H., Wang, J., Wang, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+pore+combination+on+the+mechanical+properties+of+an+open+cell+aluminum+foam%5BTitle%5D)+AND+%22Scripta+Materialia%22%5BJournal%5D)">Effect of pore combination on the mechanical properties of an open cell aluminum foam.</a> Scripta Materialia. 50 (1), 13-17 (2004).</li>
<li>Cao, X. -q, Wang, Z. -h, Ma, H. -w, Zhao, L. -m, Yang, G. -t <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effects+of+cell+size+on+compressive+properties+of+aluminum+foam%5BTitle%5D)+AND+%22Transactions+of+Nonferrous+Metals+Society+of+China%22%5BJournal%5D)">Effects of cell size on compressive properties of aluminum foam.</a> Transactions of Nonferrous Metals Society of China. 16, 351-356 (2006).</li>
<li>Abdulla, T., Yerokhin, A., Goodall, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+plasma+electrolytic+oxidation+coating+on+the+specific+strength+of+open-cell+aluminium+foams%5BTitle%5D)+AND+%22Materials+%26+Design%22%5BJournal%5D)">Effect of plasma electrolytic oxidation coating on the specific strength of open-cell aluminium foams.</a> Materials & Design. 32, 3742-3749 (2011).</li>
<li>San Marchi, C., Mortensen, A. Fabrication and Comprehensive Response of Open-cell Aluminum Foams with Sub-millimeter Pores. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aSan+Marchi%2C+C+%22Euromat99%22">Euromat99</a>. Clyne, T. W., Simancik, F. 5, DGM/Wiley-VCH. Munich, Germany. 34(1999).</li>
<li>San Marchi, C., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Deformation+of+open-cell+aluminium+foam%5BTitle%5D)+AND+%22Acta+Materialia%22%5BJournal%5D)">Deformation of open-cell aluminium foam.</a> Acta Materialia. 49 (19), 3959-3969 (2001).</li>
<li>Goodall, R., Despois, J. F., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Sintering+of+NaCl+powder%3A+Mechanisms+and+first+stage+kinetics%5BTitle%5D)+AND+%22Journal+of+the+European+Ceramic+Society%22%5BJournal%5D)">Sintering of NaCl powder: Mechanisms and first stage kinetics.</a> Journal of the European Ceramic Society. 26 (16), 3487-3497 (2006).</li>
<li>Despois, J. F., Conde, Y., San Marchi, C., Mortensen, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Tensile+Behaviour+of+Replicated+Aluminium+Foams%5BTitle%5D)+AND+%22Advanced+Engineering+Materials%22%5BJournal%5D)">Tensile Behaviour of Replicated Aluminium Foams.</a> Advanced Engineering Materials. 6 (6), 444-447 (2004).</li>
<li>Zhao, Y. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Stochastic+Modelling+of+Removability+of+NaCl+in+Sintering+and+Dissolution+Process+to+Produce+Al+Foams%5BTitle%5D)+AND+%22Journal+of+Porous+Materials%22%5BJournal%5D)">Stochastic Modelling of Removability of NaCl in Sintering and Dissolution Process to Produce Al Foams.</a> Journal of Porous Materials. 10 (2), 105-111 (2003).</li>
</ol>

The authors declare that they have no competing financial interests.

The basic method described here has been used in different forms by other researchers. Some of the key variants that allow foams of different types to be created are discussed. In characterizing these foams we have measured the porosity, as this is a quick and easy assessment to make, but characterization of other structural characteristics, such as pore size, specific surface area or strut thickness might be required to obtain a full understanding of foam characteristics for different applications. In practice, for prod...

A journal reference was corrected in the publication of <a href="http://www.jove.com/video/52268">Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity</a>. Reference 21 and 22 were originally merged together as one reference. They have been separated into references 21 and 22 in the article. The reference numbers have been updated in the article to reflect this additional reference citation. It has been updated from:
<ol start="21"><li>LeMay, J.D., Hopper, R.W., Hrubesh, L.W., &#38; Pekala, R.W. Low-Density Microcellular Materials. Materials Research Society Bulletin. 15 (12), 19&#8211;20 (1990).Seliger, H., &#38; Deuther U. Die Herstellung von Schaum- und Zellaluminium. Feiburger Forschungshefte. 103&#8211;129 (1965).</li></ol>
to:
<ol start="21"><li>LeMay, J.D., Hopper, R.W., Hrubesh, L.W., &#38; Pekala, R.W. Low-Density Microcellular Materials. Materials Research Society Bulletin. 15 (12), 19&#8211;20 (1990).</li>
<li>Seliger, H., &#38; Deuther U. Die Herstellung von Schaum- und Zellaluminium. Feiburger Forschungshefte. 103&#8211;129 (1965).</li></ol>

Erratum: Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams have attracted a large amount of interest and research effort in recent years as shown by the large body of work cited in wide ranging review articles such as Banhart1, Conde et al.2 or more recently Goodall and Mortensen3. Among the methods used for production of the material, the replication process is distinguished by its experimental simplicity and the degree of control over the final foam structure that can be offered. It should be noted that although in the literature such materials are often described as foams (and are here) as they are not produced by bubbles of gas within a liquid they are more appropriately called porous metals or microcellular metals.
The first report of the replication process was in the early 1960s4, and it has been developed further at different stages since then, with notable advances by the research group of Mortensen at the Ecole Polytechnique Federale de Lausanne in Switzerland.
The process relies on the casting of the metal around a preform of particles that defines the shape of the porosity in the final material2, 5. After cooling the preform can be removed by solvent leaching or pyrolysis that causes oxidation. A popular use of this technique utilizes NaCl as a space holder to produce aluminum5-10 or aluminum alloy foams11-14. NaCl has several advantages such as being readily accessible, non-toxic and can be removed from the foam by dissolution in water. By having a melting point of 801 &#176;C, it can be used with metals that have a melting point lower than this value, most commonly aluminum, but examples also exist of the use with materials such as bulk metallic glasses, by humidifying a mix of liquid palladium-based bulk metallic glass alloy and NaCl granules15. Substitution of the NaCl with higher melting point materials also permits the production of foams from higher melting point metals16. This may include other water-soluble materials, or insoluble ones including different types of sand. In this form the process becomes more like conventional sand casting as to remove the sand, high pressure water jets17, 18 or different forms of washing19 or agitating20 are required.
The essential process21 proceeds by taking grains of NaCl and placing them in a mold4, 22, 23. The basic method has been used to make aluminum and aluminum alloy foams24-26 for a wide range of foam behavior investigations. Additional steps have been introduced to further control the density and to increase the interconnectivity of the pores; these include the densification of the preform. To densify the preform, sintering has been employed27, 28 and has been used in different experiments since13, with the sintering behavior of NaCl based on temperature, granule size and density described by Goodall et al.29. Another method used for this purpose is cold isostatic pressing (CIP)5, 30; this is a faster technique that can achieve a larger spectrum of comparable densities. The procedure can also be performed in the solid state with metal powder and NaCl grains, and is then sometimes called the Sintering and Dissolution Process31.
A full survey of the use of the replication technique to date and comparison with other techniques is given in Goodall and Mortensen3.
In this work we report in detail equipment and experimental protocols that have been used for the processing of metal foams by the replication method, and which are relatively easy to implement in a research laboratory setting. It is important to acknowledge that other versions of the equipment, with different capabilities exist in other research groups, and that while the equipment presented here is suitable to process the material, it is not the only version or protocol that can be made to work. In any case, a thorough understanding of any particular method is essential for experimental success.
The precise protocols used are detailed below. The protocol variations (A, B, C and D) have small changes between them, principally intended to alter the density of the foams produced. The porosity has been calculated from measurements of the bulk weight of the samples, their volume and the density of aluminum (2.7 g/cm3). In developing the methods described for aluminum foam production by replication, attempts have been made to reduce the amount of advanced equipment to the smallest possible extent, such that the method is as easy to implement as possible. Other variations that may be used at different stages are discussed later.

<table><tbody><tr><td>Salt</td><td>Hydrosoft</td><td>Granular Salt 25 kg 855754</td><td>http://www.travisperkins.co.uk/p/hydrosoft-granular-salt-25kg/855754/3893446</td></tr><tr><td>Aluminum</td><td>William Rowland</td><td>Aluminum Ingots 99.87% pure 25&amp;nbsp;kg drum</td><td>http://www.william-rowland.com/products/high-purity-metals#product-id-1</td></tr><tr><td>Crucible</td><td>Morgan Advance Materials</td><td>Syncarb Crucible</td><td>http://www.morganmms.com/crucibles-foundry-products/crucibles/syncarb/</td></tr><tr><td>Furnace</td><td>Elite Thermal Systems</td><td>TLCF10/27-3216CP &amp;amp; 2116 O/T</td><td>http://www.elitefurnaces.com/eng/products/furnaces/1200%20Top%20Loading%20Furnaces.php</td></tr><tr><td>Bar Mold</td><td>The University of Sheffield</td><td>Custom Made</td><td>Stainless Steel 304, 15&amp;nbsp;cm height, 5&amp;nbsp;cm inner diameter, 6&amp;nbsp;cm outer diameter</td></tr><tr><td>Band Saw</td><td>Clarke</td><td>CBS45MD (6&quot; x 4 1/2&quot;) 370W 060710025</td><td>http://www.machinemart.co.uk/shop/product/details/cbs45md-41-2in-x-6in-metal-cutting-ban</td></tr><tr><td>Sandpaper</td><td>Wickes</td><td>Specialist wet &amp;amp; dry sandpaper 501885</td><td>http://www.wickes.co.uk/Specialist-Wet+Dry-Sandpaper-PK4/p/501885</td></tr><tr><td>Sieves</td><td>Fisher Scientific</td><td>Fisherbrand test sieves 200 mm diamater</td><td>http://www.fisher.co.uk/product/brand_listing.php/F/Fisherbrand/Sieve</td></tr><tr><td>Balance</td><td>Precisa</td><td>XB 6200C</td><td>http://www.precisa.co.uk/precision_balances.php</td></tr><tr><td>Boron Nitride</td><td>Kennametal</td><td>500 ml spray can</td><td>http://www.kennametal.com/content/dam/kennametal/kennametal/common/Resources/Catalogs-Literature/Advanced%20Materials%20and%20Wear%20Components/B-13-03401_ceramic_powders&lt;br/&gt; _brochure_EN.pdf</td></tr><tr><td>Infiltration Mold, Base and Lid</td><td>The University of Sheffield</td><td>Custom Made</td><td>Stainless Steel 304, 15&amp;nbsp;cm height, 5.1&amp;nbsp;cm inner diameter, 6&amp;nbsp;cm outer diameter</td></tr><tr><td>Cylindrical Mold</td><td>The University of Sheffield</td><td>Custom Made</td><td>Low carbon steel 1020, 15 cm height, 5 cm inner diameter, 6 cm outer diameter</td></tr><tr><td>Graphite Gasket</td><td>Gee Graphite</td><td>Geegraf Stainless Steel Reinforced Graphite 1&amp;nbsp;mm thick</td><td>http://www.geegraphite.com/steel_reinforced.html</td></tr><tr><td>Mallet</td><td>Thor Hammer Co. Ltd.</td><td>Round Solid Super Plastic Mallet</td><td>http://www.thorhammer.com/Mallets/Round/</td></tr><tr><td>Wrench</td><td>Kennedy Professional</td><td>13 mm Ratchet Combination Wrench KEN5822166K</td><td>https://www.cromwell.co.uk/KEN5822166K</td></tr><tr><td>Nuts</td><td>Matlock</td><td>M8 Steel hex full nut galvanized</td><td>https://www.cromwell.co.uk/CTL6400068J</td></tr><tr><td>Washers</td><td>Matlock</td><td>M8 Form-A steel washer bzp</td><td>https://www.cromwell.co.uk/CTL6451208H</td></tr><tr><td>SS Nuts</td><td>Matlock</td><td>M8 A2 st/st hex full nut</td><td>https://www.cromwell.co.uk/CTL6423008F</td></tr><tr><td>SS Washers</td><td>Matlock</td><td>M8 A2 st/st Form-A washer</td><td>https://www.cromwell.co.uk/CTL6464008H</td></tr><tr><td>Stainless Steel Studding</td><td>Cromwell</td><td>M8 x 1 Mtr A2 Stainless Steel Studding QFT6397080K</td><td>https://www.cromwell.co.uk/QFT6397080K</td></tr><tr><td>Valves</td><td>Edwards</td><td>C33205000 SP16K, Nitrile Diaphragm</td><td>https://www.edwardsvacuum.com/Products/View.aspx?sku=C33205000</td></tr><tr><td>Fitting Cross</td><td>Edwards</td><td>C10512412 NW16 Cross Piece Aluminum</td><td>https://www.edwardsvacuum.com/Products/C10512412/View.aspx</td></tr><tr><td>Fitting T</td><td>Edwards</td><td>C10512411 NW16 T-Piece Aluminum</td><td>https://www.edwardsvacuum.com/Products/C10512411/View.aspx</td></tr><tr><td>Vacuum Pump</td><td>Edwards</td><td>A36310940 E2M18 200-230/380-415V, 3-ph, 50 Hz</td><td>http://www.edwardsvacuum.com/Products/View.aspx?sku=A36310940</td></tr><tr><td>Dial Gauge</td><td>Edwards</td><td>D35610000 CG16K, 0-1,040 mbar</td><td>http://www.edwardsvacuum.com/Products/View.aspx?sku=D35610000</td></tr><tr><td>Argon Gas</td><td>BOC</td><td>Pureshield Argon Gas</td><td>http://www.boconline.co.uk/en/products-and-supply/industrial-gases/inert-gases/pureshield-argon/pureshield-argon.html</td></tr><tr><td>Stainless Steel Hose</td><td>BOC</td><td>Stainless Steel Hose</td><td>http://www.boconline.co.uk/en/products-and-supply/speciality-equipment/hoses-and-pigtails/index.html</td></tr><tr><td>Regulator</td><td>BOC</td><td>HP 1500 Series Regulator</td><td>http://www.boconline.co.uk/en/products-and-supply/speciality-equipment/regulators/single-stage-regulators/hp1500-series/hp1500-series.html</td></tr><tr><td>Copper Block</td><td>William Rowland</td><td>Copper Ingot 25 kg</td><td>http://www.william-rowland.com/products/high-purity-metals#product-id-18</td></tr><tr><td>Vise</td><td>Record</td><td>T84-34 H/Duty Eng Vice 4 1/2&quot; Jaws REC5658326K</td><td>https://www.cromwell.co.uk/REC5658326K</td></tr><tr><td>Beaker</td><td>Fisher Scientific</td><td>11567402 - Beaker, squat form, with graduations and spout 800 ml</td><td>https://webshop.fishersci.com/insight2_uk/getProduct.do;jsessionid=16D5812&lt;br/&gt; D71B8CB37B475E94281E2BEA&lt;br/&gt; 5.ukhigjavappp11?productCode=11567402&amp;amp;resultSet&lt;br/&gt; Position=0</td></tr><tr><td>Stirring Hot Plate</td><td>Corning</td><td>Corning stirring hot plate Model 6798-420d</td><td>http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_guid/shp/shp.aspx</td></tr><tr><td colspan="4">[header]</td></tr><tr><td>Stir Bar</td><td>Fisher Scientific</td><td>11848862 - PTFE Stir bar + Ring 25x6 mm</td><td>https://webshop.fishersci.com/insight2_uk/getProduct.do;jsessionid=16D5812&lt;br/&gt; D71B8CB37B475E94281E2BEA&lt;br/&gt; 5.ukhigjavappp11?productCode=11848862&amp;amp;resultSet&lt;br/&gt; Position=0</td></tr><tr><td>Air dryer</td><td>V05</td><td>V05 Max Air Turbo Dryer DR-120-GB</td><td>http://reviews.boots.com/2111-en_gb/1120627/v05-v05-max-air-turbo-hair-dryer-dr-120-gb-reviews/reviews.htm</td></tr><tr><td>Ceramic Sheet</td><td>Morgan Advance Materials</td><td>Kaowool Blanket 2 mm thick</td><td>http://www.morganthermalceramics.com/downloads/datasheets?f[0]=field_type%3A84</td></tr><tr><td>Vibrating Table</td><td>Peveril Machinery</td><td>Pevco Vibrating Table 1.25&amp;nbsp;m x 0.625&amp;nbsp;m x 0.6&amp;nbsp;m</td><td>https://peverilmachinery.co.uk/equipment/vibrating-tables</td></tr></tbody></table>

casting protocols for the production of open cell aluminum foams by the replication technique and the effect on porosity

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual &#8220;know-how&#8221;, and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1&#8211;2.36 mm diameter and 61% to 77% porosity can be obtained.

In Figure 4 the morphology of the NaCl grains can be seen (angular and spherical), for illustrative purposes. The foams obtained with Protocol A were made using angular shaped grains and the rest were made with the spherical grains. It was found that the use of different shape NaCl grains had no observed effect on the porosity obtained in the samples.
From the results we can determine that samples a, b, and c (made with Protocol A), are on average 63% porous (Figure 5<...

Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many ...

The overall goal of this procedure is to produce a metal foam by the infiltration method. This is accomplished by first loading a mold with fine sodium chloride at the bottom, infiltration, sodium chloride in the middle, and an aluminum bar on top. Then placing the lid on the chamber.The second step is to attach the mold to a valve system and place it in a preheated furnace to melt the aluminum. Next argon gas pressure is applied to the molten aluminum, forcing it into the free spaces between the infiltration sodium chloride grains. The final steps are to remove the mold from the furnace and retrieve the foam sample.Then cut the sample to size and remove the sodium chloride in a water bath. Ultimately, the weight and volume of the sample will indicate its density and inform modifications in the protocol to obtain foams of different characteristics. Generally, individuals new to this method will struggle because slight variations in the procedure have great effect on the outcome.As a first step, set the furnace to increase 20 degrees Celsius per minute to a final temperature of 740 degrees Celsius as it is reaching its final temperature, begin preparation of the preform, the preform will be placed in a mold. The mold in this experiment is cylindrical 150 millimeters tall and has an inner diameter of 51 millimeters. Prior to this experiment, a commercial purity aluminum ingot has been cast for use in the mold.The aluminum is formed into a cylindrical bar with a 50 millimeter diameter. The bar is cut into four equal parts sufficient for four experiments. Next, begin collecting the sodium chloride to be used for infiltration.Select a sieve with openings about the size of the smallest acceptable diameter, and another with openings about the size of the largest pore diameter. Place a container to catch filtered sodium chloride on the bench. On top of that, place the sieve with the smallest opening.Place the sieve with the larger openings above it at this point, ready, either high purity or supermarket sodium chloride. Put approximately 500 grams of sodium chloride into a container and pour it into the stacked sieves. Then agitate the sieves for a minute After the agitation, discard the contents of the top sieve.Also discard the sodium chloride from the bottom container. The sodium chloride in the middle sieve will be used for infiltration after it is weighed. The experiment in this video uses both an infiltration, sodium chloride and a fine sodium chloride.Use the sieve technique once to collect 150 grams of infiltration, sodium chloride, and a second time to collect 100 grams of fine sodium chloride. After collecting the sodium chloride, proceed by working with the infiltration mold. It should be clean and free of any impurities from previous use.Use a boron nitride aerosol spray to create a thin coating inside the cylinder. After the cylinder has dried, use fine sandpaper to remove boron nitride residue from the ends of the cylinder with the mold prepared. Work with the mold base.Place a graphite gasket on the groove of the base. Then place the bottom of the mold cylinder into the groove on top of the gasket with a mallet, tap the cylinder top to secure it in the base before continuing. Now get the 100 grams of vine sodium chloride and pour it into the mold cylinder.Place an uncut aluminum bar on the top and tap it lightly with a mallet to increase the packing density and make the surface of the sodium chloride flat. Remove the uncut bar and proceed by pouring the sodium chloride to be infiltrated into the mold. Hold the top of the cylinder in place and pick up the base to shake the assembly slightly until the sodium chloride forms a flat surface at the top.Next, place the prepared aluminum bar on top of the sodium chloride preform. Place the mold lid with gasket on top of the mold cylinder and secure it. Transport the mold to where it will be attached to a gas supply and vacuum pump.Lace the mold under the tubing for the valve system. Then properly attach the tubing to the top of the lid. The valves immediately above the mold control isolation of the mold argon gas flow, and access to the vacuum pump.Initially, all valves should be closed. To test the mold seal, open the valves to the mold and the vacuum pump. Pump to the lowest possible pressure before stopping and checking the loss rate.After testing the mold seal, return the system to ambient pressure using the pump's relief valve. Continue by closing the valve, leading to the vacuum pump. With the mold still attached to the valve system, move the mold to the preheated furnace.Let it remain there for one hour. After one hour, start the infiltration process By closing the valve to the mold, all valves in the system should be closed. Next, open the valves to the Argonne gas cylinder.To provide the infiltration pressure, prepare to open the mold valve. Quickly open the mold valve and wait for one minute. Remove the mold from the furnace and place it on a cooling surface here, a copper block.For the next five minutes, monitor the pressure on the Argonne regulator and adjust Argonne to maintain infiltration pressure. When the mold is cool enough, take appropriate steps to detach it from the valve system. When this is done, transport the mold to a workbench where the sample can be extracted.At a workbench equipped with a vice, secure the base of the mold in the vice grip and unscrew the hardware holding the lid to the top of the cylinder. To remove the top with the top removed, use a mallet to lightly tap the mold cylinder perpendicular to the vice grip in order to loosen the mold cylinder from the base groove. Next, release the vice grip to remove the mold base.Once removed, put the mold base aside and prepare to place the mold cylinder in the vice. Secure the mold cylinder in the vice grip so that the remaining aluminum at the top of the sample is accessible with the mallet. Tap the remaining aluminum at the top of the sample to push it out of the mold cylinder.The recovered material will have a foam sample, will surplus aluminum samples of a desired height can be cut using a band saw. After samples of a desired height to cut, the sodium chloride must be removed from the preform. To do this, have a beaker filled with sufficient water to cover the foam and a magnetic stir bar on a stirring hot plate.Start the stirring and add the foam. Set the temperature to 60 degrees Celsius and be prepared to change the water every 10 minutes until there is no sodium chloride left in the foam. The protocol was followed three times for different size sodium chloride grains.The foam pore sizes range from one millimeter to about 1.2 millimeters, 1.4 millimeters to 1.7 millimeters, and two millimeters to about 2.4 millimeters. The average porosity of the samples is 70%Each sample is made with 99.95%aluminum and measures 51 millimeters in diameter and about 25 millimeters in height Once mastered, this technique can be done in two hours if it is performed properly.

casting-protocols-for-production-open-cell-aluminum-foams-replication

Research

JoVE Journal

Engineering

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Microfabrication of Chip-sized Scaffolds for Three-dimensional Cell cultivation

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Extracellular Matrix-derived Foam Fabrication via Lyophilization: A Procedure to Generate Biological Scaffolds from ECM of Decellularized Tissues

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A Facile and Eco-friendly Route to Fabricate Poly(Lactic Acid) Scaffolds with Graded Pore Size

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Fabrication of Extracellular Matrix-derived Foams and Microcarriers as Tissue-specific Cell Culture and Delivery Platforms

This study presents a methodology to prepare 3D, biodegradable, foam-like cell scaffolds based on biocompatible side-chain liquid crystal elastomers (LCEs). Confocal microscopy experiments show that foam-like LCEs allow for cell attachment, proliferation, and the spontaneous alignment of C2C12s myoblasts.

Synthesis of Biocompatible Liquid Crystal Elastomer Foams as Cell Scaffolds for 3D Spatial Cell Cultures

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Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

This paper describes a protocol along with a comparative study of two microfluidic fabrication techniques, namely photolithography/wet-etching/thermal-bonding and Selective Laser-induced Etching (SLE), that are suitable for high-pressure conditions. These techniques constitute enabling platforms for direct observation of fluid flow in surrogate permeable media and fractured systems under reservoir conditions.

Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs

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Fabricating Highly Open Porous Microspheres (HOPMs) via Microfluidic Technology

Minimizing the variability in the particle fraction within granular scaffolds facilitates reproducible experimentation. This work describes methods for generating granular scaffolds with controlled particle fractions for in vitro tissue engineering applications.

Controlling Particle Fraction in Microporous Annealed Particle Scaffolds for 3D Cell Culture

This protocol presents an improved demolding procedure for the Polydimethylsiloxane (PDMS)  double casting technique by introducing silicone oil as a non-adhesive barrier between PDMS layers. Unlike plasma or chemical surface modification methods, this approach requires no specialized or costly equipment, making it a more accessible and cost-effective alternative.

Improved Polydimethylsiloxane (PDMS) Double Casting via Silicone Oil Treatment for Densely Packed Microstructure Replication

This study describes a supercritical carbon dioxide foaming method for the preparation of carbon fiber and bamboo fiber reinforced poly (butylene adipate-co-terephthalate) foams.

Preparation of Carbon Fiber and Bamboo Fiber Reinforced Poly (butylene Adipate-co-terephthalate) Foams by Supercritical Carbon Dioxide Foaming

Learn the infiltration method to produce open-celled aluminum foam using sodium chloride preforms and argon gas pressure. This protocol enables precise control of porosity for materials science applications.

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

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