A metallic microlattice is a synthetic porous metallic material consisting of an ultra-light

metal foam Regular foamed aluminium In materials science, a metal foam is a material or structure consisting of a solid metal (frequently aluminium) with gas-filled pores comprising a large portion of the volume. The pores can be sealed (closed-cell foam) ...

. With a

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

as low as 0.99 mg/cm³ (0.00561 lb/ft³), it is one of the lightest structural materials known to science. It was developed by a team of scientists from

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

-based HRL Laboratories, in collaboration with researchers at

University of California, Irvine The University of California, Irvine (UCI or UC Irvine) is a Public university, public Land-grant university, land-grant research university in Irvine, California, United States. One of the ten campuses of the University of California system, U ...

and

Caltech The California Institute of Technology (branded as Caltech) is a private university, private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small g ...

, and was first announced in November 2011. The prototype samples were made from a

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

alloy. In 2012, the microlattice prototype was declared one of 10 World-Changing Innovations by ''

Popular Mechanics ''Popular Mechanics'' (often abbreviated as ''PM'' or ''PopMech'') is a magazine of popular science and technology, featuring automotive, home, outdoor, electronics, science, do it yourself, and technology topics. Military topics, aviation an ...

''. Metallic microlattice technology has numerous potential applications in automotive and

aeronautical engineering Aerospace engineering is the primary field of engineering concerned with the development of aircraft and spacecraft. It has two major and overlapping branches: aeronautical engineering and astronautical engineering. Avionics engineering is s ...

. A detailed comparative review study among other types of metallic lattice structures showed them to be beneficial for light-weighting purposes but expensive to manufacture.

Synthesis

To produce their metallic microlattice, the HRL/UCI/Caltech team first prepared a

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

template using a technique based on self-propagating

waveguide A waveguide is a structure that guides waves by restricting the transmission of energy to one direction. Common types of waveguides include acoustic waveguides which direct sound, optical waveguides which direct light, and radio-frequency w ...

formation, though it was noted that other methods can be used to fabricate the template. The process passed UV light through a perforated mask into a reservoir of UV-curable

resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...

Fiber-optic An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...

-like "self-trapping" of the light occurred as the resin cured under each hole in the mask, forming a thin polymer fiber along the path of the light. By using multiple light beams, multiple fibers could then interconnect to form a lattice. The process was similar to

photolithography Photolithography (also known as optical lithography) is a process used in the manufacturing of integrated circuits. It involves using light to transfer a pattern onto a substrate, typically a silicon wafer. The process begins with a photosensiti ...

in that it used a two-dimensional mask to define the starting template structure, but differed in the rate of formation: where stereolithography might take hours to make a full structure, the self-forming waveguide process allowed templates to be formed in 10–100 seconds. In this way, the process enables large free-standing 3D lattice materials to be formed quickly and scalably. The template was then coated with a thin layer of metal by

electroless nickel plating Electroless Deposition, Electroless nickel-phosphorus plating, also referred to as ''E-nickel'', is a chemical engineering, chemical process that deposits an even layer of nickel-phosphorus alloy on the surface of a solid substrate, like metal o ...

, and the template is etched away, leaving a free-standing, periodic porous metallic structure. Nickel was used as the microlattice metal in the original report. Owing to the electrodeposition process, 7% of the material consisted of dissolved phosphorus atoms, and it contained no precipitates.

Properties

A metallic microlattice is composed of a network of interconnecting hollow struts. In the least-dense microlattice sample reported, each strut is about 100

micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

s in diameter, with a wall 100

nanometre 330px, Different lengths as in respect to the Molecule">molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling), is a unit of length ...

s thick. The completed structure is about 99.99% air by volume, and by convention, the mass of air is excluded when the microlattice density is calculated. Allowing for the mass of the interstitial air, the true density of the structure is approximately 2.1 mg/cm³ (2.1 kg/m³), which is only about 1.76 times the density of air itself at 25 °C. The material is described as being 100 times lighter than Styrofoam. Microlattices can also be 100 times stronger than regular polymers. Metallic microlattices are characterized by very low densities, with the 2011 record of 0.9 mg/cm³ being among the lowest values of any known solid. The previous record of 1.0 mg/cm³ was held by

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

aerogel Aerogels are a class of manufacturing, synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid wit ...

s, and aerographite is claimed to have a density of 0.2 mg/cm³. Mechanically, these microlattices are behaviorally similar to

elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus (E) and high failure strain compared with other materials. The term, a portmanteau of ''ela ...

s and almost completely recover their shape after significant compression. This gives them a significant advantage over earlier aerogels, which are brittle, glass-like substances. This elastomeric property in metallic microlattices furthermore results in efficient shock absorption. Their

Young's modulus Young's modulus (or the Young modulus) is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Youn ...

E exhibits different scaling, with the density ρ, E ~ ρ², compared to E ~ ρ³ in

s and

carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range ( nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized: * ''Single-walled carbon nanotubes'' (''S ...

foams.

Applications

Metallic microlattice may find potential applications in thermal and vibration insulators such as shock absorbers, and may also prove useful as battery electrodes and catalyst supports. Additionally, the microlattices' ability to return to their original state after being compressed may make them suitable for use in spring-like energy storage devices. Automotive and aeronautical manufacturers are using microlattice technology to develop extremely lightweight and efficient structures that combine multiple functions, such as structural reinforcement and heat transfer, into single components for high-performance vehicles.

Similar materials

A similar but denser material, consisting of an electrodeposited nanocrystalline nickel layer over a polymeric rapid-prototyped truss, was created by researchers at the

University of Toronto The University of Toronto (UToronto or U of T) is a public university, public research university whose main campus is located on the grounds that surround Queen's Park (Toronto), Queen's Park in Toronto, Ontario, Canada. It was founded by ...

in 2008. In 2012, German researchers created a

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

foam known as aerographite, with an even lower density than a metallic microlattice. In 2013, Chinese scientists developed a carbon-based

which was claimed to be lighter still. Nanolattices like tube-based nanostructures are similar structures on a smaller scale.

References

{{reflist, 30em, refs= "New carbon nanotube struructure aerographite is lightest material champ"
Phys.org. 13 July 2012. Retrieved 14 July 2012. {{cite journal, doi=10.1002/adma.200700797, title=Micro-scale Truss Structures formed from Self-Propagating Photopolymer Waveguides, year=2007, last1=Jacobsen, first1=A.J., last2=Barvosa-Carter, first2=W.B., last3=Nutt, first3=S., journal=Advanced Materials, volume=19, issue=22, pages=3892–3896, bibcode=2007AdM....19.3892J , s2cid=137188553 {{cite journal, doi=10.1126/science.1211649, title=Ultralight Metallic Microlattices, date=12 October 2011, last1=Schaedler, first1=T. A., last2=Jacobsen, first2=A. J., last3=Torrents, first3=A., last4=Sorensen, first4=A. E., last5=Lian, first5=J., last6=Greer, first6=J. R., last7=Valdevit, first7=L., last8=Carter, first8=W. B., journal=Science, volume=334, issue=6058, pages=962–5, bibcode = 2011Sci...334..962S, pmid=22096194, s2cid=23893516 {{cite patent, country=US, number=7382959, status= patent, title=Optically oriented three-dimensional polymer microstructures, fdate=13 October 2006, pridate=3 June 2008, invent1= Alan J. Jacobsen, assign1= HRL Laboratories, LLC., accessdate= {{cite journal, doi=10.1016/j.actamat.2008.10.038, title=Micro-truss nanocrystalline Ni hybrids, year=2009, last1=Gordon, first1=L.M., last2=Bouwhuis, first2=B.A., last3=Suralvo, first3=M., last4=McCrea, first4=J.L., last5=Palumbo, first5=G., last6=Hibbard, first6=G.D., journal=Acta Materialia, volume=57, issue=3, pages=932–939, bibcode=2009AcMat..57..932G {{cite journal, doi=10.1016/j.matdes.2016.01.146, title=Metallic microlattice materials: A current state of the art on manufacturing, mechanical properties and applications, year=2016, last1=Rashed, first1=M.G., last2=Ashraf, first2=Mahmud, last3=Mines, first3=R.A.W., last4=Hazell, first4=Paul J., journal=Materials & Design, volume=95, pages=518–533

External links

Video of metallic microlattice undergoing compression
via YouTube. American inventions Foams 2011 in science