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

metal foam Regular foamed aluminium A metal foam is a cellular 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) or interconnected (open-c ...

. With a

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

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 state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

-based HRL Laboratories, in collaboration with researchers at

University of California, Irvine The University of California, Irvine (UCI or UC Irvine) is a public land-grant research university in Irvine, California. One of the ten campuses of the University of California system, UCI offers 87 undergraduate degrees and 129 graduate and p ...

and

Caltech The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

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

nickel Nickel is a chemical element with 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 slow ...

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

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

Popular Mechanics ''Popular Mechanics'' (sometimes 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 and transportation o ...

''. 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 sim ...

. 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 (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

template using a technique based on self-propagating

waveguide A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...

formation, though it was noted that other methods can be used to fabricate the template. The process passed

UV light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

through a perforated mask into a reservoir of UV-curable

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on n ...

Fiber-optic An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means t ...

-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 in that it used a two-dimensional mask to define the starting template structure, but differed in the rate of formation: where

stereolithography Stereolithography (SLA or SL; also known as vat photopolymerisation, optical fabrication, photo-solidification, or resin printing) is a form of 3D printing technology used for creating models, prototypes, patterns, and production parts in a lay ...

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 nickel-phosphorus plating is a chemical process that deposits an even layer of nickel-phosphorus alloy on the surface of a solid substrate, like metal or plastic. The process involves dipping the substrate in a water solution containi ...

, 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 In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...

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 ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

s in diameter, with a wall 100 nanometres 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 Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam (XPS), commonly called "Blue Board", manufactured as foam continuous building insulation board used in walls, roofs, and foundations as thermal insulation and water barrie ...

. 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 , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

aerogels, and aerographite is claimed to have a density of 0.2 mg/cm³. Mechanically, these microlattices are behaviorally similar to elastomers 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 E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied le ...

E exhibits different scaling, with the density ρ, E ~ ρ², compared to E ~ ρ³ in aerogels and carbon nanotube 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

nanocrystal A ''nanocrystal'' is a material particle having at least one dimension smaller than 100 nanometres, based on quantum dots (a nanoparticle) and composed of atoms in either a single- or poly-crystalline arrangement. The size of nanocrystals dist ...

line 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 in Toronto, Ontario, Canada, located on the grounds that surround Queen's Park (Toronto), Queen's Park. It was founded by royal charter in 1827 ...

in 2008. In 2012, German researchers created a

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...

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