NanoFoil
Encyclopedia
NanoFoil is the trademarked name for a reactive multi-layer foil material
Reactive material
In the US military, reactive materials are a new class of materials currently being investigated by the Office of Naval Research and others as a means to increase the lethality of direct-hit or fragmentation warheads...

, sometimes referred to as a pyrotechnic initiator
Pyrotechnic composition
A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...

 of two mutually reactive metals, aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 and nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

, sputtered to form thin layers to create a laminate
Laminate
A laminate is a material that can be constructed by uniting two or more layers of material together. The process of creating a laminate is lamination, which in common parlance refers to the placing of something between layers of plastic and gluing them with heat and/or pressure, usually with an...

d foil. On initiation by a heat pulse, delivered by a bridge wire, a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 pulse, an electric spark
Electric spark
An electric spark is a type of electrostatic discharge that occurs when an electric field creates an ionized electrically conductive channel in air producing a brief emission of light and sound. A spark is formed when the electric field strength exceeds the dielectric field strength of air...

, a flame
Flame
A flame is the visible , gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone...

, or by other means, the aluminium and nickel undergo self-sustaining exothermic reaction
Exothermic reaction
An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...

, producing an intermetallic compound nickel aluminide
Nickel aluminide
Nickel aluminide is an intermetallic material with properties similar to both a ceramic and a metal.There are three materials called nickel aluminide:* NiAl, CAS number 12003-78-0 * NiAl3, CAS number 12004-71-6* Ni3Al-Ni3Al:...

 (NiAl). The reaction occurs in solid and liquid phase only, without releasing any gas.

Such multilayer materials, whether nickel-aluminium, aluminium-titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

, or titanium-amorphous silicon
Amorphous silicon
Amorphous silicon is the non-crystalline allotropic form of silicon. It can be deposited in thin films at low temperatures onto a variety of substrates, offering some unique capabilities for a variety of electronics.-Description:...

, are used for joining materials by reactive bonding
Reactive bonding
Reactive bonding describes a wafer bonding procedure using highly reactive nanoscale multilayer systems as an intermediate layer between the bonding substrates. The multilayer system consists of two alternating different thin metallic films. The self-propagating exothermic reaction within the...

.

NanoFoil is a trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

 name of Reactive NanoTechnologies. The technology was developed in Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...

 from the technology used to fabricate multilayer optics for extreme ultraviolet
Extreme ultraviolet
Extreme Ultraviolet radiation is high-energy ultraviolet radiation, generally defined to be electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 120 nm down to 10 nm, and therefore having photons with energies from 10 eV up to 124 eV...

 and x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 ranges.

The foil is made in a range of thicknesses, e.g. 60, 80, 100, and 150 micrometers. The flame front propagation rate ranges generally between 7.5–9 m/s. The reaction temperature can reach up to 1500 °C for a millisecond. The energy released is approximately 1200 to 1300 joules per gram. The velocity and temperature of the reaction can be controlled by adjusting the thickness of the layers. Typical thickness is 50 nm per a bilayer. The thin layers maximize the contact between the metal and lower the activation energy
Activation energy
In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius that is defined as the energy that must be overcome in order for a chemical reaction to occur. Activation energy may also be defined as the minimum energy required to start a chemical reaction...

 for the reaction, normally too high to allow reaction between bulk aluminium and bulk nickel. The layers are deposited by sequential sputtering
Sputtering
Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...

 of alternately nickel and aluminium.

Nanofoil will ignite on heating to at least 250 °C in rate of at least 200 °C/min. Slower heating will anneal the material, causing loss of its pyrotechnic properties. For electrical initiation, a momentary contact at 10A/5V is sufficient; for ohmic contact, 120-150 amperes is needed for a 15 micrometer diameter contact, and 250-300 A for a 300 micrometer contact. It can be also ignited by a heat paper. When the flame front reaches the edge of the material, particles of molten metal can be ejected, causing voids in the bond; this can be prevented by simultaneous ignition from more sides, so the flame fronts meet in the middle, confined by the substrates.

Nanofoil can be both cut
Laser cutting
Laser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses and hobbyists. Laser cutting works by directing the output of a high-power laser, by computer, at the...

 and ignited by a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

. The pulse width and power determines if the material will be cut or initiated.

Nanofoil is frequently used for soldering
Soldering
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...

 and brazing
Brazing
Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...

, as a heat source. When sandwiched between the components to be joined, either with a foil of solder on each side, using solder precoated components, or using solder-coated NanoFoil, it uniformly delivers significant amount of heat energy across the entire area, melting the solder
Solder
Solder is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece.Soft solder is what is most often thought of when solder or soldering are mentioned and it typically has a melting range of . It is commonly used in electronics and...

 and only locally heating the surface of the substrates, lowering the heat load on the component in comparison with soldering/brazing in a furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...

. An externally applied even pressure during reaction and cooling serves to ensure a good homogeneous joint without voids. This process is known as NanoBond. Significantly dissimilar materials can be bonded without cracking: semiconductors, metals, ceramics, and polymers. The energy is deposited very locally, without significant heating of the bulk of the substrates, which reduces problems with mismatched thermal expansion coefficients between the materials and allows their joining at room temperature.

The NanoBond process can be used in assembly of electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

, die attachment
Die attachment
Die attachment is the step during the integrated circuit packaging phase of semiconductor device fabrication during which a die is mounted and fixed to the package or support structure....

 to heatsinks where high temperature stability is required (e.g. high-power LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

s or concentrated photovoltaics
Concentrated photovoltaics
Concentrated photovoltaic technology uses optics such as lenses to concentrate a large amount of sunlight onto a small area of solar photovoltaic materials to generate electricity...

 solar panels, soldering together layers of composite armor plates, bonding of large sputtering
Sputtering
Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...

 targets made of ceramics or refractory metals where normal indium
Indium
Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...

 based solders cannot be used, and other applications where a uniform joint over large area has to be created.

NanoFoil can be used as a pyrotechnic heat source
Pyrotechnic heat source
A pyrotechnic heat source, also called heat pellet, is a pyrotechnic device based on a pyrotechnic composition with a suitable igniter. Its role is to produce controlled amount of heat...

, a replacement of potassium chlorate
Potassium chlorate
Potassium chlorate is a compound containing potassium, chlorine and oxygen atoms, with the molecular formula KClO3. In its pure form, it is a white crystalline substance. It is the most common chlorate in industrial use...

/iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 pellets, for thermal batteries. It reacts faster than the conventional composition, reaches higher temperatures, and heat buffers of inert metal (e.g. steel) are needed to lower the peak temperature and prolong the heat delivery.

NanoFoil can be also used as an electrically initiated pyrotechnic initiator
Pyrotechnic initiator
A pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, e.g. thermites, gas generators, and solid-fuel rockets...

, e.g. to ignite solid propellants, and in decoy flares.

NanoFoil is not significantly sensitive to electrostatic discharge
Electrostatic discharge
Electrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...

.

NanoFoil-like composites can be employed in weapons as reactive material
Reactive material
In the US military, reactive materials are a new class of materials currently being investigated by the Office of Naval Research and others as a means to increase the lethality of direct-hit or fragmentation warheads...

s, enhancing the energy delivery to the targets by the projectiles or their fragments.

Other similar intermetallic compositions used in pyrotechnics are titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

-boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

 and aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

-palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

("Pyrofuze").
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