News | Mar 2, 2018
10 advanced materials from defense engineers that deliver big results
Does your company need innovative ideas to improve products? Here are 10 advanced materials technologies invented in defense laboratories available now to industry for product development.
Silicon carbide coatings
Due to its covalent bonding, SiC is very difficult to densify without the use of additives that compromise its material properties. However, in many cases, a monolithic material is not needed. SiC can be deposited as a coating by techniques such as chemical vapor deposition (CVD), plasma-enhanced CVD, and direct chemical reaction between carbon and molten silicon. SiC coatings are used to protect a weaker or less resistant material by isolating it from the environment. This protection can be mechanical protection against abrasion or chemical protection in corrosive or reactive environments. Examples of mechanical protection are wear-resistant coatings on bearings and wear plates. Examples of chemical protection are coated filters for molten metals and coatings for the chemical industry. An example of combined mechanical and chemical protection is SiC coatings used in gas turbine engines.
Using CVD with SiC requires specialized equipment that can sustain temperatures of 2000°C at a pressure of 0.5 Torr+/−0.001 for up to 10 days. The growth process is slow and expensive. The gases used, methylsilane and trimethylsilane, are extremely flammable and considered hazardous.
Navy researchers have overcome these problems with a method of forming β-SiC material or coating by mixing SiO2 with carbon and heating the mixture in a vacuum. At that point, the carbon is oxidized to CO gas and reduces the SiO2 to SiO gas. The reaction occurs at a temperature range of 1300 to 1600°C. This process results in a SiC material or a SiC coating on a substrate. Link
Light-activated polymers with shape memory
Air Force researchers have identified glassy azobenzene as one such SMP (shape-memory polymer) material that can bend bi-directionally when exposed to the blue-green light of 440–514 nm. It retains the photo-deformed state upon removal of light for a significant period of time. It can then be returned to its original state by specific light activation. SMP have already found commercial utility in building materials and ophthalmic devices. They will further intrude into areas like photo-responsive switches; additional medical devices such as stents, shunts, and sutures; and self-repairing vehicle structures, to name only a few potential applications. Link
Non-toxic, high-temperature polymer
Air Force scientists have developed a new polyimide resin consisting essentially of BTDA, BPDA, 6FDA, 4-PEPA, and an aromatic diamine which overcomes the toxicity issues above and achieves a glass transition temperature of 370 degrees C.
The polyimide system may be used in the fabrication of high-temperature composite components for airframe, turbine engine, missile, rocket, and rocket motor applications. The technology is most useful for components that can be manufactured using a prepreg approach to composite fabrication with autoclave or press-molding and thick composite parts can be fabricated at relatively low pressures. The polyimide system is also suitable for numerous automotive and industrial applications that employ prepreg processes. Link
Electron conducting polymers
The Navy has invented easy-to-synthesize polymers from inexpensive starting materials, requiring only one step plus purification. Highly variable redox states and good electron-transporting properties. Oligo(AP-CN) was able to produce anodic photocurrent of magnitudes as high as 103 times that of a gold-coated electrode alone, and 43.2 times that of a fullerene-coated gold electrode. The materials are stable in their n-doped state. Link
Army researchers have developed a novel polymer supercapacitor with a simple and efficient production method. Carbon nanotube sheets are dipped in a small particle metal oxide solution and then dipped again in a polymer hydrogel electrolyte solution. Annealing may then be done if needed.
In this design, the electrolyte is bound within the polymer matrix and given this integration, mechanical distortion of the polymer does not cause loss of the electrolyte. Thus, they can be rolled, folded or otherwise shaped to fit the desired packaging. The sheet of encased carbon nanotubes that form the electrical double layer permits substantial charge storage in thin, lightweight matrices. The addition of metal oxide particles creates additional charge storage capacity. Link
Simplified boron phosphide synthesis
Army researchers have developed a high-yield process to synthesize BP where boron phosphate and magnesium metal are combined into a homogenous mixture without the need for temperature-controlling diluents, loosely packing the mixture at a pressure of 0 to 20,000 psi, and igniting the mixture using minimum energy input to create a self-propagating high-temperature synthesis reaction that produces BP. It’s cheaper, safer, and more environmentally friendly than current synthesis methods. Link
Lead azide (LA) and lead styphnate (LS) compounds are toxic and LA reacts with copper, zinc or alloys containing such metals, forming other azides that can be highly sensitive and dangerous to handle. Lead materials are cataloged on the EPA Toxic Chemical List and are additionally regulated under the Clean Air Act and the Clean Water Act. Recently, the EPA revised the National Ambient Air Quality Standard (NAAQS) to 0.15 μg/m3, which is 10 times more stringent than the previous standard. Regardless, recent studies have shown that there are no safe exposure levels for lead, in particular for children. Their use during military training and testing deposits heavy metals on munition ranges and can impact the sustainable use of these ranges. Manufacturing of any lead-based primary explosives, such as LA or lead styphnate, results in the production of significant quantities of highly toxic hazardous waste.
To address these serious issues, Army researchers have developed detonators with non-toxic energetics that achieve or exceed the performance of currently used lead-based products. The old detonators containing LA and LS are replaced with milled DBX-1 (copper(I) 5-nitrotetrazolate) as the spot charge and unmilled DBX-1 as an intermediate charge without losing any of the functionality associated with the current lead-based detonators. These lead-free detonators exceed the rigorous performance standards previously mentioned. A comparison of these materials is charted below. Link
Enhanced photomechanical polymers
A number of reports have distinguished the photo-responses of liquid crystalline polymer networks (LCN) for comparatively large magnitude responses typified by bending of cantilevers or dramatic contractions of thin films. Notably, a majority of these efforts have characterized the response of azobenzene-based LCN to exposure to UV light. But, UV-induced responses in azobenzene LCNs are limited in the need for multiple light sources to reverse the response.
Air Force researchers have developed new photochromic bis(azobenzene)-diamino monomers, for use in the preparation of new linear and crosslinked polyimides, polyamides, or poly(amide-imide)s having photomechanical properties. Representative polyimides and copolyimides, derived from the photochromic bis(azobenzene)-diamino monomers are heat resistant and possess excellent photomechanical properties. As evidence of the photomechanical properties, cantilevers of the linear polyimides show large-amplitude, photo-directed, bidirectional bending. The high-modulus and glassy nature of these materials distinguish them for highly efficient and useful light-to-work transduction. Link
Nanoparticle polymer additives
Air Force researchers have created a series of novel aromatic POSS dianiline molecules for use in the preparation of high-temperature aromatic polyimides. A general synthetic strategy was devised to improve the structure, yield, and utility of POSS dianilines over those currently available. Incorporation of these POSS mono- and dianilines into polymer hosts occurs through chemical reaction of amine moieties of the POSS compound with a variety of functionalities, including epoxies, anhydrides, and cyanate esters. The amine groups may also be further reacted with a phenylethynyl phthalic anhydride (“PEPA”) to yield POSS monomers useful as drop-in additives for high-temperature thermosets, also possessing PEPA in their chemical structures. Resulting POSS-containing polymers generally exhibit improved processing and delivered properties. Starting materials are commercially available. Synthesis is amenable to scale-up and yield is superior to current strategies. Link
Rubidium uranium fluorophosphate crystals for detecting and storing nuclear material
Air Force researchers have developed a novel process to synthesize rubidium uranium fluorophosphate crystals by combining a uranium-based feedstock with a mineralizer solution. The mineralizer solution includes an alkali nutrient, a phosphate, and a fluoride. The process takes place under pressure of approximately 25,000 psi and between 400 and 700°C. By incorporating these radioisotopes directly into the crystal structure, it is believed that resultant materials may be radiation-damage resistant, to better contain radioactive wastes without the threat of leaking or degradation over time. With a large amount of nuclear waste produced each year by medical, industrial, and military processes, these materials would fill a large void in current radioactive waste storage and disposal technology. Link
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