Materials & Chemicals : Metals


Improved Manufacture of Porous Materials for Catalysis and More

A UW–Madison researcher has developed a new method for manufacturing porous metal-oxygen based materials. The method achieves structures with controlled porosity and shape based on air oxidation.

In brief, the materials are produced from metal alloys via an oxidative dealloying process that selectively removes one or more elements from the alloy and converts remaining elements into a stable metal-oxygen matrix having a controlled porosity. Once fabricated, the porous matrices are post-treated to render them suitable for various downstream applications.

Novel 3-D Powder Refractory Materials for Investment Casting

Research emanating from the University of Wisconsin-Whitewater with collaborators at Florida State University has resulted in patented refractory mold recipes and associated methods for the investment casting and rapid prototyping industries. These novel materials and methods of manufacture are a seamless fit for current 3-D powder printers in the marketplace. This technology is capable of producing shell materials that can withstand temperatures up to 3,000°F and can be more easily removed from finished castings than products currently on the market. ‘Pattern to pour’ time and shell weight/thickness is also significantly decreased. In addition, this technology entirely eliminates the need for a sacrificial pattern for each refractory shell and further reduces the time and cost of manufacturing by way of directly printing the 3-D refractory shell from a powder printer dispensing the proprietary recipe.

Modular Investment Casting Mold Assembly

Traditional ceramic investment casting requires that patterns duplicating the desired finished product are attached directly to a wax or plastic sprue. Multiple patterns may be attached to a sprue creating an inverted tree-like structure. The pattern-sprue assembly is then encased in a ceramic mold material or refractory. The refractory containing the wax pattern-sprue assembly is then heated to melt and burn off the wax pattern and sprue in order to create a cavity in which molten metal can be poured. Volatilized hydrocarbon wax released during burnout is a major cause of pollution from investment casting foundries and wax is a major expense for foundries. There is an opportunity to markedly reduce wax usage, reduce pollution from the casting process and centralize sprue creation by making a prefabricated, modular, ceramic sprue. The wax pattern material is melted/burned off from the individual shells before they are attached to the prefabricated sprue. If a pattern breaks before it is cast, this technology allows for the broken pattern to be replaced without needing to recreate the entire sprue assembly.This reduces the amount of pattern material needed to create an end product. It also permits the use of less expensive and less precise refractory material for the prefabricated sprue than is used to coat the patterns. The technology will allow foundries to reduce infrastructure associated with traditional sprue creation and will allow for centralized production of modular sprues to decrease duplicative work within each foundry.

Improved Immiscible Alloy Formation with Stabilizing Nanoparticles

UW–Madison researchers have developed a method for controlling the size of minority phase droplets during alloy formation. The approach utilizes nanoparticles to rapidly restrict the growth of the droplets after they nucleate and to inhibit coagulation when they collide, allowing for a more uniform mixture.

The nanoparticles are made of a thermally stable ceramic or other material, and are added to the hot liquid alloy solution. Only then is the melt allowed to cool, with the nanoparticles spontaneously assembling between the growing droplets and the rest of the material. In this way, the nanoparticles act as a thin coating around the droplets to prevent them from growing, coalescing and sinking.

Improved Method for Incorporating and Uniformly Dispersing Nanoparticles into Metal-Based Materials

UW–Madison researchers have developed a method to incorporate and uniformly disperse nanoparticles into a metal matrix through a combination of liquid state processing and solid state stirring. The method comprises introducing nanomaterials into a metal-based material in a liquid state, cooling the materials to a viscous state and stirring the materials to disperse the nanomaterials therein. The metal-based material may be used to maintain dispersion as the metal cools. Ultrasonic or mechanical stirring is used to initially disperse the nanomaterials within the molten metal, with subsequent stirring in the partially solidified state to break up clusters or other agglomerations of the nanomaterials.

Production of Nanoparticle Reinforced Metal-Matrix Nanocomposites from Master Nanocomposites

UW–Madison researchers have developed a method of producing a metal-matrix nanocomposite using a master material containing a higher percentage of wetted nanoparticles than the molten metal to which the master material is introduced. The master metal-matrix nanocomposite is introduced into a molten metal at a temperature above the melting temperature of the master metal-matrix nanocomposite. The master metal-matrix nanocomposite contains a first matrix metal and selected nanoparticles dispersed in the matrix metal. The first matrix metal may be an alloy containing a primary metal element and a wettability enhancing metal element. A portion of the master metal-matrix nancomposite is introduced by immersion as a solid or semisolid, or by addition as a liquid, and the master material melts into the molten metal. Then, the mixed molten metal solidifies to provide a second metal-matrix nancomposite containing a second matrix metal and at least a portion of the nanoparticles dispersed in the second matrix metal.

The use of a master nanocomposite allows the initial volume of metal processed with the nanoparticles to be reduced to a process in which the nanoparticles are added at their intended final concentration to a melt that will be added into the final nanocomposite. This enables the sale of solid master nanocomposites to foundries where they can be used easily to cast nanocomposites with desired nanoparticle concentrations without specialized training or expertise in nanoparticle handling and processing.

Oxidation-Resistant Coatings for Ultra-High Temperature Ceramic-Based Materials

UW–Madison researchers have developed alumina coatings that form protective, oxidation-resistant scales on ceramic substrates at high temperatures. The method for coating the ceramic-based substrates involves a two-stage deposition process. This process comprises depositing a layer of molybdenum metal onto a surface of the substrate and subsequently co-depositing silicon and boron onto the layer of molybdenum in the presence of alumina to form a continuous MoSiB coating. Ceramic-based substrates that can be coated in accordance with this method include ultra-high temperature ceramics, fiber-reinforced matrix composites and refractory metal cermets.

Coating Extends Life of Catalytic System

UW–Madison researchers have developed a coating that helps catalyst support structures withstand harsh reaction conditions.

The coating is made of a chemically robust material such as niobium oxide that can be applied in extremely thin layers using a technique called ALD (atomic layer deposition). The coating may be selected purely for its structure-enhancing properties, or may comprise materials that are themselves catalytically active.

Friction-Stir Welding of Dissimilar Metals with High Weld Strength

UW-Madison researchers have developed a method to join dissimilar metals using friction-stir welding through a process that combines the strength of butt welding and the manufacturing characteristics of lap welding. One application of the method is a modification to conventional lap welding in which a small extra piece of metal is added such that three, instead of two, metal pieces are welded together. A second application is to use friction-stir spot welding to join dissimilar metals by welding a piece of metal such as aluminum with predrilled holes onto a second metal piece such as magnesium. A disc of the second metal (i.e. magnesium) is added into each predrilled hole, increasing the weld strength when the first piece of metal is friction-stir spot welded to the second piece. Both applications of friction-stir welding to join dissimilar metals improve weld strength and manufacturing characteristics over traditional friction-stir welding methods.

Nanoporous Protective Coatings for Corrosion and Wear Resistance of Metal Substrates

UW-Madison researchers have developed a method to manufacture highly corrosion- and wear-resistant metal substrates with a nanoporous oxidized surface layer. These coated substrates can be used in applications where the surface of the substrate is exposed to corrosive media.

For example, the method could be used to produce an improved stainless steel heat exchanger.   An oxidized layer is added to the surface of the stainless steel plates.  Then a nanoporous thin film comprised of titanium dioxide, silicon dioxide, zirconium dioxide and/or alumina is adhered to the oxidized layer.  The thin film has a uniform thickness less than one micrometer with porosity in the range of 26 to 80 percent.  This coating provides improved resistance to corrosion.

Low-Temperature, Corrosion-Resistant Integrated Metal Coatings to Improve Efficiency of Coal Plants

UW-Madison researchers have developed an improved method for the low-temperature synthesis of integrated, corrosion-resistant coatings for metal substrates. The low-temperature process avoids the degradation of substrate mechanical properties that occurs in traditional pack cementation processes. The new method also improves upon previous technologies by widening the scope of its application. For example, synthesis of aluminide coatings on steel alloys via low-temperature pack cementation can enhance oxidation resistance in conditions of extreme temperature and moisture, as in high-temperature operation of steam power generation plants. 

In general, the integrated coating consists of the substrate metal, a diffusion-barrier that hinders diffusion of the coating components into the substrate, a corrosion-resistant layer and an oxidation barrier. Deposition of the integrated structure can be achieved via pack cementation at a temperature lower than 700°C, or by thermal spray, vapor deposition or electrodeposition methods.

The substrate, diffusion layer and corrosion-resistant layer can consist of metals, intermetallic compounds or metalloid alloys, depending on the specific application of the integrated structure. For example, a chromium/molybdenum/steel alloy substrate could be coated with an aluminum/iron/intermetallic diffusion-barrier and an aluminum/iron corrosion-resistant layer for use in coal-fired power plants, in which the integrated coating is in contact with supercritical steam. With these techniques, coal-fired power plants can operate at higher temperatures to exploit supercritical steam properties, improving efficiency and reducing overall emissions.

Corrosion- and Wear-Resistant Coating for Vessels, Equipment and More

UW–Madison researchers and others have developed a new composite coating made of amorphous metal and ceramic particles. The coating can be applied to seagoing vessels, containers and any other surface to prevent corrosion.

Suitable metals for amorphous alloys may be iron-based and include other elements (yttrium, chromium, molybdenum, tungsten, boron or carbon). The ceramic particles are produced by a partial nanocrystallization reaction. They range in size from nanometers to microns, and are used to improve hardness and wear resistance while maintaining corrosion resistance.

The coating can be applied to surfaces by cold spray, thermal spray, physical vapor or other deposition technique.

Semi-Solid Forming of Metal-Matrix Nanocomposites

UW-Madison researchers have developed a method of incorporating nanoparticles into a semi-solid casting process, so the resulting metal-matrix nanocomposite has the appropriate globular microstructure and improved mechanical properties. The metal-matrix nanocomposite is formed by heating a metal until it reaches a liquid state and then adding nanoparticles to the liquid metal. To uniformly distribute the nanoparticles throughout the metal, the metal/nanoparticle mixture is agitated by inserting a probe that vibrates at ultrasonic frequencies into the mixture. The mixture can then be cooled, and the vibrating probe removed. When the mixture reaches a semi-solid state, it can be injected into a mold cavity for SSC.

Arc-Enhanced Friction Stir Welding

A UW-Madison materials expert has now shown that pre-heating and softening a workpiece with an arc prior to welding can significantly reduce tool wear during friction stir welding of hard materials such as steels, titanium alloys and metal-matrix composites. Arc pre-heating prior to FSW can also join materials with very different physical properties, such as aluminum and copper, or aluminum and steel, something that is difficult to do with conventional FSW.

Oxidation Resistant Coatings for Ultra-High Temperature Transition Metals and Metal Alloys

UW-Madison researchers have developed a multilayered coating for the surface of Mo-Si-B alloys, which includes a diffusion barrier layer, an oxidation resistant layer and an oxidation barrier layer. The coatings form a stable gradient of integrated layers that prevents cracking, peeling and delamination of Mo-Si-B alloys under extreme operating conditions.

Method and Additive for Improving the Properties of Thin-Wall Castings

UW-Madison researchers have developed an additive that increases the toughness of thin-wall CGI and DI castings. The additive includes a non-ferrous metal oxide that has less affinity for oxygen than iron, and a metal sulfide that has less affinity for sulfur than magnesium. Because the metals contained in the oxides and sulfides are not alkali, alkali earth or rare earth metals, the incidence of defects in the castings is also reduced.

When added to a cast iron melt, the metal oxide and metal sulfide react with magnesium to form nucleation sites composed of a core of magnesium oxide surrounded by magnesium sulfide. These nucleation sites cause increased nucleation of graphite so that the cross-section of the thin-wall iron casting is more uniform. This, in turn, decreases the amount of carbide formed in the casting, and increases the casting’s toughness.

Method for Disinfecting Liquids in a Dense Fluid Plasma Reactor

UW–Madison researchers have developed an efficient new method for disinfecting liquids, especially water, by using a dense medium plasma (DMP). Water is placed inside a DMP reaction vessel and vigorously stirred between two electrodes. Multiple spark discharges between the electrodes then produce reactive plasma species, including electrons, ions and free radicals, which inactivate any bacteria, fungi or other microbes present in the water. In a second sterilization method, which can be applied alone or in conjunction with the first, the plasma reactor is used to generate antimicrobial colloidal nanoparticles, especially silver nanoparticles, which interact with microbial cells and deactivate them.

Electro-Optic Optical Elements

UW-Madison researchers have developed electro-optic elements formed in metal oxide films, particularly lithium niobate, for use in electro-optic devices. These elements are fabricated through a process in which lithium niobate is deposited as an amorphous thin-film onto a lithium niobate substrate, patterned and etched by conventional techniques, and then annealed to a crystalline state suitable for electro-optic applications (see WARF reference number P01007US). Because amorphous lithium niobate is easily etched and otherwise manipulated, trenches and other features in the electro-optic elements can be easily designed to improve device performance. In particular, this invention includes traveling wave modulators whose topographical features can be selected to achieve higher bit rate functioning than conventional devices.

Thin-Film Lithium Niobate and a Method of Producing It

UW-Madison researchers have developed a method of growing thin, ferroelectric films of lithium niobate, which are easily etched by chemical, kinetic or optical processes. First, a uniform, amorphous, thin film of lithium niobate is grown on a substrate. Unlike the material in its crystalline state, amorphous lithium niobate is easily patterned by conventional photolithography and etched by wet or dry etchants. After etching, the remaining film can be annealed to its crystalline form, providing a material suitable for optical and electronic applications.

Method and Apparatus for Producing Colloidal Nanoparticles in a Dense Medium Plasma

UW-Madison researchers have developed a method for producing a colloidal dispersion of nanoparticles of at least one conductive material in a dense fluid medium. The dense fluid medium is a liquid at the operating conditions of a plasma reactor. Specifically, the nanoparticles of the conductive materials can be produced by generating a plasma reaction between two electrodes made of the desired conductive material, which are immersed within the dense fluid medium. Preferred materials for the electrodes include carbon, copper, silver, gold and platinum. The electrodes may also be made of different materials to produce colloidal suspensions with more than one conducting material.