http://www.flyash.info/2011/047-Itskos-2011.pdf
We've documented a couple of times that Coal Ash can be beneficially utilized in the making of what are known as "Metal Matrix Composites"; that is, a metal object wherein the metal is "filled" or "loaded" with a non-metal material that serves to impart desired properties in the finished product.
A number of metals are posited to be suitable for the manufacture of such composites, although Aluminum is the one we've seen most often described, as in our recent report of:
West Virginia Coal Association | Coal Ash & Metal Composites Save Gas, Reduce CO2 | Research & Development; concerning: "Aluminum - Fly Ash Metal Matrix Composites as Advanced Automobile Material; 2001' Cosponsors: United States Department of Energy; Wisconsin Electric Power Company; Electric Power Research Institute; Report Summary: Metal matrix composites such as silicon carbide-aluminum, alumina-aluminum and graphite-aluminum represent a class of emerging materials with significant potential for commercial use in the auto and aerospace industries. In industrial foundry trials, a joint industry and Department of Energy project demonstrated a promising new process for producing a low cost aluminum metal matrix composite containing fly ash particles".
And, we note that we have cited the above 'Wisconsin Electric Power Company", aka "We Energies", many times, relative to the productive utilization of Coal-use residuals, as in our report of:
West Virginia Coal Association | Wisconsin Coal Ash Utilization Guidebook Available | Research & Development; concerning: "Coal Combustion Products Utilization Handbook (2nd Edition); By Bruce Ramme & Mathew Tharaniyil (We Energies); 2004; We hope that this book will serve as a ready reference tool for engineers, architects, construction managers and contractors in using We Energies coal combustion products (CCPs) in various construction applications. This handbook contains chapters dedicated to major product categories and their applications. The information in this handbook will help develop an understanding of the generation, properties, construction applications and performance of CCPs. It also contains sample specifications that can be used as references in developing project specifications that utilize CCPs. A list of references is provided at the end of this handbook for the reader who is looking for a deeper understanding of the material".
As was noted in our above-cited report concerning "Aluminum - Fly Ash Metal Matrix Composites", a brand, or trade, name has even been assigned to such concoctions: "Ashalloy"(R). And herein, we wanted to further document the development of such seemingly-desirable technologies.
Unfortunately, our intent and purpose has been foiled to a certain extent by the nature of the documentation that is available.
Much of the published technical information and narrative concerning "Aluminum - Fly Ash Metal Matrix Composites" and "Ashalloy"(R), even though the core technologies are at least a decade and a half old, are treated in the same way as proprietary works of creative literature, with built-in protections against reproduction and distribution of key, or at least interesting, documents.
So, herein, in an unsatisfactory way, we'll attempt to provide an anchor for our future discussions of metal and Coal Ash composites, through links to a few key documents and summaries of several key patents.
First, the initial link in this dispatch should take you to a report demonstrating that the development of such metal matrix composites isn't limited to just the innovative scientists in Wisconsin cited in our earlier reports; but, that those Wisconsin scientists have entrained some international interest.
As demonstrated by very limited excerpts from that link to:
"Pressure Infiltration Technique for the Synthesis of Aluminum/Fly Ash Composites
Grigorios Itskos, Pradeep Rohatgi, et. al.
University of Athens, Greece, and University of Wisconsin, Milwaukee
World Of Coal Ash (WOCA) Conference; May, 2011; Denver, CO
Abstract: In the present paper eight types of A356 Aluminum-Fly Ash composites were synthesized using pressure infiltration technique, by using Class C Fly Ash. ... It was concluded that using fine Fly Ash particles can strongly advantage the properties of composites".
------------------------
The full paper is accessible via the link, and explains the advantages in wear characteristics and strength obtained in various automobile parts molded out of Aluminum into which is blended varying quantities of Class C Fly Ash, a co-product of burning Lignite Coal. The presentation is complete with experimental results and illustrations of processes and procedures. The implication is, that, such and similar improvements had already been demonstrated by incorporating Class F Fly Ash, as is co-produced by the combustion of eastern US Bituminous Coal; and, such would seem to be borne out in our above-cited previous report of: "Aluminum - Fly Ash Metal Matrix Composites as Advanced Automobile Material; 2001:", by the USDOE, et. al., wherein it is clearly specified that: "aluminum-flyash composites (provide) a high value use of ASTM Class F type fly ash".
However, following are three United States Patents issued to the above-named co-author, Pradeep Rohatgi, of the University of Wisconsin, which will hopefully be of interest and use in explaining the "pressure infiltration technique", and the use of that technique in forming "Aluminum-Fly Ash composites".
We must note, however, that our presentation herein does an injustice to the work of Dr. Rohatgi, and colleagues. The full body of developed knowledge concerning "Mixed Metal Matrix Composites" that comprise, in part, Coal Ash, is much larger than even our reference selections herein might indicate; and, we will be returning to both earlier and later work on them, as performed by Rohatgi, and others, in the future.
That said, following is the first of three examples of technology illustrating how Coal Ash can be productively consumed and utilized in the manufacture of industrial metal materials, and metal articles that offer improved properties over the base metal of their composition, while at the same time offering economies in the cost of such manufacture and better performance in the final, end-use product:
"United States Patent: 5711362 - Method of Producing Metal Matrix Composites Containing Fly Ash
Method of producing metal matrix composites containing fly ash - Electric Power Research Institute
Date: January, 1998
Inventor: Pradeep K. Rohatgi, Milwaukee, WI
(CEAS Wisconsin Distinguished Professor Pradeep Rohatgi;
Pradeep Rohatgi - Wikipedia, the free encyclopedia; "Pradeep K. Rohatgi ... is a professor of materials engineering, and Director of the Center for Composites at the University of Wisconsin-Milwaukee. He is a pioneer in the field of composite materials, particularly metal matrix composites.)
Assignee: Electric Power Research Institute (EPRI), CA
(Since Dr. Rohatgi is on the faculty of the University of Wisconsin, and that is where the development work was done, we assume that EPRI funded the research.)
Abstract: A reinforcing phase comprising fly ash is combined with an aqueous medium comprising a binder to produce a slurry. The slurry is then dried to produce a preform of the reinforcing phase. Molten metal is then introduced into the preform, resulting in a metal matrix composites. The reinforcing phase of the subject composites may be present in excess of 50%.
(In other words, a component suitable for use in an application traditionally reserved for metals, can be made to consist of more than half Coal Fly Ash.)
Claims: A method for producing a metal matrix composite, comprising steps of: combining a reinforcing phase comprising a fly ash with an aqueous medium comprising a binder to produce a slurry; drying said slurry to produce a solid, porous preform; and introducing molten metal into said preform, whereby said metal matrix composite is produced.
The method ... wherein said method further comprises pouring said slurry into a mold (and) wherein said binder is an inorganic binder (or) an organic binder (and) wherein said metal is selected from the group consisting of aluminum, copper, zinc, magnesium, iron, lead, tin and alloys thereof.
(A number of metals can be used in this technique, although most of the related literature indicates that the bulk of actual development work has been done with Aluminum; and, to a lesser extent, Magnesium.)
The method ... wherein said step of introducing molten metal into the porous preform includes infiltration of the metal into the porous preform under pressure ... in the range 100-5000 psi.
The method ... wherein said fly ash is cenosphere fly ash (or) precipitator fly ash.
(Pretty much any Fly Ash will do, although "cenosphere"s offer some unique characteristics, as we've documented, for example, in:
West Virginia Coal Association | Wisconsin Recovers "Cenospheres" from Coal Fly Ash | Research & Development; concerning, primarily: "United States Patent 8,074,804 - Separation of Cenospheres from Fly Ash; 2011; Assignee: Wisconsin Electric Power Company; Abstract: Methods for increasing the amount of cenospheres in a fly ash sample are disclosed"; and:
West Virginia Coal Association | Georgia Tech Recycles Coal Utilization Byproducts | Research & Development; concerning: "United States Patent 8,057,594 - High Strength Pozzolan Foam Materials and Methods of Making Same; 2011; Assignee: Georgia Tech Research Corporation; Abstract: The various embodiments of the present invention relate generally to high strength foam materials and methods of making the same. More particularly, various embodiments of the present invention relate to high strength foam materials comprising pozzolans, such as cenospheres derived from fly ash".
For more background, see:
Cenosphere - Wikipedia, the free encyclopedia; "A cenosphere is a lightweight, ... hollow sphere filled with inert air or gas, typically produced as a byproduct of coal combustion at thermal power plants".
And, concerning "precipitator fly ash":
Electrostatic precipitator - Wikipedia, the free encyclopedia; "Electrostatic Precipitators continue to be excellent devices for control of many industrial particulate emissions, including smoke from electricity-generating utilities (coal and oil fired)...)
The method ... wherein said metal is selected from the group consisting of aluminum and alloys of aluminum (or) lead and alloys of lead (and) wherein said reinforcing phase is selected from the group consisting of cenosphere fly ash and precipitator fly ash ... .
Background and Field: Metal matrix composites are materials which comprise a secondary, reinforcing or filler phase in combination with a metal matrix. Metal matrix composites have different, and often improved or more desirable, properties as compared to their monolithic metal counterparts. For example, depending on the particular metal and reinforcing phases present in a composite material, as well as their respective ratios in the composite material, the composite material may have improved characteristics with respect to strength, stiffness, contact wear resistance and elevated temperature strength, as compared to the corresponding monolithic metal.
Furthermore, depending on the choice of reinforcing phase present in the composite, the metal matrix materials may be less expensive to prepare than their monolithic metal counter-parts.
There are many potential applications for metal matrix composites. Significant applications of metal matrix composites are likely in automotive components, machine parts, and electronic packaging, as well as in specialized products based on unique combinations of properties.
Of particular interest are metal matrix composites comprising fly ash, because such composites are less expensive to prepare and exhibit improved properties with respect to their corresponding monolithic metal counterparts. Fly ash is an abundant by-product that results from the combustion of pulverized coal. In the past fly ash has been employed as a concrete admixture, as a soil stabilizer, as a filler for asphalt and structural materials, such as bricks.
A variety of methods for producing metal matrix composite materials have been developed. These methods include diffusion bonding, powder metallurgy, casting, pressure infiltration of loose fly ash beds, spray codisposition and the like. For fly ash metal matrix composites in particular, stir casting and pressure infiltration of loose fly ash beds have found use.
Summary: Novel metal matrix composites, as well as methods for their production, are provided. The subject method comprises combining a reinforcing phase with an aqueous medium comprising a binder to produce a slurry that is dried to produce a solid, porous preform. The resultant solid, porous preform is then infiltrated with a molten metal to produce the subject metal matrix composite."
----------------------
Following is an example of how refined the technology for forming such "metal matrix composite"s actually is, with Rohatgi defining what are, primarily, nuances in the types and ratios of various "binders" to be utilized in molding the Coal Ash "preforms" into which the molten metal is infiltrated:
"United States Patent: 5897943 - Metal Matrix Composite Including Homogeneously Distributed Fly Ash
Metal matrix composite including homogeneously distributed fly ash, binder, and metal - Electric Power Research Institute, Inc
Date: April, 1999
Inventor: Pradeep k. Rohatgi, WI
Assignee: Electric Power Research Institute, CA
Abstract: Metal matrix composites comprising of a solid preform comprising a filler phase containing fly ash and a binding material having a binder to water ratio of 1:1 to 1:9, wherein the preform contains a metal homogeneously distributed within the preform.
Summary: Novel metal matrix composites, as well as methods for their production, are provided. The subject method comprises combining a reinforcing phase with an aqueous medium comprising a binder to produce a slurry that is dried to produce a solid, porous preform. The resultant solid, porous preform is then infiltrated with a molten metal to produce the subject metal matrix composite.
The subject composites may find use in a variety of applications, such as their use as structural materials, where the properties of the metal matrix composite are more desirable than the properties of the corresponding monolithic metal."
------------------------
And, in yet a further example, Rohatgi discloses another way in which Coal Ash can be filled with, or "infiltrated" by, be encapsulated in, molten metal, most typically Aluminum, to achieve even better results:
"United States Patent: 5899256 - Metal-Fly Ash Composites and Low Pressure Infiltration Methods
Metal-fly ash composites and low pressure infiltration methods for making the same - Electric Power Research Institute, Inc.
Date: May, 1999
Inventor: Pradeep Rohatgi, WI
Assignee: Electric Power Research Institute, CA
Abstract: Metal matrix composites are made by infiltrating packed loose fly ash with molten metal or metal alloy under low pressure. In some embodiments the infiltration is driven by pressurized gas. Coating the fly ash prior to infiltration can lower the threshold of pressure required for satisfactory infiltration by the molten metal. In some embodiments nickel coated cenosphere fly ash is employed. Resulting metal-fly ash composites have high volume fractions of fly ash, and the fly ash is uniformely distributed in the metal matrix. The densities of the composites are relatively low, particularly in composites made using cenosphere fly ash.
Claims: A method for making a metal matrix composite, comprising the steps of: providing loose fly ash particles positioned in a container, said fly ash particles having a substantially spherical shape; exposing an end of the container to molten metal held in a vessel under pressure in the range from 2 kPa to 100 kPa for a time sufficient to effect infiltration of the fly ash particles by the molten metal, and permitting the infiltrated fly ash particles to cool.
The method ... wherein said fly ash particles comprise ... precipitator fly ash (or) cenosphere fly ash (and)wherein said metal comprises one of aluminum or lead or an alloy of aluminum or of lead (or) copper, zinc, manganese, magnesium, tin, iron, gold, silver, nickel, cobalt, and alloys thereof.
The method ... wherein said pressure is less than 40 kPa.
(Online Conversion - Pressure Conversion; According to calculations performed by the linked utility, the specified "40 kPa" is only about six pounds per square inch - i.e., not much.)
The method ... wherein said exposing step includes the step of immersing the end of said container into said molten metal.
(The pressure needed to saturate the Coal Ash preform with molten metal is so low, in fact, that we can just dip it into a vat of melted Aluminum, for instance. The liquid metal doesn't have to be pumped, thus greatly reducing the potential cost of the total operation.)
The method ... further comprising the step, prior to said contacting step, of applying a coating onto the surface of at least a portion of the fly ash particles ... wherein said coating alters the surface energy of the fly ash particles coated thereby (and) wherein said metal comprises a metal selected from the group consisting of nickel, copper, aluminum, cobalt, tin, gold, silver, magnesium, and alloys thereof.
The method ... wherein said step of applying said coating comprises exposing a fluidized bed of said fly ash particles to a gas of a carbonyl of said metal, whereby decomposition of said carbonyl results in coating said fly ash particles with said metal.
(The above use of "a carbonyl of said metal", for deposition of the metal, actually describes a known manufacturing technique employed primarily, as we've been given to understand it, in the electronics industry. If you wish to explore it a bit, a good place to start might be the included references in:
"United States Patent: 4929468; US Patent 4,929, 468 - Formation of Amorphous Metal Alloys by Chemical Vapor Deposition; May, 1990; The United States of America; Abstract: Amorphous alloys are deposited by a process of thermal dissociation of mixtures or organometallic compounds and metalloid hydrides, e.g., transition metal carbonyl such as nickel carbonyl, and diborane. Various sizes and shapes of deposits can be achieved, including near-net-shape free standing articles, multilayer deposits, and the like. Manipulation or absence of a magnetic field affects the nature and the structure of the deposit. The U.S. Government has rights in this invention pursuant to Contract No. DE-AC04-76DP00789 between the U.S. Department of Energy and AT&T Technologies, Inc.".)
The method ... wherein said coating comprises a ceramic (and) wherein said ceramic comprises one of an oxide or a nitride or a carbide of a metal.
The method ... wherein said method comprises exposing a fluidized bed of said particles with a carbonyl of nickel, whereby decomposition of said carbonyl results in coating said particles with nickel.
Summary: Methods according to the invention can provide for satisfactory pressure infiltration of molten metal throughout the packed unbound secondary phase over suitably short infiltration times at low pressures. Where the secondary phase material particles are coated prior to the infiltration step, even lower pressures are required for satisfactory infiltration. Lower pressure infiltration is much more commercially feasible than conventional higher-pressure infiltration, because much simpler and less costly equipment, requiring lower cost tooling, is required to generate and to maintain the lower pressures. Moreover, where the secondary phase material is cenosphere fly ash, a lesser proportion of the hollow spherical fly ash particles are ruptured at the lower pressures employed according to the invention than at conventional higher infiltration pressures, and infiltration by the molten metal into the interiors of the hollow spherical particles is reduced. The resulting composite materials have higher volume fractions of secondary phase material, and substantially lower densities."
----------------------------
There are a number of advantages to manufacturing such Coal Ash and Aluminum - - as representative, keeping in mind, as Rohatgi specifies, that a wide selection of metals can be so utilized with Coal Ash, depending on the needs of the end-use application - - Alloys; not the least of which are the conservation of valuable metal and the productive consumption of what might otherwise be considered as "waste".
Some of those are described in another document, accessible for you via the awkward-looking link:
http://download.springer.com/static/pdf/885/art%253A10.1007%252FBF03222635.pdf?auth66=1353108641_c5cbb6b1e712ebfff4ed5eee3d0ff; through which you can, hopefully, access:
"Low Cost, Fly-Ash-Containing Aluminum Matrix Composites; Pradeep K. Rohatgi; In recent years there has been considerable activity in the development of metal-matrix composites, especially for aerospace, ground transportation, and the leisure industry. and industrial applications. In a broader sense, many materials have been marketed by Japanese companies for several years. It is likely that near future cast particulate composites like aluminum-graphite, aluminum-silicon carbide, and aluminum-alumina will find widespread applications as brake rotors, in automotive drive shafts, cylinder liners, connecting rods and wrist pins. The cost of metal-matrix composites has been one of the major barriers toward their widespread application.
This paper describes the development of cast aluminum-fly ash particle composites (ash alloy). Incorporation
of fly-ash particles, which are a waste by-product of coal-based power generation, reduces the cost of aluminum castings by acting as a filler; decreases their density; and increases their hardness, abrasion resistance, and stiffness."
-------------------------
So, Coal Ash can reduce "the cost of aluminum castings by" replacing some of the Aluminum needed for those "castings"; while at the same time increasing the "hardness, abrasion resistance, and stiffness" of the final product.
And, keep in mind that much of the same can be true of other metals, as well, such as, as Rohatgi suggests, "nickel, copper, ... cobalt, tin, gold, silver, magnesium, and alloys thereof"; with such metal displacement thus conserving both the metal resources and the energy that might otherwise be needed to refine and process them.
We do note that Coal Ash nowadays, due in large part to "pollution controls" that interfere with complete combustion, is often contaminated with a certain amount of unburned Carbon; and, that Carbon, to prevent contamination of cast metal parts incorporating, as explained herein, a certain percentage of Coal Ash, would no doubt have to be removed. And, as we've documented, for just one example, in:
West Virginia Coal Association | Virginia Converts Coal Ash to Cash | Research & Development; concerning, in part: "South Carolina Electric and Gas Successful Application of Carbon Burn-Out (CBO) at the Wateree Station; 1999 International Ash Utilization Symposium; University of Kentucky; South Carolina Electric and Gas Company; Progress Materials, Inc.; and, Southeastern Ash Co., Inc. CBO combusts residual carbon in fly-ash, producing a very consistent, low-carbon, high-quality pozzolan";
and, as we will attempt to do a better job of documenting in the future, technologies do exist to efficiently remove, and maybe even derive some benefit from, such residual Carbon in the Coal Ash.
In closing, we must also observe, that, as we have previously discussed, for just one instance in:
West Virginia Coal Association | USDOE Says Coal Ash Could End Aluminum Ore Imports | Research & Development; concerning: "Economic Metal Recovery from Fly Ash; 1981; USDOE; Abstract: Although most coal combustion ash produced in the United States is discarded as a waste, results are presented to show that fly ash can be an economical source of Al2O3";
and, as we will reaffirm in more reports to follow, Coal Ash can also serve as "an economical source" of Aluminum ore.
And, thus, the Aluminum we would be making better, but less expensive, "castings" out of, by reinforcing those castings with "in excess of 50%" Coal Ash, as per the teachings of, for just one of the examples presented herein, "United States Patent 5,897,943 - Metal Matrix Composite Including Homogeneously Distributed Fly Ash", could itself be extracted from Coal Fly Ash.
This seems to be the place where we're usually motivated to attempt a little editorializing about our apparently myopic and moribund Coal Country Press.
But, we reckon we've whipped on that great sorry old gossip mill about as much as we can, and they ain't flinched yet in their seeming resolution to feed you nothing but pie-in-the-sky nonsense about endless shale gas riches that lie just over the rainbow, and pot-boiling hash about the sad personal lives of public people.
For our part, we'll do our best to keep loadin' out the Coal here, in the wan hope that someday someone will come along and start carting the stockpiles off to market.
The thing to take away from our report herein is, that:
Coal Ash, rather than being some sort of valueless, or even hazardous, waste the consumers of abundant and affordable Coal-based electric power must be extorted to ensure disposal of, is, instead, a valuable mineral resource; a mineral resource which we can utilize to extend our stockpiles of strategic metals by using Coal Ash to replace some of those metals in cast and molded articles of manufacture; metal articles that, because they do contain a significant percentage of Coal Ash, actually exhibit better and improved physical properties and are themselves, thus, more valuable.
