{"id":1934,"date":"2014-03-12T14:00:56","date_gmt":"2014-03-12T22:00:56","guid":{"rendered":"http:\/\/blogs.oregonstate.edu\/erlenmeyer\/?p=1934"},"modified":"2014-03-10T15:08:17","modified_gmt":"2014-03-10T23:08:17","slug":"aqueous-aluminum-nanoclusters","status":"publish","type":"post","link":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/2014\/03\/12\/aqueous-aluminum-nanoclusters\/","title":{"rendered":"Aqueous Aluminum Nanoclusters"},"content":{"rendered":"

“Reprinted with permission from the February 2014 issue of TLT,<\/b> the official monthly magazine of the Society of Tribologists and Lubrication Engineers, a not-for-profit professional society headquartered in Park Ridge, Ill., www.stle.org<\/a>.”<\/b><\/p>\n

Aluminum is continuing to be an important metal used in the manufacture of automobiles. Its\u00a0 lighter weight (as compared to steel alloys), good strength and ability to elongate are important factors that enable automobiles to be produced with higher levels of fuel economy.<\/p>\n

But aluminum does not have the mechanical strength of steel. In a previous TLT article, a new process\u00a0 known as high-pressure torsion was discussed that increases the strength of aluminum to a level\u00a0 comparable to carbon steel without sacrificing ductility. A well-known alloy, 7075 aluminum, was solution treated at 480 C for five hours followed by quenching in room temperature water. The resulting metal was found to display a strength of 1.0 GPa in a tensile strength test, which is comparable to a typical hardened and tempered carbon-steel alloy.<\/p>\n

\"Key<\/a>Aluminum is fabricated into components used in automobiles through a series of metalworking operations that occur mainly with water-based fluids. There are a number of challenges in finding optimum machining conditions for specific aluminum alloys.<\/p>\n

But one of the intriguing issues is what happens to the aluminum alloy when it comes into contact with water, which is the primary component in a water-based\u00a0 metalworking fluid. Aluminum can readily form a series of metal salts with other additives used in MWFs such as fatty acids. These salts can become water insoluble and form residues that are similar to greases.\u00a0 Such contaminants are undesirable because they can degrade the performance of the MWF.<\/p>\n

Chong Fang<\/a>, assistant professor of chemistry at Oregon State University in Corvallis, Ore., says, \u201cAddition of aluminum to water leads to the formation of a variety of complex species that include monomeric, oligomeric and polymeric hydroxides. These species are present in water as colloidal solutions and gels, but they can also form precipitates and crystals.\u201d<\/p>\n

Gaining a better understanding of the composition of these species is extremely difficult. Fang says, \u201cMany of these species cannot be readily identified because they are difficult to detect using techniques such as\u00a0 27Al nuclear magnetic resonance (NMR) and conventional Raman spectroscopy. The problem is water\u00a0 binds in many different positions with respect to aluminum, leading to the formation of different types of highly coordinated structures, and there may be transient species involved. The elucidation of aqueous aluminum speciation pathways demands a technique capable of monitoring molecular choreography.\u201d<\/p>\n

Some of these aluminum water species are known as hydroxide clusters that contain multiple aluminum atoms. Fang says, \u201cFormation of aluminum clusters is dependent on factors such as reagent concentration and the method and rate of solution pH change.\u201d<\/p>\n

If specific aluminum clusters can be selectively synthesized, then these clusters can be studied to gain an\u00a0 understanding of their respective properties and how they may form when water contacts aluminum metal. One specific \u201cflat\u201d aluminum cluster has now been synthesized through a pHcontrolled process monitored by a novel analytical technique.<\/p>\n

FEMTOSECOND RAMAN SPECTROSCOPY
\n\"Figure<\/a>Fang and his fellow researchers synthesized an aqueous aluminum nanocluster known as Al13 by slowly raising the pH of a solution and following the reaction using an emerging technique known as Femtosecond Stimulated Raman Spectroscopy (FSRS). He says, \u201cWe chose to produce Al13 because this species\u00a0 represents a naturally occurring mineral that is octahedral in configuration. We have also pioneered a novel technique that enables thin metal-oxide films that are a few atomic layers thick to be prepared directly from solution instead of using more expensive methods. This integrated platform will enable Al13 potentially to be used as a green solution in broad applications such as transistors, solar energy cells, catalytic converters and corrosion inhibitors.\u201d<\/p>\n

The researchers used an electrochemical process to slowly and precisely raise the pH of the reaction\u00a0 mixture to produce Al13. Fang says, \u201cIn Stage I, we started at a pH of 2.2 where the dominant aluminum species prepared from a 1 molar aluminum nitrate solution is the monomeric aluminum hexa-aqua ion.\u201d<\/p>\n

The solution is placed in a two-compartment electrochemical cell, which contains an anode compartment and a cathode compartment. Nitrate ions migrate into the anode compartment where oxygen is produced.<\/p>\n

Aluminum ions migrate into the cathode compartment where hydrogen is produced. The charge balance is maintained. An electric current is used to control the process, which exhibits a net reduction in proton\u00a0 (hydrogen ions) concentration in the cathode compartment as the pH is slowly increased, wherein\u00a0 condensation of aluminum species occurs to produce larger aluminum nanoclusters.<\/p>\n

FSRS was used to follow the reaction because of the limitation of conventional Raman spectroscopy. Fang says, \u201cWe needed to detect small changes in Raman vibrational modes down to between 300 and 500 cm-1. Unfortunately, this frequency is too close to the fundamental pulse. Instead, we used non-resonant (800 nanometer) FSRS spectroscopy with a newly developed Raman probe pulse based on our photonic\u00a0 advances to cover that spectral range.\u201d<\/p>\n

FSRS reveals that the reaction moves to stage II at a pH between 2.4 and 2.7 due to the formation of an\u00a0 intermediate identified as Al7. Fang says, \u201cAs the pH increases to between 2.7 and 3.2, further\u00a0 deprotonation strips positive charges at the outer shell of Al7, leading to the formation of the larger Al13 cluster, which represents Stage III of the process. The key is to catch a glimpse of aluminum speciation as the chemistry proceeds in water.\u201d<\/p>\n

Figure 3 shows the two-compartment electrochemical cell and the reaction process as it moves from\u00a0 monomeric aluminum in Stage I to Al13 Stage III via an octahedrally coordinated Al7 intermediate in Stage II.<\/p>\n

The researchers deliberately ran this reaction sequence at a low pH because the involving aluminum clusters could be identified using FSRS aided by computations, and they represent the onset of larger\u00a0 aluminum cluster formation. Fang says, \u201cWork is underway to characterize the different types of clusters and species that form in aqueous solution at pH values above 7. This effort might also bring us closer to the regime where dehydration and annealing yield metal oxide thin films with versatility.\u201d<\/p>\n

This work is also of interest to formulators of MWFs because they are designed to operate at a pH of 9. Potentially, the aluminum clusters identified at this alkaline pH may help formulators better understand how to prepare products that will minimize such concerns as staining.<\/p>\n

Additional information can be found in a recent article2 or by contacting Dr. Fang at chong.fang@oregonstate.edu.<\/p>\n

REFERENCES
\n1. Canter, N. (2011), \u201cSuper-Strong, Ductile Aluminum,\u201d TLT, 67 (1), pp. 10-11.
\n2. Wang, W., Liu, W., Chang, I., Wills, L., Zakharov, L., Boettcher, S., Cheong, P., Fang, C. and Keszler, D. (2013), \u201cElectrolytic Synthesis of Aqueous Aluminum Nanoclusters and In Situ Characterization by\u00a0 Femtosecond Raman Spectroscopy and Computations,\u201d Proc. Natl. Acad. Sci. U.S.A. 110 (46), pp.\u00a0 18397-18401.<\/p>\n

Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech\u00a0 Beat can be submitted to him at neilcanter@comcast.net.<\/p>\n","protected":false},"excerpt":{"rendered":"

“Reprinted with permission from the February 2014 issue of TLT, the official monthly magazine of the Society of Tribologists and Lubrication Engineers, a not-for-profit professional society headquartered in Park Ridge, Ill., www.stle.org.” Aluminum is continuing to be an important metal used in the manufacture of automobiles. Its\u00a0 lighter weight (as compared to steel alloys), good… Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":3656,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101481],"tags":[199248,199247,199250,199249,199255,199254,199251,199252,199253],"class_list":["post-1934","post","type-post","status-publish","format-standard","hentry","category-research-2","tag-aluminum","tag-aqueous","tag-chong-fang","tag-nanoclusters","tag-spectroscopy","tag-stle-org","tag-tech-beat","tag-tlt","tag-tribology-lubrication-technology"],"_links":{"self":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/posts\/1934","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/users\/3656"}],"replies":[{"embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/comments?post=1934"}],"version-history":[{"count":16,"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/posts\/1934\/revisions"}],"predecessor-version":[{"id":1961,"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/posts\/1934\/revisions\/1961"}],"wp:attachment":[{"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/media?parent=1934"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/categories?post=1934"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dev.blogs.oregonstate.edu\/erlenmeyer\/wp-json\/wp\/v2\/tags?post=1934"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}