Niles A. Fleischer

Applications of WS2(MoS2) inorganic nanotubes and fullerene-like nanoparticles for solid lubrication and for structural nanocomposites

Nanoparticles of WS2 and MoS2 with a closed cage structure (fullerene-like) that are termed IF phases are synthesized in large amounts in a pure form. These nanoparticles were shown to play a favorable role as solid lubricants under severe conditions where fluids are unable to support the heavy load and are squeezed away from the contact area. Various tribological scenarios are presented for these superior solid lubricants, demonstrating the large scale potential for applications of these materials. The mechanism of action of these solid lubricants is briefly discussed. Various other potential applications of IF phases for nanocomposites with high impact resistance; in rechargeable batteries and in optical devices are discussed in short.

Friction reduction and wear resistance of electro-co-deposited inorganic fullerene-like WS 2 coating for improved stainless steel orthodontic wires

A new type of composite metal–nanoparticle coating that significantly reduces the friction force of various surfaces, particularly archwires in orthodontic applications, is demonstrated. The coating is based on electrodeposited Ni film impregnated with inorganic fullerene-like nanospheres of tungsten disulphide. The first encouraging tests have shown reduction of up to 60% of the friction force between coated rectangular archwires and self-ligating brackets in comparison with uncoated archwires. The coating not only significantly reduces friction of commercial archwires but also maintains this low value of friction for the duration of the tests in comparison to archwires coated with nickel film without the nanoparticles. The coated surfaces of the wires were examined by scanning electron microscopy equipped with energy dispersive analyzer and by x-ray powder diffraction methods before and after the friction tests. Using these analyses, it was possible to qualitatively estimate the state of the Ni+IF-WS 2 coating before and after the friction test compared to Ni coated wires without IF-WS 2 .

Electrochemical insertion of lithium into the Bi2Sr2CaCu2O8+y high-Tc superconductor

Abstract The insertion compound LixBi2Sr2CaCu2O8+y (for lithium contents up to the studied level of x=2) was prepared by electro-chemical insertion of lithium into Bi2Sr2CaCu2O8+y pellets at room temperature in galvanic cells using 1.4 M LiAsF6 in 2Me-THF as electrolyte. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists but the superconducting fraction appears to be lower in the reacted samples. XRD data show that insertion of Li ions is accompanied by interlayer expansion between BiO planes and a small increase in the a and b cell lattice parameters. 7Li NMR measurements indicate a substantial donation of electrons to the 2212 host lattice. The changes in the a and b lattice parameters and the effect on superconductivity is consistent with some of the donated electrons entering the CuO planes and reducing holes in these layers.

Electrochemistry at High-T[sub c] Superconductors in Their Normal State

The recent discoveries of several new types of perovskite-like copper oxides as high transition temperature (T/sub c/) superconductors have led to extensive research in this field. Even though the low resistivity at room temperature of these materials enables them to be used as electrodes, electrochemical studies have been relatively scarce. Here the authors report on electron transfer reactions at room temperature at electrodes made from high-T/sub c/ superconductor materials. Electrodes were prepared from fresch YBCO and BCSCO pellets (0.25 cm/sup 2/) without any surface treatments. Used electrodes could be renewed by gentle scraping of the surface. (Resistivity measurements on the scraped surface verified that these samples had the same T/sub c/ and resistivity values as fresch pellets). Low resistance contacts to the electrodes were achieved by Ar etching and then sputtering gold pads onto the rear of the pellet. Insulated wires were attached to the gold with silver paint. The rear of the pellet was then protected with epoxy resin. The contact resistance was lower on YBCO than on BCSCO. Cyclic voltammetry was performed in 0.1M aqueous KCl, and in acetonitrile (AN) or dimethyl formamide (DMF) using 0.1M tetrabutylammonium perchlorate (TBAP) supporting electrolyte. The experiments were done at room temperature.

Electrochemical reduction of the high Tc superconductor YBA2Cu3Oy0 by lithium via new compound formation

Abstract We report on the electrochemical reduction of polycrystalline YBa 2 Cu 3 O y 0 (YBCO) pellets by lithium at room temperature in organic electrolyte galvanic cells at low current densities and its effect on superconductivity. The reaction is found to occur by irreversible new compound formation, which removes oxygen and copper from YBCO to form Li 6 CuO 4 and a reduced YBCO phase, rather than by insertion as previously thought. This conclusion is based on various types of analyses of electrochemically lithium-reacted samples which include, for the first time to be reported, their electronic transport and magnetic susceptibility behavior at superconducting temperatures, determination of their oxygen content, peak assignment of the additional phase in their powder X-ray diffraction pattern, and lithium analysis of samples reacted and after cell charging. The removal of oxygen and copper does not alter the orthorhombic symmetry of the YBCO phase nor its T c onset but progressively destroys superconductivity. Annealing at 150°C in argon causes structural rearrangement to tetragonal symmetry, restores superconductivity and the T c now depends on the reduction level. The significance of the lithium reaction technique as compared to high temperature reduction methods is that it provides an accurate means, via coulometric control, to separate changes in YBCO stoichiometry from structural rearrangements thus enabling electronic and structural contributions to superconductivity to be evaluated individually.

Structural changes upon electrochemical insertion of lithium into the Bi2Sr2CaCuO8+y high Tc superconductor

The insertion compound LixBi2Sr2CaCu2O8+y (x≤2) was prepared by electrochemical insertion of lithium into Bi2Sr2CaCu2O8+y pellets at room temperature in galvanic cells. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists, but the superconducting fraction appears to be lower in the reacted samples. The lithiated product was analyzed by crystallographic and chemical measurements. The results show that insertion of Li ions is accompanied by an expansion of the interlayer spacing between Bi‐O planes and a small increase in the a‐ and b‐cell parameters. This change is consistent with some, but not all, of the donated electrons entering the Cu‐O planes, with a corresponding reduction in hole concentration. At higher levels of Li content, a substantial breakdown of the lattice is observed.

INORGANIC FULLERENE-LIKE NANOPARTICLES AS NEW LUBRICANT ADDITIVES: A DRUG DELIVERY MECHANISM

When dispersed in a synthetic polyalphaolefin (PAO) base oil, inorganic fullerene-like (IF-MS2 ) nanoparticles of metal dichalcogenides (IF-MoS2 , IF-WS2 , IF-NbS2 ) lead to a significant reduction of both friction and wear under boundary lubrication. The effect of the contact pressure on the tribological properties of IF nanoparticles is particularly interesting. Results show that the higher is the pressure, the lower is the friction coefficient. The effect of the concentration shows that, even used at a low concentration (0.1%wt), IF-MS2 is able to decrease friction (0.05) compared to base oil only (0.08). A steady state friction coefficient of 0.04 was reached with IF-WS2 at 1%wt in PAO. Friction-induced transformation of the IF-MS2 nanoparticles into H-MS2 single sheets was evidenced by High Resolution Transmission Electron Microscopy (HRTEM). Some of these superimposed sheets are found in incommensurate positions, thus possibly explaining the very low friction coefficient of 0.04 obtained with IF-WS2 . In-situ Raman spectroscopy was performed during a friction test to follow this structural modification. The lubrication mechanism of IF-MS2 is very similar to a “drug delivery system”. A very low concentration of additives is sufficient and the activation is obtained by the opening of the nested structure, like in certain micellar structures. Furthermore, no chemical reaction is required to obtain interesting properties. Thus, fullerene-like nanoparticles are active at the very beginning of the test and even at ambient and low temperature.Copyright