Jesus Paulo L. Perez

Hypergolic Ionic Liquids to Mill, Suspend and Ignite Boron Nanoparticles

Boron nanoparticles prepared by milling in the presence of a hypergolic energetic ionic liquid (EIL) are suspendable in the EIL and the EIL retains hypergolicity leading to the ignition of the boron. This approach allows for incorporation of a variety of nanoscale additives to improve EIL properties, such as energetic density and heat of combustion, while providing stability and safe handling of the nanomaterials.

Functionalization and Passivation of Boron Nanoparticles with a Hypergolic Ionic Liquid

Abstract : Boron is a beneficial fuel for propellants and explosives because of its high energy density. However, efficient combustion of boron particles is difficult to obtain because of an inhibiting oxide layer that covers the particles. Various metal oxides are active catalysts in graphite/carbon oxidation, but no study has been carried out to investigate metal oxides as catalysts for boron oxidation. In this paper, the effects of metal oxides on boron oxidation are introduced. The instruments used in the experiments include a thermobalance, FactSage 6.2 software, and a CO2 laser ignition facility. The results reveal that Bi2O3 is the most active catalyst: it can reduce the ignition temperature by 15.2%. Fe2O3 and SnO2 are the second and third most active catalysts, respectively. The other four metal oxides used in the experiments exhibit little activity on boron thermal oxidation. The catalytic action of metal oxides possibly involves the cyclic reduction of the metal oxides and the reoxidation of the resulting metals. The catalysts help transfer oxygen from the surroundings to the B-B2O3 interface. All metal oxides used in the experiments help decrease boron ignition delay time. Two reasons are proposed to interpret the effect of metal oxides on the boron ignition delay time.

Boron nanoparticles with high hydrogen loading: mechanism for B-H binding and potential for improved combustibility and specific impulse.

Ball milling of boron in an H2 atmosphere was found to result in hydrogen uptake of up to 5% by weight (36 mol %). The nature of the hydrogen binding to boron was probed by a combination of ab initio theory, IR spectroscopy, thermogravimetric analysis, and mass spectral measurements of gases evolved during sample heating. The dominant binding mode is found to be H atoms bound to B atoms in the surface layer of the particles, and the high hydrogen loading results from production of very high surface area, indicating that gaseous H2 is an effective agent promoting size reduction in milling. Hydrogen incorporated in the samples was found to be stable for at least a month under ambient conditions. Desorption is observed beginning at ∼60 °C and continuing as the temperature is increased, with broad desorption features peaking at ∼250 and ∼450 °C, and ending at ∼800 °C. Unprotected hydrogenated boron nanoparticles were found to be reactive with O2 producing a hydrated boron oxide surface layer that decomposed readily at 100 °C leading to desorption of H2O. Hydrogenated boron nanoparticles were found to promote a higher flame height in the hypergolic ignition of ionic liquids upon contact with nitric acid.

Synthesis of nanoparticles from malleable and ductile metals using powder-free, reactant-assisted mechanical attrition

A reactant-assisted mechanochemical method was used to produce copious nanoparticles from malleable/ductile metals, demonstrated here for aluminum, iron, and copper. The milling media is intentionally degraded via a reactant-accelerated wear process, where the reactant aids particle production by binding to the metal surfaces, enhancing particle production, and reducing the tendency toward mechanochemical (cold) welding. The mechanism is explored by comparing the effects of different types of solvents and solvent mixtures on the amount and type of particles produced. Particles were functionalized with oleic acid to aid in particle size separation, enhance dispersion in hydrocarbon solvents, and protect the particles from oxidation. For aluminum and iron, the result is air-stable particles, but for copper, the suspended particles are found to dissolve when exposed to air. Characterization was performed using electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Density functional theory was used to examine the nature of carboxylic acid binding to the aluminum surface, confirming the dominance of bridging bidentate binding.

Binding of Alkenes and Ionic Liquids to B–H-Functionalized Boron Nanoparticles: Creation of Particles with Controlled Dispersibility and Minimal Surface Oxidation

The interaction of B-H-functionalized boron nanoparticles with alkenes and nitrogen-rich ionic liquids (ILs) is investigated by a combination of X-ray photoelectron spectroscopy, FTIR spectroscopy, dynamic light scattering, thermogravimetric analysis, and helium ion microscopy. Surface B-H bonds are shown to react with terminal alkenes to produce alkyl-functionalized boron particles. The interaction of nitrogen-rich ILs with the particles appears, instead, to be dominated by boron-nitrogen bonding, even for an ILs with terminal alkene functionality. This chemistry provides a convenient approach to producing and capping boron nanoparticles with a protective organic layer, which is shown to protect the particles from oxidation during air exposure. By controlling the capping group, particles with high dispersibility in nonpolar or polar liquids can be produced. For the particles capped with ILs, the effect of particle loading on hypergolic ignition of the ILs is reported.

Tuning azolium azolate ionic liquids to promote surface interactions with titanium nanoparticles leading to increased passivation and colloidal stability.

The passivation and stability of suspensions of titanium nanoparticles in azolium azolate ionic liquids can be tuned by introducing metal specific binding sites in the azolate anion.

Comparison of different types of phacoemulsification tips. I. Quantitative analysis of elemental composition and tip surface microroughness

Purpose To evaluate the elemental composition of phacoemulsification tips and their surface roughness in the microscale. Setting John A. Moran Eye Center and Utah Nanofab, College of Engineering, University of Utah, Salt Lake City, Utah, USA. Design Experimental study. Methods Seven types of phacoemulsification tips were studied. The phaco tips were examined through energy‐dispersive x‐ray spectroscopy (EDS) and x‐ray photoelectron spectroscopy (XPS) for elemental composition. In addition, the roughness of the opening in all tips was assessed through 3‐dimensional white‐light interferometry. Results Elemental analysis showed considerable differences in the surface layers between manufacturers. Alcon tips had a thinner oxidized titanium (Ti) layer in their surface. Through XPS, vanadium was not detected in the superficial layers of any tip, but only in deeper levels. The microroughness surface analysis showed comparable results regarding their root‐mean‐square (RMS) metric. Maximum peak valley distance values varied and appeared to be dependent on the quality of material process rather than the material itself. Conclusions Phacoemulsification tips are made of Ti alloys and showed differences between models, especially regarding their composition in the superficial layers. Their opening end roughness showed an overall appropriate RMS value of less than 1.0 &mgr;m in all cases. The existence of small defected areas highlights the importance of adequate quality control of these critical surgical instruments. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

Comparison of different types of phacoemulsification tips. II. Morphologic alterations induced by multiple steam sterilization cycles with and without use of enzyme detergents.

Purpose To evaluate the alterations in the morphology and elemental composition of reusable phacoemulsification tips after cleaning and sterilization. Setting John A. Moran Eye Center, Salt Lake City, Utah, USA. Design Experimental study. Methods For the main experiment, 2 types of reusable phacoemulsification needles were studied. One tip of each type underwent 1, 2, and 3 autoclave sterilizations with the use of detergents followed by thorough rinsing with sterile water between cycles. Another set of tips underwent the same procedure but without rinsing. Subsequently, phaco tips were examined through scanning electron microscopy and energy‐dispersive x‐ray spectroscopy to assess morphologic changes and surface deposits. In a second experiment, tips of 8 different types (both reusable and single use) underwent 10 sterilization autoclave cycles without detergents. Results Residues, mostly comprised of carbon‐containing material, were found in extensive areas of tips that were sterilization with enzymes and without rinsing. Smaller and fewer residues were found in tips after sterilization with the use of enzymes and thorough rinsing. Tips that underwent autoclave sterilization without detergents had no bulky deposits on their surface; they mostly had thin layers of sodium and chloride or material discoloration. Conclusions Rinsing the phaco tips significantly reduced the size and number of residues after use of enzymatic detergents. However, detergent residues were detected on phaco tip surfaces even after thorough rinsing with sterile water. No major noticeable changes were observed in either single‐use or reusable phaco tips after 10 cycles of sterilization without detergents. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.