William S. Willis

Pyrolytic Decomposition of Ammonia Borane to Boron Nitride

The thermal decomposition of ammonia borane was studied using a variety of methods to qualitatively identify gas and remnant solid phase species after thermal treatments up to 1500 °C. At about 110 °C, ammonia borane begins to decompose yielding H(2) as the major gas phase product. A two step decomposition process leading to a polymeric -[NH═BH](n)- species above 130 °C is generally accepted. In this comprehensive study of decomposition pathways, we confirm the first two decomposition steps and identify a third process initiating at 1170 °C which leads to a semicrystalline hexagonal phase boron nitride. Thermogravimetric analysis (TGA) was used to identify the onset of the third step. Temperature programmed desorption-mass spectroscopy (TPD-MS) and vacuum line methods identify molecular aminoborane (H(2)N═BH(2)) as a species that can be released in appreciable quantities with the other major impurity, borazine. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to identify the chemical states present in the solid phase material after each stage of decomposition. The boron nitride product was examined for composition, structure, and morphology using scanning Auger microscopy (SAM), powder X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Thermogravimetric Analysis-Mass Spectroscopy (TGA-MS) and Differential Scanning Calorimetry (DSC) were used to identify the onset temperature of the first two mass loss events.

CVD Mo, W and Cr oxycarbide, carbide and silicide coatings on SiC yarn

SiC yarn has been coated with molybdenum oxycarbide and tungsten oxycarbide without degrading the fibre. Conversion of the coatings to the metals has been accomplished by heat treatment in nitrogen. These metal coatings have then been converted to suicide coatings by heating in SiCl4. An SiC/WOC minicomposite has been formed by longer deposition of tungsten oxycarbide on a silicon carbide yarn.

Vanadium interactions with treated silica aluminas

Abstract Poisoning of fluid cracking catalysts by vanadium, nickel, iron and copper can decrease the selectivity and overall activity of such catalysts. Silica alumina is often used as a matrix to disperse the active zeolite component, to crack large hydrocarbons at initial stages of reaction and for stability of the fluid cracking catalyst. Vanadium poisons are particularly bothersome due to zeolite destruction by vanadium. This paper explores the interaction of vanadium with various silica aluminas including those with rare earth and magnesia contents. The effects of calcination and steaming were also determined. Spectroscopic techniques such as luminescence, diffuse reflectance, electron paramagnetic resonance, X-ray photoelectron spectroscopy and secondary ion mass spectrometry methods were used to study the oxidation state, chemical composition, and number and type of vanadium species in these materials. The results show that vanadium moves into the particle interior when magnesium or rare earth oxides are present. This is responsible for the decreased mobility of vanadium even during steaming conditions and results in higher catalytic selectivity for catalysts containing these materials.

Growth of large buserite crystals: precursors for octahedral molecular sieves

Large buserite crystals that are important in the generation of octahedral molecular sieves are prepared by crystal growth in gels.

Pulsed‐laser deposition of magnetic alloys

Targets of SmCo5 and Pr2Fe17 are ablated with a quadrupled Nd:YAG pulsed laser operating at 266 nm with fluence levels of ≊2 J cm−2. The plasmas are condensed on r‐plane sapphire (Al2O3) maintained either at ambient room temperature of ≊400 °C. Preliminary results indicate that Sm+n and Co+n recombine on room temperature substrates to form an alloy with a‐axis orientation that is consistent with an hkl〈200〉 d‐spacing for hexagonal SmCo5. Rare‐earth and Fe plasmas condense at ≊400 °C to form alloys with c‐axis orientation as indicated by a single narrow hkl〈006〉 reflection with a HHFW of about Δ(2θ)=0.4°. When codeposited with N2, an interstitial alloy Re2Fe17N3−δ can be formed. These newly discovered metastable alloys display high Curie temperatures (Tc), large magnetization and anisotropy fields desirable for permanent magnet applications. Preliminary XRD, (SQUID) magnetometry and Auger surveys are presented together with speculation about future work.