Reactive Laser Ablation Synthesis of Nanosize Alumina Powder

An aluminum (Al) target was laser ablated in an oxygen (O₂) atmosphere, producing nanosize alumina (Al₂O₃) powder. The powder surface area decreased (and the particle size increased) with both increasing oxygen pressure and laser fluence. All powders produced had surface areas between 135 and 250 m²/g, corresponding to primary particle sizes ranging from 7 to 3 nm in radius. Phase evolution with temperature was studied via X-ray diffraction. These powders showed a direct transformation from γ- to α-alumina at approximately 1200°C, bypassing other transition alumina phases, while still maintaining small particle size ( 30 nm). Despite the nanosize particles, green densities equal to 54% of the skeletal density (i.e., true density of the solid phase) were obtained by uniaxial pressing at 40 MPa.     

Reactive Laser Ablation Synthesis of Nanosize Aluminum Nitride

An aluminum (Al) target was laser ablated in a nitrogen (N₂) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm² and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase-pure AlN by X-ray diffraction (XRD). The surface area of this powder is 82 m²/g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observations.     

A novel synthesis method for the preparation of aromatic poly(imide benzoxazole) from trimellitic anhydride chloride and bis(o‐aminophenol)

A poly(imide benzoxazole) was prepared directly from trimellitic anhydride chloride and 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane (BisAPAF) monomers in a two‐step method. In the first step, a poly(hydroxyamide amic acid) precursor was synthesized by the low‐temperature solution polymerization in an organic solvent. Subsequently, thermal cyclodehydration of the poly(hydroxyamide amic acid) precursor at 350°C produced the corresponding poly(imide benzoxazole). The inherent viscosity of the precursor polymer was 0.22 dL/g. The cyclized poly(imide benzoxazole) showed a glass transition temperature (T_g) at 329°C and a 5% weight loss temperature at 530°C in nitrogen and at 525°C in air. The poly(imide benzoxazole) is amorphous as evidenced by the wide‐angle X‐ray diffraction measurement. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance spectroscopy (¹H NMR). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2388–2391, 2003     

Structure-function studies of an IGF-I analogue that can be chemically cleaved to a two-chain mini-IGF-I

The structure and biological activities of two disulphide isomersof a C-region deletion mutant of insulin-like growth factor-I(IGF-I) which has an Asn–Gly link engineered at the junctionof the A- and B-regions were studied before and after chemicalcleavage. Circular dichroism (CD) spectra and binding affinityto IGF binding protein 3 (IGFBP3) indicated that the treatmentwith hydroxylamine did not disrupt the overall tertiary foldof the hormones. Cleavage restored some binding affinity forthe IGF-I receptor in both isomers and weakly restored the abilityto stimulate incorporation of tritiated thymidine into DNA inNIH 3T3 fibroblasts transfected with the human IGF-I receptor.Cleavage also restored metabolic capacity, as measured by theability of the isomers to promote lipogenesis in isolated ratadipocytes through the insulin receptor. These results are consistentwith the theory that binding of IGF-I to the IGF-I receptorrequires a conformational change similar to that involved ininsulin binding the insulin receptor. The weak affinity forthe IGF-I receptor after cleavage is consistent with the beliefthat residues in the C-region interact with the IGF-I receptor.This structural difference between insulin and IGF-I gives eacha higher binding affinity for its own receptor.     

The effect of various fire‐exposed surface dimensions on the spalling of concrete specimens

Concrete spalling due to fire exposure is often defined as the sudden detachment of fragments from a concrete surface. It can be quantified by various parameters of which weight loss and spalling depth are the most common ones. The risk of spalling is influenced by many factors such as concrete composition, heating rate and applied testing methods. A reduced scale testing method should be developed to analyse the spalling behaviour and to understand its effectiveness in more detail. As a subsection of this development, this study aimed to analyse the effect of different‐sized, circular heated areas in semi full‐scale fire tests. Therefore, vermiculite slabs with varying cut‐outs in their centre were placed between a specimen made of a spalling‐sensitive concrete and the combustion chamber. The combustion chamber was heated following a standard fire curve. Our experimental results show that the thermal expansion inside of equal‐sized specimens is strongly dependent on the size of the heated area. In addition, this area also affects thermal stresses. They decrease as a result of lower temperature gradients for tests with smaller unheated boundary areas. Apart from this, the analysis of fragments shows no correlation between their relative volume distribution and the heated area. Copyright © 2014 John Wiley & Sons, Ltd.     

Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass-Ceramic

The devitrification kinetics and mechanism of a low-dielectric, low-temperature, cofirable K₂O–CaO–SrO–BaO–B₂O₃–SiO₂ glass-ceramic have been investigated. Crystalline phases including cristobalite (SiO₂) and pseudowollastonite ((Ca,Ba,Sr) SiO₃) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami-like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.     

Experimental study of the burner for FAA fire test: NexGen burner

The NexGen (Sonic) burner is the new burner developed by the Federal Aviation Administration, FAA, to replace old oil burners used for the required fire certification tests on power plant‐related materials, as it provides the capability to control both air and fuel flow rates. During a fire test, the burner is supposed to simulate a certain fire condition, so the flame properties should be robust and repeatable. The NexGen burner can achieve this due to the precise fuel and air controls. However, the current calibration criterion (ISO2685:1998 and AC20‐135) may not be good enough to ensure consistent flame properties. In the presented work, the sensitivity of the burner performance to air and fuel flow rate, as measured by the temperature and heat flux for calibration purposes, was studied. Additionally, the influence of the turbulator and the thermocouple size used for flame calibration was also studied. The impact of varying fuel/air ratio and thermocouple sizes was studied by conducting fire tests on aluminum samples, to show the inadequacies in the current calibration standards.     

Mechanisms of Solution Reactions of Cyclo-Penta[cd]Pyrene Oxide and Acenaphthylene Oxide

Rates and products of the acid-catalyzed and spontaneous reactions of cyclopenta[cd]pyrene oxide (2) and acenaphthalene oxide (3) in 1:3 dioxane-water and water, respectively, have been determined. Both 2 and 3 undergo acid-catalyzed hydrolyses to yield cis diol as the major product, and undergo spontaneous reactions to yield predominantly ketone products. The mechanisms of these reactions are discussed.     

Airborne Deployment of an Instrument for the Real-Time Analysis of Single Aerosol Particles

An instrument is described that provides real-time chemical analysis of the composition of individual aerosol particles. A differentially pumped aerosol inlet transfers particles from the ambient atmosphere into the source region of a time-of-flight mass spectrometer where they impact on a heated surface and the resulting vapors are ionized by electron ionization prior to mass analysis. Labora tory calibration studies demonstrated that the instrument was capable of detecting particles with diameters greater than approximately 0.4mu m. The instrument was operated on the NASA DC-8 research aircraft as part of the 1996 SUbsonic aircraft: Contrail and Cloud Effects Special Study (SUCCESS) mission with the intent of studying the chemical composition of upper tropospheric particles. More than 25,000 aerosol particle mass spectra were recorded during 19 mission flights. Although approximately 120 of those spectra showed clear evidence of sulfate, nitrate, and other inorganic materials, the remaining spectra contained only mass peaks consistent with water. Moreover, particles were detected only while traversing clouds. These results are not consistent with expectations of the size, quantity, or composition of upper tropospheric particles. It is likely, however, that a subisokinetic aircraft sampling inlet resulted in the collection of only very large ice particles. This situation would account for both the observed preponder ance of water-only spectra and the apparent lack of particles outside of clouds. Despite the sampling problem, the instrument was able to chemically speciate aerosols directly sampled from a medium altitude aircraft. These represent the first examples of aerosol particles chemically speciated in real time from an airborne platform.