Wen-Hwa Hwu

A study on the thermal decomposition of mixtures containing an energetic binder and a nitramine

Abstract In this paper, a differential thermal analyzer (DTA) and a thermogravimetric analyzer (TGA) were both employed to study the thermal decomposition of mixtures containing an energetic binder and a nitramine compound. The energetic binders investigated were polyethylene glycol (PEG) and glycidyl azide polymer (GAP). Both cyclotriethylene trinitramine (RDX) and cyclotetraethylene tetranitramine (HMX) were studied. The heating rate was set at 10°C min −1 . The purge gas was nitrogen or oxygen. It was found that the thermal decompositions of the mixtures were affected by the sample composition and the atmosphere employed. The decomposition reaction rates of PEG and GAP increased when they were heated under oxygen. Because the polymer binders are energetic, both RDX and HMX nitramine compounds in the mixtures decomposed earlier and the reaction rate was increased.

Physical and Chemical Dispersion Effects on the Preparation of Ni-AI2O3 Composite Coating

Charged alumina fine particles (80 nm) easily agglomerated into larger particles with an average diameter about 1109 nm in a well-stirred concentrated Watts bath. However, the average diameter of the agglomerated particles could be easily reduced to 162 nm and 318 nm, respectively, by means of physical dispersion through the application of supersonic energy, and by means of chemical dispersion through the addition of surfactants to this electrolyte. The volume content of alumina particles in the electrochemical composite coating depended on the dispersal effect of alumina particles in the electrolyte. Although the applied supersonic energy in the Watts bath electrolyte had a better dispersion effect than the particles promoted the attractive force between the agglomerates and the cathode surface, as well as a higher volume content of alumina particles in the Ni-Al2O3 composite coating (6.8 vol%) was obtained. Better hardness (470 Hv) was also found in this composite coating.

A Novel Method Produces Pd nanoparticles for Ink-Jet Printing Technology

The free-radical polymerization method was used in this study to synthesize three kinds of oligomers (hydrophobic PS, PS-co-PMMA, hydrophilic PVAc) with sulfate group on chain end which can be successfully applied in reduction and stabilization of Pd nanoparticles without any surfactant. Pd nanoparticles are further used as the reductant for catalyzing electroless nickel(EN). Since the Pd nanoparticles are existed on the surface of oligomer. Therefore, the oligomers can effectively prevent Pd nanoparticles from oxidation and aggregation and use in ink-jet printing process. We also demonstrated that the water-based ink containing these Pd nanoparticles can be ink-jet printed onto the PET substrate, then, a Ni pattern is fabricated successfully by the electroless Ni plating.

The mechanism of shear thickening fluid with nanoparticles applied to liquid armor

Shear thickening fluid (STF) has been reported that it can be applied in defensive and protective equipment, however, to meet the protection requirements for typical ballistic threats, approximately 20-50 layers of fabric are required. The resulting bulk and stiffness of the armor limits its comfort, and has restricted its application primarily to torso protection. Utilization of this shear thickening characteristic, the ballistic protection capability afforded by fabricated, flexible body armor can be enhanced tremendously. The ballistic protection properties of this complex system can be predicted or controlled only if the mechanism is fully understood. But the mechanism of shear thickening is still a matter of debate. It has been ascribed either to an order-disorder transition or to the formation of hydroclusters, however, our research verifies that the hydrogen bond might play an important role on the forming of STF. From our results, it is possible to interpret the occurrence of shear thickening behavior in terms of the shear-induced structure of the suspension once the critical shear strain is reached. The shear -induced structure can only be obtained for the suspension system with intensive hydrogen bonding within the system. The degree of shear thickening also depends on the concentration and temperature of the system.

Ultrafine Na–Sr–Si precursor powder for sealing glass via sol–gel route

Sealing glasses have been widely used as insulating and sealing materials in the electronics industry. In this study, ultrafine Na–Sr–Si precursor powder was synthesized from sodium nitrate (NaNO3), strontium nitrate Sr(NO3)2, and tetraethoxy orthosilicate (TEOS) via the sol–gel method. Nitric acid (HNO3) or ammonia (NH4OH) was used as acid or base catalysts, respectively, to achieve miniaturization of particles. The products were characterized by X-ray diffraction, scanning electron microscope, and thermogravimetric/differential thermal analyzer. The results showed that the mean particle size for acid-catalyzed Na–Sr–Si glass precursor powder was approximately 100–700 nm, and appeared to be smaller than that for base-catalyzed Na–Sr–Si glass precursor powder. This glass precursor powder synthesized by sol–gel process has a low processing temperature of about 850–900°C compared with the processing temperature of ∼1400°C for traditional glass precursor powder. Furthermore, the coefficient of thermal expansion of this sealing glass was in the range 6.575 × 10−6–9.136 × 10−6°C−1, measured by the thermal mechanical analyzer.

Polymer Composite Varistor

A reusable nonlinear polymeric composite varistor composed of a linear low density polyethylene (LLDPE) as the matrix and doped zinc oxide varistor powders as the functional fillers, sintered at 850, 950 and 1100℃ for 5 h, is used as a novel material to limit excess voltage, current or power. The functional fillers act as varistors due to their grain boundary characteristics which can be adjusted by different formula and sintering conditions. When applied field is above breakdown field of the filler the current density increases abrupt if a critical temperature is reached. Thereby the over voltage is limited by fillers (i.e. varistor effect) and the over current is limited by polymer matrix (i.e. PTC effect). We studied the dependence of the E-J characteristics on the preparation conditions of filler material, the filler content in the polymeric matrix and suggest possible nonlinear electrical-thermal switching mechanism.