Comparative characterization of iridium loading on catalyst assessment under different conditions

To discuss the potential role of iridium(Ir)nanoparticles loaded under atmospheric and high pressures,we prepared a series of cata-lysts with the same active phase but different contents of 10wt%,20wt%,and 30wt%on gamma-alumina for decomposition of hydrazine.Un-der atmospheric pressure,the performance of the catalyst was better when 30wt%of the Ir nanoparticles was used with chelating agent that had greater selectivity of approximately 27%.The increase in the reaction rate from 175 to 220 h^(−1)at higher Ir loading(30wt%)was due to a good dispersion of high-number active phases rather than an agglomeration surface.As a satisfactory result of this investigation at high pressure,Ir catalysts with different weight percentages showed the same stability against crushing and activity with a characteristic velocity of approxim-ately 1300 m/s.

Influence of ZrB2 Nanoparticles on the Mechanical and Thermal Behaviors of Carbon Nanotube Reinforced Resol Composite

The present study focuses on the thermal response of carbon fiber-reinforced phenolic composites, where the matrix has been modified with different reinforcements. Two types of materials, multiwalled carbon nanotubes and zirconium diboride （ZrB2）, were used in a new design of mixture to produce the heat- resistant ablative composite system. The CNT/ZrB2/carbon/phenolic nanocomposite （Z/NT-CR） system corresponding to CNT/carbon/phenolic nanocomposite （NT-CR） showed a reasonable decrease in mass loss and the ablation rate as compared to carbon/phenolic composite （CR）. However, substantial drop in two factors was found for Z/NT-CR as compared to carbon/phenolic and NT-CR. Ablation mechanisms for all three composites were investigated by thermal gravimetric analysis in conjunction with micro- structural studies using a field emission scanning electron microscope. The microstructural studies revealed that CNTs acted as an ablation resistant phase for protection against 2000 ℃, and the conversion from ZrB2 to ZrO2 played an important role as an insulator in the performance of char layer in the ablation resistance.

Using an Inhibitor to Prevent Plasticizer Migration from Polyurethane Matrix to EPDM Based Substrate

The loss of adhesion between the propellant and insulator is one of the most important problems in solid propellant motors due to migration of plasticizer to interface of propellant and insulator. In this work, the polyurethane (PU) binder containing DOP plasticizer was used as a polymeric matrix and β-cyclodextrin (β-CD) was applied as inhibitor agent to prevent plasticizer migration from the PU matrix into the ethylene propylene diene monomer (EPDM) substrate. To increase the compatibility of β-CD and PU matrix, a derivative of β-CD has been synthesized using toluene diisocyanate (β-CD-TDI). The synthesized derivative was characterized by MALDI-MS and FTIR-ATR analyses. FTIR-ATR results confirmed the formation of bonding between β-CD and the polymeric network while the MALDIMS results showed that the synthesized derivative contained two β-CD and 7 TDI molecules bonded to β-CD. Investigation of the mechanical properties of PU modified by β-CD-TDI showed a decrease in tensile strength and an increase in elongation at break with increasing β-CD-TDI content. DMTA results showed a decrement in crosslinking density by increasing the β-CD-TDI content. Also, to investigate plasticizer migration, extraction of the DOP plasticizer from samples was performed using dichloromethane solvent and its concentration was measured by gas chromatography. The results of migration evaluation after four months showed that using β-CD as an inhibitor agent in the PU binder could prevent the migration of plasticizer to EPDM substrate.