Hot corrosion behavior of Cr2AlC MAX phase and CoNiCrAlY compounds at 950 °C in presence of Na2SO4+V2O5 molten salts

In this research, a high-purity Cr₂AlC MAX phase sample was prepared via spark plasma sintering (SPS) method with the hot corrosion behavior investigated in the presence of Na₂SO₄+V₂O₅ molten salts at 950 °C. Also, the hot corrosion resistance of this MAX phase was compared with a hot corrosion-resistant SPS-processed CoNiCrAlY sample. The results of the hot corrosion test after 30 h revealed that the MAX phase sample has better hot corrosion resistance compared to CoNiCrAlY sample. According to the results, corrosion kinetics of Cr₂AlC sample followed near-cubic law with diffusion occurring along the grain boundaries. On the other hand, CoNiCrAlY sample followed parabolic kinetics where the diffusion of reactants occurred through the oxide scale. The results indicated that in the Cr₂AlC sample, upon exposure time prolongation, a dense and uniform Cr-rich alumina layer was formed in the surface and Cr₇C₃ phase was created as a sub-layer, while in the CoNiCrAlY sample the oxide layer contained Al₂O₃ and porous spinel oxide phases. In the CoNiCrAlY sample, a considerable volume change and stress occurred during the non-uniform growth of spinel oxide causing the formation of defects such as microcracks which deteriorate its hot corrosion resistance.     

Temperature Distribution in Flux Channels with Discrete Contact Boundary Conditions

An analytical approach for the thermal behavior of two-dimensional rectangular flux channels with arbitrary boundary conditions on the source plane is presented. The boundary condition along the source plane can be a combination of the first kind boundary condition (Dirichlet or prescribed temperature) and the second kind boundary condition (Neumann or prescribed heat flux). To model the boundary conditions along the source plane, the method of least squares is used. The proposed solution is in the form of Fourier series expansion and can be applied to both symmetrical and non-symmetrical channels. This method is more general than other approaches and there is no need to use equivalent heat flux distributions to model isothermal heat sources. The general approach for obtaining the multidimensional temperature profile in flux channels and the advantages of the least-square method is discussed. The proposed solution can be used to calculate the temperature at any specified point in the flux channel. Two case studies are presented. The first case study is a flux channel with five discretely specified contact temperatures along the source plane. The second case study has both of the first kind and second kind boundary conditions on the source plane. The analytical results for both systems are compared with finite element method using a commercial software package. It is shown that the proposed approach can precisely model the temperature profile over the flux channel.     

Magnesiothermic synthesis of HfB2–HfC-SiC nanocomposite by spark plasma technique

The HfB₂-HfC-SiC nanocomposite was produced using H₃BO₃, HfO₂, Si, C, and Mg as starting materials by spark plasma for the first time. The reactions during synthesis indicate that the synthesis process progressed in self-propagating mode. The reaction mechanisms were investigated by the displacement-temperature-time (DTT) diagram, which was obtained during spark plasma cycles. The synthesis process of the composite was completed at the temperature of 400 °C in less than 30 min. The tendency to form the composite was investigated by thermodynamic calculations, and the formation of HfB₂, HfC, and SiC phases was observed by X-ray diffraction. Finally, using the Rietveld method, the mean crystallites sizes of about 54, 26, and 43 nm were calculated for HfB₂, SiC, and HfC phases, respectively.     

Force control grinding of gamma titanium aluminide

This paper addresses the grinding of ordered intermetallic compounds and their brittleness at ambient temperature. The depth of plastic deformation is supposed as the measure of surface integrity. The current paper expands the work of a previously reported indentation model that correlated the depth of plastic deformation and the normal component of the grinding force. This paper studies the indentation model using force control grinding of gamma titanium aluminide (TiAl-γ). Reciprocating surface grinding is carried out for a range of normal force 15–90 N, a cutting depth of 20–40 μm and removal rate of 1–9 mm³/sec using diamond, cubic boron nitride (CBN) and aluminum oxide (Al₂O₃) abrasives. The measured depths of plastic deformation are in the range of 150–300 μm. The deviations from the indentation model are explained by changes in the ductility during the grinding process. Furthermore, a force-based model for specific energy is developed and evaluated. The measured specific energies are in the range of 40 J/mm³ (diamond) to 400 J/mm³ (CBN).     

RF CMOS transceivers for cellular telephony

This article describes system and circuit issues related to cellular transceivers, presenting design techniques that have provided high performance in CMOS technology. Following an overview of relevant GSM and WCDMA specifications, the article identifies four trends in RF design that have continued to improve the performance. Examples of CMOS transceivers, and circuit and device concepts are then described that meet the stringent requirements of cellular telephony.     

Rheology,morphology, and mechanical properties of reactive compatibilized polypropylene/polystyrene blends via Friedel–Crafts alkylation reaction in the presence of clay

Attempts were made to study the effect of reactive compatibilization via Friedel–Crafts alkylation reaction, using AlCl₃ as a catalyst, on rheology, morphology, and mechanical properties of polypropylene/polystyrene ( PP/PS) blends in the presence of an organoclay (Cloisite 15A). During the reactive compatibilization process, PS showed much more degradation than that of PP in the presence of AlCl₃. It was found that the effect of generation of PP‐g‐PS copolymer at the interface of the PP/PS blend dominates the effects of degradation of PS and PP phases, which manifested itself by increased toughness as well as uniform dispersion of the dispersed PS particles in the PP matrix. Generation of PP‐g‐PS copolymer was confirmed by using Fourier‐transform infrared analysis. By using rheological and X‐ray diffraction analyses, it was shown that the clay had higher affinity to PS than that of PP. It was also shown that the clay located at the interface of PP and PS phases, leading to increased relaxation time of the deformed PS dispersed particles, exhibited higher dispersion in PP/PS blend, which resulted in higher ductility of the blend. By using the results of rheological studies, it was concluded that during reactive compatibilization of the blend nanocomposite, the clay migrated into the dispersed PS phase, which was confirmed by scanning electron microscopy analysis. It was demonstrated that the rheological studies have a reliable sensitivity to the clay partitioning and phase morphology of the studied blends and blend nanocomposites . J. VINYL ADDIT. TECHNOL., 24:18–26, 2018. © 2015 Society of Plastics Engineers