Narrow Results

A 12-mm caliber gas gun was used to launch a high-strength steel cylindrical projectile to impact a polyurea-coated B₄C ceramic target plate to investigate the effects of the polyurea coating position and the thickness of the polyurea coating on the protective ability of the ceramic composite target plate, reveal the penetration resistance mechanism of the polyurea-coated B₄C ceramic plate and protection mechanism of polyurea coating. The result showed that the ceramic cone top diameter of the composite target plate coated with polyurea on the front side was 52.4–60.5% lower than that of the uncoated ceramic target plate, and the ceramic cone bottom diameter was 0.2–4% lower than that of the uncoated ceramic target plate. For the same area density, the ceramic target plate coated with polyurea on both sides had the largest percentage of mass remaining and the smallest mass of dislodged ceramic fragments. In addition, composite target plates coated with polyurea on the back side and both sides significantly reduced the head velocity of the post-target debris cloud. The polyurea coating on the front of the target plate utilizes the strain rate effect to dissipate the kinetic energy of the projectile and inhibit the spallation of ceramic fragments toward the front of the target plate. The polyurea coating on the back of the target plate utilizes bulge deformation to dissipate the kinetic energy of the projectile and intercepts the scattering of the post-target debris cloud. The polyurea coating effectively reduces ceramic target plate damage and improves composite target plate integrity level and resistance penetration.

In the present work, comparative study of the dielectric behavior of Mn_0.4Zn_0.6Fe₂O₄ ferrite synthesized with and without H₂O₂ (hydrogen peroxide) has been presented. The dc resistivity has been improved by the citrate precursor method as compared to the ceramic method, and it is further improved by the addition of H₂O₂, which acts as a strong oxidizing agent. We have shown by means of X-ray diffraction that the resulting ferrite is made up of nanocrystallites and the average size of these nanocrystallites–calculated by Scherrer's formula–depends on the polarizer. The average particle size was found to be ~70 nm with H₂O₂ and ~88 nm without H₂O₂. The particle size is further confirmed by scanning electron microscopy. Both the results are found to be in good agreement. The decrease in dielectric constant and dielectric loss factor by addition of oxidizing agent is justified by inverse proportionality between the resistivity and dielectric constant. Possible mechanisms contributing to these processes have been discussed.

Nanostructured alumina ceramic templates have been fabricated by anodizing annealed high-purity aluminium foil. Pore diameter, pore separation and thickness in these alumina ceramics can be controlled using a range of acid electrolytes and anodizing voltage profiles. Thermal development of the structure of these robust and optically clear templates have been compared using XRD, thermal analysis and ²⁷Al MAS NMR techniques, showing that species substituted in the alumina lattice from decomposition of the acid electrolyte play a major role in determining the chemical and physical stability of the ceramic template at elevated temperatures. Deposition of ultrathin palladium films on the surface of these alumina templates creates robust membranes that enable hydrogen separation from mixed gas streams at elevated temperatures. Gas permeability measurements through these membranes as a function of temperature have demonstrated their very high selectivity for hydrogen.

An experimental investigation was carried out to evaluate the fracture pressure and behaviors of ceramic materials for a dome port cover of an air breathing engine. The experiments were performed in a shock tube, which had a working section of 70 mm in diameter and a total length of 6 m in the shock tube. The response pressure transducers were used to measure expansion pressure and reflection pressure of working section near the end edge of the shock tube. Fractured specimens collected from the dump tank were investigated for the fracture phenomenon of ceramics after testing. The fracture pressure increases as a specimen thickness increases, and as the specimen diameter decreases, respectively. The driven gas pressures P₂ obtained from theory and experiment agree well. The reflection wave pressures P₅ agree well comparatively with both results of equation and experiment at low pressure of P₄, but they do not agree well at high pressure of P₄. The fracture phenomena of the plate and dome specimens at the same diameter are broken into small particles in various thicknesses, but the fracture phenomenon of the plate specimen is not broken into the particles as specimen diameter decreases.

The friction and wear of silicon nitride (Si₃N₄) against silicon nitride (Si₃N₄) and zirconia (Y–TZP) and chilled cast iron and Alumina sliding under dry friction at room temperature conditions were investigated with pin-on-disk tribometer at sliding speed of 0.56ms^-1 and normal load of 50N, 80N, respectively. Based on the variety regulation of the wear maps, the wear mechanisms of the two couples were analyzed. Get the result of friction coefficient and maps of wear Rate of the Pin and the Disk. The results of comparing this couple is Si₃N₄/ chilled cast iron < Si₃N₄/ ZrO₂< Si₃N₄/ Si₃N₄< Si₃N₄/ Al₂O₃.

The use of silicon-based ceramics and composites as combustor liners and turbine vanes provides the potential of improving next-generation turbine engine performance, through lower emissions and higher cycle efficiency, relative to today's use of super alloy hot-section components. As a series of research for FOD resistant, a particle erosion wear test was carried out for continuous Pre-SiC fiber-reinforced SiC matrix composites with a new concept of lab. scale fabrication by LPS process. The result shows that aperture (some form of porosity) between fiber and interface has a deleterious effect on erosion resistance. Aperture along the fiber interfaces consequently causes a severe wear in the form of fiber detachment. Wear rate increase proportional as contents of open porosity increases. For nearly full dense composite materials of about 0.5 % porosity, are about 200 % more wear-resistant than about 5 % porous composites. Grain growth and consolidate condition of matrix which directly affects to FOD resistant are also discussed.

Polycrystalline (1-x)YBa₂Cu₃O_7-y + xBaTiO₃–CoFe₂O₄(x = 0.0, 0.2, 0.4, 0.6 wt.%) superconductors were prepared by solid state route. XRD analysis reveals no significant change in "b" parameter and increase in "a" and "c" parameters. SEM micrographs show no change in grain size of the samples. With the increase of BaTiO₃–CoFe₂O₄ (BTO–CFO) addition it has been analyzed that the superconducting transition temperatures (T_c) determined from standard four-probe method was decreased and dropped sharply with higher wt.% addition. Excess conductivity fluctuation analysis using Aslamazov–Larkin model fitting reveals transition of two dominant regions (2D and 3D) above T_c. The decrease in 2D–3D crossover temperature T_LD (Lawerence–Doniach temperature) in the mean field region has been observed as a consequent dominance of 3D region to increase in wt.% in the composite. The increasing value of ρ_wl and ρ₀ and the decreasing trend in the value of zero-resistance critical temperature (T_c0) indicates that the connectivity between grains decreases gradually with the addition of magneto–electric composite BTO–CFO.

Electron paramagnetic resonance (EPR) spectra of 0.01, 0.1 and 1.0 molar percentage (mp) of CuO doped derivatives of layered Na₂Ti₃O₇ ceramic have been reported. The results show that copper substitutes as Cu²⁺ at Ti⁴⁺ octahedral sites. From the dependence of loss tangent (tan δ) and the relative permittivity (ε′) on temperature and frequency, it is concluded that all the derivatives are of polar nature. The relaxation peaks at lower temperatures have been attributed to the presence of different types of dipoles, whereas peaks in the higher temperature region indicate possible ferroelectric phase transition. The dependence of conductivity on temperature show that electron hopping (polaron) conduction exists in a wide span of temperature range. However, the associated interlayer ionic conduction exists in a small temperature range. Interlayer alkali ion hopping mechanism of conduction has been proposed toward higher temperatures. The conductivity versus frequency plots reveal that the polaron conduction plays a prominent role toward the lower temperature side that diminishes with the rise in temperature. The most probable relaxation times for 0.01 and 0.1 mp CuO doped derivatives are almost same but it records an increased value for 1.0 mp doped material. This again attributes to the possible change in the symmetry of copper environment.

The SOFC interconnect materials La${}_{0.75}$Sr${}_{0.25}$Cr${}_{1-x}$O${}_{3-\delta }$$(x=0$–$0.04)$ were prepared using an auto-ignition process. The influences of Cr deficiency on their sintering, thermal expansion and electrical properties were investigated. All the samples were pure perovskite phase after sintering at 1400${}^{\circ }$C for 4 h. The cell volume of La${}_{0.75}$Sr${}_{0.25}$Cr${}_{1-x}$O${}_{3-\delta }$ decreased with increasing Cr deficient content. The relative density of the sintered bulk samples increased from 93.2% $(x=0)$ to a maximum value of 94.7% $(x=0.02)$ and then decreased to 87.7% $(x=0.04)$. The thermal expansion coefficients of the sintered bulk samples were in the range of $10.60$–$10.98\times 10^{-6}{\mathrm{\text{K}}}^{-1}$ (30–1000${}^{\circ }$C), which are compatible with that of YSZ. Among the investigated samples, the sample with 0.02 Cr deficiency had a maximum conductivity of 40.4 Scm${}^{-1}$ and the lowest Seebeck coefficient of 154.8 $\mu$VK${}^{-1}$ at 850${}^{\circ }$C in pure He. The experimental results indicate that La${}_{0.75}$Sr${}_{0.25}$Cr${}_{0.98}$O${}_{3-\delta }$ has the best properties and is much suitable for SOFC interconnect material application.

The ceramics with the composition of $x{\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$–$(1-x){\mathrm{\text{Ba}}}_{0.66}{\mathrm{\text{Mg}}}_{0.04}{\mathrm{\text{Sr}}}_{0.3}{\mathrm{\text{TiO}}}_3$ (NBT–BMST) in which $x$ = 0.2, 0.3, 0.4 and 0.5 were prepared successfully by the solid-state reaction method. The effects of NBT-doping on phase structure, morphology, temperature stability and dielectric properties had been investigated in detail. The XRD results show that the composites are composed of tetragonal perovskite. The phase structure of NBT–BMST is observed by scanning electron microscopy. The dielectric constant of $0.3{\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$–$0.7{\mathrm{\text{Ba}}}_{0.66}{\mathrm{\text{Mg}}}_{0.04}{\mathrm{\text{Sr}}}_{0.3}{\mathrm{\text{TiO}}}_3$ ceramic is $\sim$4100, the temperature coefficients of capacitance are −15%, 15% and 22% at −55${}^{\circ }$C, 60${}^{\circ }$C and 200${}^{\circ }$C, respectively. And the dielectric loss is less than 0.13, which is obviously superior to other compositions. The results of this work showed that the component of $0.3{\mathrm{\text{Na}}}_{0.5}{\mathrm{\text{Bi}}}_{0.5}{\mathrm{\text{TiO}}}_3$–$0.7{\mathrm{\text{Ba}}}_{0.66}{\mathrm{\text{Mg}}}_{0.04}{\mathrm{\text{Sr}}}_{0.3}{\mathrm{\text{TiO}}}_3$ is a promising candidate to high-temperature stable materials.

Microstructures, electrical transport and magnetic properties of Sr${}_2$Ti${}_{1-x}$Co${}_x$O${}_4(0\le x\le 0.3)$ ceramics are investigated. With Co doping, the Sr${}_2$Ti${}_{1-x}$Co${}_x$O${}_4$ ceramics remain tetragonal structure while the grain size is decreased with doping. Magnetic moment is enhanced with Co doping and ferromagnetism is observed at low temperatures for Co-doped Sr${}_2$TiO${}_4$. The Sr${}_2$Ti${}_{0.9}$Co${}_{0.1}$O${}_4$ and Sr${}_2$Ti${}_{0.7}$Co${}_{0.3}$O${}_4$ show semiconductor-like transport properties, which can be well fitted by Mott variable range hopping model. The results will provide an effective route to synthesize Sr${}_2$Ti${}_{1-x}$Co${}_x$O${}_4$ ceramics as well as to investigate the physical properties.

The drilling of film cooling holes on gas turbine blades made out of ceramic-coated superalloy improves the efficiency of the gas turbine and prolongs the life of the turbine blade. The purpose of this study was to investigate the effects of different stand-off distances (SODs) on abrasive water jet (AWJ)-pierced holes, in which the machining time, entry and exit hole diameters, overcut, hole taper, and surface morphology were studied. In this study, the water jet pressure (WJP) of 275MPa, piercing angle of $90^{\circ }$, dwell time of 0.2s, and abrasive flow rates (AFRs) of 350g/min and 400g/min were considered for the AWJ piercing operations. The entry and exit hole diameters and overcut linearly increased with an increase of SOD with different abrasive flow rates. And hole taper was observed at the coating and substrate sections in which it decreased with an increase of SOD up to 2mm, and a further increase of SOD increased the hole taper. Besides, the drilled holes were found to have an absence of delamination, cracks, and thermal defects. It was also noted that there is a transformation from a brittle to a ductile mode of erosion that may occur in the high-erosion kinetic energy impact region in the YSZ material section. Based on the experimental results, it is confirmed that SOD of 2mm became an influencing factor in AWJ for piercing quality holes in the YSZ-coated superalloy.

The Raman spectroscopy can be used as a didactic technique in the study of the thermal expansion of Grüneisen parameter and anharmonic behavior of materials. Here, we present exemplary, the lead titanate doped with lanthanum (PLT). However, this method can be used to study various materials. The ferroelectric ceramics have been one of the most studied compounds in the literature both in obtaining the same, as in behavior of chemical and physical properties. The structural PbTiO₃ phase may change either by the application of pressure, temperature or concentration, thereby allowing a study of behavior anharmonic of the material [M. R. Joya, J. Barba and P. S. Pizani, J. Appl. Phys.113 (2013) 013512]. This paper gives a brief review of the effect of temperature and pressure on Raman spectra.

We have previously described the enhancement of piezoelectricity in low crystallinity Bi${}_{12}$TiO${}_{20}$–BaTiO₃ (BTO-BT) nanocomposites. This poses a question regarding the effect of the crystallinity on piezoelectricity. Here, the variation of crystallinity and structure that was developed along the temperature gradient was confirmed. The magnitude of the piezoelectric constant was found to have great relationship with the crystallinity and distortion of BiO₅ polyhedra of amorphous Bi${}_{12}$TiO${}_{20}$. The highest piezoelectric constant of 13pC/N was obtained together with the lowest crystallinity and highest degree of distortion of BiO₅ polyhedra. These results highlight the key role of the amorphous phase and further confirm the importance of distortion of BiO₅ polyhedra in influencing the piezoelectricity. In this view, one may also expect that macroscopic polarity could be improved by increasing the amorphous content and the degree distortion of the BiO₅ bonding units in the system.

Lead–free Sr${}_{1-x}$Ca_xTiO₃ ($x=0,0.4$) ceramics were synthesized via a solid state reaction technique at room temperature. The effects of ionic substitutions in A-sites between strontium and calcium on the structural and dielectric properties were investigated. XRD technique was used to identify the crystal structure and to demonstrate the phase purity. SEM observations have shown homogeneous morphologies for all samples. Dielectric measurements were investigated for a wide range of frequency (100Hz–1GHz) and temperature (25${}^{\circ }$C–250${}^{\circ }$C). Strontium substitution by calcium has not only led to a decrease in the dielectric permittivity value, but also to the loss tangent value by a considerable factor. Interesting values of the quality factor and the quite constant value ${\epsilon }^{\prime }\sim 200$ in extended frequency and temperature ranges show that SCT ceramic could be a real candidate for the development of monolithic ceramic capacitors dedicated to high-frequency lead-free components and/or to extremely high-temperature environments.

Ultrafine powder of CaCu_2.80Zn_0.20Ti₄O₁₂ ceramic was prepared using a novel semi-wet method. DTA/TG analysis of dry powder gives pre-information about formation of final product around 800°C. The formation of single phase was confirmed by X-ray diffraction analysis. The average particle size of sintered powder of the ceramic obtained from XRD and Transmission electron microscopy was found 59 nm and 102 nm, respectively. Energy Dispersive X-ray studies confirm the stoichiometry of the synthesized ceramic. Dielectric constant of the ceramic was found to be 2617 at room temperature at 1 kHz.

CaCu₃Ti₄O₁₂ (CCTO) ceramics which has perovskite structure gained considerable attention due to its giant permittivity. But it has high tan δ (0.1 at 1 kHz) at room temperature, which needs to be minimized to the level of practical applications. Hence, TeO₂ which is a good glass former has been deliberately added to CCTO nanoceramic (derived from the oxalate precursor route) to explore the possibility of reducing the dielectric loss while maintaining the high permittivity. The structural, morphological and dielectric properties of the pure CCTO and TeO₂ added ceramics were studied using X-ray diffraction, Scanning Electron Microscope along with Energy Dispersive X-ray Analysis (EDX), spectroscopy and Impedance analyzer. For the 2.0 wt.% TeO₂ added ceramics, there is a remarkable difference in the microstructural features as compared to that of pure CCTO ceramics. This sample exhibited permittivity values as high as 7387 at 10 KHz and low dielectric loss value of 0.037 at 10 kHz, which can be exploited for the high frequency capacitors application.

Yttrium Copper Titanate (Y_2/3Cu₃Ti₄O₁₂) nanoceramic is structurally analogous to CaCu₃Ti₄O₁₂ (CCTO). X-ray diffraction (XRD) of Y_2/3Cu₃Ti₄O₁₂ (YCTO) shows the presence of all normal peaks of CCTO. SEM micrograph exhibits the presence of bimodal grains of size ranging from 1–2 μm. Bright field TEM image clearly displays nanocrystalline particle which is supported by presence of a few clear rings in the corresponding selected area electron diffraction (SAED) pattern. It exhibits a high value of dielectric constant (ε′ = 8434) at room temperature and 100 Hz frequency with characteristic relaxation peaks. Impedance and modulus studies revealed the presence of temperature-dependent Maxwell–Wagner type of relaxation in the ceramic.

The desirable characteristics of Ba_6-3xNd_8+2xTi₁₈O₅₄ include high dielectric constant, low loss tangent, and high quality factor developed a new field for electronic applications. The microwave dielectric properties of Ba_6-3xNd_8+2xTi₁₈O₅₄, with x = 0.15 ceramics at different sintering temperatures (600–1300°C) were investigated. The phenomenon of polarization produced by the applied electric field was studied. The dielectric properties with respect to frequency from 1 MHz to 1.5 GHz were measured using Impedance Analyzer, and the results were compared and analyzed. The highest dielectric permittivity and lowest loss factor were defined among the samples. The complex dielectric modulus was evaluated from the measured parameters of dielectric measurement in the same frequency range, and used to differentiate the contribution of grain and grain boundary.

The polycrystalline ceramic Pb${}_{0.5}$Ba${}_{1.5}$BiVO₆ manifesting the complex double perovskite structure was tailored by the conventional solid state route at a moderate temperature. Qualitative phase analysis and formation of the ceramic were affirmed by XRD analysis. The X-ray powder diffraction pattern of the compound explored at room temperature affirms the single phase formation with double perovskite structure exhibiting rhombohedral phase. Microstructural analysis of the studied compound procured from the Scanning Electron Microscope (SEM) validates the formation of dense microstructures and nonuniformly distributed grains with minimal voids. Compositional analysis was shaped through the Electron Diffraction Spectroscopy (EDS) confirming the absence of contamination of any other metals apart from the mentioned ones. Dielectric (Cr and $tan\delta$) parameters of the compound were studied using the LCR analyzer at different temperatures and wide range of frequencies. The polarization and dielectric study affirms the presence of ferroelectricity in the material with transition temperature much above the room temperature. The tangent dielectric loss of this sample being almost minimal at room temperature attributes it to find applications in different grounds of electronics. Optical equities of the ceramic were further analyzed by the RAMAN, FTIR, UV–Vis and Photoluminescence spectroscopy.