Effect of pH on the Crystallization of Homogeneously Precipitated Nanosized PZT Powder

Nanosized lead zirconate titanate (PZT) powder with Zr:Ti ratio in the morphotropic phase boundary region was synthesized by homogeneous precipitation of metal ions. The powder precipitated at 90°C and at pH 6.7 resulted single-phase perovskite lead zirconate titanate powder when calcined at 550°C and above for 4 hours in air. The solution pH and the precipitation temperature strongly affect the composition of the calcined powder. The results obtained by structural characterization of homogeneously precipitated powder were compared with that obtained from the conventional precipitation method using ammonia in terms of crystallization, homogeneity, and microstructure. The homogeneously precipitated powder showed smaller particle size, minimum agglomeration and uniform shape on calcination and annealing. Powdered samples that precipitated by homogeneous precipitation crystallized directly to perovskite PZT, without any intermediate pyrochlore phase formation. In contrast, the NH₃ precipitated powder converted to perovskite PZT via metastable pyrochlore and it showed phase segregation upon annealing at higher temperatures. The reaction kinetics has been studied by X-ray diffraction, differential thermal analysis, and differential scanning calorimetry.     

Electron microscopy of shock deformation in alumina

Shock recovered samples of a coarse grain (10 μm), high density (>99.9% theoretical) alumina from asymmetric impact tests conducted at 6.5 GPa (e.g. 3.2 times its Hugoniot Elastic Limit) in a single stage gas gun and characterized by X-ray diffractometry, scanning and field emission scanning electron microscopy, and transmission electron microscopy showed prolific presence of reduced crystallite size, higher average microstrain, grain localized micro/nano-scale deformations, micro-cleavages, grain-boundary microcracks, micro-wing crack formation, extensive shear induced deformations and fractures localized at grains, grain boundaries and triple grain junctions, grain localized entanglement of dislocations and their pile up impeded at grain boundaries. A new qualitative model based on micro-shear and micro-twist induced deformation and fracture in single and/or multiple planes in suitably oriented grain and/or grain assembly was developed to explain the experimentally observed damage evolution process.     

Homogeneous and polymorphic transformations to ordered intermetallics in nanostructured Au–Cu multilayer thin films

Journal of Materials Science - Atomic arrangements in the nanostructured grains and interfaces of thermally evaporated Au/Cu multilayer thin films on polycrystalline Si substrate have been explored...     

Nanohardness of Sintered and Shock Deformed Alumina

To understand how high–strain rate, flyer-plate impact affects the nanohardness of a coarse (~10 μm) grain, high-density (~3.978 gm cc^–1) alumina, load controlled nanoindentation experiments were conducted with a Berkovich indenter on as-sintered disks and shock-recovered alumina fragments obtained from an earlier flyer-plate shock impact study. The nanohardness of the shock-recovered alumina was much lower than that of the as-sintered alumina. The indentation size effect was severe in the shock-recovered alumina but only mild in the as-sintered alumina. Extensive additional characterization by field emission scanning electron microscopy, transmission electron microscopy, and analysis of the experimental load depth data were used to provide a new explanation for the presence of strong indentation size effect in the shock-recovered alumina. Finally, a qualitative model was proposed to provide a rationale for the whole scenario of nanoindentation responses in the as-sintered and shock-recovered alumina ceramics.     

Ultrafine PZT based ceramics synthesized by auto-ignition of metal–polymer gel: Enhanced sinterablity and higher remnant polarization

PbZr_0.53Ti_0.47O₃ (PZT) nanoparticles within the size range 1–8 nm were synthesized by auto-ignition of metal–polymer gel in single step without any calcination. The auto ignitable gel was obtained by adjustment of nitrate/polymer molar ratio. The amount of the carbonaceous residue in the as-ignited powder was negligible. The as-ignited ultrafine PZT powders showed excellent sinterability and were sintered directly to about 96% of the theoretical density at 1000 °C without any further calcination. Dielectric loss of the sintered PZT sample at room temperature was very low and increased very slowly up to 300 °C, which is advantageous for dielectric application point of view. The measured value of remnant polarization of the 1100 °C-sintered sample was 54.2 μC/cm², which is considerably higher than the value reported in the literature for the same composition.     

Effect of heat treatment on morphology and thermal decomposition kinetics of multiwalled carbon nanotubes

High temperature treatment in inert atmosphere proved to be an effective way to improve high temperature stability of MWNTs in ambient condition. TEM analysis of heat-treated MWNTs confirmed successful removal of impurities and formation of ordered graphene layers and internal bamboo structure. TG–DTG curves indicated that decomposition range and rate of as-received MWNTs were narrow and notably higher, respectively, than heat-treated MWNTs mainly due to presence of impurities like metal nanoparticles in the former. Non-isothermal kinetic analysis revealed that the rate determining mechanism for as-received MWNTs was random nucleation and growth of active species. However, for heat-treated MWNTs, rate controlling mechanism was chemical reaction. Higher activation energies (～203 kJ mol^?1 and 280 kJ mol^?1) and reaction orders (3 and 4) of MWNTs heat-treated at 1200 °C and 1800 °C in inert, respectively, indicated delayed thermal decomposition than as-received MWNTs (E_a ≈ 178 kJ mol^?1; n = 1) even in oxidative atmosphere.     

Spark Plasma Sintering of Magnesia-Doped Alumina with High Hardness and Fracture Toughness

The effect of grain size of magnesia and its content as well as spark plasma sintering conditions on the density, grain size, strength, hardness, and toughness of alumina was investigated. Spark plasma sintering conditions were optimized at 1150°C/5 min/175°C/min. Addition of 100 nm magnesia gave higher density levels (99.5%), while better strength (600 MPa), hardness (25 GPa), and fracture toughness (4.5 MPa·m^1/2) were obtained with 15 nm magnesia. The good strength and hardness is attributed to the submicrometer grain size of the matrix, and the improved toughness to the presence of Mg-rich nanoparticles and nanopores at grain boundaries.     

Laser-induced self-propagating reaction synthesis of amorphous-based composite Zr-Al-Ni-Cu alloys

Strong exothermic reaction due to large negative enthalpy of mixing can occur among major components of bulk metallic glass forming alloy systems. Based on this idea, we developed a new technique to fabricate amorphous-based composite materials using Laser-induced Self-propagating Reaction Synthesis (LSRS). The LSRS of the Zr₅₅Al₁₀Ni₅Cu₃₀ alloy shows that the products mainly consist of the amorphous, Zr₃Al₂ and Zr₂Cu phases. Hardness and wear resistance of the produced composite alloys are measured and are compared to the single amorphous phase alloy of the same composition.     

钛板表面激光熔覆锆基合金涂层的组织结构

利用激光熔覆技术在Ti板上制备了非晶复合涂层,利用X射线衍射仪、能谱仪、扫描电镜和透射电子显微镜对熔覆层和结合区的组织结构进行了表征。研究发现,熔覆层组织主要由非晶、Zr的金属间化合物、氧化物及局部纳米晶组成。基体与熔覆层结合区由Ti的柱状晶和α(Ti/Zr)固溶体所构成,保证了基体与熔覆层之间有良好的冶金结合。