Development of Ti PVD Films to Limit the Carburization of Metal Powders during SPS Process

Spark plasma sintering technique is used for the fabrication of dense materials with a fine-grained microstructure. In this process, a powder is placed into a graphite mold and a uniaxial pressure is applied by two graphite punches. A graphite foil is inserted between the punches and the powder and between the mold and the powder to ensure good electrical, physical and thermal contact. One of the major drawbacks during sintering of metal powders is the carburization of the powder in contact with the graphite foils. In this study, a PVD coating of titanium was applied on the graphite foils in contact with the metal powder (pure iron). The results are promising, as the investigations show that the application of a Ti PVD film of 1.5 and 1.1 µm thickness is effective to completely avoid the carburization of iron powder. Carbon diffuses inside the PVD film during sintering. In parallel, iron diffusion was revealed inside the Ti coating of 1.5 µm thickness. On the other hand, a Ti PVD film of 0.5 µm thickness provides a protection against carbon diffusion just on the sides in contact with the mold, proving that the coating thickness represents an important parameter to consider.

The Role of the Activator Additives Introduction Method in the Cold Sintering Process of ZnO Ceramics: CSP/SPS Approach

The great prospects for introducing the cold sintering process (CSP) into industry determine the importance of finding approaches to reduce the processing time and mechanical pressure required to obtain dense ceramics using CSP. The introducing zinc acetate into the initial ZnO powder of methods, such as impregnation, thermovapor autoclave treatment (TVT), and direct injection of an aqueous solution into a die followed by cold sintering process using a spark plasma sintering unit, was studied. The effect of the introduction methods on the density and grain size of sintered ceramics was analyzed using SEM, dynamic light scattering, IR spectroscopy, and XRD. The impregnation method provides sintered samples with high relative density (over 0.90) and significant grain growth when sintered at 250 °C with a high heating rate of 100 °C/min, under a uniaxial pressure of 80 MPa in a vacuum, and a short isothermic dwell time (5 min). The TVT and aqueous solution direct injection methods showed lower relative densities (0.87 and 0.76, respectively) of CSP ZnO samples. Finally, the development of ideas about the processes occurring in an aqueous medium with CSP and TVT, which are subject to mechanical pressure, is presented.

Investigation of Structural, Morphological, Resistivity of Novel Electrical Insulator: Industrial Wastes

In the present study, the effect of china clays on the sintering, strength and dielectric behavior of electrical ceramic fly ash/china clay (FA/CC) composite insulator is investigated. The different composition of samples containing different china clay (CC) contents of 10, 20, 30, 40, and 50 % are prepared using the uniaxial pressure technique applying 10 MPa pressure. At 1200 °C, for the composition having 40 wt% china clays, the maximum resistivity is calculated and is 39.5 × 107 Ωm. The composite is highly competence with china clays-based insulators. Further, the prepared composite is also analysed using different characterization technique such as x-ray diffraction, field emission scanning electron microscopy with energy dispersive analysis, fourier transformation infra-red spectroscopy, dielctric, and thermo gravimetric analysis. Frequency dielectric value of the composite is estimated at room temperature in the frequency range of 1-500 kHz at room temperature. According to the resistivity and dielectric properties, the composite has enormous potential for the electrical insulator application.

Increasing the number of topological nodal lines in semimetals via uniaxial pressure

The application of pressure has been demonstrated to induce intriguing phase transitions in topological nodal-line semimetals. In this work we analyze how uniaxial pressure affects the topological character of BaSn$$_2$$ 2 , a Dirac nodal-line semimetal in the absence of spin-orbit coupling. Using calculations based on the density functional theory and a model tight-binding Hamiltonian, we find the emergence of a second nodal line for pressures higher than 4 GPa. We examine the topological features of both phases demonstrating that a nontrivial character is present in both of them. Thus, providing evidence of a topological-to-topological phase transition in which the number of topological nodal lines increases. The orbital overlap increase between Ba $$d_{xz}$$ d xz and $$d_{yz}$$ d yz orbitals and Sn $$p_z$$ p z orbitals and the preservation of crystal symmetries are found to be responsible for the advent of this transition. Furthermore, we pave the way to experimentally test this kind of transition by obtaining a topological relation between the zero-energy modes that arise in each phase when a magnetic field is applied.