Ultrafast Sintering Research Articles

Low field magnetoresistance of La0.7Ca0.3MnO3 ceramics fabricated by fast sintering process

Bulk perovskite manganese oxide La0.7Ca0.3MnO3 was prepared in 2 min by a novel densification method based on self-propagating reactions. The influence of temperature on the structure and transport properties has been investigated. The structures of specimens were analyzed using the Rietveld refinement technique and the specimens are observed to have orthorhombic structure with Pbnm space group. Moreover, study of magnetic transport properties reveals that the variation of the magnetization values and the Curie temperature is attributed to grain size and oxygen deficiency concentration at different sintering temperatures. In the plot of resistivity as a function of temperature, double metal-insulator transitions accompanied with a single ferromagnetic transition are observed, which is explained on the basis of inhomogeneous oxygen generated by the nonuniform temperature field. The enhanced low-field magnetoresistance (LFMR) is achieved, suggesting that it is an efficient way to obtain LFMR of La0.7Ca0.3MnO3 specimens. We explained the enhanced low field magnetoresistance by the spin-polarized tunneling model on the relaxation grain boundary induced by this ultra fast sintering process.

High Efficient Synthesis of Iron-based Superconductors

We have performed systematic investigations aimed at high efficient synthesis of the 1111 family iron-based superconductors. By using meta-stable reactive starting materials of Ln As and FeO, assisted by mechanical alloying and fast heating, high purity samples with T c onset greater than 50K can be made with sintering temperatures between 1433K-1073K, and sintering time from 20 min to 40 h. High purity phase with sintering temperature as low as 973K was demonstrated successfully although T c onset fall below 50K and weak grain boundary suppressed greatly the zero resistance temperature. Ultra fast microwave sintering brings the sintering time further down to 5 min. Samples prepared by the above high efficient methods typically posses submicron grain and very high upper critical field, indicating very high pinning power. Besides offering cost advantages, the developed methods may play important roles in the exploit of novel superconductors.

Spark Plasma Sintering of Diamond Binderless WC Composites

A new method was developed to fully consolidate binderless tungsten carbide and diamond powders by means of spark plasma sintering (SPS) in current‐control mode (CCm). Below 900°C, the 2 cm diameter sample was slowly heated by a dc current of 1000 A. Above 900°C the imposed current was suddenly raised to 4000 A. The combination of the relatively high heating rate of 2000°C/min and the relatively short holding time of 1.5 min (above 1300°C) was successful to fabricate fully dense binderless WC/diamond composite. No graphitization of diamond was detected after ultrafast sintering as confirmed by optical and SEM microstructure observations, XRD and Raman analysis. The sample showed very high wear resistance in comparison to fully dense monolithic binderless WC compacts. The developed method, unlike previously published works, did not require any diamond coating to prevent diamond graphitization.

Nanostructure Evolution of ZnO in Ultra-fast Microwave Sintering

Grain growth is inevitable in the sintering of pure nanopowder zinc oxide. Sintering depend on diffusion kinetics, thus this growth could be controlled by ultra-fast sintering techniques, as microwave sintering. The purpose of this work was to investigate the nanostructural evolution of zinc oxide nanopowder compacts (average grain size of 80 nm) subjected to ultra-rapid microwave sintering at a constant holding temperature of 900°C, applying different heating rates and temperature holding times. Fine dense microstructures were obtained, with controlled grain growth (grain size from 200 to 450nm at high heating rate) when compared to those obtained by conventional sintering (grain size around 1.13µm), which leads to excessively large average final grain sizes.

C233 Comparison of ultra-fast microwave sintering and conventional thermal sintering in manufacturing of anode support solid oxide fuel cell

C233 Comparison of ultra-fast microwave sintering and conventional thermal sintering in manufacturing of anode support solid oxide fuel cell

The Use of Near Infra Red as a Rapid Heat Treatment Process in the Manufacture of Metal-based Dye-sensitized Solar Cells

AbstractA near infrared heating method is presented which directly heats metal substrates to very high temperatures within seconds. The technique is used to heat 1mm thick titanium and stainless steel metal coupons onto which 1 cm2commercial TiO2pastes have been deposited within 12-25 seconds giving assembled dye sensitized solar cell efficiencies which are equivalent to cells prepared using a convection oven for 1800 seconds. The near infrared method is applicable to different paste thicknesses and paste types as well as different metal substrates. Near infrared sintering for the shortest times 12.5 seconds yielded cells with the highest efficiency compared to convection oven prepared samples. This ultrafast heating seems to drive off binder very effectively and lead to rapid sintering. Ultrafast sintering allows peak metal temperatures of 500-800 °C to be achieved without the massive losses in cell efficiency observed with the conventional heat treatment at temperatures over 600 ◦C.

Ultrafast sintering of La–Ca–Mn–O bulk ceramics by thermal plasma assisted heating

Abstract This paper reports a novel and low-cost thermal plasma assisted heating method for ultrafast sintering of rare-earth-based perovskite manganites. An indigenously designed DC thermal plasma reactor has been used to sinter La 0.67 Ca 0.33 MnO 3 (LCMO) colossal magnetoresistance (CMR) material. Highly dense (96% of theoretical density) crystalline bulk LCMO ceramics were prepared within 2.5 min of sintering time. Plasma-sintered LCMO bulk ceramics showed enhanced T C (272 K), which is close to T IM (275 K) as compared to the conventional sintered LCMO [J.M. De Teresa, M.R. Ibarra, J. Blasco, J. Garcia, C. Marquina, P.A. Algarabel, Z. Arnold, K. Kamenev, C. Ritter, R. von Helmolt, Phys. Rev. B 54 (1996) 1187] sample. We observe that the thermal plasma heating process offers a unique advantage for quick physical densification and hence sintering within a few minutes.