Reduction Expansion Synthesis of Sintered Metal

Abstract

Described herein is a novel method, Reduction Expansion Synthesis-Sintered Metal (RES-SM), to create a sintered metal body of a designed shape at ambient pressure, hundreds of degrees below the metal melting temperature. The precursor to the metal part is a mixture of metal oxide particles and activated metal particles, and in this study specifically nickel oxide and activated nickel metal particles. It is postulated that the metal oxide component is reduced via exposure to chemical radical species produced via thermal decomposition of urea or other organic compounds. In the study performed, the highest temperature required was 950 °C, the longest duration of high temperature treatment was 1200 s, and in all cases, the atmosphere was inert gas at ambient pressure. As discovered using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD), the metal that forms via the RES process presents necks of completely reduced metal between existing metal particles. The ‘as produced’ parts are similar in properties to ‘brown’ metal parts created using more standard methods and require ‘post processing’ to full densify. Parts treated by hot isostatic pressing show fully self-supporting, robust structures, with hardness values like others reported in literature for traditional fabrication methods. This novel method uses affordable and environmentally friendly precursors to join metallic parts at moderate temperatures, produces fully reduced metals in a very short time and has potential to make many parts simultaneously in a standard laboratory furnace.

Creating Strong Titanium/Titanium Hydride Brown Bodies at Ambient Pressure and Moderate Temperatures

“…The SEM images support the proposed model of HEAT; however, the evidence is subtle, for example there is little evidence of extensive 'neck' formation between particles. This contrasts with the less subtle SEM evidence, including extensive necking, observed in earlier RES-SM studies [6,15] of solid, designed shapes. Chief among the differences observed between HEAT and control samples is the smoother profile and edges of the particles formed in Ar/H 2 mixtures, the identification of direction joining of some particles, and the appearance, only for the Ar/H 2 -treated samples, of structures associated with multiple phases.…”

“…The development of the HEAT process represents a further evolution of reduction expansion synthesis (RES) [5][6][7][8][9][10][11][12][13][14][15][16], a set of technologies based on a "reduction" chemistry introduced by our team. RES chemistry in all cases starts with a primary step: thermal decomposition of a "reducing" solid, such as urea, under inert gas.…”

“…This primary step chemistry creates volatile reducing species that can be harnessed to create a wide range of products based on designed secondary reactions. Processes developed on the basis of the RES concept include the batch generation of sub-micron metal and metal alloy particles [7][8][9], metal thin film formation [13,14], metal part formation from mixtures of metal and metal oxide particles [6,15,16], graphene from graphite oxide [10], even stable tin/carbon anodes for batteries [11].…”

“…In all "metal" variants of RES [6][7][8][9][13][14][15][16] there is also a key secondary step: radicals, produced in the first step, interact with oxygen atoms in metal oxides or hydroxides to create products such as CO 2 and H 2 O that subsequently leave the process reactor as a gas. The heavier metal atoms/metallic clusters produced via the removal of oxygen are not volatile and do not leave the reactor.…”

Kinetic Assessment of the Dry Reforming of Methane over a Ni–La2O3Catalyst

“…The equivalence in these crystallite sizes can be related to the fact that 60 mol % out of the total amount of Ni in the catalyst was due to the reduction of the NiO present in the precursor. This also suggests that sintering of the NiO phase did not occur during the reduction treatment at 1023 K. 45,46 The temperature-programmed reduction (TPR) profile of the precursor is shown in Figure 3A. The profile displayed five reduction peaks.…”