Detection of high-valent iron species in alloyed oxidic cobaltates for catalysing the oxygen evolution reaction

Iron alloying of oxidic cobaltate catalysts results in catalytic activity for oxygen evolution on par with Ni-Fe oxides in base but at much higher alloying compositions. Zero-field 57Fe Mössbauer spectroscopy and X-ray absorption spectroscopy (XAS) are able to clearly identify Fe4+ in mixed-metal Co-Fe oxides. The highest Fe4+ population is obtained in the 40–60% Fe alloying range, and XAS identifies the ion residing in an octahedral oxide ligand field. The oxygen evolution reaction (OER) activity, as reflected in Tafel analysis of CoFeOx films in 1 M KOH, tracks the absolute concentration of Fe4+. The results reported herein suggest an important role for the formation of the Fe4+ redox state in activating cobaltate OER catalysts at high iron loadings.

Control of Retained Delta Ferrite in Type 410 Stainless Steel

Type 410 stainless steel is used in petro-chemical refineries for its high resistance to halide stress corrosion cracking, sulfide corrosion cracking, and sulfur attack at elevated temperatures. Along with its adequate corrosion resistance 410SS also exhibits low cost and hardenability making it an ideal material for hydro-processing applications. Problems related to meeting toughness and hardness code requirements within the weld metal and heat effected zone (HAZ) have been experienced during fabrication of 410SS welded components. The loss of toughness has been related to excessive amounts of delta ferrite in the weld metal and HAZ. The objective of this study was to quantify the effect of cooling rate and alloying compositions within ASTM and AWS specifications for 410SS on delta ferrite formation. C, Cr, Ni, and Mo, were used as factors in a model-based design of experiment (DOE) within CALPHAD based software DICTRA™ to simulate the effects of composition and cooling rate on delta ferrite formation. Based on the DOE results, a predictive model for quantification of retained delta ferrite in 410SS welds was developed along with evidence for cooling rate effect on retained delta ferrite. Optical metallography was also used to demonstrate possible ferrite content within the 410 composition range.

The Alloying and Aging Effects on the Wettability and Intermetallic Bonding of the Sn-Zn-Cu-Bi Soldering Alloy on a Cu Substrate

The soldered bonding between the Sn-Zn-Cu-Bi system and a Cu substrate was studied and reported herein. The alloying compositions were varied to investigate the effects of Zn, Cu, Bi contents on the solders’ melting temperature (Tm), microstructures, wettability and the intermetallic-compound (IMC) bonding with a Cu substrate. The Sn-7Zn and Sn-9Zn exhibited low Tm (198 °C), but poor wettability on the Cu substrates. Both Cu and Bi additions significantly improved the solder wettability. However, the Tm of the Sn-Zn-Cu series increased sharply to about 225 °C by the addition of 4-wt% Cu. The addition of 3-wt% Bi lowered Tm of the Sn-Zn-Cu alloys by 5 °C. The thickness of the IMC layers between solder and substrate was maximum for Sn-9Zn and significantly decreased with the Cu addition. With the addition of Bi to Sn-Zn-Cu, the IMC thickness increased. The aging of 150 °C for 150 hours minimally affected the IMC-bonding thicknesses of most samples; however, micro crack could be observed along the aged IMC layers.