Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures
In this work MnxCo1−xFe2O4 nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400–4000 cm−1 which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe2O4) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.
pH-Controlled Gating of a Porous Glass Filter by Surface Grafting of Polyelectrolyte Brushes
Poly(acrylic acid) (PAA, a polyelectrolyte brush) was grafted onto a porous glass filter in order to construct a pH-dependent system for the control of liquid permeation. The porous glass filter was treated with octadecyldimethyl(N,N-diethylamino)silane and subjected to glow-discharge treatment to facilitate graft polymerization of the acrylic acid. The surface was analyzed using measurement of the water contact angle, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The surface wettability of the glass filter decreased following silane-coupling treatment and increased following PAA grafting. Water permeation of the PAA-grafted glass filter was pH dependent. The permeation rate was high under low pH conditions and low under high pH conditions. A possible explanation for this permeation profile is that under low pH conditions protonated PAA chains shrink, thereby opening the pores of the filter, and that under high pH conditions dissociated PAA chains are extended to cover the...
Analysis of the oxidation reactions of CaS
The chemical reactions of dense pellets of solid CaS in oxidizing atmospheres were studied by using continuous thermogravimetric analysis and iodimetric titration of SO2 in the off-gas. The experiments covered a temperature range of 1223 to 1853 K, and Ar-O2 mixtures varying from 1 to 100 pct O2. The oxidation of CaS was found to be a complex process involving the formation of CaO and CaSO4. Within the experimental conditions stated, three different processes were observed: 1) Weight loss with the formation of CaO and SO2 which occurred at high temperatures and low partial pressures of O2. 2) Weight gain which occurred at low temperatures and high partial pressures of O2. 3) Combination of a) weight gain with the overall formation of CaSO4 and b) weight loss with the overall oxidation of CaS to CaO and the decomposition of CaSO4 leading to an oscillatory behavior which occurred at intermediate temperatures and intermediate to high partial pressures of O2. The boundaries between these three processes are distinct. The rate of oxidation of the sulfide is limited first by the transport of O2 across the gas boundary layer and later by the diffusion of O2 through the porous reaction product. From these results and the Ca-S-0 stability diagram, it is possible to predict the experimental conditions which will produce processes of weight gain, weight loss and oscillatory behavior.