The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. The MCE properties have been compiled and correlations have been made comparing the behaviours of the different families of magnetic materials which exhibit large or unusual MCE values. These families include: the lanthanide (R) Laves phases (RM2, where M = Al, Co and Ni), Gd5(Si1−xGex)4 ,M n(As1−xSbx), MnFe(P1−xAsx), La(Fe13−xSix) and their hydrides and the manganites (R1−xMxMnO3, where R = lanthanide and M = Ca, Sr and Ba). The potential for use of these materials in magnetic refrigeration is discussed, including a comparison with Gd as a near room temperature active magnetic regenerator material. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0034-4885/68/6/R04/pdf

Recent developments in magnetocaloric materials

Atmospheric acid leaching of nickel laterites review: Part I. Sulphuric acid technologies

Storing hydrogen in materials is based on the observation that metals can reversibly absorb hydrogen. However, the practical application of such a finding is found to be rather challenging especially for vehicular applications. The ideal material should reversibly store a significant amount of hydrogen under moderate conditions of pressures and temperatures. To date, such a material does not exist, and the high expectations of achieving the scientific discovery of a suitable material simultaneously with engineering innovations are out of reach. Of course, major breakthroughs have been achieved in the field, but the most promising materials still bind hydrogen too strongly and often suffer from poor hydrogen kinetics and/or lack of reversibility. Clearly, new approaches have to be explored, and the knowledge gained with high-energy ball milling needs to be exploited, i.e. size does matter! Herein, progress made towards the practical use of magnesium as a hydrogen store and the barriers still remaining are reviewed. In this context, the new approach of tailoring the properties of metal hydrides through size restriction at the nanoscale is discussed. Such an approach already shows great promise in leading to further breakthroughs because both thermodynamics and kinetics can be effectively controlled at molecular levels.

Hydrogen in magnesium: new perspectives toward functional stores

http://digital.csic.es/bitstream/10261/78672/1/Kinetics%20of%20redox%20reactions%20of.....2011.pdf

Kinetics of redox reactions of ilmenite for chemical-looping combustion

Thermodynamic investigation of the magnesium–hydrogen system

Thermal conductivities of dense pure hematite, magnetite and wustite measured using the laser flash method as reference value have been summarized in the form of an empirical equation k=1/(AT+B). Wustite shows an almost constant and the relatively low thermal conductivity due to the lattice imperfection. Thermal resistivities, 1/k, of three iron oxides appear to change linearly as a function of temperature up to the Tammann temperature.Effective thermal conductivities of fired, nonfired pellets and sinter, reduced into magnetite, wustite and metallic iron by CO-CO2 or H2 gas, have also been systematically measured in the temperature range from room temperature to 1273 K. The porosity of samples was found to change from 20 to 62% by the reduction from hematite to metallic iron. Measured effective thermal conductivity values of these iron ore agglomerates are remarkably smaller than those of dense materials due to the existence of pore. Effective thermal conductivities of metallic iron and hematite strongly depend on temperature. There is no significant difference in the effective thermal conductivities of reduced samples at the same reduction degree.The measured effective thermal conductivity values have been well-explained by the modified unit cell model originally proposed by Luikov when considering the structure composed of core part and connecting part in the solid phase. This model also clearly identify the distinction of solid structure in samples originated from the difference in preparation and reduction degree.

Measurement and Modeling of Thermal Conductivity for Dense Iron Oxide and Porous Iron Ore Agglomerates in Stepwise Reduction

https://www.jstage.jst.go.jp/article/isijinternational1989/31/5/31_5_434/_pdf

Pressure Loss and Hold-up Powders for Gas-Powder Two Phase Flow in Packed Beds

/pdf/reduction-kinetics-of-cement-bonded-natural-ilmenite-pellets-pd1zjv6me7.pdf

Reduction kinetics of cement-bonded natural ilmenite pellets with hydrogen

https://www.jstage.jst.go.jp/article/isijinternational1966/26/9/26_9_765/_pdf

Operation and simulation of pressurized shaft furnace for direct reduction.

The laterite ore with low nickel content deposits in Indonesia can be expected to be an alternative raw material of iron making due to its high iron content. One of the required processes is the separation of nickel and cobalt from the laterite ore by leaching it with H 2 SO 4 at the atmospheric condition. The sample containing 50.88 % iron, 0.03 % cobalt and 0.30% nickel was selectively reduced with CO/C0 2 mixed gas to obtain metallic nickel and cobalt, as well as magnetite from hematite. Accordingly, in the leaching process metallic nickel and cobalt will be dissolved by controlling the iron dissolving. The effects of various parameters have been examined. These condition include leaching time, temperature (303-343 K), H 2 S0 4 concentration (0.005-1.0) mol/l, as well as extraction rate of nickel. The result of the analysis indicated that the influence of selective reduction could speed up the nickel extraction and obstructed the iron dissolution. The extraction rate of nickel was very high for small particle and slower for larger size. The optimal condition of the test was obtained at the leaching temperature of 343 K, 0.05 mol/l H 2 S0 4 with a sample lower than 4.0 g/l. In 60 min after the test, about 93 mass% of nickel was extracted from the sample smaller than 44 μm. The nickel extraction would be higher by adding the leaching time. The rate of extraction was chemically controlled and the apparent activation energy was 42.2 kJ/mol. At the end of the leaching process, there was residual solid rich-magnetite and minimal nickel.

Reijiro Takahashi

Papers

Measurement and Modeling of Thermal Conductivity for Dense Iron Oxide and Porous Iron Ore Agglomerates in Stepwise Reduction

Pressure Loss and Hold-up Powders for Gas-Powder Two Phase Flow in Packed Beds

Reduction kinetics of cement-bonded natural ilmenite pellets with hydrogen

Operation and simulation of pressurized shaft furnace for direct reduction.

Recovery of Nickel from Selectively Reduced Laterite Ore by Sulphuric Acid Leaching