Eddy current and total power loss separation in the iron–phosphate–polyepoxy soft magnetic composites

Raman spectroscopy has in recent years been used by several research groups to study the stresses that develop in thermally grown oxide layers, particularly Cr2O3, at elevated temperatures between 700 and 900 °C. This paper presents an overview of the Raman technique and describes quantitatively the factors that, in addition to stress, affect the Raman peak shifts, including temperature, non-stoichiometry, impurities, stresses and instrumental calibration. It also summarizes and reviews published work in this area and in doing so, discusses the pros and cons of this technique for oxidation stress measurements.

Limitations and Advantages of Raman Spectroscopy for the Determination of Oxidation Stresses

Carbonyl iron powders were coated with iron phosphate using phosphating method and boehmite (γ-AlOOH) or silicon hydroxide (Si(OH)4) nanoparticles derived from the hydrolysis of tri-sec-butoxide (Al(OC4H9)3) or tetramethylsilane (Si(OCH3)4) using sol–gel method. The coated powders were dried and calcined at 400 °C for 3 h in air. Cross-section morphology of coated carbonyl iron powders were investigated by scanning electron microscopy energy dispersive X-ray analysis. Coated Fe micro-particles were spherical in shape with ‘shell/core’ structures. The shells consisted of an amorphous layer with varying thickness (100–800 nm) and the core represented a carbonyl iron.

Gelatinous morphology of dried FePO4 coating composed from nanoparticles of iron oxyhydroxides and hydrated iron phosphate with a shell thickness of ∼100 nm around iron particles was observed. In coatings based on alumina or silica xerogels with a thickness of ∼100–150 nm or ∼200–500 nm, the coatings were composed of iron oxyhydroxides and γ-AlOOH or Si(OH)4. The resulting XRD diffractograms revealed the hematite (α-Fe2O3) and magnetite (Fe3O4) that were formed in phosphated and sol–gel coated iron powders. The X-ray diffraction patterns did not verify the presence of phosphates, alumina or silica and indicate the amorphous or nanocrystalline structure of FePO4, γ-Al2O3 and SiO2. Copyright © 2009 John Wiley & Sons, Ltd.

The effect of iron phosphate, alumina and silica coatings on the morphology of carbonyl iron particles

Carbonyl iron powder was coated with phosphate layer using phosphating precipitation method. The phosphated powder was dried at 60 °C for 2 h in air and heat treated by calcination at 400 and 800 °C for 3 h in air. Cylindrical specimens density of ~6.5 g.cm−3 based on iron phosphated powder calcined at 400 °C were sintered at 820, 900, 1110 °C in N2 + 10%H2 atmosphere and 1240 °C in vacuum for 30 min. The morphology and phase composition of the phosphate coating and sintered compacts were studied by scanning electron microscopy, atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis. Gelatinous morphology of dried phosphate coating (thickness of ~100 nm) containing nanoparticles of iron oxyhydroxides and hydrated iron phosphate was observed. From XRD, diffractogram indicated the presence of goethite α-FeOOH, lepidocrocite γ-FeOOH and ludlamite Fe3(PO4)2.4H2O. The calcined phosphate coating (thickness of ~ 400 nm) contained non-homogeneous consistency of α-Fe2O3 layer on iron particles, an inter-layer of amorphous FePO4 and Fe3O4 top layer. The transformation to crystalline FePO4 structure occurred during calcination at 800 °C with the presence of α-Fe2O3 forming a light top zone (rough morphology). The microstructure of compacts sintered in solid state at temperatures up to 900 °C has retained composite network character. A fundamental change in microstructure due to the liquid phase sintering occurred after sintering at temperatures of 1100 and 1240 °C. It was confirmed that the microstructure complex consists of spheroidized α-Fe and α-Fe2O3 phases surrounded by solidified liquid phase consisting various phosphate compounds. Copyright © 2013 John Wiley & Sons, Ltd.

The effect of calcination on morphology of phosphate coating and microstructure of sintered iron phosphated powder

Microstructure and properties of FeSiCr/PA6 composites by injection molding using FeSiCr powders by phosphating and coupling treatment

On the relation between damage rate and stress level evolution in α-Cr2O3 thin films growing on Ni–33at%Cr

Consolidation of iron powders through the influence of phosphate thin films

In the present work, the morphological evolution of the iron-oxide layers growing at 400 °C on α-Fe and phosphated α-Fe in artificial air at 1 atm is investigated. The oxidation kinetics of α-Fe and phosphated α-Fe are firstly presented for various oxidation times. Then a detailed chronological study is undertaken of the microstructural states in the different stages of the complex oxidation kinetics. Correlations are established between the morphology of the oxides layers and the successive parabolic oxidation stages. It is shown that the phosphate conversion layers seem to modify the growth mechanisms of the oxides.

C. Huvier

Papers

On the relation between damage rate and stress level evolution in α-Cr2O3 thin films growing on Ni–33at%Cr

Consolidation of iron powders through the influence of phosphate thin films

Chronological study of the oxidation of phosphated α-iron