1. Introduction 20642. Synthesis of Magnetic Nanoparticles 20662.1. Classical Synthesis by Coprecipitation 20662.2. Reactions in Constrained Environments 20682.3. Hydrothermal and High-TemperatureReactions20692.4. Sol-Gel Reactions 20702.5. Polyol Methods 20712.6. Flow Injection Syntheses 20712.7. Electrochemical Methods 20712.8. Aerosol/Vapor Methods 20712.9. Sonolysis 20723. Stabilization of Magnetic Particles 20723.1. Monomeric Stabilizers 20723.1.1. Carboxylates 20733.1.2. Phosphates 20733.2. Inorganic Materials 20733.2.1. Silica 20733.2.2. Gold 20743.3. Polymer Stabilizers 20743.3.1. Dextran 20743.3.2. Polyethylene Glycol (PEG) 20753.3.3. Polyvinyl Alcohol (PVA) 20753.3.4. Alginate 20753.3.5. Chitosan 20753.3.6. Other Polymers 20753.4. Other Strategies for Stabilization 20764. Methods of Vectorization of the Particles 20765. Structural and Physicochemical Characterization 20785.1. Size, Polydispersity, Shape, and SurfaceCharacterization20795.2. Structure of Ferro- or FerrimagneticNanoparticles20805.2.1. Ferro- and Ferrimagnetic Nanoparticles 20805.3. Use of Nanoparticles as Contrast Agents forMRI20825.3.1. High Anisotropy Model 20845.3.2. Small Crystal and Low Anisotropy EnergyLimit20855.3.3. Practical Interests of Magnetic NuclearRelaxation for the Characterization ofSuperparamagnetic Colloid20855.3.4. Relaxation of Agglomerated Systems 20856. Applications 20866.1. MRI: Cellular Labeling, Molecular Imaging(Inﬂammation, Apoptose, etc.)20866.2.

Magnetic Iron Oxide Nanoparticles: Synthesis, Stabilization, Vectorization, Physicochemical Characterizations, and Biological Applications

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The attainment of both strength and toughness is a vital requirement for most structural materials; unfortunately these properties are generally mutually exclusive. Although the quest continues for stronger and harder materials, these have little to no use as bulk structural materials without appropriate fracture resistance. It is the lower-strength, and hence higher-toughness, materials that find use for most safety-critical applications where premature or, worse still, catastrophic fracture is unacceptable. For these reasons, the development of strong and tough (damage-tolerant) materials has traditionally been an exercise in compromise between hardness versus ductility. Drawing examples from metallic glasses, natural and biological materials, and structural and biomimetic ceramics, we examine some of the newer strategies in dealing with this conflict. Specifically, we focus on the interplay between the mechanisms that individually contribute to strength and toughness, noting that these phenomena can originate from very different lengthscales in a material's structural architecture. We show how these new and natural materials can defeat the conflict of strength versus toughness and achieve unprecedented levels of damage tolerance within their respective material classes.

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The conflicts between strength and toughness

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

An assessment of high voltage electron microscopy (HVEM). An invited review

The uncompensated spins on the surfaces of antiferromagnetic CoO films exhibit a thermoremanent magnetization after field cooling from ${T}_{N}$ that has the same temperature dependence as the exchange field of $\mathrm{Ni}{}_{81}\mathrm{Fe}{}_{19}/\mathrm{Co}\mathrm{O}$ bilayers after field cooling. This suggests that these interfacial uncompensated spins are responsible for unidirectional anisotropy. A model based on a calculation of the density of these interfacial uncompensated spins predicts the correct magnitude of the exchange field, as well as the observed inverse dependence on interfacial grain size.

Interfacial Uncompensated Antiferromagnetic Spins: Role in Unidirectional Anisotropy in Polycrystalline Ni 81 Fe 19 / CoO Bilayers

Transmission electron microscopy of materials

A detailed analysis of martensite transformations in 18/8 (304) stainless steel, utilizing transmission electron microscopy and diffraction in conjunction with X-ray and magnetization techniques, has established that the sequence of transformation is γ → ∈ → α. e is a thermodynamically stable hcp phase whose formation is greatly enhanced as a result of plastic deformation. Comparison with the e → α transformation in pure Fe-Mn alloys lends further support to the above sequence and suggests that a transformation line between e and α in Fe-Cr-Ni alloys can be expected. In the 304 stainless steel used in this investigation, formation of α was induced only by plastic deformation and subsequent to formation of e. Nucleation of α occurs heterogeneously at intersections of e bands or where e bands abut twin or grain boundaries (which represent unilaterally compressed regions). From electron diffraction, the Nishiyama relationship between γ and α phases appears to predominate at the start of the transformation, but then changes to that of Kurdjumov-Sachs. Based on these observations, a sequence of atom movements from the hcp structure to the bcc structure is proposed which has the basic geometric features of the martensitic transformation.

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The martensite phases in 304 stainless steel

Although high-temperature strength loss in ceramics such as silicon nitride has been attributed to the presence of intergranular amorphous phases, until now no direct proof has been offered. The present paper describes high resolution electron microscopy lattice imaging studies of an MgO fluxed hot-pressed silicon nitride. These studies indicate that intergranular second phases do indeed exist, but they are heterogeneously distributed, appearing especially at multiple grain junctions. These room temperature observations are compatible with the microstructures expected at elevated temperatures.

Grain Boundary Phases in a Hot-Pressed MgO Fluxed Silicon Nitride

The problems of detecting the distribution of small amounts (5 pct or less) of retained austenite films around the martensite in quenched and tempered experimental medium carbon Fe/c/x steels are discussed and electron optical methods of analysis are emphasized. These retained austenite films if stable seem to be beneficial to fracture toughness. It has been found that thermal instability of retained austenite on tempering produces an embrittlement due to its decomposition to interlath films of M3C carbides. The fractures are thus intergranular with respect to martensite but transgranular with respect to the prior austenite. The temperature at which this occurs depends upon alloy content. The effect is not found in Fe/Mo/C for which no retained austenite is detected after quenching, but is present in all other alloys investigated.

/pdf/retained-austenite-and-tempered-martensite-embrittlement-4als5rw8h9.pdf

Gareth Thomas

Papers

Interfacial Uncompensated Antiferromagnetic Spins: Role in Unidirectional Anisotropy in Polycrystalline Ni 81 Fe 19 / CoO Bilayers

Transmission electron microscopy of materials

The martensite phases in 304 stainless steel

Grain Boundary Phases in a Hot-Pressed MgO Fluxed Silicon Nitride

Retained austenite and tempered martensite embrittlement