Grain-size dependence of coercive force in sputtered and annealed iron films

Magnetic properties such as coercive force, initial susceptibility, etc., are structure sensitive parameters. Especially, the coercive force depends on the existence of crystal defects such as dislocations and grain boundaries. In this study, the grain-size dependence of coercive force was investigated in an iron film, 150 nm in thickness, deposited by sputtering method on a (001) KCl substrate at room temperature. The grain size of the film was changed from 15 to 120 nm by annealing in a vacuum. The coercive force increased with the increase of grain size and was proportional to the square of grain size. The magnetic domain had a ripple structure when the grain size was smaller than 50 nm. A grain size larger than 50 nm led to an irregular domain wall configuration and the formation of domain walls in the grain.     

Grain-size dependence of Snoek peaks in niobium

The effect of grain size on the oxygen and nitrogen Snoek peaks in niobium has been studied. It has been observed that the conversion factor K given by C = K _max, where C is the concentration of oxygen or nitrogen and _max the height of the corresponding Snoek peak, is concentration independent up to about 0.06 and 0.04 wt % oxygen and nitrogen respectively.The variation of K with grain size (d) obeys the relationship K = K ₀ + k_Kd^–1/2, where K ₀ represents the value of K for an aggregate of crystals without boundaries and k _K the grain size dependence of K.     

Grain-size dependence of microcrack initiation in brittle materials

In this paper, the energy criterion is extended to predict the relationship between the temperature of microcrack initiation (T _MB) caused by thermal stressing in brittle materials and the grain size. The relation can be extrapolated to room temperature to provide an estimate of the critical grain size. When the relation was compared to literature data, it was found that: (1) the predicted inverse square root relation of T _MB to grain size is satisfied; (2) the room temperature intercept on the grain-size axis agrees well with the measured critical grain sizes. Also presented is a graphical method, based on the proposed relation, by which an engineering estimate of the critical grain size may be made from a minimal set of data.     

Grain-size dependence of fracture stress in anisotropic brittle solids

The stress concentrations that occur at grain boundaries due to thermal expansion anisotropy and elastic stress concentration are discussed, and the stress intensity factor that results from these stresses is estimated. The procedure for the stress intensity factor calculation is based on the model in which a spherical crystal (grain) is forced into a cavity of equal size possessing annular or radial cracks emanating from the boundary. The stress intensity factor equation thus obtained is extended to include the effect of elastic stress concentration due to the presence of a cavity, and is subsequently used to predict the grain-size dependence of strength in anisotropic brittle ceramics. In assessing the degradation of strength with increasing grain size in non-cubic ceramics, it is shown that, in addition to grain size, the effect of pre-existing crack size must also be considered. Cubic ceramics, on the other hand, are known to exhibit no thermal expansion anisotropy and, based on the present model, their strength is predicted to be governed by the pre-existing flaw size, rather than the grain size.     

Grain-size dependence of toughness and transformability of 2mol% Y-TZP ceramics

Journal of Materials Science Letters -     

Grain-size dependence of the mechanical properties of an age-hardening Fe-1 % Cu-alloy

The contribution of grain size and precipitation hardening to the yield stress and other mechanical properties was investigated. An alloy of iron with 1 % copper was prepared as supersaturated solid solution with grain sizes between 12 and 140 μm. By ageingat 500 and 600° C different precipitation hardening conditions were produced. For small particle sizes an additive behaviour of grain-boundary and precipitation hardening was found (particle radiusr < 50 Å). For large particle sizes the yield stress is independent of grain size (r > 150 Å). A transition is found for intermediate particle sizes with grain size dependence for small and independence for large grain sizes (50 Å <r < 150 Å). The effect of grain boundaries and particles on the formation and motion of dislocations is used to explain this behaviour.     

Seed-mediated synthesis of iron oxide and gold/iron oxide nanoparticles

In this study, we prepared magnetic iron oxide and gold/iron oxide nanoparticles (NPs) and characterized their morphologies and properties by XRD, TEM, EDX, VSM and UV-vis measurements. The magnetite iron oxide NPs of 10 nm were synthesized by coprecipitation of Fe2+ and Fe+3 in the solution of NH4OH and then they were used as seed particles for the subsequent growth to prepare the magnetite NPs of different particle sizes and also to prepare gold/iron oxide composite NPs. All those magnetite NPs are superparamagnetic and the gold/iron oxide composite NPs combine the optical and magnetic properties, which are contributed by gold and iron oxide components, respectively.     

Multifunctional iron and iron oxide nanoparticles in silica

Iron and iron oxide nanoparticles in silica layers deposited by sol–gel techniques on Si wafers were formed and studied. It was shown that multifunctional nanoparticles of different iron oxides possessing various physical properties can be fabricated by means of post-growth annealing of (SiO₂:Fe)/SiO₂/Si samples in various atmospheres. The hematite, maghemite, and iron nanoparticles were found to be dominant upon annealing the samples in air, argon, and hydrogen atmosphere, respectively. The physical properties of produced hybrid structures were studied by Raman and FT-IR spectroscopy, spectroscopic ellipsometry, AFM, and magnetic measurements. The sol–gel technique with subsequent annealing procedure is demonstrated to be an effective method for the formation of multifunctional hybrid structures composed of iron or iron oxide nanoparticles in silica matrix.     

Nitric oxide donor superparamagnetic iron oxide nanoparticles

This work reports a new strategy for delivering nitric oxide (NO), based on magnetic nanoparticles (MNPs), with great potential for biomedical applications. Water-soluble magnetic nanoparticles were prepared through a co-precipitation method by using ferrous and ferric chlorides in acidic solution, followed by a mercaptosuccinic acid (MSA) coating. The thiolated nanoparticles (SH-NPs) were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The results showed that the SH-NPs have a mean diameter of 10 nm and display superparamagnetic behavior at room temperature. Free thiol groups on the magnetite surface were nitrosated through the addition of an acidified nitrite solution, yielding nitrosated magnetic nanoparticles (SNO-NPs). The amount of NO covalently bound to the nanoparticles surface was evaluated by chemiluminescense. The SNO-NPs spontaneously released NO in aqueous solution at levels required for biomedical applications. This new magnetic NO-delivery vehicle has a great potential to generate desired amounts of NO directed to the target location.     

Synthesis of monodisperse iron oxide and iron/iron oxide core/shell nanoparticles via iron-oleylamine complex

Monodisperse magnetic nanoparticles are of great scientific and technical interests. This paper reports a single-step synthesis of monodisperse magnetite nanoparticles with particle size of 8 nm. Iron/maghaemite core/shell nanoparticles with particle size of 11 nm were obtained by reducing the concentration of oleylamine. TEM and in-situ FTIR results suggested that iron-oleylamine intermediate was generated in-situ and decomposed at higher temperature. Oleylamine was also found on the surface of nanoparticles, indicating its role as capping agent which provided steric protection of as-synthesized nanoparticles from agglomeration. Both magnetite and iron/maghaemite core/shell nanoparticles were superparamagnetic at room temperature with a blocking temperature at 80 K and 67 K, respectively.     

Terahertz lenses made by compression molding of micropowders

We present a simple and versatile approach for fabricating terahertz lenses based on compression molding of micropowder polymer materials in a tabletop hydraulic press. To demonstrate the feasibility of this approach, a biconvex lens shape is calculated using a ray-tracing algorithm and lenses based on two different micropowders are fabricated. As the powder materials have different refractive indices, the resulting lenses share the same geometric shape but differ in their respective focal length. The focusing properties of the lenses are evaluated by transversal and sagittal beam profile measurements in a fiber-coupled terahertz time-domain spectroscopy system, confirming the excellent imaging qualities of the compression molded lenses.     

Temperature dependence of fracture toughness in cleavage fracture of iron and iron alloys

In order to examine the temperature dependence of fracture toughness in cleavage fracture, exploratory work was carried out. Then effects of alloying elements and micro-structure on the low temperature fracture toughness were studied quantitatively in iron and iron alloys.The results indicate that (1) the relationship between fracture toughness G_ic and testing temperature T at low temperatures is G_ic = G_o exp (T/T_e), where G_e and T_o are the material constants; (2) G_o exhibits a stro dependence on solute carbon and nitrogen contents but is independent of micro-structure and other elements; (3) G_o values increases with increasing solute carbon and nitrogen contents; (4) T_o depends on the structure; (5) $\text{1}\text{T}{}_{\mathrm{o}}$ values increase with increasing nickel and manganese contents, to the contrary, decrease with increasing carbon, silicon and phosphorus contents; and (6) $\text{1}\text{T}{}_{\mathrm{o}}$ values increase with decreasing grain size.     

Microstructural evolution of iron oxide hollow nanoparticles toward iron oxide nanotubes in a prolonged sintering condition

Prolonged sintering of iron oxide hollow nanoparticles (HNPs) during chemical vapor condensation (CVC) at 800 °C for 6 h showed some interesting morphologies of the iron oxide nanotubes. TEM and XRD studies confirmed that single-walled nanotubes of a mixed phase of α, β, and γ-Fe₂O₃, with a wall thickness of less than 10 nm and an outer diameter of approximately 50 nm were synthesized. The formation of iron oxide nanotubes was thought to be an evolution of iron oxide HNPs based on the sintering.     

Wave-vector dependence of spin-wave line-width in yttrium iron garnets

The wave-vector dependence of the spin-wave line-width in yttrium iron garnets has been studied for samples of grain diameter varying from 1·2μm to 12μm. An expression for the spin-wave line-width as a function of wave-vector and grain diameter has been obtained, which agrees satisfactorily with experiment.     

Isothermal thermal diffusivity of iron oxide

Using the flash technique, the thermal diffusivity of iron oxide has been measured as a function of time at temperatures ranging from 623 to 753 K to study the isothermal decomposition of wustite to magnetite and iron. The results are briefly discussed in terms of transformation kinetics and it is shown that the data are consistent with the growth of a fixed number of nuclei, all of which are present at the start of transformation.     

Defect spinel structure in iron oxide colloids

A structural quantitative study has been performed on iron-oxide colloids with the spinel structure prepared by a chemical way. Cation vacancies are found to occupy both octahedrally (16d) and tetrahedrally (8a) coordinated sites. Significant electron density at equipoint position(48f) is assigned to interstitial iron ions in a second tetrahedrally coordinated position.