Improving the effectiveness of boiler units with coal dust systems equipped with mill-ventilators

Problems pertinent to controlling the load of steam boilers and coal dust systems equipped with mill-ventilators are analyzed. A comprehensive set of patented technical solutions for these problems is presented. A formula for determining the ventilation output of mill-ventilators as a function of the fuel charge is proposed.     

Microwave absorbing properties of Fe powders milled in various media

Principal factors determining the microwave-absorption material parameters (shape, size, and chemical and phase compositions of the particles) and their dispersion relations in a range from 0.1 to 3 GHz were determined for composites containing milled Fe particles as the filling agent. The basic physical mechanisms of the effect of the aforementioned factors were assumed to be the domain-wall resonance and ferromagnetic resonance.     

Mechanical alloying of the Fe-Pb system immiscible in the equilibrium state

X-ray diffraction and Mössbauer spectroscopy were used to study the mechanical alloying of the Fe-Pb system, which is immiscible under equilibrium conditions, in a planetary ball mill by the example of an Fe(95)Pb(5) composition. The formation of a supersaturated bcc solid solution of Pb in α-Fe with a limiting concentration of 1.7 at. % Pb has been established. The most fraction of Pb in the mechanically alloyed samples was present as segregates at the boundaries of the nanocrystalline bcc phase. No dissolution of iron in lead has been observed. The mechanism of formation of the supersaturated solid solution includes sequential stages of the formation of a nanostructure in α-Fe, penetration of Pb along α-Fe grain boundaries and its segregation at the boundaries, and the saturation of α-Fe with lead.     

Peculiarities of Mechanical Alloying of High-Concentration Fe–Cr Alloys

The kinetics of the mechanical alloying of Fe and Cr powder mixtures with Cr contents of 20–48 at % has been studied by Mössbauer spectroscopy, X-ray diffraction analysis, and temperature measurements of dynamic magnetic susceptibility. It has been found for the first time that the processes of mechanical alloying differ for initial mixtures with chromium contents of 30 at % or more and contents of less than 30 at %. For the first case, the unidirectional dissolution of Cr in Fe is observed through the whole process of mechanical alloying of the mixture in a planetary ball mill. For the second case, the dissolution of Cr in Fe is observed at the beginning stage of milling; however, after milling for 2 h (t_mil), the reverse process, namely, the dissolution of Fe in Cr is likely to dominate. The mechanically alloyed samples are characterized by inhomogeneous Cr and Fe concentration distribution in powder particles, in particular at a Cr concentration in the initial mixture of more than 30 at %.     

Kinetics of dissolution of phases upon deformation of nanostructured metals and alloys

The kinetic features of dissolution of foreign inclusions in the bulk of nanostructured metals upon plastic deformation have been discussed. It has been shown that the rate of dissolution of inclusions substantially depends on the character of structural transformations in the subsystem of intercrystallite boundaries of nanomaterials. Equations that determine the kinetics of dissolution of chemical compounds of metals depending on the rate of structural transformations in intercrystallite boundaries upon deformation have been obtained. The behavior of the kinetic curves of dissolution has been described qualitatively. Numerical estimates of the time of dissolution of inclusions Fe₃C and Fe₂B in steels are given which are in satisfactory agreement with experimental data on the mechanical alloying of iron with nonmetals in ball planetary mills.     

Mössbauer spectroscopy of the nanocrystalline materials

X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements were used to study the magnetic properties and the parameters of hyperfine interactions in the nanocrystalline (with a grain size less than 10 nm) and microcrystalline alloys Fe₉₀Ge₁₀, Fe₇₇Al₂₃ and pure α-Fe. It has been established that the nanocrystalline state does not affect the formation of the saturation magnetization, Curie temperature, isomeric shift, and hyperfine magnetic field. No additional sextets in the Mössbauer spectra and no additional features in the temperature dependences of dynamic magnetic susceptibility of the alloys investigated have been revealed. In the Mössbauer spectrum of pure nanocrystalline iron, a slight line broadening (～20%) is observed.     

Mechanical alloying of the Mo-rich Mo-O-Fe ternary system

Using X-ray diffraction, M?ssbauer spectroscopy, and Auger spectrometry, it has been established that oxygen affects the sequence of solid-state reactions upon mechanical alloying of two types of powders mixtures consisting of an Mo/O composite and Fe with the elemental (atomic) ratios 74.4: 6.7: 18.9 (type 1) and 70.3: 11.7: 18 (type 2). For the samples of both types the process begins with the formation of a nanostructure in Mo and penetration of Fe atoms along oxygen-saturated grain boundaries. The feasibility of two types of reactions depending on the oxygen content has been considered. In the samples of the first type, a reaction Mo/O + Fe → bcc Mo + bcc Mo-O-Fe → bcc Mo_74.4O_6.7Fe_18.9 occurs. The final product is assumed to be a supersaturated solid solution in which O atoms are located in interstitial positions (lattice interstices) and Fe atoms in substitutional positions (lattice sites). For the samples of the second type, an appreciably different reaction has been suggested: Mo/O + Fe → bcc Mo + hcp Mo₆₃O₁₅Fe₂₂ → bcc Mo₈₁Fe₁₉ + Am Mo₃₁O₅₂Fe₁₇, where Am is an amorphous phase. The correlation (established by Butaygin and Povstugar (Dokl.-Chem. 398 (Part 2), 196–199 (2004)) between the rate of the consumption of the second component and the ratio of the yield strengths of the base (Mo) and second (Fe) elements has been confirmed.     

Initial stage of mechanical alloying in a binary system with composition Si70Fe30

Mössbauer spectroscopy and X-ray diffraction have been used to study the sequence of solidstate reactions that occur upon the mechanical alloying of mixtures of Si and Fe powders taken in an atomic ratio of 70: 30 in a planetary ball mill. In the course of the formation of a nanocrystalline state, the interpenetration of Si atoms into Fe particles and of Fe atoms into Si particles occurs. In the Si particles, clusters with a local neighborhood of Fe atoms that is characteristic of the deformed α-FeSi₂ phase are formed. In the Fe particles, clusters of the ?-FeSi and the β-FeSi₂ type arise. With increasing time of mechanical treatment, second phases of α-FeSi₂ in Si particles and of ?-FeSi and β-FeSi₂ in Fe particle are formed. In the latter case, a reaction ?-FeSi + Si → β-FeSi₂ occurs up to the complete disappearance of the ?-FeSi phase if the mixture under study is not contaminated by the material of the vessel (Fe) and balls.     

Magnetic Properties of Mechanically Alloyed and Annealed Powders Fe100 – X C X (X = 5 and 15 at.%)

The effect of the structural state and the phase composition on the magnetic hysteresis properties of Fe(95)C(5) and Fe(85)C(15) powders after mechanical alloying and annealing is investigated. It is shown that in the initial stage of grinding in a ball planetary mill the coercive force of the Fe–C powders is determined by the degree of defectiveness of the -Fe phase and the relative volume and dimensions of nonmagnetic graphitic inclusions in iron powder particles. As the grinding time increases, the -Fe phase goes over into a nanostructure state and carbon from graphite inclusions goes over into an amorphous Am(Fe–C) phase. After annealing on the temperature interval 300–600°C, the amorphous Am(Fe–C) phase is transformed into Fe₃C ferric carbide. The coercive force of the Fe₃C phase strongly depends on the degree of distortion of its crystal lattice and amounts to 80 A/cm for the phase with distorted lattice and 240 A/cm for the phase with equilibrium undistorted lattice. The magnetic characteristics of the powder after mechanical alloying and subsequent annealing are determined by the type, amount, and structural state of the phases containing in the samples.     

The role of cementite in the formation of magnetic hysteresis properties of plastically deformed high-carbon steels: I. Magnetic properties and structural state of cementite

Magnetic properties of cementite after strong plastic deformations and subsequent annealing in a broad range of temperatures are studied. The plastically deformed cementite is shown to exist in a soft (H _c ≈ 80 A/cm) state; the annealed cementite, in a hard (H _c ≈ 240 A/cm) state. The nature of the cementite’s soft and hard states is discussed. The field dependence of the cementite’s magnetostriction is measured. The longitudinal magnetostriction of the polycrystalline cementite’s saturated state is shown to be negative and approximately four times smaller than iron’s magnetostriction in the saturated state.