Igor Maťko

The study of phase transitions in amorphous bilayers prepared by rapid quenching

Abstract Amorphous bilayers with layers of FeNiB and CoFeCrSiB have been prepared by planar flow casting from a single crucible with two nozzles close to each other and with a partition between them forming two separate vessels. Such an arrangement has allowed us to obtain ribbons with two homogeneous layers, one on top of the other, along the whole ribbon length with high quality surface and with contact interlayer having submicron thickness. The character of the interlayer has been investigated by SEM, EMA, CS-TEM, AES and resistometry in the as-quenched state and after annealing below and after crystallization. From the results it seems evident that the process of connection of the two layers takes place below the crystallization temperature by mutual interdiffusion of component atoms, thus giving rise to mechanically solid connection.

Structure and magnetic properties of the Finemet alloy Fe73Cu1Nb3Si13.5B9.5

Abstract Structural changes taking place in the course of crystallization in nanocrystalline Fe 73 Cu 1 Nb 3 Si 13.5 B 9.5 and their influence on the initial permeability of the material have been studied as a function of ribbon thickness and thermal treatment. To obtain good magnetic properties it is necessary, as well as keeping the α(FeSi) grains to a suitable size, to ensure the appropriate Cu and Nb content. Inhomogeneous Cu distribution and eventual decrease in its content has been found to cause formation of borides or silicides in regions of Cu depletion, influencing the magnetic properties of the Finemets. It has further been determined that the content of Si in α-Fe is of great importance for the permeability of the Finemets.

The study of phase transformations in nanocrystalline materials

Abstract The structure of ferromagnetic amorphous alloys Fe 73.5 X 1 Nb 3 Si 13.5 B 9 , with X = Cu, Au, Pt, Pd, has been investigated by TEM, resistometry, dilatometry and magnetic measurements. Nanocrystalline grain formation is observed in these alloys upon crystallization. Ultrafine grains are preserved in alloys with additives which are insoluble in b.c.c.-Fe (Cu, Au), thus forming, together with niobium, a relatively stable interfacial barrier around the grains preventing their growth. In alloys with additives soluble in b.c.c.-Fe, grain sizes increase upon prolonged annealing.

Structural investigation of Fe(Cu)ZrB amorphous alloy

The crystallization process in Fes6(Cu~)ZrTB6 and FesvZr7B6 is .investigated using the methods of transmission electron microscopy, electron and X-ray diffraction and resistrometry. Two crystallization reactions take place during thermal annealing of amorphous Fe86(Cul)ZrvBe and Fes7Zr7B6 alloys. In both alloys the first crystallization begins with the formation of nanocrystalline c~-Fe at temperature to approximately 800 K. The second crystallization starts above 1000 K; the nanocrystalline phase dissolves and together with the remaining amorphous matrix form rough grains of a-Fe and dispersed Fe23Zr6 phases. From M6ssbauer spectroscopy it seems that there exist two neighbourhoods of Fe atoms in the amorphous structure. One of them is characterized by low Zr content and is responsible for the high-field component of the hyperfine field distribution p(H). The second one is rich in Zr and B and is responsible for the low-field component of p(H). This is in accord with the observation of two crystallization steps separated by a large interval of temperatures due to the existence of two chemically different regions or clusters.

Structural characterization of the finemet type alloys

Abstract Using the methods of X-ray diffraction, transmission electron microscopy and selected area electron diffraction, five finement alloys have been investigated with different chemical compositions: Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 , Fe 72 Cu 1 Nb 4.5 Si 13.5 B 9 , Fe 70.5 Cu 1 Nb 4.5 Si 16 B 8 , Fe 76 Cu 1 Si 13.5 B 9.5 and Fe 74 Nb 3 Si 13.5 B 9.5 . The formation of the crystalline phases has been studied and an attempt has been made to explain the influences of Cu on the crystallization of the nanocrystalline phase.

Combined study of confined water in controlled pore glasses by differential scanning calorimetry and positron annihilation lifetime spectroscopy

The solidification/melting of water confined in controlled pore glass CPG126 has been studied by differential scanning calorimetry (DSC) and positron annihilation lifetime spectroscopy. Samples with variable coefficient of filling of water were prepared and analysed. DSC measurements revealed, besides effects related to the melting or freezing point depression of the confined liquid, a shift of freezing peaks towards lower temperatures with decreasing water content and due to the heat treatment. An attempt of interpretation of this effect based on microstructural properties has been made, which is supported also by detected freezing of confined water by homogenous nucleation. Positron annihilation lifetime spectroscopy shows the difference between the bulk and confined water in the global trends of temperature dependence of the ortho-positronium lifetime and also confirms some results of calorimetric measurements connected with the phase transitions.

Nano-machining for advanced X-ray crystal optics

We present our recent technological achievements in development of the nano-machining of active X-ray crystal optics surfaces. This technique uses a single crystal diamond tool with extremely precise and temperature stabilized positioning system. We can prepare various simple (flat, spherical, cylindrical) as well as more complex free-form surfaces (including aspherical ones). The objective is to prepare high-quality surfaces of the desired shape with sub-nanometer surface roughness and low sub-surface damage of the crystal lattice. The final surface roughness of a flat Ge surface below 0.4 nm (RMS) was achieved for a very slow regime of the processing using feed rates≤0.25 mm/min. At such a slow feed rate, a parasitic surface grating formed due to rastering the diamond tool along the surface was minimized. Surface roughness Ra was reached well below the level of 3 nm stated by the machining device manufacturer in specifications, which is a very good result. The sub-surface damage varied periodically and ...

Crystallization in Rapidly Quenched Fe-B-Si System with Additions of C and Cu

Glass formability and phase transformations in rapidly quenched ferromagnetic nano-structured (Fe85B15-xSix)98-yC2Cuy (where x=0; 5 and y=0; 1) systems were investigated. The consecutive crystallization stages of bcc-Fe and borides were determined by resistometry, differential scanning calorimetry and by thermogravimetry, where the values of important transformation parameters were estimated and mutually correlated with the results from the structure analysis by TEM and XRD. Morphology of the nano-sized Fe grains in amorphous matrix and their transformation to borides matrix was observed by TEM in dependence on the chemical composition and thermal treatment. The effects of systematic alloying on the transformation process and on the resulting structure have been correlated with selected magnetic properties of the samples after suitable annealing.

Preparation and characterization of MnO2- SiO2 composite resin for 226Ra pre-concentration in water samples

The presented work describes an effective method for 226Ra determination using laboratory- prepared MnO2-SiO2 composite resin. Samples were traced with 133Ba for radium radiochemical recoveries monitoring which were in the range of (77 - 100%). MnO2- SiO2 composite resin was used to collect for 226Ra from water samples (pH = 6.5-7.0). Radium was eluted from the column with 50 mL of 4 mol L-1 HNO3 at a flow rate of 1.5 mL min-1. Alpha-spectrometric counting of Ba(Ra)SO4 microprecipitate was used for 226Ra determination. The new developed method was used to the 226Ra determination in samples of natural mineral, mountain spring, drinking and natural healing waters from Slovakia and Czech Republic.

Formation of a nanocrystalline phase in NiPNb amorphous alloys

Abstract The kinetics and mechanism of formation of nanocrystalline phase by heat treatment have been studied in amorphous NiP and NiPNb systems with low Nb-content by resistometry, transmision electron microscopy, electron and X-ray diffraction. In NiP alloys no orientation relationship between the forming nanocrystalline Ni3P and γ-Ni has been observed. The addition of niobium into NiP system results in the refinement of the nanocrystalline phase, which, however, is less stable and exhibits a tendency to precrystalization. In systems with 10 at.% Nb-content a major change of the crystallization kinetics is observed and phases containing NbP and NiP are formed.