A. Lovas

Amorphous alloy catalysis VIII. A new activation of an amorphous Cu41Zr59 alloy in the transformation of methyl alcohol to methyl formate

Abstract Successive oxidation of an amorphous Cu 41 Zr 59 alloy followed by reaction generates an active and selective catalyst in the dehydrogenation of methanol to methyl formate (about 80% selectivity at 40% conversion at 220°C). The high activity and selectivity of the catalyst thus formed can be maintained for a long period (over 150 h on stream). A similar activation of Cu—Ti and Cu—Hf was unsuccessful. The comparison of Cu(0) surface areas determined in situ or after reducing the used catalysts in hydrogen indicates that oxidized copper species are the active sites in the transformation.

Amorphous alloy catalysis IX. Isomerization and hydrogenation of allyl alcohol over an amorphous copper-zirconium alloy

The transformation of allyl alcohol was studied over an amorphous Cu41Zr59 alloy and, for comparison, on copper powder in the presence of hydrogen at 448–573 K. The amorphous Cuue5f8Zr alloy precursor can be activated to exhibit high activity in the isomerization and hydrogenation of allyl alcohol to produce propanal and 1-propanol as major products. The activity of the as-received alloy increases and the selectivity changes with time on stream due to the rapidly increasing copper surface area. 1-Propanol formation is correlated with the number of Cu(0) surface sites.

The role of nucleating element additives in the crystallization and soft magnetic properties of Fe-Zr-B based amorphous alloys

Abstract The role of nucleating additives (Cu, Ag, Au, Pd, Pt, Sb and, Ga) in the formation of nanocrystalline structure and in the improvement of soft magnetic properties is investigated in Fe86Zr7B6M1 type alloys by calorimetric (DSC), thermomagnetic (initial permeability) and Mossbauer spectroscopic studies. It is found that the nucleating additives lower the temperature of the first crystallization step and improve the soft magnetic properties due to the refined nanostructure of the crystallization products.

Correlation between the abrasive ability of ceramic reinforced amorphous metal matrix composites and the adhesion energy between the amorphous matrix and the ceramic particles

Abstract Ceramic reinforced amorphous metal matrix composite ribbons have been produced by the melt spinning method from Fe 40 Ni 40 Si 6 B 14 matrix and particles made of two different carbides (SiC and WC). The wear properties of the composite ribbons produced were examined. The tests proved that composite ribbons with WC particles have higher abrasive ability compared with those with SiC particles of the same size. The sessile drop method was used to measure contact angles and adhesion energies of the Fe 40 Ni 40 Si 6 B 14 liquid alloy on ceramic samples made of SiC and WC at 1300 K. The adhesion energy between the Fe 40 Ni 40 Si 6 B 14 liquid (and solid, amorphous) matrix and WC particles is about 5 times higher than between the same matrix and SiC particles. Therefore a higher abrasive ability of ribbons with WC and a higher adhesion energy between the matrix and WC is experimentally found. The correlation between these two properties is explained.

Pressure dependence of nanocrystallization in amorphous Fe86B14 and Fe85Cu1B14 alloys

Pressure effect on the nanocrystallization of amorphous Fe86B14 and Fe85Cu1B14 alloys has been investigated by means of piston-cylinder measurements within a pressure range of 0-1.0 GPa. It was found that the pressure does not alter the crystallization products but decreases the crystallization temperature of each crystallization product for both samples. Crystallization products of these amorphous alloys are bcc-Fe, metastable Fe3B and Fe2B, respectively. The crystallization and precipitation temperatures of both alloys decrease with increasing pressure but not in same manner

Viscous flow, thermal expansion and phase separation of Fe40Ni40Si6B14 amorphous alloy

Abstract The thermal behaviour (viscous flow, thermal expansion, glass transition(s), phase separation and crystallization) of Fe 40 Ni 40 Si 6 B 14 glassy alloy is studied with the aid of thermomechanical analysis and DSC. Viscous flow and thermal expansion measurements revealed two glass transition temperatures (amorphous phase separation) in the glassy alloy studied. The possibility of using these alloys as sensitive structural probes for detecting possible phase separation processes in amorphous metallic alloys is shown.

Reversible and irreversible hydrogen absorption in Ni67 − xCuxZr33 glasses monitored by in situ resistivity measurements

Abstract The process of hydrogen absorption and desorption are investigated in Ni67 − xCuxZr33 glassy alloys by in situ resistivity measurements. The cyclic charging and discharging process has been monitored by conventional DC method using a computer-controlled system, exposing the samples to hydrogen of 6 MPa pressure at 293, 328 and 373 K, respectively. Normalized resistivities as a function of charging and discharging times are compared for the first and repeated cycles. Separate samples, taken from specific points of cycling, were investigated by transmission electron microscopy (TEM) measurements. Hydrogen content (H/M ratio) was determined by weight measurements, and checked by gas chromatography, which is combined with an appropriate vacuum extraction and heating technique of the samples. A gradual hydrogen-induced phase separation could be detected on the samples by scanning transmission electron microscopy (STEM) with increasing number of the cycling.

Interface phenomena in processing of ceramic reinforced amorphous metal composites

Abstract The role of interface adhesion on the wear resistance of ceramic reinforced amorphous metal matrix composites (AMMC) was studied both theoretically and experimentally. Theoretically, the wear resistance is expected to improve with wettability. Calculations show that the Fe40Ni40Si14B6 melt should wet WC particles well, but wet SiC particles poorly. Therefore better wear resistance is expected for AMMC using WC rather than SiC particles. Evidence for better wetting, higher wear resistance and better abrasive ability of the Fe40Ni40Si14B6-WC system compared to the Fe40Ni40Si14B6-SiC system is presented.

Magnetic susceptibility and 31P nuclear magnetic resonance study of the electronic structure of amorphous and crystalline NiCuP alloys

Abstract Magnetic susceptibility and 31P nuclear magnetic resonance (NMR) measurements have been performed on amorphous (Ni1 − xCux)80P20 and crystalline (Ni1 − xCux)3P alloys to complement previous low temperature specific heat and NMR work on the Niue5f8Cuue5f8P system. After correction for ion core diamagnetism, the alloys were found to be Pauli paramagnetic. The Pauli susceptibility decreases much more rapidly with increasing copper content than does the electronic specific heat coefficient, indicating a gradual weakening of the exchange enhancement of the conduction band susceptibility of d electrons. The change in the 31P NMR parameters with copper content was also in accordance with a lowering of the d band density of states at the Fermi level toward the copper-rich side. The 31P NMR study gave useful information also on the metallurgical inhomogeneity of some of the crystalline alloys.

Combustion of M-xylene over Pd catalysts derived from amorphous Pd2Ni50Nb48 alloy

Oxidation of 0.05–0.1% m-xylene in 2.5–4.0% oxygen/nitrogen mixtures has been studied as a model reaction for the oxidation of aromatics in automotive exhaust gases over Pd catalysts derived from amorphous Pd2Ni50Nb48 alloy. The alloy in the as quenched form was inactive because its surface was covered by an NbOx layer. On etching in 40% HF the top oxide layer could be removed as well as Nb was leached from the subsurface layers resulting in a Raney-type surface layer of Pd and Ni. This layer had high initial activity but sintered during reaction. The final activity developed at 673 K in the reaction mixture during the initial 10–20 hours of operation as Pd segregated to the outermost layer of the ribbon. This resulted in a catalyst where Pd oxide was embedded in partly crystallized niobia-nickel amorphous matrix. In this high activity state light-off temperatures were 523–573 K at 50,000 h−1 space velocity depending on the xylene concentration and the temperature ramp. In some cases hysteresis loops were also observed.