Monophasic Structure Research Articles

Study of Nd-Fe-B alloys with nonstoichiometric Nd content in optimal magnetic state

Characterization of two rapid-quenched Nd-Fe-B alloys with nonstoichiometric Nd content in the optimized magnetic state was carried out using the X-ray diffractometry (XRD), 57Fe M?ssbauer spectroscopic phase analysis (MS), electron microscopy (TEM), high resolution TEM (HREM) and Superconducting Quantum Interference Device (SQUID) magnetometer. The experimental results demonstrate the fundamental difference in the structure and magnetic properties of the two investigated alloys in the optimized magnetic state. The Nd-Fe-B alloy with the reduced Nd content (Nd4.5Fe77B18.5) was found to have the nanocomposite structure of Fe3B/Nd2Fe14B and partly ?-Fe/Nd2Fe14B, with mean grain size below 30 nm. On the other side, the overstoichiometric Nd14Fe79B7 alloy has almost a monophase structure with the dominant content of the hard magnetic phase Nd2Fe14B (up to 95 wt. %) and a mean crystallite size about 60 nm, as determined by XRD and TEM analysis. The results of magnetic measurements on SQUID magnetometer also suggest the nanocomposite structure of the Nd-low alloy and nanocrystalline decoupled structure of the Nd-rich alloy after the optimal heat treatment.

Solid state structure and mechanical properties of melt mixed poly(trimethylene terephthalate)/polycarbonate blends

AbstractPoly(trimethylene terephthalate) (PTT)/poly (carbonate of bisphenol A) (PC) blends were obtained in the melt state by direct injection molding and also by extrusion followed by injection molding. The blends rich in PTT were monophasic, while the blends rich in PC were biphasic with the two components of the blends present in both phases. Both the monophasic and biphasic blends were partially miscibilized, and also partially reacted, as observed by FTIR. The extent of the reaction was greater in previously mixed blends. The observed synergism in the modulus of elasticity was attributed to the increased orientation of the blend components upon blending. Although decreases in elongation at break were observed and attributed to degradation of PTT, the blends were clearly ductile and compatible. This was a consequence of either their monophasic structure, or of the presence of the two components in the two phases of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Composition, preparation procedure and physical properties of linear homogeneous polyurethanes for membranes

AbstractLinear polyurethanes (PUs) were prepared in solution in two steps. In the first step, toluene‐diisocyanate (TDI) 80:20 (T) was reacted with a short‐chain poly(oxypropylene) diol (V) to obtain prepolymers characterized by various ratios of R = [T]°/[V]°. In the second step, the prepolymers were reacted with the extender 1,4‐cyclohexanedimethanol (E) with various extension ratios RE = (R − 1)[V]°/[E]°. The PU properties were analyzed by various techniques. In particular, the molecular weights determined by gel permeation chromatography (GPC), the thermal properties such as glass transition temperature Tg and specific heat variation ΔCp measured by differential scanning calorimetry (DSC), the chemical composition of the PUs and the various types of hydrogen bonds present in the polymers evidenced by Fourier‐transform infrared (FTIR) spectroscopy, the monophasic structure evidenced by small‐angle X‐ray scattering (SAXS), and the existence of only one Tg confirmed that these PUs were linear, amorphous and monophasic. Positron annihilation lifetime spectroscopy (PALS) analysis showed that the mean volume of the nanoholes increased with increasing temperature, but was not dependent on the composition, as expected for a monophasic system. A stoichiometric semi‐empirical model was proposed that relates the PU blocks' micro‐composition to the R and RE macro‐parameters, chosen for the synthesis. The polymer assumes various expressions of the general formula X[(TV)k(TE)n]mX for different values of the R and RE ratios. The micro‐parameters k and m have a direct connection with the experimental mean molecular weights of the prepolymer and the polymer, respectively: n depends only on R. The model could foresee the density of hydrogen bonds and distinguished the bonds connected to either V or E, which could be shown by FTIR analysis. This paper shows that, when using stereo‐irregular diols and blends of 2,4‐ and 2,6‐TDI, non‐stereoregular PUs are obtained. If low‐molecular‐weight diols are used and R < 3.3, it is quite improbable that the PU blocks separate into macrophases and therefore monophasic amorphous PUs are obtained. Monophasic PUs can be useful for applications such as in the field of membrane gas and vapour separation. Copyright © 2005 Society of Chemical Industry

RESULTS OF PRODUCTION TESTS AND ANALYSIS OF DESTRUCTION MECHANISMS OF HOT FORGING DIES COVERED BY THE COMPOSITE „NITRIDING LAYER/CrN COATING”

The paper presents the results of durability investigations of hot forging dies made of steel DIN 1.2367 and covered with the composite “nitrided layer/CrN coating”. The nitrided layer with the mono-phase structure α-Fe(N) was obtained through the plasma nitriding process and the CrN coating was deposited on the nitrided substrate by the arc-vacuum method. For the composite “nitrided layer/CrN coating” prepared in a two-stage way, the authors carried out materials investigations (i.e., roughness, microhardness, metallographic observations). After production tests, they carried out also analyses of the wear mechanisms of forging dies with the use of metallographic observations. On the basis of the obtained results and the results from earlier investigations [1], the authors determined that there is a possibility to make use of the laboratory forging tests for the determination of production durability of forging dies covered with different “nitrided layer/PAPVD coating” composites.

Structural, electrical and electromechanical sensing properties of Bi-modified PLZT ceramics

Piezoelectric ceramics lead zirconate titanate (PZT) is a material of high technological importance due to its applications in solid-state actuators, transducers and sensors. La+3 ion can be substituted for Pb+2 ion in PZT system (as called PLZT) because of its similar ionic sizes. The main aim of this work is to study the effect of trivalent Bi+3 doping on PLZT (8/65/35) on their microstructural, electrical and electromechanical sensing properties. Bismuth (Bi) content in the doped materials is varied from 0.3 to 1.0. These materials are prepared using the conventional way. Structural analysis of the materials from room temperature XRD data shows that the materials have monophasic rhombohedral structure. TEM analysis confirms the fabrication of fine (nano sized) homogeneous powder, whereas SEM microscopy shows the uniform distribution of spherical grains. Bi substitution is found to alter significantly some physical properties of the pure PLZT material, that is, lattice parameters, size of the grains, dielectric, pyro and piezoelectric properties. The sensing and actuation power of the prepared materials were found to be useful for the vibration control of a carbon composite cantilever beam.

In vitro Study of the Materials of the Components of the Implant Overdentures

To analyze the implant overdentures components as following: morphology and composition aspects of several small diameter systems, evaluating both the implant and the retention system (1); biomechanical characteristics of some of the polymers used for manufacturing the overdenture base (2). An experimental in vitro study was carried out through optic microscopy to analyze the metallic structure of dental implants components and anchor systems. The marketed products analyzed were mini1SKY (Bredent) and 3M ESPE MDI Mini dental implant (3M ESPE). A Zeiss microscope with Kohler illumination was used. Samples from polymeric materials commonly used for overdenture based (i.e. Duracryl and Superacryl) were analyzed by 3 point bending test by Tira device. In the case of the mini1SKY system (Bredent), the dental implant has the typical structure of marketed pure titanium that went through thermomechanical processing, resulting in a higher rate of granulation, and the matrix has a completely different structure, as it is a monophasic structure specific to materials that crystalize in the cubic system of the stainless steels. In the case of the 3M ESPE MDI system, the implant and the matrix have a similar microstructure, specific to a Ti-6Al-4V beta alloy annealed with an extremely fine rate of granulation. Duracryl and Superacryl samples fractured variable (frequently close to the midline) and were similar in regard to the value of breaking force. Knowledge of the materials of the components of implant overdenture guide their selection from the point of view of biocompatibility, resistance and ensuring denture retention.

Synthesis of MoSi2-TiSi2 pseudobinary alloys by reactive sintering

MoSi2-TiSi2 pseudobinary alloys are synthesized from mixtures of elemental powders of molybdenum, silicon, and titanium by reactive sintering under a pseudoisostatic pressure of 150 MPa. When the titanium content in the alloy increases from 0 to 33 at. pct, the density of the alloy decreases from approximately 6 to 4 g/cm3, while the relative density is more than 95 pct independent of the titanium content. Vickers hardness of the alloy is approximately 800 when the alloy consists of a monophase structure of α-MoSi2 or β-MoSi2. However, the hardness increases to approximately 950 when the alloy consists of a dual-phase structure of (α-MoSi2+β-MoSi2) or (β-MoSi2+γ-TiSi2). The oxidation resistance of the alloy at 773 K is approximately tripled when the titanium content increases from 0 to 1.7 at. pct, but the effect of the titanium content on the oxidation resistance becomes less remarkable as the titanium content increases.

Combustion synthesis of Al-Ni alloys by a pseudo-HIP process.

Several Al–Ni alloys containing 20 to 80 at% nickel are produced from a mixture of aluminum and nickel powders by a combustion synthesis method using a pseudo-HIP (Hot Isostatic Pressing) process. All the powder mixtures exothermically react and produce intermetallic compounds. The change in the exothermic temperature resulting from the composition of the powder mixture seems to be similar to the change in the melting temperature of the alloy. When the nickel content of the powder mixture is below 30 at% or above 70 at%, the multiphase structure including the elemental phase is formed. When an intermetallic compound phase has a relatively wide concentration range, the monophase structure of the compound is formed. The Vickers hardness of the synthesized alloy which include the elemental phase is 100 to 200 at room temperature. The hardness of Ni2Al3 is above 700. The hardness of NiAl changes with the nickel content; it decreases from 400 to 300 as the nickel content increases from 46 to 50 at%, but it increases to 400 as the nickel content increases from 50 to 56 at%.

Microstructural characterization of P/M Ni 3Al consolidated by HIP

Rapidly solidified powder of Ni 3Al doped with boron was produced by inert gas atomization and consolidated by hot isostatic pressing (HIP). Morphology and microstructure of the powder were studied. From the particle morphology, it could be deduced that the solidification time was similar at least to the time necessary for complete fragmentation of the liquid. The powder showed a two-phase microstructure that was finer the smaller the particle size. The presence of dendrites of NiAl (β) phase was consistent with the diagram proposed by Schramm and not with the traditional diagram of Singleton et al. The microstructure of the material consolidated at 1100°C and 1200°C was studied. A monophasic structure was observed after HIP, and no relevant microstructural differences were seen between the two temperatures used.

Effects of thermal annealing on the properties of zirconia films prepared by ion-assisted deposition

The effect of thermal annealing in the range 300–800 °C on the properties of zirconia films prepared by ion assisted deposition was studied. It was found that at low temperature the cubic phase is formed. This phase is stable up to 700 °C. All the films exhibit a monophasic monoclinic structure at 800 °C. The stress, estimated from X-ray patterns, shows a transition from tensile to compressive with increasing ion fluence. The refractive index and extinction coefficient do not seem to change appreciably up to 700 °C, showing a marked degradation thereafter. Single step annealing to the highest temperature was found to result in better stability than multistep annealing.

Mechanical Properties and Microstructure of Drawn High-Density Polyethylene Films by Unilateral Roller Drawing Method.

The unilateral roller-drawing (URD) method was tested to prepare high-modulus and high-strength polyethylene films. Samples were heated locally for a short period during the drawing by this method, in which only the bottom-edge of a roller was soaked with a part of the film in silicone of high temperatures. The deformation aspects of macroscopic shape and microscopic structure as well as the mechanical properties of the films drawn by the URD method were studied under the various conditions of draw-temperature (Td) and draw-ratio (λ). The values of breaking stress and Young's modulus reached 1.0GPa and 40.0GPa, respectively, at Td=120°C and λ>25. The results obtained from wide-angle X-ray diffraction indicated orientations of (110) and (200) planes as well as high degrees of c-axis orientation along the draw-direction. On the basis of small-angle X-ray scattering, it was suggested that the two-phase structure composed of crystalline and amorphous regions changed into the mono-phase structure with the extended-chain crystals when λ was increased. The folding index was evaluated from IR spectra to show that chain unfolding appreciably occurred when λ was larger than 15 and Td was in the region of between 120 and 135°C. The endothermic peak in DSC caused by the melting of the sample was found to shift to the higher temperature region with increasing λ. It was confirmed from the scanning electron microscopic observation on the fractured surface that the brittle fracture occurred for the sample drawn by the URD method, while the uniaxially cold-drawn films showed the ductile-fracture appearance. It was considered from these results that the URD method was useful to prepare high-density polyethylene films with superior mechanical properties such as high-strength and high-modulus.

I.r. spectroscopy and 1H n.m.r. broad line studies of poly( p-phenylene sulphide) doped with sulphur trioxide

I.r. spectra and temperature dependences of 1H n.m.r. linewidths were measured for poly( p-phenylene sulphide) (PPS) heavily doped with sulphur trioxide (SO 3) in the form of vapour and liquid. X-ray diffraction studies confirmed the total destruction of the crystalline phase as a result of the doping process. I.r. spectra show that doping with SO 3 leads to irreversible chemical modifications of the polymer by sulphonation. A comparison of the experimental values of the n.m.r. second moment determined for a rigid structure of the doped PPS with the poly(benzothiophene) excludes the formation of the latter as a result of doping. Doping with SO 3 in the vapour form leads to structural changes in the polymer with its two-phase character preserved. Annealing of the doped sample at 450 K results in the removal of chemically unbonded SO 3. However, the annealed polymer still has a different structure from the pristine polymer. PPS doped with liquid SO 3 shows a monophase structure indicated by a liquid-like resonance line.

Preparation of rhodium niobate compound by chemical mixing methods: Effect of preparation method on SMSI behavior of RhNbO4/SiO2 catalysts

Rhodium niobate was prepared as a complex oxide supported on silica via tetra-alkyl ammonium and citrate complexation. After calcination at 750 °C, the complex oxide was formed essentially in the monophasic columbite structure as determined by means of XRD. The two silica-supported RhNbO4 catalysts were tested for their activity toward ethane hydrogenolysis, and a large difference in SMSI behavior was observed for the two preparations.

A reinterpretation of the defect structure of L-Ta 2O 5

Studies of the L-Ta 2O 5 defect structure are reviewed. It is shown that the overall results are inconsistent with a simple oxygen-vacancy defect model. A new defect model based on infinitely adaptive structures is proposed, and according to this model a monophasic structure is maintained without site conservation in the sub-lattices. For L-Ta 2O 5-type structures it is proposed that the oxygen sub-lattice may change its density of sites independent of the metal sub-lattice. These processes may involve extremely long equilibrium periods, even at temperatures as high as 1400°C.

Experimental Evaluation of Two Operational Standard States for Montmorillonite in Metastable Hydrolysis Reactions

AbstractTwo conventions have been used to represent smectite formulas in mineral hydrolysis reactions: exchangeable cations are either included in (monophase structure) or excluded from (charged structure) the Standard State phase designation. Replicate mixtures of K‐saturated Belle Fourche montmorillonite, kaolinite, goethite, and magnesite were taken through a series of consecutive equilibrations with 0.01, 0.1 or 1.0 M KCl solutions using low solution/solid ratios. Apparent chemical equilibrium with respect to magnesite was used as an indication of system‐wide meta‐equilibrium. Following equilibration, the aqueous phases were recovered by immiscible displacement. Total soluble K, Mg, Si, pH, and ambient CO2 were measured. The solutions were chemically speciated using an ionassociation computer model. Hydrolysis reactions were developed based on the two smectite standard state phase designations. Reaction equilibrium constants and Gibbs free energies of formation (ΔG°) for montmorillonite were calculated. In the case of the monophase structure model, these parameters were functions of exchangeable cation composition. The mean ΔG° (montmorillonite) values for the charged structure and monophase structure models differed in absolute value but were equally precise. These results suggested that a characteristic metastable equilibrium was obtained in the experimental system. Justification for the selection of one convention over the other must be based on criteria other than precision.