Thermal degradation behaviour of the layer-type complexes of montmorillonite/α-naphthylamine,saponite/α-naphthylamine and their mixtures

Samples of montmorillonite/-naphthylamine complex (MNC), saponite/-naphthylamine complex (SNC) and their mixtures were heated at temperatures below 1473 K under a nitrogen atmosphere to examine macroscopic structural change and crystalline phases deposited after pyrolysis. SNC resulted in a dense structure after pyrolysis. Heating of samples of MNC/SNC mixtures gave a porous structure which became dense as the proportion of SNC increased. No porosity measured by the mercury porosimeter was detectable in samples pyrolysed from MNC containing more than 25% SNC. After pyrolysis, the MNC/SNC mixtures gave crystalline phases which were never formed in the pyrolysed pure MNC and SNC. The formation of these crystalline phases was explained by reference to the chemical compositions of the mixtures and the phase diagram.     

Ultrasonic attenuation of longitudinal and shear waves in superconducting lead

Longitudinal and shear wave ultrasonic attenuations have been measured in high-purity Pb on two single crystals obtained from the same ingot. The measurements were done at low temperatures, at different frequencies, and in transverse magnetic fields, up to a field of 7.3 kG. The propagation directions in the two crystals were along [100] and [110]. For some propagation and polarization directions the _s / _n ratio is found to be frequency-independent, while for others, large divergences in the _s / _n ratios at different frequencies are observed. A sharp decrease of _s / _n nearT _c is observed for a particular longitudinal wave propagation, but not in any shear wave propagation. In some cases _s / _n is found to be abnormally high and this feature is associated with a peak in attenuation _n and a relatively high _n at 7.2 K. None of the _s / _n curves fits closely to any BCS energy gap. For longitudinal waves the high magnetic field (H) dependence of the normal state attenuation was found to agree qualitatively with the free electron theory for propagation along [100], but not for propagation along [110]. For shear waves the high-field attenuations do not extrapolate to zero asH tends to infinity. For all propagation and polarization directions the high-field attenuations show 1/H ² field dependence.     

Evaluation of tricalciumphosphate/ hydroxyapatite cement for tooth replacement: an experimental animal study

A calciumphosphate cement, consisting mainly of tricalciumphosphate (85% -TCP and 15% -TCP), was inserted in 16 surgical defects created in the tibia of goats. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) showed that after 3 months of implantation the -TCP was transformed to hydroxyapatite (HA). Histological evaluation revealed that the presence of cement stimulated the ingrowth of bone compared with unfilled cavities. Active resorption and remodelling of cement particles was observed. The cement did not evoke an inflammatory reaction. At 6 months after implantation no further changes in the composition of the cement occurred. All remaining material was surrounded by mature bone.     

Effects of microstructure on the R-curve behaviour of sintered silicon nitride

The R-curve behaviour of sintered silicon nitride was investigated by using short bar specimens. The samples were fabricated by sintering at 1700° C for 2 or 8 h in a nitrogen atmosphere, varying the initial contents of the silicon nitride powder. The R-curve was evaluated with a loading and unloading technique to calculateK _R during stable fracture. Steep R-curves were observed in the specimens made from the high initial content powder. Thus, the grainbridging effect behind the crack seems to contribute to the R-curve, because a steep R-curve corresponds to fibrous texture development. ApparentK _c values with an assumption of linear elastic fracture mechanics for the specimens undergoing 8h sintering, are greater than those undergoing 2 h sintering. These results can be attributed to microcracking.     

An investigation of the ordered DO19 phase formation in the Ti-Al system

For the Ti-rich, Ti-AI system, the- and- ₂ phase boundaries have been obtained through differential thermal analysis for alloy compositions ranging from 10.2 to 25.2 at% Al (6 to 16 wt% Al). It has been shown that in the above mentioned composition range, a metastable disordered-phase can be quenched in. This metastable then transforms to the ordered ₂(DO)₁₉ phase upon heating and/or isothermal ageing. It has also been observed that the kinetics of this ordering phenomenon is composition dependent.     

Structure of amorphous boron

The short range order structure of amorphous boron is studied. Three sample materials of different appearances, film, whisker and fibre, are prepared by chemical vapour deposition by the reduction of BCl₃ with hydrogen. The reduced radial distribution functions (reduced RDFs) derived from their X-ray or electron diffraction patterns are found to be almost identical among the three samples. The reduced RDFs are compared with those calculated for the four crystalline modifications of boron, i.e.-rhombohedral,-tetragonal,-tetragonal and-rhombohedral boron. The reduced RDFs of amorphous boron are found to be similar to those of the-tetragonal and-rhombohedral boron. From the similarity of physical and chemical properties and co-existence in deposition, the short range order structure of amorphous boron is shown to be closer to that of the-rhombohedral modification.     

Anisotropic grain growth of R-α-sialon (R = Nd and Er)

Two R--sialon (R_0.6Si_9.3Al_2.7O_0.9N_15.1, R=Nd and Er) compositions were first fired at 1750°C/25 min and 1650°C/2 h respectively for completion of the phase transformation. Elongated -sialon grain morphology was developed in both samples after being re-fired at 1800°C for different periods of time. The growth in width of R--sialon grains is controlled by diffusion in the liquid, while the length growth tends to be interfacial reaction controlled. The anisotropic growth of R--sialon is attributed to the large difference in the growth rate constant between the length and the width directions of the grain.     

Mössbauer studies of α″-Fe16N2 and α′-Fe8N films

Conversion-electron Mössbauer spectra of epitaxial -Fe₁₆N₂ and -Fe₈N films have been studied and their differences are discussed in detail. The Mössbauer spectrum of -Fe₁₆N₂ can be decomposed into three subspectra, which correspond to the 4d, 8h and 4c sites. The Mössbauer spectrum of -Fe₈N can be fitted using four spectra based on a nitrogen-atom-random-distribution model. The average hyperfine field is larger (3%) for -Fe₁₆N₂ than for -Fe₈N, which is approximately consistent with a 4.1% enhancement of the magnetic moments for -Fe₁₆N₂. The iron moments tend to locate in the film plane for -Fe₁₆N₂ and to arrange perpendicularly to the film plane for -Fe₈N.     

The morphology of α-Fe crystals which grow in the amorphous Fe80(C1−xBx)20 alloys

Crystallization behaviour of amorphous Fe₈₀(C_1–x B _x )₂₀ alloys, obtained by splat-cooling technique, for x values ranging from zero to unity has been investigated mainly by transmission electron microscopy. The crystalline phase which first appeared in the amorphous matrix was -Fe for all alloys studied. However, the morphology of -Fe phase changed from a spherical shape for low x values to a watch-glass shape for intermediate x values and to dendritic for large x values. The nucleation of -Fe crystals was homogeneous for low x samples while preferred nucleation on edges and surfaces was noted for samples with higher x values. The final volume fraction of -Fe phase before the appearance of the second crystalline phase increased with the increase in x.     

Mechanical properties of alkoxy-derived cordierite ceramics

Mechanical properties of cordierite ceramics prepared by the controlled hydrolysis and following polycondensation of aluminium, magnesium and silicon alkoxides were investigated in great detail. Flexural strengths of- and-cordierite ceramics are about 60 and 100 MPa, respectively. The flexural strengths of these ceramics are mainly influenced by cracks arising from thermal mismatch between - and -cordierite precipitated during sintering. High fracture toughness of-cordierite ceramics prepared by this method is ascribed to the fine microstructure of the ceramics. The high-temperature flexural strength of-cordierite ceramics is little reduced below 1000° C because of high purity of the ceramics.[/p]     

Formation mechanism of Fe80Si8B12 metallic glass

In order to gain an understanding of the glass-forming mechanism during the rapid quenching of a metallic alloy, the nucleation and growth process of the crystalline phase which competes with the metallic glass must be investigated. The microstructures of melt-spun Fe₈₀Si₈B₁₂ alloy ribbons with different thicknesses were examined using optical and electron microscopy. The phase competing with the metallic glass is-(Fe, Si) ferrite, nucleated by the homogeneous nucleation. The growth process of-(Fe, Si) dendrites was explained well by Liptonet al.'s theory of dendritic growth in an undercooled alloy melt. It was concluded that the easy glass-forming ability during rapid quenching of the Fe₈₀Si₈B₁₂ alloy is due to (i) the slow growth rate of-(Fe, Si) dendrite, and (ii) the wide gap between the temperatures of the maximum nucleation rate and the maximum growth velocity.     

On dual solutions occurring in mixed convection in a porous medium

Summary The dual solutions to an equation, which arose previously in mixed convection in a porous medium, occuring for the parameter in the range 0 < < ₀ are considered. It is shown that the lower branch of solutions terminates at =0 with an essential singularity. It is also shown that both branches of solutions bifurcate out of the single solution at =₀ with an amplitude proportional to (₀-)^1/2. Then, by considering a simple time-dependent problem, it is shown that the upper branch of solutions is stable and the lower branch unstable, with the change in temporal stability at =₀ being equivalent to the bifurcation at that point.     

Calcium phosphate cement: in vitro and in vivo studies of the α-tricalcium phosphate-dicalcium phosphate dibasic-tetracalcium phosphate monoxide system

In this paper, calcium phosphate cement consisting of -tricalcium phosphate (-TCP), dicalcium phosphate dibasic (DCPD) and tetracalcium phosphate monoxide (TeCP) was investigated in vitro and in vivo. Measurements of compressive strength against soaking time in simulated body fluid (SBF) showed a rapid increase of the hardness for the first 7 days. The gained strength was retained up to 1 year and the maximal mean value was 94.7 (±14.4) MPa. X-ray diffraction (XRD) and scanning electron microscopy (SEM) presented precipitates of hydroxyapatite (HA) after mixing, also after soaking in SBF and after implantation in rat subcutaneous tissues. However, the conversion to HA happened in different ways between in vitro and in vivo exposures. Histologic examinations showed that the cement causes the same reactions at the interface with surrounding soft tissues as HA. The authors consider the cement to be a promising material as a bone substitute, bone cement or dental material, however, further studies in a paste form and in bone tissue environments are necessary.     

Eutectoid decomposition mechanisms in hypoeutectoid Ti-X alloys

A TEM study has been made of the bainite reaction in five hypoeutectoid Ti-X alloys, where X was successively cobalt, chromium, copper, iron and nickel. Rational orientation relationships were demonstrated amongst eutectoid , eutectoid intermetallic compound and the matrix in Ti-Ni, Ti-Co and Ti-Cr. Formation of Ti₂Co at : boundaries was observed. Eutectoid in bainite was found to be slightly misoriented with respect to proeutectoid , indicating that it is separately nucleated, perhaps sympathetically, rather than the result of the continued growth of proeutectoid . Eutectoid Ti₂Co and Ti₂Cu crystals in bainite were approximately equiaxed whereas Ti-Cr₂ crystals were elongated, a result ascribed to a ledge height-to-spacing ratio / at intermetallic compound crystal: boundaries approaching that of eutectoid (: boundaries in Ti-Cr but not in the other two systems. In the Ti-Fe alloy, eutectoid and eutectoid TiFe were directly observed to have ledged interphase boundaries with their matrix, but with different inter-ledge spacings and growth directions. Observation of pearlite lamellae growing normal to the broad faces of proeutectoid plates in the Ti-Ni alloy indicates that this mode of eutectoid decomposition, like that of bainite, can develop from partially coherent interphase boundaries. The suggestion was offered that pearlite forms when approachesh at the nucleating proeutectoid : interface and that bainite develops when h at this interface.     

Phase transformations in permanent-mould-cast aluminium bronze

The phases obtained in aluminium bronze (Cu-10Al-4Fe) cast into a permanent mould were investigated. The parameters examined were the pre-heating temperature of the mould and the graphite coating thickness. The phases and ₂ were detected as well as the metastable phases and . The intermetallics of the system Fe-Al were obtained in various stoichiometric compositions. The different cooling rates of the casting resulted in two mechanisms of transformation to grains out of the unstable phase, one being nucleation and growth producing needle-shaped grains, the other exhibiting a massive transformation to spherical grains. These two mechanisms determine the changes in the size of the a grains as result of changes in the cooling rate in its various ranges.     

Effects of surfactants on the precipitation and properties of colloidal particles from forced hydrolysis of FeCl3-HCl solution

The forced hydrolysis of FeCl₃-HCl solution in the presence of surfactants such as sodium dodecyl sulphate (SDS), cetyltrimethyl ammonium chloride (CTAC), polyoxyethylene (20) nonylphenyl ether (NP-20) and poly(oxyethylene-oxypropylene) (PE-64) has been carried out and the precipitated particles were characterized by various techniques. No effect on the morphology of the precipitates was observed for CTAC and NP-20. The addition of a small amount of PE-64 progressed the particle growth but PE-64 yielded small lemon-shape -Fe₂O₃ particles at high concentration. On the other hand, the morphological uniformity of -Fe₂O₃ particles was impaired and they changed to needleor rod-like -FeOOH particles with increase in the SDS concentration. The -Fe₂O₃ particles formed with SDS showed a high selective adsorption of H₂O and CO₂, although -FeOOH particles have no such selectivity. The -FeOOH particles thus prepared exhibited a low porosity on the heat treatment in vacuo.     

Relaxations in semicrystalline polyethyleneterephthalate using thermally stimulated currents

Relaxation processes at temperatures above 20 °C in semicrystalline polyethylene-terephthalate have been studied using thermally stimulated depolarization currents (TSDC). The discharge curve shows three relaxation peaks (c, c and *) whose positions and intensities depend on the polarization conditions and the crystallinity. Relaxations c and c are heteropolar, while * may be homopolar or heteropolar according to the polarization temperature used. The effect of the crystallinity on these relaxations has been analysed by the thermal steps stimulation (TSS) method applied to an amorphous sample. Results show that c is fundamentally a dipolar relaxation associated with the amorphous interlamellar zone. The relaxation c is associated with the release of a free charge trapped in the amorphous regions, and * is a Maxwell–Wagner–Sillars relaxation associated with crystalline – amorphous interphases. For polarization temperatures above 150 °C, two relaxations are observed only as a consequence of overlapping C and * relaxations. © 1998 Chapman & Hall     

The Berlekamp-Massey algorithm and linear recurring sequences over a factorial domain

We present an extended polynomial remainder sequence algorithm XPRS for R[X] whereR is a domain. From this we derive a Berlekamp-Massey algorithm BM/R overR. We show that if () is a linear recurring sequence in a factorial domainU, then the characteristic polynomials for () form aprincipal ideal which is generated by a primitive minimal polynomial. Moreover, this generator ismonic when U[[X]] is factorial (for example, whenU is Z orK[X ₁,X₂,...,X_n] whereK is a field). From XPRS we derive an algorithm MINPOL for determining the minimal polynomial of () when an upper bound on the degree of some characteristic polynomial and sufficiently many initial terms of () are known. We also show how to obtain a Berlekamp-Massey type minimal polynomial algorithm from BM/U and state BM_MINPOL/K explicitly with a further refinement. Examples are given forU=Z, GF(2)[Y].A preliminary version of this paper [7] was presented at the Third Int. Coll. on Coding Theory and Applications, Toulon, Nov. 1988.     

Thermal Conductivity Properties of Bi2-αTlαSr2Ca2Cu3O10+z Glass-ceramic HT c Superconductor Rods

The Glass rods with nominal composition of (Bi _2- Tl )Sr ₂ Ca ₂ Cu ₃ O _10+z , where =0.15, 0.25 and 0.35, have been prepared by melt casting technique. Preferably c-axis oriented grains were grown after the sintering process. The thermal conductivity (T) measurements were performed between 30K and 290K and calculations were made using Wiedemann-Franz law. The (T) values of the samples varied between 3.8 to 8.9 mW/cm.K and showed strong dependence to the heating temperatures and compositions. The best T _c and T _zero were obtained to be 122 K and 115 K respectively.     

In situ X-ray diffraction of the early stages of the crystallization of Fe80B20

A new technique has been used for the early stages of crystallization of amorphous materials, like metallic alloys. In situ X-ray diffraction has been performed during the early stages of crystallization of Fe₈₀B₂₀. The samples are resistively heated to 600°C in a customized vacuum chamber. A programmable charge-coupled device detector records simultaneously the evolution of the three phases: -Fe, Fe₃B and Fe₂B in the minute scale. This is the first in situ X-ray diffraction study of this system in these temperature and time scales. Interesting behaviours have been seen: appearance and disappearance of phases, -Fe supersaturation solution in boron (found for the first time in this compound), and migration of B out of the -Fe matrix. The two-dimensional diffraction pictures show topography irregularities indicating crystallite inhomogeneties.