Bone formation induced by calcium phosphate ceramics in soft tissue of dogs: a comparative study between porous α-TCP and β-TCP

Two kinds of tri-calcium phosphate ceramics (Ca/P = 1.50), -TCP and -TCP, which has the same macrostructure and microstructure, but different phase composition, were implanted in dorsal muscles of dogs. The samples were retrieved at 30, 45 and 150 days, respectively, after implantation, and were analyzed histologically. There were critically different tissue responses between -TCP ceramic and -TCP ceramic. Higher cell populations were observed inside the pores of -TCP than those of -TCP, bone tissue was found in -TCP at 45 and 150 days, but no bone formation could be detected in any -TCP implants in this study. On the other hand, the bone tissue in -TCP seemed to degenerate at 150 days. The results indicate that porous -TCP can induce bone formation in soft tissues of dogs; while the rapid dissolution of the ceramic and the higher local Ca²⁺, PO ₄ ^3- concentration due to the rapid dissolution of -TCP may resist bone formation in -TCP and the less rapid dissolution of -TCP may be detrimental to already formed bone in -TCP.     

Structure development in PP/CaSO2 composites: Part II Effect of filler on crystallization and morphology

The structure development in melt crystallized polypropylene (PP) containing different types and concentration of calcium sulphate has been studied by X-ray diffraction and optical polarizing microscopy. The commercial CaSO4 containing mostly the anhydrite form gives the form of PP while the CaSO4 prepared by in situ method yields the form of PP. This takes place first by conversion of the dihydrate form of CaSO4 to the form which preferentially nucleates the form of PP. The crystallization behaviour in the latter case clearly reveals two processes. The presence of PEO which is used for the in situ preparation of CaSO4, however, is found to hinder the rate of crystallization and nucleation of the form of PP but it gives a high degree of orientation of the CaSO4 needle-like crystals during extrusion of the PP–CaSO4 composites. © 1998 Chapman & Hall     

Effects of citrate ions on the formation of ferric oxide hydroxide particles

The effects of citrate ions on the formation of - and -FeOOH particles were investigated using various techniques. The formation and crystallization of both particles were inhibited by citrate ions, and their particle sizes decreased with increase in the concentration of these ions. Finally, aggregated amorphous particles were formed. The effects of citrate ions appeared to be more significant for -FeOOH than for -FeOOH. This difference could be explained by the pH dependence of the affinity of citrate ions to Fe³⁺ ions. The amorphous -FeOOH particles prepared in the presence of > 10 mol% citrate ions selectively adsorbed water molecules.     

Activated slip systems during yielding of α-β brass two-phase bicrystals

- brass two-phase bicrystals, consisting of fcc () single crystals and bee () single crystals, which were made by the solid state diffusion couple technique, were tensile-tested at room temperature in order to clarify the role of phase-interface on the deformation. The two-phase bicrystals had small concentration gradients in the- and-phases and satisfied the Kurjumov-Sach's orientation relationships i.e. {1 1 1} {1 1 0} and [1 1 0] [1 1 1] at the interface. The slip traces observed in bicrystals deformed to about 3% plastic strain showed a striking contrast between the- and-phases; the slip traces in the-phase were clear and straight, while those in the-phase were fine and wavy. The slip systems in the bicrystals were attributed to those observed in and single crystals, and were explained by a plastic strain incompatibility mechanism. The slip systems, originating at the interface or propagating from another phase, were observed on matching planes.On leave from Mechanical Engineering Department, Faculty of Engineering, Al-Azhar University, Cairo, Egypt.     

Sintering and characterization of HA and TCP bioceramics with control of their strength and phase purity

HA and -TCP-based ceramics were prepared using commercial powders. Powder characteristics were defined and the processing parameters studied, aimed at the production of samples with improved microstructural and mechanical properties. The behaviour of HA powder subjected to various thermal treatments was investigated in order to control the formation of secondary phases (- and -TCP) during sintering. The optimal thermal treatment required to prepare pure -TCP powder from the precursors (HA and DCP) was determined and the sintering method required to prepare fully dense -TCP completely free from -form, was identified. Translucent hot-pressed -TCP ceramics with potential applications in aesthetic restorative prostheses were prepared and characterized. The interval of existence of -TCP and -TCP as secondary products was also defined. Crystallographic analysis was carried out on the imperfectly known low-temperature -TCP phase, and a proper monoclinic unit cell determined.     

Phase relationships in Si3N4-AIN-MxOy systems and their implications for sialon fabrication

Phase relationships in Si₃N₄-AIN-M_xO_y systems involving -sialon, where M represents lithium, magnesium, calcium, yttrium, neodymium, samarium, gadolinium, dysprosium, erbium and ytterbium are outlined. Their implications for the formation and fabrication of single-phase -sialon and two-phase : sialon ceramics are discussed.     

Electron microscopy studies of α- andβ-form spherulites in weld lines of injection moulded polypropylene parts

The crystal morphology of the weld lines in injection moulded polypropylene parts has been investigated by X-ray scattering and transmission electron microscopy. Wide angle X-ray scattering curves reveal two crystal modifications in the samples: the monoclinic -modification and the hexagonal -modification. The fraction of the crystallinity which is due to the -modification is lower in the vicinity of the weld line and increases with the distance from the weld line.Transmission electron micrographs reveal that in the weld line no crystallization of -spherulites occurs.     

Interface characterization of a β-SiC whisker-Al composite

The nature of the interface, the orientation relationship of -SiC whisker (-SiC_w)-Al combination, and the misfit dislocation structures at the -SiC_w-Al interfaces in a -SiC_w-Al composite have been observed by a high-resolution transmission electron microscopy (HRTEM). It was shown that quite a good bonding between the whisker and the aluminium was achieved due largely to the lattice match between SiC and aluminium at the interfaces. The orientation relationship between the whisker and the aluminium was {002}_SiC{111}_Al; 110_SiC110_Al. The interface was clean, faceted and semicoherent. The misfit dislocation cores were located in the whisker side away from the -SiC_w-Al interfaces.     

Effect of high-temperature deformation on the texture of a two-phase titanium alloy

Changes in the texture of both the - and -phases of the two-phase alloy Ti-6AI-4V have been determined in order to clarify the mechanisms of high-temperature deformation. A strain of 1.5 was applied to the alloy at 928 °C, at strain rates representative of superplastic and nonsuperplastic conditions. The -phase texture changed very little with strain rate whereas that for the -phase was much more sensitive. The -phase texture was weakened at superplastic strain rates but developed a fibre texture at non-superplastic rates. It is postulated that under superplastic conditions the alloy deforms predominantly by grain boundary sliding of the soft -phase grains, with the hard primary -phase grains remaining in their original orientations and the measured loss in texture intensity being attributed to the loss in texture of the secondary -phase only. Under non-superplastic conditions there is a greater contribution from plastic deformation in the -phase which, in turn, can enhance the secondary -phase texture.     

Phase Transformations and Melt Structure of Calcium Metasilicate

The phase transition, melting, crystallization, and vitrification of calcium metasilicate were studied by high-temperature Raman scattering spectroscopy. The results demonstrate that, in the course of melting, the [Si₃O₉] metasilicate rings, which form the structural basis of the phase, transform mainly into [SiO₃] anions. The structural similarity or dissimilarity of the CaO · SiO₂ melt to crystalline phases is shown to have a crucial effect on its crystallization/vitrification behavior.     

Pressureless sintering of β-SiC with Al2O3 additions

-SiC was pressureless sintered to 98% theoretical density using Al₂O₃ as a liquid-phase forming additive. The reaction between SiC and Al₂O₃ which results in gaseous products, was inhibited by using a pressurized CO gas or, alternatively, a sealed crucible. The densification behaviour and microstructural development of this material are described. The microstructure consists of fine elongated -SiC grains (maximum length 10 m and width 2–3 m) in a matrix of fine equi-axed grains (2–3 m) and plate-like grains (2–5m). The densification behaviour, composition and phases in the sintered product were studied as a function of the sintering parameters and the initial composition. Typically, 50% of the -phase was transformed to the -phase.     

Structural effects in the superconductor NbTi65

Annealed and metallurgical processed Nb-65 wt % Ti material is extensively investigated in the temperature range of 4–300 K. By means of transmission electron microscopy the premartensitic phase and athermal martensite are shown to exist. The microscopic event of pseudoelasticity is observed when the metastable phase is strained in the cold stage. The deformation-induced morphological instabilities are discussed in view of the training behavior of superconductors.     

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.     

Suppression of Anomalous Allotropic Transformations at High Pressures

Anomalous allotropic transformations accompanied by a reduction in the density of the substance can be suppressed by applying a high pressure equal to the ratio of the heat of transition to the difference in the volumes of the phases involved. The estimated pressures necessary to suppress the (ZrO₂), (Fe), and (Sn) phase transitions are 4.34, 3.00, and 0.495 GPa, respectively.     

Further properties of the Falkner-Skan equation

Summary We present some analytical perturbation results from which the skin-friction is accurately predicted over the range 1/2<<, where is the usual Falkner-Skan parameter. The first eigenvalue for various in the range 2<< is also calculated numerically and certain properties noted. We find, analytically, the whole set of eignesolutions for the case when is large.With 1 Figure     

Crystal structure and thermal expansion of quartz-type aluminosilicates

The thermal expansion of quartz-type aluminosilicates, which is very important for their usefulness in ceramics, can be negative or positive, depending on composition. The structures of these phases are generally described as being -quartz-like, however, an analysis of T-O bond lengths and thermal parameters of the oxygen atoms indicates that in several of these aluminosilicates the local atomic arrangement is -quartz like and that the structures derived from diffraction data are average structures only. Computer modelling of the structures strongly supports this view. In the -quartz-like phases there are static atomic displacements from the -quartz positions that, as in -quartz itself, become smaller with increasing temperature. This mechanism makes a positive contribution to thermal expansion. In phases where static displacements are absent, only thermal vibrations contribute to thermal expansion. Among these, the vibrations of the oxygen atoms normal to the T-O-T bonding plane are the most important ones and make a negative contribution to thermal expansion which is dominant in -quartz as well as in some of the aluminosilicate phases like -eucryptite.     

Torsional load transfer from a rigid shaft to an elastic plane with a slit

A plane elastostatic problem for an elastic wedge loaded by a concentrated moment at its apex provides an example of violation of the Saint-Venant principle for apex angles 2 larger than . Considering the problem for a truncated wedge, Neuber demonstrated the method of construction of an applicable solution for any apex angles in the range 22, despite the failure of the Saint-Venant principle. In the present paper the particularly important case of the truncated-wedge problem is examined. The truncated wedge degenerates into a slitted elastic plane, while a rigid circular shaft, acted upon by a torsional moment, is inserted into the plane. The analytical solution of the mixed boundary-value problem is obtained. Numerical results turn out to be in complete agreement with Neuber's results for the slitted elastic plane.     

Silicon nitride ceramics with celsian as an additive

Four different Si₃N₄ ceramics using 10 wt% celsian (BaAl₂Si₂O₈) as an additive, have been prepared by hot pressing. Different celsian sources and hot-pressing conditions were used and their effects on densification, in situ crystallization of celsian, to phase transformation, microstructures and properties, were examined. The use of a presynthesized celsian as a raw material was found to enhance the rates of densification and phase transformation due to the excess silica from raw Si₃N₄ powders which, however, did not change the microstructure and crystallization behaviour of celsian. Increases in hot-pressing temperatures and times increased the total number of large elongated grains and resulted in coincidental increases in strength and toughness until the to transformation was complete. An intermediate quench-and-reheat step during hot pressing made the microstructure finer and more uniform by greatly reducing the large-sized elongated grains. The quenching step also disrupted complete crystallization of celsian which led to more grain-boundary glassy phase and compromised the material's high-temperature properties.     

The effect of explosive loading on the microstructure of some metals and alloys

The effects of explosive pulses on the microstructure of Al-4.5% Cu duralumin, tough pitch copper, pure magnetic iron and 18 chromium 8 nickel stainless steel have been studied using transmission electron microscopy. An explosive loading assembly was designed to investigate the effect of both the flanks and the length of shock pulses on the material microstructure. In copper and duralumin it was found that the microhardness increased with the duration of the rarefaction flank. The size of the shock transformed martensite particles in stainless steel also increased with rarefaction time. Three wave interactions could be related to the microstructure of baratol-loaded iron and were attributed to the double shock front caused by the a to phase transformation. Twinning was found to occur when the reflected elastic wave interacted with the first part of the double shock front. The abrupt hardness increase caused by the interaction of the first reflected wave and the second transformation shock front was observed. In addition, a second more gradual hardness increase is attributed to the interaction between the low pressure and the high pressure rarefaction waves which caused a relatively slowly increasing rarefaction shock. The microstructure of shocked stainless steel showed that hexagonal plates and twins could occur in the same grain and that martensite particles were formed at the intersection of two twins, or of plates and twins. Both Kurdjumov-Sachs and Nishyama-Wassermann orientations were observed and sometimes occurred on the same fault band. The short rise and fall times in the pulse flanks made it possible to discuss formation mechanisms for twins and martensite particles in terms of the available formation times.     

Tilted and Crossing Vortex Chains in Layered Superconductors

No Heading In presence of the Josephson vortex lattice in layered superconductors, small c-axis magnetic field penetrates in the form of vortex chains. In general, structure of a single chain is determined by the ratio of the London [] and Josephson [_J] lengths, = /_J. The chain is composed of tilted vortices at large s (tilted chain) and at small s it consists of crossing array of Josephson vortices and pancake-vortex stacks (crossing chain). We study chain structures at the intermediate s and found two types of phase transitions. For 0.6 the ground state is given by the crossing chain in a wide range of pancake separations a [2–3]_J. However, due to attractive coupling between deformed pancake stacks, the equilibrium separation can not exceed some maximum value depending on the in-plane field and . The first phase transition takes place with decreasing pancake-stack separation a at a = [1 – 2]_J, and rather wide range of the ratio , 0.4 0.65. With decreasing a, the crossing chain goes through intermediate strongly-deformed configurations and smoothly transforms into the tilted chain via the second-order phase transition. Another phase transition occurs at very small densities of pancake vortices, a [20 – 30]_J, and only when exceeds a certain critical value 0.5. In this case small c-axis field penetrates in the form of kinks. However, at very small concentration of kinks, the kinked chains are replaced with strongly deformed crossing chains via the first-order phase transition. This transition is accompanied by a very large jump in the pancake density.PACS numbers: 74.25.Qt, 74.25.Op, 74.20.De