Bone formation following implantation of fibrous calcium compounds (β−Ca(PO3)2, CaCO3(aragonite)) into bone marrow

Bone formation around three types of fibrous calcium-containing crystals has been examined histologically using rats. The implanted materials are (i) calcium metaphosphate (–Ca(PO₃)₂) fibers having aspect ratios of 15–80 with 2–20 m in diameter, (ii) –Ca(PO₃)₂) fibers surface-modified using dilute NaOH and (iii) calcium carbonate (CaCO₃; aragonite phase) whiskers having aspect ratios of 15–40 with 0.5–3 m in diameter. –Ca(PO₃)₂ fibers show a mechanically high strength with a low modulus of elasticity, and the surface-modified fibers have a thin layer consisting of a calcium orthophosphate phase. CaCO₃ whiskers were used for comparison reasons. The materials were implanted for 4, 8, and 12 weeks into bone defects created in the bone marrow of rat tibiae. Cancellous bone formation was observed around –Ca(PO₃)₂ fibers, the surface-modified fibers and CaCO₃ whiskers after implantation for 12, 4 and 4 weeks, respectively. CaCO₃ whiskers were scarcely observed after 12 weeks for resorbing. The calcium phosphate fibrous materials show combined advantages of mechanically high strength for toughening a matrix phase and biological activities; thus, these materials may prove to be useful for novel applications in the biomedical field.     

Sintering Behavior of Hot-Pressed Ca–αSialon Ceramics

On the basis of phase relationships in the Ca–Si–Al–O–N system, a Ca––sialon ceramic was synthesized using the hot-pressing technique. The reaction sequences and densifications of the Ca––sialon vs. firing temperatures have been characterized in detail. The present experiments reveal a reaction sequence as follows: at 1250°C the reactant mixture started to soften, at 1300°C a gehlenite phase was produced, at 1500°C the gehlenite phase was resolved into a liquid phase and a Ca––sialon started to form, and at 1600°C the formation of Ca––sialon was complete. The product was stable and almost entirely single phase Ca––sialon. Accompanying to the above sequences, densification also proceeded via a liquid-phase sintering, particle rearrangement, solution–reprecipitation, and grain growth process. In the final microstructure elongated grains of Ca––sialon were obtained, improving the fracture toughness of this Ca––sialon ceramic.     

Effect of heating temperature on dielectric properties of Pb(Zr,Ti)O3 [PZT] fibers

Ferroelectric Pb(Zr_0.53Ti_0.47)O₃ fibers were reproducibly fabricated by sol-gel technique using triethanolamine (TEA) complexed alkoxide. The phase transition from pyrochlore to perovskite took place about 400°C and a stable single perovskite phase was obtained at 550°C. PZT gel fibers spun through nozzle were heat-treated at 700°C, and at 1000°C for 1 h to certify the effect of heat-treatment temperature on the electrical properties. The PZT fibers had elliptical cross sections with diameter of 72 m–92 m, and dense microstructure was obtained by heating at 1000°C. In the PZT fibers heat-treated at 1000°C, a distinguishable relative permittivity peak and a pyroelectric current peak were observed at their Curie temperature. The P-E hysteresis loops of the crystalline PZT fibers were also observed.     

Effect of fiber content on the thermoelectric behavior of cement

The effect of discontinuous stainless steel fibers (diameter 60 m) as an admixture in cement paste on the thermoelectric behavior (the Seebeck effect) was systematically studied as a function of fiber volume fraction from 0 to 0.50 vol%. Without fibers, cement paste has an absolute thermoelectric power of +3 V/°C. A fiber content of up to 0.20 vol% makes the absolute thermoelectric power more negative (down to –63 V/°C), whereas a fiber content of 0.20–0.50 vol% makes the absolute thermoelectric power more positive (up to +31 V/°C)—even more positive than the positive value for the steel fiber by itself (+8 V/°C). The value is zero at a steel fiber content of 0.27 vol%. The effects are probably due to carrier scattering rather than conduction.     

Investigation of Phase Evolution During the Thermochemical Synthesis of Tricalcium Phosphate

The formation of tricalcium phosphate (TCP) from dicalcium phosphate and calcium carbonate was investigated using differential thermal analysis (DTA), thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD). DTA showed three distinct thermal events attributed to dehydration of dicalcium phosphate dihydrate (brushite, DCPD) to dicalcium phosphate anhydrous (monetite, DCPA), the formation of beta-calcium pyrophosphate (-Ca₂P₂O₇), and the calcination of calcium carbonate. TGA showed three weight losses corresponding to the three thermal events, respectively. XRD analysis showed that -TCP formed, beginning at about 900°C, by the reaction of -Ca₂P₂O₇ with CaO and -TCP changed to -TCP above 1200°C. Further examination of the formation of TCP from calcium hydroxide (Ca(OH)₂) and DCPA showed that -TCP would form only after the decomposition of Ca(OH)₂ to CaO and from the reaction of CaO with -Ca₂P₂O₇ at a fairly low temperature of 800°C. In addition, by naturally cooling -TCP, formed at 1300°C within the heating furnace, to room temperature, it was difficult to obtain a pure phase of -TCP. The proposed mechanism of the reaction to form TCP may include the dehydration of brushite to monetite, dehydration of monetite to beta-calcium pyrophosphate, decomposition of calcium carbonate, the formation of -TCP, and phase transition.     

Gelatin manipulation of latent macropores formation in brushite cement

Macroporous brushite cement was prepared from a mixture of -tricalcium phosphate (-TCP) and monocalcium phosphate monohydrate (MCPM) using gelatin powder as a latent templates. In a setting reaction coexisting with gelatin, closed packed, open-pore structure with 100–200 m macropores are obtained after immersion of the set cement into PBS buffer (pH 7.4) at 37 °C for 1–4 weeks. The macroporous brushite cement has compressive strength of 15 MPa originally, which reducing to 5.5 MPa with macropore formation gradually in comparison to that of cancellous bone (5–10 MPa).     

The effects of temperature on the behaviour of an apatitic calcium phosphate cement

An apatitic calcium phosphate cement is obtained by mixing -tricalcium phosphate (-TCP) and precipitated hydroxyapatite into a cement powder, and by then mixing this powder with an aqueous solution of Na₂HPO₄ as an accelerator. Setting times were reduced by about 30% by increasing the temperature from 22 to 37°C. Compressive strength reached higher intermediate and final values at 37 °C. Degrees of transformation of the -TCP in the resulting calcium-deficient hydroxyapatite (CDHA) were much higher at 37 °C after 24 h of storage in Ringer's solution according to X-ray diffraction. Differential scanning calorimetry indicated that the rate of reaction increased by a factor of about 5 when the temperature was increased from 25 to 37 °C. Scanning electron microscopy showed that the microstructure was more homogeneous and that a more tight entanglement of the precipitated CDHA crystals occurred after storage at 37 °C than at room temperature.     

Characterization of a δ/γ duplex stainless steel

A duplex stainless steel was investigated in both as-received sheet and after annealing at temperatures ranging from 850 to 1100°C. The sheet presents a deformation texture in both phases, austenite and ferrite, induced by cold rolling. Microstructure in the as-received material consists of island-like austenitic grains in a ferrite matrix. These austenitic grains are elongated with an average size of 6, 20 and 40 m along the normal (ND), transversal (TD) and rolling direction (RD). Quantitative texture measurements demonstrated that texture components are distributed mainly along the -fiber (ND ‹100›) and -fiber (RD ‹110›) for the ferrite and the -fiber (ND ‹110›) for the austenite. After recrystallization, a decrease in the intensity of the mean fibers and an increase in the minor components was observed in both, ferrite and austenite. Therefore, a similar texture was reached in both phases after annealing at 1050°C. Microstructural characterization after annealing at temperatures above 850°C showed that the elongated austenitic grains transform in colonies of equiaxic grains of about 10–15 m in size. These colonies are surrounded by a ferritic matrix at annealing temperatures above 1000°C or by a laminar microstructure at temperatures below 950°C. This laminar microstructure includes sigma phase and austenite formed from delta ferrite, and untransformed delta ferrite.     

Interfacial and mechanical properties of environment-friendly “green” composites made from pineapple fibers and poly(hydroxybutyrate-co-valerate) resin

Physical and tensile properties of pineapple fibers were characterized. Tensile properties of pineapple fibers, like most natural fibers, showed a large variation. The average interfacial shear strength between the pineapple fiber and poly(hydroxybutyrate-co-valerate) (PHBV) was 8.23 MPa as measured by the microbond technique. Scanning electron microscopy (SEM) photomicrographs of the microbond specimens revealed an adhesive failure of the interface. Fully degradable and environment-friendly green composites were prepared by combining pineapple fibers and PHBV with 20 and 30% weight content of fibers placed in a 0°/90°/0° fiber arrangement. Tensile and flexural properties of these green composites were compared with different types of wood specimens. Even though tensile and flexural strength and moduli of these green composites were lower than those of some wood specimens tested in grain direction, they were significantly higher than those of wood specimens tested in perpendicular to grain direction. Compared to PHBV virgin resin, both tensile and flexural strength and moduli of these green composites were significantly higher. SEM photomicrographs of the fracture surface of the green composites, in tensile mode, showed partial fiber pull-out indicating weak bonding between the fiber and the matrix.     

Phase transformation and impact properties of type 17-8-2 austenitic weld metals

The influence of stress relieving and ageing treatments in the range 600 to 900° C on the phase transformations and change in room temperature impact properties has been studied for two manual metal arc 17-8-2 weld metals. The transformation of the-ferrite in the range 600 to 800° C was found to conform to a classical Johnson-Mehl equation; the initial precipitates were M₂₃C₆ carbides followed by the intermetallic-phase. At higher temperatures a slower transformation rate was found suggesting a C curve type of behaviour and the dominant intermetallic phase changed to. Room temperature impact toughness values were found to change with ageing time. Below 800° C there was a consistent fall in these values which became very marked when the-phase developed at the/-boundaries, Above 800° C, spherodization of the carbides and intermetallic phases delayed the fall in the impact values, and led to significant increases in the early stages of ageing. Scanning electron microscopy confirmed that the change from ductile to brittle fracture mode was normally associated with the development of the and phases, but at 600° C the fall in impact properties could be atrributed to carbide development.     

Sintering behaviour and mechanical properties of hydroxyapatite and dicalcium phosphate

The sintering behaviour of powders of two calcium phosphates, namely hydroxyapatite (HA) and dicalcium phosphate (DCP), were studied at various temperatures and in various environments. The density, flexural strength and Knoop hardness of HA sintered in air for 4 h initially increased with the sintering temperature, reaching maxima at around 1150°C, and then decreased due to decomposition of HA into tri- (TCP) and tetracalcium phosphates. Sintering in vacuum caused decomposition of HA at lower temperatures, and consequently the mechanical properties were poorer than those of HA sintered in air. The densification and mechanical properties of DCP sintered in air and vacuum showed similar behaviour to those of HA. In air DCP underwent phase transformation from - to - and to -phases. In vacuum DCP started to decompose into tricalcium phosphate at 1000°C. To reduce dehydroxylation, HA powder was sintered in moisture at various temperatures up to 1350°C and X-ray diffraction study did not indicate any decomposition at the highest sintering temperature. The density, flexural strength and hardness of HA sintered in moisture increased with the sintering temperature and eventually reached plateaux at about 1300°C, but below 1200°C they were lower than those of HA sintered in air at corresponding temperatures. Thus, it is seen that dehydroxylation did not hinder sintering of HA. On the other hand, decomposition obstructed sintering of both HA and DCP.     

Influence of the high temperature treatment of zinc phosphate conversion coatings on the corrosion protection of steel

An anhydrous -Zn₃(PO₄)₂ phase converted by the dehydration of hydrous zinc phosphate, Zn₃(PO₄)₂·2H₂O, crystal coatings in air at a temperature of approximately 300 °C, significantly enhances the corrosion resistance of steel, and also reduces the susceptibility of the crystals to alkaline dissolution. A subsequent phase transition at approximately 500 °C results in a poor protection behaviour, because of the formation of numerous microcracks on the crystal faces.     

Characterization of the transformation from calcium-deficient apatite to β-tricalcium phosphate

The structural changes that occur during the transformation of a Ca-deficient apatite, prepared by a wet chemical method, to -TCP were investigated. X-ray diffraction (XRD) analysis of as-prepared samples and samples calcined at temperatures between 500 and 1100 °C showed that the transformation occurs over the temperature range 710–740 °C, under non-equilibrium conditions. The change in crystallite size with increasing calcination/sintering temperature was studied by XRD using the Scherrer formula. Fourier transform infra-red (FTIR) analysis indicated considerable structural change in samples above and below this temperature range. Changes were observed in the hydroxyl, carbonate and phosphate bands as the calcination temperature was increased from 500 to 1100 °C. Even once a single -TCP phase is obtained at 740 °C there remains a considerable amount of structural change at temperatures between 740 and 1100 °C. This effect was illustrated by an unusual change in the lattice parameters of the -TCP structure and significant changes in the phosphate bands of the FTIR spectra as the calcination temperature was increased. The results obtained in this study show that the combined experimental techniques of XRD and FTIR are excellent complimentary methods for characterizing structural changes that occur during phase transformations.     

Phase equilibria in the Ag4SSe-ZnTe system

The Ag₄SSe-ZnTe phase diagram has been determined on the basis of X-ray diffraction, differential thermal and metallographic analyses, as well as microhardness and density data. It has been divided into two subdiagrams of eutectic type by an intermediate A-phase with most probable composition of 2Ag₄SSe.ZnTe. The unit-cell parameters of the low-temperature -2Ag₄SSe·ZnTe modification have been determined (a=3.330 , b=3.010 , c=2.895 , =95.04°, =107.83°, =92.62°). It has been supposed that in the ZnTe-rich part a second intermediate B-phase with a composition of Ag₄SSe·2ZnTe is formed, which is stable in the range of 320÷500 °C.     

Carbothermal production of β′-sialon from alumina,silica and carbon mixture

Mixtures of pure nanometer-sized amorphous silica and -alumina with the atomic ratio SiAl=1 were reduced by a stoichiometric amount of carbon between 1100 and 1450 °C in flowing nitrogen in order to produce -sialon powder. Using aqueous suspensions of starting materials, compacts with different microstructures were prepared for reaction. Silica reduction to SiO occurred at a temperature as low as 1300 °C and part of it was removed with flowing nitrogen. Carbothermal reaction involving nitrogen stated at 1350 °C and Si₂N₂O was found as an intermediate together with SiC, resulting in -sialon formation. Loss of silica from the system led to AlN formation. Decomposition of -sialon into sialon polytypoids (15R, 12H) was observed as a result of sialon and AlN reaction at 1450 °C. The reaction rate of sialon formation was slowed down compared to the carbothermal reduction of kaolin because of the lack of impurities. The microstructure of the reacted pellets influenced the reaction products, and the narrow pore size distribution as well as good homogeneity enhanced -sialon formation.On leave, from Silesian Technical University, Krasiskiego 8, 40-019 Katowice, Poland.     

In-vitro forming of calcium phosphate layer on sol–gel hydroxyapatite-coated metal substrates

In-vitro deposition of calcium phosphate layer (CPL) on metallic substrate requires special surface preparation in order to provide an interfacial bond. In this work 316 stainless steel surface is modified through deposition of a thin film (0.5 m) of sol–gel hydroxyapatite (SG-HA). This well-bonded film acts as an intermediary and nucleation surface of the CPL film. The SG-HA films were annealed at 375 °C (samples coded 375-ACS) and 400 °C (400-ACS) to achieve different crystallinity of the films, and thus to affect and study the CPL nucleation process. The CPL growth was investigated in terms of deposition kinetics and microstructural development. A deposition rate of dense CPL of about 0.43 m/day was achieved on the crystallized film of 400-ACS, and 0.22 m/day of porous CPL on amorphous 375-ACS. A compositional variation of Ca/P ratio across the CPL film thickness (400-ACS) was observed. Lower Ca/P ratio of 1.2 was detected near the substrate-CPL interface and about 1.5 near the solution-CPL interface. Infrared analysis showed the CPL to be of apatitic calcium-deficient structure. Kinetic model explaining the advancement of the CPL upon the in-vitro immersion is proposed.     

Change of mechanical properties of rigid poly(vinylchloride) during photochemical ageing

Thermally stabilised, unpigmented, rigid PVC samples, were exposed to accelerated photoageing at 40°C, 55°C and 70°C. The concentration profiles of photoproducts were determined on microtome slices ( 20 m) parallel to the irradiated surface using IR (carbonyls) and UV (polyenic double bonds) spectrophotometry and by steric exclusion chromatography (Mn and Mw). They indicate that carbonyls and chain scissions predominate only in a thin superficial layer whereas polyconjugated double bonds and crosslinks predominate in a subcutaneous layer (300–400 m). Tensile measurements show that the ultimate elongation decreases after an induction period whose duration is a decreasing function of temperature. The change of mechanical behaviour can be described in terms of a ductile-brittle transition shift mechanism in which crosslinking plays an important role. A tentative explanation of a such crosslinking induced transition is proposed in the discussion.     

Structural evolution of alumina-γ-aluminium oxynitride composites during high-temperature compression creep

TEM studies of Al₂O₃--AION composites show the presence of precipitates in the -AION phase, due to a partial decomposition of this metastable phase formed during heat treatment. Thermal treatment (1650°C) has no effect on the microstructure, while compressive creep deformation (1650°C, 10–30 MPa) leads to a decrease of the -AION content. This phase decomposes, probably into alumina or alumina-poor AION. The precipitation process can be activated by the presence of dislocations, and is associated with a slight increase in strain rate during creep.     

Fabrication and properties of novel composites in the system Al–Zr–C

Composite bodies in the system Al–Zr–C, with about 95% relative density, were obtained by heating the compact body of powder mixture consisting of Al and ZrC (5 : 1 mol %) in Ar at 1100–1500°C for various lengths of time. Components of the material heated at more than 1200°C were Al, Al3Zr, ZrC and AlZrC2. The Al3Zr exhibited plate-like aggregation, and its size increased with increasing temperature. In the material heated at 1500°C for 1 h, the largest plate-like Al3Zr aggregation was 2000 m long and 133 m thick. Then the AlZrC2 was present as well-proportioned hexagonal platelet particles with a 8–9 m diameter and a 1–2 m thickness in the interior of the plate-like Al3Zr aggregation and Al matrix phase. The average three-point bending strength of the bodies was 140–190 MPa, and the maximum strength was 203 MPa in the body heated at 1300°C for 1 h. The body heated at 1500°C for 1 h showed high oxidation resistivity to air up to 1000°C.     

Solid state phase transformation of BaB2O4 during the isothermal annealing process

Solid-state phase transformation of BaB₂O₄ during the isothermal annealing process for both to and to were investigated using a platinum crucible. For the -phase crystal at the -phase stable temperature (> 925 °C), the phase transforms to the phase perfectly below the melting temperature of 1100 °C. Meanwhile, for the -phase crystal at the -phase stable temperature (< 925 °C), the phase transforms to the phase perfectly above 800 °C. There is some difference in phase transformation behaviour between bulk-shape crystals and the powder, caused by thermal stress.