Characterization of hydroxyapatite powders prepared by ultrasonic spray-pyrolysis technique

The hydroxyapatite (HAp) powder was prepared by the ultrasonic spray-pyrolysis technique; the characterization of the resulting powders was performed. Five kinds of the starting solutions with the Ca/P ratio of 1.67 were prepared by mixing Ca(NO₃)₂, (NH₄)₂HPO₄ and HNO₃; the concentrations of Ca²⁺ and PO₄ ^3– were in the ranges of 0.10 to 0.90 mol·dm^–3 and 0.06 to 0.54 mol·dm^–3, respectively. These solutions were sprayed into the heating zone to prepare the HAp powders. The heating zone was composed of two electric furnaces; the lower furnace was used for the evaporation of the solvent from the droplets (300–500°C) and the upper furnace for the pyrolysis of the precipitated metal salts (750–900°C). The easily sinterable HAp powder was prepared by spray-pyrolysing the solution with Ca²⁺ (0.50 mol·dm^–3) and PO₄ ^3– (0.30 mol·dm^–3) at the temperatures of 800°C (the upper furnaces) and 400°C (the lower furnaces). The resulting powder was composed of the spherical particles with diameters of 1 m or below. Even without the calcination and grinding operations, the relative densities of the compacts fired at 1150 and 1200°C for 5 h attained maxima 95%. The microstructure of the sintered compacts appeared to be uniform; the average grain size was 3 m. The activation energies for the grain growth of the sintered HAp compacts were 120 to 147 kJ · mol^–1 · K^–1.     

Zr-Hf interdiffusion in polycrystalline Y2O3-(Zr+Hf)O2

Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y₂O₃·84(Zr_1–x Hf _x )O₂ withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [–391 (kJ mol^–1)/RT] cm² sec^–1 and the grain-boundary diffusion parameters byD=1.5×10^–6exp [–309(kJ mol^–1)/RT] cm³ sec^–1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O₂ and MgO-(Zr+Hf)O₂ indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO₂ solid solutions.     

Electrical conductivity of iodine adducts of nylon 6 and other non-conjugated polymers

Iodine-nylon 6 adducts containing 70 to 90wt% iodine have been prepared by heating iodine and nylon 6 at 115 and 145° C. The electrical conductivity () of the adduct increases with increase in the iodine content and the iodine-nylon 6 adduct containing 90wt% iodine and prepared at 145° C gives = 10^–3 S cm^–1 at 25° C. Infrared, nuclear magnetic resonance (¹H and¹³C{1 H}), and powder X-ray diffraction analysis of the adduct show a profound change of the structure around the amide group of nylon 6 and suggest the formation of a-C=NH⁺-group in the reaction of nylon 6 with iodine. The temperature dependences of of the idoinenylon 6 adducts prepared at 115° C give activation energies of 51 to 92 kJ mol^–1 depending on the iodine content. Addition of carbon powder to the iodine-nylon 6 adduct causes an increase in electrical conductivity. Other polymers (aliphatic and aromatic nylons, poly(vinyl alcohol), poly (tetrahydrofuran), poly(N-vinylpyrrolidone), poly (4-vi nylpyridine), and poly(acrylonitrile)) which have lone pair or -electrons also form iodine adducts containing 70 to 95 wt % iodine and the adducts show an electrical conductivity in the range of 10^–5 to 10^–2 S cm^–1. Among the iodine adducts, those of poly(vinyl alcohol) and poly (tetra hydrofuran) show electrical conductivities as high as 1.5 X 10^–2 S cm^–1 when the adducts contain about 90 wt% iodine.     

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

Effect of temperature on fatigue crack growth in unplasticized polyvinyl chloride

The effect of temperature on the fatigue crack growth in a 150 mm class 12 unplasticized polyvinyl chloride (uPVC) pipe-grade material overa temperature range –30–60°C was studied. The Arrhenius relationship between fatigue crack growth rate, da/dN, and absolute temperature, T, was found to describe the experimental data very well independent of the applied stress intensity factor range, K. In the temperature range –30–10°C the activation energy was 8.8 kJ mol^–1 and between 26 and 60°C this was 30 kJ mol^–1. The two activation energies were found to be associated with two distinctly different crack growth mechanisms. In the low-temperature range there was a predominant shear mechanism, but in the high-temperature range multiple crazing was the major fatigue mechanism. Finally, a stress intensity factor—biased Arrhenius equation for fatigue crack growth was suggested and found to predict rather accurately the data of uPVC, as well as those of other polymeric materials at different temperatures.     

Formation of oxide phases in the system Fe2O3-NiO

Mixed metal oxides in the system Fe₂O₃-NiO were prepared by coprecipitation of Fe(OH)₃/Ni(OH)₂ and the thermal treatment of hydroxide coprecipitates up to 800 or 1100°C. X-ray diffraction showed the presence of -Fe₂O₃, NiO and NiFe₂O₄ in samples prepared at 800°C. The oxide phases -Fe₂O₃, NiO, NiFe₂O₄ and a phase with structure similar to NiFe₂O₄ were found in samples prepared at 1100°C. Fourier transform-infrared spectra of oxide phases formed in the system Fe₂O₃-NiO are discussed. Two very strong infrared bands at 553 and 475 cm^–1, a weak intensity infrared band at 383 cm^–1 and two shoulders at 626 and 441 cm^–1 were observed for -Fe₂O₃ prepared at 1100°C. NiFe₂O₄, prepared at the same temperature, showed two broad and very strong infrared bands at 602 and 411 cm^–1, while NiO showed a broad infrared band at 466 cm^–1. Fourier transform infrared spectroscopic results were in agreement with X-ray diffraction.     

Effect of ion implantation on the strength of sapphire at 300–600°C

Ion implantation with ¹¹B⁺ or ²⁸Si⁺ at 1000°C doubled the ring-on-ring flexure strength of c-plane sapphire disks tested at 300°C but had little effect on strength at 500 or 600°C. Disks were implanted on the tensile surface with 2 × 10¹⁷ B/cm² (half at 40 keV and half at 160 keV) or 1 × 10¹⁷ Si/cm² (80 keV). Sapphire implanted with 1 × 10¹⁸ B/cm² had only half as much flexure strength at 300° or 500°C as sapphire implanted with 2 × 10¹⁷ B/cm². Implantation with B, Si, N, Fe or Cr had no effect on the c-axis compressive strength of sapphire at 600°C. Boron ion implantation (2 × 10¹⁷ B/cm², half at 40 keV and half at 160 keV) induced a compressive surface force per unit length of 1.9 × 10² N/m at 20° and 1.4 × 10² N/m at 600°C. The infrared emittance at 550–800° of B-implanted sapphire at a wavelength of 5 m increased by 10–15% over that of unimplanted sapphire. Infrared transmittance of sapphire implanted with B, Si or N at either 1000°C or 25°C is within 1–3% of that of unimplanted material at 3.3 m. Implantation with Fe or Cr at 25°C decreases the transmittance by 4–8% at 3.3 m, but implantation at 1000°C decreased transmittance by only 2–4% compared to unimplanted material.     

Ionic conductivity of synthetic analcime,sodalite and offretite

The ionic conductivity of pressed pellets of dehydrated synthetic analcime, sodalite and offretite was determined by a.c. measurements within the range 10 Hz to 10 MHz. The ionic conductivity values of those zeolites exchanged with various monovalent cations were determined by the complex impedance plane method. The conduction activation energies range between 63 and 101 kJ mol^–1. Sodium analcime shows the best ionic conductivity, namely 1.8×10^–4–1 cm^–1 at 400° C. A comparison with the conductivity of other ion-conducting solids was made.     

Creep of (Mg,Fe)O single crystals

The creep behaviour of (Mg, Fe)O single crystals compressed along 1 0 0 has been investigated over the temperature range 1300 to 1500° C, at stresses between 20 and 70 MPa, for oxygen partial pressures between 10^–4 and 10² Pa, and with iron concentrations between 70 and 11 900 p.p.m. Under these conditions, the dependence of the steady-state strain rate on stress, temperature, oxygen partial pressure, and iron concentration can be summarized by the flow law, exp (–445 kJ mol^–1/RT. These results suggest that the steadystate strain rate is controlled by dislocation climb with a jog velocity which is limited by lattice diffusion of oxygen by a vacancy pair mechanism. The activation energy for creep, 445 kJ mol^–1 is larger than that reported for self-diffusion of oxygen, 330 kJ mol^–1, because the formation energy for jogs is relatively large, 115 kJ mol^–1.     

Kinetics and thermodynamics of intracrystalline Fe-Ga distribution in Y3(Fe,Ga)5O12

Garnets of composition Y₃Fe_5–x Ga _x O₁₂, withx=0–5, were synthesized from oxides. Samples with various Ga content were annealed at temperatures between 700–1290° C; the heating duration varied between 90 s and 1350 h. Cation distribution was measured by Mössbauer spectroscopy at room temperature. The standard free energy change for the exchange reaction Fe³⁺ (tet)+ Ga³⁺ (oct)Fe³⁺ (oct)+Ga³⁺ (tet) is about 20 kJ mol^–1, and decreases slightly with increasing Fe content. The specific rate constants for the ordering process were determined according to the Mueller model for order-disorder kinetics. The activation energies for the ordering process between 200–250 kJ mol^–1 were calculated from the temperature dependence of the specific rate constants.     

The effect of additives on the crystallization and sintering of 2MgO-2Al2O3-5SiO2 glass-ceramics

Crystallization and sintering behaviour of three cordierite (2MgO-2Al₂O₃-5SiO₂) glasses containing different amount of additives were investigated and compared by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Archimedes method. The stoichiometric 2MgO-2Al₂O₃-5SiO₂ (MAS) glass and the 2MgO-2Al₂O₃-5SiO₂ glass containing 3 wt% of B₂O₃ and 3 wt% of P₂O₅ (MASBP) showed two exotherms (one for -cordierite formation from a glass and the other for -cordierite formation from the -cordierite phase), whereas the 2MgO-2Al₂O₃-5SiO₂ glass containing 2 wt % of B₂O₃, 2 wt% of P₂O₅, and 2 wt % of TiO₂ (MASBPT) showed only a single exotherm representing -cordierite formation. By using Kissinger, Augis-Bennett, Ozawa, and modified Kissinger methods, the activation energy values for -cordierite formation in the MASBP and MASBPT glasses were determined as 310±6 and 326±13 kJ mol^–1, respectively, whereas that in the MAS glass was determined as 868±5 kJ mol^–1. The MASBPT glass showed the lowest peak temperature value for -cordierite formation (980 °C) amongst the three glasses. Both the MASBP and MASBPT glasses showed excellent sintering behaviour (> 99.7% of theoretical density).     

Coarsening of precipitates and dispersoids in aluminium alloy matrices: a consolidation of the available experimental data

Experimental data on the coarsening of precipitates and dispersoids in aluminium-based matrices are reviewed. Available data are tabulated as K=(r ³–r ₀ ³ )/t where r ₀ is the initial particle radius and r is its value after time t at temperature T, and then plotted as log (KT) against 1/T for consolidation and assessment. The considerable body of data for -A₃Li in Li-containing alloys is well represented by K=(K ₀/T) exp (–Q/RT) with K ₀=(1.3 _–0.5 ^+3.0 ) × 10^–13m³Ks^–1 and Q=115±4kJ mol^–1. The relatively limited data for and in Cucontaining alloys are representable by the same relationship with K ₀4 × 10^–8 and — 4 × 10^–10 m³ Ks^–1, respectively, and Q — 140 kJ mol^–1. Available data for coarsening of L1₂ ^– Al₃(Zr, V) and related phases in Zr-containing alloys and of Al₁₂Fe₃Si and related phases in Al-Fe based alloys indicate (i) rates of coarsening at 375 to 475 °C (0.7 to 0.8T_m) five to eight orders of magnitude less than would be expected for , and in this temperature range, and (ii) high activation energies of 300 and 180 kJ mol^–1, respectively.     

High temperature oxidation of hot-pressed aluminium nitride by water vapour

Hot pressed AIN without additives was oxidized et 1100 to 1400°C in dry air, wet air and wet nitrogen gas atmospheres with 1.5 to 20 kPa of water vapour pressure. AIN was oxidized by both air and water vapour, and formed -Al₂O₃ film on the surface above 1150°C. The oxidation kinetics in air were parabolic end were promoted by water vapour. On the other hand, the oxidation kinetics in wet nitrogen were linear below 1250°C and parabolic above 1350°C. The oxidation rate in wet nitrogen was much greater than that in wet air. The rate of oxidation increased with increasing temperature until 1350°C, and then decreased. The parabolic rate constant decreased with increasing temperature and increased linearly with increasing water vapour pressure. The linear rate constant at 1150 to 1250° C increased with increasing the temperature with the apparent activation energy of 250 kJ mol^–1. The relation between the linear rate constant and water vapour pressure was of the Langmuir type.     

Preparation of barium iron oxides by the oxidation of iron in the Fe-Ba(OH)2-NaOH-H2O-O2 system

Iron was oxidized in the Fe-Ba(OH)₂-NaOH-H₂O-O₂ system at elevated temperatures. Fe₃O₄ and -FeOOH were formed in the absence of oxygen. On the other hand, hexagonal plate-like particles of BaFe₁₂O₁₉, 1.0–4.3 m diameter, were formed as single phase by the oxidation of iron in Ba(OH)₂ and NaOH mixed solutions at 250–300°C and above 1.0 MPa oxygen. The diameter of the particle significantly depended on the NaOH concentration. Additives such as CO ₃ ^2– , SO ₄ ^2– and CH₃COO^– promoted the grain growth of BaFe₁₂O₁₉.     

Fabrication and mechanical properties of silicon carbide–silicon nitride nanocomposites

A powder mixture of ultrafine –SiC–35 wt% –Si₃N₄ containing 6 wt% Al₂O₃ and 4 wt% Y₂O₃ as sintering additives were liquid–phase sintered at 1800°C for 30 min by hot–pressing. The hot–pressed composites were subsequently annealed at 1920°C under nitrogen–gas–pressure to enhance grain growth. The average grain–size of the sintered bodies were ranged from 96 to 251 nm for SiC and from 202 to 407 nm for Si₃N₄, which were much finer than those of ordinary sintered SiC–Si₃N₄ composites. Both strength and fracture toughness of fine–grained SiC–Si₃N₄ composites increased with increasing grain size. Such results suggested that a small amount of grain growth in the fine–grained region (250 nm for SiC and 400 nm for Si₃N₄) was beneficial for mechanical properties of the composites. The room–temperature flexural strength and fracture toughness of the 8–h annealed composites were 698 MPa and 4.7 MPa · m^1/2, respectively.     

Transformation of tridymite to cristobalite below 1470° C in silica refractories

Because silica refractory has good volume stability and creep properties at high temperature, it has been used in several furnaces. However, silica has three polymorphs (quartz, tridymite and cristobalite) and each polymorph has an- type transformation. It is known that cristobalite is the stable phase of silica between 1470° C and the melting point of silica refractories. However, sometimes cristobalite was found in silica refractories used in the stable temperature region of tridymite. Therefore, the cause and mechanism of this tridymite-to-cristobalite transformation below 1470° C was studied. Although the transformation temperature of tridymite to cristobalite was also 1470° C in the sample used in this research, it decreased on addition of Al₂O₃. The apparent activation energy of the tridymite-to-cristobalite transformation was found to be 787 kJ mol^–1 above 1470° C and 176 kJ mol^–1 below 1470° C with Al₂O₃ by measuring the transformation rate. It was also observed using EPIVIA that the tridymite included CaO; however, CaO and Al₂O₃ were located on the outside of the cristobalite which was produced below 1470°C. Therefore, it is supposed that the liquid phase was produced by the penetration of Al₂O₃, and impurities in the tridymite crystal diffused outside and then silica was precipitated as cristobalite.     

The surface diffusion coefficients of MgO and Al2O3

From the measurement of neck size and neck curvature during the sintering of two spheres the surface diffusion coefficients of MgO and Al₂O₃ were determined. The spheres of both materials were machined from single crystals. The following values of surface diffusion coefficients were found: for MgO,D _{s s} = 3.7 × 10^–4 exp (407.8 kJ mol^–1/RT m³ sec^–1; for Al₂O₃,D _{s s} = 1.5 × 10^–2 exp (518.7 kJ mol^–1/RT) m³ sec^–1.     

The retention of heterocyclics by siliceous frameworks Part I The role of the heterocyclic

Flow microcalorimetry has been used to probe acid-base interactions between five-membered-ring heterocyclics and thermally pre-treated, porous silica. The adsorbates (1-methylpyrrolidin-2-one, pyridine, pyrrolidine, pyrrole, 2-methylthiophene, 2-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-octyl-4-isothiazolin-3-one and 2-cyclopentenone,) varied in basicity, polarity and -character. The amounts of the adsorbates retained by the silica were determined, along with enthalpy of adsorption (ranging from –5.5 kJ mol^–1 to –57.8 kJ mol^–1) and enthalpy of desorption (ranging from 5.6 kJ mol^–1 to 26.1 kJ mol^–1). For the majority of the adsorbates the enthalpy of adsorption is consistent with hydrogen bonding to isolated silanols. Although increasing basicity enhanced the adsorption enthalpy and hence the strength of associations, desorption was inhibited when a carbonyl, or unsaturated carbonyl, group was adjacent to the active basic centre. Bulky electron-withdrawing agents (chlorine atoms) substituted at the double bond of the unsaturated carbonyl reduced the adsorption considerably. This was attributed to steric hinderance restricting the proximity of the basic groups with the active silanol sites.     

Electrical conductivity in hot-pressed nitrogen ceramics

The a.c. and d.c. electrical conductivities of some hot-pressed polycrystalline nitrogen ceramics have been measured between 400 and 1000° C. The materials examined were Si₃N₄, 5.0% MgO/Si₃N₄ and two sialons, Si_(6–z) · Al _z · O _z · N_(8–z) having z 3.2 and z 4.0 respectively. The electrical behaviour of all the materials showed similar general features. The d.c. conductivities were about 10^{–10 –1} cm^–1 at 400° C and rose to between 10^–6 and 10^{–5 –1} cm^–1 at 1000° C. The a.c. Data, taken over the frequency range 15 Hz to 5 kHz showed that below about 500° C the a.c. conductivity ( _a.c.) varied with frequency as _a.c. ^s where 0.7 _d.c.) agreed well with the relation _d.c. = A exp(–B/T ^1/4). Above 700° C both the a.c. and d.c. conductivities followed log T ^–1. Hall effect and thermoelectric power measurements enabled the Hall mobility to be estimated as less than 10^–4 cm² V^–1 sec^–1 at 400° C and showed that the materials were all p-type below 900° C and n-type above 900° C. The electrical properties of all four materials are consistent with the presence of a glassy phase.     

High temperature bending creep of a Sm-α-β Sialon composite

The four-point bending creep behavior of a Sm-- Sialon composite, in which Sm-melilite solid solution (denoted as M) was designed as intergranular phase, was investigated in the temperature range 1260–1350°C and stresses between 85 and 290 MPa. At temperatures less than 1300°C, the stress exponents were measured to be 1.2–1.5, and the creep activation energy was 708 kJ mol^–1, the dominant creep mechanism was identified as diffusion coupled with grain boundary sliding. At temperatures above 1300°C, the stress exponents were determined to be 2.3–2.4, and creep activation energy was 507 kJ mol ^–1, the dominant creep mechanism was suggested to be diffusion cavity growth at sliding grain boundaries. Creep test at 1350°C for pre-oxidation sample showed a pure diffusion mechanism, because of a stress exponent of 1. N^3– diffusing along grain boundaries was believed to be the rate controlling mechanism for diffusion creep. The oxidation and Sialon phase transformation were analyzed and their effect on creep was evaluated.