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1.
A mechanistic model for the kinetics of hydrolysis of α-tricalcium phosphate (α–Ca3 (PO4 )2 or α-TCP) to hydroxyapatite (Ca10− x (HPO4 ) x (PO4 )6− x (OH)2− x or HAp) has been developed. The model is based on experimental hydrolysis rate data obtained using isothermal calorimetry. Analysis of the kinetic data according to the general kinetics models in terms of the fractional degree of reaction and time suggests the hydrolysis to be controlled by different rate-limiting mechanisms as reaction proceeds. Initially, the hydrolysis kinetics depend on the surface area of the anhydrous α-TCP. Subsequently, they change to a dependence on the rate of HAp product formation controlled by a nucleation and growth mechanism. The model predicts that HAp nuclei form at essentially one time and growth occurs in two dimensions, leading to a platelike morphology. The change in the reaction mechanism occurs at a fractional degree of hydrolysis, which does not change significantly with temperature in the range of 37°–56°C. 相似文献
2.
Bang-Yen Chou Edward Chang Shyue Yen Yao Jen Min Chen 《Journal of the American Ceramic Society》2002,85(3):661-669
This study aims to explore phase transformation in plasma-sprayed hydroxyapatite (HA) + 10 wt% ZrO2 –8-mol%-Y2 O3 composite coating, using separately prepared HA and ZrO2 –8-mol%-Y2 O3 coatings as a control. Changes in the phase and chemistry of the coatings are characterized by X-ray diffractometry, with lattice-constant measurement (Cohen's method), and by transmission electron microscopy. Experimental results show evidence of diffusion, in the liquid state, of calcium ions from the HA matrix into the ZrO2 . This behavior causes the formation of the following structural features in the composite coating: (i) a CaO-doped ZrO2 solid solution (ZrO2 –7.7 mol% Y2 O3 –4.4 mol% CaO); (ii) a mixture of ZrO2 and CaZrO3 having a crystal-orientation relationship; (iii) an amorphous phase containing elements of calcium, phosphorus, zirconium, and yttrium; and (iv) a remaining CaO-poor HA matrix (Ca10− x (HPO4 ) x (PO4 )6− x (OH)2− x ; x = 0.06). Rationales for the greatly decreased impurity phases of CaO and Ca4 P2 O9 found in the composite coating are discussed. 相似文献
3.
Axel Nørlund Christensen Torben R. Jensen Nicola V. Y. Scarlett Ian C. Madsen Jonathan C. Hanson 《Journal of the American Ceramic Society》2004,87(8):1488-1493
The hydrolysis of pure and sodium-substituted calcium aluminates and cement clinker phases was investigated in situ in the temperature range 25°–170°C, using the angle dispersive powder synchrotron powder X-ray diffraction technique. The final hydrolysis product in all cases was Ca3 Al2 (OH)12 . The intermediate phase Ca4 Al2 O7 ·19H2 O was formed from the pure calcium aluminates, and the intermediate phases Ca4 Al2 O7 · x H2 O, x = 11, 13, or 19, were formed from the cement clinker phases. 相似文献
4.
The phase diagram for the ternary system MgO─P2 O5 ─H2 O at 25°C has been constructed. The magnesium phosphates represented are Mg(H2 PO4 )2 · n H2 O ( n = 4, 2, 0), MgHPO4 ·3H2 O, and Mg3 (PO4 )2 · m H2 O ( m = 8, 22). Because of the large differences in the solubilities of these compounds, the technique which involves plotting the mole fractions of MgO and P2 O5 as their 10th roots has been employed. With the exception of MgHPO4 ·3H2 O, the magnesium phosphates are incongruently soluble. Because incongruency is associated with a peritectic-like reaction, the phase Mg2 (PO4 )3 · 8H2 O persists metastably for an extended period. 相似文献
5.
FREDRIK P. GLASSER ERIC E. LACHOWSKI DONALD E. MACPHEE 《Journal of the American Ceramic Society》1987,70(7):481-485
A compositional model based on available structural evidence is proposed for amorphous calcium silicate hydrogel. It is applicable to gels in the (Ca/Si),solid range 1.0 to 1.4 and is formulated to take account of dimeric silicate species in the solid. Its composition is represented by Ca x H6−2 x Si2 O7 · z Ca(OH)2 · n H2 O where x and z are not independently obtainable; x + z , however, is evaluated from the Ca/Si ratio. The model is applied to representative solubility data; Ksp and free energies of formation for C-S-H's in this composition range are evaluated. 相似文献
6.
Eaden Saw Ken H. Sandhage Patrick K. Gallagher Alan S. Litsky 《Journal of the American Ceramic Society》2000,83(4):998-1000
A novel VIMOX (volume identical metal oxidation) route to near-net-shaped calcium hydroxyapatite, Ca10 (PO4 )6 (OH)2 , is demonstrated: the oxidation of machinable Ca—Ca2 P2 O7 precursors. Mechanically alloyed mixtures of Ca and β-Ca2 P2 O7 were compacted into disk- and bar-shaped preforms. The latter preforms could be machined into cylinders using a metalworking lathe (200 rpm, hardened steel tooling). After oxidation at 600°C in O2 , and then postoxidation annealing in H2 O/O2 mixtures at 850°C and 1150°C, phase-pure hydroxyapatite was obtained. Because of offsetting volume changes from calcium oxidation and hydroxyapatite formation, porous hydroxyapatite bodies were produced that retained the shapes and dimensions (within 1%) of the machined precursors. 相似文献
7.
Raúl García Carrodeguas Antonio H. De Aza Xavier Turrillas Pilar Pena Salvador De Aza 《Journal of the American Ceramic Society》2008,91(4):1281-1286
The transformation β→α in Mg-substituted Ca3 (PO4 )2 was studied. The results obtained showed that, contrary to common belief, there is, in the system Mg3 (PO4 )2 –Ca3 (PO4 )2 , a binary phase field where β+α-Ca3 (PO4 )2 solid solutions coexist. This binary field lies between the single-phase fields of β- and α-Ca3 (PO4 )2 solid solution in the Ca3 (PO4 )2 -rich zone of the mentioned system. In the light of the results and the Palatnik–Landau's Contact Rule of Phase Regions, a corrected phase equilibrium diagram has been proposed. The practical implications of these findings with regard to the synthesis of pure α- and β- Mg-substituted Ca3 (PO4 )2 powders and to the sintering of related bioceramics with improved mechanical properties are pointed out. 相似文献
8.
Yiquan Wu Larry L. Hench Jing Du Kwang-Leong Choy Jingkun Guo 《Journal of the American Ceramic Society》2004,87(10):1988-1991
Hydroxyapatite (Ca10 (PO4 )6 (OH)2 , HA) fibers were prepared by electrospinning a precursor mixture of Ca(NO3 )2 ·4H2 O and (C2 H5 O)3 PO with a polymer additive, followed by a thermal treatment. The X-ray diffraction (XRD) analysis of the annealed composite fibers revealed that pure HA phase could be obtained by annealing at 600°C for 1 h. The scanning electron microscopy (SEM) analysis showed the surface of as-electrospun composite fibers with an average diameter of 50 μm was smooth due to the amorphous nature of the polymer. However, the surface of the calcined HA fibers was rough because of the complete removal of the polymer. The pure HA fibers obtained by electrospinning in this work were up to 10 mm in length and 10–30 μm in diameter and the hydroxyapatite grain size was ∼1 μm in the HA fibers. 相似文献
9.
Nakshatra B. Singh Awadhesh K. Singh Shashi Prabha Singh 《Journal of the American Ceramic Society》1990,73(10):3063-3068
Hydration occurring in the system Ca3 Al2 O6 –CaSO4 · 2H2 O–Ca(OH)2 –H2 O has been studied at different temperatures and it was found that the reactions are diffusion controlled. The kinetic data obeyed Jander's equation and the rate of reaction increased with increasing temperature. X-ray diffraction studies and calorimetric measurements show that when gypsum is consumed, ettringite is converted into monosulfate. The rate of this conversion also increased with the increasing temperature and decreased in the presence of citric acid. Spectroscopic studies showed that there was some interaction between citric acid and the cement and that the product of hydration is of colloidal nature. Zeta potential measurements show that retardation of Ca3 Al2 O6 hydration in the presence of gypsum and Ca(OH)2 is not due to SO2− 4 adsorption. Electrical conductivity and thermoelectric potential measurements of solid Ca3 Al2 O6 show that Ca3 Al2 O6 is an n -type semiconductor and contains defects. The retardation of Ca3 Al2 O6 may be due to poisoning of reaction sites by gypsum and Ca(OH)2. 相似文献
10.
Novel Preparation Method of Hydroxyapatite Fibers 总被引:5,自引:0,他引:5
Yoshio Ota Tetsushi Iwashita Toshihiro Kasuga Yoshihiro Abe 《Journal of the American Ceramic Society》1998,81(6):1665-1668
A novel method for preparing calcium hydroxyapatite (Ca10 (PO4 )6 (OH)2 : HAp) fibers has been developed. HAp fibers can be prepared successfully by heating a compact consisting of calcium metaphosphate (ß-Ca(PO3 )2 ) fibers with Ca(OH)2 particles in air at 1000°C and subsequently treating the resultant compact with dilute aqueous HCl solution. The ß-Ca(PO3 )2 fibers and the Ca(OH)2 in the compact were converted into fibrous HAp and CaO phases by the heating, and the CaO phase was removed by acid-leaching. HAp fibers obtained in the present work were 40-150 µm in length and 2-10 µm in diameter. The fibers had almost the same dimensions as those of the ß-Ca(PO3 )2 fibers. 相似文献
11.
Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li1+ x Ti2− x Al x (PO4 )3 (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li2 O─CaO─TiO2 ─Al2 O3 –P2 O5 system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li1+ x Ti2− x Al x (PO4 )3 and β-Ca3 (PO4 )2 phases. The median pore diameter and surface area of the resulting porous Li1+ x Ti2− x Al x (PO4 )3 glass-ceramics were approximately 0.2 μm and 50 m2 /g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K. 相似文献
12.
A. Cuneyt Tas 《Journal of the American Ceramic Society》2007,90(8):2358-2362
A novel, one-pot technique of synthesizing calcium phosphate whiskers was developed. Commercially available β-tricalcium phosphate (β-Ca3 (PO4 )2 ) powders were aged in unstirred 30% H2 O2 solutions at 90°C for 48 h in ordinary glass media bottles. Resultant samples consisted of whiskers (200 nm wide and 5 μm-long) of a biphasic mixture of octacalcium phosphate (OCP: Ca8 H2 (PO4 )6 ·5H2 O) and carbonated apatitic (apatite-like) calcium phosphate (Ap-CaP). As-formed whiskers possessed a Ca/P molar ratio of 1.46 and a BET surface area of 8 m2 /g. Upon soaking these whiskers in a Tris-HCl-buffered SBF solution of 27 mM HCO3 − for 6 days, Ca/P molar ratio and surface area values were increased to 1.60 and 52 m2 /g, respectively. The technique, owing to its simplicity, may prove useful in providing large amounts of biocompatible short whiskers for numerous technology sectors. 相似文献
13.
(Ca1− x ,Zn x )TiO3 :Pr, B red phosphor particles were prepared using the peroxide-based route and their photoluminescent (PL) properties were investigated by changing the sintering temperature, the concentration of the activator, the ratio of Ca to Zn, and the amount of H3 BO3 flux. For the CaTiO3 :Pr phosphor, a pure perovksite-type CaTiO3 phase was formed when the sintering temperature was 700°–800°C. It was found that the substitution of Zn atoms instead of Ca considerably enhanced the 614-nm red emissions. The PL intensity of (Ca1− x ,Zn x )TiO3 :Pr phosphor was also additionally improved by adding an H3 BO3 flux. Finally, the optimized phosphor Ca0.85 Zn0.15 TiO3 :0.001Pr,0.1B showed the highest PL intensity. 相似文献
14.
Mary W. Barnes Maria Klimkiewicz Paul W. Brown 《Journal of the American Ceramic Society》1992,75(6):1423-1429
Compositions along the Ca2 SiO4 –Ca3 (PO4 )2 join were hydrated at 90°C. Mixtures containing 15, 38, 50, 80, and 100 mol% Ca3 (PO4 )2 were fired at 1500°C, forming nagelschmidtite + a 1 -CaSiO4 , A -phase and silicocarnotite and a -Ca3 (PO4 )2 , respectively. Hydration of these produces hydroxylapatite regardless of composition. Calcium silicate hydrate gel is produced when Ca2 SiO4 ≠ 0 and portlandite when Ca2 SiO4 is >50%. Relative hydration reactivities are a -Ca3 (PO4 )2 > nagelschmidtite > α 1 -Ca2 SiO4 > A -phase > silicocarnotite. Hydration in the presence of silica or lime influences the amount of portlandite produced. Hydration in NaOH solution produces 14-A tobermorite rather than calcium silicate hydrate gel. 相似文献
15.
Arnaud Quintas Odile Majérus Daniel Caurant Jean-Luc Dussossoy Philippe Vermaut 《Journal of the American Ceramic Society》2007,90(3):712-719
The effect of varying R =[CaO]/([CaO]+[Na2 O]) ratio on the crystallization of a rare earth-rich aluminoborosilicate glass (16 wt% RE2 O3 , RE=Nd or La) is investigated. The crystallization of a silicate apatite with Ca2+ x RE8− x (SiO4 )6 O2−0.5 x composition ( x ≈0.4–0.7), is responsible for a drop of the rare earth solubility in the melt. When successive nucleation and growth stages are performed, crystallization processes change across the glass series as a consequence of glass-in-glass phase separation. An exotic phase of composition close to Ca10 Nd7 Si20.75 O62 grows at the expense of silicate apatite. 相似文献
16.
In this communication, we describe an inexpensive and feasible method for the preparation of hexagonal boron nitride (h–BN) nanorods in the absence of metal catalyst. Tertiary calcium phosphate (Ca3 (PO4 )2 ) and ammonium biborate hydrate (NH4 HB4 O7 ·3H2 O) were selected as starting materials where calcium phosphate was used as a diluting agent to prevent the formation of bulk B2 O3 during the thermolysis of ammonium biborate hydrate. The mixture was nitrided at 900°C in the flowing ammonia and was transformed into h–BN nanorods after subsequent crystallization. After crystallization at 1650°C for 2 h, the unique microstructure of h–BN nanorods was observed. 相似文献
17.
F. G. BUTTLER L. S. DENT GLASSER H. F. W. TAYLOR 《Journal of the American Ceramic Society》1959,42(3):121-126
Single-crystal X-ray and electron-diffraction studies show the existence in one polymorph of 4CaO.Al2 O3 . 13H2 O of a hexagonal structural element with α= 5.74 a.u., c = 7.92 a. u. and atomic contents Ca2 (OH)7 - 3H2 O. These structural elements are stacked in a complex way and there are probably two or more poly-types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A12 O3 .13H2 O, from which it is derived by substitution of CO3 2- for 20H- + 3H2 O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al2 O3 .Ca Y 2 - xH2 O and 3CaO Al2 O3 Ca Y xH2 O. On dehydration, 4CaO.Al2 O3 .13H2 O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)2 and 4CaO.3Al2 O3 .3H2 O are formed and, by 1000°C., CaO and 12CaO.7Al2 O8 . The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al2 O3 .3H2 O is formed. 相似文献
18.
Toshifumi Sugama Marita Allan Janet M. Hill 《Journal of the American Ceramic Society》1992,75(8):2076-2087
We investigated the characteristics of calcium phosphate cements (CPC) prepared by an exothermic acid–base reaction between NH4 H2 PO4 -based fertilizer (Poly-N) and calcium aluminate compounds (CAC), such as 3CaO · Al2 O3 (C3 A), CaO · Al2 O3 (CA), and CaO · 2Al2 O3 (CA2 ), in a series of integrated studies of reaction kinetics, interfacial reactions, in-situ phase transformations, and microstructure development. Two groups were compared: untreated and hydrothermally treated CPC specimens. The extent of reactivity of CAC with Poly-N at 25°C was in the following order: CA > C3 A ≫ CA2 . The formation of a NH4 CaPO4 · x H2 O salt during this reaction was responsible for the development of strength in the CPC specimens. The in-situ phase transformation of amorphous NH4 CaPO4 · x H2 O into crystalline Ca5 (PO4 )3 (OH) and the conversion of hydrous Al2 O3 gel →γ-AIOOH occur in cement bodies during exposure in an autoclave to temperatures up to 300°C. This phase transformation significantly improved mechanical strength. 相似文献
19.
Ceramic–polymer composites composed of hydroxyapatite (Ca10 (PO4 )6 (OH)2 , HAp) and calcium poly(vinyl phosphonate) salt were prepared by warm-pressing powder mixtures of tetracalcium phosphate (Ca4 (PO4 )2 O, TetCP) and poly(vinyl phosphonic acid) (PVPA) at a weight ratio of 3.5:1. The effects of temperature (to 300°C), pressure (to 690 kpsi), or compaction time (to 1 h) on the extent of conversion were studied using X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy coupled with energy dispersive spectroscopy. The conversion of TetCP to HAp and formation of the calcium poly(vinyl phosphonate) salt was enhanced at higher temperature, pressure, and/or longer compaction time. Mechanical property determinations showed both the tensile strengths and elastic moduli continuously increase with increasing temperature, pressure, and compaction time. However, the glass transition temperature values of the composites were only minimally higher than that of the unreacted polymer. 相似文献
20.
Junying Zhang Zhongtai Zhang Zilong Tang Yuanhua Lin 《Journal of the American Ceramic Society》2002,85(4):998-1000
A (Ce0.67 Tb0.33 )Mn x Mg1− x Al11 O19 phosphor powder was synthesized, using a simple sol–gel process, by mixing citric acid with CeO2 , Tb4 O7 , Al(NO3 )3 ·9H2 O, Mg(OH)2 ·4MgCO3 ·6H2 O, and Mn(CH3 COO)2 . The phosphor crystallized completely at 1200°C, and the phosphor particle size was between 1 and 5 μm. The excitation spectrum was characteristic of Ce3+ , while the emission spectrum was composed of lines from Tb3+ and Mn2+ . The Mn2+ gave a green fluorescence band, and concentration quenching occurred when x > 0.10. The luminescent properties of the phosphor were explained by a configurational coordinate model. 相似文献