Koji Ioku

Porous hydroxyapatite ceramics prepared by hydrothermal hot-pressing

Etude experimentale de la solidification de lapatite hydroxylee par pressage chaud dans des conditions hydrothermales et de la preparation de ceramiques poreuses resistantes a partir du materiau solidifie

Densification of silica gels by hydrothermal hot-pressing

Commercial silica gels (Nipsil ES and Nipsil VN3, produced by Nippon Silica Industrial Co. Ltd, Japan) which were quite different from spherical silica particles in their production method and properties, were densified by hydrothermal hot-pressing

Neck formation of spherical silica particles by hydrothermal hot pressing

On etudie le pressage de particules spheriques de SiO 2 par traitement hydrothermal. On etudie la densite de la masse solidifiee et ses proprietes mecaniques. On examine les surfaces de rupture au microscope electronique a balayage

Preparation and Characterization of Porous Apatite Ceramics Coated with β-Tricalcium Phosphate

Hydroxyapatite (Ca10(PO4)6(OH)2; HA) is one of the most biocompatible materials with bones, and porous HA is promising bone substitute materials for clinical applications. While there are reports that beta-tricalcium phosphate (Ca3(PO4)2; TCP) has higher resorbability than HA when the material is implanted in a bone defect. In the present study, porous HA coated with beta-TCP was prepared by our unique method. The porous HA of about 60% porosity with interconnecting pore structure was soaked in diammonium hydrogen phosphate solution, and then the HA was sintered at 900 degrees C for 3 h. beta-TCP was revealed by X-ray diffractometry on the surface of porous HA. It was possible to control the content of surface-formed beta-TCP arbitrary by varying the concentration of the solution. The obtained HA coated with 33 wt% beta-TCP (33TCP) had about 60% open porosity with the pore size from 150 to 400 microns. The average compressive strength of this porous ceramics was 17.5 MPa. Surface coated HA with beta-TCP deprived of the brittleness in handling. The weight of HA implanted into muscles was increased obviously at 4 weeks because of formation of carbonate hydroxyapatite on the surface of HA. The weight of 33TCP was scarcely changed up to 12 weeks, but the weight tended to increase at 24 weeks. The carbonate hydroxyapatite was not formed on 33TCP at 4 weeks, but formed on it at 24 weeks. Therefore beta-TCP coated porous HA behaved like beta-TCP initially after implantation, and then behaved like HA.

Hydrothermal crystallization mechanism of sodium beidellite from amorphous gel

Beidellite is a dioctahedral member of the smectite group and sodium beidellite can be described by the general formula, NaxA12(Si4_xAlx)O10(OH)2.nH20. Natural beidellite has an average layer charge of 0.33, although theoretically values range from 0.2 to 0.6 [1]. Beidellite has been hydrothermally synthesized from a gel by several researchers [1-5]. Their methods can be classified into two groups depending on the silica source for the gel preparation: the procedure of Luth and Ingamells [6] used colloidal silica, and that of Hamilton and Henderson [7] used tetraethyl orthosilicate (TEOS). Kloprogge et al. [1, 5] used gels prepared from TEOS to prepare sodium beidellite and presented the properties of synthesized sodium beidellite and its stability in the Na20-A1203-SiO2-H20 system. They reported that pure phase of beidellite was obtained by hydrothermal treatment of the gel only in water, but low-quartz co-existed with beidellite under basic conditions. Furthermore, kaolinite and low-quartz were crystallized at low temperatures below 250 °C but not sodium beidellite. Koizumi and Roy [2] used colloidal silica to prepare gels and showed the formation of wellcrystallized beidellite at 300-350 °C by reaction of a small amount of water with the gel with ideal beidellite composition. Plee et al. [3] synthesized sodium beidellite under basic conditions from a gel prepared by using colloidal silica. This report disagreed with the results obtained by Kloprogge et al. [1, 5]. The aim of the work reported here was to clarify the crystallization mechanism of sodium beidellite from a gel prepared from colloidal silica. The starting materials were Al(NO3)3.9H20, NaNO3 (reagent grade, Wako Pure Chemical Industries Ltd, Japan) and Ludox colloidal silica (HS-40; E.I. du Pont Nemours & Co., USA), which contains 40% SiO2 and a small amount of Na with SiOJNa20 weight ratio of 95. Starting gel (gel 1) was prepared to obtain the composition of Na0.4A12 (Si3.6A10.4) O10(OH)2nH20. Firstly, a solution was prepared by dissolving 150.052 g of Al(NO3)3.9H20

Preparation of biologically active glass ceramics with rod-shaped crystals dispersion by hydrothermal hot-pressing

Research Laboratory of Hydrothermal Chemistry, Faculty of Science, Kochi University, 2-5-1 Akebono-cho, Kochi 780, Japan Biologically active glass (Bioglass) in the system Na20-CaO-SiO2-P2Os, is used as implant mater- ials because of the ability to bond chemically to living bone [1-3], but its mechanical properties, especially toughness, are insufficient for hard tissue. Therefore, their usefulness is limited to areas with- out mechanical requirements. Recent studies have demonstrated that dense ceramics can be toughened by rod-shaped particles dispersed in them, due to the crack deflection and pull-out toughening mechan- isms [4, 5]. Fully dense glass ceramics could be prepared by mechanical pressing under hydro- thermal conditions by the hydrothermal hot-pressing technique [6-10]. The present work deals with the preparation of reinforced Bioglass ceramics with rod-shaped crystals dispersion by hydrothermal hot- pressing. The autoclave for hydrothermal hot-pressing used in this work was a steel cylinder. Bioglass powders (45S5, Nikon Co., Japan) pulverized into grains under 200 mesh (smaller than 75 gm) were kneaded with 20 wt % distilled water, then transferred into the autoclave. The starting sample in the chamber was compressed uniaxially by cast rods from above and below. The details of this autoclave [11] and related autoclaves [12] were described in the previ- ous paper. The Bioglass ceramics were prepared by hydro- thermal hot-pressing at temperatures from 100 to 350 °C under 50 MPa mechanical pressing for 2 h. The produced phases were identified by powder X-ray diffractometry (XRD, Rigaku RAD-RC) with Ni-filtered CuKo~ radiation, operating at 40 kV and 100 mA. The microstructure of the glass ceramics was observed by scanning electron microscope (SEM, Hitachi

Development of solubility measurement method under hydrothermal conditions

530) for the polished surface. According to the XRD analysis, the solidified Bioglass hot-pressed hydrothermally at 100 °C had no crystalline phases. This solidified Bioglass with- out crystalline phases had about 86% theoretical density. The Vickers hardness was determined to be 1.0 GPa by the micro-Vickers indentation method with 1.96 N loading for 15 s (Akashi MVK-EIII). The compressive strength of this glass was found to be 150 MPa by uniaxial compression perpendicular to the base of the compact in cylindrical shape with crosshead travel rate of 0.02 cmmin -1 (Shimadzu REH-100). XRD analysis (Fig. 1) revealed that the glass ceramics hot-pressed hydrothermally at above 200 °C had crystalline phases identified as NaCa2 0261-8028

Hydrothermal preparation of Na1.0Ti2(PO4)3 fine powders

We have developed a simple method for accurate solubility measurement under relatively mild hydrothermal conditions in which the vapour phase coexists with the liquid phase. The method basically consists of separation of the solid specimen from the solution under hydrothermal conditions, in order to avoid regrowth or further weight loss during quenching

Reaction of Porous Hydroxyapatite, β-TCP and β-TCP Coated Hydroxyapatite in the Bone

The NASICON-type group of materials has been investigated because of their considerable potential as high ionic conductors. NASICON, Na3Zrz-PSi2012, is one term of the solid solution Nal+xZrzP3_xSix012 with NaZr2(PO4) 3 (NZP). Since the first report on this high conductivity [1], much research has been devoted to synthesis of analogous compounds. The hydrothermal synthesis of NZP powders was successful in the presence of trimethylamine [2]. Also, work on the sintering of NZP-type materials to obtain ionic conductive ceramics has been reported [3]. NaTiz(PO4) 3 is one of the materials with a NASICON-type crystal structure of R3C consisting of a 3-dimensional network made up of TiO6-octahedra sharing corners with PO4-tetrahedra. The preparation of this material was by solid-state reaction at high temperature, 1000 °C [4], by the sol-gel method [5] and by the flux method [6]. It is necessary to produce non-aggregated, homogeneous and fine powders in order to obtain well sintered ceramic samples. Hydrothermal synthesis of ceramic powders is known as one of the most suitable methods for this purpose. In the first report of hydrothermal synthesis of NaTi2(PO4)3, crystalline anatase, TiO2, was chosen as the starting material of the Ti component [7]. Several days were required to prepare the samples. In the present work, the gel-like material, amorphous TiO2nH20, was chosen instead of crystalline TiO 2 in order to synthesise them faster than other methods. Therefore, the results of the hydrothermal faster synthesis of NaTi2(PO4)3 fine powder will be described in this report. Firstly, a starting material for the hydrothermal reaction was obtained by coprecipitation. TIC14 was added to distilled water cooled by ice under stirring. Then the yellow TIC14 solution was combined with a solution of NH3 resulting in a thick yellowish white precipitate. Thus we obtained a semipermeable white gel after washing with deionized and distilled water and air drying. For the autogenously hydrothermal reaction, 145 mg of the starting gel-like material, 85% H3PO 4 and NaOH aqueous solution were put into a Teflon-lined mini-autoclave of 30 cm 3 capacity. The reaction vessel was heated in an electric furnace for 0.5-24 h at 220 °C. After air cooling of the vessel, the white powder product was recovered by filtration, washed with deionized and distilled water, and dried in a desiccator at room temperature. XRD (RIGAKU RAD-2C with monochromated CuKo 0 measurement showed that the white powderlike gel obtained by this coprecipitation method was an amorphous phase. The water content of the sample was determined by TG-DTA (Mac Science TG-DTA2000), suggesting amorphous TiO2 nH20 (n = 2). So we used the material-like gel as the starting sample for hydrothermal crystallization. Table I shows the conditions of various ratios of starting material, TiO 2. nH20 gel, H3PO4 and NaOH, on hydrothermal treatment. As a result of XRD characterization, it turned out that the phases in the products were determined by the ratios of the starting material. NaTi2(PO4)3 was not obtained with the ratio Na20:TiO2:P2Os = 1:4:3, corresponding to its chemical composition, against our expectation; TiO2 (anatase) was obtained instead of NaTiz(PO4) 3. And with the ratio Na20:TiO2:P205 = 3:1:4, which contained relatively more Na, Na2Yi90 m was obtained. The samples synthesized where the P ratios were relatively high were shown to have the same XRD patterns as that of NaTie(PO4)3. But chemical analysis by ICP (SeikoElectron SPS7000A) showed they were NaxTiz(PO4)3:x = 1.1-1.3. The desired material, Naa.0Ti2(PO4)3, was obtained with the ratio Na20:TiO2:P205 = 0.8:1:24, where the P ratio was much higher. Fig. 1 shows an XRD pattern of t h e sample synthesized where NazO:TiO2:P205 = 0.8:1:24. All the peaks were indexed for NaTiz(PO4)3 [8], but relative intensities were different; intensities of (012) and (0 2 4) diffraction were rather stronger than that of (1 13) which was reported to have maximum intensity. The hexagonal lattice parameters calculated from that XRD pattern by the least squares method were a=0 .852nrn and c = 2.182 nm. i It turns out that pure NaTi2(PO4)3, withgut any other phases, could be obtained in only 5 h. IR spectra measured in KBr disks (Niho~abunko JASCO FT-IR5300) showed a PO4-tetrahedra band at about 1000 cm -1 and other characteristic I NaTiz(P04) 3 bands. The TG-DTA data showed ~o clear

Microstructure Designing of Hydroxyapatite Ceramics by Hip Post-Sintering

ABSTRACT This study was conducted to analyze and compare the bone ingrowth (amount of regenerated bone) and biodegradation of low-porosity (60%) hydroxyapatite (HA), 100 wt% β-tricalucim phosphate (TCP) and 33 wt% β-tricalucim phosphate-coated HA (33TCP). The results suggest that in the early in vivo stages 33TCP behaved similarly to β-TCP by showing high resorption and rapid bone ingrowth, but in the later stages behaved like HA by maintainig a high rate of the bone ingrowth, making it a more effective bone substitute material.