New development in the recent study of condensed phosphates was described in the fields of synthetic process of newly prepared short-chain origophosphates of tetra-, hexa- and octaphosphates, industrial preparation process of ammonium polyphosphates of phases II, V and VI as well as their flame retardation effect, and preparation of proton-conductive phosphate glasses as solid electrolytes.

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Aluminum and nickel ortho- and condensed phosphates were used as a catalyst for decomposition of trifluoromethane and nitrogen trifluoride. The specific surface area, acid strength, and amount of acidic sites of phosphates were also estimated. The condensation degree of phosphates, the addition of other metal cation, and the reforming by mechanical treatment were discussed on the catalytic activity of the phosphates for the design of catalyst.

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Apatites reveal specific physicochemical properties according to the substituted trace elements. Fluoridated apatites, which contribute to the caries prevention, show unexpected crystallinity phenomena in contrast to their solubility behavior. CO₃apatites, which must be closely connected with susceptibility to caries, are main inorganic components of biological hard tissues. The composites of CO₃apatites and collagen are expected as hard tissue biomaterials with excellent biocompatibility for therapeutic use.

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New syntheses of calcium phosphate ceramics and its composite materials are studied. The properties of the developed materials are from bioactive properties for medical applications to bio-functional integration for advanced applications. The newly developed syntheses; mechanochemical synthesis, coatings with interlayer forming, hydrothermal synthesis with organic molecules, phosphorylation and partially hydrolysis, and mesopores coatings into hyper structure formation, templating of macromolecules into ordered structure, are based on low energy and with conscious biological structure formation. Here the development from bioactive to biofunctional integration are descried as follow as high strength calcium phosphate ceramics prepared using mechanochemical synthesized fine powders, calcium phosphate coating on high strength materials, estimation of biocompatibility of bioceramics by tissue culture method, research on water polluted water, morphology control of HAp, stimulation of calcium phosphate growth on polymeric substrate and highly oriented collagen fibers and apatite composite materials through biomimetic route, and biointegaration for multifunctional materials..

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Calcium phosphate cements and the resulting porous hardened bodies are noticed as injectable bone pastes and scaffolds for bone ingrowth or bone cell culture, respectively. The present paper provides various calcium phosphate cement combinations, chemistry and hardened properties.

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Microstructural changes taking place during the heating of spherical calcium-phosphate (Ca₁₀(PO₄)₆(OH)₂ (HAp) and β-Ca₃(PO₄)₂) agglomerates prepared by spray-pyrolysis and freeze-drying techniques have been reviewed. The powders are prepared (1) by the spray-pyrolysis of calcium phosphate (Ca/P ratio=1.50 and 1.67) solution containing Ca(NO₃)₂, (NH₄)₂HPO₄ and concentrated HNO₃ at 600°C, and (2) by the flash freezing of droplets (Ca(CH₃COO)₂, PO(OCH₃)₃ and concentrated HNO₃) in a cryogen, subliming of water ice under reduced pressures, and finally heat-treating of freeze-dried powder at 900°C for 1 h. In both techniques the resulting powders are composed of spherical agglomerates, reflecting the outward form of the starting droplets. The spray-pyrolyzed and heat-treated powder is generally composed of hollow spherical agglomerates, except for the case of ultrasonic spraying of droplets from 0.5 mol · dm^-3 Ca(NO₃)₂/0.3 mol · dm^-3 (NH₄)₂HPO₄ or higher concentration where dense spherical agglomerates are produced. The freeze-dried β-Ca₃(PO₄)₂ and HAp powders are prepared from solutions with Ca/P ratios of 1.44 and 1.67, respectively, and comprise of agglomerates with weakly-bonded particles.

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Ultrasonic spray-pyrolysis technique may be effective for syntheses of the HAp and various substituted apatites powders with the formula of M₁₀(PO₄)₆(OH)₂ (M=Ca, Sr, Ca+Sr and Ba). We have reviewed our research for 1) syntheses of HAp and substitued apatite powders by spray-pyrolysis technique and 2) coating process for porous films with good biocompatibility based on the above technique. Spray-pyrolysis technique is also effective for porous coating of biocompatible calcium-phosphate films. We wish that novel biomaterial has been developed via spray-pyrolysis technology and then use to clinical applications.

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Living things produce hard tissues such as bones, teeth and shells through precipitation of inorganic substances such as calcium carbonate (CaCO₃), hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) and silica (SiO₂) on organic matrices at ambient conditions. This phenomenon is called biomineralization. As a novel technique to develop inorganic-organic hybrid materials, biomimetic process which mimics the mechanism of the biomineralization have been attracting much attention. This paper reviews some trials to obtain inorganic-organic hybrids based on calcium carbonate and hydroxyapatite. Crystal structure and morphology of the calcium carbonate can be easily controlled according to the kind of organic polymers and metal ions added into calcium carbonate supersaturated solutions. In addition, various hydroxyapatite-polymer hybrids can be designed by using simulated body fluid (SBF) or more concentrated solutions that is supersaturated with respect to the hydroxyapatite. This type of biomimetic process is expected as a novel material design with low energy consumption and low load on environment.

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The formation of a bone-like apatite layer is essential for glasses and glass-ceramics to show osteoconductivity, i.e., a bone-bonding property, when they are implanted in bony defects. Glasses in the CaO-SiO₂ binary system show promise in being able to deposit apatite after exposure to a body fluid, since these glasses can release Ca²⁺ ions to increase the degree of supersaturation of the surrounding body fluid with respect to apatite, as well as having the ability to form silanol groups that can induce heterogeneous nucleation of apatite on their surfaces. In this paper, we review different types of glass-ceramics that are mainly composed of CaO and SiO₂ for their potential to form apatite in a simulated body fluid that has similar ion concentrations to those found in human blood plasma.

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Based on the composition formula of Na_3+3x-yR_1-xP_ySi_3-yO₉, Na₅YSi₄O₁₂ (N5)-type glass-ceramic Na⁺ superionic conductors were successfully produced for a variety of rare earth ions, R, under the appropriate composition parameters. In the crystallization of N5-type glass-ceramics, its relatives (Na₃YSi₃O₉ (N3)- and Na₉YSi₆O₁₈ (N9)-type glass-ceramics) structurally belonging to the family of Na_24-3xY_xSi₁₂O₃₆ were found to crystallize as the precursor phase at low temperatures. In order to produce N5 single phase glass-ceramics, the concentration of both phosphorus and rare earth was found important. The meaning of the composition was evaluated by thermodynamic and kinetic studies on the phase transformation of metastable N3 or N9 phases to stable N5 phase with Na⁺ superionic conductivity.
The possible combinations of x and y became more limited for the crystallization of the superionic conducting phase as the ionic radius of R increased, while the Na⁺ conduction properties were more enhanced in the glass-ceramics of larger R. These results are discussed in view of the structure and the conduction mechanism. Also studied were the microstructural effects on the conduction properties, which were dependent upon the heating conditions of crystallization. These effects were understood in relation to the grain boundary conduction properties as well as the transmission electron microstructural morphology of grain boundaries.

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Calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂:HA, is the inorganic principle component of natural bones and teeth. It has been already suggested that the amount of OH ion in the crystal structure of HA is closely related to the biocompatibility. The amount of OH ion in current HA, however, has not been controlled. In order to prepare more functional HA ceramics, the amount of OH ion must be controlled. In this study, HA ceramics with different OH amount were prepared by spark plasma sintering (SPS). In order to reveal the ideal sintering conditions for preparation of transparent ceramics, densification process on SPS was investigated. The samples were pressed uniaxialy under 60 MPa, and then they were heated by SPS at 800 °C, 900 °C and 1000 °C for 10 min with the heating rate of 25 °C · min^-1. The quantity of OH ion in HA ceramics sintered by SPS was decreased with increasing temperature of sintering. Transparent HA ceramics were prepared by SPS at 900 °C and 1000 °C. In analysis of the densification behavior during sintering of HA by SPS, dominant sintering mechanism was plastic flow of densification. Cell attachment, proliferation, and osteogenic differentiation of rat mesenchymal stem cells on transparent HA ceramics observed by light microscopy were significantly similar to those on tissue culture polystyrene dish. The observation of living cells on transparent HA ceramics is a new significant and revealed reliable nature of the hydroxyapatite ceramics for the purpose of tissue engineering in hard tissue repair.

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Hydroxyapatite (HAP) was prepared from CaCl₂, Na₂HPO₄ and NaOH in an aqueous phase mixed with a chloroform solution of cetylphosphate (CP). The CP was incorporated mainly on the surface of HAP but not to its bulk phase, resulting in formation of a hydrophobic surface. This surface-modified HAP has various characteristic properties different from those of the intact HAP. Some of the examples are as follows; an increase in a contact angle of water droplet, a decrease in a mean diameter of the HAP particle, and increases in the amounts of adsorption of various organic compounds. The aim of this study was of characterization of the surface-modified HAP through determining the adsorption amounts of various organic compounds on the surface. As for the adsorption of a surfactant to the modified HAP, it was concluded that hydrophobic interaction between alkyl chains of a surfactant and those of CP implanted on the surface became more important than hydrophilic interaction between polar/ionic groups of a surfactant and ions exposed on the intact area of the HAP. In the adsorption of bovine serum albumin (BSA), it was denatured by the CP implanted on the surface of the modified HAP (i.e., surface denaturation). Adsorption properties of the surface-modified HAP were quite different from those of the intact HAP.

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The effect of a cationic surfactant, dodecyltrimethylammonium chloride (DTMAC), on the adsorption of bovine serum albumin (BSA) to the surface of hydroxyapatite (HAP) was studied. BSA was bound to HAP owing mainly to electrostatic interaction between opposite charges on HAP and BSA in the absence of an additive. On the other hand, the adsorption amount of BSA by HAP decreased after attaining a maximum with a concentration of DTMAC when a concentration of BSA was kept constant at 0.2w/v%. At a low concentration region of DTMAC, the adsorption amount of BSA on HAP increased with the concentration by virtue of hydrophobic interaction between hydrophobic groups of DTMAC bound to BSA and those adsorbed on HAP. The adsorption amount, however, decreased with the concentration at a high concentration region of DTMAC. This is because the expansion/denaturation of BSA molecule was caused by the binding of much amount of DTMAC, resulting in an increase in a molecular occupied area of BSA.

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Titanium cation was introduced into calcium hydroxyapatite by three different procedures; (A) stepwise precipitation, (B) coprecipitation, and (C) surface treatment with aqueous titanium. The solids (Ti-CaHAp) thus obtained were employed as a photo-catalyst for the decomposition of methylene blue. No photo-catalytic activities were observed on Ti-CaHAp obtained from the surface treatment. Although rather great photo-catalytic activities have been already reported on Ti-CaHAp prepared with the stepwise precipitation, the decomposition of methylene blue on Ti-CaHAp depended on the atomic ratio of Ti/Ca in the catalysts. The photo-catalytic activities on Ti-CaHAp obtained from the coprecipitation were evidently greater that those on the solids obtained with the stepwise precipitation.

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Barium hydroxyapatite (Ba₁₀(PO₄)₆(OH)₂; BaHAp) was successfully prepared with a sol obtained from the addition of sodium alginate ((C₅H₇O₄ · COONa)_n) to the aqueous mixture of sodium diphosphate (Na₄P₂O₇) and barium nitrate (Ba(NO₃)₂) although it has been already reported that calcium hydroxyapatite, typical hydroxyapatite, was prepared with a sol obtained from the addition of the corresponding nitrate to the aqueous mixture of sodium diphosphate and sodium alginate.

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The spherical β-calcium orthophosphate (β-Ca₃(PO₄)₂: β-TCP) agglomerates have been prepared by a spray-pyrolysis technique. The hollow spherical agglomerates were obtained by heating the spray-pyrolyzed powder at 900°C for 10 min. The cylindrical specimen was fabricated mixing the calcium-phosphate paste (CPP) with 10-50 mass% β-TCP agglomerates, using malaxation liquid. The setting time of CPP specimen increased from 8.5 to 17 min with increasing amount of β-TCP from 10 to 50 mass%. The CPP specimens with β-TCP addition were immersed into the simulated body fluid (SBF) at 37±0.2°C for various times. The compressive strengths of CPP specimens with β-TCP addition reached maxima, e.g., 42.8 MPa for 10 mass% β-TCP addition and 7.5 MPa for 50 mass% β-TCP addition, respectively, after the immersion of these specimens in SBF for 3-7 d. Crystalline phases of the CPP specimens after the immersion in SBF for 7 d were HAp and β-TCP. The total porosity of CPP specimen increased with increasing amount of β-TCP and attained 67.1% for 50 mass% β-TCP addition.

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The influence of thermal treatment on the performance of polymers as dispersants for calcium hydropxyapatite, HAP, was investigated in an aqueous system. The polymeric additives tested include: homo-polymers of acrylic acid (AA) and maleic acid (MA); co-polymer of AA:SA (2-acrylamido-2-methylpropane sulfonic acid) and ter-polymers of AA:SA:t-bAM (tertiary butyl acrylamide) and AA:SA:SS (sulfonated styrene). It was found that polymers containing SA upon exposure to heat treatment (i.e., 150° to 200°C, 1 hr to 20 hr) undergo degradation. The extent of degradation as investigated by NMR and FT-IR techniques indicates that at higher temperature and longer exposure time, SA is essentially degraded to acrylic acid. Among the ter-polymers tested, SS containing polymer exhibits more stability to thermaI treatment than the t-BuAm containing polymer. In addition, it has been found that polymer architecture strongly influences the performance of polymer as HAP dispersant.

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The influence of polymeric and non-polymeric additives as dispersants for calcium hydropxyapatite, HAP, was investigated in an aqueous system. The polymeric additives tested include: homo-polymers of acrylic acid (AA), maleic acid, methacrylic acid, 2-acrylamido 2-methylpropane sulfonic acid, (SA); co-polymer of AA:SA and ter-polymers of AA:SA:t-bAM (tertiary butyl acrylamide) and AA:SA:SS (sulfonated styrene). It was found that polymer architecture i.e., monomer type, monomer content, molecular weight, and polymerization solvent, strongly influences the performance of polymer as HAP dispersant. The non-polymeric additives investigated include: phosphonates and surfactants. The dispersancy data reveal that non-polymeric additives are inferior to polymeric additives in dispersing HAP.

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The impact of thermal stability on the performance of homo-, co-, and ter-polymers on the precipitation of calcium phosphate was investigated at pH 8.50, 50°C, calcium = 3.50 mM and phosphate = 0.095 mM. The polymers tested include: poly(acrylic acid), P-AA; poly(maleic acid), P-MA; poly(acrylic acid: 2-acrylamido-2-methyl propane sulfonic acid), P-AA:SA; P-AA:SA:t-bAm (ter-butylacrylamide), and P-AA:SA:SS (sulfonated styrene). It has been found that all polymers lose performance to a varying degree when exposed to thermal treatment. The performance data also suggest that SS containing ter-polymer is a better calcium phosphate inhibitor than t-bAm containing ter-polymer. In the case of co-polymer of AA:SA, the thermal treatment exhibits strong negative influence on the inhibitory power of polymer. The results have been explained in terms of loss of SA and t-bAM in the co- and ter-polymers leading to the formation of poly(acrylic acid).

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Hydroxyapatite was prepared by a reaction of CaWO₄ with phosphate at temperatures from 90 °C to 210 °C. High concentration of NaOH was appropriate for the formation processes of hydroxyapatite. The temperature dependence of reaction rate was related to the mass transport through a reaction layer. Very small activation energy of reaction, 25.5 kJ/mol, was attributed to the diffusion of Ca²⁺ ions in liquid among reaction products.

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Hydroxycarbonate apatite (HCA) coatings on two types of composites containing calcium carbonates were prepared by a biomimetic method using simulated body fluid (SBF). Poly(lactic acid) (PLA) composites containing calcium carbonates formed HCA on the surface after soaking in SBF for 3 h. The PLA composites had numerous carboxy groups bonded with Ca²⁺ ions. Titania composites containing calcium carbonates formed HCA on the surface after soaking in SBF for 1 d. Formation of titanium hydroxide groups was drastically promoted on the titania composite by soaking in SBF. The HCA-forming ability of these composites was much higher than that of PLA or titania crystals. Vaterite in the composites plays an important role in HCA formation in SBF. By soaking in SBF, a large amount of Ca²⁺ ions released from the vaterite increase in the supersaturation of HCA in SBF.

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This paper reports the fluorescence properties and stabilization of Ce³⁺ and Tb³⁺ codoped calcium carbonate phosphor which was treated in an ammonium phosphate solution. The reaction rate of the phosphor (Ce³⁺ and Tb³⁺ codoped calcium carbonate, CaCO₃:Ce³⁺, Tb³⁺) when treated for 60 minutes in (NH₄)₃PO₄ solution was approximately 40 mass%. Amorphous calcium phosphate (ACP) and dicalcium phosphate dihydrate (DCPD), which was obtained by the crystallization of ACP, were seen to adhere to the phosphor surface. The emission intensity of the phosphor treated for 60 minutes rose by 1.7 times that of the original phosphor and gently decreased for about 60 days. The ACP adhered on the phosphor surface was in the form of ultrafine particles and was emitted by the inclusion both Ce³⁺ and Tb³⁺ ions. It is thought that the increase of the emission intensity of the phosphor adhered ACP is based on the emission from both ACP and the phosphor.

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Phosphate glass with a composition of 15BaO-10PbO-5SrO-70P₂O₅ has been prepared by 2.45 GHz microwave heating. In the ³¹P MAS NMR spectra of this glass, we observed the strong Q₃ band corresponding to the branching PO₄ group which was not observed in the glass prepared by conventional electric furnace heating. The presence of branching points means that the glass prepared by microwave has three-dimensionally polymerized structure, which gives the higher stability of the glass.

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