Anhydrous Phosphate Research Articles

Morphological and phase characterizations of retrieved calcium phosphate cement implants.

A self-hardening calcium phosphate cement (CPC), consisting of equimolar amounts of tetracalcium phosphate and dicalcium phosphate anhydrous, hardens when mixed with water and forms a resorbable hydroxyapatite (HA) as the end-product. The objective of this study was to investigate the changes of the phase and morphology of the CPC during hardening and aging under in vivo conditions. CPC samples retrieved 12 h after hardening in vivo had already contained carbonated HA (type B), even though the initial cement mixture did not contain carbonate as one of the solid components. The mass fraction of carbonate in the 12-h sample was about 1%. The results suggested that under in vivo conditions carbonate is readily available and this allows formation of carbonated HA in favor of carbonate-free HA. The carbonate content of the CPC samples retrieved 3 months after implantation was similar to that of the 12-h samples, and the exterior surfaces of the 3-month samples appeared less crystalline than that of the 12-h samples.

New Results of Chemical Transport as a Method for the Preparation and Thermochemical Investigation of Solids

Chemical transport experiments are a valuable aid of great potential in the synthesis and thermochemical characterization of solids. Compounds of interest can often only be crystallized by this method. The use of a transport balance allows very detailed observations, particularly of the course of the experiment over time (simultaneous or sequential deposition of multiple-phase solids). The computer program CVTRANS enables a quantitative thermochemical description of the experiment based on the cooperative transport model. A compilation of recent results illustrates the development and efficiency of the method. The transport of phosphides, anhydrous phosphates and sulfates, and rare-earth oxide and oxohalide compounds are treated in detail.

New Results of Chemical Transport as a Method for the Preparation and Thermochemical Investigation of Solids

Chemical transport experiments are a valuable aid of great potential in the synthesis and thermochemical characterization of solids. Compounds of interest can often only be crystallized by this method. The use of a transport balance allows very detailed observations, particularly of the course of the experiment over time (simultaneous or sequential deposition of multiple-phase solids). The computer program CVTRANS enables a quantitative thermochemical description of the experiment based on the cooperative transport model. A compilation of recent results illustrates the development and efficiency of the method. The transport of phosphides, anhydrous phosphates and sulfates, and rare-earth oxide and oxohalide compounds are treated in detail.

Diametral tensile strength and compressive strength of a calcium phosphate cement: effect of applied pressure.

The diametral tensile strength (DTS) and compressive strength (CS) of a calcium phosphate cement comprised of tetracalcium phosphate and dicalcium phosphate anhydrous were studied. Cement powder and water were mixed at a powder/liquid ratio of 4.0. The resulting cement pastes were placed in molds and a pressure ranging from 0-2.8 MPa was applied for various lengths of time (0.5-24 h). DTS and CS measurements were conducted on 24-h wet samples. The strength was found to be significantly (p<0.05) affected by the pressure but not by the time. Samples prepared under a pressure of 0.7 MPa had a mean DTS value of 10.8+/-1.0 MPa (n = 5), which is comparable to the values reported in the literature for the same cement prepared under similar conditions. In contrast, the mean CS value obtained in the present study, 66.1+/-5.0 MPa (n = 5), was significantly higher than the value (51+/-4.5 MPa) previously reported. The higher CS may be attributed to an improved mold design that may reduce sample damage during demolding, and to the use of a loading device that applied a constant pressure to the sample during setting. The average standard deviation of the mean for the 19 DTS sample groups (n = 5 in each group) was 1.1 MPa, corresponding to 9.6% of the mean DTS value. The average standard deviation of the 7 CS sample groups (n = 5 in each group) was 4.5 MPa, corresponding to 7.1% of the mean CS value. Published 2000 John Wiley & Sons, Inc.

Metastable Equilibrium Solubility Distribution of Carbonated Apatite as a Function of Solution Composition

Previous studies have shown that carbonated apatites (CAPs) exhibit the phenomenon of metastable equilibrium solubility (MES) in weak acid media. The purpose of the present investigation was to examine two questions: first, whether the MES concept is applicable to a broader range of solution conditions and, second, whether a driving force function associated with a surface complex having a constant stoichiometry governs the dissolution of CAP and, if so, what is this stoichiometry. CAP preparations with carbonate contents of 1.8–5.7 wt% (synthesized by hydrolysis of dicalcium phosphate anhydrate in solutions of varying bicarbonate levels or by direct precipitation from supersaturated calcium/phosphate/carbonate solutions) were studied as follows. MES distributions for each of the CAP preparations were determined by equilibrating the CAP under stirred conditions in a series of acetate buffers (0.10 M) containing various levels of calcium and phosphate in the pH range 4.5–6.5 and a solution calcium/phosphate ratio in the range 0.1–10. The amount dissolved in each instance was regarded as the fraction of the CAP possessing an MES value greater than that corresponding to the ion activity product (IAP) of the equilibrating solution. The solution IAPs were calculated from the solution compositions using plausible calcium phosphate stoichiometries, viz., dicalcium phosphate dihydrate, octacalcium phosphate, tricalcium phosphate, hydroxyapatite, carbonated apatite (based on the bulk composition of the particular CAP involved in the experiment), and tetracalcium phosphate. The fraction of CAP dissolved was plotted against the solution IAPs for each experimental set using each of the six assumed stoichiometries for the surface complex. The results demonstrated that the MES concept was applicable to all of the CAP preparations in media of various solution compositions and different pH levels. The most important new outcome of this study was that MES profiles for each of the CAP preparations in all of the experiments were found to be superimposable when solution IAPs were calculated using the hydroxyapatite stoichiometry, while such was not the case when other stoichiometries were used to calculate the solution IAPs.

Crystal Growth and Characterisation of Rare Earth Phosphates

Growth of rare earth phosphates has been carried out from aqueous phosphoric acid solutions. The system K2O - La2O3 - P2O5 - H2O has been studied in detail within a temperature range 150 to 700 degrees C, and a series of hydrous and anhydrous phosphates have been obtained. The influence of several growth parameters like the ratio of the alkali metals to rare earth metals, the concentration of P2O5, H2O, the pH of the growth media, experimental temperature, etc. on the type and quality of the rare earth phosphate obtained has been studied. The growth mechanism of the formation of various hydrous and anhydrous phosphates in the system K2O - La2O3 - P2O5 - H2O has been studied, in order to obtain crystals with a desired morphology and quality, which helps in the in-situ fabrication of the crystals ready for use as solid state laser hosts. LaP5O14 and KLaP4O12 crystals were doped with Nd up to 20%.

Reaction of calcium phosphate cements with different amounts of tetracalcium phosphate and dicalcium phosphate anhydrous

Calcium phosphate cements (CPCs) with different amounts of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) (TTCP/DCPA molar ratio from 0.25 to 2.00) were prepared to further understand the setting reaction and the factors that could influence the properties of CPCs. Quantitative X-ray diffraction patterns, Fourier transform IR spectra, and diametral tensile strength of the set mass were measured along with pH measurements of the CPC suspension. Calcium-deficient hydroxyapatite (d-HAP) with a calcium to phosphate molar ratio of approximately 1.5 was formed initially in the CPC setting consisting of an equimolar mixture of TTCP and DCPA. This gradually transformed into stoichiometric HA (s-HA) with increasing incubation time. The s-HA was formed in the initial stage when the CPC contained an excess amount of TTCP. In contrast, maturation to s-HAP was slow when the CPC contained excess amounts of DCPA. The highest mechanical strength of set CPC was associated with an equimolar mixture of TTCP and DCPA, and the mechanical strength decreased as the TTCP/DCPA molar ratio deviated from 1.00. We concluded, therefore, that the setting reaction and the nature of the resulting set mass are dependent on the molar ratios of TTCP and DCPA.

Possible Mechanisms of Intercalation

Recent knowledge of the kinetics and intercalation mechanisms are summarized and accompanied by examples of intercalation reactions of water and ethanol into anhydrous vanadyl phosphate and redox intercalation of alkali metal cations into vanadyl phosphate dihydrate. Three possible mechanisms of intercalation are presented which are based on: (i) a concept of exfoliation of layers; (ii) the formation of stages and randomly stacked layers; (iii) co-existence of intercalated and non-intercalated parts of crystals of the host separated by an advancing phase boundary. The corresponding kinetic curves are ascribed to mechanisms (ii) and (iii).

5665144 Method and apparatus utilizing hydrocarbon pollutants from glycol dehydrators : Hill D Jeffre; Wiggins E Tod Edmond, OK, United States

Calcium phosphate whiskers have been suggested to be effective as the reinforcement in improving mechanical properties of composite biomaterials. Therefore, composite scaffolds of varying compositions were prepared by freeze drying of gelatin foams containing increasing amounts of calcium phosphate whiskers/fibrous spherulites, up to 50 wt%. The whiskers were attempted to synthesize in acidic solutions under thermal conditions using two different methods: aging of a highly crystalline beta-tricalcium phosphate powder in H2O2 solution, and the precipitation−hydrolysis method using aqueous solutions of calcium and phosphate ions in HNO3 solution and urea as an additive. The morphology and phase analysis of the whiskers were studied by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. The results proved that the whiskers could not be obtained by first method at an appropriate period, but using the second method, a mixed plate-like and long whiskers, and fibrous spherulites could be formed. The XRD patterns revealed the biphasic mixture of octacalcium phosphate (OCP) and dicalcium phosphate anhydrate (DCPA). The composite scaffolds containing whiskers obtained by freeze drying were characterized by SEM, Fourier transform infrared spectroscopy and compressive mechanical test. Scaffolds with interconnective pores in a range of 150–350 μm and porosity of 65–74%, as well as homogenous dispersion of the whiskers could be produced which indicates their potential to use in bone tissue engineering applications. The prepared scaffolds showed the compressive yield strength of 4.3−6.2 MPa and Young modulus of 28−38 MPa. In the view of mechanical and microstructural features, the composite of 25 wt% calcium phosphate phase was introduced as the optimal composite for bone tissue engineering.

5665149 Anti-corrosion pigment and use thereof : Gotzmann Karl; Dorn Karlheinz; Numl agerl Hans-Dieter; Guml obelbecker Sieghard Budenheim, Germany assigned to Chemische Fabrik Budenheim

Calcium phosphate whiskers have been suggested to be effective as the reinforcement in improving mechanical properties of composite biomaterials. Therefore, composite scaffolds of varying compositions were prepared by freeze drying of gelatin foams containing increasing amounts of calcium phosphate whiskers/fibrous spherulites, up to 50 wt%. The whiskers were attempted to synthesize in acidic solutions under thermal conditions using two different methods: aging of a highly crystalline beta-tricalcium phosphate powder in H2O2 solution, and the precipitation−hydrolysis method using aqueous solutions of calcium and phosphate ions in HNO3 solution and urea as an additive. The morphology and phase analysis of the whiskers were studied by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. The results proved that the whiskers could not be obtained by first method at an appropriate period, but using the second method, a mixed plate-like and long whiskers, and fibrous spherulites could be formed. The XRD patterns revealed the biphasic mixture of octacalcium phosphate (OCP) and dicalcium phosphate anhydrate (DCPA). The composite scaffolds containing whiskers obtained by freeze drying were characterized by SEM, Fourier transform infrared spectroscopy and compressive mechanical test. Scaffolds with interconnective pores in a range of 150–350 μm and porosity of 65–74%, as well as homogenous dispersion of the whiskers could be produced which indicates their potential to use in bone tissue engineering applications. The prepared scaffolds showed the compressive yield strength of 4.3−6.2 MPa and Young modulus of 28−38 MPa. In the view of mechanical and microstructural features, the composite of 25 wt% calcium phosphate phase was introduced as the optimal composite for bone tissue engineering.

On the Bonding Behaviour of Transition Metal Ions in Inorganic Solids—Optical and Epr Spectroscopic Studies on Anhydrous Phosphates and Phosphate-Silicates of Ti3+

TiPO4 (green), Ti4P6Si2O25 (purple-red) and TiP3O9 (blue) show a remarkable variety of colours . We compare the results of optical and e.p.r. spectroscopic measurements on these compounds with d-electron energy levels for Ti3+ obtained by using the angular-overlap model. Thus, a unified set of angular-overlap model bonding parameters for the description of the spectroscopic behaviour of Ti3+ in anhydrous phosphates can be derived. The σ-interaction was assumed to depend on the nth power of the Ti-O bond distance, and it was found that optimum agreement with experiment occurred with n = -4.5. For the correct reproduction of the experimentally observed ground-state splittings it is necessary to allow for anisotropic π-bonding interactions between titanium and the oxygen ligands linking Ti-O coordination polyhedra.

Novel Preparation of Free Flowing Spherically Granulated Dibasic Calcium Phosphate Anhydrous for Direct Tabletting.

Free flowing spherically granulated (average diameter, 70 or 115 μm) dibasic calcium phosphate anhydrous (DCPA) for direct tabletting was prepared by a restricted crystal growing synthesis of DCPA, followed by spray drying of its aqueous dispersions. The spherically granulated DCPA had larger specific suraface area (32 to 34 m2/g), because they had porous structures compoesd of very fine primary crystals (Heywood diameter, 0.1-1.0 μm) compared to conventionally prepared DCPA (Heywood diameter, 2.0-5.0 μm). The crystallinity of granulated DCPA was lower than that of conventional DCPA. Those micromeritic characteristics of granulated DCPA might correlated closely with their dramatically improved tablettability.

Dicalcium phosphate dihydrate and anhydrous dicalcium phosphate for direct compression: A comparative study

Dicalcium phosphate dihydrate (Emcompress) and anhydrous dicalcium phosphate (Anhydrous Emcompress) for direct compression were compared as regards particle size distribution and flow properties, which were found to be similar for the two products, and microporous structure and compression properties, which differed markedly. Specifically, intraparticular porosity and mean yield pressure of the anhydrous product were greater than for the dihydrate. Several properties of compacts of both products were also compared: compacts of the anhydrous phosphate disintegrated much more rapidly in distilled water than those of the dihydrate, which was attributed to the greater porosity of the former compacts.

Degradation of Bisoprolol Fumarate in Tablets Formulated with Dicalcium Phosphate

Degradation of Bisoprolol Fumarate in tablet dosage forms was accelerated when granular Dicalcium Phosphate Anhydrous USP was substituted for milled Dicalcium Phosphate Anhydrous USP. Studies demonstrate that instability with the granular material is due to an acidic microenvironment created by this material in the presence of moisture. Bisoprolol is less stable at this low pH compared to a neutral microenvironmental pH which is created with milled Dicalcium Phosphate Anhydrous.

Formation of a disordered layer lattice during the intercalation of water into anhydrous vanadyl phosphate

The course of intercalation of water into α1-VOPO4 has been studied by thermomechanical analysis and X-ray diffraction. Neither formation of vanadyl phosphate monohydrate nor staging were observed during the intercalation. The broadening and the shift of the positions of the lines in the diffractograms have been explained by the random stacking of intercalated and nonintercalated layers in the sample.

Intercalation of Anhydrous Vanadyl Phosphate with Aliphatic Alcohol Mixtures

The intercalation of VOPO4 with the mixtures of alcohols (ethanol and 1-butanol, methanol and ethanol, methanol and 1-propanol, methanol and 1-butanol) have been studied. The dependence of alcohols content and interlayer distance of the intercalates formed on composition of the starting mixtures of alcohols has been found. The ability of VOPO4 to form mixed intercalates with alcohols is discussed.

Mechanochemical Synthesis of Bioactive Material: Effect of Environmental Conditions on the Phase Transformation of Calcium Phosphates During Grinding

The effect of environmental conditions on the crystalline transformation of metastable calcium phosphates during grinding was investigated using X-ray diffractometry and fourier transformed infrared spectroscopy. A mixture of CoA and dicalcium phosphate anhydrate (DCPA, CaHPO4) did not transform after grinding in air. On the other hand, CaO and dicalcium phosphate dihydrate (DCPD, CaHPO4 2H2O) were converted into a noncrystalline solid. Mixtures of DCPD and Ca(OH)2 transformed into low-crystallinity hydroxyapatite after grinding in air. When ground under N2, a mixture of Ca(OH)2 and DCPD did not transform into hydroxyapatite, whereas that of DCPD: Ca(OH)2: CaCO3 = 1:0.8: 0.2 did. The results of X-ray diffraction of FT-IR spectra suggested that the presence of carbon dioxide in the grinding system was necessary for transformation from metastable calcium phosphates to hydroxyapatite.

Volumetric method for following the rate of intercalation of liquid molecular guests into layered hosts

A new experimental method is suggested for the kinetic measurements of intercalation reactions in systems formed by a polycrystalline layered host and a liquid molecular guest. The method is based on the fact that the molecular guest decreases its molar volume on entering the space between the host layers. Hence the volume of the system in which an intercalation process takes place is measurably decreased. The time course of the intercalation process can thus be monitored by measuring the volume change of the system. The method has been used to obtain kinetic data about heterogeneous intercalations of some liquid aliphatic compounds into layered structures of anhydrous vanadyl phosphate and sulfate.

ChemInform Abstract: Contributions on the Thermal Behavior of Anhydrous Phosphates. Part 9. Synthesis and Crystal Structure of Cr6(P2O7)4. A Pyrophosphate Containing Di‐ and Trivalent Chromium.

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Surface chemistry of chromia-pillared tin and zirconium phosphate materials: an X-ray photoelectron spectroscopic study

X-Ray photoelectron spectroscopy has been used to examine the surface chemical composition of chromiapillared Sn and Zr phosphates. All the materials are single-phase with CrIII ions octahedrally coordinated in a virtually anhydrous phosphate network, independent of the chromium content and preparation conditions. Quantitative analysis of the surfaces of the materials was achieved within an accuracy of ±5%. While the atomic ratios Mi:Mj(Mi,Mj= Cr, P, Sn, Zr) differ by at most 20% from the chemical composition of the starting materials, the nO:nMi(Mj) atomic ratios show a sizeable depletion (up to 50%) in oxygen content, which we interpret as being due to surface dehydration.