Preparation and study of Ca1 − xMgx(PO3)2 glassy and crystalline phases

The structure of Ca_{1 – x} Mg _x (PO₃)₂ crystalline and glassy samples was investigated in the whole concentration region of x = 0–1.0. From X-ray diffraction data it was found that, in the crystalline samples, solid solutions are formed for x < 0.3 on the calcium-side of the system, with the structure of -Ca(PO₃)₂, and for x > 0.6 on its magnesium-side, with the structure of Mg₂P₄O₁₂. Similar results were obtained from the study of their infrared and Raman spectra. In the glassy state, homogeneous glasses were formed within the whole concentration region. The values of their transformation temperatures, T _g, and crystallization temperature, T _c, change slightly with the composition and lie within the region of T _g = 529–544 °C and T _c = 631–677 °C.     

Effect of filler level and particle size on dental caries-inhibiting Ca–PO4 composite

Secondary caries and restoration fracture are common problems in restorative dentistry. The aim of this study was to develop Ca–PO₄ nanocomposite having improved stress-bearing properties and Ca and PO₄ ion release to inhibit caries, and to determine the effects of filler level. Nanoparticles of dicalcium phosphate anhydrous (DCPA), two larger DCPA powders, and reinforcing whiskers were incorporated into a resin. A 6 × 3 design was tested with six filler mass fractions (0, 30, 50, 65, 70, and 75%) and three DCPA particle sizes (112 nm, 0.88 μm, 12.0 μm). The DCPA nanocomposite at 75% fillers had a flexural strength (mean ± SD; n = 6) of 114 ± 23 MPa, matching the 112 ± 22 MPa of a commercial non-releasing, hybrid composite (P > 0.1). This was 2-fold of the 60 ± 6 MPa of a commercial releasing control. Decreasing the particle size increased the ion release. Increasing the filler level increased the ion release at a rate faster than being linear. The amount of ion release from the nanocomposite matched or exceeded those of previous composites that released supersaturating levels of Ca and PO₄ and remineralized tooth lesions. This suggests that the much stronger nanocomposite may also be effective in remineralizing tooth lesion and inhibiting caries. In summary, combining calcium phosphate nanoparticles with reinforcing co-fillers in the composite provided a way to achieving both caries-inhibiting and stress-bearing capabilities. Filler level and particle size can be tailored to achieve optimal composite properties. Disclaimer: Certain commercial materials and equipment are identified to specify the experimental procedure. This does not imply recommendation or endorsement by NIST or ADAF.     

Transformations of neat and heated struvite (MgNH4PO4⋅6H2O)

Struvite (MgNH₄PO₄?6H₂O) is the mineral phase of one of the urinary tract stones of humans and animals, besides being an important phase seen in waste water treatment and purification plants. Single-phase and highly crystalline struvite powders were synthesized in this study at room temperature in aqueous solutions containing dissolved salts of MgCl₂?6H₂O and (NH₄)₂HPO₄ at the Mg/P molar ratio of 1.00. As-synthesized, crystalline struvite powders (neat powders) completely transformed into cryptocrystalline apatitic calcium phosphate (Ap-CaP), in less than 72 h, when soaked in Ca-containing saline solutions at 37 °C. Moreover, crystalline struvite powders heated at temperatures from 90° to 200 °C became x-ray amorphous. Amorphous powders stirred for 4 h at room temperature in water containing dissolved diammonium hydrogen phosphate recrystallized back into struvite.     

Hydrothermal synthesis and electrochemical properties of Li₃V₂(PO₄)₃/C-based composites for lithium-ion batteries

To improve performance at higher rates, we developed a hydrothermal method to prepare carbon-coated monoclinic lithium vanadium phosphate (Li(3)V(2)(PO(4))(3)) powder to be used as a cathode material for Li-ion batteries. The structural, morphological and electrochemical properties were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and galvanostatic charge-discharge cycling. A superior cycle and rate behavior are demonstrated for Li(3)V(1.85)Sc(0.15)(PO(4))(3)/C and Li(2.96)Ca(0.02)V(2)(PO(4))(3)/C electrodes at charge-discharge current rates above 5C.     

Mössbauer and XRD studies on the effect of doping iron in KCaY(PO4)2

The effect of doping iron at the yttrium site in hexagonal KCaY(PO₄)₂ is studied for various concentrations ofx (0≤x≤1), of iron using Mössbauer and X-ray diffraction methods. For low iron concentrations, very little changes in structure are seen but atx≈0·1, onset of new peaks in the XRD pattern is observed. The Mössbauer study of the doped samples reveals that iron has a solubility of up to 2·5% in the parent phase with any excess iron precipitating out to form a new and unknown phase. From a detailed analysis of the X-ray diffraction pattern (corresponding tox=1) of the latter phase, it is found that this phase is rhombohedral with the possible space groupR3.     

A study of copper stoichiometry and phase relationships in the copper-zirconium phosphate system: CuZr2(PO4)3 – Cu0.5Zr2(PO4)3

CuZr₂(PO₄)₃ crystallises with the Nasicon-type structure and is a copper(I) ion conductor. The possibility of a solid solution between CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ has been a controversial issue for many years. As part of a continued study, CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ were prepared by solid state methods and used to investigate the copper stoichiometry and phase relationships between these two materials as a function of copper content, temperature and oxygen fugacity. The following reversible reaction: Cu_0.5Zr₂(PO₄)₃ (s) + CuO (s) ↔ CuZr₂(PO₄)₃ (s) + O₂(g) was studied by thermogravimetry in an atmosphere of PO₂ = 0.22 atm and was found to occur at 475 ± 10°C. Thus, CuZr₂(PO₄)₃ is a thermodynamically stable phase in air above ∼475°C, which places a lower temperature limit on its use as an electrolyte in air. The results of X-ray powder diffractometry on materials with various copper contents that had been annealed in argon at 750°C indicate that there is no evidence for a significant solid solution between CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ nor, a reductive decomposition of Cu_0.5Zr₂(PO₄)₃. The coexistence of CuZr₂(PO₄)₃ and Cu_0.5Zr₂(PO₄)₃ as discrete phases is also supported by evidence from electron spin resonance spectroscopy on these materials, which indicate the presence of copper(II) ions in CuZr₂(PO₄)₃ at a dopant and dispersed level of concentration. The results from energy dispersive X-ray analysis, as well as, the novel use of the fluorescent behaviour of CuZr₂(PO₄)₃ in ultra-violet light as an analytical tool, support the above conclusions.     

Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

The LiZr₂(AsO₄)₃ arsenate and LiZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr₂(AsO₄)₃ (sp. gr. P2₁/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) ų, Z = 4; sp. gr. R $\bar 3$ c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr₂(AsO₄)_1.5(PO₄)_1.5. Their structural frameworks are built up of AsO₄ tetrahedra—or (As,P)O₄ tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO₆ octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr₂(AsO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.     

Investigation of Spontaneous Polarization and Phase Transition Phenomena in KH2PO4-Type Crystals by Green’s Function Approach

Journal of Low Temperature Physics - In this paper, the spontaneous polarization and the phase transition of order–disorder type H-bonded KH2PO4-type crystals are theoretically investigated....     

Photoluminescence and scintillation properties of Al(PO3)3–CsPO3–CsBr–CeBr3 glass scintillators

Scintillators, which are widely used as radiation detectors, are phosphors that release absorbed ionizing radiation energy as ultraviolet or visible light. Inorganic glass scintillators have several advantages over inorganic crystal scintillators, such as ease of fabrication and low costs. However, unlike inorganic crystals, which can emit up to tens of thousands of photons/MeV, inorganic glasses exhibit less than several hundred photons/MeV in most cases. Here, we studied an inorganic glass scintillator that exhibits a light yield of 2700 photons/MeV, which exceeds those of previous inorganic glass scintillators with high light yields of approximately 2000 photons/MeV. The density of this material is 3.28 g/cm³, which is relatively high among glass scintillators. Moreover, a fast scintillation decay with a decay time constant of 30.0 ns was obtained and is attributed to the 5d–4f transition of Ce³⁺. Thus, this glass is suitable for gamma- and X-ray detection, thereby expanding the practical applicability of inorganic glass scintillators.

     

Continuous,martensitic nature of the transition ß→γ Li3PO4

The transformation Li₃PO₄ shows characteristics of both continuous and martensitic transformations. Below 340° C, no detectable transformation occurs; between 340 and 410° C, the transformation goes only partially to completion; above 410° C the transformation rapidly goes to completion. At any temperature in the range 340 to 410° C, transformation proceeds rapidly in the initial stages to attain a certain degree of transformation. With prolonged isothermal heating or grinding of the samples, further transformation does not occur. The reverse transformation could not be effected under normal, dry conditions.     

Synthesis and characterization of (Sr1−x′K2x)Zr4(PO4)6 ceramics

Single phase (Sr_1–x K_2x )Zr₄(PO₄)₆, where x lies between 0.0 and 1.0, ceramic powder with a submicron scale particle size has been synthesized successfully at calcination temperatures as low as 650–750°C by a sol-gel technique. The formation of the powder strongly depends on calcination temperature, but is independent of solution pH in the studied range. Dilatometric measurement shows an ultra-low linear coefficient of thermal expansion of 0.1×10^–6°C^–1 when x=0.5 at temperature intervals of 25–1000°C. Thermal conductivity and flexural strength of the materials were determined at ambient temperature to be 1.0 Wm^–1K^–1 and as high as 280 MPa, respectively, indicating that this material can be an excellent candidate in many applications, especially those subjected directly to severe environments.     

Effect of fluoride on apatite formation from Ca4(PO4)2O in 0.1 mol L−1 KH2PO4

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca4(PO4)2O) was investigated in 0.1 mol l–1KH2PO4 containing 0–83 mol l–1 KF. Characterization of the final apatite phase formed by the hydrolysis was made with X-ray diffraction and SEM. The initial pH was between 4.5 and 5.4, depending on the solutions, and the pH rapidly increased and was kept constant between 7.3 and 6.5. An increase in KF concentration tended to lower the pH in the final stage of hydrolysis. The calcium concentration was considerably lower than the phosphorus concentration throughout the reaction. The fluoride concentration decreased shortly after the start of hydrolysis. The hydrolysis of TTCP in 0.1 mol l–1 KH2PO4 proceeded to form hydroxyapatite via DCPD when the KF concentration was low. The hydrolysis product was a calcium-deficient non-stoichiometric hydroxyapatite with a Ca/P ratio of about 1.5. With an increase in the KF concentration in the 0.1 mol l–1 KH2PO4 solution, TTCP directly transformed into hydroxyapatite containing F- ions or fluorapatite and with improved crystallinity. The addition of fluoride in the solution initially accelerated the formation of apatite. However, the layer of newly formed apatite adhering to the TTCP particles retarded TTCP dissolution; as a result, hydrolysis was delayed. IR analysis showed that the apatite phase contained HPO2–4 ions in the structure. The formula for the hydrolysis product of TTCP in the presence of fluoride can be expressed as follows: Ca10–x(HPO4)x(PO4)10–x(OH)2–x–yFy. © 1998 Chapman & Hall.     

Intercalation of nitrogenous substances into HUO2PO4·4H2O

The laminar compound HUO₂PO₄·4H₂O (HUP) interacts with piperidine, hydrazine, pyridine, pyrazine and (dimethylamino-methyl)ferrocene to produce intercalation reactions. The intercalate materials exhibit a layered structure derived from the starting solid. The only observed structural modifications were dimensional changes in the crystal c axes.The amount of adsorbate taken up by the HUP is related to the size and geometry of the guest molecule and its basicity. The guest-host reactions are of the acid-base type as shown by i.r. spectra.     

Synthesis of Macroscopic Zr（C6H5PO3）2 Tubes

A new method of infiltration-diffusion is used to synthesize macroscopic α-Zr（C6H5PO3）2 （α-ZrBP） tube. Compared to the routine method, no HF was used and a fiberlike product with several millimeters in length was obtained. SEM （scanning electronic microscopy） result indicates that these fibers are tubes. The wall of the tubes is composed of the flake of α-ZrBP overlapped with each other. As we know, it is the first report on the synthesis of millimeter-scale supramolecular assembly of α-ZrBP.     

Production and characterization of new calcium phosphate bone cements in the CaHPOv4–α-Ca3(PO4)2 system: pH, workability and setting times

The initial setting properties of calcium phosphate cements in the CaHPOv₄–-Ca₃(PO₄)₂ (DCP–-TCP) system have been investigated. Interest was focused on the pH, workability, cohesion time and initial and final setting times. The addition of CaCO₃ modified the structure of the cement reaction product such that it became more similar to the apatite phase in bone mineral. The addition of 10% w/w of CaCO₃ reduced the viscosity of the cement pastes resulting in an increase in initial and final setting times and improved injectability. © 1999 Kluwer Academic Publishers     

Resistivity and Susceptibility of Y-Ba-Cu and Bi-Sr-Ca-Cu Oxides

The resistivity and magnetic susceptibility ofthe quenched samples for the Y-Ba-Cu oxideswere measured at room temperature.Themeasurement for the temperature dependence of theamorphous Bi-Sr-Ca-Cu oxides with differentheat treatment temperature was made.Theresistivity and the parameters C in the formulax=X_0+C/(T-0)of the quenched samples forY-Ba-Cu oxides decreased with lowering quenchtemperature,and their susceptibility did not varymonotonously with quench temperature.The tem-perature dependence of the amorphousBi-Sr-Ca-Cu oxides gradually deviates fromCurie-Weiss law with increasing heat treatmenttemperature.The local magnetic moments forY-Ba-Cu and amorphous Bi-Sr-Ca-Cu oxidesgradually decrease with decreasing quench tempera-ture or increasing heat treatment temperature.     

Strength of Materials and Structures

Book reviewAll engineering structures designed according to modern principles have to be strong and sufficiently rigid. Scientists and engineers have long recognized the importance of the strength ofmaterials and structures, and dedicated much their efforts to bothfundamental and industrial research into the theory for vast engineering materials and various structures. A lot of engineers needto be familiar with the fundamental principles of strength in materials and structures in order to desi…     

Preparation and study of in vitro bioactivity of PMMA–co–EHA composites filled with a Ca3(PO4)2–SiO2–MgO glass

The nature of the orthopaedic implant surface affects the interaction with cells and subsequent bone formation. The bone/cement interface in cement-held prostheses is considered to be the main cause of fracture leading to implant revision. It is thought that the introduction of a bioactive phase, such as bioglass, in the cement may permit a more stable interface by encouraging direct bone apposition rather then encapsulation of the implant by fibrous tissue. In this work new poly(methylmethacrylate) (PMMA) based composites filled with 0, 30, 40 and 50 (wt.%) of a Ca₃(PO₄)₂–SiO₂–MgO glass, were processed. The prepared composites consist of a poly(methylmethacrylate)–co–(ethylhexylacrylate) (PMMA–co–EHA) matrix filled with a glass (G7), with nominal composition 33.26CaO, 28.07P₂O_5, 23.03SiO_2, 15.64MgO (wt.%). The in vitro bioactivity of the composites was assessed by determining the changes in surface morphology and composition, by X-ray diffraction (XRD) and scanning electron microscopy coupled with X-ray energy dispersive spectroscopy (SEM-EDS), after soaking in a simulated body fluid (SBF) for periods of up to 21 days at 37 °C. Inductively coupled plasma (ICP) was used to assess the evolution of ionic concentrations in the SBF solution. The results obtained confirmed the growth of a hydroxyapatite (HA)-like layer on the surface of the prepared composites. As expected, HA layer formation was faster for composites prepared with higher glass content.