CaO SrO Research Articles

The effect of Sr concentration on bioactivity and biocompatibility of sol–gel derived glasses based on CaO–SrO–SiO 2–P 2O 5 quaternary system

In the present study, sol–gel derived glasses based on CaO–SrO–SiO 2–P 2O 5 system were prepared and the effect of Sr concentration on in vitro bioactivity and cellular properties of the glasses were investigated. SrO was substituted for CaO in the glass formula up to 10 mol% and in vitro bioactivity of the samples was evaluated by soaking them in simulated body fluid followed by structural characterization using XRD, FTIR and SEM techniques. The effects of various glass compositions on proliferation and differentiation of osteoblastic cells were also evaluated. The results showed that the substitution of Sr for Ca in the glass composition retarded formation of apatite layer onto the glass surfaces. Morphologies of the apatite layers were also different in which abundance of the crystals decreased with increasing Sr concentration. The bioactive glasses did not exert cytotoxic effect on the cells, however the proliferation and alkaline phosphatase activity of the cells on the samples containing low doses of Sr were higher than those of control and the samples with high dose of Sr. Glass specimen with 5 mol% of Sr exhibited appropriate bioactivity with optimal cell proliferation and ALP activity.

Analysis of γ-irradiated synthetic bone grafts by 29Si MAS-NMR spectroscopy, calorimetry and XRD

Ca–Sr–Zn–Si glasses have demonstrated excellent biocompatibility both in vitro using the MTT assay with L929 mouse fibroblast cells, and in vivo using healthy and ovariectomized female Wistar rats. However, the biological evaluation of the materials was performed on glass granules that were autoclaved, rather than γ-irradiated; the sterilisation procedure required prior to implantation of these materials in the human body. Given the fact that when a glass is exposed to ionizing radiation changes in its physical properties can take place, it is imperative to determine whether the structure of such glasses will be altered as a result of exposure to the typical amounts of γ-irradiation required to sterilise such materials prior to implantation. This paper examines the structure of Na–Ca–Sr–Zn–Si glasses using 29Si MAS-NMR, XRD and DTA and to evaluate the effect of 30 kGy γ-irradiation on their structure. The 29Si MAS-NMR results indicate that the peak maxima for each glass remains between −74 ppm and −79 ppm; a chemical shift for 29Si associated with Q 1 units in silicate glasses, and that the local environment around the 29Si isotope remains unaltered as a result of exposure. Additional analysis (DTA and XRD) showed that the onset of the glass transition temperature, T g (in the range 553 °C–619 °C depending on composition) typically remains unchanged, as a result of exposure to the ionizing radiation, as do the XRD diffractograms for each glass. Therefore it can be concluded that the use of 30 kGy γ-irradiation does not effect the local environment of the 29Si isotope in the glasses, nor does it significantly alter the XRD diffraction patterns or the T g values for CaO–SrO–NaO–ZnO–SiO 2 described in this work.

Photon interaction and energy absorption in glass: A transparent gamma ray shield

The effective atomic number, Z eff, the effective electron density, N e,eff, and the energy dependence, ED, have been calculated at photon energies from 1 keV to 1 GeV for CaO–SrO–B 2O 3, PbO–B 2O 3, Bi 2O 3–B 2O 3, and PbO–Bi 2O 3–B 2O 3 glasses with potential applications as gamma ray shielding materials. For medium- Z glasses, Z eff is about constant and equal to the mean atomic number in a wide energy range, typically 0.3 < E < 4 MeV, where Compton scattering is the main photon interaction process. In contrast, for high- Z glasses there is no energy region where Compton scattering is truly dominating. Heavy-metal oxide glasses containing PbO and/or Bi 2O 3 are promising gamma ray shielding materials due to their high effective atomic number and strong absorption of gamma rays. They compare well with concrete and other standard shielding materials and have the additional advantage of being transparent to visible light. The single-valued effective atomic number calculated by XMuDat is approximately valid at low energies where photoelectric absorption is dominating.

Fabrication of spherical CaO–SrO–ZnO–SiO2 particles by sol–gel processing

This study was concerned with the fabrication of ceramic CaO-SrO-ZnO-SiO(2) spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol-gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO-SrO-ZnO-SiO(2) particles by sol-gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H(2)O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3-5 mum homogenous spherical particles were obtained at a H(2)O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO(3)):Ca(NO(3))(2):Zn(NO(3))(2):Si(OC(2)H(5))(4) = x:0.12:(0.40 - x):0.48 (0 </= x </= 0.8). Starting composition limitations are caused by the low solubility of strontium ions in the minimal amount of water used and the acceleration of hydrolysis as well as polycondensation at higher water content.

Properties of glasses based on the CaO–MgO–SiO 2 system for low-temperature co-fired ceramic

Glass compositions based on the CaO–MgO–SiO 2 system are investigated with an aim to increase the coefficient of thermal expansion (CTE) in a low-dielectric constant layer material for low-temperature co-fired ceramics (LTCC). The effect of changing the glass composition on the CTE is examined by the addition of ZnO, Al 2O 3, BaO, and SrO. X-ray diffraction (XRD) results show that CaMgSi 2O 6 is the major crystalline phase of all sintered samples except for one composition. According to the experimental results, the substitution of BaO and SrO for CaO plays an important role in increasing the CTE.

The role of Sr2+ on the structure and reactivity of SrO–CaO–ZnO–SiO2 ionomer glasses

The suitability of Glass Polyalkenoate Cements (GPCs) for use in orthopaedics is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. To further improve their potential, and given that Strontium (Sr) based drugs have had success in the treatment of osteoporosis, the authors have substituted Calcium (Ca) with Sr in the glass phase of a series of aluminium free GPCs. However to date little data exists on the effect SrO has on the structure and reactivity of SrO-CaO-ZnO-SiO(2) glasses. The objective of this work was to characterise the effect of the Ca/Sr substitution on the structure of such glasses, and evaluate the subsequent reactivity of these glasses with an aqueous solution of Polyacrylic acid (PAA). To this end (29)Si MAS-NMR, differential scanning calorimetry (DSC), X-ray diffraction, and network connectivity calculations, were used to characterize the structure of four strontium calcium zinc silicate glasses. Following glass characterization, GPCs were produced from each glass using a 40 wt% solution of PAA (powder:liquid = 2:1.5). The working times and setting times of the GPCs were recorded as per International standard ISO9917. The results acquired as part of this research indicate that the substitution of Ca for Sr in the glasses examined did not appear to significantly affect the structure of the glasses investigated. However it was noted that increasing the amount of Ca substituted for Sr did result in a concomitant increase in setting times, a feature that may be attributable to the higher basicity of SrO over CaO.

Effects of Alumina on Densification of a Low-Temperature Cofired Crystalllizable Glass+Alumina System

The effects of alumina particle size and content on densification of a low-temperature cofired crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 (TG) glass+alumina system have been investigated. The densification is improved by decreasing alumina content, or increasing alumina particle size. This is attributed to competitive kinetic processes between the viscous flow of the TG glass, and the dissolution of alumina into the TG glass. The dissolution changes the composition of the TG glass to become aluminum-rich, which increases the viscosity of the TG glass, and then slows down the densification kinetics caused by the viscous flow of the TG glass. However, de-densification would take place if the alumina content is not sufficient, or if the alumina particle size is too large because of the bloating of the TG glass.

Compositional Design of Lead-Free, Low-Temperature Cofired Ceramic Dielectric Composite

Compositional design and properties of a lead-free, low-temperature cofired ceramic (LTCC) system containing a crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 glass, alumina and titania have been investigated. The ternary composites with a high sintered density of >95% can be obtained at 875 °C. Compositions with tailor-made properties are designed according to a working model based on the assumption of the mixing rule, and validated with experimental results. The resulting lead-free composites exhibit a dielectric constant of 7.7–20.0 at 1 MHz, and a thermal expansion coefficient of (5.37–7.22)×10-6/°C.

Gamma-ray shielding properties of CaO–SrO–B 2O 3 glasses

Mass attenuation coefficients, effective atomic numbers and effective electron densities have been determined experimentally for the glass system xCaO·(0.3– x)SrO·0.7B 2O 3 at photon energies 511, 662, 1173, and 1332 keV. The results are compared with theoretical calculations. In addition, the molar volume of the glasses has been derived from density measurements, and the excess volume has been determined as a function of composition. The reported data should be useful for potential applications of these glasses in radiation shielding.

Thermodynamic assessment of the BiO x–SrO–CaO system

The BiO x –SrO–CaO system is the most complex of the four ternary systems forming the BiO x –SrO–CaO–CuO x system where the superconducting phases Bi 2Sr 2CaCu 2O 8+ δ and Bi 2Sr 2Ca 2Cu 3O 10+ δ are found. The BiO x –SrO–CaO system has received relatively little attention since it does not contain any superconducting phases itself. Several of the phases in this system appear during processing of superconductors, though. Using the Calphad approach, we have assessed the experimental data of this system and optimised a set of thermodynamic parameters from which the phase diagram and any thermodynamic property can be calculated. The experimental data available are quite scattered and often contradictory, but the thermodynamic description presented here is consistent with most of what is known about this system.

Thermodynamic calculation of the BiO 1.5–CaO–CuO x system

The BiO 1.5–CaO–CuO x system is by far the simplest of the four ternary systems forming the BiO x –SrO–CaO–CuO x system where the superconducting phases Bi 2Sr 2CaCu 2O 8+ δ and Bi 2Sr 2Ca 2Cu 3O 10+ δ are found. The only solution phase extending into the system is the liquid phase. Using a single interaction parameter the experimentally determined [M.-L. Carvalho et al., Physica C 336 (2000) 1] eutectic temperature at 1024 K in 1 bar O 2 could be fitted and the complete phase diagram calculated.

Effects of Alumina on Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass

Effects of alumina on the devitrification kinetics and mechanism of a low-dielectric K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder have been investigated. Crystalline phases including cristobalite (SiO2) and pseudowollastonite [(Ca, Ba, Sr)SiO3] are formed during the firing of the pure glass. With added alumina content greater than a critical value, e.g., 10–20 vol% at 900–1000°C, the above crystalline phases are completely prevented but anorthite [(Ca, Sr, Ba)Al2Si2O8] is formed. This result is attributed to the dissolution of alumina into the glass. The dissolution changes the composition of the glass to become aluminum-rich, and the dissolution kinetics of alumina into the glass is far too rapid compared with the formation of cristobalite and pseudowollastonite. The crystallization kinetics of anorthite follows the analysis of the Avrami equations, and the results show an apparent activation energy close to that of the Al–O bond strength, suggesting a reaction-controlled kinetics.

Sintering of a Crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 Glass with Titania Present

Crystallization and reaction kinetics of a crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder with 17–40 vol% titania powder were investigated. The initially amorphous K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder formed cristobalite (SiO2) and pseudowollastonite [(Ca, Ba, Sr)SiO3] during firing. The above crystalline phases were completely replaced by a crystalline phase of titanite [(Ca, Sr, Ba)TiSiO5] when the amount of added titania was greater than a critical value, e.g., 10 vol%, at 99–1100 °C. A chemical reaction taking place at the interface between titania and the glass was attributed to the above observation. The dissolved titania changed the composition of the glass, and the dissolution kinetics was much faster than the formation of cristobalite and pseudowollastonite. Activation energy analysis showed that the crystallization of titanite [(Ca,Sr,Ba)TiSiO5] was controlled by a reaction-limiting kinetics of formation for the Ti–O bond.

Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass‐Ceramic

The devitrification kinetics and mechanism of a low‐dielectric, low‐temperature, cofirable K2O–CaO–SrO–BaO–B2O3–SiO2 glass‐ceramic have been investigated. Crystalline phases including cristobalite (SiO2) and pseudowollastonite ((Ca,Ba,Sr) SiO3) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami‐like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.

Liquidus phase equilibria in portions of the BSCCO system

This paper summarizes a systematic investigation of the phase equilibria in the quaternary BiO 1.5SrOCaOCuO system (BSCCO). The study combines our completed work on subset binaries and ternaries and experiments in the quaternary system, focusing on the small volume of the quaternary where the primary phase volumes of ternary and quaternary BSCCO phases exist. Known phase relations and conducted experiments within the BSCCO quaternary support the findings of this paper.

Luminous efficiency and secondary electron emission characteristics of alternating current plasma display panels with MgO–SrO–CaO protective layers

Development of protective layers with a higher secondary electron emission yield than that of the conventional MgO is necessary to attain both a lower driving voltage and a higher luminous efficiency in alternating current plasma display panels. Alkaline earth metal oxides, such as SrO and CaO were added to the pure MgO in order to improve the electrical characteristics of the conventional MgO protective layer. With addition of SrO and CaO to MgO, the intensity of the (111) peak remained unchanged but the (311) peak newly appeared in the x-ray diffraction results. The secondary electron emission yield of Mg1−x−ySrxCayO films was found to be larger than that of the MgO film and in particular, the Mg0.7Sr0.2Ca0.1O films showed the largest secondary electron emission yield among the prepared films of the Mg–Sr–Ca–O system in this work. The luminous efficiency of the panel with the Mg0.7Sr0.2Ca0.1O protective layer was also much higher than that of the panel with the MgO protective layer probably due to its lower discharging voltage. The increase in the luminous efficiency and the decrease in the driving voltage were in good agreement with the results of the secondary electron emission yield as expected.

Permanent densification behavior and 29Si MAS NMR of SiO 2–K 2O–CaO–SrO glasses

In permanent densification of xSiO 2·0.4(100− x)K 2O·0.4(100− x)CaO·0.2(100− x)SrO glasses ( x=41.2–66.7) in mol% by the 3 and 6 GPa high-pressure treatments a peculiar behavior was found in the glasses of x below 50 mol%. The skeleton structures composed of SiO 4 units in the glasses were investigated on the undensified and densified glasses by means of 29Si magic angle spinning (MAS) NMR spectroscopy. From the peak deconvolution of MAS NMR spectra the Q n fractions of SiO 4 structural-units, where n ( n=0–4) means the number of bridging oxygen, were examined. At first, the skeleton structures in the undensified glasses are clarified. Then the skeleton structures of the densified glasses are discussed in comparison with those of the undensified glasses. Irrespective of the x value, the fractions of Q n of small n-values increased with an increase in the applied pressure, indicating that some of the Si–O–Si bonds are broken under the applied pressure and the skeleton structures were kept even after a release of the applied pressure. It is concluded that other causes should be considered as the origin of the present peculiar behavior.

An In Situ Study on Phase Relation between Bi2SrO4 and SrCuO2 in the Bi2O3–SrO–CuO System

A pseudobinary phase relation of Bi2SrO4–SrCuO2 in the Bi2O3–SrO–CuO ternary system between 850 and 1100°C has been investigated in situ using an apparatus that combines high-temperature X-ray diffraction with an optical microscopy. The liquidus temperatures increase with decreasing Bi composition from 910°C to 1090°C. The lowest phase change temperature which corresponds to the solidus line of this system is 910°C in the compositions below Bi2Sr4Cu3O10. Above 910°C, the decomposition to Bi4Sr8Cu5Ox and liquefaction occurs. On further heating above 925°C, a partially molten phase with solid SrCuO2 appears in the Bi-deficient side. The results are discussed in comparison with stabilities of the Ca-added system of Bi2O3–SrO–CaO–CuO, in which Bi-based cuprate superconductors are formed.

Phase equilibria in the system BiO 1.5–SrO–CaO–CuO

Solid solution range of 2212 phase was revised. Geometrical image of this volume was designed based on experimental data. Model of incongruent melting of 2212 phase at isobaric conditions was simulated.

Phase diagram for the system Bi 2O 3CaOSrOCuO in the SrO-rich region

It has been found experimentally that phase diagram for the system Bi 2O 3CaOSrOCuO in SrO-rich region at 850°C in the open air includes three elementary tetrahedra: CaOSrOSr 6Bi 2O 11Sr 2CuO 3, CaOSr 2CuO 3Sr 6Bi 2O 11Sr 3,5Ca 0,5Bi 2O 7 and Sr 3Bi 2O 6Sr 6Bi 2O 11Sr 3,5Ca 0,5Bi 2O 7 Sr 2CuO 3. In the considered interval of corresponding oxide concentrations quaternary oxides are not formed under the above conditions.