Calcium Borate Research Articles

Can crystalline phases be self-healing sealants for solid oxide fuel cells?

The poor thermodynamic and thermal stability of self-healing glass sealants restrict their applications in planar solid oxide fuel cells (SOFCs). In this paper, a calcium borate crystalline is prepared by melting-quench and a subsequent crystallization. The crystalline phases include CaB 4O 7 and CaB 2O 4. The in situ observation reveals that the micro-indentation on the surface of such crystalline can be healed when heating from room temperature to 840 °C at a heating rate of 40 °C min −1. Combining with the improved thermal stability, the crystalline sealant with desired self-healing property, at the operational temperature of SOFCs (e.g., 700–900 °C), provides additional solution for the sealing challenge of SOFCs.

Kinetics and mechanisms of converting bioactive borate glasses to hydroxyapatite in aqueous phosphate solution

Borate bioactive glasses are receiving increasing attention as scaffold materials for bone repair and regeneration. In this study, the kinetics and mechanisms of converting three groups of sodium–calcium–borate glasses with varying CaO:B2O3 ratio to hydroxyapatite (HA) in 0.25 M K2HPO4 solution were investigated at 10–70 °C. Glass disks with the composition 2Na2O·(2 − x)CaO·(6 + x)B2O3 (x = 0, 0.5, and 1.0) were immersed for up to 8 days in the potassium phosphate solution. The conversion kinetics to HA were monitored by measuring the weight loss of the glass, while X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy were used to study structural and compositional changes. All three groups of glasses formed HA on their surfaces, showing that the glasses were bioactive. At 10–37 °C, the conversion kinetics was well fitted by the contracting sphere model. Also, the contracting sphere model has a good fit for the early stage of conversion at 70 °C, whereas a three-dimensional (3D) diffusion model provided a good fit to the data of the later stage. The results of this study provide kinetic and structural data for the design of borate bioactive glasses for potential applications in bone tissue engineering.

Dosimetric properties of rare earth doped LiCaBO 3 thermoluminescence phosphors

Lithium Calcium borate (LiCaBO 3) polycrystalline thermoluminescence (TL) phosphor doped with rare earth (RE 3+) elements has been synthesized by high temperature solid state diffusion reaction. The reaction has produced a very stable crystalline LiCaBO 3:RE 3+ phosphors. Among these RE 3+ doped phosphors thulium doped material showed maximum TL sensitivity with favorable glow curve shape. TL glow curve of gamma irradiated LiCaBO 3:Tm 3+ samples had shown two major well-separated glow peaks at 230 and 430 °C. The glow peak at 430 °C is almost thrice the intensity of the glow peak at 230 °C. The TL sensitivity of the phosphor to gamma radiation was about eight times that of TLD-100 (LiF). Photoluminescence and TL emission spectra showed the characteristic Tm 3+ peaks. TL response to gamma radiation dose was linear up to 10 3 Gy. Post-irradiation TL fading on storage in room temperature and elevated temperatures was studied in LiCaBO 3:Tm 3+ phosphor.

Dielectric and Sintering Properties of the Doping CaO-B<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> System Low Temperature Co-Fired Ceramics

. A doping CaO-B2O3-SiO2 system low temperature co-fired ceramics (LTCC) was prepared with a mixture of high temperature melting glass and sol-gel glass for different ratio. The effects of sol-gel glass content on the microstructure, crystalline phases, sintering properties and dielectric properties of CaO-B2O3-SiO2 system were investigated at 850°C. The results show that the samples with sol-gel glass doping had little change in phase composition, but contained more calcium silicates, and less calcium borate. As the amount of sol-gel glass increased, the shrinkage improved, the sintered density slightly decreased, the dielectric constant (εr) reduced, and the dielectric loss (tgδ) decreased. When the amount of sol-gel glass was 14.5wt%, εr and tgδ of the doping sample were 5.80, 4.6×10-5 (at 1 MHz), respectively. Moreover, the doping system had a good matching ability with gold slurry and Au-Pt-Pd slurry.

Synthesis of Fe–4.6 wt% B alloy via electro-deoxidation of mixed oxides

Fe–4.6 wt% B alloy was synthesized via electro-deoxidation of the mixed oxide precursor. The oxides, Fe2O3 and B2O3, mixed in suitable proportions were sintered at 900 °C yielding pellets with a two-phase structure; Fe2O3 and Fe3BO6. The sintered pellets, connected as cathode, were then electro-deoxidized in molten CaCl2 or in CaCl2–NaCl eutectic, against a graphite anode at 3.1 V. The electrolysis at 850 °C has successfully yielded a powder mixture of Fe and Fe2B. Sequence of changes during the electrolysis was followed by interrupted experiments conducted at 850 °C. This has shown that iron is extracted quite early during the electrolysis through the depletion of oxygen from the starting oxide; Fe2O3, forming the other iron oxides in the process. Boron follows a more complicated route. Fe3BO6, the initial boron-bearing phase, was depleted in the early stages due to its reaction with molten salt. This gave rise to the formation of calcium borate. Boron was extracted from calcium borate in later stages of electrolysis, which appeared to have reacted in situ with the iron forming compound Fe2B.

HIGH TEMPERATURE OXIDATION OF CaB6-28wt%Ni SINTERED BODY

The oxidation process of calcium hexaboride ( CaB 6) ceramic sintered body with 28wt% nickel as a sintering aid was investigated systematically in this paper. DTA-TG was used to analyze the oxidation behavior at various temperatures. The morphologies of the oxidation surfaces and the interface between the oxide layer and the bulk material were given by EPMA and BSE, respectively. Element distribution on cross-sections was measured by an energy spectrum analyzer. It is found that CaB 6-28 wt % Ni shows an excellent oxidation resistance below 1173K owing to the protection provided by calcium borate on the surface. Catastrophic fast oxidation begins at 1273K. The grain boundaries act as the diffusion channels for O 2 penetration. The existence of Ni doesn't affect the oxidation behavior of the matrix CaB 6. The mechanism of oxidation was also discussed in this paper.

Easy synthesis of CaB2O4 via pyrolysis of calcium fructoborate

The investigation of the thermal behavior of calcium fructoborate samples of composition Ca(C6H10O6BO)2.3.5H 2O showed that CaB2O4 is generated as the final solid pyrolysis residue. On the basis of these observations a new, very easy, synthetic procedure for the preparation of high purity samples of this calcium borate is proposed. The material was characterized by X ray powder diffractometry and IR spectroscopy.

Thermoluminescent and optical absorption properties of neodymium doped yttrium aluminoborate and yttrium calcium borate glasses

Neodymium doped yttrium aluminoborate and yttrium calcium borate glasses were prepared by the conventional melting-quenching technique with neodymium concentration varying from 0.10 to 1.0 mol%. The obtained glasses present a wide transparency in the UV–visible region (till 240 nm). The thermoluminescent (TL) emission of beta-irradiated samples was measured, showing a broad peak at ∼240 °C with intensities related to the Nd 3+ content, for both glasses. Calcium borate glass samples are about one order of magnitude less luminescent than the aluminoborate glasses. Probably the presence of Ca 2+, instead of Al 3+ and Y 3+ in the matrix, inhibits the production of the intrinsic hole centers, connected to boron and oxygen, known in the literature to act as luminescent centers in TL emission of borate glasses. We suggest that Nd 3+ ions act as electron trapping centers in both glass matrices, as they modify the temperature of emission and the light intensity. Also, the Nd:YAlB glass can be used as a dosimeter in various applications, including radiotherapy, but the sensitivity of this material to neutron should be checked.

New perspectives on calcium environments in inorganic materials containing calcium–oxygen bonds: A combined computational–experimental 43Ca NMR approach

The potential of a combined experimental–computational 43Ca solid state NMR approach for the structural analysis of different families of inorganic compounds (calcium phosphates, silicates, aluminates and borates) has been investigated. Natural-abundance 43Ca NMR data of six crystalline calcium phosphates is reported. DFT periodic calculations of 43Ca NMR parameters of an extensive number of Ca–O inorganic species have been performed, showing that the isotropic chemical shift of calcium can accurately be predicted. A strong dependence of the isotropic chemical shift on the average Ca⋯O bond distance and on the nature of the associated oxoanion is found.

Growth and assessment of physical properties of a new nonlinear optical crystal: Lanthanum calcium borate

Single crystals of La 2CaB 10O 19 (LCB) were grown by flux method. The main physical properties of using LCB as a frequency conversion device were evaluated. The crystal has a high transparency from ultraviolet (UV) to infrared range. The four nonvanished nonlinear optical coefficients measured by Maker fringes method are 0.433, 0.484, 0.437 and 0.640 pm/V for d 21, d 22, d 23 and d 14, respectively. The damage threshold of (0 0 1) plane of LCB was measured to be 11.5 GW/cm 2. Besides the good optical properties, the crystal also has good thermal and mechanical properties and stable chemical properties for processing and application. All these properties provide LCB with a good application prospect as a frequency conversion device.

A study on dissolution of ulexite in ammonium acetate solutions

Abstract Ulexite, sodium–calcium–borate hydrate, has a chemical formula of Na2O·2CaO·5B2O3·16H2O, and is found in great amounts in Turkey. In this study, the dissolution of ulexite in ammonium acetate solutions was investigated in a batch reactor. The effects of the concentration of solution, particle size, solid-to-liquid ratio, stirring speed and reaction temperature on the dissolution rate were determined. It was found that the dissolution rate increased with an increase in concentration and reaction temperature, and with a decrease in particle size and solid-to-liquid ratio. No effect of stirring speed was observed on the conversion. It was determined that the dissolution rate fit the chemical reaction control model. The activation energy of this dissolution process was found to be 55.7 kJ/mol.

Synthesis and crystal structure of a new calcium borate, CaB6O10

Abstract A new calcium borate, CaB6O10, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB6O10 crystallizes in the monoclinic space group P21/c with a = 9.799(1) A, b = 8.705(1) A, c = 9.067(1) A, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B3O7]5− triborate groups are bridged by one oxygen atom to form a [B6O13]8− group that is further condensed into a 3D [ B 6 O 10 ] 2 − ∞ 3 network, with the shorthand notation 6: ∞3[2 × (3:2Δ + T)]. The 3D [ B 6 O 10 ] 2 − ∞ 3 network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca2+ cations reside. The IR spectrum further confirms the presence of both BO3 and BO4 groups.

Pure zircon process for removing radionuclides from zircon concentrates

The presence of U and Th as impurities in zircon makes it radioactive. Provided the U and Th levels are below 500 ppm, or 70 Bq g-1 activity, the limits that allow transportation of the material as a non-radioactive substance, it is acceptable as a commercial product. However, some zircon sands contain radioactivity levels well above this limit. A new process (the pure zircon process) is described for the removal of radioactivity from zircon. Tests to identify the best flux addition, calcination temperature and time, and leaching conditions indicated that by grinding a zircon sample containing 1059 ppm U + Th to a particle size of about 15–20 μm, calcining it with 15 wt-% calcium borate (colemanite) at 1200°C for 4 h and leaching the calcine with up to 1M HCl at 80°C for 30 min gave a product with <500 ppm U + Th. While the grade of Zr of the final product was slightly increased, the levels of major impurities, Al, Fe, Ti and P were decreased. Operating costs for the pure zircon process using the optimum conditions were estimated to be A$243/t leach product.

Reaction of sodium calcium borate glasses to form hydroxyapatite

This study investigated the transformation of two sodium calcium borate glasses to hydroxyapatite (HA). The chemical reaction was between either 1CaO . 2Na(2)O . 6B(2)O(3) or 2CaO . 2Na(2)O . 6B(2)O(3) glass and a 0.25 M phosphate (K(2)HPO(4)) solution at 37, 75 and 200 degrees C. Glass samples in the form of irregular particles (125-180 microm) and microspheres (45-90 and 125-180 microm) were used in order to understand the reaction mechanism. The effect of glass composition (calcium content) on the weight loss rate and reaction temperature on crystal size, crystallinity and grain shape of the reaction products were studied. Carbonated HA was made by dissolving an appropriate amount of carbonate (K(2)CO(3)) in the 0.25 M phosphate solution. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to characterize the reaction products. The results show that sodium calcium borate glasses can be transformed to HA by reacting with a phosphate solution. It is essentially a process of dissolution of glass and precipitation of HA. The transformation begins from an amorphous state to calcium-deficient HA without changing the size and shape of the original glass sample. Glass with a lower calcium content (1CaO . 2Na(2)O . 6B(2)O(3)), or reacted at an elevated temperature (75 degrees C), has a higher reaction rate. The HA crystal size increases and grain shape changes from spheroidal to cylindrical as temperature increases from 37 to 200 degrees C. Increase in carbonate concentration can also decrease the crystal size and yield a more needle-like grain shape.

Study on the Synthetic Process of Calcium Borate

Calcium borate used for non-pollution flux of ceramic decoration materials is synthesized by using boric acid and calcium carbonate as raw materials. The effects of reaction temperature, concentration, time, pH value and additive agent on synthesis of calcium borate are studied. The synthesized products are characterized by using DTA, XRD, TEM and SEM. The results show that the better conditions are: synthesis temperature is 80-100°C, the proportion of boric acid and water is0.26 ~ 0.42 to 1(mol), the proportion of calcium carbonate and boric acid is 0.09-0.15 to 1(mol), the pH value is 5 ~ 7, reaction time is 3hs. The synthetic calcium borate is non-crystalline with particle size of 0.1 ~ 0.2 µm, when being calcinated at 300°C, the main crystal phase isCaO·3B2O3·4H2O.

Comparison of the Formation of Calcium and Barium Phosphates by the Conversion of Borate Glass in Dilute Phosphate Solution at near Room Temperature

The formation of phosphates of calcium or barium at near room temperature by the direct conversion of borate glass in dilute phosphate solution was investigated. Borate glass particles (150–300 μm), with the composition 20Na2O·20AO·60B2O3 (mol%), where A is the alkali‐earth metal Ca or Ba, were prepared by conventional processing, and immersed in 0.25M K2HPO4 solution at 37°C and with a starting pH value of 9.0 or 12.0. The effects of the borate glass composition and the solution pH on the rate of formation, the chemical composition, and the structure of the phosphate products formed in the conversion reaction were investigated using weight loss and pH measurements, X‐ray diffraction, X‐ray fluorescence, scanning electron microscopy, and Brunauer–Emmett–Teller surface area. At both pH values, the calcium borate glass particles were completely converted to hydroxyapatite, Ca10(PO4)6(OH)2, with a high surface area (160–170 m2/g). At pH=9.0, the barium borate glass particles converted completely to a barium phosphate product that was isostructural with BaHPO4, whereas at pH=12.0, the barium phosphate product was isostructural with Ba3(PO4)2, with both products having much lower surface areas (4–8 m2/g). The formation of the phosphate products was pseudomorphic, retaining the external shape of the original glass particles.

Development of the sorption-membrane “green” technology for boron removal from natural and wastewaters

An effect of the nature of electrodialysis and reverse osmosis membranes on the separation and concentration effectiveness of boron-containing solutions generated in the regeneration process of the synthetic boron-selective sorbents of N-methylglucamine type has been determined. The optimum conditions of membrane treatment and utilization of the above regeneration solutions have been established. The technological scheme providing a high purification degree of water from boron and complex processing of generated regenerating solutions with isolating valuable marketable product (calcium borate) and obtaining concentrate of the regenerating acid (that can be reused in the purification process) has been advanced. This provides a means to avert contamination of the environment by toxic boron compounds and regenerating acid as well as to reduce consumption of that acid by 40%.

An approach for interpreting thermogravimetric profiles using artificial intelligence

Expert systems are proposed in order to analyze thermogravimetric profiles. The methodology showed to be an efficient tool as a complementary procedure for experimentalists in the area of themogravimetric analysis. Several simple and complex molecules were used to validate the developed methodology. The advantage of the actual approach can be attributed to its efficient error minimization for each weigh loss and global process. In addition, the proposed expert system presents a low computational demanding. The validation analysis using compounds such as salicylato (amine) Co (III) complexes, norfloxacin complexes of manganese (II) and cobalt (II), and calcium borate produced an average confidence interval of about 2%.

Structural and acoustic investigations of calcium borate glasses

AbstractAcoustic and structural properties of x CaO · (1–x ) B2O3 (0.2 ≤ x ≥ 0.7) glass system have been studied at ambient temperature. The ultrasonic velocity and attenuation for different compositions of calcium borate glasses were measured at 5 MHz at room temperature (303 K) using a pulse echo overlap method. The elastic moduli, Debye temperature, Poisson's ratio and other acoustic parameters have been obtained from experimental data. Fourier transform infrared spectroscopic analysis has been used to further support the results of acoustic studies. The results obtained indicate that the calcium oxide enters the glass network as a modifier by occupying the interstitial spaces in the network and by increasing the nonbridging oxygen atoms (NBOs). (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Calcium borate flame retardation system for epoxy molding compounds

AbstractA new flame retardation system for epoxy molding compounds was investigated for application to semiconductor packaging. By adding a small volume of calcium borate as a flame retardant, the flammability of the epoxy molding compound decreased. The flammability was not decreased proportionally with the volume of calcium borate. To further enhance flammability, an excess amount of phenolic resin was added to the epoxy molding compound. With the effects of calcium oxide and the excess phenolic resin, we developed an epoxy molding compound which has a flame‐retardant level sufficient to satisfy the V‐0 classification of the UL94 rating. We also found that calcium oxide in the calcium borate accelerates the curing reaction of epoxy compounds due to its absorption of water from the phenolic resin hardener. Calcium hydroxide formed from calcium oxide and water was also considered to contribute to the decrease in flammability by releasing water at high temperatures. The flame retardation mechanism of this developed epoxy compound is also discussed. Finally, the developed epoxy compound was proved to have suitable moldability, mechanical properties, and durability for use as semiconductor packaging. POLYM. ENG. SCI., 46:799–806, 2006. © 2006 Society of Plastics Engineers