Calcium phosphate bioceramics synthesized from eggshell powders through a solid state reaction

Everyday millions of tons of eggshells are produced as biowaste around the world. Most of this waste is disposed of in landfills without any pretreatment. Eggshells in landfills produce odors and promote microbial growth as they biodegrade. The present invention provides an environmentally beneficial and cost-effective method of producing calcium phosphate bioceramics (hydroxyapatite or tricalcium phosphate) from eggshell waste. In this investigation, heat treatment produced solid state reactions between eggshell powders and dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) or calcium pyrophosphate (Ca₂P₂O₇). When eggshell powders (CaO) and DCPD were heat treated at 1150 °C for 3 h, only a single hydroxyapatite (HA) phase was found; no diffraction peaks of starting materials and no β-TCP were observed. The XRD patterns of the product fabricated from raw eggshell powders (CaCO₃) and Ca₂P₂O₇ heat treated at 1100 °C for 3 h showed that almost only pure β-TCP remained with a trace amount of HA. The calcium phosphate ceramic synthesized from eggshell powders contains several important trace elements such as Na, Mg and Sr.     

Characterization of Mg-substituted hydroxyapatite synthesized by wet chemical method

Mg-substituted hydroxyapatite made up of needle-like and plate-like particles containing different amounts of Mg (between 0.21 wt% and 2.11 wt%) were prepared via wet chemical precipitation method of a homogenous suspension of Mg(OH)₂/Ca(OH)₂ and an aqueous solution of H₃PO₄. According to the data of Brunauer–Emmett–Teller method and field emission scanning electron microscopy, high specific surface area Mg-substituted hydroxyapatite was obtained. Specific surface area of as-synthesized powders increased from 94.9 m² g⁻¹ to 104.3 m² g⁻¹ with increasing concentration of Mg up to 0.64 wt%. Fourier transform infrared spectroscopy, X-ray powder diffraction, differential thermal analysis, and heating microscopy, were used to evaluate thermal stability and sintering behavior of synthesis products. Increase in concentration of Mg in synthesis products (≥0.83 wt%) promoted decomposition of Mg-substituted hydroxyapatite to Mg-substituted β-tricalcium phosphate after thermal treatment.     

Synthesis of calcium phosphate-based composite nanopowders by mechanochemical process and subsequent thermal treatment

One-step mechanochemical process followed by thermal treatment has been used to produce calcium phosphate-based composite nanopowders. Effects of milling and subsequent heat treatment on the phase transition as well as structural features were investigated. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques. The results revealed that the dominant phases after mechanical activation were hydroxyapatite, anatase (TiO₂), and periclase (MgO), while after thermal annealing process at 700 °C hydroxyapatite along with geikielite (MgTiO₃) and periclase (MgO) were the major phases. In addition, decomposition of hydroxyapatite to tricalcium phosphate (β-TCP) occurred after heat treatment in the range 900–1100 °C which resulted in the formation of tricalcium phosphate-based composite nanopowders. Evaluation of structural features of the samples calculated by X-ray diffraction profiles analysis indicated that the average crystallite size of hydroxyapatite after 10 h of milling and subsequent heat treatment at 700 °C were about 21 and 34 nm, respectively. TEM and SEM studies exhibited that the considerable morphological changes at temperatures ≥900 °C had to be ascribed not only to grain growth, but also for the transformation of hydroxyapatite to β-TCP.     

Mg2+, Sr2+, Ag+, and Cu2+ co-doped β-tricalcium phosphate: Improved thermal stability and mechanical and biological properties

β-tricalcium phosphate (β-TCP, β-Ca₃(PO₄)₂) is an attractive biomaterial for bone repair applications. However, its sintering and mechanical properties are limited by a problematic phase transition to α-TCP. Cationic doping of β-TCP is able to postpone the formation of α-TCP allowing higher sintering temperatures and better mechanical properties. The co-doping of β-TCP with Mg²⁺ and Sr²⁺ has already been studied in detail, but the addition of antibacterial cations (Ag⁺ and Cu²⁺) on the Mg–Sr β-TCP co-doped composition remains unexplored. Thus, two co-doped β-TCP compositions were realized by aqueous precipitation technique without any secondary phase and compared with undoped β-TCP: Mg–Sr (2.0–2.0 mol%) and Mg–Sr–Ag–Cu (2.0–2.0–0.1–0.1 mol%). Differential thermal analysis and dilatometry analyses showed a slight decrease of the β-TCP → α-TCP phase transition temperature for the Mg–Sr–Ag–Cu (2.0–2.0–0.1–0.1% mol) composition as compared to the Mg–Sr (2.0–2.0 mol%). However, both exhibited much higher transition temperatures than undoped β-TCP. The addition of Ag⁺ and Cu²⁺ slightly reduces the grain size after sintering compared to the Mg–Sr (2.0–2.0 mol%) and the undoped compositions. The co-doped compositions also exhibited improved mechanical properties, specifically a higher Vickers hardness and elastic modulus. Finally, cell proliferation assays showed that the presence of dopants, even Ag⁺ and Cu²⁺, does not affect the survival and proliferation of cells. Thus, the use of Mg²⁺, Sr²⁺, Ag⁺, and Cu²⁺ co-doped β-TCP could be very promising for biomedical applications due to the improvements of these dopants on the thermal stability and mechanical and biological properties.     

Thermal conductivity of combustion synthesized β-sialons

To the first time, thermal conductivities of spark plasma sintered β-sialons (Si₃Al₃O₃N₅) procured from combustion synthesis (CS) with no sintering additive were measured by the laser flash method at room temperature. A full densification occurred when these materials were sintered at 1600 °C with a simultaneous pressure of 50 MPa. XRD analyses indicated that single phase β-sialons were formed after SPS though the combustion synthesized β-sialon powders had considerable amounts of silicon impurities. Thermal conductivity values increased with sintering temperature and attained a maximum of 5.49 W m⁻¹ K⁻¹ for fully densified β-sialons sintered at 1700 °C for 10 min.     

Low temperature synthesis of nanocrystalline magnesium aluminate spinel by a soft chemical method

A new simple soft chemical method – synthesizing nanocrystalline MgAl₂O₄ spinel powder with oxalic acid as organic template and nitric acid as an oxidizing agent – is described. The method was developed with the objective of obtaining phase pure nanocrystalline MgAl₂O₄ spinel powder with uniform particle size and morphology at a much lower temperature than that used by conventional methods. The synthesized powders were characterized by X-ray diffractometry (XRD), thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR), surface area analysis (BET) and field emission scanning electron microscopy (FE-SEM). The average crystallite size of the single phase material was 30 nm. Through this method, porous MgAl₂O₄ powder with a high surface area of 162.2 m²g⁻¹ and 141 m²g⁻¹ was obtained at 600 °C and 700 °C, respectively.     

Temperature-dependent morphology changes of noble metal tricalcium phosphate-nanocomposites

Calcium phosphates, functionalized with nano-sized metal particles, are a promising material class for the treatment of bone defects. However, a sintering process is required in principle to achieve sufficient strength of calcium phosphate scaffolds. In this work laser-generated nano-sized silver, gold and platinum particles were adsorbed on micro-sized β-tricalcium phosphate particles and further heat treated at temperatures between 600 and 1200 °C. Gold and platinum nanoparticles underwent exponential growth starting at about 600 °C, while sintering of β-tricalcium phosphate started at 800 °C. We hypothesise that this phenomenon is caused by a heat-induced evaporation and growth process where the decrease of the particle number is directly correlated with the size increase. The silver nanoparticles on the other hand formed a new phase with the calcium phosphate (AgCa₁₀(PO₄)₇) during the heat treatments and could not be observed within the ceramic scaffold anymore. Addressing the lack of information in nanoparticle-combined calcium phosphate scaffolds, this study contributes to the further modification of bone replacement materials with biologically relevant functions and molecules.     

Synthesis of lanthanum beta-alumina powders by the polymeric precursor technique

La-β-Al₂O₃ (LaAl₁₁O₁₈) powders were synthesized by the polymeric precursor technique using lanthanum nitrate and aluminum nitrate. The transformations during thermal treatment of the precursor solution with ethylene glycol and citric acid were evaluated by thermal analysis. Fourier transform infrared spectroscopy analysis was performed after calcinations of the polymeric resin for determination of residual carbon. The specific surface area was evaluated by the BET method. Fine powders with ∼121 m²/g specific surface area and 20 nm average particle size were obtained and observed by scanning and transmission electron microscopy. Nearly single phase LaAl₁₁O₁₈ was obtained after pressing and sintering these powders at 1600 °C with small additions of MgO. The sintered pellets were characterized by X-ray diffraction and scanning electron microscopy. Impedance spectroscopy measurements carried out in the 1000–1200 °C range show the electrolytic behavior of the La-β-Al₂O₃ pellets, suggesting their application as solid electrolytes in high temperature potentiometric oxygen sensors.     

Thermal conductivity in mullite/ZrO2 composite coatings

Mullite-based multilayered structures have been suggested as promising environmental barrier coatings for Si₃N₄ and SiC ceramics. Mullite has been used as bottom layer because its thermal expansion coefficient closely matches those of the Si-based substrates, whereas Y–ZrO₂ has been tried as top layer due to its stability in combustion environments. In addition, mullite/ZrO₂ compositions may work as middle layers to reduce the thermal expansion coefficient mismatch between the ZrO₂ and mullite layers. Present work studies the thermal behaviour of a flame sprayed mullite/ZrO₂ (75/25, v/v) composite coating. The changes in crystallinity, microstructure and thermal conductivity of free-standing coatings heat treated at two different temperatures (1000 and 1300 °C) are comparatively discussed. The as-sprayed and 1000 °C treated coatings showed an almost constant thermal conductivity (K) of 1.5 W m⁻¹ K⁻¹. The K of the 1300 °C treated specimen increased up to twice due to the extensive mullite crystallization without any cracking.     

Synthesis and characterization of LZS/α-Al2O3 glass-ceramic composites for applications in the LTCC technology

In this work, α-Al₂O₃ (1–40 vol%) particles (350 nm) were added to a 19.58Li₂O·11.10ZrO₂·69.32SiO₂ (5 µm) glass-ceramic matrix to prepare composites with the purpose of studying the influence of α-Al₂O₃ on their mechanical, thermal and electrical properties in order to obtain materials for LTCCs applications. The composites, sintered between 800 and 950 °C for 30 min, with relative densities between 85% and 93%, showed zircon and β-spodumene as main crystalline phases. The maximum bending strength (290 MPa) was achieved for composites with 1% α-Al₂O₃. For composites containing between 1% and 10% α-Al₂O₃, sintered at 900 °C/30 min, the electrical and thermal conductivities and CTE varied between 3.35 and 1.21×10⁻¹⁰ S/cm, 4.65 and 2.98 W/m K, 9.54 and 3.36×10⁻⁶ °C⁻¹, respectively.     

Preparation and properties of C/SiC/ZrO2 porous composites by hot isostatic pressing the pyrolyzed preforms

Three phase mixture of C/SiC/ZrO₂ porous composites were prepared from commercially available phenolic resin, Si and ZrO₂ powders. In the first step, mixed powders were pyrolyzed at 850 °C in vacuum to obtain a carbonized microporous material and then hot isostatically pressed at 1200, 1300 and 1350 °C for 10 min in an argon pressure of 50 MPa to prepare C/SiC/ZrO₂ porous composites, in second step. The hot isostatic pressing led to the increase in density from 3.28 to 3.48 g/cm³ and reduction in porosity (from 32 to 20%) of the composites. X-ray diffraction analyses revealed the existence of β-SiC and carbon might be amorphous in the composites. According to the results of scanning electron microscopy, the crystal growth of β-SiC with facets was observed at 1350 °C. In addition, the energy dispersive spectroscopy showed that carbon/silicon atomic ratio was 1:1 in the crystals. X-ray photoelectron spectroscopy of the composites suggested that evolved gaseous molecules, due to the decomposition of phenolic resin, reacted with molecules containing Si to form β-SiC. The formation and growth of β-SiC in addition to the densification of matrix by hot isostatic pressing led to the increase in hardness (max.: 13.99 GPa) at higher temperatures.     

LaBaCuFeO5+δ-Ce0.8Sm0.2O1.9 as composite cathode for solid oxide fuel cells

The performance of the LaBaCuFeO_5+δ-Ce_0.8Sm_0.2O_1.9 (LBCF-SDC) composite cathodes was studied in this paper. Electrical conductivity, thermal expansion and electrochemical properties were investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. The thermal expansion coefficients of the LBCF-SDC were between (16.3 and 13.4) × 10⁻⁶ K⁻¹ from 30 to 850 °C, which was lower value than LBCF (17.0 × 10⁻⁶ K⁻¹). AC Impedance spectroscopy measurements of LBCF-SDC/SDC/LBCF-SDC test cell were carried out. Polarization resistance values for the LBCF-SDC10 cathode was as low as 0.097 Ω cm² at 750 °C.     

Cefuroxime-impregnated calcium phosphates as an implantable delivery system in experimental osteomyelitis

The study aimed to investigate the effectiveness of porous calcium phosphates viz., hydroxyapatite (HAp) and a bi-phasic calcium phosphate (BCP) with predominately β-tricalcium phosphate (β-TCP) prepared by aqueous solution combustion method impregnated with cefuroxime axetil for the treatment of experimental osteomyelitis and compared with parenteral treatment. In vitro release of the drug was tested for its sustained elution characteristics for 21 days in PBS (pH 7.2) and measured by HPLC. In the in vivo study, bone infection was induced in tibia of rabbits by inoculation of 1 ml (3 × 10⁶) CFU Staphylococcus aureus. On the 21st day, after the development of osteomyelitis, six animals were treated by filling the cavity with cefuroxime-impregnated HAp blocks (Group II), six animals with the same drug-impregnated β-TCP (Group III) and in six others, only cefuroxime (15 mg/kg twice daily) was injected parenterally 6 weeks (Group IV). Group I with six animals was kept untreated. Histologically, the signs of infection were found to subside by 3 and 6 weeks. Radiological evaluation with cefuroxime-impregnated HAp and β-TCP pointed out the disappearance of sequestrum and existence of newly formed bony specules. Concentration of cefuroxime in bone and serum as estimated by HPLC showed highest value on day 21 itself which reduced marginally by day 42 in both the groups and these values were higher than minimum inhibitory concentration (MIC) against S. aureus. Our findings suggest that bi-phasic calcium phosphates with predominately β-TCP content is a very efficient carrier material for antibiotic compounds even for refractory infections by S. aureus.     

Manufacturing of highly porous calcium phosphate bioceramics via gel-casting using agarose

There is a technological need for highly porous bioceramics to be produced in an environmentally friendly manner. Gel-casting of highly porous HAp-(α-TCP) (CaP) foams using agarose as a gelling agent was investigated. Foaming of gel-cast suspension was performed at the temperature of 60 °C followed by transformation of the foams from a liquid state to a gelled state by cooling them to 15 °C. The sintered (1250 °C, 2 h soaking time) foams were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption isoterm and Hg porosimetry. XRD study revealed that additives used in the gel-casting process did not influence the phase composition of the investigated materials. The macroporous microstructure of HAp-(α-TCP) foams was typically composed of approximately spherical pores (cells) interconnected by circular windows. The foams exhibited a broad pore size distribution with cells and windows ranging from 250 to 900 μm, and from 25 to 250 μm, respectively. The mode for spherical pore size was approximately 500 μm while the above value for window was ∼100 μm. Additionally, the small amount of wall microporosity in the range of 0.2–0.9 μm was confirmed by SEM and Hg porosimetry. The obtained porous (P = 90%) HAp-(α-TCP) scaffolds with interesting two types of macropores and a small amount of micropores seem to be a promising bone substitution material.     

Changes in pore properties of phenol formaldehyde-based carbon with carbonization and oxidation conditions

Porous carbon beads were prepared by carbonizing at 700 and 1000 °C under N₂ (NN-series) or CO₂ atmospheres (CO-series) and a subsequent oxidization with boiling nitric acid solution (13%, v/v) for 3 h (ANN- and ACO-series). BET surface area of both CO- and NN-series samples tends to increase with increasing carbonization temperature, but CO-series samples show higher BET surface areas (700 °C: 610 m²/g, 1000 °C: 780 m²/g) compared with those of NN-series samples (700 °C: 380 m²/g, 1000 °C: 580 m²/g). After acid oxidation, BET surface areas of NN-series samples increased from 580 to 650 m²/g, whereas those of CO-series samples decreased from 780 to 600 m²/g. On subsequent acid oxidation, acidic surface functional groups increased in both CO- and NN-series samples, but the CO-series samples tend to have much more acidic surface functional groups. Adsorption of halogenated methanes, such as tetra-, tri- and dichloromethanes, onto the samples of CO-, NN-, ACO- and ANN-series was thought to be driven initially by the basicity, but the acidic functional groups that could attract adsorbates via dipole-dipole interaction might hinder the adsorption of subsequently incoming adsorbates.     

Co-gasification of meat and bone meal with coal in a fluidised bed reactor

After the Bovine Spongiform Encephalopathy illness appeared, the meat and bone meat (MBM) produced from animal residues became an important waste. In spite of being a possible fuel due to its heating value (around 21.4 MJ/kg), an important fraction of the meat and bone meal is being sent to landfills. The aim of this work is to evaluate the co-gasification of low percentages of meat and bone meal with coal in a fluidised bed reactor as a potential waste management alternative. The effect of the bed temperature (800-900 °C), the equivalence ratio (0.25-0.35) and the percentage of MBM in the solid fed (0-1 wt.%) on the co-gasification product yields and properties is evaluated. The results show the addition of 1 wt.% of MBM in a coal gasification process increases the gas and the liquid yield and decreases the solid yield at 900 °C and 0.35 of temperature and equivalence ratio operational conditions. At operational conditions of 900 °C and equivalence ratio of 0.35, the specific yield to gas (y_gas) increases from 3.18 m³(STP)/kg to 4.47 m³(STP)/kg. The gas energy yield decreased 24.1% and the lower heating value of the gas decreases from 3.36 MJ/m³(STP) to 2.16 MJ/m³(STP). The concentration of the main gas components (H₂, CO and CO₂) hardly varies with the addition of MBM, however the light hydrocarbon concentrations decrease and the H₂S concentration increases at the higher temperature (900 °C).     

Catalytic combustion of methane on substituted strontium ferrites

Sr-hexaferrites prepared by co-precipitation method and calcined at 700-1000 °С have been characterized by thermogravimetric and differential thermal analysis (TG-DTA), Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), and Ar adsorption techniques. It has been shown that hexaferrite phase formed after calcination at 700 °С is amorphous and its crystallization occurs at 800 °С. Specific surface area (S_BET) of the samples calcined at 700 °С is 30-60 m²/g. Reduction in hydrogen proceeds in several steps, Fe(III) in the hexaferrite structure being practically reduced to Fe⁰. Amount of hydrogen necessary for the reduction of the samples decrease in the order: SrMn₂Fe₁₀O₁₉ > SrFe₁₂O₁₉ > SrMn₆Fe₆O₁₉ > SrMn₂Al₁₀O₁₉. Surface composition of the ferrites differs from bulk. According to XPS data, the surface is enriched with strontium. Sr segregation is most probably explained by the formation of surface carbonates and hydroxocarbonates. The main components on the surface are in oxidized states: Mn³⁺ and Fe³⁺. Maximum activity in the methane oxidation is achieved for the SrMn_xFe_12−xO₁₉ (0 ? x ? 2) catalysts. These samples are characterized by highest amount of the hexaferrite phase, which promotes change of oxidation state Mn(Fe)³⁺ ↔ Mn(Fe)²⁺.     

Preparation and characterization of iron/β-tricalcium phosphate bio-cermets for load-bearing bone substitutes

Ceramic-metal composite materials, namely cermets, are provided with characteristics of both ceramic and metal. Herein, for the first time bio-cermets based on β-tricalcium phosphate (β-TCP) bioceramic with biodegradable iron being reinforcement phase, were fabricated using the powder metallurgic method. The phase composition, microstructure, mechanical properties and in vitro cell behaviors of bio-cermets were investigated. The results revealed that atomic diffusion occurred between the iron and β-TCP matrix during the sintering process. The bio-cermets attained remarkable increase in fracture toughness (1.16–1.55 MPa m^1/2) compared to the β-TCP bioceramic (0.54 MPa m^1/2). The bio-cermets with 10 vol% iron showed the highest compressive strength (640 MPa), significantly higher than that of plain β-TCP bioceramic (285 MPa). The in vitro cell behaviors test indicated that the bio-cermets did not showed any sign of toxicity; the iron ions released from bio-cermets up-regulated bone-related gene expression of bone mesenchymal stem cells. The bio-cermets developed in this study represent potential bone substitutes for application in the load-bearing bone defects.     

Sintering behavior and mechanical properties of hydroxyapatite ceramics prepared from Nile Tilapia (Oreochromis niloticus) bone and commercial powder for biomedical applications

In this work, Nile tilapia (Oreochromis niloticus) bone was calcined at 800 °C for 5 h in an air atmosphere to obtain hydroxyapatite powder (FB powder). The elemental composition, phase structure, and morphology of the FB powder were investigated and compared with commercial hydroxyapatite powder (SM powder). The FB-powder exhibited 1.01 at. % of Mg while the SM-powder showed Mg in ppm-level. Carbonate groups were detected in the two powders. Both HAp and β-tricalcium phosphate (β-TCP) structures were found in the FB powder, but the SM powder exhibit only the HAp phase. Irregular-shaped particles were observed in the FB powder. After the two HAp powders were sintered at 1200 °C and 1250 °C for 2 h (FB-1200, FB-1250, SM-1200, and SM-1250), the β-TCP intensity peaks of the FB-ceramic samples significantly increased with increasing sintering temperature. The highest relative density, well-packed grains, and β-TCP stabilization by Mg at the Ca5 site of the FB-1250 structure were the dominant factors governing the highest mechanical properties. Although high density was observed in the SM-1200 sample, Vickers hardness of the SM-1200 sample is lower than the FB-1250 sample. This may be attributed to the partial decomposition of HAp into β-TCP, α-tricalcium phosphate (α-TCP), and Ca₁₀(PO₄)₆O phases. In addition, the increase of grain size was the main factor that governs the increasing compressive strength and Young's modulus instead of density and phase decomposition of the SM-ceramic samples.     

Microstructure and ionic conductivity properties of gadolinia doped ceria (GdxCe1−xO2−x/2) electrolytes for intermediate temperature SOFCs prepared by the polyol method

Gd_0.1Ce_0.9O_1.95 and Gd_0.2Ce_0.8O_1.9 powders were prepared through the polyol process without using any protective agent. Microstructural and physical properties of the samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG) and impedance analysis methods. The results of the thermogravimetry/differential thermal analysis (TG/DTA) and XRD indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 500 °C. The XRD patterns of the samples revealed that the crystallite size of the samples increased as calcination temperatures increased. The sintering behavior and ionic conductivity of pellets prepared from gadolinia doped ceria (GDC) powders, which were calcined at 500 °C, were also investigated. The relative densities of the pellets, which were sintered at temperatures above 1300 °C, were higher than 95%. The results of the impedance spectroscopy revealed that the GDC-20 sample that was sintered at 1400 °C exhibited an ionic conductivity of 3.25×10⁻² S cm⁻¹ at 800 °C in air. This result clearly indicates that GDC powder with adequate ionic conductivity can be prepared through the polyol process at low temperatures.