Ceramic Microspheres Research Articles

Influence of the Foaming Agent on the Particle Size and Microwave Absorption Properties of Hollow Ceramic Microspheres

In this study, based on self‐reactive quenching technique, hollow ceramic microspheres (HCMs) containing barium ferrites were synthesized using Al+Fe2O3+BaO2+sucrose+ epoxy resin as the reactive system and polyethylene glycol (PEG) as the foaming agent. The influence of PEG on the particle size and microwave absorption properties of HCMs is investigated using SEM, XRD, laser particle size analyzer and vector network analyzer. Preliminary results show that the average particle size increases initially from 28 μm to 53 μm after adding PEG, as well as the particle distribution gets narrower and the surface takes on classical hexagonal crystals. BaFe2O4, the intermediate phase of M‐type barium ferrites (BaFe12O19), can be seen in XRD. The microwave absorption properties are improved greatly in the frequency range of 8–18 GHz. And the minimum reflection loss can reach −10 dB.

Flight combustion of the agglomerate powders containing energy (APCE) in making new hollow multiphase ceramic microspheres by self-reactive quenching technology

Al–TiO2–Fe–Fe2O3–MnO2, as the main reaction system, was selected to prepare the agglomerate powders containing energy (APCE) on 50–90μm by balling, drying, carbonating, grinding and sieving. Self-reactive quenching technology, which is integrated with flame spraying, self-propagating high-temperature synthesis (SHS) and rapid solidification, was used to spray and melt the APCE. Flight combustion of the APCE was analyzed by high-speed photography, water quenching, collisions and Gibbs free energy graph, and surface morphologies of quenching products were characterized by SEM. The results show that the APCE goes through three stages, which mean heat storage (0–80mm, 66–72ms), heat releasing (80–240mm, 73–83ms) and after combustion (240–400mm, 84–99ms), to form hollow ceramic droplets which decisively affect the quality of hollow multiphase ceramic microspheres. Collisions and burst may be the main reasons to produce flame retrogression and affect the particle size distribution of hollow multiphase ceramic microspheres simultaneously.

Fabrication of Ceramic Microspheres by Diffusion-Induced Sol–Gel Reaction in Double Emulsions

We demonstrate an approach to prepare zirconium dioxide (ZrO2) microspheres by carrying out a diffusion-induced sol-gel reaction inside double emulsion droplets. A glass capillary microfluidic device is introduced to generate monodisperse water-in-oil-in-water (W/O/W) double emulsions with a zirconium precursor as the inner phase. By adding ammonia to the continuous aqueous phase, the zirconium precursor solution is triggered to gel inside the emulsions. The double emulsion structure enhances the uniformity in the rate of the sol-gel reaction, resulting in sol-gel microspheres with improved size uniformity and sphericity. ZrO2 ceramic microspheres are formed following subsequent drying and sintering steps. Our approach, which combines double-emulsion-templating and sol-gel synthesis, has great potential for fabricating versatile ceramic microspheres for applications under high temperature and pressure.

Effect of heat treatment on the structure of M-Type BaFe12O19 hollow ceramic microspheres prepared by self-reactive quenching technology and microwave absorption properties

Fe–Fe2O3–BaCO3–sucrose–epoxy resin and O2 as reaction system and feeding gas, respectively, were used to prepare M-type BaFe12O19 hollow ceramic microspheres (BaM HCMs) absorbent by self-reactive quenching technology which combines flame thermal spraying, self-propagating high temperature synthesis (SHS), and rapidly solidification. The morphologies and phase composition before and after heat treatment of HCMs were studied by SEM, XRD, and EDS, and microwave absorption properties were also analyzed. The results showed that before heat treatment, the phase was composed of Fe3O4, Fe2O3, BaFe2O4, and BaCO3. And thick dendrite, eutectic of dendrite and amorphous and amorphous were formed on the surface of HCMs. After heat treatment, high purity single BaM HCMs was obtained, and the surface was transformed into nanolamella, micro-nano isometric grain, eutectic of nanolamella and isometric grain, and hexagonal crystal. Absorption test result showed that at 0.5–18 GHz, both e′ and e″ of HCMs reduced obviously, but the μ″ increased by heat treatment. Therefore, the minimum reflectivity and bandwidth less than −10 dB were improved to −22.1 dB and 5.7 GHz (12.3–18 GHz), respectively. The improvement of electromagnetic match resulted by obvious reduction of permittivity, and the magnetocrystalline anisotropy, shape anisotropy, and various polarizations generated from special surface morphologies may be the main reasons to make microwave absorption properties better.

Effect of Heat on Hollow Multiphase Ceramic Microspheres Prepared by Self-Reactive Quenching Technology

The self-reactive quenching technology, which combines flame thermal spraying technology, self-propagating high-temperature synthesis (SHS), and rapid solidification, is a new method for preparation of hollow microspheres. Based on this, the effect of heat released by different exothermic systems on preparation of hollow ceramic microspheres was studied. The results show that for low-exothermic system Si-Sucrose-NH4Cl, the self-propagating reactions cannot occur, and the quenching products are Si microspheres with porous structure. For the moderate exothermic system Al–SiO2-Sucrose, the quenching products consist of some grains, which are hollow spherical or nearly spherical particles and irregular powders. Formation of Al2O3–Si indicates possible occurrence of SHS reactions. Meanwhile, for high-exothermic system Al–Cr2O3-Sucrose-Si-Epoxy Resin, the quenching products consist of internal hollow spherical grains and irregular-shaped porous particles; the phase composition mainly contains Al2O3, Cr3C2, Cr7C3, Cr3Si, and mullite, showing completeness of SHS reactions. The higher the adiabatic combustion temperature of the system is, the more heat it releases is higher, and the ceramic droplets form easilier.

がんや骨疾患の治療に貢献する医用材料の設計

Ceramic microspheres containing yttrium and/or phosphorus are useful for intra-arterial radiotherapy. Indeed, radioactive yttrium oxide (Y2O3) microspheres with high chemical durability can remarkably suppress growth of VX2 tumor. Hollow Y2O3 microspheres and yttrium phosphate (YPO4) microspheres have been also developed. Magnetic microspheres are believed to be useful for intra-arterial hyperthermia of cancer. It is confirmed that silica (SiO2) microspheres containing magnetite (Fe3O4) and maghemite (γ – Fe2O3) nanoparticles can generate heat under alternating magnetic field. On the other hand, development of metallic biomaterials with osteoconductivity as well as antibacterial property is desired so that incidence of infection after surgery is decreased. Titanium (Ti) metal with anion-doped titania (TiO2) surface might be a novel metallic biomaterials with ex vivo antibacterial property and in vivo osteoconductivity. Further, we recently proposed that specific adsorption of proteins on hydroxyapatite (HAp) might play an important role in the expression of osteoconductivity in vivo. The fundamental reach on relationship between specific protein adoption and osteoconductivity is believed to be useful for development of bone-repairing biomaterials with extremely high osteoconductivity. Development of novel biomedical materials for treatment of cancer and bone diseases is strongly desired to contribute to better health and welfare of patients with cancer and/or bone diseases.

Thermodynamic Properties of Reflective Coatings

As a part of introducing new technologies and materials, reflective coatings are among many other materials ones, which have to be taken into account. This article presents the results of a comparative nature aiming to investigate the thermodynamic properties of selected reflective coatings on energy balance for periods of heating. In order to investigate their thermal performance at the external building surfaces dynamic outdoor testing was used. Two comparative coatings and reference standard facing coating were used for various samples. The measured data demonstrates that the representative coating consisting of hollow ceramic microspheres have the same thermodynamic properties as a standard facing coating, while the reflective coating have distinctive thermal performance effect depending on thermal insulation functions of measured samples.

An Experimental Investigation of the Dynamic Mechanical Behaviors of Hollow Spheres Filled Syntactic Foam

Dynamic mechanical behaviors are critical to the engineering applications of hollow spheres filled syntactic foams. The potential of such composites cannot be fully realized unless the effects of strain rate on their mechanical properties are fully understood. In this study, both the compressive and the tensile behaviors of an epoxy syntactic foam filled by ceramic microspheres were experimentally investigated over the strain rate range from 0.001 to 2000 s-1. The compressive and tensile tests at high strain rates were carried out by means of split Hopkinson pressure bar (SHPB) and split Hopkinson tensile bar (SHTB), respectively. The stress-strain responses and failure mechanisms were examined quantitatively and qualitatively. The experimental results indicate that both the compressive and the tensile behaviors of syntactic foam are highly sensitive to strain rate. Moreover, a comparison of the stress-strain curves suggests that the compressive and tensile behaviors are dominated by different failure mechanisms, which consequently lead to distinct effects of strain rate on the compressive and tensile behaviors of syntactic foam.

Anal bulking agents for faecal incontinence

The aim of this review was to assess and evaluate reports of studies on the efficacy of anal bulking agents used in the treatment of faecal incontinence. A systematic review of the literature was carried out to identify studies that have reported on the use of anal bulking agents. A variety of biomaterials have been employed for anal bulking. These include autologous fat, bovine glutaraldehyde cross-linked collagen, carbon-coated zirconium oxide beads, dextranomer microspheres in a gel, hydrogel cross-linked with polyacrylamide, polydimethylsiloxane elastomer in a gel, porcine dermal collagen and synthetic calcium hydroxylapatitie ceramic microspheres. Although the ideal site of injection (submucosal or intramuscular) and the mechanism of action remain the subject of debate, most published studies report a significant improvement in continence in at least 50% of subjects with mild to moderate symptoms with little or no associated morbidity.We concluded that anal bulking agents may be used to alleviate symptoms of faecal seepage and soilage.

Manufacturing, compressive behaviour and elastic modulus of Ti matrix syntactic foam fabricated by powder metallurgy

Ti matrix syntactic foam has potential in the orthopaedic application because of its good biocompatibility, corrosion resistance and varied elastic modulus. Ti matrix syntactic foams embedded with thick-wall ceramic microspheres (CMs) were prepared using a powder metallurgy method. The structure, compressive behaviour and elastic modulus of Ti matrix syntactic foam embedded with thick-wall CMs were analyzed and compared with those embedded with thin-wall CMs. Results show that the compressive strength of Ti matrix syntactic foam increases with the increase of the volume fraction of CMs clearly. However, the strength increase would not increase the elastic moduli obviously which are still similar with those of human bone.

Research on Preparation of Hollow Ceramic Microspheres Base on the Main Reaction System of Al + Cr<SUB>2</SUB>O<SUB>3</SUB>

Research on Preparation of Hollow Ceramic Microspheres Base on the Main Reaction System of Al + Cr<SUB>2</SUB>O<SUB>3</SUB>

Experimental study and numerical prediction of tensile strength properties and failure modes of hollow spheres filled syntactic foams

Tensile properties are critical to the engineering applications of hollow spheres filled syntactic foams. The potential of such composites cannot be fully realized unless their fracture modes and failure mechanisms under tension are fully understood, and appropriate modeling strategies for failure prediction are developed and verified. In this study, both experimental and numerical methods were employed to investigate the tensile behaviors of epoxy–ceramic microspheres syntactic foams with different volume fractions of filler phase. The experimental results indicate that mechanical behaviors of syntactic foams are dominated by brittle fracture mechanism under tensile load. To predict the mechanical properties of syntactic foams in terms of tensile strength and associated failure modes, a three-dimensional microstructure based finite element model was developed by means of a representative volume element (RVE). Cohesive elements were introduced into the finite element model to capture the progressive damage behavior of the microsphere-matrix interface. Complex failure modes of syntactic foams including microspheres fracture, interfacial debonding and the interaction of both features were well characterized according to the simulation results. The proposed model interprets the entire failure process from damage to fracture under tension and provides predictive capabilities for the strength properties of hollow spheres filled syntactic foams. By comparison, the simulation results and the experimental data are found to be in good agreement.

Synthesis of syntactic steel foam using gravity-fed infiltration

In this study, we report a procedure for producing syntactic steel foams by melt infiltration of millimeter-sized ceramic microspheres. The gravity-fed infiltration method yields steel foam with uniform distributions of microspheres and negligible unintended porosity. The critical parameters in the manufacturing process are the melt temperature and the preheat temperature of the microspheres prior to infiltration. Syntactic foams with relative density of 0.46 were produced using monosized microspheres (4.45mm) randomly situated in a mold. Six steel compositions were selected to produce steel foams of different inherent yield strength: five ferritic–pearlitic steels and one TRIP steel (transformation-induced plasticity). The resultant foams were characterized by chemical and microstructural analysis. The microstructure of the samples consisted of blends of ferritic and pearlitic constituents in varying proportions for the ferritic–pearlitic steels, while the cast TRIP steel matrix presented an austenitic microstructure. Simple compression behavior of the steel syntactic foams was studied, and the TRIP steel syntactic foam exhibited the highest compression strength and energy absorption capacity. Syntactic steel foams were also produced with different relative densities (0.60, 0.68 and 0.75). The steel syntactic foam with relative density of 0.60 exhibited the maximum energy absorption. Problems and challenges for achieving steel foams with lower relative densities and for scaling up the synthesis process are contemplated.

Hollow Multiphase Ceramic Microspheres of Al+Cr<sub>2</sub>O<sub>3</sub>+SiO<sub>2</sub> System Prepared by Self-Reaction Quenching Technology

This paper aims to study preparation and mechanism of hollow ceramic microspheres. With Al+Cr2O3+SiO2+sucrose+epoxy resin as reactive system, Al2O3-based hollow ceramic microspheres are synthesized and reaction mechanism of hollow ceramic microspheres is established. Results show that the quenching products consist of hollow spherical or irregularly spherical particles and irregularly powders. Spherical or irregularly spherical particles are hollow structure and constitutive of Al2O3-SiC diphase and a few Cr3Si、Cr7C3. The preparation of hollow ceramic microspheres includes igniting by heating, forming ceramic thawy droplets and fast cooling. The great deal of air produced by burning epoxy resin and sucrose is the key reason why hollow ceramic microspheres are formed.

Preparing and Characterization of Hollow Ceramic Microspheres

The hollow microsphere is a kind of new materials. It has a bright future for its excellent comprehensive performance. This article introduces a high-temperature synthetic technology on the basis of SHS to prepare new hollow ceramic microspheres. Reaction mechanism of hollow ceramic microspheres was studied. Results show that sphere, similar sphere and irregular powders constitute the spraying products. Sphere and similar sphere powders are hollow structure. Besides it also recommend the self-made equipments of collection that adopts three kinds of collections methods of static electricity, water and filter net. The total rate of collection raised above 80%.The effect is good. The hollow microsphere were analyzed through SEM and XRD, the hollow microsphere is regular spheroid or type spheroid.the size of the hollow microsphere is abort Similar. Its diameter is 20 μm or so. The equipments that experiment needs is simple, vivid craft and strong adaptability and respond that raw material and manufacturing circulate cost cheap.

Spectral emissivity properties of reflective coatings

Spectral emissivity properties of reflective coatingsThis article deals with the spectral radiative properties of coatings consisting of hollow ceramic microspheres. They were selected from the commercial coatings available in the Slovak and Czech Republics. The aim was to measure and compare their spectral emissivity properties with standard facing coatings by means of infrared spectroscopy. The measured data demonstrates that the coatings have the same radiative properties as a standard building coating. Two reflective measurement methods (DRIFT and ATR) were used for this purpose. These results have been compared, and the DRIFT method was finally recommended for determining the spectral radiative properties of the materials measured.

Performance of evacuated calcium phosphate microcarriers loaded with mesenchymal stem cells within a rat calvarium defect

Tissue engineering of stem cells in concert with 3-dimensional (3D) scaffolds is a promising approach for regeneration of bone tissues. Bioactive ceramic microspheres are considered effective 3D stem cell carriers for bone tissue engineering. Here we used evacuated calcium phosphate (CaP) microspheres as the carrier of mesenchymal stem cells (MSCs) derived from rat bone marrow. The performance of the CaP-MSCs construct in bone formation within a rat calvarium defect was evaluated. MSCs were first cultured in combination with the evacuated microcarriers for 7days in an osteogenic medium, which was then implanted in the 6mm-diameter calvarium defect for 12weeks. For comparison purposes, a control defect and cell-free CaP microspheres were also evaluated. The osteogenic differentiation of MSCs cultivated in the evacuated CaP microcarriers was confirmed by alkaline phosphatase staining and real time polymerase chain reaction. The in vivo results confirmed the highest bone formation was attained in the CaP microcarriers combined with MSCs, based on microcomputed tomography and histological assays. The results suggest that evacuated CaP microspheres have the potential to be useful as stem cell carriers for bone tissue engineering.

Compressive failure of Al alloy matrix syntactic foams manufactured by melt infiltration

a b s t r a c t Al alloy syntactic foams containing hollow or porous ceramic microspheres were fabricated by melt infiltration. Tensile, shear, confined compressive and unconfined compressive tests were performed and the failure modes in compression were studied. The tensile and shear strengths were insensitive to the types of the ceramic microspheres. In confined compression, all syntactic foams failed by progressive collapse of the microspheres. Different failure mechanisms were observed in unconfined compression. The syntactic foams with stronger ceramic microspheres failed by Griffith rupture, with cracks oriented at approximately 30◦ to the loading direction and the compressive strengths being about eight times of their tensile strengths. The syntactic foams with weaker ceramic microspheres failed by progressive collapse of the ceramic microspheres and had lower compressive strengths.

The in vivo osteogenesis of Mg or Zr‐modified silicate‐based bioceramic spheres

The use of bioactive microspheres as bone filling materials has received much attention due to their ability to fill the bone defects with irregular and complex shapes and sizes. Divalent Mg(2+) modified silicate-based diopside (DIOP: CaMgSi(2)O(6)) and tetravalent Zr(4+) modified silicate-based baghdadite (BAGD: Ca(3)ZrSi(2)O(9)) ceramics have shown excellent in vitro bioactivity for potential bone repair application. However, their in vivo osteogenesis has not been systematically investigated. The aim of this study is to prepare DIOP and BAGD ceramic microspheres and investigate their in vivo osteogenesis. DIOP and BAGD ceramic spheres with loose microstructure were successfully prepared. The dissolution ability of two silicate-based bioceramics was investigated by testing the release of SiO 44- ions after soaking them in phosphate buffered saline. The ceramic spheres were implanted into supracondylar site of the femur defects in Wistar rats and the degree of in vivo osteogenesis was evaluated by hematoxylin and eosin (H and E), Safranin O staining, tartrate-resistant acid phosphatase (TRAP) staining, and immunohistochemistry (type I collagen: Col I, osteopontin: OPN) analyses. The results have shown that BAGD spheres induced a higher rate of new bone formation in the defects than did DIOP and β-tricalcium phosphate (β-TCP) spheres. Immunohistochemical analysis showed greater expression of Col I and OPN in BAGD group compared to DIOP and β-TCP groups. The study indicates different ion modification playing an important role to regulate the in vivo osteogenesis of silicate-based bioceramics. BAGD spheres are a promising bone filler material due to their significantly enhanced osteogenesis, compared to β-TCP spheres.

Long-term conversion of 45S5 bioactive glass–ceramic microspheres in aqueous phosphate solution

The conversion of 45S5 glass and glass-ceramics to a hydroxyapatite (HA)-like material in vitro has been studied extensively, but only for short reaction times (typically <3 months). In this paper, we report for the first time on the long-term conversion of 45S5 glass-ceramic microspheres (designated 45S5c) in an aqueous phosphate solution. Microspheres of 45S5c (75-150 μm) were immersed for 10 years at room temperature (~25 °C) in K(2)HPO(4) solution with a concentration of 0.01 M or 1.0 M, and with a starting pH of 7.0 or 9.5. The reacted 45S5c microspheres and solutions were analyzed using structural and analytical techniques. Only 25-45 vol% of the 45S5c microspheres were converted to an HA-like material after the 10 year reaction. In solutions with a starting pH of 9.5, an increase in the K(2)HPO(4) concentration from 0.01 to 1.0 M resulted in a doubling of the volume of the microspheres converted to an HA-like material but had little effect on the composition of the HA-like product. In comparison, reaction of the 45S5c microspheres in the solution with a starting pH of 7.0 resulted in an HA-like product in the 0.01 M K(2)HPO(4) solution but a calcium pyrophosphate product, Ca(10)K(4)(P(2)O(7))(6).9H(2)O, in the 1.0 M solution. The consequences of these results for the long-term use of 45S5 glass-ceramics in biomedical applications are discussed.