Showing papers in "Advances in Applied Ceramics in 2008"
TL;DR: In this article, various sintering and densification strategies were adopted, including pressureless sinter, hot pressing, hot isostatic pressing, microwave sinter and spark plasma sinter.
Abstract: Observation of the unconventional properties and material behaviour expected in the nanometre grain size range necessitates the fabrication of fully dense bulk nanostructured ceramics. This is achieved by the application of ceramic nanoparticles and suitable densification conditions, both for the green and sintered compacts. Various sintering and densification strategies were adopted, including pressureless sintering, hot pressing, hot isostatic pressing, microwave sintering, sinter forging, and spark plasma sintering. The theoretical aspects and characteristics of these processing techniques, in conjunction with densification mechanisms in the nanocrystalline oxides, were discussed. Spherical nanoparticles with narrow size distribution are crucial to obtain homogeneous density and low pore-to-particle-size ratio in the green compacts, and to preserve the nanograin size at full densification. High applied pressure is beneficial via the densification mechanisms of nanoparticle rearrangement and sli...
253 citations
TL;DR: In this article, two classes of novel hard amorphous coatings: (a) Si3N4/MeNx coatings with high (≥50 vol.-%) content of Si 3N4 phase; here Me=Zr, Ta, Ti, Mo, W, etc.
Abstract: This article reports on two classes of novel hard amorphous coatings: (a) Si3N4/MeNx coatings with high (≥50 vol.-%) content of Si3N4 phase; here Me=Zr, Ta, Ti, Mo, W, etc. and x=N/Me is the stoich...
69 citations
TL;DR: In this article, a review is dedicated to the problems of nanostructured ceramics consolidation and the grain growth factor in these processes was found to be less than 10.
Abstract: This review is dedicated to the problems of nanostructured ceramics consolidation.Laboratory practice in recent years has displayed several potentially important technologies for consolidation of ceramic nanopowders, such as spark plasma sintering, high pressure sintering and rate controlled sintering. The grain growth factor in these processes was found to be less than 10. These advanced technologies have to be adapted to consolidation of nanopowders and require nanopowders specifically designed for consolidation purposes. When adapted to nanopowders, these techniques must be accomplished in rapid rate mode to eliminate residual porosity and retain nanosize grains. Practical verification, however, has exposed problems such as large residual porosity, stable pores in triple junctions, defective grain boundaries and intensive grain growth. All these problems can be avoided when the temperature–pressure–time schedule of sintering is optimised with respect to minimal grain growth.
52 citations
TL;DR: In this paper, the authors used X-ray diffraction and Fourier transform infrared spectroscopy to confirm the formation of crystalline HAp as well the presence of both constituents in the composite samples.
Abstract: Gelatin–hydroxyapatite (HAp) nanocomposites have been prepared by particulate leaching technique using glutaraldehyde (GTA) as cross-linking agent for polymer. The porosity in the scaffolds was controlled using sodium chloride as porogen agent. Microstructural investigation by scanning electron microscopy (SEM), revealed the formation of a well interconnected porous scaffold with pore size in the range of 100–200 μm. X-ray diffraction and Fourier transform infrared spectroscopy were used to confirm the formation of crystalline HAp as well the presence of both constituents in the composite samples. The bioactivity of the samples was evaluated by conducting MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay and cell adhesion tests. The results suggest that the use of GTA in excess of 0˙25% can be detrimental to cell survival. Cell attachment on the nanocomposite scaffold was verified by microscopic analysis.
35 citations
TL;DR: A glass-ceramic composition has been studied to realize a highly bioactive material, suitable for stimulate the bone regeneration, which has been subjected to a patented ion exchange process with silver ions, to impart antibacterial properties as discussed by the authors.
Abstract: A glass–ceramic composition has been studied to realise a highly bioactive material, suitable for stimulate the bone regeneration, which has been subjected to a patented ion exchange process with silver ions, to impart antibacterial properties. The obtained material has been characterised by SEM, EDS and XRD analyses, before and after the introduction of Ag+ ions, and has been subjected to mechanical tests. Ag+ release was verified by GF-AAS analysis. The influence of silver on material wettability and bioactivity was evaluated through contact angle measurements and in vitro test on SBF solution. Finally, biocompatibility with osteoblast like cells and antibacterial test on Staphylococcus Aureus, have been realised to demonstrate the effective antimicrobial behaviour and the safety of silver doped glass–ceramic. On the basis of this study, it was evinced that ion exchange technique, optimised on glasses in previous research works, allows the controlled introduction of Ag+ ions and can be transferr...
33 citations
TL;DR: In this paper, a polymer-derived SiOC microcellular foams were etched by means of a 20 vol.-%HF solution and an increase in specific surface area (SSA) values compared to the unetched samples was observed.
Abstract: Polymer derived SiOC microcellular foams were etched by means of a 20 vol.-%HF solution. An increase in one order of magnitude in specific surface area (SSA) values compared to the unetched samples was observed. This SSA increase was accompanied by micro- and mesopores formation. The limited increase in the specific surface area was attributed to several factors: the smaller dimension of the etchable SiO2 nanodomains and the more amorphous nanostructure of these polymer derived ceramics compared to the sol–gel derived ones. Moreover a possible role of the carbon residue deriving from polymethylmetacrylate (PMMA) microbeads used as porosity source was supposed. Higher SSA values (up to 65 m2 g−1) were reached by inducing a slight phase separation, accompanied by a growth of the nanodomains size, and by an oxidative treatment that partly removed the residual carbon. Microcellular ceramic foams with a bimodal pore size distribution were produced.
33 citations
TL;DR: In this article, the use of electric arc furnace steel slag as a raw material in the floor tile body was introduced and the effect of slag addition on the strength of experimental samples was evaluated by four-point bending strength test.
Abstract: In this paper, the authors have tried to introduce the use of electric arc furnace steel slag as a raw material in the floor tile body. Experimental samples were prepared with different amounts of slag (10–50 wt-%) using the die pressing method. Fabricated samples were fired in an industrial roller kiln at 1140°C. Thermal behaviour of the samples was investigated by simultaneous thermal analysis and dilatometery. X-ray diffraction analysis identified Wustite (FeO), as the major phase in the used slag. The effect of slag addition on the strength of experimental samples was evaluated by four-point bending strength test. Sintering behaviour of different samples was investigated by measuring shrinkage, relative density and water absorption. Results showed that addition of more than 40 wt-% slag to the base body generates closed porosities in the specimens due to the bloating phenomenon which reduces the bending strength. The wear resistance test on this sample confirmed that it can be used as a standa...
32 citations
TL;DR: In this article, the BZT diffused into BNKT lattice and formed a solid solution during sintering, and their crystalline structures changed from rhombohedral phase to tetragonal phase as the bZT content was increased.
Abstract: Lead free piezoelectric ceramics (1–x)Bi0˙5 (Na0˙84K0˙16)0˙5TiO3–xBa(Zr0˙04Ti0˙96)O3 (BNKT–BZT100x, wherein x ranged from 0 to 10 mol.-%) were fabricated by a conventional mixed oxide route, whose BZT content effect on electrical properties and crystalline structures was investigated. X-ray diffraction investigation showed that BZT effectively diffused into BNKT lattice and formed a solid solution during sintering, and their crystalline structures changed from rhombohedral phase to tetragonal phase as the BZT content was increased. Piezoelectric property measurements revealed that the BNKT–BZT4 ceramics had the highest piezoelectric performance: piezoelectric constant d 33 reached 178 pC N–1 and planar electromechanical coupling factor k p was up to 0˙33. The influence of Bi2O3 doped content on electrical properties and crystalline structure of the BNKT–BZT4 ceramics were also studied, and found that the piezoelectric property of the ceramics was enhanced when Bi2O3 was doped.
32 citations
TL;DR: In this article, two methods of compacting dry poly-and nanodisperse powders into compacts of a complicated shape with uniform density distribution in the volume have been developed: pressing under powerful ultrasonic action and collector pressing by the control of friction forces redistribution.
Abstract: Two methods of compacting dry poly- and nanodisperse powders into compacts of a complicated shape with uniform density distribution in the volume have been developed: pressing under powerful ultrasonic action and collector pressing by the control of friction forces redistribution. Experimental measuring and simulation of the process of deformation of a powder body by different methods show that in the case of ultrasonic pressing, the dispersion of the density distribution has decreased by 20%, and the relative differential of density along the pressing height has decreased by 35% as compared to the case of the conventional uniaxial pressing. Collector pressing allows reducing the dispersion of the density distribution (has decreased by a factor of 10), while the relative density differential along the green compact height has decreased by 60%.
32 citations
TL;DR: In this paper, a patented ion exchange process was used to introduce silver ions onto their surface and confer antibacterial properties, both treated and untreated materials have been analyzed by means of SEM, EDS and XRD in order to verify the amount of introduced silver, and also after immersion in simulated body fluid to investigate bioactivity.
Abstract: Plasma spray bioactive glass ceramic coatings on metallic substrates have been characterised and modified by a patented ion exchange process in order to introduce silver ions onto their surface and confer antibacterial properties. Both treated and untreated materials have been analysed by means of SEM, EDS and XRD in order to verify the amount of introduced silver, and also after immersion in simulated body fluid in order to investigate bioactivity. The amount of silver released in simulated body fluid has been quantified by means of graphite furnace atomic adsorption spectrophotometry analysis. Finally cellular and microbiological test have been performed in order to verify material biocompatibility and antibacterial behaviour.
20 citations
TL;DR: In this paper, a three-dimensional carbon fiber reinforced nitride composite materials were fabricated by precursor infiltration and pyrolysis using a hybrid precursor. And the results show that high pressure curing method can be used to fabricate high density composites.
Abstract: Three-dimensional carbon fibre reinforced nitride composite materials were fabricated by precursor infiltration and pyrolysis using a hybrid precursor. The curing stage of precursor infiltration and pyrolysis was investigated and improved. The densification behaviour, mechanical properties and ablation properties of the composites were studied. The results show that high pressure curing method can be used to fabricate high density composites. With the increase of density from 1˙50 to 1˙65 g cm−3, the flexural strength increases from 156˙4 to 192˙3 MPa, and the elastic modulus increases from about 45˙9 to 56˙3 GPa, while the linear ablation rate decreases from 0˙069 to 0˙056 mm s−1. The load–displacement curves show that carbon fibres cause efficient reinforcement, and the composites have good toughness.
TL;DR: In this article, a platinum (Pt) on pure ceria (CeO2) particles supported by carbon black (CB) was synthesized and the electrochemical activity of methanol oxidation reaction on synthesized Pt-Ce-O2/CB anodes was investigated.
Abstract: A Platinum (Pt) on pure ceria (CeO2) particles supported by carbon black (CB) was synthesised. The electrochemical activity of methanol oxidation reaction on synthesised Pt–CeO2/CB anodes was investigated. To develop this anode, the influence of surface area of CeO2 particles in Pt–CeO2/CB on anode properties was examined. The anode properties (i.e. onset potential and peak current density) were improved using fine CeO2 particles with high surface area. This indicates that higher activity on surface of CeO2 improves the anode properties. The anode properties on Pt high surface area CeO2/CB was better than that on Pt–Tin oxide(SnO2)/CB or Pt–Ru/carbon. The authors suggest that the rate determining steps of methanol oxidation reaction on Pt–CeO2/CB and other anodes such as Pt–SnO2/CB and Pt–Ru/carbon are different which accounts for the difference in performance. Therefore, it is concluded that a design of active surface of CeO2 is a key for development of Pt–CeO2/CB anode in polymer membrane fuel c...
TL;DR: In this paper, the authors used the theory of continuum micromechanics as a basis for a material model predicting relationships between porosity and elastic/strength properties of tissue engineering scaffolds.
Abstract: Owing to their stimulating effects on bone cells, ceramics are identified as expressly promising materials for fabrication of tissue engineering (TE) scaffolds. To ensure the mechanical competence of TE scaffolds, it is of central importance to understand the impact of pore shape and volume on the mechanical behaviour of the scaffolds, also under complex loading states. Therefore, the theory of continuum micromechanics is used as basis for a material model predicting relationships between porosity and elastic/strength properties. The model, which mathematically expresses the mechanical behaviour of a ceramic matrix (based on a glass system of the type SiO 2 -P 2 O 5 -CaO-MgO-Na 2 O-K 2 O; called CEL2) in which interconnected pores are embedded, is carefully validated through a wealth of independent experimental data. The remarkably good agreement between porosity based model predictions for the elastic and strength properties of CEL2-based porous scaffolds and corresponding experimentally determined mechanical properties underlines the great potential of micromechanical modelling for speeding up the biomaterial and tissue engineering scaffold development process - by delivering reasonable estimates for the material behaviour, also beyond experimentally observed situations.
TL;DR: Hydroxyapatite and tricalcium phosphate are bioceramic materials of special interest with regards to bone surgery, in particular the repair of bone tissue defects and bacterial colonisation on the surface of different calcium phosphate based materials is evaluated.
Abstract: Hydroxyapatite (HAp – Ca10(PO4)6(OH)2) and tricalcium phosphate (TCP – Ca3(PO4)2) are bioceramic materials of special interest with regards to bone surgery, in particular the repair of bone tissue defects. These materials are highly biocompatible with bone and soft tissue; they are bioactive, osteoconductive and resistant to sterilisation processes. In comparison with other biomaterials, particularly metallic materials, bioceramic surfaces exhibit high resistance to bacterial colonisation. This is currently considered to be one of the most important issues concerning materials used in medicine, due to the fact that bacterial biofilm is difficult to combat or remove and can be responsible for recurrent infections.The aim of the present study was to evaluate bacterial colonisation on the surface of different calcium phosphate based materials.
TL;DR: In this paper, the authors investigated the kinetics of 3Al2O3.2SiO2 formation from Algerian kaolin using differential thermal analysis (DTA) and found that bulk nucleation was dominant in mullite crystallisation followed by three-dimensional growth of mullite crystals with polyhedron-like morphology controlled by the growth morphology parameters.
Abstract: In the present work, the kinetics of mullite (3Al2O3.2SiO2) formation from Algerian kaolin was investigated using differential thermal analysis (DTA). The raw kaolin was wet ball milled for 5 h followed by attrition milling for 1 h. Differential thermal and thermogravimetric (DTA/TG) experiments were carried out on samples between room temperature and 1350°C at heating rates of 5, 10, 20 and 40°C min−1. The temperature of mullite crystallisation was found to be ∼1005°C. The activation energies measured from isothermal and non-isothermal treatments were around 1290 and 1260 kJ mol−1 respectively. The growth morphology parameters n (Avrami parameter which indicates the crystallisation mode) and m (a numerical factor which depends on the dimensionality of crystal growth) were found to be almost equal to 1˙5. Analysis of the results showed that bulk nucleation was dominant in mullite crystallisation followed by three-dimensional growth of mullite crystals with polyhedron-like morphology controlled by...
TL;DR: In this article, the authors present a design and defeat mechanism for the Ceramic Armour: Design and Defeat Mechanisms (CARM) for the application of applied ceramics: Vol. 107, No. 4, pp 232-232.
Abstract: (2008). Ceramic Armour: Design and Defeat Mechanisms. Advances in Applied Ceramics: Vol. 107, No. 4, pp. 232-232.
TL;DR: In this article, composites of polyvinyl alcohol (PVA) and calcium carbonate (CaCO3) were prepared by a sequential method involving first in situ synthesis of CaCO3 in PVA solution, then physical crosslinking of synthetic suspension and subsequently washing of resultant elastic gel followed by consolidation.
Abstract: Composites of poly(vinyl alcohol) (PVA) and calcium carbonate (CaCO3) were prepared by a sequential method involving first in situ synthesis of CaCO3 in PVA solution, then physical crosslinking of synthetic suspension and subsequently washing of resultant elastic gel followed by consolidation. The phase and composition, mechanical properties and microstructure of the composites and possible molecular interactions between both components were evaluated. X-ray diffraction analysis revealed that calcium carbonate was mainly composed of aragonite and calcite. Compression tests confirmed the composites prepared by this sequential method had good mechanical properties and that the compressive strength of the composites increased with higher content of calcium carbonate. PVA formed an interconnected network and needle-like CaCO3 crystals together with some fine grains were well compatible with PVA. In situ synthesis induced a spectral shift of hydroxyl groups and C–O bonds of PVA and the suppression of t...
TL;DR: In this paper, a polyurethane foam and slurry containing hydroxyapatite (HA) and dicalcium phosphate anhydrous (DCP) powder, water and additives were used to create a high porosity structure with ∼70% porosity.
Abstract: The aim of the present study was to obtain a biodegradable porous calcium phosphate implants as a synthetic bone graft substitute. The calcium phosphate used in the present study consisted of hydroxyapatite (HA) and dicalcium phosphate anhydrous (DCP). Porous bioceramic was fabricated by a foam casting method. By polyurethane foam and slurry containing HA/DCP (3 : 1 weight ratio) powder, water and additives a high porous structure with ∼70% was created. The X-ray diffractometry revealed that the β-tricalcium phosphate (β-TCP) formation is major phase. Surface morphology analysis and porosity evaluations were performed. The variation in the compressive strength, elastic modulus and dissolution behaviour of immersed synthetic bone graft in simulated physiological solution investigated.
TL;DR: In this article, an emerging problem related to the development of polymer surfaces resistant to calcification was addressed in the context of medical applications, where the addition of small amount of TiO 2 nanoparticles resulted in higher crystallinity and roughness of the copolymer surface.
Abstract: An emerging problem related to the development of polymer surfaces resistant to calcification was addressed in this work. Multiblock copolymers containing poly(ethylene terephthalate) (PET) (30 wt-%) as hard segment and dilinoleic acid (DLA) as soft segment were prepared in the presence of two concentrations of TiO 2 particles (23 nm diameter) as nanofiller (0.2 and 0-4 wt-%) via in situ polycondensation process. Changes of thermal properties as well as investigations of topography of these nanocomposites suggest that addition of small amount of TiO 2 nanoparticles resulted in higher crystallinity and roughness of the copolymer surface. Incubation in simulated body fluid (SBF) increased the roughness of all copolymers characterised by root mean square (rms) values; however, no hydroxyapatite layer was formed on the samples surface. The highest difference of rms values was found for the neat PET/DLA material. The addition of nanocrystalline TiO 2 seems to prevent the material surface from calcification which represents a positive effect when such nanocomposite is intended for medical applications, especially for uses in contact with soft tissue.
TL;DR: In this paper, a biomimetic composite material for bone tissue substitution and repair using a "biologically inspired" synthesis, apatite/collagen (70: 30 wt-%) biohybrid composites were developed, nucleating apatitic phases on self-assembling collagen, acting as a template.
Abstract: The present work describes the development of biomimetic composite materials for bone tissue substitution and repair Using a ‘biologically inspired’ synthesis, apatite/collagen (70: 30 wt-%) biohybrid composites were developed, nucleating apatitic phases on self-assembling collagen, acting as a template To reproduce the chemical composition of natural tissue, specific reactants were added during the synthesis process, to induce the growth of amorphous apatitic phases containing ions influent for the bone regeneration, namely, CO32−, Mg2+ and SiO44−, directly on the surface of the assembling organic fibrils To increase the stability of the composite in physiological condition, a cross-linking agent was employed The effect of natural proteins on the mineralisation process as well as the influence of the substituting ions on the crystallinity and morphology of the mineral particles was investigated The features of the final composites were thoroughly examined in comparison with those of natural
TL;DR: In this paper, a pyrolytic method for large scale production of aligned/micropatterned carbon nanotube arrays perpendicular to the substrate surface has been developed, which can be transferred onto various substrates of particular interest in either a patterned or non-patterned fashion.
Abstract: Carbon nanotubes are very attractive for a wide range of potential applications. However, many applications require the growth of aligned/micropatterned carbon nanotubes with or without a modified nanotube surface. Simple pyrolytic methods for large scale production of aligned/micropatterned carbon nanotube arrays perpendicular to the substrate surface have been developed. These aligned carbon nanotube arrays can be transferred onto various substrates of particular interest in either a patterned or non-patterned fashion. The perpendicularly-aligned structure provides advantages for not only an efficient device construction but also surface functionalisation (both the inner and outer wall) while their alignment structure can be largely retained. These aligned carbon nanotubes with tunable surface characteristics are of great significance to various practical applications, ranging from plastic optoelectronics to bioceramics. Examples include biomolecule immobilised carbon nanotube biosensors, synth...
TL;DR: In this article, the surfactants assisted colloidal processing of 1˙0 wt% carbon nanotube (CNT)-SiO2 composites using acid treated CNTs and colloidal silica has been investigated.
Abstract: The surfactants assisted colloidal processing of 1˙0 wt-% carbon nanotube (CNT)–SiO2 composites using acid treated CNTs and colloidal silica has been investigated. By using different combinations of anionic and cationic surfactants five systems were developed with the aim of coating the CNTs with silica particles and creating a homogenously dispersed composite. Sintering of CNT–SiO2 composites was performed for 3 h at 1300°C in argon atmosphere. Pressureless sintering yielded composites with a density >95% of the theoretical. X-ray diffraction analysis showed the presence of cristobalite, but no other crystalline phases were detected in the sintered composites. Microstructural observation revealed isolated CNTs in the SiO2 matrix both in the as dried powder and in the sintered samples. It is concluded that the simple colloidal process developed here can be a convenient alternative to the sol–gel based methods used for fabrication of inorganic matrix composites containing CNTs.
TL;DR: In this paper, two glasses belonging to the CaO-Al2O3-SiO2 system and corresponding to the melting of mixtures of industrial wastes (recycled glasses, mining residues, ashes, asbestos containing cements, etc.), have been successfully converted into dense glass ceramics by sintering with concurrent crystallisation.
Abstract: Two glasses, belonging to the CaO–Al2O3–SiO2 system and corresponding to the melting of mixtures of industrial wastes (recycled glasses, mining residues, ashes, asbestos containing cements, etc.), have been successfully converted into dense glass ceramics by sintering with concurrent crystallisation. The usage of fine glass powders (<37 μm) allowed very short sintering treatments, due to the enhanced nucleating activity of glass surfaces. In particular, dense glass ceramics could be produced by direct insertion of pressed glass powders in the furnace at the sintering temperature, followed by rapid cooling at room temperature after a 30 min holding time. The proposed approach evidences the feasibility of sintered glass ceramics by the fast and economic processes employed for traditional ceramics, with the advantage of superior mechanical properties (bending strength exceeding 100 MPa, Vickers' microhardness exceeding 6 GPa). Like in traditional ceramics, clay and water could be used for the shaping...
TL;DR: In this article, the effect of fluorine content on the sinterability and crystallisation of glass belonging to the CaO-Al2O3-SiO2 system was investigated.
Abstract: The effect of fluorine content on the sinterability and crystallisation of glass belonging to CaO–Al2O3–SiO2 system was investigated. It was shown that increasing fluorine content promotes sinterability and crystallisation simultaneously. The Avrami exponent and activation energy for crystallisation of the most promising specimen were determined according to the Marotta method. The calculated Avrami exponent confirms a surface crystallisation mechanism. Results in the present paper suggest that with increasing fluorine content, the sinterability, crystallisation and mechanical properties of the system are improved whereas the chemical resistance is degraded.
TL;DR: The results indicate that the developed bioassay is an appropriate approach as an alternative to conventional animal models to evaluate the biocompatibility of scaffold biomaterials for tissue engineering and regenerative medicine.
Abstract: The aim of the present study was to investigate a novel ex ovo bioassay for the first time using the chick embryo chorioallantoic membrane (CAM) for testing tissue engineering bioceramic scaffolds. Bioglass based scaffolds with porosity in the range of 90–95% were fabricated using the foam replica technique and sintering at 1100°C for 1 h. Scaffolds (5 × 5 × 2 mm3) were placed on the CAM at 10 days of total incubation. The embryos were killed 5 days after implantation. The scaffolds and CAM were explanted, fixed in formalin solution and processed for embedding in methyl methacrylate. Histological analysis using ground sections showed that the scaffolds were surrounded by CAM. There was no occurrence of macrophages or related inflammatory cells. The results described in this paper indicate that the developed bioassay is an appropriate approach as an alternative to conventional animal models to evaluate the biocompatibility of scaffold biomaterials for tissue engineering and regenerative medicine.
TL;DR: In this article, an alumina-zirconia nanocomposite powder has been synthesized by mechanical activation of a dry powder mixture of AlCl3, ZrCl4 and CaO.
Abstract: The alumina–zirconia nanocomposite powder has been synthesised by mechanical activation of a dry powder mixture of AlCl3, ZrCl4 and CaO. Mechanical milling of the above raw materials with the conditions adopted in this study resulted in the formation of a mixture consisting of crystalline CaO and amorphous aluminium and zirconium chlorides phases. There was no sign of chemical reaction occurring during milling stage as evidenced by X-ray diffraction (XRD) studies. Subsequent heat treatment of the milled powder at 350°C resulted in the occurrence of displacement reaction and the formation of ZrO2 and Al2O3 particles within a water soluble CaCl2 matrix. The effect of higher temperature calcination on the phase development in this powder mixture was followed by XRD analysis. Scanning electron microscopy and differential thermal analysis were also used in the characterisation of the powders. Perhaps the most important observation in this study was the formation of α-Al2O3 phase at a very low temperatu...
TL;DR: In this article, an injectable composite biomaterial was prepared by hot pressing of highly porous nanocrystalline calcium phosphates at the polymer's melting temperature, blocks were obtained with relatively uniform distribution of phases.
Abstract: Nanocrystalline calcium phosphates (NC CP) are suitable for the synthesis of CP/bioresorbable polymer composite biomaterials for the application in bone engineering. There are different forms of NC CP/bioresorbable polymers composite biomaterials. Calcium phosphate was synthesised in highly NC form. A NC calcium phosphate/poly-DL-lactide-co-glycolide (CP/DLPLG) composite biomaterial in filler forms was synthesised in the shape of spherical granules (150–200 mm in diameter) and nanoparticles (30–40 nm in diameter). Each CP granule or nanoparticle was coated with amorphous DLPLG polymer. Using NC and nanosized CP/DLPLG composite materials, an injectable composite biomaterial was prepared. By hot pressing of highly porous NC CP/bioresorbable polymer composite biomaterials at the polymer's melting temperature, blocks were obtained with relatively uniform distribution of phases. Designing of the properties of CP/bioresorbable polymers composite biomaterial block was provided by combining high pressure,...
TL;DR: The high temperature processing of porcelain stoneware products is attractive for the possibility to incorporate several inorganic wastes as mentioned in this paper, however, even if recycling is an environmental benefit, it...
Abstract: The high temperature processing of porcelain stoneware products is attractive for the possibility to incorporate several inorganic wastes. However, even if recycling is an environmental benefit, it...
TL;DR: In this article, a complete investigation on the sintering behavior involving ceramic transformation of volcanic ash is reported, and a suitable thermal cycle, which matches the better microstructure and mechanical properties, has been performed.
Abstract: A complete investigation on the sintering behaviour, involving ceramic transformation, of volcanic ash is reported. Sintering and softening points, vitrification and fusion of finely ground powders of volcanic ash were obtained by hot stage microscope observation. Then, a suitable thermal cycle, which matches the better microstructure and mechanical properties, has been performed. The low quartz content of the final product, the relative high density together with the particular structural complexity of the matrix consequence of the interlocking of various crystalline phases conferred to fired volcanic ash relevant ceramic characteristics. Nucleation and microcrystallisation of pyroxene together with oxidation and cation enrichment are indicated as the main sintering mechanism of fired volcanic ash. Differently from conventional vitrified ceramics, i.e. quartz and mullite in vitreous matrix, the microstructure of the fired products presents spinel, anorthite, diopside, enstatite, pyroferrite, faya...
TL;DR: In this article, the in vitro behavior of titania-hydroxyapatite graded coatings obtained by plasma spraying was investigated by a microstructural and mechanical point of view.
Abstract: The in vitro behaviour of titania-hydroxyapatite graded coatings obtained by plasma spraying was investigated by a microstructural and mechanical point of view. To verify the bioactivity of the graded coatings, as sprayed and after thermal treatment, in vitro tests were performed in simulated body fluid. Furthermore, since the mechanical properties of the coatings may be altered by the immersion in simulated body fluid, the local elastic properties were measured on the cross-section by means of a depth sensing Vickers microindentation technique before immersion (reference materials) and after soaking for 1 week (short term response) and 4 weeks (long term response), separately investigating the titania and the hydroxyapatite rich zones to account for the compositional gradient. The results proved that the presence of titania in the coating did not suppress the bioactivity, which, on the contrary, was inhibited by the heat treatment. However, the heat treated samples showed higher mechanical properties and reduced dissolution rates.