Showing papers in "Journal of Materials Science in 2000"

Bacterial cellulose—a masterpiece of nature's arts

Abstract: Ever since its remarkable mechanical properties were found fifteen years ago, interest has grown in bacterial cellulose for which the use had been more or less limited to the manufacture of nata-de-coco, an indigenous food of South-East Asia. This paper reviews the progress of relevant studies including the production of cellulose by bacteria, the formation of microfibrils and gel layer, the properties of gel and processed sheets, and some aspects of applications.

Review Carbon fibers for composites

Abstract: An attempt has been made to review and analyze the developments made during last few decades in the field of high performance carbon fibers The focus is primarily on high technology sector, which includes aerospace and nuclear engineering or other areas, where the large scale use of carbon fibers is driven by maximum performance and not by cost factors We have identified and suggested some specific areas for future research in order to minimize the gap between theoretical and practically realized tensile strengths and other mechanical properties of carbon fibers

Correlation of C1s chemical state intensities with the O1s intensity in the XPS analysis of anodically oxidized glass-like carbon samples

Abstract: An XPS study of anodic oxidized glass-like carbon (GC) was conducted in order to investigate the inconsistency between O1s/C1s and oxygen concentration (Ocal.) calculated from the curve fitting results of the C1s spectrum. Consideration of the asymmetric peak shape of the C1s spectrum is normally done in order to obtain precise curve fitting results. However, it was found that the 2nd-carbon peak should also be taken into consideration in the curve fitting process in addition to the effect of asymmetric peak shape of carbon to obtain a consistent value of O1s/C1s. The 2nd graphitic peak is normally located +0.7–+0.8 eV away from the original C1s spectrum. The ratio of the 2nd graphitic peak area in the C1s spectrum increased as the electrical charge increased. However, the peak shapes of C1s spectra of anodic oxidized GC after heat treatment at 1500 °C in argon atmosphere were almost the same as the C1s of untreated GC. Although the origin of the 2nd graphitic peak is not well understood, it may be related to the amount of oxygen on the GC surface.

Review Properties of blends and composites based on poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) copolymers

Abstract: Poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) copolymers are microbial polyesters presenting the advantages of biodegradability and biocompatibility over other thermoplastics with useful mechanical properties. However, their costs and performances must be adjusted by blending with suitable polymers. In this article the miscibility, morphology, mechanical behaviour and other prominent characteristics of a representative number of blends and composites of PHB and PHBV are summarized. In particular, blends with a few polyethers, polyesters, polyvinylacrylates and polysaccharides are illustrated. Furthermore, a brief paragraph deals with PHB/vegetal fiber composites. A wide range of properties emerges by blending with polymers having very different molecular structures and characteristics, such as crystallinity, glass transition and melting temperatures. The microstructure of the blends, resulting from thermodynamic and kinetic factors, is regarded as an important factor in controlling the mechanical and the biodegradation behaviours. Moreover, some considerations upon the nature of the “driving force” of the miscibility have been made in order to explain miscibility behaviour differences.

Mechanical buckling instability of thin coatings deposited on soft polymer substrates

Abstract: Deformation of rubber and poly(ethylene terephthalate) coated with a platinum or a gold film was studied. The thickness of the coating film was approximately ten nanometers. The polymer substrates were 104 to 105-fold softer than the coating. Folding of the coating leading to the appearance of a wave-like pattern on an originally smooth surface was observed both in tension and after shrinkage. In tension the wave crests are oriented along the elongation direction. After shrinkage the wave crests are perpendicular to the shrinkage direction. For rubber substrates, the appearance of the wave is explained by a mechanical buckling instability of the coating under compressive force. The length of the surface wave depends on the thickness of the coating layer and the rigidity of the polymer substrate. In addition to folding, regular fragmentation of the coating film on long and comparatively narrow bands is observed. The cracks are perpendicular to the wave crests both in tension and after shrinkage.

Hydration of alkali-activated ground granulated blast furnace slag

Abstract: The hydration of ground granulated blast furnace slag (GGBFS) at 25 °C in controlled pH environments was investigated during 28 days of hydration. GGBFS was activated by NaOH, and it was found that the rate of reaction depends on the pH of the starting solution. The main product was identified as C-S-H, and, in the pastes with high pH, hydrotalcite was observed at later stages of hydration. The pH of the mixing solution should be higher than pH 11.5 to effectively activate the hydration of GGBFS. As deduced from very low electrical conductivity measurements, GGBFS pastes had very tortuous and disconnected pores. The effect of the pH of the aqueous solution on the composition, microstructure and properties of alkali-activated GGBFS pastes are also discussed.

Precipitation sequence of various kinds of metastable phases in Al-1.0mass% Mg2Si-0.4mass% Si alloy

Abstract: The precipitation of three new types of metastable phases, i.e., TYPE-A, TYPE-B and TYPE-C, with different crystal structures from the β′ phase is proposed from our research on the change in crystal structures and formation sequence of metastable phases during the aging of the Al-1.0mass% Mg2Si-0.4mass% Si alloy by a combination of analytical high resolution electron microscopy and energy dispersive X-ray spectroscopy. The sequence of their formation is explained as follows. First, precipitation of the β′ phase and TYPE-B precipitate, then β′ dissolution into the matrix and degradation of the TYPE-B precipitate. Finally, predominant precipitation of the metastable TYPE-A precipitate. The TYPE-C precipitate appeared heterogeneously in the over-aged condition.

Anisotropic thermal expansion in wurtzite-type crystals

Abstract: The temperature dependence of the lattice parameters of six wurtzite-type crystals, BeO, AlN, GaN, ZnO, CdSe, and CdS, has been measured by X-ray powder diffractometry. The thermal expansion changes nonlinearly with temperature and is anisotropic; the expansion along the a-axis is larger than that along the c-axis (more than 50% larger in ZnO, CdS and CdSe), resulting in a decrease of the c/a ratio with increasing temperature. The calculated Gruneisen parameters range between 0.27 and 1.45 and have a positive correlation with the bulk moduli. The anisotropic thermal expansion is associated with the anisotropies of both elasticity and anharmonicity.

Phase transformations in Ti-Nb-Ta and Ti-Nb-Ta-Zr alloys

Abstract: Phase transformations in solution treated and quenched Ti-(13-26) Nb-(22-38) Ta (wt.%) and Ti-(13-35.5) Nb-(5-22) Ta-(4-7.2) Zr alloys have been studied. It has been observed that phase transformations in these alloys are sensitive to both composition and cooling rate. In ternary alloys, water and oil quenching resulted in the formation of orthorhombic martensite (α′′) in a retained β + ωathermal matrix, whereas slower cooling showed evidence of fine α and ωisothermal formation within the β matrix. Increase of Nb + Ta content decreases the volume percentage of martensite. Moreover, addition of Zr stabilized the β phase, lowered the martensite start temperature and suppressed ω formation. Finally, dynamic moduli of air cooled quaternary alloys showed that the modulus was sensitive to the composition, a minima at Nb/Ta ratio of 12.0 and 5 at% Zr being observed, this minimum in dynamic modulus being consistent with ω phase suppression.

Hydration of Nafion® studied by AFM and X-ray scattering

Abstract: Nafion® is a commercially available perfluorosulphonate cation exchange membrane commonly used as a perm-selective separator in chlor-alkali electrolysers and as the electrolyte in solid polymer fuel cells. This usage arises because of its high mechanical, thermal and chemical stability coupled with its high conductivity and ionic selectivity, which depend strongly on the water content. The membrane was therefore studied in different states of hydration with two complementary techniques: atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) combined with a maximum entropy (MaxEnt) reconstruction. Tapping mode phase imaging was successfully used to identify the hydrophobic and hydrophilic regions of Nafion. The images support the MaxEnt interpretation of a cluster model of ionic aggregation, with spacings between individual clusters ranging from 3 to 5 nm, aggregating to form cluster agglomerates with sizes from 5 to 30 nm. Both techniques indicate that the number density of ionic clusters changes as a function of water content, and this explains why the bulk volumetric swelling in water is observed to be significantly less than the swelling inferred from scattering measurements.

Morphology and phase transition of high melt temperature crystallized poly(vinylidene fluoride)

Abstract: When PVDF is crystallized at temperatures above 155°C it presents a multiform morphology composed of ringed, non ringed and mixed spherulites. Infrared spectroscopy showed that the ringed spherulites are formed exclusively by the α phase when crystallization takes place at temperatures below 155°C. Higher temperatures induce a solid-state α → γ phase transformation in these structures, increasing the amount of γ phase with crystallization time. The rate at which this transformation takes place increases with crystallization temperature. The non ringed spherulites, only formed at crystallization temperatures above 155°C, consist predominantly of the γ phase, crystallized from the melt, with small α phase inclusions. The melt process of the different spherulites, observed by optical microscopy and calorimetric measurements (DSC) showed that the melt temperature of the γ phase, originated from the phase transition, is 8°C higher than that crystallized directly from the melt. Optical micrographs of samples heated up to 186°C and quickly cooled allowed visualization of the ringed spherulite regions which underwent the α → γ phase transformation at different crystallization times and temperatures.

Synthesis, microstructure and properties characterization of disintegrated melt deposited Mg/SiC composites

Abstract: In the present study, elemental and silicon carbide reinforced magnesium materials were synthesized using an innovative disintegrated melt deposition method followed by hot extrusion. Microstructural characterization studies revealed the presence of minimal porosity and completely recrystallized matrix in all the unreinforced and reinforced samples. In the case of reinforced magnesium samples, a fairly uniform distribution of SiC particulates and good SiC-Mg interfacial integrity was realized. The results of microhardness measurements revealed an increase in the brittleness of the SiC-Mg interfacial region with an increase in the amount of SiC particulates. Results of physical and mechanical properties characterization revealed that the increasing presence of SiC particulates led to an increase in hardness and elastic modulus, does not affect 0.2% yield strength and reduces the ultimate tensile strength, ductility, work for fracture and coefficient of thermal expansion. An attempt is made to correlate the results of physical and mechanical properties testing with that of the microstructural characterization.

CoNi and FeCoNi fine particles prepared by the polyol process: Physico-chemical characterization and dynamic magnetic properties

Abstract: Spherical and monodisperse CoxNi100 − x and Fez[CoxNi100 − x]1 − z particles are synthezied by the polyol process over a wide size range (lying from a few micrometers to a few tens of nanometers). The whole physico-chemical characterizations, i.e. dark-field image by TEM, SAED, density, saturation magnetization and chemical analysis, are consistent with a “core-shell” model. In the CoxNi100 − x system, the particles are constituted by a ferromagnetic, almost pure and dense core surrounded by a thin coating composed of metal oxides and metallo-organic phases. On the contrary, in the Fe[CoxNi100 − x]1 − z system, the ferromagnetic core is polycrystalline, slightly porous and retains impurities in higher content, the superficial layer having almost the same composition as in the Co-Ni system, but being twice more thick. The microwave permeability of the CoxNi100 − x and Fez[CoxNi100 − x]1 − z particles, previously insulated by a superficial treatment and then mechanically compacted, is investigated in the 100 MHz-18 GHz frequency range. Whatever the composition, submicrometer-sized particles show several narrow resonance bands which are interpreted as non uniform exchange resonance modes. Iron-based particles have lower resonance frequencies than iron-free powders; they also have higher permeability levels despite their lower cristallinity and their higher impurity content. A mild thermal treatment allows to increase this permeability by eliminating the metallo-organic impurities without modifying the morphology of the particles.

Particle packing and rheological property of highly-concentrated ceramic suspensions: φm determination and viscosity prediction

Abstract: A model is proposed which is able to predict the maximum particle packing density (φm) over a wide variety of ceramic suspensions with very large difference in particle size/shape, particle surface chemistry, and solvent chemistry. This model provides a simple method to obtain φm directly through the use of a few viscosity-concentration data for a given colloidal suspension, rather than a best-fitting approach. The model is also capable of predicting the viscosity of a variety of ceramic suspensions under different conditions of shear. A comparison with some existing viscosity model is also presented.

The effect of surface treatment on the performance improvement of carbon fiber/polybenzoxazine composites

Abstract: The effects of surface treatments, such as oxygen plasma and nitric acid treatment, on the mechanical properties of carbon fiber (CF)/polybenzoxazine composites were investigated. Interlaminar shear strength (ILSS) and flexural strength of CF/polybenzoxazine composites were measured and correlated with surface area and surface functionality. Both oxygen plasma treatment and nitric acid treatment were efficient in the enhancements of the ILSS and flexural strength of CF/polybenzoxazine composites. However, nitric acid treatment was more efficient than oxygen plasma treatment due to large increment of surface roughness. Cohesive failure was observed in surface treated composite due to adhesion improvement.

Crystallisation kinetics in AO-Al2O3-SiO2-B2O3 glasses (A = Ba, Ca, Mg)

Abstract: The crystallisation kinetics of AO-Al2O3-SiO2-B2O3glasses (A = Ba, Ca, Mg) was investigated using DTA, XRD, and microstructural studies. Moreover, the influence of nucleating agentssuch as TiO2, ZrO2, Cr2O3, and Ni on MgO base glasses waselucidated. The glasses are of interest for the development ofsealants in Solid Oxide Fuel Cells (SOFC). The activation energy ofcrystal growth, E a, was evaluated for the different glassesusing the modified Kissinger equation. The preparation method of theglasses seems to determine whether surface or bulk nucleation is thedominant mechanism. The E a values vary between 330 and622 kJ/mol. The nucleating agents tend to enhance E a exceptZrO2. An increase of the Al2O3 concentration induces phaseseparation and decreases E a. The results are discussed onthe basis of the structural role and chemical properties of the Alions as well as with respect to the possible use of the glasses inSOFC.

Time and temperature dependence of the scratch properties of poly(methylmethacrylate) surfaces

Abstract: Most existing models describing the scratch properties of materials take into account forces acting at the interface between the material and a grooving tip, but do not consider the stress and strain properties of the material far beneath or ahead of the tip. In the case of polymer scratches, there are no models at all which take into account the viscoelastic viscoplastic behaviour of the material. In standard indentation tests with a non moving tip, the elastic plastic boundary and the limits of the region subjected to hydrostatic pressure beneath the tip are known. These models were used to analyse the geometry of the grooves left on the surface of a viscoelastic viscoplastic body by a moving cone-shaped diamond tip having a radius of about 40 μm. A new apparatus was built to control the velocity of the tip over the range 1 to 104 μm/s, at several different temperatures from −10°C to 100°C. The material was a commercial grade of cast poly(methylmethacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress and temperature activated process. Values of the activation energy and volume of the dynamic hardness and of the interfacial shear stress were in good agreement with those usually attributed to the mechanical properties of PMMA.

Factors controlling mechanical properties of clay mineral/polypropylene nanocomposites

Abstract: Effects of two factors on the mechanical properties of clay mineral/polypropylene nanocomposites were examined. The first factor is the presence of a small amount of poly(diacetone acrylamide) formed between clay mineral layers. This material was expected to separate effectively the stacked layer structure of the clay mineral on mixing with polypropylene. The stacked layer structure, however, was not separated sufficiently in spite of expansion of the interlayer distance of clay mineral, leading to poor improvement of the mechanical properties of the nanocomposite. Another factor is the kind of clay mineral. Montmorillonite and mica resulted in less favorable separation of the stacked structure than hectorite, but the resulting nanocomposites gave outstanding improvement of the properties. The stiffness of clay mineral layer was considered to influence the properties of the nanocomposite strongly.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and wheat straw fibre composites: thermal, mechanical properties and biodegradation behaviour

Abstract: The thermal and mechanical behaviour of a biotechnological polyester (poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) reinforced with wheat straw fibres has been investigated. In order to improve chemico-physical interactions between the components, the reinforcing agent has been previously submitted to a treatment with high temperature steam leading to fibres richer in cellulose and more reactive. The addition of straw fibres has been found to increase the rate of PHBV crystallisation, while it does not affect the crystallinity content. Furthermore, the comparison of the mechanical properties has shown that the composites exhibit higher Young moduli and lower values of both the stress (σB) and strain (∈B) to break than the neat matrix of PHBV. The biodegradability in different environments by means of short and long term tests has been studied. It has been observed that the presence of straw does not affect biodegradation rate evaluated in liquid environment and in long term soil burial tests. In the composting simulation test the rate of biodegradation is reduced for composites with more than 10% of straw content. The morphology of the composites has also been investigated and correlated to the biodegradation process.

Influence of the starting kaolin on alkali-activated materials based on metakaolin. Study of the reaction parameters by isothermal conduction calorimetry

Abstract: The properties of the product obtained through alkaline activation of metakaolin are directly influenced by the characteristics of the starting kaolin. For the study of this influence, a complete characterization of two spanish kaolins used to synthesised the material has been carried out. A JAF conduction calorimeter was used to follow metakaolin reaction with NaOH solutions. Calorimetric data were obtained isothermally at 45°C with variable solution/solid ratio and NaOH solution concentrations varying from 12 to 18 M.

The strain dependent indentation resilience of auxetic microporous polyethylene

Abstract: A series of tests have been conducted on (i) auxetic, (ii) compression moulded and (iii) sintered ultra high molecular weight polyethylene. The auxetic material possesses a negative Poisson's ratio, ν, due to its complex porous microstructure which consists of nodules interconnected by fibrils and the sintered material has a positive ν and is microporous but does not contain fibrils. It was found that the auxetic material was both more difficult to indent than the other materials at low loads (from 10–100 N) and was the least plastic with the most rapid viscoelastic creep recovery of any residual deformation. Indeed, at low loads, where the resistance to local indentation is most elastic, the hardness increased by up to a factor of 8 on changing the Poisson's ratio from ν ≈ 0 to ν ≈ −0.8. A mechanism is proposed based on local densification under the indentor of the nodules and fibrils which explains how the microstructural response of an auxetic polymer can be used to interpret the results.

C3N4: Dream or reality? Solvothermal synthesis as macroscopic samples of the C3N4 graphitic form

Abstract: In order to prepare C3N4 as macroscopic sample, two synthesis attempts of the graphitic variety were carried out. The first consists on the condensation of melamine and cyanuric chloride (P = 130 MPa, T = 250°C) with triethylamine acting as solvent in supercritical conditions. The second one consists on the pyrolysis of melamine (P = 2.5 GPa, T = 800°C) in presence of hydrazine. The two routes led to a graphite-like carbon nitride, nevertheless, the first product is poorly crystallized and contains a larger amount of hydrogen as NHx due to a partial condensation. Several analysis (XRD, SEM, TEM, FTIR, XPS, EELS) reveal that the brown black solid issued from the route 2 presents a bidimensional honey-type structure close to those expected for the theoretical g-C3N4. This synthesis represents a first step in the C3N4 synthesis and its study as macroscopic sample.

The synthesis of nanosized TiO2 powder using a sol-gel method with TiCl4 as a precursor

Abstract: Nanosized TiO2 powder with anatase structure was synthesized by a sol-gel method using TiCl4 ethanol solution as a precursor. The grain size of TiO2 powder was homogenous and was about 10 nm after the precursor was calcined at 500 °C for 1 hour. Anatase TiO2 powder formed after the precursor was calcined at a temperature ranging from 300 °C to 550 °C. The gelatinizing mechanism of TiCl4 in ethanol solution can be described as followings. When mixed with ethanol, TiCl4 reacted with ethanol to form TiCl x (OCH2CH3)4 − x species and HCl gas. During gelatinizing process, TiCl x (OCH2CH3)4 − x species absorbed water from atmosphere to form Ti(OH)4 precursor, which was polymerized to be an inorganic polymer. The formation of inorganic polymer of Ti(OH)4 was intensified with gelatinizing time. In contrast, the organic component was removed from the precursor. The formation of anatase TiO2 can also be promoted by increasing gelatinizing time. The influence of alcohol on the reacting progress and dispersivity was also studied. The size and activity of alcohol molecule were found to have influence on the polymerization and mineralization degree of the precursor and the dispersivity of TiO2 powders.

Sol-gel derived hydroxyapatite coatings on titanium substrate

Abstract: Biomaterials, in particular those used for orthopaedic prostheses, consist of a metallic substrate, exhibiting excellent mechanical properties, coated with a ceramic layer, which guarantees resistance to the corrosion and an elevated bioactivity. In this paper the preparation of sol-gel films of hydroxyapatite, HA (Ca10(PO4)6(OH)2), on titanium substrate is described. The samples were obtained through the dip-coating method, starting from a colloidal suspension of hydroxyapatite. In order to increase the adhesion between the HA film and the metallic substrate, the same substrate has been preliminarily coated either with titanium oxide, TiO2 (in the anatase or rutile phase), or calcium titanate, CaTiO3 (perovskite). Also these latter films have been deposited from a sol-gel solution. The characterization of the films through XRD, SEM, and AFM gave good results for the crystallinity of the deposited HA; for what concerns the sample morphology, the films turned out to be homogeneous and crack-free.

Surface roughness effects and their influence on the degradation of organic light emitting devices

Abstract: Organic light emitting devices typically consist of one or several organic layers which are sandwiched between two electrodes, one of which has to be transparent. In most cases indium tin oxide (ITO) is employed as the transparent, hole-injecting anode material. Usually, the functional organic layers possess a thickness of about 100 nm. For such thin films the homogeneity and the surface roughness are especially important factors for the device performance. Therefore, the surface roughness of all those layers which are the basis for subsequent deposition processes were systematically studied by atomic force microscopy (AFM). For these investigations both the ITO substrate and the layers consisting of different organic materials deposited onto the ITO substrate were analyzed. In addition, the two different basic deposition methods for the organic materials, namely the deposition from solution by spin coating and the deposition by thermal evaporation, were compared to one another with respect to their resulting surface roughness. It was found that the large surface roughness of the ITO substrate induces layer inhomogeneities, especially for the vapor deposited organic layers. They can be reduced by the incorporation of a polymeric smoothing layer.

Shape memory polyurethane containing amorphous reversible phase

Abstract: Segmented thermoplastic polyurethanes (TPUs), which consist of an amorphous soft segment from 1,3-butanediol and hexamethylene diisocyanate (HDI) and a crystalline hard segment from 4,4′-bis-(6-hydroxy hexoxy)biphenyl and tolylene 2,4-diisocyanate were synthesized. Their thermal and mechanical properties, shape memory effect, utilizing amorphous soft segment domain as reversible phase and crystalline hard segment domain as frozen phase, were examined. The reversibility observed on repeated deformation was improved as the magnitude of deformation was reduced and the hard segment content was increased, or by crosslinking with excess HDI.

Effects of addition of MnO on piezoelectric properties of lead zirconate titanate

Abstract: The effects of manganese addition on the piezoelectric properties, microstructure, sintering characteristic and Curie temperature have been studied for Pb(Zr,Ti)O3 (PZT) ceramics. The valence states of manganese are measured by Electron Spin Resonance (ESR). Those studies show that manganese coexist mainly in the way of Mn2+ and Mn3+ in PZT ceramics. When the concentration of Mn ion is below 0.5 mole%, it is preferentially incorporated in the lattice Pb site in Mn2+ or Mn3+, which gives rise to the increase of Kp and d33. In the intermediate concentration region of 0.5–1.5 mole%, Mn ion will be incorporated in the lattice of (Ti, Zr) site in Mn3+ acted as acceptor, which increases Qm without causing large changes of Kp and d33. When the concentration of Mn ion is larger than 1.5 mole%, it will accumulate at the grain boundaries and give rise to the decrease of piezoelectric properties of PZT ceramics. Small amount of Fe may decrease the solubility limit of Mn ion in PZT ceramics and it may also prevent the oxidation of Mn2+ and Mn3+.

The properties of AlN-filled epoxy molding compounds by the effects of filler size distribution

Abstract: AlN filler was compared with crystalline silica as a filler for advanced epoxy molding compounds. Properties such as the thermal conductivity, dielectric constant, CTE, flexural strength, elastic modullus and water absorption ratio of water-resistant grade AlN-filled molding compounds according to the contents or size of AlN and the filler size distribution were evaluated. A spiral flow test was also carried out to measure the change in viscosity according to the AlN size distribution for improved fluidity. The properties of EMC that is filled with a 70 vol.% of 12 micron AlN was compared with a crystalline silica-filled EMC. Thermal conductivity was improved by 2.2 times, the dielectric constant was reduced to less than one-half, the flexural strength was improved, and the CTE was also reduced. A binary mixture of an AlN-filled (65 vol.%) EMC showed improved fluidity, thermal conductivity, dielectric constant, flexural strength and water resistance compared to a single-size AlN-filled EMC. The maximum improvement was obtained when the fraction of small particles in the binary mixture of the AlN is 0.2–0.3. The CTE of EMC was decreased by increasing the volume fraction of small particles in the binary mixture of the AlN.

The effects of various hydrothermal treatments on magnesium-aluminium hydrotalcites

Abstract: Mg/Al hydrotalcites were synthesized by coprecipitation followed by hydrothermal treatment. The materials were characterized by XRD, infrared and Raman spectroscopy, electron microscopy and thermal analysis. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO, with a basal distance of approximately 23.5 angstroms. All possible CO modes were observed in the infrared and Raman spectra, at 1068 cm, 844 cm, approximately 1380 cm, and approximately 680 cm. XRD, Infrared and Raman spectroscopy complimented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity and that treatment in water rather than in the mother liquid resulted in a more crystalline material. TEM showed that crystal size increased with aging, such that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. Thermal analysis showed 3 major weight losses corresponding to the loss of interparticle water, interlayer water, and dehydroxylation of the hydroxide layers and decarbonation of the interlayer region.

Preparation and luminescence properties of sol-gel hybrid materials incorporated with europium complexes

Abstract: Microporous silica gel has been prepared by the sol-gel method utilizing the hydrolysis and polycondensation of tetraethylorthosilicate (TEOS). The gel has been doped with the luminescent ternary europium complex Eu(TTA)3·phen: where HTTA = 1-(2-thenoyl)-3,3,3-trifluoracetone and phen = 1,10-phenanthroline. By contrast to the weak f-f electron absorption bands of Eu3+, the complex organic ligand exhibits intense near ultraviolet absorption. Energy transfer from the ligand to Eu3+ enables the production of efficient, sharp visible luminescence from this material. Utilizing the polymerization of methyl methacrylate or ethyl methacrylate, the inorganic/polymer hybrid materials containing Eu(TTA)3·phen have also been obtained. SEM micrographs show uniformly dispersed particles in the nanometre range. The characteristic luminescence spectral features of europium ions are present in the emission spectra of the hybrid material doped with Eu(TTA)3·phen.