Inorganic Ceramics Research Articles

Humidity sensors principle, mechanism, and fabrication technologies: a comprehensive review.

Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

Borohydride-induced destabilization of hydrazine borane

We investigated the destabilization of 4 mol of hydrazine borane N2H4BH3 in the presence of 1 mol of an alkaline borohydride (LiBH4 or NaBH4) and, in a second step, of 1 mol of NH3BH3 in addition. The destabilization was followed by TGA, DSC and μGC. The solid residues were analyzed by solid-state 11B NMR, IR and XRD. The presence of the borohydride effectively destabilizes N2H4BH3 which is thus able to liberate H2 from 50 °C. Seeing the results from the other side, one could consider that the alkaline borohydrides are destabilized by N2H4BH3. Such destabilization approach is attractive as it involves boron-based materials only. The best decomposition results were obtained with the sample containing 4 mol of N2H4BH3 and 1 mol of LiBH4 (containing 16 equiv. H2). Upon heating up to 300 °C at 5 °C min−1, this sample releases 12.1 mol of H2 (dehydrogenation extent of 76%) and 1.1 mol of N2H4. A solid residue of empirical formulae LiB5N5.8H3.4 is formed. It is composed of polyborazylene- and/or boron nitride-like materials. This is an attractive feature as it implies recyclability of the polymer and elaboration of inorganic ceramics at relatively low temperatures. Our main results are reported herein.

Mechanically-reinforced electrospun composite silk fibroin nanofibers containing hydroxyapatite nanoparticles

Electrospun silk fibroin (SF) scaffolds provide large surface area, high porosity, and interconnection for cell adhesion and proliferation and they may replace collagen for many tissue engineering applications. Despite such advantages, electrospun SF scaffolds are still limited as bone tissue replacement due to their low mechanical strengths. While enhancement of mechanical strengths by incorporating inorganic ceramics into polymers has been demonstrated, electrospinning of a mixture of SF and inorganic ceramics such as hydroxyapatite is challenging and less studied due to the aggregation of ceramic particles within SF. In this study, we aimed to enhance the mechanical properties of electrospun SF scaffolds by uniformly dispersing hydroxyapatite (HAp) nanoparticles within SF nanofibers. HAp nanoaprticles were modified by γ-glycidoxypropyltrimethoxysilane (GPTMS) for uniform dispersion and enhanced interfacial bonding between HAp and SF fibers. Optimal conditions for electrospinning of SF and GPTMS-modified HAp nanoparticles were identified to achieve beadless nanofibers without any aggregation of HAp nanoparticles. The MTT and SEM analysis of the osteoblasts-cultured scaffolds confirmed the biocompatibility of the composite scaffolds. The mechanical properties of the composite scaffolds were analyzed by tensile tests for the scaffolds with varying contents of HAp within SF fibers. The mechanical testing showed the peak strengths at the HAp content of 20wt.%. The increase of HAp content up to 20wt.% increased the mechanical properties of the composite scaffolds, while further increase above 20wt.% disrupted the polymer chain networks within SF nanofibers and weakened the mechanical strengths.

Nanotexture influence of BaTiO 3 particles on piezoelectric behaviour of PA 11/BaTiO 3 nanocomposites

The piezoelectric activity of a hybrid ferroelectric nanocomposite, i.e. polyamide 11/barium titanate (BT), has been investigated for different loadings of BT particles. The BT volume fraction ( ϕ) was ranging from 0.024 to 0.4 with a particle size of 50, 100, 300 and 700 nm. The influence of polarization mode on the piezoelectric behaviour has been studied. The magnitude of the poling field used in this study is in the same order of magnitude of the one used for bulk BT i.e. significantly lower than for piezoelectric polymers. The optimum piezoelectric coefficient is reached when the amorphous phase of the polymeric matrix is in the liquid state i.e. for a polarization temperature higher than the glass transition and for time constant allowing macromolecular mobility. The composite piezoelectric activity decreases for particles size lower than 300 nm due to the loss of the tetragonal phase. The nanotexture of these particles has been investigated by transmission electron microscopy (TEM) and high-resolution TEM. A core shell structure has been observed. An increase of the longitudinal piezoelectric strain coefficient d 33 with the raising of BT volume fraction was shown. Contrary to inorganic piezoelectric ceramics, the dielectric permittivity of hybrid composites remains moderate; therefore it allows the piezoelectric voltage coefficient of composites to be higher than ceramics.

Combining sol–gel chemistry and millifluidic toward engineering microporous silica ceramic final sizes and shapes: An Integrative Chemistry approach

For the first time we have combined sol–gel chemistry and millifluidic to generate silica ceramic engineering their sizes and aspect ratios. The particle sizes are controlled by varying the flow rates of the continuous and disperse phases within the home-made millifluidic reactor. Also, the silica particles aspect ratio can be tuned by adjusting the constrained geometry of the millifluidic devices, leading to the production of rod-like silica ceramics. Both SAXS and nitrogen physisorption measurements reveal that final inorganic silica ceramics are essentially microporous.

PAL spectroscopy as experimental probe for extended free-volume defects in inorganic glasses and ceramics

Extended free-volume defects trapping positrons are studied in inorganic glasses and functional ceramics using positron annihilation lifetime spectroscopy. Obtained results are treated in terms of general macroscopic approach grounded on physical–chemical properties of the tested materials which depend on the value of free volume content. At the example of chalcogenide glasses of ternary Ge–Sb–S system and spinel-type mixed transition-metal manganite Cu 0.4Co 0.4Ni 0.4Mn 1.8O 4 and magnesium aluminate MgAl 2O 4 ceramics, it is shown that strict correlation exists between numerical values of free volumes of potential positron traps and lifetime parameters determined within two-state positron trapping model.

New Macroporous Crosslinked Polymer Gels Prepared via Living Radical Polymerization

ABSTRACTMacroporous crosslinked polymer gels have been prepared via TEMPO-mediated living radical polymerization of divinylbenzene (DVB) in a solvent with a counter polymer. Incorporating a counter polymer, poly(dimethylsiloxane) (PDMS), induced macroscopic spinodal-type phase separation during the course of polymerization of DVB while suppressing the segregation of DVB-derived particles from the solution by living polymerization. Well-defined macroporous morphologies comprising continuous DVB-derived skeletons have thus obtained. Macropore volume and diameter were independently controlled by altering the concentrations of PDMS and the solvent. Since the present polymer gels are prepared using only the multifunctional “crosslinker”, mechanical durability against bending and compression was found to be as high as inorganic ceramics with similar morphologies and porosities.

Bibliographical Review on Inorganic Lithium Ion Conductors

A bibliographical review of inorganic lithium ion conductors is presented with a focus on those potential candidates for lithium battery application. A wide variety of inorganic lithium ion conductors, both crystalline ceramics and non-crystalline glasses, are considered.

Mechanical loss spectroscopy on inorganic glasses and glass ceramics

While the classical mechanical loss studies on ion conducting glasses and glass ceramics were done with the help of torsional pendulums with relatively narrow frequency windows, there has been effort in the last years to make use of commercially available instrumentation for dynamic mechanical thermal analysis (DMTA) in order to perform mechanical loss spectroscopy over broader frequency ranges. This opens up the possibility to study in detail the frequency/temperature relations of mechanical losses caused by the ionic motions and so to learn more about the mechanisms of ion transport processes. Mixed mobile ion effects in different types of mixed mobile ion glasses, e.g. in mixed alkali glasses, mixed alkali alkaline-earth glasses, mixed alkaline-earth glasses, and mixed cation–anion glasses, have been studied by mechanical loss spectroscopy. Many of these effects are still poorly understood. In the theoretical description of the mechanical loss spectra of ion conducting glasses, first attempts have been made to use linear response theory in order to derive the mechanical loss of simple model systems from the microscopic dynamics of the mobile ions.

Carbon nanotube reinforced ceramics

Silicon dioxide glass rods of micrometer sizes were synthesized by using surfactant–carbon nanotube co-micelles as templates. These glass rods were used as additives to reinforce inorganic ceramics. The mechanical strength of the silicon dioxide ceramic is enhanced by ∼100% in the presence of ∼6 wt% of CNTs.

Thin film of low-crystalline calcium phosphate apatite formed at low temperature

Surface modification of biomaterials to improve biocompatibility without changing their bulk properties is desired for many clinical applications and has become an emerging technology in biomaterial research and industry. In the present study, a simple method of coating the solid surfaces of metals, organic tissue matrices, glasses, inorganic ceramics as well as organic polymers with a thin film of low-crystalline apatite crystals (LCA) was developed. Acidic solution containing calcium and phosphate ions was neutralized with alkaline solution to form calcium phosphate precipitates at low temperature. Precipitates of solid calcium phosphate particles were, then, removed by filtration. Concentration of free ions in the filtered ion solution which were not involved in the formation of calcium phosphate precipitate was high enough to induce the heterogeneous nucleation on the solid surfaces at low temperature. Thin layers of calcium phosphate crystals were formed on the surfaces of metals, glasses, inorganic ceramics, organic polymers including hydrophobic ones, and biological tissue matrices with this solution. The thin layer of crystals consisted of poorly crystalline calcium phosphate apatite crystals which contain high amount of labile ions like bone crystals and did not dissolve in the physiologic solutions. Various cells attached to this crystal layer and proliferated well.

Immobilization of lipase on a new inorganic ceramics support, toyonite, and the reactivity and enantioselectivity of the immobilized lipase

A porous ceramics support, Toyonite 200-M (TN-M), for the immobilization of lipases was prepared hydrothermally from the minerals of kaolinite. Compared with some other commercial solid supports, the TN-M one exhibited better stability and higher selectivity for lipase proteins, and lipase PS ( Pseudomonas cepacia) immobilized on the ceramics support showed higher reactivity for organic substrates than the free crude enzyme.

Inorganic‐Organic Composite Solid Polymer Electrolytes

Inorganic‐organic composite solid polymer electrolytes (CSPEs) have been prepared from the poly(ethylene oxide) (PEO)‐like electrolytes of the general formula polyvinylidene fluoride‐hexafluoropropylene and ceramic powders. In the PEO‐like electrolytes, PVdF‐HFP is the copolymer of PVdF and HFP, is a nonvolatile oligomeric polyethylene oxide of ∼400 g/mol molecular weight, and LiX is lithium bis(trifluoroethylsulfonyl) imide. Two types of inorganic oxide ceramic powders were used: a highly material of the composition 14 mol % , and the poorly Li‐silicates where M is Ca or Mg and x is 0 or 0.05. The composite electrolytes can be prepared as thin membranes in which the conductivity and good mechanical strength of the inorganic ceramics are complemented by the structural flexibility and high conductivity of organic polymer electrolytes. Excellent electrochemical and thermal stabilities have been demonstrated for the electrolyte films. Li//composite electrolyte// rechargeable cells have been fabricated and cycled at room temperature and 50°C. © 2000 The Electrochemical Society. All rights reserved.

Sol‐gel polycondensation kinetic modeling: Methylethoxysilanes

AbstractQuantitative kinetic modeling of the condensation of methylethoxysilanes {(CH3)4‐f Si(OC2H5)f} of varying functionality (f) is needed to engineer inorganic polymers, resins, and ceramics. To that end, a kinetic model that accounts for hydrolysis pseudoequilibrium, nearest‐neighbor substitution effects, and unimolecular cyclization reactions in homogeneous ethoxysilane polycondensation is presented. Condensation rate parameters are determined by fitting to 29Si NMR transients. Several important features become evident: (1) the success of the hydrolysis pseudoequilibrium approximation; (2) strong negative substitution effects with unusual dependence on connectivity; (3) a strong kinetic tendency for ring formation, growing with methyl substitution; (4) acceleration of condensation upon methyl substitution; and (5) destabilization of three silicon rings by methyl substitution. The first three observations are consistent with previous findings for ethylethoxysilanes, but the last two are strikingly different.

Space charge characterization for the 21th century

Various methods of characterizing insulating materials by their ability to take up charge, retain it, and release it, are reviewed critically in search of measurable quantities that could be used to predict material behavior under stress up to failure conditions. Space charge characterization data on different types of materials from polymers to inorganic single crystals and ceramics are surveyed. The charging behavior is found to be influenced by many details such as surface condition and residual stresses. The traditional approach of linking dielectric breakdown to an intrinsic critical field for the material is tested against the newly emerging view that breakdown could be linked to space charge trapping at defect sites and to the attendant energetics of the mechanically strained lattice. The characterization process thus requires more care than was previously thought necessary, but after more research should become more predictive.

Microstructure and Fracture Behavior of Si-Ti-C-O Fiber-Assembled Ceramics

Inorganic fiber-assembled ceramics with 5vol% silica as a matrix were fabricated by hot-pressing Si-Ti-C-O fibers in the temperature range of 1500 to 1900°C. The effects of fabrication temperature on the microstructure and fracture behavior were studied by field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray powder diffraction analysis and three-point bending test. With an increase in hot-pressing temperature, distortion of fibers became remarkable and the crystalline size of β-SiC in fibers increased. The matrix in these ceramics, silica, was cristobalite below 1700°C and amorphous above 1800°C. The fiber assembled ceramics hot-pressed at 1700 and 1900°C, which had a graphite layer between fibers and between fiber and matrix, showed higher bending strength and more excellent fracture toughness than the materials obtained at 1500 and 1800°C.

Race of new inorganic materials towards an ultra neolithic age

Three generally accepted generic groups of competitive engineering materials—metals, inorganic ceramics, as well as plastics and polymers belonging to the organic family—have been comparatively reviewed in the context of raw materials availability, energy requirements in production, engineering properties, combustibility and environmental friendliness. The intrinsic advantages of inorganic materials have been discussed. The shortcomings of engineering properties of inorganic materials and the new technologies of making chemically bonded ceramics or biomimic compounds from inorganic materials with improved toughness have been dealt with. The expanding application horizons of inorganic materials have been illustrated with the help of several novel products.

Inorganic nonlinear materials

As optical technology becomes poised to revolutionise the world of communication the need for novel nonlinear optic (NLO) and electrooptic (EO) materials is increasing rapidly. NLO and EO materials come in many shapes and sizes; there are the large, aesthetically-pleasing, optically perfect and well known inorganic single crystals such as lithium niobate (LiNbo3), and the less familiar potassium titanyl phosphate(KTiOPO4 or KTP) and β-barium borate (β-BaB2O4 or BBO). There are also crystalline thin films, organic polymer or composite thin films and transparent inorganic ceramics such as lead lanthanum zirconium titanate (PLZT) I will concentrate here on the wide range of research on inorganic, dielectric single crystals.

Limits for high-resolution electron microscopy of inorganic materials?

The era of atomic-resolution electron microscopy has finally arrived. In virtually all inorganic materials, including oxides, metals, semiconductors and ceramics, it is possible to image individual atomic columns in low-index zone-axis projections. A whole host of important materials’ problems involving defects and departures from nonstoichiometry on the atomic scale are waiting to be tackled by the new generation of intermediate voltage (300-400keV) electron microscopes. In this review, some existing problems and limitations associated with imaging inorganic materials are briefly discussed. The more immediate problems encountered with organic and biological materials are considered elsewhere.Microscope resolution. It is less than a decade since the state-of-the-art, commercially available TEM was a 200kV instrument with a spherical aberration coefficient of 1.2mm, and an interpretable resolution limit (ie. first zero crossover of the contrast transfer function) of 2.5A.

Sol-gel chemistry studied by 1H and 29Si nuclear magnetic resonance

The sol-gel process for forming inorganic glasses and ceramics can be studied uniquely at the molecular level by using 1H and 29Si nuclear magnetic resonance (NMR). A variety of reaction conditions have been investigated, and resonances for hydrolysis products, oligomers, and polymers have been identified. Differences resulting from variations in pH, water/alkoxide ratio, starting material, solvent, and addition of a second network-forming oxide are discussed. The effects of ester interchange were observed in 29Si NMR spectra. The structural makeup of the polymer formed was studied as a function of pH. The hydrolysis was followed with 1H NMR spectroscopy. All reactions were of tetramethyl or tetraethyl orthosilicate in methanol or ethanol.