Advanced Ceramics

This article provides an overview of the state-of-the-art chemistry and processing technologies for silicon nitride and silicon nitride-rich films, i.e., silicon nitride with C inclusion, both in hydrogenated (SiN x :H and SiN x :H(C)) and non-hydrogenated (SiN x and SiN x (C)) forms. The emphasis is on emerging trends and innovations in these SiN x material system technologies, with focus on Si and N source chemistries and thin film growth processes, including their primary effects on resulting film properties. It also illustrates that SiN x and its SiN x (C) derivative are the focus of an ever-growing research and manufacturing interest and that their potential usages are expanding into new technological areas.

The present article aims to give a brief overview about the advantages of the hydrothermal crystallization method for the synthesis of advanced ceramics. Emphasis is given, not only on the conventional hydrothermal crystallization, but also on some of its variants; such as ultrasound-assisted, electrochemical-assisted, microwave-assisted and surfactant-assisted hydrothermal methods which open up new opportunities for the synthesis of ceramic materials with novel properties demanded for advanced applications. In the current work the synthesis of barium titanate (BaTiO 3 ), lithium metasilicate (Li 2 SiO 3 ) and sodium-potassium niobate (Na, K)NbO 3 powders are reported as cases of study.

Barium hexaferrite (BaFe12O19) has traditionally been used in permanent magnets and more recently used for high density
magnetic recording. Fine particles of barium hexaferrite (BaFe12O19) powder have been synthesized by sol-gel based combustion
technique. In this technique, barium and iron nitrates were used as the source nitrates and D-Fructose was used as the fuel. The phase
formation, functional groups, thermal properties, particle morphology and magnetic hysteresis behavior were analyzed by X-ray
diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermo gravimetric/differential thermal analysis (TG-DTA), high
resolution scanning electron microscope (HR-SEM) and vibrating sample magnetometer (VSM). Fine crystalline particles were
obtained from calcinations of precursor relatively at 900 °C. The crystalline diffraction pattern shows the corresponding major angles
were 32.14°, 34.1196°, 30.3207°, 37.0953°, 55.0400°, 56.5423°, and 63.0425° respectively. HR-SEM studies reveal that the diameters
of the few particles were roughly about 90 to 120 nm. The calcined powder shows specific saturation magnetization (Ms), was 55.016
A·m2/kg, remanence magnetization (Mr) was 33.1286 A·m2/kg, coercive force (Hc) was 3851.4 Gauss and squereness ratio was 0.6022.
Few particles were nano meters in diameter.

The lithium titanate defect spinel, Li4Ti5O12 (LTO), is a promising “zero-strain” anode material for lithium-ion batteries in cycling-demanding applications. However, the low-rate capability limits its range of applications. Surface modifications, for example, coating and defect engineering, play an intriguing role in interfacial electrochemical processes. Herein, a novel syn-thesis of highly oxygen-deficient “defective-LTO” anode material with high-rate performance is reported. It is synthesized using conventional precursors via a one-pot thermal reduction process. A high level of oxygen vacancies of ≈6.5 at% and conformal amorphous carbon coating are achieved simul-taneously, resulting in a compounding effect for a high discharge capacity of 123 mAh g−1 with Coulombic efficiency of 99.8% at 10 C-rate. Ab initio calculations foresight that oxygen vacancies increase the electron donor den-sity of the neighboring titanium atoms, while conformal amorphous carbon significantly lowers interfacial charge-transfer resistance. The formation mechanism, as well as the origin of enhanced electrochemical properties, is elaborated in this paper.

Al2O3–ZrO2 (Y2O3) nanopowders containing 5, 10 and 15 wt% ZrO2 were synthesized by aqueous sol–gel
method using aluminum sec-butoxide and zirconium butoxide as precursors. BET analysis shows that,
increasing the zirconia content results in a decrease in surface area, 152, 125 and 121 m2/g, and an
increase in pore size, 5.63, 9.79 and 11.05 nm for 5, 10 and 15 wt% ZrO2, respectively. Furthermore, a shift
toward higher temperatures is observed for transition of transitional aluminas to stable a-alumina phase
through increasing the zirconia content. SEM micrograph of calcined nanopowders revealed nanosize
spherical particles in the range of 15–75 nm.

The alumina nanopowder was synthesized via the sol–gel method. u-Alumina with crystallite size in the range of 25–110 nm was crystallized by
calcination of the powder at 900 8C for 1 h. Sodium alginate, a natural innoxious polymer, was applied for in situ forming process of an Al2O3 green
body, using calcium phosphate as a solidifier agent. Sodium hexa metaphosphate was also utilized as a chelator. Rheological and gelation behaviors
of resultant slurry were analyzed. The viscosity of slurries with 15 vol.% alumina and 1.8 vol.% calcium phosphate dispersed by 1 wt.% sodium
alginate solution, was less than 800 mPa s. The green bodies from the gelcasting process were dried at room temperature for 36 h and pressureless
sintered at 1500 8C for 3 h. A uniform microstructure without huge grain growth was revealed by SEM.

We present the magnetic properties of magnetic glass ceramics obtained by crystallization of Fe containing borosilicate glass. Two types of nucleators have been used: Cr 2 O 3 and P 2 O 5 . The role of the nucleators proved to be crucial in the size and morphology of the crystallites developed within glassy matrix as well in the magnetic response. The former stimulates the growth of regular single crystals uniformly dispersed within the matrix whereas the latter leads to the formation of grains made of tiny (30 nm), nanocrystals. The magnetic response depends on the amount of Fe ions left dispersed within glassy matrix as paramagnetic ions. Although P 2 O 5 leads to the best structural magnetite, almost 42% of Fe ions are left dispersed in the matrix without magnetic interaction. In the case of Cr 2 O 3 , the paramagnetic Fe is decreased to 12% but structural deficiency in the occupancy of the Fe sites of magnetite is revealed by Mössbauer spectroscopy.

The alumina–zirconia–yttria (AZY) nanopowders ranging from 30–110nm were synthesized via the
sol–gel method. -Alumina and t-zirconia phases were identified in the nanopowders calcined at 900 ◦C
for 1 h. Sodium alginate was used for gelcasting process of green bodies. The viscosity of castable slurries
with highest nanopowder loading, 15 vol.%, is about 800mPa.s. The dried gels were pressureless sintered
at 1400, 1450 and 1500 ◦C for 3 h. Grain boundary diffusion seems to be the controlling sintering mechanism
with increasing zirconia content from 5 up to 10 wt.%, whereas in the range of 10–15 wt.% zirconia
content increase, lattice diffusion is the controlling.

This paper presents the findings on thermal expansion behavior of slaked lime doped rice husk silica (RHS) refractory monitored between 25 ℃ and 1500 ℃. It also reports the phase transition analysis within the temperature range of 850-1450 ℃. A sudden expansion of 0.7% noticed at 220 ℃ is due to the transformation of α-cristobalite to β-cristobalite. The highest expansion (0.85%) reached within the temperature range of 650-850 ℃, remains almost constant for the investigated temperature range, and is not high enough to cause macro cracks in the refractory. The phase transition order is similar to those reported for quartzite refractory after 600 ℃, though the crystallization temperature is lowered due to the presence of the dopant. Modulus of rupture, apparent porosity, bulk density, refractoriness and reheat change are reported and their results meet with the standards qualifying them for use in coke ovens.

Mechanical and thermal properties of SiC-porcelain ceramics were studied in the wide SiC content range of 0-95%. Microstructure evolution, shrinkage at sintering, porosity, mechanical strength, elastic modulus, coefficient of thermal expansion (CTE) and thermal conductivity were studied depending on SiC content. The optimal sintering temperature was 1200 ℃, and the maximum mechanical strength corresponded to SiC content of 90%. Parametric evaluation of the ceramic thermal shock resistance revealed its great potential for thermal cycling applications. It was demonstrated that the open-cell foam catalyst supports can be manufactured from SiC-porcelain ceramics by the polyurethane foam replication process.

Large-area polycrystalline diamond (PCD) coatings are important for fields such as thermal management, optical windows, tribological moving mechanical assemblies, harsh chemical environments, biological sensors, etc. Microwave plasma chemical vapor deposition (MPCVD) is a standard technique to grow high-quality PCD films over large area due to the absence of contact between the reactive species and the filament or the chamber wall. However, the existence of temperature gradients during growth may compromise the desired uniformity of the final diamond coatings. In the present work, a thick PCD coating was deposited on a 100-mm silicon substrate inside a 915-MHz reactor; the temperature gradient resulted in a non-uniform diamond coating. An attempt was made to relate the local temperature variation during deposition and the different properties of the final coating. It was found that there was large instability inside the system, in terms of substrate temperature (as high as ΔT = 212 ℃), that resulted in a large dispersion of the diamond coating's final properties: residual stress (15.8 GPa to +6.2 GPa), surface morphology (octahedral pyramids with (111) planes to cubo-octahedrals with (100) flat top surfaces), thickness (190 µm to 245 µm), columnar growth of diamond (with appearance of variety of nanostructures), nucleation side hardness (17 GPa to 48 GPa), quality (Raman peak FWHM varying from 5.1 cm 1 to 12.4 cm 1 with occasional splitting). This random variation in properties over large-area PCD coating may hamper reproducible diamond growth for any meaningful technological application.

C 4 photosynthesis has higher light-use, nitrogen-use, and water-use efficiencies than C 3 photosynthesis. Historically, most of C 4 plants were classified into three subtypes (NADP-malic enzyme (ME), NAD-ME, or phosphoenolpyruvate carboxykinase (PEPCK) subtypes) according to their major decarboxylation enzyme. However, a wealth of historic and recent data indicates that flexibility exists between different decarboxylation pathways in many C 4 species, and this flexibility might be controlled by developmental and environmental cues. This work used systems modelling to theoretically explore the significance of flexibility in decarboxylation mechanisms and transfer acids utilization. The results indicate that employing mixed C 4 pathways, either the NADP-ME type with the PEPCK type or the NAD-ME type with the PEPCK type, effectively decreases the need to maintain high concentrations and concentration gradients of transport metabolites. Further, maintaining a mixture of C 4 pathways robustly affords high photosynthetic efficiency under a broad range of light regimes. A pure PEPCK-type C 4 photosynthesis is not beneficial because the energy requirements in bundle sheath cells cannot be fulfilled due to them being shaded by mesophyll cells. Therefore, only two C 4 subtypes should be considered as distinct subtypes, the NADP-ME type and NAD-ME types, which both inherently involve a supplementary PEPCK cycle.

An alumina–15 wt.% zirconia (3 mol% yttria) nanopowder was synthesized by sol–gel method using salt and alkoxide as precursors.
Al(NO3)39H2O, ZrOCl28H2O and Y(NO3)36H2O were used as salt precursors and Al(OC4H9)3 and Zr(OC4H9)4 were used as alkoxide
precursors. The dried gels of two precursors were heat treated in the range of 450–1350 8C. The powders produced by alkoxide precursors calcined
at 750 8C were in the range of 15–75 nm, while those prepared by salt precursors had the size in the range of 30–90 nm. The former powders had a
higher surface area and smaller mean pore diameter compared with the later powder, i.e. 152 m2/g and 5.63 nm comparing with 121 m2/g and
9.79 nm, respectively. Therefore phase transformation in the former occurred in lower temperatures.

Hydroxymethyltriethoxysilane and hydroxymethyltrimethoxysilane, precursors by hydrolysis to a simple analog of silicic acid, hydroxymethylsilanetriol, were prepared. Hydroxymethyltrialkoxysilanes undergo condensation to form silmethyleneoxide oligomers and dimeric 2,2,5,5-tetraalkoxy-2,5-disila-1,4-dioxanes. Hydroxymethylsilanetriol undergoes condensation reactions similar to silicic acid and readily forms organosilicate structures by sol–gel processing techniques which may be converted at relatively low temperatures to silicon dioxide. Hydroxmethylsilanetriol
derived gels were subject to less stress-cracking during drying than conventional tetraethoxysilane derived gels, suggesting that Si-O-C bond equilibration during drying provides a mechanism for stress-relief. In screening experiments, hydroxymethylsilanetriol appears to be a competitive inhibitor of the growth of the diatom C. fusiformis, a silicate dependent species that produces silicate structures.

Increasing energy cost calls for exterior coatings with high near infra-red reflectance, so as to reduce heat absorption and in turn cost of air-conditioning. While modulations of substrate, use of white metal oxides as pigments or under-layers has been reported in past, reports on metal oxide or doped metal oxide pigments with high NIR reflectance is scarce. We report for the first time a blue colored cobalt aluminate type pigment prepared through doping of cerium, praseodymium or neodymium. CIELAB color measurements and calculation of E indicated that the Nd doped sample had crystal size of (36±1) nm, bandgap value of (2.4±0.2) eV and color coordinates similar to that of cobalt aluminate. The molar ratio as estimated by EDX was found to be Al : Cu : Co : Ce : Nd : O= 2 : 0.06 : 0.06 : 0.012 : 0.000 12 : 6.18. The pigment was found to have potential applications as a cool blue colorant, owing to changes in optical properties arising out of crystal chemistry changes. Incorporation of rare earth metal ions was found to enhance the NIR reflectance by 10%, when compared to a conventional cobalt aluminate pigment. The oxide has been well characterized and its performance as a pigment evaluated. We have proposed that changes in crystal lattice when neodymium enters into Ce 4+ sites enhance the NIR reflectance by about 9% as against the entry of praseodymium.

Pure-phased Li 2 MnSiO 4 /C is prepared by solegel method with Mn 3 O 4 nanoparticle. It owns nano-sized active material particle with 20e30 nm. It delivers an initial discharge capacity of 240 mAh g À1 at room temperature. Irreversible distortion might mainly effect on the cycle performance of Li 2 MnSiO 4 /C.

YBa 2 Cu 3 O y (YBCO) foam samples show an open, porous foam structure, which may have benefits for many applications of high-T c superconductors. As the basic material of these foams is a pseudo-single crystalline material with the directional growth initiated by a seed crystal similar to standard melt-textured samples, the texture of YBCO is a very important parameter. Therefore, we analysed the local texture and grain orientation of the individual struts forming the foam by means of atomic force microscopy (AFM) and electron backscatter diffraction (EBSD). Due to the processing route starting with Y 2 BaCuO 5 (211), a two-phase analysis must be performed, so a high surface quality is necessary to enable an automated EBSD scan. Good quality Kikuchi patterns were obtained from both the YBCO and 211 phases. We found an inhomogeneous distribution of the residual 211 particles, which are mainly randomly oriented and have sizes ranging between 200 nm and 15 µm. In contrast to this, the YBCO matrix shows a dominating orientation with cracks with a typical distance of 1-10 µm. Furthermore, the analysis of strut cross-sections reveals that the entire strut is converted to the YBCO phase.

A misfit layer sulfide (BiS) 1.2 (TiS 2 ) 2 with a natural superlattice structure has been shown to be a promising thermoelectric material, but its high carrier concentration should be reduced so as to further optimize the thermoelectric performance. However, ordinary acceptor doping has not succeeded because of the non-parabolic band structure. In this paper, we have successfully doped chromium ions into the Ti sites, which can maintain or even enhance the high effective mass of electrons so as to effectively improve ZT value. X-ray diffraction analysis, coupled with X-ray photoelectron spectroscopy, shows that chromium has been substituted into titanium sites in TiS 2 layers and confirms its ionic state. The chromium doping has successfully reduced the carrier concentration with the subsequent reduction of electrical conductivity. Unlike other acceptor dopants (alkaline earth metals), chromium also enhances Seebeck coefficient and the effective mass, which can possibly be attributed to the formation of additional resonant states near Fermi level. Though the power factor does not improve, the significant reduction in the electronic part of the thermal conductivity leads to a measurable improvement in ZT.

In this study, 5 mol% yttria-stabilized zirconia tubular thin film is fabricated by screen printing method. The processing parameters are investigated. The microstructure of the samples is analyzed by X-ray diffraction and scanning electron microscope. The electrical conductivity of the samples is studied by impedance spectroscopy. The microhardness, nanohardness, and Young's modulus of the thin films are measured. It is found that the proper weight ratio of zirconia powder to organic constituents of the ink is 3:2. The hardness of tubular thin film is higher than that of the planar specimen. The conductivity of 5YSZ tubular thin film at 850°C is 0.028 S/cm.

We develop a theoretical model for quantitative analysis of temperature-dependent thermoelectric power of monovalent (Na) doped La 0.97 Na 0.03 MnO 3 manganites. In the ferromagnetic regime, we have evaluated the phonon thermoelectric power by incorporating the scattering of phonons with impurities, grain boundaries, charge carriers and phonons. In doing so, we use the Mott expression to compute the carrier (hole) diffusion thermoelectric power ( diff c S ) using Fermi energy as carrier (hole)-free parameter, and diff c S shows linear temperature dependence and phonon drag drag ph S increases exponentially with temperature which is an artifact of various operating scattering mechanisms. It is also shown that for phonons the scattering and transport cross-sections are proportional to  4 in the Rayleigh regime where  is the frequency of the phonons. Numerical analysis of thermoelectric power from the present model shows similar results as those revealed from experiments.

A comparative study was carried out on the load-dependent indentation behavior with respect to hardness and induced cracks of β-SiAlON and α-silicon carbide ceramics. It is observed that silicon carbide (SiC) exhibits lower transition load, early cracking and severely crushed indentation sites, whereas β-SiAlON shows higher transition load and damage-free indentation zone even at the maximum applied load (294.19 N). Crack density is higher for α-SiC with comparison to β-SiAlON at each load. SiC exhibits both main and secondary radial types of cracking from low indentation load (0.98 N). Cracks are often associated with branching at higher load (> 9.80 N) for α-SiC. β-SiAlON exhibits cracks which are mainly radial types initiated at 4.90 N load. These opposing behaviors of β-SiAlON and α-SiC are attributed to their difference in hardness, toughness, and brittleness index. Higher brittleness of α-SiC results in early and severe cracking around its indentations. β-SiAlON shows less cracking due to its lower brittleness and higher toughness. The increased size of indentation-induced cracks of α-SiC is higher than that of β-SiAlON due to the rapid crack propagation in α-SiC with transgranular fracture behavior.

Lead-free piezoceramics based on the (Ba,Ca)(Zr,Ti)O 3 (BCZT) system exhibit excellent electromechanical properties for low-temperature actuation applications, but suffer from relatively high processing temperatures. Here we demonstrate an approach for the reduction of the sintering temperature and simultaneous increase of the electromechanical strain response of (Ba,Ca)(Zr,Ti)O 3 piezoceramics by aliovalent doping with Ce. The samples were prepared by solid state synthesis and their crystallographic structure, dielectric, ferroelectric, and electromechanical properties were investigated. The highest d * 33 value of 1189 pm/V was obtained for the sample with 0.05 mol% Ce, substituted on the A-site of the perovskite lattice. The results indicate a large potential of these materials for off-resonance piezoelectric actuators.

Polyorganoborosilazane ((B[C 2 H 4 -Si(CH 3 )NH] 3 ) n ) was synthesized via monomer route from a single-source precursor and thermolyzed at 1300 ℃ in argon atmosphere. The as-thermolyzed Si-B-C-N ceramic was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The crystallization behavior of silicon carbide in the as-thermolyzed amorphous Si-B-C-N matrix was understood by XRD studies, and the crystallite size calculated using Scherrer equation was found to increase from 2 nm to 8 nm with increase in dwelling time. Concomitantly, Raman spectroscopy was used to characterize the free carbon present in the as-thermolyzed ceramic. The peak positions, intensities and full width at half maximum (FWHM) of D and G bands in the Raman spectra were used to study and understand the structural disorder of the free carbon. The G peak shift towards 1600 cm 1 indicated the decrease in cluster size of the free carbon. The cluster diameter of the free carbon calculated using TK (Tuinstra and Koenl) equation was found to decrease from 6.2 nm to 5.4 nm with increase in dwelling time, indicating increase in structural disorder.

The objective of this study was to characterize the chemical and physical properties of bioactive ceramics prepared from an aqueous paste containing hydroxyapatite (HA) and beta tri-calcium phosphate (β-TCP). Prior to formulating the paste, HA and β-TCP were calcined at 800 ℃ and 975 ℃ (11 h), milled, and blended into 15%/85% HA/β-TCP volume-mixed paste. Fabricated cylindrical rods were subsequently sintered to 900 ℃, 1100 ℃ or 1250 ℃. The sintered specimens were characterized by helium pycnometry, X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), and inductively coupled plasma (ICP) spectroscopy for evaluation of porosity, crystalline phase, functional-groups, and Ca:P ratio, respectively. Mechanical properties were assessed via 3-point bending and diametral compression. Qualitative microstructural evaluation using scanning electron microscopy (SEM) showed larger pores and a broader pore size distribution (PSD) for materials sintered at 900 ℃ and 1100 ℃, whereas the 1250 ℃ samples showed more uniform PSD. Porosity quantification showed significantly higher porosity for materials sintered to 900 ℃ and 1250 ℃ (p < 0.05). XRD indicated substantial deviations from the 15%/85% HA/β-TCP formulation following sintering where lower amounts of HA were observed when sintering temperature was increased. Mechanical testing demonstrated significant differences between calcination temperatures and different sintering regimes (p < 0.05). Variation in chemical composition and mechanical properties of bioactive ceramics were direct consequences of calcination and sintering.

Tantalum oxynitride powder with a baddeleyite crystal structure was synthesized and densified by hot pressing in Ar and under high pressure using a belt-type high-pressure apparatus. The tantalum oxynitride powder could not be densified completely under hot-pressing conditions at 1400°C. The use of high pressure resulted in dense materials. The samples showed a hardness of 16–17 GPa and a fracture toughness of 3–4 MPa·m1/2. The hardness is higher compared with that of ZrO2 and HfO2 ceramics. The fracture toughness corresponds to the value of fully stabilized ZrO2 due to the absence of any transformation toughening mechanism.

The frequency dependent electrical parameters, such as impedance, electric modulus, dielectric constant and AC conductivity for ferroelectric Ba 0.8 Sr 0.2 TiO 3 thin film have been investigated within the range of 1 Hz and 10 6 Hz at room temperature. Z* plane shows two regions corresponding to the bulk mechanism and the distribution of the grain boundaries-electrodes process. M" versus frequency plot reveals a relaxation peak, which is not observed in the ε″ plot and it has been found that this peak is a non-Debye-type. The frequency dependent conductivity plot shows three regions of conduction processes, i. e., a low-frequency region due to DC conduction, a mid-frequency region due to translational hopping motions and a high-frequency region due to localized hopping and/or reorientational motion. (A. A. Saif) measurements were performed using an impedance/gainphase analyzer in the frequency range of 1 Hz to 1 MHz at room temperature.

Gadolinia-doped ceria ceramic pastes were formulated with different solid loadings and extruded using lab-scale equipment. The force to maintain a constant ram speed of 10 mm/min was recorded. The radial shrinkage after drying was proportional to the solid loading and this allowed the determination of the maximum solid loading by an extrapolation procedure. In order to obtain the apparent viscosity of the pastes, a novel approach based on the analysis of the slope of the extrusion pressure plot versus distance covered by the ram, was formulated for the direct determination of the shear stress upon extrusion. The agreement of the determined maximum solid loading with values calculated by two existing models confirmed that the proposed approach was an alternative and reliable method to identify the upper limit of the solid loading range for the formulation of extrudable ceramic pastes.

Ceramic materials are increasingly used in micro-electro-mechanical systems (MEMS) as they offer many advantages such as high-temperature resistance, high wear resistance, low density, and favourable mechanical and chemical properties at elevated temperature. However, with the emerging of additive manufacturing, the use of ceramics for functional and structural MEMS raises new opportunities and challenges. This paper provides an extensive review of the manufacturing processes used for ceramic-based MEMS, including additive and conventional manufacturing technologies. The review covers the micro-fabrication techniques of ceramics with the focus on their operating principles, main features, and processed materials. Challenges that need to be addressed in applying additive technologies in MEMS include ceramic printing on wafers, post-processing at the micro-level, resolution, and quality control. The paper also sheds light on the new possibilities of ceramic additive micro-fabrication ...

Ceramic materials are increasingly used in micro-electro-mechanical systems (MEMS) as they offer many advantages such as high-temperature resistance, high wear resistance, low density, and favourable mechanical and chemical properties at elevated temperature. However, with the emerging of additive manufacturing, the use of ceramics for functional and structural MEMS raises new opportunities and challenges. This paper provides an extensive review of the manufacturing processes used for ceramic-based MEMS, including additive and conventional manufacturing technologies. The review covers the micro-fabrication techniques of ceramics with the focus on their operating principles, main features, and processed materials. Challenges that need to be addressed in applying additive technologies in MEMS include ceramic printing on wafers, post-processing at the micro-level, resolution, and quality control. The paper also sheds light on the new possibilities of ceramic additive micro-fabrication ...

Ceramic materials are increasingly used in micro-electro-mechanical systems (MEMS) as they offer many advantages such as high-temperature resistance, high wear resistance, low density, and favourable mechanical and chemical properties at elevated temperature. However, with the emerging of additive manufacturing, the use of ceramics for functional and structural MEMS raises new opportunities and challenges. This paper provides an extensive review of the manufacturing processes used for ceramic-based MEMS, including additive and conventional manufacturing technologies. The review covers the micro-fabrication techniques of ceramics with the focus on their operating principles, main features, and processed materials. Challenges that need to be addressed in applying additive technologies in MEMS include ceramic printing on wafers, post-processing at the micro-level, resolution, and quality control. The paper also sheds light on the new possibilities of ceramic additive micro-fabrication ...

Highly stoichiometric hexagonal AlN films of different thicknesses ranging from ≈10 nm to >1 µm were synthetized on silicon (100) substrates under the same deposition conditions by dc reactive magnetron sputtering. The X-ray diffraction and reflectometry, ellipsometry, scanning electron and atomic force microscopies, and nanoindentation techniques were applied to study the effect of the film thickness on the structure, refractive index and hardness. Fine granular structure transforms into the ordered columnar form possessing (002) texture with increasing film thickness, the refractive index being affected only slightly. The most notable feature is the existence of a particular film thickness around 800 nm where the texture perfection reaches a maximum. This result was verified on a repeatedly deposited film of the same thickness. The texture extreme at 800 nm brings about a significant hardness enhancement which surpasses 20 GPa, presumably due to the hampered dislocation formation and/or motion.

The objective of this study was to characterize the chemical and physical properties of bioactive ceramics prepared from an aqueous paste containing hydroxyapatite (HA) and beta tri-calcium phosphate (β-TCP). Prior to formulating the paste, HA and β-TCP were calcined at 800 ℃ and 975 ℃ (11 h), milled, and blended into 15%/85% HA/β-TCP volume-mixed paste. Fabricated cylindrical rods were subsequently sintered to 900 ℃, 1100 ℃ or 1250 ℃. The sintered specimens were characterized by helium pycnometry, X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), and inductively coupled plasma (ICP) spectroscopy for evaluation of porosity, crystalline phase, functional-groups, and Ca:P ratio, respectively. Mechanical properties were assessed via 3-point bending and diametral compression. Qualitative microstructural evaluation using scanning electron microscopy (SEM) showed larger pores and a broader pore size distribution (PSD) for materials sintered at 900 ℃ and 1100 ℃, whereas the 1250 ℃ samples showed more uniform PSD. Porosity quantification showed significantly higher porosity for materials sintered to 900 ℃ and 1250 ℃ (p < 0.05). XRD indicated substantial deviations from the 15%/85% HA/β-TCP formulation following sintering where lower amounts of HA were observed when sintering temperature was increased. Mechanical testing demonstrated significant differences between calcination temperatures and different sintering regimes (p < 0.05). Variation in chemical composition and mechanical properties of bioactive ceramics were direct consequences of calcination and sintering.

Porcelain fused to metal (PFM) has received great attention over the last few years due to its importance in the dentistry. Kalsilite (K 2 O·Al 2 O 3 ·SiO 2 ) is a high thermal expansion porcelain, suitable for bonding to metals. However, kalsilite is a metastable phase which gets converted into crystalline leucite upon heating. In the current work feasibility of developing stable kalsilite phase, dispersion of MgF 2 in it as an additive and using mechanochemical synthesis are studied. Micro fine dental material has been formulated by mixing prepared kalsilite with low temperature frit (LTF) in different ratio. The crystalline phases evolved in fired powders are characterized by powder X-ray diffraction (XRD) technique. Kalsilite with different ratio of LTF has been cold pressed and heat treated to examine its coefficient of thermal expansion (CTE), flexural strength, apparent porosity (AP), bulk density (BD) and microstructure. Results indicate that MgF 2 addition and high milling duration help in kalsilite stabilization. Temperature also plays an important role in this stabilization, and at 1100 ℃ single phase kalsilite formation is observed. Present outcomes demonstrate that it is easily possible to synthesize a stable single phase kalsilite with desirable properties.

The inexpensive and green method of synthesis for self-assembled micro/nano structures is an important area of emerging research. Such structures can be chemically tuned with predesigned functional properties. Therefore, they hold very good promise for future applications, e.g., biomedicine, electronic device, solar energy, gas sensing. Here we report for the first time an inexpensive and green method for chemical deposition of magnesium hydroxide (Mg(OH) 2 ) micro/nano flowers in thin films on commercial soda lime silica glass substrates at room temperature. Under identical conditions, chemically synthesized Mg(OH) 2 powders are also prepared in absence of the soda lime silica glass substrates. The condition that favors the growth of micro/nano flowers in thin films is identified from X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX) data. Finally, the possible growth mechanism of micro/nano flowers in thin films is discussed.

YBa 2 Cu 3 O y (YBCO) foam samples show an open, porous foam structure, which may have benefits for many applications of high-T c superconductors. As the basic material of these foams is a pseudo-single crystalline material with the directional growth initiated by a seed crystal similar to standard melt-textured samples, the texture of YBCO is a very important parameter. Therefore, we analysed the local texture and grain orientation of the individual struts forming the foam by means of atomic force microscopy (AFM) and electron backscatter diffraction (EBSD). Due to the processing route starting with Y 2 BaCuO 5 (211), a two-phase analysis must be performed, so a high surface quality is necessary to enable an automated EBSD scan. Good quality Kikuchi patterns were obtained from both the YBCO and 211 phases. We found an inhomogeneous distribution of the residual 211 particles, which are mainly randomly oriented and have sizes ranging between 200 nm and 15 µm. In contrast to this, the YBCO matrix shows a dominating orientation with cracks with a typical distance of 1-10 µm. Furthermore, the analysis of strut cross-sections reveals that the entire strut is converted to the YBCO phase.

Structure, phase composition and electrical conductivity of thin yttria-stabilized zirconia (YSZ) films deposited by electron beam evaporation on a silicon (1 0 0) substrate at different temperatures i.e. room temperature (r.t.), 700 and 830°C, as well as the quality of the YSZ-Si interface have been investigated. The phase composition was verified by Raman spectroscopy and by infrared (i.r.) transmission measurements. The structure of films changed in agreement with their electrical conductivity depending on the deposition temperature. Both structure and thereby electrical conductivity were influenced by the high concentration of Y 2 O 3 stabilizer used and by the post-deposition thermal treatment of films. The deposition temperature was also important in determining the quality of the YSZ-Si interface and hence the accessible sweep of the surface potential. The capacitance-voltage characteristics of the metal-insulator-semiconductor (MIS) structures incorporating YSZ films measured at r.t. showed hysteresis and positive shifts of the flat-band voltages.