Porosity Of Ceramics Research Articles

Enhanced energy-storage performance of (1-x)(0.72Bi0.5Na0.5TiO3-0.28Bi0.2Sr0.7□0.1TiO3)-xLa ceramics

Leed-free ferroelectric (1-x)(0.72Bi0.5Na0.5TiO3-0.28Bi0.2Sr0.7□0.1TiO3)-xLa (NBST-xLa; x = 0, 0.5%, 1.5%, 2%) ceramics were synthesized using a conventional solid-state reaction method and the effect of La-doping on the microstructure and electrical properties was investigated. The introduction of La could reduce the grain size and improve the porosity of NBST ceramics. Temperature-dependent dielectric permittivity illustrated that the relaxation properties of NBST-xLa ceramics changed parabolically with the increase of La content. The introduction of La gave rise to a large dielectric breakdown strength and maximum polarization when x = 0.5%, which was attributed to the variation of the microstructure and the relaxation properties of NBST-xLa ceramics, respectively. The optimum effective energy storage density of 1.2 J/cm3 at 90 kV/cm was achieved when x = 0.5%. These results indicated that NBST-0.5%La ceramic may provide a practical perspective for energy storage ceramics research.

Effect of Y2O3 dopant on dielectric, magnetic, magnetodielectric properties of Bi0.95La0.05Fe0.95Ti0.05O3 ceramics

The Bi0.95-xLa0.05YxFe0.95Ti0.05O3 (BYFO) (x = 0, 0.04, 0.06, 0.08, 0.10) ceramics were synthesized by traditional solid phase method. The samples for BYFO ceramics were tested for X-ray diffraction (XRD) techniques, magnetic hysteresis (M–H)loops, scanning electron microscope (SEM). The leakage current were weakened because highly dense microstructure and low porosity ceramics were compounded. When x = 0.06, remanent polarization (Pr) is 0.3079 μC/cm2, and saturization polarization (Ps) is 1.3542 μC/cm2 for BYFO ceramics. Saturation magnetization (Ms) and remanent magnetization (Mr) are increased to 1.91926 emu/g, 1.43179 emu/g respectively. The obtained values of the magnetodielectric coefficient (αMD) comes to maximum value, which is 15.64% for x = 0.08.

Preparation and characterization of mullite foam ceramics with porous struts from white clay and industrial alumina

In this study, four mullite foam ceramics with porous struts and low thermal conductivities, were prepared by direct-foaming method from white clay and industrial alumina with the addition of sodium carboxymethyl cellulose (CMC) as foam stabilising agent. The effect of the CMC addition on the phase composition, pore characteristics, and strength was analysed through XRD, SEM and EDS, etc. The great part of struts for the foam ceramics was the needle-like mullite, the rest was the minor corundum and quartz. The addition of CMC decreased the apparent porosity of foam ceramics and pore area fractions of their struts, while the phase composition was nearly unaffected. Furthermore, the compressive strengths and the thermal conductivities of the foams ceramics increased. The optimized product contained 0.15 wt% CMC, which combined a high porosity of 81.3%, shown a low thermal conductivity of 0.095 W/(mK) (at 350 °C) and a minor positive reheating linear change.

Physical and mechanical properties of hot-press sintering ternary CM2A8 (CaMg2Al16O27) and C2M2A14 (Ca2Mg2Al28O46) ceramics

The new ternary CM2A8 (CaMg2Al16O27) and C2M2A14 (Ca2Mg2Al28O46) pure and dense ceramics were first prepared by a hot-press sintering technique, and their physical and mechanical properties were investigated. The purity of obtained CM2A8 and C2M2A14 ceramics reaches 98.1 wt% and 97.5 wt%, respectively. Their microstructure is dense with few observable pores, and their grain size is about a few dozen microns. For their physical properties, the average apparent porosity of CM2A8 and C2M2A14 ceramics is 0.18% and 0.13%, and their average bulk density is 3.66 g/cm3 and 3.71 g/cm3, respectively. The relative density of CM2A8 ceramic is 98.12% and that of C2M2A14 ceramic is 98.67%. The thermal expansivity (50–1400 °C) of CM2A8 and C2M2A14 ceramics is 9.24×10–6 K–1 and 8.92×10–6 K–1, respectively. The thermal conductivity of CM2A8 and C2M2A14 ceramic is 21.32 W/(m·K) and 23.25 W/(m·K) at 25 °C and 18.76 W/(m·K) and 19.42 W/(m·K) as temperature rises to 350 °C, respectively. In addition, the mechanical properties are also achieved. For CM2A8 ceramic, the flexural strength is 248 MPa, the fracture toughness is 2.17 MPa·m1/2, and the Vickers hardness is 12.26 GPa. For C2M2A14 ceramic, the flexural strength is 262 MPa, the fracture toughness is 2.23 MPa·m1/2, and the Vickers hardness is 12.95 GPa.

Preparation of Low Dielectric Constant Porous Silicon Nitride Ceramics for Radome Application

The porous silicon nitride ceramics with low dielectric constant and high flexural strength were obtained by adding pore-forming agent through partial sintering technique. The effects of pore-forming agent amount on the properties of porous silicon nitride ceramics were investigated. Microstructure was analyzed by means of scanning electron microscopy. The results show that the porous structure is formed by the overlap of pillar β-Si3N4 with high length diameter ratio. The porosity of samples rises with the increase of pore-forming agent content, which leads to the decrease of the dielectric constant and loss, but the decrease of flexural strength. When the pore-forming agent of PMMA with mass fraction of 20% was added, the volume density, porosity, dielectric constant and loss of porous silicon nitride ceramics were 1.17g/cm3, 66.5%, 2.33 and 0.8×10-3 respectively, with higher flexural strength of 75MPa which is satisfactory as low dielectric material for core layer of broadband radome.

Effect of the Mass Fraction of Ceramic Particles on the Porosity of Wear-Resistant Composites Fabricated by Combustion Synthesis

Combustion synthesis was employed to fabricate a wear-resistant composite using reactions between Ti, Al, Fe3O4, B4C, and CrO3 powders on the steel plate. CaF2 was used to improve the fluidity and decrease the melting temperature of Al2O3. A large number of holes were found in the top of the composite with different contents of ceramic particles. To elucidate the relationship between the mass fraction of ceramic particles and porosity, the adiabatic temperatures of different combustion systems were calculated. The porosity and size distribution of the holes of samples with different ceramic particle contents were studied, and the distributions and compositions of the ceramic particles were analyzed. The compositions surrounding and inside the holes were studied, and the hardness of the composite was also tested. The results show that the formation of holes is associated with the vaporization of Al and Cr. The porosity increases with an increase in the ceramic particle contents which is the combined effect of the decreasing adiabatic temperature, the increasing nucleation rate, the increasing ceramic particle sizes, the increasing viscosity of the metal, and the wetting angle between the liquid and solid phase, while the composition of ceramic particles has little effect. The hardness values of all composites exceed 60 HRC.

Fabrication of porous alumina by directional freeze casting and annealing in TBA–water–sucrose system

The volume change difference between water and tert-butyl alcohol (TBA) hydrate was approximately 10.1% when ceramic slurry with water–TBA was frozen for fabrication of porous ceramics. Residual stress may be produced at the pore walls and led to low compressive strength of the ceramics. In this regard, sucrose was used in the ceramic slurry. Several water–TBA crystals were observed in the sucrose amorphous bodies after directional freezing. Water and TBA in the sucrose amorphous bodies were recrystallized during subsequent annealing. Sucrose was used as a protective agent and annealing additive in the TBA–water–sucrose system to eliminate residual stress and change the pore structure from snowflakes and dendrites into tiny cylinders. Adding sucrose and annealing process exerted minimal effect on the open porosity of porous ceramics but remarkably improved their compressive strength. When TBA and sucrose contents were 30 and 20 wt%, respectively, in the ceramic slurry with 20 vol% alumina content, the compressive strength of porous ceramics was 49.9 MPa after annealing at − 15 °C for 2 h. The value was 3.6-fold higher than that of the ceramic without annealing. Results provide a new method for improving the mechanical properties of porous ceramics prepared by freeze casting.

Transient liquid phase diffusion process for porous mullite ceramics with excellent mechanical properties

Porous mullite ceramics were fabricated by the transient liquid phase diffusion process, using quartz and fly-ash floating bead (FABA) particles and corundum fines as starting materials. The effects of sintering temperatures on the evolution of phase composition and microstructure, linear shrinkage, porosity and compressive strength of ceramics were investigated. It is found that a large amount of quartz and FABA particles can be transformed into SiO2-rich liquid phase during the sintering process, and the liquid phase is transient in the Al2O3-SiO2 system, which can accelerate the mullitization rate and promote the growth of mullite grains. A large number of closed pores in the mullite ceramics are formed due to the transient liquid phase diffusion at elevated temperatures. The porous mullite ceramics with high closed porosity (about 30%) and excellent compressive strength (maximum 105 MPa) have been obtained after fried at 1700 °C.

Characterization Porosity on Ceramic Body Stoneware Based Kalimantan Clay

It has been made ceramic body stoneware using a mixture of Kalimantan clay, RRC feldspar, Belitung kaolin, Belitung quartz and Bukit Jimbaran limestone further coded BPC-1. This study aims to determine the value of dry shrinkage, the effect of sintering temperature of 900oC and 1200oC against firing shrinkage, and the influence of sintering temperature of 900oC and 1200oC against porosity in the ceramic body stoneware. Ceramic stoneware burned with a temperature variation of 900oC and 1200oC. The results show the value of dry shrinkage in ceramic stoneware of 2.9%. Stoneware ceramic firing shrinkage at a temperature of 900 oC combustion of 1.3%, and the combustion at a temperature 1200oC of 3.8%. Porosity ceramic stoneware at a temperature of 900oC combustion showed porosity of 10.5%, while the combustion at a temperature 1200oC of 5.5%. Show that the combustion temperature greatly affects the value of dry shrinkage, firing shrinkage and porosity of stoneware ceramics. The higher the combustion temperature the higher the shrinkage and the decreasing the porosity.

Formation mechanism of high apparent porosity ceramics prepared from fly ash cenosphere

Porous ceramics with high apparent porosity have wide applications in various fields. In this work, high apparent porosity ceramics were fabricated from fly ash cenosphere. Effects of sintering temperature and CaCO3 on the apparent porosity were investigated. More importantly, the formation mechanism of high apparent porosity was proposed. Results showed that the sintering temperature decreased the apparent porosity in densification process. The addition of CaCO3 improved the apparent porosity in two ways: one was that CO2 emission from CaCO3 decomposition promoted the formation of pores in ceramics; the other one was that CaO from decomposed CaCO3 was transformed into anorthite with fly ash cenosphere, which generated the porous structure of fly ash cenosphere shell. In this work, the apparent porosity of ceramics with 30 wt% CaCO3 sintered at 1250 °C reached 59.25%, and the corresponding compressive strength was 70 ± 2.58 MPa. Results also indicated that the skeleton structure of interconnected fly ash cenosphere guaranteed a relatively high mechanical strength of this porous ceramics.

Effect of Activator on Properties of SiC Porous Ceramics

In this study, porous silicon carbide ceramics were prepared by using silicon carbide as the main material and sodium carboxymethyl cellulose (CMC) as the pore-forming agent. SiO2-Y2O3-Al2O3 and SiO2-kaolin were used as the builders respectively. This study is about the effect of SiO2-Y2O3-Al2O3 and SiO2-kaolin content on the structure and mechanical properties of porous silicon carbide. SiO2-Y2O3-Al2O3 and SiO2-kaolin affect the porosity, hardness and flexural strength of silicon carbide porous ceramics. In this experiment, the porosity of porous ceramics was measured by Archimedes method. The hardness was measured by Rockwell hardness tester. The flexural strength was measured by universal testing machine. The results show that the properties of silicon carbide porous ceramics prepared by SiO2-Y2O3-Al2O3 are better than that of SiO2-kaolinite when the SiO2 -Y2O3-Al2O3 content is 20%. With SiO2-Y2O3-Al2O3 as the combustion agent, porous ceramic with better performance can be prepared at 1500 ℃. When the SiO2-Y2O3-Al2O3 content is 20%, the prepared silicon carbide porous ceramics has a large porosity and excellent mechanical properties, the opening porosity of 23.73%, hardness and flexural strength of 62 and 15.47MPa, from the fracture can be seen more porous and evenly distributed.

High-temperature wettability and interactions between Hf-containing NbSi-based alloys and Y2O3 ceramics with various microstructures

To obtain improved mould shells with appropriate microstructures for directional solidification casting of NbSi-based alloys, Y2O3 ceramics with various microstructures were designed and characterized. The mechanisms of high-temperature wettability and interactions between NbSi-based alloys and Y2O3 ceramics were studied. The results showed that there was a characteristic transition in the wettability between the molten alloys and ceramics when the Y2O3 microstructure changed. The spreading rate gradually decreased and the apparent equilibrium contact angle changed from 70.2° to 112.6° with the level of open porosity of Y2O3 ceramics increasing from 3.6% to 27.2%. Wetting kinetics analyses indicated that the movement of the triple line during the wetting process was driven by the formation of continuous HfO2 reaction layer in the alloy-ceramic interface. The content of HfO2 particles inner the alloy matrix with the level of open porosity of Y2O3 ceramics increasing from 3.6% to 27.2% initially gradually decreased and subsequently increased. Y2O3 with open porosity level of about 20.7% were the most beneficial for directional solidification casting of high-purity Hf-containing NbSi-based alloys.

Effect of raw materials pretreated by physical grinding method on the sintering ability and microwave dielectric properties of Li2MgTiO4 ceramics

Li2MgTiO4-1 (abbreviated as LMT-1) ceramics were synthesized via the solid state reaction method using the pretreated raw materials. The unpretreated raw materials were used in the preparation of Li2MgTiO4-2 (abbreviated as LMT-2) ceramics. The particle size of LMT-1 powders is smaller and more uniform than that of LMT-2 powders and the porosity of LMT-1 ceramics is lower than that of LMT-2 ceramics. The microwave dielectric properties of LMT-1 ceramics keep a relatively stable value at a wide sintering temperature range. The slight fluctuation of sintering temperature will lead to great changes in the microwave dielectric properties of LMT-2 ceramics. The pretreatment of raw materials enhances the sintering ability and broadens the sintering temperature range of the Li2MgTiO4 ceramics.

Effect of Sintering Atmosphere and Carbon Content on Properties of Porous Ceramic

The mullite bonded SiC porous ceramic products were prepared by pressing, molding, drying, pre sintering and sintering with alumina (Al2O3), silica (SiO2), carbon black(CB), silicon carbide (SiC), sodium carboxymethyl cellulose solution (CMC) as raw materials. The effects of sintering atmosphere and carbon black content on the flexural strength, porosity and microstructure of ceramics were investigated. The result shows that: The best sintering atmosphere of the mullite bonded SiC porous ceramic prepared is in coke bed condition; When the content of mullite is 20 % and the content of carbon black is 10 %, the flexural strength of the ceramic is 15 MPa, and the porosity is 42.6 %. At this time, the ceramic has the best performance.

MULTILAYER COMPOSITE PLASMA COATINGS ON SCREEN PROTECTION ELEMENTS BASED ON ZIRCONIUM DIOXIDE

The paper contains results of investigations pertaining to an influence of plasma jet parameters (current, spraying distance, consumption of plasma formation gas (nitrogen)), fractional composition of initial powder and degree of cooling with compressed air on anti-meteoric coating characteristics. Optimum modes (arc current 600 A; spray distance of 110 mm; consumption of plasma formation gas (nitrogen) – 50 l/min; fractional composition of zirconium dioxide powder <50 μm; compressed air consumption for cooling – 1 m3/min; p = 4 bar) make it possible to obtain anti-meteoric coatings based on zirconium dioxide with material utilization rate of 62 %, total ceramic layer porosity of 6 %. After exposure of compression plasma flows on a coating in the nitrogen atmosphere a cubic modification of zirconium oxide is considered as the main phase being present in the coating. The lattice parameter of cubic zirconium oxide modification is equal to 0.5174 nm. Taking into consideration usage of nitrogen as plasma formation substance its interaction with zirconium coating atoms occurs and zirconium nitride (ZrN) is formed with a cubic crystal lattice (lattice parameter 0.4580 nm). Melting of pre-surface layer takes place and a depth of the melted layer is about 8 μm according to the results of a scanning electron microscopy. Pre-surface layer being crystallized after exposure to compression plasma flows is characterized by a homogeneous distribution of ele-ments and absence of pores formed in the process of coating formation. The coating structure is represented by a set of lar- ge (5–7 μm) and small (1–2 μm) zirconium oxide particles sintered against each other. Melting of coating surface layer and speed crystallization occur after the impact of compression plasma flows on the formed coating. Cracking of the surface layer arises due to origination of internal mechanical stresses in the crystallized part. While using a scanning electron microscopy a detailed analysis of the surface structure has permitted to reveal a formation of a cellular structure with an average cell size of less than 1 μm in the crystallized portion and formation of the cells can be caused by speed crystallization of the melted layer.

Fabrication of porous ceramics with double-pore structure by stepwise freeze casting using water/diphenyl methane emulsion

Porous alumina with double-pore structure was fabricated by stepwise freeze casting using water/diphenyl methane (DPM) emulsion as freezing medium. The effects of DPM content in the alumina slurry on the pore structure, mechanical properties, and specific surface area of porous ceramics were investigated. The porosity of porous ceramics was not significantly affected by DPM content in the alumina slurry due to their same solid contents. The lamellar pore size decreased, and the spherical pore size increased in porous alumina with increasing DPM content in the slurry. Closed spherical pores were formed in lamellar pore walls when the DPM content was 10vol%. The compressive strength slightly increased, and the specific surface area decreased in the samples with DPM compared with those in porous ceramics with pure water as freezing medium. The specific surface area of porous alumina was 0.566m2/g, and the interception rate for titan yellow was 44.16% when the DPM content reached 25vol% because the large spherical pore was connected to the outside. Hence, the fabricated porous alumina with DPM exhibited potential as adsorption and filtration materials.

Development of microstructural and voxel based models of deformation and failure of the porous ceramics for assessment of ballistic performance

Traditionally, ceramic materials are brittle and have various internal defects. Impact strength of ceramic tiles strongly depends of defects distribution and still not fully understood. In this work, the porosity of alumina ceramics was studied using fracture surface SEM analysis. Microstructural 3D-modeling of stochastic pores distribution in ceramics was completed for strength and elastic moduli estimation by FEA. The Weibull distribution parameters of strength were determined for different porosity values. A voxel model of ceramic disks with a porosity of 12.5% was proposed and investigated for the assessment of residual velocities after local impact by LS-DYNA software. This model was created taking the heterogeneity of the structure in consideration (1–9 groups of voxels), which allows for the modeling of real thin disc-shaped structure. The experimental and numerical results agreed quite well with ballistic tests. Proposed model of porous ceramics can be effectively used for the optimization of protective structures.

The effect of nano-copper additives on the porosity, mechanical properties, and microstructure of alumina ceramics using commercial rice husk ash as a pore former

The aim of the present research is to examine the effect of Cu metal addition in nano-scale particle size on the mechanical properties and porosity of porous alumina ceramics using commercial rice husk ash as pore forming agent and silica (SiO2) source. Porous alumina ceramics reinforced were prepared using nano-scale Cu metal particles as their strengthening phase. Solid-state and sacrificial techniques were used to prepare the porous alumina reinforced ceramics. A field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and transmission and electron microscope (TEM) were used to analyze the microstructure and ceramic phases. Different ratios of Cu metal were added (3, 6, 9, and 12 wt%) at different ratios of commercial rice husk ash. The results of this investigation show that with increasing ratios of Cu metal, the porosity decreased and the mechanical properties increased. The increase in the mechanical properties could be attributed to the decrease in the porosity, the toughening mechanism, increase density of porous alumina ceramics, and formation of the tenorite (CuO) phase due to sintering at high temperature (1600 °C). Some potential applications include purging of gas filtration and thermal insulation.

Influence of acid‐treated talc and Na2CO3 flux on mineralogical phase composition and porosity in steatite ceramics

AbstractThe work aimed with the effect of preceramic mixtures containing natural talc (Tc) or acid‐treated talc (Tc‐ac) supplemented by montmorillonite (Mt) or kaolinite (Ka), and the flux Na2CO3 on the mineral phase composition, porosity and pore size distribution in the steatite ceramics prepared using solid state sintering at 1300°C. The samples were analyzed using X‐ray diffraction and porometry techniques and scanning electron microscopy. Application of Mt or Ka in preceramic mixtures with provided comparable results. The acidification of talc using hydrochloric acid resulted in partial release of Mg2+ from the structure. The ratio of SiO2:MgO in Tc was 35:65 (wt%) and 70:30 (wt%) in Tc‐ac. Tc, clay minerals, and flux Na2CO3 in the MgO–Al2O3–SiO2–Na2O glass system resulted to the separation of forsterite and protoenstatite, while Tc‐ac provided crystallization of protoenstatite at the expense of clinoenstatite in highly porous ceramics. The preceramic mixtures were precursors of bimodal pore size distribution at prepared steatite ceramics.

Plasma dynamic synthesis of ultradispersed zinc oxide and sintering ceramics on its basis by SPS method

Zinc oxide is a well-known semiconductor material having good electrical, optical and catalytic properties. It can be used in different areas from cosmetics to drug delivery and biosensors. The synthesis of nanosized zinc oxide is an urgent task for obtaining ZnO-based ceramics with enhanced physical properties. This work shows the possibility to implement the plasma dynamic synthesis of zinc oxide in one short-term process (less than 1 ms) using an electrodischarge zinc-containing plasma jet, flowing into oxygen atmosphere. It allows synthesizing a mono-crystalline powder with particle size distribution from tens to hundred nanometers. The synthesized powdered product is investigated using by X-Ray diffractometry (XRD), scanning electron microscopy and high-resolution transmission electron microscopy. According to XRD, the obtained product consists of hexagonal zinc oxide with lattice parameters a = b = 3.24982 Å, c = 5.20661 Å that is clearly confirmed by microscopy data. This powder was used to produce a bulk ceramics sample on its basis by spark plasma sintering. The influence of sintering parameters on the structure of the resulting sample was studied. The optimal parameters were found which allows obtaining the more dense ceramics with a better microstructure. It was also found that the absence of exposure time after reaching the working temperature and pressure allows decreasing the porosity of ceramics.