Effects of various rare-earth additives on the sintering and transmittance of γ-AlON

Several rare earth elements (Sc, La, Pr, Sm, Gd, Dy, Er, and Yb) were evaluated to develop a sintering additive for transparent γ-AlON. After adding 0.2 wt. % of each of the rare earth additives to the α-Al₂O₃ and AlN starting material, hot pressing was performed at 1850 °C for 1 h under 20 MPa as a screening test, whereby the γ-AlON with Pr-nitrate showed the highest transmittance of 60.4 % at 632 nm. Two-step pressureless sintering was conducted as a separate test for the same starting material after adjusting the amount of Pr-nitrate to 0, 0.1, or 0.2 wt. % to enhance transmittance. The γ-AlON with 0.1 wt. % Pr-nitrate showed the highest transmittance of 80.36 % after 1st and 2nd sintering steps at 1610 and 1940 °C, respectively, indicating that Pr can be an alternative sintering additive to conventional Y₂O₃, MgO, and La₂O₃ for the fabrication of transparent γ-AlON.     

Effects of Ca-, Mg- and Si-doping on microstructures of alumina–zirconia composites

The aim of this work was to obtain zirconia toughened alumina composites with different microstructures, using a simple process (powder mixing and natural sintering). Adjusting the amount of zirconia directly controls the size and localization of zirconia grains and the size of the alumina grains. Doping the composite with CaO, MgO and SiO₂ allows further control of the microstructures. The influence of the thermal treatments is also investigated. The composites exhibit different structures (nano/nano-, micro/nano- and micro-composites) with zirconia and alumina grains as small as 100 and 200 nm, respectively, and with the proportion of intragranular zirconia grains varying between 0% and 90%. Zirconia plays a major role on grain size distributions as compared to CaO and MgO, whose role is almost negligible. The use of SiO₂ leads to micro/nano composites with intragranular zirconia particles. The influence of these different additions is related to adjustments of the grain boundaries mobility.     

Effects of washing and calcination–milling on ionic release and surface properties of yttria stabilized zirconia

Crystallographic features, physical properties and ionic release from yttria stabilized zirconia (YSZ) in suspension were studied by means of XRD, TEM, light-scattering particle size, BET, ICP and zeta potential analysis. It was found that Zr, Y, Na, and to a lesser extent Ca, Hf and Pd leach from 8 mol% YSZ powder. The impurities present increase the zeta potential of suspensions made from as-received YSZ. A trace amount of tetragonal phase observed in 8 mol% YSZ persists following washing and calcination–milling. Dislocations and crystallographic defects together with fractured crystals which form during milling of the calcined powder should lead to the formation of more broken bonds; as a result the surface of the particles can support higher surface charge density. Washing and calcination–milling lead to a shift of the isoelectric point of 8 mol% YSZ from pH 8.4 to pH 6.3 and 6.8, respectively. Due to higher chemical stability and previously shown positive impacts on microstructure and performance of fuel cells, use of calcined YSZ can be more advantageous than as received powder.     

Effects of Z-value on physicochemical and biological properties of β-SiAlONs ceramics

This study evaluated the effects of different Z-values on the physical, chemical, and biological properties of β-SiAlON ceramics. Increasing the Z-value of the β-Si₃N₄ solid solution's main phase resulted in the replacement of Si–N bonds with Al–O bonds. The number of columnar crystals decreased, bulk density increased, and porosity decreased, thus transforming the fine-particle microstructure of β-Si₃N₄ into the columnar structure of β-SiAlON. The compressive strength increased, which facilitated sintering at 1500 °C without sintering auxiliaries. H⁺ and OH⁻ ions in deionized water broke the covalent bonds on the β-SiAlON surface, thereby forming new Si–OH, Al–OH, and N–H bonds on the β-SiAlON surface and producing SiO₄⁴⁻, AlO₂⁻, and NH₄⁺ groups in the solution. Increasing the soaking time changed the compositions of ionized H⁺ and OH⁻ ions, thus increasing the pH. MC3T3-E1 cells were cultured on the β-SiAlON surface, and it was observed that the increase in the Z-value of β-SiAlON had no influence on cell adhesion and spreading, but it may slightly suppress cell proliferation at high Z-values. At low Z-values, the low AlO₂⁻ concentration helps promote osteogenic differentiation and mineralized nodule formation. Thus, β-SiAlON ceramics possess excellent physical, chemical, and biological properties and are considered excellent bone-repairing materials.     

Effect of zirconia content on mechanical and thermal properties of mullite–zirconia composite

Abstract

Mullite–zirconia composites were prepared by adding various zirconia contents in the mullite ranging from 0 to 30 wt-% and sintering at 1400–1600°C for 2 h. The phase composition examined by X-ray diffraction showed that mullite was the major phase combined with developed t-ZrO₂ and m-ZrO₂ phase as a function of zirconia content, especially at 1600°C, wherein m-ZrO₂ predominated. Density increased when the zirconia content and sintering temperature were increased ranging from 2·2 to 3·53 g cm^?3. The morphology of mullite grain showed elongated grains, whereas dispersed zirconia showed equiaxed and intergranular grains. Flexural strength was continuously improved by adding zirconia during the sintering temperature ranging from 1400 to 1500°C, whereas flexural strength was initially improved up to 5 wt-% of zirconia addition and deteriorated with more than 5 wt-% of zirconia content during sintering between 1550 and 1600°C. The maximum strength, 190 MPa, was obtained when sintering mullite with 30 wt-% of zirconia content at 1500°C. The degradation of strength at high sintering temperature may be a result from more occurrence of m-ZrO₂ phase. Thermal expansion of sintered specimens indicated linear change and hysteresis loop change. The hysteresis loop obtained with increased zirconia content resulted in the t–m phase transformation. Martensitic start temperature M_s was determined to be 530°C for 15 wt-% zirconia sintered at 1500°C, implying that the t–m phase transformation occurred.     

Novel method for the synthesis of a β-tricalcium phosphate coating on a zirconia implant

A novel method for the synthesis of a thin β-tricalcium phosphate (β-TCP) coating on zirconia implants has been developed. The synthesis procedure involves two steps: (i) rapid wet-chemical deposition of a biomimetic CaP coating and (ii) subsequent post-deposition processing of the biomimetic CaP coating, which includes a heat treatment at 900 °C followed by a short sonication in a water bath. The obtained β-TCP coating showed a uniform and dense morphology with a thickness of ≈500 nm and displayed a roughness in the nanometre range (R_a = 28 nm). The β-TCP coating demonstrated an apatite-mineralization ability in a simulated body fluid and enhanced the adsorption of serum proteins on the zirconia. Moreover, the β-TCP coating adhered firmly to the zirconia substrate, developing a notable scratch resistance (L_c = 97 N) and tensile strength (52 MPa) and showed strong resistance towards mechanical forces present during implantation of the coated zirconia implant into the artificial bone.     

Effects of different additives on properties of magnesium aluminate Spinel–Periclase castable

Bauxite- and alumina-based spinels were employed as refractory aggregates, and sintered magnesia fine powder, calcium aluminate cement, microsilica, and activated α-Al₂O₃ were utilized as matrices. The effects of alumina powder, analytically pure zinc oxide, and analytically pure zirconia on the properties of magnesium aluminate spinel–periclase castables were studied. The results demonstrated that the addition of the three additives promoted the sintering of magnesium aluminate spinel–periclase castables. Simultaneously, the three additives significantly improved the high-temperature properties of the samples. The thermal shock resistance of the alumina powder sample increased by 200%, that of the pristine zinc oxide sample by 75%, and that of the zirconia sample by 125%. The additives effectively improved the thermal shock resistance of the magnesium aluminate spinel–periclase castable. In addition, the slag resistance depths of the samples with alumina powder and zirconia were 41% lower than that of the sample without additives, which significantly improved the slag resistance of the magnesium aluminate spinel–periclase castable.     

ZrSi2–MgO as novel additives for high thermal conductivity of β-Si3N4 ceramics

A novel ZrSi₂–MgO system was used as sintering additive for fabricating high thermal conductivity silicon nitride ceramics by gas pressure sintering at 1900°C for 12 hours. By keeping the total amount of additives at 7 mol% and adjusting the amount of ZrSi₂ in the range of 0-7 mol%, the effect of ZrSi₂ addition on sintering behaviors and thermal conductivity of silicon nitride were investigated. It was found that binary additives ZrSi₂–MgO were effective for the densification of Si₃N₄ ceramics. XRD observations demonstrated that ZrSi₂ reacted with native silica on the Si₃N₄ surface to generate ZrO₂ and β-Si₃N₄ grains. TEM and in situ dilatometry confirmed that the as formed ZrO₂ collaborated with MgO and Si₃N₄ to form Si–Zr–Mg–O–N liquid phase promoting the densification of Si₃N₄. Abnormal grain growth was promoted by in situ generated β-Si₃N₄ grains. Consequently, compared to ZrO₂-doped materials, the addition of ZrSi₂ led to enlarged grains, extremely thin grain boundary film and high contiguity of Si₃N₄–Si₃N₄ grains. Ultimately, the thermal conductivity increased by 34.6% from 84.58 to 113.91 W·(m·K)⁻¹ when ZrO₂ was substituted by ZrSi₂.     

Effects of Mn-doping on the structure and in vitro degradation of β-tricalcium phosphate

β-tricalcium phosphate (β-TCP) is an ideal biomaterial for the bone repair because of its biocompatibility and biodegradability. In this study, 0 mol%, 5 mol%, 15 mol% and 30%mol bivalent manganese ion (Mn²⁺) doped β-TCP (Mn-TCP) powders were synthesized by a sol-gel method. The amount of the dopants significantly influences the crystallinity and the parameters related with structure of β-TCP, such as the lattice parameters and crystallite dimensions. The particle size and the particle distribution of doped β-TCP powers were evaluated as well. Meanwhile, the as-synthesized powders were consolidated by sintering at 1000 °C in muffle furnace for 5 h to get Mn-TCP porous material and the degradation experiment was carried out in Simulated Body Fluid (SBF) solution for 28 days. Then, Mn-TCP porous material were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). Significantly, there were bone-like apatite materials deposited on the surface of bone-like porous materials. With the increasing doping amount of Mn²⁺, the newly formed apatite-like materials decreased, while the crystallinity increased significantly. Besides, pH results showed that alkaline environment was more favorable for the formation of sedimentary materials.     

Effects of Phosphatidylcholine on Interaction of α-Tocopherol and β-Carotene in Photosensitized Oxidation of Emulsions

The interaction between α‐tocopherol (500 mg/kg) and β‐carotene (10 mg/kg) during chlorophyll‐photosensitized oxidation of a sunflower oil emulsion was studied in the presence or absence of phosphatidylcholine (PC, 250 mg/kg) by determining peroxide (POV) and conjugated dienoic acid (CDA) values. Chlorophyll, α‐tocopherol, β‐carotene, and PC contents in the emulsion were also monitored. α‐Tocopherol and β‐carotene individually and interactively decreased the POV and CDA values of oil in the emulsion by singlet oxygen quenching. PC decreased the POV and CDA values of oil, however, the values of the emulsion with added α‐tocopherol, β‐carotene, and PC were not significantly different from those of the emulsion with added α‐tocopherol and β‐carotene without PC. Contents of α‐tocopherol did not change during 24‐h oxidation, whereas co‐present PC significantly caused α‐tocopherol and chlorophyll degradation. β‐Carotene and PC contents significantly decreased to 45.5 and 51.3 %, respectively, after 24 h, and α‐tocopherol protected β‐carotene from degradation. The results suggest that PC had no net effects on the interactive antioxidant activity of α‐tocopherol and β‐carotene during chlorophyll‐photosensitized oxidation of the emulsion through free radical generation, chlorophyll degradation, and lessening the potency of α‐tocopherol as a singlet oxygen quencher.     

Synthesis and characterisation of β-TCP/bioglass/zirconia scaffolds

Tricalcium phosphate scaffolds reinforced with bioglass were characterised morphologically, physically, and mechanically. The scaffolds were fabricated through powder technology and the polymer foaming technique using 80?wt-% of β-TCP and 20?wt-% of phosphate-based bioglass doped with zirconia in various amounts (0, 0.25, 0.5, 0.75, and 1.0?wt-%). The foaming agent was varied (1, 1.5, 2, 2.5, and 3?wt-%) to determine the optimal amount that ensured an interconnected porosity and pore size suitable for increasing osteoconduction and cell attachment. Promising samples for tissue engineering applications showed a pore size ranging from 1.41 to 303?μm, total porosity of 50–53%, compressive strength values between 0.6 and 1?MPa, Young’s modulus from 357 to 574?MPa, and excellent interconnectivity.     

Effects of β-cyclodextrin side chains on the dispersing and retarding properties of polycarboxylate superplasticizers

A modified polycarboxylate (MPC) superplasticizer was synthesized by the copolymerization of acrylic acid, methallyl sulfonic acid, allyl poly(ethylene glycol)s, and β-cyclodextrin (β-CD) grafted maleic anhydride. The molecular structure of the MPC was characterized by Fourier transform infrared spectroscopy and gel permeation chromatography. The effects of the content of β-CD on the application performance of MPC were investigated with measurements of the cement paste fluidity, setting time, amount of adsorption of MPC on the cement particles, and ζ potentials of the cement particles and differential scanning calorimetry–thermogravimetric analysis of different hydration ages of the cement pastes. The results indicate that the initial fluidities and setting times of the cement pastes increased with increasing number of β-CD side chains. The dispersion capacity of MPC on the cement particles mainly came from a steric hindrance effect and an air-entraining effect of the β-CD side chains. The better retarding performance of MPC was attributed to the solvation water film formed by the polyoxyethylene side chains and chelates formed by  OH groups on the β-CD structure combined with Ca²⁺ ions on the surface of the cement particles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of the γ-irradiation strength and basalt additive content on the mechanical performance and dielectric response of polypropylene films

In this study, we investigated the effects of high-dose γ-ray irradiation on the mechanical and dielectric properties of polypropylene (PP)–basalt thick films. PP–basalt thick-film composites with various basalt contents from 0.5 to 10.0% were prepared by a hot-press method. The samples were exposed to γ radiation at different doses in the range 3–25 kGy. The mechanical properties of the samples, such as the Young's modulus, tensile strength, percentage strain at break, and energy at break, were examined in the context of the γ-irradiation process. Although the maximum elasticity was obtained for the unirradiated 0.5% basalt-added composite, the 6 kGy γ-irradiated PP–1.0% basalt sample exhibited the highest elasticity properties among all of the composites. The best mechanical properties, including the ultimate tensile strength and energy at break values, were achieved for the 12 kGy γ-irradiated neat PP. The dielectric properties of the PP–basalt composites were also investigated in the 100 Hz to 15 MHz frequency region at room temperature. According to the analysis of the dielectric properties, the 3 kGy γ-irradiated neat PP may have potential for microelectronic device applications that require low dielectric constant and dielectric loss materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47414.     

β-TCP coatings on zirconia bioceramics: The importance of heating temperature on the bond strength and the substrate/coating interface

β-tricalcium phosphate (β-TCP) coatings were synthesized on tetragonal zirconia (Y-TZP) discs by heating the apatite coating between 800?°C and 1200?°C. The study results suggest that heating temperature has a strong influence on the coating bond strength and microstructure of the substrate/coating interface. The β-TCP coatings fired at 800?°C and 900?°C exhibited excellent tensile bond strength (～50?MPa) while heating at 1100?°C and 1200?°C led to decreased bond strength (～30?MPa) as the result of substantial structural and microstructural changes: diffusion of Y³⁺ from the zirconia substrate in the coating resulting in partial crystal transformation (t-m) of zirconia, formation of surface uplifts and nanoporosity in zirconia, as well as generation of large residual thermal stresses leading to microcracking of the β-TCP coatings. However, these structural changes did not have any measurable effect on the flexural strength of the bulk zirconia substrates.     

Effects of formaldehyde solution and nanoparticles on mechanical properties and biodegradation of gelatin/nano β-TCP scaffolds

In this study, gelatin/beta tricalcium phosphate (β-TCP) nanocomposite scaffolds were prepared by solvent casting method. The cross-linking method was carried out by adding formaldehyde to gelatin. The microparticles of sodium chloride were used as porogen agent. Characterization of nano β-TCP was performed using XRD, FTIR, and SEM. Results showed that the size of the particles is about 100 nm with spherical morphology. In addition, the scaffold characterization was carried out using FTIR and SEM techniques. Observations showed a porous texture with pore size between 100 and 400 μm. The biodegradability and bioactivity evaluations of the scaffolds were done by immersing them in a simulated body fluid solution for different time periods. The biodegradability studies demonstrated a reduction in the degradation rate of gelatin/β-TCP nanocomposite scaffolds due to the presence of β-TCP nanoparticles. The obtained results of bioactivity tests confirmed the formation of apatite layer on the surface of the scaffolds. Furthermore, the effects of porosity, cross-linking agent, and β-TCP nanoparticles on the bending and compressive properties of the composite scaffolds were examined. According to the mechanical examinations of the scaffolds, the best bending and compressive properties occurred in the presence of 10 and 20 wt% of β-TCP nanoparticles, respectively. The appropriate mechanical properties and biodegradation rate for tissue engineering applications obtained at 1 g of the formaldehyde solution.     

Optimization of SiC–ZrC high emissivity composite flexible coating for thermal protection with high interfacial bond strength and temperature resistance

Aluminum silicate fiber fabric (ASFF) has been widely used in the outer surface of flexible insulation felt on the leeward side of aerospace vehicle. In order to improve the temperature resistance of ASFF, a kind of SiC–ZrC composite coating was prepared on the surface of fiber fabric via spraying method with SiC as emittance agent and ZrC as additive. The surface morphology and mechanical properties of the coating were studied. Compared with the single-component SiC coating, the composite coating could effectively avoid coating spalling and improve the surface integrity at high temperature. After thermal treatment at 1100 °C for 2 h, the interface bond strength of the composite coating/substrate was 52.41% higher than that of SiC coating/substrate. The tensile strength of fiber fabric with SiC–ZrC composite coating could reach 91.75 MPa, which was 101.76% higher than that of raw ASFF. Therefore, the SiC–ZrC coating could greatly improve the temperature resistance of ASFF, and has an attractive application prospect in the field of thermal protection system.     

Effects of β-carotene and lycopene thermal degradation products on the oxidative stability of soybean oil

The relative oxidative stability of soybean oil samples containing either thermally degraded β-carotene or lycopene was determined by measuring peroxide value (PV) and headspace oxygen depletion (HOD) every 4 h for 24 h. Sobyean oil samples containing 50 ppm degraded β-carotene that were stored in the dark at 60°C displayed significantly (P<0.01) higher HOD values compared with controls. Lycopene degradation products (50 ppm) in soybean oil significantly (P<0.05) decreased HOD of samples when stored in the dark. PV and HOD values for samples containing 50 ppm of either β-carotene or lycopene degradation products stored under lighted conditions did not differ significantly from controls (P<0.05). However, soybean oil samples containing 50 ppm of unheated, all-trans β-carotene or lycopene stored under light showed significantly lower PV and HOD values than controls (P<0.01). These results indicated that during autoxidation of soybean oil held in the dark, β-carotene thermal degradation products acted as a prooxidant, while thermally degraded lycopene displayed antioxidant activity in similar soybean oil systems. In addition, β-carotene and lycopene degradation products exposed to singlet oxygen oxidation under light did not increase or decrease the oxidative stability of their respective soybean oil samples.     

Effects of carbon additives on the properties of ZrB2–based composites: A review

This review presents the recent achievements on carbon additives incorporated in ZrB₂ ceramics, improved properties, and their advancements. Monolithic ZrB₂ ceramics have broad potential applications, but their critical drawbacks such as poor damage tolerance, and weak oxidation and ablation resistance confines their applicability. It is an important issue to resolve these shortages in physiochemical properties by engineering the composite ingredients and process design of the ceramic counterparts for an extensive production and applications, which are especially essential in high–tech industries and products. Carbon additives have exceptional characteristics including low density, low cost, and excellent thermo–mechanical stability. These materials have been incorporated in ZrB₂ ceramics to enhance their efficiency and form practical composite ceramics. Although addition of the secondary carbonaceous phases is generally supposed to improve the mechanical properties of ZrB₂ composites, it may also result in a decrease in other aspects of performance, comparing with monolithic ZrB₂ ceramics. In this work, we reviewed the methods and strategies for the preparation of carbon modulated ZrB₂ ceramic composites. Moreover, the advantages, disadvantages, and the productivity of the introduced composite ceramics have been explored and featured.     

Influence of sulfation and structure of zirconia on catalytic isomerization of n‐hexane

Two series of sulfated zirconia have been prepared by immersing amorphous or crystalline zirconia in an H₂SO₄ solution (0.25–2.5 M). They were compared with a commercial sulfated zirconium hydroxide. Activation temperature was varied between 300 and 725°C. Sulfate density varied so that the mean surface area of an individual sulfate ranged from 0.14 to 0.54 nm². Three limiting sulfate states are evidenced and characterized by TPRMS. Catalysts are tested for isomerization of nhexane at 150°C and 3 MPa. Factors influencing the activity are discussed. The data show that a highly active and selective catalyst for producing hexane isomers requires tetragonal zirconia with a sulfate occupancy of about 0.40 nm². Preparation parameters must therefore be adapted to match these constraints.