Effect of Pb excess in sol–gel process on phase composition in PFN ceramics

Lead iron niobate Pb(Fe_0.5Nb_0.5)O₃ (PFN) precursors were prepared using sol–gel synthesis by mixing acetates Pb and Fe with Nb-ethylene glycol–tartarate (Pechini) complex at 80 °C and calcination of gels at 600 °C. Single pyrochlore phase with structure close to Pb₃Nb₄O₁₃ was formed in stoichiometric precursor and Pb₃Nb₄O₁₃ with small amount of perovskite phase Pb(Fe_0.5Nb_0.5)O₃ in nonstoichiometric precursor prepared with the excess of Pb in molar ratio (Pb:Fe:Nb = 1.2:0.5:0.5). Average particle sizes of PFN calcined powders were ～120 nm. The metastable pyrochlore phase was partially decomposed to perovskite phase at sintering temperature of 1150 °C for 2, 4 and 6 h. Excess of Pb caused increasing of the density (7.4 g/cm³) and content of the perovskite phase (～53 vol.%) in ceramics sintered for 4 h. In microstructures of PFN ceramics sintered at 1150 °C for different times, the bimodal grain size distribution was observed with small spherical grains of perovskite phase and larger octahedral grains, which represent the pyrochlore phase. Results of EDX analysis confirm that complex types of pyrochlore phases that differ in iron content were present in ceramics.     

Effects of Li2CO3 and Sm2O3 additives on low-temperature sintering and piezoelectric properties of PZN-PZT ceramics

To assist the development of applications for multilayer piezoelectric devices, the low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ with Li₂CO₃ and Sm₂O₃ additives were fabricated by a conventional solid-state reaction, and their structural and piezoelectric properties were studied. With the addition of Li₂CO₃, the minimum sintering temperature of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramics was reduced from 1125 °C to 950 °C through the formation of a liquid phase and its piezoelectric properties showed almost no degradation. When the sintering temperature was below 950 °C, however, the piezoelectric properties degraded obviously. The additional Sm₂O₃ resulted in a significant improvement in the piezoelectric properties of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ ceramic with added Li₂CO₃. When sintered at 900 °C, the optimized properties of the 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramic with 0.3 wt% Li₂CO₃ and 0.3 wt% Sm₂O₃ were obtained as d₃₃ = 483 pC/N, k₃₁ = 0.376, Q_m = 73, ɛ_r = 2524, tan δ = 0.0178.     

In situ synchrotron X-ray powder diffraction study of the early age hydration of cements blended with zeolitite and quartzite fines and water-reducing agent

A comparison was made between the early-age hydration of cements blended with micronized zeolitite and quartzite powders. The Portland cement replacement in the mixes was 30%, and the effect of introducing a superplasticiser to lower the required water to solid ratio was assessed. The cement pastes were hydrated at 40 °C and monitored in situ by time-resolved synchrotron X-ray powder diffraction combined with Rietveld quantitative phase analysis.The quantitative evolution of phase weight fractions showed that the addition of the zeolite tuff accelerated the hydration rate of the main C₃S cement component. Blending with the quartzite powder of similar fineness did not affect the C₃S hydration rate. Reduction of the water to solid ratio by introduction of the superplasticiser had a retarding effect on the hydration of the zeolitite-blended cement over the early hydration period up to 3 days.The AFt or ettringite reaction products, formed promptly after the addition of water to the mixtures, underwent a crystal structural modification over the induction period up to 4 to 6 hours of reaction. The continuous contraction of the c-cell parameter and expansion of the a-cell parameter towards the ideal values for AFt or ettringite reflects the structural adaptation of the AFt to the changing availability of sulphate over the course of the first hours of hydration. The observed structural changes were less pronounced in the zeolitite blended cement. This is related to the dilution of the overall sulphate content in the blended cement and highlights the need to control and optimise sulphate additions in blended cements.     

Effect of MgAl2O4 nanoparticles addition on the densification and properties of MgO-CaO refractories

MgAl₂O₄nanoparticles were added to MgO–CaO refractory ceramic composites in the range of 0–8 wt%. Refractory specimens were obtained by sintering at 1650 °C for 3 h in an electric furnace. Refractory specimens were characterized by measurements of bulk density, apparent porosity, hydration resistance, cold crushing strength, crystalline phase formation, and microstructural analysis. Results show that with additions of MgAl₂O₄ nanoparticles the bulk density of the samples increased. But the apparent porosity and cold crushing strength decreased and increased, respectively with addition MgAl₂O₄ nanoparticles up to 6 wt% and for further MgAl₂O₄ nanoparticles, due to the thermal expansion mismatch, the results is reversed. Also, the hydration resistance of the samples was appreciably improved by the addition of MgAl₂O₄ nanoparticles due to its effect on decreasing the amount of free CaO in the refractory composite and promotion of densification by creating a dense microstructure.     

Effects of WO3 on the microstructure and optical transmittance of PLZT ferroelectric ceramics

The influence of the WO₃ addition as sintering aids on the structural, microstructural and optical properties of (Pb,La)(Zr,Ti)O₃—PLZT based ceramics was investigated. Ferroelectric (Pb_0.9La_0.1)(Zr_0.65Ti_0.35)_0.975O₃ + x wt% WO₃ (x = 0.0, 0.5, 1.5 and 2.0) ceramics were densified by oxygen assisted uniaxial hot pressing. From the XRD results it was found that the hot pressed samples displayed single pseudocubic perovskite phase. EDS analysis evidenced the presence of WO₃ rich phase at the grain boundaries. An inhibition of grain growth and an evolution from transgranular to intergranular fracture behavior was observed, as a consequence of the formation of a PbO–WO₃ liquid phase, as the amount of WO₃ addition was increased. The optical transmittance in the visible and infrared range was decreased due to the presence of the liquid phase in grain boundaries, for WO₃ content lower than 2.0 wt%.     

Improved thermoelectric performances in textured Bi1.6Pb0.4Ba2Co2Oy/Ag composites

Bi_1.6Pb_0.4Ba₂Co₂O_y thermoelectric ceramics with small Ag additions (0, 1, 3, and 5 wt%) have been textured using the laser floating zone method. Microstructure has shown a slight decrease on the secondary phases content and a better grain alignment in Ag added samples. These microstructural features are reflected in the thermoelectric properties, which have shown a significant decrease of electrical resistivity, when the Ag content is raised. In spite of a corresponding decrease of Seebeck coefficient, all the Ag-containing samples possess higher Power Factor values than the Bi_1.6Pb_0.4Ba₂Co₂O_y ones. Moreover, the maximum Power Factor values (about 0.36 mW/K².m at 650 °C) have been measured in Bi_1.6Pb_0.4Ba₂Co₂O_y+3 wt% Ag samples, which are the best results reported in this family of materials.     

Improvement of textured Bi1.6Pb0.4Sr2Co1.8Ox thermoelectric performances by metallic Ag additions

Bi_1.6Pb_0.4Sr₂Co_1.8O_x thermoelectric ceramics with small Ag additions (0, 1, and 3 wt%) have been successfully grown from the melt, using the laser floating zone method. Microstructure has shown a reduction in the amount of secondary phases and a better grain alignment with respect to the growth direction for an Ag content of 3 wt%. The microstructural evolution, as a function of Ag content, is confirmed with the electrical resistivity values, which show an important decrease for the 3 wt% Ag samples, leading to maximum power factor values of about 0.42 mW/K² m at 650 °C, which are among the best results obtained in this type of material.     

Effects of Bi2O3–Li2CO3 additions on dielectric and pyroelectric properties of Mn doped Pb(Zr0.9Ti0.1)O3 thick films

Pb(Zr_0.9Ti_0.1)O₃ pyroelectric thick films adding various amounts of the sintering aids Bi₂O₃–Li₂CO₃ have been deposited on the substrates Al₂O₃ by the screen-printing process, and the dependence of microstructure, dielectric and pyroelectric properties on the content of sintering aids has been studied. When the amount of Bi₂O₃–Li₂CO₃ increases from 0 wt% to 5.4 wt%, the sintering temperature of the thick films decreases from 1100 °C to 900 °C, and the grain size and the lattice constant decrease either, but the density and the dielectric constant increase. The Pb(Zr_0.9Ti_0.1)O₃ thick film with 5.4 wt% of Bi₂O₃–Li₂CO₃ sintered at 900 °C has the maximum pyroelectric coefficient 10.51×10^?8 C/cm^?2 K^?1 and the highest figure-of-merit 10.58×10^?5 Pa^?0.5.     

Tribological behavior of Ti3SiC2 and Ti3SiC2/Pb composites sliding against Ni-based alloys at elevated temperatures

The Ti₃SiC₂ and Ti₃SiC₂/Pb composites were tested under dry sliding conditions against Ni-based alloys (Inconel 718) at elevated temperatures up to 800 °C using a pin-on-disk tribometer. Detailed tribo-chemical changes of Pb on sliding surface were discussed. It was found that the tribological behavior were insensitive to the temperature from 25 °C (RT) to 600 °C (friction coefficient ≈0.61–0.72, wear rate ≈10⁻³ mm³ N m⁻¹). An amount of Pb in the composites played a key role in lubricating with the temperature below 800 °C. The friction coefficient (≈0.22) and wear rate (≈10⁻⁷ mm³ N m⁻¹) at elevated temperatures were both decreased by the added PbO. The wear mechanisms of Ti₃SiC₂/Pb-Inconel 718 tribo-pair at elevated temperatures were believed to be the combined effect of abrasive wear and tribo-oxidation wear. During the sliding, two oxidization reactions proceed, 2Pb+O₂=2PbO (below 600 °C) and 6PbO+O₂=2Pb₃O₄ (800 °C). The friction coefficient and wear rate of the composites were reduced due to the self-lubricating effect of the tribo-oxidation products.     

Piezoelectric properties of highly densified 0.01Pb (Mg1/2W1/2)O3–0.41Pb (Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3+0.1 wt% Y2O3+1.5 wt% ZnO thick films on alumina substrate

This paper reports on the formation of highly densified piezoelectric thick films of 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃+0.1 wt% Y₂O₃+1.5 wt% ZnO (PMW–PNN–PT–PZ+YZ) on alumina substrate by the screen-printing method. To increase the packing density of powder in screen-printing paste, attrition milled nano-scale powder was mixed with ball milled micro-scale powder, while the particle size distribution was properly controlled. Furthermore, the cold isostatic pressing process was used to improve the green density of the piezoelectric thick films. As a result of these processes, the PMW–PNN–PT–PZ+YZ thick film, sintered at 890 °C for 2 h, showed enhanced piezoelectric properties such as P_r=42 μC/cm², E_c=25 kV/cm, and d₃₃=100 pC/N, in comparison with other reports. Such prominent piezoelectric properties of PMW–PNN–PT–PZ+YZ thick films using bi-modal particle distribution and the CIP process can be applied to functional thick films in MEMS applications such as micro actuators and sensors.     

Low temperature sintering of PZT powders coated with Pb5Ge3O11 by sol–Gel method

Low temperature sintering of PZT powders was investigated using Pb₅Ge₃O₁₁(PGO) as a sintering aid. PZT powders with 150 nm particle size were coated with PGO which was prepared from precursor solutions of Ge(OiPr)₄ and Pb(NO₃)₂ by sol–gel method. 1 wt% PGO-added PZT powders were densified at 750°C for 2 h to sintered bodies with the relative density of approximately 95%. An addition of PGO improved the sinterability of PZT powders with a reduction of sintering temperature by about 300°C. Dielectric and piezoelectric properties of PGO-added PZT ceramics sintered at ≦950°C were superior to those without PGO additives. However, a higher sintering temperature above 1000°C deteriorated the dielectric and piezoelectric properties of PGO-added PZT ceramics. This may be attributed to the change of microstructure involving the formation of solid solution between PZT and PGO. The 1 wt% PGO-added PZT bodies sintered at 750°C exhibited an electromechanical coupling factor, Kp, of about 56%.     

High-power properties of piezoelectric hard materials sintered at low temperature for multilayer ceramic actuators

0.05Pb(Mn_1/3Sb_2/3)O₃–0.05Pb(Al_1/2Nb_1/2)O₃–0.9Pb(Zr_0.48Ti_0.52)O₃ (PMS–PAN–PZT) high power piezoelectric system with both La₂O₃ as a hardener and CuO as a low sintering agent had been synthesized at 900 °C for 2 h. When La₂O₃ doping of the main composition went over 0.5 wt%, the mixed tetragonal and rhombohedral perovskite structure changed to pure rhombohedral perovskite structure. In case of the CuO, 1.0 and 1.5 wt% CuO content significantly improved the sinterability of the PMS–PAN–PZT system processed at 900 °C for 2 h. When La₂O₃ and CuO co-doped in PMS–PAN–PZT ceramics, piezoelectric constants (d₃₃), quality factor (Q_m), electromechanical coupling factor (k_p) and dielectric constant (${\epsilon }_3^{\text{T}}/{\epsilon }_0$) of the piezoelectric ceramics sintered at 900 °C for 2 h were optimized, such as 336 pC/N, 841, 60%, and 1358, respectively. New developed piezoelectric materials are promising for high power multilayer ceramic actuators.     

The effect of La2O3 on the microstructure and room temperature mechanical properties of t-ZrO2

Structural and mechanical properties of La₂O₃ added (up to 5 wt%) t-ZrO₂ compacts were examined with the aim of optimizing hardness and fracture toughness for room temperature applications. Structural examinations were performed using an X-ray diffractometer and a scanning electron microscope. Mechanical properties of the compacts were determined as modulus of elasticity, hardness and fracture toughness by conducting Vickers indentation tests under test loads of 0.5, 1 and 10 kg. Addition of 0.5 wt% La₂O₃ deteriorated the room temperature stability of t-ZrO₂ by forming m-ZrO₂ and coarse polygonal grains in the matrix. Higher concentrations (2 and 5 wt% La₂O₃) caused precipitation of La₂Zr₂O₇ at the grain boundaries, which also accompanied by a reduction in hardness. Fracture toughness increased with increasing La₂O₃ content of the compact. Finally, an optimum combination between hardness and fracture toughness was obtained for the 0.5 wt% La₂O₃ containing compact.     

Superparamagnetic zinc ferrite spinel–graphene nanostructures for fast wastewater purification

Superparamagnetic ZnFe₂O₄/reduced graphene oxide (rGO) composites containing ZnFe₂O₄ nanoparticles (with ∼5–20 nm sizes) attached onto rGO sheets (with ∼1 μm lateral dimensions) were synthesized by hydrothermal reaction method. By increasing the graphene content of the composite from 0 to 40 wt%, the size as well as the number of the ZnFe₂O₄ nanoparticles decreased and the saturated magnetization of the composites reduced from 10.2 to 1.8 emu/g, resulting in lower responses to external magnetic fields. Concerning this, the time needed for 90% separation of ZnFe₂O₄/rGO (40 wt%) composite from its solution (2 mg/mL in ethanol) was found 60 min in the presence of an external magnetic field (∼1 Tesla), while using ZnFe₂O₄/rGO (15 wt%), only 2 min was required (comparable to the separation time of pure ZnFe₂O₄ nanoparticles). Correspondingly, the magnetic separation time of 10 μM methyl orange and rhodamine B from aqueous solutions containing 2 mg/mL ZnFe₂O₄/rGO (15 wt%) was found <6 min, while using the ZnFe₂O₄/rGO (40 wt%) only 15–20% of the dyes could be separated after 16 min. Although the pure ZnFe₂O₄ nanoparticles could magnetically separate nearly whole of the dyes from the solutions, the separation time was too longer (>16 min).     

Effects of adding different morphological carbon nanomaterials on supercapacitive performance of sol–gel manganese oxide films

In this study, the supercapacitive performances of manganese oxide films were investigated by adding different carbon nanomaterials, including carbon nanocapsules (CNC), multiwalled carbon nanotubes (MWCNTs) and multi-layered graphene. The manganese oxide films were prepared with manganese acetate precursor by sol–gel method, and the post-treatment effects were also examined. With a heat-treatment above 300 °C, the as-prepared amorphous films transformed to a compound of Mn₃O₄ and Mn₂O₃ phases, and the smooth surface became rough as well. Cyclic voltammogram (CV) tests showed that the manganese oxide film, which was mixed with 0.05 wt% MWCNTs and annealed at 350 °C for 1 h, exhibited the optimized specific capacitance, 339.1 F/g. During 1000CV cycles, the specific capacitances of original manganese oxide film decreased gradually from 198.7 to 149.1 (75%) F/g. After same number of cycle tests, the modified films containing 0.025 wt% CNC, 0.05 wt% MWCNTs and 0.1 wt% graphene retained 201.8 (64.2%), 267.4 (78.9%) and 193.1 (57.4%) F/g respectively. The results indicates that the supercapacitive performance of manganese oxide films were significantly modified by carbon nanomaterials; in addition, the MWCNTs additive could also reduce the decay rate.     

Effects of glass additions on the microstructure and dielectric properties of barium strontium titanate (BST) ceramics

Commercial glass frits (lead borosilicate glasses) were employed as the sintering aids to reduce the sintering temperatures of BST ceramics. The effects of the glass content and the sintering temperature on the microstructures, dielectric properties and tunabilities of BST ceramics have been investigated. Densification of BST ceramics of 5 wt% glass content becomes significant from sintering temperature of 1000 °C. The glass content shows a strong influence on the Curie temperature T_c, permittivity and the diffuse transition. X-ray results show all BST ceramics exhibit a perovskite structure and also the formation of a secondary phase, Ba₂TiSi₂O₈. The shift of BST diffraction peaks towards higher angle with increasing the glass content indicates the substitution of Pb²⁺ in Ba²⁺ site, which mainly accounts for the diffuse transition observed in these BST ceramics. BST ceramics with 10 wt% glass additives possess the highest tunability at all four sintering temperatures. A tunability of 12.2% at a bias field of 1 kV/mm was achieved for BST ceramics with 10 wt% glass content sintered at 900 °C.     

Microwave dielectric properties of Pb2MoO5 ceramic with ultra-low sintering temperature

Ultra-low firing microwave dielectric ceramic Pb₂MoO₅ with monoclinic structure was prepared via a conventional solid state reaction method. The sintering temperature ranged from 530 °C to 650 °C. The relative densities of the ceramic samples were about 97% when the sintering temperature was greater than 570 °C. The best microwave dielectric properties were obtained in the ceramic sintered at 610 °C for 2 h with a permittivity ∼19.1, a Q × f value about 21,960 GHz (at 7.461 GHz) and a temperature coefficient value of −60 ppm/°C. From the X-ray diffraction, backscattered electron image results of the co-fired samples with 30 wt% silver and aluminum additive, the Pb₂MoO₅ ceramics were found not to react with Ag and Al at 610 °C for 4 h. The microwave dielectric properties and ultra-low sintering temperature of Pb₂MoO₅ ceramic make it a promising candidate for low temperature co-fired ceramic applications.     

In situ preparation of CoFe2O4–Pb(ZrTi)O3 multiferroic composites by gel-combustion technique

Diphase magnetoelectric composites of CoFe₂O₄–Pb(ZrTi)O₃ were prepared by citrate–nitrate combustion technique by using Pb(Zr,Ti)O₃ template powders obtained by the mixed oxide method. Pure diphase powder composites with a good crystallinity were obtained after calcination. The composition and purity were maintained after sintering at temperature of 1100 °C/2 h, which ensured limited reactions at interfaces, while by sintering at 1250 °C/2 h, some small amounts of secondary phases identified as nonstoichiometric ZrO_2?x resulted. The method allowed to produce diphase ceramics with homogeneous microstructures and a very good mixing of the two phases. The dielectric and magnetic investigation at room temperature confirmed the formation of composite ceramics with both dielectric and magnetic properties at room temperature, with permittivity and magnetization resulted as sum properties from the parent Pb(Zr,Ti)O₃ and ferrite phases.     

Formation of hollow MgO-rich spinel whiskers in low carbon MgO–C refractories with Al additives

MgO–C refractories with different carbon contents have been developed to meet the requirement of steel-making technologies. Actually, the carbon content in the refractories will affect their microstructure. In the present work, the phase compositions and microstructure of low carbon MgO–C refractories (1 wt% graphite) were investigated in comparison with those of 10 wt% and 20 wt% graphite, respectively. The results showed that Al₄C₃ whiskers and MgAl₂O₄ particles formed for all the specimens fired at 1000 °C. With the temperature up to 1400 °C, more MgAl₂O₄ particles were detected in the matrix and AlN whiskers occurred locally for high carbon MgO–C specimens (10 wt% and 20 wt% graphite). However, the hollow MgO-rich spinel whiskers began to form locally at 1200 °C and grew dramatically at 1400 °C in low carbon MgO–C refractories, whose growth mechanism was dominated by the capillary transportation from liquid Al at these temperatures.     

Densification and biocompatibility of sintering 3.0 mol% yttria-tetragonal ZrO2 polycrystal ceramics with x wt% Fe2O3 and 5.0 wt% mica powders additive

The densification and biocompatibility of sintered 3.0 mol% yttria-tetragonal zirconia polycrystal (3Y-TZP) ceramics, with X wt% Fe₂O₃ and 5.0 wt% mica powders (denoted by 3Y-TZP: X-5.0 wt% mica) have been studied. When the pellets of 3Y-TZP: X-5.0 wt% mica were sintered at 1300 °C for 1 h, the relative shrinkage increases from 19.20–19.43% with the X increased from 0.3 to 1.0. The relative shrinkage of pellets containing 1.0 wt% Fe₂O₃ (X=1.0) increased from 19.43–19.59% when sintering temperatures were raised from 1300 °C to 1450 °C. X-ray diffraction results show that the pellets of 3Y-TZP: X-5.0 wt% mica sintered at 1400 °C for 1 h only contained single phase of tetragonal ZrO₂ (t-ZrO₂). When the sintering temperature was higher than 1400 °C, the Vickers microhardness was greatest in the pellets with X=0.5. Within pellets with the same Fe₂O₃ content, the dominant wavelength (λ_d) was only slightly different for pellets sintered at 1300 °C and those sintered at 1450 °C. The results of the materials were evaluated in vitro cytotoxicity tests reveals that the powders and sintered pellets are safe materials. The oral mucosa irritation tests did not find erythema or histopathological change including normal epithelium, and was free from leucocyte infiltration, vascular congestion and oedema.