Synthesis of spherical lead zirconate titanate (PZT) nanoparticles by electrohydrodynamic atomisation

Abstract

This paper describes the production of spherical-shaped lead zirconate titanate (PZT) nanoparticles by the electrohydrodynamic atomisation (EHDA) process in order to make inks suitable for ink jet printing applications. PZT sols with different concentrations (0·1–0·6 M) were used as starting materials. Two different heating systems, gas heating and direct heating, were used in order to remove the solvent, reduce the particle size and stabilise the PZT particles. Several aspects have been considered, such as liquid flow rate, sol concentration and heat system temperature, and their influence on the particle dimension is determined. Using optimised processing parameters of direct heating at 520°C, 0·2 M precursor sol, flow rate of 0·2 mL h^?1 and field of 3 kV cm^?1, particles of 100–300 nm in diameter were synthesised. Following stabilisation at 300°C, the particles were suspended in a PZT sol to produce an ink suitable for ink jet printing.     

Firing behavior of argillites from northern Tunisia as raw materials for ceramic applications

This study reports the firing properties of clayey materials from northern Tunisia to evaluate their possible use as raw material in ceramic. Physical, chemical, and mineralogical characterization and thermal behavior were carried out by inductively coupled plasma atomic emission, X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal analysis, particle size distribution, and Atterberg limits tests. Firing properties were evaluated by color, firing shrinkage, water absorption, bulk density, apparent porosity, and flexural strength. Studied clayey materials are made up mainly by kaolinite and illite and are rich in iron. The main transformations after thermal analysis were identified from 500°C to 1000°C subsequent to the dehydroxylation of clay minerals, calcite decomposition, and the recrystallization process. Fired samples up to 1100°C showed better physical and mechanical properties related with a great densification resulting in a significant increase in linear shrinkage, bulk density, and flexural strength and a decrease in apparent porosity and water absorption up to 1100°C. This behavior is due to a crystalline and liquid phases formed at low firing temperature associated with a high content of fluxing agents. The fired ceramic materials exhibited low water absorption up to 2.26% and high flexural strength up to 32.6 MPa, which makes their potential use for some earthenware and stoneware products.     

Influence of processing parameters on the microstructure of the eco-friendly glass foam

Eco-friendly glass foam (GF) with a specific mechanical strength of 5.96 MPa g⁻¹ cm³ and thermal conductivities between 0.131 and 0.282 Wm⁻¹ K⁻¹ was produced using fluorescent lamp glass residue (FLGR) and white eggshell as foaming agent (FA). The influence of the FLGR average diameter particle, the amount of FA, and the heat treatment on the GF final properties were evaluated. The highest expansion (500%) and the lowest density (0.24 g cm⁻³) were achieved using 32.90 μm mean diameter FLGR particles, 5 wt% FA, and foaming at 700°C. The produced GF showed promising application as porous building materials with load-bearing function.     

The details of the formation of CuCl nanoparticles in photochromic glass

The details of the formation of CuCl nanoparticles in the sodium alumina-borosilicate glass for different methods of thermal treatment of the samples are studied by exciton thermal analysis. It is revealed that the formation of the CuCl phase in glass depends on the heating rate of the samples to the predetermined temperature of isothermal annealing. The concentration of the nucleating centers of the CuCl phase reaches its peak value at 600°C during slow (60 min) heating up to 650°C, due to the fast increase of the critical size of particles of the phase as a result of the fast temperature increase and the rapid decrease of supersaturation in glass. As a result, the formation of new CuCl nucleation centers terminates above 600°C, and part of the centers formed earlier whose size is less than critical dissolve, which results in the monotonic decrease of the CuCl particle concentration.     

Enhancing the physical and mechanical properties of pellet-shaped hydroxyapatite by controlling micron- and nano-sized powder ratios

Hydroxyapatite (HA) was fabricated in microns as its basic size. The particle size distribution was controlled by mixing micron- and nano-sized HA to obtain the optimum amount of mixture to improve its properties. HA powder with a size of 2.5 μm was mixed with that with a size of 200 nm, with a variety of concentrations of up to 20 wt%. A green body was fabricated using the uniaxial pressing method at a pressure of 200 MPa. The sintering process was conducted at a temperature of 1200 °C, heating rate of 3 °C/min, and holding time of 2 h in air. The physical characteristics of the HA sintered body were determined using X-ray diffraction, scanning electron microscopy, linear shrinkage, and density testing. The mechanical properties of the HA sintered body were tested using compressive strength testing. The test results indicated that the mechanical properties of the HA sintered body increased with the addition of nano-sized HA. The mechanism of the increasing strength occurred because nano-sized HA particles filled the gaps between the micron-sized particles. In this study, the highest mechanical properties were obtained by adding 20 wt% nano-sized HA. The compressive strength in the sample without added nano-sized HA was 132.2 MPa and increased significantly to 208.6 MPa with the addition of nano-sized HA of 20 wt%. No change in the phase in HA was observed within a sintering temperature of 1200 °C.     

Scaling up the cold sintering process of ceramics

The cold sintering process (CSP) densifies ceramics below 300 °C by utilizing a transient phase and applied pressure. Although CSP has been employed for densifying a variety of functional systems, their structural integrity does not always reach that of conventionally sintered parts. On the example of ZnO, this study aims to eliminate processing-induced defects that compromise the strength of cold sintered materials. Ultrasonic evaluation was employed for nondestructive detection of flaws prior to mechanical testing. Load transfer misalignments and fast heating rates were found as major sources of defects, impairing the mechanical strength. Based on these findings, multiple disc-shaped samples (13 mm diameter and ∼1.3 mm thickness) were cold sintered simultaneously using precisely aligned punches and slow heating rates. The obtained homogeneous densification, high relative density (>97%) and relatively high strength (∼120 MPa), i.e. two times superior to previously reported values, demonstrates the feasibility of scaling up the CSP towards industrial implementation.     

Evaluation of a Heated-Inlet for Calibration of the SP2

Black carbon (BC) calibration standards, such as fullerene soot, are routinely used to calibrate single-particle soot photometer (SP2) instruments. Impurities in BC standards create uncertainties in these calibrations, and thus it is desirable to remove non-BC compounds from the aerosol, though removal processes must not significantly alter BC microphysical properties. We present a series of experiments using mobility- and mass-selected fullerene soot particles to assess the performance of a high-temperature denuder system for treating BC prior to SP2 analysis. Particle mass, incandescence, and scattering properties were measured by tandem aerosol particle mass analyzers and an SP2, after thermal treatment at a range of temperatures and residence times (RT). For a longer RT (e.g., ～6 s at 300°C), monodisperse fullerene soot particles of initial mass 1.4 fg decreased in mass with increasing temperature, by 3% at 300°C to 15% at 600°C. Mass losses were similar for fullerene soot particles of initial mass 10.7 fg. The peak height of the particle laser-induced incandescence (LII) and scattering intensities of the 10.7 fg fullerene soot increased by 7% and 3%, respectively, at 300°C, and by over 15% and 10% at 400°C, possibly due to microphysical changes after heating. When sampling through a 300°C denuder with a particle RT of 2.5 s, the LII intensity of ambient BC particles of initial mass 1.1 fg increased by 8%. In light of these results, denuder temperatures of ～300°C with 0.4 s ≤ RT ≤ 2.5 s are recommended for SP2 calibration.

Copyright 2013 American Association for Aerosol Research     

Cost‐effective porous ceramic tubes fabricated through a phase inversion/casting process using calcined bauxite

Cost‐effective ceramic tubes based on low‐price commercial calcined bauxite for economical separation were fabricated by a new phase‐inversion casting method. The thermal shrinkage and weight loss during heating of the green tubes were characterized by dilatometric analysis and TG, respectively. Three shrinkage stages appear successively, corresponding to the viscous deformation of polymeric binder at 200‐300°C, significant combustion loss of ~5.2 wt% at 500‐620°C and sintering shrinkage over 800°C, respectively. However, due to high enough viscosity of the casting suspension that can guarantee the green tube against collapse or deformation during the phase inversion/casting process, the sintered tubes display nearly uniform microstructure instead of characteristic asymmetrical structure of the phase inversion process. The influence of sintering temperature on the pore property (including pore size and porosity) and mechanical strength was investigated. As the sintering temperature increases from 1200 to 1400°C, the porosity and average pore size decrease from 46.4% to 37.0% and from 0.98 to 0.81 μm, respectively, and the flexural strength increases from 25.8 to 65.1 MPa. The cost‐effective ceramic tube sintering at the range of 1250‐1400°C can be capable of functioning as a microfiltration membrane or an ultrafiltration membrane support.     

Preparation of anthracene fine particles by rapid expansion of a supercritical solution process utilizing supercritical CO<Subscript>2</Subscript>

The rapid expansion of a supercritical solution (RESS) process is an attractive technology for the production of small, uniform and solvent-free particles of low vapor pressure solutes. The RESS containing a nonvolatile solute leads to loss of solvent power by the fast expansion of the supercritical solution through an adequate nozzle, which can cause solute precipitation. A dynamic flow apparatus was used to perform RESS studies for the preparation of fine anthracene particles in pure carbon dioxide over a pressure range of 150–250 bar, an extraction temperature range of 50–70 °C, and a pre-expansion temperature range of 70–300 °C. To obtain fine particles, 100, 200 and 300 μm nozzles were used to disperse the solution inside of the crystallizer. Both average particle size and particle size distribution (PSD) were dependent on the extraction pressure and the pre-expansion temperature, whereas extractor temperature did not exert any significant effect. Smaller particles were produced with increasing extraction pressure and preexpansion temperature. In addition, the smaller the nozzle diameter, the smaller the particles and the narrower the PSD obtained.     

Sintering Mechanism and Microstructure of TaC/SiC Composites Consolidated by plasma-activated sintering

TaC/SiC composites with 5 wt% SiC addition were densified by plasma-activated sintering (PAS) at 1500–1800 °C for 5 min under 30 MPa. The effects of plasma-activated sintering on microstructures, densification and mechanical properties of the composites were investigated. The results showed that TaC/SiC composites achieved a relative density more than 99% of the theoretical density at 1600 °C. A low eutectic liquid phase generated by the oxide on the particle surface was observed in the composite to realize a relatively low temperature sintering densification. While the TaC particle size decreased insignificantly with increasing sintering temperature, the transformation of morphology of SiC particles changing from equiaxed to elongated grain was activated, accompanying with a slight particle size decreasing of the SiC phase, thus promoting a relatively high flexural strength of 550 MPa under 1800 °C. Besides, some ultra-fine 2 nm Ta₂Si was observed in the glassy pockets, strengthening the amorphous phase and thus increasing the flexural strength.     

Content and diffusion of water and gases in MgAl2O4 spinel crystals synthesized to produce ceramics

Content, evolution and diffusion characteristics of water and gases in fine-crystalline spinel MgAl₂O₄ were studied by kinetic thermodesoption mass spectrometry. Water is the main volatile component by quantity in the spinel structure. From the spinel crystals with an average size of 0.52 μm, water is released in vacuum in three temperature ranges: at 100–200 °C due to desorption from micropores, at 300–600 °C due to near-surface dehydroxylation and at 500–800 °C due to diffusion of water from the crystal bulk. The content of structural water, diffusively released from the crystals, is about 3000 ppm. The coefficients and activation energy of diffusion of water from spinel crystals in the range 500–700 °C were calculated. This allows us to estimate at any temperature the degassing time of the spinel with a certain degree of dispersion and ceramics made of it, and thereby promote the production of high-quality ceramics.     

Filtration of fly ash using fluidized bed at 300–500 °C

The filtration of the coal-burning fly ash using fluidized beds with silica sand of 770 μm under temperatures of 36, 300, 400, and 500 °C was studied. The variations of the outlet concentration and particle size distribution (PSD) with time were measured to evaluate the dynamic characteristics of the process. Experimental results showed that the overall collection efficiency decayed with the operation time, revealed the effect of the elutriation of fly ash on particle filtration. The collection efficiency rose when the temperature increased from 36 °C to 500 °C. The strong attrition at high temperature released more small particles than that at room temperature, increased the concentration of the particles less than 10 μm (PM₁₀) at high temperature. The removal efficiency of the particles in a size of 4–7 μm, not the submicron particles, is the lowest because they are most easily elutriated from fluidized beds.     

The effect of particle size of fly ash (FA) on the interfacial interaction and performance of PVC/FA composites

In this study, the effect of particle size of fly ash (FA) on the interfacial interaction between the filler particles and the polymer matrix is investigated. Structural and physical characterization of FA with different particle sizes show that its chemical composition is highly dependent on the particle size. The mechanical, dynamic‐mechanical, structural, and microstructural properties of the composites are evaluated. Interfacial interaction between FA particles and the polymer matrix is assessed experimentally using a nanoindenter and numerically using two different models developed by Pukanszky and Kubat. The composites reinforced with smaller particles exhibit better mechanical, viscoelastic, and microstructural properties. Structural and interfacial studies show that, although the characterized amount of silicon oxide in the small particles is lower than the large particles, the concentration of –OH group in SiO₂ is particle‐size and surface‐area dependent. Therefore, smaller particle inclusions result in better interfacial interaction and improved properties. This observation is consistent with the numerically estimated interfacial interaction. J. VINYL ADDIT. TECHNOL., 25:134–143, 2019. © 2018 Society of Plastics Engineers     

Processing of porous glass ceramics from highly crystallisable industrial wastes

This study was carried out to gain understanding about the sintering behaviour of highly crystallisable industrial waste derived silicate mixtures under direct heating and rapid cooling conditions. The materials used in this study were plasma vitrified air pollution control waste and rejected pharmaceutical borosilicate glass. Powder compacts sintered under direct heating conditions were highly porous; compacts with particle size <?38?μm reached a maximum density of 2.74 g?cm^??3 at 850°C, whereas compacts with particles of size <?100?and <?250?μm reached maximum densities of 2.69 and 2.72 g?cm^??3 at 875 and 900°C respectively. Further increase in sintering temperature resulted in a rapid decrease in density of the glass ceramics. Image analysis results were used to link the sudden drop in density to the increase in volume of microsized pores formed in the samples during sintering. In particular, compacts made from <?38 μm particles sintered at 950°C resulted in 65 vol.-% porosity with a pore size of ～20?μm. Such materials can be used for sound and thermal insulation purposes.     

Fast one-step carbothermal reduction and nitridation method using nano-sized Al2O3 and carbon black to prepare aluminium oxynitride powder for highly transparent ceramics

By fast heating the nano-sized Al₂O₃ and carbon black mixtures at 50°C/min to 1750°C for 30–120 min, single-phase AlON powders were successfully obtained by a fast one-step carbothermal reduction and nitridation (CRN) method. The AlON ceramics pressureless sintered at 1880°C for 150 min by these powders show high transmittances up to 83%–84%, which indicates that the proposed fast one-step CRN method is an effective and efficient way with strong robustness to synthesize single-phase AlON powder for highly transparent AlON ceramics. It was found that α-Al₂O₃ particles do not have enough time to aggregate and coalesce during heating due to the tremendously shortened heating span, which significantly inhibited particle coarsening until the formation of AlON starts. The fast-formed AlON further inhibits the coarsening of α-Al₂O₃ during dwelling. Consequently, single-phase AlON powder of small primary particles can be obtained after 30 min dwelling at 1750°C.     

Mullite development on firing in porcelain stoneware bodies

Microstructural evolution on heating was investigated in a reference industrial composition (50% kaolinitic clay, 40% feldspar and 10% quartz) of porcelain stoneware, fast fired at different temperatures (500–1400 °C). The evolution of mullite crystals, regarding shape and size progress, was examined by scanning electron microscopy (SEM). The proportion of Type I mullite crystals decreases with firing temperature and simultaneously, the size of crystals increases, reaching the maximum value of aspect ratio (3:1) at 1400 °C. Type II and Type III secondary mullite needles increase with temperature in both number and length, which leads to an increase in the aspect ratio from 5:1 to ～20:1 in Type II crystals and from ～33:1 to 50:1 in Type III mullite needles. Finally, clusters of Type III mullite fibres are observed in porcelain stoneware samples fast fired in the 1250–1280 °C interval.     

Synthesis and application of multilayered core shell particles for toughening of unsaturated polyester resin

Toughening particles, comprising two radially alternating rubbery and glassy layers, were prepared by using sequential emulsion polymerization. The conditions which led to controlled particle size and morphology are discussed. A relatively new type of inert core shell particle [fly‐ash (FA)] and surface‐activated FA, by two different silane coupling agents, namely 3‐aminopropyltrimethoxy silane (AMP) and vinyltriethoxysilane (VES)‐based multilayered toughening particles, which radially comprise rubbery and glassy layers, were also prepared. The toughening particles were used with general purpose polyester resin (GPR) for making composite sheets. Formation of multiple layers in the core‐shell particles and their morphology were confirmed by transmission electron microscopy (TEM). The mechanical properties such as tensile, flexural, impact, and hardness of the toughened GPR are discussed critically. The tensile fractured surfaces were studied by scanning electron microscopy (SEM). Thermal property such as thermogravimetric analysis (TGA) were also discussed. The composites were exposed to various adverse environmental conditions such as water, boiling water, salt water, acid, alkali, toluene, weather, and freezing–thawing for 30 days. The mechanical properties (viz. the tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus, impact strength and hardness of FA/GPR, FA.AMP core/GPR, and FA.VEScore/GPR) were studied before and after exposure to adverse environmental conditions. The results indicate that the mechanical properties of FA/GPR composite are improved by surface treatment of FA and their resistance to the various environmental stresses is also enhanced substantially on modification by toughening particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 511–528, 2004     

Effectiveness of gases in desulphurization of coal

The effect of air, steam and hydrogen on the desulphurization of 10 U.S. high-volatile bituminous coals was investigated. Air treatment was most effective at 450 °C where an average of 38% total sulphur, comprising 51% of the inorganic sulphur and 20% of the organic sulphur, was removed. With steam at 600 °C, 61% of the total sulphur, 87% of inorganic and 25% of organic was lost. Hydrogen was not effective below 850 °C, but at 900 °C 86% of the total sulphur was dispelled, i.e. 94% of the inorganic and 76% of the organic sulphur. Without oxidative pretreatment the sulphur was much more difficult to remove; after oxidative pretreatment at 300 °C for 10 min followed by treatment with hydrogen at 900 °C, as much sulphur was removed in 4 min as in 60 min without the pretreatment. With raw coal, heating under nitrogen ‘cooked-in’ or fixed some of the sulphur making it more difficult to remove with hydrogen; whereas following oxidative pretreatment, heating for up to 1 h did not lessen the reduction of sulphur with hydrogen. For temperature-swelling coals with large quantities of organic sulphur, heating at 300 °C in air followed by reduction with hydrogen at 900 °C appears to permit rapid discharge (3–10 min) of the organic as well as the inorganic sulphur, to produce a smokeless product with a CV (per unit of product) similar to the fuel value of the untreated coal.     

Thin fly ash/ ladle furnace slag geopolymer: Effect of elevated temperature exposure on flexural properties and morphological characteristics

The flexural properties and thermal performance of 10 mm-thin geopolymers made from fly ash and ladle furnace slag were evaluated before and after exposure to elevated temperatures (300 °C, 600 °C, 900 °C, 1100 °C and 1150 °C). Class F fly ash was mixed with liquid sodium silicate (Na₂SiO₃) and 12 M sodium hydroxide (NaOH) solution using aluminosilicate/activator ratio of 1:2.5 and Na₂SiO₃/NaOH ratio of 1:4 to synthesise thin fly ash (FA) geopolymers. 40 wt% of ladle furnace slag was partially replacing fly ash to produce fly ash/slag-based (FAS) geopolymers. Thermal treatment enhanced the flexural strength of thin geopolymers. In comparison to the unexposed specimen, the flexural strength of FA geopolymers at 1150 °C and FAS geopolymers 1100 °C was increased by 161.3% to 16.2 MPa and 208.9% to 24.1 MPa, respectively. A more uniform heating was achieved in thin geopolymers which favoured the phase transformation at high temperatures and contributed to the substantial increase in flexural strength. The joint effect of elevated temperature exposure and the incorporation of ladle furnace slag further improved the flexural strength of thin geopolymers. The calcium-rich slag refined the pore structure and increased the crystallinity of thin geopolymers which aided in high strength development.     

Thermal dehydroxylation of kaolinite under isothermal conditions

The dehydroxylation reaction of kaolinite from the industrial kaolin Sl-K (Germany) has been studied by thermal analyses (TG, DTA) and ex situ annealing experiments. Heating experiments were performed at 450, 500, 550 and 600 °C. At each working temperature, different heating times were used in order to follow the evolution of the dehydroxylation process with time until completion of the reaction. Every heating run was performed on a new batch of sample, which was weighted before and after the heat-treatment. At the end of the heating run, each sample was characterised by X-ray powder diffraction (XRPD) and FT-infrared attenuated total reflectance spectroscopy (FTIR-ATR). The dehydroxylation process was followed by monitoring the gradual mass loss and the corresponding decrease in intensity of the most significant peaks both in the diffraction patterns (disappearing of kaolinite peaks) and in the FTIR-ATR spectra (disappearing and changes in OH and SiOAl bands), as determined by peak-profile and autocorrelation analyses. A kinetic analysis was performed using the Avrami method on the basis of sample mass loss and changes in the intensities of XRPD and FTIR-ATR peaks under isothermal conditions. Two temperature regimes are found, with only the data in range 500–600 °C being isokinetic. The activation energy values obtained in this temperature range on the basis of the three measured parameters are comparable and are between 127 and 139 kJ mol^− 1.