Colour performance of ceramic nano-pigments

Ceramic nano-pigments have been recently developed for ink-jet decoration of ceramic tiles using quadrichromic technology (cyan, magenta, yellow, and black colours). The colouring mechanisms and performance of CoAl₂O₄, Au, (Ti,Cr,Sb)O₂ and CoFe₂O₄ nano-pigments were investigated by DRS, XRD and colorimetry. The nano-pigments were dispersed in several ceramic glazes and glassy coatings and their colour performance was compared with that of conventional micro-pigments. Each nano-pigment was characterized in terms of its colour mechanism and chemico-physical stability. Although the micro-pigments provided more saturated hues, intense colours were achievable in nano-pigments despite their very small particle size (<50 nm). Limitations to the use of nano-pigments arose for very high firing temperatures (>1200 °C) due to particle growth (e.g. Au) or dissolution in the glassy phase (e.g. titania).     

Synthesis of black pigments containing chromium from leather sludge

The black ceramic pigments with spinel structure have been prepared by using Cr-rich leather sludge in this paper. The washed Cr-rich leather sludge calcined at 1100 °C for 1 h as chromium oxide precursor (named as CA) was mixed with an appropriate proportion of other industrial metallic oxides, followed synthesizing black ceramic pigment by sintering. Both non-washed and washed sludge fired at 1100 °C were characterized by X-ray fluorescence (XRF) in order to determine their chemical compositions and X-ray diffraction (XRD) analysis to confirm that CA mainly contains Cr₂O₃ crystal phase. The results show that CA could be used as a source of chromium to prepare black pigment. The crystalline phases of obtained pigments were characterized by XRD. Furthermore, the morphology as well as the composition of pigments was investigated by scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The color coordinates of pigments were examined and compared with the commercial pigments based on CIE-L* a* b* values measured using UV–vis spectroscopy. The obtained pigments sintered at 1200 °C with 35–55 wt% content of CA possess the excellent black spinel structure and color effect. Under optimized conditions, the pigment has low average spectral reflectance (7%).     

Encapsulated carbon black prepared by sol–gel-spraying: A new black ceramic pigment

As a new black ceramic pigment, encapsulated carbon black pigment has been prepared by a sol–gel-spraying method. The obtained pigment sintered at 900 °C for 2 h in air has a deep black hue (L* = 19), indicating carbon black can be fully covered. In the pigment, a dense coating layer on carbon black is formed due to the fast transformation from sol into gel by rapid extraction of solvent. The transparent silica phase spaces out the fine crystalline (zirconia or zircon), which permits to display the color of carbon black. This preparation method provides a way to prepare the encapsulated pigments. It will provide more colorful ceramic pigment applied in ceramic decoration by encapsulating.     

Effect of high energy milling process on microstructure and piezoelectric/dielectric properties of K0.475Na0.475Li0.05NbO3 solid solution

K_0.475Na_0.475Li_0.05NbO₃ (abbreviated as NKLN) ceramic of near the morphotropic phase boundary (MPB) composition was synthesized by two different processes. The first one is the high energy milling [sometimes abbreviated as HEM hereafter] process, which involves mixing the starting materials and milling the calcined powder using a high energy nano-mill, in order to obtain nano-sized particles. The second one is a conventional mixed oxide method. The HEM process of the starting materials lowered the calcination temperature to the extent of 200 °C as compared with conventionally fabricated NKLN. The particle size of the powder, exposed to the HEM process, reduced to 40 nm, whereas the conventionally ball-milled powder had a larger size of 420 nm after the mixing process. Furthermore, the HEM process improved the reaction activity and homogeneity of the materials used throughout the process, accompanying the enhancement of the sintering density, grain uniformity, and the decrease of grain size. In order to investigate the effects of the HEM process on the electric properties of NKLN ceramics, the dielectric and piezoelectric properties of sintered specimens fabricated by two different processes were evaluated. It was found that the properties of the nano-sized NKLN ceramic near the MPB composition were increased by the modified method, showing the maximum values of d₃₃=179 pC/N, k_p=34% and K₃₃^T=440 compared with 132 pC/N, 29%, and 400, respectively in the conventional process. Further evidence for the grain size effect was investigated by the polarization–electric field curve at room temperature. The remnant polarization for the nano-sized NKLN specimen had a higher value of 24.3 μC/cm² compared with that of 13.7 μC/cm² for conventional NKLN, whereas the coercive field had a similar value. The modified mixing and milling method was considered to be a new and promising process for lead-free piezoelectric ceramics owing to their excellent piezoelectric/dielectric properties.     

Development of a yellow ceramic pigment based on silver nanoparticles

In this study a yellow pigment was obtained for third-fire ceramic decorations, based on silver nanoparticles synthesised by the method of chemical reduction in aqueous phase, using silver nitrate and polyvinylpyrrolidone as raw materials. Monitoring of the nanoparticle synthesis reaction by UV–vis spectroscopy allowed optimum operating conditions to be defined in preparing these particles for use as chromophores. Under these conditions, a stable suspension of Ag nanoparticles, which were well dispersed and had an average diameter of 20–30 nm, was obtained. Polyvinyl alcohol and tetraethyl orthosilicate were then added to the nanoparticle suspension to obtain the pigment precursor. The pigment precursor was directly applied on to fired glazed ceramic tile. Subsequent thermal treatment at moderate temperature (700 °C) yielded a layer less than one micron thick, which generated an intense yellow colour.     

Effect of milling time and pH on the dispersibility of lead zirconate titanate in aqueous media for inkjet printing

Micrometre-sized Pb(Zr_0.53Ti_0.47)O₃ (PZT) powder was dispersed in water, stabilized with the ammonium polyacrylate (PAANH₄) and milled to reduce the particle size. The influence of the pH, the amount of PAANH₄, and the milling time on the zeta potential, the PZT particle size and the particle size distribution was studied. The agglomeration took place regardless the milling time at pH 3. The suspension, containing 5 vol.% of PZT and 5 wt.% of PAANH₄, milled at pH 10 for 240 min, was stable and contained particles with a narrow, log-normal particle size distribution with the median size of 160 nm. The dissociated carboxyl groups from the PAANH₄ interacted with the PZT particles as evidenced by Fourier transform infrared spectroscopy and electrosterically stabilized the particles in water at pH 10. The PZT particle size and the stability of the suspension fitted the requirements for the ink, suitable for ink-jet printing.     

Influence of milling time on the synthesis,microstructure and mechanical properties of ZrB2SiCZrO2f ceramic composites

Zirconium diboride toughened by silicon carbide and zirconia fiber (ZrB₂SiCZrO_2f) was prepared by using planetary ball mill and the effect of milling time was investigated. The results showed that both the length of fiber and particle size of ZrB₂SiC-matrix were reduced as the ball milling time increased. When milling time varied from 8 h to 12 h, the accumulated fibers and agglomerated particles were observed. The production of a homogeneous ceramic could be successfully achieved by using a combination of 20 h milling time and hot-pressing at 1850 °C for 60 min under a uniaxial load of 30 MPa. The optimal flexural strength and fracture toughness of the hot-pressed ZrB₂SiCZrO_2f ceramics reached 1084 MPa and 6.8 MPa m^1/2, respectively. The main toughening mechanisms were fiber debonding, fiber pull-out and transformation toughening. The results indicated that the ball milling technique was proposed as a potential and simple method to obtain usable quantities of ZrB₂SiCZrO_2f ceramic.     

Preparation and characterization of micron and submicron-sized vermiculite powders by ultrasonic irradiation

Micron and submicron-sized vermiculite lamellar particles with nanometric thickness (< 10 nm) were prepared by ultrasonic treatments (< 12 h) of aqueous and hydrogen peroxide suspensions of thermally exfoliated vermiculite. Laser granulometry characterizations showed that the particles size distribution was dependent on the treatment time and that the use of H₂O₂ afforded smaller particles than H₂O. In both media, an exfoliation and a size reduction were observed after only 1 h of ultrasonic treatment by Scanning Electron Microscopy, X-ray diffraction, and Nitrogen Adsorption Measurements at 77 K. X-ray diffraction studies showed the absence of damage in crystals structure after sonication and also a reduction of crystallites size along the basal direction (00l). The different ultrasonic treatments also induced modifications of the surface properties of the vermiculite particles, brought out by BET surface measurements, infrared spectroscopy, pH modifications of the materials and zeta potential analyses. Sonication of the vermiculites yielded to the formation of carbonate anions from the dissolved CO₂ and hydroxide anions released from the clay layers. The long ultrasound irradiation of the vermiculite in hydrogen peroxide (> 5 h) generated the decrease of the surface charge, pointed out by pH and zeta potential modifications, allowing an aggregation of the submicron particles in the suspensions.     

Microstructure evolution of Ti3SiC2 powder during high-energy ball milling

Ti₃SiC₂ powder was milled by high-energy ball milling under argon atmosphere and subsequently thermally annealed. The microstructure evolution of Ti₃SiC₂ after milling was investigated. It was found that 200 nm particle size Ti₃SiC₂ powder could be achieved by 9 h milling whereas a longer milling time would induce Ti₃SiC₂ decomposition. After 18 h milling, the particle size gradually decreased to 150 nm and TiC appeared in the XRD pattern. It is suggested that the collision of the milling balls triggered the formation of TiC from the amorphous phase which was generated in the milling process.     

Effect of mechanical milling on structural,dielectric and magnetic properties of BaTiO3–Ni0.5Co0.5Fe2O4 multiferroic nanocomposites

The coexistence of ferroelectricity and ferromagnetism has triggered great interest in multiferroic materials. Multiferroic with strong room temperature magnetoelectric (ME) coupling can provide a platform for future technologies. In this paper, we have investigated the effect of mechanical milling on the properties of multiferroic nanocomposites synthesized by mixing barium titanate (BaTiO₃) (BT) and nickel cobalt ferrite (Ni_0.5Co_0.5Fe₂O₄) (NCF). This process has resulted into reliable disposal of a given quantity of NCF nanoparticles in BT grid and composite samples of different particle sizes (<500 nm) have been obtained by varying the duration of ball-milling for 12, 24, and 48 h. The presence of NCF within BT powder has been confirmed by X-ray Diffraction (XRD) and magnetization measurements (MH). Structural analysis was performed by using Reitveld refinement method that shows that the tetragonality of BaTiO₃ structure get reduced in submicron range. Variations in ferroelectric and dielectric properties with reduction in particle size/milling duration have been studied by P-E loop tracer and Impedance analyzer. The dielectric constant value of 400 has been observed for BT-NCF0 that increases to 9.7 K for composite sample ball mill at 48 h whereas remnant polarization increases to 4.2 μC/cm². These composites with high dielectric constant that changes with temperature and particles size find application in energy storage devices, sensor and memory devices.     

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Environmental-friendly yellow pigment based on Tb and M (M = Ca or Ba) co-doped Y2O3

A yellow inorganic ceramic pigment with general formula Y_1.86?xM_xTb_0.14O_3?x/2 (M = Ca and/or Zn) with x = 0.06, 0.32 and 0.64 were synthesized by a modified Pechini method. XRD, SEM and HRTEM/EDX analysis showed the formation of solid solution at 1300 °C when x = 0.06 and 0.32. The best b* yellow coordinates were obtained for Ca and Zn co-doped Y_1.86Tb_0.14O₃ samples. The intensity of the yellow colour in the samples is related to the presence of Tb⁴⁺ ions. Samples with higher concentration of Tb⁴⁺ ions lead to a better yellow colour. The chemical stability of these pigments was determinate in an industrial glaze. The glazing tests indicated that the powder samples with x = 0.06 and 0.32 fired at 1300 °C were stable in the glaze. These results make it a potential candidate for environmental friendly yellow ceramic pigment to be used in applications such as pigment for glazes or inkjet printers.     

The formation of Y5V-type fine-grained ceramics based on spherical submicron BaZr0.1Ti0.9O3@Al2O3 particles

To improve multilayer ceramic capacitors (MLCCs), thinner dielectric layers are necessary. To achieve this goal, both grain size and uniformity of the MLCC particles must be controlled effectively. In this study, the core-shell structure of submicron-sized multi-function ceramic capacitors powder was synthesized using a novel precipitation route, which controls both dispersion and particle size of BaZr_0.1Ti_0.9O₃ and BaZr_0.1Ti_0.9O₃@Al₂O₃ particles. In this paper, we investigate the effect of Al₂O₃ coating on the microstructure and the dielectric properties of BaZr_0.1Ti_0.9O₃. We found that both average grain size and maximum dielectric constant (ε_max) of the ceramics decrease with increasing concentration of Al₂O₃. Our results demonstrate that fine-grained ceramic materials can meet the specifications of the Electronic Industries Alliance Y5V with a concentration of Al₂O₃-coated of 0.25 mol percent, a permittivity of 3393 at room temperature, and an average particle size of about 400 nm.     

Synthesis of nanocrystalline cerium oxide by high energy ball milling

We have synthesized pure nanocrystalline CeO₂ powders of nearly spherical shape using high-energy attritor ball mill. Milling parameters such as the milling speed of 400 rpm, ball to powder ratio (40:1), milling time (30 h) and water cooled media were determined to be suitable for synthesizing nanosize (～10 nm) powders of CeO₂. The powders after milling for various durations (up-to 50 h) were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy-dispersive X-ray Spectrometry and Transmission Electron Microscopy. An average particle size of 10 nm was obtained at 30 h milling, after which the particle agglomeration started, and a mixture of nanocrystalline and amorphous phase was observed after 50 h milling.     

Solution combustion of spinel CuMn2O4 ceramic pigments for thickness sensitive spectrally selective (TSSS) paint coatings

A series of spinel-type CuMn₂O₄ ceramic pigments were prepared by a facile and low-cost sol-gel solution combustion method and used as cost-effective materials to fabricate thickness sensitive spectrally selective (TSSS) paint coatings by a convenient spray-coating technique. The chemical component, crystalline morphology, and optical property of the copper manganese oxide ceramic pigment could be accurately controlled by altering the annealing temperature. X-ray diffraction (XRD) analysis confirmed that the ceramic pigments annealed at 500 °C for 1 h coincided well with the XRD patterns of crystalline CuMn₂O₄ in the JCPDS database, and there were segregated phases of CuO and Mn₂O₃. Furthermore, the pure spinel CuMn₂O₄ phase could be achieved at 900 °C for 1 h. The copper manganese oxide ceramic pigments could serve as an effective pigment for fabricating the TSSS paint coating, and the TSSS paint coatings based on ceramic pigments calcined at 900 °C showed solar absorptance of 0.895–0.905 and thermal emittance of 0.186–0.310. In addition, the accelerated thermal stability test revealed that the TSSS paint coating exhibited good thermal stability when it was exposed to air at a temperature of 300 °C for 300 h. Hence, the fabricated TSSS paint coating could be used as a solar absorber coating in the low-to-mid temperature domain.     

Ball milling assisted hydrothermal synthesis of ZrO2 nanopowders

The formation of ZrO₂ nanopowders under various hydrothermal conditions such as temperature, time, autoclave rotation speed, heating rate and particularly assistance of ball milling during reaction was investigated. Full ZrO₂ formation (with monoclinic phase) from zirconium solution was completed at shorter times with increasing temperature such as after 4 h at 150 °C, 2 h at 175 °C and less than 2 h at 200 °C. Crystallite size increased from 2.9 to 4 nm with increasing reaction temperature from 125 °C to 200 °C, respectively. Ball milling assisted hydrothermal runs were performed to understand the effect of mechanical force on phase formation, crystallinity and particle size distribution. Monoclinic ZrO₂ was formed in both milled and non-milled runs when zirconium solution was used. Mean particle size for the 2 M solution was measured to be 94 nm for the milled and 117 nm for the non-milled powders. However, when amorphous aqueous zirconia gels (precipitated at pH 5.8) were used, tetragonal phase was also formed in addition to monoclinic phase. Mean particle size was measured to be 0.7 μm (d₉₀≅1.3 μm) for the milled and 7.9 μm (d₉₀≅13 μm) for the non-milled powders. Ball milling during hydrothermal reactions of both zirconium solution and aqueous zirconium gel resulted in smaller crystallite size and mean particle size and, at the same time, effectively controlled particle size distribution (or agglomeration) of nanopowders.     

The production of β-SiAlON ceramics with low amounts of additive,at low sintering temperature

In the present work nano-sized powder of β-SiAlON was produced using a wet milling process. Different milling times and mediums (methyl ethyl keton, ethanol and toluene as solvents, polyethyleneglicol, oleic acid, sodium tripolyphosphate and polyvinylpyrrolidon as dispersants) were performed for the determination of the most efficient milling system. The powders were produced using a conventional process (the ball to powder ratio was 1:1.5, at 300 rpm, for 1.5 h) having a few hundred nanometer particle size, and these were used as standard powders in this study. The nano-sized β-SiAlON starting powders (<100 nm) were sintered at lower temperatures than that of the conventional powders. The amount of Y₂O₃ in powders (～130 nm), produced by high energy milling process, was fewer than conventional powders (5 wt.%). The results of the powder size, sintering behavior and mechanical properties of this sample were compared to those of the standard powder and its sintered sample. This sample, produced using the nano-powder, was investigated, and densified at 150 °C lower than that of the standard sample. Even though the amount of Y₂O₃ was decreased, the hardness of the samples was better than that of the standard sample.     

Synthesis of nano-titanium diboride powders by carbothermal reduction

The nano-sized titanium diboride particles were synthesized by carbothermal reduction process. In this study, carbothermal reduction process was used by controlling reaction rate and duration time. TiO₂, B₂O₃ and carbon resin were used as starting materials with a molar composition; TiO₂:B₂O₃:C = 1:2:5. The mixture was placed in a graphite crucible and pushed into a heating zone maintained at 1500 °C and Ar was flown for a period of 20 min. After reaction, the crucible was pulled out from the heating zone to cooling zone of the furnace for the rapid cooling. The average particle size of the agglomerated product was found to be ∼500 nm, which was composed with small primary particles of <100 nm in size. After milling, the large agglomerate was reduced to primary particles.     

Microstructure of TiO2 porous ceramics by freeze casting of nanoparticle suspensions

During freeze casting of TiO₂ porous ceramics, the porous architecture is strongly influenced by TiO₂ particle size, solids loading, and cooling temperature. This work investigates the influences of particle size, freezing substrate, and cooling temperature on the TiO₂ green bodies prepared by freeze casting. The results show that the lamellar channel width with 100 nm particles is larger than that of 25 nm particles, yet the ceramic wall thickness is noticeably decreased. The lamellar structure is more ordered when using a copper sheet than glass as its freezing substrate. A finer microstructure results when frozen at − 50 ℃ than − 30 ℃. Such porous materials have application potentials in a wide range of areas such as photocatalysis, solar cells, and pollutant removal and should be further studied.     

Shift of morphotropic phase boundary in high-performance fine-grained PZN–PZT ceramics

The fine-grained xPb(Zn_1/3Nb_2/3)O₃–(1 − x)Pb(Zr_0.47Ti_0.53)O₃ system has been prepared from submicron precursor powders obtained by high-energy ball milling method. The addition of PZN induces a decrease of grain size from an initial micron scale to a submicron scale, accompanying with the phase transition from tetragonal to morphotropic phase boundary (MPB), and then rhombohedral side. Interestingly, compared to the former published data for coarse-grained ceramic, the MPB has shifted from 50% to 30% PZN content side due to the enhancement of the internal stress for fine-grained ceramic. The enhanced electrical and mechanical performances are closely associated with the phase structure and grain size. A high piezoelectric property (d₃₃ = 380 pC/N and k_p = 0.49) as well as mechanical performance (H_v = 5.0 GPa and K_IC = 1.33 MPa m^1/2) were obtained simultaneously for the MPB 0.3PZN–0.7PZT ceramics with an average grain size of 0.65 μm.