Heterogeneous Precipitation Method Research Articles

Preparation of lanthanide aluminate‐encapsulated silica nanoparticles toward long‐persistent photoluminescent polymer paint with superhydrophobic and anticorrosion properties

AbstractSmart afterglow paints can function as energy‐saving products that are able to persist lighting in the dark. Additionally, polyurethane paints (PURPs) have shown some limitations, including weak adhesion, poor mechanical performance, poor corrosion, and low water resistance as compared with solvent‐based paints. Herein, nanoparticles of lanthanide aluminate (NLA; 16–24 nm) were mixed with polyurethane and silica to develop novel photoluminescent nanocomposite paints. A precursor of NLA‐encapsulated silica nanoparticles (NLA@Silica; 200–225 nm) can be described as a SiO2‐coated NLA pigment prepared by the heterogeneous precipitation method. Steel was coated with nanocomposite paints made of PURP, silica, and NLA. Using emission spectra and Commission Internationale de l'Eclairage (CIE) Lab coordinates, the coloring and transparency of painted films were investigated. Upon excitation at 365 nm, the UV‐irradiation of transparent painted films showed green emission at 518 nm. The hydrophobic activity and hardness properties were examined. Using electrochemical impedance spectroscopy (EIS), the anticorrosion of coatings applied to mild steel was studied. Improved anticorrosion characteristics were observed due to the fluorescence of NLA@Silica in the applied coatings. The optimal long‐lasting luminous characteristics were observed for nanocomposite films containing 12.5% of NLA@Silica.

Evolution of the precursor structure during the preparation of the nanopowders with perovskite-type LnLn’O3 (Ln, Ln’ = REE) complex oxide phase in the La2O3-Lu2O3-Yb2O3 system

The thermal decomposition of complex oxide phases, such as perovskite, in the La2O3-Lu2O3-Yb2O3 systemwith a specific surface area of 37 m2/g, synthesised by the heterogeneous precipitation method under non-isothermal conditions of linear heating at a rate of 5 deg/min, was studied to reveal the features of structure changes in intermediate products. Thermogravimetric and adsorption-structural analyses, infrared spectroscopy, powder diffraction and electron microscopy revealed that the decomposition of precursors occurs in two main stages. Up to 700 °C, the initial coordination spheres are destroyed in a sequential manner, resulting in the powders remaining amorphous in phase composition. However, with a gradual increase in the order of the atoms, the change in the pore structure is non-monotonic, with an inflection point observed at 450 and 675 °C. At 675 °C, the system undergoes a collapse, accompanied with decrease in both the pore volume (V∑) and the specific surface area (SBET), which attain the lowest values of 0.0415 cm3/g and 16.5 m2/g, respectively. The second stage of decomposition of the precursor in the temperature range of 750-825 °C is associated with the formation and accumulation of the crystalline phase of perovskite in the form of a nanodispersed mesoporous powder with a specific surface area of 18 m2/g and the average mesopore diameter of 17 nm corresponding to a particle size of 40 nm when using the calculated X-ray density of 8.26 g/cm3.

Immobilization of rare-earth doped aluminate nanoparticles encapsulated with silica into polylactic acid-based color-tunable smart plastic window

An inorganic/organic nanocomposite was used to develop an afterglow and color-tunable smart window. A combination of polylactic acid (PLA) plastic waste as an environmentally-friendly hosting agent, and lanthanide-activated strontium aluminum oxide nanoparticles (SAON) encapsulated with silica nanoparticles (SAON@Silica) as a photoluminescent efficient agent resulted in a smart organic/inorganic nanocomposite. In order to prepare SAON-encapsulated silica nanoparticles (SAON@Silica), the SAON nanoparticles were coated with silica using the heterogeneous precipitation method. By using transmission electron microscopy (TEM), SAON showed a diameter range of 5–12 nm, while the SAON@Silica nanoparticles showed a diameter range of 50–100 nm. In order to ensure the development of a colorless plastic film, a homogeneous dispersion of the phosphorescent Phosphor@Silica nanoparticles throughout the plastic bulk was confirmed. CIE Lab coordinates and luminescence spectra were used to study the color shift characteristics. Under visible light conditions, the plastic films were transparent. The photoluminescent films emitted green light at 525 nm when excited at 375 nm. The hydrophobicity and ultraviolet protection were enhanced without altering the fundamental physico-mechanical performance of the plastic sheet. The current color-tunable plastic can be used in many potential applications, such as warning signs, anti-counterfeiting barcodes, smart windows, and protective apparel.

Preparation of BaSi2O2N2:Eu2+ cyan phosphor with excellent luminescence properties via heterogeneous precipitation method for high-CRI white LED applications

Preparation of BaSi2O2N2:Eu2+ cyan phosphor with excellent luminescence properties via heterogeneous precipitation method for high-CRI white LED applications

Promoting thermal stability and acid resistance of rare earth sulfide powders by coating ZnO and SiO2 double shells

AbstractAs an environment‐friendly powder with good coloring performance, rare earth sulfide is one kind of the important choices to replace cadmium and lead colorants. In particular, γ‐Ce2S3 belongs to rare earth sesquisulfide, which has a bright red color. However, the uncoated γ‐Ce2S3 is easy to decompose and release H2S in a humid or acidic environment, and its air thermal stability is limited to 350°C. In this work, γ‐Ce2S3 powders coated with zinc oxide were prepared by heterogeneous precipitation method, and a dense protective layer was formed by ZnO to improve chemical and thermal stability. Moreover, silicon dioxide was deposited on the surface of the zinc oxide coating using the microemulsion process to strengthen the powder's acid resistance. The double shells structure greatly promoted thermal stability and acid resistance of γ‐Ce2S3 powders. The results showed that rare earth sulfide powders with double shells have good stability for coloring applications.

Enhanced strength and synergistic flame retardancy of PE-base nanocomposites with coating-modified palygorskite clay

Polyethylene (PE) - base nanocomposites composed of high density polyethylene (HDPE) as matrix and coating-modified palygorskite clay (MAT) as functional filler and fire resistance was prepared by melt blending method. The MAT powder was prepared by solution heterogeneous precipitation method combined with spray drying processes. The microstructure observation shows that the particle size of the obtained MAT powder was concentrated and even. Both mechanical properties and thermal behaviors of the nanocomposites containing MAT were compared to those with commercial ceramic fillers (naming as S type flame retardants) at the same addition mass ratios level. The added MAT mass fractions in the composite were defined as 5 wt%, 10 wt%, 15 wt%, and 20 wt%, respectively. When the addition amount of MAT is 15 wt%, the impact toughness of MAT/HDPE composites approaches 13.41 kJ/m2, which is better than that with commercial fillers. The added fractions of MAT increases to 19.1 wt%, and the elongation at break of nanocomposite reaches 495%, which is much higher than that with S type flame retardants. The differential scanning calorimeter (DSC) test results show that MAT can enhance the melting point range of HDPE and improve the thermal stability of the composite. The LOI (limiting oxygen index) results confirm that MAT can effectively improve the flame retardancy of HDPE composites, and the LOI value increases with the MAT addition. The enhancement of mechanical and thermal properties of the PE-base composite is essentially originated from the uniform dispersion of MAT in polymer matrix and the strong interactions with inorganic – organic interface compatibility.

An anticounterfeiting strategy based on photochromic nonwoven polyester fabric by plasma‐assisting spray coating with ultraviolet‐responsive silica@strontium aluminate nanoparticles

Photochromism is an interesting method to enhance the anticounterfeiting activity of commercial products. Polyester fibers have been significant polymers for a variety of applications; however, they have been known to resist staining due to the absence of reactive dyeing site on their fibrous surface. Herein, we present recycled nonwoven polyester immobilized with rare‐earth activated aluminate nanoparticles for anticounterfeiting applications. Using the heterogeneous precipitation method, the lanthanide‐doped aluminate pigment was firstly coated with silica to give phosphor‐encapsulated within silica nanoparticles (Silica@Phosphor). The produced Silica@Phosphor particles were mixed with an adhesive binder in an aqueous medium, which was then spray‐coated directly onto plasma‐pretreated nonwoven polyester fabric. The fibrous composite demonstrated ultraviolet‐induced photochromism. Both phosphor and Silica@Phosphor morphologies demonstrated particle diameter of 4–12 and 90–105 nm, respectively. Various techniques were utilized to examine both morphologies and compositions of the photochromic nonwoven fabrics. The antibacterial activity, cytotoxicity, comfortability, colorfastness, and ultraviolet shielding of the prepared polyesters immobilized with Silica@Phosphor were also reported. The luminescent fabrics demonstrated two emission wavelengths at 435 and 514 nm (green) upon excitation at 369 nm (colorless). The nonwoven fabrics showed an enhanced superhydrophobicity as an improved contact angle up to 129.9° was detected upon increasing the Silica@Phosphor ratio.

Heterogenous Iron Oxide Assemblages for Use in Catalytic Ozonation: Reactivity, Kinetics, and Reaction Mechanism.

Heterogeneous catalytic ozonation (HCO) has gained increasing attention as an effective process to remove refractory organic pollutants from industrial effluents. However, widespread application of HCO is still limited due to the typically low efficacy of catalysts used and matrix passivation effects. To this end, we prepared an Al2O3-supported Fe catalyst with high reactivity via a facile urea-based heterogeneous precipitation method. Due to the nonsintering nature of the preparation method, a heterogeneous catalytic layer comprised of γ-FeOOH and α-Fe2O3 is formed on the Al2O3 support (termed NS-Fe-Al2O3). On treatment of a real industrial effluent by HCO, the presence of NS-Fe-Al2O3 increased the removal of organics by ∼100% compared to that achieved with a control catalyst (i.e., α-Fe2O3/Al2O3 or γ-FeOOH/Al2O3) that was prepared by a conventional impregnation and calcination method. Furthermore, our results confirmed that the novel NS-Fe-Al2O3 catalyst demonstrated resistance to the inhibitory effect of high concentration of chloride and sulfate ions usually present in industrial effluent. A mathematical kinetic model was developed that adequately describes the mechanism of HCO process in the presence of NS-Fe-Al2O3. Overall, the results presented here provide valuable guidance for the synthesis of effective and robust catalysts that will facilitate the wider industrial application of HCO.

Synthesis of Aluminum Phosphate-Coated Halloysite Nanotubes: Effects on Morphological, Mechanical, and Rheological Properties of PEO/PBAT Blends.

Polymer blending has been widely used to fabricate polymeric films in the last decade due to its superior properties to a single component. In this study, an aluminum phosphate-coated halloysite nanotube (HNTs@AlPO4) was fabricated using a one-pot heterogeneous precipitation method, organically modified HNTs@AlPO4 (o-HNTs@AlPO4) was used to improve the performance of polyethylene oxide/poly(butylene adipate-co-terephthalate) (PEO/PBAT) blends, and the mechanical and rheological properties of the PEO/PBAT/o-HNTs@AlPO4 films were systematically discussed. According to our results, there is an optimal addition for adequate AlPO4 nanoparticle dispersion and coating on the surface of HNTs, and organic modification could improve the interfacial compatibility of HNTs@AlPO4 and the polymeric matrix. Moreover, o-HNTs@AlPO4 may serve as a compatibilizer between PEO and PBAT, and PEO/PBAT/o-HNTs@AlPO4 films have better mechanical and rheological properties than the PEO/PBAT blends without the o-HNTs@AlPO4 component.

Surface coating preparation of spherical magnetic materials

Magnetic materials are being increasingly used in anti-counterfeiting coatings, but the dark colors of magnetic materials greatly limit their applications. This necessitates the development of light-colored magnetic materials. In this study, the heterogeneous precipitation method was used to deposit a layer of titanium dioxide (TiO2) on the surface of magnetic spherical metal particles, followed by the deposition of a layer of Ag by the reduction method, in order to achieve a light color. In the experiment, the particles were initially coated with a few tens of nanometers of TiO2 with a strong shading effect, followed by a further coating of Ag of the same thickness with a similar shading performance. Not only did this achieve a lighter color, but there was no reduction in the magnetic properties of the material after the application of the coating. Scanning electron microscopy (SEM), scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometry (XRD), and other methods were used to study the changes in morphology and composition before and after the magnetic material was coated. A magnetic tester was used to study the changes in magnetic strength before and after the magnetic material was coated.

LaPO4 coating on alumina-based fiber: Strength retention of fiber and improvement of interfacial performances

The characteristics of the interface are the key factors that determine the mechanical properties and fracture behavior of fiber-reinforced ceramic matrix composites. Design and preparation of coatings which can preserve fiber strength and maintain appropriate interfacial bonding strength are of great challenges. LaPO4 coating is a promising weak interface coating for oxide fiber reinforced oxide ceramic matrix composites. Through this coating, the toughening mechanism of the composite such as fiber pulling out and fiber debonding is triggered. The LaPO4 coating was deposited on the surface of alumina-based fibers by a solution precursor heterogeneous precipitation method. The effects of different precursors and different deposition temperatures on fiber strength were studied, and the mechanism of the strength degradation of the coated fiber was analyzed. It was found that the fibers coated with phytic acid precursor and deposited at 90 °C had the highest tensile strength compared to other coated fibers. The retention of strength is attributed to its loosely stacked coating. Besides, a single fiber pullout test was carried out to evaluate the effect of the coating on the interface of the composites. The results show that the composites coated by depositing citric acid precursor and phytic acid precursor at 90 °C can reduce the interfacial bonding strength by 32.5% and 46.7%, respectively compared to uncoated composites. This study has potential application value in the preparation of ceramic matrix composites used in oxidation and high temperature environments.

Low velocity drop weight impact behaviour of Al2O3-Ni-ZrO2 and Al2O3-Ni-Cr2O3 ceramic composites

Particulate Al2O3 matrix nanocomposites containing 1 vol.%Ni were prepared by the heterogeneous precipitation method and the addition of 5 vol.% ZrO2 (ANZ) or 1 vol.% Cr2O3 (ANC). The prepared samples were subjected to the low energy drop weight impact tests to compare the behaviour of the composites under low energy impact and to investigate the damage mechanisms. The pure Al2O3, Al2O3/Ni, Al2O3/ZrO2 and Al2O3/Cr2O3 compositions with the same additive ratios were also produced to make the comparison systematically. Also, the Vickers hardness measurements were carried out and a significant increase in hardness was attained for both ANZ and ANC composites. The average hardness value around 24.8?1.0GPa was measured for the ANZ and ANC composites which means ~15% improvement compared to the pure Al2O3. Between all the compositions, the maximum force (Fmax) value was obtained for the ANZ (for 12 J impact energy level Fmax = 26617N) according to the low energy drop weight impact test results. Tensile radial crack network formation, cone formation, fracture and crushing of the cone structure were observed as damage mechanisms for all compositions. The volume of conical frustum structure was evaluated for each composition and the effect of microstructure on possible ballistic performance was also discussed.

Enhanced interfacial wettability and mechanical properties of Ni@Al2O3/Cu ceramic matrix composites using spark plasma sintering of Ni coated Al2O3 powders

Poor wettability and weak interfacial bonding between Cu and Al2O3 have been critical issues for sintering of high-quality Ni@Al2O3/Cu composites. In this paper, we explore an interfacial engineering design methodology to achieve good mechanical properties of Ni@Al2O3/Cu composites using spark plasma sintering method. The Ni coated powders were prepared using a heterogeneous precipitation method, which can significantly improve wettability between Cu and Al2O3 and enhance their interfacial bonding. The sintered Ni@Al2O3/Cu composites with a copper content of 15 vol% showed a compact network structure of alumina well-infiltrated with metallic Cu, and achieved good mechanical (e.g., fracture toughness of 6.72 MPam1/2) and physical properties (e.g., relative density of 99.3% and electrical resistivity of 1.2810−3 Ω m). The key mechanisms for the enhanced properties of the composites synthesized using the Ni coated composite powders have been identified as: (1) well-formed ceramic/metal interfacial structures which improve wettability of Al2O3 with Cu, and promote the formation of a homogeneous network structure; (2) enhanced elemental diffusion and interfacial reactions, which result in formation of Cu2O and CuAlO2 and thus improve interfacial wetting and bonding properties.

Effect of water resistant SiO2 coated SrAl2O4: Eu2+ Dy3+ persistent luminescence phosphor on the properties of Portland cement pastes

The present study investigates the effect of water-resistant SiO2 coated SrAl2O4: Eu2+, Dy3+ (SSA) phosphor on the properties of Portland cement pastes. In order to investigate it, firstly, SrAl2O4: Eu2+, Dy3+ phosphor was coated with SiO2 using heterogeneous precipitation method. Afterward, coated phosphor was admixed with Portland cement in varying proportions to prepare cement pastes. The setting time, hydration reaction, compressive strength, and luminescence intensity analysis were carried out. Moreover, water resistance performance of SSA phosphor based cement pastes was assessed in terms of afterglow test. Based on the results of setting time and hydration studies, it was deduced that SSA phosphor has set acceleration effect on cement pastes. Use of SSA phosphor improved the compressive strength of cement pastes due to the greater degree of hydration. Moreover, the afterglow study results confirmed the hydrolysis stability of SSA phosphor in water cured cement pastes. The XRD, SEM, EDX, TG-DTG, and FTIR analyses confirmed the formation of excessive amount of hydration products in SSA phosphor based cement pastes. Based on the results obtained, it is concluded that using SSA phosphor could be a promising approach for producing water-resistant persistent luminescence light emitting cement composites.

An investigation of equibiaxial flexural strength and hardness properties of Al2O3–Ni nanocomposites based microstructures with ZrO2 and Cr2O3 additives

The investigation of new ceramics and ceramic composites to overcome the inadequacies of monolithic ceramics without using costly techniques and equipment is essential for developing ceramic armor components. The aim of the research was analyzing the mechanical properties (elastic modulus, flexural strength, and hardness) of Al2O3/1 vol% Ni nanocomposites with 5 vol% ZrO2 or 1 vol% Cr2O3 additives and estimating their performance by comparing with the pure Al2O3, Al2O3/ZrO2 composite, and Al2O3/Cr2O3 ceramic system for armor applications. The heterogeneous precipitation method was used to obtain nano-sized metal particles in the ceramic matrix for the Ni-containing compositions. Equibiaxial flexural tests were conducted for strength measurements and stored energy at failure was estimated by using the theoretical deflection of the cylindrical plate; also, post-failure total crack lengths were measured. Simultaneous addition of Ni and ZrO2 on Al2O3 matrix resulted in the highest hardness (25.5 ± 1.0 GPa) and flexural strength (367 ± 34 MPa) compared to other compositions because of the hardening effect of Ni and the grain boundary strengthening mechanism. Moreover, this composition showed the highest resistance to fragmentation as evidenced by the shortest crack length per stored energy at failure. Cr2O3 addition also provided remarkable results related to the solid solution formation for both the pure Al2O3 and Al2O3/Ni composites. By this comparative study, different compositions with high mechanical properties have been introduced as the potential candidates to be used in armor applications with static tests giving an indication about ballistic performance.

Improved thermal stability of Y3Al5O12:Ce3+ phosphor by SiO2 coating

In this paper, a heterogeneous precipitation method was adopted to coat a SiO2 layer on the surface of Y3Al5O12:Ce3+ phosphor. The surface morphologies, crystal phases, defect concentrations, luminescent properties and thermal stability of coated phosphors were investigated and compared with those of uncoated phosphor. A compact and homogeneous SiO2 layer on the surface of phosphor was determined by SEM-EDS, TEM, XRD and FT-IR results. Two thermoluminescent peaks were found at 112 °C and 248 °C on the thermoluminescence spectrum. Their intensities decreased slowly with the increasing coating amounts. It indicated that their corresponding defect concentrations were gradually reduced. Improved thermal stability was obtained by SiO2 coating in spite of a slight weakening of the emission intensity. The optimum theoretical coating amount was identified as 4%. Moreover, a structural modification mechanism on improved thermal stability of SiO2 coated Y3Al5O12:Ce3+ was proposed.

Enhanced thermal and mechanical properties of Sr0.2Ba0.8TiO3/Cu composites by introducing Cu2O interface coating

Ferroelectric ceramic with negative thermal expansion during the phase transformation from T-phase to C-phase can be used as reinforcement to obtain low thermal expansion metal matrix composites. Interface bonding plays an important role in determining thermal and mechanical properties of the composites. Here, we designed and applied Cu2O coating on the surface of Sr0.2Ba0.8TiO3 (SBT) particles by heterogeneous precipitation method, and subsequently obtained low thermal expansion Cu2O/SBT/Cu composites with excellent mechanical properties. It was found that the semi-coherent relationship can be formed in both Cu/Cu2O and Cu2O/SBT interfaces, which benefits the reduction of composites thermal expansion. The relationship among Cu2O content, SBT phase transformation and thermal expansion has been discussed. Compared with SBT/Cu composite, the average coefficient of thermal expansion of 6%Cu2O/SBT/Cu composite can be reduced from 12.97 × 10−6 °C−1 to 11.44 × 10−6 °C−1. Moreover, with the introduction of Cu2O coating, the compressive strength of the composite can reach up to 722.7 MPa. This work provides a promising method to improve the thermal expansion and mechanical property of ferroelectric reinforcement metal matrix composites.

Fabrication of Al2O3@BaFe12O19 core-shell powder by a modified heterogeneous precipitation method

Core-shell structural composites are promising to quench the desire for low-cost, lightweight and multifunctional magnetic materials, but the fabrication of highly pure shell nanoparticles with a desired morphology on a heterogeneous nuclear is still a big challenge. This study gives a successful illustration by in-situ synthesizing BaFe12O19 nanoparticles as a shell on Al2O3 core powders using BaCl2 and FeCl3 as precursors, instead of commonly used Ba(NO3)2 and Fe(NO3)3, by a modified heterogeneous precipitation process followed by calcination for crystallization. After calcination of the precipitants from the raw precursor mixture of BaCl2:FeCl3 for 1:10 at 800 °C, and for 1:8.5 at 900 °C, respectively, pure BaFe12O19 formed on pristine Al2O3, mostly with a hexagonal plane, about 100–200 nm in basal diameter and 20–100 nm in thickness. The highest saturation magnetization and coercivity of the coated Al2O3 @ BaFe12O19 powders was 23.3 emu/g and 5149 Oe, quite higher than that of the direct-mixed Al2O3-BaFe12O19 composite powder, and BaFe12O19-containing composites reported in literature, which could be attributed to the hexagonal shape of BaFe12O19 and uniform shell dispersion on Al2O3 core. The formation mechanism for the Al2O3@BaFe12O19 powders was discussed in detail.

Effect of Cu Doping on the SCR Activity of Mn‒Ce/ATP Catalyst

In this study, the Cu-doped Ce‒Mn/ATP denitration catalyst was prepared by impregnation method and heterogeneous precipitation method and its denitrification performance was tested. It was found that the denitrification effect was obviously improved after Cu doping. And the denitration effect of the catalyst prepared by the heterogeneous precipitation method was better and the denitrification rate was above 98%. Under this method, n(Cu: Mn) = 1 had the best denitration effect, with a maximum of 99.76%. The prepared catalysts were characterized by means of XRD, XPS, BET, and SEM. The results showed that CuMn2O4 and CuO appeared in the Cu doped catalysts. Moreover, the doping of Cu enriched the pore structure and surface morphology of the catalyst, so that the catalyst showed good denitrification performance.

Processing and mechanical characterization of Al2O3/Ni and Al2O3/C0 composites by pressureless sintering of nanocomposite powders

Al2O3/Ni and Al2O3/Co nanopowder mixtures (with 3 vol.% of metallic phase) were synthesized by heterogeneous precipitation method. In order to increase the green strength, polypropylene carbonate (PPC) was used as a binder while preparing green compacts. Uniaxially pressed powder mixtures were sintered at 1550?C for 2 h in a reducing atmosphere. The effects of Ni and Co nanophases on the microstructure and mechanical properties of Al2O3 ceramics were studied by X-ray diffraction, scanning electron microscopy, Vickers indentation technique and three-point bending tests. The metallic phase hindered the densification of alumina matrix, yet hardness values of Al2O3, Al2O3/Ni, and Al2O3/Co composites were comparable. Vickers fracture toughness results indicate that the composites have higher fracture toughness, but the characteristic flexural strength and Weibull modulus are higher for the pure Al2O3.