Nano-sized Nickel Particles Research Articles

The effect of different atmosphere treatments on the performance of Ni/Nb–Al2O3 catalysts for methane steam reforming

Methane steam reforming is currently the most widely used hydrogen production reaction in industry today. Ni/Nb–Al2O3 catalysts were prepared by treatment under H2, N2, and air atmosphere prior to reduction and applied for methane steam reforming reaction at low temperature (400–600 °C). The hydrogen-treated catalysts increased catalytic activity, with 55.74% methane conversion at S/C = 2, GSVH of 14400 mL g−1 h−1 and 550 °C. The H2 atmosphere treatment enhanced the Ni–Nb interaction and the formation of stable, tiny, homogeneous Ni particles (6 nm), contributing to good activity and stability. In contrast, the catalysts treated with nitrogen and air showed weaker interactions between Ni and Nb species, whereas the added Nb covered the active sites, which caused the decrease in activity. Meanwhile, carbon accumulation was also observed. This work is informative for preserving small nano-sized nickel particles to enhance catalytic performance.

Preparation and characterization of nano magnetic fluid for automotive applications

Purpose: of this paper is to prepare a nano magnetic fluids with nano additives to have the combined characteristics of high yield stress and better magnetic properties for smart vehicles. This study focuses on increasing the sedimentation time of the fluid using suitable nano additive nickel along with graphene as fillers. Design/methodology/approach: Magnetic nano sized nickel particle based electro- magneto-rheological fluid was prepared and graphene nanoparticle with thickness less than 10nm was introduced as an additive to reduce its sedimentation. This added plate like graphene acts as filler which seals the interfaces of nickel particles and thereby it improves the resistance to sedimentation. Triton X 100 was added as the surfactant for the fluid to reduce the agglomeration of the particles. Findings: Morphology of pure nickel and graphene were examined using scanning electron microscopy (SEM) images. Research limitations/implications: The important limitations is that freely dispersed micron sized iron particles could settle over a period of time, in the form of cakes at the bottommost, and it is tedious to recuperate as dispersed phase. In this investigation, nano sized nickel particles were used as additive to reduce the sedimentation of micron sized iron particles so that, the mixture is homogeneous for extended period of time. In future, addition of different types composite additives in the magnetorheological fluid could be made for the better sedimentation control. Practical implications: The sedimentation problem is one of the major drawback in the smart fluids, which can be eliminated by adding nano particles. For conventional fluid, the complete sedimentation will occur in 2 hours while the improved nano magnetic fluid with additive has good resistance to settle the micron sized iron particle up to 10 hours. Originality/value: To prepare a low cost magnetorheological fluid with nano additives like nickel particles along with fillers as graphene nano particles. With this addition of nickel and inclusion of graphene, the sedimentation problem in magnetorheological fluids is significantly reduced. This magnetorheological fluids can be used in brakes and dampers of automobiles.

Preparation and characterization of nano magnetic fluid for automotive applications

Purpose: of this paper is to prepare a nano magnetic fluids with nano additives to have the combined characteristics of high yield stress and better magnetic properties for smart vehicles. This study focuses on increasing the sedimentation time of the fluid using suitable nano additive nickel along with graphene as fillers. Design/methodology/approach: Magnetic nano sized nickel particle based electro- magneto-rheological fluid was prepared and graphene nanoparticle with thickness less than 10nm was introduced as an additive to reduce its sedimentation. This added plate like graphene acts as filler which seals the interfaces of nickel particles and thereby it improves the resistance to sedimentation. Triton X 100 was added as the surfactant for the fluid to reduce the agglomeration of the particles. Findings: Morphology of pure nickel and graphene were examined using scanning electron microscopy (SEM) images. Research limitations/implications: The important limitations is that freely dispersed micron sized iron particles could settle over a period of time, in the form of cakes at the bottommost, and it is tedious to recuperate as dispersed phase. In this investigation, nano sized nickel particles were used as additive to reduce the sedimentation of micron sized iron particles so that, the mixture is homogeneous for extended period of time. In future, addition of different types composite additives in the magnetorheological fluid could be made for the better sedimentation control. Practical implications: The sedimentation problem is one of the major drawback in the smart fluids, which can be eliminated by adding nano particles. For conventional fluid, the complete sedimentation will occur in 2 hours while the improved nano magnetic fluid with additive has good resistance to settle the micron sized iron particle up to 10 hours. Originality/value: To prepare a low cost magnetorheological fluid with nano additives like nickel particles along with fillers as graphene nano particles. With this addition of nickel and inclusion of graphene, the sedimentation problem in magnetorheological fluids is significantly reduced. This magnetorheological fluids can be used in brakes and dampers of automobiles.

Optical properties of nickel nanoparticles in systems with a statistically inhomogeneous structure

The analysis and further development of the experimental-analytical approach for determining the values of the optical parameters of nanosized particles for a system with a statistically inhomogeneous structure is presented. An improved experimental-analytical method for determining the complex specific electric polarizability of nanosized particles in systems with a statistically inhomogeneous structure is based on spectrophotometric and electron-microscopic measurements on two-dimensional structures and application of analytical solution of Rosenberg’s spectrophotometric equations with the consideration of analysis of particle size distribution.Experimental spectrophotometric and electron-microscopic studies of nickel islet films with weight thickness from 0.3 nm to 2.0 nm deposited by high-vacuum sputtering on quartz substrates in the range of the spectrum 0.2 ÷ 1, 1 μm are performed. Islands nickel film presented morphological microstructure in the form of monolayers isolated from each other nanoislands spherical surface nickel concentration (0.8 ÷ 2.0) · 1012 cm-2 and an average particle diameter 2.5 ÷ 7 nm.The optical characteristics, namely, the complex specific electric polarizability, optical electric conductivity of nanosized nickel particles are determined in the spectral range 0.2 ÷ 1.1 μm with the help of the improved experimental-analytical method. A significant increase to one order of magnitude of the absolute values of complex specific electric polarizability of nickel particles with a decrease in their size and in comparison with absolute values of complex specific electric polarizability of model spheres with refractive index and absorption index of nickel in macroscopic volumes was revealed. It is established that in the spectral dependences of optical electric conductivity of nickel nanoparticles in the range 0.2 ÷ 1.1 μm there is a band that diminishing size is shifted to a high-frequency region. In this case, the value of optical electric conductivity of nickel nanoparticles monotonically decreases with a decrease in the size by 1-2 orders of magnitude. Comparison of the obtained values of optical electric conductivity of particles in the range of the considered interval with the values of optical electric conductivity of macroscopic samples of nickel in the studied range of the spectrum shows that in particles the value of optical electric conductivity is 2-3 orders of magnitude smaller than that of massive metals. It is shown that in the nanoparticles of nickel absorption of “Drude” type in the near infrared region the spectrum is suppressed. The reason for this phenomenon may be the change of the mechanism of low-frequency electromagnetic response in nanosized metal particles in comparison with macroscopic metals.The research results are of interest for the development and optimization of nanostructured systems with the inclusion of nanosized nickel particles and functional devices based on them with given electromagnetic characteristics.Ref. 22, fig. 4.

Self-organized nickel nanoparticles on nanostructured silicon substrate intermediated by a titanium oxynitride (TiNxOy) interface

In this work we report an experimental approach by combining in situ sequential top-down and bottom-up processes to induce the organization of nanosized nickel particles. The top-down process consists in xenon ion bombardment of a crystalline silicon substrate to generate a pattern, followed by depositing a ∼15 nm titanium oxynitride thin film to act as a metallic diffusion barrier. Then, metallic nanoparticles are deposited by argon ion sputtering a pure nickel target, and the sample is annealed to promote the organization of the nickel nanoparticles (a bottom-up process). According to the experimental results, the surface pattern and the substrate biaxial surface strain are the driving forces behind the alignment and organization of the nickel nanoparticles. Moreover, the ratio between the F of metallic atoms arriving at the substrate relative to its surface diffusion mobility determines the nucleation regime of the nickel nanoparticles. These features are presented and discussed considering the existing technical literature on the subject.

The role of nanosized nickel particles in microwave-assisted dry reforming of lignin

Dry reforming (DR) of lignin with supported Ni nanoparticles under microwave irradiation (MWI) with plasma generation has been studied. Nickel depositing on the lignin surface was carried out by two different procedures. According to the first procedure, Ni was deposited from an aqueous solution of nickel acetate by impregnation. The second procedure included depositing a colloid solution of nickel particles in toluene preliminary obtained by metal vapor synthesis (MVS). As a result in both cases Ni particles of 6nm size were formed on the lignin surface. Both types of nanocatalysts govern the microwave (MW)-assisted DR of lignin. MW treatment of the mechanical mixture of a carbon sorbent with a high dielectric loss factor, and a Ni-containing lignin sample obtained by the first method resulted in the 65wt.% lignin conversion to synthesis gas with the H2/CO ratio of ∼1/1. The content of syngas in the products was 8090wt.%. It was found that MW treatment sharply increases the yield of syngas in the reforming as compared with the convective heating. The Ni-containing lignin samples before and after reforming were investigated by XRD, TEM, EDA, and magnetic measurements. It was established that different depositing procedures lead to the formation of X-ray amorphous Ni particles with markedly different magnetic properties. In contrast to entirely paramagnetic sample obtained from nickel acetate solution, superparamagnetic Ni0 particles formed by MVS exhibited a high capacity for absorption of MWI, sufficient for plasma to be generated and the reforming temperature to be reached without an additional sorbent.

Durablility of Methane Steam Reforming Catalysts Prepared By Exsolution and Infiltration

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems. In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern. In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes.

Radio Frequency-Thermal Plasma Synthesis of Metal Nano-Thin Exfoliated Graphite Hybrid.

Nano-metal with nano-thin exfoliated (NTE) graphite hybrid material has been synthesized by radio frequency (RF) thermal plasma. A micro-sized nickel powder and the NTE graphite powder were fed into the RF plasma and nano sized nickel particles attached to the surface of the NTE graphite were found. In the high temperature of RF thermal plasma that is of higher than 10,000 K, the NTE graphite was not vaporized or damaged, while the metal powder was vaporized. The size of nickel nanoparticles on the NTE graphite was 40 80 nme. The size and number density of produced metal nanoparticle can be controlled by the process pressure in a reactor, the feeding ratio of raw materials, and the flow rate of working gas. X-ray diffraction results of the produced hybrid nano material indicate that there was a bonding between the nano metal and the NTE graphite. The inert nature of surface of the NTE graphite has been a barrier for the NTE graphite to be used a compounding additive. The nano metal covered NTE graphite will open up many potential applications of NTE graphite and polymer compound materials.

Fabrication of a Ni/MgO Nanocomposite Catalyst by Exolution

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems. In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern. In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes. Figure 1

Self-organized 2D Ni particles deposited on titanium oxynitride-coated Si sculpted by a low energy ion beam

Self-ordered Ni nanoparticles grown on TiNxOy-coated crystalline silicon previously sculpted by ion beam bombardment are reported. The samples are obtained following a sequential in situ routine deposition procedure. First, crystalline Si is Xe+ bombarded, generating regular patterns. Second, a thin TiNxOy film is grown on the patterned Si substrate. Immediately, nano-sized nickel particles are deposited by ion beam sputtering and temperature-annealed forming a 2D lattice. The self-organized Ni islands are induced by preferential Ni site nucleation on the coated sculpted Si grooves.

Effect of nickel introduced by electroplating on pyrocarbon deposition of carbon-fiber preforms

In order to improve the deposition rate and microstructure of pyrocarbon, nickel was introduced by electroplating on carbon fibers and used as a catalyst during the deposition of pyrocarbon at 1000°C using methane as a precursor gas. The distribution of nickel catalyst and the microstructure of pyrocarbon were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Raman micro-spectrometry. Results show that nano-sized nickel particles could be well distributed on carbon fibers and the pyrocarbon deposited catalytically had a smaller d002 value and a higher graphitization degree compared with that without catalyst. In addition, the deposition rate of pyrocarbon in each hour was measured. The deposition rate of pyrocarbon in the first hour was more than 10 times when carbon cloth substrates were doped with nickel catalysts as compared to the pure carbon cloths. The pyrocarbon gained by rapid deposition may include two parts, which are generation directly on the nickel catalyst and formation with the carbon nanofibers as crystal nucleus.

Effect of Temperature on the Synthesis of Nano-Nickel Particles

<b> </b><b> </b>The focus of this study is to observe the effect of temperature on the size and morphology of nano-nickel particles. Nano-nickel particles have been prepared by a simple polymer-surfactant interaction of a cationic polymer poly vinyl pyrrolidone (PVP) with an anionic surfactant, sodium-dodecyl-sulphate SDS at different temperatures i.e. 60℃, 80℃ and 100℃. Nano-sized nickel particles were synthesized by using nickel chloride as the precursor, hydrazine as the reducing agent in the presence of SDS and PVP in a strong basic medium (pH-10.2). Our research shows that the rate of reduction increases as the reaction temperature was increased from 60℃ to 100℃. Finer particles of diameters less than 10nm were formed as the temperature was increased from 60 to 100℃. The morphology of the synthesized nano-nickel particles also varied as the temperature was increased. The concentration of nickel chloride and SDS/PVP was kept constant in all these experiments. The nano-sized nickel particles synthesized were characterized by using SEM and HRTEM.

Enhancement of electrocatalytic activity towards hydrogen evolution reaction by boron-modified nickel nanoparticles

Nanosized nickel particles have been synthesized by three different routes: polyol, microemulsion and precipitation/reduction methods. Nickel nanoparticles have been evaluated as electrocatalysts for the hydrogen evolution reaction (HER). The electrocatalysts have been characterized by using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Their electrocatalytic performance in the hydrogen evolution reaction has been evaluated by means of the Tafel curves recorded in alkaline medium. The activity for the hydrogen evolution reaction increases with the increasing amount of reduced Ni in the electrocatalysts. Remarkably, the formation of a nickel-boride alloyed phase (Ni3B) is responsible for the higher activity of the sample prepared by the precipitation/reduction method for the HER. The crystalline phase Ni3B appears to be responsible for the very high activity in hydrogen production.

Aqueous solution-chemical derived Ni–Al2O3 solar selective absorbing coatings

Here we report the preparation of Ni–Al2O3 absorbing coatings by a facile aqueous solution-chemical method. In this approach, aluminum nitrate and nickel nitrate were simply mixed in water as precursor solution together with a chelating agent and a wetting agent, all of which were of low cost and available commercially. At high temperature and in N2 atmosphere, aluminum ions were converted into an Al2O3 matrix and nickel ions were in situ reduced into nano-size nickel particles embedded in the Al2O3 matrix. The optimum single layer attained a high normal solar absorptance of 0.85 and a low normal thermal emittance of 0.03. A three-layer coating, i.e. double absorption layers together with one top anti-reflection layer, exhibited better optical properties of absorptance/thermal emittance=0.93/0.05, respectively, and was stable in air up to 300°C.

A Novel Method for the Preparation of Nano-Sized Nickle Powders

Nano-sized nickel powders were prepared through a wet chemical reduction, of NiCl2 by sodium in liquid ammonia at -45 °C, and a subsequent heat-treatment in vacuum at 300 °C. The prepared product was systematically characterized by X-ray diffraction (XRD), scan electron microscopy (SEM), transmission electron microscopy (TEM), and BET specific surface area measurement. The results show that the product was composed of nano-sized nickel particles, with average particle diameter of about 20 nm, and specific surface area of about 30 m2g-1. The possible formation mechanism of the nano-sized nickel powder was also discussed briefly.

Nanoporous Silicon Oxycarbonitride Ceramics Derived from Polysilazanes In situ Modified with Nickel Nanoparticles

Ni–polysilazane precursors were synthesized from polysilazane and trans- [bis(2-aminoetanol-N,O)diacetato-nickel(II)]. The Ni–polysilazane precursors are superparamagnetic indicating formation of nanosized nickel particles (∼2−3 nm) confirmed by HRTEM as well. The as-obtained Ni–polysilazane precursors were thermolized at 700 °C and transformed to ceramic nanocomposites, manifesting a nanoporous structure, revealing a BET surface area of 215 m2 g–1, a micropore surface area of 205 m2 g–1, and a micropore volume of 0.113 cm3 g–1. Although Si–C–N–(O) ceramics derived from the native polysilazane are nonporous, the pronounced development of porosity in the Ni/Si–C–N–(O) system was attributed to (i) the stabilizing effect of carbosilane bonds, which prohibit the formation of macropores during thermolysis; (ii) the reduced barrier for heterogeneous pore nucleation as a result of in situ created nickel nanoparticles; and (iii) the reduced viscous flow of the pores due to the presence of nickel nanoparticles and turbostratic carbon. The formation of turbostratic carbon is due to the reactions catalyzed by nickel nanoparticles that result in graphene stacking as inferred from the STA–MS studies.

Carbon Nanotubes Guides for Nickel Electrical Interconnects

We present an innovative approach for interconnections based on aligning nanosized nickel particles along single-walled carbon nanotubes bundles. The nanotubes are first deposited to connect normal gold contacts or niobium nitride superconducting pads and a successive step in fabrication, based on an electrochemical method, enables us to “coat” the nanotubes with nickel particles. This technique, as shown by field-emission SEM analysis, generates chains of nickel particles aligned along the nanotubes connecting the contact electrodes. The temperature dependence of the resistance of the chains of Ni nanoparticles evidences the metallic nature of the obtained interconnection and shows values of the resistances up to three orders of magnitudes lower than those of the bare nanotubes bundles. The ease of the fabrication process and its reliability candidate our technique as a possible solution for interconnects applications.

The role of hypoxia inducible factor-1α in the increased MMP-2 and MMP-9 production by human monocytes exposed to nickel nanoparticles

Nickel is an important economic commodity, but it can cause skin sensitization and may cause lung diseases such as lung fibrosis, pneumonitis, bronchial asthma and lung cancer. With development of nanotechnology, nano-sized nickel (Nano-Ni) and nano-sized titanium dioxide (Nano-TiO2) particles have been developed and produced for many years with new formulations and surface properties to meet novel demands. Our previous studies have shown that Nano-Ni instilled into rat lungs caused a greater inflammatory response as compared with standard-sized nickel (5 μm) at equivalent mass concentrations. Nano-Ni caused a persistent high level of inflammation in lungs even at low doses. Recently, several studies have shown that nanoparticles can translocate from the lungs to the circulatory system. To evaluate the potential systemic effects of metal nanoparticles, we compared the effects of Nano-Ni and Nano-TiO2 on matrix metalloproteinases 2 and 9 (MMP-2 and MMP-9) gene expression and activity. Our results showed that exposure of human monocyte U937 to Nano-Ni caused dose- and time- dependent increase in MMP-2 and MMP-9 mRNA expression and pro-MMP-2 and pro-MMP-9 activity, but Nano-TiO2 did not. Nano-Ni also caused dose- and time- related increase in tissue inhibitor of metalloproteinases 1 (TIMP-1), but Nano-TiO2 did not. To determine the potential mechanisms involved, we measured the expression of hypoxia inducible factor 1α (HIF-1α) in U937 cells exposed to Nano-Ni and Nano-TiO2. Our results showed that exposure to Nano-Ni caused HIF-1α accumulation in the nucleus. Furthermore, pre-treatment of U937 cells with heat shock protein 90 (Hsp90) inhibitor, 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG), prior to exposure to Nano-Ni significantly abolished Nano-Ni-induced MMP-2 and MMP-9 mRNA upregulation and increased pro-MMP-2 and pro-MMP-9 activity. Our results suggest that HIF-1α accumulation may be involved in the increased MMP-2 and MMP-9 production in U937 cells exposed to Nano-Ni.

Low-Temperature Metal Induced Crystallization of Amorphous Silicon Using Nano-Nickel Particles

A simple method was presented to conduct the low-temperature metal induced crystallization of an amorphous silicon (a-Si) film using nano-sized nickel particles. The effects of the annealing temperature and the duration on the morphology and the crystallized size of the induced polycrystalline silicon (poly-Si) film were investigated using a field emission scanning electron microscope (FE-SEM), a twin thin-film X-ray diffractometer (XRD), a Raman spectrometer, and an energy dispersive spectrum (EDS). In addition, the residual nickel and the I-V characteristics of the poly-Si film were measured using a secondary ion mass spectrometer and a semiconductor parameter analyzer, respectively. The crystalline peak of Si (311) was obviously detected even at an annealing temperature of 400°C and the duration of 1 h. The crystallization temperature was lowered due to the high activity of the nano-nickel particles. Therefore, this study supports the feasibility of applying nano-nickel particles to crystallize the a-Si film.

Nano-sized agglomerated Ni particles synthesised by a phase transformation method

Nano-sized nickel particles have been prepared by using a 'phase transformation' method. Nickel chloride was used as a precursor, hydrazine as a reducing agent in the presence of an anionic surfactant sodium-dodecyl-sulphate (SDS) and PVP (polyvinylpyrrolidone – a cationic polymer) in a strong basic medium. Initially the effect of SDS and SDS-PVP on the particle size formation was studied, then hydrazine only and then followed by the effect of adding SDS to the solution. SEM characterisation showed that in the absence of SDS-PVP the Ni particles were almost spherical but when SDS and SDS-PVP were present the particles showed very spiky morphology. Much finer particles were produced when SDS was used on its own. However, the combination of SDS-PVP had produced the finest particles in our research work. Froth contained Ni particles; TEM characterisation showed these Ni particles were much finer than the particles collected from the precipitated particles.