Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2021 Oct 13;6(42):27842–27850. doi: 10.1021/acsomega.1c03468

Chemical Vapor Synthesis of Nonagglomerated Nickel Nanoparticles by In-Flight Coating

Yong-Su Jo †,‡, Hui-Jung Lee †,§, Hye-Min Park †,∥, Tae-Wook Na †, Jin-Seung Jung §, Seok-Hong Min §, Young Keun Kim ‡, Seung-Min Yang †,*
PMCID: PMC8552332  PMID: 34722984

Abstract

graphic file with name ao1c03468_0013.jpg

Nickel (Ni) nanoparticles (NPs) prepared through vapor-phase synthesis (VPS) are preferred for multilayer ceramic capacitor electrodes due to their high purity and crystallinity advantages. Agglomerated Ni NPs are usually generated using VPS but are undesirable because they cause various problems such as low packing density and electrical shorts. This study proposes the use of coating-assisted chemical vapor synthesis (CVS) for agglomerate inhibition using NaCl or KCl as a coating agent. We have found that the agglomeration ratio, 34.40%, for conventional CVS, can be reduced to 4.80% in the proposed method by in-flight coating with KCl at 900 °C by image analysis using field-emission scanning electron microscopy. Furthermore, the X-ray diffraction and X-ray fluorescence analyses confirm that the NaCl and KCl coating agent can be removed by washing with distilled water. We believe that this coating process can be used to inhibit the formation of agglomerates during the CVS of Ni NPs.

Introduction

Nickel (Ni) nanoparticles (NPs) have been widely used in various applications, including electrodes,1,2 catalysts,3,4 batteries,5,6 and supercapacitors.7,8 More specifically, they have been used extensively as electrode materials for multilayer ceramic capacitors (MLCCs). Various methods, including wet chemical synthesis9,10 and vapor-phase synthesis (VPS),11−15 have been used to produce Ni NPs. Those prepared by VPS, including spray pyrolysis, physical vapor synthesis, and chemical vapor synthesis (CVS), are preferred for MLCC electrodes due to their high purity and crystallinity advantages.

The formation of agglomerates during VPS is typical due to the high process temperature and absence of surfactants.16−18 Agglomerated particles are preferred in applications, such as catalysts and sensors, because they have a large surface area.19 However, such particles are undesirable for use in MLCC electrodes, as they cause various problems such as low packing density and electric shorts. Therefore, a classification process is performed to remove agglomerates from Ni NPs prepared by VPS, resulting in a low yield.20

In VPS, particles are formed by nucleation, surface growth, and coagulation. The coagulation frequency increases when the temperature or number density of the particles increases or the mass of individual particles decreases. Coagulated particles usually evolve into spherical particles through full coalescence or into chain-like agglomerated particles through partial coalescence. Complete coalescence occurs with enough temperature and residence time and when the size of the particles is smaller than the critical size depending on the material.16,17,21−23

The trend toward increasing the capacitance and miniaturization of MLCCs has been driving a reduction in the Ni NP size requirements.24 If the particle size decreases while maintaining the production rate, the coagulation rate increases because the number density of particles increases exponentially. Thus, this miniaturization trend has caused the agglomerate formation to become more problematic.

Many researchers have studied and developed methods to inhibit agglomeration during VPS. Gas quenching has been studied most actively.25,26 However, the cost of this method is high due to excessive gas usage, and it is technically challenging to reduce the temperature rapidly and uniformly when the reactor scale is increased. Another promising method is vapor phase coating.27,28 In this method, Na and NaCl are used as a reducing agent and a coating, respectively, to produce NaCl-coated NPs during flame synthesis. However, it is difficult to control this process because it is necessary to use highly reactive Na, and coating is performed by NaCl as a byproduct. We, therefore, chose to study the coating process using CVS, as shown in Figure 1, which should allow easier control by using a nonreactive coating agent such as NaCl and KCl.

Figure 1.

Figure 1

Open in a new tab

Schematic of coating-assisted CVS.

Theoretical Basis

In this study, we tried to inhibit agglomeration using in-flight coating in the cooling section. The intent was to perform in-flight coating in a temperature range of 800–900 °C. We considered metal chlorides as coating agent candidates for the following reasons. First, they have an appropriate vapor pressure for condensation to occur between 800 and 900 °C. Second, their thermal decomposition does not occur at a reactor temperature of 1000 °C. Third, we can easily remove them by water washing.

Among the various metal chlorides, we selected MgCl2, LiCl, NaCl, KCl, ZnCl2, and CaCl2 as candidates from the following steps. First, metal chlorides reacting with H2 and Ni were excluded, which eliminated chlorides such as FeCl3, CuCl, and CoCl2. Second, chlorides of radioelements were excluded. Third, chlorides of rare-earth elements were excluded due to their high price. Fourth, metal chlorides with a boiling point lower than 800 °C were excluded, resulting in the elimination of chlorides such as AlCl3 and GaCl3.

Gibbs free energy changes for the hydrogen reduction reactions of NiCl2(g), MgCl2(g), LiCl(g), NaCl(g), KCl(g), ZnCl2(g), and CaCl2(g) were calculated by Thermo-Calc DB to determine reactivities of the selected candidates, as shown in Figure 2. Note that if a particular metal chloride does not react with H2, it also does not react with Ni. Figure 2 shows that only NiCl2(g) should be expected to react with H2.

Figure 2.

Figure 2

Open in a new tab

Hydrogen reduction Gibbs free energies for various metal chlorides as a function of temperature.

Saturated vapor pressures of NiCl2, MgCl2, LiCl, NaCl, KCl, ZnCl2, and CaCl2 were calculated by the Antoine coefficients,29 as shown in Figure 3. As the vapor pressure of the coating agent increases, the distance between the Ni cores increases. The higher the vapor pressure of the coating agent, the lower is the formation of the agglomerates. In contrast, if the vapor pressure of the coating agent is too high, homogeneous nucleation of the coating agent may be induced in the cooling section, which does not help to inhibit agglomeration but rather may cause the clogging of the reactor. Therefore, it is appropriate to use the smallest amount of the coating agent that can inhibit agglomeration.

Figure 3.

Figure 3

Open in a new tab

Saturated vapor pressure of various metal chlorides as a function of temperature.

Among the metal chlorides, NaCl and KCl, which are earth abundant, were selected in this study to investigate the effect of in-flight coating on the formation of agglomerates during CVS. We determined that the agglomeration inhibition behavior according to the vapor pressure could be observed because the vapor pressures of NaCl and KCl differ more than twice at 900 °C.

Results and Discussion

CVS of Uncoated Ni NPs

The field-emission scanning electron microscopy (FESEM) image of uncoated Ni NPs (sample 1) prepared by conventional CVS is shown in Figure 4a and the corresponding particle size distribution histogram is shown in Figure 4b. The count median diameter (CMD) and geometric standard deviation (GSD) of the Ni NPs in this sample were 75.60 nm and 1.24, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 38, 19, 6, and 3, respectively, and the agglomeration ratio was 34.40%. The CMD, GSD, and agglomeration ratios of samples 1–7 are summarized in Table 2.

Figure 4.

Figure 4

Open in a new tab

(a) FESEM image, (b) particle size distribution histogram, (c) XRD, and (d) XRF results of uncoated Ni NPs (sample 1) prepared by conventional CVS.

Table 2. CMD, GSD, and Agglomeration Ratio of Samples.

sample number CMD (nm) GSD agglomeration ratio (%)
1 75.60 1.24 34.40
2 81.80 1.25 23.60
3 64.50 1.24 20.20
4 63.70 1.33 17.40
5 74.20 1.25 16.40
6 72.10 1.28 16.00
7 71.90 1.33 4.80
Open in a new tab

The X-ray diffraction (XRD) result of sample 1 in Figure 4c shows peaks of Ni matching with JCPDS 04-0850. The X-ray fluorescence (XRF) result of sample 1 in Figure 4d shows that the Ni and Cl contents were 98.47 and 1.53 wt %, respectively. The XRF results of samples 1–7 are summarized in Table 3. It is assumed that NiCl2 was deposited on the surface of the Ni NPs as an unreacted residual precursor. As this is a trace amount, it was likely not detected by XRD.

Table 3. XRF Results of Samples.

  chemical composition (wt %)
  as-prepared
 after washing
sample number Ni Na K Cl Ni Na K Cl
1 98.47     1.53 99.64     0.36
2 95.20 0.97   3.83        
3 91.10 2.34   6.57        
4 86.56 4.30   9.13 99.39     0.61
5 91.61   3.97 4.43        
6 81.17   8.93 9.90        
7 64.69   17.96 17.36 99.89     0.11
Open in a new tab

CVS of NaCl-Coated Ni NPs

Figure 5a–c shows SEM images of NaCl-coated Ni NPs (samples 2–4) prepared by coating-assisted CVS. The size distribution histograms of the Ni cores are shown in Figure 5d–f. When the coating temperature was 800 °C, the CMD and GSD values for the coated NP Ni cores were 81.80 nm and 1.25, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 34, 15, 5, and 0, respectively, and the agglomeration ratio was 23.60%. When the coating temperature was 850 °C, the CMD and GSD values were 64.50 nm and 1.24, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 27, 13, 2, and 0, respectively, and the agglomeration ratio was 20.20%. When the coating temperature was 900 °C, the CMD and GSD values were 63.70 nm and 1.33, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 27, 9, 1, and 0, respectively, and the agglomeration ratio was 17.40%.

Figure 5.

Figure 5

Open in a new tab

(a–c) FESEM images and (d–f) size distribution histograms of NaCl-coated Ni NPs (samples 2–4) with coating temperatures of (a,d) 800, (b,e) 850, and (c,f) 900 °C. (CMD: count median diameter, GSD: geometric standard deviation).

The agglomeration ratio decreased from 23.60 to 17.40% as the coating temperature was increased from 800 to 900 °C. It was determined that the agglomeration ratio, which was 34.40% when not coated, was reduced to 17.40% by coating with NaCl. However, the agglomeration ratio is still high even when Ni NPs are coated with NaCl. To further reduce the agglomeration ratio, it may be possible to increase the coating temperature or use a metal chloride with a vapor pressure higher than that of NaCl.

The XRD results of samples 2–4 in Figure 6a show peaks of Ni and NaCl matching with JCPDS 04-0850 and 72-1668, respectively. The XRF results are shown in Figure 6b. When the coating temperatures were 800, 850, and 900 °C, the Ni contents were 95.20, 91.10, and 86.56 wt %, the Na contents were 0.97, 2.34, and 4.30 wt %, and the Cl contents were 3.83, 6.57, and 9.13 wt %, respectively. These results show that as the temperature increased, the amount of the remaining coating agent also increased.

Figure 6.

Figure 6

Open in a new tab

(a) XRD and (b) XRF results of NaCl-coated Ni NPs (samples 2–4) with coating temperatures of 800, 850, and 900 °C.

CVS of KCl-Coated Ni NPs

FESEM images of KCl-coated Ni NPs (samples 5–7) prepared through coating-assisted CVS are shown in Figure 7a–c. The size distribution histograms of the Ni cores are shown in Figure 7d–f. When the coating temperature was 800 °C, the CMD and GSD values for the coated NP Ni cores were 74.20 nm and 1.25, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 27, 8, 1, and 0, respectively, and the agglomeration ratio was 16.40%. When the coating temperature was 850 °C, the CMD and GSD values were 72.10 nm and 1.28, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 28, 8, 0, and 0, respectively, and the agglomeration ratio was 16.00%. When the coating temperature of KCl was 900 °C, the CMD and GSD values were 71.9 nm and 1.33, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 9, 2, 0, and 0, respectively, and the agglomeration ratio was 4.80%.

Figure 7.

Figure 7

Open in a new tab

(a–c) FESEM images and (d–f) size distribution histogram of Ni cores of KCl-coated Ni NPs (samples 5–7) with coating temperatures of (a,d) 800, (b,e) 850, and (c,f) 900 °C.

The agglomeration ratio decreased from 16.40 to 4.80% as the coating temperature was increased from 800 to 900 °C. It was determined that agglomeration could be effectively inhibited by coating with KCl. As the saturated vapor pressure of KCl is higher than that of NaCl, the distance between the nickel cores is sufficient to inhibit agglomeration when a relatively large amount of KCl is deposited.

Figure 8 shows FESEM and energy-dispersive X-ray spectroscopy (EDS) results of sample 7. It was observed that the KCl coating layer surrounding the Ni core looks transparent. This can be explained because the penetration depth is large when the accelerating voltage is high and the atomic number is low.30,31

Figure 8.

Figure 8

Open in a new tab

EDS mapping of sample 7, including (a) FESEM image, (b) Cl, (c) K, and (d) Ni elements.

The XRD results of samples 5–7 in Figure 9a show the peaks of Ni and KCl matching with JCPDS 04-0850 and 41-1476, respectively. The XRF results are shown in Figure 9b. When the coating temperatures were 800, 850, and 900 °C, the Ni contents were 91.61, 81.17, and 64.69 wt %, the K contents were 3.97, 8.93, and 17.96 wt %, and the Cl contents were 4.43, 9.90, and 17.36 wt %, respectively. Again, more of the coating agent remained as the temperature increased, but the effect was more pronounced with KCl.

Figure 9.

Figure 9

Open in a new tab

(a) XRD and (b) XRF results of KCl-coated Ni NPs (samples 5–7) with coating temperatures of 800, 850, and 900 °C.

Removal of Chlorides

The XRD and XRF results of samples 1, 4, and 7 after washing with distilled water are shown in Figure 10. The XRD results in Figure 10a show only the peaks of Ni in all samples. The XRF results are shown in Figure 10b. Ni contents of 99.64, 99.39, and 99.89 wt % and Cl contents of 0.36, 0.61, and 0.11 wt % were found in samples 1, 4, and 7, respectively. It was determined that we can remove NaCl and KCl used for coating using distilled water, as the Na and K contents were not detected in samples 4 and 7.

Figure 10.

Figure 10

Open in a new tab

(a) XRD and (b) XRF results of washed samples 1, 4, and 7.

The FESEM image and size distribution histogram of sample 7 after washing with distilled water are shown in Figure 11. The CMD and GSD values were 70.50 nm and 1.30, respectively. The number of agglomerates consisting of 2, 3, 4, and 5 primary particles was identified as 12, 1, 0, and 0, respectively, and the agglomeration ratio was 5.40%.

Figure 11.

Figure 11

Open in a new tab

(a) FESEM image and (b) particle size distribution results of washed sample 7.

Conclusions

We carried out the coating-assisted CVS using NaCl and KCl as agglomeration inhibitors. Compared to conventional CVS with an agglomeration ratio of 34.4%, NaCl and KCl inhibitors reduced the ratio to 17.4 and 4.8%, respectively, when processed at 900 °C. KCl is a more effective agglomeration inhibitor than NaCl, presumably due to its higher vapor pressure. Therefore, we expect that a further increase in the inhibitor vapor pressure would be helpful during NP manufacturing with a higher number density. The NaCl and KCl inhibitors used in this study were easily removed with distilled water. Thus, we believe that coating-assisted CVS can inhibit the formation of agglomerates in the manufacture of Ni NPs.

Experimental Section

Preparation of Feedstock for the Synthesis of Uncoated Ni NPs

NiCl2·6(H2O) (Alfa Aesar, 98%) was dissolved in deionized water, and the resulting solution was spray-dried at 180 °C (B-290, BUCHI Labortechnik). NiCl2·2(H2O) powder collected from a spray-dryer was dried at 250 °C under a pressure of 10–5 Torr to obtain an anhydrous NiCl2 powder.

Preparation of Feedstock for the Synthesis of Coated Ni NPs

NiCl2·6(H2O) and NaCl (Sigma-Aldrich, 99.5%) or KCl (Sigma-Aldrich, 99.0%) were dissolved together in distilled water followed by spray-drying of the mixed solution at 180 °C. The composite powder collected from the spray-dryer was dried at 250 °C under a pressure of 10–5 Torr.

CVS of Uncoated and Coated Ni NPs

The vertical hot-wall reactor shown in Figure 1 was used for CVS at a fixed heating zone temperature of 1000 °C (Figure 1a). Because the vapor pressure of NiCl2 and the H2 reduction rate are proportional to the temperature, increasing the process temperature has the advantage of increasing the Ni powder production rate. However, due to the limit of the operating temperature of the reactor material, quartz, all process temperatures in this study were performed at 1000 °C with a precision of ±2 °C. The feedstock was introduced to a reactor by a powder feeder (Fine Techniques) with an N2 carrier gas flow rate of 5.6 standard liter per minute (SLM). Table 1 shows that the coating agent content and feed rate changed with the coating temperature. The amount of the coating agent content was determined by the saturated vapor pressure at the coating temperature. Note that the feed rate was increased to increase only the injection amount of the coating agent while maintaining the injection amount of NiCl2 at 10 g/h. H2 reducing gas was injected directly into the particle formation section at a flow rate of 0.5 SLM (Figure 1b). The temperature decreased through the cooling section due to air cooling of the reactor outer wall (Figure 1c).

Table 1. Samples Prepared in This Study.

    content of the coating agent in the feedstock (wt %)
 vapor pressure of (kPa)
  
sample number feed rate of feedstock (g/h) NaCl KCl NaCl KCl coating temperature (°C)
1 10          
2 10.30 2.91   0.04   800
3 10.75 6.99   0.11   850
4 11.78 15.06   0.24   900
5 10.85   7.83   0.09 800
6 12.17   17.83   0.23 850
7 15.51   35.49   0.54 900
Open in a new tab

Metal chlorides evaporate in the top section while H2 reduction of NiCl2 vapor occurs in the particle formation section, leading to nucleation, growth, and coagulation of Ni NPs. Complete coalescence of coagulated NPs mainly occurs in the particle formation section, and partial coalescence primarily occurs in the cooling section. The in-flight coating was performed in this cooling section to inhibit partial coalescence in the coating temperature range of 800–900 °C.

Ni NPs produced by CVS were retrieved from the collector and characterized by FESEM (Quanta 250 FEG, FEI), XRD (Empyrean, Panalytical), and XRF (M4 TORNADO, Bruker). Each sample was sputter-coated with a thin film of Au–Pd before FESEM analyses to improve the resolution on the FESEM images. The inner electrode of MLCC is made of Ni NPs and its thickness is only hundreds nm. Hence, the average particle size and size distribution of the Ni NPs are important and were expressed as CMD and GSD, respectively. CMD and GSD were determined by a randomly sampling of 200 particles from FESEM images. The agglomeration ratio was calculated by dividing the number of primary particles constituting agglomerates by the sum of the primary particles constituting agglomerates plus non-agglomerated particles, as determined by the randomly sampling of more than 500 particles from FESEM images. The content ratio and phase of the coating agent and Ni were determined by XRD analysis. The residual amount before and after the removal of the coating agent was determined by XRF analysis.

Removal of Chlorides

Samples 1, 4, and 7 were sonicated in distilled water (Q500, Qsonica) for the removal of chlorides. Three samples were selected to determine whether the coating agent could be removed. Sample 1 without using a coating agent and samples 4 and 7 with the highest amount of each coating agent were selected as a control. After washing, NPs were obtained by centrifugal separation at 10,000 rpm and characterized by XRD and XRF. CMD and GSD were determined by randomly sampling of 200 particles from the FESEM image of washed sample 7. Also, the agglomeration ratio was determined by randomly sampling more than 500 particles from FESEM images.

Acknowledgments

This study was supported by the Korea Institute of Industrial Technology (no. JB-21-0004).

The authors declare no competing financial interest.

References

  1. Im T.; Pyo J.; Lee J.-s.; Lee C. S. Fabrication of homogeneous nanosized nickel powders using a planetary ball mill: Applications to multilayer ceramic capacitors (MLCCs). Powder Technol. 2021, 382, 118–125. 10.1016/j.powtec.2020.12.043. [DOI] [Google Scholar]
  2. Songping W. Preparation of ultra fine nickel-copper bimetallic powder for BME-MLCC. Microelectron. J. 2007, 38, 41–46. 10.1016/j.mejo.2006.09.013. [DOI] [Google Scholar]
  3. Wang A.; Yin H.; Lu H.; Xue J.; Ren M.; Jiang T. Effect of organic modifiers on the structure of nickel nanoparticles and catalytic activity in the hydrogenation of p-nitrophenol to p-aminophenol. Langmuir 2009, 25, 12736–12741. 10.1021/la901815b. [DOI] [PubMed] [Google Scholar]
  4. Wang H. Y.; Lua A. C. Development of metallic nickel nanoparticle catalyst for the decomposition of methane into hydrogen and carbon nanofibers. J. Phys. Chem. C 2012, 116, 26765–26775. 10.1021/jp306519t. [DOI] [Google Scholar]
  5. Oh Y. J.; Kim J. H.; Park S.-K.; Park J.-S.; Lee J.-K.; Kang Y. C. Highly efficient hierarchical multiroom-structured molybdenum carbide/carbon composite microspheres grafted with nickel-nanoparticle-embedded nitrogen-doped carbon nanotubes as air electrode for lithium-oxygen batteries. Chem. Eng. J. 2018, 351, 886–896. 10.1016/j.cej.2018.06.166. [DOI] [Google Scholar]
  6. Zhong G.; Li S.; Xu S.; Liao W.; Fu X.; Peng F. Nickel Nanoparticles Encapsulated in Nitrogen-Doped Carbon Nanotubes as Excellent Bifunctional Oxygen Electrode for Fuel Cell and Metal-Air Battery. ACS Sustainable Chem. Eng. 2018, 6, 15108–15118. 10.1021/acssuschemeng.8b03582. [DOI] [Google Scholar]
  7. Jiang Y.; Zhou C.; Liu J. A non-polarity flexible asymmetric supercapacitor with nickel nanoparticle@ carbon nanotube three-dimensional network electrodes. Energy Storage Mater. 2018, 11, 75–82. 10.1016/j.ensm.2017.09.013. [DOI] [Google Scholar]
  8. Wu X.; Xing W.; Zhang L.; Zhuo S.; Zhou J.; Wang G.; Qiao S. Nickel nanoparticles prepared by hydrazine hydrate reduction and their application in supercapacitor. Powder Technol. 2012, 224, 162–167. 10.1016/j.powtec.2012.02.048. [DOI] [Google Scholar]
  9. Park J. W.; Chae E. H.; Kim S. H.; Lee J. H.; Kim J. W.; Yoon S. M.; Choi J.-Y. Preparation of fine Ni powders from nickel hydrazine complex. Mater. Chem. Phys. 2006, 97, 371–378. 10.1016/j.matchemphys.2005.08.028. [DOI] [Google Scholar]
  10. Carenco S.; Boissière C.; Nicole L.; Sanchez C.; Le Floch P.; Mézailles N. Controlled design of size-tunable monodisperse nickel nanoparticles. Chem. Mater. 2010, 22, 1340–1349. 10.1021/cm902007g. [DOI] [Google Scholar]
  11. He Y.; Li X.; Swihart M. T. Laser-driven aerosol synthesis of nickel nanoparticles. Chem. Mater. 2005, 17, 1017–1026. 10.1021/cm048128t. [DOI] [Google Scholar]
  12. Jung K. Y.; Lee J. H.; Koo H. Y.; Kang Y. C.; Park S. B. Preparation of solid nickel nanoparticles by large-scale spray pyrolysis of Ni(NO3)2·6H2O precursor: Effect of temperature and nickel acetate on the particle morphology. Mater. Sci. Eng. B 2007, 137, 10–19. 10.1016/j.mseb.2006.09.025. [DOI] [Google Scholar]
  13. Jung D.-W.; Oh S.-M.; Park D.-W. Preparation of Nickel Nanopowder using the Transferred Arc Plasma for MLCCs. Korean Chem. Eng. Res. 2008, 46, 701–706. [Google Scholar]
  14. Bai L.; Fan J.; Hu P.; Yuan F.; Li J.; Tang Q. RF plasma synthesis of nickel nanopowders via hydrogen reduction of nickel hydroxide/carbonate. J. Alloys Compd. 2009, 481, 563–567. 10.1016/j.jallcom.2009.03.054. [DOI] [Google Scholar]
  15. Yang S.-M.; Kim D.-S.; Choi H.; Kim K.-H.; Hwang N.-M. Shape change of submicron nickel particles under hydrogen and nickel chloride vapor. Appl. Surf. Sci. 2020, 509, 145274. 10.1016/j.apsusc.2020.145274. [DOI] [Google Scholar]
  16. Tsantilis S.; Pratsinis S. E. Soft- and Hard-Agglomerate Aerosols Made at High Temperatures. Langmuir 2004, 20, 5933–5939. 10.1021/la036389w. [DOI] [PubMed] [Google Scholar]
  17. Feng J.; Huang L.; Ludvigsson L.; Messing M. E.; Maisser A.; Biskos G.; Schmidt-Ott A. General approach to the evolution of singlet nanoparticles from a rapidly quenched point source. J. Phys. Chem. C 2016, 120, 621–630. 10.1021/acs.jpcc.5b06503. [DOI] [Google Scholar]
  18. Malekzadeh M.; Swihart M. T. Vapor-phase production of nanomaterials. Chem. Soc. Rev. 2021, 50, 7132–7249. 10.1039/d0cs01212b. [DOI] [PubMed] [Google Scholar]
  19. Eggersdorfer M. L.; Pratsinis S. E. Agglomerates and aggregates of nanoparticles made in the gas phase. Adv. Powder Technol. 2014, 25, 71–90. 10.1016/j.apt.2013.10.010. [DOI] [Google Scholar]
  20. Bai L.; Yuan F.; Tang Q. Synthesis of nickel nanoparticles with uniform size via a modified hydrazine reduction route. Mater. Lett. 2008, 62, 2267–2270. 10.1016/j.matlet.2007.11.061. [DOI] [Google Scholar]
  21. Lehtinen K. E. J.; Zachariah M. R. Energy accumulation in nanoparticle collision and coalescence processes. J. Aerosol Sci. 2002, 33, 357–368. 10.1016/s0021-8502(01)00177-x. [DOI] [Google Scholar]
  22. Swihart M. T. Vapor-phase synthesis of nanoparticles. Curr. Opin. Colloid Interface Sci. 2003, 8, 127–133. 10.1016/s1359-0294(03)00007-4. [DOI] [Google Scholar]
  23. Grass R. N.; Tsantilis S.; Pratsinis S. E. Design of high-temperature, gas-phase synthesis of hard or soft TiO2 agglomerates. AIChE J. 2006, 52, 1318–1325. 10.1002/aic.10739. [DOI] [Google Scholar]
  24. Suzuki S.; Yamaguchi S.; Doi A.; Abe S.; Matsuda M.; Nakamura T.; Ando A.; Sano H. Effect of alloying Ni inner electrodes on the leakage current degradation of BaTiO3-based multilayer ceramic capacitors. Appl. Phys. Lett. 2020, 116, 132903. 10.1063/5.0002701. [DOI] [Google Scholar]
  25. Zhang X.; Liu Z.; Tanaka M.; Watanabe T. Formation mechanism of amorphous silicon nanoparticles with additional counter-flow quenching gas by induction thermal plasma. Chem. Eng. Sci. 2021, 230, 116217. 10.1016/j.ces.2020.116217. [DOI] [Google Scholar]
  26. Wegner K.; Pratsinis S. E. Nozzle-quenching process for controlled flame synthesis of titania nanoparticles. AIChE J. 2003, 49, 1667–1675. 10.1002/aic.690490707. [DOI] [Google Scholar]
  27. Ehrman S. H.; Aquino-Class M. I.; Zachariah M. R. Effect of Temperature and Vapor-phase Encapsulation on Particle Growth and Morphology. J. Mater. Res. 1999, 14, 1664–1671. 10.1557/jmr.1999.0224. [DOI] [Google Scholar]
  28. DuFaux D.; Axelbaum R. Nanoscale unagglomerated nonoxide particles from a sodium coflow flame,. Combust. Flame 1995, 100, 350–358. 10.1016/0010-2180(94)00097-c. [DOI] [Google Scholar]
  29. Yaws C.The Yaws Handbook of Vapor Pressure: Antoine Coefficients; Gulf Professional Publishing, 2015 10.1016/C2014-0-03590-3. [DOI] [Google Scholar]
  30. Krumeich F.Properties of electrons, their interactions with matter and application in electron microscopy; Laboratory of Inorganic Chemistry, ETH Zurich, 2015. https://www.microscopy.ethz.ch/downloads/Interactions.pdf (accessed 2021-10-11). [Google Scholar]
  31. Zarraoa L.; González M. U.; Paulo A. S. Imaging low-dimensional nanostructures by very low voltage scanning electron microscopy: ultra-shallow topography and depth-tunable material contrast. Sci. Rep. 2019, 9, 16263. 10.1038/s41598-019-52690-9. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES