Mechanistic Investigation of the Formation of Nickel Nanocrystallites Embedded in Amorphous Silicon Nitride Nanocomposites

Abstract

Herein, we report the mechanistic investigation of the formation of nickel (Ni) nanocrystallites during the formation of amorphous silicon nitride at a temperature as low as 400 °C, using perhydropolysilazane (PHPS) as a preformed precursor and further coordinated by nickel chloride (NiCl2); thus, forming the non-noble transition metal (TM) as a potential catalyst and the support in an one-step process. It was demonstrated that NiCl2 catalyzed dehydrocoupling reactions between Si-H and N-H bonds in PHPS to afford ternary silylamino groups, which resulted in the formation of a nanocomposite precursor via complex formation: Ni(II) cation of NiCl2 coordinated the ternary silylamino ligands formed in situ. By monitoring intrinsic chemical reactions during the precursor pyrolysis under inert gas atmosphere, it was revealed that the Ni-N bond formed by a nucleophilic attack of the N atom on the Ni(II) cation center, followed by Ni nucleation below 300 °C, which was promoted by the decomposition of Ni nitride species. The latter was facilitated under the hydrogen-containing atmosphere generated by the NiCl2-catalyzed dehydrocoupling reaction. The increase of the temperature to 400 °C led to the formation of a covalently-bonded amorphous Si3N4 matrix surrounding Ni nanocrystallites.

Chemical route for synthesis of β-SiAlON:Eu2+ phosphors combining polymer-derived ceramics route with non-hydrolytic sol-gel chemistry

“…1(c), A09E1 shows an apparent red shift of the Si-N-Si peak. These changes in the ATR-IR spectra reveal the formation of a typical Lewis acid-base adduct via the coordination of the lone pair of =NH in ≡Si-NH-Si≡ to AlCl 3 as previously suggested for chemical modification of PHPS with cobalt (II) chloride (CoCl 2 ) [24] and NiCl 2 [25]. In addition, the peak intensity at 920 cm −1 (observed on the left shoulder of the broad peak attributed to νSi-N-Si) increases consistently with the amount of AlCl 3 used for the chemical modification of PHPS (A36E1 and A09E1 in Fig.…”

“…As suggested by the ATR-IR spectroscopic analysis, the excess AlCl 3 was coordinated with NH groups of PHPS, which could allow the Al-N bond formation via the nucleophilic attack of N of the NH groups to Al cation center of AlCl 3 followed by elimination of HCl. As another possible reaction, the released chloride anion (Cl − ) attacked other electrophiles such as the Si center of PHPS moieties to release chlorosilanes as previously discussed for chemical modification of PHPS with MCl 2 (M = Co [24], Ni [25]).…”

“…In this route, polysilazane derivatives are frequently used as a starting polymer precursor, especially perhydropolysilazane (PHPS) composed of only Si, N, and H elements has some advantages in high purity and high ceramic yield for Si 3 N 4 ceramics synthesis [14][15][16]. Moreover, PHPS is highly reactive and easily modified with various monomeric organometallic compounds including metal alkoxides (M(OR) x , M = B [17], Al [18,19], Y [20][21][22][23]), metal chlorides (MCl n , M = Ti [23], Co [24], Ni [25]) and metal amides (M(NR 2 ) x , M = Ti [26][27][28], B [29]).…”

Advanced nanocomposite materials made of TiC nanocrystals in situ immobilized in SiC foams with boosted spectral selectivity

“…Although the hydrosilylation reaction usually takes place above 120 1C in pure polysilazanes, 29 previous works showed that the presence of inorganic catalysts such as transition metals or metal complexes could remarkably lower this reaction temperature. 25,[30][31][32] However, taken separately, this can also reflect the reaction of Si-H units with TDMAT while vinyl groups polymerize.…”

Hierarchically Porous Ceramic and Metal‐Ceramic Hybrid Materials Structured by Vat Photopolymerization‐Induced Phase Separation

“…[53] As Ni-and Co-precursors are typically reduced at temperatures beneath 400 and 500 °C, respectively, the presence of elemental metal is expected. [60,62,63] This reducibility is well reflected in the Gibbs free energy change of the different metal oxidation reactions versus the oxidation of carbon. [64] Therefore, the expected presence of metallic face-centered (fcc) Ni and Co phases could be determined by XRD measurements (Figure S12, Supporting Information) and selected area electron diffraction (SAED) (Figure S13, Supporting Information).…”