Deposition of a SiO2 Shell of Variable Thickness and Chemical Composition to Carbonyl Iron: Synthesis and Microwave Measurements

Protective SiO2 coating deposited to iron microparticles is highly demanded both for the chemical and magnetic performance of the latter. Hydrolysis of tetraethoxysilane is the crucial method for SiO2 deposition from a solution. The capabilities of this technique have not been thoroughly studied yet. Here, two factors were tested to affect the chemical composition and the thickness of the SiO2 shell. It was found that an increase in the hydrolysis reaction time thickened the SiO2 shell from 100 to 200 nm. Moreover, a decrease in the acidity of the reaction mixture not only thickened the shell but also varied the chemical composition from SiO3.0 to SiO8.6. The thickness and composition of the dielectric layer were studied by scanning electron microscopy and energy-dispersive X-ray analysis. Microwave permeability and permittivity of the SiO2-coated iron particles mixed with a paraffin wax matrix were measured by the coaxial line technique. An increase in thickness of the silica layer decreased the real quasi-static permittivity. The changes observed were shown to agree with the Maxwell Garnett effective medium theory. The new method developed to fine-tune the chemical properties of the protective SiO2 shell may be helpful for new magnetic biosensor designs as it allows for biocompatibility adjustment.

[1]  M. Hayashi,et al.  Complex Permittivity and Permeability of SiO2 and Fe3O4 Powders in Microwave Frequency Range between 0.2 and 13.5 GHz , 2009 .

[2]  W. Feng,et al.  Impact of silica-coating on the microwave absorption properties of carbonyl iron powder , 2015 .

[3]  R. Adnan,et al.  Effect of anion electrolytes on the formation of silica nanoparticles via the sol–gel process , 2006 .

[4]  G. Wen,et al.  A new type of catalyst allows carbonyl iron powder to be coated with SiO2 for tuned microwave absorption , 2020 .

[5]  Michael T. Harris,et al.  Chemical reaction kinetics leading to the first Stober silica nanoparticles – NMR and SAXS investigation , 2003 .

[6]  F. González,et al.  Electromagnetic Effective Medium Modelling of Composites with Metal-Semiconductor Core-Shell Type Inclusions , 2019, Catalysts.

[7]  G. F. Engen,et al.  Thru-Reflect-Line: An Improved Technique for Calibrating the Dual Six-Port Automatic Network Analyzer , 1979 .

[8]  S. Havriliak,et al.  A complex plane analysis of α‐dispersions in some polymer systems , 2007 .

[9]  M. Khodzitsky,et al.  Effective Medium Theory for Multi-Component Materials Based on Iterative Method , 2020 .

[10]  Enis Tuncer,et al.  Dielectric mixtures-importance and theoretical approaches , 2013, IEEE Electrical Insulation Magazine.

[11]  M. Koledintseva,et al.  Influence of Higher-order Modes in Coaxial Waveguide on Measurements of Material Parameters , 2018, 2018 IEEE Symposium on Electromagnetic Compatibility, Signal Integrity and Power Integrity (EMC, SI & PI).

[12]  Liuying Wang,et al.  Enhanced electromagnetic properties of carbon nanotubes and SiO2-coated carbonyl iron microwave absorber , 2018, Journal of Alloys and Compounds.

[13]  I. O. Wallinder,et al.  Mechanical surface smoothing of micron-sized iron powder for improved silica coating performance as soft magnetic composites , 2020 .

[14]  Guangqiang Li,et al.  Core loss reduction in Fe–6.5 wt.%Si/SiO2 core–shell composites by ball milling coating and spark plasma sintering , 2014 .

[15]  D. Pasquet,et al.  A new model for microwave characterization of composite materials in guided-wave medium , 1996 .

[16]  Ari Henrik Sihvola,et al.  Analysis of a three-dimensional dielectric mixture with finite difference method , 2001, IEEE Trans. Geosci. Remote. Sens..

[17]  G. Dionne,et al.  Dielectric constants of paraffin‐wax–TiO2 mixtures , 1976 .

[18]  Z. Lu,et al.  Fabrication and properties of iron-based soft magnetic composites coated with parylene via chemical vapor deposition polymerization , 2015 .

[19]  A. M. Nicolson,et al.  Measurement of the Intrinsic Properties of Materials by Time-Domain Techniques , 1970 .

[20]  Sheng-Li Chen,et al.  Kinetics of Formation of Monodisperse Colloidal Silica Particles through the Hydrolysis and Condensation of Tetraethylorthosilicate , 1996 .

[21]  S. Sankaran,et al.  Recent advances in electromagnetic interference shielding properties of metal and carbon filler reinforced flexible polymer composites: A review , 2018, Composites Part A: Applied Science and Manufacturing.

[22]  A. K. Mandal,et al.  Microwave Absorption of Barium Borosilicate, Zinc Borate, Fe-Doped Alumino-Phosphate Glasses and Its Raw Materials , 2015 .

[23]  Fu-hui Wang,et al.  Enhanced electromagnetic wave absorption of hybrid-architectures Co@ SiOxC , 2020, Journal of Alloys and Compounds.

[24]  Sergey S. Maklakov,et al.  Low Weight Hollow Microspheres of Iron with Thin Dielectric Coating: Synthesis and Microwave Permeability , 2020 .

[25]  Qing Yuchang,et al.  Microwave electromagnetic property of SiO2-coated carbonyl iron particles with higher oxidation resistance , 2011 .

[26]  W. Weir.  Automatic measurement of complex dielectric constant and permeability at microwave frequencies , 1974 .

[27]  Roberto Cingolani,et al.  SiO2 nanoparticles biocompatibility and their potential for gene delivery and silencing. , 2012, Nanoscale.

[28]  Liya Li,et al.  Fe@SiO2@(MnZn)Fe2O4 soft magnetic composites with enhanced permeability and low core loss for high-frequency applications , 2019, Journal of Alloys and Compounds.

[29]  Woo-Sik Kim,et al.  Effect of electrolyte additives on sol-precipitated nano silica particles , 2004 .

[30]  D. Polder,et al.  The effective permeability of mixtures of solids , 1946 .

[31]  Dayang Wang,et al.  Unraveling the Growth Mechanism of Silica Particles in the Stöber Method: In Situ Seeded Growth Model. , 2017, Langmuir : the ACS journal of surfaces and colloids.

[32]  U. Chettiar,et al.  Internal homogenization: effective permittivity of a coated sphere. , 2012, Optics express.

[33]  J. Robertson.  High dielectric constant oxides , 2004 .

[34]  V. Shukla.  Review of electromagnetic interference shielding materials fabricated by iron ingredients , 2019, Nanoscale advances.

[35]  V. Pavlínek,et al.  Synthesis of Silicone Elastomers Containing Silyl-Based Polymer-Grafted Carbonyl Iron Particles: An Efficient Way To Improve Magnetorheological, Damping, and Sensing Performances , 2017 .

[36]  N. Ghalichechian,et al.  Permittivity and dielectric loss measurement of paraffin films for mmW and THz applications , 2016, 2016 International Workshop on Antenna Technology (iWAT).

[37]  X. Gong,et al.  Flexible, self-powered, magnetism/pressure dual-mode sensor based on magnetorheological plastomer , 2019, Composites Science and Technology.

[38]  Julian R. Jones,et al.  Controlling particle size in the Stöber process and incorporation of calcium. , 2016, Journal of colloid and interface science.

[39]  Sergey S. Maklakov,et al.  Corrosion-resistive magnetic powder Fe@SiO2 for microwave applications , 2017 .