Next Article in Journal
Experimental Thermal Study of the Materials Used in the Construction of Combustion Chamber of Firewood Stoves in Southern Mexico and Central America
Previous Article in Journal
On the Heat Transfer Process in a System of Two Convex Bodies Separated by a Vacuum—Mathematical Description and Solution Construction
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Thermo
Volume 6
Issue 1
10.3390/thermo6010007
thermo-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

The Influence of Mechanochemical Activation on the Properties of a Double Complex Salt [Co(NH3)6][Fe(CN)6] and Its Thermolysis Products

by
Alevtina Gosteva
1,
Alexander M. Kalinkin
1,
Vladimir Vinogradov
1,
Diana Manukovskaya
1,*,
Viktor Nikolaev
2,
Vasilii Semushin
3 and
Maria Teplonogova
4
1
Tananaev Institute of Chemistry—Subdivision of the Federal Research Centre «Kola Science Centre of the Russian Academy of Sciences» (ICT KSC RAS), Akademgorodok, 26a, 184209 Apatity, Russia
2
Department of Physics, Biology and Engineering Technology, MASU Branch in Apatity, 29, Lesnaya str., 184209 Apatity, Russia
3
Company Group Rusredmet, Kingiseppskoe Highway, 47, Letter “R”, Krasnoe Selo, 198320 Saint Petersburg, Russia
4
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences (JRC PMR IGIC RAS), Leninskii Prospect, 31, 119991 Moscow, Russia
*
Author to whom correspondence should be addressed.
Thermo 2026, 6(1), 7; https://doi.org/10.3390/thermo6010007
Submission received: 10 November 2025 / Revised: 11 January 2026 / Accepted: 13 January 2026 / Published: 19 January 2026
(This article belongs to the Topic Clean Energy Technologies and Assessment, 2nd Edition)
Browse Figures
Review Reports Versions Notes

Abstract

Double complex salts (DCSs) of the composition [Co(NH3)6][Fe(CN)6] are a promising precursor for the preparation of catalysts for the hydrogenation of carbon oxides (CO and CO2) by Fischer–Tropsch synthesis. The specific surface area is an important parameter for catalysts. Our article investigates the influence of mechanochemical activation (MCA) on this DCS in order to determine the conditions for obtaining the largest specific surface area of the intermetallic compound, a product of the DCS thermolysis. In this work, the effect of MCA on the physicochemical properties of the DCS [Co(NH3)6][Fe(CN)6] and the products of its thermal decomposition in an argon atmosphere were investigated. It was shown that MCA leads to partial reduction of Fe+3 to Fe+2, changes in the coordination of ammonia, amorphization of the structure and a decrease in the thermal stability of DCS. Thermolysis at 650 °C of samples subjected to MCA for 10 min results in the formation of nanocrystalline intermetallic compound Co0.5Fe0.5. The results demonstrate the potential of using MCA to control the properties of functional materials based on DCS.

1. Introduction

Fischer–Tropsch synthesis, the hydrogenation of carbon oxides to produce hydrocarbons, is considered an important green technology in modern science. These hydrocarbons can then be used as synthetic fuels. The most suitable catalysts for this synthesis are Co and Fe. Co initiates synthesis via one pathway, Fe via another, and by using double complex salts (DCSs), we aim to achieve synergy between the active phases. We have previously shown that the thermolysis product [Co(NH3)6][Fe(CN)6] exhibits promising catalytic properties in argon [1] and hydrogen [2]. However, studies on the pretreatment of DCS prior to thermolysis are currently rare. One of the goals of this work is to fill this gap.
The result of the thermal decomposition of [Co(NH3)6][Fe(CN)6] is an intermetallic compound of the composition Co0.5Fe0.5. The intermetallic compound differs from the solid solution CoFe by its strict stoichiometry and properties that are different from those of the solid solution, for example, increased hardness [3].
It should be noted that the solid calcination product, in addition to Co0.5Fe0.5, also contains X-ray amorphous carbon. FeCo alloys of various origins are actively studied due to their promising magnetic properties. Let us consider some methods for producing such alloys. In the study [4], polyhedral FeCo alloys were obtained using hydrothermal synthesis. Treatment was carried out at a temperature of 160 °C, with a maximum duration of 15 h. Toxic N2H4∙H2O was used in the study. The alloys exhibited excellent electromagnetic absorption performances over the X-band and the entire Ku-band. The grain sizes of the FeCo alloys were 1–2 mm. In the work [5], Fe-Co alloy nanoparticles were also obtained using hydrothermal synthesis. Unsafe ammonium fluoride was used. This is a very long, multi-step synthesis. It is noteworthy that the lattice parameter α in the article [5] and in this work are almost the same—about 2.86 Å. To obtain FeCo alloy parts, the authors of [6] used electrical field-activated sintering technology combined with micro-forming as a new rapid powder-sintering/forming method. The grain sizes of the FeCo alloys were in a range of 5–6 µm. A Co-Fe alloy was prepared through an extended soft chemical solution process [7]. A mixture of Co(acac)2, Fe(acac)3, and additional reagents was processed by rotary evaporation, drying, and calcination in a nitrogen gas atmosphere. The grain size was 35.8 and 47.7 nm, depending on the decomposition temperature. Using the polyvinyl pyrrolidone-assisted liquid-phase reduction method, it is possible to obtain Co7Fe3 in the form of nanospheres [8]. Using organometallic precursors such as HFeCo3(CO)12 and its mixtures with other carbonyls, it is also possible to produce iron–cobalt intermetallics. Depending on the composition of the starting mixture and the processing temperature, particle sizes ranging from 0.2 to 200 μm can be obtained [9]. FeCo colloidal magnetic nanoalloys in the range of 11.5–37.2 nm were synthesized by the surfactant-assisted ball-milling method. The processing time ranged from 20 to 45 h [10]. The authors of [11] used a similar technique; they used the same surfactant and 30 h treatment in a planetary-ball mill system. The resulting suspension was sonicated, then settled, and separated using a magnet. The resulting nanoscale FeCo alloy was obtained by vacuum-drying. By applying all the methods listed above, an alloy or intermetallic compound, CoFe, was obtained. The article [12] is very close to our work (obtaining the intermetallic compound Co0.5Fe0.5 with a large amount of X-ray amorphous carbon). It discusses a two-step hydrothermal/annealing synthesis approach using CoFe alloy nanoparticles on nitrogen-doped ultrathin carbon nanosheets. The intricate architecture, featuring interlayer gaps and mesoporous channels within the ultrathin carbon layers, establishes an optimal network for efficient mass transfer. Furthermore, the significant interfacial interaction between alloy nanoparticles and carbon shells enables the optimization of the electronic structure.
Thus, it is clear that there are numerous methods for producing the CoFe alloy or intermetallic compound. By varying the synthesis method, it is possible to obtain a compound with the properties required for each specific research objective. However, virtually every approach has its own limitations. For example, the need for complex equipment, toxic reagents, or lengthy synthesis procedures. Therefore, developing an improved method for producing the CoFe intermetallic compound is a pressing issue.
The study of DCSs is a rapidly developing area of general chemistry and materials science. DCSs can have interesting structures [13]; magnetic properties [14,15]; biological activity, especially DCSs with urea [16,17]; mixed-valence species [18]; metal-to-metal charge transfer [19]; and other interesting and useful properties [20,21,22]. Despite the virtually unlimited number of complex compounds that have already been discovered or may be synthesized in the future, the number of DCSs is significantly limited. The limitations are caused by the low stability of some initial complex compounds, which limits the possibilities of synthesizing DCSs. Many monocomplexes are poorly stable in protic solvents, and the use of aprotic analogs significantly increases the synthesis cost and reduces the environmental friendliness of the laboratory procedures. Furthermore, for large-scale implementation, relatively simple syntheses with quantitative yields are required. All of the above impose certain limitations on DCSs, which can be considered as precursors for functional materials with potential industrial applications.
Thermal decomposition (thermolysis) of complex compounds is actively used to obtain functional materials [23]. Thermolysis is relatively simple and inexpensive in terms of instrumentation, allowing for a wide range of solid decomposition products to be obtained without significantly altering or complicating the setup. For example, by varying the experimental gas atmosphere within a single experimental setup, it is possible to obtain simple and complex oxides (thermolysis in air) and mixtures of metals and intermetallics with virtually no carbon admixture (thermal destruction in a hydrogen stream), or with a large amount of X-ray amorphous carbon when calcined in an inert atmosphere [24].
Existing research on solid products of DCS thermolysis can be divided into several directions. The first one is demonstrated by Domonov et al.: the group investigated metal–carbon composites (MCCs). MCCs were obtained by calcining the DCS in an argon flow at temperatures of 600–900 °C, while alternative methods of obtaining products with similar properties require synthesis conditions at 1500–2000 °C [25,26]. Acid treatment (HCl) of these products increases the specific surface area to 470 m2/g with a residual content of total metals of 10–20%. Varying the temperature of DCS thermolysis allows obtaining products with different specific surface areas (Ssp). Various DCS precursors, even with the same complexing metals, make it possible to obtain MCCs with different morphologies (Table 1) [27]. Table 1 shows the data after acid treatment with 6 M HCl of the thermolysis products of DCS.
The second direction considers that not only is the synthesis of new, previously unexplored DCSs important, but also the development of new methods for processing the salts. Therefore, the group of authors in [28,29,30] examined the autoclave decomposition of DCS containing platinum and one 3D metal. In subcritical water (190 °C; 1.25 MPa; pH 8–9), black powders are formed from the DCS: [Co(NH3)5Cl][PtCl4], [Ni(NH3)6][PtCl4] and [Cr(NH3)5Cl][PtCl4]. The complex compounds undergo almost complete conversion into solid products if the ratio of platinum and one of the transition metals is equimolar, which is ensured by the stoichiometry of the binary complex. Scanning electron microscopy (SEM), electron probe X-ray microanalysis, and X-ray diffraction (XRD) phase analysis demonstrated that the products of chemical transformation of the DCS in subcritical water consist of particles of oxide and hydroxide forms of transition metals (Co3O4, Ni(OH)2, or CrOOH, respectively). Spherical particles of metallic platinum up to 100 nm in size are reduced on the surface of the oxide or hydroxides.
Transformations of platinum and 3D-metal complexes in subcritical water in the presence of a metal carrier result in particles depositing predominantly on the substrate surface. The particles form a heterogeneous catalyst consisting of a carrier and a catalytically active platinum phase and an oxide form of the transition metal: Pt/Ni(OH)2, Pt/Co3O4, Pt/CrOOH. Catalysts based on crushed stainless steel chips or nichrome “metal rubber” block material demonstrate activity and stability in the complete oxidation of hydrocarbons (n-hexane and propane) [28,29,30].
The third direction of DCS pyrolysis is the development of methods for various pretreatments of the precursor. One example of this direction is the work [31]. Using [Co(NH3)6][Fe(CN)6] as an example, this article demonstrates the effect of plasma discharge of varying power and exposure time on the physicochemical properties of DCS and its thermolysis products. Under the following exposure conditions (maximum conditions are given)—three cycles of 15 min each at 25 W and one cycle of 15 min at 100 W—it is not possible to achieve a homogeneous structure of the resulting powder. During processing with two cycles of 10 min each at 100 W, a homogeneous black powder is formed, which is why this mode is considered to be optimal for this DCS. A single-phase spinel with a CoFe2O4 structure forms during pyrolysis of DCS, previously subjected to plasma treatment at 1000 °C for 1 h, in air. The crystallite sizes of the obtained spinel are 40 nm, with a lattice constant of 8.38 Å [31].
MCA (mechanochemical activation) is a promising method for modifying the properties of materials by mechanical action, leading to structural changes at the molecular level [32,33]. MCA has the advantage of allowing both component mixing and solid-phase reactions to occur simultaneously, directly in the grinding drum. In addition to intensifying solid-phase synthesis processes, MCA is also used to intensify sintering processes [34] and change catalytic properties [35,36,37,38]. MCA’s effectiveness is due to both the acceleration of mass transfer and the accumulation of excess energy in solids due to various structural disturbances, such as point defects, dislocations, changes in bond lengths, etc., which increase the reactivity of the reagents [39,40,41]. The works [42,43] consider mechanocatalysis, i.e., catalytic reactions under the simultaneous effect of mechanical loading. Mechanochemical catalysis increased the selectivity of catalysts. A promising method for carrying out mechanochemical reactions at high pressures (10 MPa) of hydrogen, oxygen, or ammonia was developed. Studies of mechanochemical transformations in Fe-X systems (X = C, B, Al, Si, Ge, Sn, Cr) are illustrated in the works [44,45].
The work [46] is devoted to ensuring enhanced performance of bimetallic Co-based catalysts and their activity in the deposition of carbon nanofibers. Most studies of carbon nanofiber catalysis use coprecipitation to create alloys, but recent work has demonstrated the suitability of mechanical alloying using ball milling to reduce costs and enhance catalytic activity. This work established the unique ability of mechanochemical alloying to control the microstructure to produce bimetallic composites that retain individual metallic phases, which enhances catalytic activity. The preparation of catalysts using mechanochemical approaches, as well as their applications, is discussed in reviews [47,48,49,50].
This paper attempts to combine the advantages of DCS and MCA. MCA of complex compounds (not DCS) has been discussed in review papers [51,52,53]. By analogy with the mechanical processing of some solid oxide compounds, the following parameters of mechanical processing were selected: mechanical processing time—1–10 min; centrifugal factor—40 g (50 Hz); ratio of grinding media/object being ground = 20:1 [54,55,56,57]. When using these MCA parameters for the centrifugal-planetary mill AGO-2, the required efficiency of mechanical processing is ensured, which is necessary for intensifying the reaction and improving the physicochemical characteristics.
The study is devoted to the investigation of the influence of mechanical activation using the example of the DCS [Co(NH3)6][Fe(CN)6]. This complex can find wide application in catalysis, electronics, and medicine due to its physicochemical properties [13,58,59,60].
The article [1] examines the catalytic activity of the thermolysis product of [Co(NH3)6][Fe(CN)6] in argon at 650 °C for 1 h in the hydrogenation of CO2, a greenhouse gas. It is shown that at 230 °C, the selectivity for converting CO2 to CH4 reaches 68% for the sample without activation. The selectivity of the same sample after activation in a flow of H2 reaches 78% for C5+ saturated hydrocarbons. For the same catalyst, but during CO hydrogenation, conversion is observed to be 93%, and the selectivity for C1–C4 hydrocarbons is 61% [2].
The aim of this work is to study MCA’s effect on the physicochemical properties of [Co(NH3)6][Fe(CN)6] DCS and the products of its thermolysis.

2. Materials and Methods

All experiments were performed at least three times; the data presented in this article are averaged.
The starting binary compound [Co(NH3)6][Fe(CN)6] (hereinafter referred to as DCS) was obtained in quantitative yield by mixing aqueous solutions of cationic and anionic complexes. Chemicals [Co(NH3)6]Cl3 and K3[Fe(CN)6] (Vecton Ltd., Saint Petersburg, Russia) were used. Powder XRD, IR spectroscopy, and elemental analysis for DCS are the same as described in [1].
After merging the cationic [Co(NH3)6]Cl3 and anionic K3[Fe(CN)6] complexes, the target [Co(NH3)6][Fe(CN)6] DCS precipitates, while KCl remains in the mother liquor. The DCS is filtered off under vacuum, and the wet residue is washed with ice-cold water until the silver nitrate reacts negatively with the chloride ions. The DCS is then washed with ethanol.
MCA was carried out in a laboratory centrifugal-planetary mill AGO-2 (NPO NOVIC, Novosibirsk, Russia, 2013) in an air atmosphere using steel drums and balls with a diameter of 8 mm for 5 min at a centrifugal factor of 40 g. The ball-to-load ratio was 20:1. To ensure macrohomogeneity of the powders, the mill was turned off every 60 s of MCA and the contents of the drums were mixed with a metal spatula [61]. Before the MCA, lining was carried out with a smaller amount of composition.
XRD was carried out at room temperature in the 2θ range of 5–70° using a powder diffractometer XRD 6000 (Shimadzu, Kyoto, Japan, 2008) with a Cu-Kα source (λ = 1.5418 Å) and a graphite monochromator. XRD patterns of products calcined in argon at 200–650 °C were obtained on a powder diffractometer MiniFlex 600 (RIGAKU, Tokyo, Japan, 2021) with a Cu-Kα source (λ = 1.5418 Å) and a graphite monochromator in the 2θ range 2–140°. The crystal lattice parameters were refined using the Rietveld refinement and the fundamental parameters method. The method error was generally 5%. The decoding was performed using a database JCPDS-ICDD PDF 4+ (International Center for Diffraction Data, Philadelphia, PA, USA, 2020).
Infrared (IR) spectra were recorded on a spectrometer Nicolet 6700 FT-IR (Thermo Fisher Scientific Inc., Hillsboro, OR, USA, 2010) in KBr tablets, with a recording interval of 400–4000 cm−1, 16 skans, resolution 4. The carbon content of the samples was determined using an ELTRA CS–2000 analyzer (Alpha Resources, LLC, Stevensville, MI, USA, 2004). The porous structure of the samples was determined by the method of low-temperature nitrogen sorption on the Tristar 3020 instrument (Norcross, GA, USA, 2009). The measurement error was 5%.
Synchronous thermal analysis (STA) was carried out on a STA 409 PCLuxx (NETZSCH-Gerätebau GmbH, Selb, Germany, 2009) in an argon flow (protective gas, 20 mL/min; gas flow into the heating chamber, 50 mL/min) at a heating rate of 10 °C/min in the range of 30–1000 °C in Al2O3 crucibles with lids, with a sample weight of 15 mg. STA in our case included obtaining simultaneous results with thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses.
Thermolysis at 220, 450, and 650 °C was carried out under isothermal conditions in a tubular furnace Nabertherm RT 50-250/11 (Nabertherm GmbH, Lilienthal, Germany, 2013) in an argon flow of 15 L/min with a heating rate of 10 °C/min in a quartz bed with a sample weight of ~0.5 g. Argon of 99.99% purity was used with additional purification of oxygen impurities by passing through a manganese suspension and drying from traces of water by passing through concentrated H2SO4. Thermolysis time was 1 h.
A scanning electron microscope, SEM LEO 420 (Carl Zeiss, Oberkochen, Germany, 1998), was also used in some cases.
Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) images were taken using a Tescan Amber GMH (Brno, Czech Republic, 2021) scanning electron microscope. Images were obtained using an Everhart–Thornley SE detector at ×3000–300,000 magnification and at an accelerating voltage of 1 kV. EDX spectra and elemental maps were recorded using an Ultim MAX EDS detector with a 100 mm2 active area (Oxford Instruments, Abingdon, UK, 2021) and at an accelerating voltage of 20 kV using AZtec 5.0 SP1 software.
CHN elemental analysis was performed on a EuroVector EA3000 (Pavia, Italy, 2008) elemental analyzer at a temperature of up to 1000 °C.

3. Results and Discussion

3.1. Characterization of Samples Before Thermolysis

After the MCA, the DCS samples were analyzed using elemental analysis, XRD, and IR spectrometry. We will designate these samples as MCA-X, where X is the MCA time in minutes.

3.1.1. Elemental Analysis

Table 2 shows data on the carbon content of the complex anion before and after MCA. The carbon content changes slightly with increasing MCA time, and this change is within the error limits of the carbon-content determination instrument. Therefore, performing MCA for 10 min did not significantly alter the chemical composition of the complex anion.
To assess the chemical state of the cation, additional elemental analysis was performed (Table 3). The observed discrepancy in carbon content can be explained by the different instruments used for the analyses. As in Table 2, in this case, the discrepancy in carbon content does not exceed the instrumental error of 5%.
Since the cation and anion each contain six nitrogen atoms, this corresponds to 22.5 wt%. After 5 min of MCA, the cation contains 35.5–22.5 = 13.0 wt%, i.e., 13.0/22.5 = 57.8% nitrogen. During MCA, a decrease in the nitrogen and hydrogen content is observed; therefore, some of the ammonia is removed unchanged. However, since the decrease in the N and H content does not occur symbatically, we can speak of the partial destruction of NH3 during MCA. Therefore, we will assume that the cation ligand is in the form “NHx≤3”.

3.1.2. XRD Analysis

Changes in the phase composition of the DCS were monitored using XRD (Figure 1). After 1 min of MCA, peaks at 10, 28, 56.5, 58, 61, and 62° (2θ) were no longer detected, while the intensity of peaks at 25, 26.5, and 38° decreased significantly. As the MCA time increased, amorphization of the sample occurred. By 10 min MCA, a virtually X-ray amorphous phase was observed.
The degree of crystallinity was determined according to Segal [62], shown in Table 4. The data confirm that amorphization occurs due to MCA.

3.1.3. IR Analysis

IR spectrometric analysis also confirms the strong influence of MCA on the structure of the DCS sample (Figure 2). Here, and in later designations near the band frequencies, ν = stretching, δ = bending, r = rocking, st = strong, m = medium, w = weak, sym = symmetric, as = antisymmetric, and sh = shoulder.
IR spectrum of the original DCS: 3292 st, 3265 st ν as (NH3); 3110 st ν sym (NH3); 2112 st ν(Fe+3-CN); 1662–1670 sh, 1628 m, 1581 m, 1551 m δ as (HNH); 1492–1503 sh (NH3); 1364 st δ s (HNH); 839 st r (HNH) [63,64,65,66,67]. IR spectroscopy can unambiguously identify the oxidation state of iron (+3 or +2) in complexes with cyano groups [68]. This is widely used to confirm the structure of DCSs [13,23,25,26,27,60,69,70].
In the spectra of both the initial DCS and all MCA DCSs, a band at 2112 st cm−1 was recorded, which corresponds to the vibration (Fe+3-CN) [71]. Starting from the first minute of MCA, vibrations of 2043–2045 cm−1 appear, which are characteristic of the bond Fe+2-CN. As the MCA time increases, the intensity of Fe+2 vibrations increases, and by 7 min of MCA, it becomes equal to the intensity of Fe+3 vibrations. Further increases in processing time do not affect the ratio of Fe+3 and Fe+2 intensities. Iron reduction likely occurs through the reaction of Fe+3 with ammonia.
This assumption confirms the change in ammonia coordination. The IR spectrum of the untreated DCS contains the following ammonia absorption bands: 1662–1670 sh, 1628 m, 1581 m, 1551 w, 1492–1503 sh cm−1. This part of the spectrum (1475–1700 cm−1), after 1 min of MCA, becomes less intense. The peaks acquire the following frequencies: 1666 w, 1623 m, 1570 m, 1532 w cm−1—δ as (HNH), mode 1469 w cm−1 (NH3). It is evident that with increasing MCA time, the spectral range of ammonia molecule vibrations in the region of 1475–1700 cm−1 narrows, and by 6 min of MCA, only one wide band remains at 1619 cm−1.
The band at 1364 st cm−1 in the initial compound, also showing vibrations of NH3 atoms, splits into low-intensity peaks at 1406 w and 1359 st cm−1 (it is strong, but relative to the band at 1364 in the initial DCS, it is less intense) after 1 min of MCA; by 6 min MCA, their intensities become the same.
By 10 min of MCA, the 1364 w cm−1 δ s (HNH) band is practically not recorded in the spectrum (a very weak peak remains); the intensity of the peak at ~1400 st cm−1 increases significantly, and this band becomes one of the strongest in the spectrum.
From the second minute of MCA, a band at 590 w cm−1 appears, its intensity increases until the fourth minute of MCA, and then the intensity and wave number do not change. From the fourth minute of MCA, a new band appears at 1282 m cm−1. By the 10th minute of MCA, the band shifts to 1271 st cm−1 and its intensity increases significantly. Up to the 10th minute of MCA, the bands in the range of 3150–3280 cm−1 remain, although they become more diffuse. Consequently, a new type of bond coordinated through nitrogen is formed—NH2 (stretching NHx≤3 3150–3280 cm−1, NHx≤3 wagging ~1280 cm−1, NHx≤3 as rocking 590 cm−1) [63]. However, it should be noted that the band at 575 cm−1 can also be attributed to vibrations (Fe+2-CN) in this system.

3.1.4. Synchronous Thermal Analysis

The STA was carried out for the untreated DCS and samples after 5 and 10 min of MCA. The analysis was carried out in an argon flow to remove the influence of the oxidizing action of atmospheric oxygen (Figure 3). MCA reduced the thermal stability of the DCS and shifted the main stages of mass loss and thermal effects towards lower temperatures.
MCA-0 is stable when heated to 215 °C; the samples MCA-5 and MCA-10 show no weight loss only up to 80 °C. Up to 180 °C, the TG curves of the MCA samples coincide and show a weight loss of 12 wt%; after this temperature, the TG curves diverge. When all samples are heated above 220 °C, the TG curves of all three samples do not coincide, but the course of the curves remains almost identical. The end of the last sharp step of weight loss is observed at 621 °C for MCA-0, at 603 °C for MCA-5, and at 595 °C for MCA-10. The residual weight at 1000 °C is 35.0% for MCA-0, 33.8% for MCA-5, and 40.1% for MCA-10. The discrepancy can be explained by the removal of part of the coordinated ammonia during the MCA process—the sample begins to smell of ammonia immediately after one minute of MCA, after removal from the reaction beakers. The DSC curve also undergoes changes as the MCA time increases. Although the general course of the curves remains unchanged, new thermal effects appear (Table 5).
Mass loss is accompanied by thermal effects. For greater data clarity and ease of comparison, we divided thermolysis into stages. Experiments have shown that the response on the DCS curve is somewhat delayed compared to the mass loss on the TG curve. Thus, the T-extremum in Table 3 is the temperature of the maximum or minimum thermal effect corresponding to each stage of mass loss.
An analysis of Figure 3 and Table 5 reveals the following. The thermal effects, i.e., the number of peaks, are identical for samples MCA-0 and MCA-10. However, sample MCA-5 exhibits an additional endothermic effect in the temperature range of 70–200 °C, as well as an exothermic effect in the temperature range of 565–625 °C. Therefore, with MCA for 5 min, intermediate processes occur, and the state of this sample is relatively metastable, as the first effect is already observed at a temperature of 108 °C. A 10 min MCA is sufficient to achieve a more stable state in terms of the number of thermal effects.

3.2. Characterization of Samples After Thermolysis

The samples in this section are designated MCA-X-Y, where X is the MCA time in min and Y is the thermolysis temperature.

3.2.1. Static Thermal Analysis

Static thermolysis was performed for the characteristic points on the STA curves. The catalytic properties of the thermolysis products of [Co(NH3)6][Fe(CN)6] in a flow of argon at 650 °C for 1 h were studied in [1,2]. Therefore, in this work, special attention is paid to the physicochemical properties of the residues from the calcination of DCS after 5 and 10 min MCA, obtained under similar conditions of thermal destruction. The crystal lattice parameters were refined using the Rietveld method, IR spectra were recorded, the specific surface area and pore structure were determined, the morphology was determined by SEM, and the elemental distribution was determined by EDX. For comparison, similar data for the thermolysis product of untreated DCS are also presented in Table 6.

3.2.2. XRD Analysis with Rietveld Refinement

The XRD patterns of the thermolysis products in argon of DCS at 650 °C, prepared with and without MCA, are shown in Figure 4. According to the obtained data, the thermolysis of all precursors leads to the formation of the intermetallic compound Co0.5Fe0.5 (PDF 01-071-5029) with a cubic lattice. Calculations using the Rietveld method and the Rigaku SmartLab Studio II program revealed the following trends, shown in Table 7. MCA increases the lattice parameter. This indicates a slight increase in the Fe content, probably due to the formation of milled iron (finely dispersed iron resulting from the self-abrasion of the balls and drum during MCA). Intensive mechanical processing of precursors in a planetary mill leads not only to the chemical changes described above but also to the accumulation of excess energy in the form of various structural defects. This is the reason why the reactivity of the reagents increases under the influence of preliminary MCA. This probably contributes to the formation of more perfect crystals during heat treatment, which is manifested in some reduction in lattice microdeformation, shown in Table 7. Clarification of the reasons for the significant decrease in the size of coherent scattering regions (CSR), shown in Table 7, requires additional research. MCA of DCS for 10 min allows one to obtain an intermetallic compound in a nanocrystalline state, seen in Table 7.

3.2.3. Physical Analysis

In Figure 4, a low-intensity peak in the region of 26–27° 2θ is observed in the residues from the calcination of MCA-0-650 and MCA-5-650. In the IR spectra for all three samples obtained by pyrolysis at 650 °C, a peak in the region of 2160–2180 cm−1 is observed (Figure 5). Based on the card from the PDF database number 32–1073 (the peak at 26–27° 2θ is observed for a salt with a similar composition (Co,Na)Zn(Fe(CN)6)·3H2O and [68], this can be attributed to the Fe bridge–CN bond. However, similar IR spectrometry patterns of calcination residues were observed in articles [1,2]. It was determined in [1] that the residual nitrogen content was equal to 0.94 wt%, which corresponds to the gross formula of the resulting residue for MCA-0-650—CoFeC3.5N0.1. Consequently, residual cyano groups are present in the residue from the calcination of MCA-0-650 in extremely small quantities.
Table 6 shows that the values of residues after ignition and residual carbon contents for MCA-0-650, MCA-5-650, and MCA-10-650, as well as the results of XRD and IR analyses, are extremely similar. Therefore, it can be assumed that residual cyano groups are also present in extremely small quantities in both MCA-5-650 and MCA-10-650 samples.

3.2.4. Morphology and Porosity Structure

Sorption Isotherms
The sorption isotherms exhibit pronounced hysteresis loops. These loops are caused by capillary condensation within the pores. These loops indicate sorption isotherms characteristic of mesoporous structures (Figure 6). This type of hysteresis loop is typical of materials with a complex porous structure. The increase in the adsorption isotherm in the medium-pressure region indicates intense capillary condensation, and hence the presence of a large mesopore volume in the MCA-0-650 sample. The adsorption isotherm of the MCA-5-650 sample suggests a slower and possibly uniform pore filling. We believe that the pronounced hysteresis loops give us the right to classify the isotherms as type IV according to the Brunauer classification.
Description of Pore Size Distribution
Figure 7 shows a single intense and narrow peak for the MCA-5-650 sample in the ~3.8–4.0 nm region, indicating a highly developed mesoporous structure with a predominance of pores of this diameter. The peak magnitude indicates a large pore volume, confirming the results obtained with the hysteresis loop. The MCA-0-650 sample also has a relatively low peak in the mesopore region (4.2–4.4 nm), indicating a less uniform pore distribution and a smaller total pore volume than that of MCA-5-650. The absence of this peak for MCA-10-650 indicates the presence of only a small number of pores up to 20 nm in size. It can be concluded that this effect is achieved through the use of 10 min MCA due to a significant decrease in crystallite size and an increase in the specific surface area. The increased pore size in the 50–55 nm range for the MCA-10-650 sample is most likely explained by the distance between the carbon nanotubes (see discussion below). The most interesting conclusion here is the following: all calcined products have similar specific surface areas and porous structures (Table 8).
SEM and EDX Results
Initially, SEM was performed for DCS before MCA and with MCA for 5 and 10 min, without thermolysis (Figure 8 and Figure 9). According to the SEM results, the initial sample before MCA (MCA-0) consists of long, faceted needles with a pronounced hexagonal symmetry, which corresponds to the symmetry of the unit cell, which has a six-fold axis (Figure 8). Samples MCA-5 and MCA-10 consist of micron-sized plates and smaller fragments of initial needles (Figure 9). Therefore, MCA substantially changed particle morphology and resulted in particle grinding.
Figure 10 shows SEM images of the studied samples after calcination at 650 °C. The calcination product, the precursor of which was not subjected to MCA (MCA-0-650), is long, hollow tubes with a spherical tip (Figure 10a,b). If the DCS were subjected to MCA before thermolysis, the calcination products (Figure 10c,d) retain the original morphology of irregularly shaped particles (see Figure 9). The residues from thermolysis of MCA-5-650 are flat plate-like particles of irregular shape (Figure 10e,f). MCA-10-650 is a three-dimensional agglomerate of various shapes, but each fragment is covered with very small, long particles (whiskers, Figure 10e,f).
EDX maps determined that the whiskers of the sample DCS-0-650, approximately 0.5–2 µm in diameter, consist of carbon, and the spherical particles at their ends are made of iron and cobalt (Figure 11).
The SEM results confirm the data on the pore distribution (Figure 7). We see that if the DCS is simply heated (sample MCA-0-650), large, round columns (Figure 10a,b) of carbon whiskers grow (according to the EDX data, Figure 11). Consequently, the maximum number of pores in the region of their size of 2–3 nm indicates that the surface of these whiskers is dotted with small pores. This is a consequence of the fact that when gaseous products are released during thermolysis, gases make a way through the thickness of these whiskers and leave pores when cooling. With MCA for 5 min (sample MCA-5-650), another process occurs (see Figure 10c,d). The long needles of the original DCS break into well-cut crumbs (Figure 9a), which inherit the shape of the original needles. The size of the resulting crumbs varies greatly—from very small pieces less than 1 µm to large individual grains (50 µm). During thermolysis of these crumbs, parts of the crushed grains sinter to form flakes. The shape of the resulting substance remains unchanged—faceted grains remain, the size of which also remains unchanged by thermolysis, remaining within the range of 1–50 µm (Figure 10b). Thermolysis also releases gases, which likely form a large number of pores with a diameter of 2–3 nm on the surface of these particles.
With MCA of the DCS for 10 min (sample MCA-10), the shape and size of the resulting crumbs are no different from those obtained with MCA for 5 min (Figure 9). However, during thermolysis of this sample, the SEM image changed dramatically (Figure 10e,f). Very thin (no more than 5 nm in diameter) tubular structures (whiskers) grew on the surface of the particles. This explains the pore size distribution for sample MCA-10-650 (Figure 7): small pores (2–3 nm) disappear to a minimum, and a sharp increase in the number of pores in the 50 nm region corresponds to the distance between the whiskers.
The growth of the whiskers can possibly be explained as follows: with increasing MCA time, there is a significant reduction in crystallite size, an increase in specific surface area, energy accumulation, and the formation of active centers. These centers presumably form a structure similar to the carbon tubes in the MCA-0-650 sample, but on a significantly smaller scale (by three orders of magnitude).
EDX analysis was performed on sample MCA-10-650 (Figure 12). The method clearly showed that particles 2–3 µm in size contained carbon, iron, and cobalt. Therefore, the overall particle composition of sample MCA-10-650 is identical to that of sample MCA-0-650 (Figure 11).
Figure 12 includes the EDX data for K and Cl. We present these data to demonstrate the accuracy and purity of the synthesis. A low-intensity silicon signal was also recorded for sample MCA-10-650. We explain this by addition when grinding the sample in an agate mortar, as in [31]. Si can also be inherited from the stage of thermolysis in quartz bed and pipe.
We determined that 10 min of MCA is sufficient to obtain tubes similar to those obtained without MCA. At 10 min of MCA, the obtained tubes are much smaller, by at least three orders of magnitude. Further MCA is not advisable. Furthermore, excessive MCA can lead to particle agglomeration, which is undesirable for our purposes (maximizing the specific surface area). Excessive MCA is also associated with increased energy consumption. Thus, we have achieved scalability of the carbon tube growth mechanism.

4. Conclusions

  • Mechanochemical activation (MCA) leads to structural and chemical changes in the [Co(NH3)6][Fe(CN)6] complex. Partial reduction of Fe+3 to Fe+2 is observed, which is confirmed by IR spectroscopy data. The coordination of ammonia ligands changes, and new bonds are formed. The degree of structural amorphization increases, which is recorded by XRD. The thermal stability of the complex decreases, and the main decomposition stages shift to lower temperatures.
  • Preliminary MCA affects the properties of the final thermolysis products. In all cases, thermolysis at 650 °C in argon leads to the formation of the intermetallic compound Co0.5Fe0.5. MCA promotes a reduction in the crystallite size (CSR) and the formation of a nanocrystalline state of the intermetallic compound. We obtained a significant (two-fold) increase in the specific surface area of solid thermolysis products with the chemical composition of the intermetallic compound Co0.5Fe0.5.
  • MCA significantly alters the morphology and porous structure of thermolysis products. The product from unactivated DCS (MCA-0-650) has the form of hollow carbon tubes. After 5 min of MCA (MCA-5-650), the product consists of tablet-shaped particles with a developed mesoporous structure. After 10 min of MCA (MCA-10-650), aggregates are covered with whiskers, which fundamentally changes the pore size distribution and allows for the scalability of obtaining such structures.
  • The optimal duration of mechanochemical treatment was determined. A 10 min MCA is sufficient to achieve significant changes in the product’s structure and morphology. Further increases in treatment time were deemed inadvisable due to the risk of particle agglomeration and increased energy consumption.
  • Thus, the possibility of controlling the properties of functional materials (intermetallic carbon) by combining synthesis via DCS and MCA has been demonstrated, opening up prospects for their application in catalysis and materials science. Further studies of the resulting compounds as catalysts are planned. The obtained results also suggest further investigation into the causes of the significant reduction in the size of the CSR.

Author Contributions

Conceptualization, A.G.; methodology, A.G., V.S., V.V. and V.N.; validation, V.V.; investigation, A.G., V.V., V.S. and M.T.; resources, A.G. and D.M.; data curation, A.G., V.V. and D.M.; writing—original draft preparation, A.G., V.V., A.M.K. and D.M.; writing—review and editing, A.G., V.V., A.M.K., D.M. and M.T.; visualization, V.V., V.S. and M.T.; supervision, A.G. and V.V.; project administration, A.G.; funding acquisition, A.G. and D.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Russian Science Foundation project 24-29-20076 (A.G.).

Data Availability Statement

The raw data required to reproduce these findings are available from the authors on reasonable request.

Acknowledgments

The analysis of the structure of the materials (M.A. Teplonogova) obtained was carried out using the equipment of the JRC PMR IGIC RAS. The authors thank Kirill Yakovlev from ICT KSC RAS for help with obtaining SEM, XRD, and EDX data. The authors are grateful to E.V. Fatushina for HCN-analysis. Analysis of the composition was carried out using the equipment of the JRC PMR IGIC RAS.

Conflicts of Interest

Vasilii Semushin was employed by the company Company group Rusredmet. He declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Abbreviations

The following abbreviations are used in this manuscript:
DCSDouble complex salt
MCAmechanochemical activation
MCCmetal–carbon composites
SEMScanning electron microscopy
EDXenergy-dispersive X-ray spectroscopy
XRDX-ray diffraction
IRInfrared
STASynchronous thermal analysis
TGthermogravimetry
DSCdifferential scanning calorimetry
CSRcoherent scattering regions

References

  1. Gosteva, A.N.; Kulikova, M.V.; Ivantsov, M.I.; Grabchak, A.A.; Semushina, Y.P.; Lapuk, S.E.; Gerasimov, A.V.; Tsvetov, N.S. CO2 hydrogenation over Fe-Co bimetallic catalyst derived from the thermolysis of [Co(NH3)6][Fe(CN)6]. Catalysts 2023, 13, 1475. [Google Scholar] [CrossRef]
  2. Gosteva, A.N.; Kulikova, M.V.; Semushina, Y.P.; Chudakova, M.V.; Tsvetov, N.S.; Semushin, V.V. Catalytic activity of thermolyzed [Co(NH3)6][Fe(CN)6] in CO hydrogenation reaction. Molecules 2021, 26, 3782. [Google Scholar] [CrossRef] [PubMed]
  3. Askeland, D.R.; Wright, W.J. 11-2 Intermetallic Compounds. In The Science and Engineering of Materials, 7th ed.; CL Engineering: Boston, MA, USA, 2015; pp. 387–389. ISBN 978-1-305-07676-1. [Google Scholar]
  4. Zhou, J.; Shu, X.; Wang, Z.; Liu, Y.; Wang, Y.; Zhou, C.; Kong, L. Hydrothermal synthesis of polyhedral FeCo alloys with enhanced electromagnetic absorption performances. J. Alloys Comp. 2019, 794, 68–75. [Google Scholar] [CrossRef]
  5. Klencsár, Z.; Németh, P.; Sándor, Z.; Horváth, T.; Sajó, I.E.; Mészáros, S.; Mantilla, J.; Coaquira, J.A.H.; Garg, V.K.; Kuzmann, E.; et al. Structure and magnetism of Fe–Co alloy nanoparticles. J. Alloys Comp. 2016, 674, 153–161. [Google Scholar] [CrossRef]
  6. Zhou, B.; Yang, Y.; Qin, Y.; Yang, G.; Wu, M. Fabrication of equiatomic FeCo alloy parts with high magnetic properties by fields activated sintering. Manuf. Rev. 2022, 9, 7. [Google Scholar] [CrossRef]
  7. Zhu, K.; Jin, C.; Klencsár, Z.; Ganeshraja, A.S.; Wang, J. Cobalt-iron oxide, alloy and nitride: Synthesis, characterization and application in catalytic peroxymonosulfate activation for orange II degradation. Catalysts 2017, 7, 138. [Google Scholar] [CrossRef]
  8. Chen, N.; Jiang, J.T.; Xu, C.Y.; Yuan, Y.; Gong, Y.X.; Zhen, L. Co7Fe3 and Co7Fe3 x SiO2 nanospheres with tunable diameters for high-performance electromagnetic wave absorption. ACS Appl. Mater. Interf. 2017, 9, 21933–21941. [Google Scholar] [CrossRef]
  9. Gonsalves, K.E.; Kembaiyan, K.T. Synthesis of iron-cobalt intermetallics from organometallic precursors. J. Mater. Sci. Lett. 1990, 9, 59–62. [Google Scholar] [CrossRef]
  10. Çelik, O.; Fırat, T. Synthesis of FeCo Magnetic Nanoalloys and Investigation of Heating Properties for Magnetic Fluid Hyperthermia. J. Magn. Magn. Mater. 2018, 456, 11–16. [Google Scholar] [CrossRef]
  11. Yang, X.; Ji, L.; Yan, N.; Sun, Z.; Lu, X.; Zhang, L.; Zhu, X.; Chen, L. Superior catalytic effects of FeCo nanosheets on MgH2 for hydrogen storage. Dalton Trans. 2019, 48, 12699–12706. [Google Scholar] [CrossRef]
  12. Liu, P.; Sun, Y.; Luo, J.; Dong, Z.; Zhang, P.; Zhong, S.; Wei, Y.; Song, W.; Wang, Y.; Li, Z.; et al. CoFe alloy embedded in ultra-thin nitrogen-doped carbon nanosheets derived from CoFe LDH as efficient oxygen reduction electrocatalyst for Zn-air batteries. Nano Res. 2025, 18, 94907139. [Google Scholar] [CrossRef]
  13. Domonov, D.P.; Kuratieva, N.V.; Pechenyuk, S.I. Structure and properties of double complex salts [Co(NH3)6][Fe(CN)6] and [Co(NH3)6]2[Cu(C2O4)2]3. J. Struct. Chem. 2011, 52, 358–364. [Google Scholar] [CrossRef]
  14. Sun, J.-S.; Zhao, H.; Ouyang, X.; Clérac, R.; Smith, J.A.; Clemente-Juan, J.M.; Gómez-Garcia, C.; Coronado, E.; Dunbar, K.R. Structures, magnetic properties, and reactivity studies of salts containing the dinuclear anion [M2Cl6]2− (M= Mn, Fe, Co). Inorg. Chem. 1999, 38, 5841–5855. [Google Scholar] [CrossRef]
  15. Kahani, S.A.; Shahrokh, M. Preparation and characterization of Cu–Co alloy nanoparticles from double complex salts by chemical reduction. N. J. Chem. 2015, 39, 7916–7922. [Google Scholar] [CrossRef]
  16. Karadağ, A.; Korkmaz, N.; Aydın, A.; Tekin, Ş.; Yanar, Y.; Yerlif, Y.; Korkmaz, Ş.A. In vitro biological properties and predicted DNA–BSA interaction of three new dicyanidoargentate (I)-based complexes: Synthesis and characterization. N. J. Chem. 2018, 42, 4679–4692. [Google Scholar] [CrossRef]
  17. Hogarth, G. Metal-dithiocarbamate complexes: Chemistry and biological activity. Mini-Rev. Med. Chem. 2012, 12, 1202–1215. [Google Scholar] [CrossRef]
  18. Oshio, H.; Onodera, H.; Tamada, O.; Mizutani, H.; Hikichi, T.; Ito, T. Cyanide-bridged Fe−Fe and Fe−Co molecular squares: Structures and electrochemistry of [Fe4II(μ-CN)4(bpy)8](PF6)4⋅4 H2O, [Fe2IICo2II(μ-CN)4(bpy)8](PF6)4⋅3 CHCl3⋅2 CH3CN, and [Fe2IICo2III(μ-CN)4(bpy)8](PF6)6⋅2 CHCl3⋅4 CH3NO2. Chem. Eur. J. 2000, 6, 2523–2530. [Google Scholar] [CrossRef]
  19. Wang, Y.; Ma, X.; Hu, S.; Wen, Y.; Xue, Z.; Zhu, X.; Zhang, X.; Sheng, T.; Wu, X. Syntheses, crystal structures, MMCT and magnetic properties of four one-dimensional cyanide-bridged complexes comprised of MII–CN–FeIII (M = Fe, Ru, Os). Dalton Trans. 2014, 43, 17453–17462. [Google Scholar] [CrossRef]
  20. Schmidtke, H.H.; Mink, H.J. Luminescence properties of transition-metal ions in double complex salts. Z. Naturforsch. A Phys. Sci. 1990, 45, 771–778. [Google Scholar] [CrossRef]
  21. Yang, J.G.; Li, K.; Wang, J.; Sun, S.; Chi, W.; Wang, C.; Chang, X.; Zou, C.; To, W.-P.; Li, M.-D.; et al. Controlling metallophilic interactions in chiral gold (I) double salts towards excitation wavelength-tunable circularly polarized luminescence. Angew. Chem. Int. Ed. 2020, 59, 6915–6922. [Google Scholar] [CrossRef]
  22. Palion-Gazda, J.; Machura, B.; Kruszynski, R.; Grancha, T.; Moliner, N.; Lloret, F.; Julve, M. Spin crossover in double salts containing six-and four-coordinate Cobalt (II) ions. Inorg. Chem. 2017, 56, 6281–6296. [Google Scholar] [CrossRef] [PubMed]
  23. Pechenyuk, S.I.; Domonov, D.P.; Gosteva, A.N. Thermal decomposition of cationic, anionic, and double complex compounds of 3d-metals. Russ. J. Gen. Chem. 2021, 91, 1834–1861. [Google Scholar] [CrossRef]
  24. Rudneva, Y.V.; Korenev, S.V. Dispersed metal alloys: Synthesis methods and catalytic properties (A review). Russ. J. Inorg. Chem. 2024, 69, 1247–1264. [Google Scholar] [CrossRef]
  25. Domonov, D.P.; Pechenyuk, S.I.; Semushina, Y.P.; Yusenko, K.V. Solid-state transformations in inner coordination sphere of [Co(NH3)6][Fe(C2O4)3]∙3H2O as a route to access catalytically active Co-Fe materials. Materials 2019, 12, 221. [Google Scholar] [CrossRef] [PubMed]
  26. Domonov, D.P.; Pechenyuk, S.I.; Belyaevskii, A.T.; Yusenko, K.V. Formation of nanostructured carbon from [Ni(NH3)6]3[Fe(CN)6]2. Nanomaterials 2020, 10, 389. [Google Scholar] [CrossRef]
  27. Domonov, D.P.; Pechenyuk, S.I. Products of double complex compounds as precursors of metal-carbon composites. J. Mater. Sci. Appl. 2024, 8, 1–10. [Google Scholar] [CrossRef]
  28. Tupikova, E.N.; Platonov, I.A.; Khabarova, D.S. Hydrothermal synthesis of platinum-chromium oxidation catalysts on metal supports. Kinet. Catal. 2019, 60, 366–371. [Google Scholar] [CrossRef]
  29. Tupikova, E.N.; Platonov, I.A.; Bondareva, O.S.; Khabarova, D.S. Catalytic activity of the autoclave thermolysis products of [Co(NH3)5Cl][PtCl4] in the complete oxidation of propane and their morphology and phase composition. Kinet. Catal. 2021, 62, 838–844. [Google Scholar] [CrossRef]
  30. Tupikova, E.N.; Platonov, I.A.; Khabarova, D.S. Nano catalysts obtained from platinum and cobalt or nickel binary complexes. AIP Conf. Proc. 2018, 1989, 030017. [Google Scholar] [CrossRef]
  31. Gosteva, A.N.; Golubev, O.V.; Vinogradov, V.Y.; Svidersky, S.N.; Grabchak, A.A.; Manukovskaya, D.V.; Ivantsov, M.I.; Kulikova, M.V. Double complex salt [Co(NH3)6][Fe(CN)6] plasma treatment. Thermo 2025, 5, 36. [Google Scholar] [CrossRef]
  32. Boldyrev, V.V. Mechanochemistry and mechanical activation of solids. Russ. Chem. Rev. 2006, 75, 177–189. [Google Scholar] [CrossRef]
  33. Baklanova, O.N.; Knyazheva, O.A.; Vasilevich, A.V.; Drozdov, V.A.; Leontyeva, N.N.; Lavrenov, A.V. Mechanochemical activation as an efficient way to obtain catalytic materials. Chem. Sustain. Dev. 2022, 30, 15–25. [Google Scholar] [CrossRef]
  34. Stankiewicz, A.I.; Moulijn, J.A. Process intensification: Transforming chemical engineering. Chem. Eng. Prog. 2000, 96, 22–34. [Google Scholar]
  35. Gordina, N.E. Mechanochemical activation as method of intensifying synthesis processes of low-modulus zeolites. Izv. Vyssh. Uchebn. Zaved. Khim. Tekhnol. 2018, 61, 4–22. (In Russian) [Google Scholar] [CrossRef]
  36. Leonardi, M.; Villacampa, M.; Menéndez, J.C. Multicomponent mechanochemical synthesis. Chem. Sci. 2018, 9, 2042–2064. [Google Scholar] [CrossRef] [PubMed]
  37. Molchanov, V.V.; Buyanov, R.A. Scientific grounds for the application of mechanochemistry to catalyst preparation. Kinet. Catal. 2001, 42, 366–374. [Google Scholar] [CrossRef]
  38. Buyanov, R.A.; Molchanov, V.V.; Boldyrev, V.V. Mechanochemical activation as a tool of increasing catalytic activity. Catal. Today 2009, 144, 212–218. [Google Scholar] [CrossRef]
  39. Baláž, P. Mechanochemistry in Nanoscience and Minerals Engineering; Springer: Berlin/Heidelberg, Germany, 2008; p. 413. [Google Scholar] [CrossRef]
  40. Fuentes, A.F. Preface to the special section on mechanochemical synthesis. J. Mater. Sci. 2017, 52, 11785–11788. [Google Scholar] [CrossRef]
  41. Zhang, Q.; Saito, F. A review on mechanochemical syntheses of functional materials. Adv. Powder Technol. 2012, 23, 523–531. [Google Scholar] [CrossRef]
  42. Buyanov, R.A. Mechanism of deactivation of heterogeneous catalysts. Kinet. Catal. 1987, 28, 138–145. [Google Scholar]
  43. Molchanov, V.V.; Buyanov, R.A. Mechanochemistry of catalysts. Russ. Chem. Rev. 2000, 69, 435–450. [Google Scholar] [CrossRef]
  44. Yelsukov, E.P.; Dorofeev, G.A. Mechanical alloying in binary Fe-M (M = C, B, Al, Si, Ge, Sn) systems. J. Mater. Sci. 2004, 39, 5071–5079. [Google Scholar] [CrossRef]
  45. Elsukov, E.P.; Ul’yanov, A.L.; Porsev, V.E.; Kolodkin, D.A.; Zagainov, A.V.; Nemtsova, O.M. Peculiarities of mechanical alloying of high-concentration Fe–Cr alloys. Phys. Met. Metallogr. 2018, 119, 153–160. [Google Scholar] [CrossRef]
  46. Knauss, S.J.; Guevara, L.N.; Atwater, M.A. Enhanced performance of bimetallic Co-Pd catalysts prepared by mechanical alloying. Metals 2019, 9, 335. [Google Scholar] [CrossRef]
  47. Ralphs, K.; Hardacre, C.; James, S.L. Application of heterogeneous catalysts prepared by mechanochemical synthesis. Chem. Soc. Rev. 2013, 42, 7701–7718. [Google Scholar] [CrossRef] [PubMed]
  48. Amrute, A.P.; De Bellis, J.; Felderhoff, M.; Schüth, F. Mechanochemical synthesis of catalytic materials. Chem. Eur. J. 2021, 27, 6819–6847. [Google Scholar] [CrossRef]
  49. Xu, C.; De, S.; Balu, A.M.; Ojeda, M.; Luque, R. Mechanochemical synthesis of advanced nanomaterials for catalytic applications. Chem. Commun. 2015, 51, 6698–6713. [Google Scholar] [CrossRef]
  50. Yang, L.; Pan, Z.; Tian, Z. Mechanochemical synthesis of solid catalysts and application in catalytic reaction. ChemCatChem 2024, 16, e202301519. [Google Scholar] [CrossRef]
  51. Aleksanyan, D.V.; Kozlov, V.A. Mechanochemical tools in the synthesis of organometallic compounds. Mendeleev Commun. 2023, 33, 287–301. [Google Scholar] [CrossRef]
  52. Friščić, T.; Mottillo, C.; Titi, H.M. Mechanochemistry for synthesis. Angew. Chem. 2020, 132, 1030–1041. [Google Scholar] [CrossRef]
  53. Zhang, H.; Davison, N.; Lu, E. Conquering the impossible: Mechanochemistry as a tool for tackling coordination chemistry challenges. RSC Mechanochem. 2025, 2, 370–388. [Google Scholar] [CrossRef]
  54. Avvakumov, E.G.; Kalinkin, A.M.; Kalinkina, E.V. Experience of using a continuous action centrifugal mill for mechanical activation of titanite. Chem. Technol. 2008, 9, 590–594. [Google Scholar]
  55. Kalinkin, A.M.; Vinogradov, V.Y.; Kalinkina, E.V.; Nevedomskii, V.N. Preparation of nanocrysralline Gd2Zr2O7 from mechanically activated coprecipitated precursor. Chem. Pap. 2019, 74, 1161–1170. [Google Scholar] [CrossRef]
  56. Kalinkin, A.M.; Vinogradov, V.Y. Solid state synthesis of Ce-doped zircon from the mechanically activated CeO2-ZrO2-SiO2 mixture. J. Nucl. Mater. 2024, 601, 155350. [Google Scholar] [CrossRef]
  57. Vinogradov, V.Y.; Kasikov, A.G.; Kalinkin, A.M. Preparation of zircon on the basis of raw materials of the Kola peninsula using mechanical activation. Theor. Found. Chem. Eng. 2025, 59, 133–138. [Google Scholar] [CrossRef]
  58. Khalil, L.H.; Mousssa, N.A.; Mikhail, S. Thermal, structural and textural studies on the double complex salt [Co(NH3)6][Fe(CN)6] and on its silica-supported catalysts. J. Mater. Sci. 1992, 27, 557–568. [Google Scholar] [CrossRef]
  59. Khassin, A.A.; Pechenyuk, S.I.; Domonov, D.P.; Minyukova, T.P.; Chermashentseva, G.K.; Kustova, G.N.; Plysova, L.M. Catalytic properties of bimetallic catalysts based on binary complexes of transition metals in Fischer-Tropsch synthesis. Chem. Sustain. Dev. 2007, 15, 673–683. [Google Scholar] [CrossRef]
  60. Pechenyuk, S.I.; Domonov, D.P.; Rogachev, D.L.; Belyavskii, A.T. Anion effect on the thermolysis of double complexes [Co(NH3)6][Fe(CN)6] and [Co(NH3)6]4[Fe(CN)6]3. Russ. J. Inorg. Chem. 2007, 52, 1033–1038. [Google Scholar] [CrossRef]
  61. Zyryanov, V.V. Mechanochemical synthesis of complex oxides. Russ. Chem. Rev. 2008, 77, 105–135. [Google Scholar] [CrossRef]
  62. Salem, K.S.; Kasera, N.K.; Rahman, M.A.; Jameel, H.; Habibi, Y.; Eichhorn, S.J.; French, A.D.; Pal, L.; Lucia, L.A. Comparison and assessment of methods for cellulose crystallinity determination. Chem. Soc. Rev. 2023, 52, 6417–6446. [Google Scholar] [CrossRef]
  63. Sacconi, L.; Sabatini, A. The infra-red spectra of metal(II)-hydrazine complexes. J. Inorg. Nucl. Chem. 1963, 25, 1389–1393. [Google Scholar] [CrossRef]
  64. Smirnov, P.; Filatov, E.; Kuratieva, N.; Plyusnin, P.; Korenev, S. Crystal Structure and Thermal Properties of Double-Complex Salts [M1(NH3)6][M2(C2O4)3] (M1, M2 = Co,Rh) and K3[Rh(NH3)6][Rh(C2O4)3]2·6H2O. Int. J. Mol. Sci. 2023, 24, 12279. [Google Scholar] [CrossRef] [PubMed]
  65. John, A.; Philip, D.; Morgan, K.R.; Devanarayanan, S. IR and Raman spectra of two layered aluminium phosphates Co(en)3Al3P4O16·3H2O and [NH4]3[Co(NH3)6]3[Al2(PO4)4]2·2H2O. Spectroch. Acta A Molec. Biomolec. Spectrosc. 2000, 56, 2715–2723. [Google Scholar] [CrossRef] [PubMed]
  66. Volchkova, E.V.; Churakov, A.V.; Pyatakhina, E.S. Crystal Structure and Properties of [Co(NH3)6][PdCl4]Cl. Russ. J. Coord. Chem. 2019, 45, 215–221. [Google Scholar] [CrossRef]
  67. Makotchenko, E.V.; Baidina, I.A.; Plyusnin, P.E. Synthesis and crystal structure of [Co(NH3)6][AuX4]X2 (X = Cl−, Br−). J. Struct. Chem. 2007, 48, 275–281. [Google Scholar] [CrossRef]
  68. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry, 6th ed.; John Wiley & Sons: Hoboken, NJ, USA, 2009; p. 484. [Google Scholar]
  69. Matiková Maľarová, M.; Černák, J.; Matik, M.; Briančin, J.; Varret, F. Thermal properties of four Co/Fe complexes based on amine-type and cyanido ligands. J. Therm. Anal. Calorim. 2019, 136, 703–715. [Google Scholar] [CrossRef]
  70. Matiková-Maľarová, M.; Matik, M.; Briančin, J.; Kuchár, J.; Žák, Z.; Černák, J. Cd(II)/Fe(III) heterobimetallic complexes with dien and cyanido ligands as precursors of ferrite-type oxides: Syntheses, crystal structures, thermal properties and identification of the oxides. Polyhedron 2021, 200, 115101. [Google Scholar] [CrossRef]
  71. Nakagawa, I. Far infrared and Raman spectra of K3[Co(CN)6] and [Co(NH3)3][Co(CnN)6]. Bull. Chem. Soc. Jpn. 1973, 46, 3690–3693. [Google Scholar] [CrossRef]
Thermo 06 00007 g001
Figure 1. XRD patterns of the initial complex [Co(NH3)6][Fe(CN)6] (sample MCA-0) and the MCA complex from 1 min to 10 min (samples MCA-1–MCA-10).
Figure 1. XRD patterns of the initial complex [Co(NH3)6][Fe(CN)6] (sample MCA-0) and the MCA complex from 1 min to 10 min (samples MCA-1–MCA-10).
Thermo 06 00007 g001
Thermo 06 00007 g002
Figure 2. IR spectra of the initial complex [Co(NH3)6][Fe(CN)6] (sample MCA-0) and the MCA complex from 1 min to 10 min (samples MCA-1–MCA-10).
Figure 2. IR spectra of the initial complex [Co(NH3)6][Fe(CN)6] (sample MCA-0) and the MCA complex from 1 min to 10 min (samples MCA-1–MCA-10).
Thermo 06 00007 g002
Thermo 06 00007 g003
Figure 3. STA (TG + DSC) of samples MCA-0, MCA-5, and MCA-10.
Figure 3. STA (TG + DSC) of samples MCA-0, MCA-5, and MCA-10.
Thermo 06 00007 g003
Thermo 06 00007 g004
Figure 4. XRD patterns of thermolysis products in argon at 650 °C of DCS prepared without the use of MCA (sample MCA-0-650) and with the use of MCA for 5 (sample MCA-5-650) and 10 min (sample MCA-10-650). The main phase is Co0.5Fe0.5 (PDF 01-071-5029).
Figure 4. XRD patterns of thermolysis products in argon at 650 °C of DCS prepared without the use of MCA (sample MCA-0-650) and with the use of MCA for 5 (sample MCA-5-650) and 10 min (sample MCA-10-650). The main phase is Co0.5Fe0.5 (PDF 01-071-5029).
Thermo 06 00007 g004
Thermo 06 00007 g005
Figure 5. IR spectra of the initial compound [Co(NH3)6][Fe(CN)6] (sample DCS-0) and thermolysis products in an argon atmosphere of the MCA complex (samples MCA-0-220–MCA-10-650).
Figure 5. IR spectra of the initial compound [Co(NH3)6][Fe(CN)6] (sample DCS-0) and thermolysis products in an argon atmosphere of the MCA complex (samples MCA-0-220–MCA-10-650).
Thermo 06 00007 g005
Thermo 06 00007 g006
Figure 6. Sorption isotherms of samples MCA-0-650, MCA-5-650, and MCA-10-650.
Figure 6. Sorption isotherms of samples MCA-0-650, MCA-5-650, and MCA-10-650.
Thermo 06 00007 g006
Thermo 06 00007 g007
Figure 7. Description of pore size distribution of samples MCA-0-650, MCA-5-650, and MCA-10-650.
Figure 7. Description of pore size distribution of samples MCA-0-650, MCA-5-650, and MCA-10-650.
Thermo 06 00007 g007
Thermo 06 00007 g008
Figure 8. SEM images of MCA-0 sample, i.e., DCS right after the synthesis. (a)—scale of 30 μm, (b)—the same area, scale 7 μm.
Figure 8. SEM images of MCA-0 sample, i.e., DCS right after the synthesis. (a)—scale of 30 μm, (b)—the same area, scale 7 μm.
Thermo 06 00007 g008
Thermo 06 00007 g009
Figure 9. SEM images of (a) MCA-5 and (b) MCA-10 samples.
Figure 9. SEM images of (a) MCA-5 and (b) MCA-10 samples.
Thermo 06 00007 g009
Thermo 06 00007 g010
Figure 10. SEM images of (a,b) MCA-0-650 sample, (c,d) MCA-5-650 sample, (e,f) MCA-10-650 sample.
Figure 10. SEM images of (a,b) MCA-0-650 sample, (c,d) MCA-5-650 sample, (e,f) MCA-10-650 sample.
Thermo 06 00007 g010
Thermo 06 00007 g011
Figure 11. Sample MCA-0-650: (a)—SEM image. EDX maps: (b)—C (Kα1/2), (c)—Co (Lα1/2), (d)—Fe (Lα1/2).
Figure 11. Sample MCA-0-650: (a)—SEM image. EDX maps: (b)—C (Kα1/2), (c)—Co (Lα1/2), (d)—Fe (Lα1/2).
Thermo 06 00007 g011
Thermo 06 00007 g012
Figure 12. Sample MCA-10-650: (a)—SEM image; EDX maps (Kα1/2): (b)—C, (c)—Si, (d)—Fe, (e)—Co, (f)—K, (g)—Cl.
Figure 12. Sample MCA-10-650: (a)—SEM image; EDX maps (Kα1/2): (b)—C, (c)—Si, (d)—Fe, (e)—Co, (f)—K, (g)—Cl.
Thermo 06 00007 g012
Table 1. Characteristics of MCCs obtained by acid DCS treatment [27].
Table 1. Characteristics of MCCs obtained by acid DCS treatment [27].
DCST, °CContent Co + Fe, wt%Ssp, m2/gMorphology Details
[Co(NH3)6][Fe(CN)6]6303.8 + 4.8109rod-like particles
[Co(NH3)6]4[Fe(CN)6]367513.0 + 11.0176spongy masses
[Co(en)3][Fe(CN)6]70013.0 + 10.4230elongated nodules
[Co(en)3]4[Fe(CN)6]356025.4 + 9.540irregularly shaped
Table 2. Results of elemental analysis of samples MCA-0–MCA-10.
Table 2. Results of elemental analysis of samples MCA-0–MCA-10.
MCA Time, min012345678910Average
C Content, wt%19.119.619.219.419.219.118.818.418.718.518.719.0 ± 0.6
Table 3. Results of elemental analysis of samples MCA-0–MCA-10.
Table 3. Results of elemental analysis of samples MCA-0–MCA-10.
MCA Time, minC Content, wt%N Content, wt%H Content, wt%
0 (calculated)19.345.14.80
0 (measured)19.1 ± 0.144.3 ± 0.14.60 ± 0.09
519.7 ± 0.135.5 ± 0.14.09 ± 0.05
1019.4 ± 0.135.1 ± 0.24.22 ± 0.03
Table 4. Dependence of the degree of crystallinity on MCA time.
Table 4. Dependence of the degree of crystallinity on MCA time.
MCA Time, min012345678910
The Degree of Crystallinity, %86.667.535.833.214.814.514.09.43.93.43.0
Table 5. DSC details for samples MCA-0, MCA-5, and MCA-10.
Table 5. DSC details for samples MCA-0, MCA-5, and MCA-10.
SampleRange T, °CTextremum, °CThe Effect Type
MCA-0190–250223Endothermic
580–650612Exothermic
MCA-570–165108Endothermic
165–200185Endothermic
565–600588Exothermic
600–625604Exothermic
MCA-1075–150114Endothermic
540–610583Exothermic
Table 6. Results of static thermal analysis.
Table 6. Results of static thermal analysis.
MCA Time, minXRDCalcination Temperature, °CResidue of Calcination (wt%)C Content, wt%Color After CalcinationSample
0Amorph *22077.118.3Dark greenMCA-0-220
Amorph45065.515.6BlackMCA-0-450
CoFe65043.325.4BlackMCA-0-650
5Amorph22071.219.0Dark greenMCA-5-220
Amorph45059.419.6BlackMCA-5-450
CoFe65043.925.7BlackMCA-5-650
10Amorph22077.119.7BlackMCA-10-220
Amorph45063.917.6BlackMCA-10-450
CoFe65044.525.0BlackMCA-10-650
* Amorph = XRD amorphous.
Table 7. Lattice parameter α, microdeformations of the lattice, CSR, and content of C, H, and N of thermolysis products in argon at 650 °C of DCS prepared without the use of MCA (sample MCA-0-650) and with the use of MCA for 5 (sample MCA-5-650) and 10 min (sample MCA-10-650).
Table 7. Lattice parameter α, microdeformations of the lattice, CSR, and content of C, H, and N of thermolysis products in argon at 650 °C of DCS prepared without the use of MCA (sample MCA-0-650) and with the use of MCA for 5 (sample MCA-5-650) and 10 min (sample MCA-10-650).
SampleMCA-0-650MCA-5-650MCA-10-650
MCA Time, min0510
Lattice Parameter α, Å2.858502.859412.85970
Microdeformations of the Lattice, %0.131 ± 0.0030.109 ± 0.0040.095 1 ± 0.012
CSR, nm384.3 ± 51.0154.2 ± 9.085.0 ± 7.0
Content of C, %25.425.725.0
Table 8. Porous structure of the sample.
Table 8. Porous structure of the sample.
MCA-0-650MCA-5-650MCA-10-650
Ssp m2/g39.652.559.6
V pore cm3/g0.1090.1600.194
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Gosteva, A.; Kalinkin, A.M.; Vinogradov, V.; Manukovskaya, D.; Nikolaev, V.; Semushin, V.; Teplonogova, M. The Influence of Mechanochemical Activation on the Properties of a Double Complex Salt [Co(NH3)6][Fe(CN)6] and Its Thermolysis Products. Thermo 2026, 6, 7. https://doi.org/10.3390/thermo6010007

AMA Style

Gosteva A, Kalinkin AM, Vinogradov V, Manukovskaya D, Nikolaev V, Semushin V, Teplonogova M. The Influence of Mechanochemical Activation on the Properties of a Double Complex Salt [Co(NH3)6][Fe(CN)6] and Its Thermolysis Products. Thermo. 2026; 6(1):7. https://doi.org/10.3390/thermo6010007

Chicago/Turabian Style

Gosteva, Alevtina, Alexander M. Kalinkin, Vladimir Vinogradov, Diana Manukovskaya, Viktor Nikolaev, Vasilii Semushin, and Maria Teplonogova. 2026. "The Influence of Mechanochemical Activation on the Properties of a Double Complex Salt [Co(NH3)6][Fe(CN)6] and Its Thermolysis Products" Thermo 6, no. 1: 7. https://doi.org/10.3390/thermo6010007

APA Style

Gosteva, A., Kalinkin, A. M., Vinogradov, V., Manukovskaya, D., Nikolaev, V., Semushin, V., & Teplonogova, M. (2026). The Influence of Mechanochemical Activation on the Properties of a Double Complex Salt [Co(NH3)6][Fe(CN)6] and Its Thermolysis Products. Thermo, 6(1), 7. https://doi.org/10.3390/thermo6010007

Article Metrics

Back to TopTop