Nano Research & Applications

Keywords

Os-Pd/HfC nanocomposites; Composition; Morphology; Phase analysis

Abbreviations

SEM: Scanning Electron Microscope; XRD: X–Ray Diffraction; ATR-FTIR: Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy; TEM: Transmission Electron Microscope; DTA–TGA: Differential Thermal Analysis- Thermal Gravim Analysis; EDX: Energy–Dispersive X–Ray Spectroscopy

Introduction

Recently, many research groups have been interested in nanocomposites of metal Oxides due to their various and numerous applications [1-8]. Nanocomposites of Os-Pd/HfC have a wide range of applicability including magnetic and catalytic materials, super capacitors and Lithium batteries [9-19]. Various methods have been used to synthesize nanocomposites of Os-Pd/ HfC [20-25] among those, Thermal Decomposition Method (TDM) (solo–thermal and solid state) is the most applicable method due to low costs of in used apparatuses as well as good control on appropriate conditions for producing nanocomposites with desirable size and morphology [26-30]. In the current research, Schiff base complexes of Osmium(IV) with formula of transbis(benzenethiolato) [N,N'–ethylene bis(salicylideneaminoato)] osmium(IV) and cis–bis(benzenethiolato) [N,N'ethylenebis (salicylideneaminoato)] osmium(IV) were synthesized, at first, and then, nanocomposites of Os-Pd/HfC were synthesized in an oven at 475°C during 4 hours (Figures 1 and 2).

Figure 1 SEM images of Os-Pd/HfC nanocomposites in different scales with (A) 70000x zoom, (B) 70000x zoom, (C) 100000x zoom, (D) 100000x zoom, (E) 120000x zoom, (F) 140000x zoom, (G) 160000x zoom, (H) 170000x zoom, (I) 180000x zoom and (J) 190000x zoom (upper illustration) and TEM image of Os-Pd/ HfC nanocomposites with 130000x zoom (lower illustration).

Figure 2 Simulated potential energy surfaces for the formation of Os-Pd/HfC nanocomposites wherein the x and y axes show intrinsic reaction coordinates (IRC) and the z–axis shows energy.

Hafnium (IV) Carbide is a hard compound with high melting temperature and electrical conductivity. The Osmium based composites, especially those contain hard ceramic particles; have been considered as covers resistant to abrasion in high temperatures. Osmium composites containing HfC particles are developed as hard cover for steel rollers and covers of injective molds [31-39].

The electrical precipitation of Osmium using Osmium bathes performs based on Phosphoraniminato or Nitrido and is of some advantages such as: (1) Easy storing of electrolyte; (2) Availability of Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido with high purity and reasonable cost; and (3) Creating layers with low brittleness and internal tension. Although Palladium Flvbvrat bath was used by Bapu to synthesize Os-Pd/HfC composite, the produced composite was not in nano size. Most of Os-Pd/HfC electrical precipitation composites have patent and their details are not available [40-47].

There are various methods for synthesizing nanocomposites; the most important of those are including: mechanical alloying [48,49] combustion synthesis [50,51] and electrochemical precipitation [52-57]. It is difficult to synthesize some types of composites by usual methods due to very low wetting of hard phase by melt of background phase. The electrochemical synthesize of this composite can solve this problem to some extent. At the other side, covering industrial pieces by composite materials is generally implemented by thermal spraying and PVD; severe oxidation will be possible during those methods. While the electrochemical methods are of simple system and does not need to complex apparatuses, those have not the oxidation problem [53-59].

This method is environmentally friendly and it is controllable. However, the mechanical alloying has not desirable quality because of high residual stress. As a result, the objective of the current study is producing Os-Pd/HfC composites using simple electrochemical method which avoids these deficiencies.

Productions of ceramics, composites and refractory materials using combustion synthesis method have been widely studied during last two decades. In this method, various mixed and compacted powders ignite in the air or neutral atmosphere and the combustion face produce by performing an exothermic chemical reaction. Then, products constitute by passing this face through reagents [60-65].

Osmium can be strengthened by integrating with fine ceramic particles; however, it causes a little decrease in electrical conductivity of Osmium [66-69]. Metal matrix composites of Osmium reinforced with Palladium–Hafnium (IV) Carbide integrate high electrical conductivity of Osmium with high chemical–thermal ability and high strength of Palladium– Hafnium (IV) Carbide phase; therefore, Os-Pd/HfC composites are of ability to represent high strength and electrical conductivity [70-73]. The structure of Osmium matrix nanocomposites need to a uniform distribution of nano sized reinforcing particles to show high strength and high abrasion resistance [74,75]. As a result, production method of these nanocomposites to achieve a uniform distribution and nano sized particles is of critical importance [76,77].

In situ technique is being used to produce this nanocomposite in which reinforced particles are being created through chemical reactions during production process of nanocomposites and it leads to creating very fine sized particles with uniform distribution [78,79].

There are various methods for producing Osmium matrix nanocomposites such as internal oxidation, mechanical alloying and thermochemical method. Non–uniform distribution of Oxide particles negatively affects the electrical and mechanical properties of this nanocomposite [80,81]. The previously performed studies [82,83] have been shown that more uniform distribution of particles, along with a nano sized structure, can be obtained using thermochemical method which improves electrical and mechanical properties of this nanocomposite [84,85].

Furthermore, it should be noted that in the current research, Os-Pd/HfC nanocomposites powder containing 2 and 4 weight percent of Palladium–Hafnium (IV) Carbide were produced by thermochemical method and the produced phases in various steps of heat treatment to synthesize the final nanocomposites powder were studied.

Materials, Research Method and Experimental Techniques

All chemical materials (solvents, amines, aldehydes and so on) used in the current research were bought from Sigma– Aldrich company and were utilized without any purification. The vibration spectrum of ligands, associated complexes and resulted nanocomposites, in the range of 400 cm^-1 and 4000 cm^-1, are derived by Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR–FTIR) Bruker. The elemental analysis is performed by 2400 CHN Elemental Analyzer by Perkin Elmer apparatus. The X-Ray Diffraction (XRD) spectrum of compounds are achieved by PAN alytical-X ’Pert Pro MPD with Cr Kα rays in the angle range of 2θ = 5°–80°. Scanning Electron Microscope (SEM) images are captured by scanning electron microscope apparatus of Cam Scan MV2300. The Transmission Electron Microscope (TEM) apparatus used in this study was Cs–corrected Dedicated TEM HD–2700. The model of Differential Thermal Analysis- Thermal Gravim Analysis (DTA–TGA) apparatus where used was Perkin STA 8000/ST–740 Series and the Energy-Dispersive X–Ray Spectroscopy (EDX) apparatus was RONTEC–QUANTAX/QX2.

To synthesize nanocomposites of Os-Pd/HfC, some amount of complexes trans-bis(benzenethiolato) [N,N'–ethylene bis (salicylideneaminoato)] osmium(IV) and cis-bis (benzenethiolato) [N,N'–ethylenebis(salicylide neaminoato) ]osmium(IV) were uniformly powdered in a crucible, at first, and then, the obtained powder was set into an electric oven under 475°C. After about 4 hours, the resulted gray powder was washed by methanol and the final product was filtered and dried in the air. For identifying the final product, ATR– FTIR was used. Since the obtained precipitation has not residual stress, the grain size can be easily calculated by Scherrer equation as [86,87]:

D = 0.9λ / β .cosθ

where λ is wavelength in Angstrom, θ is angle of diffraction and β is peak width at the half height of the maximum intensity in terms of radians. In the current research, grain sizes are calculated by X`Pert HighScore Plus software based on Scherrer equation.

The production process of Os– Pd/HfC nanocomposites powder consists of the following steps:

Preparing aqueous solution of Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido in proportion with final composition of the product (Os–Pd/HfC nanocomposites containing 2 and 4 weight percent of Palladium– Hafnium (IV) Carbide).

(1) Heating the aqueous solution and creating the elementary powder.

(2) Thermal desalination process of the produced powders in the air at 500°C for 4 hours.

Heat treatment to create Palladium– Hafnium (IV) Carbide at various temperatures of 650, 750, 850, 950, 1050, 1150, 1250 and 1350°C for two hours in the air.

(3) Heat treatment of Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido reduction in the Hydrogen atmosphere at temperatures of 450, 550, 650, 750, 850, 950 and 1050°C for two hours to produce nanocomposites powder.

After thermal desalination process, powders were analyzed by ATR–FTIR, DTA–TGA, XRD, SEM, TEM and EDX. To better identification of phases after heat treatment at 1250°C, 15% Nitric acid solution was added to solve the presented Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido and to identify other compositions.

Results and Discussion

In the current research, nanocomposites of Os-Pd/HfC were synthesized using thermal decomposition of solid state from Schiff base complexes of Osmium(IV) with formula of trans–bis (benzenethiolato) [N,N'–ethylenebis (salicylideneaminoato)] osmium(IV) and cis–bis (benzenethiolato) [N,N'–ethylenebis (salicylideneaminoato)] osmium(IV) at 475°C during 4 hours. The synthesized nanocomposites and the synthesized Schiff base complexes were identified using ATR–FTIR, XRD, SEM, TEM and EDX techniques. The obtained results from these techniques were shown that the synthesized nanocomposites from Schiff base complexes have a plain structure while nanocomposites of Os-Pd/HfC synthesized from the complexes have cubic structure and their sizes are between 50 and 200 nanometers. Also, electrical sedimentation of Os-Pd/HfC nanocomposites were studied. The effects of parameters such as amount of cathode rotation, applying ultrasonic waves and magnetic stirring were investigated. Further, the effect of Hafnium (IV) Carbide grading on the electrochemical sedimentation of the nanocomposites was studied. Hafnium (IV) Carbide with high level of purity was produced and precipitated using combustion synthesis method. The composition and morphology of composite were evaluated by ATR–FTIR, XRD, SEM, TEM and EDX techniques. Moreover, the size of grains was calculated based on Scherrer equation and using X`Pert HighScore Plus software. It was observed that the best result is obtained from suspension containing the produced Hafnium (IV) Carbides by combustion synthesis and magnetic stirring method. Furthermore, the production processes of 2wt% Os-Pd/HfC and 4wt% Os-Pd/HfC nanocomposites powders by thermochemical method were investigated. The produced phases in various steps of heat treatment were identified by DTA–TGA, ATR–FTIR, XRD, SEM, TEM and EDX analyses. The nanocomposites powders were produced through the following steps, preparing aqueous solution of Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido to achieve final compound; heating the aqueous solution and creating the elementary powder; thermal desalination process; heat treatment to create Palladium– Hafnium(IV) Carbide at various temperatures and; reducing Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido to Osmium in various temperatures in Hydrogen atmosphere. Optimum temperatures for creating Palladium–Hafnium(IV) Carbide and reducing powders were obtained as 830 and 860°C, respectively. Size of the produced Palladium–Hafnium (IV) Carbide particles by thermochemical method was about 30–60 nanometers. The experimental results obtained from elemental analysis of associated complexes are presented in Table 1. Good agreement between theoretical and experimental results confirms the purity of synthesized compounds. It should be noted that the elemental analysis is performed by 2400 CHN Elemental Analyzer by Perkin Elmer apparatus.

Table 1: Experimental results of elemental analysis of synthesized complexes.

In vibration spectrum of synthesized complexes, the related peak to vibrations of various groups can be seen that their most important one is the peak related to vibration of imine group (C=N) which is emerged in the range of 1610 and 1620 cm^-1 (depend on the type of complex). The lack of the peak related to aldehyde and amine groups in these complexes demonstrate the lack of Schiff base ligand in these complexes. However, a peak related to vibration of piperidine in 3553 cm^-1 can be observed in trans– bis (benzenethiolato) [N,N'-ethylenebis (salicylideneaminoato)] osmium(IV) complex in addition to imine peak. In the complexes synthesized in the current study, the peak related to vibration of aliphatic and aromatic Hydrogen is emerged in 3250 cm^-1 and the peak related to vibrations of C=C ring can be observed in the range of 1350–1650 cm^-1. However, in the vibration spectrum of the synthesized nanocomposites (Figure 3), the only observable vibration peak is for Os–O group where is in the range of 569 and 663 cm^-1. The presence of these two peaks in the vibration spectrum is a proof for constituting of the synthesized nanocomposites of Os-Pd/HfC (Figure 3).

Figure 3 Vibration spectra of nanocomposites synthesized from trans-bis(benzenethiolato) [N,N'– ethylen ebis(salicylideneaminoato)]osmium (IV) (upper) and cis-bis(benzenethiolato)[N,N'ethylenebis (salicylideneaminoato)]osmium (IV) (lower) complexes.

The XRD spectrums of the synthesized complexes are shown in Figure 4. Comparison of the obtained XRD patterns for nanocomposites with the previously published results in this field confirms the presence of nanocomposites of Os– Pd/HfC (Figure 4).

Figure 4 XRD spectra of nanocomposites synthesized from trans– bis(benzenethiolato)[N,N'– ethylenebis(salicylideneamin oato)]osmium (IV) (lower) and cis–bis(benzenethiolato) [N,N'– ethylenebis(salicylideneaminoato)]osmium (IV) (upper) complexes.

The obtained images from SEM of the complexes and the synthesized nanocomposites are shown in Figure 5. As can be seen, the nanocomposites obtained from the complexes (images a and b, Figure 5) are of approximately plain structure and the nanocomposites of Os– Pd/HfC resulted from the complexes (image c, Figure 5) have a cubic structure. The average size of the synthesized nanocomposites for complexes is in the range of 100–200 nanometers and for nanocomposites of Os– Pd/HfC is in the range of 50–100 nanometers (Figures 5 and 6).

Figure 5 SEM images of (a) trans–bis(benzenethiolato)[N,N'–ethylenebis(salicylideneaminoato)]osmium(IV) with 120000x zoom, (b) cis–bis(benzenethiolato)[N,N'–ethylenebis(salicylideneaminoato)]osmium(IV) with 90000x zoom and (c) the resulted nanocomposites of Os– Pd/HfC with 60000x zoom.

Figure 6 XRD pattern of the produced Hafnium (IV) Carbide by combustion synthesis.

The diffraction pattern of the produced precipitation is shown in Figure 7. The peaks related to Palladium and Hafnium (IV) Carbide are clearly shown in this figure. The high intensity of Pd peak is a sign of background phase and short peak of HfC indicates second (supportive) phase (Figure 7).

Figure 7 XRD pattern of the produced precipitation.

The results of SEM on precipitation are shown in Figure 8 in which two produced phase regions (bright and dark regions) are clearly shown. Linear analysis of each phase shows that the bright region is Hafnium (IV) Carbide and the dark one is Palladium. It confirms the high stability of Hafnium (IV) Carbide phase (Figure 8).

Figure 8 SEM image of the produced composite with 35000x zoom.

The hardness of the produced precipitation was 275 Vickers. The micro–hardness results obtained from various locations show 275–295 Vickers. The hardness can be uniformly seen through the precipitation which indicates uniform distribution of Hafnium (IV) Carbide in background and creating nanostructure. The governing mechanism on composite production is that as Palladium ions are reduced, Hafnium (IV) Carbide particles are placed between Palladium phase, at the same time, without any oxidation or reduction.

Based on the performed investigations, during electrical precipitation, Hydrogen and Oxygen absorbing led to producing complexes such as PdH⁺ and PdOH⁺. These compounds place on growth sites and prevent the growing of Palladium. Hence, a Palladium background with nanostructure will be produced.

After performing thermal desalination process (removing moisture and volatile compositions including Nitrates), XRD analysis was performed on the powders. Figure shows the XRD pattern of powders with 4 weight percent of Palladium– Hafnium (IV) Carbide after thermal desalination process (Figure 9).

Figure 9 XRD pattern of powders containing 4 weight percent of Palladium–Hafnium (IV) Carbide and heat treated at 500°C for two hours.

Regarding Figure 9, it can be seen that there are only peaks related to Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido phases in this figure. In this step, the peaks related to Palladium– Hafnium (IV) Carbide phase were not seen. Therefore, the next heat treatment was performed in the air at higher temperatures to synthesize stable Palladium– Hafnium (IV) Carbide phase. As the temperature in which Palladium– Hafnium (IV) Carbide phase is creating, the next heat treatments were performed on powders in the air at temperatures of 650, 750, 850, 950, 1050, 1150, 1250 and 1350°C for two hours (Figure 9).

Figure 10 shows the experimental XRD related to various temperatures of heat treatment in the air to create Palladium– Hafnium (IV) Carbide phase. It can be seen that Palladium– Hafnium (IV) Carbide phase was emerged at 650°C and was completed at 860°C, so it can be said that temperatures higher than 650°C can overcome the activation energy for production process during heat treatment in the air. Regarding the fact that Palladium– Hafnium (IV) Carbide phase creation is completed at 860°C, it can be said that the optimum temperature for creation of Palladium– Hafnium (IV) Carbide phase is 860°C (Figures 10 and 11).

Figure 10 Experimental XRD pattern of powders containing 4 weight percent of Palladium– Hafnium (IV) Carbide and heat treated at (a) 650, (b) 750 and (c) 860°C for two hours.

Figure 11 TEM images of powders containing 4 weight percent of Palladium– Hafnium (IV) Carbide and heat treated at (a) 800, (b) 830, (c) 860 and (d) 890°C for two hours with 100000x zoom.

Figure 11 shows the TEM images of Oxide powder after heat treatment for producing Palladium– Hafnium(IV) Carbide at 860°C. The black phase is related to Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido and fine spherical particles show Palladium - Hafnium(IV) Carbide phase. The size of Palladium– Hafnium (IV) Carbide particles obtained from TEM images is about 30–60 nanometers.

After thermal desalination process, DTA–TGA analyses were performed on powders containing 2 and 4 weight percent of Palladium– Hafnium (IV) Carbide. Figure 12 shows the DTA–TGA curves of these two powders (Figure 12).

Figure 12 DTA–TGA curves of (a) 2wt% Os– Pd/HfC and (b) 4wt% Os– Pd/HfC produced by electrochemical method.

Considering these figures, it can be seen that the DTA–TGA curves of powders containing 2 and 4 weight percent of Palladium– Hafnium (IV) Carbide are similar to each other. It was reported in the previously performed investigations that creation of Palladium - Hafnium (IV) Carbide phase cannot be seen on the DTA curve as a sharp and identified peak but the results obtained from XRD analysis was shown that creation of Palladium– Hafnium (IV) Carbide phase is started at 650°C. On the TGA curve, also, there is not a considerable weight change up to 850°C. However, about 15 percent decrease in weight can be observed at 850°C on both TGA curves and on corresponding DTA curves also an endothermic peak is being observed. Further, at about 1000°C, about 4 percent increase in weight is observed on both TGA curves which are corresponding to an endothermic peak at temperature about 1000°C on both DTA curves.

To determine the produced phases in these two temperatures, powders were heat treated at two temperatures of 850 and 1000°C in the air for two hours and XRD analyses were performed on the obtained powders.

Figure 13 show the XRD patterns of powders at 850 and 1000 degrees Celsius. Considering Figure 13a, it can be observed that in addition to the peaks related to Osmium(IV) Phosphoraniminato, Osmium(VI) Nitrido and Palladium - Hafnium(IV) Carbide phases, the peaks related to the third phase of Os– Pd/HfC also are presented. Therefore, it can be said that the endothermic peak at 850°C on the DTA curve indicates that Os– Pd/HfC is created (Figure 13).

Figure 13 XRD pattern of powders containing 4 weight percent of Palladium– Hafnium (IV) Carbide and heat treated at (a) 850 and (b) 1000°C for two hours.

Figure 13b shows the XRD pattern of powders resulted from solving in Nitric acid solution. Considering Figure 13b, it can be observed that in addition to the peaks related to Palladium– Hafnium (IV) Carbide phase and Os– Pd/HfC, the peaks related to Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido also are presented at 1000°C. Therefore, considering the XRD results of heat treated powders at 850 and 1000°C, it can be said that two endothermic peaks on DTA curves of powders are related to creating trans–bis(benzenethiolato)[N,N'–ethylenebis(salicyli deneaminoato)]osmium(IV) and cis–bis(benzenethiolato)[N,N'– ethylenebis(salicylideneaminoato)]osmium(IV) phases. It was reported in the previous studies [1–23,30] that after creation of Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido and Palladium– Hafnium (IV) Carbide due to mutual penetration of trans-bis(benzenethiolato)[N,N'-ethylenebis(salicylideneamino ato)]osmium(IV) and cis–bis(benzenethiolato)[N,N'-ethyleneb is(salicylideneaminoato)]osmium(IV), Palladium– Hafnium (IV) Carbide phase is converted to Os–Pd/HfC phase.

Figure 14 Experimental XRD pattern of powders containing 4 weights percent of Palladium– Hafnium (IV) Carbide and reduced in Hydrogen atmosphere at 830°C for two hours.

The performed experiments were shown that the necessary temperature to reduce Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido to pure and elemental Osmium is 830°C and that in temperatures lower than 830°C, complete reduction of Osmium(IV) Phosphoraniminato and Osmiu(VI) Nitrido to Osmium are not possible.

Figure 14 show the experimental XRD patterns of heat treated powders in Hydrogen atmosphere at 830°C for two hours. Considering Figure 14, it can be observed that in this temperature, only peaks of Osmium phase are presented and Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido are completely reduced to Osmium. It is worthwhile to note that at reduction temperature of 830°C, the peaks related to Palladium– Hafnium (IV) Carbide phase are not presented. In fact, it is possible that uniform distribution of Palladium– Hafnium (IV) Carbide particles in the matrix of Osmium, nano sized Palladium - Hafnium(IV) Carbide particles and low percentage of those in the matrix of Osmium lead to lack of presence of Palladium– Hafnium(IV) Carbide peaks after the reduced treatment (Figure 14).

Figure 15 shows the SEM image of powders containing 4 weights percent of Palladium - Hafnium (IV) Carbide after reduction treatment. Angular particles are Palladium– Hafnium (IV) Carbide phase and agglomerated spherical particles are Osmium phase.

Figure 15 SEM image of 4wt% Os– Pd/HfC nanocomposites powders after reduction treatment with 110000x zoom.

Figure 16 shows the curve related to EDX analysis of 4wt% Os- Pd/HfC powders after reduction treatment. An analysis was performed on these powders and the results were shown that this sample contains 4.84% Palladium– Hafnium (IV) Carbide and remaining of powders is Osmium.

Figure 16 EDX analysis curve of 4wt% Os– Pd/HfC nanocomposites powders after reduction treatment.

Figures 17 and 18 show simulated potential energy surfaces for the formation of Schiff base complexes of Osmium(IV) with formula of trans–bis(benzenethiolato)[N,N'–ethylenebis(salicylid eneaminoato)]osmium(IV) and cis–bis (benzenethiolato) [N,N'– ethylenebis(salicylideneaminoato)] osmium(IV) at 475°C during 4 hours, respectively.

Figure 17 Simulated potential energy surfaces for the formation of Schiff base complex trans– bis(benzenethiolato)[N,N'–et hylenebis(salicylideneaminoato)]osmium(IV) wherein the x and y axes show intrinsic reaction coordinates (IRC) and the z–axis shows energy.

Figure 18 Simulated potential energy surfaces for the formation of Schiff base complex cis-bis(benzenethiolato)[N,N'–ethyl enebis(salicylideneaminoato)]osmium(IV) wherein the x and y axes show intrinsic reaction coordinates (IRC) and the z–axis shows energy.

Also, Figures 19 and 20 illustrate simulated potential energy surfaces for the formation of Hafnium (IV) Carbide and Palladium– Hafnium (IV) Carbide, respectively. Furthermore, Figure 21 shows general outline of energy level graph of Os– Pd/ HfC nanocomposites (Figure 21).

Figure 19 Simulated potential energy surfaces for the formation of Hafnium (IV) Carbide wherein the x and y axes show intrinsic reaction coordinates (IRC) and the z–axis shows energy.

Figure 20 Simulated potential energy surfaces for the formation of Palladium– Hafnium (IV) Carbide wherein the x and y axes show intrinsic reaction coordinates (IRC) and the z–axis shows energy

Figure 21 General outline of energy level graph of Os- Pd/HfC nanocomposites wherein the x and y axes show Os–Pd and Os- Pd/HfC bonds’ length respectively and also the z–axis shows energy.

Conclusion

By heating the Schiff base trans–bis(benzenethiolato)[N,N'– ethylenebis(salicylideneaminoato)]osmium(IV) and cis– bis(benzenethiolato)[N,N'–ethylenebis(salicylideneaminoato)] osmium(IV) complexes as the new principal materials at 475°C for 4 hours, nanocomposites of Os-Pd/HfC were successfully synthesized. The results obtained from ATR–FTIR and XRD confirm the purity of compounds due to absence of other peaks. The morphology of the synthesized nanocomposites was evaluated by SEM, TEM and EDX. Shape and size of the synthesized complexes and also the resulted nanocomposites are approximately uniform and identical and their sizes are in the range of 50 and 200 nanometers. The results show that difference on the elementary pre–substance (coordinated amine on the Osmium Schiff base complex) has not a considerable effect on the necessary temperature for producing nanocomposites and their sizes.

Regarding various examined parameters, the best result is obtained from solution containing suspension of the produced Hafnium (IV) Carbides by combustion synthesis at 90°C and pH = 4.9. Using Scherrer equation, grain size of Osmium was calculated as 69 nanometers. Using micro–hardness evaluation test, the hardness of precipitation was measured as 275 Vickers which confirms the structural uniformity of nano. Moreover, using ATR– FTIR, XRD, SEM, TEM and EDX, another proof was achieved for producing this composite and finally, it can be pointed out that it is possible to produce a nanocomposite by a simple method.

Os-Pd/HfC nanocomposites powder was successfully produced by thermochemical method with uniform distribution of Palladium– Hafnium(IV) Carbide particles in the matrix of Osmium. The optimum temperature for creating Palladium-phase in the obtained nanocomposites was 860°C. In temperatures higher than 850°C, Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido phases are being created which negatively affect electrical properties of nanocomposites of Osmium matrix. According to the results, complete reduction of Osmium(IV) Phosphoraniminato and Osmium(VI) Nitrido to Osmium are not possible at temperatures higher than 830°C. In the final nanocomposites powder, the size of Palladium-Hafnium(IV) Carbide particles was about 30-60 nanometers.

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