Novel insight into the chemical analysis of light elements in oxycarbides

doi:10.1016/j.actamat.2018.07.023

Acta Materialia

Volume 157, 15 September 2018, Pages 11-20

https://doi.org/10.1016/j.actamat.2018.07.023 Get rights and content

Abstract

Pure powders of TiC_xO_(1-x) solid solution were synthesized through the carbothermal route. The chemical analysis of the light elements in the as-obtained TiC_xO_(1-x) oxycarbides powders were performed by Instrumented Gas Analysis (IGA). The cell parameters of the samples were determined with an accuracy of about 2% by means of X-ray powder diffraction and the internal standard method. As a result, a model correlating the cell parameters to the chemical composition was established. These reference TiC_xO_(1-x) oxycarbides powders were then sintered in order to obtain pellets of dense ceramics. After having determined that the sintering process does not change the chemical composition of the starting powder, chemical analysis of the different samples of the solid solution were successfully undertaken by Ion Beam Analysis techniques (IBA). The Nuclear Reaction Analysis (NRA) method - that was used to analyse light elements with very high sensitivity - was coupled with Rutherford Back Scattering (RBS) analysis in order to accurately determine the metallic over light elements ratio and to determine the stoichiometry of the phase on massive samples. Exhaustive simulations of the NRA spectra were performed and demonstrated that discrete compositions of the TiC_xO_(1-x) can be efficiently measured locally for bulk samples. Compared to IGA results, the relative amounts of carbon and oxygen of bulk materials were determined with a bias lower than 5%. This protocol being implemented for the TiC_xO_(1-x) system was then tested on HfC_xO_(1-x)with the same success.

Graphical abstract

Introduction

The quantitative analysis of light elements remains one of the ongoing issues in the field of ceramic materials. As an example, this topic is commonly a pending issue for searchers working in the field of carbide based ceramics as carbo-nitrides (MC_xN_y: M = Si, Ti, Zr, Hf …) or oxycarbides (MC_xO_y) for which macroscopical properties depend strongly on their respective amounts of light elements [1]. In the present paper, we report and compare different investigation techniques aiming at characterizing directly or indirectly the chemical composition of both powders and bulk samples of MC_xO_y oxycarbides compounds.

The oxycarbide is a frequently encountered compound. Indeed, as the most used route to elaborate carbides, the carbothermal reduction reaction which consists in the progressive reduction of dioxides with carbon generally leads to an oxycarbide final product [[2], [3], [4]] whose composition is largely dependent on the synthesis conditions. Besides, these ultrarefractory carbides are ideally suited for ultra-high temperature applications [5], thanks to their favorable properties: high hardness, good wear resistance and high decomposition temperature [6]. These properties allow them to be used for example as barriers retaining the fission products in nuclear reactors [7], or as wear-resistant coatings [8]. However, the application field of zirconium carbide is limited under air due to its low oxidation resistance [9]. As a consequence, they are progressively transformed into oxycarbides during their use through carbon-oxygen substitution [[10], [11], [12]]. Therefore, the accurate quantification of light elements (C and O) in heavier matrices is a topic of significant interest in order to define the actual stoichiometry of the studied oxycarbides and to connect these compositions to their expected properties.

The analysis of oxycarbides meets two different kinds of issues depending on whether the sample is a powder or a bulk-type ceramics. When assuming homogeneous samples, powders are generally characterized by coupling X-ray powder diffraction (XRD) and X-Ray Fluorescence (XRF) or Instrumented Gas Analysis (IGA), which provide information averaged over macroscopic sample volumes only. This is for example the case with commercial powders that are mostly considered as homogeneous starting raw materials. The case of bulk type carbide ceramics is, however, more complicated. The high hardness of bulk type carbide materials makes complicated their quantitative analysis because the crushing of ceramics can lead to the incorporation of some impurities. In addition these samples are most often encountered under the form of composite materials and in this case, the global techniques of chemical analysis by IGA or XRF are no longer valid as they will solely provide an average analysis of the sample. For these reasons, numerous fields of research on ceramics could, however, take advantage of analytical methods allowing to perform accurate quantitative analysis of light element at local scale (micrometer to nanometer scale). In this paper, the Nuclear Reaction Analysis (NRA) method was used on bulk type oxycarbides to locally analyse light elements such as carbon and oxygen with very high sensitivity in transition metal oxycarbides of the IVb-group. NRA was associated with Rutherford Back Scattering (RBS) analysis which gives the ratio of metallic over light elements and makes it possible to determine the phase stoichiometry with good accuracy.

Concerning the choice of the chemical system, the focus was set on TiO₂-C. Indeed, the stability domain of the TiC_xO_y solid solution has already been investigated in the literature and it has been shown that the solid solution was complete between TiC and TiO [13,14], giving rise to a wide compositional range of TiC_xO_y compounds. This chemical system was also retained because some of the authors of this publication share a long standing experience in synthesis and characterization of these compounds [3,15,16]. In the present study, the synthesis of the starting powders was achieved through the carbothermal reduction of TiO₂ by carbon black [3]. After having controlled the phase and purity of each synthesized powder sample by XRD and Transmission Electron Microscopy (TEM) and their chemical composition by Instrumented Gas Analysis (IGA) with an accuracy of a few atomic percent, the high purity powders obtained were considered as reference materials to test the accuracy of the Ion Beam Analysis techniques (IBA) on bulk samples that were obtained from the powders.

The first part of this paper is devoted to the establishment of a model that can be further on used by the readers to correlate the evolution of the cell parameter of the solid solution with the oxygen and carbon content. In this part, a special attention has been paid to accurately determine the cell parameters by minimizing systematic errors related to X-ray powder diffraction measurements. In the past, several models linking the oxycarbide cell parameter with its chemical composition had already been proposed in the literature [13,14,17]. However, none of these works used an internal standard to correct for sample positioning errors, which results in large uncertainties in the measurement of the cell parameters. In addition, in none of these previous works the targeted compositions were checked by elemental analysis, so that the mentioned compositions are not fully reliable.

The second part of the paper deals with the local analysis of bulk ceramic materials by IBA. In this work, bulk oxycarbides sintered by Spark Plasma Sintering (SPS) from well controlled powders are used as references in order to evaluate IBA capabilities for light elements quantification in ceramics. The expected results were first simulated and discussed and the obtained results were then compared to those obtained by IGA on powder samples.

The methodology was first implemented on TiC_xO_y and was further on applied to an HfC_xO_y sample.

Section snippets

Synthesis and characterization of powders

The synthesis protocol of powders was described in a previous paper [3]. Summarily, TiO₂ powder (99.9% wt.%, Anatase, Alfa Aesar) and carbon black (Prolabo, France, ashes < 0.75% wt.%) were weighted to the desired final composition of oxycarbide according to the global reaction: ${TiO}_{2}_{(s)} + (1 + 2x) C_{(s)} ⇄ {TiC}_{x} {O_{1 - x}}_{(s)} + (1 + x) {CO}_{(g)}$

The theoretical targeted compositions were calculated assuming that the sum of the C/Ti and O/Ti ratios is equal to 1. In such a condition the amount of possible vacancies is neglected and in

XRD and TEM analyses

Cell parameters measurements were performed using X-ray powder diffraction (XRD) and the Rietveld method. The XRD patterns of all the samples were collected from 10 to 125° (2θ) with CuKα₁ radiation using a Bruker D8 Advance diffractometer (Karlsruhe, Germany) with Bragg-Brentano geometry, LynxEye PSD detector and Ge (111) primary monochromator. A step size of 0.02° (2θ) and an effective acquisition time of 208s per step were chosen to get data with well-defined peaks and good counting

Powder samples: establishing a model linking parameter cell versus composition

Fig. 5 shows the XRD patterns obtained on the titanium oxycarbide samples synthesized at 1600 °C (Fig. 5). For all compositions, the diffraction peaks correspond to those of the PDF-ICDD 00-032-1283 [25] file of the titanium carbide. On the right hand side of the figure, the enlargements on the 422 diffraction peak emphasize a shift towards high angles when the amount of the oxygen rises in the crystalline structure. For samples with a theoretical C/Ti ratio >0.50 a heat treatment of 4 h was

Conclusion and perspectives

1.
Different pure and homogeneous powder samples of TiC_xO_(1-x) oxycarbides solid solution have been synthesized via the carbothermal route at 1500 °C and 1600 °C. This study confirms that the solid solution is complete at least in the compositional range TiC_0.97O_0.02/TiC_0.21O_0.79.
2.
Each of the eight synthesized samples were first chemically analysed by IGA with an accuracy of a few atomic percent. The results obtained show that the measured phase stoichiometry is in very good agreement with the

Acknowledgements

The authors are grateful to the French GdR CNRS 3584 called Thermodynamique des Matériaux à Haute Température (TherMatHT) for the support and the opportunity to collaborate on this particular topic. All authors are also very grateful to the two referees who made excellent comments and remarks to improve the quality of the article.

References (41)

M. Gendre et al.
Synthesis of zirconium oxycarbide (ZrCxOy) powders: influence of stoichiometry on densification kinetics during spark plasma sintering and on mechanical properties
J. Eur. Ceram. Soc.
(2011)
J. David et al.
TEM study of the reaction mechanisms involved in the carbothermal reduction of zirconia
J. Eur. Ceram. Soc.
(2013)
J. David et al.
Transmission electron microscopy study of the reaction mechanisms involved in the carbothermal reduction of anatase
Acta Mater.
(2013)
Y. Katoh et al.
Properties of zirconium carbide for nuclear fuel applications
J. Nucl. Mater.
(2013)
Ö.N. Doǧan et al.
Wear of titanium carbide reinforced metal matrix composites
Wear
(1999)
M.M. Opeka et al.
Mechanical, thermal, and oxidation properties of refractory hafnium and zirconium compounds
J. Eur. Ceram. Soc.
(1999)
I.L. Shabalin et al.
Initial stages of oxidation of near-stoichiometric titanium carbide at low oxygen pressures
J. Alloy. Comp.
(2009)
B. Jiang et al.
Structural studies of TiC1−xOx solid solution by Rietveld refinement and first-principles calculations
J. Solid State Chem.
(2013)
A. Maitre et al.
Role of some technological parameters during carburizing titanium dioxide
J. Eur. Ceram. Soc.
(2000)
P. Lefort et al.
Influence of the grain size on the reactivity of TiO2/C mixtures
J. Alloy. Comp.
(2000)

K.H. Kim et al.

The effect of lanthanum on the fabrication of ZrB2–ZrC composites by spark plasma sintering

Mater. Char.

(2003)

F. Goutier et al.

Role of impurities on the spark plasma sintering of ZrCx–ZrB2 composites

J. Eur. Ceram. Soc.

(2008)

J. Rodríguez-Carvajal

Recent advances in magnetic structure determination by neutron powder diffraction

Phys. B Condens. Matter

(1993)

F. Réjasse et al.

Study of the TiC1-x - TiO2 reactive interface

Acta Mater.

(2018)

H. Khodja et al.

The Pierre Süe Laboratory nuclear microprobe as a multi-disciplinary analysis tool

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

(2001)

A.F. Gurbich

SigmaCalc recent development and present status of the evaluated cross-sections for IBA

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

(2016)

W.A. Lanford et al.

Nuclear reaction analysis for H, Li, Be, B, C, N, O and F with an RBS check

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

(2016)

A.C. Fernandes et al.

Influence of the O/C ratio in the behaviour of TiCxOy thin films

Surf. Coating. Technol.

(2007)

D.A. Pejaković et al.

Synthesis of carbon-rich hafnia thin films by pulsed laser deposition

J. Eur. Ceram. Soc.

(2010)

M. Kokkoris et al.

A detailed study of the 12C(d,p0)13C reaction at detector angles between 135° and 170°, for the energy range Ed,lab=900–2000keV

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

(2006)

Cited by (9)

Microstructure and wear resistance of in-situ TiC reinforced AlCoCrFeNi-based coatings by laser cladding
2022, Applied Surface Science
Citation Excerpt :
Table 2 shows the crystal lattice parameters of TiC1-xOx calculated by XRD diffraction. Compared with the TiC1-xOx crystal lattice parameters in other studies [30,50], the lattice parameters of the TiC1-xOx phase existing in the AlCoCrFeNi-10% TiC coating are most similar to the lattice parameters of TiC0.8O0.2. However, the lattice parameters of the TiC1-xOx phase existing in the AlCoCrFeNi-20% TiC and AlCoCrFeNi-30% TiC coating are most similar to those of TiC0.7O0.3.
High-entropy alloy (HEA) coatings of AlCoCrFeNi are being investigated as potential wear-resistance materials due to their excellent hardness and wear resistance. In this work, AlCoCrFeNi-based coatings were reinforced by in-situ TiC particles via laser cladding. The microstructure and wear resistance were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and wear resistance tests. In addition, the hardness of oxidation TiC particles was analyzed by first principles calculations. The results show that the dominant phase of AlCoCrFeNi-based coatings is BCC phase. In-situ TiC particles present a flower-shaped morphology with Al₂O₃ core. Based on the calculated hardness, the hardness of TiC decreases with the increase of oxygen atoms in TiC. The hardness and wear resistance are improved considerably with the generation of the in-situ TiC particles. The AlCoCrFeNi-20% TiC coating exhibits the best wear resistance with an average hardness of 684.4 HV_0.3, and the main wear mechanism is abrasive wear.
Cracks, porosity and microstructure of Ti modified polymer-derived SiOC revealed by absorption-, XRD- and XRF-contrast 2D and 3D imaging
2020, Acta Materialia
Citation Excerpt :
When Ti is added, the crystallization process is more complex and three phases are expected: TiC, TiO (both in rock salt structure, space group Fm3-m) and β-SiC (zinc blende, space group F-43 m), as it was shown in [26,27]. It is well known that the isostructural compounds TiC and TiO can form a solid solution TiO1-xCx [28–33]. TiC – SiC systems can create solid solution either in zinc blende, or in rock salt structure [34–36].
Morphology, phase composition, cracks and porosity are investigated in monolithic Ti modified SiOC polymer-derived ceramics pyrolyzed at 1000 °C and 1400 °C using synchrotron X-ray full field absorption-contrast tomographic microscopy and scanning XRF- and XRD-contrast microscopy. Samples pyrolyzed at 1000 °C show a crack-free structure, but pyrolysis at 1400 °C results in formation of cracks and at higher Ti content also shows porosity. Tomography revealed the formation of a layered morphology that varies in terms of crystallographic structure and/or Ti stoichiometric concentration. The microstructural observations and electrical conductivity are discussed in terms of pyrolysis temperature and Ti content.
Ti(C, N)-based cermets by vacuum sintering using Commercial Composite powders: Morphology evolution, Composition and related properties
2019, Vacuum
Citation Excerpt :
Oxygen atoms can easily occupy the lattices of cubic carbides of (Ti/Ta/Nb)C, leading to the formation of (Ti/Ta/Nb)CxOy solid solutions. Chemical bonded oxygen is rather stable in these solid solutions and much more energy needs to be consumed during the carbothermal reduction [20,21]. It is noteworthy that the eliminating of oxygen should occur at the solid-state sintering, during which, the gases can go out of the body.
The Composite powders of Commercial TNGG160402R–S inserts were used to prepare Ti(C, N)-based cermets, in order to investigate the morphology evolution, Composition, Com and Hc properties. Mo₂C and WC were first dissolved in Ni–Co binder at 1150 °C, resulting in the formation of M₆C (Co₃W₃C). Precipitation of (Ti, W, Mo, Ta, Nb)(C, N) solid solutions occurred around 1300 °C, with totally dissolved WC/Mo₂C/TaC/NbC in Ni–Co binder. With increasing the sintering temperature from 800 °C to 1460 °C, the mass content of carbon, oxygen and nitrogen was decreased from 7.73%, 1.81% and 6.21%–7.24%, 0.32% and 6.05%, respectively. The value of Com was inversely proportional to the lattice parameter of Co. The sudden decreased Hc from 1350 °C to 1400 °C was caused by the rapid densification via the liquid sintering. Compared with the Commercial products, cermets contained residual M₆C after vacuum sintering, with nonuniform morphology, thinner rims on black cores, and finer grains. Vacuum sintering for Ti(C, N)-based cermets favors an increased internal stress at the core-rim interface. Promising Ti(C, N)-based cermets need carefully controlling the sintering atmosphere, in order to decrease or even avoid the rapid loss of nitrogen during the solid-state sintering.
Mechanical properties of submicronic and nanometric boron carbides obtained by Spark Plasma Sintering: Influence of B/C ratio and oxygen content
2019, Ceramics International
Citation Excerpt :
However, the remaining oxygen in the monoliths is involved in boron oxycarbide ceramics, B3.83CO0.04 and B4.59CO0.18 for HD and TK respectively. The position of the oxygen atom within the boron oxycarbide is unknown from the literature as it could fill a vacancy or, as for TiCO or ZrCO, substitutes the carbon [40,41]. The lower apparent hardness and elasticity of TK material is a consequence of the lower intrinsic properties of the oxycarbide phase.
Boron carbide samples exhibiting nanometric and submicronic microstructure were sintered by Spark Plasma Sintering to investigate the effect of grain size on mechanical properties. The mechanical properties of sintered monoliths were characterized at the grain and macroscopic scales. Although nanostructured material exhibits finer grains than the submicronic material (i.e. mean diameter of 82 vs. 474 nm), its apparent rigidity and hardness are found to be reduced by 6.8% and 8.4% respectively. This contradiction with the Hall-Petch law is linked to the chemical compositions of both materials, which show significant difference in terms of B/C ratio and higher structural oxygen content especially for nanostructured material.
SiC-TiC nanocomposite for bulk solar absorbers applications: Effect of density and surface roughness on the optical properties
2019, Solar Energy Materials and Solar Cells
Citation Excerpt :
This increase in volume is consistent with the higher atomic radius of C compared to O. This result is in agreement with several studies about the evolution of lattice parameter of TiCxO(1-x) oxycarbide materials as a function of the composition [87,89]. For both series of samples, the reflectance increases with the increase in the relative density in the whole range of analyzed wavelengths (Fig. 5).
In this study, the potential of SiC-TiC nano-composites as solar absorbers has been studied. For solar thermal applications, materials with high solar absorptance and low emittance are ideally sought for (spectral selectivity). A semi-molecular sol-gel synthesis route leading to nanometric homogenous composites was described. The resulting SiC-TiC nanocomposite powder was sintered at different temperatures to produce samples with various relative densities (from 57% to 96%). The samples morphology and composition were characterized by several techniques including Scanning Electron Microscopy (SEM), Energy-Dispersive X-Ray Spectroscopy (EDX), X-Ray Diffraction (XRD), carbon and oxygen elemental analyses. The link between the surface roughness and the relative density was precised and the effects on the optical properties (0.25–25 µm wavelength range) were studied. Comparisons were made with pure SiC and pure TiC samples with various relative densities.
Overall, the sample emittance was found to strongly decrease with the increase in the relative density, leading to a great increase in the spectral selectivity, despite a little decrease in the solar absorptance. The TiC-SiC composite has an intermediate reflectance compared to the pure SiC and the pure TiC samples. With an absorptance of 0.76, an emittance of 0.44 and a selectivity of 1.74, the denser SiC-TiC could be a good candidate for bulk solar applications.
Zirconium oxycarbides and oxycarbonitrides: A review
2023, International Journal of Applied Ceramic Technology

View all citing articles on Scopus

View full text

Full length articleNovel insight into the chemical analysis of light elements in oxycarbides

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis and characterization of powders

XRD and TEM analyses

Powder samples: establishing a model linking parameter cell versus composition

Conclusion and perspectives

Acknowledgements

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Acta Mater.

J. Nucl. Mater.

Wear

J. Eur. Ceram. Soc.

J. Alloy. Comp.

J. Solid State Chem.

J. Eur. Ceram. Soc.

J. Alloy. Comp.

Mater. Char.

J. Eur. Ceram. Soc.

Phys. B Condens. Matter

Acta Mater.

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

Surf. Coating. Technol.

J. Eur. Ceram. Soc.

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

Full length article
Novel insight into the chemical analysis of light elements in oxycarbides