Titanium Carbide TiCx Research Articles

Neutron Diffraction Study of Phase Transformations at the Lower Boundary of the Homogeneity Range of Cubic Titanium Carbide TiCx

Neutron Diffraction Study of Phase Transformations at the Lower Boundary of the Homogeneity Range of Cubic Titanium Carbide TiCx

Combustion characteristics and structure of carbon nanotube/titanium composites

Reactivity of nanosized objects is a hot topic in modern solid-state chemistry and materials science. The present work is focused on the interaction between multi-walled carbon nanotubes (MWCNTs) and metallic titanium during high-energy ball milling and thermal explosion, a rapid temperature rise in a mixture caused by an exothermic reaction ignited by external heating and occurring throughout the sample volume. A fundamental property of the nanocomposite mixture—the ability of its components to react in the combustion mode—is explained; an analysis of the dependence of the combustion characteristics of the nanocomposites on the milling duration of powder mixtures is provided. The phase and structural transformations of the Ti-MWCNT mixtures have been analyzed using X-ray diffraction and transmission electron microscopy. It was found that the ball-milled powders contain nanostructured titanium, nanotube fragments, amorphous carbon and nanosized carbon-deficient titanium carbide TiCx. Within the nanocomposite powder particles, TiCx nanoparticles are covered with layers of amorphous carbon. Thermal explosion was observed in Ti-4mass%MWCNT mixtures milled for 1.5–7 min. Shorter milling times were apparently not sufficient for establishing a proper interfacial contact, while longer milling times led to the extensive formation of titanium carbide TiCx, which acted as a barrier lowering the heat release by the mixture upon ignition. Both the ignition temperature of Ti-4mass%MWCNT and the maximum temperature developed during thermal explosion decrease with the milling time. A comparison of the behavior of MWCNT with that of carbon black under conditions of thermal explosion in the mixtures with titanium is also presented.

ABOUT HEAT CAPACITY OF TITANIUM CARBIDE TiCx

This work relates to the field of thermophysical parameters of refractory interstitial alloys. The isochoric heat capacity of cubic titanium carbide TiCx has been calculated within the Debye approximation in the carbon concentration range x = 0.70–0.97 at room temperature (300 K) and at liquid nitrogen temperature (80 K) through the Debye temperature established on the basis of neutron diffraction analysis data. It has been found out that at room temperature with decrease of carbon concentration the heat capacity significantly increases from 29.40 J/mol·K to 34.20 J/mol·K, and at T = 80 K – from 3.08 J/mol·K to 8.20 J/mol·K. The work analyzes the literature data and gives the results of the evaluation of the high-temperature dependence of the heat capacity СV of the cubic titanium carbide TiC0.97 based on the data of neutron structural analysis. It has been proposed to amend in the Neumann–Kopp formula to describe the high-temperature dependence of the titanium carbide heat capacity. After the amendment, the Neumann–Kopp formula describes the results of well-known experiments on the high-temperature dependence of the heat capacity of the titanium carbide TiCx. The proposed formula takes into account the degree of thermal excitation (a quantized number) that increases in steps with increasing temperature.The results allow us to predict the thermodynamic characteristics of titanium carbide in the temperature range of 300–3000 K and can be useful for materials scientists.

Neutron Diffraction Study of the Phase Transformations in Titanium Carbohydride TiC0.50Hy

It is shown that the ordered phase of titanium carbohydride TiC0.50H0.31 with a face-centered cubic lattice (sp. gr. Fd $$\bar {3}$$ m), obtained by self-propagating high-temperature synthesis, has an ordered antiphase domain structure with a period P = 16. This period is much larger than that in TiC0.50Hy (y ≤ 0.22), with a lower hydrogen content (P ≈ 11). It is shown that TiC0.50H0.31 decomposes at temperatures T ≤ 900°C into the cubic phase of titanium carbide TiCx (x ≥ 0.70) (sp. gr. Fm $$\bar {3}$$ m) and the trigonal phase of titanium carbohydride Ti2Cv′Hz′ (sp. gr. P $$\bar {3}$$ m1).

Effects of Duty Cycle on Texture Orientation and Composition of TiCx Nanostructured coatings

Nanostructured titanium carbide (TiCx) coatings are deposited on steel substrates by plasma chemical vapor deposition using three different duty cycles of 33, 40, and 50% and characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The relationship between the texture orientation/elemental concentration and duty cycle can be divided into two regimes, carbide (TiCx) state and oxycarbide (TiCxOy) state. The coatings crystallize into a TiC NaCl-type crystal structure (FCC) in the carbide and oxycarbide states and a smaller “x” in the TiCx coatings causes the transformation of the preferred orientation of (200) in the carbide state to (111) in the oxycarbide state. A poorly crystallized anatase phase is also observed from the coatings deposited using duty cycles of 40 and 50% and this anatase phase is detected from the oxycarbide state.

Ceramic Materials in a Ti–C–Co–Ca3(PO4)2–Ag–Mg System Obtained by MA SHS for the Deposition of Biomedical Coatings

This study aimed to obtain biocompatible ceramic materials in a Ti–C–Co–Ca3(PO4)2–Ag–Mg system by the combustion mode of mechanically activated (MA) reaction mixtures. The influence of the MA time on the reaction ability capability of the mixtures, on their structural and chemical homogeneity, on the combustion parameters and structural-phase conversions in the combustion wave, as well as on the structure and phase composition of the electrode materials has been researched. It was found that the intense treatment of powder mixtures causes plastic deformation of components, the formation of lamellar composite granules, a reduction in the sizes of coherent scattering regions, and also the formation of minor amounts of products. The influence of the activation duration of the ignition temperature and heat release during the combustion of the reaction mixtures was studied. By the method of quenching the combustion front, it was demonstrated that in a combustion wave, chemical transformations occur within the lamellar structures formed during the process of mechanoactivation. It was shown that in the combustion wave, parallel chemical reactions of Ti with C as well as Ti with Co and Ca3(PO4)2 occur, with a Ti–Co-based melt forming the reaction surface. Ceramic electrodes with different contents of Ag and Mg were synthesized by force self-propagating high-temperature synthesis (SHS)-pressing technology using the MA mixtures. The microstructure of the materials consisted of round-shaped grains of nonstoichiometric titanium carbide TiCx grains, intermetallic matrix (TiCo, TiCo2, CoTiP), inclusions of Ca and Mg oxides, and grains of the Ag-based solid solution. An increased content of Ag and Mg in the composition of the electrodes, as well as an increased MA duration, leads to an enlargement of the inclusions of the Ag-containing phase size and deterioration in the uniformity of their distribution.

Neutron diffraction study of titanium carbide TiC x prepared from hydrogen-containing titanium powder

We show that self-propagating high-temperature synthesis can serve to prepare not only stoichiometric or near-stoichiometric hydrogen-containing titanium carbide TiCx from powdery titanium containing minor hydrogen. The hydrogen percentage in the crystal lattice increases linearly as the TiCx composition progressively deviates from the 1: 1 stoichiometry. A small amount of hydrogen atoms (within 0.38 wt %) in the crystal lattice of nonstoichiometric FCC titanium carbide TiCx appreciably increases the unit cell parameter without having any affect on the concentration dependence trend. This result makes it possible to attest titanium carbide for hydrogen content from the unit cell versus concentration curve.

Phase Composition and Mechanical Properties Modification in Cr/Ti System by Short-Pulsed High Intensity Ion Beams Treatment

In the present the results of research of structure, phase composition and microhardness measurement of the surface layers of the Cr/Ti system treated by short-pulsed high intensity ion beams (HPIB) are presented. It was shown that the HPIB impact on a “coating/substrate” system can serve as an affective way to produce near-surface alloys in the metals. In particular, in the Cr/Ti system the formation of solid solution β-Ti (Cr) as well as titanium carbide TiCx was revealed. The found changes in structure and phase composition of titanium caused by the HPIB impact allow to increase its microhardness in 2 times.

Synthesis of Tic Thin Films by CVD from Toluene and Titanium Tetrachloride with Nickel as Catalyst

Titanium Carbide TiCx was deposited onto quartz substrates by the chemical vapour deposition (CVD) method. TiCx thin films were obtained from titanium tetrachloride (TiCl4) and toluene (C6H5CH3) as carbon source. Deposits were carried out in the range of substrate temperatures from 300 to 1100 C, with a source gas molar ratio (C6H5CH3/TiCl4 + C6H5CH3 ) of 0.8. There was two deposit processes; the first was to carry out without nickel as catalyst and the second with nickel as catalyst. Results showed that the effect of nickel as catalyst is very relevant to obtain TiCx. TiC0.87 thin films, 0.5 m thickness, were obtained for deposition temperatures above 900C using nickel as catalyst. In this case a cubic structure, with a lattice parameter of 4.327 A and a hardness of 2900 Vickers, was obtained at 11000C. whilst for substrate temperatures between 300 to 900°C with nickel as catalyst amorphous carbon samples were obtained. For the samples prepared without the presence of the nickel as catalyst only C amorphous thin films were obtained for all deposit temperatures.

Atomic structure, comparative stability and electronic properties of hydroxylated Ti2C and Ti3C2 nanotubes

Recently, hydroxylated and fluorinated graphene-like titanium carbide TiCx layers have been solvothermally fabricated in large amounts from so-called MAX phase Ti3AlC2. We assume, that a wide family of novel planar and tubular forms of titanium carbides may exist and design the atomic models for monolayers and nanotubes with nominal stoichiometry Ti2C, Ti3C2 and for their hydroxylated forms Ti2C(OH)2, Ti3C2(OH)2. The stability and electronic properties of these nanostructures are examined by means of density-functional theory tight-binding method depending on the composition and the type of OH arrangement. We reveal that the type of OH termination plays a minor role in the variation of nanotubes’ strain energies, but causes a difference in the relative stability of their parent planar phases. The electronic structure for all nanotubes studied has metallic-like character, while their precursors (planar layers) demonstrate either metallic-like or semiconducting behavior depending on the arrangement of the surface OH groups.

Separate determination of the amplitude of thermal vibrations and static atomic displacements in titanium carbide by neutron diffraction

The amplitude of thermal (dynamic) atomic vibrations and meansquare static atomic displacements in titanium carbide TiCx (x = 0.97, 0.88, 0.70) have been separately determined by measuring neutron diffraction patterns at two temperatures (T1 = 300 K and T2 = 80 K). The static lattice distortions in stoichiometric titanium carbide are experimentally found to be negligible. In the TiCx homogeneity range, the amplitude \(\sqrt {\overline {u_{dyn}^2 } } \) of thermal atomic vibrations significantly increases with a decrease in the carbon concentration. The Debye temperature has been determined for the first time in the TiCx homogeneity range at both room and liquid-nitrogen temperatures.

Changes in structure and properties of carbide-steel cermets resulted from a heat treatment

Abstract Cermets were produced by a technology including pressing and sintering of titanium carbide TiCx (0.7 < × < 0.98) preforms and molten tool steel infiltration. So-called “graded” cermets were produced using a controlled distribution of TiCx with different x. The resultant redistribution of alloying elements between the steel and TiCx during both the infiltration and following heat treatment was very essential. The changes of both steel and TiCx compositions produce changes in the process of austenitization, carbide dissolution and precipitation, and martensitic transformation. Both the strength of the material and the gradient of properties in graded cermets can be controlled using both kinetic factors of element redistribution and structure changes caused by the heat treatment.

Synthesis of TiC thin films by CVD from toluene and titanium tetrachloride with nickel as catalyst

Titanium Carbide TiCx was deposited onto quartz substrates by the chemical vapour deposition (CVD) method. TiCx thin films were obtained from titanium tetrachloride (TiCl4) and toluene (C6H5CH3) as carbon source. Deposits were carried out in the range of substrate temperatures from 300 to 1100 °C, with a source gas molar ratio (C6H5CH3/TiCl4 + C6H5CH3 ) of 0.8. There was two deposit processes; the first was to carry out without nickel as catalyst and the second with nickel as catalyst. Results showed that the effect of nickel as catalyst is very relevant to obtain TiCx. TiC0.87 thin films, 0.5 mum thickness, were obtained for deposition temperatures above 900°C using nickel as catalyst. In this case a cubic structure, with a lattice parameter of 4.327 Å and a hardness of 2900 Vickers, was obtained at 1100(0)C. whilst for substrate temperatures between 300 to 900°C with nickel as catalyst amorphous carbon samples were obtained. For the samples prepared without the presence of the nickel as catalyst only C amorphous thin films were obtained for all deposit temperatures.

Effect of Active Fillers on Properties of Heat-Resistant Composites

The effect of active fillers such as titanium nitrides TiN x , carbides TiC x , and carbonitrides TiC x N y (0.5 < x or x + y ≤ 1.0) on properties of polymeric composites based on thermostable binders PAIS-104, SFP-012 AK-30, and ED-20 is studied.

Magnetization of the unsegregated and segregated (100) surface of MoV binary alloys

The present thesis concerns applications of first principles electronic structure calculations in conjunction with methods of statistical mechanics for simulations of transition metal alloys both in the bulk and at surfaces.A fully relativistic generalization of the exact muffin-tin orbitals (EMTO) method has been developed. The method accurately takes into account spin-orbit coupling and allows one to calculate orbital polarization and magneto-crystalline anisotropy in magnetic systems as well as increasing the range of applicability of the EMTO method to heavy elements. A new direct-exchange Monte Carlo (DEMC) method has been proposed, which is capable to tackling effectively statistical simulations of surface segregations in disordered and ordered alloys.The applications of relativistic methods include calculations of spin and orbital magnetization in iron-cobalt disordered and partially ordered alloys, as well as computation of the core-level shifts (CLS) in transition metal alloys. It has been found, that relativistic corrections are important for CLS calculations in 5-d metal alloys. Properties of a Ni monolayer deposited on a Cu surface have been studied. The monolayer is found to be unstable in the top layer, and its magnetization depends greatly on the surface orientation. Two distinct energy levels have been found to exist Co/Cu/Ni trilayers deposited on the (100) Cu surface, which correspond to a completely paramagnetic trilayer and the case when only Ni is paramagnetic.Vacancy ordering in substoichometric titanium carbides TiCx have been simulated. Existence of three ordered phases in the range of carbon concentration x=0.5 ÷1.0 has been revealed and a theoretical phase diagram has been proposed. Surface segregations have been calculated in disordered Ni50Pt50 and Ni50Pd50 as well as in ordered NiPt alloys. Segregation reversal has been observed in the Ni50Pt50 alloy with Pt segregation at the (111) surface and Ni segregation at the (110). In the ordered NiPt alloys segregation behaviour is found to be affected greatly by small deviations from the exact stoichiometric composition in bulk. Surface magnetization in PdV and MoV bcc alloys have been studied. It has been found, that in PdV alloys surface segregations suppress magnetic order at the surface, while in MoV alloys magnetization is substantially enhanced due to the segregation.

Magnetic properties of a Co/Cu/Ni trilayer on the Cu(100) surface

The present thesis concerns applications of first principles electronic structure calculations in conjunction with methods of statistical mechanics for simulations of transition metal alloys both in the bulk and at surfaces.A fully relativistic generalization of the exact muffin-tin orbitals (EMTO) method has been developed. The method accurately takes into account spin-orbit coupling and allows one to calculate orbital polarization and magneto-crystalline anisotropy in magnetic systems as well as increasing the range of applicability of the EMTO method to heavy elements. A new direct-exchange Monte Carlo (DEMC) method has been proposed, which is capable to tackling effectively statistical simulations of surface segregations in disordered and ordered alloys.The applications of relativistic methods include calculations of spin and orbital magnetization in iron-cobalt disordered and partially ordered alloys, as well as computation of the core-level shifts (CLS) in transition metal alloys. It has been found, that relativistic corrections are important for CLS calculations in 5-d metal alloys. Properties of a Ni monolayer deposited on a Cu surface have been studied. The monolayer is found to be unstable in the top layer, and its magnetization depends greatly on the surface orientation. Two distinct energy levels have been found to exist Co/Cu/Ni trilayers deposited on the (100) Cu surface, which correspond to a completely paramagnetic trilayer and the case when only Ni is paramagnetic.Vacancy ordering in substoichometric titanium carbides TiCx have been simulated. Existence of three ordered phases in the range of carbon concentration x=0.5 ÷1.0 has been revealed and a theoretical phase diagram has been proposed. Surface segregations have been calculated in disordered Ni50Pt50 and Ni50Pd50 as well as in ordered NiPt alloys. Segregation reversal has been observed in the Ni50Pt50 alloy with Pt segregation at the (111) surface and Ni segregation at the (110). In the ordered NiPt alloys segregation behaviour is found to be affected greatly by small deviations from the exact stoichiometric composition in bulk. Surface magnetization in PdV and MoV bcc alloys have been studied. It has been found, that in PdV alloys surface segregations suppress magnetic order at the surface, while in MoV alloys magnetization is substantially enhanced due to the segregation.

Formation process of mixed silicon and titanium carbide from copyrolysis of polysilane and metallic titanium : Part II

In part I we reported a copyrolysis of polysilane with metallic tungsten [1]. Now copyrolysis of chlorine containing polysilane with metallic titanium addition in the range of 0–10 at % Ti was performed. A significant decrease of the mass loss during the polysilane pyrolysis was observed. Also the specific surface area, gas evolution and occuring phase formation changes. The titanium forms preferently carbides and temporary silicides depending on the applied pyrolysis temperature. The reactions are controlled by transport phenomena of carbon and titanium. In the end of the process silicon carbide (SiC) and titanium carbide (TiCx) are stable.

Density Functional and Complete Active Space Self-Consistent Field Investigations on the Structure and Electronic Properties of TiCx (x = 2−4) Clusters

The structures and energies of the previously not studied titanium carbide TiCx (x = 3−4) clusters have been investigated by density functional theory (DFT) using the hybrid B3LYP functional in their singlet, triplet, and quintet potential energy surfaces. The planar four-membered ring structure VIs, otherwise called the “fan” structure, with a transannular Ti−C bond is the global TiC3 minimum and 21.5 kcal/mol more stable than the transannular C−C bond structure, VIIt (“kite” structure) at the DFT level. Both cyclic structures are energetically favored over a linear quintet minimum. Electronic structure and the nature of bonding in the various electronic states of the fan and kite structures of TiC3 have been well-characterized at the complete active space self-consistent field (CAS(12,12)) level. For the TiC4 cluster, two nonplanar structures have been considered in addition to three linear, fan, and kite geometries. Nonplanar structures are characterized as higher energy minima. The harmonic frequencie...

Preparation of titanium carbide plates by chemical vapour deposition

Thick titanium carbide (TiCx) plates were prepared by chemical vapour deposition using TiCl4, CCl4 and H2 as source gases at deposition temperatures (Tdep) of 1573 to 1873 K, total gas pressures (Ptot) of 4 and 40 kPa, and source gas molar ratio (CCl4/(TiCl4 + CCl4)) (mc) of 0.13 to 0.91. The effects of deposition conditions on the microstructure, preferred orientation, deposition rate, lattice parameter and composition were investigated.