Formation Of Zirconium Carbide Research Articles

Effect of zirconia coating on Ti6Al4V at elevated substrate temperature on its wear, corrosion and hemocompatibility properties

Titanium and its alloys have been recognized as biocompatible materials since decades although these materials can at times show wear, corrosion and thrombosis leading to various health complications. Surface coating has been found to be one of the effective techniques to overcome this issue in-vitro as well as in-vivo. In this paper, thin film coating of zirconia (ZrO2) on Ti6Al4V is reported using pulsed laser deposition (PLD) technique at elevated substrate temperatures ranging from room temperature to 800 °C (TiZr800). The morphology, composition, wettability and average surface roughness of the samples were analyzed by scanning electron microscope, Raman spectrometer, water contact angle (WCA) and profilometer, respectively. Adhesion between film and substrate was qualified using Elcometer. The tribological studies were performed in ball-on-disc against ZrO2 counterpart, the electrochemical potential analysis was done in simulated body fluid to replicate body environment and the hemocompatibility test was evaluated on the basis of human whole blood adsorption and distribution of Red Blood Cells (RBCs) on the samples. The results revealed an increase in WCA and film adhesion with increased substrate temperature. At 800 °C, formation of zirconium carbide, a relatively harder material, was observed due to diffusion of substrate carbon into ZrO2 film, as confirmed by the Raman analysis. In comparison to pristine, TiZr800 sample showed a reduction in wear rate from 3.5 × 10−3 mm3/Nm to 1.1 × 10−3 mm3/Nm indicating improved resistance of the sample against abrasive wear. Further, drop in Icorr from 4.96 × 10−7 A/cm2 to 2.75 × 10−7 A/cm2 resulted in a 44 % increase in corrosion protective efficiency of the sample coated at 800 °C. Additionally, a 4.5 fold increase in RBC counts was observed on TiZr800 sample. Therefore, it is inferred that while ZrO2 coating can improve overall surface properties of Ti–6Al–4V, additional benefits can be obtained by performing PLD at higher substrate temperatures, more so when the temperature is such as to promote formation of ZrC in the coating.

Preparation of zirconium carbide nanofibers by electrospinning of pure zirconium-containing polymer

Zirconium carbide (ZrC) nanofibers were prepared from a pure zirconium-containing polymer by electrospinning without a spinning aid. The product possessed a lower carbon content, which helped in improving its oxidation resistance. The factors affecting the morphology of precursor fibers, such as the concentration of zirconium-containing polymer, spinning voltage, and spinning distance, were further investigated. The zirconium-containing polymer got partially oxidized during the electrospinning process, which led to the requirement of a high conversion temperature from zirconium oxide to ZrC. The pyrolysis of zirconium-containing polymers under vacuum resulted in the formation of ZrC due to the lower activation energy under vacuum compared with that under an argon atmosphere.

Low-Temperature Synthesis of Zirconium Carbonitrode via the Reduction of Zirconia with Magnesium in the Presence of Sodium Carbonate in a Nitrogen Atmosphere

Physicochemical transformations that occur during the low-temperature synthesis of zirconium carbonitride via the reduction of zirconia with magnesium in the presence of sodium carbonate in a nitrogen atmosphere are studied. Both reactions leading to the formation of Zr2CN and side processes occurring in the charge are studied by means of differential scanning calorimetry. Based in the results, it is concluded that zirconium carbonitride can be synthesized in the temperature range of 600–675°C. It is shown that using graphite does not lead to the formation of zirconium carbide or zirconium carbonitride in the investigated range of temperatures, while the use of urea has hardly any effect on the final product.

The study of physico-chemical transformations in the process of low-temperature synthesis of zirconium carbide

The joint reduction of zirconium oxide and sodium carbonate with the formation of zirconium carbide was studied. It was shown that with magnesium thermomes ZrO2 and Na2CO3, the reduction of ZrO2 occurs in the range of 600‒620 °C, and Na2CO3 ― in the range of 590‒610 °C. Thermodynamic calculations and the results of X-ray diffraction analysis allowed us to judge the transformations occurring in the synthesis process and the resulting reaction products. It has been established that the use of graphite as a carbon source does not lead to the formation of ZrC in the range of 700‒900 °C, unlike Na2CO3. Ill. 6. Ref. 9. Tab. 1.

The study of carbothermic reduction–sintering of ZrO2–ZrC–C composite microspheres prepared by internal gelation

ZrO2–ZrC–C (ZrCO) ceramic microspheres were fabricated by a combination of internal gelation and carbothermic reduction. The effects of temperature on carbothermic reduction of ZrO2 and the CO content in the heat treatment atmosphere on the phase composition, microstructure and properties of the microspheres were studied. The effects of different concentrations of CO in the reaction atmosphere on the formation of zirconium carbide were analyzed. The results indicate that addition of a small concentration of CO in the heat treatment atmosphere refined the microstructure, and high concentration of CO inhibited the formation of ZrC. Crack-free ZrCO ceramic microspheres with uniform microstructure, improved crush strength and density were successfully fabricated with C/Zr = 3 in the broth and heat treated at 1550 °C for 4 h in argon containing 5%CO.

Pressureless sintering of ZrC with variable stoichiometry

This paper presents the experiments on the synthesis of zirconium carbide (ZrC) using carbothermal reduction of zirconia (ZrO2). The ratio of ZrO2:C is used to adapt ZrCxOy with x < 1 or ZrC + C. The modification of ZrCxOy and the total carbon amount allows the use of pressureless sintering method in combination with sintering temperatures ≤ 2000 °C. Fully densified ZrC products are obtained. The relevant details of ZrC formation are investigated by X-ray diffraction (XRD). The sintered products are characterized by XRD, field emission scanning electron microscopy (FESEM), as well as mechanical and electrical methods. XRD and FESEM investigations show that ZrCxOy is formed during the manufacturing process. The grain size and additional zirconia or carbon are related to the ZrO2:C ratio of the starting powder mixture. Bending strength up to 300 MPa, Young’s modulus up to 400 GPa, fracture toughness up to 4.1 MPa·m1/2, and electrical resistance at room temperature around 10−4 Ω·cm are reached by the pressureless sintered ZrC.

X-ray absorption spectroscopy studies on the carbothermal reduction reaction products of 3 mol% yttria-stabilized zirconia

Extended X-ray absorption spectroscopy (EXAFS) at the ZrKedge has been used to determine changes in various bond lengths in 3 mol% yttria-stabilized zirconia (YSZ) during zirconium carbide (ZrC) formation. The principal objective of this study was to determine if ZrC formation at the YSZ/carbon interface alters the zirconia structure. A mixed-phase sample (YSZ and graphite) was carbothermally reduced to form ZrC. X-ray diffraction phase quantification by Rietveld analysis confirmed the formation of ∼50% ZrC in the analyzed sample volume. EXAFS data of ZrC and YSZ powders and a sintered YSZ pellet (∼96.7% density) were used as standards to compare with the carbothermally reduced sample.Ab initocalculations using these spectra quantified various Zr—O, Zr—C and Zr—Zr bond distances in the system. Best fit results revealed Zr—OI(tetragonal), Zr—O (monoclinic), Zr—Zr (tetragonal) and Zr—Zr (monoclinic) bond length values of 2.10, 2.25, 3.65 and 3.52 Å, respectively, in the YSZ powder, Zr—OI(tetragonal) and Zr—Zr (tetragonal) bond length values of 2.12 and 3.62 Å, respectively, in the sintered pellet, and Zr—C and Zr—Zr bond lengths of 2.32 and 3.33 Å, respectively, in the ZrC powder. Similar fitting procedures were carried out on the carbothermally reduced pellet, with measured Zr—O, Zr—Zr (of YSZ), Zr—C and Zr—Zr (of ZrC) bond lengths of 2.13, 3.62, 2.36 and 3.33 Å, respectively. These bond lengths indicate that the formation of ZrC in the YSZ matrix does not influence the local structure when compared to pure standards. Therefore, carbothermal reduction does not induce any apparent strain or thermally induced effects on the first and second coordination shells of Zr as measured by the X-ray absorption spectra of the carbothermally reduced sample. Interestingly, the results indicated that sintering of the YSZ powder into pellets did not result in any significant change in the Zr—O and Zr—Zr distances for tetragonal YSZ.

Physicomechanical properties of the surface of a zirconium alloy modified by a pulsed ion beam

The physicomechanical properties of the surface of the Zr-1% Nb zirconium alloy modified by a pulsed carbon ion beam with a pulse duration of 80 ns, an energy of 200 keV, and a current density of 120 A/cm2 are studied at four regimes having different numbers of pulses. Irradiation by a carbon ion beam results in hardening of the surface layer to a depth of 2 μm, grain refinement to 0.15–0.8 μm, zirconium carbide formation, and a decrease in the hydrogen permeability of the zirconium alloy.

Nanozirconium Carbide Powder Synthesis via Carbothermal Route

Zirconium carbide (ZrC) has extended application in many ceramic and metal matrix composites especially used for ultra high temperature conditions. The synthesis of zirconium carbide powder is costly and difficult because of its high refractoriness and chemically inert properties. In this research, the synthesis of zirconium carbide nanopowder at low temperature via carbothermal reduction route was investigated according to thermodynamic data. The starting materials were zirconium acetate and sucrose as zirconium and carbon sources, respectively. After preparation of different carbon/zirconium ratio containing precursors, the dried precursors were heat treated at 1400°C and vacuum atmosphere. Also the ZrC formation was followed by thermal analysis of the produced precursors. The phase evolutions and microstructural studies were carried out using X-ray diffraction and scanning electron microscopy. The results showed that it is possible to synthesis zirconium carbide nanopowder with round shape and crystallite sizes smaller than 20 nm at low temperatures. Also according to thermodynamic calculations, it was concluded that by applying vacuum condition, the zirconium carbide formation can occur at less than 1000°C which is very effective on the size reducing of produced ZrC nanopowders.

Synthesis of Nanosized Zirconium Carbide (ZrC) by a Polymeric Precursor Route

Based on the basic principle of carbothermal reduction reactions in the ZrO2-C system, nanosized ZrC powders were synthesized by the preceramic method using Polyzirconoxane (PZO) and salicyl alcohol (SA) as sources of zirconia and carbon respectively. The obtained polymeric precursor exhibited excellent solubility and rheology for the processing of ceramic matrix composites. Thermal dynamic change process, phase composition, crystallite size and morphology of the synthesized powders were characterized by Thermogravimetric analysis (TGA)、 Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). When heat-treated at 900 °C under flowing argon, precursors transformed into intimately mixed amorphous carbon and nanosized tetragonal ZrO2. Further heat treatments (1300 °C) led to the formation of zirconium carbide with a yield of 70.6 %. The obtained ZrC particles exhibit cubic morphology with size ranged in 50-100 nm. This study displays the preparation of nanosized ZrC materials from the preceramic polymers.

Microstructural Control of Zirconium Carbide Coating Prepared by Chemical Vapor Deposition

To obtain Zirconium Carbide (ZrC) coating with columnar structure, which is optimal for resistance to heat shocks, chemical vapor deposition was used. Three series of multi-steps were carried to decrease the degree of supersaturation of active [C]: reducing concentration of C3H6, substituting C3H6 by lower-carbon-content hydrocarbons and the last increasing the flow rate of H2. Scanning electron microscopy show the morphology evolution of ZrC coatings from two-dimensional platelets, to fine grains, to polycrystals with different shapes and to columnar with domed tops. When the flow rate of H2 reach maximum (0.3m3/h), the columnar grains have a width of 1-2μm and a preferred orientation of (220). It is regarded as the change of limiting step of active [C] involving the reaction of formation of ZrC is the key factor for evolution.

Decreased molybdenum emission in a carbon arc caused by zirconium carbide formation on the sample electrode

The presence of about 10% zirconium (as oxide) in alumina samples obtained by the ignition of aluminum 8-quinolinolate (precipitated as a trace-element collector) greatly dereased the intensity of molybdenum emission when the alumina was analysed by means of a cathode-layer carbon arc. Retention of the molybdenum on the sample electrode was confirmed with radioactive molybdenum-99. A prominent crystalline residue on the cathode, identified as ZrC by x-ray powder diffraction, was probably responsible for the decreased emission. Thus, zirconium crucibles cannot be used for the sodium carbonate fusion of samples in a spectrochemical procedure for determining traces of molybdenum in soils and plants.