Non-isothermal Oxidation Research Articles

Non-isothermal oxidation kinetics of WC–6Co cemented carbides in air

The oxidation of WC–Co cemented carbides cutting tools is a key factor in determining tools' life during dry and high speed cutting. Thus, its investigation is of great importance to the design and development of cutting tool materials. In this paper, the non-isothermal oxidation of WC–6Co cemented carbides was carried out on simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) thermal analyzer (Netzsch STA 449C) between room temperature and 1273K at different heating rates (β=5, 10, 15 and 20K/min) in a dry air atmosphere under the atmospheric pressure. The results show that, with the heating rate increasing from 5K/min to 20K/min, the extrapolated initial temperature (Tei), the peak temperature (Tp), and the extrapolated final temperature (Tef) of the oxidation of WC–6Co cemented carbides increased from 957K to 997K, from 1014K to 1079K, and from 1030K to 1094K, respectively. The apparent activation energy (Ea) of the oxidation of WC–6Co cemented carbides was 206.85kJ/mol calculated by Flynn–Wall–Ozawa (FWO) method, and preexponential factor (A) was 5.02×109min−1. The oxidation experiment data of WC-6Co was in good agreement with R2 kinetic model. The reaction rate can be described by dα/dt=1010exp(−24,879/T)(1−α)1/2.

Non-isothermal oxidation of aluminum nanopowder coated by hydrocarbons and fluorohydrocarbons

Aluminum nanopowder (nAl) obtained by electrical explosion of wires and passivated/coated with hydrocarbons and fluorohydrocarbons is comprehensively characterized. Coatings of different natures (octadecanoic and hexadecanoic acid, (1,1,11) trihydroperfluoro-undecan-1-ol, Fluorel™+ester from esterification of (1,1,11) trihydroperfluoro-undecan-1-ol with furan-2,5-dione) were applied on the particle surface. The powders were studied by TEM, SEM, DSC-TGA, and BET specific surface area. The active aluminum content was determined by volumetric analyses. Coated nAl particles were compared to non-coated powder by the corresponding reactivity parameters obtained from DSC-TGA. It was found that while fatty acids have a weak effect on the non-isothermal oxidation behavior, fluoroelastomers shift the oxidation onset of nAl to higher temperatures by ∼20°C for the first oxidation stage and by ∼100°C for the second oxidation stage.

Non-isothermal oxidation and ignition prediction of Ti-Cr alloys

The non-isothermal oxidation behavior and oxide scale microstructure of Ti-Cr alloy (0≤w(Cr)≤25%) were studied from room temperature to 1723 K by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influencing mechanism of chromium on the oxidation resistance of Ti-Cr alloys was discussed. The results show that the oxidation resistance of the alloys decreases with Cr below a critical chromium content wC and increases above wC; above 1000 K, the oxidation kinetics obeys parabolic rule and titanium dominates the oxidation process; after oxidation, the oxygen-diffusing layer is present in the alloy matrix, the oxide scale is mainly composed of rutile whose internal layer is rich in chromium, and chromium oxides separated out from TiO2 near the alloy-oxide interface improve the oxidation resistance. Ignition of metals and alloys is a fast non-isothermal oxidation process and the oxidation mechanism of Ti-Cr alloys during ignition is predicted.

High-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air

The high-temperature oxidation of ZrB2–SiC and ZrB2–SiC–ZrSi2 ceramics up to 1700°C in air has shown their high corrosion resistance. A five-stage nonisothermal oxidation mechanism is established for the samples when heated at a rate of 20°C/min: 1) oxygen adsorption–desorption; 2) formation of ZrO2 and B2O3 oxides; 3) formation of α-SiO2 cristobalite and ZrSiO4 zircon; 4) formation of amorphous SiO2; and 5) formation of upper protective borosilicate film with ZrSiO4 inclusions at less than 40 wt.% SiC. It is shown that small ZrSi2 admixtures (<6–8 wt.%) substantially slow down the oxidation of the ceramics in initial heating stages due to diffusion-hindered formation of ZrO2 and B2O3. The 67.3 wt.% ZrB2–26 wt.% SiC–6.7 wt.% ZrSi2 ceramics are characterized by the highest corrosion resistance since their upper scale layer represents borosilicate glass stabilized with ZrO2 (tetragonal) inclusions.

Calix[4]pyrogallolarenes as novel high temperature inhibitors of oxidative degradation of polymers

Oxidative stability of high density polyethylene containing C-alkylcalix[4]pyrogallolarenes was studied by Differential Scanning Calorimetry. The kinetic parameters of non-isothermal oxidation indicate that pyrogallolarenes are effective antioxidants at temperatures above 150 °C.

High temperature oxidation behavior of electroconductive TiN/O′-Sialon ceramics prepared from high titania slag-based mixture

The oxidation behavior of electroconductive TiN/O′-Sialon ceramics prepared using high titania slag as main starting material was studied at 1 200–1 300 °C in air. The isothermal and non-isothermal oxidation processes were investigated by DTA-TG. Phase compositions and morphologies of the oxidized products were analyzed by XRD, SEM and EDS. The results indicate that the oxidation of TiN and O′-Sialon occurs at about 500 °C and 1 050 °C, respectively. After oxidation at 1 200–1 300 °C, a protective scale that consists of Fe 2MgTi 3O 10, SiO 2 and TiO 2 is formed on the surface of the materials, which effectively prevents the oxidation process. The formation of a protective scale is relative to TiN content and apparent porosity of the samples, the amount of SiO 2 and amorphous phase in the oxidation product. At the initial oxidation stage, the oxidation kinetics of the materials follows perfectly the linear law with the apparent activation energy of 1.574×10 5 J/mol, and at the late-mid stage, the oxidation of the samples obeys the parabolic law with the apparent activation energy of 2.693×10 5 J/mol. With the increase of TiN content, mass gain of the materials increases significantly.

Examination of the oxidation resistance of Cr–Mo–V tool steel by thermal analysis

In the present study, the oxidation behavior of Cr–Mo–V tool steel was examined at different temperatures in air. The examination was conducted by means of thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction (XRD). After non-isothermal oxidation from ambient temperature to 1000 °C, it was revealed that the specimen begins to oxidize over 700 °C, while over 800 °C the oxidation rate increases significantly. Finally over 900 °C, this rate has a considerable value, and the specimen's oxidation resistance is inadequate. From these results, four different oxidation temperatures (805, 835, 865, and 895 °C) were selected for the isothermal test, as referred above, which correspond to different oxidation rates, to determine the oxidation activation energy of the Cr–Mo–V specimens. Energy dispersive X-ray spectroscopy (EDX) and XRD phase identification of the as-formed scales showed that in every case, it contains two distinguishable regions. The inner layer is a mixture of chrome and iron oxides and the outer layer contains iron oxides and is also characterized by high porosity. This phenomenon was explained by the different diffusion coefficients of every element in the steel matrix.

On the oxidation of electrolytic carbon nanomaterials

The non-isothermal oxidation behaviour of molten salt electrolytically produced carbon material in air has been studied using various thermal analysis techniques, complemented by electron microscopy and X-ray diffraction analysis. It was observed that the oxidation of the carbon nanostructures in the electrolytic carbon material proceeds at considerably lower temperatures than those typically needed for the oxidation of carbon nanomaterials. This has been attributed to the effect of lithium carbonate crystals that were found to be located on the walls of the carbon nanostructures. The results are of importance to understanding the properties of, and identifying suitable applications for, this new material.

Non-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes up to 1273 K in ambient

Non-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes (CNTs) have been studied using thermogravimetry up to 1273 K in ambient using multiple heating rates. One single heating rate based model-fitting technique and four multiple heating rates based model-free isoconversional methods were used for this purpose. Depending on nanotube structure and impurity content, average activation energy (Ea), pre-exponential factor (A), reaction order (n), and degradation mechanism changed considerably. For multi-walled CNTs, Ea and A evaluated using model-fitting technique were ranged from 142.31 to 178.19 kJ mol−1, respectively, and from 1.71 × 105 to 5.81 × 107 s−1, respectively, whereas, Ea for single-walled CNTs ranged from 83.84 to 148.68 kJ mol−1 and A from 2.55 × 102 to 1.18 × 107 s−1. Although, irrespective of CNT type, the model-fitting method resulted in a single kinetic triplet i.e., Ea, A, and reaction mechanism, model-free isoconversional methods suggested that thermal oxidation of these nanotubes could be either a simple single-step mechanism with almost constant activation energy throughout the reaction span or a complex process involving multiple mechanisms that offered varying Ea with extent of conversion. Criado method was employed to predict degradation mechanism(s) of these CNTs.

Kinetics of non-isothermal oxidation of anhydrous milk fat rich in conjugated linoleic acid using differential scanning calorimetry

Abstract Anhydrous milk fat (AMF) with low, medium, and high content of conjugated linoleic acid (L-, M-, and H-CLA) was oxidized using differential scanning calorimetry (DSC) at five different heating rates (3, 6, 9, 12, and 15 °C min−1) in a temperature range of 100–350 °C. For the first time, kinetic oxidation parameters of AMF rich in CLA are reported. DSC spectra were analyzed to locate the start temperature (Ts), onset temperature (Ton), and maximum heat flow temperature (Tp). These reference points were further used to calculate the effective activation energy (E) and pre-exponential factor (z) using the Ozawa-Flynn-Wall method. The Ts shifts to lower values as the CLA content increases, while the Ton and Tp were less affected by the CLA content. The calculated kinetic parameters not only depend on the ratio between unsaturated to saturated fatty acids but also on the selected reference points. For the L-CLA sample, the E values calculated from Ts, Ton, and Tp were 146.51, 114.11, and 121.31 kJ mol...

Preparation of composites in the ZrB2-Si system and investigation of their properties

The refractory glass-ceramic materials based on the ZrB2-Si composite have been prepared by nonisothermal oxidation in air, and their structure, phase composition, and properties (porosity, thermal expansion, and refractoriness) have been investigated. The composite materials have a complex heterogeneous structure: crystalline particles of the initial phases (ZrB2, Si) and the phases formed as a result of oxidation in air (ZrO2, ZrSiO4, and α-cristobalite) are encapsulated in the vitreous matrix.

Characterization and oxidation properties of biomorphic porous carbon with SiC gradient coating prepared by PIP method

A biomorphic porous carbon coated with SiC (SiC/BPC) was prepared by controlled carbonizing native pine under Ar atmosphere and then processed with precursor infiltration-pyrolysis (PIP) of organosilane. Microstructure and component of SiC/BPC were analyzed by FT-IR, XRD, SEM and EDS (attached with line scanning program). The non-isothermal oxidation properties and mechanism of SiC/BPC were studied by TGA. The kinetic parameters were calculated through model-free kinetics methods. Experimental results showed that SiC/BPC had a topologically uniform interconnected porous network microstructure; the obtained gradient SiC coating on BPC surface was amorphous and combined well with the carbon surface, which can improve the oxidation resistance of BPC clearly. The non-isothermal oxidation reaction of SiC/BPC exhibited a partial self-accelerating characteristic. The oxidation process was complicated, firstly it was controlled by gas diffusion in coating, then controlled by chemical reaction, and at last it was controlled by gas diffusion and chemical reaction together, the corresponding effective activation energy was calculated also.

Research on Oxidation Reaction of AlN Powder

The process of non-isothermal oxidation of AlN powder (d50=15μm, 5μm and 0.5μm) were studied by TG-DTA and XRD in atmosphere of 80%N2 and 20%O2 mixture at flowrate of 55ml/min and heating rate of 10 /min. The experimental results reveal that the AlN powder obviously began to be oxidated and its weight increased at 900-1000°С . The process of dynamics of oxidation reaction between AlN and O2 was controlled alternately by reaction and diffusion. Non-isothermal oxidation dynamic parameters (activation energy E, reaction orders n and pre-exponential factor A) of d50=5μm AlN powder were obtained by the experimental data. E equals about 417.4kJ/mol, n about 2.9 and A about 3.47×1012. Due to smaller activation energy E and larger pre-exponential factor A in dynamic parameters of AlN powder non-isothermal oxidation, powdery AlN is easily oxidated at high temperature and in air and has a larger oxidation reaction rate. If AlN material with high thermal conductivity characteristics is introduced to prepare composite with high thermal shock resistance, the AlN powder must be treated for oxidation resistance.

Preparation and oxidation properties of biomorphic porous carbon derived from native bamboo

A biomorphic porous carbon (BPC) was prepared by carbonized native bamboo under an Ar atmosphere through a controlled heating process. Microstructural properties of BPC were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The pyrolytic behavior of bamboo and non-isothermal oxidation properties of BPC were studied by thermogravimetric analysis (TGA). Experimental results show that BPC has a porous interconnected honeycomb microstructure, with a multi-peak pore size distribution, and is a typical non-graphitizable carbon. With an increasing carbonization temperature, the (002) peak of the XRD spectrum becomes stronger, the interplanar spacing decreases, the structure of BPC slowly evolved towards that of ideal graphite, and also the density increases, and bulk porosity decreases. The non-isothermal oxidation properties of BPC exhibit a self-catalytic characteristic, which is discussed through a schematic model.

Kinetics of Thermal Oxidation of Titanium Nitride Powder at Different Oxidizing Atmospheres

The oxidation behavior of titanium nitride powder at different oxidizing atmospheres was investigated using thermogravimetric analysis, X‐ray diffraction, and scanning electron microscopy. Oxidation experiments have been carried out both in isothermal as well as nonisothermal modes. The nonisothermal oxidation result showed that the oxidation rate was affected by temperature, heating rate, and oxygen partial pressure. The isothermal oxidation result showed that the diffusion of oxygen through the oxide product layer to the oxide/titanium nitride interface was the rate‐controlling step and the oxidation product became obviously porous at elevated temperature. In view of the oxidation kinetics, Chou model, which quantitatively expresses the oxidation weight increment as a function of time, heating rate, temperature, and oxygen partial pressure, has been employed and gotten a good agreement.

Effect of SiC Particle Size on Anti-Oxidation Behavior of C/B&lt;sub&gt;4&lt;/sub&gt;C/SiC Composite

B4C and SiC particle-dispersed carbon composite were fabricated from calcined pitch coke, B4C and SiC with various particle size by grinding and then pressureless sintering. During non-isothermal oxidation test up to 1400°C in air atmosphere, oxidation behavior of the C/B4C/SiC composite was clarified by means of calculation of kinetic parameters using experimental data of mass change, gas formation of CO2, and oxygen gas consumption. Amount of the matrix carbon oxidized above 800°C in the composite with SiC particle of 0.4 µm and 0.9 µm in size was less than that in the composite with SiC particle of 50 nm and 1.8 µm in size. The oxidation of the matrix carbon was shown to depend upon the formation of B2O3 glass below 800°C oxidation, and that of SiO2 glass above 800°C. The composite containing SiC with 20 nm in size was stable against oxidation above 1400°C except the temperature ranging from 900°C to 1100°C.

Kinetics of non-isothermal oxidation of AlN powder

The non-isothermal oxidation of AlN powder has been studied, based on which a new formula has been suggested to express the reacted fraction of the oxidation as a function of oxidation time, oxygen partial pressure, the particle size, as well as the temperature increasing rate explicitly. The application of this new model to the oxidation of AlN powder shows that this new model can give a more accurate and reasonable result. The diffusion activation energy of AlN powder is extracted to be 356.3 kJ/mol.

Nonisothermal and Cyclic Oxidation Behavior of Mo-Si-B and Mo-Si-B-Al Alloys

A study on nonisothermal and cyclic oxidation behavior of the reaction-hot-pressed 76Mo-14Si-10B, 77Mo-12Si-8B-3Al, and 73.4Mo-11.2Si-8.1B-7.3Al alloys has been carried out in dry air, and the results have been compared with those of isothermal tests. Nonisothermal studies by thermogravimetric (TG) analysis up to 1300 °C have shown a transient mass gain between 700 °C and 860 °C, followed by a sharp mass loss with increased temperature, with the amount of mass change dependent on the heating rate (5 °C/min to 35 °C/min). The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies of oxide scales formed on the alloys held at 790 °C and 820 °C for 10 or 20 minutes suggest that the oxidation of α-Mo and Mo3Si precedes that of Mo5SiB2. Thermal cyclic tests involving exposure at 1150 °C for 1 hour, followed by either air cooling to room temperature (RT) or furnace cooling to 700 °C, 800 °C, or 900 °C, and the subsequent examination of oxidation products, have confirmed that the formation of B2O3-SiO2 scale provides complete and partial protection for the Mo-Si-B and Mo-Si-B-Al alloys, respectively. The results of this study show that oxidation resistance is deteriorated upon Al addition. Residual stress measured by XRD is found to be largely compressive in Mo and in mullite phases of oxide scales. Thermal shock and the mismatch in the coefficients of thermal expansion (CTEs) between the constituent phases of the oxide scale appear to be the main causes of damage.

Microstructure characterisation and non-isothermal oxidation kinetics study of biomorphic carbon template derived from native aspen

A biomorphic carbon template (BCT), which retained its pore morphology, was prepared by carbonising aspen under Ar atmosphere. The effect of carbonisation temperature on chemical composition, the microstructure and the non-isothermal oxidation kinetics and mechanism of BCT were characterised and studied. Experimental results show that the template has a honeycomb interconnected porous network and double peaked porous diameter distribution; it is a typical non-graphitisable carbon. When carbonisation temperature increases from 900 to 1300°C, the C=C, C–O–C and C–H bonds existing in BCT transform into C–C bonds slowly and the transformation finishes at 1300°C. The oxidation reaction of carbon template carbonised at 1300°C begins at 421·5°C, and reaction rate reaches a maximum when temperature is 465·4°C. The oxidation mechanism is random nucleation.

Preparation, Characterization and Oxidation Mechanism Study of Biomorphic Porous Carbon Coated with SiC Gradient Coating

A biomorphic porous carbon coated with gradient SiC coating (SiC/BPC) was prepared by controlled carbonizing native pine under Ar atmosphere and then processed with precursor infiltration-pyrolysis (PIP) of organosilan. Microstructure and component of SiC/BPC were performed by SEM, EDS (attached with line scanning program) and XRD. The non-isothermal oxidation properties and mechanism of SiC/BPC were studied by TGA. The kinetic parameters were calculated through model-functions methods. Experimental results showed that SiC/BPC has a topologically uniform interconnected porous network microstructure, the SiC coating was amorphous and combines well with the carbon surface, which improved the oxidation resistance of BPC material about 150K. The non-isothermal oxidation reaction of SiC/BPC exhibited the characteristic of self-catalytic, the oxidation mechanism of SiC/BPC was 2-D diffusion, decelerator -t curve, the kinetic parameters are lgA/min-1= 15.483；E/kJ•mol-1 = 287.49.