Oxidation Onset Temperature Research Articles

Motor oil degradation during urban cycle road tests

Several civilian vehicles in China operate in urban traffic conditions and have their motor oil changed every 5,000 km. This study investigates the variations in oil properties after servicing at 5,000 km, based on systematic road tests (including a repeated test, a parallel test, and a new vehicle test). The physicochemical properties, changes in components, oxidation stability, detergent-dispersant performance, and tribological properties of motor oils were analyzed. The results showed that the total acid number (TAN) of oils increased with the operation mileage, by up to 1.41 mgKOH/g. The total base number (TBN) decreased after the road tests were completed, and the decrease was less than 44.6%. The kinematic viscosity (KV) of most oils decreased initially and then stabilized in the middle stage, before starting to increase later in the experiment. The change in KV at 100 °C was less than 15.96%. The oxidation onset temperature (OOT) of the oils diminished gradually with the operation mileage. All OOT values of the used oils were higher than 210 °C. A spot test indicated that the used oils retained their detergent-dispersant performance to an appropriate extent. The four-ball wear scar diameters and friction coefficient of the used oils did not increase significantly after the road tests were completed. This study can serve as a reference for end-users when changing motor oils.

Natural compounds from Punica granatum peel as multiple stabilizers for polyethylene

AbstractPunica granatum peel extractive (PPE), a novel stabilizer of polyethylene, is investigated in this study. Oxidation onset temperature (OOT), carbonyl index (CI), melt flow rate (MFR), tensile strength, and elongation at break are used to characterize the effects of PPE, which are also compared with commercial antioxidant (Irganox 1010) with the presence of tetrakis (2,4‐di‐tert‐butylphenol)[1,1‐biphenyl]‐4,4′‐diylbisphosphite (PEPQ). Long‐term and short‐term aging results show that samples modified by PPE or Irganox 1010 (PE‐PPE0.12%‐P and PE‐10100.12%‐P samples) have comparable CI value and stability of OOT. However, compared with PE‐PPE0.12%‐P sample, much higher CI and larger change of MFR is detected for PE‐10100.12%‐P after UV irradiation and five extrusions. It suggests that PPE is better protector for PE against UV light and mechanical shear force. All results indicate that the effect of PPE in protecting PE is comparable or much better than Irganox 1010 and it can be used as multiple stabilizers for PE. Moreover, the stabilities of PE modified with PPE alone (PE‐PPE2%) is also investigated. Results show that PE‐PPE2% sample has good thermo‐oxidative, UV and processing stabilities. All results reveal that PPE is a good candidate of PE stabilizer and it could avoid the usage of PEPQ in protecting PE.

Evaluation of the Durability of PE-HD Geosynthetic Barriers Using High-Pressure Autoclave Tests

To evaluate the resistance of a 2 mm thick polymeric geosynthetic barrier (GBR-P) made of high-density polyethylene (PE-HD), oxidation tests at 80 °C using high-pressure autoclaves at three different oxygen pressures were carried out. After different times, 18 different evaluations were performed on the aged test specimens of the GBR-P. The following characteristics were considered: thermoanalytical methods like oxidation induction time (OIT), crystallinity and oxidation onset temperature (OOT), viscosity measurements like melt mass-flow rate (MFR) and viscosity, mechanical properties of the short term tensile test as well as stress crack resistance methods with the notched constant tensile load (NCTL) test and the strain hardening test (SHT). The failure times extrapolated to atmospheric conditions at the test temperature of 80 °C were in the range of 450–550 days for the stress crack tests. For the analytical methods, the failure times were 620–780 days and for the tests in the short-time tensile test, the failure times were between 700 and 900 days, depending on the property. To evaluate the OIT measurements, investigations were carried out on the influence of the sampling, preparation and treatment of the OIT measurement samples. Furthermore, the influence of oxidation on the thickness of the test samples was investigated. For this purpose, test specimens with thicknesses of 1 mm, 2 mm, 4 mm and 10 mm were produced and tested with the same material. The consumption of antioxidants on the surface of the test specimens was twice as high as inside the specimens. It was shown that a wide range of parameters is suitable for representing the ageing states of a PE-HD GBR-P. With very few exceptions, it was possible to determine the time transitions up to which the properties hardly changed and from which a steep rise or steep fall occurred. The most reliable and practicable test methods for ageing tests in the study were: elongation at break in the tensile test, the strain hardening modulus, OIT and OOT.

The thermal oxidation evolution and relationship of unsaturated fatty acids and characteristic functional groups in blended oils with raspberry seed oil during deep-frying process by low field nuclear magnetic resonance and 1H nuclear magnetic resonance

To demonstrate the oxidation evolution and thermal stability of blended oils during the deep-frying process, the relationship between unsaturated fatty acids, the distribution and migration of H protons and functional groups was investigated. The results showed that blended oils had high onset and peak oxidation temperature, and the peroxide value, p-anisidine value and polar compounds were low due to high tocopherols, which implied that blended oils had better thermal stability. The levels of linoleic and linolenic acids decreased significantly, as well as the ratio of C18:2/C16:0 except sunflower seed oil blended with raspberry seed oil. Moreover, there was also a significant decrease in relaxation times T22 and T23. The ratios of olefinic H, bisallylic CH2, allylic CH2 relative to glyceride CH2 slowly decreased along with the increase of Rab and Rao, except corn oil blended with raspberry seed oil. For corn oil blended with raspberry seed oil, the ratio of olefinic H, bisallylic CH2, allylic CH2 increased and then slowly decreased. Rao, Rab and Raa reached the highest value on the forth day, then decreased, and Rab was higher than Rao and Raa. In addition, T22,T23 and functional groups significantly correlated with unsaturated fatty acids.

Intensification of bituminous coal and lignite oxidation by copper-based activating additives

The oxidation of lignite and bituminous coal samples modified by 5 wt% (in terms of dry salt) addition of copper salts Cu(NO3)2, CuSO4, and Cu(CH3COO)2 was studied. The samples’ reactivity was studied by thermogravimetry within a temperature range of 45–600 °C at a heating rate of 2.5 °C/min in an oxidizing environment. The introduction of activating additives has resulted in a significant decrease in the temperature of intense oxidation onset (ΔTi = 20/94 °C), in a reduction in the sample residence time in the volatile matter release region (Δte = 2/22 min) and the total duration of the coal combustible mass oxidation (Δtf = 8/14 min). The Friedman method was used to calculate the activation energy values for the oxidation process of the modified samples. The maximum change in activation energy values was observed for the bituminous coal sample. The possible mechanism behind the action of the copper-salt additives, which activate the oxidation of lignite and bituminous coal, is discussed. According to the data of mass spectrometric analysis, the concentration of NOx in the reaction products decreases as the temperature of the activated oxidation process is shifted towards the low-temperature region.

UO2 + 5 ​vol% ZrB2 nano composite nuclear fuels with full boron retention and enhanced oxidation resistance

The boron isotope (10B) can be used as a neutron absorber in UO2 to control the reactivity of nuclear fuel pellets, however, the boron source can react with oxygen source in UO2 to form B2O3 that vaporize readily at temperatures above 1200 °C. Unfortunately, the sintering of UO2 fuel requires hours holding at high temperature (>1700 °C), resulting in an inevitable B loss during sintering and unpredictable B concentration in final product. It is challenging to incorporate boron through a conventional sintering method. In this work, we demonstrated that spark plasma sintering (SPS), a field assisted sintering technology, can effectively densify UO2 ​+ ​5 ​vol% ZrB2 composite fuel pellets by rapid consolidation at 1600 °C for a short duration of 5 min under an applied pressure of 40 MPa. Thermogravimetric analysis (TGA) measurements confirm that ZrB2 is fully retained inside the composite fuel pellets. Inside the composite fuel pellets, nano sized ZrB2 particles are uniformly distributed along the grain boundaries of the UO2 matrix. The ZrB2 particle transforms to a glassy B2O3 phase covering the sample surface and grain boundaries of UO2 matrix after a simple post-sintering annealing at 1000 °C in flowing Argon gas for 4 h. The formed glassy B2O3 slows down the diffusion of oxygen ions and postpones the onset temperature for oxidation of UO2 from 400 °C to 550 °C. This study demonstrates the capability of SPS, an advanced fuel manufacturing technique, to achieve a full retention of ZrB2 in UO2 oxide fuel and increase oxidation resistance through a simple post-sintering annealing. The reported work holds great engineering potential for development of advanced oxide fuel for nuclear application.

Thermal characteristics and hazard of 1,3-Butadiene (BD) polymerization and oxidation

Accelerated calorimeter (ARC) is widely used to evaluate the hazard of solid or liquid materials, however, there are few literatures on the investigation of gas hazard. In this paper, thermal polymerization and oxidation characteristics of BD were investigated using an ARC. The onset temperature of BD polymerization is 408.5 K under nitrogen atmosphere. Under oxygen atmosphere, the oxidation characteristics of BD with oxygen are: first, pressure is reduced when oxygen reacts with BD, and peroxide is formed; second, an exothermic oxidation reaction has occurred, and the onset temperature of oxidation is 343.2 K, and the activation energy (Ea) of BD oxidation is 112.6 kJ/mol. The products of polymerization and oxidation were analyzed by gas chromatography - mass spectrometry (GC–MS). The brief mechanism of oxidation reaction is described. These results are helpful to understand the characteristics of chemical engineering, and to research and develop the safety technology of BD.

Reduced graphene oxide enhanced emulsification for one-pot synthesis of high-density jet fuel

Synthesis of jet fuel with high density, good low-temperature property and high thermal stability is significant to aerospace industry. Here, a great-performance jet fuel blending including bi- and tri-cyclic hydrocarbons (C10 ~ C16) is synthesized with high yield through reduced graphene oxide (rGO) assisted H2SO4 catalytic one-pot reaction of cyclopentanol and methylcyclopentane. The reaction occurs through a consecutive way of dehydration, alkylation, rearrangement and hydrogen transfer. Carbon-based materials especially rGO are used as additive to increase the carbon yield by promoting the emulsification of reactants in sulfuric acid. Promoted emulsification improves the alkylation of cyclopentanol with methylcyclopentane and makes the hydrogen transfer easier, which highly increases the conversion of methylcyclopentane (54.9%), the carbon yield (83.2%) and the selectivity (97.3%) of products. Finally, a jet-fuel-ranged blending with overall yield of 71.8% is obtained by distillation, which shows high density of 0.90 g/mL, low freezing point of ＜-72 °C and a high oxidation onset temperature of 195.0 °C. This work provides a simple, efficient and low-cost way to synthesize high performance jet fuel from biomass.

(Ni,Cu)/hexagonal BN nanohybrids – New efficient catalysts for methanol steam reforming and carbon monoxide oxidation

This work is aimed at the development of bimetallic (Ni0.2Cu0.8) catalysts with hexagonal boron nitride (h-BN) nanosheet (BNNS) supports and elucidating their catalytic activity in the methanol steam reforming and CO oxidation reactions. The hybrid Ni0.2Cu0.8/BN catalysts consist of curved h-BN nanosheets, up to 10–20 nm in lateral size, decorated with metallic nanoparticles, 3.0–8.2 nm in dimensions. The methanol conversion starts at ~20 °C and is nearly completed at 320 °C. The (Ni0.2Cu0.8)/BN nanohybrids exhibit high catalytic stability and high selectivity for CO2 over the whole temperature range. No carbon monoxide is detected during full methanol conversion. The possible mechanism of CO utilization during methanol reforming is proposed using ab initio calculations. The onset temperature of catalytic CO oxidation is 100 °C and full conversion is completed at 200 °C. These results indicate high catalytic efficiency of (Ni0.2Cu0.8)/BN nanohybrids in methanol steam reforming and CO oxidation reactions.

Sulfurized Methyl Esters of Soya Fatty Acids: Synthesis and Characterization

Soy-based fatty acid methyl ester disulfide (FAME-S2) was synthesized in good yield by oxidation of polymercaptanized soybean oil fatty acid methyl ester (PM-FAME). The chemical structure of FAME-S2 is of interest because of its potential as a biobased multi-functional additive in lubricant formulations. Neat FAME-S2 and their blends (1–10% w/w) in polyalphaolefin (PAO-6) and high oleic sunflower oil (HOSuO) were characterized for its chemical, physical and tribological properties. Blends of FAME-S2 in HOSuO relative to similar blends of PM-FAME displayed higher oxidation onset temperature (> 15 °C) that remained constant with increasing concentration. Evaluation of FAME-S2 as an extreme pressure (EP) additive on a 4-ball tribometer showed increasing weld point (WP) with increasing concentration to a maximum of 220 and 180 kgf in HOSuO and PAO-6, respectively, at 10% w/w concentration. The results indicate that FAME-S2 has both anti-oxidant and EP properties and can be applied as a multi-functional biobased additive in lubricant formulation. This work demonstrates an encouraging progress towards the development of effective biobased lubricant additives.

U3Si2 and UO2 composites densified by spark plasma sintering for accident-tolerant fuels

This work reports the synthesis and characterization of the U3Si2 and UO2 composites sintered by spark plasma sintering (SPS) with controlled microstructures for accident-tolerant fuel application. The U3Si2 and UO2 composites with different silicide and oxide ratios were synthesized by SPS at temperatures from 1000 to 1300 °C for 5 minutes. The microstructure and phase composition of the SPS densified composite fuels were characterized with scanning electron microscopy, X-ray diffraction (XRD), and energy dispersed spectroscopy (EDS). A systematic study of the thermal and mechanical properties was conducted using microhardness testing and laser flash apparatus, along with oxidation resistance measurements using thermogravimetric analysis (TGA). The results show that the synthesis of composite fuels can be achieved with a 90% theoretical density (TD) at 1000 °C and over 95% TD when sintered at 1300 °C. XRD and EDS results confirmed that the dominant phases in the composites are U3Si2 and UO2. Improved physical density generally leads to improved hardness, fracture toughness, thermal diffusivity, and onset temperature during the oxidation process. U3Si2 was found to play a dominant role in determining the mechanical and oxidation properties of the composite fuels, whereas UO2 had a more important impact on controlling the thermal diffusivity of the composites. The composite with 50 wt% UO2 sintered at 1300 °C displayed the onset oxidation temperature of 500 °C by dynamic oxidation testing using TGA at a ramp degree of 10 °C/min. The composite also achieved a high fracture toughness of ∼3.5 MPa m½. These results highlight the potential of composite fuel forms densified by SPS with simultaneously enhanced fissile element density, fracture toughness, thermal transport properties, and oxidation resistance.

Low-temperature thermocatalytic particulate carbon decomposition via urea solution-combustion derived CeO2 nanostructures

A facile, one-pot, urea solution combustion route was utilized to synthesize highly catalytic CeO2 nanostructures. CeO2 prepared under varying thermal conditions was characterized by electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, infrared and Raman techniques. As the synthesis temperature is raised from 400 to 1000 °C, the crystallite size and d-spacing of nanoparticles are observed to reduce while cell parameters remain in the same range. Particle size exhibits an accession from ∼20 to ∼50 nm along the process. Initial CeO2 nanoparticles are detected as a composite structure of CeO2 and graphitic carbon nitride (g-C3N4) produced by the pyrolysis of urea. Concerning the solid carbon particulate oxidation capacity, an outstanding performance is exhibited by CeO2 synthesized at 800 °C where the oxidation onset temperature is reduced by 27% compared with the others. The superior performance is attributed to the carbon nitride-generated unique CeO2 nanomorphology consolidating ample reactive sites and facilitated oxygen delivery for a highly efficient thermocatalytic process. Concerning atmospheric pollution mitigation, synthesis of these CeO2 nanostructures represents a cost effective and convenient abatement technique for carbon particulates in comparison to cost-intensive, environmentally detrimental and noble-metal based techniques.

Spark plasma sintering (SPS) densified U3Si2 pellets: Microstructure control and enhanced mechanical and oxidation properties

Dense U3Si2 pellets with controlled grain structure and enhanced thermal-mechanical and oxidation properties are synthesized with spark plasma sintering (SPS). Microstructure and phase composition of the SPS densified pellets are characterized systematically using SEM, EDS, and XRD. Thermal-mechanical properties and oxidation behavior of the sintered silicide fuel pellets are analyzed by laser flash, indentation, and dynamic thermogravimetric analysis. Dense U3Si2 pellets are consolidated by combining high energy ball milling and rapid sintering by SPS, and the microstructure structures are controlled from micron-sized (∼5.7 μm grain size) for conventional silicide to a nanocrystalline matrix with an average grain size of ∼280 nm. A dominant phase of distorted U3Si2 was identified with lattice expansion due to residual thermal stress upon SPS consolidation and rapid cooling processes. Both micron-sized and nano-sized pellets show exceptional thermal transport properties, consistent with monolithic silicides reported in literature. The SPS-densified pellets possess simultaneously high hardness and fracture toughness. The SPS-densified silicide pellets also demonstrate exceptional oxidation performance with extended onset oxidation temperature above 500 °C and reduced oxidation kinetics, particularly for nano-sized pellets. A strong strain effect was proposed in which compressive stress in nano-sized pellets enhances the oxidation resistance of silicide fuels, as evidenced by the degradation of oxidation performance upon strain relaxation by isothermal annealing. The correlation among the sintering process – microstructure control – physical properties and fuel behavior is established. A new concept of strain engineering is proposed further properties optimization, enabling the development of potential oxidation and corrosion-resistant silicides with extended performance, the key technological challenge of U3Si2 as the leading concept of accident tolerant fuels.

Microstructure and properties of in-situ Ti5Si3-TiC composite coatings by reactive plasma spraying

Ti powders, Si powders, and sucrose as a carbonaceous precursor were used to prepare Ti-Si-C composite powders by a spray-drying/precursor-pyrolysis technology. Ti-Si-C composite coatings were in-situ synthesized by reactive plasma spraying of Ti-Si-C composite powders. The microstructure and properties of the composite coatings were investigated. The results showed that the composite coatings consisted of in-situ formed Ti5Si3, TiC and Ti3O. The TiC particles with a diameter of hundreds of microns formed into clusters. The Ti5Si3 and Ti3O with sizes of about 20–40 nm coexisted in the lamellae. The microhardness of Ti5Si3-TiC composite coatings is up to 1906 HV0.1, about 4 times higher than that of TC4 alloys because of the nano Ti5Si3 and the submicron TiC grains. The composite coatings showed excellent wear resistance at room temperature and high temperature (600 °C), about 170 times and 40 times that of TC4 alloys, respectively. The oxidation tests suggested that the Ti5Si3-TiC composite coatings improved the oxidation onset temperature and have an oxidation weight change half of that of the TC4 alloys.

Kinetic Parameters of the Thermal Oxidation and Degradation Reactions in Soybean Oil and Palm Olein

Partially hydrogenated soybean oil and palm olein are oils that are widely used in the food industry. Continuous contact with air may cause changes of the triglycerides chemical structure, to eventually produce substances of lower molar masses that may be toxic to mammals. This study aimed to determine the kinetic parameters for the thermal oxidation of these oils and of their residual used oils from the pre-frying industrial step on preparing breaded chicken meat. The main reactions were followed by thermogravimetry (TG) and differential scanning calorimetry (DSC); the formation of the produced substances was monitored by gas chromatography flame ionization detector (GC-FID) and Fourier transform infrared spectroscopy (FTIR). These analyses indicated different chemical pathways, according to the type of unsaturation and changes in the molecular structures of the fatty acids in the oils. From the thermal analysis, more than one decomposition event was observed during the thermal oxidation process. As the soybean oil has a lower oxidation onset temperature than palm olein, it has lower rate of mass loss, with a higher activation energy value.

Improving the heat transfer capability and thermal stability of vehicle engine oils using Al2O3/TiO2 nanomaterials

ABSTRACT One of the key reasons for the failure of lube oils is their thermal degradation owing to elevated heat conditions in vehicle engines. In this study, the thermal degradation studies of the lube oils were performed using a simultaneous thermal analyzer (TGA/DTG/DSC). Furthermore, the engine thermal efficiency was determined experimentally using an AVL dynamometer under different operating conditions. TGA results showed that the oxidation onset temperature and burnout temperature of Al2O3/TiO2 hybrid nanolubricants could be delayed by 54.9 °C and 38.7 °C, respectively, as compared with the reference oil (5W-30). Comparing the engine results, the Al2O3/TiO2 nanolubricants presented enhancement of heat transport characteristics and brake thermal efficiency by 9–14% and 3.9–8.6%, respectively, compared with the reference oil. Hence, the high thermal stability of Al2O3/TiO2 nanolubricants allows to be used in a wide temperatures range with a higher fuel economy, optimize lube oil drain intervals and reduce maintenance costs in vehicles.

On the Use of Gallic Acid as a Potential Natural Antioxidant and Ultraviolet Light Stabilizer in Cast-Extruded Bio-Based High-Density Polyethylene Films.

This study originally explores the use of gallic acid (GA) as a natural additive in bio-based high-density polyethylene (bio-HDPE) formulations. Thus, bio-HDPE was first melt-compounded with two different loadings of GA, namely 0.3 and 0.8 parts per hundred resin (phr) of biopolymer, by twin-screw extrusion and thereafter shaped into films using a cast-roll machine. The resultant bio-HDPE films containing GA were characterized in terms of their mechanical, morphological, and thermal performance as well as ultraviolet (UV) light stability to evaluate their potential application in food packaging. The incorporation of 0.3 and 0.8 phr of GA reduced the mechanical ductility and crystallinity of bio-HDPE, but it positively contributed to delaying the onset oxidation temperature (OOT) by 36.5 °C and nearly 44 °C, respectively. Moreover, the oxidation induction time (OIT) of bio-HDPE, measured at 210 °C, was delayed for up to approximately 56 and 240 min, respectively. Furthermore, the UV light stability of the bio-HDPE films was remarkably improved, remaining stable for an exposure time of 10 h even at the lowest GA content. The addition of the natural antioxidant slightly induced a yellow color in the bio-HDPE films and it also reduced their transparency, although a high contact transparency level was maintained. This property can be desirable in some packaging materials for light protection, especially UV radiation, which causes lipid oxidation in food products. Therefore, GA can successfully improve the thermal resistance and UV light stability of green polyolefins and will potentially promote the use of natural additives for sustainable food packaging applications.

Fabrication of bilayer antioxidant microcapsule and evaluation of its efficiency in stabilization of polypropylene

In recent years, there has been increasing interest on maintaining the efficiency of Polypropylene (PP) fibers by various methods during its application. In this paper, bilayer antioxidant microcapsules were successfully prepared with Irgafos168 as inner core, hindered polyphenol as inner shell, and TEMPO as outer shell via in situ polymerization method combined with water phase separation method. Structure and property of microcapsules were investigated by FT-IR, XPS, SEM, and TGA analysis. Results showed that microcapsules were successfully prepared with bilayer structure. Microcapsules had spherical shape with particle sizes of 1.09 ± 0.35 μm. They also had good thermal stability to ensure stable structure and property during melt-spinning process. These microcapsules were then blended with PP melts to fabricate composite PP fibers via melt-spinning technique. DSC measurement and accelerated aging treatment was performed to investigate the effect of microcapsules on aging resistance of composite PP fibers. Results showed that the addition of bilayer microcapsules significantly increased the onset oxidation temperature and decreased the aging rate of PP fibers, indicating that the addition of bilayer microcapsule effectively improved the aging resistance of PP fibers. Furthermore, the addition of microcapsules contributed to maintain sound surface morphology of PP fibers.

Synthesis and physicochemical properties of novel lauric acid capped estolide esters and amides made from oleic acid and their evaluations for biolubricant basestock

Vegetable oils have been used as environmentally friendly biolubricants because of their inherent biodegradability, good lubricity, higher viscosity index and low evaporative loss. However, their use is limited due to significantly poor cold flow properties and inferior oxidative stability. This paper presents an approach to modify vegetable oil derivatives namely oleic acid to yield biolubricant with good cold flow properties and oxidation stability. Oleic acid was converted to polyhydroxy estolide through reaction with only hydrogen peroxide, which is considered a ‘green’ oxidant. The synthesized polyhydroxy estolide was further reacted with appropriate amount of lauric acid to end-cap its hydroxy groups, which yielded lauric acid capped estolide as the product. Subsequently, the prepared lauric acid capped estolide was reacted with branched and straight chain alcohols as well as secondary amines to afford estolide esters and amides. In general, most of the prepared samples showed improved cold flow properties as compared to vegetable oil-based lubricants, where the best pour point (−41 °C) was achieved by 4-methyl-2-pentyl estolide ester. Meanwhile, estolide amides exhibited the best oxidative stability among samples evaluated with an oxidation onset temperature of 205 °C, which is significantly higher than vegetable oil-based lubricants. Generally, the oxidative stability, viscosity index and anti-wear properties of prepared estolide esters and amides were found to be comparable to the properties of commercial samples used as benchmark.

Chlorine induced high-temperature corrosion mechanisms in HVOF and HVAF sprayed Cr3C2-based hardmetal coatings

A novel method that combines thermal analysis and traditional furnace corrosion tests was used to study the corrosion behaviour of thermally sprayed Cr3C2-based hardmetal coatings at 450 °C and 550 °C under a KCl deposit. This method enabled the identification of the onset temperature of chlorine-induced oxidation to be within 450–500 °C. Two corrosion mechanisms were suggested for these temperatures. At 450 °C, the corrosion rate was slow and mainly controlled by the formation of K2CrO4. Exposure at 550 °C caused the formation of fine interconnected secondary-carbide precipitates in the metal matrix. Their fast corrosion was identified as the major cause of degradation.