Papers by Vinothini Venkatachalam
Journal of Composites Science, 2022
Ultra high-temperature ceramic matrix composites (UHTCMCs) based on carbon fibre (Cf) have been s... more Ultra high-temperature ceramic matrix composites (UHTCMCs) based on carbon fibre (Cf) have been shown to offer excellent temperature stability exceeding 2000 °C in highly corrosive environments, which are prime requirements for various aerospace applications. In C3Harme, a recent European Union-funded Horizon 2020 project, an experimental campaign has been carried out to assess and screen a range of UHTCMC materials for near-zero ablation rocket nozzle and thermal protection systems. Samples with ZrB2-impregnated pyrolytic carbon matrices and 2.5D woven continuous carbon fibre preforms, produced by slurry impregnation and radio frequency aided chemical vapour infiltration (RF-CVI), were tested using the vertical free jet facility at DLR, Cologne using solid propellants. When compared to standard CVI, RFCVI accelerates pyrolytic carbon densification, resulting in a much shorter manufacturing time. The samples survived the initial thermal shock and subsequent surface temperatures of &...
American Society for Composites 2021, 2021
Carbon fibre (Cf) reinforced Ultra High Temperature Ceramic (UHTC) Matrix Composites (UHTCMCs) ha... more Carbon fibre (Cf) reinforced Ultra High Temperature Ceramic (UHTC) Matrix Composites (UHTCMCs) have proven to be excellent materials that can survive nearly 3000°C in highly oxidizing environments along with a good specific strength. Consequently, they have excellent potential for use in aerospace applications such as rocket nozzle throats and thermal protection systems (TPS). Due to the presence of the carbon fibres, UHTCMCs offer high strength and modulus combined with excellent thermal shock behaviour whilst the presence of the ultra-high temperature ceramic phase protects the carbon fibres at the application temperatures. High temperature oxidation, thermal ablation behaviour and mechanical properties of the UHTCMC’s relies heavily on the bonding between the carbon fibre and matrices especially the oxides formed to avoid any progressive failure and predict the life of the components. In the present investigation, a radio frequency assisted chemical vapor infiltration (RF-CVI) te...
IOP Conference Series: Materials Science and Engineering, 2016
In this work (Mn,Co)3O4 spinel powders with different Mn:Co ratio (1:1 and 1:2) and from differen... more In this work (Mn,Co)3O4 spinel powders with different Mn:Co ratio (1:1 and 1:2) and from different commercial suppliers are evaluated for possible powder for production of interconnect coatings. Sinterability of the powders is evaluated on pressed pellets sintered in oxidizing and in reducing/oxidizing atmospheres. For selected powder, coatings are then prepared by the electrophoretic deposition method on Crofer 22 APU stainless steel coupons. Effects of dispersant/iodine content and deposition voltage and times are evaluated. Thickness as a function of deposition parameters is described. Results show that with appropriate powder it is possible to produce adherent protective coating with a well-controlled thickness.
Metal supported protonic fuel cells (PCFC) offer one major advantage over standard solid oxide fu... more Metal supported protonic fuel cells (PCFC) offer one major advantage over standard solid oxide fuel cells (SOFC) with oxygen conducting electrolytes, namely that the product, water, is produced on the cathode (air) side. This feature simplifies the engineering of the stack, boosts efficiency, and is particularly helpful for a porous metal supported cell because it limits the corrosion of the metal by exposure to water vapor in the anode gas. In this work, we show the effect of composition and microstructure on the high temperature corrosion and phase stability (formation of sigma phase/Laves phase) of porous alloys. Alloys in the compositional range Fe-20%Cr to Fe-32%Cr were evaluated and the effects of surface modification on corrosion resistance were studied using thermogravimetry, x-ray diffractometry and electron microscopy. The results show that surface modified porous ferritic steels are very promising materials for cost effective protonic fuel cells operating at 600°C.
Chromia forming ferritic stainless steels (SS) are being considered for intermediate temperature ... more Chromia forming ferritic stainless steels (SS) are being considered for intermediate temperature solid oxide fuel cell interconnect applications. However, protective coatings are in general needed to avoid chromium volatilization and poisoning of cathodes from chromium species. Mn-Co spinel is one of the promising candidates to prevent chromium outward diffusion, improve oxidation resistance and ensure high electrical conductivity over the lifetime of interconnects. In the present study, uniform and well adherent Mn-Co spinel coatings were produced on Crofer 22APU using electrophoretic deposition (EPD). The oxidation behavior of both the coated and bare alloy was evaluated at 800°C in air for 1000 h. The oxidation kinetics were investigated using weight gain and scale thickness measurements. The weight gain per unit surface area of the bare alloy exhibited parabolic oxidation behavior. The influence of Mn-Co spinel coating on chromia scale formation and corrosion rate of different f...
Journal of Materials Science, 2010
Ceramics International, 2006
... This solution was heated at 90 °C with a constant stirring until it became clear transparent ... more ... This solution was heated at 90 °C with a constant stirring until it became clear transparent yellow solution. This solution was heated at 200 °C for 5 h in an oven to promote polymerization and remove solvents. With continued ...
Composites Part A: Applied Science and Manufacturing, 2021
Link to publication on Research at Birmingham portal General rights Unless a licence is specified... more Link to publication on Research at Birmingham portal General rights Unless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or the copyright holders. The express permission of the copyright holder must be obtained for any use of this material other than for purposes permitted by law. •Users may freely distribute the URL that is used to identify this publication. •Users may download and/or print one copy of the publication from the University of Birmingham research portal for the purpose of private study or non-commercial research. •User may use extracts from the document in line with the concept of 'fair dealing' under the Copyright, Designs and Patents Act 1988 (?) •Users may not further distribute the material nor use it for the purposes of commercial gain. Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.
Journal of the European Ceramic Society
Journal of Alloys and Compounds
International Materials Reviews
Materials & Design
A functionally graded composite based on ZrB 2 and 0-50 vol% of short carbon fibres was prepared ... more A functionally graded composite based on ZrB 2 and 0-50 vol% of short carbon fibres was prepared via a deliberately simple approach that involved creating a suitable stacking sequence of layers with different sintering agents and fibre contents. This led to an excellent combination of failure tolerance and oxidation resistance in a light material with a density below that of alumina. The graded architecture outperformed other related composites when tested at 1500°C and, separately, achieved a toughness of 10 MPa m ½. In addition, the composite withstood the ablation effect of an oxyacetylene torch at 2500°C, undergoing minimal recession. Moreover, the true nature of the "tubular" zirconium oxide formed upon oxidation at extreme temperatures is reported for the first time. The functionally graded concept applied to a ultra-refractory matrix seems to be a promising route to obtain even complex shaped components with functional symmetry for use in severe environments.
Journal of Power Sources
Manganese cobalt spinel oxides are promising materials for protective coatings for solid oxide fu... more Manganese cobalt spinel oxides are promising materials for protective coatings for solid oxide fuel cell (SOFC) interconnects. To achieve high density such coatings are often sintered in a two-step procedure, involving heat treatment first in reducing and then in oxidizing atmospheres. Sintering the coating inside the SOFC stack during heating would reduce production costs, but may 2 result in a lower coating density. The importance of coating density is here assessed by characterization of the oxidation kinetics and Cr evaporation of Crofer 22 APU with MnCo 1.7 Fe 0.3 O 4 spinel coatings of different density. The coating density is shown to have minor influence on the longterm oxidation behavior in air at 800 °C, evaluated over 5000 h. Sintering the spinel coating in air at 900 °C, equivalent to an in-situ heat treatment, leads to an 88 % reduction of the Cr evaporation rate of Crofer 22 APU in air-3% H 2 O at 800 °C. The air sintered spinel coating is initially highly porous, however, densifies with time in interaction with the alloy. A two-step reduction and re-oxidation heat treatment results in a denser coating, which reduces Cr evaporation by 97 %.
Journal of Materials Science, 2006
Dispersion of barium titanate nano powder of average particle size~30 nm in different solvent sys... more Dispersion of barium titanate nano powder of average particle size~30 nm in different solvent systems of tape casting (toluene-ethanol, methyl ethyl ketone-ethanol, xylene-ethanol) along with Triton x-100 or phosphate ester as dispersants has been studied using sedimentation experiments. The influence of different parameters such as type of solvent system, dispersant and concentration of dispersant on BaTiO 3 slip dispersion, viscosity and the properties of green tape were studied. The optimal concentration of dispersant was determined from the minimum slip viscosity. Xylene-ethanol with phosphate ester was found to be the best solvent and dispersant system for tape casting. Defect free, denser and smooth green tapes are formed with this system.
Tape casting is the feasible method for preparing ceramic tapes with different electrical and mag... more Tape casting is the feasible method for preparing ceramic tapes with different electrical and magnetic properties for multi layer ceramic devices. The preparation of stable, well-dispersed slip is a critical step in tape casting technology. As the miniaturization stresses the use of nano size powders and less and less thickness of tape to increase the effective surface area in the same volume of material with improved properties, the optimization of suitable parameters to achieve the defect free tape with specified properties is a difficult task. Dispersion of barium titanate nano powder of average particle size ~ 30nm in different solvent systems of tape casting (toluene-ethanol, methyl ethyl ketone-ethanol, xylene-ethanol) along with Triton x-100, phosphate ester as dispersants has been studied using sedimentation experiments. The optimal concentration of dispersant was determined from the minimum in slip viscosity. Poly vinyl butyral was used as a binder. The influence of differe...
Metal supported protonic fuel cells (PCFC) offer one major advantage over standard solid oxide fu... more Metal supported protonic fuel cells (PCFC) offer one major advantage over standard solid oxide fuel cells (SOFC) with oxygen conducting electrolytes, namely that the product, water, is produced on the cathode (air) side. This feature simplifies the engineering of the stack and is particularly helpful for a porous metal supported cell because it limits the exposure of the metal to highly oxidising atmospheres.
In this work, we show the effect of composition and microstructure on the high temperature corrosion and phase stability (formation of sigma phase/Laves phase) of porous alloys. Alloys in the compositional range Fe20Cr to Fe32Cr were evaluated and the effects of surface modification on corrosion resistance were studied, using thermogravimetry, x-ray diffractometry and electron microscopy. The results show that surface modified porous ferritic steels are a very promising material for cost effective protonic fuel cells operating at 600°C.
Chromia forming ferritic stainless steels (SS) are being considered for intermediate temperature
... more Chromia forming ferritic stainless steels (SS) are being considered for intermediate temperature
solid oxide fuel cell interconnect applications. However, protective coatings are in general
needed to avoid chromium volatilization and poisoning of cathodes from chromium species.
Mn-Co spinel is one of the promising candidates to prevent chromium outward diffusion,
improve oxidation resistance and ensure high electrical conductivity over the lifetime of
interconnects. In the present study, uniform and well adherent Mn-Co spinel coatings were
produced on Crofer 22APU using electrophoretic deposition (EPD). The oxidation behavior of
both the coated and bare alloy was evaluated at 800°C in air for 1000 h. The oxidation kinetics
were investigated using weight gain and scale thickness measurements. The weight gain per unit
surface area of the bare alloy exhibited parabolic oxidation behavior. The influence of Mn-Co
spinel coating on chromia scale formation and corrosion rate of different ferritic stainless steels
is also elucidated.
The paper reports the synthesis, structural and high frequency dielectric properties of Ba(Zr x T... more The paper reports the synthesis, structural and high frequency dielectric properties of Ba(Zr x Ti 1-x ) O 3, BZT, nanopowders where x = 0, 0.1, 0.2, 0.3. These powders were synthesized using both microwave assisted and conventional heating, with the former requiring lower temperature and shorter times compared to the latter, viz., 700°C for 30 min versus 900°C for 5 h. The synthesized nanopowders were characterized using X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, BET surface area analysis, differential scanning calorimetry and high frequency dielectric measurements. All the microwave synthesized BZT compositions were found to have well crystallized, finer nanoparticles with less agglomeration and higher dielectric permittivity compared to the conventionally prepared powders. The rapidity and less demanding processing conditions associated with the microwave assisted method augers well for the general applicability of the technique for the production of nanocrystalline powders.
Dispersion of barium titanate nano powder of average particle size~30 nm in different solvent sys... more Dispersion of barium titanate nano powder of average particle size~30 nm in different solvent systems of tape casting (toluene-ethanol, methyl ethyl ketone-ethanol, xylene-ethanol) along with Triton x-100 or phosphate ester as dispersants has been studied using sedimentation experiments. The influence of different parameters such as type of solvent system, dispersant and concentration of dispersant on BaTiO 3 slip dispersion, viscosity and the properties of green tape were studied. The optimal concentration of dispersant was determined from the minimum slip viscosity. Xylene-ethanol with phosphate ester was found to be the best solvent and dispersant system for tape casting. Defect free, denser and smooth green tapes are formed with this system.
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Papers by Vinothini Venkatachalam
In this work, we show the effect of composition and microstructure on the high temperature corrosion and phase stability (formation of sigma phase/Laves phase) of porous alloys. Alloys in the compositional range Fe20Cr to Fe32Cr were evaluated and the effects of surface modification on corrosion resistance were studied, using thermogravimetry, x-ray diffractometry and electron microscopy. The results show that surface modified porous ferritic steels are a very promising material for cost effective protonic fuel cells operating at 600°C.
solid oxide fuel cell interconnect applications. However, protective coatings are in general
needed to avoid chromium volatilization and poisoning of cathodes from chromium species.
Mn-Co spinel is one of the promising candidates to prevent chromium outward diffusion,
improve oxidation resistance and ensure high electrical conductivity over the lifetime of
interconnects. In the present study, uniform and well adherent Mn-Co spinel coatings were
produced on Crofer 22APU using electrophoretic deposition (EPD). The oxidation behavior of
both the coated and bare alloy was evaluated at 800°C in air for 1000 h. The oxidation kinetics
were investigated using weight gain and scale thickness measurements. The weight gain per unit
surface area of the bare alloy exhibited parabolic oxidation behavior. The influence of Mn-Co
spinel coating on chromia scale formation and corrosion rate of different ferritic stainless steels
is also elucidated.
In this work, we show the effect of composition and microstructure on the high temperature corrosion and phase stability (formation of sigma phase/Laves phase) of porous alloys. Alloys in the compositional range Fe20Cr to Fe32Cr were evaluated and the effects of surface modification on corrosion resistance were studied, using thermogravimetry, x-ray diffractometry and electron microscopy. The results show that surface modified porous ferritic steels are a very promising material for cost effective protonic fuel cells operating at 600°C.
solid oxide fuel cell interconnect applications. However, protective coatings are in general
needed to avoid chromium volatilization and poisoning of cathodes from chromium species.
Mn-Co spinel is one of the promising candidates to prevent chromium outward diffusion,
improve oxidation resistance and ensure high electrical conductivity over the lifetime of
interconnects. In the present study, uniform and well adherent Mn-Co spinel coatings were
produced on Crofer 22APU using electrophoretic deposition (EPD). The oxidation behavior of
both the coated and bare alloy was evaluated at 800°C in air for 1000 h. The oxidation kinetics
were investigated using weight gain and scale thickness measurements. The weight gain per unit
surface area of the bare alloy exhibited parabolic oxidation behavior. The influence of Mn-Co
spinel coating on chromia scale formation and corrosion rate of different ferritic stainless steels
is also elucidated.