Binner, Jon

Vaidhyanathan, Bala

Zheng, Pengxiang

English

Engineering Conferences International

Engineering Conferences InternationalECI Digital ArchivesUltra-High Temperature Ceramics: Materials forExtreme Environment Applications III ProceedingsSpring 4-13-2015Synthesis and Static Oxidation Testing of DopedHf B2 PowdersPengxiang ZhengLoughborough UniversityJon BinnerUniversity of BirminghamBala VaidhyanathanLoughborough UniversityFollow this and additional works at: http://dc.engconfintl.org/uhtc-iiiPart of the Materials Science and Engineering CommonsThis Conference Proceeding is brought to you for free and open access by the Proceedings at ECI Digital Archives. It has been accepted for inclusion inUltra-High Temperature Ceramics: Materials for Extreme Environment Applications III by an authorized administrator of ECI Digital Archives. Formore information, please contact franco@bepress.com.Recommended CitationPengxiang Zheng, Jon Binner, and Bala Vaidhyanathan, "Synthesis and Static Oxidation Testing of Doped Hf B2 Powders" in "Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications III", G. Franks and C. Tallon, University of MelbourneEds, ECI Symposium Series, (2015). http://dc.engconfintl.org/uhtc-iii/8© 2014 University  of Birmingham  The information in this document is the property of The University of Birmingham and may not be copied or communicated to a third party, or used for any purpose other than that for which it is supplied without the express written consent of The University of Birmingham. Synthesis and Static Oxidation Testing of Doped HfB2 Powders Pengxiang Zheng, Jon Binner* and Bala Vaidhyanathan   Loughborough University *University of Birmingham UK  © 2015 University of Birmingham The information in this document is the property of The University of Birmingham and may not be copied or communicated to a third party, or used for any purpose other than that for which it is supplied without the express written consent of The University of ir ingha . HfB2 oxidises to HfO2 readily; whilst not a problem in itself, like ZrO2, HfO2 undergoes a phase transformation with an associated volume change that opens up porosity. Phase transformation of the oxide product of HfB2 One solution is to dope the HfB2 so that on oxidation it forms stabilised, tetragonal HfO2 Problems with HfB2 Ceramic Oxidation Materials Systems for Extreme Environments 2 TaB2 was chosen because of its similar crystal structure and atomic radius to that of HfB2 Dopant Selection Compound Melting point /oC Crystal structure Covalent radius of the metal atom / pm HfB2 3250 Hexagonal 175±10 YB4 2150 Tetragonal 190±7 TaB2 2850 Hexagonal 170±8 LaB6 2250 Cubic 207±8 MgB2 830 Hexagonal 141±7 Materials Systems for Extreme Environments 3 Addition of Ta-Dopant Materials Systems for Extreme Environments 4 HfO2 + B2O3 + 5C → HfB2 + 5CO ↑ G<0 at >1350 oC Ta2O5 + 2B2O3 + 11C → 2TaB2 + 11CO ↑ G<0 at >1327 oC TaCl5 dispersed in ethanol, HfCl4 in de-ionised water. Ammonia used to form hydroxides & remove Cl –ions. H3BO3 HfCl4  Refluxing & stirring (100oC for 24 h) Drying & calcining (200oC for 2 h) Grinding Carbo/borothermal reduction (1600oC for 2 h) Phenolic resin Dissolved in ethanol TaCl5  Co-precipitates EDX mapping shows the Ta distributed homogeneously. The particle size was ~0.5 µm, but the final product contained hard agglomerates.  Hf Ta 10 wt% Ta-doped HfB2 powder Ta-Doped HfB2 Powder Materials Systems for Extreme Environments 5 All the peaks correspond to HfB2 confirming the formation of (Ta,Hf)B2 solid solution XRD of Ta-Doped HfB2 Powder Materials Systems for Extreme Environments 6 0 wt% Ta-doped HfB2 5 wt% Ta-doped HfB2 10 wt% Ta-doped HfB2 ●  HfB2 Lattice parameter HfB2 (literature) HfB2 (this study) 5% TaB2-doped HfB2 10% TaB2-doped HfB2 15% TaB2-doped HfB2 TaB2 a / nm 0.3141 0.3142 0.3140 0.3139 0.3138 0.3088 c / nm 0.3470 0.3470 0.3468 0.3466 0.3464 0.3241 Lattice Parameter of Pure and Doped HfB2 Materials Systems for Extreme Environments 7 XRD Results after 1600oC Oxidation of Powder After 1600oC oxidation, pure HfB2 yielded entirely monoclinic HfO2 whilst the 10%TaB2-doped HfB2 gave almost phase pure tetragonal HfO2. Materials Systems for Extreme Environments 8 0 wt% Ta-doped HfB2 10 wt% Ta-doped HfB2 XRD Results after 1600oC Oxidation of Powder After 1600oC oxidation, pure HfB2 yielded entirely monoclinic HfO2 whilst the 10%TaB2-doped HfB2 gave almost phase pure tetragonal HfO2. Materials Systems for Extreme Environments 9 0 wt% Ta-doped HfB2 10 wt% Ta-doped HfB2 Modelling TA Parthasarathy Predicted: recession rates, scale thicknesses, weight gain (all validated against expts)  Phase transformation of ZrO2 and HfO2 plays a significant role (increases pore volume) Materials Systems for Extreme Environments 10 Modelling TA Parthasarathy Predicted: recession rates, scale thicknesses, weight gain (all validated against expts)  Phase transformation of ZrO2 and HfO2 plays a significant role (increases pore volume) Materials Systems for Extreme Environments 11 HfB2 HfO2 B2O3 20 mm Treibacher  HfB2 5 wt% Ta-  doped HfB2 10 wt% Ta- doped HfB2 15 wt% Ta- doped HfB2 0 wt% Ta-  doped HfB2 Ta-Doped Samples after SPS at 2100oC, 50 MPa Materials Systems for Extreme Environments 12 Ta-Doped Samples after SPS at 2100oC, 50 MPa  Peak shifts shows that Ta atoms remain in solid solution   No residual TaB2 in the 15 wt% Ta-doped HfB2 sample Materials Systems for Extreme Environments 13 Samples  Density  / g cm-3 Relative density Treibacher HfB2  9.83 93.62% 0 wt% Ta-doped HfB2 8.93 85.04% 5 wt% Ta-doped HfB2 9.24 87.73% 10 wt% Ta-doped HfB2 9.36 88.59% 15 wt% Ta-doped HfB2 9.55 90.12% Ta-Doped Samples after SPS at 2100oC, 50 MPa Theoretical value for HfB2  10.50 Theoretical value for TaB2  11.15 The addition of Ta improves the sinterability of HfB2 Materials Systems for Extreme Environments 14 5 wt% Ta-doped HfB2 Treibacher HfB2 10 wt% Ta-doped HfB2 15 wt% Ta-doped HfB2 0 wt% Ta-doped HfB2 Ta-Doped Samples after SPS at 2100oC, 50 MPa The addition of Ta improves the sinterability of HfB2 Materials Systems for Extreme Environments 15 10 wt% Ta-doped HfB2 Ta homogeneously distributed. Carbon was found in all the samples (including the commercial HfB2). It is probably from the protective graphite sheet used for SPS. Compositional Analysis C K series Hf M series Ta M series Materials Systems for Extreme Environments 16  High purity, sub-micron (~0.5 µm) Ta-doped HfB2 has been synthesized.  The 10 wt% Ta-doped HfB2 was able to almost fully stabilize HfO2 in the tetragonal phase after oxidation of the powder at 1600oC.  The addition of Ta-dopants improve the sinterability of HfB2.  In order to achieve higher density, the 10 wt% Ta-doped HfB2 powders will be SPSed at 2400oC and 500 MPa at QML.  Samples with satisfactory density (>98%) will be oxidized to investigate TAPs’ model. Ta-Doping of HfB2 – Summary & Future Work Materials Systems for Extreme Environments 17 18 ECerS XIII Thank You Materials Systems for Extreme Environments 18 

Synthesis and Static Oxidation Testing of Doped HfB2 Powders

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Synthesis and Static Oxidation Testing of Doped HfB2 Powders

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