Micro-Raman spectroscopy of indentation induced phase transformation in nanozirconia ceramics

Micro-Raman spectroscopy has been employed as an effective technique to determine the phase transformations in nanostructured yttria stabilised zirconia (YSZ) ceramics with different yttria content. Samples have been prepared with varying mean grain sizes by a slip casting route followed by a microwave assisted two-step sintering cycle starting with aqueous nanozirconia suspensions. Indents were generated using a Vickers pyramidal indenter at different loads and the resulting phase transformations were mapped using micro-Raman spectroscopy. The results were compared to those of a commercial submicron 3YSZ. The amount of transformation was found to be much lower for nanozirconia compared to the submicron zirconia with similar yttria content

Evaluation of the high temperature performance of HfB2 UHTC particulate filled Cf/C composites

This is the peer reviewed version of the following article: PAUL, A. ... et al, 2017. Evaluation of the high temperature performance of HfB2 UHTC particulate filled Cf/C composites. International Journal of Applied Ceramic Technology, 14 (3), pp. 344–353, which has been published in final form at https://doi.org/10.1111/ijac.12659. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Room and high temperature flexural strength and coefficient of thermal expansion (CTE) of HfB2 ultra-high temperature ceramic (UHTC) particulate filled Cf/C composites are determined along with UHT oxidation behavior. Both room and high temperature strength of the composites were found to be broadly comparable to those of other thermal protection system materials currently being investigated. The CTE of the composites was measured both along and perpendicular to the fiber direction up to 1700°C and the values were found to depend on fiber orientation by approximately a factor of 3. Arc-jet testing of the UHTC composites highlighted the excellent ultra-high temperature oxidation performance of these materials

High strain rate characteristics of 3-3 metal–ceramic interpenetrating composites

3-3 interpenetrating composites (IPCs) are novel materials with potentially superior multifunctional properties compared with traditional metal matrix composites. The aim of the present work was to evaluate the high strain rate performance of the metal–ceramic IPCs produced using a pressureless infiltration technique through dynamic property testing, viz. the split Hopkinson’s pressure bar (SHPB) technique and depth of penetration (DoP) analysis, and subsequent damage assessment. Though the IPCs contained rigid ceramic struts, the samples plastically deformed with only localised fracture in the ceramic phase following SHPB. Metal was observed to bridge the cracks formed during high strain rate testing, this latter behaviour must have contributed to the structural integrity and performance of the IPCs. Whilst the IPCs were not suitable for resisting high velocity, armour piercing rounds on their own, when bonded to a 3mm thick, dense Al2O3 front face, they caused significant deflection and the depth of penetration was reduced

Compositional effects in nanostructured yttria partially stabilised zirconia

There is a considerable current interest in learning how to process genuinely nanostructured ceramics as they offer the potential for significantly enhanced properties; however, it is often difficult to make large enough components to allow more than the most basic of property measurements. In this work, densified components measuring up to 50 mm in size have been produced and a number of very interesting properties have been measured and demonstrated

Evaluation of the high temperature performance of HfB2 UHTC particulate filled Cf/C composites

Room and high temperature flexural strength and coefficient of thermal expansion (CTE) of HfB2 ultra-high temperature ceramic (UHTC) particulate filled Cf/C composites are determined along with UHT oxidation behavior. Both room and high temperature strength of the composites were found to be broadly comparable to those of other thermal protection system materials currently being investigated. The CTE of the composites was measured both along and perpendicular to the fiber direction up to 1700°C and the values were found to depend on fiber orientation by approximately a factor of 3. Arc-jet testing of the UHTC composites highlighted the excellent ultra-high temperature oxidation performance of these materials

No Association between Clinical Periodontal Conditions and Microbiological Findings on Driveline of Patients with Left-Ventricular Assist Devices (LVAD)

The aim of this retrospective study was to investigate whether there would be an association between periodontal disease parameters and positive bacterial findings at the driveline of patients with a left ventricular assist device (LVAD). Patients with an LVAD, who underwent a full oral and microbiological examination between 2016 and 2018, were included. During oral examination, periodontitis severity (stage and grade) and the periodontal inflamed surface area (PISA) were evaluated. A microbiological analysis was performed from swabs of the driveline, whereby different bacterial species were cultivated and analyzed. A total of 73 patients were included in the current study. The majority of participants (80.8%) had at least one positive bacterial finding during the study period. Most patients had a periodontitis stage of III-IV (80.9%). The determined PISA of the total group was 284.78 ± 352.29 mm2. No associations were found between the periodontal disease parameters and the bacterial findings in general, the bacterial findings on the day of oral examination or the bacterial findings 12 months prior to/after the oral examination (p > 0.05). Periodontitis is not associated with cultivated microbiological findings at the driveline of patients with an LVAD and thus appears not to be a risk indicator for driveline colonization. Nevertheless, the high periodontal burden in LVAD patients underlines the need for their improved periodontal care