Thermodynamics of the oxidation of ZrB2-TiB2, ZrB2-SiC and ZrB2-B4C ceramics

The thermodynamics of the oxidation of three-high temperature ZrB2-based ceramics (ZrB2-TiB2, ZrB2-SiC and ZrB2-B4C) has been studied in order to find the stability domain of zirconium diboride, in terms of temperature, partial pressure of oxygen and composition, in which it is protected against oxidation. In the case of the ZrB2-TiB2 binary system, a plot of log pO2vs. 1/T in the temperature range of 500-2000 K and another plot of pO2 (x1014) vs.xTiB2 for T=2000 K are made taking into account the two-extreme possibilities of no solubility and 100% solid solubility between ZrB2 and TiB2, respectively. A plot of log pCOvs. log pO2 is made for 1773 K for the systems ZrB2-SiC and ZrB2-B4C. It was found that the ZrB2-TiB2 ceramics does not have sufficient oxidation resistance in the temperature range of 500-2000 K. ZrB2 of ZrB2-SiC ceramics can be protected under 1 atmosphere oxygen or in air if the liquid borosilicate (with the chosen composition, 70% B2O3-30% SiO2), which is an intermediate product, provides a kinetic barrier to the continuation of oxidation by forming an impervious layer on the exposed surfaces. In contrast, the ZrB2-B4C ceramics does not produce the borosilicate upon oxidation. In view of the volatility of pure liquid B2O3, it is recommended that the ZrB2-B4C ceramics can be used at a lower temperature, perhaps below 1373 K, when the vapour pressure of B2O3 is significantly small

Detection of biomarker in breath: A step towards noninvasive diabetes monitoring

Along with more than two hundred volatile organic compounds (VOCs), acetone is also a normal constituent of breath of healthy individuals, albeit in the sub-ppm range, and its concentration increases in diabetic patients. Considering the importance of breath acetone as a biomarker of diabetes, some studies have already been made to measure breath acetone concentration (and correlate with blood sugar level) using GC-MS. There are a few reports of measuring breath acetone concentration using semiconductor sensor in the background of air (i.e. in the absence of VOCs present in normal breath and hence the question of selectivity remains in the real situation) and at a higher concentration (above 10 ppm). We report excellent sensitivity of sonochemically prepared nanosized gamma-Fe2O3 sensors towards sub-ppm acetone (pathological range) in the background of human breath. Our preliminary results should stimulate further research towards developing cheap, rugged and compact semiconductor sensors for noninvasive monitoring of diabetes

A study of mechanical properties and WEDM machinability of spark plasma sintered ZrB2-B4C ceramic composites

Four different compositions of ZrB2-B4C composites (i.e., 5, 15, 20, 25 Wt. % of B4C) were fabricated by Spark Plasma Sintering Technique (SPS) at 2000 degrees C temperature. The composites were characterized by the evolution of physical and mechanical properties; X-Ray Diffraction (XRD) analysis was also done for phase analysis of the composites. The relative density values were obtained in the range of 96.14-97.78 % of all the composites. The addition of B4C in ZrB2 matrix led to an enhancement in hardness (15.38 GPa at 5 wt.% B4C to 20.49 GPa at 25 wt.% B4C measured at 1.0 kgf load) and fracture toughness (from 2.93 MPa-m(0.5) at 5 wt.% B4C to 4.13 MPa-m(0.5) at 25 wt.% B4C measured at 1.0 kgf load). The composite samples were processed by wire electrical discharge machining (WEDM) process with three different parameters set for the study of machining speed, surface roughness. The composite with 25 wt.% of B4C shows highest machining speed of 10.56 mm(2)/min. The average surface roughness (R-a) of the WEDM processed composite surfaces lies in the range of 1.26-5.64 mu m

Phase determination of ZrB2-B4C ceramic composite material using XRD and rietveld refinement analysis

In this work, the Spark plasma sintering technique has been used to sinter ZrB2-B4C (20 wt%) composite at 2100 degrees C and 50 MPa uniaxial pressure for 15 min soaking in an argon atmosphere. XRD analysis has been carried out on the sintered sample to analyze the different phases present in the ZrB2-B4C composite. The Rietveld refinement technique has been used to analyze the crystal structure, the unit cell information such as space group, cell position, cell angles and atomic distances of the composite material using FULLPROF software. (C) 2019 Elsevier Ltd. All rights reserved

Room temperature synthesis of nanocrystalline SnO through sonochemical route

Nanocrystalline tin monoxide (SnO) has been synthesized through sonication-assisted precipitation technique at room temperature. The key in obtaining phase pure SnO at room temperature lies in exploiting high-power ultrasound (450W). The physical phenomenon responsible for the sonochemical process is acoustic cavitation. A mixed phase is formed on decreasing the ultrasonic power.-The heat generated during sonication does not explain the difference in phase formation under varying ultrasonic power as the difference in temperatures of the solutions during sonication under different power ratings was within 10-15 degrees C. SEM and XRD analysis were carried out for the investigation of powder morphology and crystalline structure of the material. (C) 2007 Published by Elsevier B.V

Mechanical, Tribological, and Thermal Properties of Hot-Pressed ZrB2-B4C Composite

The effect of addition of submicrometer-sized B4C (5,10 and 15 wt%) on microstructure, phase composition, hardness, fracture toughness, scratch resistance, wear resistance, and thermal behavior of hot-pressed ZrB2-B4C composites is reported. ZrB2-B4C (10 wt%) composite has V-H1 of 20.81 GPa and fracture toughness of 3.93 at 1kgf, scratch resistance coefficient of 0.40, wear resistance coefficient of 0.01, and ware rate of 0.49x10(-3)mm(3)/Nm at 10N. Crack deflection by homogeneously dispersed submicrometer-sized B4C in ZrB2 matrix can improve the mechanical and tribological properties. Thermal conductivity of ZrB2-B4C composites varied from 70.13 to 45.30W/mK between 100 degrees C and 1000 degrees C which is encouraging for making ultra-high temperature ceramics (UHTC) component

Severe wear behaviour of alumina balls sliding against diamond ceramic coatings

At present alumina is the most widely used bio-ceramic material for implants. However, diamond surface offers very good solid lubricant for different machinery, equipment including biomedical implants (hip implants, knee implants, etc.), since the coefficient of friction (COF) of diamond is lower than alumina. In this tribological study, alumina ball was chosen as the counter body material to show better performance of the polycrystalline diamond (PCD) coatings in biomedical load-bearing applications. Wear and friction data were recorded for microwave plasma chemical vapour deposition (MWCVD) grown PCD coatings of four different types, out of which two samples were as-deposited coatings, one was chemo-mechanically polished and the other diamond sample was made free standing by wet-chemical etching of the silicon wafer. The coefficient of friction of the MWCVD grown PCD against Al2O3 ball under dry ambient condition was found in the range of 0.29-0.7, but in the presence of simulated body fluid, the COF reduces significantly, in the range of 0.03-0.36. The samples were then characterized by Raman spectroscopy for their quality, by coherence scanning profilometer for surface roughness and by electron microscopy for their microstructural properties. Alumina balls worn out (14.2 x 10(-1) mm(3)) very rapidly with zero wear for diamond ceramic coatings. Since the generation of wear particle is the main problem for load-bearing prosthetic joints, it was concluded that the PCD material can potentially replace existing alumina bio-ceramic for their better tribological properties

Mechanical and Thermal Properties of Hot-Pressed ZrB2-SiC Composites

ZrB2-SiC composites were hot pressed at 2473 K (2200 A degrees C) with graded amounts (5 to 20 wt pct) of SiC and the effect of the SiC addition on mechanical properties like hardness, fracture toughness, scratch and wear resistances, and thermal conductivity were studied. Addition of submicron-sized SiC particles in ZrB2 matrices enhanced mechanical properties like hardness (15.6 to 19.1 GPa at 1 kgf), fracture toughness (2 to 3.6 MPa(m)(1/2)) by second phase dispersion toughening mechanism, and also improved scratch and wear resistances. Thermal conductivity of ZrB2-SiC (5 wt pct) composite was higher 121 to 93 W/m K from 373 K to 1273 K (100 A degrees C to 1000 A degrees C)] and decreased slowly upto 1273 K (1000 A degrees C) in comparison to monolithic ZrB2 providing better resistance to thermal fluctuation of the composite and improved service life in UHTC applications. At higher loading of SiC (15 wt pct and above), increased thermal barrier at the grain boundaries probably reduced the thermal conductivity of the composite