Study of the Effect of Doping ZrO2 Ceramics with MgO to Increase the Resistance to Polymorphic Transformations under the Action of Irradiation

The purpose of this study is to assess the effect of doping ZrO2 ceramics with MgO on radiation swelling and polymorphic transformations, as a result of irradiation with heavy ions. Interest in these types of materials is due to the great prospects for their use as structural materials for new-generation reactors. The study established the dependences of the phase composition formation and changes in the structural parameters following a change in the concentration of MgO. It has been established that the main mechanism for changing the structural properties of ceramics is the displacement of the cubic c-ZrO2 phase by the Zr0.9Mg0.1O2 substitution phase, which leads to an increase in the stability of ceramic properties to irradiation. It has been determined that an increase in MgO concentration leads to the formation of an impurity phase Zr0.9Mg0.1O2 due to the type of substitution, resulting in changes to the structural parameters of ceramics. During studies of changes in the strength properties of irradiated ceramics, it was found that the formation of a phase in the Zr0.9Mg0.1O2 structure leads to an increase in the resistance to cracking and embrittlement of the surface layers of ceramics.

THE EFFECT OF PH AND CALCINATION TEMPERATURE ON THE ZrO2 PHASE FORMATION FROM NATURAL ZIRCON SAND OF KERENG PANGI

In this research ZrO2 has been synthesized from Kereng Pangi zircon sand in Central Kalimantan through alkali fusion-coprecipitation method. Firstly, zircon sand (ZrSiO4) was purified to reduce impurities by magnetic separation, cleaned using an ultrasonic cleaner, soaked/leached with HCl 2 M for 12 hours and leached with HCl at 60 ºC for 3 hours. Secondly, alkali fusion was done with KOH as an alkali. This product was then washed by water and dried before leached with HCl 30% at 90 ºC for 30 minutes to precipitate and seperate Silica from Zircon. ZrO2 filtrate (ZrOCl2) precipitated with NH4OH at pH 4, pH 7, and pH 10 forms Zr(OH)4 gel. Zr(OH)4 gel was dried and characterized by DTA-TGA, which was then followed by calcination based on DTA TGA results at temperature ranges of 550 ºC - 700 ºC to produce ZrO2. XRD results show that single tetragonal phase of ZrO2 is formed in all variations of pH precipitation and calcination temperature. An analysis using MAUD software show that crystal size reduces as the increase in precipitation of pH. The crystal size results are 110 nm, 66 nm and 48 nm at pH 4, pH 7 dan pH 10 at 700 ºC, respectively. Moreover, XRF results show that ZrO2 with purity is at around 95.8 % at pH 4 and 96.3 % at pH 7 and pH 10.

In Situ Investigation of the Oxidation Behaviour of Chemical Vapour Deposited Zr(C,N) Hard Coatings Using Synchrotron X–ray Diffraction

The oxidation behaviour of chemical vapour deposited ZrN, ZrC and ZrCN coatings was investigated using in-situ synchrotron X–ray diffraction (XRD). To obtain a precise analysis of the temperature–dependent phase evolution during oxidation, coating powders were annealed in air between 100 °C and 1000 °C. Simultaneously, 2D XRD patterns were recorded in ~2 °C increments, which were subsequently evaluated using parametric Rietveld refinement. The results were correlated with differential scanning calorimetry and thermogravimetric analysis measurements, to further illuminate the oxidation mechanism of each coating system. ZrCN exhibited the highest oxidation onset temperature, followed by ZrC and ZrN. Furthermore, ZrCN was completely oxidised at a temperature of ~720 °C, which was ~50–70 °C higher than for ZrN and ZrC. The in–situ experiments revealed a similar oxidation sequence for all three samples: first, tetragonal and/or cubic (c/t)–ZrO2 is formed, which subsequently transforms into the more stable monoclinic (m)–ZrO2 phase. ZrCN and ZrC showed a higher c/t–ZrO2 fraction than the ZrN sample at 1000 °C. Furthermore, ex–situ Raman and XRD investigations of the oxidised samples revealed the ongoing c/t–ZrO2 → m–ZrO2 phase transformation during cooling.

Thermal Stability of PS-PVD YSZ Coatings with Typical Dense Layered and Columnar Structures

Yttria-stabilized zirconia (YSZ) coatings with typical pyramid columnar and dense layered structure were prepared by plasma spray-physical vapor deposition (PS-PVD). The evolution behavior of microstructure and crystallography of the coatings before and after thermal aging treatment were observed by electron backscatter diffraction (EBSD) and field emission scanning electron microscopy (FE-SEM). Results showed that the as-deposited coatings exhibited many types of structures and were mainly composed of a nonequilibrium tetragonal (t’-ZrO2) phase. With the prolonging of thermal exposure time, the initial nonequilibrium tetragonal phase of YSZ coatings gradually transformed into a monoclinic (m-ZrO2) phase. During the process of stationary deposition, at a proper spraying distance, each column exhibited a certain preferred orientation, but the ceramic topcoat did not exhibit distinct preferred orientation statistically.

Carbide-Modified Pd on ZrO2 as Active Phase for CO2-Reforming of Methane—A Model Phase Boundary Approach

Starting from subsurface Zr0-doped “inverse” Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state.

R-curve of La2O3 doped Zirconia Toughened Alumina Composites Prepared via Stereolithography based 3D Printing

In this study, we combined liquid precursor infiltration of high introduction amounts of bi-additives (20wt%) and stereolithography-based 3D printing to fabricate zirconia toughened alumina, and the infiltration systems consist of the four following systems Zr4+/La3+, Zr4+/Er3+, Zr4+/Gd3+, and Zr4+/Ce4+. The sample immersed with Zr4+/La3+ shows intense peaks of m-ZrO2 phase compared to the other samples while a new phase of flake-like LaAl11O18 occurs in the Zr4+/La3+ immersed sample, the existence of which could be confirmed by XRD and EDS. The fracture toughness of the Zr4+/Er3+, Zr4+/Gd3+, and Zr4+/Ce4+ samples remained basically unchanged versus the crack size, while the measured fracture toughness values for the Zr4+/La3+ system could be fitted as a rising R-curve behavior with the steady-state fracture toughness of 17.76 MPa·m1/2. The enormous enhancement of the toughness could be attributed to thermal expansion misfit and flake-like LaAl11O18 in the Zr4+/La3+ system. The effect of residual stresses on the fracture mode and thus the toughness is discussed on the basis of theoretical calculation and analysis. It is the first time a rising R-curve behavior is observed in the 3D printed ceramics. The shocking discovery provides a highly effective toughening way in 3D printing combined infiltration approach.