MgO ZrO2 Research Articles

Improved sinterability and thermal shock resistance of MgO–ZrO2 composites due to in-situ formed MgAl2O4

To solve the problems of high cost and high firing temperature of ZrO2 inserted rings of slide plates, the in-situ MgAl2O4 (MA) toughened MgO–ZrO2 new ring materials were prepared using lightly calcined MgO, m-ZrO2 and nanoscale Al2O3. The effects of MgO/ZrO2 ratio and the amount of nanoscale Al2O3 on properties of samples were investigated. The results showed that the sinterability and mechanical properties of MgO–ZrO2 composites improved significantly due to the MA formed in situ by reaction between MgO and Al2O3, which promoted reactive sintering and densification of the samples. The improved thermal shock resistance (TSR) in MA-toughened MgO–ZrO2 composites was attributed to microcracks developed due to thermal expansion mismatch, MA and ZrO2 also acted as bridging particles, improving the ability to prevent crack propagation of the composites. The optimum MgO/ZrO2 ratio and addition amount of nanoscale Al2O3 were 7/3 and 3 wt%, respectively.

Influence of ZrO2 on the phase composition and mechano-physical properties of MgO–ZrO2 refractories prepared by cold isostatic pressing

MgO–ZrO2 refractories were produced by combining MgO refractories (with a CaO/SiO2 ratio of 2.1) with monoclinic ZrO2 powder using wet-bag cold isostatic pressing. The phase composition and mechano-physical properties of the MgO–ZrO2 materials were influenced by the interaction between ZrO2 and MgO refractories. ZrO2 enhanced the cold modulus of fracture of MgO refractories but decreased the hot modulus of fracture due to changes in bonding phases. The addition of 1 wt% ZrO2 transformed Ca2SiO4 into CaMgSiO4 and CaZrO3. CaMgSiO4 with a low melting point deteriorated the hot modulus of fracture of MgO–ZrO2 refractories from 13.3 to 2.97 MPa. With an increase in ZrO2 to 3–5 wt.%, CaMgSiO4 remained while CaZrO3 gradually transformed into the solid-solution Ca0.2Zr0.8O1.8. This transformation occurred because ZrO2 seized CaO from CaZrO3 to stabilize itself. Based on thermodynamic equilibrium ZrO2 preferentially reacts with CaO-containing phases in the MgO matrix in the following order: Ca3SiO5 > Ca2SiO4 > CaZrO3 > CaMgSiO4. The thermal shock resistance of MgO–ZrO2 refractories with less than 5 wt% ZrO2 was not significantly improved by assessing their strength loss and coefficient of thermal expansion. In conclusion, it is recommended to incorporate ZrO2 into MgO refractories with low SiO2 or CaO to develop high-performance MgO–ZrO2 refractories.

Microstructure evolution, mechanical characteristics and erosion behavior of Cr2O3–Al2O3–MgO–ZrO2 refractories in molten reduction slag

In order to overcome the serious corrosion problem of furnace hearth refractory materials for smelting reduction ironmaking, the Cr2O3–Al2O3–MgO–ZrO2 refractories were synthesized, and the phase component, microstructure, mechanical characteristics, and slag erosion behavior of composite refractories were investigated and evaluated. The results indicate that the composite refractories mainly consist of Mg(Al, Cr)2O4 spinel phase, (Al, Cr)2O3 solid solution and ZrO2. The content of Mg (Al, Cr)2O4 spinel significantly increases with the increasing MgO content, while the content of (Al, Cr)2O3 obviously decreases. Furthermore, the comprehensive mechanical properties of the MgO modified composite refractories can be obviously enhanced by increasing the MgO content, and sample S4 presents the best mechanical characteristics when the MgO addition is 10 wt%. The corresponding hardness, compressive strength and bending strength are 14.22 GPa, 267.14 MPa and 80.0 MPa, respectively. This is mainly because the formation of Mg(Al, Cr)2O4 significantly improves the densification of composite refractories, and a large number of high-strength Mg (Al, Cr)2O4 spinel “bridge” formed between the large-sized (Al, Cr)2O3 grains. The erosion test results indicate that increasing the MgO content can significantly improve the slag infiltration resistance of composite refractories, because the formation of Mg (Al, Cr)2O4 spinel layer significantly improves the densification of MgO reinforced composite refractories. Although the slag corrosion resistance of Mg(Al, Cr)2O4 is lower than that of (Al, Cr)2O3, the Cr2O3–Al2O3–MgO–ZrO2 refractories still presents good erosion resistance, permeability resistance, and excellent mechanical characteristics.

Partial Oxidation of Bio-methane over Nickel Supported on MgO–ZrO2 Solid Solutions

Syngas can be produced from biomethane via Partial Oxidation of Methane (POM), being an attractive route since it is ecofriendly and sustainable. In this work, catalysts of Ni supported on MgO–ZrO2 solid solutions, prepared by a one-step polymerization method, were characterized by HRTEM/EDX, XRD, XPS, H2-TPR, and in situ XRD. All catalysts, including Ni/ZrO2 and Ni/MgO as reference, were tested for POM (CH4:O2 molar ratio 2, 750 ºC, 1 atm). NiO/MgO/ZrO2 contained two solid-solutions, MgO–ZrO2 and NiO-MgO, as revealed by XRD and XPS. Ni (30 wt%) supported on MgO–ZrO2 solid solution exhibited high methane conversion and hydrogen selectivity. However, depending on the MgO amount (0, 4, 20, 40, 100 molar percent) major differences in NiO reducibility, growth of Ni0 crystallite size during H2 reduction and POM, and in carbon deposition rates were observed. Interestingly, catalysts with lower MgO content achieved the highest CH4 conversion (~ 95%), high selectivity to H2 (1.7) and CO (0.8), and low carbon deposition rates (0.024 g carbon.gcat−1 h−1) with Ni4MgZr (4 mol% MgO) turning out to be the best catalyst. In situ XRD during POM indicated metallic Ni nanoparticles (average crystallite size of 31 nm), supported by MgO–ZrO2 solid solution, with small amounts of NiO–MgO being present as well. The presence of MgO also influenced the morphology of the carbon deposits, leading to filaments instead of amorphous carbon. A combustion-reforming mechanism is suggested and using a MgO–ZrO2 solid solution support strongly improves catalytic performance, which is attributed to effective O2, CO2 and H2O activation at the Ni/MgO–ZrO2 interface.

Mechanical properties of TiC reinforced MgO–ZrO2 composites via spark plasma sintering

We develop the MgO–ZrO2–TiC (MSZ-TiC) composite for improving the mechanical properties. To increase the mechanical hardness, spark plasma sintering technique was used, enabling rapid heating and subsequent quenching for the stabilization of tetragonal zirconia as well as the formation of the composites. Titanium carbide was applied as reinforcing material to improve the fracture toughness. Also, effect of the sintering temperature on phase evolution of the composite is investigated; with increasing sintering temperature, the monoclinic ZrO2 (m-ZrO2) gradually transforms to tetragonal ZrO2 (t-ZrO2), while maintaining the TiC structure. Combined with material characterization, mechanical properties depending on ZrO2 phase in MSZ-TiC are discussed. As a result, increased hardness (16.3 GPa) and fracture toughness (5.2 MPa m1/2) were observed from optimized MSZ-TiC sintered at 1400 °C mainly due to phase transformation of ZrO2. This work can provide an engineering strategy to improve the mechanical properties of ZrO2 based composites, which can be widely applied for industrial application.

Effect of CaCO3 addition on thermal shock resistance of MgO-ZrO2 composites

The effects of CaCO3addition on phase composition, microstructure, sintering and mechanical properties as well as thermal shock resistance (TSR) of MgO–ZrO2 composites were investigated.The results showed that appropriate amount(1-3 wt%) of CaCO3addition could promote sintering and enhance the density and cold strength. However, excessiveCaCO3 addition (5 wt%) led to the increased CO2 derived from CaCO3 decomposition, which had slightly negative effect on sintering.The fracture toughness and residual strength ratio of the samples after thermal shock increased with CaCO3addition, indicating that adding CaCO3 could improve TSR of MgO–ZrO2 composites, and the optimum amount of CaCO3 addition was 3 wt%.The improved TSR of MgO–ZrO2 composites in presence of CaCO3was attributed to the micropores formed by CO2 discharging. Meanwhile, crack deflection and branching increased fracture energy and ZrO2 acted as the bridging particles improving the ability to prevent crack propagation of the composites.

Mechanical properties and machinability of lithium silicate glass-ceramics with varying MgO content

This study focused on the role of lithium metasilicate crystalline phase and microstructural evolution on altering the mechanical properties and machinability of two glass-ceramic system, (Li2O–K2O–Na2O–CaO–MgO–ZrO2–Al2O3–P2O5–SiO2), previously developed by our research group. Our previous study showed that increasing MgO content introduced phase separation and thus controlling the crystallization and microstructure of the glass-ceramics. For this study we chose the glass ceramic system with 1.5 and 4.5 mol% MgO. The glass-ceramics were prepared by melt cast method followed by heat treatment at 650 °C to induce partial crystallization. The crystalline phase in the glass-ceramics was identified by x-ray diffraction and the quantification of crystalline and amorphous phase content was done using Rietveld refinement. The hardness and elastic moduli were measured by nanoindentation. Vickers hardness and fracture toughness were determined by micro indentation. Nano scratch test was performed and scratch morphology was characterized using AFM and FEG-SEM. In order to compare the machinability of the prepared glass-ceramic samples, milling experiments were carried out using CNC milling machine, and machining characteristics were compared by analysing machining force, surface roughness and microstructure of the machined surface. Presence of higher amount of lithium metasilicate (LS) crystals in higher magnesia containing glass-ceramic (G2) resulted in lower average force (Fyrms) as compared to lower MgO containing glass-ceramic. However, due to a wide range of variation in crystal size (150 nm - 2 μm) in higher MgO containing glass-ceramic, the force fluctuation was more than lower MgO containing glass-ceramics.

Fabrication of highly dense Si3N4 via record low‐content additive system for low‐temperature pressureless sintering

AbstractDense Si3N4 ceramics were fabricated by pressureless sintering at a low temperature of 1650°C with a short holding period of 1 h under a nitrogen atmosphere. The role of ternary oxide additives (Y2O3–MgO–Al2O3, Y2O3–MgO–SiO2, Y2O3–MgO–ZrO2) on the phase, microstructure, and mechanical properties of Si3N4 was examined. Only 5 wt.% of Y2O3–MgO–Al2O3 additive was sufficient to achieve >98% of theoretical density with remarkably high biaxial strength (∼1200 MPa) and prominent hardness (∼15.5 GPa). Among the three additives used, Y2O3–MgO–Al2O3 displayed the finest grain diameter (0.54 μm), whereas Y2O3–MgO–ZrO2 produced the largest average grain diameter (∼0.95 μm); the influence was seen on their mechanical properties. The low additive content Si3N4 system is expected to have superior high‐temperature properties compared to the system with high additive content. This study shows a cost‐effective fabrication of highly dense Si3N4 with excellent mechanical properties.

MgO-ZrO2 Ceramic Composites for Silicomanganese Production.

The deterioration of the refractory lining represents a significant problem for the smooth operation in the ferroalloys industry, particularly in the production of silicomanganese, due to the periodic requirements of substitution of the damaged refractory. Within this context, magnesia refractories are commonly employed in the critical zones of the furnaces used in silicomanganese production since the slag involved in the process has a basic character. The behavior of MgO–ZrO2 ceramic composites with different ZrO2 nanoparticles (0, 1, 3, and 5 wt.%) contents in the presence of silicomanganese slags is proposed in this manuscript. XPS, XRD and SEM–EDX were used to evaluate the properties of the ceramic composite against the silicomanganese slag. The static corrosion test was used to evaluate the corrosion of the refractory. Results suggest that corrosion is controlled by the change in slag viscosity due to the reaction between CaZrO3 and the melted slag. Besides, ZrO2 nanoparticles located at both triple points and grain boundaries act as a barrier for the slag advance within the refractory. The utilization of MgO refractories with ZrO2 nanoparticles can extend the life of furnaces used to produce silicomanganese.

Enhancement of thermal shock and slag corrosion resistance of MgO–ZrO2 ceramics by doping CeO2

The purpose of this paper was to develop ceramics materials with high thermal shock resistance and corrosion resistance for preparing gas blowing components. In this paper, MgO-rich MgO–ZrO2 ceramics were obtained by using MgO powder and ZrO2 powder as starting materials and CeO2 as an additive. Changes in the properties in terms of thermal shock resistance, mechanical properties, and slag corrosion-resistance with chemical compositions were examined correlated to microstructure and phase changes. Especially, the effect of doping CeO2 on phase transition of zirconia in MgO-rich system was discussed. The results showed that doping amount of CeO2 significantly improved properties of MgO–ZrO2 ceramics. Especially when doping amount of CeO2 was 2 wt%, residual strength ratio was enhanced over 100% after thermal shock testing. In samples doped with CeO2, ZrO2 was stable in cubic or tetragonal form due to complete solution of CeO2, which was important reason for the improvement of various properties of MgO–ZrO2 ceramics.

Role of MgO in lowering glass transition temperature and increasing hardness of lithium silicate glass and glass-ceramics

The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li2O–K2O–Na2O–CaO–MgO–ZrO2–Al2O3–P2O5–SiO2 glass system has been reported here. Increased amount of MgO enhanced the participation of Al2O3 as a glass network former along with [SiO4] tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (∼10 GPa) and elastic modulus (∼127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.

The main role of the ZrO2–MgO–CaO and ZrO2–MgO–CaO–SiO2 systems in the field of refractories

The increasing severity of the working conditions of refractories together with the necessity of available and economically feasible raw materials have changed the design approaches towards materials experiencing “in situ” modifications during use.The systems ZrO2–MgO–CaO and ZrO2–MgO–CaO–SiO2 are key ones in refractory technology due to the high temperatures for liquid formation involved. Apart from the well-known ZrO2, MgO, MgO-C and MgO·CaO commercial refractories, calcium zirconate (CZ, CaZrO3)-based materials have been proposed due to the low thermal conductivity and high refractoriness of CZ. Naturally occurring minerals as dolomite, baddeleyite or zircon are potential raw material candidates for the fabrication of relatively low cost MgO-CZ-based refractories.This work discusses guidelines for the formulation of basic refractories with CZ-based matrices. The effect of composition on the microstructural development, the mechanical behaviour and the corrosion resistance against cement clinker are discussed.

A combined phase evolution, mechanical and electrical analysis of Mg-PSZ with TiO2 addition

The phase evolution, mechanical properties and electrical properties of 8 mol% MgO–ZrO2 (8 Mg-PSZ) with different amounts of TiO2 are characterized using phase, morphological and electrochemical analyses. The mechanisms for mechanical performance improvement and electrical degradation are also investigated. The addition of TiO2 causes lattice distortion, the appearance of Mg-rich phases at the grain boundaries, grain growth and phase transformation in 8 Mg-PSZ. A significant increase in thermal shock resistance and compressive strength is observed in specimens with 0.5 mol% TiO2. The observed behaviors are explained in terms of second phase (Mg-rich phase) toughness and the creation of microcracks caused by phase transformation and the Mg-rich phase formation. These specimens exhibit a decrease in ionic conductivity due to lattice distortion affecting the mobility of oxygen, Mg-rich phase acting as a barrier to the movement of oxygen vacancies, and the presence of a grain boundary liquid phase acting as a barrier to the diffusion of oxygen.

The Preparation of Dense Materials in the MgO-ZrO2 System by the Application of Nanometric Powders.

Crystallization under hydrothermal conditions allowed us to prepare nanometric powders in the MgO–ZrO2 system of different magnesia concentrations. Sintering runs of these powder compacts studied using dilatometry measurements during heating and cooling revealed essential differences in their behavior. The microstructure of the resulting polycrystal is strongly related to the magnesia content in the starting powder, which strongly influences the phase composition of the resulting material and its mechanical properties. It should be emphasized that the novel processing method of such materials differs from the usual applied technology and leads to magnesia–zirconia materials of a different microstructure than that of “classical” materials of this kind.

Sintering, microstructure, and mechanical properties of vitrified bond diamond composite

The demand for high-performance grinding wheels is gradually increasing due to rapid industrial development. Vitrified bond diamond composite is a versatile material for grinding wheels used in the backside grinding step of Si wafer production. However, the properties of the vitrified bond diamond composite are controlled by the characteristics of the diamond particles, the vitrified bond, and pores and are very complicated. The main objective of this study was to investigate the effects of SiO2–Na2O–B2O3–Al2O3–Li2O–K2O–CaO–MgO–ZrO2–TiO2–Bi2O3 glass powder on the sintering, microstructure, and mechanical properties of the vitrified bond diamond composite. The elemental distributions of the composite were analyzed using electron probe micro-analysis (EPMA) to clarify the diffusion behaviors of various elements during sintering.The results showed that the relative density and transverse rupture strength of the composite sintered at 620 °C were 91.7% and 126 MPa, respectively. After sintering at 680 °C, the glass powder used in this study exhibited a superior forming ability without an additional pore foaming agent. The relative density and transverse rupture strength of the composite decreased to 48.2% and 49 MPa, respectively. Moreover, the low sintering temperature of this glass powder protected the diamond particles from graphitization during sintering, as determined by X-ray diffraction and Raman spectrum. Furthermore, the EPMA results indicate that Na diffused and segregated at the interface between the diamond particles and vitrified bond, contributing to the improved bonding. The diamond particles can remain effectively bonded by the vitrified bond even after fracture.

Interfacial microstructure and strengthening mechanisms of Cf/Mg composite with double-layer interface

In order to overcome the interfacial incompatibility of carbon fiber reinforced magnesium matrix (Cf/Mg) composites, a double-layer interface (ZrO2–MgO) is designed in this work. Carbon fiber was modified with ZrO2 coating by sol-gel process. Microstructural examination reveals that MgO layer forms on the surface of ZrO2 coating by ZrO2 reacting with Mg during the composite fabrication. Such double-layer interface could inhibit Al4C3 and hence prevent fiber damage. Meanwhile, the wettability was improved for the reaction between ZrO2 and Mg. Thus the tensile strength of ZrO2-Cf/AZ91D composite was 68.0% higher than that of the unmodified one. Due to the fiber bundle pull-out, debonding and crack deflection, the toughness of Cf/Mg composite with double-layer interface is increased simultaneously.

МЕХАНИЧЕСКИЕ И ТРИБОЛОГИЧЕСКИЕ СВОЙСТВА ЗАЩИТНО-ВОССТАНОВИТЕЛЬНЫХ ПОКРЫТИЙ РАБОЧЕЙ ФАСКИ КЛАПАНОВ ДВИГАТЕЛЕЙ ВНУТРЕННЕГО СГОРАНИЯ

Over the past 7-10 years, there has been a steady increase in the cost of gasoline and gas fuel. This circumstance forces the enterprises operating automotive equipment to switch to the use of gas-powered fuel. (Research purpose) The research purpose is in creating a protective and recovering coating that can withstand the wear of the working chamfer of the valve caused by high operating temperatures, dry friction in the valve–seat interface, as well as high flow rates of exhaust gas. (Materials and methods) The article presents an analysis of a priori information, which resulted in the following powder compositions: Ni- ZrO2-SiC; Ni–B4C–BN–ZrO2; Ni–B4C–ZrO2–MgO; Ni-B4C. The samples were subjected to tests on the SMT 2070 friction machine under boundary friction conditions to determine the tribological parameters of coatings made of these materials. The parameters of the friction moment and the coefficient of friction were taken during the tests, depending on the applied load on the tribo-coupling. (Results and discussion) At the first stage of the research, the microhardness of the coatings was analyzed. Tribological studies were performed depending on the microhardness of the coatings. Along with the economic effect, there are negative factors that affect the performance of the valve-seat coupling: increased temperatures up to 750-800 degrees Celsius, the transition to dry friction, high exhaust rates of combustion products (over 1000 meters per second). The best value of the coefficient of friction obtained during the tests belongs to the composition Ni–ZrO2–SiC, which takes values below 0.1. (Conclusions) The use of standard and well-known methods of protecting the working chamfer of the valve in this case is ineffective, since it does not provide the required operating conditions. The article recommens the use of Ni-ZrO2-SiC as the material of the protective and restorative coating of the working chamfer of the valve.

Porous Zirconia/Magnesia Ceramics Support Osteogenic Potential In Vitro.

Porous zirconia (ZrO2), magnesia (MgO) and zirconia/magnesia (ZrO2/MgO) ceramics were synthesised by sintering and designated as ZrO2(100), ZrO2(75)MgO(25), ZrO2(50)MgO(50), ZrO2(25)MgO(75), MgO(100) based on their composition. The ceramic samples were characterised by means of scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and atomic absorption spectrometry to explore the incorporation of Mg atoms into the zirconia lattice. The resulting porosity of the samples was calculated based on the composition and density. The final porosity of the cylinder-shaped ceramic samples ranged between 30 and 37%. The mechanical analysis exhibited that the Young modulus increased and the microstress decreased with increasing magnesia amount, with values ranging from 175 GPa for zirconia to 301 GPa for magnesia. The adhesion, viability, proliferation and osteogenic activity of MC3T3-E1 pre-osteoblastic cells cultured on the zirconia/magnesia ceramics was found to increase, with the magnesia-containing ceramics exhibiting higher values of calcium mineralisation. The results from the mechanical analysis, the ALP activity, the calcium and collagen production demonstrate that the zirconia/magnesia ceramics possess robust osteoinductive capacity, therefore holding great potential for bone tissue engineering.

High performance and stable mesoporous MgO–ZrO2 supported Ni catalysts for dry reforming of methane

Catalysts for dry reforming of methane (DRM) based on Ni are used widely. However, due to carbon deposition or active metal sintering, deactivation is inevitably attached to these catalysts. Ni catalysts supported on mesoporous MgO–ZrO2 have been synthesized by surfactant-assisted route and impregnation method, and their catalytic performance for DRM reaction has been investigated in this study. The specific surface area of the mesoporous support is approximately 64.7 ​m2 ​g−1 after calcination at 700° for 2 ​h. Catalyst with 10 ​wt% Ni content shows the best catalytic performance. The conversion rates of CH4 and CO2 are higher than 80%, while the selectivity values of CO and H2 are higher than 90%. After a long-term DRM test, according to the weight loss by TG, the catalysts carbon deposition with 7.5 ​wt% and 10 ​wt% content are 46.2% and 19.9%, respectively.

Fractal Dimension of the Fracture Surface of Porous ZrO2–MgO Composite

Fractal Dimension of the Fracture Surface of Porous ZrO2–MgO Composite