Sintering Of MgO Research Articles

Effect of MgO sintering additive on mullite structures manufactured by fused deposition modeling (FDM) technology

An optimized recipe for 3D printing of Mullite-based structures was used to investigate the effect of MgO sintering additive on the processing stages and final ceramic properties. To achieve dense 3:2 mullite, ceramic filaments were prepared based on an alumina powder, a methyl silicone resin, EVA elastomeric binder and MgO powder. Using 1 wt% MgO and a dwell time of 5 h at 1600 °C, a dense mullite structure could be obtained from filaments with a diameter of 1.75 mm. Ceramic structures with and without sintering additive were printed in vertical and horizontal direction, to investigate the effect of printing direction on mechanical strength after sintering. Using four-point bending test, it was demonstrated that by using MgO, the printing orientation did not affect the mechanical strength significantly anymore. The low Weibull modulus could be explained by the closed porosity that emerge during the degassing of the preceramic polymer due to cross-linking.

BRUCITE-BASED MAGNESIUM PHOSPHATE BONDING AGENT, ITS ANALYSIS AND APPLICATION FOR PERICLASE SINTERING

Some results on magnesium phosphate binder obtained from natural brucite (mainly Mg(OH)2) and H3PO4 were discussed. Hereafter, it was named brucite phosphate (BPB). This binder then was used to the sintering of MgO (periclase). MgO is one of the most high-refractory materials and chemically stable to various aggressive mediums, so the aim was presented as actual. To determine the phase composition data on sample weight loss in different temperature intervals were compared. All weight losses were related to the multistage water moving away. Up to 140 °С it was the removal of crystalline hydrate water. Then monosubstituted magnesium hydrophosphate transformed into MgH2P2O7 and Mg2P4O12, that in principle was in accordance with literature data. Dehydration was accompanied with appropriate endothermal effects. There was a slight exothermal effect which could relate to a structure rearrangement (cyclization) of primary magnesium metaphosphates and/or some crystallization of anhydrous cyclophosphates from primarily obtained amorphous phase non-connected with a weight loss in the interval of 450-575 °С. At 500–1000 °С the phase composition remained constant that was in a good accordance with data obtained by other methods. By means of IR-spectroscopy, it was confirmed the formation of structure cycles composed from oxygen-phosphor tetrahedrons. To determine kinetics parameters of periclase sintering with BPB it was used a model being proposed that took the role of a physical consolidation and a chemical binding in the presence of binder into account under heating. The obtained parameters analysis showed that the forming conglomerate strength was provided with the sintering properly as well as with binder action; an estimated chemical factor contribution was maximal at low temperatures (1100-1200 °C). The activation energy value was practically identical to the activation energy of oxygen diffusion in MgO.

Effect of MgO doping on the structure and optical properties of YAG transparent ceramics

The paper studies the features of Mg2+ ions as sintering aid for reactive solid-state sintering of YAG transparent ceramics. Phase composition, microstructure and optical properties of YAG ceramics, doped by 0 ÷ 0.15 wt.% MgO, were investigated. Solubility limit of Mg2+ ions in YAG crystal lattice was found to be in the range of 0.06 ÷ 0.1 wt.% of MgO additive. Substitution mechanism of Mg2+ in ceramic YAG was identified by comparison of XRD data and ab initio calculation. It was shown that within the solubility limit Mg2+ ions most likely substitute Al3+ sites. Doping by MgO above solubility limit led to precipitation of spinel secondary phases. It was found that doping by Mg2+ ions increases concentration of oxygen vacancies in YAG lattice that effectively promote sintering. The optimal concentration range of MgO sintering aid that allow to achieve YAG transparent ceramics was defined as 0.03 ÷ 0.06 wt.%.

Effects of B2O3 and MgO on the microwave dielectric properties of MgTa2O6 ceramics

MgTa2O6 is a very promising microwave dielectric material, but the residual Ta2O5 which produced during the reaction process of MgO and Ta2O5 with stoichiometric ratio limits its further development. In this study, B2O3 and MgO sintering additives were applied to reduce Ta2O5 phase and enhance the microstructure and microwave dielectric properties. Results show that B2O3 has an advantages over MgO in improving the material properties, the best microwave dielectric properties (εr = 27.8, Qf = 184000 GHz, τf = 53 ppm/oC) were acquired at x(B2O3) = 0.5 wt%. The mechanisms of both B2O3 and MgO additives were analyzed in detail.

High thermal conductivity silicon nitride ceramics prepared by pressureless sintering with ternary sintering additives

AbstractSilicon nitride ceramics were pressureless sintered at low temperature using ternary sintering additives (TiO2, MgO and Y2O3), and the effects of sintering aids on thermal conductivity and mechanical properties were studied. TiO2–Y2O3–MgO sintering additives will react with the surface silica present on the silicon nitride particles to form a low melting temperature liquid phase which allows liquid phase sintering to occur and densification of the Si3N4. The highest flexural strength was 791(±20) MPa with 12 wt% additives sintered at 1780°C for 2 hours, comparable to the samples prepared by gas pressure sintering. Fracture toughness of all the specimens was higher than 7.2 MPa·m1/2 as the sintering temperature was increased to 1810°C. Thermal conductivity was improved by prolonging the dwelling time and adopting the annealing process. The highest thermal conductivity of 74 W/(m∙K) was achieved with 9 wt% sintering additives sintered at 1810°C with 4 hours holding followed by postannealing.

Mechanical and thermal properties of graphene nanosheets/magnesia composites

Abstract Highly dense graphene nanosheets (GNSs)/magnesia (MgO) composites were prepared by hot-pressing. The effect of GNSs content (0 vol%–7 vol%) on microstructural, mechanical and thermal properties was evaluated, and the mechanisms were identified. Incorporating GNSs inhibited the sintering and grain growth of MgO and produced a significant strengthening and toughening effect. With the increase in GNSs content, both flexural strength and fracture toughness increased and then decreased: the highest strength of 265 MPa and toughness of 3.3 MPa m 1/2 were obtained at 2 vol%, increasing by 37.3% and 32%, respectively, compared with monolithic MgO. Vickers hardness and modulus declined linearly. Thermal conductivity in the hot pressing direction decreased from 55.8 W/(m K) for MgO to 33.9 W/(m K) for 7 vol% GNSs/MgO. With the increase in temperature, both monolithic MgO and 2 vol% GNSs/MgO exhibited a decrease in thermal conductivity, which tended to be consistent and constant beyond 700 °C. The 2 vol% GNSs/MgO composite also showed nearly the same CTE as that of monolithic MgO.

Rapid and uniform in-situ solidification of alumina suspension via a non-contamination DCC-HVCI method using MgO sintering additive as coagulating agent

Abstract A novel rapid, uniform and non-contamination in-situ solidification method for alumina suspension by DCC-HVCI method using MgO sintering additive as coagulating agent was reported. MgO was used to release Mg2+ in suspensions via reaction with acetic acid generated from glycerol diacetate (GDA) at elevated temperature as well as to improve density and suppress grain growth of alumina ceramics during sintering. Influence of adding 0.7 wt% MgO with 2.0 vol% GDA in alumina suspension on coagulation process and properties of green bodies and sintered samples were investigated. It was indicated that the controlled coagulation of the suspension could be achieved after treating at 70 °C for 10 min. Homogeneous composition distribution of Mg element in EDS result indicated the uniform solidification of suspensions. Compressive strength of wet-coagulated bodies is 2.09±0.25 MPa. Dense alumina ceramics with relative density of 99.2% and flexural strength of 354±16 MPa sintered at 1650 °C for 4 h present homogeneous microstructure. The result indicated that the novel DCC-HVCI method via a sintering additive reaction with no contamination, short coagulation time and uniform in-situ solidification is a promising colloidal forming method for preparing high-performance ceramic components with complex shape.

Highest UV–vis transparency of MgAl2O4 spinel ceramics prepared by hot pressing with LiF

Reaction sintering of MgO and Al2O3 with addition of LiF as sintering additive was used to prepare MgAl2O4 spinel ceramic by hot pressing. The process parameter (temperature, pressure, dwell time), the stoichiometric ratio of MgO to Al2O3 and the selection of the alumina raw powder are equally important for highest transparency of the spinel ceramic. With this optimization highest transparency of 86% in the visible range at λ=640nm together with UV transmission of 62% at 200nm for spinel ceramic with 4mm thickness was reached.

Effect of ball milling on reactive microwave sintering of MgO-TiO2 System

Abstarct In this paper, effect of mechanical activation on microwave reactive sintering of MgO - TiO2 system was investigated. Mixtures of MgO and TiO2 were milled at different times. Mixed powders along with 10 h milled powders were chosen for microwave sintering between 1000- 1400⁰C. Results showed that increasing of temperature up to 1400C for mixed powders could not give rise to complete formation of Magnesium titanate phases and raw materials were in the products. Also the densities of these samples were about 3 g/Cm3. With milling of reactants up to 10 h, it seems reactions could be completed at 1000⁰C and the density was augmented to 3.58 g/Cm3. The samples were sintered at 1400⁰C in a microwave furnace exhibited good microwave dielectric properties while er and tan δ were 16.3 and 0.0001 respectively.

Effect of N2 pretreatment on the basicity, structural change, and isomerization activity of MgO and MgO/Mg(OH)2 catalysts

AbstractAs revealed by the X‐ray diffraction, basicity titration, and Fourier transform infrared spectroscopy results, changes in the structural properties, basicity, and isomerization activities were observed on the MgO catalysts upon N2 pretreatment at 325 °C followed by isomerization reaction at 125 °C. These changes became less pronounced when the starting catalysts contained Mg(OH)2 phase or when the catalysts were pretreated under N2 at high temperature alone (without reaction). Because of the limited amount of O2 during 1‐butene isomerization, the single‐phase MgO could transform into the mixed MgO/Mg(OH)2 catalysts, and the basicity and the isomerization activity were enhanced. Higher temperature pretreatment (i.e. 527 °C), however, led to the changes of Mg(OH)2 back to the single MgO phase and/or sintering of MgO. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.

The Influence of Magnesia Addition and Sintering Temperature on The Properties of Synthesized Electrical Porcelain

The influence ofmagnesia (MgO) content at different sintering temperatures on the physical and dielectric properties of synthesized electrical porcelain was investigatied.Feldspar is one of the major components of porcelain,since feldspar is not available in Iraq, so it was synthesized from Iraqi raw materials.MgO was progressively added in the range (2-30 wt. %) into electrical porcelain. The composed bodies were sintered at temperature in the range(1200-1350 C),Physical properties such bulk density, open porosity beside the Vickers microhardness and dielectric properties such as dielectric constant, loss tangent and dielectric loss factor were measured. The improvement of these properties could associate with an increasing of MgOadditive and sintering temperatures. Bulk density, microhardness and dielectric constant are increased with the increasing of MgO content and sintering temperatures. The results reveal that the highest value of density at 30wt. %MgO and at 1350 C for density, hardness and dielectric constant, while it has the lowest value for porosity and loss tangent.

Preparation and properties of Al2O3–MgAl2O4 ceramic foams

In this work, a series of alumina (Al2O3)–magnesium aluminate (MgAl2O4) ceramic foams (AMCFs) were fabricated from powders of fused white corundum and magnesia (MgO) by a polymeric foam replication method combined with a reaction sintering process. The effects of MgO content and sintering temperature on the sintering properties and post-sintering properties of the AMCFs such as phase composition, appearance, microstructure, cold compressive strength and thermal shock resistance have been investigated. During the sintering process, MgO reacted with Al2O3 to form MgAl2O4 ceramic phase, which contributed to the improvement in sintering properties, cold compressive strength and thermal shock resistance of the AMCFs. The AMCFs doped with 8wt% MgO and sintered at 1450°C for 2h displayed high cold compressive strength of 0.89MPa, good sintering properties and thermal shock resistance. Although their apparent porosities were about 87%, the cold compressive strength of as-prepared foam was about 1.3 times higher than that of commercial Al2O3 foam.

Effects of Li2O3–B2O3–SiO2 addition on dielectric properties and microstructure of MgO–TiO2–ZnO–CaO ceramics

The effect of Li2O3–B2O3–SiO2 (LBS) liquid-phase additives on the sintering, microstructures, and dielectric properties of MgO–TiO2–ZnO–CaO (MTZC) ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the dielectric properties of MTZC ceramics could be greatly improved by adding a small amount of LBS solution additives. With the addition of 10 wt% LBS, the ceramics sintered at 900 °C showed favorable dielectric properties with er = 21.7, Qf = 5.0 × 104 GHz, and TCF = −21.6 ppm/ °C. The distructive physical analysis showed an excellent co-firing interfacial behavior between the MTZC ceramic and the Ag electrode. It indicated that MTZC ceramics with LBS solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology.

앵커용 알루미나 세라믹의 기계적 강도에 대한 MgO 첨가제와 소결온도 영향

앵커용 알루미나 세라믹의 기계적 강도에 대한 MgO 첨가제와 소결온도 영향

Sintering and Performance of MgO from Bischofite with ZrO<sub>2</sub> Additive

Effect of ZrO2 on sintering properties of MgO prepared from natural brine from Qarhan Salt Lake, crystalline bischofite and MgCl2·6H2O(AR) was studied. The results showed that ZrO2 of addition exceeded 1 wt% had promotive effect on sintering of magnesia prepared from MgCl2·6H2O(AR). While 1.5 wt% ZrO2 was added, the bulk density of sample was 3.37 g/cm3, and relative density was 94.1%. With 1 wt% ZrO2, the bulk densities of magnesia prepared from crystalline bischofite and brine were 3.10 and 3.27 g/cm3, and the relative densities increased by 10.0% and 19.6%, respectively. The main reasons for promoting MgO sintering with ZrO2 were that monoclinic phase ZrO2 converted to cubic phase Zr2O and excess ZrO2 reacted with MgO to generate Mg0.13Zr0.87O1.87, which activated lattice and promoted the diffusion of ions during sintering process. In addition, liquid phase sintering was also one of the main reasons for promoting the sintering of brine magnesia.

Effect of LiCl·H<sub>2</sub>O on Sintering Properties of MgO from Bischofite

Effect of LiCl·H2O on sintering properties of MgO prepared from natural brine from Qarhan Salt Lake, crystalline bischofite and MgCl2·6H2O(AR) was studied. The results showed that LiCl·H2O of addition exceeded 1 wt% had promoting effect on sintering of magnesia prepared from MgCl2·6H2O(AR). While 1.5 wt% LiCl·H2O was added, the bulk density of magnesia was 3.40 g/cm3, and the relative density was 95.0%. With 0.5 wt% LiCl·H2O, the bulk densities of magnesia prepared from crystalline bischofite and brine were 3.04 and 3.10 g/cm3, and the relative densities increased by 8.4% and 14.8%, respectively. The main mechanism for promoting MgO sintering with LiCl·H2O was that Li2O produced by hydrolysis solubilized in MgO to form solid solutions and oxygen vacancies which were favorable to sintering. The main reasons for promoting sintering of brine magnesia with LiCl·H2O were solid solution and liquid phase sintering, while the main reason was solid solution for magnesia from crystalline bischofite and MgCl2·6H2O(AR).

Effect of TiO2 on Sintering and Grain Growth Kinetics of MgO from MgCl2·6H2O

The effect of TiO2 on the grain growth kinetics of MgO prepared from MgCl2·6H2O was studied by the tradition phenomenological rate equation. The results showed that the addition of TiO2 decreased the activation energy of MgO grain growth, accelerated the growth rate of MgO grain, and markedly promoted the sintering of MgO. Without TiO2 addition, the MgO grain growth exponent \( n \) was 3, the grain growth activation energy \( Q \) was 556.9 kJ·mol−1, and the process was considered as volume diffusion controlled. With 0.2 wt pct TiO2 addition, the MgO grain growth exponent \( n \) was 2, the grain growth activation energy \( Q \) was 272.8 kJ·mol−1, and the process was considered as interface diffusion controlled. The apparent and closed porosities of MgO-0.2 wt pct TiO2 sample were decreased significantly, and the bulk density increased to 3.49 g·cm−3 (relative density is 97.5 pct). The main mechanism of TiO2 promoting the sintering of MgO was that TiO2 solubilized in MgO to form unequivalence substitutional solid solutions and cation vacancies that were favorable to cation diffusion.

Properties and rapid consolidation of nanostructured MgO–MgAl 2O 4 composites

The rapid sintering of nanostructured MgO–MgAl 2O 4 composites was investigated with a high-frequency induction heated sintering process. The advantage of this process is that it allows for very quick densification to near theoretical density and prohibits grain growth in nanostructured materials. Highly dense nanostructured MgO–MgAl 2O 4 composites were produced with simultaneous application of 80 MPa pressure and an induced output current of total power capacity (15 kW) within 2 min. The sintering behaviors, grain sizes and mechanical properties of MgO–MgAl 2O 4 composites were investigated.

Influence of intergranular phases on edge integrity of Si 3N 4/SiC wood cutting tools

Si 3N 4/SiC composites used for industrial wood cutting were processed by a near net shape route involving gas pressure sintering with sintering additives such as Al 2O 3, La 2O 3, Y 2O 3 and MgO. The cutting edge integrity of these knives was tested in a cutting trial and compared to knives made by a hot pressing route. It was found that the intergranular phase has a crucial influence on the cutting edge integrity. The boundary phase was analysed by EFTEM and EDX mapping on TEM samples: in gas pressure sintered composites the crystallisation of the apatite Y 5Si 3O 12N phase was identified. In the hot pressed composite the boundary phase consisted only of silicates. These composites showed better edge stability than cutting tools with a Y–N-apatite phase. The formation of the type of intergranular phase was found to be determined by the amount of MgO sintering aid and the temperature of the post sintering heat treatment.

The effects of MgO doping and sintering temperature on the microstructure of the lead-free piezoelectric ceramic of Bi 0.5Na 0.5TiO 3

This study investigates the effects of adding MgO and a sintering temperature on the microstructure, as well as the relative density of a disk of the lead-free piezoelectric ceramic of Bi 0.5Na 0.5TiO 3 doped with MgO (BNT-MgO), prepared using the mixed oxide method. Three kinds of starting powders (such as Bi 2O 3, Na 2CO 3 and TiO 2) were mixed and calcined. This calcined BNT powder and a certain weight percentage of MgO were mixed, sintered, and compressed into a green compact of BNT-MgO. This green compact of BNT-MgO was sintered to be a disk doped with MgO, and its characteristics (such as density and microstructure) were measured. At a fixed wt.% of MgO, as the sintering temperature increased, the grain size of the disk increased, but the relative density of the disk decreased. The largest relative density of the disk obtained in this study was 98.0% at a sintering temperature of 1000 °C and with 1.0 wt.% of MgO. This study shows that adding MgO to the BNT not only improves the relative density of the disk, but it also lowers the sintering temperature.