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1.
《Ceramics International》2022,48(4):5162-5167
Calcium alumino-titanate (CAT), a secondary material obtained from ferrotitanium slag, was used as a hibonite source to prepare CaAl12O19–MgAl2O4–Al2O3 castables. The restructuring effect of CAT aggregate was compared by replacing tabular alumina aggregates with CAT aggregates of different particle sizes. The effects of CAT particle size on cold mechanical strength and thermal shock resistance of CaAl12O19–MgAl2O4–Al2O3 castables were studied. The results showed that CAT aggregates with particle size of 5–3 or 3–1 mm led to more internal cracks or pores and reduced the cold mechanical strength of the castable samples fired at 1600 °C for 3 h. The use of CAT aggregates with particle size of 1–0 mm led to the formation of a well-bonded CAT aggregate and matrix, improving the cold mechanical strength and thermal shock resistance of the castable samples fired at 1600 °C for 3 h. The enhancement mechanism of fine CAT aggregates in this process was proposed based on the sintering of the matrix–aggregate interface with the formation of Ca(Al, Mg, Ti)12O19. 相似文献
2.
《Journal of the European Ceramic Society》2022,42(6):2994-3003
Transparent MgAl2O4 ceramics were bonded by using CaO-Al2O3-SiO2 (CAS) glass filler. The CAS glass filler exhibited the same thermal expansion behavior as MgAl2O4 ceramic and excellent wetting ability on the surface of MgAl2O4 ceramic. When the cooling rate of 15 °C/min was used, no interfacial reaction was observed and the amorphous brazing seam could be obtained. However, low joining temperature (1250 °C) led to the formation of pores and high joining temperature (1400 °C) resulted in the formation of cracks. Furthermore, the slow cooling rate of 5–10 °C/min induced the crystallization of CaAl2Si2O8 and Mg2Al4Si5O18 due to the dissolution of MgAl2O4 substrate. The optimal flexural strength of 181–189 MPa was obtained when the joining temperature and cooling rate were 1300–1350 °C and 15 °C/min respectively. Moreover, the in-line transmittance of the joint at 1000 nm was 82.1%, which was slightly lower than that of MgAl2O4 ceramic (85.6%). 相似文献
3.
Yury V. Bykov Sergei V. Egorov Anatolii G. Eremeev Vladislav V. Kholoptsev Ivan V. Plotnikov Kirill I. Rybakov Andrei A. Sorokin Stanislav S. Balabanov Alexander V. Belyaev 《Journal of the American Ceramic Society》2019,102(2):559-568
MgAl2O4 samples were microwave sintered to near-full density in rapid processes with heating rates on the order of 100°C/min and zero isothermal hold. The experiments were carried out using a gyrotron system for microwave processing of materials operating at a frequency of 24 GHz with a maximum power of 6 kW. In the regimes with a preset heating rate sustained by the automatically regulated microwave power, the maximum achieved density was about 95% of the theoretical value in pristine MgAl2O4 samples (maximum sintering temperature 1650°C) and about 97% in 1 wt.% Y2O3-doped samples (1700°C). In the regimes with a fixed microwave power (about 3.5 kW), translucent spinel samples with a relative density above 99% were obtained at 1700°C. The duration of the high-temperature stage of sintering was 1.5-10 minutes. The suggested mechanism responsible for the enhanced densification involves development of a thermal instability and formation of transient liquid phases at grain boundaries. The estimated specific absorbed power in the samples during the high-temperature stage of ultra-rapid microwave sintering was 27-80 W/cm3, similar to the values observed in dc field-assisted flash sintering experiments. 相似文献
4.
《Journal of the European Ceramic Society》2023,43(12):5330-5338
The La2O3-SiO2-B2O3 (LSB) glass filler with high softening temperature was first used to join MgAl2O4 ceramic. An interfacial layer composed of Al2O3 was formed due to the solubility difference of MgO and Al2O3 in the LSB glass filler. As a result, the addition of Al2O3 into the LSB glass filler caused the increase of interfacial layer thickness. On the contrary, the addition of MgO into the LSB glass filler led to the decrease of interfacial layer thickness. When the adding content of MgO was 6 wt%, the interfacial layer disappeared and completely amorphous brazing seam was obtained. The in-line transmittance of joints decreased with the increase of the thickness of interfacial layer. The optimal in-line transmittance of joint bonded with La2O3-SiO2-B2O3-MgO (LSB6M) glass filler reached 82.9% at 1000 nm. Meanwhile, the average flexural strength of joints was about 196.2 MPa, which was equal to the strength of MgAl2O4 substrate. 相似文献
5.
《Ceramics International》2023,49(8):12551-12562
Magnesium aluminate (MgAl2O4) spinel has grasped considerable attention in high-temperature application by right of its excellent properties. However, the poor sintering behavior of MgAl2O4 is detrimental to its further development. In the present work, the application of isostructural heterogeneous nucleation method provides a novel idea for optimizing the sintering behavior of refractory materials. A series of (1-x)MgAl2O4-xMg2TiO4 (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) spinel solid solutions with a present ration of components were fabricated from light calcined magnesia, reactive alumina and pre-preparation Mg2TiO4. The effect of Mg2TiO4 heterogeneous nucleating agent on the crystalline phase, densification, and microstructure evolution of MgAl2O4–Mg2TiO4 spinel solid solutions was studied. The XRD, XPS, and EDS results showed that Mg2TiO4 entered the lattice of MgAl2O4 to form a spinel solid solution, and the heterovalent substitution process was identified, where Ti4+ and Mg2+ ions of larger radius in the Mg2TiO4 replaced the Al3+ of smaller radius in the MgAl2O4. For the sample at x = 0.08, the spinel solid solutions exhibited the optimized densification with a relative density of 93.3%, an apparent porosity of 1.2%, and a compressive strength of 84.5 MPa. A significant increase in densification was related to the lattice distortion induced by ion size mismatch during the heterovalent substitution, thus accelerating the diffusion rate of Mg2+ and Al3+ ions in the spinelisation state. Moreover, the solid solubility content of Ti4+ in the MgAl2O4–Mg2TiO4 spinel solid solutions had a significant effect on the grain morphologies. The Mg2TiO4 heterogeneous nucleating agent significantly increased the spinelisation rate of MgAl2O4 spinel with negligible effect on densification. 相似文献
6.
《Ceramics International》2020,46(13):21351-21359
The luminescence properties of ceramic phosphors based on two spinel hosts MgAl2O4 and ZnAl2O4 doped with manganese ions have been studied. It has been found that the spectral properties of these phosphors can be strongly varied by changing synthesis conditions. Both types of doped ceramic spinel can serve as efficient Mn2+ green-emitting phosphors having peak emissions at 525 and 510 nm, respectively. Mn-doped MgAl2O4 spinel can also be prepared as an efficient Mn4+ red-emitting phosphor having peak emission at ~651 nm by using specific temperatures of heat treatment in air. It has also been shown that the conversion of Mn2+ to Mn4+ and viсe versa, as well as the coexistence of Mn2+ green and Mn4+ red emissions, can be accomplished by properly chosen annealing conditions of the same initially synthesized MgAl2O4:Mn sample. Manganese doped MgAl2O4 spinel with an optimal intensity ratio of green and red emissions can be a promising single-phase bicolor phosphor suitable for the development of warm white phosphor-converted LED lamps. On the other hand, it has been determined that perfectly normal ZnAl2O4 spinel cannot be doped with Mn4+ ions in contrast to partially inverse MgAl2O4 spinel. However, ZnAl2O4 samples unintentionally doped with impurity Cr3+ ions show emission spectra in the far-red region with well pronounced R, N and vibronic lines of Cr3+ luminescence due to the perfect normal spinel structure of synthesized ZnAl2O4 ceramics. Also, by partially substituting Al3+ cations for Mg2+ in ZnAl2O4 there is an opportunity to obtain Mn4+ doped or Mn4+/Cr3+ codoped far-red emitting phosphors which can be suitable for indoor plant growth lighting sources. 相似文献
7.
N. N. Eremin R. A. Talis A. E. Grechanovskii V. S. Urusov 《Glass Physics and Chemistry》2013,39(5):555-562
An original method of the atomistic computer modeling of substitutional solid solutions is applied to the noble spinel MgAl2O4-magnesia chromite MgCr2O4 binary system. The parameters of the interatomic potentials in the partially ionic approximation are optimized using the experimental values of the structural, elastic, and thermodynamic characteristics of these minerals. The point defect formation energy is estimated. The modeling of Mg(Al x Cr1 ? x )2O4 solid solutions is carried out in a supercell of the 4 × 4 × 4 structural type of spinel that contains 3584 atoms; the GULP 3.4.9 program, which is implemented in the SKIF Chebyshev supercomputer (Moscow State University), is used. The mixing properties of the solid solution such as the mixing enthalpy, the interaction parameters, the mixing volumes, the deviations of the compression moduli from additivity, and the oscillatory entropy were determined. Calculations of the Gibbs energy have yielded the assessments of the stability fields of the MgAl2O4-MgCr2O4 solid solution and the comparisons of these assessments with the experimental data. Histograms of interatomic spacings are plotted and the values of the relaxation parameters of the Cr-O and Al-O bonds are estimated; these values agree well with the experimental values obtained by measuring the optical absorption spectra on a Cr3+ ion. 相似文献
8.
9.
Jeffrey D. Smith James G. Hemrick 《International Journal of Applied Ceramic Technology》2014,11(6):1020-1024
Aluminum oxide must take a spinel form (γ‐Al2O3) at increased temperatures in order for extensive solid solution to form between MgAl2O4 and α‐Al2O3. The solvus line between MgAl2O4 and Al2O3 has been defined at 79.6 wt% Al2O3 at 1500°C, 83.0 wt% Al2O3 at 1600°C, and 86.5 wt% Al2O3 at 1700°C. A metastable region has been defined at temperatures up to 1700°C which could have significant implications for material processing and properties. Additionally, initial processing could have major implications on final chemistry. 相似文献
10.
《Ceramics International》2023,49(2):2486-2494
Co-doped CaCu3Ti4O12 samples were synthesized by solid-phase reaction. Electrical properties were studied by impedance spectroscopy in wide temperature (25–450 °C) and frequency (10 Hz–10 MHz) intervals. It was shown that the presence of the copper oxide interlayer significantly reduces the value of the dielectric constant. The amount of impurity copper in the CaCu3Ti4-хCoхO12-δ samples (x = 0.06; 0.12; 0.24) rise with an increase in the cobalt content. The samples are characterized by a granular microstructure, with an average grain size ranging from 2 to 10 μm. The impedance of the samples was simulated at a temperature of 25 °C and in the range of 100–450 °C. It was found that the samples are characterized by low- and high-frequency polarization. The conductivity activation energy varied from 0.94 to 0.87 eV depending on the cobalt content. The CaCu3Ti3.94Co0.06O12-δ sample are characterized by the best values of the dielectric permittivity and the dielectric loss tangent, ε = 400 and tanδ = 0.2 (at 1 MHz and room temperature), respectively. 相似文献
11.
《Ceramics International》2023,49(10):15164-15175
Magnesium aluminate spinel (MgAl2O4) ceramics are high-performance and carbon-free materials widely used in both military and civilian fields. However, it is usually challenging to densify during the solid-state sintering process. The excellent properties of some rare earth oxides have been proved to promote the densification of MgAl2O4 spinel ceramics. But the mechanism of promoting sintering is not clear. In the present work, MgAl2O4 spinel ceramics have been successfully fabricated by co-doping CeO2 and La2O3 via a single-stage solid-state reaction sintering. The effects of addition amounts of CeO2 and La2O3 on phase compositions, microstructures, sintering characteristics, cold compressive strength, and thermal shock resistance of as-prepared MgAl2O4 spinel ceramics were systematically investigated. The results show that by co-doping CeO2 and La2O3 can increase the defect concentration due to the lattice distortion. This could promote the movement of Al3+ and Mg2+ at high temperature, which is beneficial to the formation of more secondary MgAl2O4 spinel. t-ZrO2 with more Ce4+ filling between spinel grains could prevent the growth of grains and promote the densification, besides the new-formed LaAlO3 that was mainly distributed along the grain boundary of the MgAl2O4 phase, both of which were favorable for the formation of dense microstructure of MgAl2O4 spinel materials. At the same time, the formation of more secondary MgAl2O4 spinel and sintering densification also improve the mechanical properties of spinel ceramics. La3+ will segregate to the spinel grain boundary, preventing grain boundary movement and absorbing the main crack's fracture energy. With 3 wt% CeO2 and 3 wt% La2O3 co-doping, the bulk density of the sample increased from 3.02 g∙cm−3 to 3.55 g∙cm−3; the apparent porosity decreased from 12.21% to 9.97%; the cold compressive strength increased from 172.88 MPa to 189.54 MPa; and the residual strength retention ratio after thermal shock increased from 84.92% to 89.15%. 相似文献
12.
Conclusions The interaction was studied between MgAl2O4 and MgCr2O4 spinels (and their solid solutions and compositions with periclase) with calcoferruginous melts, which are the essential constituents of various slag reagents.On exposure to a highly basic calcoferruginous melt, the magnesium-aluminum spinel forms magnesio-ferrite, brownmillerite, and some calcium aluminate.On interaction of magnesiochromite with calcium ferrite, chiefly high-temperature compounds form.With the action of highly ferruginous melts on magnesiochromite, the resulting solid solution increases in volume, and a distortion is observed at the boundary of the reaction and little-change zones of the samples.The addition of granular MgO to spinels or their solid solutions improves the chemical stability of the compositions against calcoferruginous melts [4].During use in contact with highly basic calcoferruginous melts, the addition of periclase to chromium spinellide additives is recommended; for use in contact with highly ferruginous melts, periclase and aluminum spinellide compositions are recommended.Translated from Ogneupory, No. 7, pp. 44–47, July, 1969. 相似文献
13.
V. M. Ust'yantsev M. G. Tretnikova L. B. Khoroshavin I. L. Shchetnikova D. S. Rutman 《Refractories and Industrial Ceramics》1973,14(1-2):122-124
Conclusions A study was made of the reaction between spinels MgAl2O4 and MgCr2O4 with orthophosphoric acid and sodium chromophosphate bond. The setting of the material is related to the formation of various hydrated phosphates and hydrates. During heating complex phase inversions take place, with the formation of intermediate compounds. At elevated temperatures the stable phases are spinels.Translated from Ogneupory, No. 2, pp. 53–55, February, 1973. 相似文献
14.
The addition of C/MgAl2O4 composite powders can improve the thermal shock resistance of low-carbon Al2O3–C refractories attribute to the formation of microcracks in the agglomerated structure, thus consuming more thermal stress and strain energy. Moreover, C/MgAl2O4 composite powders additive promote the formation of short fibrous ceramic phases in the refractories, which suggest a bridging role in the interior of the refractories and increase its toughness. Furthermore, the C/MgAl2O4 composite powders also result in a remarkable enhancement of the slag corrosion resistance in the refractories. 相似文献
15.
《应用陶瓷进展》2013,112(6):242-246
AbstractUsually, Nd2O3 shows a polymorphism based on the hexagonal Ln2O3 A type and cubic Ln2O3 C type structures, which have coordination numbers of 7 and 6 respectively. The Nd3+ (4f2) ion in an octahedral environment produces a reddish shade. In the present study, EuxNd2-xO3 compositions were prepared by ceramic and coprecipitation (from chloride solution) methods using several flux agents. Using the ceramic route, Nd2O3 C type structure was detected and the samples were colourless, but using coprecipitation, NdOCl crystallised from an amorphous coprecipitate at low temperature, developing the unusual monoclinic EuNd2O3 B type doped polymorph which is blue in colour. When enamelled using a conventional industrial tile glaze, these blue coprecipitated samples gave L*a*b* = 75/1/-11 in the CIE colour convention. Samples were characterised by X RD, U V-V-NIR spectroscopy, and SEM-EDX techniques. 相似文献
16.
本文采用MgO粉和金属Al粉为原料,在氮气气氛下制备MgAl2O4晶须,研究了TiO2、SiO2或Cr2O3等供氧添加剂和制备条件对晶须合成率的影响并分析了晶须的物相组成和结构.结果表明:最佳MgO/Al=2/3;添加SiO2或Cr2O3不利于晶须合成;添加TiO2对合成晶须有促进作用,最佳TiO2加入量为40%;采用氧化铝坩埚比采用釉面陶瓷坩埚好,最佳保温时间为6 h.合成的晶须为MgAl2O4,空间群Fd3M,晶格常数a=b=c=0.8083 nm,MgO 28.3%,Al2O3 71.7%;晶须呈透明柱状,最大长度为20~30 mm,长径比20~400. 相似文献
17.
《Ceramics International》2017,43(18):16258-16263
A rod-like microcrystalline reinforced MgAl2O4 (MA) based ceramic with high strength and good thermal shock resistance has been successfully prepared by co-doping Sm2O3 and La2O3 via a single-stage solid-state reaction sintering (SRS) process. The effects of addition amounts of Sm2O3 and La2O3 on the phase compositions, microstructures, shrinkage ratio, apparent porosity, bulk density, high temperature compressive strength and thermal shock resistance of the MA based ceramics have been investigated. The results showed that MA, SmAlO3, La10Al4O21, Sm4.67(SiO4)3O and La4.67(SiO4)3O phases could be found in the ceramics after co-doping additives. The new formed rare earth compounds could prevent the growth of MA grains leading to a densification microstructure of the MA based ceramics. The Sm4.67(SiO4)3O and La4.67(SiO4)3O were formed by the reaction between additives and impurities of raw materials, which presented as rod-like microcrystallines to effectively clean the impurities in the grain boundaries of the MA based ceramics. Accordingly, the sintering properties, high temperature compressive strength and thermal shock resistance of the MA based ceramics were improved markedly. 相似文献
18.
19.
Lorena B. Caliman Andre Luiz da Silva Douglas Gouvêa 《Journal of the American Ceramic Society》2022,105(7):4994-5002
Magnesium aluminate spinel (MAS) has a wide range of technological applications owing to its exceptional mechanical properties and good chemical stability. MAS phase diagrams indicate that only stoichiometric MgAl2O4 is stable at ∼25°C and Mg2+ and Al3+ exhibit solubility in nonstoichiometric MAS only at temperatures higher than ∼1200°C. In this study, the synthesis of nonstoichiometric single-phase spinel nanopowders at low temperatures is reported, and the role of the chemical distribution of Al3+ and Mg2+ excess on the stability of these nanopowders is examined. We performed selective lixiviation to examine the surface segregation of Mg2+ and Al3+ in nonstoichiometric MAS to investigate its effect on interfacial solubility and consequently the stability of nonstoichiometric MAS. Furthermore, we plotted an experimental phase diagram of nano MAS that predicts the crystallite size limits for the nonstoichiometric single-phase MAS. 相似文献
20.
《Ceramics International》2023,49(4):5770-5775
In this work, MgAl2O4: Cr3+ transparent ceramics have been synthesized by the hot press sintering techniques, and the effect of the sintering aid Gd2O3 and its content on the densification, microstructure, and optical, photoluminescence was studied and discussed. The relative density reached 99.29% with 0.8 wt% Gd2O3 as a sintering aid, and the optical transmittance at 686 nm and 1446 nm were approximately 76%. As Gd2O3 content continued to increase, the grain size of the ceramics became smaller and uniform, accompanied by some pores with the size of ~1 μm. The ceramics with 4.0 wt% Gd2O3 showed a higher transmittance, of 82% at 1446 nm. Additionally, Gd2O3 was helpful for Cr3+ in the sites of octahedral symmetry, which increased the quantum yield. The quantum yield of MgAl2O4: Cr3+ with 0.8 wt% Gd2O3 was about 0.175, which was 36% higher than that of ceramic without Gd2O3. In short, the sintering aid Gd2O3 not only contributed to improving the densification, homogenizing the grain size, and heightening the optical transmittance but also enhanced the quantum yield of Cr3+. 相似文献