铝镁双醇盐制备MgAl2O4尖晶石陶瓷超滤膜

Spinel (MgAl2O4) ultrafiltration membranes were prepared on porous α-Al2O3 plates via the sol-gel route. Mg-Al double alkoxide [MgAl2(iprO)s] was first synthesized as the precursor, then hydrolyzed and peptized in aqueous solution. The gel layer was coated from the colloidal sol on the intermediate layer (α-Al2O3), which was formerly prepared to modify the porous substrate, and then thermally treated at 900℃. The processing parameters such as pH, temperature and sol composition during the sol preparation were optimized for controlling particle size. The pore size of the 2μm thick top layer is about 13 nm as estimated by both the BSA (Bovine Serum Albumin)retention test and an empirical equation.The water permeability of the obtained spinel membrane is 55～143 kg/(min.cm2.Pa).     

透明MgAl2O4晶须的制备与表征

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.     

Fabrication and properties of Co:MgAl2O4 transparent ceramics for a saturable absorber from coprecipitated nanopowder

The 0.05 at.% Co:MgAl₂O₄ precursor was synthesized by the coprecipitation method from a mixed solution of magnesium, aluminum, and cobalt nitrates using ammonium carbonate as the precipitant. 0.05 at.% Co:MgAl₂O₄ transparent ceramics were successfully obtained via vacuum sintering and hot isostatic pressing (HIP) of 0.05 at.% Co:MgAl₂O₄ nanopowder calcined at 1100°C for 4 hours. The properties of powder and ceramics were comprehensively investigated. X-ray diffraction (XRD) results showed that Co:MgAl₂O₄ nanopowder had a pure spinel phase. Also, the in-line transmittances of the HIP posttreated Co:MgAl₂O₄ ceramics with the thickness of 1.2 mm were 82% at 400 nm and 84.7% at 900 nm. The average grain sizes of 0.05 at.% Co:MgAl₂O₄ ceramics before and after the HIP posttreatment were 11 and 28 μm, respectively. The calculated ground state absorption cross section of 0.05 at.% Co:MgAl₂O₄ ceramics was 2.9 × 10⁻¹⁹ cm², indicating that this ceramics is a promising material applied as a saturable absorber for passive laser Q-switches in the 1.3-1.7 μm domain.     

Self-segregation and solubility in nonstoichiometric MgAl2O4 nanoparticles

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.     

TiO2含量对镁铝尖晶石烧结性能的影响

以分析纯氧化镁、氧化铝、氧化钛为原料,按氧化镁与氧化铝质量比28.33∶71.67配料,在合成体系中分别引入质量分数为0、0.5％、1％、2％、4％、6％、8％和10％的氧化钛,在钼丝炉中1600℃保温2h,烧结法合成镁铝尖晶石.用X射线衍射、扫描电子显微镜和能谱对烧后试样进行分析.结果表明:引入适量的TiO2可显著提高镁铝尖晶石的烧结性能;当TiO2含量低于4％时,随着TiO2的含量增加,试样的线变化率减小,显气孔率下降,体积密度增大,常温耐压强度增大.TiO2的引入提高了镁铝尖晶石晶体空位浓度,活化了晶格,促进镁铝尖晶石的烧结.当TiO2含量高于4％时,试样的线变化率、显气孔率和体积密度没有显著变化,常温耐压强度有所下降;尖晶石晶粒尺寸没有明显变化,且生成了一定量的Mg0.6Al0.8Ti1.6O5,阻碍了镁铝尖晶石之间的接触,影响镁铝尖晶石烧结性能的提高.     

Microwave dielectric properties and crystal structures of spinel-structured MgAl2O4 ceramics synthesized by a molten-salt method

The microwave dielectric properties and crystal structures of MgAl₂O₄ ceramics synthesized using either molten-salt (MA-M) or solid-state reaction (MA-S) methods were characterized in this study. Raman and ²⁷Al solid-state nuclear magnetic resonance spectra indicated that Al³⁺ cations primarily occupied in tetrahedral sites of the MA-M ceramic. The degree of inversion x, i.e., degree of cation disorder in tetrahedral and octahedral sites, of the MA-M was higher than that of MA-S; such the preferential site occupation of Al³⁺ cations enhanced the covalency of the MO bonds in the MO₄ tetrahedra (M = Mg and Al), leading to a decrease in the lattice parameters. The Q·f of the MA-M fired at 1600 °C was 201,690 GHz, while the MA-S synthesized at 1600 °C exhibited a Q·f of just 85,100 GHz. Based on these results, an intermediate spinel structure with a greater x evidently has a higher Q·f, and therefore the cation distribution is closely related to the Q·f of the ceramic.     

MgAl2O4透明陶瓷粉体的研究进展

透明镁铝尖晶石陶瓷的制备,对粉体有特殊的要求.高纯、超细、分散性好、高活性的粉体是制备镁铝尖晶石透明陶瓷的首要条件.本文以制备镁铝尖晶石透明陶瓷为目标,从粉体的纯度和粉体颗粒特征两方面分析了粉体的性能对制备透明镁铝尖晶石陶瓷的影响,介绍了几种可用于制备镁铝尖晶石透明陶瓷粉体的方法,分析比较了每种方法的优缺点.     

化学共沉淀法制备镁铝尖晶石粉末的研究

以ＭｇＣｌ２·６Ｈ２Ｏ和ＡｌＣｌ３·６Ｈ２Ｏ为主要原料,利用化学共沉淀法制备ＭｇＯ－Ａｌ２Ｏ３系中唯一稳定的二元化合物ＭｇＡｌ２Ｏ４粉末。与机械球磨混合法相比,湿化学法制备的均匀超细ＭｇＡｌ２Ｏ４粉末,具有纯度高、比表面积大、且活性高、易于较低温度（９００℃）下煅烧获得等特点。     

Growth-microstructure relationship in MgO-MgAl2O4 eutectic fabricated by micro-pulling down method with MgAl2O4 seed crystals

The MgO-MgAl₂O₄ eutectic was directionally solidified via micro-pulling down method in the form of rods with 2–3 mm diameter. MgAl₂O₄ single crystals (with <111> orientation) were used as crystallization seeds. At low pulling rates, especially 0.15 mm/min triangle-like cross-section was observed, which was linked to the eutectic MgAl₂O₄ following the crystallographic direction of the seed. MgO precipitates in the form of lamellae and rods with median equivalent diameter ranging from 0.19 to 0.85 μm, depending on the pulling rate. The preferred crystallization direction was <111> for both phases, however notable traces of other directions, e.g. <100>, <110> and <331> were found as well.     

Sintering behavior and morphology control of porous Al2O3-SiO2 ceramics for radome applications

Ceramics from porous Si₃N₄ and its derivatives SiAlON and Si₂N₂O were once considered the most promising high-temperature wave-transmitting materials. However, their large-scale application in the field of radomes is greatly restricted due to their poor oxidation resistance, high preparation costs, and expensive raw materials. Therefore, the development of low-cost porous oxide ceramics remains of significant interest to the field of high-temperature wave transmission. Surprisingly, mullite ceramics, which are representative of the Al₂O₃-SiO₂-system of ceramics, are ultra-low-cost materials with the potential to replace ceramics from Si₃N₄ and its derivatives. In this paper, integrated porous Al₂O₃-SiO₂-system ceramics were successfully prepared for load-bearing/wave-transmitting applications, using inexpensive calcined kaolin and alumina powder as the main raw materials. Calcined kaolin can provide seeds for the growth and development of mullite crystals in the ceramic system. High-strength and high-porosity ceramics were obtained with the mullite morphology controlled through the molar ratio of Al₂O₃ to SiO₂ and the resulting content of mullite seeds. With increasing of mullite seed content, the length and radial width of mullite whiskers with “interlocking structure” gradually change from rod-shaped “long and thick” to needle-like “short and thin.” The prepared porous Al₂O₃-SiO₂ ceramics have high flexural strength, fracture toughness, and good dielectric properties.     

氮气气氛下MgAl2O4/SiC材料的反应性能研究

为了研究氮气气氛下MgAl2O4/SiC材料的反应性能及硅粉的影响,将添加硅粉前后的MgAl2O4-SiC材料在流动氮气中经1600℃保温3h烧成,对烧结后的试样进行XRD、SEM和EDS分析.研究发现:两者材料的主要物相均为镁铝尖晶石、碳化硅、氮化硅.不添加硅粉的试样中生成的氮化硅呈长径比较大的纤维状,其生长过程符合VS生长机制;添加硅粉后的试样中生成的氮化硅根部呈柱状,顶部呈锥状,其生长是LS和VS生长机制共同作用的结果.另外,氮化烧成时MgAl2O4/SiC反应界面层中会发生离子互扩散,可能生成少量堇青石,并且C4-、Al3+、Mg2+较O2-、Si4+具有更大的扩散速度.     

Solid-state NMR for the analysis of interface excesses in Li-doped MgAl2O4 nanocrystals

Interface segregation plays a governing role in nanocrystalline ceramics properties due to the relative increase in the interfacial volume fraction. However, due to the complexity of the detection and quantification of interfacial excesses at the nanoscale, the role of ionic dopants or additives on microstructural evolution and thermodynamics can be easily underestimated. In this work, we address the spatial distribution of Li⁺ as a dopant in magnesium aluminate spinel nanoparticles. This is achieved through a novel method for the detection and quantification of Li⁺ across the surface, grain boundary, and bulk (crystal lattice). Based on selective lixiviation combined with chemical analysis, we were able to quantify the amount of Li⁺ forming surface excess, whereas the quantitative solid-state nuclear magnetic resonance technique enabled the quantification of Li⁺ segregated in the grain boundaries and dissolved in the lattice. This comprehensive understanding of the Li⁺ distribution across the nanoparticles makes possible an unprecedented interpretation of coarsening and sintering, with a clear correlation between the microstructure and the Li⁺ distribution. Although the work focuses on MgAl₂O₄, the proposed combination of techniques is expected to have a positive impact on the understanding of other multicomponent nanoscale systems.     

MgAl2O4:Ce荧光粉辐照合成及发光机理研究

通过伽马射线辐照辅助聚丙烯酰胺凝胶法合成了MgAl₂O₄和MgAl₂O₄:Ce荧光粉。通过X射线粉末衍射仪（XRD）、透射电子显微镜（TEM）、紫外可见分光光度计和荧光分光光度计研究了MgAl₂O₄:Ce荧光粉的晶体结构、表面形貌、光学性质和发光性质;基于实验所获得的结果,分析了纳米级MgAl₂O₄:Ce荧光粉的发光机理。实验结果表明:采用伽马射线辐照辅助聚丙烯酰胺凝胶法制备纯相MgAl₂O₄和MgAl₂O₄:Ce荧光粉的结晶温度要比传统聚丙烯酰胺凝胶法低100 ℃左右;MgAl₂O₄:Ce荧光粉的平均颗粒尺寸为14 nm,Ce离子掺杂后导致样品颗粒细化;Ce离子的掺入,降低了MgAl₂O₄的能带值,改善了其颜色性质和发光性质;当采用275 nm的光去激发MgAl₂O₄:Ce荧光粉时,获得了425 nm和464 nm的蓝光发射。通过能量传递原理分析认为,杂质缺陷（Ce³⁺）在整个发光过程中扮演了重要角色。MgAl₂O₄:Ce作为一种抗辐射能力强的荧光粉,在空间照明领域具有很好的应用前景。     

Combustion synthesis of C/MgAl2O4 composite powders using magnesium oxalate as carbon source

In order to solve the bottleneck problems including uniform distribution, and oxidation resistance of nano carbons in oxide ceramics, C/MgAl₂O₄ composite powders were prepared with MgC₂O₄·2H₂O, MgO₂, Al₂O₃, and Al as raw materials via combustion method under argon atmosphere. The maximum adding amount of MgC₂O₄·2H₂O is 34.34 wt%. The phase compositions and microstructures of combustion products were characterized through X-ray diffraction (XRD), scanning electron microscope (SEM)/EDX, and Raman spectroscopy. The results showed that the phases of products are mainly composed of MgAl₂O₄ and carbon. The prepared MgAl₂O₄ has granular and rod-like morphologies, and the free carbon (1.172 wt%) exists between particles of MgAl₂O₄. Moreover, the addition of FeC₂O₄ as catalyst in raw materials ratio would be beneficial for improving crystallization of in situ carbon generated in the products. The oxidation activation energy of the prepared C/MgAl₂O₄ composite powders was calculated as 143.01 kJ/mol which was 22.17% higher than that of carbon black/MgAl₂O₄ powders (117.06 kJ/mol), suggesting that the C/MgAl₂O₄ composite powders prepared by combustion synthesis have excellent oxidation resistance.     

Preparation of MgAl2O4 solar thermal storage ceramics from different magnesium sources

In order to study the performance and feasibility of magnesia-alumina spinel (MgAl₂O₄) ceramics for thermal storage in solar thermal power generation, MgAl₂O₄ was prepared by theoretical composition using α-Al₂O₃ as aluminium source, fused magnesia, magnesite, and light burned magnesia as different magnesium sources and kaolin as additive. The effects of magnesium source and the additive on sintering properties, thermal shock resistance and thermal properties of MgAl₂O₄ ceramics were researched. The results shown sample A1 (with fused magnesia) sintered at 1670°C possessed the optimum comprehensive properties, the bending strength increased by 7.71% after 30 thermal shock times (room temperature-1000°C, air cooling), the specific heat capacity was 1.05 J/ (g·K). Therefore, the MgAl₂O₄ ceramics exhibited great potential in high-temperature thermal storage material.     

球磨法制备NiO/MgAl2O4催化剂用于低浓度甲烷催化燃烧

用球磨法制备了MgAl_2O_4尖晶石负载的NiO催化剂NiO/MgAl_2O_4,考察了镍源、NiO负载量、球料比、球磨转速、焙烧温度对低浓度甲烷催化燃烧的影响,并用H_2-TPR、BET、XRD、SEM等手段对催化剂进行了表征。结果表明,与沉淀-沉积法或浸渍法相比,球磨法制备的催化剂前驱体与载体的相互作用较弱,焙烧后生成了高活性NiO物种。球磨法制备时,镍盐种类及NiO负载量、球料比、转速以及焙烧温度均会改变载体表面NiO晶粒的大小和结合状态,从而影响其活性。以乙酸镍为镍源、NiO质量分数10%、球料比2∶1、球磨转速400 r/min、经700℃焙烧,制得的NiO/MgAl_2O_4催化剂稳定性和活性较好;600℃下,700℃焙烧制得催化剂的拟一级反应速率常数(k600)为0.489 L/(g·s),高于MgAl_2O_4尖晶石负载的La_(0.8)Ca_(0.2)FeO_3或La_(0.8)Sr_(0.2)MnO_3钙钛矿催化剂。     

Selective removal of antibiotics over MgAl2O4/C3N4/YMnO3 photocatalysts: Performance prediction and mechanism insight

A simple polyacrylamide gel method combined with low temperature sintering technology has been used to synthesize the C–O functional groups grafted MgAl₂O₄/C₃N₄/YMnO₃ (MAO–CN–YMO) heterojunction photocatalysts with enhanced visible-light-induced photodegradation toward oxytetracycline hydrochloride (OTC-HCl). A variety of characterization methods are used to gain insight into the phase purity, crystal structure, microstructure, functional group information, elemental composition, surface defect, light response capability, and photocatalytic activity of the as-synthesized samples. The influences of the mass ratios of m_CN/m_YMO, m_CN/m_MAO, and m_MAO/(m_CN + m_YMO) in CN–YMO, CN–MAO, and MAO–CN–YMO heterojunction photocatalysts on the photocatalytic activity for the degradation of OTC-HCl was also discussed, and the optimal mass ratio of m_MAO/(m_CN + m_YMO) is identified as 15 wt%. The photocatalytic experiments confirmed that the MAO–CN–YMO heterojunction photocatalysts had high selectivity for the degradation of antibiotics. The prediction of the photocatalytic activity of the MAO–CN–YMO heterojunction photocatalysts for the degradation of OTC-HCl was made by a variety of intelligent algorithm models. The results of the whale optimization algorithm are highly consistent with the experimental results. Combined with the energy band theory and the characterization results of high-performance liquid chromatography–tandem mass spectrometry, the free radicals in the reaction solution preferentially attacked the –CH₃, –NCH₂, and –OH of OTC-HCl during the degradation of OTC-HCl by MAO–CN–YMO heterostructure photocatalysts, and then attack –C=O and –C=O–NH₂, and finally perform ring-opening reaction to degrade OTC-HCl into nontoxic and harmless products of small molecules such as CO₂, H₂O, and NH₄⁺. This work provides a new idea for the development of novel double p–n junction MAO–CN–YMO heterojunction photocatalysts for antibiotic degradation and the prediction of photocatalytic activity of multiple heterojunction photocatalysts by intelligent algorithms.     

Improved properties of low-carbon MgO-C refractories with the addition of multilayer graphene/MgAl2O4 composite powders

The paper investigated the effects of different amounts (0%, 3%, 6%, 9%) of in situ multilayer graphene/MgAl₂O₄ composite powders on the slag resistance, thermal shock resistance, and oxidation resistance of low-carbon MgO-C refractories. Comparing with commercial MgAl₂O₄, the MgAl₂O₄ in in situ multilayer graphene/MgAl₂O₄ composite powders has higher lattice strain of crystal, which can trap more Mn and Fe ions, resulting in the better slag resistance. The oxidation decarbonation layer of MgO-C specimen with 3% composite powders is 9.71 mm, which is lower than not only the specimen with other contents but also specimen containing carbon black/MgAl₂O₄ powders. Moreover, the residual strength ratio of the specimen C/MA-3 was 47.47%, which is 28.5% and 8.08% higher than specimens with no additive and with carbon black/MgAl₂O₄ powders, respectively. Both improving thermal shock and oxidation resistance properties are related with the unique nano structure, multilayer graphene in situ formed between MgAl₂O₄ grains, of added composite powders. The former is due to higher strain energy consumed by multi-deflection of cracks inside the multilayer graphene/MgAl₂O₄ composite powders. And the latter is due to the higher energy of oxidation activation of multilayer graphene/MgAl₂O₄ composite powders due to effective protection of multilayer graphene by MgAl₂O₄.     

Fabrication and characterizations of Cr3+-doped ZnGa2O4 transparent ceramics with persistent luminescence

0.5 at.% Cr:ZnGa₂O₄ precursor was synthesized by the co-precipitation method with nitrates as raw materials, using ammonium carbonate as the precipitant. Low-agglomerated Cr:ZnGa₂O₄ powders with an average particle size of 43 nm were obtained by calcining the precursor at 900℃ for 4 h. Using the powders as starting materials, 0.5 at.% Cr:ZnGa₂O₄ ceramics with an average grain size of about 515 nm were prepared by presintering at 1150℃ for 5 h in air and HIP post-treatment at 1100℃ for 3 h under 200 MPa Ar. The in-line transmittance of 0.5 at.% Cr:ZnGa₂O₄ ceramics with a thickness of 1.3 mm reaches 59.5% at the wavelength of 700 nm. The Cr:ZnGa₂O₄ ceramics can be effectively excited by visible light and produce persistent luminescence at 700 nm. For Cr:ZnGa₂O₄ transparent ceramics, the brightness of afterglow was larger than 0.32 mcd/m² after 30 min, which is far superior to that of Cr:ZnGa₂O₄ persistent luminescence powders.