Processing of High‐Density Magnesia Spinel Electro‐Conducting Ceramic Composite and its Oxidation at 1400°C

Dense conductive ceramic composites of MgAl₂O₄ and MoSi₂ were processed using combustion synthesis under‐load methodology. The starting reactants were blends of MoO₃, SiO₂, MgO, and Al powders. The study revealed that to obtain dense composite with homogeneous microstructure, 30 wt. % of MoSi₂, 18.5 μm Al average particle size, and 175 MPa load are required. The produced dense composite was found to have a low apparent porosity (<1.0 vol. %), moderate density 4.61 g/cm³, and low electrical resistivity 0.3 Ωcm. The dense composite exhibited excellent thermodynamic stability between its phases at 1400°C in open atmosphere.     

铜铈改性镁铝尖晶石作为助催化剂同时脱除FCC烟气中的SOx,Nox

为降低催化裂化烟气中的SO_x、No_x,采用溶胶凝胶法合成了Mg-Al尖晶石,并通过共胶法进行金属氧化物改性制备得到催化裂化烟气脱硫脱硝助催化剂。在小型固定床反应装置上考察了铜铈改性以及烟气中O₂含量对尖晶石脱硫脱硝性能的影响,并在小型提升管装置上考察了铜铈复合改性后尖晶石同时脱硫脱硝的性能。结果表明：经铜铈复合改性后的尖晶石脱硫活性最高,40min内仍能保持90.67%的SO₂脱除率;含铜尖晶石的脱硝性能最优,450℃后NO转化率达100%。烟气中O₂含量对脱硫有利而对脱硝不利,当O₂含量过高时,NO不能有效脱除。原位红外漫反射分析表明：含铜尖晶石良好的脱硝性能是因为其含有的Cu⁺对CO优异的吸附性能,O₂的影响在于其与CO的反应,导致CO消耗。提升管装置评价实验结果表明：主风量为0.6m³/h时,CuCe-MgAl脱硫效率为59.96%,脱硝效率为87.63%。当主风量为0.8m³/h时,脱硫效果提升至74.50%而失去了脱硝功能。     

Fabrication of porous magnesium spinel with directional pores by unidirectional solidification

A porous magnesium spinel (MgAl₂O₄) with directional pores was fabricated by unidirectional solidification in pressurized argon and hydrogen mixed gases. Two different kinds of pores with large directional and small facet shape were formed in the solidified samples. The former pores were dominant in the porous structure. A small amount of free corundum phase was formed in the solidified porous spinel as a secondary phase by vaporization of MgO component during the solidification process. With increasing total gas pressure, the pore size of the solidified samples decreased while no change in the porosity. The porosity and pore size of the samples increased with increasing hydrogen partial pressure. The porosities of the samples fabricated under 10%H₂–90%Ar and 1%H₂–99%Ar mixed gases were 30 and 10%, respectively, and that under Ar atmosphere was very low, non-porous.     

Origin of rate bistability in Mn–O/Al2O3 catalysts for carbon monoxide oxidation: role of the Jahn–Teller effect

Peculiarities in catalytic activity in carbon monoxide oxidation as well as some structure, electronic and magnetic properties of the three oxide catalysts, Mn³⁺–O/Al₂O₃ (1), Mn³⁺–O–Fe/Al₂O₃ (Mn-substituted spinel, 2) and -Fe₂O₃/Al₂O₃ (3), were studied by kinetic measurements and by Mössbauer spectroscopy. The catalysts 1 and 2 showed a kinetic bistability with a sharp transition towards more reactive state at 200°C (ignition point). In contrast, for catalyst 3, at 200–250°C, the behavior of reaction rate against temperature did not display noticeable hysteresis. On cooling the catalysts 1 and 2, extinction was observed at about 170 and 120°C, respectively, i.e., at 30–80°C lower than the corresponding ignition points. Proximity of activation energy for the high and low activity (15–19 kJ/mol) for both Mn-containing catalysts suggests an increase in the number of active sites at high temperature with no changes in the reaction mechanism. The considerable difference between Mn-containing catalysts 1, 2 and Fe-containing catalyst 3 may be caused by Jahn–Teller (JT) type distortions of the oxygen polyhedron around Mn³⁺. A significant spontaneous axial bond stretching within the local polyhedron seems to diminish Mn–O binding energy, facilitate the participation of surface oxygen species, O_S, in the oxidation of CO by a redox mechanism and promote oxygen vacancies at the surface that would cause considerable effect on the activity. An increase in the width of the counterclockwise hysteresis loop for the catalyst 2 compared to the catalyst 1 indicates that clusters of mixed spinel provide more active sites and more labile O_S species than clusters of the binary Mn oxide.     

自组装法合成介孔铝酸锌尖晶石陶瓷纳米粉

采用硝酸铝和硝酸锌为无机原料,以嵌段聚合物P123为表面活性剂,自组装法合成了介孔结构的铝酸锌尖晶石纳米粉体。利用X射线衍射、透射电镜、氮气吸附-脱附比表面测定仪对铝酸锌样品进行表征,样品为单一尖晶石相,而且具有介孔结构,500℃焙烧的铝酸锌样品比表面积最大,比表面积为98.4m2·g-1。     

Composition and microstructure of a periclase–composite spinel brick used in the burning zone of a cement rotary kiln

The composition and microstructure of a periclase–composite spinel brick used in the burning zone of a cement rotary kiln were investigated and compared to the original brick. The results indicate that cement clinker and alkali salts are two important agents that cause corrosion especially of the bonding phase of refractories in cement rotary kilns. When the molar ratio of alkalis to anions ((Na+K)/(Cl+2S)) is more than one, alkali salts accumulated in the pores, cracks and grain boundaries of the refractory but the severe corrosion of the bonding phase of the refractory did not occur in zones with lower temperatures. The interaction between the cement clinker and the refractory formed a liquid, which, together with alkali salts, improved sintering. The reaction between the cement clinker and the refractory formed a dense reaction layer. Cracks formed in the dense layer and extended through the boundary between the reaction and non-reaction (penetrated) layers by mechanical and thermal stress, which caused the spalling of the reaction and coating layer from the refractory. The recurrence of this process during service leads to degradation of the refractory.     

纳米尖晶石型涂复材料吸波性能的研究

选用化学共沉淀法制备纳米粒子(Ni,Zn)1-xFexFe2O4铁氧体吸波材料。用扫描电子显微镜、透射电子显微镜等对产品进行表征,并研究了材料的介电损耗和磁损耗。实验表明,以二价铁离子、三价铁离子的氯化物为原料,以氢氧化物作沉淀剂,制备出的纳米晶体粒度均匀、平均粒径小于40nm。从10～1000kHz的频率范围内,其吸波性能随着频率的增加而增加,随着材料厚度增加而增加。     

NiFe2O4隋性阳极的制备及其电解腐蚀机理

以Fe2O3和NiO为主要原料，添加2％（按质量计）MnO2，采用固相烧结工艺制备了NiFe2O4惰性阳极。用X射线衍射和扫描电子显微镜对材料的组成和微观结构进行了研究，测量了样品在冰晶石熔盐中不同电流密度下的电解腐蚀速率，并对其腐蚀机理作了初步探讨。结果表明：惰性阳极由NiO和NiFe2O4尖晶石两相组成，MnO2作为固溶体在尖晶石晶界处富集。电解腐蚀呈现出物理化学溶解过程，熔盐对试样的电解腐蚀首先要在晶界处发生反应生成更稳定的FeAl2O4相，而FeAl2O4相结构致密，冰晶石熔盐通过该相向NiFe2O4尖晶石晶粒内扩散速度减慢，从而降低了腐蚀速率。     

尖晶石型CuAl2O4纳米粉体的制备及其可见光催化性能

采用无机盐溶胶-凝胶法,由700℃热处理制备了纳米级尖晶石型CuAl2O4粉体.用X射线衍射和透射电子显微镜对材料的结构、形貌进行了分析和表征.结果表明:CuAl2O4为尖晶石型结构,呈现球型颗粒状,粒径大约为10～30 nm.利用紫外-可见漫反射吸收光谱,得到吸收极限波长约为700 nm,计算得到禁带宽度为1.77 eV.在荧光汞灯(λ＞400 nm)照射下,纳米CuAl2O4粉体对甲基橙、酸性红B、活性艳红K-2G等有机物的2 h脱色降解率均可达到97%.通过紫外光、荧光汞灯和太阳光等不同光照条件对甲基橙的光催化降解的比较表明:CuAl2O4光催化剂具有优异的可见光催化活性.     

掺杂元素La、F对尖晶石LiMn2O4材料结构及性能的影响

采用X-射线衍射仪(XRK)、扫描电子显微镜(SEM)、电池测试系统等研究了掺杂元素La、F对高温固相合成尖晶石型LiMn2O4材料的相结构、貌、活化性能、循环稳定性能的影响.结果表明:掺杂元素La、F可有效地提高LiMn2O4样品的充放电效率、循环稳定性能:随着掺杂元素F含量的增加,LiMn2O4-xFx样品的初始容量降低、循环稳定性能呈现出先增后减的变化规律;当掺杂元素La、F的含量较少时,LiLay,Mn2-yO4-xFx样品具有纯的尖晶石LMn2O4结构,样品呈球形或近球形,粒径范围为0.5～2.5 μm,LiLa0.02Mn1.98O3.95F0.05样品的初始放电容量为123.6mAh/g,经30次循环充放电后的容量为114.6mAh/g,容量保持率为92.7%,具有较好的活化性能和循环稳定性能.