Segregation of Aliovalent Solutes Adjacent Surfaces in MgO

The segregation of ferrous iron, ferric iron, chromium, and scandium solutes adjacent {100} surfaces of MgO crystals in the single-phase region was studied by ion microprobe mass spec-troscopy. Excess concentration in a region near the surface was found for Fe³⁺, Cr³⁺, and Sc³⁺, but none for Fe²⁺. This segregation is the type predicted as necessary to balance the negative surface charge.     

Segregation Isotherms at the Surfaces of Oxides

A non-Arrhenius segregation isotherm is derived which includes the change in the heat of segregation with surface coverage due to impurity—impurity interactions. It is shown that a linear dependence of log ( X_s ) on the reciprocal temperature, where X_s is the surface atomic ratio, can derive either from a constant heat of segregation, i.e., Arrhenius behavior, or from a heat of segregation that varies as X⁻¹_s . This isotherm is then used to calculate the equilibrium surface coverages of Ca at the {001} surface of MgO₁ Mg at the {0001} surface of α-Al₂O₃, γ at the {1012} and {1120} surfaces of α-Al₂O₃, and Na at the {111} and {110} surfaces of Li₂O from the calculated heats of segregation. Where possible, comparisons are made with experiment. The more useful operational definition of the heat of segregation, namely, that derived from the measured coverage or that defined atomistically and obtained by calculation, is discussed.     

Segregation at Special Boundaries in MgO

Segregation of Ca to three high-angle boundaries in MgO was analyzed using scanning transmission electron microscopy. Two boundaries were special [001] twist boundaries (Σ=5 (Σ=36.9°), Σ=17 (Σ=28.5°)) and one was nonspecial. The concentration of Ca at the special boundaries was approximately half that at the nonspecial boundary.     

Characterization of Grain-Boundary Segregation in MgO

Using Auger electron spectroscopy, segregation of Ca and Si corresponding to the adsorption of a partial monolayer adjacent the boundary in polycrystalline MgO was observed. Segregation of Sc is different in nature; the distribution consists of a 3.0-nm wide region corresponding to a positive space charge layer balancing a negative boundary charge. Various segregation models are applied to the observed behavior.     

连铸中间包镁钙质涂料的研制

研制的连铸中间包镁钙质涂料施工便利,粘附性强, 不水化,隔热效果好,烘烤过程中不爆裂,且抗侵蚀性较好,使用后在冷却过程中能自动从中间包永久衬上脱落。     

Thermal Segregation of Cations in Iron Aluminate Spinels

Thermal segregation experiments were performed on open and encapsulated wafers of Fe(Fe_1.51Al_0.49)O₄ spinels using CO₂ laser radiation as a heat source. The correlation of "apparent" marker movement and cation segregation led to the conclusion that the free exchange of gaseous oxygen at the external spinel surfaces is necessary to cause significant redistribution of aluminum and iron in a temperature gradient. This was explained by the different mobilities of different cations in a net vacancy (low. Effectively no segregation was observed for the zero vacancy flux condition.     

镁钙砂细粉碳酸化反应的热分析动力学研究

采用单一扫描速率法对镁钙砂细粉的碳酸化反应进行了热分析动力学研究,为镁钙砂颗粒表面碳酸化改性动力学研究提供相关信息。结果表明:镁钙砂中的MgO仅发生轻微碳酸化,因其碳酸化温度较低、反应量较小,且反应产物MgCO3在400℃后即开始分解,因此不会对镁钙砂中CaO的碳酸化反应产生太大影响;镁钙砂中CaO碳酸化反应的最大转化速率出现在700℃左右,碳酸化反应前期(相对转化率约小于38%)机理可用n=2的Avrami-Erofeev成核生长模式(机理)函数描述,后期(相对转化率约大于38%)则可用Ginstling-Brounshtein三维扩散模式(机理)函数描述。     

抗水化型MgO-CaO材料烧结性研究

研究低杂质高钙型菱镁矿在不同试验条件下的烧结情况，试验证明：煅烧温度以及粉料的细度对烧结性能有较明显影响，而同一煅烧温度下烧结活化剂对烧结性影响不大；烧结后的试样由于具有直接结合的稳定性和连续基体相的存在具有良好的抗水化性。     

添加剂对MgO-CaO浇注料性能的影响

以36%(质量分数,下同)的镁钙砂(5~3 mm)、16%的镁钙砂(3~1 mm)和20%中档镁砂(≤1 mm)为骨料,21%~28%的高纯镁砂粉(≤0.088 mm)为细粉,外加3%的硅灰为结合剂,分别比较了不同量的3种添加剂ZrO2(分别为2%、4%、6%)、Al2O3(分别为3%、5%、7%)、TiO2(分别为2%、4%、6%)对MgO-CaO浇注料性能的影响。结果表明:加入ZrO2可提高MgO-CaO浇注料的体积密度和常温抗折强度,ZrO2含量为4%的效果最好;加入Al2O3时,随Al2O3量的增加,MgO-CaO浇注料的体积密度和常温抗折强度增大,但高温下形成的低熔点铝酸盐相也较多,可能导致材料的高温性能下降,综合考虑认为,Al2O3以添加3%较好;加入TiO2可显著促进材料的烧结,使其结构致密,体积密度提高,常温抗折强度提高,TiO2含量为2%~4%时,对改善材料性能的作用较理想,但超过4%时,材料的性能开始变差;添加剂ZrO2、Al2O3、TiO2均能改善MgO-CaO浇注料的抗热震性,其中,添加ZrO2的试样抗热震性最好,其次为加Al2O3的,加TiO2的稍差。     

Simulation of Segregation to Free Surfaces in Cubic Oxides

Segregation of isovalent solute cations to (001) and (001) free surfaces in cubic metal oxides is investigated using atomistic computer simulations. Solute concentrations are represented by a mean-field approximation, and equilibrium distributions of solute are calculated by minimizing the free energy. Surface energy effects are found to dominate segregation behavior, even when in competition with misfit strain energy effects. Results are compared with a conventional Langmuir-McLean (LM) analysis. The two approaches are found to agree well in certain cases, but the LM treatment fails to reproduce important phenomena revealed using the free energy method (i.e., segregation to subsurface atomic layers).     

Effect of steam in the oxidative coupling of methane over MgO and CaO based catalysts

Influence of the initial methane-oxygen mixture dilution with steam on the parameters of the oxidative coupling of methane is studied. Catalytic tests of Pb---Mg, Sm---Mg, Bi---Ca, Zr---Mg and Na---Ca oxide systems are carried out with steam content 50–70% at 700–850°C and P(CH₄)/P(O₂)= 1,5–4,9. It is shown that the addition of steam gives increase of ethylene yield up to 12–16 mol%. The role of steam is investigated.     

高铝质耐火材料中CaO和MgO测定方法的对比研究

分别使用3种方法对高铝质耐火材料进行前处理,并采用火焰原子吸收光谱法和电感耦合等离子体发射光谱法测定高铝质耐火材料中Ca O和Mg O含量,结果发现测定结果十分接近,都可取得相对准确的测定结果。     

Reaction thermodynamics for ZrO2, MgO,and CaO with refractory metals

Conclusions We made a thermodynamic analysis of the reactions between ZrO₂, MgO, CaO with Mo, W, Nb,Ta, and Zr at 2000–3000°K on the basis of which the basic reactions of this interaction were determined. We determined the relative intensity of the reactions of ZrO₂, MgO and CaO with refractory metals Mo, W, Nb, Ta, Zr and also the temperatures of initial reaction in regard to the pressure of the surroundings.Translated from Ogneupory, No.7, pp.46–52, July, 1967.     

Surface Segregation of Aluminum (Spinel Precipitation) in MgO Crystals

MgO single crystals containing 0.006 and 0.187 wt% Al in solid solution at 1850°C were quenched and slow cooled. Analysis of the Al distribution near the surface with ion microprobe mass analysis indicated an increased Al concentration and near-surface precipitation within a region × to 4 μ thick in the slow-cooled samples and a much smaller enhanced concentration in the region 0.1 to 0.2 μ from the surface in the quenched samples.     

玻璃分相结构形态与MgO/CaO摩尔比的相互关系

本文研究MgO/CaO比值不同的两种玻璃的分相结构。结果发现高MgO/CaO比的玻璃在热处理的过程中分相液滴由连通结构逐渐长大而转变为孤立的液滴结构。而低MgO/CaO比的玻璃在热处理的过程中分相液滴则由小尺度的连通结构长大为大尺度的连通结构。     

Thermal and catalytic cracking of n-Heptane in presence of CaO,MgO and Calcined Dolomites

Experimental kinetic data on n-heptane pyrolytic and catalytic steam cracking, and product distribution data were obtained at reaction temperatures from 700° to 800°C at atmospheric pressure. The overall thermal cracking of n-heptane was compared to the cracking in presence of the basic catalysts MgO, CaO (low surface quicklime), and calcined dolomites.     

新型镁钙铝浇注料的脱磷作用研究

将等质量而磷含量不同的铁粉分别置于以高铝水泥为结合剂浇注成型的镁钙铝质坩埚内 ,并将坩埚埋入石墨粉中经 1 6 0 0℃保温 2h ,冷却后测定金属样中和坩埚衬表层的磷含量 ,发现金属样中磷含量显著下降而坩埚衬中磷含量增多 ,表明该浇注料有脱磷作用。采用SEM和EDAX方法探讨了浇注料脱磷机理和过程。其脱磷作用是由于镁钙砂中游离态的氧化钙能逐步吸收转化磷杂质为磷硅酸钙的固溶体存在于浇注料中     

水泥回转窑用MgO-CaO砖添加ZrO2后的性能改进

介绍了白云石砖、白云石-二氧化锆砖、白云石-氧化镁-二氧化锆砖和MgO-C-ZrO2砖等无铬砖的开发和改进的情况，尤其是新开发的MgO-CaO-ZrO2砖具有优异的性能，在水泥回转窑上使用取得了非常好的效果。     

Comparison of the Role of MgO and CaO Additives on the Microstructures of Reaction‐Sintered Zirconia–Mullite Composite

Isostatically pressed dense reaction‐sintered zirconia–mullite composites were prepared from zircon flour and reactive alumina with different proportions of MgO and CaO additives. The pressed compacts were sintered at elevated temperatures with variable soaking times. Development of different phases and microstructures of the sintered compacts were analyzed to assess the relative influence of the additives on the formation of the zirconia–mullite.