Physico-Chemical Investigation of Component Interactions of the Si ― Al ― O ― N ― Ti System in the Region Si3N4 ― AlN ― Al2O3 ― SiO2 ― TiN ― TiO2. Part 1. Subsystems Si3N4 ― Al2O3, Si3N4 ― TiN,and Al2O3 ― TiN

Using the methods of differential thermal and x-ray diffraction analysis an investigation was made of component reactions in the Si Al O N Ti system, particularly between the compounds Si ₃N₄ Al₂O₃, Si₃N₄ TiN, and Al₂O TiN under conditions approximating those used in the hot pressing of composites. It was established that in the reaction of Si₃N₄ with Al₂O₃, -sialon, SiO₂, AlN, and the intermediate reaction products (mullite and X-phase) are formed. In the reaction of Si₃N₄ with TiN, as a result of the decomposition of Si₃N₄ at 1650-1900°C titanium disilicide is produced, which forms eutectics with free silicon and residual TiN at 1320 and 1280°C, respectively. The reaction of Al₂O₃ with TiN similarly leads to the formation of a eutectic between Al₂O₃ and spinel at 1850°C. The presence of eutectic liquids in the specimens after sintering promotes densification of the material, and improves certain of its mechanical properties.     

Nitriding Powders in the System SiO2 ― Al2O3 ― C

Chemical and x-ray analysis methods are used to study features of carbothermal reduction and simultaneous nitriding of a powder mixture of crystalline SiO₂ (α-quartz) and amorphous SiO₂ (Aerosil). It is established that the use of amorphous SiO₂ leads to accelerated formation of SiC and a shift in the direction of nitriding towards AlN formation. It is also shown that both phases are the solid solutions SiC ― AlN and AlN ― SiC.     

Study of Phase Formation Processes in the Systems Li ― N,Si3N4 ― Li3N,Si3N4 ― Li3N ― Y2O3

We have studied phase formation processes in the systems Li N and Si₃N₄ Li₃N. By nitriding lithium powder at temperatures of 400-600°C, we obtained lithium nitride Li₃N with a composition approaching stoichiometric. In the system Si₃N₄ Li₃N in the temperature range 300-1300°C, the ternary compounds Li₈SiN₄ (500°C), Li₅SiN₃, Li₂SiN₂ (900°C), and LiSi₂N₃ (1300°C) are formed. The studied properties of the hot-pressed composite material of the system Si₃N₄ Li₃N Y₂O₃ allow us to provisionally assign it to the class of solid electrolytes.     

Effect of K2O on Phase Relation and Viscosity of the CaO–SiO2—ZnO—FeO–Al2O3 System Slags

Russian Journal of Non-Ferrous Metals - The effect of K2O on phase relation and viscosity of the CaO–SiO2–25 wt % “FeO”–12 wt % ZnO–3 wt % Al2O3 slags...     

Formation of a Corrosion-Resistant Layer on Steel by Reaction with a Si3N 4 ― Al2O3 Composite under the Conditions of Light-Thermal Treatment

The formation of a surface layer on low-alloyed steel during light-thermal treatment with a composite material based on Si₃N₄ Al₂O₃ was investigated. The working surfaces were studied using metallographic, x-ray diffraction, and electron-probe microanalysis. It was found that the corrosion-resistant phases Al₂SiO₅, (Fe, Cr)₂O₃, (Cr, Al) ₂O₃, and NiCrO₄ formed in the alloyed layer, increasing its microhardness by 2-5 times and its corrosion resistance in sea water by more than two orders of magnitude.     

Effect of Y2O3, CeO2 on Sintering Properties of Si3N4 Ceramics

The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride.     

Quasi-Chemical Viscosity Model for Fully Liquid Slag in the Al2O3-CaO-MgO-SiO2 System—Part I: Revision of the Model

A model has been developed that enables the viscosities of the fully liquid slag in the multi-component Al₂O₃-CaO-FeO-Fe₂O₃-MgO-Na₂O-SiO₂ system to be predicted within experimental uncertainties over a wide range of compositions and temperatures. The Eyring equation is used to express viscosity as a function of temperature and composition. The model links the activation and pre-exponential energy terms in the viscosity expression to the slag internal structure through the concentrations of various Si_0.5O, $ {\text{Me}}^{n + }_{2/n} {\text{O}} $ , and $ {\text{Me}}^{n + }_{ 1/n} {\text{Si}}_{0. 2 5} {\text{O}} $ viscous flow structural units (SUs). The concentrations of these SUs are derived from a quasi-chemical thermodynamic model of the liquid slag using the thermodynamic computer package FactSage. The model describes a number of slag viscosity features including the charge compensation effect specific for the Al₂O₃-containing systems. The predictive capability of the model is enhanced by the physical aspects of the model parameters—the correlation with other physicochemical properties as well as experimental viscosity data is used to determine model parameters. The present series of two papers outlines (a) recent significant improvements introduced into the model formalism and (b) application of the model to the Al₂O₃-CaO-MgO-SiO₂ system, review of experimental viscosity data, and optimization of the corresponding model parameters for this system.     

氮化硅新型耐火材料中游离Si,Si3N4,SiO2,SiC的测定

测定Si_3N_4时,用NaOH熔融试样,硼酸吸收,硫酸标准溶液滴定。游离硅的测定用氟硅酸钾法。采用HF(HNO_3存在下)冷溶的方法测定(Si SiO_2)。碳化硅的含量用100%—(Si游% Si_3N_4% SiO_2)而得。     

Corrosion of Titanium-Aluminum Intermetallides. Part 2. Electrolytic Oxidation of γ‐TiAl,TiAl3, and α2‐Ti3Al in Sea Water

Potentiodynamic polarization, XRD, Auger electron spectroscopy, and scanning electron microscopy have been applied to determine the mechanisms of electrolytic corrosion of the intermetallides TiAl, TiAl₃, and ₂Ti₃Al in 3% NaCl solution with the addition of MgSO₄ in comparison with the corrosion of the pure metals (Al and Ti). There is comparatively high corrosion resistance in TiAl and Ti₃Al because of the protective action from thin films of rutile TiO₂. Evidence is obtained for the differences between these intermetallides from the appearance of pure titanium on deep anodic polarization (above +0.15 V for TiAl and +0.7 V for Ti₃Al): the aluminum and titanium enter the solution in the forms of Al³⁺ and TiO²⁺ and intermetallides dissolve rapidly. The final solid-state products from anodic oxidation in that case are rutile, magnesium aluminate, and also magnesium and sodium titanates. In addition to pure titanium, TiAl and ₂Ti₃Al as constructional materials may be recommended for use in sea water.     

氮化硅（Si3N4＋5Y2O3＋2Al2O3）在热压过程中的α—β相变

在氮化硅陶瓷中α-Si_3N_4、β-Si_3N_4的相含量,对氮化硅陶瓷的性能有直接的影响。本文用X射线定量相分析的方法,测试了热压Si_3N_4+5％Y_2O_3+2％A1_2O_3的α/β相变的相分数。研究了热压温度及时间对该成分Si_3N_4的α/β相变的影响。结果表明,α/β相变强烈依赖于温度。用本试验原料(β相含量11.0％),在升温速度45℃/min,压力41.1MPa的条件下,在1450℃×10min,13相达14.7％;在1650℃×10min,β相达41.9％;在1750℃×10min,β相达95.2％;从1650℃开始,α/β相变显著。热压时间对α→β相变的影响随温度的变化而不同:在1450～1550℃,热压时间延长,β相含量逐渐增加;在1550～1650℃,热压时间延长,β相含量增加显著;在1650～1750℃,随温度升高,热压时间对α/β相变的影响逐渐减小。用膨胀仪测得Si_3N_4陶瓷液相生成温度为1410℃。用扫描电镜观察了在1650℃时的α-β相变,由等轴状α转变为斜方β晶粒。     

The Influence of the ZrO2 Solid Solution Amount on the Physicochemical Properties of Al2O3–ZrO2–Y2O3–CeO2 Powders

Powder Metallurgy and Metal Ceramics - Alumina-based nanocrystalline powders with different ZrO2 amounts were produced for the first time by hydrothermal synthesis in an alkaline environment for...     

Thermodynamic activity of the liquid-phase components in the CaO · SiO2-CaO · Al2O3 · 2SiO2-CaO · TiO2 · SiO2 system with four-phase invariant equilibrium

The CaO · SiO₂-CaO · Al₂O₃ · 2SiO₂-CaO · TiO₂ · SiO₂ system is analyzed. Thermodynamic analysis of monovariant and invariant solidification shows that, for invariant equilibrium and for solidification along the boundary curve between the solidification fields of anorthite and sphene, peritectic processes are observed. The invariant-state parameters of the system are determined: t = 1513 K; a _CaO = 0.0407; $a_{SiO_2 } = 0.5268$ ; $a_{Al_2 O_3 } = 0.00003$ , $a_{TiO_2 } = 0.005$ ). A corrected phase diagram is presented.     

Some Characteristic Features of Formation of Ceramics Based on Composite Powders SiC ― Si3N4 ― Si2N2O

We have studied the characteristic features of synthesis of composite powders SiC Si₃N₄ Si₂N₂O. We have investigated processes involving hot pressing of these powders without activating additives and a protective atmosphere. We consider the mechanical properties of ceramics obtained on the basis of these composite powders.     

ICP-AES法测定铁矿石中SiO2,CaO,MgO,Al2O3,MnO,P,TiO2等成分

采用碳酸钠和硼酸混合熔剂,用碱融法处理试样,并通过实验条件的优化,克服了引入大量基体对测定的干扰,实现了ICP-AES法对铁矿石、烧结矿中SiO2,CaO,MgO,Al2O3,MnO,P,TiO2等成分的同时测定.本方法试剂用量少,分析速度快,线性范围宽,分析结果准确、可靠.     

Phase transformations in the (Ti,Nb)3 Al section of the TiAlNb system—II. Experimental tem study of microstructures

In Part I of this paper possible transformation paths that involve no long range diffusion and their corresponding microstructural details were predicted for TiAlNb alloys cooled from the high temperature b.c.c./B2 phase field into close-packed orthorhombic or hexagonal phase fields. In the present paper experimental TEM results show that two of the predicted transformation paths are indeed followed for different alloy compositions. For Ti25Al12.5Nb (at.%), the path includes the formation of intermediate hexagonal phases, A3 and D0₁₉, and subsequent formation of a metastable domain structure of the low-temperature O phase. For alloys close to Ti25Al25Nb (at. %), path involves an intermediate B19 structure and subsequent formation of a translational domain structure of the O phase. The path selection depends on whether B2 order forms in the high temperature cubic phase prior to transformation to the close-packed structure. The paper also analyzes the formation of a two-phase modulated microstructure during long term annealing 700°C. The thermodynamics underlying the path selection and the two-phase formation are also discussed.     

Kinetics of Na2O evaporation from CaO–Al2O3–SiO2–MgO–TiO2–Na2O slags

The present work is carried out to study the evaporation of Na₂O from CaO–Al₂O₃–SiO₂–TiO₂–MgO–Na₂O slags with high basicity and high alumina in the temperature range of 1500–1560°C. The ratio of evaporation was determined by monitoring the Na₂O content change of the slag melt under isothermal reduction conditions. The results show that the evaporation ratio increases with increasing the temperature. Higher basicity and increasing concentrations of Na₂O, Al₂O₃ are also found to increase the evaporation ratio of Na₂O, while MgO addition only slightly enhances the evaporation ratio. With TiO₂ content increasing, the evaporation ratio first increases and then decreases. The evaporation rate of Na₂O appears to be controlled by chemical reaction at the slag/gas interface in the beginning, followed by a mixed reaction-mass transfer regime, and finally a liquid-phase mass transport step. The apparent activation energy is 134.74?kJ?mol^?1 for the chemical reaction regime and 268.53?kJ?mol^?1 for the liquid-phase mass diffusion step.     

Effect of Heat Treatment on the Physicochemical Properties of Ultrafine ZrO2–Y2O3–CeO2–Al2O3–CoO Powders

Powder Metallurgy and Metal Ceramics - Variations in the phase composition, specific surface area, and morphology of structural components in the ultrafine powder of composition (wt.%) 70 (90 ZrO2...     

Formation and Evolution Mechanism of the Inclusions of Al2O3·SiO2·CaO and Al2O3·SiO2·CaO·MgO in Seamless Steel Tube Steel

Herein, the formation and evolution mechanism of inclusions of Al₂O₃·SiO₂·CaO and Al₂O₃·SiO₂·CaO·MgO in seamless steel tube steel are investigated. In the long strip defects on the longitudinal cross section of the steel tube after the rolling bar piercing, the defect is mainly formed by Al₂O₃·SiO₂·CaO·MgO inclusions and Al₂O₃·SiO₂·CaO·inclusions dotted with·CaS inclusions after the rolling. The typical inclusions in the different steelmaking stages are mainly composed of CaS, Al₂O₃·(SiO₂), CaO·(SiO₂), MnS·(TiN), Al₂O₃·SiO₂·CaO·(CaS)·(MnS), Al₂O₃·SiO₂·CaO·MgO·(MnO), Al₂O₃·SiO₂·CaO·MgO·(CaS)·(MnS), etc. In the billet, the average sizes of Al₂O₃·SiO₂·CaO-based and Al₂O₃·SiO₂·CaO·MgO-based inclusions are much larger than those of the other types of inclusions. Part of SiO₂ in the deoxidized products SiO₂ can be reduced by [Al], resulting in the formation of the Al₂O₃·SiO₂ composite inclusions. The SiO₂ in Al₂O₃·SiO₂ inclusions can continuously be reduced by the dissolved [Ca] to form the Al₂O₃·SiO₂·CaO composite inclusions. The SiO₂ in the Al₂O₃·SiO₂·CaO inclusions can be reduced by the dissolved [Mg] to form the Al₂O₃·SiO₂·CaO·MgO composite inclusions. Another formation process of Al₂O₃·SiO₂·CaO·MgO inclusions is the entrapment of ladle slag in the vacuum degassing (VD) stage, due to the strong agitation of the rising Ar bubbles in the vacuum condition of the VD stage.     

Wear-Resistant TiN–20 wt.% Si3N4 and TiN–20 wt.% TiB2 Composites Produced by Microwave Sintering

Powder Metallurgy and Metal Ceramics - Comprehensive research on microwave sintering of the TiN–20 wt.% TiB2 and TiN–20 wt.% Si3N4 composites was conducted. At a constant microwave...     

CaO—SiO2—Al2O3—MgO—TiO2—FeO渣系熔融还原过程中TiC的生成机理

在实验室条件下，测定了熔融还原过程中ＣａＯ－ＳｉＯ２－Ａｌ２Ｏ３－ＭｇＯ－ＴｉＯ２－ＦｅＯ系炉渣组成以及不同供碳对ＴｉＣ生成的影响，并进行了热力学分析。研究结果表明：ＴｉＣ的生成机理与工艺条件密切相关。