High Chrome Refractory Characterization: Part II. Accumulation of Spinel Corrosion Deposits in Radioactive Waste Glass Melters

High Cr₂O₃ containing Monofrax^™ K-3 is a robust refractory that is used in radioactive waste glass melters worldwide. Monofrax^™ K-3 contains highly reduced phases. Conversely, many of the radioactive feeds being processed are highly oxidizing. The K-3 refractory corrosion rates in oxidizing (high nitrate) feeds were ~1.8–2.8 times higher than the rates determined using reducing feeds. The corrosion product formed is a mixture of spinel and glass (slag) that can accumulate on the melter floor. A methodology to calculate the depth of slag deposits from refractory corrosion is presented and verified with slag measurements from the Defense Waste Processing Facility (DWPF) melter after it had processed oxidized feeds for 1.75 years. The calculations show that had the facility continued to process oxidized feeds the melter lifetime (based on when the deposits could have reached and blocked the pour spout riser) would have been ~4.5 years. The DWPF changed to a reducing flow sheet after ~3 years of operation. The lifetimes of Melter #1 and Melter #2, assuming a failure due to pour spout blockage, are calculated as 7.7–12 years based on corrosion rates measured with reducing feeds. Lifetimes of 9 and >11 years have actually been achieved.     

铬砖在蓝色浮法玻璃液中的耐侵蚀机制

用广东石井特种耐火材料厂生产的铬砖(Cr2O3>94%)和洛阳浮法玻璃有限公司生产的蓝色浮法玻璃为实验材料,参照GB 1020488<玻璃熔窑用耐火材料在静态下抗玻璃液侵蚀实验方法>,使用扫描电子显微镜测试分析手段.研究了侵蚀前后铬砖显微结构和侵蚀界面附近元素组成的变化,探索了铬砖的耐侵蚀机制.实验结果表明:铬砖的耐侵蚀性与其显微结构有关,也与玻璃的组成有关,碱金属氧化物能降低其耐侵蚀性.     

Study on Microstructure and Slag Corrosion Mechanism of High Chrome Bricks for Gasifier

1 Introduction The gasifier like Texaco style is of important tech- nical equipment for ammonia synthesis and production of carbamide, carbinol and ethylene etc. Due to differ- ent energy resource structure, petroleum coke is adopt- ed as rawmaterial in A…     

An injection molding study. Part I: Melt and barrel temperature dynamics

The dynamics of the key variables in the plastication phase of injection molding were studied using a microcomputer controlled laboratory scale injection molding machine. Interfaces for the measurement and manipulation of suitable variables were developed. An approximate theoretical analysis provided a preliminary understanding of the effect of a step input in heating power on melt and barrel temperatures. Deterministic and stochastic models were derived from experimental data for the melt and the front and rear zone barrel temperatures with heater power manipulation. Experiments were performed for evaluating the effects of back pressure manipulation, heating zone interaction, and process disturbances on the melt and barrel temperatures. Experiments showed that it is desirable to directly control the melt temperature rather than the barrel temperatures.     

Catalytic Partial Oxidation. Part I. Catalytic Processes to Convert Methane: Partial or Total Oxidation

The presence of large reserves of natural gas has stimulated research to utilize methane, its principal component, as an alternative energy source and to convert it to other fuels and industrially important chemicals. The reserves of natural gas in the world are estimated to be 1.4 × 10¹⁴ Nm³, while new gas fields are being discovered every year. Although this natural gas is available under pressure for piping and transport, extensive research efforts have been directed to develop gas-to-liquid (GTL) technology for the conversion of remote natural gas reserves into high-added-value liquid products, such as methanol and synthetic fuels, that can be more easily transported. A further incentive for natural gas utilization originates from environmental concerns that drive the search for cleaner energy sources. Catalytic combustion of methane offers an attractive alternative to gas-phase homogeneous combustion since it can stabilize flames at lower fuel-to-air ratios, thereby lowering flame temperatures and reducing NO_x emission. Another alternative can be found in the conversion of natural gas into hydrogen, which can be used to generate electricity in fuel cells. Fuel cells have a much higher energy efficiency compared to current combustion-based power plants. Also, hydrogen is a much cleaner fuel than hydrocarbon feedstocks since the only product from hydrogen fuel cells is water.     

Oxidation of hydrosulphide ions on gold Part II: Characterization of gold/aqueous hydrosulphide solution interface

The results of studies to characterize the gold/aqueous hydrosulphide solution interface are presented in this paper. The interface was characterized with impedance spectroscopy, contact angle and cathodic charge transfer measurements. The studies complement the cyclic voltammetry investigations presented in Part I. A detailed mechanism of the oxidation and reduction of sulphur species at gold electrodes has been suggested on the basis of this investigation. The results show that the surface becomes hydrophobic under the conditions when polysulphide ions or elemental sulphur are present at the interface.     

Rheology of PVC. Part 5: Melt elasticity

The behavior of PVC changes drastically with the temperature and the method of sample preparation. In the steady-state shear mode, upon a decrease of the rate of deformation, the data may show either a steady increase of the shear viscosity or a leveling off to a Newtonian plateau. In the dynamic test mode, both the storage modulus, G′, and the loss modulus, G″, show an effect of the yield stress. Only at temperatures above 210°C are flow curves normal for polymer melts obtained. Rigid and nonrigid PVC formulations have been tested in Weissenberg Rheogoniometer, using steady-state or dynamic test modes at temperatures from 140 to 220°C. It was observed that yield affects elasticity more (measured by the first normal stress difference or the storage modulus) than viscosity (expressed by the shear stress or the loss modulus). The corrected for yield plots of elastic vs. viscous parameter can be easily interpreted in terms of a composite flow.     

Hydroisomerization of long-chain paraffins: Mechanism and catalysts. Part I

A review of the literature on the catalysts of hydroisomerization of long-chain paraffins is presented. Part I describes the mechanisms of paraffin hydroisomerizations and presents an analysis of data on the catalysts of hydroisomerization based on zeolites of various types. Part II is devoted to catalysts based on structured mesoporous materials, partially reduced molybdenum oxides and oxycarbides, and mixtures of tungsten and zirconium oxides. Industrial catalysts that have found use in isodewaxing of diesel fuels and oils are described.     

Corrosion of nickel in sodium sulphate-sodium chloride melts. Part I

The corrosion behaviour of Ni in molten Na₂SO₄, NaCl, and in mixtures of these two salts, at 900° C, in laboratory air and under O₂+SO₂/SO₃ atmospheres has been examined by electrochemical curves and topochemical analysis of corrosion products.Ni passivity in pure Na₂SO₄ was observed under potentiodynamic and potentiometric conditions, the passive film corresponding to NiO. Passivity was not so easy to achieve in chloride melts as in sulphate alone, but once a thick oxide film forms on the specimen, the Cl^– addition is accompanied by an increase in the film stability. The inhibiting role of NaCl on Ni in the passive-transpassive area was also evidenced. In opposition, halide additions (especially those up to 25%) increased the dissolution current densities of Ni in the active region. These higher dissolution rates are represented by the equation Ni₃S₂+4NaCl+1/2 O₂ = 2NiCl₂+2Na₂S + NiO which is also suggested as a critical factor in the Ni passivation.The passive capability found for Ni in Na₂SO₄/NaCl melts, in air, is destroyed by SO₃ atmospheres. This corrosion-stimulation is due to the SO₃ role in promoting reactions such as NiS + 3O^2– = Ni²⁺+SO₃+8e which would be potential-determining at the Ni surface until Ni²⁺ precipitates or the conjugate oxygen cathodic reduction process takes place. Microprobe analysis also evidenced S penetration which might be the reason for the Ni embrittlement.The polarization curves for Ni in pure NaCl showed the lack of a passive region; occurrence of extensive intergranular attack was also indicated by metallographic observation. The observed dissolution must occur at the expense of the Ni interactions with the species which intervene in the reaction equilibrium between O₂ and molten NaCl (O₂, Cl^–, Cl₂ and O^2–) as well as with the Na⁺ cations, as has been discussed elsewhere. Its self-sustaining nature is enhanced by the continuous reduction of the nickel ion content of the melt by NiCl₂ evaporation.     

AZS耐火材料侵蚀形成玻璃缺陷的机理浅析

论述了因AZS耐火材料侵蚀形成玻璃缺陷的机理,以及AZS耐火材料在玻璃窑炉中的蚀变特征。     

Interfacial properties in commingled yarn thermoplastic composites. Part I: Characterization of the fiber/matrix adhesion

The paper aims to assess the fiber/matrix interface and adhesion quality in commingled GF/PP composites by means of complementary experimental methods. For this purpose, different interfacial qualities were obtained by a modification of the sizing of the fiber reinforcement (polypropylene specific sizing, non-specific sizing and no sizing), and of the matrix (with or without coupling agent). Transverse tensile stress-strain curves have been recorded while monitoring acoustic emissions. An analysis of acoustic emission data associated with fracture surface examinations has helped explain the differences observed in mechanical properties and damage mechanisms, emphasizing the importance of the interphase in the performance of these new composites. Thus it has been shown that the association of three experimental investigation methods (transverse tension, acoustic emission, and fracture surface analysis) makes it possible to characterize both the glass/silane bond (so-called fiber/matrix interface) and the global fiber/matrix adhesion (addition of several different zones and interfaces). Polym. Compos. 25:577–588, 2004. © 2004 Society of Plastics Engineers.     

Microstructural Evolution of Silica on Single-Crystal Silicon Carbide. Part I: Devitrification and Oxidation Rates

Dry thermal oxidation of single-crystal silicon carbide (6H-SiC) at 1400°C in low-water oxygen using an alumina tube furnace initially yields a predominantly vitreous oxide scale. After 28 h, approximately one quarter of the oxide scale's surface becomes crystalline, with disk-like cristobalite aggregates (radialites) statistically distributed within the vitreous matrix. Crystalline areas were found to be thinner than vitreous regions using optical microscopy and atomic force microscopy/hydrofluoric acid (AFM/HF)-etching analysis, providing evidence for different oxidation rates of SiC covered by vitreous silica and cristobalite. As the bulk oxide scale continues to grow during devitrification, the radialites assume their characteristic morphology with a deepened center. Line profiles of the oxide scale's thickness across radialites obtained from AFM/HF etching were used to determine the oxidation rate of SiC covered by crystalline silica and the crystallisation rate applying a two-stage parabolic equation. As a result, it was found that the parabolic rate-constant B_vitreous is ≈4.2 times larger than the corresponding rate-constant in crystalline areas (B_cristobalite), suggesting similar differences in effective oxygen diffusion coefficients. For the crystallization rate ν, we determined a value of 1.5±0.1 μm/h.     

Discussion on Wear Mechanism of High Chrome Brick Used in Coal Slurry Gasifier

The microstructure and phase composition of high chrome brick used in coal slurry gasifier has been analyzed by means of SEM and Energy Spectrum. The results indicate that the used brick can be divided into different zones as slag-adhered zone, reaction zone, penetration zone and unaltered zone. The phase composition and microstructure are different and cracks occurred in different degree at these zones. A dense ring belt was formed with complex spinel ( Mg, Fe)( Cr,Al, Fe2O4) in the reaction zone near the hot face. The wear mechanism of the brick during its employment has been discussed. It is considered that the reaction and penetration of coal slag and strong reduetant bring about the composition change of the brick and destroys its original network inlayed structure and consequently result in its structure spalling and weakening strength, which is the main wear mechanism of the brick and followed by temperature fluctuation and high mechanical im-pact of flowing fluid with high-speed.     

高韧性和高流动性PP／EPDM共混材料的研制

研究了乙丙橡胶的门尼粘度和结晶性对聚丙烯增韧效果的影响，结果表明，高门尼粘度，部分结晶性橡胶在获得较好韧性的同时不保持较高的刚性，但流动性较差，通过加入ＨＤＰＥ能在复合增韧的同时提高共混物的流动性，添加少量油酸酰胺和硬脂酰胺敢能适当提高共混物的流动性，采用过氧化物降解聚丙烯可以显著提高共混物的流动性，但韧性明显下降，采用可控降解和动态硫化相结合的技术是在得到高韧性，高流动性共混ＰＰ的有效途径。     

Corrosion product transport in water-cooled. nuclear reactors Part I: Pressurized water operation

Corrosion of out-core piping in the primary circuit of nuclear power reactors adds both dissolved and particulate metals and their oxides to the water coolant. The particles deposit on the fuel sheaths and pressure tubes in the reactor core and are irradiated there while they dissolve in the heated water. Transport of now-radioactive solute around the circuit makes the out-core surfaces radioactive, which increases radiation exposure to operators and maintainers. A mathematical model has been developed to describe these processes of deposition, irradiation and release of corrosion products on the fuel bundles and pressure tubes of CANDU pressurized water reactors. The model's predictions compare well with data from in-reactor loop fuel, and data from fuel and pressure tubes from Pickering Generating Station. The model suggests ways to control the growth of out-core radiation fields and keep them at the current low levels of Pickering. Hot filtration of the reactor water and an increase in water pH are two solutions analyzed with the model.     

Oxidation of hydrosulphide ions on gold Part I: A cyclic voltammetry study

The results of an investigation to determine the mechanism(s) of oxidation of sulphide ions on a gold electrode are discussed. The cyclic voltammetry results are presented in Part I and characterization results after various electrochemical pretreatments are to follow in Part II. The cyclic voltammetry studies show that several stages are involved in oxidation of sulphide ions to form elemental sulphur. Initially, sulphide ions undergo underpotential deposition to form chemisorbed sulphur as isolated atoms. As oxidation proceeds, a monolayer of chemisorbed atoms is formed which reacts with sulphide ions in solution to form polysulphides at higher potentials. As the potential for oxidation is further increased elemental sulphur is produced. The reduction of polysulphide to hydrosulphide ions occurs by a 2-electron transfer process whereas the reduction of elemental sulphur occurs by a l-electron transfer process. The latter reaction involves the formation of an activated complex which is a relatively slow process.     

Preparation of active carbons from coal Part I. Oxidation of coal

The oxidation of coals of different rank, origin and particle size has been studied at temperatures between 423 and 543 K and for time intervals between 6 h and 42 days. The chemical composition of the oxidised coal depends upon the coal rank, its particle size and the degree of oxidation as determined by the temperature and the time of oxidation. At higher degrees of oxidation, whether at higher temperatures for shorter time intervals or at lower temperatures for longer time intervals, the oxidised coal tends to approach similar chemical compositions. The weight of coal also changes on oxidation, the increase or decrease in weight depending upon the rank and the oxidation conditions. The rate and extent of oxidation decrease with increase in particle size because the larger particles slow down the diffusion of oxygen into the coal particles. The oxidation can eliminate completely the plastic properties of bituminous coal which inhibit the formation of anisotropic structures and enhance the development of a primary pore structure. The helium density increases with the degree of oxidation but the mercury density initially increases and then decreases. A minimum in the mercury density is obtained when the carbon content of the oxidised coal is around 85–90%. The oxidation significantly enhances the porosity and the surface area, the extent of increase depending upon the nature of the coal and the degree of oxidation. The changes in chemical composition, porosity and surface area with the degree of oxidation indicate that the oxidation of coal involves two different mechanisms, one operating at lower temperatures and the other at higher temperatures.