Study on phase structures and compositions,microstructures, and dielectric characteristics of (1-x)NdGaO3-xBi0.5Na0.5TiO3 microwave ceramic systems

(1–x)NdGaO₃-xBi_0.5Na_0.5TiO₃ [(1–x)NdGaO₃-xBNT, 0.05 ≤ x ≤ 0.7)] ceramic systems were fabricated using a conventional solid-state reaction, and their phase structures, microstructures, and microwave dielectric characteristics were systematically investigated. The XRD patterns results showed an orthorhombic perovskite structure as the main phase with a Pbnm space group at x = 0.05. In a range of x = 0.1–0.3, the main Nd₃Ga₅O₁₂ cubic structure phases (Ia-3d space group) had been formed due to the increase in the cation vacancies resulting from the Na and Bi ion volatilization at the higher densification sintering temperatures (1400–1450 °C). As (Na_0.5Bi_0.5)²⁺ ions increased and the sintering temperatures decreased, the orthorhombic perovskite-type Pnma space group solid solutions (the main phases) were detected at x = 0.4 and 0.5, accompanied with a certain amount of second phase Bi₂O₃ in the samples at x = 0.6 and 0.7. The results of Raman spectroscopy analysis, EDS data analysis, and surface morphologies observations were basically in keeping well with the XRD analysis results, wherein the Raman-active modes also implied that the crystal structure of the main phase actually had a tendency to change the perovskite structure when x = 0.3. The ε_r value increased gradually as the x value increased from 0.05 to 0.5 because of the increase in the ionic polarizability, and increased slowly at x = 0.6, then decreased slightly as the x value further increased to 0.7 due to the formation of the second phase. The Q × f values of the (1-x)NdGaO₃-xBNT (x = 0.05–0.7) ceramic systems were strongly influenced by the densification, lattice defects, and phase composition and content. The τ_f values could be well predicted by replacing Na, Bi and Ti ions with suitable substitutions for these ceramic systems. As a result, the new temperature-stable ceramics with optimal dielectric properties of ε_r ~43.1, Q × f ~6700 GHz (at 5.85 GHz), and τ_f ~ −24.5 ppm/°C and ε_r ~ 44.5, Q × f ~ 5600 GHz (6.12 GHz), and τ_f ~ +2.4 ppm/°C were obtained in the (1-x)NdGaO₃-xBNT composite series at x = 0.5 and x = 0.6 sintered at 1320 °C and 1250 °C for 4 h, respectively.     

Experimental study on direct reduction of lead- zinc oxide ore

Lead- zinc ore is a polymetallic mineral resource rich in lead, zinc and iron. Due to its complex mineral structure, low lead and zinc grades and large amount of slime, it is difficult for traditional flotation methods to efficiently orient lead and zinc, the obtained flotation concentrate has a low grade. Although direct reduction of rotary kiln can recover lead and zinc resources, there are problems such as low iron recovery rate, high equipment failure rate, and low operating rate. In order to extract iron, lead and zinc from the raw material efficiently, a direct reduction method of rotary hearth furnace was put forward. This method has the characteristics of high reduction temperature, fast reduction rate and high metal recovery. The influences of the direct reduction technological parameters on the carbon containing pellets of the lead- zinc oxide ore were experimentally investigated. The results show that the optimum reaction parameters are reduction temperature of 1300?棬 reaction time of 30min, carbon and oxygen ratio of 1. 2 and w(Ca(OH)2)=5 mass%. Under above reaction parameters, the metallization rate of pellets is 95. 89%, the volatilization rate of lead and zinc is 95. 23% and 98. 56%, respectively.     

Mineralization and nitrification of ureaform fertilizers

In an attempt to produce N materials that exhibit some delayed-release character and yet make all the N available in one growing season, ureaform (UF) fertilizers were prepared using low amounts of paraformaldehyde (PFA) (6% to 15% PFA w/w). Mineralization and nitrification of the various water-soluble components of these UF materials were studied over a period of 35 days by use of¹⁵N and high pressure liquid chromatographic techniques. Only the dimethylenetriurea (DMTU) fraction and a fraction tentatively identified as triuret showed any slow-release character, whereas other water-soluble components mineralized rapidly. Less soluble fractions did not mineralize appreciably during the experiment. Due to their reduced solubility, these ureaforms were shown to be less susceptible to volatilization than was urea, and a 37% reduction in loss was found.     

Calculation of Reactive-evaporation Rates of Chromia

A methodology is developed to calculate Cr-evaporation rates from Cr₂O₃ with a flat planar geometry. Variables include temperature, total pressure, gas velocity, and gas composition. The methodology was applied to solid-oxide, fuel-cell conditions for metallic interconnects and to advanced-steam turbines conditions. The high velocities and pressures of the advanced steam turbine led to evaporation predictions as high as 5.18 × 10⁻⁸ kg/m²/s of CrO₂(OH)₂(g) at 760 °C and 34.5 MPa. This is equivalent to 0.080 mm per year of solid Cr loss. Chromium evaporation is expected to be an important oxidation mechanism with the types of nickel-base alloys proposed for use above 650 °C in advanced-steam boilers and turbines. It is shown that laboratory experiments, with much lower steam velocities and usually much lower total pressure than found in advanced steam turbines, would best reproduce chromium-evaporation behavior with atmospheres that approach either O₂ + H₂O or air + H₂O with 57% H₂O.     

Persistent chemicals in pulp mill effluents: Occurrence and behaviour in an activated sludge treatment plant

In wastewater effluents of a Swiss pulp mill more than 50 organic chemicals were identified including chlorinated phenols, chloroform, chlorinated terpenoids and chlorinated resin acids. Quantitative determinations were carried out to investigate the behaviour of the most abundant constituents during wastewater treatment in an activated sludge process. In particular, the chlorinated compounds were only partly eliminated. The lipophilic chlorinated phenols were physically absorbed to some extent into the activated sludge biomass. The importance of this nonbiological elimination mechanism was evaluated by applying distribution coefficients between activated sludge particles and water which were determined for a series of chlorinated phenols. Chloroform and other purgeable compounds were removed mainly by transfer into the ambient air. The impact of the persistent wastewater constituents on the water quality in the receiving River Aare was assessed. It was estimated that the concentrations of chlorinated phenols in the river caused by the discharge of the treated pulp mill wastewater are about 10 times lower than the levels of pentachlorophenol which typically occur in Swiss rivers receiving effluents from municipal wastewater treatment plants.     

Ammonia losses from surface-placed mixtures of urea-calcium-potassium salts in the presence of phosphorus

Phosphorus compounds frequently are mixed with urea containing materials for economy in fertilizer operations. There is little published information on NH₃ losses from surface application of these mixtures. However, there is evidence that P can react and precipitate with adsorbed and added Ca and increase the potential for NH₃ loss. This paper compares NH₃ losses from surface applied urea plus KCl or CaCl₂ in the presence of 5 common P sources. The N, with Ca, K, and P salts, was surface-applied to a calcareous (Harkey) and an acid soil (Cuthbert) in a laboratory and the NH₃ losses determined by passage of the exhaust air through a 2% boric acid solution. Ammonia losses were increased with (in the presence of KCl or CaCl₂) KH₂PO₄ (KP) (calcareous soil only) and K₂HPO₄ (K₂P), unaffected by Na₅P₃O₁₀ (PP) but decreased with Ca(H₂PO₄)₂ (CaP) and H₃PO₄ (HP) (No HP or PP applied to the acid soil). Urea which hydrolyses in environments with lower soluble and desorbable Ca levels is susceptible to higher NH₃ losses. The effectiveness of KCl for control of NH₃ loss depended on the existence of desorbable Ca to react with the decomposing urea. Therefore the deleterious impact of P on NH₃ loss was greater with KCl than with CaCl₂. Adding Ca directly with the urea made additional Ca available for reaction with P and urea. Monocalcium phosphate (CaP) alone with urea, in a calcareous soil, did not reduce NH₃ loss; however, NH₃ loss was reduced in the acid soil. The addition of CaCl₂ with urea + CaP reduced NH₃ loss more than CaCl₂ with urea. The HP reaction with CaCO₃ was more rapid and complete than occurred with the acidic CaP. Sodium tripolyphosphate (PP) with urea had little impact on NH₃ loss over that produced by the KCl or CaCl₂ salts alone. The HP and CaP chemicals did not appear to function strictly as acid sources (calcareous soil). The Harkey soil has 8% CaCO₃ which would appear adequate to neutralize any acidity introduced by the P fertilizers. The explanation may lie in double salt formation between the Ca-urea-P materials. Contribution from the Texas Agric. Expt. Sta., Texas A&M Univ. System, College Station, TX 77843, USA     

Recent developments on the use of urease inhibitors in the tropics

Urea has become the most widely used form of N fertilizer in the world, particularly in the tropics. Its efficiency, however, is decreased by losses of N through ammonia volatilization when the urea is not incorporated into the soil. High temperatures and high biological activity at the soil surface promote rapid hydrolysis of urea to ammonia and carbonate species by the soil enzyme urease, leading to large ammonia losses. These conditions have generated interest in materials that can inhibit the urease enzyme, slowing urea hydrolysis and allowing the urea to move away from the soil surface to where it is not as susceptible to ammonia loss. The phosphoryl di- and triamides, which are structural analogs of urea, meet the requirements for effective soil urease inhibition to varying degrees depending on the conditions of their use. Until the discovery of these compounds, there was little hope that urease inhibition could be achieved either economically or in an environmentally acceptable way. Included in this group is N-(n-butyl) thiophosphoric triamide (NBTPT), which is that most widely tested proinhibitor or precursor of the actual inhibitor N-(n-butyl) phosphoric triamide. Recent research in tropical rice systems indicates that urease inhibitors such as N-(n-butyl) phosphoric triamide and cyclohexylphosphoric triamide can play an important role in increasing urea efficiency. In some experiments where urease inhibition was only partially successful, better results were obtained when the phosphoroamides were used in conjunction with an algicide, to restrict ammonia loss, and nitrification inhibitors, to reduce loss of N by denitrification. Further research on tropical soils in different environments is required to determine the most suitable combination of inhibitors to reduce N loss and increase the efficiency of fertilizer N use.     

电收尘器在锌浸出渣挥发窑烟气收尘中的应用

针对锌浸出渣挥发窑烟气的特点,及在传统收尘流程中存在的问题,结合实际生产经验,对云南冶炼厂锌系统环境治理改造工程中,电收尘器在锌浸出渣挥发窑烟气收尘中的应用情况进行了探讨。     

Volatilization of metal powders in plasma sprays

Ideally, plasma spraying of metal powders must take place within a narrow processing “window” where the particles become fully molten before they hit the substrate, but are not overheated to the point that substantial volatilization occurs. Metal evaporation in flight results in a decrease in the deposition efficiency. In addiiton, the emission of vapors leads to the formation of metal and oxide fumes that are undesirable from the viewpoints of both resource conservation and environmental control. This study examines the vaporization and fume formation in the plasma spraying of iron powders of different size ranges. The experimental part involves the determination of the population (number density) of metal atoms at different cross sections along the trajectory of the plasma jet, and the collection of the submicronic particles resulting from vapor condensation. The experimental results are compared with the projections of a mathematical model that computes the gas/particle velocity and temperature fields within the jet envelope, projects the rate of heat/mass transfer at the surface of individual particles, and determines the rate of volatilization that results in the formation of metal and metal oxide fumes. This paper was presented at the International Thermal Spray Conference sponsored by the ASM Thermal Spray Society, the DVS-German Welding Society and the IIW International Institute of Welding, May 8–11, 2000 in Montreal, Canada.     

金属直接氧化过程中的镁挥发机制

研究发现Al Mg Si合金直接氧化时存在层状Al/Al2 O3 复合结构 ,揭示了直接氧化过程的本质特征 ,证实了Mg挥发对直接氧化过程的重要作用 ,提出了Mg挥发机制并据此讨论了已有研究中尚未解决的几个重要问题。