微波焙烧预处理难浸含金硫精矿

对难浸含金硫精矿进行微波焙烧,考察微波功率、矿量(即样品质量)和焙烧时间对样品质量损失率和浸出率的影响。结果表明:当微波功率为16 k W、焙烧时间为50 min、矿量为900 g时,样品质量损失率可达28.12%,浸出率可达71.56%,较原矿直接碘化浸出率(9.82%)有了大幅提高。利用XRD和SEM技术分析焙烧前后样品的成分和表面形貌,微波焙烧后的样品较原矿更为松散、多孔,更利于浸出。     

某高硫微细粒金矿选冶试验研究

某高硫金矿中金矿物与黄铁矿紧密共生,金矿物和黄铁矿平均粒径分别为3.58和32.80μm,嵌布粒度较细,在实际生产中精矿品位和回收率均不理想。为进一步提高精矿品位和回收率,针对该矿特点,确定黄铁矿为浮选目标矿物,通过系统条件试验和精选试验得到了最优浮选工艺流程和参数,继而开展开路试验和闭路试验,得到的浮选指标并不理想。基于中矿中黄铁矿多是连生体的判断,对浮选中矿进行再磨处理,获得了精矿金品位17.4 g/t、金回收率80.66%的满意指标。同时,结合“超细磨”、“碱浸预处理”工艺,对浮选精矿进行浸出试验,得到金浸出率77%的满意指标,为生产现场提供了具有指导意义的技术方案。     

Nature of indigenous sulfur segregated to the free metal surface and to the scale-metal interface

Sulfur segregation to the free metal surface of a Ni-20(wt.%)Cr-12(wt.%)Al alloy has been documented by high-temperature scanning Auger electron microscopy. Preferential enrichment of sulfur occurs to the surface of the chromium-rich phase in the two-phase y nickel- (NiAl) alloy. Electron spectroscopy for chemical analysis (ESCA) studies have indicated that for a free metal surface, i.e., metal without an overlying thermally grown oxide scale, the surface segregated sulfur correlated with both S^–2 and elemental sulfur. Energy-dispersive X-ray analysis (EDAX) characterization of fractured oxide films thermally grown on the Ni-Cr-Al alloy indicated that both a labile, i.e., relatively volatile, and a refractory sulfur species exist at the scale-metal interface. Elemental sulfur as detected by ESCA has the volatility characteristics found for the labile sulfur species found in the scanning electron microscopy (SEM)-EDAX studies.     

Influence of sulfur on the nature and morphology of carbides formed on the surfaces of Fe-Ni-Cr alloys at high temperatures

The influence of sulfur upon surface carbide formation on a range of Fe-Ni-Cr alloys has been investigated at a temperature of 1273 K. The addition of small amounts of H₂S, up to 100 ppm (range of = 2.2×10^–12 to 5.5×10 su–11 bar), to a H₂-CH₄ carburizing atmosphere (a_c=0.8) was found to significantly modify the behavior from that normally observed in the sulfur-free environment. The carburization of these alloys in the H₂-CH₄ atmosphere led to the formation of globular particles of M₇C₃ on the surface of the alloy, but the addition of H₂S affected the type, morphology, and distribution of the surface carbides. Initially, the lower carbon containing M₂₃C₆ was formed, which transformed to M₇C₃ at a rate determined by the concentration of sulfur in the environment. The morphology of the M₇C₃ was modified by the presence of sulfur, and the carbide exhibited a preferred crystallographic orientation in the [001] direction. Particles of manganese sulfide were formed on the commercial alloys at > 2.3 × 10^–11 bar at 1273 K, and these served as nucleation sites for carbides sothat, in contrast to the behavior in sulfur-free conditions, complete surfacecarbide layers were formed.     

The initial oxidation of iron at 200° and 300° C and the effect of surface sulfur

The growth of thin (0–200 Å) oxide films on iron at 200 and 300 °C has been studied as a function of time and oxygen partial pressure using proton-induced X-ray emission (PIXE) and Auger electron spectroscopy (AES). Oxidation was found to be initially retarded by sulfur which had segregated onto the iron surfaces during preoxidation annealing, but only if the iron surface contained the maximum or near-maximum sulfur coverage (ca. one-half monolayer). During and immediately following the oxygen-sulfur interaction, oxide buildup appeared to be limited by a surface reaction (adsorption, ionization, or dissociation). For most of the oxidation period, pressure-dependent logarithmic oxide growth was observed at 200°C, and pressure-independent parabolic oxide growth at 300°C. Interpretation of the data indicated that oxide growth at 200°C may be limited by quantum mechanical tunneling of electronic species through the previously formed oxide film, and oxide growth at 300°C may be limited by ionic diffusion through the previously formed oxide film. Comparison of AES and PIXE data indicated that the oxide films formed at 200°C were uniform in thickness over the surface of the metal, whereas films formed at 300°C had relatively thin areas where sulfur had remained.     

The effect of surface condition and sulfur on the environmental resistance of airfoils

The environmental protection of aircraft engine high-pressure turbine blades is dependent upon the formation of a thin, slow-growing, external alumina scale. The adherence of alumina (Al₂O₃) scales to superalloys or coatings has been shown to be improved by adding an oxygen-active element (Y) or by desulfurization. Studies will be presented that show that cast surfaces are contaminated with sulfur and are more susceptible to high-velocity oxidation than machined surfaces regardless of an oxygen-active-element addition. In addition, the positive effect of oxygen-active elements and desulfurization on the performance of a single-crystal and directionally solidified Ni-base super-alloy in a 1149°C cyclic oxidation test and a 927°C/5 ppm sea-salt Type-I hot-corrosion test will be discussed.