新疆北部蛇绿岩型铬铁矿床铬尖晶石的类型及其矿物化学成分

作为蛇绿岩型铬铁矿的重要产区,新疆北部地区发育多处中小型铬铁矿矿床。铬尖晶石一直以来是作为研究地幔橄榄岩成因与铬铁矿形成过程的重要载体之一。本文在对萨尔托海、鲸鱼、阿克塔斯和清水等地区的造矿铬尖晶石与副矿物铬尖晶石进行了形态学与矿物化学成分的研究,发现造矿铬尖晶石产出特征以中粗粒半自形-自形结构为主,自形程度较好,Cr#值较高;副矿物铬尖晶石自形程度较差,多表现为中细粒半自形-他形结构,呈粒状-蠕虫港湾状,边缘蚀变程度很强烈,Cr#值较低。造矿铬尖晶石成分相对均一,副矿物铬尖晶石成分变化较大,暗示铬铁矿的形成,并不是地幔橄榄岩中副矿物铬尖晶石的简单聚集,而是复杂多期次多阶段熔融的结果。     

有机阴离子和溶解氧对稳定纳米铁去除水中铬(Ⅵ)的影响

以硼氢化钾为还原剂,壳聚糖为稳定剂制备纳米零价铁,研究有机阴离子(柠檬酸根、草酸根和乙二胺四乙酸根)和溶解氧对壳聚糖稳定纳米铁去除Cr(Ⅵ)的影响,并探讨其影响机理.结果表明,5.357 mmol·L-1的铁与0.769mmol·L-1的Cr(Ⅵ)反应80 min后,在有机阴离子浓度为4mmol·L-1时,柠檬酸根和草...     

赤铁矿对模拟污水中重金属铬(Ⅵ)离子的吸附及固定化

铬(Ⅵ) 是水资源中重要的污染物之一,具有很强的氧化能力和迁移能力。本文对赤铁矿(α-Fe2O3)去除铬(Ⅵ)的性能和固定化能力进行了系统研究。赤铁矿的添加量、吸附时间、铬(Ⅵ)溶液浓度、溶液pH值会影响铬(Ⅵ)的去除效果。吸附热力学和动力学计算均证明了赤铁矿去除铬(Ⅵ)主要是依靠吸附作用,即表面吸附和内部颗粒扩散作用。赤铁矿吸附铬(Ⅵ)后可以通过焙烧实现铬(Ⅵ)的固定,降低其迁移能力,在800 ℃以上焙烧即可实现无解吸。XRD、SEM等测试表征表明,赤铁矿吸附铬(Ⅵ)并将其固定后并不会产生新的物相,而是通过表面收缩、致密化将吸附在表面的铬(Ⅵ)离子包覆在其中,达到固定化的效果。赤铁矿作为优势吸附材料,最大吸附量可达到4.80 mg/g,是无二次污染、可固定化污染物的良好环保型矿物材料。     

基于硝化泥炭对含铬废水的正交实验研究

采用稀硝酸处理天然泥炭,考察硝化泥炭的投加量、溶液中铬的初始浓度、溶液的初始pH和吸附接触时间对硝化泥炭的去除效果的影响。实验结果表明:实验因素影响顺序是:含铬废水的初始浓度>pH>硝化泥炭投加量>吸附时间。最佳的实验组合是:硝化泥炭投加量0.5 g、含铬废水的初始浓度20 mg/L、吸附时间80 min、pH 6。在最佳的实验条件下,溶液中的铬离子的去除率达到91.49%。     

复合铬高温暂堵剂体系影响因素分析

复合铬高温暂堵体系由部分水解聚丙烯酰胺、交联剂Y、交联剂G及破胶剂等添加剂组成。在120℃下通过测定成胶时间和破胶时间评价了聚合物、交联剂种类及浓度对暂堵剂体系性能的影响,确定暂堵剂配方为：0.4%～0.55%聚合物PAM-1＋0.2%～0.3%复配铬（G/Y=1～2）交联剂＋0.03%破胶剂。进一步考察了盐度、剪切、地层岩性对暂堵体系的影响。结果表明,在盐度小于25 000 mg/L时,盐度对暂堵体系影响不大;在经过诸如管线和岩心剪切后,该体系的粘度保持率依然很高,保持在83%左右;与空白实验比较,该体系在砂岩及碳酸盐环境下成胶时间及破胶时间、成胶强度基本保持稳定。     

硫酸盐三价铬电镀新体系的研究

研究了一种全硫酸体系的三价铬电镀工艺,并对该体系的镀液和镀层进行了性能测试。测试结果显示,该体系无需陈化镀液即可正常工作,所得镀层外观光泽明亮,光亮范围可从4A/dm2至25A/dm2以上;镀液的pH值容易控制,无需调整就能在最佳pH值范围内工作;直角阴极法测试所得覆盖能力可达90%;Tafel测试和NSS试验表明,三价铬镀铬层具有较好的耐蚀性,较六价铬镀层略差,需要进一步改善。     

Comparison of internal nitridation reactions in ammonia and in nitrogen

Nine commercial high-temperature alloys were reacted with NH₃ and with N₂-5%H₂ at temperatures of 1000–1200°C. In all cases extensive internal nitridation developed according to parabolic kinetics. Reaction with N₂ produced precipitates of Cr₂N plus, at 1000°C, some external CrN, in accordance with thermodynamic prediction. However NH₃ produced an external scale of CrN and a near-surface zone of internal CrN as well as a deeper zone of Cr₂N at 1100 and 1200°C. The CrN phase is metastable, and results from catalytic dissociation of NH₃, which produces a high effective nitrogen activity. This high activity also leads to faster internal-precipitation reactions, whereas reaction rates in nitrogen are in reasonable agreement with Wagner's model of rate control by inwardly diffusing nitrogen at its equilibrium solubility. Precipitate morphologies are complex, reflecting the importance of the energy barrier to homogeneous nucleation.     

The influence of a titanium nitride dispersion on the oxidation behavior of 20%Cr-25%Ni stainless steel

The oxidation behavior of 20%Cr-25%Ni stainless steels and a similar but stronger alloy containing a dispersion of titanium nitride particles has been studied over the temperature range 1023 to 1173°K. The dispersion-strengthened steel oxidized slightly more slowly than its dispersion-free counterpart at 1023°K, but above this temperature it was inferior in terms of gross weight gain. The parabolic growth kinetics of the chromic oxide layer in each alloy were similar, however, with an activation energy compatible with the rate-controlling step being chromium ion diffusion across the oxide. The evidence suggests that the role of the dispersed phase is to produce an oxide of finer grain size than that of the standard steel, which increases the rate of oxygen transport inward. The consequent formation of internal oxide increases the tendency for oxide rupture and spalling with subsequent enhanced local attack. This leads to the observed higher overall weight gains compared with the dispersion-free alloy.     

Study of an alternative phosphate sealer for replacement of hexavalent chromium

This study evaluates the possibility of replacing the hexavalent chromium passivation treatment used as a sealer after phosphating of carbon steel (SAE 1010) by a treatment with niobium ammonium oxalate (Ox). Samples of carbon steel (SAE 1010) after being phosphated in a zinc phosphate bath (PZn + Ni) were immersed in solution of niobium ammonium oxalate (250 mg L⁻¹ of Nb) either at pH 3.0 or pH 8.0. A passivation treatment with a solution with CrO₃ (200 mg L⁻¹ of Cr⁶⁺) was also used for reference.The corrosion resistance of the phosphated samples after passivation treatments was analyzed in a NaCl 0.5 mol L⁻¹ solution using electrochemical impedance spectroscopy (EIS) and anodic polarization curves. Salt spray tests were also performed to evaluate their corrosion resistance. The results showed that the highest corrosion resistance was obtained by passivation in a solution with (250 mg L⁻¹ of Nb) at pH 8.0.     

等温淬火温度对CADI组织及性能的影响

针对含一定碳化物等温淬火球墨铸铁(CADI),研究了等温淬火温度对贝氏体相形貌、残余奥氏体量、力学性能及耐磨性能的影响,分析了冲击断裂机理。结果表明,对于铸态组织为75%珠光体+铁素体+10%碳化物试样,经920℃×1.5 h奥氏体化后,在240℃、280℃及320℃进行等温淬火处理2 h,随着等淬温度的提高,贝氏体的形貌由针状变粗至羽毛状,残余奥氏体量增加,硬度减低,冲击韧度提高,相对耐磨性降低。最佳等温淬火温度为280℃,此热处理工艺后组织为贝氏体+22.33%残余奥氏体+10%碳化物,硬度HRC 50.9,冲击韧度32.72 J/cm2,断口呈混合断裂特征,相对耐磨性比320℃时增加11%。