热镀锌钢板低铬钝化工艺的研究

对三价铬钝化的机理进行了研究，并通过初步实验，确定了低铬型钝化剂的配方，分析了钝化工艺参数对钝化膜耐蚀性的影响，确定最佳钝化工艺配方和工艺条件范围。     

热镀锌钢板钼酸盐钝化膜的改性及耐蚀性

 为了探寻一种热镀锌钢板用环保型无铬钝化剂，采用在钼酸盐钝化液中加入适量H3PO4、SiO2、Ti(Ⅳ)盐等添加剂对钼酸盐钝化膜改性，并利用SEM、EDS、XRD和中性盐雾试验等测试手段研究了所得钝化膜的表面形态、成分、组成和抗盐雾性能，同时讨论了钝化膜的成膜机理与防蚀机理。结果表明，改性钼酸盐钝化膜是一种复合钝化膜，其表面呈现出良好的抗白锈能力。它可以有效地提高镀锌板的耐蚀性能，其中Mo P Si Ti体系钝化膜的防护性能比热镀锌板提高5倍，这是由于膜中各组分协同作用所致。     

The trans-syn-I thymine dimer bends DNA by approximately 22 degrees and unwinds DNA by approximately 15 degrees

Chromium metabolism of lactating women was evaluated by measuring diet, breast milk, urine, and serum chromium in 17 subjects 60 d postpartum. Breast milk chromium concentration was similar for the 3 d of collection with a mean +/- SE concentration of 3.54 +/- 0.40 nmol/L (0.18 ng/mL). Dietary intake and urinary chromium values were also similar for each of the 3 collection days. Total chromium intake of lactating mothers (0.79 +/- 0.08 mumol/d) was greater than that of reference female subjects (0.48 +/- 0.02). There was a significant correlation (r = 0.84) between serum chromium and urinary chromium excretion. If a breast milk volume of 715 mL is assumed, chromium intake of exclusively breast-fed infants is < 2% of the estimated safe and adequate daily intake of 10 micrograms. In summary, breast milk chromium content is independent of dietary chromium intake and serum or urinary chromium values. Chromium intake also did not correlate with serum or urine chromium but there was a significant relationship between serum and urinary chromium concentrations.     

Bond strength of adhesive resin to three nickel-chromium alloys with varying chromium content

This in vitro study evaluated the influence of chromium content on bond strength and durability between nickel-chromium alloys and an adhesive resin that contained 4-methacryloxyethyl trimellitate anhydride. Three nickel-chromium alloys with different chromium content, as well as pure chromium and pure nickel metals, were bonded and tested for shear strength. After repeated thermocycling, shear bond strength decrease was lower in alloys containing high chromium content. Pure chromium metal demonstrated a 15.2% decrease, whereas pure nickel metal demonstrated the greatest (53.7%) decrease. The results suggest that nickel-chromium alloys with higher chromium content are desirable for 4-methacryloxy-ethyl trimellitate anhydride resin-bonded restorations.     

A phase II study of high-dose epirubicin (EPI) plus cyclophosphamide (CPA) with G-CSF for breast cancer patients with visceral metastases or hormone-independent tumors: a trial of the Japan Clinical Oncology Group

In a previous study, we found that oral chromium nicotinate overcame sucrose-induced hypertension in spontaneously hypertensive rats (SHR). Accordingly, we examined more chromium compounds to determine if others were more or less effective in regulating blood pressure (BP) of SHR. Since chromium is postulated to be an antioxidant, we also assessed the ability of different chromium compounds to alter free radical formation measured by determining thiobarbituric acid reactive substances (TBARS). The control group of SHR ingested a diet low in chromium, and 5 other groups ate the same diet with various chromium compounds added at 5 ppm-chloride, acetate, nicotinic acid-glycine-cysteine-glutamic acid (NA-AA), picolinate, and nicotinate. Following this, the rats were challenged with drinking water containing 5% and 10% w/v sucrose. Except for NA-AA, all chromium compounds inhibited the sucrose-induced elevation of systolic BP; and acetate, picolinate, and nicotinate chromium compounds lowered HbAIC below control. Only chromium acetate and nicotinate significantly lowered both hepatic and renal TBARS. Chromium picolinate lowered hepatic TBARS, and chromium chloride and NA-AA lowered neither. We conclude that chromium, rather than a specific ligand, plays a major role in ameliorating sucrose-induced BP elevations and can act as an antioxidant.     

Effect of Al2O3 modification on enrichment and stabilization of chromium in stainless steel slag

Spinel phase is considered to be the optimal phase for stabilization of chromium in stainless steel slag.In order to restrain chromium leaching from slag for the effective environmental protection,Al2O3 was utilized for the modification treatment,and the effects on the enrichment and stabilization of chromium were investigated.The mineral phases and the existence state of chromium in slag with various Al2O3 contents at different basicities (wCaO/w SiO2) were analyzed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD).The results showed that chromium mainly existed in the glass and spinel phases at basicity of 1.0 and 1.5.As the slag basicity increased to 2.0,chromium was also found in periclase phase.Al2O3 in the stainless steel slag reacted with MgO and Cr2O3,which could generate the Al-rich Mg(CrxAl1-x)2O4 solid solution.Moreover,the addition of Al2O3 was favorable to reduce the solubility of chromium oxide in liquid phase and suppress the precipitation of periclase phase.The experimental results demonstrated that Al2O3 modification has a positive influence on the enrichment and the stabilization of chromium in the stainless steel slag.     

硫酸亚铁铵滴定法连续测定铝钒锡铬合金中钒和铬

铝钒锡铬合金是冶炼钛合金的一种中间合金,为了准确、快速测定该合金中钒和铬,对硫酸亚铁铵滴定法连续测定该合金中高含量钒和高含量铬的条件进行研究并建立了测定方法。试样以硫酸-磷酸-硝酸的混酸分解后,在常温下,以高锰酸钾氧化钒,亚硝酸钠还原过量的高锰酸钾,同时用尿素分解多余的亚硝酸钠,用硫酸亚铁铵标准滴定液滴定钒,根据消耗的硫酸亚铁铵标准滴定液体积,求得钒含量;在加热情况下,将滴定钒后的溶液在硝酸银的催化作用下,用过硫酸铵溶液将钒和铬同时氧化至高价,再用硫酸亚铁铵标准滴定液滴定钒和铬的合量,两次滴定所消耗滴定液的体积之差即为滴定铬所需滴定液的体积,据此求得铬的含量。方法用于铝钒锡铬合金样品中钒和铬的测定,测定结果的相对标准偏差(RSD,n=10)分别为0.22%和0.75%,加标回收率分别在101%～105％和96％～101％之间。     

转炉铬矿熔融还原法冶炼不锈钢母液过程的热力学

针对转炉铬矿熔融还原法冶炼不锈钢母液工艺,利用冶金热力学原理对该过程中涉及的几个重要问题进行了理论分析和计算,为在转炉中用铬矿实现钢的直接合金化的热力学可行性提供了理论依据.得到结论:①铬矿石在熔融还原转炉中是完全可以被还原的;②金属熔体中铬的活度随金属中铬质量分数的增加而增大,温度对金属铬活度的影响较小;③在1500...     

氢化物发生-原子荧光光谱法测定铬矿中砷

铬矿中砷的测定方法对完善铬矿检测方法和质量评价手段有重要意义。在0.5 g样品中加入2 g过氧化钠,于650 ℃熔融20 min,熔融物经盐酸酸化溶解,以10%盐酸为载流,15 g/L硼氢化钾溶液为还原剂,采用氢化物发生-原子荧光光谱法(HG-AFS)进行测定,建立了铬矿中砷测定的新方法。实验表明,砷质量浓度在0.025～100 μg/L范围内与荧光强度呈线性关系,相关系数为1.000 0,方法检出限为0.05 μg/g,定量限为0.17 μg/g。对产地为南非、土耳其、巴基斯坦等19个国家共2 649个铬矿样品的成分进行统计,发现铬矿主要成分为铬、铁、镁、铝和硅;干扰试验表明,这些样品中的共存元素均不干扰测定。按照实验方法对3个不同砷含量的铬矿样品进行精密度和加标回收试验,结果的相对标准偏差(RSD,n=11)为1.4%～6.0%,回收率为96%~109%。将实验方法应用于与铬矿基体近似的铁矿标准物质中砷的测定,测定值与认定值基本一致。     

改进工艺生产低硅金属铬

为满足市场对低硅金属铬的需求,针对金属铬生产的特点,增加了铬酸钠中和工序,更换了氢氧化铬煅烧窑窑衬材质,使金属铬中杂质硅的质量分数有了大幅度的降低,满足了市场的需求.     

三价铬电沉积过程强化规律研究

铬镀层具有优异的机械和抗腐蚀性能，传统六价铬电镀存在高毒、高污染等问题，三价铬绿色电镀工艺受到普遍关注，但铬镀层不能持续增厚和镀液稳定性差是关键瓶颈.文中研究了脉冲电流和镀液流动对铬电沉积的影响规律，发现两者均可促进电镀过程中生成的副产物向镀液主体的传递.然而，脉冲电镀会降低铬电沉积效率，镀液流动可以提高铬电沉积效率，并能促进铬镀层的持续增厚.在50 mL/min的镀液流动条件下，直流电镀60 min，可获得41 μm的厚铬镀层，沉积速率为0.68 μm/min，镀层表面平整致密.      

二苯卡巴肼光度法测定镀铬板表面铬氧化物含量

测定镀铬板表面镀层中铬氧化物及金属铬意义重大,但以往测定的大都是镀铬板表面铬氧化物量(以铬计,下同)和金属铬量的总和。实验在A657/A657M-03标准附录中测定镀铬板表面铬氧化物方法的基础上,通过采用辉光光谱法对氢氧化钠溶液浸泡镀铬板前后的表面进行对比分析,证实了氢氧化钠溶液仅对镀铬板表面的铬氧化物有溶解作用,而不能溶解金属铬,同时优化了铬氧化物的溶解条件和光度法测定条件。实验表明:将镀铬板浸泡到300 g/L 90 ℃的NaOH溶液中20 min可将镀铬板表面铬氧化物溶解完全;在样品溶液中加入H₂SO₄(1+1)中和至pH为7,再加入5.0 mL硫磷混酸(3+3+4)、2.0 mL AgNO₃溶液以及5.0 mL(NH₄)₂S₂O₈溶液,加热至沸腾并保持约10 min以破坏过氧化物,冷却至室温后加入3.0 mL二苯卡巴肼溶液并稀释至100 mL,在542 nm处于2 cm比色皿中测定,Cr质量在0.24～100 μg之间有较好的线性关系,其线性方程为A=0.002 1+0.013 m_Cr(μg),相关系数为0.999 7。方法检出限为0.24 μg,测定下限为1.2 μg。将最终所测得镀铬板表面铬氧化物的量除以镀铬板试样面积,最终可计算出单位面积内镀铬板表面铬氧化物的含量。采用实验方法对两类镀铬板表面铬氧化物进行测定,所得平均含量分别为12.8 mg/m²和11.1 mg/m²,其相对标准偏差分别为3.1%(n=5)和3.6%(n=5)。对镀铬板试样进行加标回收,测得铬氧化物的加标回收率在92%～101%之间。     

监测环境水样中总铬和铬(Ⅵ)的相关标准、规范存在问题及修订建议

日常工作发现,现行标准、规范在总铬、铬(Ⅵ)水质样品的采集、保存和监测环节存在不一致或不科学的问题。建议总铬、铬(Ⅵ)水质样品均采用非玻璃材质的采样容器和保存容器;1 000 mL总铬样品中添加入10 mL硝酸进行保存;鉴于铬(Ⅵ)样品的复杂性,其保存条件及保存期建议重新研究确定;排放标准中,污染物配套检测方法的规定不宜过于死板;采用二苯碳酰二肼分光光度法检测总铬和铬(Ⅵ)时,针对浊度、还原性物质、氧化性物质等干扰物的预处理需进一步完善。建议水质现行标准、规范在颁布实施后,长期公开征求修改建议并作相应修订。     

电热法高碳铬铁生产铬污染防治浅析

通过介绍电热法高碳铬铁生产原理和铬元素毒理性特性,分析高碳铬铁冶炼过程中铬元素流向,剖析可能引起铬污染的工序环节及途径,提出高碳铬铁生产中供今后可参考的铬污染防治措施。     

Melting of Pre-Reduced Chromite Pellet Bearing Carbon

Carbonferrochromeusedforstainlesssteelpro ductionismainlyproducedinelectricheatingfurnacewiththelumporeasrawmaterial.Finechromitemustbepretreatedbeforeapplication ,butchromiteresourceregardedasfineoreaccountsfor 75 %to 80 %ofthetotalintheworld[1] .Nowaday…     

A Coupling Dynamic Model for Dissolution and Reduction of Chromium Ore in a Smelting Reduction Converter

 For describing and resolving the process of chromium ore smelting reduction in a converter preferably, the coupling dynamic model was established based on the kinetic models of chromium ore dissolution and interfacial reducing reaction between the slag and metal. When 150 t stainless steel crude melts with chromium of 12% are produced in a smelting reduction converter with no initial chromium in metal at 1560 ℃, the results of the coupling dynamic model show that the mean reduction rate and injection rate of chromium ore are 0091 %·min-1 and 467 kg·min-1, respectively. The foundation of the coupling dynamic model provides a reference and basis on the constitution of rational processing route for a practical stainless steelmaking.     

高氯酸处理-硫酸亚铁铵滴定法测定铜合金中铬

使用硝酸溶解样品,冒高氯酸烟至150 mL锥形瓶瓶口0～5 s,在硫酸-磷酸介质中,以苯代邻氨基苯甲酸作指示剂,硫酸亚铁铵标准溶液滴定溶液中铬,建立了一种高氯酸处理、硫酸亚铁铵滴定铜合金中铬的分析方法。试验探讨了铜合金以及指示剂的溶解方法,结果表明,硝酸与高氯酸联用,能够完全溶解铜合金基体、铬及铬的化合物,冒HClO₄·2H₂O烟氧化铬到铬;而苯代邻氨基苯甲酸和碳酸钠研匀后加水溶解,可以作为指示剂,由于试液中铜离子的背景蓝色与指示剂的颜色复合,构成滴定终点前后的紫色-绿色互补色,指示剂变色敏锐。铈、锰等不干扰铬的测定。按照实验方法测定标准样品中铬,结果的相对标准偏差(RSD,n=8)为0.46%,测定值和认定值基本一致。方法用于铜合金样品中铬的测定,结果与过硫酸铵氧化、硫酸亚铁铵滴定法测定结果相吻合。     

Behavior of grain boundary chemistry and precipitates upon thermal treatment of controlled purity alloy 690

Grain boundary composition and carbide composition and structure were characterized for various microstructures of controlled purity alloy 690. Heat treatments produced varying degrees of grain boundary chromium depletion and precipitate distributions which were characterizedvia scanning transmission electron microscopy (STEM). Convergent beam electron diffraction revealed that the dominant carbide is M₂₃C₆, and energy dispersive X-ray analysis (EDAX) determined that the metallic content was about 90 at. pct chromium. A discontinuous precipitation reaction was observed and is attributed to a high degree of carbon supersaturation. Grain boundary composition measurements confirm that chromium depletion is controlled by volume diffusion of chromium to chromium-rich grain boundary carbides in the temperature range of 873 to 1073 K. Grain boundary chromium levels as low as 18.8 at. pct were obtained by thermal treatment at 873 K for 250 hours and 973 K for 1 hour. A thermodynamic and kinetic model developed for alloy 600 was modified to describe the development of the chromium depletion profile in alloy 690 during thermal treatment. Experimentally measured chromium profiles agree well with the model results for the dependence of the chromium depletion zone width and depth on various input parameters. The establishment of the model for alloy 690 allows the chromium depletion zone width and depth to be computed as a function of alloy composition, grain size, and temperature. The chromium depletion profiles and the precipitate structure and composition of controlled purity 690 are compared to those of controlled purity 600. A thermodynamic analysis of the carbide stability indicates that other factors, such as favorable orientation relationships, play an important role in controlling the precipitation of Cr₂₃C₆ in nickel-base alloys.     

碳化钨掺钒掺铬粉末中铬的测定

碳化钨掺钒掺铬粉末经过灼烧后转化为氧化钨,氧化钒与三氧化二铬的混合物,采用氢氧化钠溶解,过滤,分离钨和钒。将沉淀灰化后,氢氧化钠熔融,在酸性条件下用过硫酸铵将三价铬氧化成六价铬,用标准硫酸亚铁铵溶液滴定。