碳热还原法制备单硫化铈的反应机理探讨

碳热还原法制备单硫化铈的反应机理探讨姜银举，秦凤启，郝占忠（包钢稀土研究院包头０１４０１０）单硫化铈是高熔点（２４５０℃）难熔材料，并具有导电性，对许多熔融金属及盐类具有稳定性。因此，单硫化铈在电子工业、冶金工业及尖端技术等领域有广阔的应用前景。单硫...     

溶剂萃取铈的某些问题

研究了由过氯酸盐水溶液与含某种β-二酮的四氯化碳溶液组成的溶剂萃取体系中铈的萃取与反萃取。由于萃取的螯合物中的铈(Ⅲ)易受空气中氧的氧化,所以延长两相搅拌时间可提高铈(Ⅲ)的萃取率。即使将有机相与水相分开,仍发现该整合物中的铈(Ⅲ)会发生这种氧化现象。对于不同的β-二酮螯合物,其铈(Ⅲ)的氧化速率大不相同。当所生成的这种金属螯合物与有机相中的三辛基氧膦(TCPO)形成加成物时,则其氧化速率要低得多。四氯化碳中β-二酮铈(Ⅳ)螯合物的反萃取速率与水相中的氢离子浓度及β-二酮浓度有关。由此可以断定,反萃取的控制反应应是水相中铈(Ⅳ)的还原反应。     

钨粉稀释—异标校正高频-红外吸收法测定硫化铈中高硫含量

以美国力可LECO-CS400型高频-红外碳硫分析仪为测量仪器,用钨稀释-异标校正法建立了快速测定硫化铈中高含量硫的高频-红外吸收法.通过对分析电流、称样量、助熔剂配比等进行研究,确定分析电流175 mA,称样量0.16 g～0.19 g,助熔剂配比0.5 g Fe、0.6 g W、0.1 g Sn为最佳分析条件.硫的...     

用于熔盐电解的碳酸铈的冶金基础特性研究

采用差热-热重分析法研究了碳酸铈的热分解特性,确定了碳酸铈在Ar气和CO/CO2气氛中的热分解产物;考察了碱式碳酸铈在室温和大气下的稳定性,研究了碱式碳酸铈与氟化铈的高温反应.在此基础上,提出碱式碳酸铈取代氧化铈用作熔盐电解原料,可以一定程度上抑制氧化铈的预还原反应,减少石墨材料消耗;同时探讨了碱式碳酸铈合理的加料方法.     

镧热和铈热还原法制取金属钐影响因素的研究

本文通过大量实验和生产实践,找出并讨论了镧热和铈热还原法制取金属钐的主要影响因素——反应温度、保温时间、还原剂用量、真空度、原料团块压力等因素与金属钐收率和质量之间的关系,简略地描述了铈热和镧热还原的热力学原理和动力学过程。     

铈系列产品的研究、应用及市场展望

稀土精矿中含有大量的铈,因其具有特殊的发光、磁学和电学性质,在发光材料、稀土催化领域、无机颜料以及玻璃工业等行业有着广阔的应用前景;本文详细介绍了铈系列化合物在稀土中的应用概况;简述了氧化铈、铈铽氧化物、铈锆复合氧化物以及三硫化二铈等铈系列化合物的制备工艺;同时展望了铈系列产品在稀土新材料中的应用前景。稀土新材料是当今世界各国发展高新技术和国防尖端技术、改造传统产业不可缺的关键材料之一,"十二五"期间,我国将加快培育和发展战略性新兴产业,传统铈富集物及氧化铈的应用越来越受到局限,而研究开发和展望含铈系列稀土新产品十分有必要。     

硝酸高铈铵的热分解动力学研究

采用热重分析、差热分析及X射线衍射等技术研究了硝酸高铈铵的热分解过程 ,特别是用差热分析仪测试了不同升温速率下硝酸高铈铵在静止的空气气氛中的差热曲线 ,结合Kissinger法和Coats -Redfern法研究硝酸高铈铵的热分解动力学 ,计算了两个主要的反应阶段的表观活化能为 1 4 4 .61 ,1 2 4 .31kJ·mol- 1 ,并确定了反应级数、频率因子、速率常数 ,推导出每个反应阶段的动力学方程 ,控制反应过程的步骤分别为随机成核和随后生长 ,符合Arrami Erofeer方程。     

高纯氢氧化铈制备工艺研究

研究了氨水-双氧水氧化沉淀法制备高纯氢氧化铈,考察了各条件对氢氧化铈氧化率、收率、重金属杂质质量分数的影响,并与Ce2(SO4)3-Na2SO4-氢氧化钠转化、Ce2(CO3)3-氢氧化钠转化2种方法制备的产品进行对比。结果表明,氨水-双氧水氧化沉淀法所制备的氢氧化铈的组成为Ce(OH)4,最佳工艺条件下制备的氢氧化铈产品中∑REO质量分数为82%~83%,氧化率大于98.5%,重金属杂质质量分数小于1.0×10-5。     

电感耦合等离子体原子发射光谱法测定镧铁合金、铈铁合金和镧铈铁合金中主量稀土

镧铁合金、铈铁合金和镧铈铁合金主要用作钕铁硼永磁材料或钢铁材料的稀土添加剂，而快速准确测定镧铁合金、铈铁合金和镧铈铁合金中主量稀土含量对产品的质量控制具有重要意义。采用盐酸-过氧化氢溶解样品，选择La 492.098 nm、Ce 447.124 nm为分析谱线，建立了电感耦合等离子体原子发射光谱法(ICP-AES)测定镧铁合金、铈铁合金和镧铈铁合金中主量稀土的分析方法。讨论了基体浓度、共存元素干扰等对测定的影响。结果表明，当铁质量浓度不大于0.2 mg/mL和镧(铈)质量浓度不大于20μg/mL时，基体效应可以忽略。样品中共存稀土元素和钙、镁、铝、锰、镍、硅、硫、磷等非稀土元素对稀土测定的影响可以忽略。镧、铈质量浓度在1.00～20.00μg/mL范围内与其对应的发射强度呈线性关系，校准曲线线性相关系数均为0.999 9。按照实验方法测定镧铁合金样品中镧，铈铁合金样品中铈，镧铈铁合金样品中镧、铈，结果的相对标准偏差为(RSD,n=11)均小于3%。按照实验方法测定镧铁合金、铈铁合金和镧铈铁合金内控样品的主量稀土含量，结果与草酸盐重量法测定结果一致。     

自模板法制备高热稳定铈锆固溶体

为解决纳米铈锆固溶体高温易烧结、合成过程添加大量表面活性剂、制备步骤繁琐等问题，开发了一种自模板法、不需添加表面活性剂，且操作简单易行的制备高热稳定铈锆固溶体的方法。通过该方法，制备了不同碳酸铵浓度刻蚀得到的铈锆固溶体，并通过XRD、HRTEM、ICP-OES、XPS、N₂吸附脱附测试等表征手段来确认刻蚀步骤对所得铈锆固溶体的影响。结果表明，碳酸铵能选择性地将Ce和Zr的氢氧化物沉淀混合物中的部分Zr刻蚀进溶液中，以此达到在固溶体原位造孔的目的。所得的刻蚀铈锆固溶体在1000℃老化5 h后的比表面积高达30 m²/g,远高于普通共沉淀法制备的具有相同铈锆比的样品，表明碳酸铵刻蚀处理能够提高铈锆固溶体的热稳定性，对高性能铈锆固溶体的可控合成具有较好的指导意义。     

Ce对2.9%Si-0.8%Al无取向硅钢夹杂物变质的影响

研究了添加单一稀土元素Ce后2.9%Si-0.8%Al无取向硅钢中夹杂物的变质机理。依据冶金热力学理论计算了Ce添加后,钢液中可能生成的夹杂物种类,分析了各种夹杂物存在的稳定性和相互转化的条件。在此基础上,利用SEM、EDS研究了Ce对无取向硅钢中夹杂物数量、尺寸、形貌及类型的影响。结果表明:适量的Ce显著降低了无取向硅钢中微细夹夹杂物(小于1μm)的数量,增加了粗大夹杂物(2~5μm)数量;Ce使AlN、Al_2O_3等夹杂物变性为球状的CeO_2S_2+AlN、CeS+CeAlO_3和CeS+Al_2O_3等复合夹杂物,有效抑制了钢中MnS的析出。     

Effect of Ce on Inclusions and Impact Property of 2Cr13 Stainless Steel

 The effect of Ce on inclusions and impact toughness of 2Cr13 stainless steel were studied by SEM and electron spectroscopy. Thermodynamic calculation was used to analyze the formation of RE inclusions in 2Cr13 stainless steel. The result shows that Al2O3 and MnS can be entirely replaced by Ce2O2S and CeS. Fracture is changed from cleavage to ductile fracture by adding Ce to the 2Cr13 stainless steel, and the spherical rare earth oxysulfide inclusions-Ce2O2S in the dimple are the main factors. The transverse impact value of 2Cr13 stainless steel has been improved obviously by rare earth. The transverse impact value of RE-2Cr13 is increased 55.46% at the temperature of -40℃, comparing with 0RE-2Cr13.     

Influence of Ce on Characteristics of Inclusions and Microstructure of Pure Iron

 The experiments on adding Ce, Mn and S to molten iron have been carried out by means of the electric furnace, and the concentration of oxygen, the evolution of inclusions and microstructures of samples are analyzed, indicating that the concentration of dissolved oxygen decreases greatly after adding Ce. The calculated thermodynamics results at 1273 K performed on Factsage show that Ce2O2S and CeAlO3 are formed with the increase of Ce content for w(Ce)＞00002 and w(S)＜00001, while three cerium sulphides (CeS, Ce3S4 and Ce2S3, in sequence), MnS and Ce2O2S are formed with the increase of S content and the decrease of Ce content for w(Ce)＞00002 and w(S)＞00001. These results are consistent with the SEM observations. Finally, some possible reasons are given to explain the formation of intragranular ferrite in the pure iron.     

Discussion of RE Inclusions as Heterogeneous Nuclei of Primary Austenite in Hardfacing Metals of Medium-High Carbon Steels

Duringthewelding0fl0wcarb0nsteels,theinclusions0fRE0xidesandREsulphidesaddedintothec0atingofelectrodescanactasthenu-cleiofprimaryfetritephase(8phase).Thelat-ticemisfittheoryhasbeenappliedt0calculatetheeffectivenessofinclusionsasthenucleiinlowcarbonsteelandprovedbyexperiments["'].InFe-Cequilibriumphasediagram,theprimaryphaseisaustenite(Yphase)insteadoffenite(6phase)whenthecarboncontentislargerthan0-53%.Forthehardfacing0fmedium-highcar-bonsteels,theprimaryphaseisYphaseduet0theirhighcarboncont…     

A Coupled Thermodynamic Model for Prediction of Inclusions Precipitation during Solidification of Heat-resistant Steel Containing Cerium

A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microsegregation of solute elements during solidification of heat-resistant steel containing cerium was established.Then the model was validated by the SEM analysis of the industrial products.The type and amount of inclusions in solidification structure of 253 MA heat-resistant steel were predicted by the model,and the valuable results for the inclusions controlling in 253 MA steel were obtained.When the cerium addition increases,the types of inclusions transform from SiO2 and MnS to Ce2O3 and Ce2O2S in 253 MA steel and the precipitation temperature of SiO2 and MnS decreases.The inclusions CeS and CeN convert to Ce2O3 and Ce2O2S as the oxygen content increases and Ce2O3 and CeN convert to Ce2O2 S,Ce3S4,and MnS as the sulfur content increases.The formation temperature of SiO2 increases when the oxygen content increases and the MnS precipitation temperature increases when the sulfur content increases.There is only a small quantity of inclusions containing cerium in 253 MA steel with high cleanliness,i.e.,low oxygen and sulfur contents.By contrast,a mass of SiO2,MnS and Ce2O2 S are formed in steel when the oxygen and sulfur contents are high enough.The condition that MnS precipitates in 253 MA steel is 1.2 w[O]+w[S]0.01%and SiO2 precipitates when 2 w[O]+w[S]0.017%(w[S]0.005%)and w[O]0.006%(w[S]0.005%).     

Effects of Cerium Addition on Inclusions and Solidification Structure of a Low-Nickel Si–Mn-Killed Stainless Steel

The effect of cerium on inclusions and solidification structure of a low-nickel Si–Mn-killed stainless steel is studied using laboratory experiments. When the cerium content in steel increased from 0 to 250 ppm, modification sequence of inclusions is Si–Mn(–Al)–O and MnS → Ce–Si–Mn–O–S → Ce(–Si)–O–S → CeS and CeC₂. The number density and area fraction of inclusion first decrease with the increase in the cerium content and then increase due to the formation of CeC₂ inclusions when the cerium content is bigger than 150 ppm, which is precipitated in solid steel during solidification. When the cerium content increases from 0 to 250 ppm, the fraction of equiaxed grain zones of steel ingot first increases and reaches a maximum value when the cerium content is 54 ppm; then the fraction of equiaxed grain zones decreases with the increase of the cerium content. 2D lattice misfit calculations are performed and it is found that there are no heterogeneous nucleation cores in the steel without cerium during solidification. For the steel with cerium, Ce_4.67Si₃O₁₃, Ce₂O₂S, and CeS inclusions act as heterogeneous nucleation cores, increasing the fraction of the equiaxed grain zone. Bigger effective heterogeneous nucleation cores number density leads to a larger fraction of the equiaxed grain zone.     

Effects of Cerium Content on the Nonmetallic Inclusions and Impact Toughness of Transformation-Induced Plasticity Steel

The effects of Ce treatment on the inclusion evolution and impact toughness of as-cast transformation-induced plasticity (TRIP) steel are systematically investigated by scanning electron microscope (SEM) and impact toughness testing. The results reveal that in Fe-2Mn-1.5Al-1Si-0.2C steel without Ce, the primary inclusions consist of AlN, MnS, and Al₂O₃. After Ce addition, the inclusions evolve into Ce-Al-O, Ce₂O₂S, CeS, and Ce₂O₃ inclusions. The evolution of inclusions exhibits an initial reduction in both quantity and size with increasing Ce content, followed by a subsequent increase. In cases of excessive Ce content, there is an observable rise in the overall inclusion count, marked by the emergence of CeAs, CeP, and CeC₂ inclusions. The segregation model suggests that P-containing inclusions predominantly precipitate in the late solidification process, while As- and C-containing inclusions form during the solid phase. When the Ce content reaches 0.0075 wt%, the minimum values of the number density and average diameter are 96.7 mm⁻² and 1.6 μm, respectively. Furthermore, the influence of the size, morphology, quantity, and type of inclusions on the impact toughness are analyzed. The highest recorded impact energy is 6.8 J with a Ce content of 0.0075 wt%.     

Ce对Fe-Ni膨胀合金凝固组织的影响

Ce对Fe-Ni膨胀合金凝固组织的影响研究结果表明:经Ce处理后,Fe-Ni膨胀合金中形成了大量的高熔点Ce₂O₃包芯Al₂O₃复合物,尺寸约为2μm.错配度理论计算表明,Ce₂O₃的某些低指数面与Fe-Ni膨胀合金的低指数面具有7.1%的较低错配度,因此Ce₂O₃作为非均匀形核核心使膨胀合金凝固组织由完全的柱状晶变为完全的等轴晶组织.Ce在凝固组织的等轴晶晶界上以Ce₂O₃、Ce₂O₂S和CeS形式存在,具有阻止晶粒长大的作用.     

Correlation Between Nonmetallic Inclusions and Localized Corrosion of a Low-Nickel Stainless Steel with Cerium Treatment

The localized corrosion induced by different kinds of inclusions in low-nickel stainless steel is studied through immersion tests and first-principles calculations. The galvanic corrosion between the steel matrix and different kinds of inclusions occurs in the corrosive environment due to the difference in the electron work function of the steel matrix and inclusions. The electron work function of MnS, CeS, and Ce-O-S is smaller than that of the steel matrix, thus, these inclusions first dissolve as the anode. However, the electron work function of cerium-containing oxides is bigger than that of the steel matrix, and the steel matrix dissolves prior to cerium-containing oxides. The order of the volume expansion rate of pits induced by inclusions is CeS > Si-Mn(-Al)-O > MnS > Ce-C-O-S > Ce-Si-Mn(-Al)-O > Ce-O-S. For cerium-containing inclusions, the electron work function of inclusions increases with the increase of the O/Ce ratio and the S/Ce ratio of inclusions. The order of the electron work function of cerium-containing inclusions is cerium oxides > cerium sulfides > cerium oxysulfide.     

稀土铈对钛微合金钢中TiC和Ti（C，N）析出的影响

摘要：采用扫描电镜对不同稀土含量钢中的稀土碳化物复合相进行观察，随着稀土含量的增加，在晶界析出的稀土夹杂物数量不断增加，抑制了在晶界连续析出的TiC，降低了大尺寸TiC，Ti(C,N)的数量。稀土与碳化物主要复合相变化顺序为CeAlO3-TiC→Ce2O2S-TiC/CeS-TiC→CeP-TiC；其中CeAlO3、Ce2O2S和CeS复合相主要为5μm以下的球形、近球形；CeP复合相主要为大于5μm的条状。采用OTS夹杂物统计软件对不同稀土含量的实验钢进行统计，随着稀土含量的上升，2μm以下的TiC、Ti(C,N)数量先上升后下降，在稀土质量分数为130×10-6时达到最佳；10μm以上的大尺寸TiC、Ti(C,N)呈下降趋势。TiC、Ti(C,N)颗粒的平均尺寸在降低。但是当稀土质量分数达到190×10-6时，小尺寸TiC、Ti(C,N)的数量下降；颗粒平均尺寸上升。