Effects of Mixture Components on Sialon Composition Homogeneity on Synthesis from Kaolins

Carbothermal reduction has been combined with nitriding of kaolin with various free SiO₂ contents in the presence of additional silicon-bearing components under experimental industrial conditions to make β-sialons with Z = 0.73-3.78. It is possible to make a sialon with a given Z by means of additional silicon-bearing components, and also a sialon with Z = 2 directly from raw material kaolin. X-ray diffraction indicates that the composition inhomogeneity in the sialon is dependent on the content of free SiO₂ in the mixture.     

Metastable Phase Formation and Its Transformation in Highly Undercooled Ni75B25 Alloy

Ni₇₅B₂₅ alloy was solidified at various undercooling. The formation and subsequent transformation of metastable Ni₂₃B₆ phase were clearly identified. If undercooling prior to nucleation is less than a critical value of 240 K (240 °C), the alloy solidifies completely into Ni₃B phase. At larger undercooling, metastable Ni₂₃B₆ phase primarily forms in the melt but then is decomposed into α-Ni and Ni₃B through a eutectoid reaction. The decomposition simultaneously triggers the rapid solidification of residual liquid, due to which a second temperature recalescence occurs. The α-Ni/Ni₃B eutectoid is partially remelted if temperature exceeds the eutectic temperature during the second recalescence. Then, residual Ni₃B grows into coarse round grains while the remaining liquid re-solidifies into α-Ni/Ni₃B eutectic structure in the remelted region. In the case that the eutectic temperature is not reached, the eutectoid product with dot α-Ni distributing in Ni₃B matrix is retained in the solidification structure. A longer delay time between the two temperature recalescence events means less residual liquid, lower recalescence temperature and thus depressed remelting. The formation competition between Ni₃B and Ni₂₃B₆ phases in the alloy melt is nucleation controlled. The heterogeneous site in Ni₇₅B₂₅ alloy melt is a better nucleation substrate for Ni₂₃B₆ phase than for Ni₃B phase.

Graphical abstract

     

利用标准生成焓由相图提取活度

本文在前述近似公式的基础上,进一步推导了其精确表达式,并利用新公式计算了In-Sb二元系的活度,与实验值吻合很好,证实了公式的可靠性。     

α'相形成与铁铬铝合金的脆性

应用电子显微镜、X射线衍射技术,对低温长期使用的铁铬铝电热合金进行分析。结果表明:晶粒长大以及铬原子含量为75%左右的铁铬二元α'相在晶界和基体中析出,是导致合金变脆的主要原因;通常微量碳化物Cr₂₃C₆相以及σ相总是沿晶界分布。     

烧结过程中二恶英的排放和生成机理研究进展

利用"辨别和量化二恶英及呋喃排放标准工具包"估算出2005年我国钢铁行业排放的二恶英总量达到1847.26 g TEQ.对当前已经开展的有关烧结过程中二恶英的分布和排放规律的研究进展进行了综述.提出了典型烧结烟气中二恶英同系物的分布规律,并以焚烧过程中二恶英的生成机理为基础讨论了烧结过程中二恶英的生成机理.目前的研究表明:烧结过程中二恶英的生成机理是"从头合成"、"前驱物合成"、"原生二恶英物质未完全分解"这三种生成机理综合作用的结果.     

赛隆(Sialon)体系热力学性质评估与预报

利用拟抛物面规则编制了评估和预报热力学性质的计算机程序,较为系统地预报了β‘－Ｓｉａｌｏｎ,ｏ’－Ｓｉａｌｏｎ,Ｘ－Ｓｉａｌｏｎ,Ｓｉａｌｏｎ多形体以及α－Ｓｉａｌｏｎ等化合物的标准吉布斯自由能与温度的关系式,以及等温条件下标准吉布自由能与组份的关系式。这为赛隆材料的设计提供了热力学数据。     

Phase Transformations in Zirconium and Its Alloys

Abstract

A critical review is presented of all published data on phase transformation in zirconium and its alloys. Topics discussed include: The α → β transformation; factors affecting the stability of α and β zirconium; transformations in the β-phase including ω-phase formation, eutectoidal decomposition and strain induced transformations; transformations in the α-phase including the tempering of martensite and supersaturated alpha, and peritectoid formation of ordered Zr₃Al. The review concludes with examples of phase transformations in commercial zirconium alloys and the effects of these transformations on the mechanical properties of the alloys.

Résumé

Une revue critique de toutes les donnees publiees sur les transformations de phase du zirconium et de ses alliages est présentée. Les sujets traités sont: la transformation α → β, les facteurs influençant la stabilité des phases α et β, les transformations ayant lieu dans la phase β incluant la formation de la phase ω, la décomposition eutectoîdique et les transformations induites par une déformation, les transformations ayant lieu dans la phase α incluant le revenu de la martensite et de la phase α sursaturée, et la formation péritectoïdique d'une phase ordonnee Zr₃Al. Cette revue se termine sur la présentation de plusieurs exemples de transformation de phases des alliages commerciaux de zirconium et l'effet de ces transformations sur les propriétés mécaniques de ces alliages.     

二恶英从头合成机理研究进展

介绍了二恶英的从头合成机理.影响二恶英从头合成的因素有碳源、氯源、氧气、水、颗粒表面特性、温度、停留时间、催化剂和抑制剂等.     

碳离子注入金属的相形成

用碳离子注入到金属Fe和Ni中形成六方相。在Co中第一次形成了六方碳化物,晶格常数为a=0.268nm,c=0.433nm。同常规热处理方法比较,离子注入更倾向于形成简单晶体结构相、非晶相,而不容易形成复杂结构相。这一规律可以指导一般的离了注入实验并预期其他新相的形成。     

Amorphous Phase Formation Analysis of Rapidly Solidified CoCr Droplets

This paper investigates amorphous phase formation and rapid solidification characteristics of a CoCr alloy. High cooling rate and high undercooling-induced rapid solidification of the alloy was achieved by impulse atomization in helium atmosphere. Two atomization experiments were carried out to generate powders of a wide size range from liquid CoCr at two different temperatures. Amorphous fraction and kinetic crystallization properties of impulse atomized powders were systematically quantified by means of differential scanning calorimetry. In addition, different but complementary characterization tools were used to analyze the powders microstructures. The fraction of amorphous phase within the investigated powders is found to be promoted by high cooling rate or smaller powder size. The critical cooling rate for amorphous phase formation, which is influenced by the oxygen content in the melt, is found to be ~3 × 10⁴ K s^?1 and corresponds to a 160-µm-diameter powder atomized in helium. Hardness of the powders is found to follow a trend that is described by the Hall–Petch relation when a relatively high fraction of crystalline structures is present and decreases with the fraction of amorphous phase.     

纳米氧化锌的固相合成

以七水硫酸锌和无水草酸钠为原料,用室温固相化学反应首先合成出前驱物草酸锌,草酸锌在400℃分解3h,得到产物纳米氧化锌。用X-射线粉末衍射和透射电镜对产物的组成、大小、型貌进行表征。结果表明,产物纳米氧化锌为粒度分布均匀的球形六角晶系结构,平均粒径28nm。     

锌氧压渣中铁复相强化溶出规律及浸出动力学

在锌冶炼的氧压浸出工艺中,由于铁复杂相的存在,使得铁浸出率不高,导致锌氧压浸出渣中仍存在一定量铁资源未能有效回收。以广东某冶炼厂锌氧压渣为研究对象,首先进行详细的工艺矿物学研究,然后采用硫酸化焙烧-溶液浸出的方法对锌氧压渣中的铁复相进行强化分解及高效溶出。得到了较优的试验条件为:焙烧温度300℃、酸渣质量比0.4、焙烧时间2.0 h、浸出时间1.0 h、浸出温度80℃,液固比L/S=5/1,此时铁浸出率为83.31%,锌浸出率达到97.06%。最后,对铁复相的溶液浸出动力学进行了研究,得到了浸出反应的表观活化能为23.18 kJ/mol,并建立了半经验动力学方程。     

二噁英(PCDD/Fs)的形成途径与控制措施

众多研究表明：当今世界环境中的二噁英（PCDD/Fs）主要来自废物焚烧,而我国则主要来自含氯化学品的生产和使用,其次是造纸和金属冶炼。为此,本文论述了废物焚烧、冶金工业、造纸工业和含氯化学品生产过程中PCDD／Fs的形成途径：并论述了主要行业PCDD/Fs的控制措施。     

纳米β-PbO粉体的固相合成

以醋酸铅和碳酸钠为原料,用室温固相化学反应首先合成前驱物碳酸铅,在此基础上通过620℃高温分解4h,得到了黄色纳米β PbO粉体。利用元素分析、热重-差热分析对固相反应的可行性作了讨论;借助X 射线粉末衍射和透射电镜对产物的组成、大小、形貌进行表征。结果表明,纳米β PbO粉体为球形,粒径大小为5～30nm左右。     

铅物相分析方法研究及应用

高杂质粗铅在电解过程中产生的阳极泥含铅在8％～20％之间,通过分析铅在阳极泥中可能存在的状态有可溶于水Ph的化合物、PbSO4、PbO、Pb3O4、Pb、PbSiO3、PbS、PbF2等,用化学物相分析方法对各相进行测定,结果表明阳极泥中铅主要以PbSiO,形式存在,从铅电解生产工艺分析出PbSiO3生成原因为PbSiF6水解所得,通过提高电解液中的H^＋浓度抑制水解反应的发生,达到降低铅阳极泥含铅的目的。     

富硼相及其在Nd-Fe-B合金中的行为

本文利用1000kV超高压电镜、穆斯堡尔谱仪、X射线衍射仪和磁测量仪等对Nd-Fe-B永磁合金中的富硼相进行了研究。结果表明:富硼相以1个孤立的相存在于Nd-Fe-B永磁合金中,它一般位于基体相Nd₂Fe₁₄B的三角晶界处,占据的体积份数为4.6%,富硼相中有高密度的缺陷存在,这些缺陷的方向垂直于$\\vec C$轴。
富硼相的化学式可以写为Nd_1+εFe₄B₄(s≈0.1),该化合物由2套亚结构,即Fe-B亚结构和Nd亚结构相互套穿而成。2个亚结构均具有四方对称,在四方基面上的晶格常数相同,但沿$\\vec C$方向却有不同的周期,所以富硼相可能为一维的成分变化型无公度结构。在室温下富硼相呈顺磁性,能够在磁体中钉扎畴壁而提高矫顽力,富硼相的显微结构和温度有关,由矫顽力对温度的依赖关系和电镜观察表明富硼相对畴壁的钉扎可能属于强钉扎。     

铁酸盐形成中钴的行为与控制

研究了硫酸亚铁溶液经空气氧化水解生成铁酸盐的过程，以及此过程中钴的行为与控制。所获得的产物经X射线衍射分析与红外光谱测定表明，在pH=11下部分氧化的亚铁溶液沉淀出绿锈中间产物并吸收溶液中的钴离子，绿锈中的亚铁继续氧化、水解、脱水，可获得尖晶石型钴铁酸盐CoxFe3-xO4。随着初始溶液中铁钴配比R从27降低到3，x的取值由0．13增大到0．45，但进入铁酸盐的钴的比例(沉淀率)则有近100％降至近53％。温度的升高不利于钴取代铁酸盐中的铁。     

Removal of Hexachlorobenzene from Kaolin by Electrokinetics Coupled with Cu/Fe PRB

This study deals with the remediation of clayed soils contaminated with hydrophobic organic compounds (HOCs) by using electrokinetics (EK) coupled with a permeable reactive barrier (PRB) technique. Hexachlorobenzene (HCB) and kaolin were selected as the typical HOCs and clay, respectively, and microscale Cu/Fe particles were synthesized as the functional materials of PRB. Furthermore, Triton X-100 was used as the solubility-enhanced agent to promote the movement and removal of contaminants. Four bench-scale EK tests were conducted with or without Cu/Fe PRB. The results reveal that coupling EK with Cu/Fe PRB greatly promoted the overall removal of HCB from soil, compared with EK alone. Other than the electroosmotic flow, the adsorption/reductive degradation by Cu/Fe PRB may also be responsible for the HCB removal (over 82% of HCB passing by the PRB was removed). Our investigation suggests that the integration of EK and Cu/Fe PRB is of great promise to promote the application of EK technique in the remediation of HOC-contaminated soils.