Structures of some 17% Cr(Mn,N) stainless steels

A study of the structures of 17 wt.% Cr(Mn, N) stainless steels has been made with the help of X-ray diffraction, optical and electron microscopic techniques. It reveals that these steels become entirely austenitic when 10% manganese or more is present in a steel that contains about 0.4% nitrogen and 0.1% carbon. No precipitation other than the grain boundary carbides is observed on prolonged exposure to high temperatures. Below 10% manganese, an unstable austenite is formed which undergoes a series of transformations at different temperatures. The mode of these transformations has been studied in detail from 1400 to 700‡C. A possible mechanism of transformation is discussed.     

Bi_(12)SiO_(20)∶Mn,Cr晶体的杂质诱导光色特性

采用提拉法、电阻炉加热铂坩埚,a 轴取向生长纯的 Bi_(12)SiO_(20)和 Bi_(12)SiO_(20)∶0.05wt·%MnO_2,0.02wt·%Cr_2O_3(BSO∶Mn,Cr)晶体。电子顺磁共振谱指出:光照后激活心电荷态各自为 Mn~(5+)和 Cr~(4+);其 g 因子大小分别为2.0009和1.9616。光照前 BSO∶Mn 在410～750nm 有吸收带,并和吸收边重叠,它相应于 Mn~(5+)离子 ~3A_2→~3T_2,~3T_1跃迁,Mn~(5+)和 Mn~(4+)同时在晶体里存在。光照后,Mn~(5+)离子吸收增加。另外,BSO∶Cr 光色效应可通过 Cr~(5+)→Cr~(4+)电荷传输过程来解释。纯 BSO 晶体粉末有一个 g=2.0109峰宽为75G 的 ESR 带,这带被归为本征捕获空穴心。     

Ion-exchange equilibria between (Mn,Co)O solid solution and (Mn,Co) Cr2O4 and (Mn,Co) Al2O4 spinel solid solutions at 1100° C

The compositions of the (Mn,Co)O solid solution with rock salt structure in equilibrium with (Mn,Co)Cr₂O₄ and (Mn,Co)Al₂O₄ spinel solid solutions have been determined by X-ray diffraction measurements at 1100° C and an oxygen partial pressure of 10^–10 atm. The ion exchange equilibria are quantitatively analysed, using values for activities in the (Mn,Co)O solid solution available in the literature, in order to obtain activities in the spinel solid solutions. The MnAl₂O₄-CoAl₂O₄ solid solution exhibits negative deviations from Raoult's law, consistent with the estimated cation disorder in the solid solution, while the MnCr₂O₄-CoCr₂O₄ solid solution shows slightly positive deviations. The difference in the Gibbs free energy of formation of the two pure chromites and aluminates derived from the results of this study are in good agreement with recent results obtained from solid oxide galvanic cells and gas-equilibrium techniques.On leave from the Institute for Metals Research, Polish Academy of Sciences, 25 Reymonta St, 30-059 Krakow, Poland.     

Investigation of strontium-doped La(Cr,Mn)O3 for solid oxide fuel cells

The (La, Sr) (Cr, Mn)O₃ system was investigated in an effort to develop an interconnect and cathode materials for solid oxide fuel cells. Sintering studies were done in air at temperatures below 1500°C. Significant improvements in densification were observed with substitution of 50 mol% Mn for chromium and a density of 95% theoretical was achieved with the substitution of 70 mol% Mn for chromium in the La(Cr, Mn)O₃ system. Electrical conductivity (d.c.) measurements were made as a function of temperature and oxygen activity. At 1000°C and 1 atm oxygen, the electrical conductivity ranged from 2.2–20 S cm^–1 for LaCr_0.8Mn_0.4O₃ and La_0.9Sr_0.1Cr_0.2Mn_0.8O₃, respectively. All of the compositions showed similar dependence of electrical conductivity on the oxygen activity. Dependence was small at high oxygen activities; as the oxygen activity decreased, a break in electrical conductivity at 10^–12 atm and 1000°C was observed, and then the electrical conductivity decreased asP _O2 ^1/4 . Sintering and electrical conductivity studies indicate that La_0.9Sr_0.1Cr_0.2Mn_0.8O₃ appears to be a candidate for solid oxide fuel cell applications.     

Structure transition and enhanced ferroelectric properties of (Mn, Cr) co-doped BiFeO3 thin films

Pure BiFeO₃ (BFO) and (Mn, Cr) co-doped BiFe_0.96?yMn_0.04Cr_yO₃ thin films were prepared on FTO/glass (SnO₂:F) substrates by using a sol–gel method. The effects of (Mn, Cr) co-doped on the microstructure and electric properties of the BiFeO₃ thin films were studied. The result indicates that the co-doped BiFe_0.94Mn_0.04Cr_0.02O₃ (BFMCO) thin film has a structure transition and better ferroelectric properties compared with the pure BFO thin film. The Rietveld refined XRD patterns of BFO and BFMCO thin films conform the trigonal (R3c:H) and the biphasic (R3c:H + R3m:R) structure, respectively. The co-existence of two phases and the mixed valences of Cr^3+/6+ and Mn^2+/3+, which apparently improves the electric properties of the (Mn, Cr) co-doped BFMCO thin films. The remnant polarization (P _r) of the BFMCO thin film was 93.58 μC/cm² at 1 kHz in the applied electric field of 636 kV/cm. At an applied electric field of 100 kV/cm, the leakage current density of (Mn, Cr) co-doped BFMCO thin film is 6.2 × 10^?6 A/cm². It is about three orders much lower than that of the BFO thin film (1.43 × 10^?3 A/cm²).     

Cr替代Mn对La0.4Ca0.6MnO3磁性质的影响

用固相反应法制备了La0.4Ca0.6Mn1-xCrxO3(x=0.00,0.02,0.04,0.06,0.08,0.10,0.15)多晶样品,通过X射线衍射(XRD)图谱、磁化强度-温度(M-T)曲线、电子自旋共振(ESR)谱线,研究了Cr替代Mn对La0.4Ca0.6MnO3磁性质的影响.实验结果表明:La0.4Ca0.6MnO3存在复杂的磁结构,在258 K出现电荷有序相,从175 K到50 K,产生强关联CO-AFM(电荷有序?反铁磁)相,温度降到41 K左右出现自旋玻璃态;当替代量x≥0.06时,电荷有序相被融化;当x≥0.10时,自旋玻璃态被融化.对实验结果进行了初步解释:电荷有序相被融化主要原因是Cr3+与Mn4+具有相同的电子结构,Cr3+替代Mn3+破坏了CE型反铁磁的自旋序,从而引起电荷序的坍塌,实验证明了电荷序CE型反铁磁体系中,电荷序和自旋序之间存在强耦合相互作用;自旋玻璃态的融化,是由于Cr替代Mn破坏了自旋玻璃态的生成条件,即反铁磁背景下有少量铁磁成分.     

Nanoparticles of pure and substituted maghemites (gamma-M(x)Fe(2_x)O3 where M = Al, Cr, Mn, Zn and 0 < or = x < or = 1.3): a comparative study

Magnetic nanoparticles of pure and substituted iron oxides are prepared by single step autocombustion or by wet chemical methods. The nanoparticles prepared by the first process had mixed phase of hematite and maghemite whereas the later essentially gives maghemite phase. XRD patterns and TEM micrographs of the pure and substituted maghemites samples suggest about their monophasic nature and inverse spinel structure. Further, the size of the particles for the above iron oxide samples was found to be in the range of 4 to 30 nm. Saturation magnetization value for the samples was observed to be varying with the type and the amount of substitution. For example, magnetization value initially increased and then decreased for Al- and Mn-substitutions but it continuously decreased for Cr- and Zn-substitutions. Contrary to the saturation magnetization value, the Curie temperature decreased continuously with increased substitutions irrespective of the type of substitutions. Due to higher magnetization value of Mn-substituted maghemite (for x = 0.2, 78 Am2/kg), it has higher heating ability and specific absorption rate compared to Al-substituted maghemite (for x = 0.07, 70 Am2/kg) and pure maghemite (62 Am2/kg).     

Elevated temperature creep behavior of three rapidly solidified Al-Fe-Si materials containing Cr, Mn, or Mo

Research on the high temperature creep behavior of three rapidly solidified Al-Fe-X-Si (where X = Cr, Mn or Mo) dispersion strengthened materials with three different alloying compositions has been conducted. Firstly, microstructural examinations have been carried out on the as-received, thermally treated and tested samples. The microstructure consists of a fine Al matrix embedding small round-shaped Al₁₂(Fe,X)₃Si and Al₁₃(Fe,X)₄ dispersoids. Grain sizes ranging from 0.85 to 1.45 μm and dispersoid sizes ranging from 45 to 54 nm were observed. Secondly, tensile tests were performed at high temperature from 573 to 823 K at strain rates ranging from 2.5×10⁻⁶ to 10⁻²s⁻¹. The experimental data exhibited high apparent stress exponent, n_ap, and high activation energy, Q_ap. The rnicrostructure remained stable and fine after testing. The results are analyzed by means of various models used in the literature.     

Release of Cr(III) from Cr(III) picolinate upon metabolic activation

Hexavalent and trivalent chromium are released into the environment from a number of different industrial activities. It is known that Cr(VI) can be reduced and subsequently complexed by humic acids to produce Cr(III) humic acid complexes in the soil and aquatic environments. The metabolic fate of Cr(III) humic acid complexes and other Cr(III) organic complexes in mammalian systems is unknown. Therefore, Cr(III) picolinate was chosen as a model complex for Cr(III) humic acid complexes and other environmentally relevant Cr(III) complexes. Both human hepatocyte microsomes and primary cultures of chick hepatocytes were used to generate metabolites of Cr(III) picolinate. The results from both of these treatments show that a significant amount of Cr(III) is released (66 and 100%, respectively) and that N-1-methylpicotinamide is the primary organic metabolite from this compound. These data suggest that the populations of humans who are exposed Cr(III) picolinate or other environmentally relevant organic Cr(III) complexes, such as Cr(III) humic acid complexes, are potentially accumulating high levels of Cr(III) intracellularly. This intracellular accumulation of Cr(III) can result in the formation of covalent bonds between Cr(III) and DNA and/or other macromolecules, causing genotoxic effects. These data should be considered when assessing the risk of an area contaminated with chromium.     

Composition dependence of magnetocaloric effect in Pr0.6Ca0.4Mn(1-x)Cr(x)O3 (x = 0.02-0.08)

We report the effect of varying Cr content on magnetic and magnetocaloric properties of Pr0.6Ca0.4Mn(1-x)Cr(x)O3 samples (x = 0, 0.02, 0.04, 0.06 and 0.08). While the parent compound (x = 0) is a charge ordered and antiferromagnetic insulator, Cr doped compounds are ferromagnetic metals with nearly same Curie temperature (T(c) approximately 140 K). We find unusual field-induced meta-magnetic transition above T(c) in x = 0.02 and 0.04 which is absent in x = 0.06 and 0.08. It is suggested that the paramagnetic phase in these compounds is inhomogeneous with coexistence of nano-size ferromagnetic clusters and short range charge ordered clusters. Field induced growth of ferromagnetic nano-clusters and destruction of short-range charge ordering leads to the observed metamagnetic transition, which results in large magnetic entropy change of -deltaS(M) = 5.043, 6, 5.509 and 4.375 J/kg K under deltaH = 5 T, for x = 0.02, 0.04, 0.06 and 0.08, respectively. In addition, large relative cooling power (RCP) found in these materials (327.384, 286.36, 272.22 and 279.936 J/kg) makes it interesting for practical applications. Our study suggests that creation of ferromagnetic nano-clusters in the paramagnetic phase by Mn-site doping in charge ordered compounds provides an alternative approach to achieve high AS(M) and RCP values.     

Alloying (In,Mn)As and (Ga,Mn)As: Ferromagnetic (In,Ga,Mn)As Lattice-Matched to InP

An effect of alloying two ferromagnetic semiconductors (In,Mn)As and (Ga,Mn)As on the ferromagnetic properties of resultant (In,Ga,Mn)As alloys is reported. For conditions close to lattice-matching to InP substrates, y = 0.53 in (In _y Ga_1–y )_1–x Mn _x As, ferromagnetism up to Curie temperatures T _C = 100–110 K could be achieved for a Mn composition x = 0.13. Trends in the Curie temperature in (In,Ga,Mn)As are compared with (Ga,Mn)As and (In,Mn)As as a function of Mn content. Hole concentrations determined from magnetotransport, taking into account the anomalous Hall contribution to Hall resistance, gives p/Mn = 0.03 ratio to Mn composition in metallic case for x = 0.13. We mention the possible role of chemical ordering (short range) of Mn impurity atoms on hole concentration and, consequently, for the ferromagnetic properties.     

On the possibility of incorporating Mn(II) and Cr(III) in SAPO-34 in the presence of isopropylamine as a template

Hydrothermal synthesis of SAPO materials using isopropylamine (i-PrNH₂) as the template leads to the formation of MnAPSO-34 if Mn(II) is present. In the presence of Cr(III), the synthesis yields SAPO-34 containing chromium(III), which is not incorporated in the silicoaluminophosphate lattice. Calcination of MnAPSO-34 results in oxidation of Mn(II); the calcinated product can be subsequently reduced back to MnAPSO-34. The MnAPSO-34 material catalyzes dehydration of methanol, and its catalytic activity is higher than that of SAPO-34.     

YAl3(BO3)4:TM (TM = Mn, Co, Cr) nanocrystals synthesis for laser operated nonlinear optics

An attempt to synthesize YAB matrices doped with cobalt, manganese, and chromium ions by means of the Pechini method for photo-induced nonlinear optics was performed. The best results were obtained for the Cr doped samples. It may be related with the fact that YAB:Cr main absorption peak is situated near the photo-inducing green second harmonics of Nd:YAG laser at 532 nm. It was established that after 600 s of samples illumination there was observed some maximum of the SHG. With the further treatment of the materials the SHG starts to decrease. The maximal enhancement was achieved at 150 K. After the switching off of the photo-inducing treatment the output SHG was relaxed to initial state during 2–3 min. Local increase of temperature due to heating did not exceed 6 K. For the Mn doped YAB NC the behavior is quite non-monotonic. The SHG changes are within the accuracy of the YAB NC NLO measurements. One can see two slight maxima at 200 and 800 s. At the same time Co suppress the output SHG, which may be caused by specific features of Co ions.     

Mathematical models applied to the Cr(III) and Cr(VI) breakthrough curves

Trivalent and hexavalent chromium continuous biosorption was studied using residual brewer Saccharomyces cerevisiae immobilized in volcanic rock. The columns used in the process had a diameter of 4.5 cm and a length of 140 cm, working at an inlet flow rate of 15 mL/min. Breakthrough curves were used to study the yeast biosorption behavior in the process. The saturation time (ts) was 21 and 45 h for Cr(III) and Cr(VI), respectively, and a breakthrough time (tb) of 4 h for Cr(III) and 5 h for Cr(VI). The uptake capacity of the biosorbent for Cr(III) and Cr(VI) were 48 and 60 mg/g, respectively. Two non-diffusional mathematical models with parameters t0 and sigma were used to adjust the experimental data obtained. Microsoft Excel tools were used for the mathematical solution of the two parameters used.     

Phase relationships in the ternary systems (V,Cr, Mo,W, Mn,Re)-Al-N

Phase equilibria in the ternary systems of aluminum and nitrogen with vanadium, chromium, molybdenum, tungsten, manganese and rhenium are investigated by X-ray diffraction of sintered alloys. No ternary phase is observed. AIN does not show solubility for these metals, and coexists either with the solid solution of these metals with aluminium (in the case of vanadium, chromium and manganese) or with the pure metal (for molybdenum, tungsten and rhenium). Isothermal sections are presented for 1073 K (Mn-Al-N), 1273 K (V-Al-N, Cr-Al-N, Mn-Al-N and Re-Al-N), 1573 K (V-Al-N) and 1773 K (Mo-Al-N, W-Al-N and Re-Al-N).     

Adsorption characteristics and separation of Cr(III) and Cr(VI) on hydrous titanium(IV) oxide

A hydrous titanium(IV) oxide was prepared to study the adsorption characteristics and the separation of chromium species. Batch sorption studies have been carried out to determine the effect of pH on the sorption of Cr(III) and Cr(VI) on hydrous TiO2. An excellent separation efficiency of Cr(III) and Cr(VI) was obtained at pH 2. The adsorption percentage of Cr(VI) was above 99%, whereas that of the Cr(III) was less than 1% at this pH. The adsorption isotherm of Cr(VI) on hydrous TiO2 at pH 2 was in good agreement with the Langmuir isotherm. The maximum adsorption capacity of Cr(VI) on TiO2 was 5 mg g(-1). The rate of adsorption of Cr(VI) by hydrous TiO2 with average particle diameter 250 and 500 microm has been studied under particle diffusion controlled conditions. The diffusion coefficients of Cr(VI) for both hydrous TiO2 having average particle diameter of 250 and 500 microm was calculated at pH 2 as 3.84 x 10(-10) m2 s(-1) and 8.86 x 10(-10) m2 s(-1), respectively.     

Comparison of CrAlN layers obtained with one (CrAl) or two targets (Cr and Al) by magnetron sputtering

The aim of this study is to compare the properties of CrAlN coatings obtained by magnetron sputtering with one (CrAl) or two targets (Cr and Al). The influence of parameters such as the target bias voltage, the working pressure, the deposition time and the bias voltage applied on the Cr or Al targets on the properties of the layers was studied. We characterized the films by X-ray Diffraction, Scanning Electron Microscopy, coupled with Energy Dispersive Spectroscopy, nanoindentation and their residual stresses were also determined. The optimal films obtained with both methods are well crystallized, well-adherent to the substrate, and contained similar amounts of Al (20-30 at.%). The optimal coatings synthesized with one target presented properties not as good as those realized with two targets. Nevertheless, films made with one target showed a lower frictional coefficient probably due to composition control. The lack of compositional control with the use of one target limits the optimization process. With two targets, we have greater control over the film composition. This leads to higher hardness, lower stresses, and improved Young's modulus over films produced with a single CrAl target. Additionally, the morphologies are different (columnar with CrAl and dense with Cr and Al). To conclude, it seems more justified to work if possible with two independent targets.