The effect of sequential and continuous high-energy impact mode on the mechano-chemical synthesis of nanostructured complex hydride Mg2FeH6

The effect of sequential and continuous high-energy impact mode in the magneto-mill Uni-Ball-Mill 5 on the mechano-chemical synthesis of nanostructured ternary complex hydride Mg₂FeH₆ was studied by controlled reactive mechanical alloying (CRMA). In the sequential mode the milling vial was periodically opened under a protective gas and samples of the milled powder were extracted for microstructural examination whereas during continuous CRMA the vial was never opened up to 270 h duration. MgO was detected by XRD in sequentially milled powders while no MgO was detected in the continuously milled powder. The abundance of the nanostructured ternary complex hydride Mg₂FeH₆, produced during sequential milling, and estimated from DSC reached 44 wt.% after 188 h, and afterwards it slightly decreased to 42 wt.% after 210 and 270 h. In contrast, the DSC yield of Mg₂FeH₆ after continuous CRMA for 270 h was 57 wt.%. Much higher yield after continuous milling is attributed to the absence of MgO. This behavior provides strong evidence that MgO is a primary factor suppressing formation of Mg₂FeH₆. The DSC hydrogen desorption onset temperatures are close to 200 °C while the desorption peak temperatures for all powders are below 300 °C and the desorption process is completed within the range 10–20 min. Within the investigated nanograin size range of 5–13 nm, the DSC desorption onset and peak temperatures of β-MgH₂ and Mg₂FeH₆ do not exhibit any trend with nanograin (crystallite) size of hydrides. TPD hydrogen desorption peaks from the powders containing a single ternary complex hydride Mg₂FeH₆, are very narrow, which indicates the presence of small but well-crystallized hydride particles. Their narrowness provides good evidence that the phase composition, bulk hydrogen distribution and hydride particle size distribution are very homogeneous. The overall amount of hydrogen desorbed in TPD from single-hydride Mg₂FeH₆ powders is somewhat higher than that observed in DSC and TGA desorption.

The powder milled sequentially for 270 h and desorbed in a Sieverts-type apparatus at 250 and 290 °C, yielded about a half of the hydrogen content obtained during DSC and TGA tests. No desorption of hydrogen was detected in a Sieverts-type apparatus at 250 and 290 °C after 128 and 70 min, respectively, from the powder continuously milled for 270 h. The latter easily desorbed 3.13 and 2.83 wt.% hydrogen in DSC and TGA tests, respectively.     

Properties of chemically prepared MmNi4.52Mn0.49 alloy

MmNi_4.52Mn_0.49 (Mm is mischmetal) alloy was prepared by a coprecipitation-reduction process. The alloy structure, chemical composition, particle size and surface properties were investigated by using the analysis of X-ray diffraction, inductively coupled plasma emission spectroscopy, particle size analysis and X-ray photoemission spectroscopy. Pressure-composition isotherms of the chemically prepared alloy were measured. The alloy powder was evaluated as the active material of a metal hydride electrode. It is found that the alloy thus obtained has larger specific surface area, different surface states, lower activation energy for hydrogen absorption/desorption and better electrode characteristics than the alloy prepared by conventional arc-melting.     

Hydrogen absorption–desorption properties of Ti0.32Cr0.43V0.25 alloy

Ti_0.32Cr_0.43V_0.25 alloy specimens were heat treated, and its various hydrogen storage properties were measured at 303 K to examine its potential as a hydrogen storage material. The heat treatment improved not only the total and the effective hydrogen storage capacities, but also the plateau flatness. The heat of hydride formation was approximately −36 kJ/mol H₂. The effective hydrogen storage capacity remained at approximately 2 wt% after 1000 cycles of pressure swing cyclic tests. The hydrogen storage capacity could be recovered almost to the initial state by reactivating the alloy. The hydrogen absorption rate increased with the repetition of cycling for the first several cycles and remained almost constant afterward. At the 504th cycle, more than 98% of the hydrogen was absorbed within the first 2 min. X-ray diffraction (XRD) patterns showed that the crystal structure of the alloy became more amorphous as the number of cycles increased.     

Another unusual phenomenon for Zr7Ni10: structural change in hydrogen solid solution and its conditions

Zr₇Ni₁₀ has three hydrogen occlusion phases, , β and γ, and the following unusual features are known for the phase transitions in the Zr₇Ni₁₀–H₂ system: (1) The intermediate hydride phase (β) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase () exhibits a much higher hydrogen solubility during hydrogenation than during dehydrogenation. In order to clarify the mechanism about the difference in the hydrogen solubility of the phase, the relation between the pressure-composition isotherms and corresponding structural change has been examined by a conventional volumetric method and X-ray diffraction. Through the examination, we discovered that the crystal structure of the phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated phase changes from an orthorhombic structure to a tetragonal structure. The conditions causing the structural change were then examined, and it has been found that the phase maintains its original orthorhombic structure as long as it is hydrogenated so as not to absorb enough hydrogen to change it to the hydride with a higher hydrogen content (γ). The phenomenon can be understood as one of the hydrogen-assisted phase transitions such as hydrogen-induced amorphization (HIA) in the sense that the phase transition requires hydrogenation under special conditions.     

Interaction of hydrogen with the LaNi4.9In0.1, LaNi4.8In0.2 and LaNi4.8 alloys and their Nd analogues

The single phase nature of the alloys LaNi_4.9In_0.1, LaNi_4.8In_0.2, NdNi_4.9In_0.1, NdNi_4.8In_0.2 of the systems LaNi_5−xIn_x and NdNi_5−xIn_x was confirmed by means of X-ray powder diffractometry. Nonstoichiometric alloys LaNi_4.8 and NdNi_4.8 were prepared and were also found to be good single phase materials. All these alloys crystallize with the same hexagonal structure of the CaCu₅ type (space group P6/mmm) as do their prototypes LaNi₅ and NdNi₅. In order to determine the interaction with hydrogen the alloys were exposed to hydrogen gas and the pressure composition desorption isotherms were measured. It was found that all alloys react readily and reversibly absorb large amounts of up to 6.54 hydrogen atoms per alloy formula unit. Generally the equilibrium pressure and the hydrogen capacity decrease with the decreasing nickel content. Presence of indium in the alloy acts in favour of these trends. Furthermore, the increasing content of indium in the alloy system drastically alters the slope and the pressure of the plateau observed at higher pressure of the two isotherm plateaux of the NdNi₅–hydrogen system. The final result is a merge of both plateaux into a single one for the hydrogen desorption isotherms of NdNi_4.8In_0.2. However, the isotherms of nonstoichiometric NdNi_4.8 still exhibit two separated pressure plateau regions. The thermodynamic parameters of hydride formation, i.e., the entropy change, the enthalpy and the Gibbs free energy of formation have also been extracted for all alloy–hydrogen systems.     

二氧化铈抛光液化学机械抛光微晶玻璃的机理及优化

以纳米CeO₂为磨料自制抛光液,研究磨料质量分数、pH值、抛光液流量、抛光盘转速、表面活性剂种类和氟化铵质量分数等因素对微晶玻璃化学机械抛光的影响,分析总结CeO₂在微晶玻璃化学机械抛光中的作用机理,利用原子力显微镜（AFM）检测微晶玻璃抛光后的表面粗糙度。结果表明:当CeO₂质量分数为3%、抛光液流量为25mL/min、抛光盘转速为100r/min、pH=8.0、十二烷基硫酸钠质量分数为0.01%,氟化铵质量分数为0.7%时,抛光后微晶玻璃表面粗糙度（R_a）最低为0.72nm,材料去除速率达到180.91nm/min。      

Hydrogen absorption of slurry system composed of different MgNi alloy and benzene

The hydrogen absorption amount and kinetics of the slurry formed by suspending the MgNi alloy powder in liquid benzene were studied.It is discovered that hydrogen is absorbed by both the solid phase(alloy) and liquid phase(C6H6)and the hydrogen absorption rate varies with the temperature and the content of the Mg-Ni in the slurry.Most hydrogen absorption curves of the slurry fall into two regions.in which the mechanism of hydriding reaction in the slurry system is different.In the former region,the hydriding of the alloy proceeds with hydrogen diffusing through C6H6.The part in the second region is the outcome of the hydrogenation of C6H6.At 548K and under the hydrogen pressure of 4.5MPa saturation capacity for the slurry of 80% C6H69mass fraction) 20%Mg Ni(mass fraction)is 5.9%(mass fraction)hydrogen,which is 97% of the theoretic capacity of the slurry system. The hydride of the alloy MgNi,which is only the hydride of Mg2 Ni phase,Mg2NiH4,is an efficent catalyst for the hydrogenation of C6H6into C6H12(C6H6 3H2→C6H12)in the slurry system.     

A向蓝宝石化学机械抛光研究

以纳米氧化铝为磨料对A向蓝宝石进行化学机械抛光,实验中考察了磨料浓度、磨料粒径、抛光时间、抛光压力以及NH₄F浓度等因素对A向蓝宝石的材料去除速率和表面粗糙度的影响。利用原子力显微镜（AFM）检测抛光后A向蓝宝石的表面粗糙度,系统分析抛光过程中各影响因素,优化实验条件,结果表明:当抛光液中磨料质量分数为1%、磨料粒度尺寸为50nm、抛光时间为40 min、抛光压力为16.39 kPa、NH₄F质量分数为0.6%、pH=4.0时,抛光后材料去除速率（MRR）为18.2 nm/min,表面粗糙度值R_a 22.3 nm,抛光效果最好。      

Mg6Ir2H11, a new metal hydride containing saddle-like [IrH4] and square-pyramidal [IrH5] hydrido complexes

Mg₆Ir₂H₁₁ has been synthesised by both hydrogenation of the intermetallic compound Mg₃Ir at 20 bar and 300 °C, and sintering of the elements at 500 °C under 50 bar hydrogen pressure. Neutron powder diffraction on the deuteride indicates a monoclinic structure (space group P2₁/c, Mg₆Ir₂D₁₁: a=10.226(1), b=19.234(2), c=8.3345(9) Å, β=91.00(1)°, T=20 °C) that is closely related to orthorhombic Mg₆Co₂H₁₁. It contains a square-pyramidal [IrH₅]⁴⁻ complex and three saddle-like [IrH₄]⁵⁻ complexes of which one is ordered and two are disordered. Five hydride anions H⁻ are exclusively bonded to magnesium. The compound has a red colour, is presumably non-metallic and decomposes under 3 bar argon at 500 °C into Mg₃Ir, iridium and a previously unreported intermetallic compound of composition Mg₅Ir₂.     

Synthese und Struktur von SrPdH2, 7

The copper-red hydride SrPdH_2.7 has been obtained by heating an Sr-Pd alloy at 200 °C under a hydrogen atmosphere. The alloy was prepared from fusing equimolar amounts of the individual metals. X-ray and neutron diffraction experiments led to the perovskite-type structure in which the hydrogen atoms statistically occupy the threefold site with an occupancy factor of 0.91(4). Correlations between the volume increments of the hydrogen atoms and the bonding properties will be discussed for SrPdH_2.7 and structurally related hydrides.

Résumé

Aus einer durch Zusammenschmelzen äquimolarer Mengen von Palladium- und Strontiummetall erhaltenen Legierung konnte in einer Wasserstoffatmosphäre bei 200 °C das kupferrote Hydrid SrPdH_2,7 erhalten werden. Röntgen- und Neutronenbeugungsexperimente führten zum Perowskitstrukturtyp, in dem die Wasserstoffatome die dreizählige Punktlage statistisch mit einem Besetzungsfaktor von 0,91(4) belegen. Für SrPdH_2,7 und strukturverwandte Hydride werden Korrelationen zwischen den jeweiligen Volumeninkrementen der Wasserstoffatome und den Bindungsverhältnissen diskutiert.     

Improvement in hydrogen sorption properties of Mg by reactive mechanical grinding with Cr2O3, Al2O3 and CeO2

We tried to improve the hydrogen sorption properties of Mg by mechanical grinding under H₂ (reactive mechanical grinding) with oxides Cr₂O₃, Al₂O₃ and CeO₂. The hydriding rates of Mg are reportedly controlled by the diffusion of hydrogen through a growing Mg hydride layer. The added oxides can help pulverization of Mg during mechanical grinding. A part of Mg is transformed into MgH₂ during reactive mechanical grinding. The Mg+10wt.%Cr₂O₃ powder has the largest transformed fraction 0.215, followed in order by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. The Mg+10wt.%Cr₂O₃ powder has the largest hydriding rates at the first and fifth hydriding cycle, followed in order by Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. Mg+10wt.%Cr₂O₃ absorbs 5.87wt.% H at 573 K, 11 bar H₂ during 60 min at the first cycle. The Mg+10wt.%Cr₂O₃ powder has the largest dehydriding rates at the first and fifth dehydriding cycle, followed by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. It desorbs 4.44 wt.% H at 573 K, 0.5 bar H₂ during 60 min at the first cycle. All the samples absorb and desorb less hydrogen at the fifth cycle than at the first cycle. It is considered that this results from the agglomeration of the particles during hydriding–dehydriding cycling. The average particle sizes of the as-milled and cycled powders increase in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of hydrogen absorbed or desorbed for 1 h for the first and fifth cycles decrease in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of absorbed or desorbed hydrogen increase as the average particle sizes decrease. As the particle size decreases, the diffusion distance shortens. This leads to the larger hydriding and dehydriding rates. The Cr₂O₃ in the Mg+10wt.%Cr₂O₃ powder is reduced after hydriding–dehydriding cycling. The much larger chemical affinity of Mg than Cr for oxygen leads to a reduction of Cr₂O₃ after cycling.     

Disintegration and fine powder preparation of Nb75Si25 via hydrogenation

Hydrogenation of Nb₇₅Si₂₅ directly in an arc-melting chamber after arc-melting was investigated. A Nb₇₅Si₂₅ ingot absorbs hydrogen rapidly and simultaneously disintegrates into fine hydride powder. After dehydriding at 1073 K for 10.8 ks, fine Nb₇₅Si₂₅ particles with an irregular angular shape are obtained. The collecting efficiency of powder under 100 mesh is 56.1 wt.%.     

Properties of copper matrix reinforced with various size and amount of Al2O3 particles

Copper matrix was reinforced with Al₂O₃ particles of different size and amount by internal oxidation and mechanical alloying accomplished using high-energy ball milling in air. The inert gas-atomised prealloyed copper powder containing 1 wt.% Al as well as a mixture of electrolytic copper powder and 3 wt.% commercial Al₂O₃ powder served as starting materials. Milling of Cu-1 wt.% Al prealloyed powder promoted formation of fine dispersed particles (1.9 wt.% Al₂O₃, approximately 100 nm in size) by internal oxidation. During milling of Cu-3 wt.% Al₂O₃ powder mixture the uniform distribution of commercial Al₂O₃ particles has been obtained. Following milling, powders were treated in hydrogen at 400 °C for 1 h in order to eliminate copper oxides formed at the surface during milling. Compaction was executed by hot-pressing. Compacts processed from 5 to 20 h-milled powders were additionally subjected to high-temperature exposure at 800 °C in order to examine their thermal stability and electrical conductivity. Compacts of Cu-1 wt.% Al prealloyed powders with finer Al₂O₃ particles and smaller grain size exhibited higher microhardness than compacts of Cu-3 wt.% Al₂O₃ powder mixture. This indicates that nano-sized Al₂O₃ particles act as a stronger reinforcing parameter of the copper matrix than micro-sized commercial Al₂O₃ particles. Improved thermal stability of Cu-1 wt.% Al compacts compared to Cu-3 wt.% Al₂O₃ compacts implies that nano-sized Al₂O₃ particles act more efficiently as barriers obstructing grain growth than micro-sized particles. Contrary, the lower electrical conductivity of Cu-1 wt.% Al compacts is the result of higher electron scatter caused by nano-sized Al₂O₃ particles.     

Hydrogen storage characteristics of composite TiCr1.8 + X wt.% LaNi5 alloys

In this paper, phase constituent, hydrogen storage characteristics and electrochemical performances of composite TiCr_1.8 + X wt.% LaNi₅ alloys with different stoichiometry were investigated. X-ray diffraction (XRD) tests reveal that these alloys still remain Laves phase constituent despite the increase of LaNi₅ content in alloys. Electrochemistry performance is improved whereas the maximum hydrogen storage capacity of pressure composition temperatures (PCT) test slightly decreases at the same time. One kind of alloy with capacity up to 55 mAh/g has been developed.     

Hydriding combustion synthesis of Mg–CaNi5 composites

The composites of Mg–x wt.% CaNi₅ (x = 20, 30 and 50) were prepared by hydriding combustion synthesis (HCS) and the phase evolution during HCS as well as the hydriding properties of the products were investigated. It was found that Mg reacted with CaNi₅ forming Mg₂Ni and Ca during the heating period of HCS. Afterwards, the resultant Mg₂Ni and Ca as well as the remnant Mg reacted with hydrogen during the cooling period. The lower platform in the P–C isotherms corresponds to the hydriding of Mg, and the higher one corresponds to Mg₂Ni. With the increase of the content of CaNi₅ from 20 to 50 wt.%, the hydrogen content of the HCS products increases at first and then decreases. The Mg–30 wt.% CaNi₅ composite has the maximum hydrogen capacity of 4.74 wt.%, and it can absorb 3.51 wt.% of hydrogen in the first hydriding process without activation.     

A facile route to VN and V2O3 nanocrystals from single precursor NH4VO3

V₂O₃ and VN nanocrystals have been synthesized by the decomposition of the precursor NH₄VO₃ and following nitridation in an autoclave with metallic Na flux at 450–600 °C. X-ray powder diffraction (XRD) recorded the evolution process of the reaction from precursor NH₄VO₃ to hexagonal V₂O₃ and then to NaCl-type VN. In addition, the products were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).     

Microstructure and electrochemical properties of mechanically ground Ce2Mg17 + x wt.% Ni (x = 0, 50, 100, 200) composites

The effects of mechanical grinding with or without nickel powder on microstructure and electrochemical properties of Ce₂Mg₁₇ hydrogen storage alloy in 6 M KOH solution were investigated. The microstructure and electrochemical properties depend greatly on the amount of nickel powder introduced during mechanical grinding. For the alloy ball-milled with nickel powder, the more nickel powder added, the more advantageous it is for the formation of a homogeneous amorphous structure, and the larger discharge capacity obtained. After 90 h ball-milling, the Ce₂Mg₁₇ + 200 wt.% Ni composite exhibited a large discharge capacity of 1014 mAh g(Ce₂Mg₁₇)⁻¹[338 mAh g(Ce₂Mg₁₇ + 200 wt.% Ni)⁻¹] at 303 K. The improvement of electrochemical capacity can be attributed to the formation of a homogeneous amorphous structure as well as the modification of the surface state by Ni addition.     

LiMg2RuH7, a new quaternary metal hydride containing octahedral [Ru(H)H6] complex anions

LiMg₂RuH₇ and its deuteride were synthesized by sintering mixtures of LiH, magnesium and ruthenium powders at 500–550 °C and a hydrogen (deuterium) pressure of 120–155 bar, and characterized by X-ray and neutron powder diffraction. The yellow powder crystallizes with hexagonal symmetry (space group, P6₃/mmc; hydride - A = 4.7060(1) Å, C = 10.6960(2) Å; deuteride - A = 4.6998(1) Å, C = 10.6674(3) Å). The structure is an ordered substitution variant of Mg₃ReH₇. It contains a nearly regular octahedral 18-electron [Ru(II)D₆]⁴⁻ complex with bond distances [Ru-6D1] = 1.704(7) Å, and a deuteride anion D⁻ coordinated in a trigonal bipyramidal configuration by two close magnesium and three distant lithium cations with bond distances [D2-2Mg] = 1.852(6) Å and [D2−3Li] = 2.7134(1) Å respectively.     

Na2SiF6活性激光焊接TC4钛合金焊缝成形和组织

采用Na₂SiF₆作为表面活性剂激光焊接TC4钛合金,通过观察焊缝表面,确定了Na₂SiF₆对TC4钛合金激光焊焊缝表面成形的影响;采用高速摄像技术,观察分析了焊件上方高温光致等离子体形态特征变化;借助光学显微镜观察分析了焊缝熔深和熔宽的变化及微观组织. 结果表明,涂覆Na₂SiF₆活性剂后TC4钛合金激光焊焊缝表面成形良好,可使焊缝熔深增加约0.8% ~ 12%,焊缝表面熔宽降低约10% ~ 29%,能够有效提高焊缝的深宽比;Na₂SiF₆活性剂改善了焊缝微观组织的不均匀性,改变了焊缝上部β柱状晶的结晶方向,细化了焊缝的晶粒尺寸和微观组织.     

电解液浓度对镁合金微弧氧化层耐蚀性与溶血率的影响

在电解液中加入 (NaPO₃)₆并在镁合金表面制备微弧氧化层,研究 (NaPO₃)₆浓度对镁合金微弧氧化层的影响.结果显示,微弧氧化层中含有MgO,Mg₂SiO₄,Mg₃(PO₄)₂等物质;随 (NaPO₃)₆浓度增加,微弧氧化层厚度增加,表面微孔孔径变大,当 (NaPO₃)₆浓度达到7 g/L时,微弧氧化层截面出现较明显的微裂纹;微弧氧化处理后的镁合金的耐蚀性明显高于基体的.当 (NaPO₃)₆浓度为5 g/L时其耐蚀性最佳;镁合金基体溶血率为72.3%,在不同浓度 (NaPO₃)₆下微弧氧化处理的镁合金溶血率均在1%~2.5%之间,溶血作用消除.