Review on the temperature memory effect in shape memory alloys

Shape memory alloys (SMAs) are well known for their unique shape memory effect (SME) and superelasticity (SE) behavior. The SME and SE have been extensively investigated in past decades due to their potential use in many applications, especially for smart materials. The unique effects of the SME and SE originate from martensitic transformation and its reverse transformation. Apart from the SME and SE, SMAs also exhibit a unique property of memorizing the point of interruption of martensite to parent phase transformation. If a reverse transformation of a SMA is arrested at a temperature between reverse transformation start temperature (A _s) and reverse transformation finish temperature (A _f), a kinetic stop will appear in the next complete transformation cycle. The kinetic stop temperature is a ‘memory’ of the previous arrested temperature. This unique phenomenon in SMAs is called temperature memory effect (TME). The TME can be wiped out by heating the SMAs to a temperature higher than A _f. The TME is a specific characteristic of the SMAs, which can be observed in TiNi-based and Cu-based alloys. TME can also occur in the R-phase transformation. However, the TME in the R-phase transformation is much weaker than that in the martensite to parent transformation. The decrease of elastic energy after incomplete cycle on heating procedure and the motion of domain walls have significant contributions to the TME. In this paper, the TME in the TiNi-based and Cu-based alloys including wires, slabs and films is characterized by electronic-resistance, elongation and DSC methods. The mechanism of the TME is discussed.     

High‐performance HTLcs‐derived CuZnAl catalysts for hydrogen production via methanol steam reforming

A series of CuZnAl oxide‐composite catalysts were prepared via decomposition of CuZnAl hydrotalcite‐like compounds (HTLcs). The catalysts derived from CuZnAl HTLcs (Cu: 37%, Zn: 15%, Al: 48% mol; using metal nitrate or acetate precursors) at 600°C provided excellent activity and stability for the methanol steam reforming. CuZnAl HTLcs were almost decomposed completely at 600°C to form highly dispersed CuO with large specific surface area while forming CuAl₂O₄ spinel that played a key role in separating and stabilizing the nano‐sized Cu and ZnO during the reaction. The CuZnAl catalyst prepared from metal acetates could highly convert H₂O/MeOH (1.3/1, mol/mol) mixture into hydrogen with only ～0.05% CO at 250°C or ～0.005% at 210°C. It is evidenced that the former afforded stronger Cu‐ZnO interaction, which might be the intrinsic reason for the significant promotion of catalyst selectivity. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

In Situ Hydrogenation of CO2 by Al/Fe and Zn/Cu Alloy Catalysts under Mild Conditions

The development of efficient metal catalysts for in situ hydrogenation of CO₂ in water under mild conditions has gained considerable attention. Three Al alloys (Al/Fe, Al/Fe/Cu, Al/Cu) and three Zn/Cu alloys for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions were investigated. Hydrogen was generated by reaction of Al, Fe, and Zn in the alloys with water. In situ hydrogenation of CO₂ was likely to be catalyzed by intermetallic compounds and generated metal oxides. Al alloys catalyzed the hydrogenation to methane while Zn/Cu alloys produced CO and formic acid. Zn/Cu5 possessed the highest catalytic activity, which was attributed to the CuZn5 crystal planes in the alloys. Insights are provided into the importance of compositions and structures of alloys for the selectivity for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions.     

Selective production of hydrogen by partial oxidation of methanol over catalysts derived from CuZnAl‐layered double hydroxides

Hydrogen production by partial oxidation of methanol (POM) reaction (CH₃OH + (1/2)O₂ ⇌ ₂H₂ + CO₂) was investigated over a series of CuZnAl ternary oxide catalysts derived from CuZnAl hydroxycarbonate precursors containing hydrotalcite‐like layered double hydroxide as a major phase. These catalysts exhibited a good catalytic activity and high H₂ selectivity. A methanol conversion of about 40–60% was obtained at 200°C with high selectivity of H₂ and CO₂. The undesirable by‐product, CO was virtually not produced over most of the catalysts at this temperature. The catalytic activity was found to decrease with increasing (Cu + Zn)/Al atomic ratio in the precursor and, was correlated with Cu metal surface areas, Cu dispersion and Cu particle sizes, which were calculated by both XRD and TPR‐N₂O passivation methods. The catalyst with higher Cu surface areas and Cu dispersion displayed a higher catalytic activity. Lifetime experiments showed that these catalysts were stable over a period of 24 h of continuous operation. Catalyst precursors containing hydroxycarbonates other than LDH as a major phase offered considerable amount of dimethyl ether as a by‐product. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure and physicochemical properties of glasses in the (As2Se3)1 ? z-(SnSe2)z ? x-(Tl2Se)x and (As2Se3)1 ? z-(SnSe)z ? x-(Tl2Se)x systems

A comparative investigation of glasses in the As₂Se₃)_{1 − z} -(SnSe₂) _{z − x} -(Tl₂Se) _x and (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x systems has been performed. In both systems, the glass formation regions are shifted toward the As₂Se₃ compound. Only tin(IV) in the structure of glasses in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system is identified by M?ssbauer spectroscopy, whereas glasses in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system contain both Sn(II) and Sn(IV). The presence of tin in the oxidation state 2+ in the structural network of the glasses does not lead to impurity conduction. The dependences of the density, the microhardness, and the glass transition temperature on the glass composition are explained in the framework of the model according to which the structure of these glasses is built up of structural units corresponding to the As₂Se₃, AsSe, TlAsSe₂, Tl₂Se, SnSe, and SnSe₂ compounds. It is established that, for crystalline alloys in the (As₂Se₃)_{1 − z} -(SnSe) _{z − x} -(Tl₂Se) _x system, there exist two compounds (Tl₂SnSe₃ and Tl₄SnSe₄), which are formed by the peritectic reactions; however, structural units of these compounds are not formed in the structural network of glasses.     

SHS-produced β-sialons as supports for oxidation catalysts

SHS-produced β-sialons Si_6−z Al _z O _z N_8−z (z = 1, 3, 4) were tested as supports for oxidation catalysts comprising of unary, binary or ternary mixtures of transition metal (Cr, Mn, Fe, Co, Ni, Cu) oxides and also KMnO₄ and K₂Cr₂O₇. In oxidation of CO and propane (C₃H₈), the highest activity was exhibited by the catalysts based on cobalt oxides. Suggested are some methods for activation of the above catalysts.      

Influence of alloying and microstructure on the electrochemical hydriding of TiNi-based ternary alloys

Nanostructured ternary TiNi-type alloys, namely Ti_0.8M_0.2Ni (M = Zr, V), TiNi_0.8N_0.2 (N = Cu, Mn) and TiNi_1−x Mn _x (x = 0.2, 0.4, 0.6, 1.0), were synthesized by mechanical alloying. Depending on the intensity and time of milling alloys with different microstructure were obtained. The as-milled TiNi_1−x Mn _x alloys contain substantial amount of amorphous phase, which crystallizes during annealing. Annealing of the as-milled fine nanocrystalline materials at 500 °C results only in slight coarsening of the microstructure, which remains still nanocrystalline. Fully crystalline material (with crystal size larger than 50 nm), consisting of mainly cubic TiNi was obtained by annealing the ball-milled alloys at T ≥ 700 °C. Electrochemical hydrogen charge/discharge cycling of the as-milled as well as of annealed alloys were carried out at galvanostatic conditions. It was found that among the nanocrystalline Ti_0.8M_0.2Ni_0.8N_0.2 (M = Zr, V; N = Cu, Mn) alloys TiNi_0.8Mn_0.2 revealed the highest discharge capacity of 56 mAh g⁻¹ in the as-milled state and 75 mAh g⁻¹ after short-time annealing at 500 °C. Annealing at higher temperature does not increase the capacity further. The as-milled TiNi_1−x Mn _x alloys with x ≤ 0.4 reveal noticeably higher discharge capacity and better cycle life than the Mn-richer alloys. Based on potentiostatic experiments the diffusion coefficients of hydrogen into TiNi alloys in two different microstructural states (fine and coarser nanocrystalline) as well as in as-milled amorphous/nanocrystalline and nanocrystalline TiNi_0.8Mn_0.2 were determined. The hydrogen diffusion coefficients of the TiNi alloys are comparable (1.9–2.7 × 10⁻¹² cm² s⁻¹). The diffusion coefficient in the as-milled amorphous/nanocrystalline TiNi_0.8Mn_0.2 was found to be 3–4 times higher than that of the as-milled nanocrystalline alloy.     

Thermal explosion in mechanoactivated 3Ni + Al mixtures

Explored was thermal explosion in mechanoactivated 3Ni + Al mixtures. Mechanoactivation was found to result in an abnormal decrease in the effective activation energy E and ignition temperature T_ign for thermal explosion. Analysis of reaction thermogram allowed us to find out the kinetic function. Mechanoactivation conditions for synthesis of Ni₃Al in thermal explosion mode have been optimized. SHS reaction in 3Ni + Al mixtures mechanoactivated for 180 s was found to obey the first-order kinetics.      

Phase Equilibria of the Zinc Oxide–Cobalt Oxide System in Air

Phase equilibria of the zinc oxide–cobalt oxide system were studied by a combination of X‐ray diffraction and in situ electrical conductivity and thermopower measurements of bulk ceramic specimens up to 1000°C in air. Rietveld refinement of X‐ray diffraction patterns demonstrated increasing solubility of Co in ZnO with increasing temperature, which is supported by the slight increase in wurtzite (Zn_1?xCo_xO) cell volume and lattice parameter a versus temperature determined for the phase boundary compositions. Similarly, the solubility of Zn in CoO increased with increasing temperature. In contrast, the spinel phase (Zn_zCo_3?zO₄) exhibited retrograde solubility for Zn. Electrical measurements showed that the eutectoid temperature for transformation of rocksalt Co_1?yZn_yO into wurtzite and spinel is 894 ± 3°C, and the upper temperature limit of the stability of the spinel phase is 894°C–898°C for the compositions Co/(Zn+Co) = 0.82–1. The resulting composition‐temperature phase diagram is presented and compared to the earlier (1955) diagram by Robin.     

The effect of aluminum substitution on the mechanically induced self-sustaining reaction of molybdenum-silicon powders

The effect of Al concentration on the ignition of mechanically-induced self-sustaining reaction (MSR) in Mo + (2 ? x)Si + 2xAl powder mixtures has been investigated. When MoSi₂ is prepared by SHS method, Al addition results in the formation of Si-Al eutectic and consequently lowers the ignition temperature. In the case of MSR, replacing brittle Si with ductile Al also affects the activation process. The ignition of MSR was investigated as a function of the Al content in a SPEX 8000 Mixer Mill. The ignition time decreased by 30% between x = 0 and 0.08. At the same time, the grain size increased by about 50% according to XRD linewidth measurements. Comparison of SEM images suggests that Al substitution promotes the formation of agglomerates and lamellar structures, although the differences between the binary Mo-Si and Alcontaining samples are very small. Al substitution encourages the formation of hexagonal Mo(SiAl)₂ over the tetragonal form of MoSi₂. It also promotes more complete conversion during MSR.     

Electrochemical properties of Li1?z(Ni1?yFey)1+zO2 synthesized by the combustion method in an air atmosphere

For the syntheses of LiNi_1−y Fe _y O₂ (0.000 ≤ y ≤ 0.300), mixtures of the starting materials with the desired compositions were preheated in an air atmosphere at 400 °C for 30 min and calcined in air at 700 °C for 48 h. The phases appearing in the intermediate reaction steps for the formation of lithium nickel oxide are deduced from the DTA analysis. XRD analysis, FE-SEM observation, FTIR analysis and electrochemical measurement were performed for the synthesized Li_1−z (Ni_1−y Fe _y )_1+z O₂ (0.000 ≤ y ≤ 0.300) samples. The samples of Li_1−z (Ni_1−y Fe _y )_1+z O₂ with y = 0.025 and 0.050 have higher first discharge capacities than Li_1−z (Ni_1−y Fe _y )_1+z O₂ with y = 0.000 and better or similar cycling performance at the 0.1 C rate in the voltage range of 2.7–4.2 V. Similar results have not previously been reported except for Co-substituted LiNiO₂. The sample Li_1−z (Ni_0.975Fe_0.025)_1+z O₂ has the highest first discharge capacity (176.5 mAh g⁻¹). Rietveld refinement of the XRD patterns of LiNi_1−y Fe _y O₂ (0.000 < y ≤ 0.100) from a starting structure model [Li,Ni]_3b[Li,Ni,Fe]_3a[O₂]_6c showed that cation disordering occurred in the samples.     

Redox and transport behaviors of Cu(I) ions in TMHA-Tf<Subscript>2</Subscript>N ionic liquid solution

The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf₂N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf₂N containing 12 mmol dm⁻³ Cu(I) ions was 1.2 × 10⁻⁶ cm² s⁻¹ and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I ⁻/I ₃⁻ at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10⁻⁵ cm² s⁻¹ at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO₄ solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol⁻¹ in the ionic liquid solution.     

Effective MgO surface doping of Cu/Zn/Al oxides as water–gas shift catalysts

Trace amounts of MgO were doped on Cu/ZnO/Al₂O₃ catalysts with the Cu/Zn/Al molar ratio of 45/45/10 and tested for the water–gas shift (WGS) reaction. A mixture of Zn(Cu)–Al hydrotalcite (HT) and Cu/Zn aurichalcite was prepared by co-precipitation (cp) of the metal nitrates and calcined at 300 °C to form the catalyst precursor. When the precursor was dispersed in an aqueous solution of Mg(II) nitrate, HT was reconstituted by the “memory effect.” During this procedure, the catalyst particle surface was modified by MgO-doping, leading to a high sustainability. Contrarily, cp-Mg/Cu/Zn/Al prepared by Mg²⁺, Cu²⁺, Zn²⁺ and Al³⁺ co-precipitation as a control exhibited high activity but low sustainability. Mg²⁺ ions were enriched in the surface layer of m-Mg–Cu/Zn/Al, whereas Mg²⁺ ions were homogeneously distributed throughout the particles of cp-Mg/Cu/Zn/Al. CuO particles were significantly sintered on the m-catalyst during the dispersion, whereas CuO particles were highly dispersed on the cp-catalyst. However, the m-catalyst was more sustainable against sintering than the cp-catalyst. Judging from TOF, the surface doping of MgO more efficiently enhanced an intrinsic activity of the m-catalyst than the cp-catalyst. Trace amounts of MgO on the catalyst surface were enough to enhance both activity and sustainability of the m-catalyst by accelerating the reduction–oxidation between Cu⁰ and Cu⁺ and by suppressing Cu⁰ (or Cu⁺) oxidation to Cu²⁺.     

Copolymerization of 1-butene and 1-hexene with supported titanium catalyst

With TiCl₄/MgCl₂ (Ti) and Al(i-Bu)₃ (Al) as catalysts, the thermoplastic copolymer of 1-butene(Bt) and 1-hexene(He) was synthesized successfully. The effects of Bt/He, Ti/(He+Bt), Al/Ti, temperature and reaction time on conversion, catalyst efficiency(CE), intrinsic viscosity([η]) and insoluble content were studied. The copolymer was analyzed with Fourier transform-infrared (FTIR) and nuclear magnetic resonance (¹H-NMR). Results showed that the optimal polymerization conditions were: He/Bt = 0.25, temperature 40°C−50°C, Al/Ti = 400−500, Ti/(Bt+He) = 3 × 10⁻⁵ − 4 × 10⁻⁵, time 4 h. Intrinsic viscosity was found to increase with increasing Ti/(Bt+He) and decreasing Al/Ti and polymerization temperature. When the molar content of He, Al/Ti and polymerization temperature increased, the insoluble content in CH₂Cl₂ of copolymers decreased. When Ti/(Bt+He) and reaction time increased, the insoluble content in CH₂Cl₂ of copolymers also increased. The crystallization and stereoregularity of poly(1-butene) decreased with the addition of He. Translated from China Synthetic Rubber Industry, 2006, 29(6): 429–434 [译自: 合成橡胶工业]     

Simultaneous determination of trace aluminum (III), copper (II) and cadmium (II) in water samples by square-wave adsorptive cathodic stripping voltammetry in the presence of oxine

A validated adsorptive cathodic stripping voltammetry method is described for simultaneous determination of Al(III), Cu(II) and Cd(II) in water samples. In acetate buffer (pH 5) containing 10 μM oxine, these metal ions were determined as oxine complexes following adsorptive accumulation onto the HMDE at −0.05 V versus Ag/AgCl/KCl_s. The best signal to noise ratio was obtained using a square wave of scan increment 10 mV, frequency 120 Hz, and pulse-amplitude 25 mV. Limits of detection as low as 0.020 μg L⁻¹ Al(III), 0.012 μg L⁻¹ Cu(II) and 0.028 μg L⁻¹ Cd(II) were achieved. Interference due to various cations (K(I), Na(I), Mg(II), Ca(II), Mn(II), Fe(III), Bi(III), Sb(III), Se(IV), Pb(II), Zn(II), Ni(II), Co(II)), anions (Cl⁻, NO³⁻, SO₄ ²⁻, PO₄ ³⁻) and ascorbic acid was minimal as the measured signals change by 4% at the maximum. The stripping voltammetry method was successfully applied for simultaneous determination of Al(III), Cu(II) and Cd(II) in tap and natural bottled water samples.     

Effect of Cu and Zn elements on morphology of ceramic particles and interfacial bonding in TiB2/Al composites

The 50 vol% TiB₂/Al composites with different alloying elements (Cu and Zn) were prepared by hot pressing sintering. The effects of Zn and Cu on the micromorphology of TiB₂ ceramic particles and interfacial behavior between TiB₂ ceramic and Al matrix as well as the mechanical properties of composites were investigated. Results indicated that the addition of Zn and Cu not only significantly enhanced the interfacial bonding strength between TiB₂ ceramic particles and Al matrix but also facilitated the reaction by reducing the reaction temperature in the Al–Ti–B system. Furthermore, the yield strength (719 MPa) and ultimate compressive strength (1130 MPa) of TiB₂/Al-6wt.%Cu composite increased by 48.8% and 26.4%, respectively, compared with that of the composite without alloy element. For the TiB₂/Al-6wt.%Zn composite, the yield strength and ultimate compressive strength increased by 15.3% and 7.8%, respectively. The improvement on the mechanical properties can be attributed to solid solution strengthening and second phase strengthening.     

Study of TiC/Ni3Al composites by laser ignited self-propagating high-temperature synthesis (LISHS)

TiC/Ni₃Al composites have been obtained in situ by laser ignited self-propagating high-temperature synthesis (LISHS) of an intimate mixture of compacted powders of elemental C, Ti, Ni and Al. Ignition temperature (T_ig) and combustion temperature (T_c) are investigated; the effects of Ni₃Al content on density, phase composition, microstructure of the reaction products and particle size of the synthesized TiC were studied. The results show the density of the products varies with Ni₃Al content, and a maximum value of density appears at 50 wt.% Ni₃Al; TiC and Ni₃Al are the two stable phases after SHS, TiC particle size decreases with the increasing of Ni₃Al content, however, the decreasing of grain size is unobvious when Ni₃Al content is over 60 wt.%.     

In situ synthesis mechanism of ZrC-ZrB2/Cu composites prepared by SHS-casting method

The self-propogating high-temperature syntheis (SHS) experiments in the glove box indicated that the combustion temperature decreased and the ignition time increased with increasing B₄C size in Cu-Zr-B₄C system. Once B₄C size exceeded 28 μm, the full conversion of ZrC and ZrB₂ failed. In situ ZrC and ZrB₂ ceramic particle-reinforced Cu matrix composites were produced by the self-propagating high-temperature synthesis reaction of Cu-Zr-B₄C system in molten Cu. Moreover, the phase formation mechanism was investigated by the combustion wave quenching experiment of Cu-Zr-B₄C powder compact in Cu liquid. Results showed that ZrC and ZrB₂ were mainly formed by the dissolution-reaction-precipitation mechanism. A developed method arresting the combustion front of a reactant in molten metal was proposed.     

Surface strengthening aluminum alloy by in-situ TiC-TiB2 composite coating

An integration technology was employed to prepare TiC-TiB₂ strengthening coating on aluminum alloys, with the combination of Self-propagating high-temperature synthesis (SHS) and Vacuum-expendable pattern casting (VEPC). During the VEPC process, the Ti-C-B₄C-TP SHS reaction was ignited by molten Al alloy, resulting in the simultaneous obtainment of TiC-TiB₂ SHS coating with the cast Al alloy. Specifically, Teflon (PTFE) as reaction promoter was introduced into the SHS system to guarantee the reaction to be ignited successfully. With 3.8?wt% PTFE addition, homogeneous and dense TiC-TiB₂ coating microstructure was obtained. Compared to the matrix, the hardness of the surface coating increased from 80 HB to 284 HB. And, the weight loss decreased from 533?mg to 52?mg at load of 20?N, indicating the significant improvement of wear resistance. In addition, a comprehensive bonding strength of 160?MPa was achieved. The proposed method for preparing hard coating on Al alloys broadens their industry application, where higher hardness and better wear resistance are required.     

The development of nonchromium catalyst for fatty alcohol production

Fatty alcohols are obtained by hydrogenation of fatty acid methyl esters derived from coconut oil and palm kernel oil. Cu−Cr has been widely used as a hydrogenation catalyst. We have developed a new environment-friendly catalyst that could substitute for the conventional Cu−Cr catalyst, preventing the release of toxic hexavalent Cr. Here we report the development of Cr-free, Cu−Fe−Al oxide catalyst. We found that iron has a strong promoting effect nearly equivalent to that of Cr and that the addition of Al significantly improved the reuse property (durability) through a study of trivalent metal addition to Cu. Powder X-ray diffraction analysis of the used catalyst revealed that the Al addition suppressed the transformation of the CuFe₂O₄ component (Cu−Fe spinel) to α-Fe. It was concluded that the stabilization of CuFe₂O₄ during reduction improved the catalyst durability. A plant-scale experiment confirmed that the Cu−Fe−Al oxide catalyst performs as well as the conventional Cu−Cr catalyst.