Room Temperature Aging Research Articles

Highly active P-doped sulfided NiMo/alumina HDS catalysts from Mo-blue by using saccharose as reducing agents precursor

Saccharose (SA) was used as organic additive in simultaneously impregnated P-doped NiMo/Al2O3 hydrodesulfurization (HDS) catalysts (Mo, Ni and P at 12, 3, and 1.6 wt%, respectively). One-pot impregnating solutions were prepared by MoO3 digestion (∼353 K) in diluted aqueous H3PO4, followed by 2NiCO3·3Ni(OH)2·4H2O addition. Saccharose (SA, SA/Ni = 0.5, 1–3) was dissolved in originally emerald-green impregnating solutions which changed to cobalt blue by room-temperature aging (2–4 days, depending on SA concentration) due to Mo-blue formation by partial molybdenum species reduction. After sulfiding of samples impregnated with SA shorter MoS2 slabs of enhanced stacking were observed (by HR-TEM). Ni and Mo dispersion and nickel sulfidability (as determined by XPS) increased with the amount of organic modifier. Enhanced hydrodesulfurization activity in dibenzothiophene HDS was registered for catalyst obtained from Mo-blue precursor as to that of corresponding materials obtained from conventional emerald-green NiMoP impregnating solutions (with or without SA). However, in solids at high saccharose content (SA/Ni = 3) enhanced “NiMoS” phase amount was not reflected in improved activity. Probably, excessive amount of carbonaceous deposits from SA residua decomposition during catalyst activation provoked partially plugged porous network (as determined by N2 physisorption) in sulfided formulations. That fact seemed to limit accessibility of reactant molecules to surface active sites. Mo-blue precursor obtained through monosaccharides partial reduction seemed to play decisive role in obtaining HDS catalysts of improved properties. Saccharose results a highly soluble, cheap and non-toxic environmentally-friendly additive to produce catalysts of enhanced HDS activity.

Effect of Long-Term Room Temperature Aging on the Fatigue Properties of SnAgCu Solder Joint

Solder joints in electronic assemblies are subjected to mechanical and thermal cycling. These cyclic loadings lead to the fatigue failure of solder joints involving damage accumulation, crack initiation, crack propagation, and failure. Aging leads to significant changes on the microstructure and mechanical behavior of solder joints. While the effect of thermal aging on solder behavior has been examined, no prior studies have focused on the effect of long-term room temperature aging (25 °C) on the solder failure and fatigue behavior. In this paper, the effects of long-term room temperature aging on the fatigue behavior of five common lead-free solder alloys, i.e., SAC305, SAC105, SAC-Ni, SAC-X-Plus, and Innolot, have been investigated. Several individual lead-free solder joints on printed circuited boards with two aging conditions (no aging and 4 years of aging) have been prepared and subjected to shear cyclic stress–strain loadings until the complete failure. Fatigue life was recorded for each solder alloy. From the stress–strain hysteresis loop, inelastic work and plastic strain ranges were measured and empirically modeled with the fatigue life. The results indicated that 4 years of room temperature aging significantly decreases the fatigue life of the solder joints. Also, inelastic work per cycle and plastic strain range are increased after 4 years of room temperature aging. The fatigue life degradation for the solder alloys with doped elements (Ni, Bi, Sb) was relatively less compared to the traditional SAC105 and SAC305.

On cryothermal cycling as a method for inducing structural changes in metallic glasses

The influence of cryothermal treatment on the mechanical properties of metallic glasses with different compositions was investigated in the present work. It was found that cryothermal cycling can induce rejuvenation as well as relaxation of the metallic glasses. The local apparent Young’s modulus and its spatial distribution width on the surface of the metallic glass increase after cryothermal cycling, while in the bulk the effect depends on the glass composition. It appeared that this increase is temporary and disappears after a period of room temperature aging. This effect is connected with a large distribution of relaxation times in the metallic glasses due to their heterogeneous structure and the formation of complex native oxides on the outer surfaces of the glasses. Our findings reveal that a cryothermal cycling treatment can improve or degrade the plasticity of a metallic glass, and the atomic bond structure appears to be very important for the outcome of the treatment.

Strain Aging Behavior of an Austenitic High‐Mn Steel

The bake hardening treatment shows great potential for increasing the yield strength of steel components for automotive applications. This study investigates the effects of bake hardening on the yield strength and ductility of an austenitic high‐Mn steel. In order to identify a promising process window, the prestrain, the bake hardening temperature, and the annealing time are varied. The bake hardening effect is evaluated by the uniaxial tensile tests with digital image correlation (DIC) in situ monitoring. The results show strong bake hardening effect on the high‐Mn steel when certain amount of prestrain is applied. Large amounts of prestrain even leads to room temperature aging. Small angle neutron scattering (SANS) measurements indicate the absence of Mn–C short range ordering (SRO) after the prestrain; however, the nano‐sized Mn–C SRO re‐occurs after the annealing. At high prestrain degree, an increase in the number density of the Mn–C SRO is found in both cases, after annealing at elevated temperature and aging at room temperature, indicating an accelerated Mn–C SRO formation. The results suggest that SRO is responsible for an increase in the yield strength and a pronounced yielding of the high‐Mn steel after bake hardening treatment.

Effect of welding thermal cycle on microstructural evolution of Al–Zn–Mg–Cu alloy

Al–Zn–Mg–Cu alloys are used extensively in high-speed train applications; however, the occurrence of softening in the heat-affected zone after welding limits their development. In this work, the effect of the welding thermal cycle on the softening and aging behaviors of a 7xxx aluminum alloy was investigated by examining the state of the strengthening precipitates. The microstructure and solvus temperature range of the precipitates of 7N01P-T4 were characterized using TEM and DSC analysis, respectively. It was found that the softening behavior of the aluminum alloys was closely related to the volume fraction and size of the hardening precipitates, which were greatly affected by the peak temperature of the welding thermal cycle. In addition, η′ and η precipitates were observed to be primarily responsible for the increase in the mechanical and electrical properties during the room-temperature natural aging. A phenomenological connection was thus uncovered between the characteristic parameters of the thermal cycle and the precipitation behavior, providing insight for the design of the welding process for 7N01 alloys.

"Infinite Sensitivity" of Black Silicon Ammonia Sensor Achieved by Optical and Electric Dual Drives.

The microstructured and hyperdoped silicon as a superior photoelectric and photovoltaic material is first studied as a gas-sensing material. The material is prepared by femtosecond-laser irradiation on selenium-coated silicon and then fabricated as a conductive gas sensor, targeting ammonia. At room temperature, the sensitivity, response time, repeatability, distinguishability, selectivity, and natural aging effect of the sensor have been systematically studied. Results show that such black silicon has good potential for application as an ammonia-sensing material. On the basis of its unique optoelectronic properties, an additional optical drive is proposed for the formation of an optical and electric dual-driven sensor, which is achieved by asymmetric light illumination between the two electrode regions. In a certain range of applied voltage, the sensitivity is enhanced dramatically and even tends to be infinite. For the aged device with degraded sensitivity, a two-order increment is obtained for 500 ppm of NH3 under the extra optical drive. A mechanism based on Dember effect is proposed for explaining such a phenomenon.

Structure and Mechanical and Corrosion Properties of a Magnesium Mg–Y–Nd–Zr Alloy after High Pressure Torsion

The structure and the properties of an Mg–Y–Nd–Zr alloy (WE43) are studied after high pressure torsion (HPT) in the temperature range 20–300°C. Structure refinement proceeds mainly by deformation twinning with the formation of a partial nanocrystalline structure with a grain size of 30–100 nm inside deformation twins. The WE43 alloy is shown to be aged during heating after HPT due to the decomposition of a magnesium solid solution. HPT at room temperature and subsequent aging causes maximum hardening. It is shown that HPT significantly accelerates the decomposition of a magnesium solid solution. HPT at all temperatures considerably increases the tensile strength and the yield strength upon tensile tests and significantly decreases plasticity. Subsequent aging additionally hardens the WE43 alloy. A potentiodynamic study shows that the corrosion resistance of this alloy after HPT increases. However, subsequent aging degrades the corrosion properties of the alloy.

Effect of Composition and Distribution of Phases after Aging on Stamp Ability for Aluminum Alloy D16 (AA2014) Sheets

The relevance of this research is connected to the increasing requirements for accuracy in stamped parts produced from aged aluminum alloys, and can also be applied for making layered composites. Indexed requirements can be provided by controlling the structure of sheet blanks, particularly by the phase composition and distribution behavior. Results of experimental research into the effect of aging modes on composition, dispersion behavior, and stamping number of sheet samples of the D16 aluminum alloy (AA2014) are presented. Heat treatment includes quenching from a temperature of 500°С into water of room temperature and further aging: natural aging for 7 days and artificial aging at temperatures of 50, 100, 150, and 200°С with a duration at each temperature of 15, 30, 60, 120, and 240 min. A method of estimating the quantity of the characteristics of dispersion phases is proposed for the microstructural picture. Stamp ability is evaluated using the stamping number, which is the ration between yield stress and tensile strength. It is found that increasing aging temperature and durance leads to the growth of the stamping number, which shows a low ability for sheet-stamping operations of alloy. Aging at 50°С did not lead to the sedimentation of dispersion phases for either optical metallography or scan electron microscopy. The inhomogeneity of phase dispersion inside the grain grows at the initial stages of aging, when durance is less than 1 h and temperature is 100, 150 and 200°С. Further increasing durance to 4 h leads to inhomogeneity decreasing. There is no correlation between the uniformity of phase dispersion and the stamping number. The chemical composition of phases plays the main role in stamping number, outside of phase-dispersion uniformity. The phase-composition changes depend on the mode of heat treatment: at an annealed and naturally aged state, the θ and S phase is sediment. After aging at a temperature lower 150°С after a short durance of less than 1 h, the θ, S and T phases are revealed; the θ phase appears after aging at temperatures higher than 150°C and long durance reaching 4 h.

Microstructural design considerations in Fe-Mn-Al-Ni shape memory alloy wires: Effects of natural aging

In this study, FeMnAlNi shape memory alloys are demonstrated to experience room temperature (RT) aging, which manifests itself as a gradual increase in critical transformation stress with time when the sample is kept in a stress-free condition. This effect is sufficient to create superelasticity in the solution treated condition, which does not normally show superelasticity soon after heat treatment. This phenomenon is due to the nucleation and coarsening of nanoprecipitates at room temperature despite the high melting point of the alloy. RT aging also influenced precipitation hardened FeMnAlNi samples by causing an increase in stress hysteresis and hardening rate.

(Invited) Room Temperature Aging Effect Improvement for Device Stability and Manufacturability of FinFET Technologies

In CMOS manufacturing industry, device threshold voltage (Vt) stability is a pre-requisite for volume manufacturing. Device architectural elements, process parameters and room temperature aging (Q-time) are the main source of Vt instability. In FinFET technology with metal/high-K gate, device Vt is controlled through effective work function engineering by optimal metal layer thickness as well as controlled Aluminum (Al) doping/diffusion within the gate stack [1-4]. The device Vtcan also be influenced by its architectural elements and process parameters [5] which should be well controlled during the volume manufacturing. However, room-temperature Q-time effects at several stages of the manufacturing process are practically unavoidable. This work demonstrates post n-work function (WF) deposition Q-time impact on device Vt instability. Longer Q-time induced Vt shifts that are independent of gate length and number of fins, as seen in Figure 1. The root cause investigations were performed using device characterization followed by elemental analysis of the gate stack (Figure 2). It was found that, the content of oxygen (O2) and Al in the gate stack is well correlated to post n-WF deposition Q-time. The device Vt instability can be explained by oxygen incorporation due to n-WF layer oxidation during the Q-time post n-WF deposition and the corresponding reduction of Al diffusion into the high-K capping layer [2, 6]. In this work, n-WF layer thickness/composition was optimized to enable immunity to a larger Q-time limit for volume manufacturing, as demonstrated in Figure 3 from n-WF layer recipe group A to group C. The reliability impact of the gate stack was also assessed. Device benefits such as Tinv scaling and thereby Ion-Ioffperformance improvement was also demonstrated without compromising the reliability. Reference [1] L.P.B. Lima et al, J. Appl. Phys., 115, 074504, 2014 [2] A. Veloso et al, Jpn. J. Appl. Phys.52. 04CA02, 2013 [3] L. Kornblum et al, Appl. Phys. Lett., 100, 062907, 2012 [4] C.L. Hinkle et al, Appl. Phys. Lett.,96, 103502, 2010 [5] M. Togo et al, VLSI tech. Symp. Dig.pp. 140-141, 2014 [6] A. Veloso et al, VLSI Tech. Symp. Dig. pp. 34-35, 2011. Figure 1

(Invited) Room Temperature Aging Effect Improvement for Device Stability and Manufacturability of FinFET Technologies

In FinFET technology, device threshold voltage (Vt) stability is a pre-requisite for volume manufacturing. Device architectural elements, process parameters and room temperature aging (Q-time) are the main source of Vt instability. For the first time, we report a method to minimize Vt instability due to Q-time in gate stack work function (n-WF) layer film depositions. Underlying mechanism was investigated using elemental analysis. The optimized n-WF layer recipes were developed that are less sensitive to the Q-time. Device benefits such as Tinv scaling and thereby Ion-Ioff performance improvement is demonstrated without compromising the reliability.

Investigation of Mechanical Properties and Dry Sliding Wear Behaviour of Graphite Reinforced Al7068 Alloy

The aim is to study the mechanical property and dry sliding wear behaviour of Al7068/graphite composite with various weight fractions (5%, 10%, 15%) were prepared by liquid metallurgy route was investigated. The average particle size of graphite is 40 μm. In addition, Al7068 alloys were cast for comparison purposes. The alloys and composites were given a T6 heat treatment process (solution treatment at 540 oC, water quenching at room temperature and artificial ageing at 170 oC) .Microstructure, hardness and tensile properties of these composites were evaluated and compared with as-cast alloy and the composites without T6 heat treatment. In addition, tribological properties of these composites were evaluated using a Pin-on-Disc apparatus with different parameters (constant velocity of 2m/s and varying loads as follows 10N, 15N, 20N, 25N, 30N) .The microstructure of the composites shows homogenous distribution of graphite particles in the Al matrix except in the Al7068/15% graphite composite. The wear and mechanical properties of composites improve with increasing the weight fraction of graphite upto 10% and then decreases gradually. This study provides an alternative way to enhance the tribological behaviour of Al7068/graphite composite. The study also highlights the different contribution of different input process parameters (like: composition of Al-graphite, molding technique and particle size of reinforcement material) on wear properties of Al-graphite MMCs.

Fabrication and Characterization of Al-0.4%Si-0.5%Mg - SiCp Using Permanent Mould Casting Technique

Production of A6063/SiC composite with various weight fractions (3%, 6%, 9%) were prepared by using permanent mould casting was investigated. The preferred mean particle size of SiC is 60 μm. In addition, A6063 alloys were cast for comparison purposes. The alloys and composites were given a T6 heat treatment process (solution treatment at 520 °C, water quenching at room temperature and artificial ageing at 180 °C), Also Microstructure, hardness and tensile properties of these composites were evaluated and compared. In addition, tribological properties of these composites were evaluated using a Pin-on-Disc apparatus with various parameters (constant load of 10N and varying velocities as follows 0.5m/s, 1m/s, 1.5m/s, 2m/s) .The microstructure of the composites shows homogenous distribution of SiC particles in the Al matrix except in the A6063/9% SiC composite. The wear and mechanical properties of composites improve with increasing the weight fraction of SiC Wear morphology studies show that higher wear rate in case of unreinforced specimen compared to heat treated composites. Whereas with the increase in SiC content, the material tends to fail in brittle mode. The aim of present study is to evaluate the effect of heat treatment on the mechanical and tribological properties of aluminum alloy A6063 /SiC metal matrix composite.

Molecular origin of aging of pure Se glass: Growth of inter-chain structural correlations, network compaction, and partial ordering.

Glass transition width W of pure Se narrows from 7.1(3) °C to 1.5(2) °C and the non-reversing enthalpy of relaxation (ΔHnr) at Tg increases from 0.23(5) cal/g to 0.90(5) cal/g upon room temperature aging for 4 months in the dark as examined in modulated differential scanning colorimetry (MDSC) at low scan rates. In Raman scattering, such aging leads the A1 mode of Sen-chains (near 250 cm-1) to narrow by 26% and its scattering strength to decrease as the strength of modes of correlated chains (near 235 cm-1) and of Se8 rings (near 264 cm-1) systematically grows. These calorimetric and Raman scattering results are consistent with the "molecular" chains of Sen, predominant in the fresh glass, reconstructing with each other to compact and partially order the network. Consequences of the aging induced reconstruction of the long super-flexible and uncorrelated Sen-chains are also manifested upon alloying up to 4 mol. % of Ge as revealed by a qualitative narrowing (by 25%) of the Raman vibrational mode of the corner-sharing GeSe4 tetrahedra and a blue-shift of the said mode by nearly 1 cm-1 in 194 cm-1. But, at higher Ge content (x> 6%), as the length of Sen chain-segments across Ge cross-links decreases qualitatively (⟨n⟩ < 8), these aging induced chain-reconstruction effects are suppressed. The width of Tg increases beyond 15 °C in binary GexSe100-x glasses as x> 10% to acquire values observed earlier as alloying concentration approaches 20% and networks become spontaneously rigid.

Additive and Aging Effects on Methylalumoxane Oligomers

In the presence of the weak donor octamethyltrisiloxane (OMTS), methylalumoxane (MAO) undergoes ionization through [Me2Al]+ abstraction. The [Me2Al·OMTS]+[(MeAlO)x(Me3Al)yMe]− ion pairs formed can conveniently be studied by electrospray ionization mass spectrometry. The anion distribution changes with OMTS:Al ratio, with low molecular weight (MW) anions forming at high ratios due to oligomer degradation. Monitoring of room-temperature aging shows that MAO oligomers of low MW are slowly and systematically converted to species with higher MW through addition of (MeAlO) units, and intermediate oligomers are observed and assigned. This process occurs at room temperature but does not occur significantly over a period of months at low temperatures. Computational investigations of these species show large cagelike clusters with four-coordinate Al and three-coordinate O. All neutral structures have sites that could readily give up [Me2Al]+ to form the observed ions, though sites that can lose [Me2Al]+ without lea...

Accelerated precipitation and growth of phases in an Al-Zn-Mg-Cu alloy processed by surface abrasion

The surface microstructure and its evolution during long-term room-temperature storage were studied using transmission electron microscopy for an Al-Zn-Mg-Cu alloy processed by surface abrasion with grinding paper. An altered surface layer (ASL) with thickness of 0.4–0.8 μm was present on the alloy after abrasion. Ultrafine subgrains with width of about 50–120 nm and a high density of dislocations were observed in the ASL. The pre-existing aging-induced η′ and η precipitates dissolved during surface abrasion. During room-temperature aging, relatively pure Zn, Al2Cu and AlCu phases were observed to precipitate at the extreme surface and subgrain boundaries in the ASL. These phases are very unusual in that they are typically not formed in Al-Zn-Mg-Cu alloys. Mg was not found in these particles, as it remained dissolved in the solid solution of the ASL. Al2Cu and AlCu phases also precipitated at the grain boundaries in the underlying substrate right below the ASL, as far as 6 μm in depth from the extreme surface. Considerable growth and coarsening of these phases occurred during natural aging over a period of 42 months. The enhanced diffusion accelerated by vacancies, dislocations, and subgrain/grain boundaries was considered to be mainly responsible for the accelerated precipitation and growth of these atypical phases.

High-Performance Formamidinium-Based Perovskite Solar Cells via Microstructure-Mediated δ-to-α Phase Transformation

The δ → α phase transformation is a crucial step in the solution-growth process of formamidinium-based lead triiodide (FAPbI3) hybrid organic–inorganic perovskite (HOIP) thin films for perovskite solar cells (PSCs). Because the addition of cesium (Cs) stabilizes the α phase of FAPbI3-based HOIPs, here our research focuses on FAPbI3(Cs) thin films. We show that having a large grain size in the δ-FAPbI3(Cs) non-perovskite intermediate films is essential for the growth of high-quality α-FAPbI3(Cs) HOIP thin films. Here grain coarsening and phase transformation occur simultaneously during the thermal annealing step. A large starting grain size in the δ-FAPbI3(Cs) thin films suppresses grain coarsening, precluding the formation of voids at the final α-FAPbI3(Cs)–substrate interfaces. PSCs based on the interface void-free α-FAPbI3(Cs) HOIP thin films are much more efficient and stable in the ambient atmosphere. This interesting finding inspired us to develop a simple room-temperature aging method for preparing ...

Cavity Formation in Molybdenum Studied In Situ in TEM

We investigated the microstructural response of molybdenum, with and without prior exposure to gaseous deuterium, during helium irradiation and subsequent annealing. Ion irradiations and annealing experiments were performed in situ in a transmission electron microscope, enabling real time observation of the microstructural evolution. Cavities approximately 0.5 nm in diameter were formed in deuterium-exposed molybdenum at a fluence of 1.7 × 1015 helium cm−2, but did not grow appreciably after increasing the fluence by two orders of magnitude or after brief room temperature aging. Similar cavities were not apparent in pristine molybdenum. Larger cavities appeared in both samples during in situ annealing to 1063 K, without any clear differences between the two samples. The evolving cavity morphologies are discussed in terms of defect production, microstructure, and sample geometry.

Effect of different electrolytes on the microstructure, corrosion and whisker growth of pulse plated tin coatings

Pulse electrodeposited tin coatings are produced from different electrolytic baths (acidic stannous sulfate, alkaline sodium stannate, stannous chloride-citrate, methyl sulfonic acid (MSA), and potassium pyrophosphate based baths). The structure and morphology of the coatings are investigated by X-ray diffraction (XRD), and scanning electron microscopy (SEM). The corrosion resistance of the coatings plated from each bath is investigated by potentiodynamic polarization method. The as deposited samples from each bath are also subjected to room temperature ageing for a period of 1year, and the extent of whisker growth is accessed. The results show that the coating prepared from the citrate bath has the highest corrosion and whisker growth resistance followed by the sulfate bath among all the plating baths investigated.

Evaluation of some intercalation methods of dimethylsulphoxide onto HCl-treated and untreated Egyptian kaolinite

Dimethylsulphoxide (DMSO)-kaolinite interlayer complexes are important precursors for the organo-modifications of kaolinite. DMSO intercalation into HCl activated (HK) and untreated (UnK) Egyptian kaolinites via four different techniques; reflux of DMSO/water mixture at 70°C (R1), ball-milling with DMSO followed by reflux at 140°C (R2) as well as room temperature ageing for two months in absence and in presence of water (2m and 2mW) were performed and compared. The complexes were investigated by IR spectroscopy, thermogravimetric analysis (TGA), X-ray diffractometry (XRD), mass spectroscopy (MS), elemental analysis, scanning electron microscopy – energy dispersive x-ray spectroscopy (SEM-EDX), and transmission electron microscopy (TEM). Fourier transform infra-red (FTIR) spectra showed a blue-shift in OH vibrations of the modified kaolinite due to the hydrogen bonds formed between DMSO molecules and the inner-surface hydroxyls of kaolinite with the order 2mW>2m>R2>R1 of DMSO loading. In addition, XRD, TGA and elemental analysis supported the same conclusion by high degree. HCl-treatment of clay was shown to reduce the intercalation of DMSO probably due to the reduction in its Al percentage. DMSO was suggested to be loaded onto kaolinite mainly via two mechanisms; intercalation and adsorption processes. The 2mW and 2m methods were recommended for higher adsorption and intercalation efficiencies of DMSO onto kaolinite.