Aging and mechanical properties of NR/BR blends

The mechanical properties and post-thermal aging properties of natural rubber (NR) and polybutadiene rubber (BR) blends at different blending ratios are investigated herein. The experimental results show that both tensile and tear strengths of NR/BR blends increase with increasing NR content. BR has a higher compression stiffness than NR. The deformation of BR is less than that of NR under the same load conditions. With regard to aging properties, both tensile stress and strain of NR/BR blends decrease after prolonged aging. In addition, the stress loss of BR is lower than that of NR, meaning that the aging resistance property of BR is superior to that of NR. Furthermore, accumulated thermal history has shifted the glass transition temperature (T _g) of NR/BR blends toward lower temperatures while the loss tangent (tan δ) value increases with prolonged thermal aging.     

Application of harmonic analysis in measuring the corrosion rate of rebar in concrete

The corrosion rate (CR) of rebar embedded in cement mortar, concrete and cement extract is determined using harmonic analysis technique (HA). Simultaneously using other electrochemical techniques such as impedance spectroscopy (EIS) and Tafel extrapolation (TET), the CR was determined and compared with the weight loss method. CR obtained from HA is comparable to that of EIS provided that the Stern–Geary constant (B value) obtained from HA is used in the calculation. In concrete, comparable corrosion rates are obtained between TET and HA only under active condition of the rebar whereas under passive state, the corrosion current (i_corr) by TET is 10 times lower than that of HA. A good agreement is obtained between the HA and weight loss method. The outcome of the result suggests that HA is capable of providing a higher degree of accuracy than that of EIS and TET in the determination of i_corr in the medium like rebar in concrete having very low rate of corrosion.     

玻璃渣性质对熔炼富集法回收废催化剂中钯的影响

利用热化学软件FactSage6.4计算了SiO₂-CaO-Al₂O₃渣系的等温相图,进而通过固定辅料MgO的含量为8%（质量分数,下同）并控制Al₂O₃含量低于35%,可以得到合理的玻璃渣系液相区温度和矿物学物相组成。采用旋转柱体法和模拟计算相结合的方法研究了温度、二元碱度w_CaO/w_SiO2和Al₂O₃含量对SiO₂-CaO-Al₂O₃-MgO熔渣黏度的影响。依据单因素实验结果可知,随温度逐渐升高、Al₂O₃含量由15%增加至35%以及二元碱度由0.3增加到1.0,熔渣粘度呈减小的变化趋势。通过以铁作为捕集剂的熔炼实验可知,钯的回收率随着废催化剂在物料体系中质量分数的增加而增大,但随着持续增大二元碱度和升高温度,其先增大而后减小。采用选取的Pd/Al₂O₃废催化剂和实验优化后的玻璃渣组分进行回收实验,即Al₂O₃和MgO含量分别约为30%和8%、二元碱度为0.5,钯的回收率可达99%,玻璃态尾渣中钯的残留量小于4.50 g/t。     

Electrochemical impedance spectroscopy investigation of chlorinated rubber‐based coatings containing polyaniline as anticorrosion agent

Corrosion protection of mild steel by a newly developed chlorinated rubber (CR)‐based coating system containing the inherently conductive polymer polyaniline (PAni) as an anticorrosion agent was studied. The synthesis of PAni and preparation of CR‐based paint containing this polymer are described herein. The corrosion behavior of mild steel samples coated with a CR resin, CR/PAni‐EB (emeraldine base), CR/PAni‐ES (emeraldine salt), and CR/DBSA‐doped PAni were investigated in 3.5% NaCl solution. For this purpose, electrochemical impedance spectroscopy and corrosion potential versus time measurements were utilized. It was found that the addition of the two forms of PAni, doped and undoped, to the CR resin increased its corrosion protection efficiency.     

Sulfidation behavior of Al-modified MP35N alloys

A commercial superalloy, MP35N, which was modified by adding various amounts of Al up to 10 wt.%, has been studied over the temperature range of 600–900°C in 0.01 atm sulfur vapor. The Al-modified alloys contained a second phase whose amount increased with increasing Al. The sulfidation rate followed the parabolic rate law and decreased with increasing Al content. An activation energy of 46 kcal/mol was obtained for MP35N, MP35N-5Al, and MP35N-7Al, while a value of 56 kcal/mol was found for MP35N-10Al at 700–800°C. Triplex sulfide scales formed on MP35N, consisting of an outer layer of solid solution (Co, Ni) ₃S₄,an intermediate layer of Cr ₂S₃,and a complex, heterophasic inner layer of mostly MoS ₂.The Al-modified alloys also formed an outer scale of (Co, Ni) ₃S₄,and an inner layer containing a mixture of CoCr ₂S₄ and Al ₂S₃.An internal-sulfidation zone containing an Al-rich sulfide was formed in the substrate. Only a moderate beneficial effect of Al additions to MP35N was observed at 600°C. The observation of the location of platinum markers suggests that cobalt, nickel, chromium, and aluminum diffuse outward to form the major part of scale, and sulfur diffuses inward to produce an internal-sulfidation zone. Transport processes in the internal-sulfidation zone governed the sulfidation rate of the alloys.     

Correlation between free-volume parameters and physical properties of polyethylene-nitrile rubber blend

Positron annihilation lifetime spectroscopy (PALS) was used to study the immiscibility of a polar nitrile rubber (NBR) that had been blended with pure and waste, low- and high-density polyethylene (PE). The effect of the weight percent of the rubber added to the PE was also investigated. It was found that a complicated variation (positive and negative) in both free-volume parameters (τ₃ and I ₃) from the values of the initial polymers forms an immiscible blend. These results are supported by a significant broadening in the free-volume hole size distributions. This has been interpreted in terms of interfacial spaces created between the boundaries of the two phases. Furthermore, a correlation was established between the free-volume parameters (τ₃ and I ₃) and the electrical and mechanical properties of the before mentioned polymer blends as a function of the weight percent of waste PE.     

Effect of annealing and heating/cooling rate on the transformation temperatures of NiFeGa alloy

In this work, Ni₅₅Fe₁₈Ga₂₇ ferromagnetic shape memory alloy was prepared through a suck-casting method. The effects of annealing and heating/cooling rate on the martensitic transformation temperatures were investigated by differential scanning calorimetry (DSC). The results showed that the phase transformation temperatures increase with increasing the annealing temperature, upon the heating and cooling process. However, the start and the finish temperatures (M_s and M_f) of martensitic phase transformation increased firstly and then decreased upon the cooling process with the increase the annealing time at 300 °C. The start and the finish temperatures (A_s and A_f) of inverse phase transformation increased slightly upon the heating process with the increase of the annealing time. The results can be explained by the evolution of the microstructure after heat treatment. It was also found that the phase temperatures show great dependence on the heating/cooling rate of the DSC test, A_s and A_f increased and M_s and M_f decreased with the increase of the heating/cooling rate.     

The effect of Al on the corrosion behavior of Ni-Mo in a H2/H2O/H2S gas mixture

The corrosion behavior of seven Ni-Mo-Al alloys was investigated over the temperature range of 600–950°C in a mixed-gas atmosphere of H ₂/H ₂O/H ₂ S. The parabolic law was followed at low temperatures, while linear kinetics were generally observed at higher temperatures. At a fixed Mo content, the transition from parabolic to linear kinetics shifted to higher temperature with increasing Al concentration. Double-layered scales generally formed on alloys having a low Al content, consisting of an outer layer of nickel sulfide and a complex inner scale. The thickness of the outer scale and the inner scale decreased as the Al content increased. The outer scale became porous and discontinuous with increasing Al content and temperature. Al ₂ O ₃ was detected in the scales of all alloys corroded at higher temperatures ( 800°C), even though the amount of Al ₂ O ₃ was very small in some cases. The decrease in corrosion rate with increasing Al content may be attributed to the formation of Al ₂ O ₃,Al _0.55 Mo ₂ S ₄,and Al ₂ S ₃ in the inner scale.     

Internal nitridation of nickel-chromium alloys

The nitriding behavior of nickel-chromium alloys was studied in ammonia-hydrogen mixtures over the range of 700–900°C. Nitridation rates decreased with increasing chromium content, but the critical amount of chromium for transition from internal nitridation to continuous-nitride film formation was found to be much greater than the critical value to form a continuous-Cr ₂O₃ film during oxidation. In general, internal-nitridation rates were found to obey the parabolic rate law. Parabolic rate constants and activation energies for the diffusion of nitrogen were measured. Very fine precipitates formed at the lowest temperature, increasing in size with increasing temperature. The precipitate number density was found to vary within the internally nitrided zone, decreasing with distance from the gas/metal surface. The precipitate morphology changed also with temperature and distance, becoming Widmanstätten at higher temperatures and/or increasing distance within the zone. CrN formed for all exposure conditions. No Cr ₂ N was detected under any conditions studied.     

Assessment of the effect of cooling rate on dendrite coherency point and hot tearing susceptibility of AZ magnesium alloys using thermal analysis

Dendrite coherency point (DCP) is an important parameter for examining the solidification structure and castability of alloys. In this research, the DCP of AZ magnesium alloys (AZ31, AZ61 and AZ91) is measured in the range of 0.22 °Cs^?1 to 8.13 °Cs^?1 cooling rates using the two-thermocouple thermal analysis technique. The results show that when cooling rate increased, temperature interval of coherency (T_{N –} T_DCP) and coherency time (t_DCP) are decreased; and it can postpone dendrite coherency. Also, by increasing the cooling rate, solid fraction at dendrite coherency increases initially and then decreases at higher cooling rates. To estimate the hot tearing susceptibility, Clyne and Davies’ criterion is used. Hot tearing susceptibility calculations exhibit initially reduce by increasing the cooling rate and then it increases at higher cooling rates. These results were explained based on the solidification principles.     

The flowability of particulate TiB2-containing metal matrix composite

This paper reports a study of the flow behaviour of a particulate TiB₂-containing metal matrix composite (MMC) and a SiC particulate MMC containing the same matrix alloy, both in comparison with the unreinforced matrix alloy, Al-7Si-0.4Mg.

Both the MMCs exhibited a similar extreme sensitivity to surface turbulence during casting, to the point at which it was not easily possible to produce good-quality castings using a conventional gravity-poured filling system. Further results obtained from fluidity measurements showed that the fluidity is not so different to conventional casting alloys, although the fluidity of the TiB₂ MMC was slightly less good than the Al-SiC metal matrix composite, which in turn was poorer than the matrix alloy. A surprising result was that increasing the casting temperature did not significantly improve the fluidity of either of the MMCs.

The relatively low fluidity and the high density of major defects appears to be associated with the high viscosity of the mixture and the fact that the mixture exhibits thixotropy, i.e. the apparent viscosity decreases with increasing rate of shear. Thus to assist the flowability of the mixture a number of experiments have been carried out to assess the effect of high rates of imposed shear, applied by vibration and stirring actions. Results show that shearing is only marginally effective in fluidity enhancement but it has no influence on casting quality. The only method which was eventually identified as giving a practically defect-free casting was the low-turbulence casting technique adapted from the Alcan-Kingston laboratory development.     

The aqueous corrosion behaviour of an ion implanted 12% chromium steel

Ion implantation has shown beneficial effects in the field of wear and oxidation. This paper is a study of the influence of ion implantation on the corrosion performance of a 12% chromium ferritic steel, 3CR12. 80 keV ions were implanted at concentrations of 5 × 10¹² to 1 × 10¹⁷ ions cm^?2. The effect of implantation of 4 ion types (Mo, V, Ph, N) each at 4 dosages was studied potentiostatically in 1 N H₂SO₄ and 0.1 N NaCl solutions. Uniform corrosion loss calculations would imply that the effect of implantation is not long lasting in 1 N H₂SO₄. This could imply that changes in the potentiostatic curves are brought about by ions in solution. Pb-Implanted 3CR12 showed increased pitting resistance with increasing dosage, whereas Pb-implanted 3CR12 showed poorer pitting resistance. Mo and V implantation showed similar behaviour for the lower doses in that both species enhanced pitting resistance but the results showed poorer pitting resistance for the higher doses. The most important limitation of ion implantation is the shallow depth of penetration and whether or not implantation effects last over sufficent periods of time for practical application is still in question.     

Effects of polarisation on mechanical properties and stress corrosion cracking susceptibility of 7050 aluminium alloy

The effects of polarisation (including cathodic and anodic polarisation) on mechanical properties and stress corrosion cracking (SCC) susceptibility (I_SCC) of 7050 aluminium alloy have been investigated by means of polarisation and slow strain rate test. The results of cathodic polarisation experiments showed that the I_SCC increased with shifting negatively the polarisation potential when the cathodic potential E_C≧?1100 mV(SCE), while it decreased with shifting negatively the polarisation potential when the cathodic potential E_CI_SCC increased severely with increasing the polarisation potential. In addition, the extents for the effect of polarisation potential on I_SCC were different among the 7050 aluminium alloy under various aging states. Polarisation was of the biggest effect on the I_SCC of under aged state, the smallest effect of over aged state and the middle effect of peak aged state. The SCC mechanism of aluminium alloy was a combination of anodic dissolution and hydrogen embrittlement, and the effects of hydrogen on SCC increased with increasing the hydrogen concentration.     

电渣重熔中TiO2对低氟CaF2-CaO-Al2O3-MgO-Li2O渣黏度和结构的影响

本文研究了连续冷却条件下电渣重熔中TiO₂对低氟CaF₂-CaO-Al₂O₃-MgO-Li₂O渣黏度的影响,并利用傅里叶变换红外光谱和拉曼光谱分析水淬渣和对应结构的关系。结果表明,渣的黏度随着TiO₂的增加而降低,当TiO₂含量达到13.1%,随着温度从1743K, 1793K, 1843K 增加至1893K时, 对应黏度从0.067 Pa?s, 0.059 Pa?s, 0.056 Pa?s 降低到0.054 Pa?s;当温度达到1843K或之上时,TiO₂的加入对降低黏度有较小的影响。随着TiO₂含量从0,4.3%,8.7%增加至13.1%,黏流活化能从58.0 kJ/mol,47.7 kJ/mol,42.8 kJ/mol降低到38.6 kJ/mol。此外,红外光谱结果表明,随着TiO₂的加入,渣中[AlOnF_4-n]-四面体络合物和[AlO₄]-四面体网状结构被解聚,但[AlO₆]-八面体结构没有发现;同时,拉曼光谱分析表明,TiO₂加入可解聚[AlO₄]-四面体网状结构中Al-O-Al键, 并且Q^₄单元转化为Q^₂单元,同时形成O-Ti-O和Ti-O-Ti键。这些结果都表明TiO₂可降低渣的聚合度,并且有利于渣的结构简单化。最终,黏度变化与渣的对应结构有很好的一致性。     

Viscosity and Structure of CaO-SiO<Subscript>2</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript>-Fe<Subscript>t</Subscript>O System with Varying P<Subscript>2</Subscript>O<Subscript>5</Subscript> and FeO Content

A rotary viscosimeter and Raman spectrum were employed to measure the viscosity and structural information of the CaO-SiO₂-P₂O₅-Fe_tO system at 1673 K. The experimental data have been compared with the calculated results using different viscosity models. It shows that the National Physical Laboratory (NPL) and Pal models fit the CaO-SiO₂-P₂O₅-FeO_t system better. With the P₂O₅ content increasing from 5% to 14%, the viscosity increases from 0.12 Pa s to 0.27 Pa s. With the FeO content increasing from 30% to 40%, the viscosity decreases from 0.21 Pa s to 0.12 Pa s. Increasing FeO content makes the complicated molten melts become simple, and increasing P₂O₅ content will complicate the molten melts. The linear relation between viscosity and structure parameter Q(Si + P) was obtained by regression analysis. The calculated viscosity by using the optimized NPL and Pal model are almost identical with the fitted values.     

1‐Methyl‐3‐pyridine‐2‐yl‐thiourea as inhibitor for acid corrosion of stainless steel

The inhibiting effect of 1‐methyl‐3‐pyridine‐2‐yl‐thiourea (MPT) on the corrosion of stainless steel in 0.5 M H₂SO₄ solution was investigated using weight loss and potentiostatic polarization techniques. The percentage inhibition efficiencies and surface coverage degrees increased with increasing additive concentration. Potentiostatic polarization studies revealed that MPT is of the mixed‐type inhibitor in 0.5 M H₂SO₄ solution. The adsorption of this inhibitor is also found to obey the Langmuir adsorption isotherm. From the adsorption isotherm, value of the ΔG_ads for the adsorption process was calculated. From the corrosion rate obtained at 25–55 °C E_a, ΔH_a and possible mechanism have been proposed. Scanning electron microscopy (SEM) was done from the surface of the exposed sample indicating uniform film on the surface.     

Processing and Mechanical Properties of Natural Rubber-ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanocomposites

We present preliminary results concerning natural rubber reinforced with nanometric ZnFe₂O₄ obtained from an industrial solid waste. The study investigate the influence of these nanometric ceramic particles on the processing as well as the mechanical properties of the obtained rubber composite, opening the possibility of partial replacement of carbon black and exposing a new potential composite material. The hardness of unfilled and reinforced rubber increased as nanometric ZnFe₂O₄ was increased. Besides, tensile properties of the reinforced rubber were measured, observing once again that as the amount of nanometric ZnFe₂O₄ particles was increased, ultimate strength improved from 2.5 MPa to almost 20 MPa.     

Effect of viscosity on lubricating and protective action of a glassy melt on hot rolling of 30XΓCA steel

Variation of the viscosity of molten glasses xNa₂O yCaO zB₂O₃ nSiO₂ in a temperature range of 1300–1700 K and the effect of the viscosity and Na₂O content on the steel oxidation rate are considered.Translated from Zashchita Metallov, Vol. 41, No. 2, 2005, pp. 218–220.Original Russian Text Copyright © 2005 by Lazutkina, Buler, Odegova.     

Tin-modified gold-based bulk metallic glasses

Tin was selected as a modifying element in low-gold-content (50 at.%) bulk metallic glasses (BMGs) aiming at developing alloys with cost-effective performance. New gold-based Au–Sn–Cu–Si alloys were fabricated by injection-casting into a copper mold. The as-cast BMG Au₅₀Sn₆Cu₂₆Si₁₈ with 18.6-karat gold and a diameter of 1 mm possessed a lower glass transition temperature (T _g) of 82°C (355 K), a lower liquid temperature of 330°C (603 K), and a super-cooled liquid region of 31°C. The viscosity range of this BMG Au₅₀Sn₆Cu₂₆Si₁₈ was from 10⁸ to 10⁹ Pa s measured at a low applied stress of 13 kPa. To compare the viscosity with different applied stresses, its viscosity clearly increased with applied stress below T _g but not so obvious above T _g. The low viscosity of this BMG Au₅₀Sn₆Cu₂₆Si₁₈ at around 102°C, which is very close to the boiling temperature of water (100°C), rendered easy thermal–mechanical deformation in a boiling water-bath by hand-pressing and tweezers-bending. Such a deformation capability in boiling water is beneficial to the further applications in various fields.     

Minute deformations and nonlinear effects in nanodisperse structured systems

Ever since P. A. Rebinder and his collaborators [1, 2, 4] published their article, it has been commonly accepted that in the range of minute deformation rates, the Newton character of a flow of structured disperse systems (pastes and suspensions) prevails. According to [1, 2], this region of viscosity is called the highest Newton viscosity of almost undisturbed structure, η₀. In the present study, it was revealed that for, systems with lyophobic interactions between particles, in the region previously considered to be a region of Newton viscosity η₀, a nonlinear dependence of the viscosity on shear stress is observed as the shear rate increases in the range $ 0 \leqslant \dot \varepsilon \leqslant 10^{ - 3} s^{ - 1} $ 0 \leqslant \dot \varepsilon \leqslant 10^{ - 3} s^{ - 1} . Thus, the viscosity increases up to the yield point P _k , at which point the avalanche decomposition of the structure begins, first into coarse aggregates and, subsequently, as their decomposition develops, into the smaller aggregates.