Analysis of pitting corrosion failure of copper tubes in an apartment fire sprinkler system

Microscopical and structural analyses as well as visual inspection of copper tubes were used to investigate the cause of pitting corrosion failure of copper tubes in the wet pipe sprinkler system. Chemical analysis of the water in the copper tubing and XRF/XRD analysis of its sediments were also used to obtain hints on what was happening in the copper tubing during the progress of the pitting corrosion. It was found from the failed copper tube that a significant amount of pressurized air was present over the water in the copper tubing during operation and a series of corrosion pits were aligned adjacent to the water/air line. The waterline localized corrosion, a type of differential oxygen concentration cell corrosion, induced by pressurized air over the water in the copper tubing was identified as the cause of the pitting corrosion failure. A state of a very low oxygen concentration was maintained under the envelope of a dense layer of malachite, the corrosion byproduct, which was evidenced by the formation of Cu₂O crystalline particles inside the corrosion pit. CuO particles observed on the inside surface of the copper tube do not seem to help prevent local as well as general corrosion. Accelerated pitting corrosion of the copper tube in the wet fire sprinkler system was simulated using a differential aeration cell. Finally, measures for stopping or delaying the pitting corrosion of the copper tube in the wet sprinkler system are suggested.     

Corrosion of M1 copper in an aqueous ethylene-glycol heat carrier under conditions of heat transfer

We have proposed an equation for calculating the mean temperature of the wall of a copper channel depending on the heat-flux density and solution velocity in the channel. We have assumed that the formation of corrosion products on copper and in the solution includes reactions leading to the appearance of complex compounds of copper with components of the solution as well as of solvated and desolvated oxides, and the shift of dynamic equilibrium in these reactions depends on the temperature of the copper surface. Under conditions of the ion-exchange purification of 66% ethylene-glycol solution, the coefficient of protective action (Z) decreases with increase in the heat-flux density and the corresponding growth of the temperature of the copper surface. A decrease in the rate of copper dissolution (Z > 40%) can be reached in 66% ethylene-glycol solution with a specific electric resistance of 25 kΩ·m and a concentration of dissolved oxygen of 0.9–1 g/m³. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 5, pp. 41–48, September–October, 2005.     

磷脱氧铜管焊接漏气失效分析

针对磷脱氧铜管与低碳钢储罐钎焊后漏气失效问题,采用金相、扫描电镜（SEM）和能谱分析（EDAX）对失效器件进行分析,发现铜管漏气的主要原因是由于钎焊过程中,预热和钎焊工艺不恰当,导致焊接气氛交替出现氧化性和还原性,使得铜管发生氢脆,产生裂纹。同时在加热和冷却时,由于异种材料的热胀系数差别过大,产生的较大热应力作用于已存在的裂纹,促使裂纹二次扩展,甚至使得晶粒脱落产生空洞,最终导致焊接接头漏气失效。提出了合理控制燃气比、钎焊加热时间和焊后冷却时间,以改善钎焊质量的建议。     

The adhesion of copper films deposited onto aluminum nitride

Good adhesion between copper film and AlN substrate is obtained when the surface of AlN is laser-irradiated prior to copper film deposition and post deposition annealing is conducted. Surface chemistry of AlN substrates before and after laser irradiation and the interfacial reactions of copper film/AlN couples were studied with Auger Electron Spectroscopy (AES) to understand the adhesion mechanisms. The surface of as-received AlN substrates was covered with a thin sheath of Al₂O₃. Laser irradiation removed the surface Al₂O₃ layers, smoothened the surface, and decomposed AlN leaving metallic aluminum on the surface. The interfacial reactions in the copper film/AlN couple are affected by the amounts of oxygen and metallic aluminum available at the interface. The adhesion mechanism is the formation of a Cu-O-Al compound at the interface of copper film/AlN couple. Since copper does not react with AlN, laser induced decomposition of AlN seems to be the driving force for the formation of the compound. This revised version was published online in September 2006 with corrections to the Cover Date.     

Thermal desorption/pyrolysis coupled with photoionization time-of-flight mass spectrometry for the analysis of molecular organic compounds and oligomeric and polymeric fractions in urban particulate matter

Atmospheric aerosols are subject to be responsible for human health effects. In this context, besides mass and number concentration of particles, their chemical composition has gained interest recently. However, knowledge about the organic content of particulate matter is still relatively scarce; i.e., only 10-40% of compounds present in the aerosol are as yet identified. By means of a newly developed measurement technique, thermal desorption/photoionization time-of-flight mass spectrometry (TOFMS), organic species evolved from urban aerosol samples collected at Augsburg, Germany, are analyzed. Thereby, compounds desorbed according to a temperature protocol following procedures for OC/EC analysis (120, 250, and 340 degrees C as desorbing temperatures) are ionized by soft, fragmentationless resonance multiphoton ionization (REMPI) and single photon ionization (SPI), respectively. With REMPI-TOFMS, a large variety of PAH is detectable. A comprehensive analysis is enabled by adding SPI-TOFMS, which gives access to aliphatic and carbonylic hydrocarbons as well as alkanoic acids and esters. Analysis of the data showed a high abundance of phenol and guiacol as well as retene, which are known markers for wood combustion. Similar patterns were found with ash from spruce wood combustion. An increase of volatile substances at 340 degrees C gave rise to the suggestion that these compounds are re-formed by pyrolytic decomposition reactions from oligomeric, polymeric, and polyfunctional oxygenated species. This was corroborated by the investigation of the behavior of cellulose acetate, which exhibited a similar pattern in its SPI-TOFMS spectrum at 340 degrees C as the aerosol. More thorough investigations of urban aerosol and source material with respect to problems such as the mass closure of carbonaceous material, indications for source apportionment, and allotment of organic species on a molecular level to fractions of organic and elemental carbon seem feasible with this measurement method.     

Thermodynamics of Copper Uranogermanate

The standard enthalpy of formation of crystalline copper uranogermanate at 298.15 K and the standard enthalpies of dehydration of its crystal hydrates were determined by reaction calorimetry. The heat capacity of Cu(HGeUO₆)₂·6H₂O was measured by adiabatic vacuum calorimetry in the range 80-300 K, and the thermodynamic functions of this compound, as well as the standard entropy and Gibbs energy of its formation at 298.15 K, were calculated. The standard thermodynamic functions of the reactions of synthesis and thermal decomposition of copper uranogermanate were calculated and discussed.     

The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion

Extensive localized or pitting corrosion of copper pipes used in household drinking water plumbing can eventually lead to pinhole water leaks that may result in water damage, mold growth, and costly repairs. Water chemistry has been recognized as the cause of some community-wide copper pinhole leak outbreaks. A large drinking water system in Florida recently switched from pH adjustment and orthophosphate addition to a blended ortho-polyphosphate chemical to address this problem. The objective of this study was to examine the impact of phosphates on the morphology and elemental composition of the interior surface of failed copper pipes removed from homes in the community. Scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis of pipe surfaces revealed the build-up of phosphorus over time. Phosphorus was most greatly concentrated over areas of localized corrosion attack. Examination of the corrosion by-product mounds that covered corroding pits showed that phosphorus had migrated to the region adjacent to the copper pipe wall. Distinct copper–phosphorus solids were identified under SEM magnification; however, no crystalline copper–phosphate compound was identified by x-ray diffraction analysis.     

紫铜-碳钢磁脉冲焊接接头界面形貌研究

为探索紫铜-碳钢磁脉冲焊接(MPW)接头界面形貌等微观特征,本文进行了T2紫铜管和50#钢管的磁脉冲焊接试验,在电压11 k V、径向间隙2.2 mm、重叠面积比3/4的条件下,获得了T2铜管-50#钢管冶金连接接头.通过光学金相、SEM/EDS、显微硬度和纳米压痕试验,重点研究了接头界面形貌、基体元素扩散和硬度分布.结果表明:接头由未焊合区、波状界面结合区、平直界面结合区等特征区域构成,连接区长度达到5 mm;波状结合区界面波长约为60μm,波峰幅值高约20μm;平直界面结合区基体元素扩散区(过渡区)宽度约2μm,而在波状界面结合区,扩散区宽度可达6μm;接头铜侧硬度相对初始值提高50%,最高硬度值出现在靠近界面的50号钢侧,而界面硬度介于两种母材之间.     

Friction stir welding of dissimilar metal joints

Friction stir welding is a solid‐state welding technology, which is suitable for joining dissimilar metals such as aluminium and copper. Because the solidus temperature is typically not exceeded, the formation of intermetallic phases can be reduced when compared to fusion welding processes. In friction stir welding, the intermetallic layer thickness, which determines the seam properties, is influenced by the welding temperature and is formed in correspondence with the Arrhenius law. It is typically in the range of a few hundred nanometers thick. In turn, the process temperature is determined by the process parameters, primarily the rotational speed and the feed rate of the machine tool. In this study, a temperature‐controlled friction stir welding process has been applied to lap joints of aluminium and copper. Welding experiments with various welding speeds and probe lengths were performed in order to assess the effect of the temperature‐time profile near the welding interface. The joints were investigated by tensile shear tests as well as optical microscopy and scanning electron microscopy.     

A METHOD TO MEASURE ELECTROCHEMICAL POTENTIAL AT THE TIP OF A GROWING CRACK DURING AN ENVIRONMENTAL FATIGUE TEST

Abstract— Electrochemical potential at the tip of a fatigue crack was measured in a compact tension specimen, situated in demineralized, oxygen saturated water at 93°C.
Results show that the crack tip region is active with respect to the external specimen surface. Passivation occurs on the crack surfaces by the formation of an oxide layer. The oxygen concentration inside the crack is likely to be lower than in the bulk solution.     

The influence of substrate temperature and sputtering gas atmosphere on the electrical properties of reactively sputtered indium tin oxide films

Tin-doped indium oxide (ITO) films were prepared by d.c. magnetron sputtering of an In-Sn alloy target, and the influence of the sputtering gas atmosphere and substrate temperature on their electrical properties was studied.The conditions for the deposition of the transparent ITO films were divided into three regions by varying the sputtering gas pressure. The first region was characterized by a high efficiency of oxygen gas consumption for film formation and a high deposition rate. In the second region the as-deposited films contained slightly less than the stoichiometric amount of oxygen. The third region was characterized by a low efficiency of oxygen consumption and a low deposition rate. The ratio of the amount of oxygen consumed to the amount of oxygen admitted to the sputtering chamber was about 15% when films with resistivities as low as 6 × 10^-4Ω cm were prepared at the optimum oxygen partial pressure.In the case of metallic deposited in an oxygen-poor atmosphere the carrier mobility, which mainly depends on the crystal structure, increased and the carrier concentration, which depends on the number of oxygen vacancies and donor centres, decreased with increasing substrate temperature. The opposite results were obtained for films deposited in an oxygen-rich atmosphere. Well-defined grain growth was observed, particularly for metallic films deposited at high substrate temperatures, and this caused the low carrier mobility.Subsequent heat treatment improved the resistivity of films deposited at substrate temperatures below 100°C, mainly because of the increase in carrier mobility, but it had little effect on the resistivity of films deposited at substrate temperatures above 150 °C because the increase in carrier mobility was cancelled by the decrease in carrier concentration.     

Equilibrium and kinetic studies of copper adsorption by activated carbon

Copper adsorption by granular activated carbon is reported in this paper. The experimental section includes titrations of activated carbon, as well as equilibrium and kinetic studies of copper adsorption. The potentiometric titration results show that the point of zero charge is 9.5, and that the surface charge increases with decreasing pH. The adsorption of copper strongly depends on solution pH and increases from 10 to 95% at pH ranging from 2.3 to 8. A dramatic increase in pH and emission of small gas bubbles are observed during the experiments, which may result from adsorption of hydrogen ion and/or reduction-oxidation reactions. The two-pK triple-layer model is employed to describe copper adsorption. KINEQL, an adsorption kinetics algorithm, is used to represent the experimental data, and it is found that the model can describe reasonably well the experimental measurements of surface charge, adsorption equilibrium, and adsorption kinetics. Calculations show that formation of the surface-metal complexes SO⁻Cu²⁺ and SO⁻CuOH⁺ (a hydrolysis product of SO⁻Cu ²⁺) in the outer layer around the surface of carbon results in removal of copper ion. It is also found that mass transfer controls the adsorption rate, and that adsorption occurs in the micropore region where both external mass transfer and diffusion are important.     

Intergranular cracking of Hastelloy C-276 in the socket welded assemblies

Abstract

The cause of thermal cracking about a socket welded tube was investigated by stress simulation and its comparison to hardness distribution of welding seam, HAZ and matrix of the tube. In the condition of heat-input in melting range of 1349°C, the stress was concentrated in HAZ at the opposite side of welding area by ANSYS program, which corresponded to the distribution of real hardness values of the tube. The high stress concentration in HAZ might be induced from fine carbide precipitation which formed during welding process. It could cause, therefore, tube cracking in operating condition simultaneously followed by bulging inside of the welded tube. In the crack propagation through all the tube originated from inside HAZ, it might be accelerated by thermal fatigue, and propagated along grain boundaries accompanied by the metal dust formation.     

旋转速度与焊接速度对铝铜异种材料搅拌摩擦焊接头成形的影响

目的为了获得较好的铝铜异种材料搅拌摩擦焊焊缝,研究旋转速度与焊接速度对焊缝成形的影响规律。方法采用对接的方式对4mm厚的纯铝和紫铜进行搅拌摩擦焊,对比了不同旋转速度和焊接速度对铝铜异种金属焊缝表面的影响,并对焊缝内部成形变化进行了分析。结果旋转速度和焊接速度对焊缝的成形影响较大,当旋转速度为1200 r/min,焊接速度为10 mm/min时,焊缝表面成形美观,焊缝表面相对较为光滑,焊缝内部存在相互交叠的片层结构和漩涡状结构,焊缝内部未见明显缺陷;与旋转速度1200 r/min,焊接速度10mm/min相比,在焊接旋转速度减小或者焊接速度变大时,由于焊接热输入减小,造成焊缝表面出现沟槽、孔洞等焊接缺陷,同时搅拌针的旋转搅拌作用影响焊缝成形和焊缝内部缺陷的产生。结论选择合适的旋转速度和焊接速度能够获得宏观成形较好和内部缺陷较少的焊缝。     

Effects of the deposition temperature on the resistivity of copper films produced by low-pressure metal-organic chemical vapour deposition on a TiN barrier layer

Copper was deposited on to TiN by low-pressure metal-organic chemical vapour deposition, using hexafluoroacetylacetonate-Cu⁺¹-trimethylvinylsilane (hfacCu(I)TMVS) and argon carrier gas. The resistivity of the deposited copper films was investigated by observing the effects of the deposition temperature on the composition, microstructure and surface morphology of the copper films. The resistivity of the copper films decreases as the deposition temperature decreases. The copper films deposited at high temperatures, tend to contain the pores and or/ channels as well as carbon and oxygen, which results in the increase of the resistivity of the deposited films. The pores and/or channels come from the island-like growth of the copper films, while carbon and oxygen are due to the concurrent thermal decomposition of hfac during the disproportionation reaction between hfacCu(I) molecules.     

Nanorobotic spot welding: controlled metal deposition with attogram precision from copper-filled carbon nanotubes

With the continuing development of bottom-up nanotechnology fabrication processes, spot welding can play a role similar to its macro counterpart for the interconnection of nano building blocks for the assembly of nanoelectronics and nanoelectromechanical systems (NEMS). Spot welding using single-crystalline copper-filled carbon nanotubes (CNTs) is investigated experimentally using nanorobotic manipulation inside a transmission electron microscope (TEM). Controlled melting and flowing of copper inside nanotube shells are realized by applying bias voltages between 1.5 and 2.5 V. The average mass flow rate of the copper was found to be 120 ag/s according to TEM video imaging (measured visually at approximately 11.6 nm/s through the CNT). Successful soldering of a copper-filled CNT onto another CNT shows promise for nano spot welding and thermal dip-pen lithography.     

金刚石制品用FeCoCu预合金粉末的制备及应用研究

采用共沉淀法制备了金刚石制品用FeCoCu预合金粉末,研究了共沉淀反应溶液的浓度、反应温度与还原温度、时间对粉末收得率与粒度的影响,并对其使用性能进行实用性研究.结果表明:采用共沉淀法可以制备出良好的预合金化粉末,随着混合金属盐溶液与沉淀剂溶液的浓度的增大,预合金粉未的粒度呈现明显的增加趋势,同时收得率也随之缓慢增加;...     

紫铜焊接脆化原因分析

通过对材料的金相组织和断口的SEM观察,对压缩机贮液罐用铜导管的脆断进行了分析,认为铜管氧含量过高,钎焊时被C2H2还原是造成脆化的重要原因。     

Characterization of solid-phase welds between Ti---6A1---2Sn---4Zr---2Mo---0.1Si and Ti---13.5A1---21.5Nb titanium aluminide

Dissimilar-alloy welds have been produced between Ti---6Al---2Sn---Z4---2Mo---0.1Si (wt. %) and Ti---13.5Al---21.5 NB (wt.%) titanium aluminde using the three different solid-phase welding processes that create significantly different thermo-mechanical conditions at the weld interface. Exposure to supertransus temperatures, appreciable deformation and rapid cooling of the weld interface region during linear-friction welding promote dynamic recrystallization of beta grains and beta decomposition to fine martensitic products. In contrast, diffusion welding at temperatures below the base metal beta transus temperatures and at relatively low pressures minimizes deformation and microstructural variations in the weld interface region relative to the unaffected base metal. During capacitor-discharge resistance spot welding, extremely rapid heating of the weld interface region to near-solidus temperatures, and subsequent rapid cooling, result in the formation of a metastable, ordered-beta microstructure in the Ti---s13.5Al---21.6Nb and fine alpha-prime martensite in the Ti---6Al---2Sn---4Zr---2Mo-0.1Si.     

Microstructural development of dissimilar weldments: case of MIG welding of Cu with Fe filler

Microstructure development during MIG welding of copper with iron filler has been studied to gain insight to the process of dissimilar welding. The microstructure of the iron rich bids consist of martensitic bcc iron with cellular network of fcc copper. The scale of network depends on the processing conditions. However, the average composition remains fairly uniform with 20at% Cu excepting at the boundary regions of the bid and the copper plates. A characteristic banded structure could be observed in these regions whose width scales with traverse speed. Evidence of phase separated copper globule suggests access to the submerged miscibility gap and significant undercooling of the melt during welding.