垃圾焚烧电厂过热器腐蚀影响因素及防护涂层研究进展

垃圾焚烧电厂过热器管道的高温腐蚀一直是制约电厂焚烧温度的关键问题,因此研究开发耐高温、耐腐蚀、长寿命的关键服役材料是保证垃圾焚烧炉正常有序运转及安全生产的关键。对近年来垃圾焚烧电厂腐蚀问题的研究现状进行了梳理,对近期垃圾焚烧电厂过热器腐蚀与防护的研究成果进行了综述。首先,从过热器腐蚀影响因素的角度,归纳了焚烧环境中存在氯、硫、温度、水蒸气等诸多因素影响下的腐蚀特点,对各个影响因素下的腐蚀机理进行了概述,氯作为影响腐蚀的关键因素,重点对氯导致腐蚀的活性氧化机理和电化学机理进行了阐述。其次,讨论了应用在过热器表面的涂层制备技术的发展,包括热喷涂、热扩散、堆焊、激光熔覆等,探讨了制备方法,以及应用技术的优缺点。分析了材料成分(Ni、Mo、Cr、Al、Si、Pt等元素)的添加与涂层耐腐蚀性能之间的关系。再次,从焚烧垃圾预处理的角度,进一步讨论前期可通过对垃圾脱水、添加共燃剂等方法,达到脱硫、脱氯的目的,以此降低烟气中硫、氯的含量,减小其对腐蚀的影响。最后,对垃圾焚烧电厂过热器管道材料和涂层的选择进行了总结和展望。     

Qualifizierung metallischer Werkstoffe für die Eindampfung von Abwässern aus der Rauchgasentschwefelung

Qualification of metallic materials for evaporation of waste water from flue gas desulfurization plants The ecologically-minded processing of waste water from the wet scrubbing of flue gases of coal-fired power plants to produce environmentally acceptable products is carried out in a two-step evaporater operating in closed loop mode. The evaporating process leads to high concentration of chlorides in the two evaporation steps: up to about 100 g/l in the 1st step and up to about 350 g/l in the 2nd step. Therefore in case of metallic design of the evaporation equipment materials of construction with exceptional resistance to chloride induced pitting are required. The corrosion resistance of the high-alloyed stainless steel Alloy 31 (X1NiCrMoCu32-28-7 – UNS N 08031) and of the NiCrMo-alloys Alloy C-276 (NiMo16Cr15W – UNS N 10276) and Alloy 59 (NiCr23Mo16Al – UNS N 06059) including their weldments were to be tested for this application both in the laboratory and in field tests. In addition the behaviour of Alloy 59 heat exchanger tubes had to be determined in field tests under heat-transfer service conditions. The critical pitting corrosion temperatures of the 3 materials after having been GTAW welded under uniform conditions with FM 59 (ERNiCrMo–12) filler were determined in potentiostatic tests in model solutions imitating concentrated waste water products as they may occur in practice, using 5 K temperature intervals. As to be expected the critical corrosion resistance limits of the materials lie at 85 °C at chloride concentrations of 100 g/l Cl⁻ for the Alloy 31 and of 300 g/l Cl⁻ for both the Alloy 59 and the Alloy C–276 respectively. Field tests in waste water evaporation units of flue gas desulfurization plants of coal-fired power stations are carried out as immersion tests with the welded materials and as heat-exchange experiments using longitudinally welded tubes of Alloy 59 (2.4605). The immersion tests over a period of 32 months show the Alloy 31 (1.4562) to be a corrosion resistant construction material for tubes and containers in the first evaporation step, whereas the Alloy 59 (2.4605) and the Alloy C–276 (2.4819) have to be used for the second evaporation step, where the chloride contents are much higher. The Alloy 59 is to value as the most resistant material according to its lower tendency to crevice corrosion. The heat-exchange experiments over a test period of 9 months cause to expect the Alloy 59 to be a suitable construction material for heat-exchanger tubes in both evaporation steps in comparison to graphite which is more succeptible to mechanical destroying.     

Increased Lifetime for Biomass and Waste to Energy Power Plant Boilers with HVOF Coatings: High Temperature Corrosion Testing Under Chlorine-Containing Molten Salt

Heat exchanger surfaces of waste to energy and biomass power plant boilers experience often severe corrosion due to very aggressive components in the used fuels. High velocity oxy-fuel (HVOF) coatings offer excellent protection for boiler tubes against high temperature corrosion due to their high density and good adherence to the substrate material. Several thermal spray coatings with high chromium content were sprayed with HVOF technique. Their mechanical properties and high temperature corrosion resistance were tested and analyzed. The coating materials included NiCr, IN625, Ni-21Cr-10W-9Mo-4Cu, and iron-based partly amorphous alloy SHS9172 (Fe-25Cr-15W-12Nb-6Mo). High temperature corrosion testing was performed in NaCl-KCl-Na₂SO₄ salt with controlled H₂O atmosphere at 575 and 625 °C. The corrosion test results of the coatings were compared to corrosion resistance of tube materials (X20, Alloy 263 and Sanicro 25).     

Preparation of TiAlN/ZrN and TiCrN/ZrN multilayers by RF magnetron sputtering

Titanium-based nitride coatings on cutting tools, press molds and dies can be used to prolong their life cycle because of their superior corrosion and oxidation resistance. TiAlN/ZrN and TiCrN/ZrN multilayer coatings were prepared by RF magnetron sputtering, and their microstructural evolution and corrosion resistance during heat treatment were investigated. The TiAlN/ZrN and TiCrN/ZrN multilayer coatings are degraded by heating up to 600 °C with the formation of oxides particles on the surface. During the heat treatment, the TiCrN/ZrN and TiAlN/ZrN multilayer coatings show the lowest corrosion current density and the highest polarization resistance at temperature range of 400–500 °C. Consequently, the TiAlN/ZrN and TiCrN/ZrN multilayer coatings show good corrosion resistance at temperature range of 400–500 °C during heating.     

超细锌粉无机硅酸锌涂层的结构及耐蚀性研究

制备了3种超细锌粉作填料的无机硅酸锌涂层,用FTIR、SEM对涂层的固化机理和结构进行了研究,对3.5%NaCl溶液浸泡腐蚀后的试样表面形貌进行了观察,通过电化学试验研究了涂层的耐蚀性.结果表明,无机硅酸锌涂层的结构为:Zn粉颗粒间以Si-O-Zn聚合物网络键合,涂层与底材钢基体间是以化学键结合的微观多孔的涂层结构;涂层的耐蚀性随Zn粉颗粒度的减小而显著提高.涂层的耐蚀机理主要是电化学阴极保护作用以及腐蚀产物填塞涂层孔隙的物理屏蔽作用.     

高速电弧喷涂铝涂层在模拟深水下的腐蚀行为

目的探究高速电弧喷涂铝涂层在深水压力环境下的腐蚀行为。方法利用电化学阻抗谱、扫描电镜微观形貌观察、物相衍射和红外光谱等锈层分析手段,分析高速电弧喷涂铝涂层在不同实验条件下的腐蚀行为,并对实验结果进行了对比研究。结果 3 MPa高压浸泡72 h的铝涂层表面腐蚀产物呈现疏松粉状,并出现了腐蚀坑洞,铝涂层快速失效。常压浸泡72 h后的铝涂层表面腐蚀较轻,常压浸泡720 h后的铝涂层表面则已被腐蚀产物完全覆盖。经XRD分析,三种条件下的铝涂层腐蚀产物基本一致。进一步利用傅里叶变换红外光谱(FTIR)分析可知,3 MPa高压条件下,压力加速了碱式氯化铝水合物Al9Cl6(OH)21·18H_2O、Al5Cl3(OH)12·4H_2O等腐蚀产物的形成。这些腐蚀产物在高压下不能有效结合,且易于流失,致使涂层耐蚀性能快速下降。结论铝涂层在高压条件下形成的腐蚀产物不能有效覆盖在涂层表面阻止腐蚀介质侵入,导致铝涂层的耐蚀性能下降。     

镁合金微弧氧化膜耐蚀性表征方法的对比研究

制备结构、性能相近的AZ91D镁合金微弧氧化膜,通过浸泡、点滴及电化学实验表征膜层的耐蚀性,并结合SEM分析膜层腐蚀前后的表面形貌。本研究中6种耐蚀性检测方法的结果均表明：AZ91D镁合金经微弧氧化处理后耐蚀性显著提高; 失重与增重现象的共存使浸泡实验不能准确评定微弧氧化膜层耐蚀性的优劣; 点滴实验可以较快较准确地反映膜层的耐蚀性,但采纳点滴液开始变色的时间点为评价依据更合适,且测试耐蚀性较好的膜层时,点滴液中硝酸的含量提高到标准中的至少两倍时,才能达到快速检测的目的; 循环伏安、Tafel 极化、开路电位和电化学阻抗谱4种电化学实验能反映诸如腐蚀电位、腐蚀电流密度、阻抗值等更多的信息,可以进一步研究膜层的耐蚀原因。膜层的耐蚀性除了与膜厚、化学成分有关外,还与微观结构膜层内部和表面的密切相关。     

Corrosion behaviors of arc spraying single and double layer coatings in simulated Dagang soil solution

Three kinds of single layer coatings of Zn, Zn15Al, 316L stainless steel and two kinds of double layer coatings with inner layer of Zn or Zn15Al and outer layer of 316L stainless steel by arc spraying were developed to protect the metal ends of prestressed high-strength concrete (PHC) pipe piles against soil corrosion. The corrosion behaviors of the coated Q235 steel samples in the simulated Dagang soil solution were investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and natural immersion tests. The results show that the corrosion of the matrix Q235 steel is effectively inhibited by Zn, Zn15Al, Zn+316L and Zn15Al+316L coatings. The corrosion rate value of Zn15Al coated samples is negative. The corrosion products on Zn and Zn15Al coated samples are compact and firm. The corrosion resistance indexes of both Zn and Zn15Al coated samples are improved significantly with corrosion time, and the latter are more outstanding than the former. But the corrosion resistance of 316L coated samples is decreased quickly with the increase in immersion time. When the coatings are sealed with epoxy resin, the corrosion resistance of the coatings will be enhanced significantly.     

Corrosion Behaviors of Nitride Coatings on Titanium Alloy in NaCl-Induced Hot Corrosion

TiN and TiAlN coatings were deposited by arc ion plating on titanium alloys to study their hot corrosion resistance when they were exposed to NaCl at 600 ℃.The microstructure and corrosion behaviors of nitride coatings were studied using scanning electron microscope,X-ray diffraction,electro-probe microanalyzer and X-ray photoelectron spectroscopy.The results showed that nitride coatings with the different compositions and the ones with the same composition but different thicknesses presented different hot corrosion resistance.TiN and thin TiAlN coatings showed poor corrosion resistance.Serious internal oxidation attacked the alloy substrate.Their corrosion products were mainly consisted of non-protective TiO2 and sodium salt.By contrast,the thick TiAlN coating presented outstanding corrosion resistance.Besides sodium salt,the corrosion products were composed of protective Al2O3.The increasing thickness of TiAlN significantly enhanced the hot corrosion resistance.The corrosion mechanisms of alloy,TiN and TiAlN coatings were discussed in detail.     

Effect of silicate pretreatment, post-sealing and additives on corrosion resistance of phosphated galvanized steel

Sodium silicate （water glass） pretreatment before phosphating, silicate post-sealing after phosphating and adding silicate to a traditional phosphating solution were respectively carried out to obtain the improved phosphate coatings with high corrosion resistance and coverage on hot-dip galvanized（HDG） steel. The corrosion resistance, morphology and chemical composition of the coatings were investigated using neutral salt spray（NSS） tests, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results show that pretreatment HDG steel with silicate solutions, phosphate coatings with finer crystals and higher coverage are formed and the corrosion resistance is enhanced. Adding silicate to a traditional phosphating solution, the surface morphology of the coatings is nearly unchanged. The corrosion resistance of the coatings is mainly dependent on phosphating time. Phosphating for a longer time （such as 5 min）, the corrosion resistance, increasing with concentration of silicate, is improved significantly. Post-sealing the phosphated HDG steel with silicate solutions, the pores among the zinc phosphate crystals are sealed with the films containing Si, P, O and Zn and the continuous composite coatings are formed. The corrosion resistance of the composite coatings, related to the pH value, contents of hydrated gel of silica and Si2O^2- 5 and post-sealing time, is increased markedly. The improved coatings with optimal corrosion resistance are obtained for phosphating 5 min and post-sealing with 5 g/L silicate solution for 10 min.     

Hot Corrosion Behavior of a High Velocity Arc-Sprayed Fe-Cr-B-C Coating

A Fe-Cr-B-C coating was prepared by electric arc spraying process to prevent the boiler tubes from hot corrosion at elevated temperatures.A hot corrosion resistance test was conducted in a mixed molten salt of Na2SO4 and K2SO4(7:3)at 700 ℃for a total period of 156 h.The microstructure and phases of the coatings before and after exposed to the hot corrosion were investigated by scanning election microscopy(SEM),optical microscopy(OM)and X-ray diffraction(XRD).The hardness and porosity were analyzed.The hot corrosion behavior of the coatings was examined by the measurement of corrosion mass gain and the observation of corrosion morphology.The results show that some splats of particles are formed on flat substrate surfaces and the coatings have a dense typical layer structure of electric arc thermally spraying deposits.Some amorphous phase exist in the coating.The coatings have an excellent resistance to hot corrosion.The formation of oxides of chromium on the exposed surface may be contributing better resistance to hot corrosion.The corrosion of the coatings follows the oxidation and sulfidation mechanism.     

Improvement of corrosion resistance of high-velocity oxyfuel-sprayed stainless steel coatings by addition of molybdenum

To improve the marine corrosion resistance of stainless steel coatings fabricated by high-velocity oxyfuel (HVOF) spraying with a gas shroud attachment, the molybdenum (Mo) content of stainless steel was increased to form coatings with a chemical composition of Fe balance-18mass%Cr-22mass%Ni-2∼8mass%Mo. These coatings were highly dense, with <0.1 vol.% in porosity, and less oxidized, with 0.5 mass% in oxygen content at most. The corrosion mechanism and resistance of the coatings were investigated by electrochemical measurement, chemical analysis, and statistical processing. The general corrosion resistance of the coatings in 0.5 mol/dm³ sulfuric acid was improved with increases in Mo content, and the corrosion rate could be decreased to 8.8 × 10⁻² mg/cm² per hour (∼1 mm/year) at 8 mass% Mo. The pitting corrosion resistance of the coatings in artificial seawater was improved with increases in Mo content and was superior to that of the 316L stainless steel coating. The crevice corrosion resistance of the coatings in artificial seawater was improved and the number of rust spots at 4 mass% Mo was decreased to 38% of that for the 316L coating. Accordingly, Mo is highly effective in improving the corrosion resistance of the stainless steel coatings by HVOF spraying.     

电弧喷涂锌基防腐涂层在洞室环境中的耐蚀性研究

采用高速电弧喷涂技术在16MnR钢上制备了Zn和Zn-Al涂层,通过盐雾加速实验考核涂层在5％NaCl溶液中的腐蚀性能,并对涂层腐蚀前后的组织结构进行分析.结果表明,两种Zn基涂层致密,在盐雾实验40 d后未出现红锈,表现出优异的耐腐蚀性能.喷涂纯Zn涂层,其腐蚀产物疏松,对基体主要起到牺牲阳极的保护作用;喷涂Zn-Al涂层,其腐蚀产物致密,起到牺牲阳极和隔离的双重保护作用.     

Zn-Fe-SiO2复合镀层的耐蚀性研究

采用电沉积的方法，制备了Zn-Fe-SiO2复合镀层，对比了该镀层与Zn-Fe合金镀层及Zn镀层的耐蚀性，并研究了镀层成分对镀层耐蚀性的影响，发现该复合镀层无需钝化处理即具有很高的耐蚀性，而且镀层在酸性溶液中的耐蚀性随着镀层中Fe含量的增大而提高，在中性溶液中的耐蚀性随着镀层中SiO2含量的增大而提高.      

耐锌液腐蚀热喷涂涂层的研发现状

生产镀锌板的热浸镀机组中的各种轴承、沉没辊等受锌液的强烈腐蚀,对热镀锌的生产和产品质量有很大影响．热喷涂耐锌液腐蚀涂层是解决这一难题的一种重要的防护方法．本文主要介绍了近年来国内外关于耐锌液腐蚀热喷涂涂层材料的开发及相应的涂层制备技术,系统分析了各涂层材料在锌液中的腐蚀机理和封孔剂在热喷涂涂层耐锌液腐蚀中的重要性,并指...     

Corrosion effects of plasma immersion ion implantation-enhanced Cr deposition on SAE 1070 carbon steel

Chromium electroplated coatings are the most common coatings used for several decades in the general industry as a protective layer against corrosion and wear. The waste of Cr plating is an environmental problem because of the toxic and carcinogenic Cr⁶⁺ compounds resulting from the Cr baths. In this study, we suggest an alternative method for thin Cr films deposition: plasma immersion ion implantation-enhanced deposition (PIIIeD) that aims at achieving highly adherent films to carbon steel surfaces with very high resistance to corrosion attacks. Chromium films formed by PIIIeD were studied with respect to corrosion resistance, surface morphology and elements profile. Potentiodynamic scans showed a decrease in the corrosion current density, promoting higher corrosion resistance, and a hydrophobic character of the PIIIeD Cr films, turning the samples less susceptible to saline corrosion. GDOES depth profiles showed the increase of film and mixing layer thicknesses with the increase of GD power.     

Corrosion Properties of Cold-Sprayed Tantalum Coatings

Cold spraying enables the production of pure and dense metallic coatings. Denseness (impermeability) plays an important role in the corrosion resistance of coatings, and good corrosion resistance is based on the formation of a protective oxide layer in case of passivating metals and metal alloys. The aim of this study was to investigate the microstructural details, denseness, and corrosion resistance of two cold-sprayed tantalum coatings with a scanning electron microscope and corrosion tests. Polarization measurements were taken to gain information on the corrosion properties of the coatings in 3.5 wt.% NaCl and 40 wt.% H₂SO₄ solutions at room temperature and temperature of 80 °C. Standard and improved tantalum powders were tested with different spraying conditions. The cold-sprayed tantalum coating prepared from improved tantalum powder with advanced cold spray system showed excellent corrosion resistance: in microstructural analysis, it showed a uniformly dense microstructure, and, in addition, performed well in all corrosion tests.     

Understanding corrosion via corrosion product characterization: II. Role of alloying elements in improving the corrosion resistance of Zn–Al–Mg coatings on steel

Corrosion products are identified on Zn, ZnMg and ZnAlMg coatings in cyclic corrosion tests with NaCl or Na₂SO₄ containing atmospheres. For Mg-containing alloys the improved corrosion resistance is achieved by stabilization of protective simonkolleite and zinc hydroxysulfate. At later stages, the formation of layered double hydroxides (LDH) is observed for ZnAlMg. According to thermodynamic modeling, Mg²⁺ ions bind the excess of carbonate or sulfate anions preventing the formation of soluble or less-protective products. A preferential dissolution of Zn and Mg at initial stages of corrosion is confirmed by in situ dissolution measurement. The physicochemical properties of different corrosion products are compared.     

离子轰击镀对铀上铝镀层组织及防腐蚀性能的影响

研究了偏压镀、循环氩离子轰击镀和间歇式镀对铀上铝镀层组织及防腐蚀性能的影响．结果表明,3种离子轰击镀方法对铝镀层的组织产生强烈影响，且组织的致密程度与其防腐蚀性能呈现了较好的一致性．在-100V、-200V和-500V偏压条件下，镀层组织致密、防腐蚀性好；在-300V偏压下，镀层的致密性和防腐蚀性均差，未加偏压(0V)的次之；循环氩离子轰击镀和间歇式镀对提高镀层的致密性和防腐蚀性更为显著．离子轰击镀沉积的铝镀层均可不同程度地为铀提供好的保护效果．     

Self healing ability of silicate conversion coatings on hot dip galvanized steels

The self-healing ability of a coating is an important aspect for evaluating its corrosion resistance. Chromate conversion coatings show excellent anti-corrosion properties because of their compact microstructure and their strong self-healing ability. Silicate conversion coatings, which are potential replacement candidates for chromate conversion coatings, have good corrosion resistance, but their self-healing abilities have not been determined. In this paper, silicate conversion coatings are prepared by immersing hot dip galvanized steel sheets in sodium silicate solutions with SiO₂:Na₂O molar ratio of 1.00 and 3.50. The coatings are scratched with a blunt knife edge and corroded in a neutral salt spray chamber for certain lengths of time. The corrosion products in and near the scratched area are investigated by scanning electron microscopy and energy-dispersive spectroscopy. The self-healing ability of silicate conversion coatings is discussed. The results show that silicate conversion coatings have self-healing abilities under the experimental conditions. Higher SiO₂:Na₂O molar ratios lead to improved self-healing abilities. During the corrosion process, the silicate anions in the coating migrate to the scratched area, where a new conversion coating composed of Zn, O, and Si is formed. This delays corrosion in the scratched area.