Hot-corrosion mechanism of Ni-Cr coatings at 650℃ under different simulated corrosion conditions

The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings pro-duced by high velocity arc spray (HVAS) were studied. Several different conditions were studied under simulated boiler conditions at 650 ℃. The protection effect of an Al coating deposited by HVAS onto the Ni-Cr coating was also investigated. Microscope, X-ray diffraction and corrosion rate curves have been used to analyze corrosion mechanisms. The experimental results show that: 1) The oxidation rates are almost superposed in both air (no SO3) and in simulated coal-fired gas (containing SO3) as long as no salt was present on the surface. These rate curves show a logarithmic relationship. 2) When the surface is coated with salt (75%K2SO3 + 25%Na2SO3) the rate curve for LTHC of the Ni-Cr coated surface shows a parabolic shape in the simulated coal-fire flue gas. In air only the oxidation reaction takes place, the second type of LTHC was not seen. And 3) the Al over coating on the Ni-Cr enhances resistance to LTHC because an inter-metallic compound, Al3Ni2, forms at the Al/Ni-Cr interface and because of the increase in coating thickness.

Effect of pattern coating thickness on characteristics of lost foam Al-Si-Cu alloy casting

An experimental study on lost foam casting of an Al-Si-Cu alloy was conducted. The main objective was to study the effect of pattern coating thickness on casting imperfection and porosity percentage as well as eutectic silicon spacing of the alloy. The results showed that increasing slurry viscosity and flask dipping time influenced the casting integrity and microstructural characteristics. It was found that thinner pattern coating produced improved mould filling, refined microstructure and higher quality castings containing less porosity.

A study on the effect of coating's sorption capacity on the porosity in lost foam aluminum alloy casting

Effects of coating constituent, coating density, coating layer thickness and temperature on coating sorption capacity for polystyrene decomposition products have been studied systematically. It has been found that the effect of attapulgite clay on sorption capacity is the largest among coating constituents. The sorption capacity of the coating with 2% attapulgite clay is elevated by 81%. The relationship between casting porosity and coating sorption capacity has been studied. It has been pointed out that higher coating sorption capacity for polystyrene decomposition products is helpful to decrease the casting porosity. Results also show that the sorption capacity of self-developed HW-1 coating for polystyrene decomposition products is as good as that of Ashland coating from America.

Radiation Efficiency of Surface Burning on a Foam Metal Matrix with Ceramic Coating

The modified empirical two-temperature model of surface burning on a foam metal matrix was proposed. The comparative experimental studies of radiation properties of both matrices without and with ceramic coating (alumina) were carried out. Measurement was conducted in different spectral ranges. The experimental results were compared with theoretical calculations. It was shown that the integral radiation efficiency of the matrix with ceramic coating was comparable with radiation efficiency of the matrix without any coating in the wide range of the firing rate and surpassed it on 30% - 40% at firing rate above 50 W/cm2.

Preparation and oxidation resistance of B_2O_3-coated boron-modified carbon foams

To improve the oxidation resistance of boron-modified carbon foams, the B2O3 coating was prepared on boron-modified carbon foams by low-cost slurry method. The microstructures and phase compositions of the coated carbon foams were characterized by scanning electron microscopy and X-ray diffraction, respectively. Oxidation resistances of uncoated and coated boron-modified carbon foams were investigated at 873 K in air. The results showed that as-received B2O3 coating could protect boron-modified carbon foams from oxidation at 873 K. B2O3-coated carbon foam doped with 7% B2O3 （mass fraction） （BO-7） had better oxidation resistance, exhibiting mass loss of 17.40% after oxidation at 873 K for 120 min. The melting glass layer formed on the surface of BO-7 could prevent oxygen from diffusing into boron-modified carbon foams substrate during oxidation to some extent.

High-temperature Compressive Performance of Mg Alloy Foams Coated with Ni-P Layer

Mg/Ni hybrid foams were fabricated by the electroless method.The Ni-P(Nickel-Phosphorous)coatings were deposited on the surface of closed-cell Mg alloy foams.The composition,microstructure and phases of the Ni-P coatings were characterized by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD),respectively.The compressive tests were performed on the Mg/Ni hybrid foams at 400℃using the Mg alloy foams as a reference.The experimental results show that the yield strength,plateau stress and energy absorption capacity of the closed-cell Mg alloy foams at high temperature were improved by the Ni-P coating.And there are four main modes for the Mg/Ni hybrid foam failure at 400℃,i e,shearing in cell wall,bending in cell edge,shedding and cracking in Ni-P coating.

Temperature stability of SmCo(2:17) magnets modified by Ni-Cr two-layer coating

The oxidation resistance behavior of SmCo(2:17)-type high-temperature magnets modified with Ni-Cr two-layer coating was studied. The study depicts the mass gain kinetics and magnetic properties of uncoated and NiCr-modified magnets oxidized at high temperature(500 ℃) in air for 200 h. The oxidation test results illustrate that the mass gain of uncoated magnet is6.95 mg·cm^(-2) which is more than that(0.08 mg·cm^(-2)) of coated magnet after 200 h. For the magnetic properties concerned, there is a great loss for uncoated magnet, while for coated magnet, magnetic properties do not change much. The study of uncoated magnet through X-ray diffraction(XRD) and electron probe microanalysis(EPMA) shows that the invasion of oxygen at high temperature leads to the loss of magnetic properties by changing the microstructure of magnet.

A novel approach to fabricate Zn coating on Mg foam through a modified thermal evaporation technique

Zn enriched coatings with distinct microstructures and properties were fabricated on Mg foams by a modified thermal evaporation technique using a tubular resistance furnace. As the temperature and kinetic energy of Zn vapor varied along the tubular system, a spatial variation of preparation conditions was created and the obtained coatings were found to follow two growth mechanisms： a thermal diffusion pattern in high-temperature zone and the a relatively low-temperature deposition model. AZn-based deposition coating with dense texture and nearly uniform structure was acquired while Mg foam was placed 20 cm far from the evaporation source, where the Zn vapor deposition model dominated the coating growth.Mechanical properties and bio-corrosion behaviors of the samples were investigated. Results showed that the Zn coatings brought dramatic improvements in compression strength, but exhibited differently in biodegradation performance. It was confirmed that the diffusion layer accelerated corrosion of Mg foam due to the galvanic effect, while the Zn-based deposition coating displayed excellent anti-corrosion performance, showing great potential as bone implant materials. This technique provides a novel and convenient approach to tailor the biodegradability of Mg foams for biomedical applications.

MODULUS PREDICTION AND DISCUSSION OF REINFORCED SYNTACTIC FOAMS WITH COATED HOLLOW SPHERICAL INCLUSIONS

The elastic properties of syntactic foams with coated hollow spherical inclusions have been studied by means of Mori and Tanaka's concept of average stress in the matrix and Eshelby's equivalent inclusion theories.Some formulae to predict the effective modulus of this material have been derived theoretically.Based on these formulae,the influences of coating parameters such as the thickness and (Poisson's) ratio on the modulus of the syntactic foams have been discussed at the same time.

Scalable and Heavy Foam Functionalization by Electrode-Inspired Sticky Jammed Fluids for Efficient Indoor Air-Quality Management

Functionalization of polymer foams by surface coating is of great interest for advanced flow-interactive materials working with well-controlled 3D open channels.However,realizing heavy functional coating via a fast and recyclable way remains a big challenge.Here,inspired by the battery electrodes,we propose a scalable mechanic-assisted heavy coating strategy based on the design of sticky jammed fluid(SJF)to conquer the above challenge.Similar to the electrode slurry,the SJF is dominated by a high concentration of active material(≥20 wt%of active carbon,for instance)uniformly dispersed in a protein binder solution.Due to the sticky and solidrich nature of the SJF,one can realize a high coating efficiency of 60 wt%gain per coating.The critical factors controlling the coating processing and quality are further identified and discussed.Furthermore,the functionalized foam is demonstrated as a high-performance shape-customizable toxic gas remover,which can absorb formaldehyde very efficiently at different circumstances,including static adsorption,flow-based filtration,and source interception.Finally,the foam skeleton and the active materials are easily recycled by a facile solvent treatment.This study may inspire new scalable way for fast,heavy,and customizable functionalization of polymeric foams.

低甲醛脲醛树脂基钢结构防火涂料的制备

本试验制备了一种低甲醛脲醛树脂基膨胀型钢结构防火涂料,探究了脲醛树脂加入量对防火涂料性能的影响,并分析其耐火机理。结果表明,在甲醛与尿素低摩尔比(0.8∶1)时,加入0.1%过氧化氢,制备低甲醛脲醛树脂,甲醛含量符合GB 18582-2020规定;加入脲醛树脂对膨胀型钢结构防火涂料的基本性能无影响,对涂层发泡性能和耐火性能影响显著,当脲醛树脂加入量在6%~10%时,涂层发泡厚度在3 cm以上,钢板背面温度在300℃以下,最低为271.9℃;脲醛树脂发生热解,分子链断裂产生大量阻燃气体,形成致密碳层,起到气源、碳源的作用。

木质素基聚氨酯的发展现状

聚氨酯是一种产品形态较多、性能较好的高分子材料,适用于各个行业的应用。由于石油资源逐渐枯竭,出现了环境问题,利用可再生资源合成高分子聚合物成为人们关注的热点。由于木质素可再生、可生物降解、非食用价值较高、功能性较强,可作为羟基提供源,替代石油基多元醇合成聚氨酯,而得到了广泛关注。近年来,木质素作为多元醇替代品被广泛地应用于聚氨酯领域(泡沫、涂料、胶粘剂),证明了木质素或改性木质素能赋予聚氨酯材料额外的功能,例如,提升了材料力学性能,赋予了材料疏水性、耐候性和热稳定性等。通过概述木质素结构、性质的多样性及木质素的功能化改性方法,分析木质素添加至聚氨酯产品中的潜在方法及其发展潜力和挑战,得到木质素应用于聚氨酯领域的潜在解决方案。最后,阐述了将木质素添加至聚氨酯产品(聚氨酯泡沫、涂料、胶粘剂)后,具有较大的发展潜力,提升了聚氨酯的性能。

泡沫基材-Ni-石墨烯复合镀层制备及电催化析氢性能研究

目的 采用电沉积技术在泡沫基材上沉积制备Ni-石墨烯复合镀层,期望借助泡沫基材的三维多孔结构和石墨烯的超高比表面积来改变复合材料的表面状态,进而获得高镀层的电催化析氢性能。方法 采用电沉积技术将石墨烯作为第二相粒子沉积,制备了泡沫基材-Ni-石墨烯复合电极,通过SEM和EDS研究了其微观形貌及成分,并利用电化学工作站完成了镀层电极的极化曲线、交流阻抗和电解水稳定性测试,使用控制变量法探究了镀层厚度、镀液石墨烯浓度和基材形貌对镀层电催化析氢活性的影响。结果 SEM和EDS表征发现,镀层表面形貌受镀液中石墨烯浓度影响较大,石墨烯作为第二相嵌入镀层后,明显改变了复合镀层的表面形貌,其存在形态为颗粒状,在150 mg·L^(–1)时颗粒堆积最多。进一步利用电化学分析技术探究了镀层厚度、镀液石墨烯浓度和基材形貌对电极电催化析氢性能的影响,发现在一定范围内,不同厚度镀层的电催化析氢活性基本相同;石墨烯质量浓度为150mg·L^(–1)时制得的电极的电催化析氢性能最优,析氢过电位为211.2m V(vs.RHE),且电解水稳定性良好;泡沫基材镀层的电催化析氢活性明显优于平板基材镀层。结论 石墨烯的引入和泡沫基材三维多孔结构均增大了复合镀层的比表面积,是电极表现良好的电催化析氢活性的关键。

三维开孔Ni-Cr-Fe合金泡沫的准静态压缩性能和能量吸收特性(英文)

采用固体粉末法在1050°C下对三维网状开孔泡沫Ni表面进行CrFe共沉积,然后经过1200°C高温固相扩散处理对开孔泡沫NiCrFe进行表面合金化。研究不同保温条件下Cr、Fe含量对NiCrFe合金泡沫的准静态压缩性能和能量吸收性能。同时,将开孔NiCrFe合金泡沫的真实力学性能与纯泡沫Ni和假设的NiCrFe合金泡沫模型进行比较。结果表明:不同Cr、Fe含量的开孔NiCrFe合金泡沫骨架显示出相似的硬度,整体上开孔NiCrFe合金泡沫的压缩强度和能量吸收性能随着合金泡沫中Cr、Fe含量的增加而明显增大。开孔NiCrFe合金泡沫的应力—应变行为与纯泡沫Ni相似,表明NiCrFe合金泡沫具有典型韧性金属泡沫的变形特性。同时,单位体积开孔NiCrFe合金泡沫的能量吸收最大值与泡沫Ni相比增加了22倍。经计算得出的NiFeCr合金泡沫的理论屈服强度与实际屈服强度大体一致。

Coating particles using liquids and foams based on viscous formulations with industrial mixers: Batch operation

Particle or powder coating with viscous liquids has been essential in industry for surface modification purposes to induce and enhance specific functionalities.This paper evaluates the performance of using foams (of different bubble diameters) versus liquids as a means of coating powder beds based on viscous liquid formulations.Coating with viscous liquids present numerous industrial challenges and therefore preparing foam equivalents can render the liquid component weak enough (through pre shearing to form the foam),to allow it to break up and coat particles under the shear forces exerted in a mixing device.In this study,two shear mixers are used;the first type consists of paddles in different configurations attached to a single rotating shaft,whilst the second type is a commercial twin screw mixer (TSM).The quality of coating achieved on the bulk powder bed using liquids and foams (stained with a dye) is assessed by image analysis to determine the homogeneity of the color distribution.In addition,scanning electron microscopy provides a tool to further investigate the coating quality of individual particles from the bulk product.The results show that large bubble (centimeter size) foams are much more effective at distributing within the fluidized powder bed compared to the starting viscous liquid and small bubble foams (submillimeter size).Furthermore,there is a maximum ratio of foam to powder beyond which agglomeration occurs and is insufficient to fully coat the particles.Coating of individual particles is achieved in the case of the TSM,whereas SEM proves that the single shaft paddle mixer crushes the particles and subsequently granulates them together to form granules of a size comparable to the size of coated particles seen after coating with the TSM.

无溶剂聚氨酯合成革发泡涂层的制备和性能

双组分无溶剂聚氨酯(SFPU)合成革发泡方法局限性较大,为开发一种新型的封闭型SFPU以及探索其新的发泡技术,采用聚醚多元醇与二苯基甲烷二异氰酸酯(MDI)共聚,丙酮肟(DMKO)进行封端,制备了封闭型SFPU,并与热膨胀聚合物微球(TEM)复合制备了一种无溶剂聚氨酯合成革发泡涂层,对涂层的力学性能、发泡倍率、柔软度、回弹性能、剥离强度和微观结构进行了表征。结果表明,原料中三元醇/二元醇最佳物质的量比为1∶1,在80℃下,合适的封端时间为30 min,最佳固化温度为120~130℃,最佳TEM质量分数为1%~2%,所获得涂层的断裂伸长率高于600%,发泡倍率介于2.0~2.5之间,泡孔细密均匀,柔软度和回弹性提高20%以上,剥离强度高于60 N/3cm,达到了合成革的应用要求。

起泡剂对高灰尾煤泥浮选的影响及机理研究

以贵州某焦煤选厂浮选尾煤泥为研究对象,考察了甲基异丁基甲醇(MIBC)、仲辛醇、2号油、正戊醇等起泡剂对浮选尾煤泥再选提质的影响及作用机理。结果表明,用量相近时,MIBC为起泡剂所获得的浮选指标优于其他3种起泡剂。煤油用量1000 g/t、MIBC用量350 g/t时,灰分56.90%的原煤经一粗一精一扫浮选可获得灰分11.47%、产率32.03%的合格炼焦精煤产品。利用充气法研究了4种起泡剂的起泡能力及泡沫稳定性,发现2号油起泡能力和气泡稳定性均较强,正戊醇起泡能力和气泡稳定性均较弱,MIBC和仲辛醇表现适中。利用气泡-颗粒包覆角及诱导时间测量仪进一步分析了不同起泡剂作用下气泡与煤粒黏附作用过程,发现MIBC可以提升气泡的载矿能力,缩短颗粒与气泡间的诱导时间,从而获得较好的浮选效果。

寒区公路泡沫混凝土抗冻融性能试验研究

通过改变泡沫混凝土的水胶比、水泥掺量、粉煤灰掺量及矿粉掺量,测试冻融循环作用下试件抗压强度,利用正交实验选出最优方案和最显著因素,并通过F50冻融循环试验,分析冻融循环后的冻融质量损失率与冻融强度损失率规律。结果表明:经历冻融循环作用后,相较未涂防水涂料的泡沫混凝土,外涂有机硅烷防水涂料的泡沫混凝土抗压强度高出10%左右;无论试件涂刷有机硅烷防水涂料与否,正交实验选出的最优组合均为A1B3C3D1;所设计的9组试样均满足F50冻融循环试验要求。

改性淀粉基碳氮硫硅环钢结构防火涂料的研究

本试验对淀粉进行改性,制备了改性淀粉基碳氮硫硅环保钢结构防火涂料,探究了改性淀粉加入量对涂料性能的影响,并对其进行阻燃机理分析。结果表明,改性淀粉的加入能显著增强涂层黏结性能,对其余基本性能无影响,符合GB 14907—2018的规定;改性淀粉能显著提高涂层发泡性能和耐火性能,改性淀粉加入量为2%~6%时,涂层发泡厚度大于3.0 cm,涂层背面温度小于183.6℃;改性淀粉在受热时形成熔融状态钠醚盐,具有较好传质传热作用,有利于气源物质同步气化,与碳源炭化协调一致,改性淀粉在289.1℃左右时开始分解,相变结束后残碳量约为36.5%,在涂层中主要起碳源和小部分气源作用,且能改善涂层的成膜性能,降低成本,具有较好应用前景。

基于石墨涂层传热技术制备界面冶金结合泡沫铝夹芯板

提出一种通过石墨涂敷处理(GCT)泡沫铝夹芯板(AFS)前驱体来提高其在粉末冶金发泡过程中传热效率的新方法。研究不同传热方法的升温和膨胀特征以及对泡孔结构和抗弯性能的影响。结果表明,前驱体在采用GCT后,升温速度增加近2倍,这提高了AFS的膨胀率、改善了泡孔尺寸均匀性和外部面板形态。此外,在发泡后期阶段具有更加平稳的升温速率,这有助于提高泡孔圆度,并减少泡壁内微孔缺陷。这些改变使AFS的弯曲强度和吸能性能得以显著提高。值得注意的是,因为热传递速率不受板幅尺寸的影响,GCT技术在大尺寸AFS的生产中具有巨大潜力。