Preparation of coated sand for selective laser sintering and optimization of baking process of sand moulds

A cold method was used to prepare coated sand for application in the selective laser sintering(SLS)process.Tensile strength,loss on ignition,gas evolution,and accuracy of the SLS samples were tested and analyzed,and the baking process was thoroughly investigated.Compared with coated sand prepared by the hot method,the cold method yields a more uniform and complete resin film on the sand's surface,resulting in enhanced tensile strength and accuracy.Additionally,the cold method requires a lower binder content to meet the same strength requirements,thereby minimizing gas evolution,reducing porosity defects,and ultimately improving casting quality.The coated sand samples prepared through the cold method exhibit superior accuracy,with a size error of within±0.4 mm.In contrast,the coated sand samples prepared by the hot method display a lower accuracy,with an average negative error of 2.1993 mm.The highest tensile strength could be attained by controlling the baking temperature within a suitable range(180-190°C),which can effectively reduce the generation of gas,thus contributing to improved overall performance.

Preparation and optical properties of Nb-NbN multilayer films as solar selective absorptive coatings

Based on the cermet double layer structure, Nb-NbN multi-layer films for solar selective coatings were deposited by direct current reactive magnetron sputtering. The Nb/Nb-NbN/Al2O3 trilayered structure was deposited on a stainless steel (SS) substrate by using a single niobium target. The expected components were adjusted by changing the gas flowing ratios of Ar: N2. The Al2O3 antireflective layer on the top of the film was produced by r. f. magnetron sputtering using Al2O3 ceramic target. A solar absorptivity of 0.94 and a normal emissivity of 0.16 at room temperature have been achieved for the coating. Thermal vacuum aging to the samples was carried out at 350 and 500 ℃ for 1 h. The results show a good thermal stability. Microstructure and its dependence on temperature of the Nb, NbN and Nb-NbN single layers were investigated, respectively.

Comparison of Five Selection Procedures for Seed Coat and Hilum Color in Interspecific Crossing of Soybeans

Five selection procedures for seed coat and hilum color were studied with F4 progenies in two interspecific crossing of soybeans. The seed coat and hilum color indicated that pedigree, 5% and 10% mass selection method were equally successful, and were better than picking-pod and 25% mass selection in cross S17. However, no significant differences in seed coat and hilum color were found in cross G18.

Effects of laser energy density on forming accuracy and tensile strength of selective laser sintering resin coated sands

Baozhu sand particles with size between 75 μm and 150 μm were coated by resin with the ratio of 1.5 wt.% of sands. Laser sintering experiments were carried out to investigate the effects of laser energy density(E = P/v), with different laser power(P) and scanning velocity(v), on the dimensional accuracy and tensile strength of sintered parts. The experimental results indicate that with the constant scanning velocity, the tensile strength of sintered samples increases with an increase in laser energy density; while the dimensional accuracy apparently decreases when the laser energy density is larger than 0.032 J·mm-2. When the laser energy density is 0.024 J·mm-2, the tensile strength shows no obvious change; but when the laser energy density is larger than 0.024 J·mm-2, the sample strength is featured by the initial increase and subsequent decrease with simultaneous increase of both laser power and scanning velocity. In this study, the optimal energy density range for laser sintering is 0.024-0.032 J·mm-2. Moreover, samples with the best tensile strength and dimensional accuracy can be obtained when P = 30-40 W and v = 1.5-2.0 m·s-1. Using the optimized laser energy density, laser power and scanning speed, a complex coated sand mould with clear contour and excellent forming accuracy has been successfully fabricated.

Scavenging of Cd through Fe/Mn oxides within natural surface coatings

The dynamics of Cd scavenging from solutions by Fe/Mn oxides in natural surface coatings （NSCs） was investigated under laboratory conditions. Selective extraction methods were employed to estimate the contributions of Fe/Mn oxides, where hydroxylamine hydrochloride （0.01 mol/L NH2OH-HCl ＋ 0.01 mol/L HNO3）, sodium dithionite （0.4 mol/L Na2S2O4） and nitric acid （10% HNO3） were used as extraction reagents. The Cd scavenging was accomplished with developing periods of the NSCs （totally 21 data sets）. The resulting process dynamics fitted well to the Elovich equation, demonstrating that the amount of Cd scavenged was proportional to the increments of Fe/Mn oxides that were accumulated in the NSCs. The amount of Cd bound to Fe oxides （MCdFe） and Mn oxides （MCdMn） could be quantified by solving two equations based on the properties of two extraction reagents. The amount of Cd scavenged by Fe/Mn oxides could also be estimated using MCdFe and MCdMn divided by the total amounts of Fe and Mn oxides in the NSCs, respectively. The results indicated that the Cd scavenging by Fe/Mn oxides was dominated by Fe oxides, with less roles attributed to Mn oxides. The estimated levels of Cd scavenging through Fe and Mn oxides agreed well with those predicted through additive-adsorption and linear-regression models.

The Effect of Annealing under Non-vacuum on the Optical Properties of TiAlN Non-vacuum Solar Selective Absorbing Coating Prepared by Cathodic Arc Evaporation

TiAIN solar selective absorbing coatings which were deposited on 304L stainless steel using cathodic arc evaporation method were annealed under non-vacuum at different temperatures with different times. The optical properties （absorptance and emittance） of the coatings were measured by a spectrophotometer. It was found that, after being annealed for 2 hours at different temperatures, the absorptance of the coatings reached the highest value of 0.92 at 700 ℃ while the emittance got the lowest value of 0.38 at 800 ℃. When the coatings were annealed at 600 ℃ for 24 hours, the optical properties changed to 0.92/0.44 （absorptance/ emittance）. By measuring the structure, morphology, elements and surface roughness of the coatings, it was found that both the elemental composition and the surface roughness of the coatings changed as a result of annealing, and these changes caused the change of the optical properties of the coatings.

Spray coating of polysulfone/poly(ethylene glycol) block polymer on macroporous substrates followed by selective swelling for composite ultrafiltration membranes

Polysulfone(PSF) is extensively used for the production of ultrafiltration(UF) membranes thanks to its high strength,chemical stability,and good processibility.However,PSF is intrinsically hydrophobic,and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems.Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded.Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes.The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol(PEG) on both ends,that is,PEG-b-PSF-b-PEG.We use the technique of spray coa ting to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports,instantly resulting in uniform,defect-free polymer coating layers with the thickness down to ~1.2 μm.The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation,thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers.This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods.The pore sizes,porositie s,hydrophilicity,and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath.This strategy combining spray coating and selective swelling is upscalable for the production of highperformance PSF UF membranes.

Selective laser sintering mechanism of polymer-coated molybdenum powder

A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.

Numerical simulation of temperature field during selective laser sintering of polymer-coated molybdenum powder

The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the temperature field during length-alterable line-scanning and laser sintering of polymer-coated molybdenum powder was presented. Finite element method (FEM) was used to simulate the temperature field during laser sintering process. In order to verify the simulated results, a measuring system was developed to study the laser sintering temperature field. Infrared meter was introduced to measure the surface temperature of sintering powder; the temperature of its inside part was measured by thermocouple. The measured results were compared with the numerical simulation results; the conformity between them is good and the relative error is less than 5%.

Coating processes towards selective laser sintering of energetic material composites

This research aims to contribute to the safe methodology for additive manufacturing(AM)of energetic materials.Coating formulation processes were investigated and evaluated to find a suitable method that may enable selective laser sintering(SLS)as the safe method for fabrication of high explosive(HE)compositions.For safety and co nvenie nce reasons,the co ncept demonstration was conducted using inert explosive simulants with properties quasi-similar to the real HE.Coating processes for simulant RDXbased microparticles by means of PCL and 3,4,5-trimethoxybenzaldehyde(as TNT simulant)are reported.These processes were evaluated for uniformity of coating the HE inert simulant particles with binder materials to facilitate the SLS as the adequate binding and fabrication method.Suspension system and single emulsion methods gave required particle near spherical morphology,size and uniform coating.The suspension process appears to be suitable for the SLS of HE mocks and potential formulation methods for active HE composites.The density is estimated to be comparable with the current HE compositions and plastic bonded explosives(PBXs)such as C4 and PE4,produced from traditional methods.The formulation method developed and understanding of the science behind the processes paves the way toward safe SLS of the active HE compositions and may open avenues for further research and development of munitions of the future.

Optical Properties of Window Coatings

Window coating used for the building in recent years is described. Important design principles, practical coating materials, and attainable optical properties for research-type coatings are introduced. Discussion is carried out on the spectrally selective coatings, the electrochromic coatings, and the thermochromic coatings.

Selective laser sintering of polymer-coated Al_2O_3/ZrO_2/TiC ceramic powder

A type of polymer-coated Al2O3/ZrO2/TiC ceramic powder was prepared. The laser sintering mechanism of polymer-coated Al2O3/ZrO2/TiC powder was investigated by studying the dynamic laser sintering process. It is found that the mechanism is viscous flow when the sintering temperature is between 80 ℃ and 120 ℃, and it is melting/solidification when the temperature is above 120 ℃. The process parameters of selective laser sintering were optimized by using ortho-design method. The results show that the optimal parameters include laser power of 14 W, scanning velocity of 1 400 mm/s, preheating temperature of 50 ℃ and powder depth of 0.15 mm. A two-step post-treatment process is adopted to improve the mechanical properties of laser sintered part, which includes polymer debinding and high temperature sintering. After vacuum sintering for 2 h at 1 650 ℃, the bending strength and fracture toughness of Al2O3/ZrO2/TiC ceramic part reach 358 MPa and 6.9 MPa·m1/2, respectively.

解草啶包衣减轻丙草胺对栽培稻药害的技术

为了探寻高效防除杂草稻且对栽培稻安全的杂草治理技术,研究解草啶包衣对减轻丙草胺药害以及防治杂草稻的潜力。对栽培稻种子进行不同浓度(4%、7%、10%、13%、16%)解草啶包衣处理,以不含解草啶的种衣剂处理为对照(CK),分别研究不同浓度解草啶包衣处理对栽培稻种子萌发、幼苗生长发育和茎叶重、根重的影响,以及10%解草啶包衣处理对丙草胺防控杂草稻的药效的影响。结果表明,不同浓度解草啶包衣对栽培稻种子萌发均无显著差异;除最高浓度(16%)解草啶包衣处理之外,其他浓度处理对栽培稻幼苗的生长发育均无显著影响;解草啶添加浓度为10%时,栽培稻茎叶、根的鲜重抑制率均最低,说明其对栽培稻的保护效果最好。丙草胺防效结果表明,10%解草啶种子包衣处理对丙草胺防除杂草稻药效无显著影响。因此,推荐对栽培稻种子进行10%解草啶种子包衣处理,并在播后苗前施用丙草胺防除水稻田杂草稻。

全玻璃真空太阳集热管关键技术参数研究进展

全玻璃真空太阳集热管是太阳能热利用系统的重要组成部分,其性能参数的优劣直接影响到太阳能热利用系统的热性能、耐久可靠性和节能效果。文章从真空管基本结构和工作原理的介绍出发,对影响真空管性能的光学性能、热性能等关键技术参数及玻璃管材料、真空性能等其他技术要求的研究进展做了详细分析,并在长期从事科研和检测工作的基础上,给出了提升真空管的产品性能可从玻璃管生产优化、新涂层开发、真空性能加强、技术创新、先进设备开发、标准修订等方面的建议。

某电机印制板组件用三防胶选用不当案例分析

三防胶质量的好坏直接影响印刷电路板组件的防护效果和产品的可靠性,因此,科学有效地选用合适的三防胶就显得尤为重要。从失效案例入手,首先,通过外观观察和SEM&EDS分析对三防胶的外观及元素成分进行了分析;随后,通过FT-IR分析、TGA分析和DSC分析对三防胶的材质进行了分析;最后,通过离子色谱分析测试了三防胶的离子含量,深入分析了某产品印制板组件因三防胶引起短路打火导致电机失效的问题,并对电路板上三防胶的失效原因和机理进行了详细的阐述,同时提出了切实可行的解决方法与改善建议,对于三防胶的合理选用具有一定的参考意义。

Molecular Dynamic Simulation on the Absorbing Process of Isolating and Coating of α-olefin Drag Reducing Polymer

The absorbing process in isolating and coating process of α-olefin drag reducing polymer was studied by molecular dynamic simulation method, on basis of coating theory of α-olefin drag reducing polymer particles with polyurethane as coating material. The distributions of sodium laurate, sodium dodeeyl sulfate, and sodium dodeeyl benzene sulfonate on the surface of α-olefin drag reducing polymer particles were almost the same, but the bending degrees of them were obviously different. The bending degree of SLA molecules was greater than those of the other two surfactant molecules. Simulation results of absorbing and accumulating structure showed that, though hydrophobie properties of surfactant molecules were almost the same, water density around long chain sulfonate sodium was bigger than that around alkyl sulfate sodium. This property goes against useful absorbing and accumulating on the surface of α-olefin drag reducing polymer particles; simulation results of interactions of different surfactant and multiple hydroxyl compounds on surface of particles showed that, interactions of different surfaetant and one kind of multiple hydroxyl compound were similar to those of one kind of surfaetant and different multiple hydroxyl compounds. These two contrast types of interactions also exhibited the differences of absorbing distribution and closing degrees to surface of particles. The sequence of closing degrees was derived from simulation; control step of addition polymerization interaction in coating process was absorbing mass transfer process, so the more closed to surface of particle the multiple hydroxyl compounds were, the easier interactions With isoeyanate were. Simulation results represented the compatibility relationship between surfactant and multiple hydroxyl compounds. The isolating and coating processes of α-olefin drag reducing polymer were further understood on molecule and atom level through above simulation research, and based on the simulation, a referenced theoretical basis was provided for practical optimal selection and experimental preparation of α-olefin drag reducing polymer particles suspension isolation agent.

改良森吉米尔法热镀锌带钢针状漏镀缺陷原因分析及控制

[目的]探究改良森吉米尔法连续热镀锌生产线上高强支架钢表面针状漏镀缺陷的产生机理,提出相应的控制措施。[方法]通过激光共聚焦显微镜、扫描电镜等对针状漏镀缺陷的形貌特征和元素分布进行了分析。[结果]漏镀缺陷在带钢表面随机分布,呈黑色针眼状。在漏镀缺陷的亚表面存在Cr、Mn等合金元素富集现象,这些合金元素在带钢表面发生外氧化,使得表面可镀性下降,从而产生针状漏镀缺陷。[结论]在明火加热段对带钢预氧化,以及在退火段促进合金元素发生内氧化,可以有效预防针状漏镀缺陷的产生。

光伏镀膜玻璃安全性能评价方法

光伏镀膜玻璃作为晶体硅光伏组件的重要支撑部件之一,其产品质量和安全性能直接关系组件产品的整体安全性能。从不同安全性能指标、不同标准及要求等方面阐述了各安全性能指标对光伏镀膜玻璃安全性能的影响、评价方法及标准要求,结果可为不同类型光伏组件产品在原辅材料光伏镀膜玻璃的选型提供参考和便利。

太阳能选择性吸收涂层的失效机制及优化策略

在光热系统中,集热器作为光热转化的核心部件通过光谱选择性吸收涂层将太阳能转化为热能。因此,对选择性吸收涂层进行优化能够有效提高集热器的工作效率。选择性吸收涂层的主要吸收机理为本征吸收和干涉吸收,提升涂层吸收效率的策略有材料掺杂、等离激元、光学陷阱等。在集热器实际工作过程中,选择性吸收涂层的失效是影响其效率的主要因素,明确失效原因和寻找解决方案是进一步研究选择性吸收涂层的重点。综述了太阳能选择性吸收涂层的种类及原理,梳理了涂层的失效机制,总结了抑制涂层失效的方法。

TiN/TiNO/SiO_(2)太阳能选择性吸收涂层的优化设计及热稳定性评价

目的太阳能选择性吸收涂层是太阳能热利用的核心材料。方法采用磁控溅射法制备Ti N/TiNO/SiO_(2)太阳能选择性吸收涂层,测定红外反射层Ti N、吸收层Ti NO的折射率n、消光系数k,对Ti N层建立Tauc-Lorentz模型进行数据迭代优化拟合,对Ti NO层建立Drude模型进行数据迭代优化拟合。通过TFCalc光学镀膜设计软件,设置连续目标在300~1500 nm光谱区反射率低于5%,得到软件优化的反射率曲线、各层的最优厚度,确定优化的工艺参数。利用UV-VIS-NIR、FTIR、SEM、XRD、EDS、AFM和XPS表征优化涂层的光学性能、评价热稳定性。结果优化后的涂层,吸收率为0.906、发射率为0.0852;经265℃、600 h热处理后,涂层的吸收率和发射率分别为0.933和0.1033,PC值小于0.01。随热处理时间的增长,α有小幅上升;热处理时间对ε的影响较小;这与表面Si O_(2)氧化物薄膜层在一定程度上阻止了晶粒的长大有关。热处理后,发现涂层表面局部位置有少量的小坑,但涂层的表面成分不变。非晶基质Si O_(2)和Ti O_(2)的再结晶是吸收率提高的主要原因;热处理后的涂层表面非常致密,粗糙度的降低有利于阻碍氧原子向内层的扩散,可以有效提高涂层的热稳定性。结论优化的Ti N/TiNO/SiO_(2)涂层,选择性吸收性能及热稳定性得到有效提高,具有较好的实际应用前景。