3D打印氧化硅陶瓷的制备及性能研究

随着陶瓷3D打印技术的发展,3D打印高性能陶瓷越来越受关注,在航空航天领域得到快速应用.通过研究分散剂、浆料pH、氧化硅粉体粒径和固相含量对浆料粘度和流动性的影响,可制备出粘度低、固相含量高、流动性好的陶瓷浆料.测试了不同固相含量对SiO2陶瓷的弯曲强度、烧成收缩率、气孔率和致密度的影响.结果表明:在68vol%的固相含量条件下,烧结后SiO2陶瓷的致密度达到74.32%,烧成收缩率为0.95%.     

基于溶剂挥发的陶瓷直写成型工艺

提出了一种基于溶剂挥发的陶瓷直写成型制备方法,通过调节工艺参数来改变陶瓷浆料在打印过程中的溶剂挥发速率,以实现陶瓷坯体成型。以氧化锆陶瓷为例,研究了高固相氧化锆陶瓷浆料的制备,分析了不同固含量氧化锆陶瓷浆料的流变特性和可打印性。结果表明:固相含量54%～58%(体积分数)的氧化锆陶瓷浆料通过改变溶剂挥发速率,可以实现陶瓷坯体成型且不发生变形或塌陷。最后,通过陶瓷义齿和长方体样件的制备与表征,验证了该方法可以制备出高强度、复杂形貌的陶瓷零部件。     

树脂基三维立体光刻陶瓷浆料性能研究

UV固化3D打印陶瓷是采用光敏树脂、活性稀释剂、分散剂、光引发剂及各种助剂配制成可用于三维立体光刻成型的陶瓷浆料。UV固化陶瓷浆料的粘度和固含量在成型过程中起到决定性的作用。通过研究活性稀释剂对光敏树脂的稀释性和分散剂对纳米粉体在树脂体系中的分散性能优化了光固化陶瓷浆料的配方。得到了固含量40%以上满足工艺要求的陶瓷浆料,成功的采用该浆料进行打印并烧结。     

PEG对双组分AM-MBAM-YSZ凝胶打印浆料性能的影响

通过在水基AM-MBAM-YSZ浆料中加入水溶性高分子PEG,并将可反应单体与引发剂分离,制备了固相含量为52vol%,室温下可稳定储存数天、混合后固化可控的双组份打印浆料.浆料粘度为11.2 Pa·s(剪切速率100 s-1),屈服应力为510.7 Pa,浆料打印的线条尺寸均匀、边缘平整,坯体表面无剥离,烧结后显微结构均匀致密.打印线条烧结后的相对密度为99.3%,圆柱试样烧结后的相对密度为95.6%.     

分散剂及粉体粒径对光固化氧化铝陶瓷浆料粘度及制件性能的影响

针对光固化氧化铝陶瓷3D打印过程中的浆料粘度及制件性能,通过旋转粘度计测量得到不同分散剂及氧化铝粉体级配条件下的陶瓷浆料的粘度,优化了分散剂的选择及氧化铝粉体级配;通过对光固化3D打印、脱脂和烧结氧化铝陶瓷样件的弯曲强度和收缩率、致密度测试,得到了粉体级配前后不同固相含量氧化铝的抗弯曲性能、收缩率及致密度.研究结果表明,光固化氧化铝陶瓷3D打印浆料制备过程,选择PMA25作为其分散剂,选择10μm(60wt％)+5μm(10wt％)+2μm(30wt％)的粉体级配的氧化铝粉体,可以有效降低浆料粘度.同时,通过选择不同粒径的氧化铝陶瓷粉体,可以减小粉体之间的间隙,增加了粉体之间的有效粘接面积,使得氧化铝粉体之间的粘接更加牢固,陶瓷制件的抗弯曲性能更好、致密度更高.     

光固化3D打印钇铝石榴石透明陶瓷及其微结构调控

成型是钇铝石榴石(YAG)透明陶瓷研制的关键环节,对透明陶瓷的致密化过程及其力学、热学和光学性能有重要影响。本工作围绕YAG透明陶瓷的基于数字光处理(DLP)技术的光固化3D打印成型,系统地开展了YAG陶瓷浆料的研制、陶瓷生坯的构筑及坯体脱脂和烧结工艺研究。采用流变仪分析了固含量对陶瓷浆料流变特性的影响,借助分析曝光参数对单层陶瓷膜特性的影响,确立了最佳的光固化工艺参数。结合TG–DTA分析,对陶瓷坯体脱脂制度进行了精准控制。采用真空高温烧结工艺制备得到高致密YAG透明陶瓷,讨论了固含量、烧结温度等工艺参数对YAG透明陶瓷微结构演变及光学质量的影响,基于DLP光固化成型技术成功制备出可见光透过率高达82.9%的高性能YAG透明陶瓷。     

硅烷偶联剂对氧化铝陶瓷浆料流动性能和3D打印性能的影响

基于光固化3D打印技术需要高固相含量、低黏度的陶瓷浆料以防止烧结陶瓷部件产生裂纹、孔洞、翘曲等缺陷,通过测试流变性能与固化性能,本文优化了树脂单体的选用及配比,采用KH550、KH560、KH570三种硅烷偶联剂对Al₂O₃粉体表面改性,以改善陶瓷浆料的流变性能和稳定性,探讨了硅烷偶联剂降低Al₂O₃陶瓷浆料体系黏度的机理,获得了固相含量为75%(质量分数)(体积分数为45.5%)、黏度为4 540 mPa·s的Al₂O₃陶瓷浆料,并提出了一种光固化Al₂O₃陶瓷浆料制备的优化方法,这有望对用于制备复杂陶瓷的高固含量、低黏度的3D打印Al₂O₃陶瓷浆料提供帮助。     

硅酸锆凝胶注模成型工艺的研究

主要以降低ZrSiO4陶瓷浆料的粘度和提高固相含量为目的,利用正交实验研究了硅酸锆陶瓷凝胶注模成型工艺中固相含量、pH值和分散剂3个因素对料浆粘度的影响,并根据实验结果拟合出回归方程;同时通过电镜分析了坯体微观形貌的差异,制备出固相体积含量55%、粘度0.57Pa·s的硅酸锆陶瓷浆体,所得坯体微观结构均匀、团聚少.     

TiB2泡沫陶瓷浆料的制备

通过沉降实验、Zeta电位的测定及粘度和流变性能测量的方法研究了制备高固相含量TiB2泡沫陶瓷浆料的工艺条件;通过挂挂浆量的测定及烧结体的扫描照片分析研究了浸渍工艺的条件。研究表明：浆料最佳pH值为9,分散剂的引入有效提高了悬浮粒子的Zeta电位,改善浆料的分散性,最佳的分散剂含量为0.3wt%,最佳固相含量为77wt%。     

泡沫凝胶注模成型工艺在多孔氧化铝陶瓷制备中的应用研究

本文介绍了泡沫凝胶注模成型工艺,研究了分散剂、固相含量等工艺参数对浆料粘度的影响,研究得出浆料中固相含量为55%时,以PMAANa为分散剂,可获得100 mPa·S低粘度高固相的陶瓷浓悬浮液;同时还研究了引发剂对凝胶固化反应的影响,实验结果表明引发剂在0.3~0.4%时聚合时间较适宜;重点探讨了发泡剂、固相含量、引发剂等对多孔氧化铝陶瓷性能的影响。     

An investigation on gas hydrate formation and slurry viscosity in the presence of wax crystals

Clarifying the interaction effect between hydrate and wax is of great significance to guarantee operation safety in deep water petroleum fields. Experiments in a high‐pressure hydrate slurry rheological measurement system were carried out to investigate hydrate formation and slurry viscosity in the presence of wax crystals. Results indicate that the presence of wax crystals can prolong hydrate nucleation induction time, and its influence on hydrate growth depends on multiple factors. Higher stirring rate can obviously promote hydrate growth rate, while its influence on hydrate nucleation induction time is complicated. Higher initial pressure will promote hydrate formation. Gas hydrate slurry shows a shear‐thinning behavior, and slurry viscosity increases with the increase of wax content and initial pressure. A semiempirical viscosity model showing a well‐fitting is established for hydrate slurry with wax crystals by considering the aggregation and breakage of hydrate particles, wax crystals, and water droplets. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3502–3518, 2018     

制备条件对聚酰胺蜡触流变剂性能的影响

研究了聚酰胺蜡粉末的粒径和活化试剂的种类对聚酰胺蜡触流变剂改善涂料流变性能的影响。在环氧树脂体系中,与未研磨的聚酰胺蜡相比较,研磨后的聚酰胺蜡使体系具有更好的流变性能。考察了活化剂正丁醇、异丙醇、乙醇和甲醇的加入对聚酰胺蜡流变性能的影响,发现将乙醇与异丙醇按质量比5∶7复配后活化的聚酰胺蜡浆,能使环氧树脂体系具有更高低剪切黏度和更低高剪切黏度的触流变性能。     

低挥发分水煤浆工业燃烧试验研究

通过对常村煤矿低挥发分煤泥水煤浆的燃烧试验研究,描述了其成浆特性和燃烧特性,重点对试验流程、过程和结果进行了分析,为潞安集体煤炭深加工和综合利用探索了一条新途径。     

High quality diesel via the Fischer–Tropsch process – a review

The Fischer–Tropsch (FT) synthesis is used to produce chemicals, gasoline and diesel fuel. The FT products are predominantly linear, hence the quality of the diesel fuel is very high, having cetane numbers of up to 75. Since purified synthesis gas is used in the FT process all the products are S‐ and N‐free. In this review the production of syngas and the various options used in the FT process (reactors and catalyst types, and high and low temperature operation) are discussed. The best FT option for producing high quality diesel is using cobalt‐based catalyst in slurry phase reactor, gearing the process for high wax production and then selectively hydrocracking the wax to diesel fuel. The overall diesel pool has a high cetane number, the aromatic S and N contents are zero and the exhaust emissions are significantly lower than for standard diesel fuels. © 2001 Society of Chemical Industry     

Development of alumina primary coat for single crystal investment casting ceramic mould

Abstract

The use of an alumina primary coat to eliminate the interaction between aluminium in NiAl single crystal alloy and silica in the ceramic investment casting mould has been examined in this study. The properties of the alumina slurry were characterised and the main factors controlling stability identified. It was found that the pH of the slurry must be carefully controlled to avoid polycondensation reactions. The most stable slurry was produced using filler with lower mean particle size and alkalinity. Alumina primary coat produced with low filler loading does not survive completely during wax removal. The surface condition can be improved by increasing the plate weight, which corresponds to a higher filler loading in the slurry. Moulds with a consistent alumina primary coat exhibit slightly higher green and sintered strength than moulds with the standard zircon-silica primary coat.     

Structures of the distillates obtained from hydrogenation and pyrolysis of Liddell coal

The structures of the distillable fractions (oils, b.p. >200 °C and volatile fractions, b.p. <200 °C) of the products from hydrogenation and pyrolysis of an Australian bituminous coal (Liddell) were investigated by gas chromatography-mass spectrometry (g.c.-m.s.) and nuclear magnetic resonance spectroscopy (n.m.r.). The distillable oil generated from hydrogenation of Liddell coal at 400 °C, using nickel molybdenum ortin (II) chloride as catalyst and tetralin or recycle oil as vehicle, consisted of a wide range of compounds. Long straight-chain alkanes were important components together with alkyl-substituted benzenes and tetralins, phenols and polycyclic material. When yields were low, as in the case of catalytic experiments with nickel molybdenum catalysts and no vehicle, isoprenoids could be identified. When a substantial proportion of the coal was converted to oil, branched-chain alkanes were not important components of the product. The replacement of tetralin and nickel molybdenum catalyst with stannous chloride reduced the amounts of methyl tetralins in the product. When tetralin was replaced by recycle oil, alkanes were more important components of the liquid products. Although alkenes were absent in oils generated by hydrogenation, they were important components of oils generated by pyrolysis. The highly volatile fractions (b.p. <200 °C) produced during hydrogenation consisted of alkyl-substituted benzenes, decalins, methylindan and straight-chain alkanes. Straight-chain alkanes were more abundant in those volatile fractions generated by hydrogenation with recycle vehicle than with tetralin. The Brown-Ladner method of estimating the fraction of aromatic carbon in distillable oils was adequate for less volatile fractions but was inadequate for the highly volatile fractions because of the large amounts of α-CH₃ and β-CH₃ alkyl groups present.     

EXHAUST EMISSIONS OF PAHs OF PASSENGER CARS

Exhaust emissions of 16 PAHs, listed by the U.S. Environmental Protection Agency (USEPA) as priority pollutants, are measured using a vehicle bench on a sample of passenger cars. Thirteen gasoline vehicles and 17 diesel vehicles are tested, complying with ECE 1504 to Euro 3 emission standards, according to three real-world driving cycles based on European driving behavior (2 urban and 1 motorway). HPLC with fluorometric detection is used for their quantification.

The effect of cold or hot start is put to the fore with the short urban INRETS cycle.

The particle and gas-phase distribution is studied for all the vehicles and the hot driving cycles.

In this study, the cars' emissions are shown to be reduced, according to the legislative level (Euro-1, 2, 3 …). The majority of volatile PAHs is mainly observed in the gas phase whereas the less volatile and carcinogenic PAHs are especially adsorbed on particles.     

Extractable waxes from Greek lignites

An investigation on the solvent-extraction yields of Greek lignites has shown that the yields are generally low compared with the yields from certain American and German lignites, and similar to the yields from Czechoslovakian lignites. The highest yields were obtained from lignites of the Psachna deposit. The only extract which resembled rather closely in its nature the Riebeck crude montan wax was obtained by benzene extraction from Ptolemais lignite. The most significant differences between benzene extracts from Greek lignites and Riebeck crude montan wax were the differences in melting points and the greater resin content of the Greek waxes. Extraction with benzene/methanol mixture instead of benzene gave higher yields and extracts characterized by higher melting points, and higher acid and ester values. The compatibility of the extracts with paraffin wax was low; only benzene extract from Ptolemais lignite was completely miscible. No relation was found between the wax yield and the ratio volatile matter/fixed carbon of the coal. We also conclude that extraction of waxes from Greek lignites is not commercially attractive.     

Performance of a slurry bubble column reactor for Fischer-Tropsch synthesis: Determination of optimum condition

The CO conversion and selectivity to C₁+ and C₁₁+ wax products over Co/Al₂O₃ as well as Ru/Co/Al₂O₃ Fischer-Tropsch (F-T)catalysts were investigated by varying reaction temperature (210-250 °C), system pressure (1.0-3.0 MPa), GHSV (1000-6000 L/kg/h), superficial gas velocity (1.7-13.6 cm/s) and slurry concentration (9.09-26.67 wt.%) in a slurry bubble column reactor (0.05 m diameter × 1.5 m height) to determine the optimum operating conditions. Squalane or paraffin wax was used as initial liquid media. The overall CO conversion increased with increasing reaction temperature, system pressure and catalyst concentration. However, the local maximum CO conversion was exhibited at GHSV of 1500-2000 L/kg/h and superficial gas velocity of 3.4-5.0 cm/s. The CO conversion in the case of Ru/Co/Al₂O₃ was much higher and stable than that in the case of Co/Al₂O₃. The selectivity to C₁₁+ wax products increased slightly with increasing GHSV; on the other hand, it decreased with increasing reaction temperature, system pressure, and solid concentration in a slurry bubble column reactor. It could be concluded that the optimum operating conditions based on the yield of hydrocarbons and wax products were; U_G = 6.8-10 cm/s, Cs = 15 wt.%, T = 220-230 °C, P = 2.0 MPa in a slurry bubble column reactor for F-T synthesis.     

Disruptive burning of precursor/solvent droplets in flame‐spray synthesis of nanoparticles

Flame spray pyrolysis is an established technique for synthesizing nanoparticles in the gas phase through aerosol combustion of precursor/solvent droplets. The combustion characteristics of isolated micron‐sized precursor/solvent droplets are investigated experimentally. Pure solvent droplets burn uniformly and classically quasisteady, whereas precursor/solvent droplets manifest disruptive combustion behavior. The fast onset of droplet disruption, which occurs only for solutions with dissolved metal precursors, is not due to solid‐particle precipitation within the droplet. Instead, the mechanism of disruptive droplet burning is similar to that of slurry droplets, consisting of three main steps: (1) diffusion‐controlled burning of the high‐volatile solvent, (2) viscous‐shell formation due to decomposition of the low‐volatile metal precursor, and (3) subsequent disruption due to heterogeneous nucleation. The time sequence of the three steps depends on the concentration and decomposition characteristics of the metal precursor, shortening with increased concentration and higher incremental decomposition temperature. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4553–4566, 2013