Preparation and Properties of Macroporous Silicon Nitride Ceramics by Gelcasting and Carbonthermal Reaction

1. IntroductionIn recent years, porous Si3N4 ceramics have re-ceived increasing attention for their extensive applicationin many high-tech areas such as bio ceramics[1], cata-lyst supports[2], hot gases filter[3], liquid purification[4],sensors[5], and membrane reactors[6]. Their appeal ismainly because of their unique and inherent proper-ties. Si3N4 ceramics are materials with excellent me-chanical properties, good corrosion resistance and oxida-tion resistance[7]. Since better performance …     

微波低温烧结制备氮化铝透明陶瓷

微波烧结(Microwave Sintering)是一种新型、高效的烧结技术, 具有传统烧结技术无可比拟的优越性. 本文在不添加任何烧结助剂的前提下, 采用高纯微米级氮化铝(AlN)粉, 在1700℃/2h的微波低温烧结工艺条件下制备出透明度较高的AlN透明陶瓷. 分析结果表明, 采用微波低温烧结工艺制备的AlN透明陶瓷晶粒尺寸细小(<10μm), 晶粒发育完善且分布均匀, 晶界平直光滑且无第二相分布, 从而证明用微波烧结可以实现AlN透明陶瓷的低温烧结.     

Preparation of Alumina Fiber-Reinforced Aluminum by Squeeze Casting and Their Machinability

Alumina fiber-reinforced aluminum alloy composites were prepared by squeeze casting, and the effect of the reinforcement on the machinability of the alloy was investigated. Two kinds of short alumina fibers, which have the same fiber size but different hardness, were used. Preform in which the fibers were in a random arrangement was formed with SiO₂ binder, and then was infiltrated with the alloy melt to prepare the composite. The fiber–matrix interfacial bond via the binder is sufficient and no reaction product was detected. The cutting force of the alloy was reduced by the fiber-reinforcement. The lower the hardness of the fiber in the composite, the lower the cutting force of the composite. The roughness of the machined surface was drastically decreased by the reinforcement. Observation of the chip formed on the machined surface indicated that the fiber suppressed the formation of the built-up-edge, and this fact would lead to the reduction in the surface roughness by the reinforcement. The chips were shortened by the reinforcement. The difference in hardness of the alumina fiber hardly affected the roughness and the chip morphology. The hardness of the fiber has a strong effect to decrease the tool life.     

Surface Preparation of Aluminum Nitride for Metallization

Currently, the surface preparation of aluminum nitride (AlN) substrates prior to metallization includes an aqueous cleaning step. Surface reactions that occur in this step cause performance and reliability issues with AlN substrates to be used in microelectronic packaging. There is a lack of published data on the reactivity of AlN substrates with common solvents. This study investigated the effects of different solvents on the surface corrosion of AlN substrates. The variables studied were pH, aqueous vs. organic solutions, prior surface condition, and time (up to 3.6 Ms or 42 days). The solvents tested were hydrochloric acid (HCl) with pH values ranging from 2 to 5, sulfuric acid (H₂SO₄) with pH values ranging from 2 to 5, sodium hydroxide (NaOH) with pH values ranging from 8 to 12, 1 M citric acid, oleic acid, Micro-90, methanol, ethanol, isopropanol, acetone, and deionized water. Three types of surface reaction behavior were observed in this study. The substrates either showed no reaction (HCl pH = 2, methanol, ethanol, isopropanol, acetone, citric acid, and oleic acid), slight corrosion without spalling (Micro-90, HCl pH = 3, H₂SO₄pH = 3), or they were severely corroded and spalled (HCl pH = 5, H₂SO₄pH = 5, all NaOH solutions, and deionized water).     

流延法制备AlN陶瓷基板的研究

从颗粒尺寸、浆料流体类型、干燥条件、排胶机制等方面对流延法制备ＡｌＮ陶瓷基板展开了较为系统的研究．结果表明,颗粒尺寸的不同直接影响到浆料粘度及分散剂用量．适于ＡｌＮ流延成型的浆料流体类型属于假塑性流体．保持一定的溶剂气氛有利于获得表面平整光滑的流延素坯膜．二次排胶有利于排除ＡｌＮ流延素坯膜中的残余碳．烧结后基板的断口ＳＥＭ照片表明晶粒发育较为完善,无明显开气孔,断裂模式为沿晶断裂．     

水溶性胶态成型工艺制备氮化硅耐磨结构陶瓷

以氮化硅粉末为原料, 采用水溶性胶态成型工艺制备高耐磨氮化硅陶瓷. 采用正交设计的方法来优化制备高品质注浆料, 并研究了掺杂分散剂后Zeta电位的变化. 同时, 还对氮化硅陶瓷烧结体的显微结构、力学性能和耐磨性能进行了研究. 结果表明: 当氮化硅浆料中固相体积分数为45%时, 可制得体积密度较高的精细氮化硅陶瓷材料, 断裂韧性可达7.21MPa·m^1/2, 硬度为9.30GPa. 通过抗耐磨损实验研究表明: 干摩擦条件下, 氮化硅陶瓷发生了晶粒脆性断裂和脱落; 水润滑条件下, 摩擦表面产生了氢氧化硅 反应膜, 降低了磨损, 主要是化学腐蚀磨损.     

直接凝固注模成型氮化硅陶瓷

直接凝固注模成型是一种新颖的原位凝固成型工艺,特别适合于复杂形状陶瓷部件的成型．通过粉体的表面改性、浆料ｐＨ值的调节以及引入高效分散剂等途径制备出了低粘度高固含量的氮化硅浆料,通过直接凝固注模成型可以获得适当的素坯密度和强度．坯体气孔分布均匀,为较窄的单峰分布,断口光滑平整,坯体各部位密度具有很好的均匀性．在相对较低的烧结温度下（１７５０℃）,成型坯体经过无压烧结可达到理论密度的９８％,基本实现致密化．烧结体结构均匀,晶粒均匀生长,发育良好．经１８００℃烧结２ｈ后,抗折强度达７５８．４ ＭＰａ,断裂韧性为６．３ＭＰａ·ｍ^１／２．     

Preparation of Lanthanum-Doped Pb(Zr,Ti)O3 Ceramics Sheets by Tape Casting

The physical and electrical properties of lanthanum doped Pb（Zr,Ti）O3 ceramic sheets （PLZT） which were prepared by tape casting method were carried out. Tape casting of lanthanum modified PZT was performed using commercial cellulose acetate binders and poly（ethylene glycol） plasticizers in ethanol solvent. Tapes from these slips were casted on a polymer substrate. The PLZT green tapes were stacked for 5 units and sintered in air at 1050℃ for 1 h with heating rate 5℃/min. SEM micrographs show that the tape is dense （90.26% of theoretical density） and rather uniform with grain size of approximately 1.1 9 m. The dielectric permittivity and loss tangent of PLZT ceramics as a function of temperature at 1 kHz suggest that the compounds exhibit a phase transition of diffuse type. The transition temperature （Tm ） and piezoelectric coefficient （ d33 ） were 110℃ and 117 pC/N, respectively.     

双层流延法制备BTO-STO多层复合陶瓷及其性能研究

钛酸锶钡是一种具有钙钛矿结构的铁电材料,在外加直流偏置电场作用下,钛酸锶钡(BSTO)的介电常数随着电场强度增加而降低,是目前相控阵天线移相器材料的研究热点.本工作以双层流延法制备了具有STO-BTO-STO-BTO-STO-…的多层叠合钛酸锶钡陶瓷,并通过控制多层陶瓷材料的烧结温度、烧结时间,以获得烧结后钛酸锶、钛酸钡双层扩散成分梯度分布的陶瓷材料,从而达到调节介电性能的目的.双层流延法制备的钛酸锶钡叠层材料通过介电性能测试发现,BTO-STO复合结构大大降低了材料的介电常数,样品介电常数均可降至300以下,最低可达210,介电损耗tanδ可降至0.02以下.BTO-STO多层陶瓷的介电可调性也有较大幅度的降低,该现象可由介质混合法则解释.通过SEM的分析结果可以看到清晰BTO-STO周期层状结构,经烧结后流延层间结合紧密.随着烧结温度的提高,烧结时间的增加,试样晶粒明显长大,而层间界线也更为模糊.     

聚砜超滤膜铸膜液中良溶剂效应的粘流性表征

聚砜超滤膜铸膜液中,良溶剂的影响是决定超滤膜的主要因素之一。我们测定了聚砜在六种良溶剂里的特性粘数,聚矾浓度为9—24g/mol时不同良溶剂铸膜液的粘度,温度在30—80℃时聚砜浓度为15g/mol不同良溶剂的粘流活化能和不同种类有机添加剂对聚砜——DMAC体系引起粘流活化能的变化。经综合分析得出:相同条件下的铸膜液粘度可表征良溶剂间的差别,良溶剂的极性是产生这一差别的根源,筛选出的极性质子性溶剂吗啉是制备聚砜超滤膜较好的良溶剂。     

Preparation of Aluminum Nitride Thin Films by CVD

AlN films were prepared by CVD using aluminum halide (AlCl₃) and aluminum alkyl ((CH₃)3Al) precursors. The appropriate deposition conditions to obtain polycrystalline AlN films using A1C1₃ precursor were found at T_dep = 1173 K, P_tot = 66.6 Pa and N₂/NH₃ = 0.75. It was found that AlN films of different crystallinity can be obtained from (CH₃)₃Al precursor at T_de = 973-1023 K, P_tot = 1.99 kPa, only under a H₂ atmosphere. AlN films can be grown highly oriented in the (210) direction on amorphous quartz substrates depending on their thicknesses. The 0.1 -0.2 μm thick AlN films were transparent and their refractive indexes were about 1.4-1.6.     

陶瓷材料水基流延成型工艺研究进展

简要介绍了水基流延成型工艺的特点,综述了水基流延成型工艺的浆料组成、流变性能以及干燥过程的研究现状,指出了水基流延成型今后的发展趋势.     

Co-firing of LNT/Ag Multilayer Sheets Prepared by Aqueous Tape Casting

Multilayer ceramic sheets composed of Li1.075Nb0.625Ti0.45O3 (LNT) layers and silver metal layers were fabricated by aqueous tape-casting method. LNT green tape was prepared using PVA (polyvinyl alcohol) as binder and ethylene glycol as plasticizer. The influence of the slurry composition on the theological properties of the slurries and the properties of the resultant green tapes were studied. The slurry exhibited a typical shear thinning behavior. The increase in the PVA content increased the tensile strength of the tapes. The slip compositions with 5 wt pct PVA produced green tapes with satisfactory tensile strength. Ethylene glycol additions enhanced the flexibility of the green tapes but also produced a decrease in the tensile strength. Sliver inner-electrode was pasted on LNT green tapes and the sheets were stacked, pressed and sintered at 900℃ for 2 h. SEM (scanning electron microscopy) micrographs showed that the multilayer sheets were fully dense with fairly uniform microstructure and no reaction was observed between LNT and sliver layers.     

凝胶浇注成型制备致密 SiC陶瓷材料

采用一种凝胶浇注成型预配液作为陶瓷粉体的分散介质,将亚微米级SiC粉体和烧结助剂Y2O3、Al2O3直接混合,制得了固含量>50vol％的凝胶浇注浆料,在100s-1的剪切速率下,浆料粘度<1Pa·s,可以顺利实现凝胶浇注成型;对得到的SiC素坯进行了无压烧结．在2000℃保温1h(氩气氛)的烧结条件下,烧结体相对密度为(98．1±0．2)％,抗折强度、硬度和韧性分别为(722±70)MPa、(20．18±0．75)GPa、(4．00±0．20)MPa·m1／2．     

可发性甲基丙烯酸甲酯-苯乙烯共聚物的制备及铸模性能

用3种可行的配方对中试所得的甲基丙烯酸甲酯(MMA) 苯乙烯(ST)共聚物进行可发性处理,制得可发性共聚物,通过铸模性能的测定,确定出实用型可发性处理配方,并得到质量较高的铸件。     

氮化铝陶瓷浆料流变性能的研究

系统地研究了流延法制备氮化铝基片过程中影响流延浆料粘度的主要因素.分析了研磨时间、有机混合溶剂掺量、分散剂掺量及粘结剂、塑性剂对氮化铝浆料流变性能的影响,并对实验条件下测得的流变曲线采用Hershel Bulkley模型进行拟合,拟合出的Hershel Bulkley屈服应力τc较好地反映了浆料的稳定性,研究结果表明:分散剂掺量为2.5%(体积分数)时,浆料的τc较低;浆料的τc随固相体积分数的增加而增加;研磨时间为4h制备的浆料τc最低,流动性能最好;浆料的粘度随着塑性剂与粘结剂的比值R的增加而急剧减小,流变性能得到明显改善.     

Thermal Conductivity of Ceramics Based on Aluminum Nitride Prepared by Self-Propagating High-Temperature Synthesis

AlN-based ceramics containing different additions were prepared by sintering powders obtained by self-propagating high-temperature synthesis and differing in morphology and oxygen content. The thermal conductivity of the ceramics was measured near room temperature by a radial-heat-flux standardless technique.     

镍铝青铜的熔铸工艺特点

介绍了镍铝青铜的铸造工艺性能,对镍铝青铜在熔铸过程中的常见缺陷及成因进行了详细分析,重点探讨了镍铝青铜的熔铸工艺方法,提出了能够提高铸件质量的多种工艺措施和建议。     

Surface Preparation of Aluminum Nitride for Metallization: Effect of Temperature on Surface Reactivity

The current aqueous cleaning step in the surface preparation of aluminum nitride (AlN) prior to metallization causes performance and reliability issues for the substrates used for microelectronic packaging due to surface reactions. These issues limit the use of AlN and its replacing of BeO, an environmentally hazardous material currently used. The aim of this investigation was to determine the effects of different solutions on the surface of AlN substrates under varying conditions at times up to 2419.2 ks (28 days). Concentration of the solutions, temperature, and immersion time were varied for the AlN samples in the solutions. Both elevated temperatures (50°C and 90°C) and low temperatures (5°C) were investigated.

Four general types of behavior were observed: minor changes in average surface roughness and microstructure, linear change in average surface roughness and pitted grains, nonlinear change in average surface roughness and product formation on AlN surface, and miscellaneous change in average surface roughness with surface product formation.

The surface roughening kinetics were very complex due to changes in both the reaction product morphology and reaction mechanism with temperature, solvent, and pH for a specific solvent. Minor changes in average surface roughness and microstructure were observed for HCl pH = 5, H₂ SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, deionized water and Alfred tap water at 5°C, HCl pH = 3 and oleic acid at 50°C and citric acid and oleic acid at 90°C. Linear changes in average surface roughness and pitted grains were observed for HCl pH = 2 and H₂SO₄ pH = 3 at 50°C and HCl pH = 2, H₂SO₄ pH = 3, and deionized water at 90°C. Non-linear change in average surface roughness and product formation on AlN surface was observed for HCl pH = 5, NaOH pH = 8 and Alfred tap water at 50°C and HCl pH = 5 and H₂SO₄ pH = 2 at 90°C. Miscellaneous changes in average surface roughness with surface product formation were observed for H₂SO₄ pH = 2, H₂SO₄ pH = 5, NaOH pH = 10, NaOH pH = 12, citric acid, Micro-90 and deionized water at 50°C and HCl pH = 3, H₂SO₄ pH = 5, NaOH pH = 8, NaOH pH = 10, NaOH pH = 12, Micro-90 and Alfred tap water at 90°C.     

The Role of Particles in Fatigue Crack Propagation of Aluminum Matrix Composites and Casting Aluminum Alloys

Fatigue crack propagation （FCP） behaviors were studied to understand the role of SiC particles in 10 wt pct SiCp/A2024 composites and Si particles in casting aluminum alloy A356. The results show that a few particles appeared on the fracture surfaces in SiCp/Al composites even at high △K region, which indicates that cracks propagated predominantly within the matrix avoiding SiC particles due to the high strength of the particles and the strong particle/matrix interface. In casting aluminum alloy, Si particle debonding was more prominent.Compared with SiCp/Al composite, the casting aluminum alloy exhibited lower FCP rates, but had a slight steeper slope in the Paris region. Crack deflection and branching were found to be more remarkable in the casting aluminum alloy than that in the SiCp/Al composites, which may be contributed to higher FCP resistance in casting aluminum alloy.