成型方式对反应烧结碳化硼基复合材料性能的影响

本文针对干压成型结合冷等静压成型对反应烧结碳化硼基复合材料样品性能的影响进行研究.考察了成型压力、保压时间、加压方式对压坯密度和强度的影响.结果表明:采用100 MPa干压2 min,再经过150 MPa冷等静压保压1 min,压坯密度由干压压制时最大密度1.86 g/cm3升高到1.96 g/cm3,压坯强度可达到2.0 MPa.保压时间和加压方式对压坯的密度、强度的影响不大.干压结合冷等静压相对于干压成型,在相同的烧结温度下样品性能有明显的提高,烧结后样品密度为2.44 g/cm3,显微硬度为2394 kg/cm2,三点抗弯强度为241 MPa.     

压力对凝胶注模成型95氧化铝陶瓷性能的影响

本文采用低毒的MAM-MBAM凝胶体系代替AM-MBAM有毒体系制备95氧化铝陶瓷,为改善成型后坯体的性能,在凝胶注模成型过程中给予浆料压力.研究发现在压力为0.3 MPa时获得的坯体表面光洁,线收缩率大,体密度高,结构均匀,成品率高,质量好.本文还并研究了压力对95氧化铝陶瓷烧结体线收缩率和体密度以及洛氏硬度的影响.实验结果表明:压力辅助凝胶注模成型所得坯体烧结后性能优于无压直接注模成型坯体,压力为0.3MPa时线收缩率最小,体密度最高可达3.81 g/cm3,洛氏硬度最高.坯体显微结构显示,陶瓷粉料被有机高分子网络很好地粘结在一起,并且压力注模的坯体中陶瓷粉料堆积紧密,结构均匀致密.烧结后,压力注模成型坯体晶粒发育良好,气孔较无压直接注模烧结体少,烧结致密性能优异.     

等静压成形工艺的优化研究

本文研究了等静压成形工艺过程中氧化铝造粒粉料成形后的坯体相对密度和强度随着各成形参数的变化而变化的规律,并进一步研究了其对烧结收缩的影响。实验表明:随着压力的增大,坯体密度逐渐提高,强度也相应增大;保压时间对坯体的相对密度影响不明显;在成形压力范围内,坯体相对密度对烧结之后的试样致密度影响不大。     

固相烧结--Ⅲ实验:超细氧化锆素坯烧结过程中的晶粒与气孔生长及致密化行为

研究了超细Y-TZP和YSZ粉料成型体在烧结中期的晶粒生长、气孔生长和致密化行为.根据作者前文[1,2]提出的致密化方程,可以满意地解释粉体及其成型体的性质,如初始颗粒尺寸、成型密度和气孔尺寸分布等对烧结的影响. 实验发现:成型体中的晶粒生长基本不受成型体性质的影响,但气孔生长同时受晶粒生长和致密化的影响,前者使气孔尺寸与晶粒尺寸同步生长,后者导致气孔收缩. 晶粒生长和致密化虽受不同的机制驱动,但通过同样扩散途径完成,使烧结中期的晶粒尺寸与密度呈线性关系. 理论分析和实验结果表明,成型体性质不改变这一线性关系,但可以改变直线的斜率,而升温速率对直线斜率的影响不大. 较大的二面角、较高的素坯密度、较窄的颗粒和气孔尺寸分布有利于获得较小的晶粒生长和较高的烧结密度.     

掺杂Al的纳米ZrO2无压烧结致密化过程的研究

采用无压烧结对平均粒径为30～50nm的ZrO2纳米粉,及掺Al的ZrO2纳米粉的烧结致密化进行研究。实验结果表明ZrO2坯休的致密化主要发生在1150～1250℃范围内。理论分析表明,通过掺杂Al改善其显微结蛄构．提高生坯密度,能降低该粉体的烧结致密化温度。     

直接干压成型与真空烧结技术制备Nd:YAG透明陶瓷

以高纯氧化物粉体为原料,采用直接干压成型与固相反应烧结技术制备Nd:YAG透明陶瓷,并对其光学透过率和烧结致密化行为进行了研究。结果表明,经1 760℃烧结10 h后,250 MPa成型压力下的样品透过率最高,在1 064 nm处达到83.8%。其素坯的气孔率为40.5%,气孔平均孔径74.5 nm。烧结后陶瓷的显微结构致密,晶界干净清晰,断裂方式为沿晶断裂。将250 MPa成型压力下获得的陶瓷素坯在不同温度和时间下烧结,得到致密化轨迹、晶粒生长曲线以及显微结构演变等信息。通过理论拟合,得出低温下陶瓷致密化和晶粒生长的控制机制为晶界扩散。     

六方氮化硼陶瓷的烧结及其结构与性能EI北大核心CSCD

以亚微米级h-BN粉体为原料,在不添加任何烧结助剂的情况下,分别采用无压烧结、热压烧结和放电等离子烧结（SPS）制备h-BN陶瓷,采用X射线衍射和扫描电子显微镜对烧结后样品的物相组成和显微结构进行测试和观察,研究不同烧结方法对h-BN陶瓷的致密度、晶粒取向、显微形貌及力学性能的影响,对比分析了不同烧结方法下坯体初始致密度对h-BN陶瓷性能的影响。结果表明：无压烧结无法实现h-BN陶瓷烧结致密化,力学性能较差,而通过热压和放电等离子烧结的方法均能得到结构致密、力学性能较好的h-BN陶瓷。相比于传统的无压和热压烧结,放电等离子烧结方法制备的h-BN陶瓷具有更高的致密度和更好的力学性能,而且晶粒更均匀细小,烧结温度可降低200℃以上。此外,坯体初始致密度的提高能显著提高h-BN陶瓷的抗弯强度和断裂韧性,但对热压和放电等离子烧结制备的h-BN陶瓷致密化的影响较小。     

六方氮化硼陶瓷的烧结及其结构与性能

以亚微米级h-BN粉体为原料,在不添加任何烧结助剂的情况下,分别采用无压烧结、热压烧结和放电等离子烧结(SPS)制备h-BN陶瓷,采用X射线衍射和扫描电子显微镜对烧结后样品的物相组成和显微结构进行测试和观察,研究不同烧结方法对h-BN陶瓷的致密度、晶粒取向、显微形貌及力学性能的影响,对比分析了不同烧结方法下坯体初始致密度对h-BN陶瓷性能的影响。结果表明:无压烧结无法实现h-BN陶瓷烧结致密化,力学性能较差,而通过热压和放电等离子烧结的方法均能得到结构致密、力学性能较好的h-BN陶瓷。相比于传统的无压和热压烧结,放电等离子烧结方法制备的h-BN陶瓷具有更高的致密度和更好的力学性能,而且晶粒更均匀细小,烧结温度可降低200℃以上。此外,坯体初始致密度的提高能显著提高h-BN陶瓷的抗弯强度和断裂韧性,但对热压和放电等离子烧结制备的h-BN陶瓷致密化的影响较小。     

粉煤灰-赤泥孔隙陶瓷的坯釉一体化制备工艺研究

采用粉煤灰、赤泥等类粘土质的工业固废制备建筑陶瓷是其生态高值化利用的有效途径.本文研究了陶瓷坯体主要成分粉煤灰和赤泥配比为3:2时优化的烧成温度、保温时间等工艺参数,研究了成孔剂含量对陶瓷体积密度、孔隙率及微观组织结构的影响,研究了与该坯体相适宜的釉料配方及涂布方式对坯釉结合性能的影响,并重点探讨了具有自保温性能的陶瓷坯釉一次干压成型和一次烧成的制备工艺.研究结果表明,较优化的烧成温度为1100℃,保温时间为2h;适宜的成孔剂含量为5％,釉料配方和涂布工艺对坯釉结合性能和釉层质量具有决定性作用,坯釉一次干压成型是解决坯釉适应性和提高结合强度的有效技术途径;陶瓷基体中加入成孔剂并不会对釉质层的质量造成影响,且坯釉一次干压成型和一次烧成的制备工艺可实现以粉煤灰、赤泥为主要原料的陶瓷的一体化生产,具有显著的生态、节能和经济性.     

SiC陶瓷的浇注成型初探

从Ｚｅｔａ电位的角度出发，对泥浆粘度、泥浆稳定性以及素坯密度进行了调整和比较，解决了ＳｉＣ泥浆制备及其浇注中的一些问题。用３种ＳｉＣ原料，浇注成型后素坯密度、无压烧结后烧结密度和烧结样品的抗弯强度分别达１．６６ｇ／ｃｍ＾３（５１．７％），２．９３ｇ／ｃｍ＾３（９１．３％）和２６８ＭＰａ。     

固相烧结——Ⅲ 实验：超细氧化锆素坯烧结过程中的 晶粒与气孔生长及致密化行为

研究了超细Y-TZP和YSZ粉料成型体在烧结中期的晶粒生长、气孔生长和致密化行为.根据作者前文     

High velocity compaction of ferrous powder

Water atomized pure iron powder was pressed by high velocity compaction technology. The influences of impact velocity on green density, shock wave, compacting and ejection forces, radial springback and strength of compacts were studied. Cross-section images of green compacts were observed by scanning electron microscopy (SEM). A computer controlled universal testing machine was used to measure the green strength of compacts. The results show that impact velocity intensively affects the green density of specimen. As impact velocity increases, the green density and the strength of compacts increase gradually, especially the green strength. In addition, the compacting force and the actuation duration of shock wave increase obviously with the augment of impact velocity, which leads to densification of powder body. No specific relation was found between the ejection force, the radial springback and the impact velocity.     

Fabrication and characterization of silica ceramic compact prepared using Aloe-Vera mucilage as a binder

In this study, silica compacts were fabricated through a powder processing route at different compaction pressure, using Aloe-Vera (AV) mucilage as a binder. The silica compacts were prepared at 90, 100, and 110 MPa compaction pressure using 0%–16 wt% of AV binder. The optimum amount of AV binder was 14 wt% for both 90 and 100 MPa and 12 wt% for 110 MPa. The maximum achieved green density and green strength of silica compacts at the optimum binder amount were 62.3% and 4 MPa, respectively at 110 MPa compaction pressure. The green silica compacts prepared at 110 MPa compaction pressure exhibited a minimum porosity of 21% and maximum flexural strength of 15 MPa after sintering at 1400°C. The green silica compacts with the optimum amount of binder were strong enough for machining. The Fourier transform infrared spectroscopy analysis revealed the functional groups present in AV mucilage. The binder burnout characteristic of AV mucilage in the silica compact was determined by thermogravimetric analysis and differential thermal analysis. Additionally, AV gel acted as a binder and solvent simultaneously for ceramic compaction.     

Sintering and densification of nanocrystalline ceramic oxide powders: a review

Abstract

Observation of the unconventional properties and material behaviour expected in the nanometre grain size range necessitates the fabrication of fully dense bulk nanostructured ceramics. This is achieved by the application of ceramic nanoparticles and suitable densification conditions, both for the green and sintered compacts. Various sintering and densification strategies were adopted, including pressureless sintering, hot pressing, hot isostatic pressing, microwave sintering, sinter forging, and spark plasma sintering. The theoretical aspects and characteristics of these processing techniques, in conjunction with densification mechanisms in the nanocrystalline oxides, were discussed. Spherical nanoparticles with narrow size distribution are crucial to obtain homogeneous density and low pore-to-particle-size ratio in the green compacts, and to preserve the nanograin size at full densification. High applied pressure is beneficial via the densification mechanisms of nanoparticle rearrangement and sliding, plastic deformation, and pore shrinkage. Low temperature mass transport by surface diffusion during the spark plasma sintering of nanoparticles can lead to rapid densification kinetics with negligible grain growth.     

Effect of spray-dried powder granulometry on the porous microstructure of polished porcelain tile

The low porosity of porcelain tile is the result of strict control of the material's processing conditions (milling of raw materials, compaction and sintering) and the characteristics of the raw materials used in its formulation (formation of liquid phases). Sealed pores remaining after the manufacturing process are revealed at the surface after polishing and are the main factor responsible for staining the product. The porous microstructure of the sintered material depends on the characteristics of the porous microstructure of the green compact and on how the densification process evolves during sintering. The present work evaluated how the size distribution of spray-dried granules acts upon the porous microstructure of green compacts and of polished porcelain tile. The results revealed that minor adjustments in the granulometric distribution curve can reduce the visibility of stains on the polished surface, thus improving this property.     

团聚体含量对氧化锆粉料烧结性能的影响

用共沉淀－喷雾干燥的方法制得了具有不同团聚性质的氧化锆粉料。粉料成型后团聚体可能破碎，也可能继续存在。通过团聚体对烧结影响的研究发现，烧结过程中团聚体含量是影响烧结密度和显微结构形成的主要因素，而成型后素坯中团聚体含量又取决于团聚体的强度。讨论了团聚体之间及团聚体与基体之间的相互作用对烧结的影响。     

Cold compaction molding and sintering of polystyrene

It is the objective of this paper to demonstrate the applicability of cold compaction molding followed by a sintering treatment to the processing of polystyrene powders. The influence of pressure, compaction speed, and peak pressure dwell time on the green (as compacted) density and the green tensile strength, as well as the effect of sintering on the tensile strength and dimensional change, were evaluated. The resulting data indicate that room temperature compaction alone is insufficient to provide adequate tensile strength for the compacts. Sintering the green compacts at temperatures of 150 to 173°C markedly improves the tensile strength while simultaneously causing a thickness change in the compacts. This thickness change results from gas evolution, pore shrinkage, and viscoelastic recovery of the residual stresses induced by pressure. For compacts of 0.225 in. thickness, an optimum sintering treatment of 173°C for 30 mins is recommended to provide a tensile strength of 4,000 psi and a thickness change of less than + 7 percent. Coining (repressing) the green compacts does not appreciably affect the sintered strength. However, a finer particle size improves the sintered properties. A review of the literature on the flow behavior of polystyrene suggests that a non-Newtonian viscous flow mechanism is followed by a Newtonian one as sintering progresses.     

Adhesion Effects of Intermediate Layers on the Densification of Ceramic Powders

In the ceramic technology the first step to produce sintered bodies is the manufacturing of powders which then are densified. The adhesion mechanisms between the single particles and the agglomerates produced from them determine the densification process. Starting from theoretical considerations adhesion mechanisms, such as solid bridge formation, adhesive bonding and glide-promoting effects, are discussed in principle. Subsequently, the effects of surface-active substances on the densification behaviour of clay-ceramics and oxide-ceramic bodies are discussed. Further, the evaluation of the action of additives to the powder mixtures on the microstructure of the compacts, such as porsity and texture, leads to a compaction equation which describes the transition from the powder pile to a densified green body.     

Influence of particles packing in granules on the particles orientation in compacts

Particles orientation during compaction was studied in alumina granules of different packing structures and deformation properties. These granules were classified mainly in two types: loose granules prepared with flocculated slurries and dense granules prepared with dispersed slurries. Particles orientations in the granules and in the compacts were examined quantitatively with the cross-polarized light microscopy. A large difference was noted in the packing structures of granules and compacts. Orientation of particles was detected only in the surface vicinity of the dense granules. These dense granules show only a slight change in particle orientation locally and its initial structures were mostly preserved even after compaction. As a result, the green compacts containing these granules also show very low net particles orientation. In contrast, loose granules show no orientated particles. However, a major rearrangement of the particles was noted during compaction, resulting in a high net particle orientation in the compacts. The particles orientation in the green compacts affected the anisotropy in the sintering shrinkage significantly; high anisotropy was observed in compacts of high particle orientation fabricated from the loose granules.     

Porosimeter as a Means to Measure the Compactibility of Powders

Samples of silica fume ponder prepressed in the form of slabs under relatively small pressures and cut in spheres were coated with a thin flexible latex film by dipping them into the water emulsion of the natural latex, and their densification behavior was studied using the common mercury intrusion porosimeter. The samples were compacted at isostatic pressure conditions by increasing the mercury pressure, and the volume changes as a function of pressure were recorded. The recorded pressure/volume changes provided information about the compaction course of the original green powder compacts in a continuous fashion.