硅粉粒径对反应烧结多孔氮化硅陶瓷介电性能的影响

以硅粉为原料,添加质量分数为30%的成孔剂(苯甲酸)球形颗粒,反应烧结制备了气孔率为55%,具有球形宏观孔的低密度多孔氮化硅陶瓷.研究了硅粉粒径对反应烧结多孔氮化硅陶瓷介电性能的影响.结果表明:烧结后样品的介电常数ε'和介电损耗tanδ随着初始硅粉粒径的减小都有明显的降低.平均颗粒尺寸为7μm的硅粉制备的样品的ε'嘬小,约为2.5.原料硅粉的粒径变化将影响反应烧结的反应速率,从而影响反应烧结后样品的生成相和微观结构.随着平均颗粒尺寸的减小,反应烧结后Si3N4相含量增加,Si2ON2相和游离硅含量减少,气孔变小.     

烧成温度和成孔剂掺量对烧结制备保温材料性能的影响

本文对利用新疆页岩加入兰炭成孔剂制备的烧结保温材料的各项性能进行研究.首先对原料的理化指标进行实验分析,分析结果为:新疆页岩的化学成分适宜制备烧结保温砌块,页岩烧成温度范围为850 ～ 1050℃,最佳烧成温度为950℃.其次,向页岩中添加不同比例的兰炭成孔剂,在不同温度下烧成,测试其抗压强度、体积密度及显气孔率.结果表明:随着烧成温度的升高,试样抗压强度增大,体积密度增加,显气孔率降低;随着成孔剂掺量的增加,试样抗压强度下降,体积密度减小,显气孔率提高.当造孔剂添加量为12％,烧成湿度为1040℃时,试样抗压强度等级达到MU20,导热系数下降至0.3598 W/(m·K),比不加成孔剂降低了20％以上.SEM分析结果表明,加入成孔剂后可使试样内部产生微孔,使导热系数降低.     

制备工艺对Al2O3多孔陶瓷性能的影响

研究了Ａｌ２Ｏ３粉料粒径、烧成温度及有机造孔剂对Ａｌ２Ｏ３多孔陶瓷的气孔率、孔径大小及分布的影响，结果表明，随造孔剂加入量的增加，气孔率呈线性增大，加入造孔剂后，平均气孔孔径变大，孔径分布范围变宽。     

用于净化高温煤气的陶瓷过滤元件的制备及其研究

以氧化铝为基体材料，采用添加成孔剂法，并结合注浆成型和凝胶注模成型制备出用于过滤高温煤气的陶瓷过滤元件。研究了料浆的配方及流动性能等对成型坯体性能的影响、成孔剂的种类及用量对气孔率、抗压强度及过滤元件外形的影响以及适应于该过滤元件的烧结工艺。实验结果表明，采用有机成孔剂AUM和无机成孔剂活性炭混合使用效果好：在成孔剂用量为25vol％、添加适量添加剂条件下，注浆成型和注凝成型后在1360℃下烧结40min，可得到气孔率高达47.4％、抗压强度迭32.26MPa，气孔的孔径为6～10μm的高温煤气过滤元件。     

镁渣多孔陶瓷滤球气孔率的调控

以镁工业废渣为主原料,添加一些成孔剂及天然矿物烧结助剂,制备了可用于工业废水及废气处理的高性能镁渣多孔陶瓷滤球。讨论了3种成孔剂的成孔效果和影响气孔率、强度的因素。理化性能和显微结构测试表明,高温成孔剂石墨添加量为20%,烧成温度为1100℃时,样品的显气孔率为56.17%,吸水率为43.76%,体积密度为1.28g/cm3,抗压碎强度为34.21MPa,耐酸性为99.59%,耐碱性为99.81%;低温成孔剂煤粉和白云石的加入也能起到气孔率调控的作用。镁渣多孔陶瓷滤球的气孔分布均匀,呈三维连通状,有利于实现其过滤性能。     

累托石合成孔梯度多孔陶瓷的研究

以累托石为主要原料，煤粉为成孔剂，采用压制成形，在1220℃温度下烧成，制得具有一定孔梯度的多孔陶瓷，研究表明，不同的骨粒粒径及不同的成孔剂粒径的相互混合可制得具有成连续变化孔梯度分布的多孔陶瓷，且随着成孔剂含量的提高，显气孔率增加，强度和体积密度均降低。     

明胶对多孔磷酸钙骨水泥结构及性能的影响

采用高温固相烧结法,在1250℃烧结并保温2h后迅速冷却得到斜方相磷酸钙骨水泥(calcium phosphate cement,CPC)粉体.向CPC粉体中加入不同含量、粒径不等的明胶颗粒得到多孔材料.考察了多孔材料的微观结构、力学性能和气孔率的变化,并分析明胶的成孔机制.结果表明:在CPC粉体中添加明胶后,随着明胶含量的增加,CPC水化体的气孔率逐渐增大,力学性能逐渐降低且粒径较大明胶颗粒的影响更为明显.CPC水化产物中孔隙周围结晶形态有明显变化,加入明胶之前为针状晶体;加入明胶之后为片状晶体.明胶大分子在羟基磷灰石生成过程中起固定作用,水化后溶于水,明胶微球原本占据的空间将被保留从而形成大孔.     

ZrO_2微孔陶瓷支撑体的研制

以微细的ＺｒＯ＿２为原料，研究了粉料粒径及有机造孔剂对ＺｒＯ＿２微孔陶瓷支撑体的气孔率．孔径大小及分布的影响．结果表明：粉料越细，气孔孔径越小．加入有机造孔剂可以有效地提高气孔率，但气孔孔径变大，孔径分布范围变宽．本研究可以得到平均气扎扎径为０．１～６．０μｍ，气孔率在１５％～７０％的ＺｒＯ＿２微孔陶瓷支撑体．     

影响多孔玻璃孔结构的因素

研究表明,利用填充法制备的多孔玻璃的孔参数(气孔率、孔径分布)可进行设计与控制,多孔玻璃的气孔率和孔径分布主要取决于成孔剂的体积比及其颗粒分布,前者与后者之间的偏差取决于生坯制备及烧结过程.     

冻干法制备多孔氮化硼陶瓷及其成孔机理

以h-BN为原料、MC为分散剂、PVA为结合剂、B2O3为烧结助剂,利用冷冻干燥法制备多孔BN陶瓷。对多孔陶瓷的物相和微观结构进行表征,分析了p H值对孔结构的影响。结果表明:冷冻干燥后的样品孔结构由树枝状孔和直通孔组成,平均孔径为30~150μm。p H值为10时,悬浮液Zeta电位最大,悬浮液分散性最好,冰晶生长过程中受到的阻力最小,样品平均孔径分布最均匀,体积密度和气孔率分别为0.4 g/cm3和81.82%。1 500℃烧结后,只有氮化硼的特征衍射峰。成孔机理为:冻干过程中水结冰后冰晶升华成孔,调节p H可改变浆料中颗粒的分散性以及冰晶生长过程中受到的阻力,从而影响孔结构的形成。     

制备工艺对多孔Si_3N_4陶瓷介电性能的影响(英文)

采用添加成孔剂和冰冻-干燥法制备具有不同气孔率(30%～60%)的多孔Si3N4陶瓷,研究了不同制备工艺对多孔Si3N4陶瓷介电性能的影响.结果表明:不同的成型工艺制备出具有不同孔分布的氮化硅多孔陶瓷,添加成孔剂制备的多孔陶瓷具有较大的孔,洞分布在致密的基体上:冰冻-干燥法制备的多孔陶瓷具有复合孔分布.对样品的介电特性的研究表明,随着样品的气孔率增加,其介电常数和介电损耗减小;添加成孔剂制各样品的介电常数小于冰冻-干燥法制备样品,而其介电损耗较大,多孔Si3N4陶瓷的介电常数和介电损耗分别在5.21～2.91和9.6×10-3～2.92×10-3范围内变化.     

烧结助剂对多孔氮化硅陶瓷的力学性能及介电性能的影响

通过添加烧结助剂,采用常压烧结工艺制备出不同气孔率(19%～54%)的氮化硅陶瓷.采用Archimedes法、三点弯曲法和Vickers硬度测试法测量了材料的密度、气孔率、抗弯强度及硬度.用X射线衍射及扫描电镜检测了相组成和显微结构.用谐振腔法测试了氮化硅陶瓷在10.2 GHz的介电特性.结果表明:材料具有优良的介电性能.随着烧结助剂的减少,样品中气孔率增加,力学性能有所下降,介电常数和介电损耗降低.添加Lu2O3所制备的氮化硅陶瓷的力学性能和介电性能优于添加Eu2O3或Y2O3制备的氮化硅陶瓷.当气孔率高于50%时,多孔氮化硅陶瓷(添加入5%的Y2O3或Lu2O3,或Eu2O3,质量分数)的抗弯强度可达170 MPa,介电常数为3.0～3.2,介电损耗为0.000 6～0.002.     

High performance porous Si3N4 ceramics prepared by coated pore-forming agent method

Coated pore-forming agent method (CPFAM) was introduced to improve the pore-forming agent method (PFAM) for the preparation of porous silicon nitride ceramics. Using SEM in combination with measurements of porosity and flexural strength, it has been found that the flexural strength of the porous silicon nitride ceramics produced with the CPFAM method is significantly higher than those without the coating process: a 100% increase in flexural strength for samples with a porosity of 50%. The porous silicon nitride ceramics also have a very low dielectric constant, which is ideal for applications in wave-transmitting systems. The enhanced mechanical strength of the silicon nitride made by the CPFAM method is a result of a more uniform distribution of the spherical pores and the formation of a dense layer of rod-like microstructures near the surface of the pores.     

Preparation of near net size porous alumina-calcium aluminate ceramics by gelcasting-pore-forming agent processs

In the processing of porous ceramics, shrinkage from green body to sintered compact during drying and sintering is one of the key concerns which affect microstructure and properties of porous ceramics. Through releasing gases from the burning of the pore forming agents, and volume expansion from the formation of low density resultants during sintering, the sintering shrinkage can be effectively compensated and near net size preparation can be achieved. Herein, near net size porous alumina-calcium aluminate ceramics with controllable shrinkage have been prepared using a combination of gelcasting and pore-forming agent process by adjusting the amount of CaCO₃ and polymethyl methacrylate (PMMA) microspheres added. Al₂O₃ and CaCO₃ were used as raw materials, PMMA microspheres were used as pore-forming agent, isobutylene/maleic anhydride copolymer (Isobam104) was used as gelling agent and dispersing agent. The effects of the addition amounts of CaCO₃ and PMMA in the slurry on the phase composition, shrinkage, porosity, and strength of porous alumina-calcium aluminate ceramics were investigated. The results show that as the CaCO₃ addition amount increases from 0 to 20 wt%, the shrinkage of the samples gradually decreases from 7.3% to −1.4%, and the consequent porosity increases from 58% to 66%, while the compressive strength increases from 5.9 to 15.5 MPa. When PMMA content increases from 10 to 50 wt%, the shrinkage of the samples decreases first and then increases, the porosity increases from 51% to 74%, and the compressive strength decreases from 12.5 to 5.3 MPa. The mechanisms for controlling shrinkages during preparation of porous alumina-calcium aluminate ceramics can be attributed to the following aspects: on one hand, gas release from burning of PMMA and decomposition of CaCO₃ during sintering; on the other hand, volume expansion due to the formation of lower density calcium aluminates which come from the reactions between CaO and Al₂O₃. The near net size preparation technique is of great significance for the manufacture of porous ceramics since the subsequent machining cost can be effectively reduced.     

Ultra-low cost porous mullite ceramics with excellent dielectric properties and low thermal conductivity fabricated from kaolin for radome applications

Near-net-shape mullite ceramics with high porosity were prepared from ultra-low cost natural aluminosilicate mineral kaolin as raw material and polystyrene micro-sphere (PS) as pore-forming agent. Microstructure, flexural strength, thermal conductivity and dielectric properties of the ceramics were systematically researched. Results show that the porous mullite ceramics possess fibrous skeleton structure formed by a large quantity of interlocked mullite whiskers, which results in good mechanical properties and low-to-zero sintering shrinkage. Flexural strength of the porous mullite ceramics can be up to 41.01 ± 1.12 MPa, even if the porosity is as high as 62.44%. The dielectric constant and loss tangent of the porous mullite ceramics at room temperature are lower than 2.61 and 5.9 × 10⁻³, respectively. Besides, dielectric constant is very stable with the rising of temperature, and the dielectric loss can be consistently lower than 10⁻² when the temperature is not higher than 800 °C. In addition, thermal conductivity at room temperature is as low as 0.163 W/m/K when the porosity of mullite ceramics is 80.05%. The infiltration of SiO₂ aerogels (SiO₂ AGs) can further decrease the thermal conductivity to 0.075 W/m/K, while has just little effects on the dielectric properties. Excellent mechanical, thermal and dielectric properties show that the porous mullite ceramics have potential applications in radome fields. The porous mullite ceramics prepared from kaolin not only have low cost, but also can achieve near-net-shape.     

Preparation and properties of porous Al5BO9 for high-temperature wave-transparent and thermal insulating applications

Porous Al₅BO₉ is a promising high-temperature wave-transparent material. However, method for the preparation of this material is not readily available. Herein, porous Al₅BO₉ ceramics with controlled porosity and small volume shrinkage are successfully prepared by using Al₂O₃ and B₂O₃ as starting materials without pore formers. The SEM and pore size distribution studies show that the as-prepared porous Al₅BO₉ ceramics exhibit a uniform pore structure and a narrow pore size distribution. Intriguingly, simply adjusting the densities of the green bodies, the density and porosity of the porous Al₅BO₉ ceramics can be controlled. The pore-forming mechanism is presumed to be a combination of boron oxide volatilization during the high-temperature synthesis and lap of elongated grains. Porous Al₅BO₉ ceramics have good high-temperature stability, which can maintain dimensional and composition stability up to 1673 K. The compressive strength can reach 211 MPa at 32.4% porosity and the dielectric constant can be as low as 3.02 at 43.2% porosity. In addition, the dielectric constant and loss tangent keep almost unchanged with temperature.     

梯度多孔载Ag羟基磷灰石陶瓷的制备和性能研究

本文采用添加造孔剂法制备孔隙呈现梯度分布的多孔载Ag羟基磷灰石(Ag-HA)陶瓷。研究了造孔剂分布、烧结温度和载Ag含量对梯度多孔Ag-HA陶瓷孔隙度的影响。分析了烧结产物的物相组成和微观形貌,测量了烧结后梯度多孔Ag-HA陶瓷的压缩性能和抗菌性能。研究结果表明:随着中间层造孔剂含量增加,梯度多孔Ag-HA陶瓷的孔隙度增大,抗压强度减小;随着烧结温度的增大,梯度多孔Ag-HA陶瓷的孔隙度减小,抗压强度增大;当造孔剂分布为20%-10%-20%(质量分数),压制压力为100 MPa,烧结温度为1 150 ℃,Ag含量为2.0%(摩尔分数)时,烧结后梯度多孔2.0Ag-HA陶瓷的孔隙度为24.7%,抗压强度为12.6 MPa。XRD分析表明烧结产物为掺杂Ag离子的HA相。SEM观察表明烧结样品的孔隙呈现梯度分布。梯度多孔Ag-HA陶瓷的抗菌实验表明:随载Ag含量和孔隙度的增大,梯度多孔Ag-HA陶瓷对于大肠杆菌和金黄色葡萄球菌的抑菌圈直径增加,表现出较强的抗菌性能,而纯HA陶瓷未表现出抗菌性能。     

以硼砂为助熔剂使用含钛高炉渣制备发泡陶瓷

以紫色页岩、含钛高炉渣为原料,硼砂为助熔剂,碳化硅为发泡剂制备发泡陶瓷,通过对气孔率、闭孔率、孔径分布、表观密度、抗压强度、导热系数进行测量,研究了原料配比和硼砂添加量对发泡陶瓷气孔结构和物理性能的影响。结果显示:当原料中含钛高炉渣比例增加时,试样的平均孔径增加,气孔均匀性下降;硼砂的加入会使试样抗压强度降低,孔隙率增大,导热系数变小。当发泡陶瓷原料配比(质量分数)为高炉渣30%,页岩70%,添加4%的硼砂和0.2%的碳化硅时,制备出的发泡陶瓷的表观密度为0.374 g·cm^-3,导热系数为0.121 W·m^-1·K^-1,抗压强度为2.59 MPa,满足建筑外墙保温发泡陶瓷的要求。发泡陶瓷主要晶相为斜长石,同时伴有部分透辉石、石英和少量的铁板钛矿。     

On the role of the pore morphology on the electrical conductivity of porous yttria-stabilized zirconia

Yttria Stabilized Zirconia ceramics with well-controlled porosity, pore size and shape were prepared using well-calibrated poly-methyl-methacrylate (PMMA) micro-beads (MB) as a pore-forming agent. The microstructure was observed by Scanning Electron Microscopy. Impedance spectroscopy was used to evaluate the effect of pore morphology (pore size, pore size distribution, pore shape and interconnectivity) on the electrical properties of YSZ ceramics. Archie's law based analyzes to express the dependence of conductivity on porosity have shown that Archie's law is independent of pore size for a pore diameter of between 1 and 7 μm. The Bruggeman model could be used to predict the bulk conductivity if the porosity was less than 25%, thus showing that the impedance response included the effect of sinuousness and constriction induced by pores. Therefore, the tortuosity factor calculated from the bulk conductivity was higher than that predicted by the Bruggeman model for porosities greater than 25% and spherical pores wide (>20 μm). Another point relates to the comparison between tortuosity factors obtained for pore samples fabricated with pore-forming PMMA or by sub-sintering.     

多孔低介电氧化硅陶瓷材料的制备

采用氧化硅为原料,木屑作为造孔剂制备了多孔的氧化硅陶瓷材料。借助于气孔率测试、抗弯强度测试、介电性能测试和SEM测试手段分析了造孔剂和烧结助剂的添加量对材料性能的影响。结果表明:加入BN作为添加剂烧成的氧化硅抗弯强度最大可达到14.80MPa。加入木屑作为造孔剂制备的陶瓷可以形成明显的气孔,气孔率最高可达到48.40%,介电常数最低可以达到3.0。