Preparation, Crystallization and Mechanical Properties of Potassium Aluminosilicate Glass-ceramics

In this study,transparent K_(2)O-Al_(2)O_(3)-SiO_(2)(KAS)glass-ceramics with leucite as the main crystalline phase were prepared by melting-quench method and two-step heat treatment.The effects of SiO_(2)/Al_(2)O_(3) ratio and heat treatment on crystallization and mechanical properties were studied.The crystallization kinetics and X-Ray Diffraction(XRD)results showed that SiO_(2)/Al_(2)O_(3) ratio and heat treatment system had a direct impact on the crystallization behavior of potassium aluminosilicate glass-ceramics.When heat-treated at 680℃/2 h and 780℃/1 h,cracks generated on the surface of the sample with the addition of SiO_(2)/Al_(2)O_(3)=4.8(in mol)due to the huge difference in the coefficient of thermal expansion between glass matrix and surface.When the addition of SiO_(2)/Al_(2)O_(3)(in mol)was 4,the sample with leucite as the main crystalline phase showed an excellent fracture toughness(1.46 MPa·m^(0.5))after the heat treatment of 680℃/2 h and 780℃/5 h.And there was a phase transformation from kaliophilite to leucite.The crystalline phases of the sample heat-treated at 680℃/8 h and 780℃/1 h were leucite and kaliophilite,which resulted in the visible light transmittance of 63%and the fracture toughness of 0.91 MPa·m^(0.5).Furthermore,after the heat treatment of 680℃/2 h and 780℃/5 h,the main crystalline phase of the sample with SiO_(2)/Al_(2)O_(3)=3.2(in mol)was still kaliophilite.Because leucite only grows on the surface of the sample and is hard to grow inward,it is hard to achieve the bulk crystallization of leucite in the sample with SiO_(2)/Al_(2)O_(3)=3.2(in mol).

Glass-Ceramics with High Strength and High Transmittance Obtained by Multi-Factor Controlling

The presence of Li_(2)Si_(2)O_(5) and LiAlSi_(4)O_(10) could effectively improve the elastic modulus and transmittance of lithium disilicate(LD)glass-ceramics.Through synergistically modulation of the crystal content and grain size,we obtained high strength and high transmittance of LD glass-ceramics.The optimal sample had a high transmittance of 90.3%,the hardness was 7.72 GPa,the fracture toughness was 1.07 MPa·m^(1/2),and the elastic modulus was 103.1 GPa.

Effect of CaO Impurity on Mullite Formation from SiO_(2) Gel and Al_(2)O_(3) Powders

To broaden the application of SiO_(2) sol-bonded castables,using micro-or nano-Al_(2)O_(3) powder and SiO_(2) gel powder as the main raw materials,the effects of CaO impurity on the formation of mullite by the reaction of Al_(2)O_(3) and SiO_(2) at different temperatures(1350,1400,1500,and 1600℃)in different atmospheres(oxidation atmosphere and reduction atmosphere)were studied.The results show that in the oxidizing atmosphere,the introduction of CaO can promote the formation of mullite.When the temperature increases from 1350℃to 1600℃,the amount of mullite formed gradually increases.In the reducing atmosphere,the introduction of CaO is not conducive to the formation of mullite,and the amount of mullite decreases with the increasing temperature.The smaller the particle size of Al_(2)O_(3),the more easily it reacts with SiO_(2) gel powder to form mullite.

Properties of Ultra-low Thermal Expansion LAS Transparent Glass-ceramics Prepared by Spodumene

The glass-ceramics were prepared with the spodumene mineral as the main raw material,and the effects of ZrO_(2)replacing TiO_(2)on the samples were systematically investigated.The results show that the substitution of ZrO_(2)for TiO_(2)is not conductive to precipitate𝛽β-quartz solid solution phase,but can improve the transparency and flexural strength of glass-ceramics.And the glass-ceramic with the highest visible light transmittance(87%)and flexural strength(231.80 MPa)exhibits an ultra-low thermal expansion of-0.028×10^(-7)K^(-1)in the region of 30-700℃.

TiO_(2)/FACs与TiO_(2)/Mullite复合材料的制备及其光催化性能

分别以粉煤灰漂珠(简记为FACs)与海胆状莫来石球(简记为Mullite)为基体,采用溶胶浸渍工艺制备了TiO_(2)/FACs与TiO_(2)/Mullite型复合材料。通过X射线衍射(XRD)、扫描电子显微镜(SEM)以及电子能谱(EDS)对制备的材料进行了表征。研究了TiO_(2)/FACs与TiO_(2)/Mullite型复合材料在紫外光照射下对罗丹明B(RhB)的光催化性能。结果表明:经500℃煅烧后形成的锐钛矿型TiO_(2)均成功负载到粉煤灰漂珠与莫来石晶体上,在粉煤灰漂珠表面覆盖了一层厚薄不均的纳米级别的TiO_(2)薄膜,而在莫来石晶体上则出现了大量细小的TiO_(2)颗粒;在降解染料时间为180 min,TiO_(2)/FACs与TiO_(2)/Mullite复合材料对罗丹明B染料的降解率分别为84.8%和96.4%,降解速率为0.01088min-1和0.02885 min-1。

Preparation and Thermal Shock Resistance of Mullite Ceramics for High Temperature Solar Thermal Storage

Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.

煅烧温度对TiO_(2)/FACs与TiO_(2)/Mullite复合材料物相结构及其光催化性能的影响

采用溶胶浸渍工艺于不同煅烧温度下(300~700℃)制备了二氧化钛/粉煤灰漂珠(简称Ti O_(2)/FACs)与二氧化钛/莫来石(简称Ti O_(2)/Mullite)复合材料,采用X射线衍射仪(XRD)、场发射扫描电子显微镜(SEM)、红外吸收光谱、紫外-可见分光光度计表征了材料的物相结构和光催化性能,研究了煅烧温度对Ti O_(2)/FACs与Ti O_(2)/Mullite复合材料物相结构和光催化性能的影响。结果表明:煅烧温度的高低对Ti O_(2)的形成产生重要影响,在400~600℃可获得单一的锐钛矿晶型,温度过高会产生金红石相,过低则不利于Ti O_(2)的形成;Ti O_(2)/FACs与Ti O_(2)/Mullite复合材料对罗丹明B染料的光催化降解效率随着煅烧温度的升高先上升后降低,经500℃煅烧制备的复合材料光催化性能最佳,锐钛矿型Ti O_(2)分别以纳米级的Ti O_(2)薄膜以及纳米级的颗粒负载于粉煤灰漂珠与莫来石晶体上;Ti O_(2)在粉煤灰漂珠与莫来石晶体上均属于物理吸附,并未形成相应的化学键。

Strengthening Mullite Ceramic Materials by Gas Infiltration

In order to improve the high-temperature performance of mullite ceramic materials,mullite ceramic bodies were placed in closed containers with AlF_(3)·3H_(2)O powder and kept at 1 600 ℃ for 6 h.AlF_(3)·3H_(2)O reacts with O_(2) to produce gaseous compounds AlOF and F,which penetrate into the bodies,promote Al2O3 and SiO_(2) to form mullite whiskers,and strengthen the mullite ceramic materials.The results show that the mullite ceramics have enhanced hot strength,increased bulk density and declined apparent porosity by adding a certain amount of AlF_(3)·3H_(2)O in a closed container.When the addition of AlF_(3)·3H_(2)O is 6%,the bulk density of the ceramic material reaches the maximum and the apparent porosity is the lowest;and when the addition of AlF_(3)·3H_(2)O is 8%,the hot strength of the material is the highest.

Effect of Porogenic Agents on Properties of Microporous Mullite Aggregates

Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1700℃for 3 h with corn starch,PMMA microspheres or rice husk powder as the porogenic agent.The effects of some porogenic agents and their additions(mass fraction of 0,5%,10%,15%and 20%,respectively)on the properties of the microporous mullite aggregates were analyzed by XRD,SEM and Image-Pro Plus software.The results show that the comprehensive performance of the sample with 10%rice husk powder is the best:the closed porosity is 7.1%;the bulk density is 2.63 g·cm^(-3);the compressive strength is 122 MPa;the median pore size is 15.16μm;and the thermal conductivity at 500℃is 2.30 W·m^(-1)·K^(-1).

Isotropic sintering shrinkage of 3D glass-ceramic nanolattices:backbone preforming and mechanical enhancement

There is a perpetual pursuit for free-form glasses and ceramics featuring outstanding mechanical properties as well as chemical and thermal resistance.It is a promising idea to shape inorganic materials in three-dimensional(3D)forms to reduce their weight while maintaining high mechanical properties.A popular strategy for the preparation of 3D inorganic materials is to mold the organic–inorganic hybrid photoresists into 3D micro-and nano-structures and remove the organic components by subsequent sintering.However,due to the discrete arrangement of inorganic components in the organic-inorganic hybrid photoresists,it remains a huge challenge to attain isotropic shrinkage during sintering.Herein,we demonstrate the isotropic sintering shrinkage by forming the consecutive–Si–O–Si–O–Zr–O–inorganic backbone in photoresists and fabricating 3D glass–ceramic nanolattices with enhanced mechanical properties.The femtosecond(fs)laser is used in two-photon polymerization(TPP)to fabricate 3D green body structures.After subsequent sintering at 1000℃,high-quality 3D glass–ceramic microstructures can be obtained with perfectly intact and smooth morphology.In-suit compression experiments and finite-element simulations reveal that octahedral-truss(oct-truss)lattices possess remarkable adeptness in bearing stress concentration and maintain the structural integrity to resist rod bending,indicating that this structure is a candidate for preparing lightweight and high stiffness glass–ceramic nanolattices.3D printing of such glasses and ceramics has significant implications in a number of industrial applications,including metamaterials,microelectromechanical systems,photonic crystals,and damage-tolerant lightweight materials.

Cu含量对Mullite/Al-Cu复合材料时效硬化行为的影响

用挤压铸造方法制备了Mullite/Al Cu复合材料。用硬度测试仪、差示扫描量热仪 (DSC)和透射电镜(TEM)等设备研究了铝基复合材料及其基体合金中Cu含量变化对时效硬化行为的影响 ,同时还研究了增强纤维对时效相的析出序列、析出相和位错结构的影响。结果表明 ,无论是在复合材料中还是在基体合金中 ,随着Al Cu合金中Cu含量的增加 ,时效硬化过程均有不同程度的加速 ;Mullite纤维的引入提高了Al Cu合金的时效硬度 ,明显加速了Al Cu合金的时效硬化过程 ,对GP区的形成有抑制作用 。

SiC晶须在Mullite浆料中的分散特性及流变学表征

研究了SiC 晶须在Ｍｕｌｌｉｔｅ浆料中的分散行为．通过沉降实验和流变学测试讨论了ｐＨ值，分散剂对SiC 晶须分散性质的影响．结果发现，晶须的加入影响了浆料的流变性能．当ＰＨ＝１１，分散剂含量为5wｔ％时，可获得分散性较好的浆料．本分散工艺促进了晶须在Ｍuｌｌｉｔe浆料中的分散，提高了浆料的结构均匀性．

PIP法制备3D Nextel^(TM) 720/Mullite复合材料

采用先驱体浸渗热解法制备了 3DNextelTM 72 0 Mullite复合材料 ,并对基体的组分控制、复合材料致密化以及热处理温度对复合材料强度的影响进行了研究。结果表明 ,采用正硅酸已酯和异丙醇铝作为先驱体可以在相对低温 (≤ 12 0 0℃ )通过循环浸渗热解制备孔隙率低于 2 0 %的复合材料。

含Si量对Mullite纤维/Al-Cu-Si复合材料及其基体合金时效行为的影响

用挤压铸造方法制备了Mullite/Al Cu Si复合材料。用硬度 (HB)测试仪、差示扫描量热仪 (DSC)和显微镜研究含Si量变化和Mullite纤维对Al Cu Si合金时效硬化行为的影响 ;元素Si、Mullite纤维以及二者同时存在对Al Cu Si合金时效析出序列的影响。结果表明 :Si和Mullite纤维明显抑制了Al Cu合金GP区的形成 ;随着含Si量增加 ,Al Cu Si合金的时效硬化过程加快 ;Mullite纤维对Al Cu和Al Cu Si合金的时效硬化过程都具有加速作用 ,同时提高了基体合金的时效硬度 ,但相对而言 ,Mullite纤维对无Si的Al Cu合金的时效硬化加速作用更为明显一些。

Preparation and oxidation resistance of mullite/SiC coating for carbon materials at 1150 ℃

To protect carbon materials from oxidation, mullite/SiC coatings were prepared on graphite by chemical vapor reaction (CVR) and slurry sintering. The XRD analyses show that the phase of the outer-layer coating is composed of SiO2 and mullite, and the inner-layer coating is mainly composed of β-SiC. The anti-oxidation behavior of the coating and the Rockwell hardness (HRB) of the coating after oxidation were investigated. The oxidation test shows that the as-prepared multi-layer coating exhibits excellent antioxidation and thermal shock resistance at high temperature. After oxidation at 1150 ℃ for 109 h and thermal shock cycling between 1150 ℃ and room temperature for 12 times, the mass gain of the coated sample is 0.085%. Meanwhile, the indentation tests also demonstrate that the as-prepared coating has good bonding ability between the layers.

Crystallization kinetics and temperature dependence of energy storage properties of niobate glass-ceramics

Glass-ceramic materials of strontium barium niobate system were prepared through a melt-quenching method. The effects of crystallization temperature on the mierostructure, dielectric property, breakdown strength and energy storage density of barium strontium niobate glass-ceramics were studied. The crystallization mechanism of the glass-ceramics was discussed and should be one-dimensional interfacial growth. The results indicate that the breakdown strength remarkably increases with the increase of crystallization temperature. The glass-ceramic heat treated at 900 ℃ was found to possess optimal properties with breakdown strength of 1300 kV/cm and energy storage density of 2.8 J/cm3, which is promising dielectric materials for high energy storage density dielectrics.

温度对Mullite/Al-4.0Cu复合材料及其基体合金时效行为的影响

用挤压铸造方法制备Mullite Al 4 0Cu复合材料及其基体合金。用硬度测试 (HB)、差示扫描量热仪 (DSC)和透射电镜 (TEM )等手段 ,研究了温度对复合材料及其基体合金时效行为的影响。结果表明 :复合材料和基体合金具有相似的时效硬化曲线及相同的时效析出序列 ,随时效温度的升高 ,峰值硬度降低、时析析出过程加快 ;莫来石纤维除了能明显提高Al 4 0Cu合金的时效硬度外 ,还能加速其时效析出进程 ,但对GP区的形成具有明显的抑制作用 ,而对θ相的析出影响不大。

3Y-TZP/mullite-Alumina复合陶瓷的韧性及增韧机制

为了研究3Y TZP为基体的3Y TZP/mullite Alumina复合陶瓷的断裂韧性及其增韧机制,将3Y TZP、mullite、Alumina3种粉料球磨混合,经干压、等静压成型,在1480℃,4h无压烧结,通过改变Alumina/mullite体积比,得到了不同断裂韧性的陶瓷复合材料,利用XRD与SEM技术分析了复合材料的成分及微观结构.研究结果表明:Al2O3/mullite体积比影响复合材料中四方氧化锆(t ZrO2)向单斜氧化锆(m ZrO2)转变的相变量、复合材料的微观结构和t ZrO2晶面间距,进而影响材料的断裂韧性;用单边切口梁法测试复合材料断裂韧性(KIC)为9 26～10 4MPa·m1/2;此系统中存在ZrO2相变增韧、非相变第二相颗粒增韧等机制.

C/Mullite/Si-C-N复合材料的组织结构及其弯曲行为研究

本研究制备出了以莫来石为界面层的炭纤维增强Si-C-N陶瓷基复合材料(C/Mullite/Si-C-N)。使用三点弯曲法研究了复合材料在室温、1300℃和1600℃时的弯曲断裂行为,利用扫描电镜(SEM)和透射电镜(TEM)观察了复合材料的组织和弯曲断口形貌。结果表明:在室温和1300℃时,C/Mullite/Si-C-N复合材料的断口呈现出明显的脆性断裂特征;而在1600℃时,则呈现出韧性断裂特征。1300℃时的弯曲强度高于室温强度,模量则与室温下的基本相等。1600℃时,复合材料的弯曲强度和模量都明显下降。与具有热解炭界面层的C/Si-C-N复合材料相比,采用莫来石界面后,C/Si-C-N复合材料的强度明显下降。

DSC法研究Mullite/Al-Cu-Mg复合材料及其基体合金的时效析出行为

用差示扫描量热仪 (DSC)对Al 4 0Cu 1.85Mg合金和莫来石 (Mullite)纤维增强Al 4 0Cu 1.85Mg复合材料的时效行为进行了研究。结果表明 :Mullite /Al 4 .0Cu 1.85Mg复合材料及其基体合金Al 4 .0Cu 1.85Mg固溶淬火试样的DSC扫描曲线上存在较大的不同 ,GPB区形成和溶解的信息在基体合金的DSC曲线上容易辨别 ,但在复合材料的DSC曲线上则较难确认 ,表明纤维推迟和抑制了GPB区的形成。S″相和S′的析出由于纤维的引入而得到明显加快 ,放热峰值温度降低 ,激活能减小 。