晶化温度对R2O-MgO-Al2O3-SiO2系微晶玻璃析晶和力学性能的影响

采用整体析晶法,以花岗岩废渣为主要原料,TiO2和P2O5作复合晶核剂,制备了R2O-MgO-Al2O3-SiO2系微晶玻璃.用DSC、XRD、SEM等表征方法研究了晶化温度对微晶玻璃的晶相组成、显微结构和力学性能的影响.实验结果表明:晶化温度为900℃时,析出镁铝钛酸盐和顽辉石晶相.晶化温度在1080～ 1200℃之间时,微晶玻璃中析出棒状假蓝宝石、镁铝钛酸盐、顽辉石的复合晶相,随晶化温度的升高,晶相含量增加,晶粒尺寸增大.晶化温度为1240℃时,假蓝宝石相减少,尖晶石相析出.在1200℃晶化2h后的微晶玻璃四点抗弯强度最高,达到109.25 MPa.     

晶化制度对矿渣微晶玻璃析晶行为的影响作用研究

以铁尾矿、硼泥和粉煤灰为原料,采用熔融法工艺制备微晶玻璃,借助XRD、SEM和显微硬度等测试方法,研究了晶化制度对微晶玻璃结构和性能的影响。试验结果表明:随着晶化温度的升高和晶化时间的延长,微晶玻璃中主晶相均为辉石相,且随着晶化温度的升高和晶化时间的延长,晶体尺寸逐渐增大,而微晶玻璃的表观体积密度和显微硬度呈升高后降低的趋势。     

TiO2对CaO-MgO-Al2O3-SiO2微晶玻璃析晶的影响

本文运用差示扫描量热分析(DSC)、X射线衍射(XRD)和场发射扫描电镜(FESEM)研究了TiO2含量对CaO-MgO-Al2O3-SiO2系微晶玻璃析晶过程和析晶动力学的影响.结果表明:随着TiO2含量的增加,玻璃转变温Ts和析晶峰温度Tp逐渐降低.当不加TiO2或者添加5wt％的TiO2时,玻璃发生表面析晶,析出的晶相为斜长石.当添加10wt％的TiO2时,玻璃样品在800℃热处理后发生剧烈分相,910℃晶化后出现整体析晶,晶相为普通辉石.随着TiO2含量的增加,析晶动力学常数k值增大.当添加10wt％的TiO2时,k值达到最大,为0.545,此时玻璃最容易析晶,相应的析晶活化能E和析晶指数n分别为643.329 kJ/mol和3.25.     

晶化温度对钨尾矿微晶玻璃析晶性能的影响

以广东韶关梅子钨尾矿和相应化学试剂为原料,通过熔融法制备了硅灰石为主晶相,钙长石为次晶相的微晶玻璃。采用差热扫描(DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)等手段研究了晶化温度对微晶玻璃样品的析晶性能、微观结构的影响,测试了样品的耐酸耐碱性、密度、抗弯强度、显微硬度等性能。结果表明:随着晶化温度的升高,微晶玻璃样品中晶粒逐渐长大,由球型晶体发育成杆状晶体;在850~1050℃热处理的微晶玻璃,其密度、抗弯强度和显微硬度都随着晶化温度的升高逐渐增加,950℃时微晶玻璃性能最优,耐酸性为0.19%、耐碱性为0.18%、密度达2.82g/cm~3、抗弯强度达97.52 MPa、显微硬度达527 MPa,1000℃时,微晶玻璃的性能不同程度的降低可能是因为晶相转变或晶相分布造成不致密结构引起的。     

转炉渣微晶玻璃的析晶行为

以转炉渣为原料,利用熔融法制备矿渣微晶玻璃.利用X射线衍射、扫描电镜和红外光谱分析研究了转炉渣含量变化对微晶玻璃析晶行为的影响.结果表明:随着转炉渣含量的增加,微晶玻璃的主晶相为透辉石和钙铁辉石;晶体尺寸呈先增加后减小的趋势,表面的晶体尺寸大于内部的晶体,晶体析出量逐渐增加;玻璃红外光谱的最强吸收带窄化,在800～1000cm-1范围内出现新的吸收峰,且强度逐渐增强.微晶玻璃中存在[SiO4]和[Fe3 O4]四面体单元,析出相具有和透辉石和钙铁辉石类似的结构.     

利用镍铁渣及粉煤灰制备CMSA系微晶玻璃的研究

铁合金渣数量多,利用率低,已经成为制约铁合金行业可持续发展的重要因素.为了拓宽铁合金渣新的利用途径,本文以镍铁渣为主要原料,协同利用粉煤灰制备了CaO-MgO-Al2O3-SiO2 (CMAS)系微晶玻璃.试验结果表明,完全利用镍铁渣和粉煤灰两种固废能够制备出性能良好的微晶玻璃.随着镍铁渣掺量从40％增加到55％时,微晶玻璃最佳成核、晶化温度变化不明显,但其抗折强度从66 MPa增加到87 MPa,相应体积密度增大3％,收缩率增大15％,吸水率降低95％.当镍铁渣掺量增加时,微晶玻璃中钙长石和顽辉石相对含量随着增大,而石英和尖晶石相对含量减少.晶相变化和微观结构致密性增加是导致微晶玻璃性能变化的一个主要原因.当镍铁渣掺量为55wt％,粉煤灰掺量为45wt％时,所制备的微晶玻璃抗弯强度为86.76 MPa,吸水率为0.09％,析出的主晶相为钙长石和顽辉石,辅晶相为尖晶石.     

铁对R2O-CaO-MgO-Al2O3-SiO2系玻璃微晶化的影响

就石材锯切粉在微晶玻璃中应用的主要问题-铁对析晶的影响展开研究。结果表明，少量铁（〈2mol％）的引入，可能引起析晶参数的升高，但外加铁含量超过2mol％时均可降低析晶参数，并使起始析晶至析晶峰的温度区间（Tp-Tg）变窄；外加铁量〈2mol％时，不同含铁量配方的（Tp—Tg）区间重叠显著，可以采用同一温度晶化处理；配方含铁与否对主晶相没有明显影响，但影响玻璃的析晶能力，铁含量〈2mol％时，使玻璃体析晶能力增加，接近或大于3mol％时，玻璃析晶能力降低；微粉制备微晶玻璃可以大幅度缩短晶化时间。     

Li_2O-ZnO-Al_2O_3-SiO_2微晶玻璃热处理制度的研究

通过两步法制备Li2O-Zn O-Al2O3-Si O2(LZAS)系微晶玻璃,并通过正交实验探究不同热处理工艺参数对微晶玻璃致密化的影响,使用P2O5作为晶核剂。结果表明;玻璃转化温度为492℃,析晶温度为560℃和714℃,材料软化点为685℃。各参数对微晶玻璃致密化的影响顺序为晶化温度晶化时间核化温度核化时间;析晶量主要受晶化温度和晶化时间影响;当温度为560℃时,开始有少量晶体析出,当温度超过580℃,主晶相为锂辉石,并且还有少量锂霞石;锂辉石的增多导致材料致密度下降。     

CaF2含量对熔融态高炉渣微晶玻璃析晶及性能的影响

利用液态高炉渣为主要原料,采用熔融法制备了微晶玻璃.借助DSC、XRD、SEM等分析测试方法研究了CaF2含量对高炉渣微晶玻璃析晶及性能的影响.试验结果表明,CaF2能够有效降低微晶玻璃的形核析晶温度,促进微晶玻璃析晶.微晶玻璃中晶体含量随着CaF2含量的增加而增加.当CaF2含量小于4％时,微晶玻璃的晶相为透辉石、普通辉石和钙镁黄长石;当CaF2含量大于4％时,析出了新晶相枪晶石.最终确定CaF2的最佳添加量为6％,此时微晶玻璃结晶度高,平均晶粒粒度100 nm,体积密度2.81 g/cm3,吸水率0.04％,耐酸腐蚀性98.92％,耐碱腐蚀性99.98％,抗弯强度173.41MPa.     

SiO2/MgO摩尔比对MgO-Al2O3-SiO2微晶玻璃析晶和晶相转变的影响

采用熔融法制备了MgO–Al_2O_3–SiO_2(MAS)微晶玻璃,研究了SiO_2/MgO摩尔比对MAS微晶玻璃析晶和晶相转变的影响。结果表明:微晶玻璃初晶相为亚稳Mg_(0.6)Al_(1.2)Si_(1.8)O_6相,终晶相为堇青石相,随晶化温度升高,Mg_(0.6)Al_(1.2)Si_(1.8)O_6向堇青石相转变。SiO_2/MgO摩尔比对微晶玻璃析晶过程影响显著,随SiO_2/MgO摩尔比从2.5增加至3.6,晶相转变开始温度从1 000℃升高到1 150℃,晶相转变结束温度从1 050℃升高到1 180℃,Mg_(0.6)Al_(1.2)Si_(1.8)O_6相热稳定性提高,堇青石相析晶难度增大,晶相转变过程变慢。当SiO_2/MgO摩尔比为3.6时,1 080℃晶化后的微晶玻璃Vickers硬度达到最大10.4 GPa。     

Influence of Nano-Nd2O3 on Crystallization Mechanism of Fused Quartz

The isothermal crystallization kinetics of pure fused quartz of blank specimen N- 0 and specimen N- 3 in troduced with 3 mass% nano-Nd2O3 was researched by means of XRD and Avrami equation. The results show that crystallization mechanisms of fused quartz in two specimens are both heterogeneous nucleation type caused by surface structure defects,and the grain growth mode of two specimens are both two-dimensional growth ac companied by one-dimensional and three-dimensiona growths,specimen N- 3 has the higher degree of grain growth in one-dimensional and three-dimensional than specimen N- 0; introducing nano-Nd2O3 can obviously reduce the "active nucleation sites"of glass structure on the fused quartz particles surface,enhance the stability o glass structure,increase the activation energy of fused quartz crystallization from 874 k J · mol- 1to 1 270 k J·mol- 1,and decrease the crystallization rate of fused quartz obviously.     

Crystallization of zeolite L from Na2O-K2O-Al2O3-SiO2-H2O system

Zeolite L powder was prepared from the substrate mixture of Na₂O-K₂O-Al₂O₃-SiO₂-H₂O system at temperatures of 373-443 K. In order to investigate the factors which influence the synthesis outcome, a reference system which yields zeolite L in a reproducible manner was chosen and subjected to controlled changes in synthesis parameters. The crystalline zeolite L samples obtained were characterized by elemental chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). It was established that phase purity, morphology, and the size of crystals of crystalline product were affected by molar ratios of the substrate, such as SiO₂/Al₂O₃, (K₂O+Na₂O)/SiO₂, Na₂O/(K₂O+Na₂O), and H₂O/(K₂O+Na₂O). Amorphous silica powder (Zeosil) was the preferred silica source, and the crystallization rate was promoted by introducing gel aging, seeding, and rapid heating rate.     

Preparation and characterization of Cr2O3-TiO2-Al2O3-V2O5 green pigment

Green pigments with high near infrared reflectance based on a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition have been synthesized. Cr₂O₃ was used as the host component and mixtures of TiO₂, Al₂O₃ and V₂O₅ were used as the guest components. TiO₂, Al₂O₃, and V₂O₅ were mixed into 39 different compositions. The spectral reflectance and the distribution of pigment powder were determined using a spectrophotometer and a scanning electron microscope, respectively. It was found that a pigment powder sample S9 with a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition of 80, 4, 14 and 2 wt%, respectively, gives a maximum near infrared solar reflectance of 82.8% compared with 49.0% for pure Cr₂O₃. The dispersion of pigment powders in a ceramic glaze was also studied. The results show that the pigment powder sample S9 is suitable for use as a coating material for ceramic-based roofs.     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

Microstructure, electrical properties, and aging behavior of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-Er2O3 varistor ceramics

The microstructure, electrical properties, and aging behavior of the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃-Er₂O₃ varistor ceramics were investigated for different contents of Er₂O₃. The microstructure consisted of ZnO grain and an intergranular layer (Pr, Y, and Er-rich phases) as a secondary phase. The increase of Er₂O₃ content decreased the average grain size and increased the sintered density. As the Er₂O₃ content increased, the breakdown field increased from 4206 V/cm to 5857 V/cm and the nonlinear coefficient increased from 32.6 to 48.6. The varistor ceramics added with 1.0 mol% Er₂O₃ exhibited excellent stability by exhibiting −0.2% in the variation rate of the breakdown field and −2.7% in the variation rate of the nonlinear coefficient for aging stress of 0.95 E_1 mA/150 °C/24 h.     

Sodium impurities in ZnO-Bi2O3-Sb2O3 based varistors

Sodium impurities are frequently present in the raw oxides that constitute the complex formulation of ZnO-Bi₂O₃-Sb₂O₃ based varistors. But actually little is known about their effect on the microstructure and the electrical response of these materials. This is the main goal of the present contribution and according to the obtained results an excessive presence of this alkaline impurity can lead to a compositional change in the Bi-rich skeleton of the varistor microstructure. As a consequence the grain growth kinetics, the densification rate and the characteristic non-linear I-V response of these electroceramics are seriously affected.     

Yb2O3 and Y2O3 co-doped zirconia ceramics

A suspension stabilizer-coating technique was employed to prepare x mol% Yb₂O₃ (x = 1.0, 2.0, 3.0 and 4.0) and 1.0 mol% Y₂O₃ co-doped ZrO₂ powder. A systematic study was conducted on the sintering behaviour, phase assemblage, microstructural development and mechanical properties of Yb₂O₃ and Y₂O₃ co-doped zirconia ceramics. Fully dense ZrO₂ ceramics were obtained by means of pressureless sintering in air for 1 h at 1450 °C. The phase composition of the ceramics could be controlled by tuning the Yb₂O₃ content and the sintering parameters. Polycrystalline tetragonal ZrO₂ (TZP) and fully stabilised cubic ZrO₂ (FSZ) were achieved in the 1.0 mol% Y₂O₃ stabilised ceramic, co-doped with 1.0 mol% Yb₂O₃ and 4.0 mol% Yb₂O₃, respectively. The amount of stabilizer needed to form cubic ZrO₂ phase in the Yb₂O₃ and Y₂O₃ co-doped ZrO₂ ceramics was lower than that of single phase Y₂O₃-doped materials. The indentation fracture toughness could be tailored up to 8.5 MPa m^1/2 in combination with a hardness of 12 GPa by sintering a 1.0 mol% Yb₂O₃ and 1.0 mol% Y₂O₃ ceramic at 1450 °C for 1 h.     

Crystal structure and properties of Al2O3-Cr2O3 solid solutions with different Cr2O3 contents

To enable the comprehensive application of Al₂O₃-Cr₂O₃ solid solutions, the crystal structures and properties of Al₂O₃-Cr₂O₃ solid solutions with different Cr₂O₃ contents were studied. It was observed that Al₂O₃ and Cr₂O₃ form a complete substitutional solid solution over the entire composition range at 1650 °C, with no compounds being formed. Lattice parameters “a” and “c” both increase linearly with an increase in the Cr₂O₃ content. The doping of the Cr³⁺ ions causes a more severe lattice strain in the c-axis direction. The diffraction angles of the diffraction peaks decrease in a linear manner with the increase in the Cr₂O₃ content. The relationship between the theoretical density of the solid solution and the Cr₂O₃ content could be fitted using a second-order polynomial. It was also observed that the linear expansion coefficient of the solid solutions decreases with an increase in the Cr₂O₃ content.     

Crystallization behaviour and properties of BaO-CaO-B2O3-SiO2 glasses and glass-ceramics for LTCC applications

The influence of BaO content (up to 15?mol%) on the crystallization behaviour, structure, thermal properties and microwave dielectric properties of the BaO-CaO-B₂O₃-SiO₂ glasses and glass-ceramics system was investigated. The glasses were produced by melting at 1400?°C and quenching into water, and the glass-ceramics were produced via heat treatment at temperatures between 750 and 800?°C. The results of X-ray diffraction analysis showed that increasing the BaO content raised the resistance of the glass against crystallization and favoured the transformation of β-CaSiO₃ and α-CaSiO₃ phases, which crystallized in the Ba-free and in low BaO content compositions, into SiO₂ and Ba₄Si₆O₁₆, which crystallized in compositions with higher concentrations of BaO. The BaO content had little influence on the glass transition temperature (T_g) and the linear coefficient of thermal expansion (CTE), but strongly reduced the softening point (T_s). Even the addition of BaO as minor additives resulted in a dramatic reduction of the T_s; for example, the T_s decreased from 902?°C for the Ba-free composition to 682?°C for the BaO-containing one (5%). Low values of the dielectric constant (5.9?≤?ε_r ≤?6.63) and dielectric loss (1.12?×?10^?3 ≤?tanδ?≤?3.15?×?10^?3) were measured.     

Phase stability and electric conductivity of Er2O3-Nb2O5 co-doped Bi2O3 electrolyte

Two oxides, Er₂O₃ and Nb₂O₃, are used to stabilize delta-phase Bi₂O₃ used as electrolyte of solid oxide fuel cell. Optimization of dopant ratio and total doping concentration (TDC) is determined by X-ray diffraction, and successfully reduce the TDC (Er + Nb) to 10-15 mol.%. Conductivities of different compositions are measured by two-probe method. The results show that highest conductivity appears at the minimum doping concentrations. Phase stability of ENSB samples with Er/Nb ratio of 2/1 and TDC of 10-20 mol.% at 650 °C up to 300 h is analyzed showing two newly formed (alpha- and gamma-) phases in the samples. Degradation of conductivity at 650 °C is studied in detail by DTA and TEM. The abnormity of lattice contraction of delta-phase is discussed.