Fe2O3含量对SiO2-Al2O3-MgO-F系微晶玻璃析晶特征的影响

为研究Fe2O3含量对SiO2-Al2O3-MgO-F系微晶玻璃析晶特征的影响,采用高温熔融法制备不同Fe2O3含量的基础玻璃,利用差示扫描量热仪(DSC)、x射线衍射(XRD)及扫描电子显微镜(SEM)分别研究此基础玻璃的热效应、相组成及组织形貌.结果表明:在不同Fe2O3含量的样品中析出的晶相主要有云母、ZrO2莫来石及柱晶石,Fe2O3含量超过0.5;时莫来石相消失.随着Fe2O3含量的增加,云母的析出量逐渐提高,且晶体尺寸逐渐变大.但是当样品中Fe2O3含量超过0.8;时,云母晶体析出量反而减少且晶体尺寸变小.     

CaO-MgO-Al2O3-SiO2-P2O5-(F)微晶玻璃的析晶及特征

采用熔融法制备了不同P2O5及F含量的CaO-MgO-Al2O3-SiO2-P2O5-(F)基础玻璃试样,研究了CaO-MgO- Al2O3-SiO2-P2O5-(F)系微晶玻璃的析晶及特征.结果表明:在CaO-MgO-Al2O3-SiO2-8.0wt;P2O5玻璃中,表面析晶和内部析晶同时存在,析出晶体主要为钙长石(CaAl2Si2O8)相、硅灰石(CaSiO3)和α-磷酸钙(Ca3(PO4)2).玻璃中P2O5含量的提高抑制玻璃的表面析晶,同时促进了玻璃的整体析晶和α-磷酸钙晶体析出.同时添加P2O5和F的玻璃试样以整体析晶为主,析出晶体为块状氟磷灰石和粒状钙长石相.     

SiO2-Al2O3-MgO-F系微晶玻璃的受压析晶

用X射线衍射(XRD)和扫描电子显微镜(SEM)研究了SiO2-Al2 O3-MgO-F系块状玻璃在受压条件下的析晶特征.采用高温熔融法制备基础玻璃,在热处理过程中施加压力制备微晶玻璃.结果表明:样品在热压过程中析出主要晶体为云母相,施加压力对析出晶体的种类影响不大.但是不同阶段施加压力对析出晶体的形态有显著的影响,在核化阶段施压可以形成晶体的定向生长,在晶化阶段施压对晶体的择优生长有较大影响.但是仅在核化阶段施压,卸载后再析晶则会降低晶体择优长大的趋势.     

TiO2和Cr2O3作晶核剂对金矿尾砂微晶玻璃结晶性能的影响

以金矿尾砂为主要原料,方解石、硼砂等为添加原料,采用熔融法制备CaO-Al2O3-SiO2系微晶玻璃.采用X射线衍射分析(XRD)、差热分析(DSC)、扫描电镜(SEM)等分析手段对所制备样品进行性能测试与结构表征,研究了TiO2和Cr2O3对金矿尾砂微晶玻璃结晶性能的影响.结果表明,以2; TiO2为晶核剂,金矿尾砂微晶玻璃只有表面析晶,晶相从表面向内部生长;以4; TiO2为晶核剂,样品内部析出少量团聚晶体;以2; Cr2O3为晶核剂,样品内部析出少量团聚粒状晶体;以2; TiO2和2; Cr2O3为复合晶核剂,样品内部析出大量均匀分布的颗粒状晶体,极大地提高了金矿尾砂微晶玻璃的整体析晶能力,主晶相为透辉石(CaMgSi2O6),次晶相为钙长石(CaAl2Si2O8).     

基础成分配比对白云鄂博尾矿微晶玻璃结构及性能的影响

以白云鄂博二次选后尾矿和粉煤灰为主要原料,采用熔融法制备得到了CaO-MgO-Al2O3-SiO2系尾矿微晶玻璃.制备流程包括熔融、退火、核化及晶化过程.其中玻璃熔融温度为1450℃,核化温度为720℃,晶化温度为850℃.利用XRD研究了基础玻璃成分配比对微晶玻璃结构的影响.结果表明基础玻璃成分配比直接决定微晶玻璃的主晶相形成.随着基础玻璃成分配比的变化,微晶玻璃可能形成辉石相、钙长石相、镁铁尖晶石相或磁铁矿相.当其他元素固定,CaO/MgO和CaO/Al2O3比值的减小会导致微晶玻璃由辉石相转变为镁铁尖晶石相和钙长石相.而当SiO2/CaO比值大于2时,主晶相则由辉石相转变为磁铁矿相.DTA测试结果表明CaO有利于析晶温度的降低,而MgO、Al2O3和SiO2相对提高了析晶温度.力学性能测试表明抗折强度、密度、耐酸碱度与微晶玻璃主晶相有直接关系.主晶相为辉石相的微晶玻璃具有更高的抗折强度、密度和耐酸性.     

Fe2O3掺杂对MgO-Al2O3-SiO2系玻璃析晶和性能的影响

采用高温熔融法和两步法微晶热处理制备了MgO-Al2O3-SiO2系堇青石微晶玻璃和铁尖晶石微晶玻璃.利用DSC分析、X射线衍射、FTIR和扫描电子显微镜等手段研究了Fe2O3对玻璃的析晶性能、显微结构和物理性能的影响.结果表明,Fe2 O3的加入可有效降低析晶活化能,促进晶体的析出.当Fe2O3含量达到7.44;时,主晶相由堇青石变为铁尖晶石.Fe2O3掺杂使样品的介电常数由3.2增大至5.8、热膨胀系数由1.941× 10-7增大至7.74×10-6、维氏硬度由7.131GPa增大至11.655 GPa,同时介电损耗由0.05降低至0.015.     

P2O5对CaO-MgO-Al2O3-SiO2系微晶玻璃析晶的影响

采用熔融法制备了不同P2O5含量的CaO-MgO-Al2O3-SiO2玻璃样品,研究了P2O5对该系微晶玻璃析晶的影响规律.结果表明:在所研究的CaO-MgO-Al2O3-SiO2玻璃中,P2O5的最大溶解量在10.0;质量分数左右,超过其饱和溶解度后将析出α-磷酸钙相.玻璃中添加4.0;质量分数P2O5时以表面析晶为主,析出晶体为钙长石和少量硅灰石.随着P2O5含量的提高, α-磷酸钙逐渐析出,同时钙长石和硅灰石的析出逐渐降低.进一步提高P2O5含量抑制了玻璃的表面析晶,促进了玻璃的分相和整体析晶.当P2O5的含量达到10;时,玻璃以整体析晶为主,在分相区内外区域析出晶体的形态非常相似,均呈现为细小粒状.     

复合晶核剂对黄磷炉渣微晶玻璃析晶的影响

以黄磷炉渣为主要原料,通过添加不同种类的复合晶核剂,采用熔融法制备了黄磷炉渣微晶玻璃.借助化学热力学软件FactSage 6.4模拟计算晶相类型,借助Kissinger方程分析析晶能力,利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)进行验证.结果表明:相比添加单一晶核剂TiO2,复合晶核剂TiO2+CaF2或复合晶核剂TiO2+P2O5均能够降低黄磷炉渣基础玻璃的析晶活化能E,促进其析晶,复合晶核剂TiO2+Cr2O3能够提高黄磷炉渣基础玻璃的析晶活化能E,抑制其析晶;无论添加单一晶核剂TiO2,还是添加复合晶核剂TiO2+CaF2、复合晶核剂TiO2+P2O5或复合晶核剂TiO2+Cr2O3,黄磷炉渣微晶玻璃晶相类型相同,主晶相为硅灰石(CaSiO3),副晶相为铝透辉石(Ca(Mg,Al)(Si,Al)2O6)和氟磷灰石(Ca5(PO4)3F),这与化学热力学软件FactSage 6.4模拟计算结果基本一致.     

晶核剂对锂锌硅系微晶玻璃析晶及显微结构的影响

采用差热分析方法研究了LZS系玻璃陶瓷的析晶动力学,讨论了晶核剂对微晶玻璃的晶相、显微结构及析晶动力学参数的影响.结果表明:与TiO2相比,P2O5能够更加有效地促进玻璃析晶,但两者效果相差不大.使用不同的晶核剂不会影响玻璃析出的晶相,但使用P2O5作为晶核剂能得到均匀细小的晶体.     

高热膨胀Na2O-MgO-Al2O3-SiO2微晶玻璃的制备及性能研究

采用传统熔体冷却法制备了Na2O-MgO-Al2 O3-SiO2玻璃并采用整体析晶工艺制备了微晶玻璃.利用DSC、XRD、SEM等测试手段研究了微晶玻璃的析晶行为和显微结构,探讨了热处理制度对该体系微晶玻璃热膨胀系数、密度、抗弯强度、显微硬度等性能的影响.研究结果表明,当晶化温度为800℃时该体系微晶玻璃主晶相为颗粒状霞石晶体(NaAlSiO4);当晶化温度达到900℃时玻璃中开始析出镁橄榄石(Mg2SiO4)晶体;延长保温时间可显著促进析晶但对晶体种类没有影响.析晶后微晶玻璃的密度、热膨胀系数、抗弯强度和显微硬度值显著增加,其最高热膨胀系数可达14.1×10-6℃-1.所制备的微晶玻璃具有很好的机械性能,当热处理温度为1000℃时,其抗弯强度和显微硬度分别达160 MPa和7.8 GPa.     

Phase segregation of non-stoichiometric aluminosilicate gels characterized by Al and Si MAS-NMR

Polymeric aluminosilicate gels with Al₂O₃/SiO₂ molar ratios of 1.3/2, 2.5/2, 3/2 and 4.7/2 were prepared by gelling a mixture of tetraethoxysilane and ethyl acetoacetate aluminium diisopropoxide. Mullite, without any other crystalline phase, directly crystallizes from the gel matrix at about 1000 °C for all investigated samples. The Al₂O₃ or SiO₂ crystalline phase can only be detected at relatively high temperatures accompanying the modification of mullite in the lattice structure. ²⁷Al and ²⁹Si MAS-NMR studies indicate that segregation of Al and Si atoms occurs in all samples below 900 °C in the amorphous state, regardless of the gel composition. However, the species of segregated units are very different and strongly dependent on the composition of the starting gels. This segregation may not cause the exothermic effect in differential thermal analysis examination, but it appears to be responsible for the composition change behavior of crystalline mullite with different heat treatment.     

New evidence for tetrahedral triclusters in aluminosilicate glasses

The formation of thermodynamically stable 3/2-mullite (3 Al₂OAl₃·2 SiO₂) was investigated by scanning electron microscopy using reaction couples consisting of 2/1-mullite (2 Al₂O₃·1 SiO₂) plus SiO₂ glass, or Na₂O-SiO₂ glass, respectively. The mullite substrates were partially dissolved, thus leading to Al incorporation in the siliceous phases. In both reaction couples thin layers of stoichiometric 3/2-mullite form on the 2/1-mullite substrates. However, the major mullitization steps are different: The 2/1-mullite/SiO₂ reaction couple gives rise to 3/2-mullite crystallization within the bulk of the glass, whereas epitactic growth of c-axis orientated 3/2-mullite needles on the 2/1-mullite substrate was observed in the presence of Na₂O-SiO₂ glass. The differences in mullite nucleation were attributed to the existence or non-existence of tetrahedral triclusters in the as-reacted non-crystalline Al₂O₃-SiO₂ and Na₂O-Al₂O₃-SiO₂ phases, respectively. Triclusters of (Si,Al)O₄-tetrahedra in the Al₂O₃-SiO₂ glass may act as nuclei for 3/2-mullite crystallization in the bulk of the glass since these structural units also occur in mullite. In Na₂O-Al₂O₃-SiO₂ glasses triclusters are absent, and epitactical 3/2-mullite formation on the mullite substrate becomes more favorable energetically.     

Crystallization kinetic of glass particles prepared from a mixture of coal ash and soda-lime cullet glass

The crystallization capability of a parent glass made from a mixture of coal ash (40 wt%) and soda-lime glass was investigated using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy. Different glass particle size distributions were considered in the range 20-500 μm. Two crystallization exotherms in DTA were attributed to the formation of both pyroxenes (diopside Ca(Mg,Al)(Si,Al)₂O₆ and augite Ca(Mg,Fe)Si₂O₆) and plagioclase (Na,Ca)(Si,Al)₄O₈. These phases were confirmed by XRD analyses. Analysis of non-isothermal DTA data yielded values of 545 kJ/mol and 1.8 for the activation energy of crystallization and the Avrami exponent, respectively. This value for the Avrami exponent was consistent with a decreasing nucleation rate and the observed dendritic morphology. The data on crystallization kinetics obtained in this study are relevant for the production of glass-ceramic materials by a sintering/crystallization method from powder compacts made of this parent glass.     

Determination of the influence of TiO2 on the elastic properties of a mica based glass ceramic by ultrasonic velocity measurements

The influence of small amount (1 or 2 wt%) of TiO₂ additions and crystallization heat treatment on the elastic properties of a mica based glass ceramic have been investigated by ultrasonic velocity measurements. The mica based glass ceramic was prepared through controlled crystallization of a glass in the SiO₂, Al₂O₃, CaO, MgO, K₂O and F system. Evidences of TiO₂ acting as a nucleating agent in this system was demonstrated. The longitudinal and transversal wave velocities of the as-prepared glass and the mica based glass ceramic were measured by using 5 MHz probes at room temperature. Elastic properties namely; longitudinal modulus, Young’s modulus, bulk modulus, and shear modulus were calculated from the ultrasonic velocity values measured and density values obtained experimentally. It has been observed that small amount of TiO₂ additions caused a notable but not significant; however, the crystallization heat treatment had a profound effect on the elastic properties of the glass in the system studied.     

Phase separation and crystallization in amorphous Pd-Si-Sb

It is found that replacing some of the Si in a Pd-Si-Sb glass with Sb can make it more resistant to crystallization than the pure binary material. This is shown by the calorimetric results, in which the crystallization temperature increases and the glass temperature decreases with increasing Sb substitution, and also by the finding that certain alloys, such as Pd_80.5 Si_16.5Sb₃ may be quenched into amorphous rods (by the gradient-quench method) up to 0.5 mm thick.

Calorimetry and small-angle X-ray scattering data show that certain alloys in this system phase separate in the amorphous state. The two phases thus produced independently crystallize. Isothermal measurements indicate that the rate of crystallization of one of the phases is interface-limited, with most nuclei initially present. The other crystallization process does not fit an Avrami law, possibly due to a transformation of the crystalline phase.

A method called “gradient-quenching” (GQ) was used to prepare samples from the melt in such a way that the quench-rate was non-uniform, so all stages of crystallization in slowly-quenched alloys are displayed. Nucleation was frequently found to take place on voids and inclusions.

The use of the calorimetric and GQ methods in conjunction to gather information about crystallization processes in metallic glasses is discussed.     

The thermal evolution of metakaolin geopolymers: Part 2 – Phase stability and structural development

The structural evolution of a systematic series of geopolymers derived from metakaolin is explored. The onset temperature of crystallization, phase composition and densification of the specimens in the current work are determined by quantitative XRD, FTIR and dilatometric analyses. Alkali cation is observed to have no significant effect on the onset temperature of crystallization and quantity of crystalline phase developed in geopolymers, though the phase composition of NaK- and K-geopolymers is more complex than Na-geopolymers, as is expected from phase diagrams. The amount of crystalline phase decreases in all systems with increasing Si/Al ratio, which is proportionally related to the extent of densification observed in Part 1 of the work. Despite similar phase composition of all geopolymers, the onset temperature of densification is observed to be higher in all K-geopolymers compared to the NaK- and Na-specimens of analogous Si/Al ratio. It is proposed that the increase in densification temperature is due to the increase in gel viscosity of K-geopolymer compared to Na- and NaK-geopolymers. The effect of heating rate on the densification mechanisms of geopolymers is analyzed, showing that the amount of crystalline phase and gel viscosity of geopolymers are critical in determining the extent of shrinkage during densification.     

Crystallization of the amorphous phase and martensitic transformations in multicomponent (Ti,Hf,Zr)(Ni,Cu)-based alloys

Shape memory materials with specific microstructure can be obtained from amorphous precursors. Rapidly solidified amorphous and crystalline–amorphous ribbons have been produced by planar flow casting for a number of multicomponent TiNi-based alloys of pseudobinary 50:50 and 55:45 compositions with substitutions of Zr, Hf, Nb for Ti and Cu, Co, Pd, Ag, Al for Ni. The glass transition and crystallization behavior of the amorphous phase as well as the martensitic transformations in the crystallized materials have been studied by differential scanning calorimetry. To control the crystal structure at different stages of crystallization, X-ray diffractometry and transmission electron microscopy were used. The effects of crystallization conditions and the resulting microstructural state on the martensitic transformation characteristics have been investigated. The transformation temperature intervals are shown to depend on the mean size of the parent phase crystals.     

Mechanism of crystallization of fast fired mullite-based glass–ceramic glazes for floor-tiles

The mechanism of crystallization from a B₂O₃-containing glass, with composition based in the CaO–MgO–Al₂O₃–SiO₂ system, to a glass–ceramic glaze was studied by different techniques. Glass powder pellets were fast heated, simulating current industrial tile processing methods, at several temperatures from 700 to 1200 °C with a 5 min hold. Microstructural study by field emission scanning electron microscopy revealed that a phase separation phenomenon occurred in the glass, which promoted the onset of mullite crystallization at 900 °C. The amount of mullite in the glass heated between 1100 and 1200 °C was around 20 wt%, as determined by Rietveld refinement. The microstructure of the glass–ceramic glaze heated at 1160 °C consisted of interlocked, well-shaped, acicular mullite crystals longer than 4 μm, immersed in a residual glassy phase.     

莫来石轻质球形料结构与性能

对以铝矾土为主要原料制备获得的莫来石轻质球形料进行了系统的结构与性能研究,研究结果表明:轻质莫来石球形料的主要化学成分为Al2O3和SiO2,物相为莫来石相,球形颗粒表面莫来石柱状结晶交织排布,内部含有大量气孔,堆积密度为1.60 g/cm3,颗粒体积密度为1.75 g/cm3,显气孔率为38;,耐火度大于1790℃,800℃下导热系数为0.245 W/(m· K),热震5次后球形保持率大于95;.     

Structural changes of mullite precursors in presence of polyethyleneimine

Thermal properties of two powders derived from the same calcined gel with a stoichiometric mullite composition (atomic ratio Al/Si =3/1) wet milled in different solutions were studied by simultaneous differential thermal analysis, thermogravimetry and evolved gas analysis (DTA,TG,EGA, respectively), by density measurements and by ²⁹Si MAS NMR spectroscopy and X-ray diffraction (XRD). Calcined gel was milled either in ethanol or in ethanol with the addition of 0.03 g of polyethyleneimine (PEI) per gram of mullite. DTA, TG and mass spectrometry revealed esterification of unhydrated surface of particles formed by milling in ethanol. The difference in the structural evolution of powders and their dependence on annealing temperature seen in ²⁹Si MAS NMR spectra and XRD patterns is attributed to different degrees of segregation of alumina and silica components, and to differing compositions of transitory spinel phase. In both samples the segregation of silica and alumina was observed at temperatures less than that for mullite crystallization. The degree of segregation was much smaller in the sample milled in ethanol. Therefore, in the latter sample spinel with larger silica content incorporated in γ-Al₂O₃ will crystallize by annealing at 900°C, and Al-rich mullite at 1100°C. Due to greater segregation of silica and alumina component in the presence of PEI, the crystallization of spinel with smaller amounts of silica incorporated into γ-Al₂O₃ is shifted to 1100°C, and orthorhombic mullite to about 1200°C. The influence of PEI is indicated by a larger sintering density at lower temperatures.