磁选分离玄武岩熔融体及玻璃的析晶性能研究

攀西某地磁选分离得到的贫磁玄武岩、富磁玄武岩与原矿作为研究对象,玄武岩样品在1 450℃熔融3 h后,通过快速冷却和程序降温冷却,探究了熔融体的析晶性能,发现贫磁玄武岩熔融体的析晶能力明显降低。结合X射线衍射(XRD)和扫描电镜(SEM)及能谱分析知道快速冷却和程序降温冷却熔融体的主要析晶相有赤铁矿及类质同象混晶钛铁矿和镁铁矿和辉石。将熔融体快速冷却到室温制得贫磁玄武岩玻璃、富磁玄武岩玻璃与原矿玻璃,利用差示扫描量热法(DSC)研究了玻璃样品在加热过程中的析晶行为。将玻璃样品分别在915℃、1 100℃和1 155℃进行晶化热处理,通过XRD、SEM及能谱分析发现玻璃在915℃的主要析晶相是赤铁矿、钛铁矿及镁铁矿类质同象混晶和辉石,在1 100℃和1 155℃的主要析晶相是赤铁矿、钛铁矿及镁铁矿类质同象混晶和斜长石。样品中铁含量越高,越容易析晶。研究结果可以为工业生产玄武岩连续纤维提供理论参考。     

玄武岩玻璃析晶性能的研究

以玄武岩纤维生产企业常用的河北玄武岩作为实验材料,用偏光显微镜和X射线衍射(XRD)分析得到其主要矿物组成是斜长石和辉石,伴有铁质及玻璃质、少许石英和绿泥石。通过1450℃高温熔制快速冷却制成玄武岩玻璃,用差示扫描量热法(DSC)研究其析晶动力学。得到玄武岩玻璃在890℃、1 100℃和1 190℃的析晶活化能(E)分别是165.23kJ/mol、352.21 kJ/mol和3 415.34 kJ/mol,主要晶化方式在890℃和1 100℃是体积晶化、1 190℃是表面晶化。对玄武岩玻璃分别在890℃、1100℃和1190℃进行晶化热处理,用XRD和扫描电镜(SEM)及能谱进行分析获得的主要析晶相有镁铁尖晶石相、斜长石相和辉石相,其形态有发育较好的板状微晶,球粒状雏晶、大小不等的粒状雏晶和骸晶及链状的串雏晶。研究结果可以为工业生产玄武岩纤维工艺条件的控制提供理论依据。     

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.     

TiO2对R2O-CaO-MgO-Al2O3-SiO2系微晶玻璃显微结构及性能的影响

用熔融法制备了R2O-CaO-MgO-Al2O3-SiO2系微晶玻璃,采用差示扫描量热法(DSC)、X-射线衍射仪(XRD)、扫描电子显微镜(SEM)等测试方法,研究了TiO2对微晶玻璃显微结构和性能的影响.结果表明,TiO2在热处理过程中有降低基础玻璃成核位垒,促进析晶的作用,TiO2的添加量为4.5％(质量分数)和5.0％时,样品的主晶相为镁橄榄石,次晶相为透辉石和斜顽辉石.随着TiO2添加量的进一步增加,镁橄榄石晶相的衍射峰逐渐减弱,斜顽辉石晶相的衍射峰逐渐增强;TiO2的添加量为5.5％和6.0％时,样品的主晶相为斜顽辉石,次晶相为镁橄榄石和透辉石;样品的力学性能有先增大后稳定的趋势,抗弯强度最大为87.08 MPa,显微硬度最大为7.16 GPa.     

碱土金属氧化物含量对模拟高放废液玻璃固化体析晶行为的影响

以硼硅酸盐玻璃作为基础玻璃基材,通过熔融法制备了含16%(质量分数)模拟高放废液的玻璃固化体,探究了碱土金属氧化物含量对玻璃固化体析晶行为的影响,以期在保证玻璃固化体性能要求的前提下,通过控制碱土金属氧化物的含量抑制玻璃固化体的析晶倾向。结果显示:碱土金属氧化物(CaO+MgO+BaO)含量在7%~19%(质量分数)时,玻璃固化体析晶上限温度和析晶率随碱土金属氧化物含量的降低而逐渐降低;玻璃网络聚合度的增加能够显著增强玻璃固化体的抗析晶性能,当碱土金属氧化物含量低于11%(质量分数)时玻璃固化体中硫酸盐的溶解度明显下降。基于包容0.7%(质量分数)SO₃的要求,碱土金属氧化物含量适宜组成应控制在11%(质量分数)以上。     

利用垃圾焚烧飞灰电弧炉熔渣制备微晶玻璃

垃圾焚烧飞灰电弧炉熔渣经核化、晶化两步处理制备微晶玻璃,采用差热分析法研究了基础玻璃的晶化行为,考察了晶化时间对微晶玻璃微观结构及理化特性的影响。结果表明:基础玻璃的晶化指数为1.48,以表面析晶为主,其最佳热处理制度为:核化温度679℃、核化时间1.5h、晶化温度985℃、晶化时间1.5h。微晶玻璃的主晶相为透辉石Ca(Mg,Al)(Si,Al)_2O_6和少量普通辉石Ca(Mg,Fe,Al)-(Si,Al)_2O_6,在最佳热处理条件下制得的微晶玻璃具有较高的抗弯强度、硬度、韧性及耐酸碱性等性能,有替代天然建材的潜力。     

钙硅比对钙铁硅铁磁体微晶玻璃核化与晶化的影响

为了研制用作温热治疗癌症的铁磁体微晶玻璃热种子材料,制备了一组化学组成为40Fe2O3xCaO(60-x)SiO23B2O33P2O5玻璃(x=20、25、30、35质量分数),用XRD、DTA、VSM对其核化与晶化过程进行了研究.研究发现,钙铁硅微晶玻璃在还原气氛下热处理后,除了磁铁矿和硅灰石及少量赤铁矿晶相外,还会出现钙铁辉石、方石英晶相.钙硅比较小的玻璃,热处理温度-时间相图中钙铁辉石相区范围较大;钙硅比较大的,钙铁辉石相区范围较小.另外,钙硅比不同,玻璃的成核机理、开始析出磁铁矿的温度也不同.     

钙硅比对钙铁硅铁磁体微晶玻璃核化与晶化的影响

为了研制用作温热治疗癌症的铁磁体微晶玻璃热种子材料,制备了一组化学组成为40Fe2O3xCaO(60-x)SiO23B2O33P2O5玻璃(x=20、25、30、35质量分数),用XRD、DTA、VSM对其核化与晶化过程进行了研究.研究发现,钙铁硅微晶玻璃在还原气氛下热处理后,除了磁铁矿和硅灰石及少量赤铁矿晶相外,还会出现钙铁辉石、方石英晶相.钙硅比较小的玻璃,热处理温度-时间相图中钙铁辉石相区范围较大;钙硅比较大的,钙铁辉石相区范围较小.另外,钙硅比不同,玻璃的成核机理、开始析出磁铁矿的温度也不同.     

热处理制度对SiO_2-CaO-Al_2O_3-MgO-ZnO-Fe_2O_3系玻璃陶瓷析晶的影响

为了探讨热处理制度对SiO2-CaO-Al2O3-MgO-ZnO-Fe2O3系玻璃陶瓷析晶的影响,利用高温熔融法制备基础玻璃,并用扫描电子显微镜(SEM)和X射线衍射(XRD)等技术考察玻璃陶瓷的析晶特征。结果表明:在所研究的玻璃体系中析出主晶相为锌橄榄石(Ca2ZnSi2O7),部分氧化锌和氧化铁固溶到硅灰石(CaSiO3)中,形成辉石类晶体(Ca(Fe,Zn)Si2O6)。热处理制度对析出晶体的种类影响不大,但是对析出晶体的形态有较大程度的影响。在随炉升温的情况下,试样表面形成枝状Ca(Fe,Zn)Si2O6晶体,而在内部形成Ca2ZnSi2O7和Ca(Fe,Zn)Si2O6。两种晶体相互交替析出,形成条带状组织。在750℃的保温有利于晶体的整体析出。     

Fe_2O_3对尾矿微晶玻璃析晶及磁学特性影响的机理研究

以白云鄂博尾矿及粉煤灰等固体废弃物为主要原料,利用熔融法制备得到了CAMS系尾矿微晶玻璃,通过DSC、XRD、SEM、TEM及振动样品磁强计等测试手段研究了Fe_2O_3对微晶玻璃析晶及磁学特性的影响规律。结果表明,微晶玻璃的初始形核相为磁铁矿相,随着热处理温度的升高,辉石相在磁铁矿晶核的基础上形成并逐渐生长。富铁微晶玻璃中磁铁矿相和辉石主晶相可同时存在,室温磁滞回线的测试结果表明磁铁矿相直接影响微晶玻璃的磁学特性。     

Transient melt formation and its effect on conversion phenomena during nuclear waste vitrification – HT-ESEM analysis

Although the vitrification of nuclear waste has a decades-long history, numerous opportunities still exist to improve its efficiency and to increase the waste loading in glass. This is especially true for the vitrification of low-activity waste (LAW), which has been historically treated by other immobilization technologies and is less mature than high-level waste (HLW) vitrification. In this work, we address one of the least understood phenomena during the conversion of nuclear waste feeds to glass—the formation of molten salt and transient glass-forming melt. Using high-temperature environmental scanning electron microscopy (HT-ESEM) in combination with X-ray diffraction, thermogravimetry, and evolved gas analysis, we have analyzed the complex chemical reactions and phase transitions as they occur during melting of representative HLW and LAW melter feeds. We evaluated the compositions of amorphous phases and the fractions of salt components, and estimated the fractions of molten salt phases present in the feeds as a function of temperature. We show that the maximum fraction of molten salts is ∼4 % and ∼28 % during HLW and LAW feed melting, respectively, and discuss the possibility of molten salt migration in LAW feeds. We also argue that the presence of significant fractions of molten salt phase can hinder the retention of rhenium (and, hence, radioactive technetium), and discuss how the properties of molten salt phase and transient glass-forming melt are related to primary foam formation and behavior. Finally, we summarize key unanswered questions requiring further research to increase the understanding of the conversion process and enhance the nuclear waste vitrification efficiency.     

Melter feed viscosity during conversion to glass: Comparison between low‐activity waste and high‐level waste feeds

During nuclear waste vitrification, a melter feed (a slurry mixture of a nuclear waste and various glass forming and modifying additives) is charged into the melter where undissolved refractory constituents are suspended together with evolved gas bubbles from complex reactions. Knowledge of flow properties of various reacting melter feeds is necessary to understand their unique feed‐to‐glass conversion processes occurring within a floating layer of melter feed called a cold cap. The viscosity of two low‐activity waste (LAW) melter feeds were studied during heating and correlated with volume fractions of undissolved solid phase and gas phase. In contrast to the high‐level waste (HLW) melter feed, the effects of undissolved solid and gas phases play comparable roles and are required to represent the viscosity of LAW melter feeds. This study can help bring physical insights to feed viscosity of reacting melter feeds with different compositions and foaming behavior in nuclear waste vitrification.     

TiO2加入量对高炉渣微晶玻璃析晶的影响

以高炉渣微晶玻璃为研究对象,改变配料中晶核剂TiO2的含量,制得微晶玻璃样品. 以不同的升温速率对样品进行差热分析,根据升温速率和差热分析曲线上的晶化峰温度,采用3种不同的方法计算微晶玻璃样品的析晶活化能. 结果表明,随着TiO2含量的增加,析晶活化能呈现出先减小后增大的趋势,在TiO2的加入量为3.1%时,微晶玻璃的析晶活化能最低,此时拟合出的3种析晶活化能最小值分别为135.7, 143.9, 151.7 kJ/mol. 样品的红外谱图表明,TiO2的含量为3%~4%时析出晶体较多. TiO2含量为3%和4%的样品的X射线衍射图谱表明,样品中析出了以透辉石为主晶相、金红石为次晶相的晶体.     

Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3

The effect of Y₂O₃ on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO–30B₂O₃–10SiO₂ glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies E_g calculated by using both Kissinger and Moynihan model decrease from 668?kJ/mol to 573?kJ/mol for Kissinger model, and 682?kJ/mol to 587?kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6?mol%. And the glass crystallization kinetics parameters, crystallization activation energy E_c and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58?kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6?mol% yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO–30B₂O₃–10SiO₂ glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893?K and 993?K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.     

Crystallization of Titanosilicate Glasses for Nuclear Waste Immobilization

The effects of different cooling and reheating rates on the phase constitutions of Na₂O–Al₂O₃–TiO₂–SiO₂ glass-ceramics containing up to 20 wt% of simulated nuclear fuel recycle waste have been studied using X-ray diffraction, differential thermal analysis, and scanning and transmission electron microscopy. The metastable formation of a perovskite-structured phase (nominally CaTiO₃, but containing ionic substituents) was observed in samples with up to 15 wt% of simulated waste after cooling from the melt at rates between 0.25 and 50°C/min. When the partially devitrified glass was reheated to 1050°C, incomplete conversion of this phase to sphene (nominally CaTiSiO₅) occurred by reaction with the silica-rich glass matrix. The conversion was completed by heating further to 1150°C. Waste loadings ⋝10 wt% produced crystallization of powellite (nominally CaMoO₄) in addition to sphene and perovskite, whereas metastable perrierite (a rare-earth titanosilicate) was also crystallized at waste loadings ⋝15 wt%. New data on elemental partitioning between the crystalline and vitreous phases confirmed earlier results obtained in different atmospheres and with simplified waste compositions and were largely in accord with crystal-chemical predictions.     

Polyphase Ceramic for Consolidating Nuclear Waste Compositions with High Zr-Cd-Na Content

The development of dense polyphase tailored ceramic forms for the immobilization of high-level nuclear wastes has been extended to an Idaho Chemical Processing Plant Fluorinel composition. The ceramic was designed to maximize waste loading and subsequent waste volume reduction without sacrificing chemical durability in aqueous environments. The ceramic, fabricated by hot isostatic pressing, consists of four main crystalline phases, calcium fluoride, zirconia, an apatite-structured solid-solution phase, and sphene. The form also contains a designed borosilicate glass phase, a Ni-Cd alloy, and a minor amount of crystalline zircon. The crystalline apatite solid-solution phase is the major host for incorporating the actinide simulants U, Ce, and Y, while the glass phase contains Cs and Sr. The calcium fluoride and sphene phases provide microstructural isolation of the radionuclide-containing phases. Since the glass and crystalline components of the ceramic are not phase compatible at all temperatures, the exact phase content is determined by the tailoring additives, consolidation temperature, and oxidation state control during processing. The simulated HLW ceramic has a density of 3.3 g/cm³ at a waste loading of 73 wt%.     

耐磨微晶玻璃的组成与晶化特性的研究

探讨制备耐磨微晶玻璃的成分范围及主晶相和晶核剂的选择，在此基础上，采用DTA，XRD，SEM等测试手段分析了材料的晶化动力学、晶相和显微结构。所得到的微晶玻璃的主晶相为透辉石，其组织致密、结构均匀、晶粒尺寸在100nm左右。该材料具有优良的晶化特性，析晶活化能为E=78.81kJ／mol，晶体生长指数为3.01。对该材料与高铝瓷的耐磨性进行了比较，其耐磨性是90％Al2O3瓷球的1．5倍。     

Differential Thermal Analysis on the Crystallization Kinetics of K2O-B2O3-MgO-Al2O3-SiO2-TiO2-F Glass

The crystallization kinetics of a glass based on one type of mica, NaMg₃AlSi₃O₁₀F₂, with the addition of a nucleating agent, TiO₂, has been studied using differential thermal analysis (DTA) under both isothermal and nonisothermal conditions. Two distinct crystallization exotherms in the DTA curve are observed and resolved that correspond to the initial formation of magnesium titanate (MgTi₂O₅) and the later formation of mica. The activation energy for precipitation of each crystalline phase has been evaluated, and the crystallization mechanism has been studied. The results indicate that the growth of mica is a two-dimensional process, controlled by the crystal-glass interface reaction. The average calculated values of activation energies are 256 ± 11 kJ/mol and 275 ± 6 kJ/mol for the precipitation of MgTi₂O₅ and mica from the glass matrix, respectively.     

Crystallization Kinetics and Phase Development of PbO–BaO–SrO–Nb2O5–B2O3–SiO2-Based Glass–Ceramics

The nucleation and crystallization kinetics of PbO–BaO–SrO–Nb₂O₅–B₂O₃–SiO₂-based glass–ceramics have been investigated. Strontium barium niobate (Sr_0.33Ba_0.67Nb₂O₆) with a tetragonal tungsten–bronze structure formed as the major crystalline phase, which nucleates and grows on the surface region of samples. The results of the present study showed an apparent activation energy of 193 kJ/mol for nucleation, which was controlled by the viscous flow of the glass. Quantitative X-ray analysis and differential thermal analysis showed that the rate-limiting mechanism of crystallization appeared to be a three-dimensional interfacial growth, which has an apparent activation energy of 386–430 kJ/mol, a value that is close to the dissociation of Si–O bonds in the glass system.