Effect of ZnO content on the physical,mechanical and chemical properties of glass-ceramics in the CaO–SiO2–Al2O3 system

The objective of this study was to evaluate the effect of ZnO content on the physical, mechanical and chemical properties of CaO–Al₂O₃–SiO₂ (CAS) glass-ceramics produced from Colombian wastes, such as fly ash, granulated blast furnace slag and glass cullet. The CaO/SiO₂ molar ratio of the mixtures was held constant (0.36). ZnO was added to the mixtures in proportions of 4, 7 and 10 wt%. The glass-ceramics were produced by the controlled crystallization of a parent glass. The values of crystallization temperature (T_p) show a fall up to 7 wt% and then shoots up with 10 wt% concentration of ZnO, but in general, ZnO addition lowers the temperature required for the formation of crystalline phases. In general, anorthite (CaAl₂Si₂O₈) is the main phase observed in all heat treated samples, in addition to albite (Na(AlSi₃O₈)) and labradorite (Na_0.45 Ca_0.55 Al_1.55 Si_2.45 O₈). The crystalline phases hardystonite (Ca₂ZnSi₂O₇) and willemite (Zn₂SiO₄) were also identified in the samples with 7 and 10 wt% ZnO. The densities of the glass-ceramics were between 2658 and 2848 kg/m³, and it was found that ZnO helps to increase the density of glass-ceramics. The elastic modulus was in the 100–105 GPa range, the fracture toughness was between 0.45 and 0.64 MPa m^1/2, and the Vickers microhardness was between 632 and 653 MPa. With regards to the durability, the weight loss of the glass-ceramics immersed in alkaline solution (NaOH) did not exceed 1.5 wt% after immersion for 6 h at 80 °C. The results of this study confirm that the vitrification process is a favorable option to utilize these industrial wastes.     

NCAS系统玻璃陶瓷烧结晶化模型探讨

文章通过ＮＣＡＳ体系尾矿玻璃陶瓷体系设计基础讨论,确定了合理的配方化学组成,进行了烧结晶化实验和动力学分析。从有限结晶体系出发,提出将时间参数引入晶体生长速度公式,结合试验结果,通过数学拟合,得到了晶化率公式ｐ＝３（γ／ｒ）．ａ０．（１－ｅ＾－ｔ）「１－ｅｘｐ（－ΔＧ／ＫＴ）」,可更准确地反映实际玻璃陶瓷体系晶化行为。     

透辉石玻璃陶瓷的制备及其析晶特性研究

以废玻璃粉为原料,采用反应析晶烧结法制备了透辉石玻璃陶瓷。采用差热分析、X射线衍射分析、扫描电镜、能谱、高分辨透射电镜等方法研究了顽辉石-堇青石粉和废玻璃粉混合样品等温烧结过程中顽辉石-堇青石向透辉石转变的演变过程。结果表明:顽辉石-堇青石与玻璃粉在815°C下即可发生反应析晶;900°C保温2 h可获得透辉石为主晶相的玻璃陶瓷。在保温过程中,顽辉石的Mg~(2+)和O~(2-)向玻璃中扩散,玻璃中的Si~(4+)和Ca~(2+)向顽辉石中移动,使顽辉石晶体在b轴方向交替排列的两条链沿c轴方向断开,转变成单链,由Mg~(2+)和Ca~(2+)连接生成透辉石。保温0 h时,由于堇青石[MgO_6]八面体膨胀较小,玻璃中的Si~(4+)、Ca~(2+)、Na~+向堇青石中移动,反应析晶生成钠长石与透辉石;当保温时间延长至2 h时,堇青石[MgO_6]八面体骨架进一步扭曲,生成主晶相为透辉石的玻璃陶瓷。     

微晶玻璃板材工业化生产的探讨

本文探讨烧结成形的微晶玻璃板材的化学成分、原料、工艺流程、生产线设计、合理生产规模、产品成本、工业生产前景.     

过渡相析出对SiO2-Al2O3-MgO-F系玻璃陶瓷析晶的影响

应用Kissinger法研究了过渡相析出对SiO2-Al2O3-MgO-F系玻璃陶瓷析晶动力学的影响。结果表明：过渡相析出后，将促进主晶相的整体析出。根据John-Mehl-Avrami(JMA)方程，得到玻璃结晶转变的反应生长指数n为2，活化能A为214．03KJ．mol^-1。     

高炉渣含量与热处理制度对矿渣微晶玻璃性能的影响

运用DTA、XRD和SEM等现代分析技术对CaO(MgO)-Al2O3-SiO2系矿渣微晶玻璃的核化晶化温度、物相组成和显微结构进行了分析，探讨了高炉渣引入量和热处理制度的影响。试验结果表明，当高炉渣加入量为45wt％时，主晶相为普通辉石(CaSiO3)和透辉石(CaMg(SiO3)2)，材料结构均匀致密，性能良好。本文适宜的热处理工艺参数为：退火温度670℃；核化温度850℃，晶化温度970℃，各保温1h。     

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.     

Glass structure and crystallization via two distinct thermal histories: Melt crystallization and glass crystallization

This study focuses on the effect of structural inhomogeneity of 44.4CaO-33.2SiO₂-8.8Na₂O-6.2Al₂O₃-7.4B₂O₃ glass on its crystallization behavior. The crystallization behavior of the investigated lime-sodium aluminoborosilicate glass system is explored for the two thermal histories of melt crystallization and the heat treatment of quenched glass. The results show that sodium melilite (CaNaAlSi₂O₇) and larnite (β-Ca₂SiO₄) are the dominant crystalline phases during heating (glass crystallization) and cooling (melt crystallization), respectively. In the glass structure from the heat treatment at 610 °C, both Si₂O₇ and AlO₄ units (i.e., four-coordinated Al) are dominant. This may induce sodium melilite (CaNaAlSi₂O₇) crystallization, connecting Si₂O₇ and AlO₄ units with O and linking Ca and Na between interlayers. The melt structure, meanwhile, has more SiO₄ and AlO₆ units in its silicate and aluminate. Therefore, larnite (β-Ca₂SiO₄) crystallizes on cooling by combining SiO₄ units and Ca. The crystallization behavior is further discussed considering the inhomogeneity structure of supercooled liquids before nucleation.     

A novel process of preparing glass-ceramics with pseudo-bioclastic texture

Water quenching-induced cracked-glass was used as parent glass to prepare glass-ceramics in this work. The cracked-glass panel was first heat-treated through two-step method, i.e. sintering for 1 h at 860 °C and subsequent crystallization for 1.5 h at 1080 °C, and then naturally cooled down to room temperature to be transformed into glass-ceramics. XRD and SEM observations confirm that the cracked-glass can be used as parent glass to deposit β-wollastonite crystals depending on crack crystallization mechanism. The volume densities, porosities and bending strengths of the glass-ceramics are respectively around 2.7 g/cm³, 0.5% and 40 MPa. As compared with glass-ceramics prepared by conventional glass grain sintering process, the new type of glass-ceramics produced by CGC process shows pseudo-bioclastic texture and has less gas pore flaws, and may therefore become an alternative for materials of architectural decoration.     

钙铁硅铁磁体微晶玻璃热处理气氛的研究

使用XRD,DTA,VSM和穆斯堡尔谱等分析测试手段,对不同气氛下晶化热处理的含水量的B2O3,P2O5钙铁硅微晶玻璃的晶相结构和性质进行了比较深入的研究,研究结果表明,在氧化性气氛下热处理的钙铁硅微晶玻璃以赤铁矿为主;必须在还原性气氛下热处理才能得到以磁铁矿为主要晶相的铁磁体微晶玻璃。     

The effect of chromite ore addition on crystallization kinetics of basalt based machinable glass-ceramics

In this study, the properties of machinable glass-ceramic materials produced from basalt and chromite ore were investigated. Three different compositions by adding chromite ore in different ratios to the main composition produced from basalt and MgF₂ were prepared. In this way, the effects on the machinable glass-ceramic of chromium and iron oxides in the chromite ore were investigated. Thermal degradation of chromite ore and the effect of its compounds on the crystallization of machinable glass-ceramics were investigated. The samples were subjected to machinability testing. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used for characterization. The results show that chromite addition has positive effects on crystallization and machinability. Also, crystallization kinetic studies were realized. It was seen that the effect of iron oxide in chromite ore on crystallization is higher than that of chromium oxide for the crystallization conditions that used chromite ore as a nucleating agent.     

Crystallization mechanisms of cordierite glass-ceramics with “surface-center” crystallization behavior

Cordierite glass-ceramics usually begin to crystallize from the surface. As an efficient nucleating agent, TiO₂ can promote the rapid transformation of glass to bulk crystallization, but it is easy to cause the increase of dielectric constant and light absorption. High crystallinity cordierite glass-ceramics were prepared by optimizing the heat treatment process without or with different nucleating agents in stoichiometric cordierite glasses. The results show that the crystallization mechanisms of glasses without and with ZrO₂+P₂O₅ as nucleation agents are controlled by surface crystallization. While, the glass with TiO₂+ZrO₂+P₂O₅ as nucleation agents have the tendency to be bulk crystallization. The studied glasses are crystallized from surface and have different crystallization orientations with the inner glass. The thickness of crystalline layer increased with the increasing of heating temperatures, but the “surface-center” crystallization process cannot complete by further increasing heating temperatures because of softening deformation of glasses. At 1020 ℃, the glasses complete the “surface-center” crystallization for long durations. The glasses without nucleation agents and with ZrO₂+P₂O₅ require 10 h, but the glass with TiO₂+ZrO₂+P₂O₅ complete for 5 h. Although all the three glasses complete the “surface-center” crystallization, the glasses with nucleation agents show the higher crystallinity upon the same heat treatments. Finally, glass-ceramics with excellent performance were obtained, for example, the Z1# glass-ceramic have the high microhardness ∼7.4 GPa, low thermal expansion coefficient ∼1.4☓10⁻⁶ ℃⁻¹ at 20–300 ℃, and relatively high thermal conductivity ∼2.4 W/mK. It also exhibits low dielectric constant and loss, which was ∼4.5 and ∼1.2☓10⁻³ at 1 MHz, ∼ 4.9 and 2.3☓10⁻³ at 10.5 GHz..     

Physical and structural properties of Ge-rich chalcogenide glass sandwiched by GeS crystalline layers

Ge-rich glass-ceramics sandwiched by GeS crystalline layers were fabricated through 10?h thermal treatments at different temperatures. Surface crystallization is evidenced by XRD investigation of glass-ceramic samples polished by different times. SEM observation shows that the thickness of the crystalline layer is about 100?µm for the sample thermally treated at 395?°C for 10?h. The physical properties, including transmission spectra, density, Vickers hardness, and thermal expansion coefficient, were characterized and discussed with the evolution of GeS crystalline layers. This work not only establishes the correlation between microstructure and physical properties of chalcogenide glass-ceramics sandwiched by GeS, but also provides important evidence of structural similarity for understanding the network structure of Ge-S chalcogenide glasses.     

热处理制度对氟金云母系微晶玻璃结构和性能的影响

对烧结法制备氟金云母系微晶玻璃的热处理工艺制度进行了系统的研究。研究结果表明，在晶化温度为．750℃，晶化时间为2h的热处理制度下，微晶玻璃具有最高的抗折强度(107．5MPa)。     

Effect of CuO addition on crystallization and thermal expansion properties of Li2O–ZnO–SiO2 glass-ceramics

A Li₂O-ZnO-SiO₂ (LZS) glass system was modified with CuO, and its phase development, microstructure evolution, crystallization kinetics and thermal expansion properties were investigated as a function of heat treatment temperature. As a result of the X-ray diffraction study and microstructure observation, lithium zinc silicate formed as the first crystalline phase with increasing heat treatment temperature. Silica polymorph developed as minor crystalline phase at higher temperatures. From the X-ray diffraction patterns, CuO addition led to a decrease in both the crystallization temperature of lithium zinc silicate phase and the volume fraction of quartz phase. According to the crystallization kinetics, the crystallization activation energy for lithium zinc silicates is almost equal to the diffusion activation energy of Zn²⁺ in glass, it suggests that the diffusion of network modifier Zn²⁺ dominates the crystallization of lithium zinc silicates. Additionally, CuO addition caused the transition of Zn²⁺ from network modifiers to network formers. From the thermal expansion coefficient measurements, two abrupt changes in slope of the thermal expansion curves were observed and attributed to the phase transitions of cristobalite and lithium zinc silicate, respectively. Comparison of the thermal expansion coefficient of two types of glass-ceramics revealed that CuO addition in the LZS system can partly inhibit the formation of cristobalite at high temperatures.     

Fe2+、Fe3+对CASM系微晶玻璃析晶性能的影响

为了能够利用冶金行业中的大量含铁固体废弃物制备高附加值的微晶玻璃,采用差热分析法(DTA)研究了Fe2+、Fe3+对CASM系微晶玻璃析晶性能影响。研究结果显示,Fe2+可以降低微晶玻璃的热处理温度,但是少量的Fe3+则会使热处理温度升高。同时计算了不同含量的Fe3+和Fe2+玻璃料的析晶动力学参数K(Tp)。分析结果表明,Fe2+对该配方下的微晶玻璃的析晶能力影响较小,当其含量为0～7.5%时Fe3+对析晶能力影响也较小;当Fe3+含量高于7.5%时其能够显著提高玻璃的析晶能力,但对于采用烧结法制备微晶玻璃工艺,析晶能力太强不利于微晶玻璃的烧结。因此固体废弃物中的铁含量较高时,其以Fe2+的形式存在时较为有利。综合微晶玻璃的力学性能,在该配方体系中Fe2+和Fe3+含量应分别不高于4.5%和3.0%。     

高掺量赤泥-粉煤灰微晶玻璃研究

赤泥是氧化铝生产中排放的碱性废渣,粉煤灰是燃煤电厂排放的高SiO2含量废渣.综合利用两种废渣制备高性能的微晶玻璃材料,控制SiO2含量在31%～44%,CaO含量在25%～31%,两种废渣总吃渣量能够达到90wt%以上,具有显著经济效益和环境效益.