Quartz Solid Solution Research Articles

Structural features and thermal expansion of zinc aluminosilicate quartz solid solutions

Zinc aluminosilicate (ZAS) glasses were synthesized along the peraluminous join (SiO2 contents between 95 and 50 mol%) by melt-quenching or sol-gel spray-drying and subjected to controlled heat treatments to obtain ZAS quartz solid solutions (Zn-Qz-ss). The precipitation of Zn-Qz-ss is non-stoichiometric with respect to their parent glass and the crystals undergo a compositional evolution during annealing, even in absence of secondary crystalline phases. Near-hexagonal high-quartz-like crystals with negative thermal expansion (down to −3 × 10−6 K−1) can be obtained in the range 50–80 mol% SiO2, while SiO2-richer crystals exhibit positive thermal expansion at room temperature (up to 29 × 10−6 K−1). Zn2+ ions occupy two distinct positions within the structural channels of quartz, with a strong preference for 4-fold coordination. In analogy to lithium aluminosilicate quartz solid solutions (Li-Qz-ss), the low-to-high phase transition exhibits a linear correlation to the composition of the crystals.

Impacts of substituting magnesium with zinc on crystallization behaviors in an aluminosilicate glass.

A series of zinc-magnesium mixed aluminosilicate glasses with the molar composition (1-r)MgO·rZnO·Al2O3·2.5SiO2, where r = 0.00, 0.25, 0.50, 0.65, 0.75, and 1.00, were fabricated to probe the effects of substitution of magnesium with zinc on crystallization behaviors. Based on the evolution of phase compositions as revealed by calorimetric behaviors and X-ray diffraction patterns, a series of transparent surface crystallized glasses ranging from high transparency for the pure Zn-end member to heavy translucency for the pure Mg-end member were fabricated through heat treatment at the first crystallization peak temperature for 20 min. With the substitution of Mg with Zn, the evolution of morphology unveiled by optical microscopy is ascribed to the alteration of crystal phases formed from the sole metastable Zn-β quartz solid solution to the coexistence of polycrystal phases containing Zn-β quartz solid solution, μ-cordierite, or α-cordierite. These findings are very helpful for optimizing the performance of crystallized aluminosilicate glasses.

Co2+-Stuffed Quartz Solid Solutions With Zero Thermal Expansion Synthesized by Sol-Gel Spray-Drying

Glassy nanobeads of nominal composition CoO·Al2O3·4SiO2, doped with some Li2O to foster their crystallization, were synthesized by spray-drying from a methanol-based solution. Heat treatments at 850 °C and 900 °C successfully induced the formation of quartz solid solution crystals, whose thermal expansion was found to be very close to zero between 25 °C and 625 °C (average linear coefficient of thermal expansion CTE = 0.3 x 10-6 K-1). Annealing at higher temperatures induced structural unstuffing of the solid solutions, accompanied by the parallel formation of CoAl2O4 spinel and by a color shift of the powders from purple to blue. Sol-gel spray-drying stands out as a highly versatile synthesis method that can harness the thermal expansion tunability of quartz solid solution phases within a (quasi) lithium-free compositional landscape.

Towards new zero-thermal-expansion materials: Li-free quartz solid solutions stuffed with transition metal cations

Stuffed aluminosilicate quartz solid solutions (Qss) represent the main functional component of state-of-the-art zero-thermal-expansion glass-ceramics. For the first time, we present the synthesis of Li-, Mg- and Zn-free Qss solely stuffed with transition metal cations (Fe2+, Ni2+, Co2+); partial Li+ co-doping enables also significant Mn2+ incorporation. They were obtained by glass powder crystallization; Qss crystals exhibit compositionally tunable coefficients of thermal expansion (CTEs), from − 2 × 10−6 K−1 to ∼10 × 10−6 K−1 in the range 30–300 °C. Co2+-bearing crystals exhibit the closest-to-zero CTE value (0.2 ×10−6 K−1) and the most isotropic behavior in the whole Qss family, opening up new perspectives for the development of Li-free low-expansion materials. From a structural point of view, we identified the unit cell volume (and not the pseudo-hexagonality of the aluminosilicate framework) as the key structural parameter leading to low or negative CTEs in Qss, with a linear correlation extending to non-stuffed non-silicate quartz-like phases.

On the assignment of quartz-like LiAlSi2O6 - SiO2 solid solutions in dental lithium silicate glass-ceramics: Virgilite, high quartz, low quartz or stuffed quartz derivatives?

ObjectivesHere we aim to provide a background on X-Ray Diffraction analysis of quartz-like crystal structures with varying amounts of Al3+ and Li+ substitution, existing confusions on their nomenclature and its implications for novel lithium silicate glass-ceramics. MethodsWe reviewed the literature dealing with modifications of the quartz crystal structure and their stuffed LiAlSi2O6 derivates, LiAlSi2O6 – SiO2 solid solutions, the terminology of such phases and criteria used to define the structure known as virgilite. Based on this information, we attempted to allocate the quartz-like phases found in CEREC TesseraTM, InitialTM LiSi Block and Amber® Mill in the range of LiAlO2 - SiO2 solid solutions. For this purpose, their lattice parameters obtained from Rietveld refinement were compared with the lattice parameters of members of the corresponding solid solutions with defined SiO2 molar fraction found in the literature. ResultsBased on the lattice parameters available for low quartz, high quartz and its stuffed derivatives, including LiAlSi2O6 and the mineral virgilite, a plot of the a- and c-parameters vs. the mol% SiO2 related to LiAlO2 was constructed with the literature data and the data found for the three dental lithium silicates. As per the definitions of virgilite as either LixAlxSi3-xO6, with 0.5 < x < 1 or especially as members of the LiAlSi2O6 – SiO2 solid-solution series with more than 50 mol% LiAlSi2O6, the crystal structures in CEREC TesseraTM, InitialTM LiSi Block and Amber® Mill failed to fall within the ranges of mol% SiO2 confined for virgilite. SignificanceBased on available literature and definitions, the quartz-like phases found in the three dental lithium silicates should be addressed as stuffed (probably low) quartz solid solutions instead of “virgilite”. However determined by mineralogical practices, the term “virgilite” for parts of the LiAlSi2O6 – SiO2 solid solution is ambiguous and can be considered as arbitrary.

Glass formation and devitrification behavior of alkali (Li, Na) aluminosilicate melts containing TiO2

The impact of TiO2 additions on the quenchability of melts derived from the stoichiometry of spodumene (LiAlSi2O6), eucryptite (LiAlSiO4) and nepheline (NaAlSiO4) was investigated by containerless melting. The results reveal a compositional dependence (Al2O3/SiO2 and M2O/Al2O3 ratios, M = Na or Li) of the role of TiO2 during devitrification. Amorphous samples incorporating up to 10 mol% TiO2 could be produced, above which devitrification invariably took place. Interaction of TiO2 with other glass components (such as Al2O3 and Na2O in nepheline glass) perceivably reduced glass stability, while eucryptite and spodumene glasses appeared only affected to the extent to which nanosized TiO2 polymorphs (TiO2(B), anatase and rutile) served as heterogeneous nucleation sites for quartz solid solutions, in which we inferred a substantial incorporation of Ti4+. A reduction in SiO2 content and a preference for peraluminous compositions stand out as viable compositional strategies to foster the glass-forming ability of TiO2-rich aluminosilicate melts.

Spray‐dried sol‐gel glass‐ceramic powders based on the tunable thermal expansion of quartz and keatite solid solutions

AbstractLithium aluminosilicate glass‐ceramic powders were synthesized by the heat treatment of spray‐dried sol‐gel glassy nanobeads, obtaining quartz solid solution (Qss) and keatite solid solution (Kss) crystals. Their composition ranged between 75 mol% SiO2 and pure silica along the spodumene join. The metastable crystals displayed tunable coefficients of thermal expansion ranging from +30 × 10−6 to −2.7 × 10−6 K−1 at room temperature, as obtained from their crystallographic characterization. The solid solution boundaries of Kss could be extended to 85 mol% SiO2. Concurrently, X‐ray diffraction measurements performed in situ at high temperature and at cryogenic conditions confirmed the known linear shift of the high‐low quartz inversion temperature upon increasing Al+Li doping. The obtained results qualify aerosol synthesis as a very versatile method for the production of glass‐ceramic powders in the LAS system.

A threshold heating rate for single‐stage heat treatments in glass‐ceramics containing seed formers

AbstractThe development of glass‐ceramic materials is often achieved using an elementary microstructural strategy that splits the tasks of seed formation and functionality between two types of crystals. This strategy requires customized time‐temperature ceramization protocols, which have been so far implemented using empirical parameters. Here, a more fundamental approach is proposed: the extent of overlap Oe between seed formation and volume crystallization is evaluated by calorimetric and dilatometric measurements, targeting the computation of a threshold heating rate qt for effective single‐stage heat treatments. The applicability of this novel parameter is tested in TiO2‐doped lithium magnesium aluminosilicate glass‐ceramics, whose seed formation stage is thoroughly characterized by Raman spectroscopy and STEM. High‐temperature X‐ray diffraction demonstrates that insufficient seeding results in potentially weaker performances of the final products, due to large sizes and silica deficiency of the functional quartz solid solution crystals.

The effects of a Li2O excess on the crystallization sequence of lithium aluminosilicate glass powders

The surface crystallization of melt-quenched lithium aluminosilicate (LAS) glasses with SiO2-contents between 77 and 79 mol% was investigated by high-temperature X-ray diffractometry. Glasses possessing a ratio Li/Al > 1 underwent far earlier crystallization (starting from 750°C) than their stoichiometric counterparts, developing solely quartz solid solution (Qss) and keatite solid solution (Kss) crystals during a heat treatment up to 1200°C. In turn, samples with Li/Al = 1 devitrified only above 900°C and exhibited the transient formation of cristobalite, whose lattice constants hint at a slight Li+Al stuffing. The composition, structural parameters and critical inversion temperature Tc of the obtained Qss crystals were analyzed and compared with the available literature sources, reaffirming the established mutually linear dependence between these properties.

Liberation and Enrichment of Metallic Iron from Reductively Roasted Copper Slag

Iron recovery from copper slag generated during copper production by the pyrometallurgical method has been widely investigated to achieve resource utilization. Liberation and enrichment of metallic iron from reductively roasted copper slag were explored in this work. Results show that metallic iron, quartz solid solution, and cristobalite solid solution are the main phases in reductively roasted copper slag, and most metallic iron particles are wrapped by silica. A concentrate with 74.39% Fe content and 83.14% Fe recovery is obtained through grinding–magnetic separation. For comparison, the metallic iron particles are liberated through alkali leaching of silica. The Fe content in leaching residue reaches 78.17% by removing 88.96% SiO2 and further increases to 90.45% by magnetic separation with Fe recovery of 85.20%. Therefore, alkali leaching–magnetic separation is suitable for treating reductively roasted copper slag because of the high Fe content in concentrate and comprehensive recovery of silica.

Investigation of Solid-State Carbothermal Reduction of Fayalite with and Without Added Metallic Iron

Copper slag (CS) with Fe-bearing fayalite and magnetite is the main waste generated during the pyrometallurgical processing of metallic copper. In this paper, the solid-state reduction kinetics of fayalite with and without addition of 10 wt.% metallic iron were studied using the isothermal method. The phase transformation of fayalite was verified by x-ray diffraction, scanning electron microscopy, and energy dispersive spectrometer. Results show that the carbothermal reduction of fayalite is controlled by phase boundary reaction (tridimensional shape), and the activation energy decreases from 165.22 kJ mol−1 to 145.74 kJ mol−1 after adding 10 wt.% metallic iron. During the carbothermal reduction process, fayalite decomposes into metallic iron and quartz solid solution, followed by the conversion of quartz solid solution into cristobalite solid solution with increasing temperature. The addition of metallic iron creates a nucleating effect and accelerates the decomposition of fayalite. This work contributes to efforts to optimize the carbothermal reduction of CS.

Mg‐bearing quartz solid solutions as structural intermediates between low and high quartz

AbstractGlass powder samples of cordierite composition (doped with 8 mol% TiO2) were heat‐treated to produce a series of increasingly SiO2‐enriched Mg‐bearing quartz solid solutions (Qss). The obtained materials were then analyzed by X‐ray diffraction: Rietveld structural refinements revealed that Mg‐bearing Qss phases possess trigonal symmetry and a compositionally dependent intermediate structural arrangement between those of low and high quartz. High‐temperature diffraction measurements were performed up to 700°C to characterize the thermal expansion behavior of the crystals. At SiO2‐rich compositions, a reversible high‐to‐intermediate inversion of the quartz structure is observed, which shifts with increasing stuffing to lower temperatures than the conventional 573°C for pure quartz. Similarities and differences to the better‐established Li‐bearing Qss are discussed in the text.

Effect of Soaking Time on Crystal Structure of Lithium Aluminosilicate Glass Ceramic

Formation of crystal structures in glass ceramic is influenced by the heat treatment of parent glass. Most of research often studied on the important of sintering temperature and its soaking time. In this study, the effect of soaking time (3, 4 and 5 hours) during melting process (1550 °C) on crystal structures of Lithium Aluminosilicate (LAS) glass ceramic was conducted. All samples were then sintered at 900 °C for 30 minutes. The amorphous phase was identified prior to sintering process and transformed into crystalline phase for all samples after sintering process in XRD analysis. Major crystalline phase of high quartz solid solution and β-spodumene (LiAlSi2O6) were observed and higher intensity peak is found as the soaking time is longer. The microstructure of the sintered samples was observed under SEM and the particles were displayed an evidently growth of the grain as function to the soaking time. The functional groups of Si-O-Si and Si-O(Si, Al) bonding were appeared in fourier-transform infrared spectroscopy (FTIR) analysis corresponding to the silicates and aluminosilicate bonding. The results achieved present 5 hours soaking time during melting process was the optimum soaking time for melting LAS glass at 1550 °C.

Inversion of quartz solid solutions at cryogenic temperatures

AbstractQuartz solid solution crystals of six different compositions were obtained from crystallization of glass powders belonging to the Li2O–Al2O3‐SiO2 (LAS) system. They were analyzed in situ by laboratory‐based X‐ray diffraction down to cryogenic temperatures (−190°C). Temperature‐resolved analysis of their lattice parameters allowed determination of the critical inversion temperature Tc in these materials, marking the displacive phase transition from a high‐quartz‐ to a low‐quartz‐like lattice. Integrating available data from other literature sources, an updated phase diagram for the occurrence of high and low quartz solid solution phases is provided for the LAS system; these data are expected to support future development of functional materials relying on these crystalline phases.

Separation of silicon and iron in copper slag by carbothermic reduction-alkaline leaching process

Approximately 2.0–3.0 t of copper slag (CS) containing 35%–45% iron is generated for every ton of copper produced during the pyrometallurgical process from copper concentrate. Therefore, the recovery of iron from CS utilizes a valuable metal and alleviates the environmental stress caused by stockpile. In this paper, a new method has been developed to realize the enrichment of iron in CS through the selective removal of silica. The thermodynamic analyses and experimental results show that the iron in CS can be fully reduced into metallic iron by carbothermic reduction at 1473 K for 60 min. The silica was converted into free quartz solid solution (QSS) and cristobalite solid solution (CSS). QSS and CSS are readily soluble, whereas metallic iron is insoluble, in NaOH solution. Under optimal leaching conditions, a residue containing 87.32% iron is obtained by decreasing the silica content to 6.02% in the reduction roasted product. The zinc content in the residue is less than 0.05%. This study lays the foundation for the development of a new method to comprehensively extract silicon and iron in CS while avoiding the generation of secondary tailing.

TiO2(B) nanocrystals in Ti-doped lithium aluminosilicate glasses

Abstract Three different compositions of TiO2-doped lithium aluminosilicate glass were annealed and analyzed to investigate their first stages of crystallization. After phase separation had occurred, monoclinic TiO2(B) was invariably observed as the first seed forming phase. Phase identification was confirmed by Raman spectroscopy and transmission electron microscopy, disproving its interpretation as pseudobrookite in previous literature sources. The phase was observed to undergo gradual transformation into anatase with increasing temperature, but its persistence was longer in the Si-richer samples. It disappeared right before the volume crystallization of high quartz solid solution and keatite solid solution.

Efficient separation of silica and alumina in simulated CFB slag by reduction roasting-alkaline leaching process

Although circulating fluidized bed (CFB) combustion technology is regarded as an efficient technology to use abundant coal gangue as fuel, large amounts of CFB slag has to be stockpiled and raises the environmental stress. This work focused on the comprehensive utilization of silica and alumina in CFB slag. The combustion process of coal gangue and the subsequent separation of alumina and silica by alkaline leaching of the simulated CFB slag were investigated. The results show that, in the combustion process, kaolinite in coal gangue firstly converts into meta-kaolinite at 600–900 °C due to dehydroxylation, and then the meta-kaolinite splits into mullite and amorphous silica at ≥1000 °C. Whereas by reduction roasting with hematite, the CFB slag simulated at 800–1100 °C can be completely converted into hercynite and free silica in forms of quartz solid solution and cristobalite solid solution. However, the conversion reaction rate for the CFB slag simulated at 1200 °C decreases significantly due to the formation of well crystallized mullite prior to the reduction roasting. Additionally, either quartz solid solution or cristobalite solid solution is readily soluble and hercynite is insoluble in alkaline solution. Under optimal conditions, more than 95% of silica inthe reduction roasted product can be dissolved in alkaline solution and the mass ratio of alumina to silica in the leached residue can increase from 0.85 to above 20. This study lays a foundation for developing a novel technique to efficiently recycle the carbon, silica and alumina in coal gangue and thus to alleviate the environmental stress.

Reaction behavior of kaolinite with ferric oxide during reduction roasting

Abstract The pre-separation of silica and alumina in aluminosilicates is of great significance for efficiently treating alumina-/silica-bearing minerals for alumina production. In this work, the reaction behavior of kaolinite with ferric oxide during reduction roasting was investigated. The results of thermodynamic analyses and reduction roasting experiments show that ferrous oxide obtained from ferric oxide reduction preferentially reacts with alumina in kaolinite to form hercynite, meanwhile the silica in kaolinite is transformed into quartz solid solution and/or cristobalite solid solution. With increasing roasting temperature, fayalite formed by reaction of surplus ferrous oxide with silica at low temperature is reduced to silica and metallic iron in the presence of sufficient carbon dosage. However, increasing roasting temperature and decreasing Fe2O3/Al2O3 molar ratio favor mullite formation. The complete conversion of kaolinte into free silica and hercynite can be obtained by roasting raw meal of kaolin, ferric oxide and coal powder with Fe2O3/Al2O3/C molar ratio of 1.2:2.0:1.2 at 1373 K for 60 min. This work may facilitate the development of a technique for comprehensively utilizing silica and alumina in aluminosilicates.

Crystallization sequence within the keatite solid solution – cordierite mixed compositional triangle with TiO2 as nucleating agent

Sixteen glasses of mixed keatite solid solution – cordierite stoichiometry, with 4 mol% TiO2 as nucleating agent, were produced and ceramized to investigate their crystallization sequence. Employed analytical methods included differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. Differences were identified already during the first ceramization stages: Al2O3/(Al2O3 + SiO2) and Li2O/(Li2O + MgO) ratios were crucial to determine which seed former phases would precipitate and the nucleation efficiency of each glass, reaching its maximum at Mg-free composition. Metastable formation of high quartz solid solution was observed in all samples; this phase was most persistent at Li2O/(Li2O + MgO) ratio equal to 0.33 and high SiO2-enrichment. Its destabilization led to the appearance of keatite solid solution and/or indialite, whose crystallization sequence and final relative amounts, as well as the microstructure of the glass-ceramics, were strongly influenced by the composition of the parent glasses.

Effect of Y2O3 content on the crystallization behaviors and physical properties of glasses based on MgO-Al2O3-SiO2 system

Different concentrations of Y2O3 doped MgO-Al2O3-SiO2 system glasses were prepared by melting method. The effects of Y2O3 content on the physical properties, crystallizability, and the resultant microstructures of the glass samples were investigated. With the increase of Y2O3 content, the glass transition temperature, dilatometric softening temperature and micro hardness all increased. Low concentrations of Y2O3 (0–1.0 mol%) favored the formation of quartz solid solution at 840 °C for 1.5 h, and phase transformation from β- to α-quartz solid solution happened after heat treatment at 1000 °C with subsequent cooling process. While high concentration of Y2O3 (1.5 mol%) inhibited the crystallization process, and quartz solid solution formed at a high temperature ~ 940 °C. The phase transformation from β- to α-quartz solid solution happened after heat treatment at 1060 °C with subsequent cooling process. Average crystal sizes were increased significantly with the crystallization temperature increasing from 940 °C to 1120 °C. The coefficient of thermal expansion of the glass treated at 1120 °C decreased obviously around temperature ~ 300 °C, which indicated that the phase transformation from α- to β-quartz solid solution happened in the heating process.