Ⅱ型无水磷石膏凝结硬化过程调控技术

为改善Ⅱ型无水磷石膏水化活性低、凝结硬化缓慢的问题,研制了一种复合助剂(β-半水石膏6%、改性钢渣3%、K₂SO₄ 2%、铝酸钙水泥0.5%)。研究表明,掺入复合助剂后Ⅱ型无水磷石膏初凝时间由744min (空白样)缩短至76min (改性样)。在此基础上添加25%的高炉矿渣微粉改善力学性能和耐水性,改性后的胶凝材料绝干抗压强度达到15.4MPa,软化系数达到0.83。研究了胶凝体系的水化率、液相离子浓度随时间的变化规律,结合X射线衍射(XRD)和扫描电子显微镜(SEM)对水化产物和水化硬化机理进行了分析。复合助剂加速了Ⅱ型无水磷石膏的溶解及二水石膏晶核的生成和长大,提高了Ⅱ型无水磷石膏的水化率,与矿渣协同作用促进生成3CaO·Al₂O₃·3CaSO₄·32H₂O、3CaO·Fe₂O₃·3CaSO₄·32H₂O等多种低溶度积复盐,改善了胶凝材料的凝结硬化性能和耐水性。     

Hydration of 3CaO·Al2O3 and 3CaO·Al2O3+] Gypsum With and Without CaCl2

Paste samples of tricalcium aluminate alone, with CaCl₂, with gypsum, and with gypsum and CaCl₂ were hydrated for up to 6 months and the hydration products characterized by SEM, XRD, and DTA. Tricalcium aluminate hydrated initially to a hexagonal hydroaluminate phase which then changed to the cubic form; the transformation rate depended on the size and shape of the sample and on temperature. The addition of CaCl₂ to tricalcium aluminate resulted in the formation of 3CaO · Al₂O₃· CaCl₂·10H₂O and 4CaO · Al₂O₃· 13H₂O, or a solid solution of the two. The chloride retarded the formation of the cubic phase 3CaO · Al₂O₃· 6H₂O; the addition of gypsum resulted in the formation of monosulfoaluminate with a minor amount of ettringite. When chloride was added to tricalcium aluminate and gypsum, more ettringite was formed, although 3CaO · Al₂O₃· CaSO₄· 12H₂O and 3CaO · Al₂O₃· CaCl₂· 10H₂O were the main hydration products.     

Formation of Ettringite from Monosubstituted Calcium Sulfoaluminate Hydrate and Gypsum

The formation of ettringite (3CaO·Al₂O₃·3CaSO₄·32H₂O) from monosulfate (3CaO·Al₂O₃·CaSO₄·12H₂O) and gypsum (CaSO₄·2H₂O) was investigated by isothermal calorimetry and X-ray diffraction (XRD) analyses. Hydration was carried out at constant temperatures from 30° to 80°C using deionized water and 0.2 M , 0.5 M , and 1.0 M sodium hydroxide (NaOH) solutions. Ettringite was found to be the dominant crystalline phase over the entire temperature range and at all sodium hydroxide concentrations. A sodium-substituted monosulfate phase was formed as a hydration product in the 1.0 M sodium hydroxide solution regardless of temperature. XRD and calorimetry demonstrate that hydration in increasing sodium hydroxide concentrations decreases the amount of ettringite formed and retards the rate of reaction. The apparent activation energy for the conversion of the monosulfate/gypsum mixture to ettringite was observed to vary depending on the sodium hydroxide concentration. Ettringite formation was observed to depend upon the concentration of calcium in solution; thus the formation of calcium hydroxide and sodium-substituted monosulfate phase competes with ettringite formation.     

Expansion associated with ettringite formation at different temperatures

Expansion of hydrated mixtures made with C₃A, CaSO₄ · 2H₂O, Ca(OH)₂ and SiO₂, at 22, 30, 40, 50, 60°C, was studied to verify if expansion is associated with colloidal ettringite formation or with the solid state conversion of C₄AH₁₃ to monosulfate hydrate in presence of calcium hydroxide. From the results of our investigation it can be drawn the conclusion that mortars expansion is in connection with colloidal ettringite formation and the monosulfate hydrate is formed only when the greatest expansion is ended. The increase in hydration temperature seem to be favorable to the formation of colloidal ettringite.     

The synthesis and characterization of calcium aluminate monoiodide

The hydrated calcium aluminate AFt and AFm phases are known hosts for a wide variety of chemical species. This characteristic is beneficial to those using portland cement to solidify/encapsulate radioactive waste which more often than not contains a wide variety of elements. In order to investigate the potential of the calcium aluminate hydrates as host phases for selected ions, the following experiments were carried out. Bottle hydration studies (water/solid > 1) were used to investigate the suitability of the AFt and AFm phases as hosts for iodine, one of the more mobile radioactive waste elements. Trial compositions along the AFt and AFm joins in the systems 3CaO·Al₂O₃---CaSO₄---CaI₂---H₂O were investigated. No stable iodine end-member AFt phase was formed at room temperature. The end-member AFm phase, 3CaO·Al₂O₃·CaI₂·12H₂O, was synthesized and was designated monoiodide. Characterization was carried out using chemical analysis, scanning electron microscopy, x-ray diffraction (conventional and high temperature), thermogravimetric analysis and differential thermal analysis. Monoiodide was indexed as hexagonal and thus isostructural with previously described AFm phases. Monoiodide is stable to about 85°C. A loss of approximately four molecules of water occurs between 71° and 101°C. The lower hydrate, tentatively identified as 3CaO·Al₂O₃·CaI₂·8H₂O, is stable to approximately 300°C. The latter hydrate was observed to revert to the original hydrate on exposure to the relative humidity in the laboratory.     

Hydrothermal transformation of the calcium aluminum oxide hydrates CaAl2O4·10H2O and Ca2Al2O5·8H2O to Ca3Al2(OH)12 investigated by in situ synchrotron X-ray powder diffraction

The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl₂O₄·10H₂O converted to Ca₃Al₂(OH)₁₂ and amorphous aluminum hydroxide. Ca₂Al₂O₅·8H₂O transformed via the intermediate phase Ca₄Al₂O₇·13H₂O to Ca₃Al₂(OH)₁₂ and gibbsite, Al(OH)₃. The phase Ca₄Al₂O₇·19H₂O reacted via the same intermediate phase to Ca₃Al₂(OH)₁₂ and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.     

Na2O掺杂铝酸钙化合物物相转化与浸出性能

以分析纯试剂CaCO₃、Al₂O₃和Na₂CO₃为原料,在1350℃烧结1 h合成了Na₂O掺杂铝酸钙熟料,并采用XRD、SEM和EDS等方法研究了Na₂O掺杂CaO-Al₂O₃体系铝酸钙化合物的物相演变规律及熟料浸出性能。结果表明:当CaO和Al₂O₃的摩尔比为1.0时,CaO-Al₂O₃体系铝酸钙由CaO·Al₂O₃和12CaO·7Al₂O₃组成,而Na₂O掺杂铝酸钙熟料由CaO·Al₂O₃、12CaO·7Al₂O₃、Na₂O·Al₂O₃和Na₄Ca₃(AlO₂)₁₀组成。除形成含Na₂O化合物外,熟料中掺杂的Na₂O固溶于12CaO·7Al₂O₃中,而CaO·Al₂O₃中几乎不含Na₂O。随着熟料中Na₂O掺杂量的升高,12CaO·7Al₂O₃和Na₄Ca₃(AlO₂)₁₀的含量逐渐增加,CaO·Al₂O₃的含量逐渐降低;12CaO·7Al₂O₃和Na₄Ca₃(AlO₂)₁₀的结晶度逐渐降低,CaO·Al₂O₃的结晶度逐渐升高。Na₂O的掺杂提高了熟料在碳酸钠溶液中的浸出性能,并且使浸出渣中CaCO₃的空间群由R-3CH、P63/MMC两种转变为只含有R-3CH一种。     

Retardation of Tricalcium Aluminate Hydration by Calcium Sulfate

The influence of calcium sulfate on the hydration of 3CaO· Al₂O₃ in the presence of Ca(OH)₂ was studied using conduction calorimetry, differential thermogravimetry, and X-ray diffraction. Sodium sulfate was also used instead of calcium sulfate. A substantial retardation of tricalcium aluminate hydration in the presence of sulfate occurs only when calcium sulfate is used and enough ettringite is formed. When ettringite disappears due to the consumption of gypsum, tricalcium aluminate hydration is renewed. Sodium sulfate does not significantly retard this hydration. The results confirm the hypothesis that ettringite formation is essential for coating 3CaO·Al₂O₃ grains and then retarding their hydration.     

In-situ growth of needlelike LaAl11O18 for reinforcement of alumina composites

In situ growth of needlelike LaAl₁₁O₁₈ grains reinforcing Al₂O₃ composites can be fabricated by a coprecipitation method using La(NO₃)₃√6H₂O and Al(NO₃)₃√9H₂O as starting materials. The new two-step process involved firstly preparing needlelike LaAl₁₁O₁₈ grains distributed homogeneously in Al₂O₃ powder and then pressureless sintering the composite powders. The Al₂O₃/25 vol.%LaAl₁₁O₁₈ samples pressureless sintered at 1550°C for 4 h achieve relative density up to 96.5% and exhibit a bending strength of 420±30 MPa and a fracture toughness of 4.3±0.4 MPa m^1/2.     

Porous structures constructed from [SiMo12O40] and [SiW12O40] Keggin units

Three compounds, K₂(H₂O)₄H₂SiMo₁₂O₄₀ · 7H₂O (1), K₂Na₂(H₂O)₄SiW₁₂O₄₀ · 4H₂O (2), and Na₄(H₂O)₈SiMo₁₂O₄₀ · 6H₂O (3) have been synthesized and structurally characterized by single-crystal X-ray analysis, IR, and thermogravimetry. Compounds 1 and 2 both show the high symmetry trigonal space group P3₂21 and a novel 3D network structure. The Keggin anions [SiM₁₂O₄₀]⁴⁻(M = Mo, W) are linked by potassium or sodium cations to generate hexagon-shaped channels along the c-axis, in which water molecules are accommodated. Compound 3 is tetragonal, space group P4/mnc constructed from [SiMo₁₂O₄₀]⁴⁻ anions and Na ions.     

Modification on the tricalcium aluminate phase in cements by manganese substitution

The effect of manganese substitution into the crystal structure of the tricalcium aluminate Ca₃Al₂O₆ has been studied by X-ray, analytical electron microscopy, IR spectroscopy and electronic spin resonance. The limit of solid solution of manganese in this phase was determined. The formula proposed for this solubility is (Ca_2.984Mn_0.016)(Al_1.979Mn_0.021)O₆. In presence of CaO and Al₂O₃ the manganese reacts to give Ca₂AlMnO₅ phase, reducing appreciably tricalcium aluminate contents.     

Subsolidus phase relationships in part of the system Si, Al, Ca/N, O

Subsolidus phase relationships in the region bounded by Si₃N₄, SiO₂, CaSiO₃, 2CaO.Al₂O₃.SiO₂, CaO.Al₂O₃, Al₂O₃ and β'-Si₂Al₄O₄N₄(β₆₀) have been studied. A new quinary phase with composition near to CaO. 1·33Al₂O₃.0·67Si₂N₂O (designated as S-phase) and a complete series of solid solution between S-phase and CaO.2Al₂O₃ were found. Fourteen compatible tetrahedra, of which five contain S-phase, occur in the region explored. They are as follows: X₁-SiO₂-anorthite-mullite; X₁-anorthite-mullite-Al₂O₃; X₁-anorthite-Al₂O₃-β₆₀; X₁-anorthite-β₆₀-Si₃N₄; X₁-anorthite-Si₃N₄-Si₂N₂O; X₁-anorthite-Si₂N₂O-SiO₂; anorthite-Si₂N₂O-SiO₂-CaSiO₃; anorthite-Si₂N₂O-CaSiO₃-gehlenite; anorthite-Si₂N₂O-gehlenite-Si₃N₄; S-anorthite-Al₂O₃-β₆₀; S-Al₂O₃-CaO.2Al₂O₃-gehlenite; S-Al₂O₃-gehlenite-anorthite; S-gehlenite-anorthite-Si₃N₄; S-anorthite-Si₃N₄-β₆₀.     

Resistance of sodium polyphosphate-modified fly ash/calcium aluminate blend cements to hot H2SO4 solution

Sodium polyphosphate-modified Class F fly ash/calcium aluminate blend (SFCB) cements were prepared at room temperature and their resistance to hot acid erosion was evaluated by submerging them in H₂SO₄ solution (pH 1.6) at 90°C. Sodium polyphosphate preferentially reacted with calcium aluminate cement (CAC) to form amorphous Ca(HPO₄).xH₂O and Al₂O₃.xH₂O gel, rather than fly ash. These amorphous reaction products, which bound the partially reacted and unreacted CAC and fly ash particles into a coherent mass, were responsible for strengthening and densifying the SFCB specimens at room temperature, playing an essential role in mitigating their acid erosion. In these cements, the extent of acid erosion depended primarily on the ratio of fly ash/CAC; namely, those with a higher ratio underwent a severe erosion. This effect was due to the formation of a porous structure, which allowed acid to permeate the cement easily, diminishing the protective activity of Ca(HPO₄).xH₂O and Al₂O₃.xH₂O gel against H₂SO₄.     

Structural phase transition and high temperature phase structure of Friedels salt, 3CaO · Al2O3 · CaCl2 · 10H2O

Friedels salt, the chlorinated compound 3CaO · Al₂O₃ · CaCl₂ · 10H₂O (AFm phase), presents a structural phase transition at about 30°C from a monoclinic to a rhombohedral phase. It has been studied by X-ray powder diffraction and optical microscopy in transmitted light with crossed polarisers on single crystals prepared by hydrothermal synthesis. The high temperature phase was determined at 37°C from X-ray single crystal diffraction data. The compound crystallises in the space group R c with lattice parameters of a = 5.7358(6)Å and c = 46.849(9)Å (Z = 3 and D_x = 2.111 g/cm³). The refinement of 498 independent reflections with I > 2σ(I) led to a residual factor of 7.1%. The Friedels salt can be described as a layered structure with positively charged main layers of composition [Ca₂Al(OH)₆]⁺ and negatively charged layers of composition [Cl⁻,2H₂O]. The chloride anions are surrounded by 10 hydrogen atoms, of which six belong to hydroxyl groups and four to water molecules. The structural phase transition may be related to the size of the chloride anions, which are not adapted to the octahedral cavity formed by bonded water molecules.     

四元体系CaCl2-CaSO4-CaB6O10-H2O 308.15 K相平衡研究

采用等温溶解平衡法研究了四元体系CaCl₂-CaSO₄-CaB₆O₁₀-H₂O在308.15 K下的稳定相平衡。测定了该体系的溶解度及平衡溶液的物化性质(包括折射率、密度和pH)。根据实验数据,分别绘制了该四元体系的干基图、水图以及相应的物化性质–组成图。研究结果表明：该体系在308.15 K时有1个共饱点(CaCl₂·4H₂O + CaSO₄·2H₂O + CaB₆O₁₀·5H₂O),3条单变量溶解度曲线,3个单盐结晶区,分别对应于CaCl₂·4H₂O、硬石膏(CaSO₄·2H₂O)和高硼钙石(CaB₆O₁₀·5H₂O)。其中,硬石膏CaSO₄·2H₂O结晶区最大、高硼钙石CaB₆O₁₀·5H₂O结晶区次之,而CaCl₂·4H₂O结晶区最小,表明硬石膏最易于结晶析出。此外,该四元体系在308.15 K下没有复盐和固溶体生成,属于简单水合物I型。平衡液相的物化性质随着CaCl₂浓度的增大呈规律性变化,并在共饱点处发生转折。其中,折射率和密度的变化规律相近,而pH的变化规律则与之相反。对该四元体系的稳定相平衡进行研究,将为综合开发利用油田卤水中的钙、硼等资源提供理论依据。     

Activity enhancement of SnO2-doped Ga2O3–Al2O3 catalysts by coexisting H2O for the selective reduction of NO with propene

Catalytic reduction of NO by propene in the presence of oxygen was studied over SnO₂-doped Ga₂O₃–Al₂O₃ prepared by sol–gel method. Although SnO₂-doped Ga₂O₃–Al₂O₃ gave lower NO conversion than Ga₂O₃–Al₂O₃ in the absence of H₂O, the activity was enhanced considerably by the presence of H₂O and much higher than that of Ga₂O₃–Al₂O₃. The presence of SnO₂ and Ga₂O₃–Al₂O₃ species having intimate Ga–O–Al bondings was found to be essential for the promotional effect of H₂O. The promotional effect of H₂O was interpreted by the following two reasons. The first one is the removal of carbonaceous materials deposited on the catalyst surface by H₂O. The other is the selective inhibition by H₂O of the reaction steps resulting in propene oxidation to CO_x without reducing NO.     

Ru-Fe/Al_2O_3氧化-还原性能探究

以Al_2O_3为载体,RuCl_3·xH_2O和FeCl_3·6H_2O为活性组分前驱体,采用吸附-沉淀法制备了Ru-Fe/Al_2O_3和Ru/Al_2O_3催化剂,以马来酸二甲酯加氢合成丁二酸二甲酯为探针反应,结合H_2-TPR和XRD表征技术,考察Fe改性Ru基催化剂的氧化-还原性能及催化活性。经氧化-还原循环处理后,催化剂Ru-Fe/Al_2O_3上马来酸二甲酯加氢活性高于Ru/Al_2O_3。XRD结果显示,经处理的Ru-Fe/Al_2O_3上未见金属Ru的特征衍射峰,而Ru/Al_2O_3上出现了金属Ru的特征衍射峰。结合H_2-TPR结果推断,Ru与Fe之间发生了相互作用,这种协同作用可以改善Ru/Al_2O_3催化剂的热稳定性。     

Enhanced activity of metal oxide-doped Ga2O3–Al2O3 for NO reduction by propene

Effect of additives, In₂O₃, SnO₂, CoO, CuO and Ag, on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H₂O, CoO, CuO and Ag showed good additive effect. When H₂O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga₂O₃–Al₂O₃ was depressed considerably, while an intensifying effect of H₂O was observed for In₂O₃- and SnO₂-doped Ga₂O₃–Al₂O₃. Of several metal oxide additives, In₂O₃-doped Ga₂O₃–Al₂O₃ showed the highest activity for NO reduction by propene in the presence of H₂O. Kinetic studies on NO reduction over In₂O₃–Ga₂O₃–Al₂O₃ revealed that the rate-determining step in the absence of H₂O is the reaction of NO₂ formed on Ga₂O₃–Al₂O₃ with C₃H₆-derived species, whereas that in the presence of H₂O is the formation of C₃H₆-derived species. We presumed the reason for the promotional effect of H₂O as follows: the rate for the formation of C₃H₆-derived species in the presence of H₂O is sufficiently fast compared with that for the reaction of NO₂ with C₃H₆-derived species in the absence of H₂O. Although the retarding effect of SO₂ on the activity was observed for all of the catalysts, SnO₂–Ga₂O₃–Al₂O₃ showed still relatively high activity in the lower temperature region.     

Devitrification of a glass obtained from porphyric sands, MgO (15%) and TiO2 (4%)

A glass of composition: SiO₂ = 59·84%; Al₂O₃ = 11·45%; MgO = 15·34%; TiO₂ = 4·23%; K₂O = 3·80%; Na₂O = 2·48%; CaO = 1·08%; Fe₂O₃ = 1·78%; was prepared from porphyric sands by addition of MgO and TiO₂. The quenched glass is demixed on a very fine scale. The non-isothermal devitrification has been studied. Three-dimensional crystal growth has been observed. The experimental data suggest a mechanism controlled by the crystal-glass interface reaction. The crystal growth activation energy E_c = 467 ± 20 kJ/mole has been evaluated. The temperature of most efficient nucleation is approximately T_N = 720°C.     

Quantified NOx adsorption on Pt/K/gamma-Al2O3 and the effects of CO2 and H2O

A multi-component NO_x-trap catalyst consisting of Pt and K supported on γ-Al₂O₃ was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H₂O and CO₂ on NO_x storage. The Al₂O₃ support was shown to have NO_x trapping capability with and without Pt present (at 250 °C Pt/Al₂O₃ adsorbs 2.3 μmols NO_x/m²). NO_x is primarily trapped on Al₂O₃ in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NO_x/m², and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al₂O₃ catalyst are coordinated on the Al₂O₃ support at saturation.

When 5% CO₂ was included in a feed stream with 300 ppm NO and 12% O₂, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H₂O was included in a feed stream with 300 ppm NO and 12% O₂, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al₂O₃-based nitrates decreased by 92%. Interestingly, with both 5% CO₂ and 5% H₂O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al₂O₃ destabilized the K–CO₂ bond; specifically, H₂O mitigates the NO_x storage capacity losses associated with carboxylate competition.