Study of the early hydration of Ca3SiO5 by X-ray photoelectron spectrometry

C₃S pastes (W/S = 0.5), have been studied from 5 seconds to 4 hours by X-ray Photoelectron Spectrometry. XPS reveals surface transformations of C₃S grains from very early ages of hydration. The modifications have been evidenced by a change in the environment of Si atoms and a variation of the Ca/Si ratio. A Primary Hydrate (C/S << 3), a Secondary Hydrate ($\text{C/S}\text{?2}$) and a Tertiary Hydrate (CSH type I) have been identified. XPS is a sensitive and reproducible method for the study of the surface C₃S hydration.     

Absorption spectra of CrO44− in Ca3SiO5 and Ca3Al2O6

C₃S and C₃A are synthesized with chromium oxide in solid solution. The optical spectrum recorded in the range 8000 to 30000 cm^? can be interpreted by assuming that chromium substitutes for silicon and aluminum in C₃S and C₃A, respectively, as Cr^IV and Cr^V in tetrahedral coordination.     

Mechanical properties of directionally solidified Al2O3/Y3Al5O12 eutectic ceramic prepared by optical floating zone technique

Al₂O₃/Y₃Al₅O₁₂(YAG) directionally solidified eutectic (DSE) crystal was prepared by optical floating zone technique. Al₂O₃/YAG DSE consists of continuous entangled Al₂O₃ and the YAG forming a three-dimensional networks structure. The volume fraction of porosity is ultra-low (0.013%) and the average equivalent diameters of most pores (>84%) are smaller than 4?μm. The Al₂O₃/YAG DSE shows excellent high-temperature elastic stiffness. The Young’s modulus at 1500?°C maintains more than 85% of the value at room temperature. Bending strength exhibits excellent retention up to high temperature as well. High-temperature ball indentation testing shows plastic deformation involving dislocations and twinning, which predominantly occur in Al₂O₃ phase, while the YAG phase is stable. Evaluation on H_v/E index predicts Al₂O₃/YAG DSE with moderate capability to accommodate damages. Our results highlight Al₂O₃/YAG DSE as excellent high-temperature structural materials.     

Si NMR Study of the Hydration of Ca3SiO5 and ß-Ca2SiO4 in the Presence of Silica Fume

²⁹Si magic-angle spinning nuclear magnetic resonance (MASNMR) was used to study the room-temperature hydration of C₃S, ß-C₂S, and reactive ß-C₂S mixed with different amounts of silica fume (SF) that had been hydrated up to nine months and longer. The overall CaO:SiO₂ molar ratios of the mixes were 0.12, 0.20, 0.35, 0.50, and 0.80. NMR spectroscopy was used to quantify the remaining starting materials and the resulting hydration products of different species. A broad peak assigned to Q³, appearing in both the fourier transform (FT) and the cross-polarization (CP) modes, increased in intensity with increased SF content and with age. This Q³ species was attributed to two sources: (1) the surface hydroxylation of SF and (2) the cross-linking of dreierketten (chains of silicate tetrahedra arranged in a repeating three-unit conformation) in the calcium silicate hydrate (C-S-H) structure. A Q⁴ species also appeared in the CP spectra of samples with large SF additions after extended hydration and was attributed to cross-polarization by adjacent hydroxylated Q³ species at the surface of amorphous SiO₂.     

溶胶-凝胶法合成纳米Ca3SiO5:Eu2+荧光粉

用溶胶-凝胶法在弱还原气氛下合成了纳米级Ca3SiO5:Eu2 绿色荧光粉.研究了Eu2 浓度的含量对发光强度的影响,表明在Ca3SiO3:Eu2 中添加Eu2 的最佳含量为0.005 mol.x射线衍射分析表明:在1000～1200 ℃合成的Ca3SiO5:0.005 Eu2 样品为单相Ca3SiO5晶体.根据Scherrer公式计算样品的平均晶粒尺寸为30 nm左右,与扫描电镜分析结果基本相符.样品的发射光谱与激发光谱都为宽带谱,其中发射光谱是峰值为505 nm的不对称宽带谱,而激发光谱是主峰为374 nm的连续光谱.     

Influence of additives on the autoclave reactions of β-Ca2SiO4 and Ca3SiO5 at 170 °C

The products formed from β-Ca₂SiO₄ and Ca₃SiO₅ in the autoclave at 170°C are influenced by the presence of Al₂O₃, Fe₂O₃, Na₂O and B₂O₃, whether in solid solution in the starting material or added to the mix in suitably reactive compounds. The most important conclusion is that Al₂O₃, Fe₂O₃ and Na₂O all favour the formation of the orthorhombic α-2CaO.SiO₂.H₂O as against hillebrandite or tricalcium silicate hydrate. Addition of Na₂O, or especially of B₂O₃, retards the hydration of both β-Ca₂SiO₄ and Ca₃SiO₅.     

Synthesis of MgSiO3 ceramics using natural desert sand as SiO2 source

High-quality inorganic minerals are being increasingly consumed in the fabrication of ceramics. In the present work, desert sand was adopted as the source of SiO₂ to synthesize MgSiO₃ and MgSiO₃SiC composite ceramics in an endeavor to economize on mineral resources and improve the desert ecosystem through the industrial application of desert sand. Experimental results show that the use of drift sand enabled the formation of glass phase at lower temperatures, which promoted protoenstatite transformation, prevented sintering cracking, and densified the ceramic bodies. The composites consisted of MgSiO₃ (protoenstatite), SiC, glass phase, and small amounts of forsterite and SiO₂. The addition of SiC particles caused the green bodies to resist densification, but this was improved by increasing the sintering temperature. The composite ceramic containing 30 wt % of SiC and sintered at 1350 °C had the highest bending strength, whereas that containing 50 wt% of SiC and sintered at 1400 °C had the highest hardness and the lowest coefficient of thermal expansion among all the samples.     

Hydration of calcium chlorosilicate Ca3SiO4Cl2

The investigations of the hydration of the calcium chlorosilicate have shown that this phase dissolves congruently. However, unlike in the case of calcium orthosilicate, a high content of silica is retained in the solution. The dissolution process proceeds at first rather slowly and after 60 minutes its rate becomes considerably increased. On the calorimetric curve this corresponds to a short induction period. After 2 hours the hydrates are already detectable by X-ray examination. They are for H₂O/dry sample = 10, CSH and CH, and for H₂O/dry sample ratio = 1, CSH, CaCl₂CHH and CH. An addition of the SiO₂ gel or CSH phase considerably accelerates the process, reducing simultaneously the induction period. Under these conditions the hydrates are detectable by X-ray examination after 1 hour. It is probable that the induction period occuring in the hydration of chlorosilicate is due to the nucleation of the CSH phase.     

Hydration of polyphase Ca3SiO5-Ca3Al2O6 in the presence of gypsum and Na2SO4

Alite (Ca₃SiO₅: C₃S^*) and calcium aluminate (Ca₃Al₂O₆: C₃A) are the major phases in Portland cement, which have an essential role in the development of early age properties. The effects of gypsum content, fineness, and Na₂SO₄ addition on the early-stage hydration kinetics are investigated for polyphase (co-sintered) Ca₃SiO₅-Ca₃Al₂O₆ model systems using calorimetry, X- ray diffraction, thermal analysis, and solid-state ²⁷Al and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. The results demonstrate that the hydration of C₃A significantly affects the hydration of C₃S. The C₃S and C₃A hydration is hindered considerably in severely over-sulfated systems (where C₃A hydration is suppressed due to a very high gypsum content) and systems with additional Na₂SO₄. Although there is a considerable amount of Al incorporation in the C-S-H phase, no clear trends with respect to gypsum content, hydration age or Na₂SO₄ addition are observed for the Al_IV/Si ratios of the C-S-H phase determined from ²⁹Si NMR. With the addition of Na₂SO₄, recrystallization of ettringite from the AFm phases is postponed from 1 day to 7 days. *Cement chemistry notation: C-CaO, S-SiO₂, A-Al₂O₃, -SO₃, N-Na₂O.     

Single- and multi-wall carbon nanotubes produced using the floating catalyst method: Synthesis, purification and hydrogen up-take

The floating catalyst (FC) method for synthesis of single- and multi-wall carbon nanotubes was optimized and scaled up to yield 6 g/h and 20 g/h of products, respectively. Different CNTs purification methods were compared. It was found that the procedure involving room temperature bromination is the most effective to purify the FC-CNTs. The hydrogen up-take capacities of the different products were measured using the quasi-equilibrium volumetric method. It was shown that, at room temperature and gas pressure up to 150 atm for both SWCNTs and MWCNTs, hydrogen up-take does not exceed 1.5 wt.% and is weakly dependent on the product purity.     

Mechanical properties up to 1900 K of Al2O3/Er3Al5O12/ZrO2 eutectic ceramics grown by the laser floating zone method

Directionally solidified Al₂O₃–Er₃Al₅O₁₂–ZrO₂ eutectic rods were processed using the laser floating zone method at growth rates of 25, 350 and 750 mm/h to obtain microstructures with different domain size. The mechanical properties were investigated as a function of the processing rate. The hardness, ∼15.6 GPa, and the fracture toughness, ∼4 MPa m^1/2, obtained from Vickers indentation at room temperature were practically independent of the size of the eutectic phases. However, the flexural strength increased as the domain size decreased, reaching outstanding strength values close to 3 GPa in the samples grown at 750 mm/h. A high retention of the flexural strength was observed up to 1500 K in the materials processed at 25 and 350 mm/h, while superplastic behaviour was observed at 1700 K in the eutectic rods solidified at the highest rate of 750 mm/h.     

Synthesis of Ca2SiO4:Dy3+ phosphors from agricultural waste for solid state lighting applications

Trivalent dysprosium (Dy³⁺) ions -doped calcium silicate (Ca₂SiO₄) phosphors have been synthesized by utilizing agricultural waste of egg shell and rice husk through solid-state reaction method. The synthesized Ca₂SiO₄ powders thus obtained are crystallized in monoclinic structure with unit cell parameters of a = 5.53 Å; b = 6.67 Å; c = 9.13 Å; β = 87.43° and irregular shape morphology. Luminescent properties of Dy³⁺:Ca₂SiO₄ phosphors were studied by varying active ion concentration. The phosphors emit characteristic blue and yellow emissions of Dy³⁺ ions corresponding to the ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 transitions, respectively. Color coordinates evaluated from emission spectra are found to fall in the white light region. Decay curves for the ⁴F_9/2 level of Dy³⁺ ions exhibit single exponential nature and turn into non-exponential with shortening of lifetime from 739 µs to 510 µs when Dy³⁺ ion concentration is increased from 0.001 to 0.5 mol%. All these results confirm that Ca₂SiO₄:Dy³⁺ phosphors are suitable for the use as low cost white light emitting phosphors.     

Bi2SiO5/SiO2的合成及催化丙烯气相环氧化反应

水热法合成了具有介孔特征的系列Bi2SiO5/SiO2催化剂（记为SBn,n为Si与Bi物质的量比,n=0.5、5、10、20、50）,并通过X射线粉末衍射、N2物理吸附-脱附和扫描电镜等技术对SBn催化剂进行表征。结果表明,以O2为氧源,SBn催化剂在气相丙烯环氧化反应中具有良好的催化活性。在温度330 ℃,SB20催化剂上环氧丙烷选择性达50%,对应丙烯转化率为0.6%;而在温度470 ℃时,SB20催化剂上丙烯转化率接近20%,但环氧丙烷选择性降至20%。     

Synthesis of tinidazole by condensation–oxidation sequence using MoO3/SiO2 bifunctional catalyst

Antimicrobial drug, tinidazole has been synthesized by condensation of 2-methyl,5-nitro-imidazole and 2-ethyl-thio-ethanol over MoO₃/SiO₂ catalyst to obtain 1-(2-ethyl-thio-ethanol)-2-methyl-5-nitro-imidazole which is further oxidized using hydrogen peroxide using the same MoO₃/SiO₂ catalyst to obtain tinidazole. MoO₃/SiO₂ catalyst (20%), synthesized by sol–gel process showed the highest acid strength and was successfully demonstrated to catalyze both condensation and oxidation in the synthesis of tinidazole. Due to the bifunctional activity of the catalyst, the use of acetic acid for condensation step and tungstic acid or ammonium molybdate for oxidation step in the conventional synthesis of tinidazole could be eliminated, thus making it an environmentally benign process. The catalysts could be recycled five times without any appreciable loss in the conversion and selectivity showing the potential for the use of MoO₃/SiO₂ as bifunctional catalyst for the production of this industrially important compound.     

H3PW12O40/SiO2催化合成糠醛乙二醇缩醛的研究

采用溶胶-凝胶法制备出具有Keggin结构的杂多酸H3PW12O40/SiO2复合催化剂,用FT-IR,XRD等手段表征了其结构形态。考察了复合催化剂催化合成糠醛乙二醇缩醛的工艺条件,其中重点考察了反应物配比、催化剂用量、反应时间及催化剂的重复使用性能等对产品收率的影响。结果表明:合成糠醛乙二醇缩醛的较优反应条件为:n(醛)/n(醇)=1.0/1.2,催化剂的用量为糠醛质量的6.0%,环己烷为带水剂,反应时间4.0 h。上述条件下,产物的收率可达85.0%以上。     

The thermal decomposition of Ca3SiO5 at temperatures below 125o°: Part 3. The influence of water and sulphate on the decomposition

The presence of water vapor is shown markedly to increase the rate of decomposition of Ca₃SiO₅. Molten K₂SO₄-CaSO₄ eutectic mixture also drastically increases the rate of decomposition of Ca₃SiO₅ at temperatures as low as $\text{ca}$ 800°.     

沉淀法SiO2包覆纳米CaCO3吸附剂性能

以CO₂为沉淀剂,Na₂SiO₃为硅源,制备了SiO₂包覆纳米CaCO₃吸附剂。TEM测试证实纳米CaCO₃表面包覆一层SiO₂膜, 用SEM & EDX 测试5个包硅样品Si含量为0.67%～4.93%。采用TGA考察吸附剂的分解温度及600℃、20% CO₂条件下的吸附性能。结果表明：采用CO₂沉淀法包覆SiO₂后,与未包硅的纳米CaCO₃相比,分解温度降低9～42℃。纳米SiO₂/CaCO₃吸附剂的循环吸附率、吸附容量、吸附速率均随Si含量的减小先增加后降低。Si含量为1.05%的纳米SiO₂/CaCO₃吸附剂显示最佳吸附性能,第1、5次循环吸附容量分别为8.9、6.0 mol·kg^-1,与未包覆SiO2的纳米CaCO₃相比,分别提高11%、50%,同时在第5次循环快反应段吸附速率较纳米CaCO₃提高10%。与纳米CaCO₃相比,包硅后的吸附剂具有较高的吸附容量和循环吸附率,循环稳定性较好。     

超增溶自组装法合成纳米AlPO_4-5分子筛

采用超增溶自组装法合成纳米级AlPO4-5分子筛,考察了焙烧温度、乳化剂质量分数对分子筛粒径及其分布的影响,结果表明在超增溶纳米自组装的条件下能够合成出类球形的纳米磷铝分子筛,并且通过调节乳化剂的质量分数可以控制纳米分子筛的粒径大小,纳米磷铝分子筛直径为10~80 nm,长度为0.1~0.2μm。     

Crystal growth and ferroelectric property of Na0.5K0.5NbO3 and Mn-doped Na0.5K0.5NbO3 crystals grown by floating zone method

Na_0.5K_0.5NbO₃ (NKN) and Mn-doped NKN crystals, which are one of the promising candidates of lead-free piezoelectric materials, were grown by using a floating zone (FZ) method. The resulting crystal growth was compared with crystal growth that resulted from using a flux method in a previous study. In the crystal grown by FZ method under where the growth rate was controlled to 3 mm/h, thin layers formed parallel and perpendicular directions to the growth direction. In the crystal grown by FZ method, the crystal structure could not be classified as having the orthorhombic lattice of Amm2, which was observed in the crystal grown using a flux method. It was found that doped Mn was substituted in the perovskite-type lattice of NKN. Pure NKN crystals showed 90° domains that had a zig-zag shape, whereas Mn-doped NKN crystals were aligned to the domain layers in straight lines. It was confirmed that Mn-doped NKN crystal showed a square P–E hysteresis loop.     

Microstructure and mechanical properties of Al2O3/Er3Al5O12 eutectic rods grown by the laser-heated floating zone method

Eutectic rods of Al₂O₃-Er₃Al₅O₁₂ were grown by directional solidification using the laser-heated floating zone method at rates in the range 25-1500 mm/h. Their microstructure and mechanical properties (hardness, toughness and strength) were investigated as a function of the growth rate. A homogeneous and interpenetrated microstructure was found in most cases, and interphase spacing decreased with growth rate following the Hunt-Jackson law. Hardness increased slightly as the interphase spacing decreased while toughness was low and independent of the microstructure. The rods presented very high bending strength as a result of the homogeneous microstructure, and their strength increased rapidly as the interphase spacing decreased, reaching a maximum of 2.7 GPa for the rods grown at 750 mm/h. The bending strength remained constant up to 1300 K and decreased above this temperature. The relationship between the microstructure and the mechanical properties was established from the analysis of the microstructure and of the fracture mechanisms.