Photosensitive Characteristics of Dopant-Free, Ultraviolet-Sensitive Calcium Aluminate Glasses

Calcium aluminate glasses show high sensitivity to ultraviolet radiation without the doping of optically active components. In this paper, photosensitive characteristics and the cause of UV-induced coloring were investigated for these glasses. Ultraviolet rays below 270 nm were effective for inducing the coloring. The most effective wavelength agreed with that of the apparent absorption edge. In the ternary system with SiO₂ or GeO₂, the sensitivity was monotonically reduced with the amount of the third component and almost vanished for the compositions containing 40 mol%. On the basis of the establishment of a close correlation between two optical absorption bands and two electron spin resonance signals induced by UV illumination, the UV-induced coloring was concluded to be due to the emergence of an aluminum-oxygen hole center (Al-OHC) and an ozonide (O₃^-).     

Dopant-Free Ultraviolet-Sensitive Calcium Aluminate Glasses

Dopant-free calcium aluminate glasses are very sensitive to ultraviolet radiation; new optical absorption bands rapidly appear around 400 nm on illumination and are easily bleached when the glass is heated to >100° to 250°C. This coloringbleaching process is reversible when the illumination and heating cycles are repeated, A clear correlation was found between the intensities of the uv-induced optical absorption and the ESR signal of Al-OHC.     

Optical and Physical Properties of Some Calcium Aluminate Glasses

Calcium aluminate glasses containing alkali oxides and iron oxide will transmit infrared radiation to about 6 μ and still have satisfactory working properties. Their refractive index, density, expansion, Young's modulus, modulus of rupture, fracture velocity, Knoop hardness, and some electrical and chemical properties are evaluated.     

铝酸钙玻璃中羟基对红外透过性能的影响

采用不同熔化方法制备了铝酸钙红外玻璃并考察了其红外透过性能。研究了结构中的羟基对玻璃红外透过性能的影响。通过红外光谱和固体核磁共振技术对玻璃中羟基的结构特征、氢键结合状态以及红外吸收情况进行了研究和探讨。结果表明:羟基会引起铝酸钙玻璃在近红外2.9μm左右的宽带吸收,这是由于玻璃中羟基结构形式的多样化所造成的;在玻璃结构中,羟基与氢键结合会造成振动频率下降,红外吸收峰向长波移动,羟基氢键结合强度越大,长波移动越严重,羟基与氢键结合形式越多,羟基的红外吸收范围越宽;在铝酸钙红外玻璃中主要存在3种羟基存在形式:孤立羟基基团、邻近的羟基对和带有氢键的单个羟基。不同制备方法获得的玻璃结构中羟基存在形式基本相同。     

The Influence of Some Transition Elements on Visible and Infrared Transmission of Calcium Aluminate Glasses

A number of calcium aluminate glasses have been developed for use as infrared-transmitting window materials. These glasses have been stabilized with respect to devitrification by introducing alkali and iron into the batch composition. The iron reduced visible transmission of these glasses and at the same time to a lesser extent tends to decrease infrared transmission as the iron concentration increases. In a study of the influence of transition elements, Mn and particularly Cu are found to increase significantly the infrared transmission of these iron-alkali stabilized calcium aluminate glasses.     

Silicon-Free Oxynitride Glasses Via Nitridation of Aluminate Glassmelts

Aluminate-oxynitride glasses were synthesized by melting calcium-aluminate-based compositions with various amounts of AlN in a nitrogen atmosphere. X-ray amorphous Ca-Al-Mg-Ba-O-N oxynitride glasses free of metallic inclusions containing up to ∼1 at. % N were obtained. Nitride additions increased the glass transition temperatures while decreasing thermal expansion, as in other Sicontaining oxynitride systems.     

钙铝酸盐红外玻璃的微晶化

采用真空熔制方法制备出钙铝酸盐红外玻璃,通过热处理方法对玻璃进行微晶化获得钙铝酸盐微晶玻璃。研究了晶核剂ZrO_2对钙铝酸盐玻璃析晶机制的影响,以及不同微晶化条件下钙铝酸盐玻璃的析晶情况和红外透过性能。结果表明:晶核剂的引入改变了钙铝酸盐玻璃的析晶机制,未添加ZrO_2的铝酸钙玻璃的析晶主要为表面析晶,析出晶相主要是BaAl_2O_4、Ba_3Al_2O_6;添加ZrO_2后,玻璃向整体析晶转化,析出晶相以Ca_3Al_2O_6为主;在930~970℃范围内,通过控制处理温度和时间可以获得透明的含ZrO_2铝酸钙微晶玻璃,在3~5μm波段具有良好的红外透过性能,玻璃硬度达到8.04 GPa以上。     

高炉铝酸钙炉渣浸出过程动力学

研究了高炉铝酸钙炉渣的浸出动力学,考察了搅拌强度、浸出反应温度、浸出剂初始浓度及炉渣粒度对浸出速率的影响. 结果表明,浸出过程符合一级反应的收缩未反应核模型,宏观动力学方程为1+2(1-xB)-3(1-xB)2/3= 1.108exp(-1906/T)t,表观活化能为15.84 kJ/mol,过程速率为固膜内扩散速率控制. 通过实验数据验证,表明所得模型能较好地描述炉渣的浸出过程.     

Mechanism of the Blue Up-Conversion in Tm3+/Nd3+-doped Calcium Aluminate Glasses

Blue up-conversion fluorescence from the Tm³⁺:¹ G ₄→³ H ₆ (480 nm) transition has been observed from calcium aluminate glass codoped with Tm³⁺/Nd³⁺. The mechanism for the up-conversion process consists of a two-photon process. An excitation beam with a wavelength of 791 nm first excites Tm³⁺ to the ³ H ₄ level, where Tm³⁺ again absorbs the 1060 nm emission from Nd³⁺:⁴ F _3/2→⁴ I _11/2 to attain the Tm³⁺:¹G₄ level. Lifetime and intensity variations with compositions suggest the presence of an efficient energy transfer from Nd³⁺ to Tm³⁺. The highest 480 nm emission intensity has been obtained from the glass with 0.1 mol% of Nd₂O₃ and 0.2 mol% of Tm₂O₃.     

Properties of Some Calcium Aluminate Cement Compositions

The properties of some high-purity calcium aluminate cement compositions in that portion of the lime-alumina system from 64 to 86% alumina were investigated. The laboratory preparation of seven hydraulic compositions in this system is described. Methods of appraising the properties, both in the neat cement and in castable formulations, are given. Data on bond strength, setting properties, heat of hydration, refractoriness, and aging characteristics are presented. A cement composition represented by the empirical molar formula CaO 2. 5Al₂O₃ was found to be optimum for balanced bond strength and refractoriness in high-temperature castables.     

Interaction Between Superplasticizers and Calcium Aluminate Hydrates

Sodium lignosulfonate and naphthalene and melamine sulfonate formaldehyde condensates, dissolved in lime water, are adsorbed on C₄AH₁₃ and C₃AH₆. When dissolved in dimethylsulfoxide the same admixtures are adsorbed on C₄AH₁₃ but, apparently, not on C₃AH₆. The adsorption isotherms of the two polycondensates are very similar but different from those of lignosulfonate. This fact can be attributed to the considerable structural difference between the synthetic admixtures and the lignine derivative. The particle zeta potential is modified by the presence of the admixtures, minimum additions of which are enough to bring the zeta potential to negative constant values. Nevertheless, the values of the potential cannot be correlated with the viscosity of the aluminate hydrate pastes, since the viscosity first increases and then decreases as the admixture increases. This behavior can be explained by a bridging effect among the particles, which overcomes the repulsive effect due to zeta potential.     

Properties of Calcium, Strontium, and Barium Galliosilicate Glasses

Glasses in three alkaline-earth (Ca, Sr, and Ba) galliosilicate systems were prepared, and the density, viscosity, thermal expansion coefficient, and glass transformation temperature were measured. All glasses contain 30 mol% alkaline-earth oxide. It is suggested that alkaline-earth ions can play a role in the glass structure which is similar to that of an intermediate ion.     

Strength Development in Phosphate-Bonded Calcium Aluminate Cements

The chemical reaction at room temperature between calcium aluminate cement (CAC) and NH₄H₂PO₄-based fertilizer solution causes the formation of ammonium calcium pyrophosphate (AmCPP) as an amorphous cementitious phase. This phase was responsible for the development of strength in rapid-setting phosphate-bonded cement (PBC) specimens. Hydrothermal treatment of PBC at 200°C led to phase transformations of AmCPP and CAC into crystalline hydroxyapatite as the major phase and anorthite as the minor one. The moderate growth of these interlocked crystals in the interspaces of amorphous phases played an important role in creating a dense microstructure, thereby conferring a very high strength to the PBC. In contrast, an excessive crystal growth, which caused the formation of porous microstructure, resulted in a reduction in strength.     

Chemical Synthesis and Characterization of Calcium Aluminate Powders

The Pechini process was used to produce high-purity, monocalcium aluminate (CaAl₂O₄) powders at temperatures as low as 900°C. Absorption spectrometry and BET measurements revealed particles with sizes ranging from submicrometer to 100 μm, with specific surface areas as high as 10 m²/g. Auger electron spectrometry (AES) was used to study the progressive elimination of surface carbon from the organic burnout as a function of temperature. The growth kinetics of calcium aluminate crystallites from a polymeric precursor were studied during calcination as a function of temperature, using transmission electron microscopy (TEM). At the early stages of crystallization, the activation energy for crystallite growth was found to be 118 kJ/mol. This is substantially less than the 356 kJ/mol previously reported. A growth kinetic exponent of n = 1.68 was determined for the amorphous-to-crystalline transformation in the temperature range 700° to 850°C. These values were consistent with growth by short-range diffusion.     

氧化镁在铝酸钙盐中的固溶性

氧化镁在水泥熟料中的存在对安定性有直接的影响,因此了解氧化镁在各熟料矿物的固溶性至关重要.铝酸三钙是水泥熟料的主要溶剂型矿物之一,本文研究氧化镁在铝酸钙中的固溶性:空白试样3CaO+Al2O3,使用0. 5 mol和1 mol的氧化镁取代对应含量的氧化钙烧制铝酸盐矿物,与空白样进行研究对比.分别采用了XRD定性、精修XRD、岩相及SEM-EDS等分析方法进行研究对比.结果显示:本实验条件下,氧化镁的加入影响矿物的产物含量,更多的氧化镁固溶于过渡相C12A7中,氧化镁在它形晶比自形晶固溶量更大,Mg2+的含量与Al3+的含量呈正相关,氧化镁的局部最大固溶量可以达到9.28%,氧化镁固溶量还会使铝酸钙盐的衬度颜色改变.     

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.     

水合硫铝酸钙对脱硫效果的影响

通过研究铝酸钠溶液添加石灰进行脱硫反应,考察铝酸钠溶液浓度、石灰添加量、反应温度、反应时间对铝酸钠溶液脱硫效果的影响,给出各影响因素的最佳脱硫效果,利用XRD和化学分析确定含水硫铝酸钙存在的依据.     

Alkaline Activation of Blends of Metakaolin and Calcium Aluminate

The present paper reports the preliminary results obtained and analyzed in the framework of a joint Spanish–Japanese project on the behavior of blends of alkali-activated metakaolin (MK) and calcium aluminate cement (CAC). In these experiments, the materials were activated with an 8 M solution of NaOH, poured into molds, and subjected to brief thermal curing (2 or 20 h at 85°C). The hardened pastes were tested for mechanical strength and characterized for mineralogy and microstructure by a number of techniques (XRD, FTIR, BSEM, and MAS-NMR). The results showed that under the above conditions, the Al and Ca in the CAC were taken up into the aluminosilicate formed as the main product of the alkali activation of MK. None of the CAC hydration compounds (CAH₁₀; C₂AH₈; C₃AH₆; AH₃) normally formed were detected in any of the cases studied.     

Low-Silica Glasses Based on Calcium Aluminates

An exploratory study of the effects of compositional variation on glass formation in low-silica aluminate compositions revealed that CaO is essential for glass formation at ordinary quenching rates. Other oxides, such as Li₂O, MgO, BaO, ZnO, Na₂O, K₂O, BeO, B₂O₃, and PbO, can be present in the glass in limited amounts (in some cases up to 30 mol%). A necessary, but insufficient, condition for easy glass formation is that the ratio of oxygen ions to network-forming cations (assumed to be Si⁴⁺ and Al³⁺) be ∼2.5. The glass-forming compositions were also characterized by liquidus temperatures below ∼1500°C (2732°F). Young's modulus ranged from 13.0 to 17.8×10⁶ psi. Glasses containing network-modifying cations with high field strengths generally had the higher moduli. Strength (420,000 to 650,000 psi in 0.3-mil fibers), static fatigue, viscosity, annealing, and surface tension were studied to a limited extent for the composition (in mol%) 30Al₂O₃-4SiO₂-60CaO-6MgO.