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31.
François Rassineux Jean Claude Petit Alain Meunier 《Journal of the American Ceramic Society》1989,72(6):1026-1032
The long-term durability of cementbased materials over periods of time not directly accessible to laboratory experiments has to be thoroughly assessed to guarantee the safety of a radioactive waste repository. In this work, archaeological mortars and concretes have been studied to check whether their use as analogues of actual technological cements used for waste disposal is possible. Samples of mortar and concrete have been collected from several Gallo-Roman thermae of western France; they were examined as petrographically thin sections with optical microscopy and were analyzed by X-ray diffraction of microsamples (10−3 mg) and by electron probe microanalysis. The masonry cement appears to be entirely carbonated with large voids and fissures. In contrast, the use of lime with additional crushed brick or tile for the bath structure concrete and coating mortar induced pozzuolanic reactions. Despite the fact that the matrices are essentially composed of calcium carbonate, calcium aluminosilicates with compositions close to those of hydrogrossular, hydrated calcium silicates with composition and a structure comparable with those of calcium hydrosilicate formed in modern cement, and ettringite deposits in voids of concretes could also be identified. It is suggestea that these ancient artifacts can help identify very slow processes that rule cement alteration over long periods of time. The artifacts may be considered as possible analogues of present-day materials whenever sufficient care is taken in interpreting and extrapolating data. 相似文献
32.
D. Karami S. Rohani 《Chemical Engineering and Processing: Process Intensification》2009,48(8):1288-1292
Four methods were used for the synthesis of pure zeolite Y using soluble silicate as a silica source: (1) the gelling of soluble silicate to silica–alumina gel, by aluminate (or aluminium sulphate), (2) the precipitation of soluble silicate to precipitated silica–alumina gel, by aluminate (or aluminium sulphate), (3) the gelling of soluble silicate by sulphuric acid plus alumina impregnation, and (4) the precipitation of soluble silicate by sulphuric acid plus alumina impregnation. A 24 two-level factorial design was used to study the influence of four different variables on the purity of zeolite Y (expressed in terms of degree of crystallinity). The ageing time turned out to be the most significant variable. Synthesis time, alkalinity and mixing rate were also found to be statistically significant. X-ray diffraction patterns were used to characterize the samples, which ranged from well-crystallized faujasite structures to amorphous materials. The highest purity achieved in method (1) was 38%. The best synthesis condition derived from method (1) was applied to the other three methods. Only method (4) yielded the pure zeolite Y. Therefore, the effect of silica–alumina precursor preparation on producing the pure zeolite Y is extremely important. 相似文献
33.
Nanoclays for polymer nanocomposites, paints, inks, greases and cosmetics formulations, drug delivery vehicle and waste water treatment 总被引:2,自引:0,他引:2
Hasmukh A. Patel Rajesh S. Somani Hari C. Bajaj Raksh V. Jasra 《Bulletin of Materials Science》2006,29(2):133-145
An overview of nanoclays or organically modified layered silicates (organoclays) is presented with emphasis placed on the
use of nanoclays as the reinforcement phase in polymer matrices for preparation of polymer/layered silicates nanocomposites,
rheological modifier for paints, inks and greases, drug delivery vehicle for controlled release of therapeutic agents, and
nanoclays for industrial waste water as well as potable water treatment to make further step into green environment. A little
amount of nanoclay can alter the entire properties of polymers, paints, inks and greases to a great extent by dispersing 1nm
thick layered silicate throughout the matrices. The flexibility of interlayer spacing of layered silicates accommodates therapeutic
agents which can later on be released to damaged cell. Because the release of drugs in drug-intercalated layered materials
is controllable, these new materials have a great potential as a delivery host in the pharmaceutical field. The problem of
clean water can be solved by treating industrial and municipal waste water with organoclays in combination with other sorbents
like activated carbon and alum. Organoclays have proven to be superior to any other water treatment technology in applications
where the water to be treated contains substantial amounts of oil and grease or humic acid. 相似文献
34.
Hing Wah Chan David G. Howitt Alan B. Harker 《Journal of the American Ceramic Society》1989,72(6):1040-1043
The microstructures of simulated tailored ceramic forms for the Idaho Chemical Processing Plant (ICPP) high-level waste were characterized by TEM. The ceramic forms were consolidated from simulated ICPP waste calcines with either silicayttria-based or silica–lithia-based additives by hot isostatic pressing. The hot isostatically pressed ceramic waste forms are composed of cubic CaF2 , monoclinic ZrO2 , stabilized cubic ZrO2 , tetragonal ZrSiO4 , and amorphous silicate phases which can be phase separated. The phaseseparated glass is a result of phase immiscibility in the soda aluminosilicate glass to the compositions of albite and mullite. 相似文献
35.
Cynthia A. Powell-Doan Arthur H. Heuer 《Journal of the American Ceramic Society》1990,73(12):3670-3676
Characterization of the microstructure and microchemistry of a group of commercial 96% Al2 O3 ceramics, using analytical and conventional electron microscopy techniques, was conducted. A continuous glassy grain-boundary phase was found in all samples, in addition to a number of intragranular and intergranular crystalline second phases; the phases present depended on the original boundary-glass composition. The faceted nature of many of the Al2 O3 -glass interfaces was studied and is thought to be an equilibrium structure. 相似文献
36.
Saturated solutions rerely form when the anhydrous constituents of aluminous and portland cement are stirred in water or in lime solutions of increasing concentrations. Apart from monocalcium aluminate, concentration of ions in solution cannot exceed maximum supersaturation with respect to the hydrate most likely to precipitate. The present work shows such a behavior for β-C2 S suspended in water and in lime solutions at low concentration. In more concentrated lime solutions, a short lifetime saturation state with respect to β-C2 S seems to be reached. 相似文献
37.
38.
针对矽酸盐型镍矿石采用目前成熟的浮选方法回收其中的镍,在产出合格镍精矿的前提下,通过强化矿浆分散、脱泥的小型试验和工业试验,镍回收率提高有限.为进一步提高镍回收率,对工艺条件、流程结构和选矿设备进行分析,提出建议,以期充分利用有限的镍资源. 相似文献
39.
采用水热电泳沉积法在SiC-C/C复合材料SiC内涂层表面制备了硅酸钇抗氧化外涂层,并借助X射线衍射(XRD)、扫描电子显微镜(SEM)对涂层的相组成及显微结构进行了表征.讨论了沉积电压对硅酸钇涂层沉积量及显微结构的影响,并研究了不同沉积电压下涂层沉积量与时间的关系,同时测试了涂层试样的抗氧化性能.研究结果表明,随着沉积电压的升高,涂层的沉积量有所增加,涂层的致密性和均匀性也逐渐得到改善.当电压为210V时达到最佳,继续升高沉积电压,涂层的均匀性变差,当沉积电压为240V时,涂层出现明显开裂;不同沉积电压下涂层沉积量随时间呈抛物线变化;涂层在1500℃静态空气中经过10h氧化后,失重仍然小于2%. 相似文献
40.
C.B Samantaray 《Microelectronics Journal》2004,35(8):655-658
The energy band gaps and total density of states of different transitional metal (Sc, Zr) silicates have been studied using density functional theory and local density approximation. The problem of a decreasing band gap in Zr silicate predicts the band offset reduction from the introduction of 4d state below the conduction band edge. While, in case of Sc silicate, there is no such decrease in the band gap and it becomes more suitable for the device performances. 相似文献