Technical Note Reactive silica and strength of fly ashes

The use of fly ash in geotechnical engineering depends greatly on its pozzolanic reactivity. Though many factors influence the reactivity of fly ash it is well recognized that reactive silica and lime content play a major role. A new, accurate and reliable method for the determination of reactive silica content of fly ash has been established. The reactive silica content, obtained as acid soluble silica in about 2 to 3 N hydrochloric acid, is found to correlate well with unconfined compressive strength of fly ashes. The reactive silica content of fly ash is also important in the stabilization of soils using fly ash. © Rapid Science Ltd. 1998     

Formation of Colloidal Silica and Alumina During Experimental Granodiorite Weathering

The role of aluminum and silica in the formation of colloids during granodiorite weathering was studied on the basis of long-term experiments in batch reactors. Rock samples were dissolved in un-buffered solutions of initial pH 3.2, 5.4, and 9.9 at ambient conditions for 500 days. During weathering, extremely high supersaturation with respect to various secondary solids was attained in the solutions. Consequently, new solids, part of which was conserved in solutions as colloids, condensed. The mean concentrations of colloidal Si reached values of 70, 50, and 48 mol 1^–1 in the alkaline, neutral, and acid solutions, respectively. The mean concentrations of colloidal Al, reached values of 34, 22, and 12 mol 1^–1 in the alkaline, neutral, and acid solutions, respectively. The concentration of colloids gradually decreased after 200-400 days of experiment. This phenomenon was interpreted as being due to the competition between homogeneous nucleation and crystal growth. At the initial stages of the experiments, the colloidal species (predominantly colloidal Al) comprised a large proportion of the total amounts of aqueous species. Their share, however, decreased with time. The molar Al/Si-ratios of colloids were as high as 2–2.5 at the early stages of the experiment. After 250–300 days of experiments, on the other hand, these ratios decreased to values of about 0.5 in both the neutral and alkaline solutions and to a value of 0.15 in the acid solution. The evolution of colloids was consistent with the evolution of secondary solids in the sequence Al-hydroxides – clay minerals (illite, chlorite), in both the neutral and alkaline solutions. In acid solutions, the evolution of Al/Si-colloids was influenced by the presence of sulfate ion and Al-sulfate precipitation. Besides Al and Si, other elements, in particular Ca or Mg as a major component and Na, K, P, S, and Cl as minor components, readily participated in the formation of colloids.     

纳米硅粉水泥土的强度特性及固化机理研究

将性能优异的纳米硅粉作为外掺剂应用于水泥土改性研究。通过室内试验，探讨了纳米硅粉水泥土的强度特性。试验表明，一定掺量下的纳米硅粉能够显著提高水泥土的各个龄期强度。结合试验测试和理论分析，探讨了纳米硅粉在水泥水化硬化过程中的作用以及纳米硅粉与土之间的作用，在此基础上，分析了纳米硅粉改性水泥土工程性状的机理，旨在为纳米硅粉应用于工程实践开展理论和试验研究探索。     

液液萃取-固相萃取富集地下水中毒杀芬的对比研究

应用液液萃取、固相萃取柱、固相萃取盘等传统和现代富集技术,对半挥发性有机物进行提取,建立了气相色谱-负化学电离质谱测定地下水中毒杀芬的方法。对性能较好的自制GDX-502固相萃取柱进行了条件优化。结果表明,使用填制的GDX-502固相萃取柱富集地下水中的毒杀芬,基体加标回收率为92.3%～98.5%,优于商品固相苯取柱LC-C18、ENVITM-C18以及固相萃取盘(92.8%～96.8%)和液液萃取(80.3%～88.5%);GDX-502固相萃取柱富集速度低于固相萃取盘,但远高于LC-C18和ENVITM-C18;GDX-502固相萃取柱的批量处理样品能力(12个)高于固相萃取盘(6个);同时所使用的有机试剂量远低于液液萃取。GDX-502固相萃取柱的萃取效率、分析通量、经济性和环保性具有更大的优势。     

Time dependence of organic matter decay and mixing processes in Framvaren, a permanently anoxic fjord in South Norway

Three different layers have been identified in Framvaren, which has a maximum water depth of 184 m. One oxic layer above the redoxcline at 18–20 m. One anoxic layer from 20 to 100 m which is occasionally ventilated by a flow over the sill (which has a depth of 2.5 m), and finally a stagnant layer below 100 m. Using the release rate of silica from the bottom and measurements of the concentration of HTO it is possible to make some calculations on the annual volume of interleaving in the layers 25–50 m, 50–75 m, and 75–100 m together with the advective flows. Reliable values of the sulfide concentration were obtained by precipitating and weighing HgS together with careful protection of all anoxic water samples with argon. The light yellow color of the precipitate in the depth range 25 to 80 m indicates that the occasional ventilation will cause such reactions as 0.50₂ + H₂S S(colloidal) + H₂O. The elemental sulfur, being stabilized with HS^–, is set free upon the precipitation of HgS. The new data for the concentration of sulfide give an acceptable stoichiometry for the decay reaction of organic matter. This is not the case with the data of Yao and Millero. The mean values for the concentrations of ammonium and phosphate agree with the new data of Yao and Millero. The mol/mol C/N ratio of 10.1 found in trapped material by Naess and coworkers (1988) agrees with the stoichiometry of the dissolved constituents, i.e. C/N = 9.92 ± 0.45. A denitrification reaction is suggested to explain the high values of C/N. The vertical diffusion coefficient at 100 m calculated from the depth profile of silica was 0.92 × 10^–6 m² s^–1 which lies in the range of values given by Fröyland. Finally, the ¹⁴C age of the total dissolved inorganic carbon (Ct) in the water below 90 m was about 1600 years indicating a bioproduction in the period 8000 years B.P. to A.D. 1853 when a channel was opened between the fjord outside (Helvikfjord) and Framvaren.     

二氧化硅溶解度方程和地温计

对地表至下地壳和上地幔温压条件下二氧化硅溶解度实验研究的进展进行了综述，并给出了石英和非晶质ＳｉＯ２在纯水和盐水溶液中的溶解度定量方程，介绍了估算地热库温度的ＳｉＯ２地质温度计。     

硅灰石合成多孔二氧化硅 ——工艺条件与产物性质研究

在一系列硅灰石酸处理实验基础上，研究了产物性质与反应速度、反应时间、中和最终pH值等工艺条件的关系。结果表明，工艺条件不同，物理性质也大不相同。     

辽-蒙交界地区晚侏罗世高硅花岗岩:岩石成因与地质意义

高硅(SiO2 ＞70％)花岗岩不仅是指示大陆地壳成熟度的重要标志,而且蕴含大陆地壳分异机制和稀有金属元素运移行为的关键信息.跨越辽宁-内蒙古两地分布的白音花岩基是沿华北克拉通与中亚造山带边界断裂带侵位的重要的中生代高硅花岗岩,但其形成时代和岩石地球化学特征一直缺乏系统刻画.本次离子探针(SIMS)锆石U-Pb测年指示...     

浅谈影响铝土矿中二氧化硅测试质量的因素

文章分析、总结了影响铝土矿中二氧化硅测试质量的因素 ,即操作因素、样品因素、温度及试剂因素 ,提出了提高铝土矿中二氧化硅测试质量的办法     

口径20厘米蜂窝熔石英平面镜制造及加工情况简介

本文叙述了口径２０．７厘米，厚３厘米，采用蜂窝结构的熔石英平面镜坯的制造与磨制情况。给出了最后面形的干涉图及阴影图。