几种乙酸铵离心法测定土壤阳离子交换量的方法探讨

乙酸铵离心交换法测定酸性和中性土壤阳离子交换量是经典方法,但此方法的蒸馏过程繁琐、时间长、效率低。本文引用纳氏试剂分光光度法测定土壤CEC值,并将结果与乙酸铵离心法常用的几种传统测定方法进行了实验对比和总结。通过对国家标准样品及实际土壤样品的CEC值测定,纳氏试剂比色法的精密度在2-4%之间,准确度与经典方法一致。与传统滴定法比较,取代了蒸馏的步骤,测定方法简单,干扰少,结果可靠,可操作性强。     

Oil in Louisiana's estuarine environments: A development model

Coastal erosion, accelerated by sea level rise, and subsidence are major Louisiana issues. With current sea-level-rise projections, coupled with the state's eroding barrier islands and coastal wetlands, the region's estuarine environments are in jeopardy of being lost, redefined, or permanently altered. As the coast erodes, Louisiana is endangered of losing valuable wetland's habitat. In addition, if the barrier islands disappear, the region's wetland-oriented oil and gas wells and associated infrastructure will be at risk to open Gulf conditions. If this should occur, each well, pipeline, and storage battery represents a potential environmental catastrophe.     

Controlled Fabrication of Cd-Bi Nanoparticles via Sonochemical Method

IntroductionMetal or alloy nanoparticles,because of their con-spicuous physicochemical properties,have been widelyapplied to various fields such as electronics,catalysis,magnetism,and corrosion-resistant materialsfields[1—4].It has been estimated that the particle sizeand the properties of nanoparticles depend strongly onthe specific method of fabrication and the applied ex-periment conditions,which makes the controlled syn-thesis of nanomaterials become an increasingly activeand important ar…     

素理想完全分裂的一个判别法则

本文给出了数域K内一个素理想在K的有限次正规扩域L内完全分裂的一个判别法则。     

Effect of Light on the Electrokinetic Behavior of TiO(2) Particles in Contact with Cr(VI) Aqueous Solutions

The electrokinetic behavior of titanium dioxide particles (Degussa P25, mainly composed of anatase) put in contact with chromium(VI) aqueous solutions is highly sensitive to light exposure under normal laboratory conditions. In the dark, adsorption of Cr(VI) gives rise to substantial decrements in the mobilities, especially in the acidic branch, and, at higher concentrations, to shifts in the isoelectric point (pH(piep)) to lower values, as expected for anionic chemisorption. A two-mode adsorption model accounts qualitatively for the results. Under light, pH(piep) shifts in the opposite direction as the Cr(VI) concentration increases. A maximum value is attained at [Cr(VI)] approximately 10(-3) mol dm(-3), pH(piep) 8.2, which coincides with values reported for hydrous chromium(III) oxides. At higher concentrations, Cr(VI) adsorption defines a shift of pH(piep) to lower values. It is concluded that light absorption by titanium dioxide promotes the reduction of Cr(VI) and the surface precipitation of the hydrous Cr(III) oxide. The values of pH(piep) for partially covered surfaces are well described by a simple model of surface ionization derived earlier. FTIR/ATR analysis of the surfaces supports this interpretation, and further suggests that one of the modes of Cr(VI) adsorption implies surface dimerization to yield adsorbed dichromate. Copyright 2000 Academic Press.     

A Robust, Environmentally Benign Catalyst for Highly Selective Hydroformylation

By a sol-gel process a rhodium complex containing a diphosphane with a large natural P-Rh-P bite angle is covalently anchored in a silica matrix (see picture). The immobilized catalyst is a very selective hydroformylation catalyst that is completely and conveniently separated from the product and can be reused in numerous cycles.     

Passages through resonance in weakly nonlinear systems

A method of determining asymptotic expansions for weakly couplednonlinearly perturbed systems of harmonic oscillators with slowlyvarying frequencies is presented. In an example with two oscillators,each one experiences a separate resonance passage that producesa first-order amplitude change. Simultaneously, second-orderadjustments occur to both oscillators. The determination isachieved by carrying the calculations to third order.     

Sol-gel coatings for chemical protection of stainless steel

Sol-gel thin coatings of ZrO₂, SiO₂, 70SiO₂-30TiO₂ and 88SiO₂-12Al₂O₃ compositions (mole %) have been prepared from sonocatalyzed sols and deposited by dip-coating technique on 316L stainless steel foils. The influence of the coatings on the chemical corrosion of the substrate has been measured through potentiodynamic polarization curves in aqueous 15% H₂SO₄ solution between 25 and 50°C. The values of the corrosion potential, polarization resistance and corrosion rate have been determined. Analysis of the data combined with scanning electron microscopy studies indicate that the films act as a geometric blocking against exposure to the corrosive media and increase the lifetime of the substrate up to a factor 8.5.