一种新型光度探头的研制及铁的自动光度滴定

光度滴定不但能滴定常量物质,而且也能准确滴定浓度<1×10~(-5)mol·L~(-1)的微量物质.但目前光度滴定的应用还不很广泛,其主要原因在于,光度滴定计量点的判断一般要借助于分光光度计、液体循环池,并由绘制滴定曲线求得,相当麻烦.我们利用最大透光度570～600nm的黄色滤光片、小钨灯、光敏二极管,制成了一种高灵敏度的光度探头.配合MX-5型多功能化学分析仪,实现了自动光度滴定,并用于铁的测定取得了满意的效果.1 主要仪器与试剂     

Distinct Superconducting Gap on Two Bilayer-Split Fermi Surface Sheets in Bi_2Sr_2CaCu_2O_(8+δ) Superconductor

High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels:the bonding sheet corresponds to a doping level of 0.14,which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped,giving an overall doping level of 0.20 for the sample.Different superconducting gap sizes on the two Fermi surface sheets are revealed.The superconducting gap on the antibonding Fermi surface sheet follows a standard d-wave form while it deviates from the standard d-wave form for the bonding Fermi surface sheet.The maximum gap difference between the two Fermi surface sheets near the antinodal region is～2 meV.These observations provide important information for studying the relationship between the Fermi surface topology and superconductivity,and the layer-dependent superconductivity in high temperature cuprate superconductors.     

CI~-Br~-I~-混合液中Br~-I~-鉴定的改进

在鉴定Cl~-、Br~-、I~-混合液中Br~-、I~-时,大都采用饱和氯水氧化、四氯化碳萃取法。该法存在几个问题:制取氯气并通入水中制成饱和氯水时,逸出大量巨毒的氯气,污染环境,危害人体健康;氯水极不稳定,很易失效,一般存放不能超过24h,给工作带来不便;氯水浓度不易测定,是否达到饱和难以判定;使用饱和氯水时,加量不好控制,稍多加一点,就有可能将I~-直接氧化成无色的碘酸,而将I~-漏检。