Bengt Skrifvars

Stepwise photometric titrations

Abstract Stepwise titrations of several metals with photometric end-point detection are described. The equivalence points when 2 metal ions are titrated compleximetrically, can be detected if the conditional stability constants are sufficiently high in value even if there are only slight differences between the colours of the different species of the indicator compounds. The following systems were analysed by stepwise photometric titration using either metalphthalein or eriochrome black T as indicator: manganese-calcium; manganese-magnesium; calcium-magnesium; manganese-calcium-magnesium; zinc-magnesium, EDTA, DTPA and EGTA were used as titrants. A satisfactory accuracy was attained in each case. The results agreed with conclusions drawn from the theory of stepwise photometric titrations based on equilibrium calculations and absorbance values.

Detailed Studies on the High Temperature Corrosion Reactions between Potassium Chloride and Metallic Chromium

Recovery of energy from biomass and various waste–derived fuels by combustion has become important due to reduction of detrimental CO2 emissions. Biomass does, however, release significant amounts of chlorine and alkali metals, as e.g. HCl(g), KCl(g), KOH(g) and NaCl(g), into the gas phase during combustion. The alkali chlorides may cause deposits on superheater tubes, which interfere with operation and can lead to corrosion and/or blockage of the gas path. To prevent and diminish the problems mentioned above, better and more detailed knowledge of the reactions between potassium chloride and the tube materials during combustion is needed. These materials commonly contain, among other metals, chromium, which is thought to protect the rest of the material since it forms a very dense but thin oxide layer on the surface of the tube material. It has been suggested that the reaction between solid or partly molten KCl and chromium oxide is the one responsible for starting the complex series of corrosion reactions. In this work, the overall reaction between potassium chloride and chromium was studied through partial reactions with compounds known to participate to the overall reaction or to be formed during it. The reactions were studied in synthetic air by heating sample mixtures in a DTA/TGA (Differential Thermal Analysis/ Thermogravimetric Analysis) apparatus. Selected samples were also studied and analyzed with a scanning electron microscope equipped with an energy dispersive x-ray analyzer (SEM/EDXA). Under the used conditions both potassium chloride and potassium chromate reacted with pure chromium and chromium oxide. In the case of chromium, chromium oxide was formed via the formation of potassium chromate. In reactions including chromium oxide as reactant also potassium dichromate was detected.

APPLICATION OF THE RINGBOM ECR (EXACTLY CORRECT REFERENCE SOLUTION) PRINCIPLE TO TITRATIONS

Abstract The ECR (Exactly Correct Reference solution) principle suggested by Ringbom to increase the precision of titrations to a preset end point value is applied to Potentiometrie and spectrophotometric titrations of sulphate as hydrogen sulphate with a strong acid. In the Potentiometric titrations the relative error was ca. 0.2% and in the spectrophotometric titrations somewhat higher. The result means that it is possible to analyse binary mixtures of sulphuric acid and a second strong acid, e.g., hydrochloric, perchloric or nitric acid, by acid-base titrations. The potentialities of the principle for analysis of multicomponent systems, automation etc. are also discussed.