Determination of the activation parameters ∆H≠ and ∆S≠ via a kinetic study of d,l-mandelic acid oxidation by using chromic acid in the presence of 1,10-phenanthroline as a promoter in an aqueous micellar acid medium

Chromic acid oxidation of d,l-mandelic acid in the presence and absence of 1,10-phenanthroline (Phen) is studied in an aqueous micellar medium under kinetic conditions, [d,l-mandelic acid] >> [Phen]T >> [Cr(VI)]T at different temperatures. From studies on the effect of temperature on the rate constant (k), the activation parameters ∆H≠ (enthalpy of activation) and ∆S≠ (entropy of activation) are evaluated by using the Eyring equation [−ln (kh/kBT) = ∆H≠/RT − ∆S≠/R]. The high value of ∆H≠ indicates that the phen-catalysed path is favoured mainly due to very high negative value of ∆S≠. The negative value of ∆S≠ and the composite rate constant kcat support the suggested cyclic transition state. Both the catalysed and uncatalysed paths show a first-order dependence on [H+], and both also show a first-order dependence on [d,l-mandelic acid]T and [Cr(VI)]T. The Phen-catalysed path is first order in [Phen]T. These observations remain unaltered in the presence of externally added surfactants. The cationic surfactant N-cetylpyridinium chloride is found to retard the rate of the reaction.

Effects of chromic acid anodizing on fatigue behavior of 7050 T7451 aluminum alloy

The effect of chromic acid anodizing (CAA) surface treatment on 7050 T7451 aluminum alloy was presented in this study in terms of fatigue behavior. CAA is a treatment against corrosion by producing aluminum oxide layer (Al2O3) at the surface. However, fatigue performance of 7050 T7451 is affected by the coating. In this study, eight different CAA processes were examined with regard to etching stage of pre-treatments by using an alkaline etchant and/or acid etchants with various immersion times. Optical microscopic examinations were applied in order to determine pitting characteristics for the selection of CAA process parameters before fatigue tests. A CAA process was selected among eight processes in terms of pitting characteristics in order to apply fatigue specimens. Four fatigue test groups were determined to investigate bare condition of 7050 T7451 and sub-stages of the CAA particularly. Constant amplitude axial fatigue tests were conducted on specimens at 91 Hz at stress ratio (R) -1 until run-out criteria, which was 106 cycles. Fatigue life reduction was determined due to pretreatments of CAA. Fracture surfaces of the specimens were examined by scanning electron microscope (SEM) to investigate morphology and crack initiation sites.

Effect of Zn content on corrosion behavior of Mg-Y-Zn alloys

The microstructure, corrosion behavior and electrochemical behavior of as-cast Mg-4Y-xZn (x=1,2,3,4 wt.%) are studied by SEM, weight loss and electrochemical tests. Mg12YZn (X), Mg3Y2Zn3 (W) and Mg24Y5 constitute the phase composition system of the alloy. When Zn content is 1 wt.%, all tests reveal that alloy has the optimal corrosion performance. The second phase in these alloys, due to their nobler nature than ?-Mg, exists as cathode during corrosion process, so that ?-Mg preferentially occurs corrosion to accelerate the formation of corrosion pits. After soaking in 3.5 wt.% NaCl solution for some time, the stability of the W phase changed, and gradually dissolved, which was finally removed by chromic acid used for removal of corrosion products. In addition, X phase can be used as an anode in the micro-galvanic cells formed with W phase to reduce the corrosion rate of ?-Mg and thus improve the corrosion performance of the alloy.

Chemo-enzymatic oxidative cleavage of isosafrole for the synthesis of piperonal

Piperonal is a key ingredient of flavour and fragrance industry and a useful intermediate for the synthesis of fine chemicals. It is currently prepared by either ozonolysis or chromic acid...

ESTIMATION OF SOIL ORGANIC CARBON PERCENTAGE IN ORGANIC FARMING SOIL SAMPLES OF TANUKU REGION, ANDHRAPRADESH, INDIA BY WALKLEY-BLACK CHROMIC ACID WET OXIDATION METHOD

The Estimation of Soil Organic Carbon (SOC) Percentage is done in Organic farming Soil samples from various places in Tanuku Region, Andhra Pradesh, India. It provides all the necessary information about, effect of Organic farming on the concentration of soil organic carbon and also assess the amount of organic matter in soil. The result depends on the quality of soil. The Soil samples were collected systematically from organic farming lands, Sieved the soil samples through 2mm sieves. The determination of SOC is based on the Walkley-Black Chromic acid Wet oxidatiom method. The method measures the amount of carbon in plant and animal remains, including soil humus but not charcoal or coal

Nissl. Die Hypothese der specifischen Nervensellenfundion. (Allg. Zeitschr. f. Psychiat. Bd. 54. pg. 1—107)

It is known that Nissle managed to use alcohol for compaction and by a simple staining method to prove a special structure in the nervous cells, unknown until then, opening new horizons in the histopathology of the nervous system. The old method of condensation by means of chromic acid artificially alters the nerve lumen and therefore is not applicable to the study of the structure of cells.

Chromate Conversion Coating and Alternatives as Corrosion-Resistant Treatments for Metal Parts

<p>Chromate conversion coating is an efficacious and fast means of protecting metal parts from corrosion, but problematic in that it uses the toxic and carcinogenic chromic acid as the reagent. This short report covers some key considerations and alternatives.</p>