Oxalic acid tests

Oxalic acid test 100gH2C204-H20 + 900 mL H20 Anodically etched at 1 A/cm2for 1.5 min Geometry of attack on polished surface at 250 x or 500 x + 1.70 to 2.0 or greater Various carbides... 

There are a number of tests available for the evaluation of the sensitivity of a given stainless steel to intergranular corrosion (Table 7.41). They differ in severity of corrosion conditions and therefore do not reveal the same phenomena. The oxalic acid test consists of an electrochemical attack at constant current. The morphology of the corroded surface is then compared with reference samples. The main advantage of this technique is its rapidity (the attack takes about one minute). The applied potential lies in the transpassive region, where the chromium easily dissolves. The oxalic acid test therefore does not reveal the zones depleted in chromium, but rather exposes the presence of carbides and intermetallic phases. 

DL data have been plotted in Fig. 17 as a function of corrosion rates in the ASTM standard ferric sulfate test and the classifications obtained in the oxalic acid etch test. They show that the current ratio is very sensitive for detecting the absence of sensitization and for differentiating mild degrees of sensitization for which the oxalic acid test shows step or dual structures. Current ratios are in the range of 0.0001-0.001 for step structures and between 0.001-0.05 for dual structures. Corrosion rates in the ferric sulfate test do not differentiate between these small levels of sensitization, However, for severely sensitized materials with ditch structures, current ratios become less effective in making distinctions between medium and severe levels of sensitization, while the corrosion rates vary over a wide range. These specimens have DL ratios in a wide band extending from 0.05-0.3. 

ASTM A 262 Practice A is a rapid procedure in which specimens are electrolytically etched and examined metal-lographically for attack at the grain boundaries. It has been widely used as a quality control screening test to approve acceptable material. Specimens that fail the oxalic acid test are then evaluated by one of the other tests in ASTM A 262 and are accepted or rejected based on these results. Although the oxalic acid etch test is done quickly, it can be tedious, because examination of all fields is required. 

Note. Methyl oxalate, unlike most other esters, hydrolyses very rapidly in aqueous solution hence it will evolve CO in the above test, owing to the formation of methanol and free oxalic acid. 

Glycol gives the non-volatile oxalic acid. After heating the mixture under reflux for 10 minutes, transfer 2 ml. of the cold product to a test-tube and add 4 ml. of cone. H2SO4. Note the production of carbon monoxide and carbon dioxide on heating (p. 350). 

Sulphuric add test. To 0-5 g. of oxalic acid or of an oxalate, add I ml. of cone. H2SO4 and warm CO and COg are evolved (cf. formic acid). The CO burns with a blue flame. Detect the COg by passing the mixed gases evolved into lime-water. It is essential to test for the COj in a separate reaction, or (if the same test-tube is used) before testing for CO. 

The calcium carbonate precipitate was removed by filtration, and the filtered solution was found to contain 1,436 g of fructose as determined by optical rotation. A small amount of calcium bicarbonate was present as an impurity in solution and was removed by the addition of oxalic acid solution until a test for both calcium and oxalic acid was negative. The insoluble calcium oxalate precipitate was removed by filtration. 

Twenty-four hundred grams (25.6 mol) of phenol, 1645 g of 37 wt % formaldehyde (20.3 mol), and 30 g (0.33 mol) of oxalic acid were charged to a 5-L, three-necked resin kettle. The mixture was stirred and refluxed until the distillate was free of formaldehyde (1-3 h) then water was distilled from the mixture until the resin temperature reached 154°C. The viscosity of the resin at this point at 150°C was such diat 105 s was required for flow in an inclined plate test. The pressure was slowly reduced while a slow current of nitrogen was bubbled through the resin, and the mixture was heated to 175°C at 6 mm Hg. Approximately 6 wt % phenol was recovered then the resin was poured into an aluminum dish and cooled. The resin had a melt viscosity of 510 s at 150°C. 

Self-Test F.5B The molar mass of oxalic acid, an acid present in rhubarb, is 90.0 g-mol , and its empirical formula is CH02. What is its molecular formula ... 

Self-Test G.2B Calculate the mass of oxalic acid needed to prepare 50.00 mL of 0.125 M C2H204(aq). 

Fig. 26 —Corrosion test of the magnetic heads immersing in oxalic acid solution with a concentration of 0.05 mol/L for 4 min at a temperature of 25°C.

This analytical procedure is based on an optimum analysis condition for segmented continuous flow analysis. The sample is combined with a molybdate solution at a pH between 1.4 and 1.8 to form the //-molybdosilicic acid. After an appropriate time for reaction, a solution of oxalic acid is added, which transforms the excess molybdate to a non-reducible form. The oxalic acid also suppresses the interference from phosphate by decomposing phosphomolyb-dic acid. Finally, a reductant is added to form molybdenum blue. Both ascorbic acid and stannous chloride were tested as reductants. 

A depressant system developed for beneficiation of Ta/Nb-Zr ores involves oxalic acid-hydro fluoro silicic acid and depressant SHQ. SHQ is a mixture of a low-molecular-weight acrylic acid and condensation product of disulphonic acid (Suspendol PKK, manufactured by Cognis, Germany). After the development of the final reagent scheme, a series of locked-cycle tests were performed using the flowsheet shown in Figure 23.7. 

A number of different depressant combinations were examined during a laboratory development test programme. Oxalic acid, citric acid and fluorosilicic acid were among the... 

Bricker et al. (30) reported that there were no statistically significant differences between the calcium balances of eight women on cocoa and non-cocoa diets. The women were studied for three to seven 4-day periods. Calcium intake was 670 mg/day with the addition of milk and 679 and 755 mg/day with the addition of milk and cocoa. Five levels of cocoa, supplying from 5.6-52.6 g/day, were tested. These amounts would likely contain from 25-280 mg of oxalic acid, which was not nearly as much as was added when spinach was fed. With the inclusion of cocoa in the diet, the urinary calcium fell and fecal calcium rose. There were also increases in the fecal excretion of dry matter and nitrogen. 

In studies on test meals, Walker et al. (32) discovered that the calcium of Swiss chard, which has a high oxalic acid content, was poorly absorbed. Children excreted more calcium during the 6 hours after a test meal of milk, Pumpkin leaves, cassava leaves, or pigweed leaves than after Swiss chard. All supplements contained 200 mg calcium. 

In the studies on humans there appeared to be decreased calcium balances when 200 g or more of spinach per day was included in the diet. In two of the studies in which women were fed spinach, calcium intakes were below the Recommended Dietary Allowance of 800 mg/day (37). Some studies were conducted for short period of a week or less, which may not be sufficient time to adjust to a change in diet. From measurement of calcium excretion in urine after a test meal, it was shown that the calcium in oxalate-containing vegetables was less well-absorbed than that of milk or of vegetables not containing oxalic acid. However, this would not necessarily affect calcium balance, since the total amount of calcium in the diet would have to be considered. The effect of a combination of oxalic acid and fiber on calcium bioavailability should be further investigated. 

Anhydrous Citric Acid Dissolve 0.8 g in 4 ml DW, add 3 ml HC1 and boil for 1 minute with 1 g granulated zinc. Allow to stand for 2 minutes, decant the liquid into a test-tube containing 0.25 ml phenyl-hydrazine HC1 and heat to boiling. Cool rapdily, transfer to a graduated cylinder, add an equal volume of HC1 and 0.25 ml potassium hexacyanoferrate (III), shake and allow to stand for 30 minutes. Any pink colour produced is not more intense than that produced by treating 4 ml of a 0.01% w/v soln. of oxalic acid at the same time and the same manner (360 ppm, calculated as anhydrous oxalic acid). 

A series of organic acids, inorganic acids and their salts have been tested as possible activators for the flotation of lime depressed p3oite. The results are presented in Fig. 6.23 and Fig. 6.24. It can be seen from Fig. 6.23 that oxalic acid is the strongest activator in the organic acid series. When the concentration of... 

The feasibility of benzenic ring amines, benzenic ring structures and aliphatic acids oxidation by means of Fenton chemistiy was tested in synthetic, acidic wastewaters by Fenton s reagent electrogenerated at a reticulated vitreous carbon cathode using the flow-cell. The organic molecules considered were phenol (Ph), cresol (Cr), aniline (An) hydroquinone (HQ), catechol (Cat), parabenzoquinone (pBQ) and oxalic acid (OxAc). Their initial... 

The bottom antireflective coating solution test consisted of the step 1 product, poly(4-hydroxystyrene-9-anthracenyl-methacrylate) (1.5 g), 55/45 molar ratio, respectively, oxalic acid/triethylamine (0.075 g) 1 1, triphenylsulfonium triflate (0.06 g), and Vectomer 5015 (0.225 g) dissolved in ethyl lactate (98.5 g) and then filtered through... 

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