Nitric-hydrofluoric acid test

Nitric-hydrofluoric acid test 1 10% HNO3 -1- 3% HF 4 h exptosure to 70° C solution Comparison of ratio of mass loss of laboratory annealed and as-received samples of same material Corrosion potential of 304 steel = -l-O-14 to -I-0-54 1. Chromium-depleted areas 2. Not for 0-phase 3. Used only for Mo-bearing steels... 

Vanadium is resistant to attack by hydrochloric or dilute sulfuric acid and to alkali solutions. It is also quite resistant to corrosion by seawater but is reactive toward nitric, hydrofluoric, or concentrated sulfuric acids. Galvanic corrosion tests mn in simulated seawater indicate that vanadium is anodic with respect to stainless steel and copper but cathodic to aluminum and magnesium. Vanadium exhibits corrosion resistance to Hquid metals, eg, bismuth and low oxygen sodium. 

In the test method, the coal or coke to be analyzed is ashed under controlled conditions, digested by a mixture of aqua regia and hydrofluoric acid, and finally dissolved in 1% nitric acid. The concentration of individual trace elements is determined by either inductively coupled plasma-atomic emission spectrometry (ICPAES) or inductively coupled plasma-mass spectrometry (ICPMS). Selected elements that occur at concentrations below the detection limits of ICPAES can be analyzed quantitatively by graphite furnace atomic absorption spectrometry (GFAA). 

Acids and Ammonium Hydroxide When ammonium hydroxide, glacial acetic acid, hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid, or sulfuric acid is called for in tests and assays, reagents of ACS grade and strengths are to be used. (These reagents sometimes are called concentrated, but this term is not used in the Food Chemicals Codex.)... 

Molybdenum does not dissolve in most common chemical reagents. A chemical reagent is a substance that takes part in a chemical reaction, such as an acid or an alkali. For example, molybdenum does not dissolve in hydrochloric acid, hydrofluoric acid, ammonia, sodium hydroxide, or dilute sulfuric acid. These chemicals are reagents often used to test how reactive a substance is. Molybdenum does dissolve in hot strong sulfuric or nitric acids, however. The metal does not react with oxygen at room temperatures, but does react with oxygen at high temperatures. 

Sulfur cements are resistant to attack from water, hydrochloric, nitric, hydrofluoric, sulfuric, phosphoric, and most organic acids. When tested as linings for storing acids at concentrations of 5-90% and at temperatures up to 90 °C, the sulfur coatings were unaflFected generally after several years of service. 

D 10% Nitric-3% Hydrofluoric Acids (This test is being removed from A 262) 70°C 4h Chromium carbide in316, 316L, 317, 317L Ratio of corrosion Rates of "unknown over that of a solution annealed specimen... 

The test apparatus comprises a heat-of-solution calorimeter with accessories (Dewar flask, stirrer, funnel, etc.), an officially calibrated Beckmann thermometer and an appropriate acid mixture (nitric acid -l- hydrofluoric acid). The cement paste samples (their mix proportions, mixing procedure and temperature are specified) are stored in a water bath at 20° 0.5 C. The heats of solution of the unhydrated and of the hydrated cement are determined from the rise in temperature occurring when the samples dissolve (the test should be performed in constant-temperature surroundings) and from the determinations of the CaO content (or the losses on ignition, if applicable). Formulas for calculating the heat of solution from the test data are given in the Standard. It is an elaborate procedure. 

Procedure. A little (several mill igi ams) of the rock is pulverized and heated in a platinum crucible or spoon with several drops of hydrofluoric and concentrated sulfuric acid. Solid ammonium fluoride may be used in place of the hydrofluoric acid. When no more acid fumes are evolved, the residue is ignited briefly, allowed to cool, and scraped from the reaction vessel with a nickel spatula. The test portion is placed on orange-red dipicrylamine paper, moistened with 1 drop water, and dried in a current of heated air. The paper is then bathed in 0.1 iST nitric acid. If potassium is present, a red fleck is left on the paper which is turned bright yellow by the acid. The preparation of the dipicrylamine paper is described on page 398. 

There is also a standard test method for determination of major and minor elements in coal ash by inductively coupled plasma (ICP)-atomic emission spectrometry (ASTM D-6349). In the test method, the sample to be analyzed is ashed under standard conditions and ignited to constant weight. The ash is fused with a fluxing agent followed by dissolution of the melt in dilute acid solution. Alternatively, the ash is digested in a mixture of hydrofluoric, nitric, and hydrochloric acids. The solution is analyzed by (ICP)-atomic emission spectrometry for the elements. The basis of the method is the measurement of atomic emissions. Aqueous solutions of the samples are nebulized, and a portion of the aerosol that is produced is transported to the plasma torch, where excitation and emission occurs. Characteristic line emission spectra are produced by a radio-frequency inductively coupled plasma. A grating monochromator system is used to separate the emission lines, and the intensities of the lines are monitored by photomultiplier tube or photodiode array detection. The photocurrents from the detector... 

---