Boron is a nonmetallic element, boron in nature mainly exist in boric acid and borate, elemental boron has not been found. Adding a small amount of boron powder in steel can increase hardenability of steel, this is boron’s unique role.
Boron can also improve the mechanical properties of the steel, and improved weldability. Boron in steel mainly exists in solid solution, also can form boron nitride, boron oxide and boron iron carbon boride. About the form of boron in steel, yet no unified division. The metal school is divided into effective boron and ineffective boron; metallography divided into boron and borides; solid melting into acid-soluble of boron and acid insoluble boron chemical analysis. Some contact among different.
The form of boron in steel is very complex, and the various forms of boron acid stability were different, which gives the decomposition of boron steel and determination some difficulties. Thus appears in the analysis of the "acid soluble boron" and "acid insoluble boron", full-boron distinction. There is no strictly defined in acid-soluble boron initially, but generally refers to that part of boron for acid decomposition, due to the type of acid, concentration and heating of the different ways, often make the results of the analysis of the acid-soluble boron different. 1971 recommended that uniform provisions C (1/2H2SO4) = 5mol / l sulfuric acid (without any oxidant) dissolving the sample, the measured boron is acid soluble boron. Acid soluble boron is mainly the solid solution of boron, boron oxide, iron carbon boron compounds; acid insoluble boron, is mainly the boron oxide. Since boron oxide has a high degree of stability, the decomposition of the acid insoluble boron generally use sodium carbonate melt method. Usually high-alloy steel, nickel-based superalloy containing elements such as niobium, tantalum, titanium, aluminum, the affinity of nitrogen is much larger than boron, and therefore rarely form boron nitride, the full amount of boron can be obtained by sulfuric smoke. Carbon steel, low-alloy steel is sometimes available the full amount of boron, sometimes range between acid-soluble boron and boron. Therefore, for the direct decomposition of the acid-insoluble boron, is still needing majority of workers continue to explore. In addition, it was pointed out that although the acid-soluble boron is not equal to effective boron, but the acid-soluble boron with good correspondence between hardenability, for routine chemical analysis, analyze the acid-soluble boron is appropriate, but this proposal not yet been recognized, and thus the analysis of boron, is still need measured, the difference between the acid-insoluble boron.
According to metal powder supplier, there are three methods to separate boron from steel, precipitation method, the sample use alkali melt or increase alkaline in the test solution, so that the vast majority of iron, chromium, manganese, nickel, cobalt, titanium, copper and other interfering elements removed by precipitation, then dry the filter portion of the test solution of boron determination. This method is simple, fast, applicable to the separation of the higher content of boron, but can not remove silicon, aluminum, molybdenum, tungsten and other elements.
The distillation method, is boron’s classical separation methods. This method is the use of boric acid with methanol to generate trimethyl borate methanol [B (OCH3) 3], the boron and other elements to obtain efficient separation, applicable to more complex components of the high-alloy steels, and various other alloys, is the current international standard separation means of the method of the main. The main drawback is that the separation time is long, and need quartz ware. However, if use boron-free glass or plastic devices instead of quartz vessel, also can obtained the same separation effect.
Extraction method, make boron reacting with hydrofluoric acid, [BF4] - anion is formed, then adding the basic dye, such as methylene blue, ethyl violet, brilliant green, etc., to generate a ternary complex, and then use two tetrachloroethane, benzene, chlorobenzene and other solvent to extract, achieve the purpose of separation and color. The disadvantage is that when the total amount of niobium, tantalum, is less than 0.5%, can use washing method to eliminate interference.
Source:http://www.mhcmp.com
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