JPS6235480B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvements in nitrogen oxide gas generation inhibitors for use in nitric acid pickling baths for metals. When pickling metals with nitric acid or an acid containing nitric acid, nitrogen oxide gas is generated from the acid bath. 1973-
It has been proposed to add compounds with amino groups, such as 102232), to acid solutions. However, when adding urea to suppress the generation of nitrogen oxide gas, if the amount of urea added in the pickling bath is too small, there will be no suppressing effect;
If the amount added is too large, there will be problems such as precipitation and separation of explosive urea nitrate and significant aging of the pickling bath, making it extremely difficult to manage the pickling bath. Furthermore, in the case of adding sulfamic acid to suppress the suppression, it is known that nitrous acid in the acid bath is decomposed by the sulfamic acid and becomes nitrogen as shown in the following equation, HNO ₂ +NH ₂ SO ₃ H →N ₂ +H ₂ SO ₄ +H ₂ O In this case, since nitrous acid and sulfamic acid participate in the reaction in equal moles, in order to put sulfamic acid into practical use as a nitrogen oxide gas generation inhibitor,
It is necessary to produce this product industrially and efficiently. However, conventional methods for producing sulfamic acid involve, for example, reacting urea with sulfuric anhydride and sulfuric acid in a stoichiometric amount or more, and then reacting with sulfamic acid at a concentration of 70 to 80%, since sulfamic acid has the lowest solubility in sulfuric acid at a concentration of 70 to 80%. diluted to
The method used was to dry it and make it into a product. However, this method inevitably increases the cost of the product due to the price of the raw materials used and the manufacturing method that requires a large number of steps. In addition, the pickling process is carried out in some large-scale factories.
Although pickling is carried out in a continuous pickling line with sufficient bath control, pickling is actually carried out in batches in the majority of small and medium-sized metal surface treatment factories. As mentioned above, in the method of adding a compound having an amino group such as urea or sulfamic acid to an acid bath to suppress the generation of nitrogen oxide gas, it is difficult to manage the acid bath or the product cost of the amino compound used is high. Due to problems such as these, it has not been practical until now. The present inventors added urea to an acid bath containing nitric acid and hydrofluoric acid.
Also, as a result of various studies on the descaling properties, finishing properties, and suppression of nitrogen oxide gas generation of stainless steel pipes when amino compounds such as sulfamic acids are added, we found that sulfamic acids 85-95
%, acidic ammonium sulfate 3-10%, urea 0.1-
A composition consisting of 5% sulfuric acid and 2-5% sulfuric acid is extremely soluble in an acid bath, and therefore, it is possible to quickly decompose nitrous acid generated in the liquid during descaling into nitrogen, and to reduce the amount of nitrite generated. As long as it is added in equal moles or more as sulfamic acid, the effect of suppressing the generation of nitrogen oxide gas is excellent regardless of slight variations in the amount added, and the decasing property and finishing properties are also good. The present invention was completed based on the discovery that the present invention has superior performance in practice compared to the case where sulfamic acid or urea is added alone. An object of the present invention is to provide an additive that is easy to manage in a nitric acid pickling bath for metals and that exhibits an excellent nitrogen oxide gas generation suppressing effect even for batch pickling. The object of the present invention is to provide a nitrogen oxide gas generation inhibitor for use in a nitric acid pickling bath for metals, which dissolves rapidly in the nitric acid pickling bath. The nitrogen oxide gas generation inhibitor for metal nitric acid pickling bath of the present invention has sulfamic acid 85 to 85% as a main component.
95% by weight, acidic ammonium sulfate 3-10% by weight,
It is characterized by containing 0.1-5% by weight of urea and 2-5% by weight of sulfuric acid. When the nitrogen oxide gas generation inhibitor of the present invention is added to a nitric acid pickling bath, it dissolves extremely quickly, and even when a large amount of metal to be pickled is immersed in the bath or continuously, it can be added sequentially. By doing so, the generation of nitrogen oxide gas can be almost completely suppressed. The sulfamic acid contained in the nitrogen oxide gas generation inhibitor of the present invention is consumed in the decomposition of nitrous acid when metals are pickled with nitric acid, the acidic ammonium sulfate improves the finish gloss of pickled metals, and the urea is decomposed. It has the effect of improving scalability. Even if any one of the four components contained in the nitrogen oxide gas generation inhibitor of the present invention is missing or its content is insufficient, the object of the present invention will not be achieved. Further, even if any one of the four components is included in excess, the object of the present invention cannot be preferably achieved. The nitrogen oxide gas generation inhibitor of the present invention is prepared by charging urea, sulfuric anhydride, and sulfuric acid into a reactor in approximately stoichiometric proportions, causing a powder reaction, and then taking them out of the reactor as they are. Therefore, it can be easily obtained as an industrial product. That is, according to this method,
There is no need for waste sulfuric acid treatment, the number of manufacturing steps is small, and the ratio of components in the nitrogen oxide gas generation inhibitor of the present invention can be easily changed by changing the ratio of the above-mentioned raw materials. The target product can be produced efficiently. Normally, when produced by the above method, the nitrogen oxide gas generation inhibitor of the present invention is obtained as a granular product, but this product may be further crushed into a fine powder product or tablet-shaped. It can also be made into tablets, both of which can be put to practical use for metal pickling. Further, the nitrogen oxide gas generation inhibitor of the present invention may contain other arbitrary components such as rust preventives, surfactants, etc., as long as the object of the present invention is achieved. Examples will be described below along with comparisons, but the technical scope of the present invention is not limited thereto. Example 1 Put 150 g of an acid solution containing 15% nitric acid and 2% hydrofluoric acid into a 300 c.c. styrene container, add 90% sulfamic acid, 5% acidic ammonium nitrate, and 2% urea.
%, and a nitrogen oxide gas generation inhibitor consisting of 3% sulfuric acid was added to the acid solution at a concentration of 2%. Before pickling, SUS-304 seamless pipes with an outer diameter of 8 mm and an inner diameter of 3.7 mm were cut into lengths of 50 mm, and 10 of these were tied into a bundle. After this bundle of steel materials was placed in the acid solution, the container was covered with a lid, and the steel materials were immersed at room temperature until descaling. After the concentration of nitrogen oxide gas in the gas phase inside the container was measured using a detection tube at the end of the immersion, the descaled steel material was taken out and another bundle was put into the acid solution. In this way, the immersion treatment of the steel material and the measurement of the concentration of nitrogen oxide gas were repeated. As a comparison, immersion treatment and concentration measurement of nitrogen oxide gas were carried out in the same manner when the above-mentioned inhibitor was not added and when urea and sulfamic acid (purity 99%) were added. As shown in Table 1, the results show that the examples of the present invention have an outstanding effect of suppressing the generation of nitrogen oxide gas.

[Table] Example 2 Put 100 g of an acid solution containing 10% nitric acid and 5% hydrofluoric acid into a 300 c.c. styrene container, and add 85% sulfamic acid, 10% acidic ammonium nitrate, and 1% urea.
A nitrogen oxide gas generation inhibitor consisting of 4% sulfuric acid was added to the acid solution at a concentration of 0.1%. A welded SUS-304 pipe with an outer diameter of 8 mm and an inner diameter of 5 mm before pickling was cut into a length of 50 mm. One of the steel materials was placed in the acid solution, the container was covered, and the steel material was immersed at room temperature until it was descaled. After measuring the concentration of nitrogen oxides in the gas phase inside the container using a detection tube, the descaled steel material was taken out and another one was placed in the acid solution. In this way, the immersion treatment of the steel material and the measurement of the nitrogen oxide concentration were repeated. As a comparison, the same immersion treatment and measurement of nitrogen oxide concentration were performed in the case where the above-mentioned inhibitor was not added and in the case where urea was added. As shown in Table 2, the results show that the examples of the present invention are excellent in suppressing the generation of nitrogen oxide gas.

【table】

Claims (1)

[Claims] 1 Main components: 85 to 95% by weight of sulfamic acid, 3 to 10% by weight of acidic ammonium sulfate, and urea.
A nitrogen oxide gas generation inhibitor for a nitric acid pickling bath, characterized by containing 0.1 to 5% by weight and 2 to 5% by weight of sulfuric acid.