CN111948369B - Passivation NTO coating quality evaluation method prepared by supercritical method - Google Patents

Passivation NTO coating quality evaluation method prepared by supercritical method Download PDF

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CN111948369B
CN111948369B CN202010717191.9A CN202010717191A CN111948369B CN 111948369 B CN111948369 B CN 111948369B CN 202010717191 A CN202010717191 A CN 202010717191A CN 111948369 B CN111948369 B CN 111948369B
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CN111948369A (en
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贾林
蒋忠亮
于思龙
王琼
张冬梅
王芳芳
顾妍
张林军
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Xian Modern Chemistry Research Institute
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/22—Fuels, explosives
    • G01N33/227—Explosives, e.g. combustive properties thereof
    • C—CHEMISTRY; METALLURGY
    • C06—EXPLOSIVES; MATCHES
    • C06B—EXPLOSIVES OR THERMIC COMPOSITIONS; MANUFACTURE THEREOF; USE OF SINGLE SUBSTANCES AS EXPLOSIVES
    • C06B21/00—Apparatus or methods for working-up explosives, e.g. forming, cutting, drying
    • C06B21/0083—Treatment of solid structures, e.g. for coating or impregnating with a modifier
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
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    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids

Abstract

The invention discloses a passivation NTO coating quality evaluation method prepared by a supercritical method. Observing the viscosity number of the passivated NTO particles through a magnifier, detecting the pH value by preparing an NTO aqueous solution, and detecting the corrosion degree of the passivated NTO on the Al sheet in a 60 ℃ RH65% damp-heat environment for 30 days, and judging the coating quality of the passivated NTO to be poor, IV grade, III grade, II grade and I grade. The method is mainly used for evaluating the passivated NTO prepared by the supercritical method. The passivated NTO with good coating quality does not show acidity, is suitable for manufacturing Al-containing pressed explosive, and does not corrode a metal shell of a warhead. In addition, passivation process parameters can be determined and desensitizers can be screened by comparing the detection values of the passivated NTO.

Description

Passivation NTO coating quality evaluation method prepared by supercritical method
Technical Field
The invention belongs to the field of detection and research of physical and chemical properties of explosive and powder samples, mainly relates to detection and research of passivation NTO coating quality, and particularly relates to evaluation of passivation NTO coating quality prepared by a supercritical method.
Background
The NTO (chemical name is 3-nitro-1,2,4-triazole-5-ketone) is an elementary explosive with excellent comprehensive performance, high energy and low sensitivity, is white or light yellow solid particles, has better thermal stability, has a melting point of more than or equal to 260 ℃ (decomposition), has a DSC decomposition peak of Wen ℃, and has certain acidic pKa = 3.67). The NTO crude product is prepared by nitrifying 1,2,4-triazole-5-ketone (TO for short), and then the NTO crude product can be applied only by improving the purity and the crystal form through technologies such as recrystallization and the like.
Various mixed explosive formulations based on NTO have been studied abroad and find application in some weapon systems. The research on the formula in China is started later.
Currently, NTO-based explosive formulations are mainly classified into 3 types: fusion cast explosives, plastic bonded explosives (PBX) and molded explosives. Dozens of NTO-based explosive formulations have been developed in Fahrenheit, american, english, etc. (see tables 1,2, 3, 4).
TABLE 1 US and Switzerland NTO-based fusion cast explosive formulations
Figure BDA0002598653530000011
Figure BDA0002598653530000021
TABLE 2 NTO-based PBX formulations in France and USA
Name (R) NTO RDX HMX AP Aluminium Adhesive agent
B2214 72 — 12 — — 16(HTPB)
B2245 8 12 — 43 25 12(HTPB)
B3017 74 — — — — 26 (energy-containing adhesive)
PBXW-121 63 10 — — 15 12(HTPB)
PBXW-121 47 5 — 20 15 13(HTPB)
PBXW-121 22 20 — 20 26 12(PU)
TABLE 3 England, switzerland, germany and Canada NTO-based PBX formulations
Name (R) NTO HMX Additive agent Energetic plasticizer Adhesive agent
CPX 412 50 30 — 10(K10) 10(PolyNIMMO)
CPX 450 40 20 20 (aluminum) 10(K10) 10(PolyNIMMO)
CPX 458 30 30 20 (aluminum) 10(K10) 10(PolyNIMMO)
GD-3 72 12 — — 16(HTPB)
GD-5 40 43 — 10(BDNPA/F) 7(PGA)
HX 310 25 47 10(NG) — 18(HTPB)
CHN-037 76 — — — 24(GAP)
TABLE 4 NTO-based compression molded explosive formulations
Name (R) NTO HMX BDNPA/F Adhesive agent
GD-9 47.5 47.5 2.5 2.5(Cariflex1101)
GD-11 48 48 — 4(Cariflex1101)
GD-13 48 48 — 2/2(Hy Temp/DOA)
France 1 55.5 37 — 7/0.5 (Kelf/graphite)
From tables 1,2, 3, and 4, it can be seen that NTO can be used in 11 formulations of Al containing explosives, 6 of which are Al containing pressed charges.
The explosive containing Al is also called high power explosive. A class of explosives prepared by adding Al powder in different proportions into the explosive is called Al-containing explosives. Because Al powder emits high heat in the secondary reaction after the detonation wave front, the explosive can generate high detonation heat and high specific volume during detonation, thereby having higher work capacity, and still being an important series forming mixed explosives.
The Al-containing mixed explosive is used in some countries in the first world war, and during the second world war, al-containing explosives are used in all warfare countries on a large scale to load underwater weapons and ammunitions, air weapons and air bombs. At present, many tactical missiles are filled with Al-containing mixed explosives. With the development of cosmonautic industry, al-containing heat-resistant explosive is also appeared and applied to an Apollo spacecraft system. The main explosive in the Al-containing mixed explosive is also greatly developed, and from the end of world war II to the present, the main explosive used in the Al-containing mixed explosive is not only various in variety, but also greatly improved in performance, and starts to appear as a heat-resistant or insensitive explosive. Since the last 70 s, al-containing explosives with low vulnerability have been developed abroad and are used for equipping navy, air force and tank troops.
The Al-containing explosive using heat-resistant explosive as main explosive is characterized by three high and one low (high density, high melting point, high explosion heat and low explosion speed). The main explosive has high melting point, low vapor pressure and no obvious physical and chemical change. The ammunition filled with the high-power explosive can bear the aerodynamic heating and space low-pressure action of the projectile, the warhead and the aircraft during high-speed flight, and can also bear the high-temperature action generated in a chamber during the continuous firing of a quick-firing weapon.
The Al powder in the mixed explosive has the function that the Al powder is combined with oxygen or reacts with an explosion product for the second time to generate Al 2 O 3 Thereby releasing a large amount of heat, and improving the explosion heat of the explosive. Some high-temperature and high-pressure reducing gas generated by the reaction of the Al powder and the explosion products is mixed with the surrounding air to generate secondary explosion, so that the duration of the explosion action is greatly prolonged. It can be seen that if the Al powder is largely inactivated, it is oxidized to Al in advance 2 O 3 The explosive detonation heat is reduced.
NTO is a typical high energy low sensitivity explosive with thermal stability and insensitivity to external stimuli. NTO is added into an explosive containing Al in French EURENCO, insensitive explosives containing Al XP3264 and PBXW-126 are developed, the performance and the insensitivity of the explosive are superior to those of a common explosive H-6, and the air explosion performance is obviously higher than that of PBXN-109.
Al powder can react with water, and the production process is unsafe, so if the Al powder is not strictly treated, the water suspension method process is not generally adopted to manufacture the Al-containing explosive, and the dry mixing method can be used for manufacturing the Al-containing explosive. For safety of blending, the main explosive is required to be insensitive. For example, 95% of passivated RDX (A-IX-I) and 5% of Al powder are mechanically mixed in an aluminum drum, the rotation speed of the drum is 30-40 r/m, and the mixture is mixed for 30 minutes to prepare the passivated black aluminum explosive (A-IX-II).
The quality of the desensitizer coating has an effect on the sensitivity of the passivated NTO. Because the occurrence of hot spots between explosive particles or between the explosive and contact materials under the mechanical action is the first step of initiating the explosive to rapidly react chemically, the probability of hot spots generated and propagated under the mechanical action is reduced, and the explosive reaction of the explosive is reduced.
The desensitizer is mainly made of materials with good plasticity, low hardness and easy deformation. When the explosive coated with the insensitive agent is subjected to mechanical action, the substances are easily filled among explosive crystal grains, and the substances have the functions of heat absorption and heat insulation and reduce bubbles among the explosive crystal grains, so that hot spots are reduced, and the detonation probability is reduced. Meanwhile, under the action of external force, the fillers can not make explosive grains directly contact with each other, so that the fillers play a role in buffering and lubricating, the phenomena of friction and stress concentration among the explosive grains are reduced, the probability of hot spots is reduced, and the mechanical sensitivity of the explosive is also reduced. If the coating of the insensitive agent on the surface of the explosive crystal is incomplete, the duration time of the hot spot is longer than the heat conduction time of the hot spot propagating through the insensitive agent layer, and the self-acceleration reaction of the explosive is easy to cause.
The conventional explosive charging method comprises the following steps: tamping, injection, press, screw, and plastic loading. The invention uses passivated NTO, which can be added with Al powder and pressed into Al-containing explosive column.
The explosive grain size ratio of the pressed explosive columns has strict requirements, so that the energy and density of a mixed explosive product can be improved, and the content of a main explosive can be improved as much as possible. In order to ensure that explosive particles are arranged as tightly as possible, the main explosive of the shaped explosive in foreign countries almost adopts the particle grading technology, namely the solid explosive particles are matched in size appropriately, so that small particles can be filled in gaps among large particles, the particles can be arranged more tightly, and the requirement of improving the filling density of the product is met. When the particle size distribution is adopted, the large particles account for 3/4 and the small particles account for 1/4. The particle grading can improve the pressed density and the compressive strength of the product.
According to the requirement of particle grading, the produced NTO particle products are classified according to particle size intervals, NTO with the particle size of 30-60 meshes (250 mu m-600 mu m) belongs to the class I, and NTO with the particle size of 60-80 meshes (180 mu m-250 mu m) belongs to the class II.
Currently, most of the methods for manufacturing insensitive explosives by adopting a water suspension method process, for example, the manufacturing method of passivated RDX comprises the following steps: firstly, putting RDX into water, heating, then adding a desensitizer, adhering the desensitizer to the surface of the RDX in a molten state, and cooling to form a coating layer on the surface of the RDX to form passivated RDX.
The water suspension method is simple to operate, short in production period and easy for mass production. In the production process, water is used as a dispersion medium and a heat transfer medium, so that the production safety can be ensured. If the temperature, the vacuum degree and the stirring speed are well controlled, the particles with smooth and compact appearance and quite uniform size can be obtained. However, because NTO has strong solubility in hot water, a part of NTO is lost when the water suspension method is adopted to prepare passivated NTO, and the loss amount is difficult to control.
The supercritical fluid coating (SCF) technology has been developed rapidly in recent years, and the main products include pharmaceuticals, foods, fertilizers and the like, so as to achieve the purpose of covering the unpleasant odor of the drugs or improving the stability of the products so as to facilitate application and storage. The SCF coating technique has the characteristics of high diffusion coefficient of the gas phase and strong solvency of the liquid phase. The technique is used to produce passivated NTO due to supercritical CO 2 Has high-efficiency mass transfer and low surface tension, and can coat NTO particles with desensitizer.
Mixing NTO with desensitizer solution at a certain proportion to form suspension, placing in a high-pressure autoclave heated in water bath, introducing CO from bottom of the autoclave 2 Stirring the suspension until the temperature and pressure in the kettle reach a certain stable supercritical state (T) C ＝31℃，P C =7.39 MPa), then the upper valve of the kettle is opened, and the lower part is continuously filled with CO 2 Regulating upper valve to maintain constant pressure in reactor, supercritical CO 2 The organic solvent (ethyl acetate) in the suspension is extracted, the residual solvent is taken away, and finally the passivated NTO is obtained through quick release. By using supercritical CO 2 The preparation of the passivated NTO can avoid a large amount of loss of the NTO due to no participation of water, and the processes of stirring, coating, drying and the like are completed at one time, so that the preparation method is time-saving, efficient and safe, and can meet the requirement of large-scale production.
But supercritical CO 2 Part of NTO crystals in the passivated NTO prepared by coatingThe body debonds, which is the result of the final rapid depressurization (quick release). The analysis reason is as follows: the NTO crystal has defects in quality (the crystal quality refers to the neatness of arrangement of crystal micro-regions, and the existence of structural defects such as micro-pores, micro-cracks, crystal dislocation, twin crystals and the like in the crystal can reduce the crystal quality), and the crystal is cracked from the defects through rapid pressure relief, and at the moment, the insensitive layer is cured and formed and cannot cover a newly generated crystal fracture surface; secondly, a plurality of NTO crystals are stacked together and coated, gaps exist among the crystals, the crystals are dispersed during rapid pressure relief, and new crystal surfaces appear, but the desensitizer is solidified, so that the new crystal surfaces cannot be coated.
When Al-containing explosive columns are manufactured by press fitting in the subsequent process, the debonded NTO crystals are in rigid contact under higher pressure, are easy to become heat accumulation points due to friction, and have higher potential safety hazards. In addition, the NTO crystals de-bond, reducing the tensile and compressive strength of the compacted charge, and environmental stresses can cause the charge to crack at the de-bonded crystal grains during subsequent shipping and storage. In use, the column cracks can also affect the detonation properties of the explosive.
In addition, NTO has certain acidity, the pH value of an NTO aqueous solution with the concentration of 0.1mol/L at 20 ℃ is 2.67, and the NTO has corrosiveness to metals under the damp and hot environment. If Al powder in the explosive is oxidized by NTO, the explosive power is reduced; if the warhead shell is oxidized and corroded, the use safety of the ammunition is affected.
Therefore, the project group adds a temperature cycle process to the passivation NTO prepared by the supercritical method, so that the desensitizer is heated, softened and extended, and effectively coated on the surface of the newly generated NTO crystal, and the coating quality of the desensitizer is improved.
In view of the above, it can be seen that the coating quality of passivated NTO is more important than other non-acid explosives. Aiming at the high requirement of the coating quality of the desensitizer, the following problems need to be solved:
(1) There is no accurate quantitative characterization method, which is not favorable for determining coating process parameters and finely adjusting the formula of the desensitizer;
(2) The desensitizer does not contain energy, so that the power of the grain is not reduced, the adding amount of the desensitizer cannot be too much, the passivating coating quality is good, the grain is not acidic at all, and the passivating NTO with the best cost performance can be obtained, so that the passivating NTO can be classified according to the coating quality and is favorable for subsequent selection.
Disclosure of Invention
The specific technical solution of the present invention is summarized as follows.
The method for evaluating the quality of the passivation NTO coating prepared by the supercritical method is characterized by comprising the following steps:
(1) Laying 3-5 g of passivated NTO particles on a glass surface dish with the diameter being more than or equal to 125mm, slightly shaking to enable large particles to be gathered to the upper layer and small particles to the bottom layer, stirring the large particles to the periphery by using a horn spoon, spreading the small particles on the upper layer and the bottom layer of the glass surface dish, randomly selecting 12 particles from the large particles, observing the particles by using a microscope with the magnification of 50 times, comparing the particles with an unpassivated NTO recrystallized product, considering that the passivated NTO is debonded if the passivated NTO particles have a reflective crystal surface similar to the unpassivated NTO recrystallized product, and recording the number n of debonded particles; judging that the coating quality of the passivated NTO is poor when n is more than or equal to 4; judging the passivation NTO coating quality IV grade when n is more than 0 and less than or equal to 3; judging that the passivated NTO is not debonded when n = 0;
(2) Detecting the passivated NTO with n =0 in the step (1), uniformly mixing 8-10 g of the passivated NTO, taking out the passivated NTO containing 1g of NTO according to a quartering method, preparing an aqueous solution with the concentration of 0.1mol/L by using neutral deionized water at the temperature of 20 ℃, stirring for 10 minutes, and detecting the pH value of the aqueous solution; judging the passivation NTO coating quality level III when the pH value is less than 6; the pH value is more than or equal to 6, and the aqueous solution is neutral;
(3) Uniformly mixing 40-60 g of passivated NTO with the pH value of more than or equal to 6 in the step (2), and taking out the passivated NTO containing 10.0 +/-0.1 g of NTO according to a quartering method; taking 2 round smooth Al sheets with the diameter of 20mm and the height of 2mm, and grinding oxide layers on two surfaces of the Al sheets by using No. 240 fine gauze; firstly, pouring half of passivated NTO into a glass container with the diameter of 30mm, then putting 1 polished Al sheet, and then pouring the other half of passivated NTO into the glass container; another empty glass container is taken and another 1 polished Al sheet is put in the empty glass container to be used as a blank test; placing the two glass containers into a 60 ℃ and RH65% damp-heat environment test box; after 30 days of continuous constant temperature and humidity, taking out 2 Al sheets, and wiping off NTO powder stuck on the Al sheets by absorbent cotton; detecting the element content of the Al sheet by using an electron microscope-energy spectrometer; detecting at least 6 points of each Al sheet, detecting the central point of the unsmooth area, and averaging the oxygen element content obtained from all the detection points to obtain the oxygen element content of the Al sheet; calculating the oxygen content of the Al sheet in the blank test of alpha = contact passivation NTO; and judging the passivation NTO coating quality level I when the alpha is less than or equal to 1.5 times, and judging the passivation NTO coating quality level II when the alpha is more than 1.5 times.
The method for evaluating the coating quality of the passivated NTO prepared by the supercritical method is characterized in that the reflected light on the surface of the NTO particles is observed by a microscope in the step one.
The method of the invention has the following advantages:
(1) The characterization method can be used for accurately quantifying, has comparable data, and can be used for determining coating process parameters and finely adjusting the formula of the desensitizer.
(2) The passivation NTO was classified into five grades based on the test results. The I-level passivation NTO has the best coating quality, does not show acidity at all and does not corrode metal. The passivated NTO with the best selective price ratio can be used for producing Al-containing explosive according to the use requirement and the combination of the process conditions.
Drawings
FIG. 1 is a graph showing the change of oxygen content with time of Al pieces exposed to 4NTO samples in a 60 ℃ RH65% moist heat environment, wherein # 1 is an Al piece of a blank test, # 2 is an Al piece in contact with passivated NTO subjected to a temperature cycle of 5 times after supercritical coating, # 3 is an Al piece in contact with passivated NTO subjected to a temperature cycle of 2 times after supercritical coating, and # 4 is an Al piece in contact with unpassivated NTO.
The present invention will be described in further detail with reference to examples.
Detailed Description
Example 1
The desensitizer has no acid-base property, and is insoluble in water. NTO (chemical name is 3-nitro-1,2,4-triazole-5-ketone) is white or light yellow crystal particles and has certain acidity. The coating quality of the passivation NTO desensitizer can be distinguished according to the crystal reflectivity and acidity of the NTO, and an evaluation method is established.
The inventive idea of the patent is elaborated by taking a certain batch of passivated NTO prepared by a supercritical heat preservation method as an example.
The preparation method of the passivation NTO to be detected comprises the following steps: mixing NTO recrystallized products with two granularity ranges of 30-60 meshes and 60-80 meshes according to the mass ratio of 3:1 to obtain mixed granularity NTO recrystallized products; preparing a desensitizer from the polyvinyl acetate and the purified ozokerite in a mass ratio of 1:1, and adding ethyl acetate into the desensitizer to prepare a desensitizer solution with the concentration of 20 percent/ml; adding the mixed particle size NTO recrystallized product into the desensitizer solution according to the mass ratio of 95g of the mixed particle size NTO recrystallized product to the desensitizer to form a suspension, and placing the suspension into a high-pressure kettle heated in a water bath, wherein the water bath heating temperature is 50-60 ℃; introducing CO from the bottom of the kettle 2 Gas, stirring the suspension until the temperature and the pressure in the kettle reach a supercritical state, wherein the supercritical state is T C ＝31.1℃、P C After that, the upper valve of the kettle is partially opened, and CO is continuously introduced into the lower part of the kettle 2 Gas, adjusting an upper valve to keep the pressure in the kettle constant, and stopping introducing CO after 1 hour 2 Gas is filled and a valve at the upper part of the kettle is completely opened, thus obtaining a passivated NTO semi-finished product; preserving the heat of the passivated NTO semi-finished product for 1 hour at 70 ℃, then heating to 85 ℃ at the heating rate of 20 ℃/hour, and then cooling to 70 ℃ at the cooling rate of 20 ℃/hour to finish 1 time of temperature cycle; and 5 times of circulation is carried out totally, then the temperature is reduced to the room temperature at the rate of 20 ℃/hour, and the passivation NTO semi-finished product is stirred once every 0.5 hour in the whole temperature treatment process, so that the passivation NTO is finally obtained.
The following are the research ideas and detection results of the coating quality evaluation method for the passivated NTO.
1. Determination of coating quality based on crystal reflectivity of NTO
NTO is a white or yellowish crystalline particle, and the crystal plane can be seen by reflecting light. The desensitizer is polyvinyl acetate and ceresin, has soft reflected light and is greatly different from NTO crystal surface. The microscope can only observe 1 particle at a time, and for the whole material, the test volume is small, and the phenomenon that the detection particle cannot represent the whole material is easy to occur, so that a plurality of particles need to be measured, but too many detection particles can cause larger workload, so that the weakest part in the whole material is preferably detected in a concentrated mode, and when the most possibly debonded particles cannot see the NTO crystal surface, the whole batch of material can be judged to be well coated.
The supercritical method is used for coating and passivating NTO, and finally the pressure is quickly released from 7.38MPa to normal pressure, so that NTO particles originally with large defects are extremely easy to break, and NTO particles which can be debonded are generally small, so that attention is focused on small NTO particles. Therefore, the design of the patent is as follows: laying 3-5 g of passivated NTO particles on a glass watch glass with the diameter being more than or equal to 125mm, slightly shaking to enable large particles to gather to an upper layer and small particles to a bottom layer, stirring the large particles to the periphery by using a horn spoon, spreading the small particles on the upper layer and the bottom layer of the watch glass, randomly selecting 12 particles from the large particles, observing the particles by magnifying the microscope by 50 times, comparing the particles with an unpassivated NTO recrystallized product, considering that the passivated NTO is debonded if the passivated NTO particles have a reflective crystal surface similar to the unpassivated NTO recrystallized product, and recording the number n of debonded particles.
In order to determine a criterion (n represents that the coating quality of the desensitizer is poor), a little Sudan red is added into the desensitizer, then the desensitizer is coated by a supercritical method, a person for detecting passivation RDX (A-IX-I) judges whether the passivation NTO is coated qualified or not according to colors (the passivation RDX is a conventional product, the coating quality is always judged by the method), then the number n of debonded particles of the passivation NTO prepared by the same supercritical process without the Sudan red is detected by the microscope method of the patent, two detection results are corresponding, and finally the judgment is carried out: when n is more than or equal to 4, the passivation NTO coating quality is poor; when n is more than 0 and less than or equal to 3, passivating the coating quality IV grade of the NTO desensitizer; when n =0, the passivated NTO is judged not to be debonded.
2. Determining the coating quality according to the pH value of NTO aqueous solution
Even in the material with n =0, the insensitive agent may have uneven thickness and poor coating effect, so the passivation agent coating quality can be judged by using the acidity of the NTO itself and adopting a method of dissolving the passivated NTO into an aqueous solution to detect the pH value. Since the amount of sample is much larger than that of the microscope method when dissolving, the whole material can be represented more comprehensively.
And (3) the temperature of the passivated NTO semi-finished product is cycled for 1 time, and the passivated NTO is observed by a microscope to have no debonded NTO crystal, namely the standard of n = 0. The NTO and the NTO semi-finished product after passivation are respectively prepared into water solutions with the concentration of 0.1mol/L by circulating the temperature for 1 time, and the pH value detection results at 20 ℃ are respectively 2.7, 4.3 and 7.2. The desensitizer is insoluble in water and has no acidity or alkalinity, so if the coating effect of the desensitizer is better, NTO can be prevented from contacting with water. The aqueous solution of well-coated passivated NTO should therefore be shown to be neutral. The detection results show that: (1) the passivation NTO coating quality is good, the contact between the NTO and water is blocked, the aqueous solution is neutral, and the pH value is 7.2; (2) after the temperature of the passivated NTO semi-finished product is cycled for 1 time, the coating quality is not good enough, partial NTO is dissolved in water, so that the aqueous solution is acid, and the pH value of the aqueous solution is between 2.7 of the aqueous solution of NTO and 7.2 of the passivated NTO.
3. Determining the coating quality according to the corrosivity of passivated NTO on Al in a damp and hot environment
The accelerated test is carried out in a damp and hot environment, the speed of the physical and chemical reaction of the passivated NTO can be accelerated, and the safe storage performance of the passivated NTO for a long time can be observed in a short time. However, the damp heat test is longer, so that only the passivation NTO with the pH value of more than or equal to 6 in the water solution test is examined.
3.1 selection of humidity and temperature
The humidity is selected primarily to provide a relative humidity of typically 65% (RH) in a normal storage environment.
The temperature is selected taking into account: on one hand, the speed of physical and chemical changes can be increased and the detection time can be shortened by increasing the temperature, so that a slightly higher temperature is generally selected for laboratory detection; on the other hand, too high a temperature will melt the desensitizer into a fluid. The test result of "putting the passivated NTO on a glass dish, keeping the temperature at 50, 60 and 70 ℃ for 30 days respectively, observing whether the desensitizer obviously seeps and sticks on the glass" is obtained, and finally determining the test temperature to be 60 ℃.
3.2 selection of incubation time
Al sheets (1 # is an Al sheet for a blank test, 2# is an Al sheet in contact with passivated NTO subjected to 5 temperature cycles after supercritical coating, 3# is an Al sheet in contact with passivated NTO subjected to 2 temperature cycles after supercritical coating, and 4# is an Al sheet in contact with unpassivated NTO) in different environments were heated at 60 ℃ and RH65%, taken out for 0, 7, 16, 26, 40, and 52 days, respectively, and the oxygen element content of the Al sheets was measured. The oxygen content was plotted on the ordinate and the heating time on the abscissa (see FIG. 1). As can be seen from fig. 1, the oxygen content of the Al sheet rapidly increased in the first few days of heating, and substantially did not change after 26 days. The heating time for the damp heat test was thus determined to be 30 days.
3.3 sheet Metal for selection test and criteria
NTO is acidic and can corrode metals in hot and humid environments. The passivated NTO is mainly used for manufacturing pressed Al-containing explosive, and the NTO can contact Al powder and can oxidize partial Al into Al 2 O 3 . NTO base explosive is put in the metal shell of the warhead, and the metal which the NTO can possibly contact is Al, cu, stainless steel.
Mixing the NTO recrystallized product with Al, cu and stainless steel metal test pieces for a damp-heat test, continuously keeping the temperature and the humidity for 30 days, taking out 3 metal test pieces, putting the 3 metal test pieces together with the 3 metal test pieces for a blank test, and observing under natural light. It can be seen that 3 kinds of metal test pieces contacted with NTO are dark in color, have corrosion spots of different degrees, have rough edges of corroded areas, and are adhered to corroded edges after a small amount of NTO absorbs moisture.
The NTO powder adhered on the metal test piece was wiped off with absorbent cotton, and the corroded parts of the metal test piece contacting with NTO were detected with a combined electron microscope and energy spectrometer, while the metal test piece of the blank test was detected with an electron microscope and energy spectrometer, and the detection data are shown in tables 5, 6 and 7.
TABLE 5 Electron microscope-Spectroscopy combination instrument for detecting elements of Al sheet
O/％ Mg/％ Al/％ Zn/％
Blank test 2.72 2.24 88.04 7.01
Contact NTO 10.24 2.10 82.13 5.54
TABLE 6 element detection of Cu plate by electron microscope-energy spectrum combined instrument
C/％ O/％ Cu/％ Zn/％
Blank test 16.72 2.10 46.35 34.84
Contact NTO 12.24 4.05 49.34 34.38
TABLE 7 Electron microscope-energy spectrum combined instrument for detecting elements of stainless steel sheet
C/％ O/％ Cr/％ Fe/％ Ni/％
Blank test 2.90 0.97 16.55 75.27 4.31
Contact NTO 5.23 2.51 15.37 73.54 3.35
From the data in table 5, it can be calculated that the oxidation degree of the aluminum sheet contacting with NTO is 3.8 times that of the aluminum sheet in the blank test, from the data in table 6, it can be calculated that the oxidation degree of the copper sheet contacting with NTO is 1.9 times that of the copper sheet in the blank test, and from the data in table 7, it can be calculated that the oxidation degree of the stainless steel sheet contacting with NTO is 2.6 times that of the stainless steel sheet in the blank test.
It can be seen that under hot and humid environments, NTO is corrosive to metals (aluminum, copper, stainless steel) due to its acidic nature. The Al sheet has the greatest oxidation degree, and Al is still in the Al-containing explosive, so that attention can be focused on whether the Al sheet is corroded in a damp and hot environment to judge whether the coating layer of the passivated NTO can withstand the test.
Considering that Cu is a relatively inert element, the copper sheet in contact with NTO oxidizes 1.9 times as much as the blank test copper sheet. And (3) artificially equating the metal test piece with alpha less than or equal to 1.5 times as a boundary to be not corroded, namely after the Al sheet is embedded into certain passivated NTO to carry out a damp-heat test, calculating that the oxidation degree of the Al sheet contacting with the NTO is the multiple alpha of the blank test Al sheet, and if the alpha is less than or equal to 1.5 times, judging that the passivated NTO meets the I grade.
FIG. 1 is a graph showing the change of oxygen content with time of Al pieces exposed to 4NTO samples in a 60 ℃ RH65% moist heat environment, wherein # 1 is an Al piece of a blank test, # 2 is an Al piece in contact with passivated NTO subjected to a temperature cycle of 5 times after supercritical coating, # 3 is an Al piece in contact with passivated NTO subjected to a temperature cycle of 2 times after supercritical coating, and # 4 is an Al piece in contact with unpassivated NTO.
From the data in fig. 1, it can be calculated that the multiples of the oxygen content of the remaining 3 Al sheets after heating at 60 ℃ and RH65% for 30 days, relative to the Al sheet of the blank test, are: α (2 #) =1.1 times, α (3 #) =1.7, α (4 #) =3.9. Therefore, the passivation NTO (contacting with No. 2 Al plate) which is subjected to temperature cycle for 5 times after the supercritical coating is I grade, and the passivation NTO (contacting with No. 3 Al plate) which is subjected to temperature cycle for 2 times after the supercritical coating is II grade.
4. Verification test
The heat sensitivity of NTO is characterized by calculating activation energy by using an explosion point test with a 5-second delay period. The calculation results of the apparent activation energy of the passivated NTO semi-finished product and the passivated NTO are 93616 and 99327J/mol respectively. The apparent activation energy of the passivated NTO increases due to the higher thermal safety of the higher quality coating samples, and therefore the higher value of the apparent activation energy. This proof test shows that the coating quality of passivated NTO is higher than that of passivated NTO semi-finished products.
5. Conclusion
The embodiment shows that the characterization method of the patent can accurately quantify, has comparable data, and can be used for determining coating process parameters and finely adjusting the formula of the desensitizer. The passivation NTO was classified into five grades based on the test results. The I-level passivation NTO has the best coating quality, does not show acidity at all and does not corrode metal. The Al-containing explosive can be produced by passivating NTO with the best selective price ratio according to the use requirements and the process conditions.

Claims (2)

1. The method for evaluating the quality of the passivated NTO coating prepared by the supercritical method is characterized by comprising the following steps of:
step one, laying 3-5 g of passivated NTO particles on a glass surface dish with the diameter being more than or equal to 125mm, slightly shaking to enable large particles to be gathered to the upper layer and small particles to the bottom layer, stirring the large particles to the periphery by using a horn spoon, spreading the small particles on the upper layer and the bottom layer of the glass surface dish, randomly selecting 12 particles from the large particles, observing the particles by magnifying the particles by 50 times by using a microscope, comparing the particles with an unpassivated NTO recrystallized product, considering that the passivated NTO is debonded if the passivated NTO particles have a reflective crystal surface similar to the unpassivated NTO recrystallized product, and recording the number n of debonded particles; judging that the passivation NTO coating quality is poor when n is more than or equal to 4; judging the passivation NTO coating quality IV grade when n is more than 0 and less than or equal to 3; judging that the passivated NTO is not debonded when n = 0;
step two, detecting the passivated NTO with the n =0 in the step one, uniformly mixing 8-10 g of the passivated NTO, taking out the passivated NTO containing 1g of the NTO according to a quartering method, preparing an aqueous solution with the concentration of 0.1mol/L by using neutral deionized water at the temperature of 20 ℃, stirring for 10 minutes, and detecting the pH value of the aqueous solution; judging the passivation NTO coating quality level III when the pH value is less than 6; the pH value is more than or equal to 6, and the aqueous solution is neutral;
step three, uniformly mixing another 40-60 g of passivated NTO with the pH value more than or equal to 6 in the step two, and taking out the passivated NTO containing 10.0 +/-0.1 g of NTO according to a quartering method; taking 2 round smooth Al sheets with the diameter of 20mm and the height of 2mm, and grinding oxide layers on two surfaces of the Al sheets by using No. 240 fine gauze; firstly, pouring half of passivated NTO into a glass container with the diameter of 30mm, then putting 1 polished Al sheet, and then pouring the other half of passivated NTO into the glass container; another empty glass container is taken and another 1 polished Al sheet is put in the empty glass container to be used as a blank test; placing the two glass containers into a 60 ℃ and RH65% damp-heat environment test box; after 30 days of continuous constant temperature and humidity, taking out 2 Al sheets, and wiping off NTO powder stuck on the Al sheets by absorbent cotton; detecting the element content of the Al sheet by using an electron microscope-energy spectrometer; detecting at least 6 points of each Al sheet, detecting the central point of the unsmooth area, and averaging the oxygen element content obtained from all the detection points to obtain the oxygen element content of the Al sheet; calculating the oxygen content of the Al sheet in the blank test of alpha = contact passivation NTO; when alpha is less than or equal to 1.5 times, judging the passivation NTO coating quality I grade, and when alpha is more than 1.5 times, judging the passivation NTO coating quality II grade.
2. The method for evaluating the quality of the passivated NTO coating prepared by the supercritical method as claimed in claim 1, wherein the light reflected from the surface of the NTO particles is observed by a microscope in the first step.
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