What Is Zinc Oxide?

Zinc oxide is an oxide of zinc. Hardly soluble in water, soluble in acids and strong bases. Zinc oxide is a commonly used chemical additive, widely used in the production of plastics, silicate products, synthetic rubber, lubricants, paints, ointments, adhesives, food, batteries, flame retardants and other products. Zinc oxide has a large band gap and exciton binding energy, high transparency, and excellent room temperature luminous properties. It is used in liquid crystal displays, thin film transistors, light emitting diodes and other products in the semiconductor field. In addition, microparticle zinc oxide has also begun to play a role in related fields as a nanomaterial.

Physical properties

Appearance and properties: white powder or hexagonal crystal. Odorless, tasteless, and sandless. When heated, it turns yellow, after cooling, it turns white again. When heated to 1800

Zinc oxide is an important and widely used physical sunscreen. The principle of shielding ultraviolet rays is absorption and scattering. Zinc oxide is an N-type semiconductor, and the electrons on the valence band can accept the energy transition in ultraviolet rays, which is also the principle of their absorption of ultraviolet rays. The function of scattering ultraviolet rays is related to the particle size of the material. When the size is far smaller than the wavelength of ultraviolet rays, the particles can scatter the ultraviolet rays acting on them in all directions, thereby reducing the intensity of ultraviolet rays in the irradiation direction. In addition, if the particle size of this raw material is too large, unnatural whitening will occur on the skin. As a result, nanoscale particles have significant advantages over conventional sizes.

Nanometer zinc oxide is a stable compound that can provide broad-spectrum ultraviolet protection (UVA and UVB), as well as antibacterial and anti-inflammatory effects. It is by far the safest and most effective ingredient in the evaluation of sunscreens in various countries. However, their extremely small size makes them have higher chemical activity and may be absorbed by the human body, which is potentially harmful to the human body and the environment. Therefore, there is still a lot of controversy regarding the use of nanoscale zinc oxide. For example, the European Union said in 2004 that nano-sized zinc oxide would be absorbed and could cause DNA damage. In a 2006 review, Australia stated that it did not consider the nanoparticles to be absorbed in the skin. The United States DNA approved the use of zinc oxide in 1999, but believed that nano-zinc oxide had safety issues and was not allowed to use it. In 2006, nano-zinc oxide was approved as a new active ingredient.

The most worrying aspect of nanoparticles is that they release free radicals, which increases oxidative stress and damages proteins, esters and DNA in the body. Oxygen free radicals produced by titanium may cause damage to DNA and cells, and hydroxyl radicals produced by zinc may damage DNA and cellular structures in the skin. In addition, when you apply sunscreen to wash your face or swim, or use lipstick with a sun protection factor, there is a great possibility that the nano-level sunscreen contained in it can be directly eaten, so that the human body can directly absorb it. of. Studies have shown that the intestines can absorb titanium dioxide particles with a diameter of 150-500nm (slightly higher than the nanometer level, which is equivalent to micron particles, which is also used in sunscreens of this size), and these particles can then reach the liver and spleen. There is controversy as to whether nanoparticles can enter the blood directly through the skin. Experiments in animals and human hands show that nano-zinc oxide has an absorption of 1.5-2.3%. However, some people think that the skin on the human hand is much thicker than the lips, eyelids, inner thighs, underarms and other places, and if the absorption condition of the skin damage will be different, it is quickly concluded that almost zero absorption of such particles is too much Sloppy, lacking more experimental evidence. ^[6]

1.It is mainly used as a reinforcing agent in the rubber or cable industry and

Rats were injected intraperitoneally with LD ₅₀ : 240 mg / kg. poisonous. Poisoned people will have many symptoms such as poor appetite, thirst, tiredness, and severe cases will show pulmonary interstitial edema and alveolar epithelium destruction.

After inhaling zinc oxide dust for 4-8 hours, metal fume fever may occur.

Poisoned persons may have poor appetite, thirst, tiredness, chest tightness and tenderness, lethargy, dry cough, and increased body temperature, enlarged pupils, conjunctiva and pharynx, facial congestion, diabetes, and sometimes hepatomegaly. In severe cases, pulmonary interstitial edema and alveolar epithelium were destroyed. ^[7]

I. Direct method:

1. From zinc carbonate

Leak handling

Isolate the leakage pollution area and set warning signs around it. It is recommended that emergency handlers wear masks, goggles, and work clothes. Sweep carefully to avoid dust, and bury it in an open area. It can also be washed with a large amount of water, and the diluted washing water is put into the waste water system. If a large amount of leakage, collect and recycle or discard after harmless treatment. ^[8]

General rules for chemical classification and hazard communication (published on May 21, 2009) ^[10]

Experimental name: Determination of zinc oxide.

Application range /: This method uses a titration method to determine the content of zinc oxide. This method is suitable for zinc oxide.

Experimental principle: Dilute hydrochloric acid to dissolve the test sample, add 0.025% methyl red ethanol solution and ammonia test solution, add ammonia-ammonium chloride buffer solution (pH 10.0) and chrome black T indicator, and use ethylenediamine Tetrasodium acetate titration solution (content 0.05mol / L) was titrated until the solution changed from purple to pure blue. Read out the amount of ethylenediamine tetraacetic acid disodium titrant used to calculate the zinc oxide content.

Experimental reagents:

1. Water (fresh to room temperature).

2. Disodium ethylenediamine tetraacetate titration solution (0.05mol / L).

3. Baseline zinc oxide.

4. Dilute hydrochloric acid.

5. Methyl red in ethanol (0.025%).

6. Ammonia test solution.

7. Chrome black T indicator.

8. Ammonia-ammonium chloride buffer (pH 10.0).

Experimental preparation:

1. Disodium ethylenediamine tetraacetate titration solution (0.05mol / L).

Preparation: Take 19 g of disodium ethylenediamine tetraacetate, add freshly boiled cold water to 1000 mL, and shake well.

Calibration: Take 0.12g of reference zinc oxide which is burned to constant weight at 800 , accurately weigh, add 3mL of dilute hydrochloric acid to dissolve, add 25mL of water, add 1 drop of 0.025% methyl red ethanol solution, and dropwise add ammonia test solution to The solution was slightly yellow. Add 25 mL of water and 10 mL of ammonia-ammonium chloride buffer (pH 10.0), and then add a small amount of chrome black T indicator. Titrate the solution until the solution changes from purple to pure blue. Blank test correction. Each 1mL of ethylenediaminetetraacetic acid disodium titration (0.05mol / L) is equivalent to 4.069mg of zinc oxide. The concentration of the liquid was calculated from the consumption of the liquid and the amount of zinc oxide taken.

Storage: Keep in glass stopper bottle, avoid contact with rubber stopper, rubber tube, etc.

2. Dilute hydrochloric acid: Take 234mL of hydrochloric acid and dilute to 1000mL with water, that's it. The solution should contain HCl at 9.5-10.5%.

3. Ammonia test solution: Take 400mL of concentrated ammonia solution and add water to make it into 1000mL.

4. Chrome black T indicator: Take 0.1g of chromium black T, add 10g of sodium chloride, grind evenly, that is, you can get.

5. Ammonia-ammonium chloride buffer solution (pH10.0): Take 5.4g of ammonium chloride, add 20mL of water to dissolve, add 35mL of concentrated ammonia solution, and dilute to 100mL with water.

Experimental steps: Weigh precisely about 0.1g of the test sample, add 2mL of dilute hydrochloric acid to dissolve, add 25mL of water, add 1 drop of 0.025% methyl red ethanol solution, dropwise add the ammonia test solution to the solution yellow, add 25mL of water, ammonia -10mL of ammonium chloride buffer (pH 10.0) and chrome black T indicator, titrate with ethylenediamine tetraacetic acid disodium titration solution (0.05mol / L) until the solution changes from purple to pure blue. Record the volume (mL) of ethylenediaminetetraacetic acid disodium titrant titration solution. Each 1mL of ethylenediaminetetraacetic acid disodium titrant titration solution (0.05mol / L) is equivalent to 4.069mg of ZnO.

Note 1: "Precise weighing" means that the weighed weight should be accurate to one thousandth of the weighed weight. "Precision weighing" means that the accuracy of the measured volume should conform to the national standard for the volume of the pipette. Precision requirements. ^[13]