Application scope: mostly used for the connection of smaller parts. Cross Recessed Tapping Screws,Pan Head Tapping Screws,Stainless Steel Screws,Steel Head Tapping Screw Kunshan Zhonggu Precision Hardware Co., Ltd. , https://www.zgfastener.com
It has pan head Screws, countersunk head screws, half countersunk head screws and large flat head screws. Pan head screws and large flat head screws are used in the occasion where the nail head is allowed to be exposed;
Half countersunk head screws have an arc-shaped head, and its top is slightly exposed after installation, and beautiful and smooth, generally used in instruments or precision machinery; countersunk head screws are used in places where the nail head is not allowed to be exposed.
2. Reference standard: Reference standard
Cross recessed pan head screws GB818-85
Cross recessed countersunk head screws GB819-85
Cross recessed umbrella head screws GB820-85
Three major production processes of glyphosate
Glyphosate, commonly known as Roundup or Other trade names, is a non-selective, broad-spectrum herbicide that is highly effective after plant emergence. It is widely used in agriculture due to its low toxicity, lack of residue, and effectiveness against a wide range of weeds. Glyphosate is particularly popular in the cultivation of genetically modified crops, where it helps farmers manage weed growth efficiently.
There are three main production methods for glyphosate:
1. **The Iminodiacetic Acid Method**
- **Preparation of Iminodiacetic Acid**: Chloroacetic acid is reacted with aqueous ammonia in the presence of calcium hydroxide, then acidified and neutralized with sodium hydroxide to produce iminodiacetic acid with an 85% yield. Alternatively, cyanogenic acid can be used as a starting material, reacting with formaldehyde and ammonia to achieve a 90% yield.
- **Synthesis of Glyphosate**: Iminodiacetic acid is reacted with formaldehyde and phosphorous acid in the presence of sulfuric acid to form glyphosate, with a yield of around 90%.
- **Alternative Synthesis**: A mixture of water and excess hydrogen peroxide is heated with equimolar sulfuric acid to produce glyphosate, yielding 90–95%.
2. **The Chloromethylphosphonic Acid Method**
- **Preparation of Chloromethylphosphonic Acid**: Phosphorus trichloride reacts with paraformaldehyde at 200–250°C (2.5–3.0 MPa) for 3–5 hours to produce chloromethylphosphonic dichloride. The molar ratio of phosphorus trichloride to paraformaldehyde is typically 1.2–1.5:1, with a yield of 67% without a catalyst and up to 80–89% with a Lewis acid catalyst. Hydrolysis of the intermediate yields chloromethylphosphonic acid.
- **Synthesis of Glyphosate**: Equimolar amounts of chloromethylphosphonic acid and glycine are dissolved in a sodium hydroxide solution (pH > 10), then refluxed for 10–20 hours. Afterward, the product is acidified with hydrochloric acid. Depending on the pH, the final product can be either a monosodium salt (at pH = 4) or a disodium salt (at pH = 8.5).
3. **The Dialkyl Phosphite Method**
This method involves the addition, condensation, and hydrolysis of glycine, dialkyl phosphite, and paraformaldehyde. It results in a product with 95% purity and an overall yield of 80%, making it a cost-effective option for large-scale production.
When using glyphosate, it's important to apply it carefully to avoid contaminating crops, which could lead to phytotoxicity. As glyphosate is acidic, it should be stored and handled properly to maintain its effectiveness and safety. Always follow the manufacturer’s guidelines and local regulations when applying this herbicide.
Whether you're a farmer, agricultural professional, or someone interested in modern farming techniques, understanding how glyphosate is produced and used can help you make more informed decisions about crop management and environmental impact.