สถิติ
เปิดเมื่อ28/01/2015
อัพเดท3/05/2022
ผู้เข้าชม918355
แสดงหน้า1191136
ปฎิทิน
February 2023
Sun Mon Tue Wed Thu Fri Sat
   
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
    
สมาชิก

สมัครสมาชิก | ลืมรหัสผ่าน

ทังสเตนคาร์ไบด์

อ่าน 169663 | ตอบ 3498
ทังสเตนคาร์ไบด์
       ทังสเตนคาร์ไบด์ (อังกฤษ: tungsten carbide) มีสูตรเคมีคือ WC ในรูปพื้นฐานจะมีลักษณะเป็นผงสีเทาละเอียด มี 2 โครงสร้างคือแบบหกเหลี่ยม (α-WC) และแบบลูกบาศก์ (β-WC)
 
       ทังสเตนคาร์ไบด์เตรียมได้จากการทำปฏิกิริยาระหว่างทังสเตนกับคาร์บอนที่อุณหภูมิ 1400–2000 °C[3] หรือให้ความร้อนกับทังสเตนไตรออกไซด์และแกรไฟต์โดยตรงที่ 900 °C หรือในแก๊สไฮโดรเจนที่ 670 °C ตามด้วยการคาร์บิวไรเซชันในแก๊สอาร์กอนที่ 1000 °C[4] หรือใช้วิธีการเคลือบด้วยไอเคมี เช่น
  • ทำปฏิกิริยาระหว่างทังสเตนเฮกซะคลอไรด์กับไฮโดรเจนและมีเทนที่อุณหภูมิ 670 °C (1,238 °F)
 WCl6 + H2 + CH4 WC + 6 HCl
  • ทำปฏิกิริยาระหว่างทังสเตนเฮกซะฟลูออไรด์กับไฮโดรเจนและเมทานอลที่อุณหภูมิ 350 °C (662 °F)
                WF6 + 2 H2 + CH3OH → WC + 6 HF + H2O
       ทังสเตนคาร์ไบด์มีจุดหลอมเหลวที่ 2,870 °C (5,200 °F) และจุดเดือดที่ 6,000 °C (10,830 °F) มีความแข็งระดับ 9 ตามมาตราโมสและประมาณ 2600 ตามมาตราวิกเคอส์[5] ทังสเตนคาร์ไบด์มีความแข็งเกร็งมากกว่าเหล็กกล้าประมาณ 2 เท่า มีค่ามอดุลัสของยังประมาณ 530–700 GPa (77,000–102,000 ksi)[2][6][5][7] โมดูลัสของแรงบีบอัด 630–655 GPa และโมดูลัสของแรงเฉือน 274 GPa[8]
 
ด้วยคุณสมบัติความแข็งและทนความร้อนสูง ทังสเตนคาร์ไบด์จึงใช้ทำเป็นเครื่องมือตัดหรือหัวเจาะ ใช้ทำกระสุนเจาะเกราะ เครื่องมือผ่าตัด อุปกรณ์กีฬา เครื่องประดับและอื่น ๆ
 
 
 
 
 
 
 
 
 
 
อ้างอิง
 
  1. Kurlov, p. 22
  2. Blau, Peter J. (2003). Wear of Materials. Elsevier. p. 1345. ISBN 978-0-08-044301-0.
  3. Pierson, Hugh O. (1992). Handbook of Chemical Vapor Deposition (CVD): Principles, Technology, and Applications. William Andrew Inc. ISBN 0-8155-1300-3.
  4. Zhong, Y.; Shaw, L. (2011). 'A study on the synthesis of nanostructured WC–10 wt% Co particles from WO3 , Co3O4 , and graphite'. Journal of Materials Science 46 (19): 6323–6331. Bibcode:2011JMatS..46.6323Z. doi:10.1007/s10853-010-4937-y.
  5. Groover, Mikell P. (2010). Fundamentals of Modern Manufacturing: Materials, Processes, and Systems. John Wiley & Sons. p. 135. ISBN 978-0-470-46700-8.
  6. Kurlov, p. 3
  7. Cardarelli, François (2008). Materials Handbook: A Concise Desktop Reference. Springer Science & Business Media. pp. 640–. ISBN 978-1-84628-669-8.
  8. Kurlov, pp. 30, 135
  9. Sprince, NL.; Chamberlin, RI.; Hales, CA.; Weber, AL.; Kazemi, H. (1984). 'Respiratory disease in tungsten carbide production workers'. Chest 86 (4): 549–557. PMID 6434250. doi:10.1378/chest.86.4.549.
  10. 12th Report on Carcinogens'. National Toxicology Program. http://ntp.niehs.nih.gov/go/roc12. เรียกข้อมูลเมื่อ 2011-06-24.
ความคิดเห็น :
3020
อ้างอิง

aishasharmaxx1
We have a vigorous sort of drain like outsider young ladies from all through the globe, with their conventional perfection and inherent quality; they in the purpose of truth serve the customer inside the best methodology. Town Night Escort in  Foreign Escorts In Delhi feels happy to fulfill our customers and ensure you have a problem-free staggering sexual time.
 
ลิงค์ที่เกี่ยวข้อง : https://www.aishaescorts.com
aishasharmaxx1 [103.159.43.xxx] เมื่อ 7/12/2022 13:50
3021
อ้างอิง

카지노사이트추천
I'm writing on this topic these days, 카지노사이트추천 , but I have stopped writing because there is no reference material. Then I accidentally found your article. I can refer to a variety of materials, so I think the work I was preparing will work! Thank you for your efforts. 
 
카지노사이트추천 [202.165.70.xxx] เมื่อ 7/12/2022 14:42
3022
อ้างอิง

Lilly
เว็บDooballvip เรามี ราคาบอล ให้ทุกท่านได้ติดตามแบบ Real Time
 
Lilly [103.107.196.xxx] เมื่อ 7/12/2022 17:27
3023
อ้างอิง

Online assignment help in Australia
We want to make certain our research and private pride with the assistance of best pay a person to do my homework online. Save some time with the assistance of assignments in all feasible subjects! Original, superb essay creator homework assist with inside the AU, Our mission offerings are to be had 24×7. Bright mission assists let you get the pleasant best carrier at less expensive expenses and be 100% lost from plagiarism. Contact 'Online assignment help in Australia' for Top Quality mission professional students can also additionally discover the mission trouble and supervisors' expectancies tough to grasp, or they'll now no longer have time to paint at the complicated wishes of the whole mission or lack the sturdy writing skills to ace online classes homework. We appear after your capabilities and permit you to collect awesome grades in each aspect. Get Assignment Help that makes a specialty of college students happiness and immediate pride.
 
Online assignment help in Australia [23.19.74.xxx] เมื่อ 7/12/2022 18:56
3024
อ้างอิง

Surbhirana

MEET OUR HORNY COLLEGE Delhi ESCORT BABES Our horny female Delhi escort college babes are also available for recreation. They are absolutely sensuous and desirable from every aspect. The sensuous gestures and absolutely amazing seduction offered by the young and ravishing divas will always make things erotic to the core for you. So, get in touch with the girls and add some really entertaining and youthful spice to your life. We are available throughout the day. So, one can dial our number any time and ask the executives to offer college escort companionship for a perfectly enjoyable moment ahead. You are surely going to have some amazing fun with the professional escorts in Delhi , associated with tiakapoor.in. Surbhi Rana BEST INDEPENDENT DELHI ESCORTS GIRL FROM DELHI CITY AREA The girls in Delhi are always there to get rid of stress and worries form their clients' life. This is the reason they escort girls are always preferred and appreciated by some of the most elite class clients on various occasions and events. The sexy escort girls in Delhi are really excellent when it comes to providing amazing out call and in call services with satisfactory treatments and other erotic offerings. The clients simply love spending time with the sexy escort girls in Delhi for various reasons. Most importantly, the Delhi escorts girls do have that ability to get rid of all sorts of negativity and stress from the life of their clients in a really amazing way.I am Surbhi Rana as of Delhi , 21 years more seasoned brilliant Contact woman in Delhi weight fledgling occupation as free Delhi female escorts in Delhi here high-class resort. You control be genuine fulfilled toward distinguish to I am presently close proffer you by my dreadfully enchanting with eye-getting relationship of universal regular since I am among the horrendously small fascinating with gorgeous Delhi escorts customers of astounding circumstance. I am Surbhi Rana.
More here partner url: Gurgaon escorts
 
ลิงค์ที่เกี่ยวข้อง : https://www.surbhirana.club
Surbhirana [139.167.242.xxx] เมื่อ 7/12/2022 19:28
3025
อ้างอิง

neetudecoz
I'm a very sweet girl, and anyone who meets me should want to do so privately. Most of the time, I'm not sure if they know I'm Hot girl, who provides call girl service in this location, and if they need to meet me and remember the time they'll spend with me. I am always accessible to my client, who loves me and wants to change his entire perspective by spending the night with such a hot and seductive girl. So if you want to have fun overnight and forget your tension, contact the independent call gir. Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services Escort Escorts Escorts Near me Escort Number Sexy Escorts Hot Escorts Independent Escorts Escort Number Escorts Services Escort Mobile Number Escorts Photo Escort Agency Escorts Services Near me Model Escort Vip Escorts Escort Services Contact Number Escort Number Justdial Online Escorts Sasti Escorts prostitute Services Cash Payment Escort Services Escorts Photo Escort Red Light Area Professional Escorts Escorts Agencies Escorts in Hotel Escort Services Agency Online Escort Number Erotic Escorts Elite Escort Services  
neetudecoz [223.225.62.xxx] เมื่อ 7/12/2022 19:50
3026
อ้างอิง

Online Dispensary

Your ideas in this blog site were extra ordinary and well presented, Good job!

Online Dispensary

 
ลิงค์ที่เกี่ยวข้อง : https://herbapproach.org
Online Dispensary [122.52.176.xxx] เมื่อ 8/12/2022 08:23
3027
อ้างอิง

cbd coffee
A great website without any doubt.
cbd coffee
 
cbd coffee [180.194.0.xxx] เมื่อ 8/12/2022 10:44
3028
อ้างอิง

CCTV Camera Installation In Delhi
Camsense India private Limited Well Known Company for Best CCTV Camera Installation in Delhi. you are planning to install CCTV cameras in your property, you should know where to find the best installation services in Delhi.  Another option for CCTV Camera Installation In Delhi is through a reputed CCTV dealer in Delhi. A reputable CCTV dealer in Delhi, Camsense India  is experienced in CCTV camera installation in homes and businesses. Their CCTV technicians are young, creative, and enthusiastic about their work. CCTV installers should also have the right expertise to properly install the system. You should also make sure to read the warranty information on the security system and consider this when choosing a CCTV Camera Installation In Delhi
 
ลิงค์ที่เกี่ยวข้อง : https://www.camsenseindia.com/best-cctv-camera-installation-in-delhi/
CCTV Camera Installation In Delhi [122.162.148.xxx] เมื่อ 8/12/2022 15:39
3029
อ้างอิง

neha singh

Get Unlimited Hot Model Delhi Call Girls

Our famous call girls in delhi are full of fun from our escort agency located in Delhi. These hot call girls are famous for their flexibility and antics that leave you in awe all night long. Are you ready to dance all night and have a blast with our escorts from Delhi? If yes, as we hear, then you have to call us and learn more about our top agents and escorts. Call us now to reserve today. It is essential to be fast when booking sexy escorts in Delhi because people reserve the escorts months in advance so that they can be fun with them. The Delhi Celebrity Escorts are categorized for you. Escorts, Bollywood Escorts, and the house of many other Delhi Escorts. You don't need to fall in love with sexual mutilation since you are aware that our sexy escorts can give sexual pleasure. 

Contact us today and experience endless orgasms from our model escorts available in Delhi. They are available 24 hours a day to cater to the physical requirements of our customers. Are you interested in booking one? Then you can go to the independent agency for escorting or arrange an escort from Delhi through WhatsApp. Our delhi call girls are able to fulfill the desires of each person they meet during the night. If you're looking for an evening of hot fun with our hot ladies, and you want to contact us today and start planning you're evening date by chatting with our Delhi escorts.

Delhi Call girl is directly at your disposal

If you are, then you can get their numbers from the escort company in Delhi. Take advantage of Delhi services for escorting by contacting our escort company. Call girls are ready to stay close to you all night long. You are now the one to get your groove back. the night. You can relax and enjoy having the companionship of our girls. Are you looking to win an award for Best Taste? If yes, then call our escort agency's number to make an appointment with the top class model call girls in delhi. 

One of our hot Escorts in Delhi Do not miss out on this fantastic opportunity to enjoy an unforgettable romantic night with friends. Are you interested in knowing the secret to providing these girls with a fun and exciting techniques? To find out, you need to contact our delhi call girl service and reserve your hot female escort for amusement. If you'd like to meet him in the hotel or make an escort from your home depending on your mood and availability. can be arranged to select your preferred date and location. Please tell us that you want to remain discreet and we'll never reveal your identity to anyone.

Book Our preoius escort service

Do you want to meet our super-sexy as well as hot and young Delhi model today? You don't need to be concerned about meeting our hot-call escorts from Delhi. We've put together for you the most escorts at our call girl in delhi. If you are feeling intimate with one of our sexy ladies' escorts, come to our Delhi agency for escorts. Just call the number and inform us that you'd like Sexy and Hot Girls to book for you. We'll handle our best to make the hot Delhi sightseeing girls' bookings for you immediately. Hot girls from Delhi are sure to get you to want to be around their attractiveness. It is then possible to spend a few minutes dressing them up before you approach them. Once they arrive at your location, make sure to be like them. Do not use abusive language before your Delhi escort and treat them as a princess.

Delhi call girls for delightful experience

Dedication to the highest degree and a desire to be a hard worker in this field has made each of the Delhi escort experience the ultimate satisfaction right from the beginning. Their journey has been smooth, but it required a lot of hard work and commitment to ensure an enjoyable career. call girls delhi are very friendly with their customers and strive to keep them satisfied and content with their exciting variety of escorts available. The services offered by independent Delhi escorts are equally appreciated. There is an increasing demand for independent Delhi Escorts, especially among individuals who wish to use a cost-effective Delhi escort with total satisfaction. 

They provide top-quality services. you're probably wondering what is a premium service. In reality, premium services are ones that aren't just spending time with your female escort, but they will be a lover as if you're the only thing in their life. This is one of the most attractive things about Delhi escorts.

 
neha singh [182.68.136.xxx] เมื่อ 8/12/2022 16:47
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350
ความคิดเห็นของผู้เข้าชม
ชื่อผู้แสดงความคิดเห็น :
สถานะ : รหัสผ่าน :
ลิงค์ที่เกี่ยวข้อง :
รหัสความปลอดภัย :