請用此 Handle URI 來引用此文件：
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/65985完整後設資料紀錄
| DC 欄位 | 值 | 語言 |
|---|---|---|
| dc.contributor.advisor | 黃神祥 | |
| dc.contributor.author | Chi-Kin Cheong | en |
| dc.contributor.author | 張子健 | zh_TW |
| dc.date.accessioned | 2021-06-17T00:17:59Z | - |
| dc.date.available | 2017-08-09 | |
| dc.date.copyright | 2012-08-09 | |
| dc.date.issued | 2012 | |
| dc.date.submitted | 2012-06-29 | |
| dc.identifier.citation | [1] J. R. Davis, Stainless Steel, ASM International, Ohio, 1994, pp. 3-315.
[2] H. Nakagawa, T. Miyazaki and H. Yokota, “Effects of aging temperature on the microstructure and mechanical properties of 1.8Cu-7.3Ni-15.9Cr-1.2Mo-low C, N martensitic precipitation hardening stainless steel”,Journal of Materials Science, 2000, Vol. 35, No. 9. pp. 2245-2253. [3] 陳柏翰，“金屬射出成形17-4PH不銹鋼之機械性質及加工性之改進”，碩士論文，國立臺灣大學材料科學與工程學研究所，2010。 [4] 王繼敏，不銹鋼與金屬腐蝕，科技圖書股份有限公司，1990。 [5] P. Lancombe, B. Baroux and G. Beranger, Stainless Steel, Les Editions de Physique Les Ulis, France, 1993, pp. 661-676. [6] E. Klar and P. Samal, Powder Metallurgy Stainless Steel, ASM International, Materials Parks, Ohio, 2007, pp. 1-35 [7] C. T. Schade and A. Lawley, “Development of a High-Strength-Dual-Phase P/M Stainless Steel”, Advances in Powder Metallurgy & Particulate Materials, MPIF, Princeton, NJ, 2005, Vol. 1, Part 7. [8] 楊世偉，郭亞歡，張天宇，趙鵬成，“固溶處理對Cr17Ni4Cu4Nb鋼耐腐蝕性能及組織的影響”，材料開發與應用，2010，第25卷，第6期，1-5頁。 [9] C. T. Schade, T. F. Murphy, A. Lawley and R. Doherty, “Development of a Dual-Phase Precipitation -Hardening PM Stainless Steel”, International Journal of Powder Metallurgy, 2009, Vol. 45, No. 1, pp. 38-46. [10] S. Xiang, J. P. Wang, Y. L. Sun, Y. Y. Yan and S. G. Hung, “Effect of Aging Process on Mechanical Properties of Martensite Precipitation-hardening Stainless Steel”, Advanced Materials Research, 2011, Vol. 146-147, pp. 382-385. [11] P. Li, Q. Z. Cai, B. K. Wei and X. Z. Zhang, “Effect of Aging Temperature on Erosion-Corrosion Behavior of 17-4PH Stainless Steels in Dilute Sulphuric Acid Slurry”, Journal of Iron and Steel Research, 2006, Vol. 13, No. 5, pp. 73-78. [12] J. Wang, H. Zou, C. Li, S. Y. Qiu and B. L. Shen, “The Effect of Microstructural Evolution on Hardening Behavior of type 17-4PH Stainless Steel in long-term aging at 350oC”, Materials Characterization, 2006, Vol. 57, No. 4-5, pp. 274-280. [13] M. Murayama, K. Hono and Y. Katayama, “Microstructural evolution in a 17-4 PH stainless steel after aging at 400 °C”, Metallurgical and Materials Transactions A, 1999, Vol. 30, No. 2, pp. 345-353. [14] J. H. Reinshagen and J. C. Witsberger, “Properties of Precipitation Hardening Stainless Steel Processed by Conventional Powder Metallurgy Techniques”, Advances in Powder Metallurgy and Particulate Materials, MPIF, Princeton, NJ,1994, Vol. 7, pp. 313-323. [15] P. K. Samal and N. Nandivada, “Properties of 17-4PH Stainless steel Produced via Press and Sinter Route”, Advances in Powder Metallurgy and Particulate Materials, MPIF, Princeton, NJ, 2008, Vol. 3, part 7. [16] J. Capus, “Seeking High Strength in PM Stainless Steels”, Metal Powder Report, 2010, Vol. 65, No. 6, pp. 30-35. [17] C. Schade, P. Stears, A. Lawley and R. Doherty, “Precipitaion Hardening P/M Stainless Steels”, International Journal of Powder Metallurgy, 2007, Vol. 43, No. 4, pp. 51-59. [18] R. Mariappan, S. Kumaran, T. S. Rao and S. B. Chandrasekar, “Microstructure and Mechanical Properties of Duplex Stainless Steels Sintered in Different Atmospheres”, Powder Metallurgy, 2011, Vol. 54, No. 3, pp. 236-241. [19] L. A. Dobrzanski, Z. Brytan, M. A. Grande, M. Rosso and E. J. Pallavicini, “Properties of Vacuum Sintered Duplex Stainless Steels”, Journal of Materials Processing Technology, 2005, Vol. 162-163, pp. 286-292. [20] D. C. Blaine, Y. Wu, C. E. Schlaefer, B. Marx and R. M. German, “Sintering Shrinkage and Microstructure Evolution during Densification of a Martensitic Stainless Steel”, Metallurgical and Materials Transactions A, 2002, Vol. 33, No.7, pp. 2185-2194. [21] C. Garcia, F. Martin, Y. Blanco, M. P, de Tiedra and M. L. Aparicio, “Corrosion Behaviour of Duplex Stainless Steels Sintered in Nitrogen”, Corrosion Science, 2009, Vol. 51, No. 1, pp. 76-86. [22] Z. Brytan, L. A. Dobrzanski, M. A. Grande, M. Rosso, “The Influence of Sintering time on the Properties of PM Duplex Stainless steel”, Journal of Achievements in Materials and Manufacturing Engineering, 2009, Vol. 37, No. 2, pp. 387-396. [23] 宋慧琳，“噴霧造粒鐵粉之性質及其熱脫脂行為”，碩士論文，國立臺灣大學材料科學與工程學研究所，2006。 [24] K. Masters, Spray Drying Handbook, 5th ed, John Wiley & Sons, Inc., New York, 1991. [25] 大川原公司資料，“噴霧乾燥機(Spray Dryer)中的微粒化與造粒(曾寶貞譯) ”，國立臺灣大學材料科學與工程學研究所。 [26] 大川原公司資料，“L-8教育訓練內容”，國立臺灣大學材料科學與工程學研究所。 [27] 黃坤祥，粉末冶金學，中華民國粉末冶金協會，第二版，2003，97-133頁。 [28] W. J. Walker Jr., J. S. Reed and S. K. Verma, “Influence of Slurry Parameters on the Characteristics of Spray-Dried Granules”, Journal of the American Ceramic Society, 1999, Vol. 82, No. 7, pp. 1711-1719. [29] R. P. Patel, M. P. Patel and A.M. Suthar, “Spray drying technology: an overiew”, Indian Journal of Science and Technology, 2009, Vol. 2, No. 10, pp. 44-47. [30] M. Mezhericher, A. Levy and I. Borde, “Spray drying modeling based on advanced droplet drying kinetics”, Chemical Engineering and Processing, 2010, Vol. 49, No. 11, pp. 1205-1213. [31] J. S. Reed, Principles of Ceramic Processing, 2nd Ed. Wiley-Interscience, New York, 1995 [32] P. P. Nampi, S. Kume, Y. Hotta, K. Watari, M. Itoh, H. Toda and A. Matsutani, “The effect of polyvinyl alcohol as a binder and stearic acid as an internal lubricant in the formation, and subsequent sintering of spray-dried alumina”, Ceramics International, 2011, Vol. 37, No. 8, pp. 3445-3451. [33] S. Balasubramanian, D. J. Shanefield and D. E. Niesz, “Effect of Internal Lubricants on Defects in Compacts Made from Spray-Dried Powder”, Journal of the American Ceramic Society, 2002, Vol. 85, No. 1, pp. 134-138. [34] D. Souriou, P. Goeuriot, O. Bonnefoy, G. Thomas and F. Dore, “Influence of the formulation of an alumina powder on compaction”, Powder Technology, 2009, Vol. 190, pp. 152-159. [35] M. R. B. Romdhane, T. Chartier, S. Baklouti, J. Bouaziz, C. Pagnoux and J. F. Baumard, “A new processing aid for dry-pressing: A copolymer acting as dispersant and binder”, Journal of the European Ceramic Society, 2007, Vol. 27, No. 7, pp. 2687-2695. [36] S. Baklouti, P. Coupelle, T. Chartier and J. F. Baumard, “Compaction Behaviour of Alumina Powders Spray-Dried with Organic Binders”, Journal de Physique III, 1996, Vol. 6, No. 10, pp. 1283-1291. [37] S. Baklouti, T. Chartier, C. Gault and J. F. Baumard, “Young’s Modulus of Dry-pressed Ceramics: The Effect of the Binder”, Journal of the European Ceramic Society, 1999, Vol. 19, Issue 8, pp. 1569-1574. [38] K. J. Konsztowicz, G. Maksym, T. Maksym, H. W. King, W. F. Caley and E. Vargha-Butler, “The Role of Surface Tension in the Formation of Donut-Shaped Granules during Spray-Drying”, Ceramic Transactions, 1992, Vol. 26, pp. 46-53. [39] K. J. Konsztowicz, E. Vargha-Butler, T. Maksym and H. W. King, “The Effect of Aparent Surface Tension of Colloidal Suspensions on the Shape of the Products of Spray-Drying”, Ceramic Transactions, 1991, Vol. 22, pp. 363-369. [40] S. J. Lukasiewicz, Granulation and Spray-Drying, In Engineered Materials Handbook, Ceramics and Glasses, ASM International, Metals Park, OH, 1991, Vol. 4, pp. 100-108 [41] S. J. Lukasiewicz, “Spray-Drying Ceramic Powders”, Journal of the American Ceramic Society, 1989, Vol. 72, No. 4, pp. 617-624. [42] G. Bertrand, G. Filiatre, H. Mahdjoub, A. Foissy and C. Coddet, “Influence of slurry characteristics on the morphology of spray-dried alumina powders”, Journal of the European Ceramic Society, 2003, Vol. 23, No. 2, pp. 263-271. [43] Metal Handbook: properties and selection: irons, steels, and high performance alloys, vol. 1, 10nd Ed. American Society for Metals, OH, 1990. [44] Y. Li, Theory and technology of warm compaction of metal powders[In Chinese], Press of South China University of Technology, Guangzhou, 2008. [45] G. F. Bocchini, “Warm compaction of metal powders: why it works, why it requires a sophisticated engineering approach”, Powder Metallurgy, 1999, Vol. 42. No. 2, pp. 171-180. [46] Y. Y. Li, T. W. Ngai, Z. Y. Xiao, D. T. Zhang and W. P. Chen, “Study on mechanical properties of warm compacted iron-base materials”, Journal of Central South University of Technology, 2002, Vol. 9, No. 3, pp. 154-158. [47] 李春香，曹順華，鄒仕民，張秀芳，“316L不銹鋼粉末的溫壓工藝研究”， 粉末冶金材料科學與工程，2008，第13卷，第1期，35-39頁。 [48] 果世駒，李明怡，林涛，趙燕斌，“無黏結劑鐵粉的溫壓工藝研究”，粉末冶金工業，1996，第6卷，第6期，5-9頁。 [49] 果世駒，林涛，李明怡，“粉末燒結鋼溫壓黏結劑玻璃化溫度調整的預測方程”，粉末冶金技術，1997，第15卷，第2期，85-88頁。 [50] Z. Y. Xiao, M. Y. Ke, W. P. Chen, D. H. Ni and Y. Y. Li, “A Study on Warm Compacting Behaviors of 316L Stainless Steel Powder”, Materials Science Forum, 2004, Vol. 471-472, pp. 443-447. [51] P. A. Davies, G. R. Dunstan, R. I. L. Howells and A. C. Hayward, “Aerospace adds luster to appeal of master alloy MIM feedstocks”, Metal Powder Report, 2004, Vol. 59, No. 10, pp. 14-19. [52] P. A. Davies, D. Heaney, G. R. Dunstan and T. J. Mueller, “Comparison of master alloy and pre-alloyed 316L stainless steel powders for Metal Injection Molding (MIM)”, Advances in Powder Metallurgy & Particulate materials, MPIF, Princeton, NJ, 2004, Vol. 1, part 4. [53] T. A. Tingskog, G. J. Del Corso, M. L. Schmitd and D. T. Whychell, Sr., “Diffusion of alloying during sintering of MIM master alloys”, Advances in Powder Metallurgy & Particulate Materials –2002, MPIF, Princeton, NJ, 2002, Part 10, pp. 156-166. [54] D. T. Whychell, Sr. and T. A. Tingskog, “Additional studies on distortion of 316L and 17-4PH MIM parts made from 1.5 master alloy/carbonyl iron blended powder.”, Advances in Powder Metallurgy & Particulate Materials- 2002, MPIF, Princeton, NJ, 2002, Part 10, pp. 199-209. [55] S. Banerjee and C. J. Joens, “A Comparison of Techniques for Processing Powder Metal Injection Molded 17-4PH Materials”, World Congress of Powder Metallurgy 2008, MPIF, Washington, DC. [56] K. S. Hwang and M. Y. Shiau, “Effects of Nickel on the Sintering Behavior of Fe-Ni Compacts made from Composite and Elemental Powders”, Metallurgical and Materials Trans., 1996, Vol. 27B, pp. 203-211. [57] 王婧，苑會林，霍艷麗，“聚乙烯醇的熱老化機理研究”，北京化工大學學報，2005，第32卷，第2期，pp. 68-71。 [58] T. A. Deis and J. J. Lannutti, “X-ray Computed Tomography for Evaluation of Density Gradient Formation during the Compaction of Spray-Dried Granules”, Journal of the American Ceramic Society, 1998, Vol. 81, No.5, pp. 1237-1247. [59] A. Shui, N. Uchida and K. Uematsu, “Origin of Shrinkage Anisotropy during Sintering for Uniaxially Pressed Alumina Compacts”, Powder Technology, 2002, Vol. 127, No. 1, pp. 9-18. [60] J. Nam, W. Li and J. J. Lannutti, “Density Gradient and Springback: Environmental Influences”, Powder Technology, 2003, Vol. 133, No. 1-3, pp. 23-32. | |
| dc.identifier.uri | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/65985 | - |
| dc.description.abstract | 一般的17-4PH粉末硬度高 (~320HV)，在加壓時不易塑性變形，粉末壓縮性差，不易達到理想之生胚密度及燒結密度。若採用粒徑較小的17-4PH粉末雖能得到高密度的燒結工件，但粉末間的摩擦力過高，導致其流動性差，粉末充填困難。由於上述的問題使17-4PH不銹鋼在傳統乾壓燒結製程上的應用受限。本實驗選用粉末硬度較低的430L混合系統(430L+Ni+Cu+Nb)和母合金混合系統(Fe+17-4PH母合金)，嘗試提高其壓縮性，再利用噴霧造粒製程，改善粉末的流動性，此造粒粉還會用於乾壓和溫壓製程。本文之第一部份在瞭解成形壓力、溫度和黏結劑對造粒粉生胚密度的影響，第二部份則在瞭解生胚燒結後的性質並與使用17-4PH預合金粉之試片作比較。
研究發現以430L為基礎粉，添加適量之鎳、銅、鈮元素粉混合成17-4PH之成分，燒結後試片的孔隙率較17-4PH預合金高的多。若使用316L作為鎳元素之來源後，能有效改善此情況，燒結後之性質與採用17-4PH預合金粉者相似，相對密度達97%以上；在母合金混合系中因母合金粉含有大量的鉻元素，在含氮氣氛下燒結容易生成氧化鉻或氮化鉻，阻礙元素之擴散，產生因鎳聚集而生成的奧斯田鐵區域，若使用真空燒結則能使組織均勻，相對密度達97%。此外，使用430L和母合金混合系統均具有較高的粉末壓縮性，使用800MPa之成形壓力時生胚密度最高可達6.44g/cm3和6.38g/cm3。 430L和母合金混合系統經過噴霧造粒製程後，造粒粉之粒徑為預合金的6至7倍，粉末流動性改善至11sec/50g，乾壓後生胚密度可進一步提高到6.51g/cm3和6.50g/cm3，燒結後試片可達97%相對密度，且工件收縮率在6%以下;若使用溫壓成形，在黏結劑Tg以上之溫度加壓均能改善生胚密度，可分別達6.64g/cm3和6.57g/cm3，燒結後收縮率小於5%，試片性質均與使用17-4PH預合金粉者相似。所以利用430L混合系統與母合金混合系統之造粒粉適合取代17-4PH預合金粉，能改善17-4PH預合金之壓縮性、流動性和尺寸穩定性等問題。並能應用在傳統乾壓燒結製程上。 | zh_TW |
| dc.description.abstract | 17-4PH is seldom produced using conventionally press-and-sinter process because the high hardness and poor compressibility of the powders cannot obtain high green density and thus cannot obtain high sintered density. Although fine powders have high sinterability and can solve this problem, they are not easy to flow because of the interparticle friction. That’s why 17-4PH is limited in conventionally press-and-sinter route. In this study, 17-4PH was prepared by using soft fine base powders, 430L system (430L+Ni+Cu+Nb) and master alloy system (Fe+17-4PH master alloy), to improve the compressibility. Spray drying process was also applied to improve the flow rate. The effects of compaction pressure, temperature and binder on green density and sintered density were examined. All the results were compared to those of using 17-4PH pre-alloyed samples.
It was observed that using 430L base powder with elemental powder additions of nickel, copper and niobium had low sintered density. After using 316L as the source of nickel, the densificaition problem was solved. Relative density reaches 97% or greater. It was observed that the master alloy system was not suitable for sintering in atmospheres containing nitrogen because chromium oxide / nitride easily formed and inhibited diffusion. Vacuum or hydrogen sintering can solve this problem. Both 430L and master alloy systems provide high compressibility and the green density reaches 6.44g/cm3 and 6.38g/cm3 respectively. After spray drying process, the green density of spray dried powder increased to about 6.50g/cm3. After sintering, the density reached 97% and the shrinkage was below 6%. Warm compaction at a temperature above the Tg of the PVA, further increased the green density of spray dried powder to about 6.57g/cm3 and the flow rate was not affected. After sintering, shrinkage was below 5% and the mechanical properties were similar to those of using 17-4PH pre-alloyed powders. Therefore, spray dried powders made of 430L system and master alloy system solve the problems of using 17-4PH pre-alloyed powders and could open up a new market for conventional press-and-sinter industry. | en |
| dc.description.provenance | Made available in DSpace on 2021-06-17T00:17:59Z (GMT). No. of bitstreams: 1 ntu-101-R99527038-1.pdf: 15284705 bytes, checksum: e96e68dcaef24d70717dc4aceb6b4785 (MD5) Previous issue date: 2012 | en |
| dc.description.tableofcontents | 摘要…………………………………………………………………………………… i
Abstract…………………………………………………………………………….... iii 目錄…………………………………………………………………………………... v 表目錄…………………………………………………………………………….... viii 圖目錄..……………………………………………………………………………… ix 第一章 文獻回顧…………………………………………………………….…….. 1 1.1 17-4PH析出硬化型不銹鋼簡介……………………………………… 1 1.2熱處理條件對17-4PH不銹鋼之影響………………………………… 1 1.2.1固溶處理對17-4PH不銹鋼之影響……………………………... 3 1.2.2時效處理對17-4PH不銹鋼之影響……………………………... 4 1.3 17-4PH不銹鋼在傳統粉末冶金製程之應用………………………… 7 1.3.1探討17-4PH不銹鋼粉末之壓縮性……………………………... 7 1.3.2 燒結條件對17-4PH不銹鋼之影響……………………………. 8 1.4噴霧造粒製程與設備………………………………………………... 11 1.4.1噴霧造粒機與製程簡介……………………………………….. 12 1.4.2影響造粒後粉末特性之參數………………………………….. 17 1.5 溫壓成形…………………………………………………………….. 21 1.6 以母合金製作17-4PH工件………………………………………… 25 1.7研究動機……………………………………………………………... 29 第二章 實驗步驟…………………………………………………………………. 32 2.1 實驗設計…………………………………………………………….. 32 2.2 原料………………………………………………………………….. 33 2.2.1 基礎粉………………………………………………………… 33 2.2.2 黏結劑………………………………………………………… 38 2.3 噴霧造粒製程……………………………………………………….. 39 2.3.1 噴霧造粒機………………………………………………….… 39 2.3.2 泥漿製備…………………………………………………….… 42 2.3.3 造粒參數設計………………………………………………… 42 2.4 乾壓成形…………………………………………………………….. 42 2.5 溫壓成形…………………………………………………………….. 42 2.6 熱脫脂……………………………………………………………….. 43 2.7 燒結………………………………………………………………….. 44 2.8 熱處理……………………………………………………………….. 44 2.9 性質量測及分析…………………………………………………….. 45 2.9.1 燒結密度……………………………………………………… 45 2.9.2 硬度…………………………………………………………… 45 2.9.3 碳氧氮含量測定……………………………………………… 46 2.9.4 金相製備……………………………………………………… 46 2.9.5 微結構分析…………………………………………………… 46 2.9.6 收縮率………………………………………………………….47 2.9.7 回彈…………………………………………………………….47 2.10 實驗儀器…………………………………………………………… 47 第三章 結果與討論………………………………………………………………. 49 3.1 17-4PH乾壓成形製程……………………………………………….. 49 3.1.1 以430L不銹鋼作基礎粉……………………………………... 49 3.1.1.1 添加鎳、銅、鈮元素粉末之系統………………………. 50 3.1.1.2 以316L取代鎳元素之系統…………………………… 54 3.1.1.3 調整鎳與銅元素比例之影響…………………….……. 58 3.1.2 以羰基鐵粉作基礎粉添加17-4PH母合金之系統…………... 60 3.1.3 比較各種混合系統對17-4PH壓縮性之影響………………... 64 3.2 17-4PH之噴霧造粒製程…………………………………………….. 66 3.2.1 霧化盤轉速與蠕動幫浦轉速對造粒粉性質之影響…………. 66 3.2.2 黏結劑含量對造粒粉性質之影響……………………………. 70 3.2.3 泥漿水分含量對造粒粉性質之影響…………………………. 73 3.2.4 綜合討論各製程參數對造粒粉性質之改進…………………. 75 3.3 17-4PH造粒粉之乾壓燒結製程…………………………………….. 78 3.3.1 成形壓力對生胚密度之影響…………………………………. 78 3.3.2 生胚密度對燒結後工件收縮率之影響………………………. 82 3.4 17-4PH造粒粉之溫壓燒結製程…………………………………...... 85 3.4.1 溫壓溫度對造粒粉流動性之影響……………………………. 85 3.4.2 溫壓溫度對造粒粉生胚密度之影響…………………………. 87 3.4.3 溫壓成形對生胚回彈之影響…………………………………. 89 3.4.4 溫壓成形對燒結後工作收縮率之影響………………………. 91 3.5 17-4PH造粒粉與預合金粉性質之比較…………………………….. 93 3.5.1 燒結前粉末與生胚性質之比較………………………………. 93 3.5.2 燒結後試片性質之比較………………………………………. 97 第四章 結論……………………………………………………………………... 103 第五章 未來工作………………………………………………………………... 107 第六章 參考文獻………………………………………………………………... 108 | |
| dc.language.iso | zh-TW | |
| dc.title | 17-4PH不銹鋼之乾壓燒結製程研究 | zh_TW |
| dc.title | Press-and-Sinter Process of 17-4PH Stainless Steels | en |
| dc.type | Thesis | |
| dc.date.schoolyear | 100-2 | |
| dc.description.degree | 碩士 | |
| dc.contributor.oralexamcommittee | 陳貞光,范揚樑,吳明偉 | |
| dc.subject.keyword | 乾壓燒結,溫壓成形,17-4PH不銹鋼, | zh_TW |
| dc.subject.keyword | Press and sinter process,Warm compaction,17-4PH Stainless steel,Spray drying,Compressibility, | en |
| dc.relation.page | 114 | |
| dc.rights.note | 有償授權 | |
| dc.date.accepted | 2012-06-29 | |
| dc.contributor.author-college | 工學院 | zh_TW |
| dc.contributor.author-dept | 材料科學與工程學研究所 | zh_TW |
| 顯示於系所單位： | 材料科學與工程學系 | |
文件中的檔案：
| 檔案 | 大小 | 格式 | |
|---|---|---|---|
| ntu-101-1.pdf 目前未授權公開取用 | 14.93 MB | Adobe PDF |
系統中的文件，除了特別指名其著作權條款之外，均受到著作權保護，並且保留所有的權利。