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Corrosion Definition - Corrosion and Galvanic Compatibility
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Corrosion is the deterioration of a material due to interaction with its environment. It is the process in which metallic atoms leave the metal or form compounds in the presence of water and gases. Metal atoms are removed from a structural element until it fails, or oxides build up inside a pipe until it is plugged. All metals and alloys are subject to corrosion. Even the noble metals, such as gold, are subject to corrosive attack in some environments.
The corrosion of metals is a natural process. Most metals are not
thermodynamically stable in the metallic form; they want to corrode and revert to the more stable forms that are normally found in ores, such as oxides. Corrosion is of primary concern in engineering and design Corrosion occurs in every metal is subject to it. Even though this corrosion cannot be eliminated, it can be controlled.
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General corrosion involving water and steel generally results from chemical action where the steel surface oxidizes, forming iron oxide (rust). Many of the systems and components in the plant are made from iron.
Some standard methods associated with material selection that protect against
general corrosion include:The use of corrosion-resistant materials such as stainless steel and nickel, chromium, and molybdenum alloys. (Keep in mind that
the corrosion is electrochemical by nature, and the corrosion resistance of the
stainless steels results from surface oxide films that interfere with the electrochemical process.)
The use of protective coatings such as paints and epoxies.
The application of metallic and nonmetallic coatings or linings to the surface which protects against corrosion, but allows the material to retain its structural strength (for example, a carbon steel pressure vessel with stainless steel cladding as a liner).
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Localized corrosion is defined as the selective removal of metal by corrosion at small areas or zones on a metal surface in contact with a corrosive environment, usually a liquid. It usually takes place when small local sites are attacked at a much higher rate than the rest of the original surface. Localized corrosion takes place when corrosion works with other destructive processes such as stress, fatigue, erosion, and other forms of chemical attack. Localized corrosion
mechanisms can cause more damage than any one of those destructive processes individually. There are many different types of localized corrosion. Pitting, stress corrosion cracking, chloride stress corrosion, caustic stress corrosion, primary side stress corrosion, heat exchanger tube denting, wastage, and intergranular attack corrosion.
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Design Guidelines - Corrosion and Galvanic Compatibility
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There are many design decisions and compromises to be made in the course of developing a product. The specifications and requirements may leave room for a wide range of engineering practices to meet not only the performance, cost and schedule, but also the reliability and maintainability requirements. Only with an understanding of the ultimate environment and its effects on equipment can these engineering practices include design characteristics that will result in equipment that will best survive and operate in that “real world ” environment. Throughout the developmental period, the materials specialist, the metallurgist, the reliability and maintainability engineers, and the electronic design
engineers, must all understand the environment implications and interact fully among these disciplines.
The design techniques discussed in this section are a summary of recommended “Do ’s ” and “Don ’ts ” based on features that have displayed significant impact on the durability and reliability of your product and equipment in service. Select on of the following links:
l Design for Corrosion - Best Practices
l
Design for Corrosion - Practices not Recommended
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There are many design decisions and compromises to be made in the course of developing a product. The specifications and requirements may leave room for a wide range of engineering practices to meet not only the performance, cost and schedule, but also the reliability and maintainability requirements. Only with an understanding of the ultimate environment and its effects on equipment can these engineering practices include design characteristics that will result in equipment that will best survive and operate in that “real world ” environment. Throughout the developmental period, the materials specialist, the metallurgist, the reliability and maintainability engineers, and the electronic design
engineers, must all understand the environment implications and interact fully among these disciplines.
The design techniques discussed in this section are a summary of recommended “Do ’s ” and “Don ’ts ” based on features that have displayed significant impact on the durability and reliability of your product and equipment in service. Select on of the following links:
l Design for Corrosion - Best Practices
l
Design for Corrosion - Practices not Recommended
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Design for Corrosion - Best Practices
The design techniques discussed in this section are a summary of recommended “Don'ts ” based on features that have displayed significant impact on the durability and reliability of your product and equipment in service.
“Don ’ts ”
l Don ’t use dissimilar metal (galvanic) couples if it can be avoided. l Don ’t use RTV that contains acetic acid.
l Don ’t use heat shrink (non-sealed) electrical connector boots to stop moisture fluid intrusion. l Don ’t mate magnesium to a metal more cathodic than aluminum. l Don ’t use acrylic, RTV or varnish type conformal coatings. l Don ’t use gold over silver or copper.
l
Don ’t use organic materials that outgas, support fungi, absorb moisture or are degraded by maintenance and operational fluids.
l Don ’t use an EMI gasket without a seal on both sides of the conductive element. l Don ’t use top mounted lid fasteners. l Don ’t mount PWBs horizontally.
l Don ’t mount electrical connectors (multicontact or coaxial) vertically. l Don ’t place edge connectors on the bottom edge of a vertically PWB.
l Don ’t create side loads or cable tension on the rear seal of electrical connectors. l Don ’t use direct air cooling on active electronic components.
l Don ’t mount equipment less than 1/2 inch above the compartment floor. l Don ’t use hygroscopic materials.
l
Don ’t use nickel plated electrical connector shells in salt or high humidity environments. (Use cadmium plated shell).
l Don ’t use foam cushioning material that can deteriorate (revert). l
Don ’t permit the presence of water trap areas.
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Design for Corrosion - Pratices not Recommended
The design techniques discussed in this section are a summary of recommended “Do ’s ” based on features that have displayed significant impact on the durability and reliability of your product and equipment in service.
“Dos ”
l
Design on the assumption that moisture and other corrosive mechanism will be present.
l Seal all dissimilar metal (galvanic) couples. l Use conformal coating on printed wiring boards.
l
Use as easily replaceable anodic (consumable) part in assembling grounding or bonding connections.
l Use only electrical connector boots that can be sealed with adhesives. l Carefully select a protective system for use on magnesium.
l
Complete the working of aluminum, steel, etc (drilling, cutting, grinding) prior to surface treatment.
l Use surface treatments (anodize and conversion coatings) on aluminum. l
Carefully select the metal plating use to provide sacrificial protection, barrier protection, as a third metal between two otherwise incompatible metals, or as a substitute surface.
l Use a nickel strike under gold plating.
l Use solder flux with lowest possible acid content.
l
Use metallic materials with the most corrosion resistant configuration (passivated) with minimum possible residual stressing.
l
Use fluorocarbon or fluorosilicone type materials for gaskets, “O ” rings an seals. l Use low point drains.
l
Mount equipment an components at least 1/2 inch above potential standing water
level.
l Use hermetic sealing where possible.
l Design for maintainability.
l Use shoe box lids on enclosures.
l
Mount PWBs vertically with the edge connectors on vertical edge or back of board.
l Mount electrical connectors horizontally.
l Use drip loops on electrical cables and piping. l Use desiccant systems with visual indicators.
l Use cooling systems that remove moisture and particulate matter.
l
Use “O ” rings to seal around control shafts that must penetrate into an corrosive environment.
l
Be aware of various interior and exterior fluids which your product will be exposed to.
l Recognize the operational environment. l Recognize the maintenance environment.
l Be aware of maintenance procedures and materials. l
Listen to feedback!
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Galvanic Compatibility Corrosion
Dissimilar Metal Corrosion
Corrosion / Galvanic Compatibility Table of Contents
Metal Products Supplier
Engineering Metals and Materials Table of Contents
Quality engineering and design requires an understanding of material compatibility. Galvanic corrosion (some times called dissimilar metal corrosion) is the process by which the materials in contact with each other oxidizes or corrodes. There are three conditions that must exist for galvanic corrosion to occur. First there must be two electrochemically dissimilar metals present. Second, there must be an electrically conductive path between the two metals. And third, there must be a conductive path for the metal ions to move from the more anodic metal to the more cathodic metal. If any one of these three conditions does not exist, galvanic corrosion will not occur. Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by finishes and plating. The finishing and plating selected facilitate the dissimilar materials being in contact and protect the base materials from corrosion.
For harsh environments, such as outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the "Anodic Index". For example; gold – silver would have a difference of 0.15V being acceptable.
For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the "Anodic Index".
For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions
METALLURGICAL CATEGORY
ANODIC
INDEX (V) Gold, solid and plated, Gold-platinum alloy0.00
Rhodium plated on silver-plated copper0.05 Silver, solid or plated; monel metal. High nickel-copper alloys0.15 Nickel, solid or plated, titanium an s alloys, Monel0.30 Copper, solid or plated; low brasses or bronzes; silver solder; German
silvery high copper-nickel alloys; nickel-chromium alloys
0.35
Brass and bronzes0.40
High brasses and bronzes0.45 18% chromium type corrosion-resistant steels0.50
Chromium plated; tin plated; 12% chromium type corrosion-resistant
steels
0.60
Tin-plate; tin-lead solder0.65
Lead, solid or plated; high lead alloys0.70 Aluminum, wrought alloys of the 2000 Series0.75 Iron, wrought, gray or malleable, plain carbon and low alloy steels0.85
Aluminum, wrought alloys other than 2000 Series aluminum, cast
alloys of the silicon type
0.90
Aluminum, cast alloys other than silicon type, cadmium, plated and
chromate
0.95
Hot-dip-zinc plate; galvanized steel 1.20 Zinc, wrought; zinc-base die-casting alloys; zinc plated 1.25
Magnesium & magnesium-base alloys, cast or wrought 1.75
Beryllium 1.85
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Galvanic Corrosion - Corrosion and Galvanic Compatibility
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Galvanic corrosion occurs when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte. It may also take place with one metal with heterogeneities (dissimilarities) (for example, impurity inclusions, grains of different sizes, difference in composition of grains, or differences in mechanical stress). A difference in electrical potential exists between the different metals and serves as the driving force for electrical current flow through the corrodant or electrolyte. This current results in corrosion of one of the metals. The larger the potential difference, the greater the probability of galvanic corrosion. Galvanic corrosion only causes deterioration of one of the metals. The less resistant, more active one becomes the anodic (negative) corrosion site. The stronger, more noble one is cathodic (positive) and protected. If there were no
electrical contact, the two metals would be uniformly attacked by the corrosive medium. This would then be called general corrosion. For any particular medium, a list can be made arranging metals sequentially from most active, or least noble, to passive, or most noble. See Galvanic Compatibility for design applicability. Galvanic corrosion is of particular concern in design and material selection. Material selection is important because different metals come into contact with each other and may form galvanic cells. Design is important to minimize differing flow conditions and resultant areas of corrosion buildup.
In some instances, galvanic corrosion can be helpful in some
applications. For example, if pieces of zinc are attached to the bottom of a steel water tank, the zinc will become the anode, and it will
corrode. The steel in the tank becomes the cathode, and it will not be effected by the corrosion. This technique is known as cathodic
protection. The metal to be protected is forced to become a cathode, and it will corrode at a much slower rate than the other metal, which is used as a sacrificial anode.
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l Engineering Materials Stress Corrosion Cracking - Corrosion and Galvanic Compatibility Corrosion and Galvanic Compatibility Knowledge
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One of the most serious metallurgical problems and one that is a major concern in most industries is stress-corrosion cracking (SCC). SCC is a type of intergranular attack corrosion that occurs at the grain boundaries under tensile stress. It tends to propagate as stress opens cracks that are subject to corrosion, which are then corroded further, weakening the metal by further cracking. The cracks can follow intergranular or transgranular paths, and there is often a tendency for crack branching.
The cracks form and propagate approximately at right angles to the direction of the tensile stresses at stress levels much lower than those required to fracture the material in the absence of the corrosive environment. As cracking penetrates further into the material, it eventually reduces the supporting cross section of the material to the point of structural failure from overload.
Stresses that cause cracking arise from residual cold work, welding, grinding, thermal treatment, or may be externally applied during service and, to be effective, must be tensile (as opposed to compressive).
SCC occurs in metals exposed to an environment where, if the stress was not present or was at much lower levels, there would be no damage. If the structure, subject to the same stresses, were in a different environment (noncorrosive for that material), there would be no failure. Examples of SCC in industry are cracks in stainless steel piping systems and stainless steel valve stems.
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Engineering Materials Corrosion Resistant Coatings Overview Industrial Coating Processes and Design Industrial Coating Services Directory
Corrosion resistance coatings are available for most materials, surface types, and application environments. Corrosion resistant coatings can significantly increase the usable lifetime of materials while reducing maintenance and replacement costs. There are many possible operating
applications which will result in corrosion. The following are many types of common corrosions which occur in applications;
l Galvanic Corrosion
l Stress Corrosion Cracking l General Corrosion l Localized Corrosion l
Caustic Agent Corrosion
Galvanic corrosion is one of the most common forms of corrosions which does occur in products. There are three conditions that must exist for galvanic corrosion to occur. First there must be two electrochemically dissimilar
metals present. Second, there must be an electrically conductive path between the two metals. And third, there must be a conductive path for the metal ions to move from the more anodic metal to the more cathodic metal. Corrosion resistant coatings would be applied to eliminate one or more of the corrosion causing conditions.
Caustic agent corrosion is caused by corrosive impurities in gases, liquids, solids or any combination of the three, which come in contact with a material.
Most petrochemical process gases contain a certain amount of impurities, which may dissolve into the water and become corrosive. For example, hydrogen sulfide is a common impurity in cracked gas. Usually these impurities are not corrosive in a dry condition, but when moisture is present, they will dissolve into the water and form hazardous acidic vapor or droplets. With these conditions present in the petrochemical process, applying corrosion resistant coatings is imperative
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脐带间充质干细胞的研究进展 间充质干细胞（mesenchymal stem cells,MSC S ）是来源于发育早期中胚层 的一类多能干细胞[1-5]，MSC S 由于它的自我更新和多项分化潜能，而具有巨大的 治疗价值 ,日益受到关注。MSC S 有以下特点：(1)多向分化潜能，在适当的诱导条件下可分化为肌细胞[2]、成骨细胞[3、4]、脂肪细胞、神经细胞[9]、肝细胞[6]、心肌细胞[10]和表皮细胞[11, 12]；(2)通过分泌可溶性因子和转分化促进创面愈合；(3) 免疫调控功能，骨髓源（bone marrow ）MSC S 表达MHC-I类分子，不表达MHC-II 类分子，不表达CD80、CD86、CD40等协同刺激分子，体外抑制混合淋巴细胞反应，体内诱导免疫耐受[11, 15]，在预防和治疗移植物抗宿主病、诱导器官移植免疫耐受等领域有较好的应用前景；(4)连续传代培养和冷冻保存后仍具有多向分化潜能，可作为理想的种子细胞用于组织工程和细胞替代治疗。1974年Friedenstein [16] 首先证明了骨髓中存在MSC S ，以后的研究证明MSC S 不仅存在于骨髓中，也存在 于其他一些组织与器官的间质中：如外周血[17]，脐血[5]，松质骨[1, 18]，脂肪组织[1]，滑膜[18]和脐带。在所有这些来源中，脐血(umbilical cord blood)和脐带(umbilical cord)是MSC S 最理想的来源，因为它们可以通过非侵入性手段容易获 得，并且病毒污染的风险低，还可冷冻保存后行自体移植。然而，脐血MSC的培养成功率不高[19, 23-24]，Shetty 的研究认为只有6%，而脐带MSC的培养成功率可 达100%[25]。另外从脐血中分离MSC S ，就浪费了其中的造血干/祖细胞(hematopoietic stem cells/hematopoietic progenitor cells,HSCs/HPCs) [26, 27]，因此，脐带MSC S (umbilical cord mesenchymal stem cells, UC-MSC S )就成 为重要来源。 一．概述 人脐带约40 g, 它的长度约60–65 cm, 足月脐带的平均直径约1.5 cm[28, 29]。脐带被覆着鳞状上皮，叫脐带上皮，是单层或复层结构，这层上皮由羊膜延续过来[30, 31]。脐带的内部是两根动脉和一根静脉，血管之间是粘液样的结缔组织，叫做沃顿胶质，充当血管外膜的功能。脐带中无毛细血管和淋巴系统。沃顿胶质的网状系统是糖蛋白微纤维和胶原纤维。沃顿胶质中最多的葡萄糖胺聚糖是透明质酸，它是包绕在成纤维样细胞和胶原纤维周围的并维持脐带形状的水合凝胶，使脐带免受挤压。沃顿胶质的基质细胞是成纤维样细胞[32]，这种中间丝蛋白表达于间充质来源的细胞如成纤维细胞的，而不表达于平滑肌细胞。共表达波形蛋白和索蛋白提示这些细胞本质上肌纤维母细胞。 脐带基质细胞也是一种具有多能干细胞特点的细胞，具有多项分化潜能，其 形态和生物学特点与骨髓源性MSC S 相似[5, 20, 21, 38, 46]，但脐带MSC S 更原始，是介 于成体干细胞和胚胎干细胞之间的一种干细胞，表达Oct-4, Sox-2和Nanog等多
电缆载流量对照表（勿转） 2009年07月23日星期四 22:19
电缆载流量口决： 估算口诀： 二点五下乘以九，往上减一顺号走。三十五乘三点五，双双成组减点五。条件有变加折算，高温九折铜升级。穿管根数二三四，八七六折满载流。
说明： (1)本节口诀对各种绝缘线(橡皮和塑料绝缘线)的载流量(安全电流)不是直接指出，而是”截面乘上一定的倍数”来表示，通过心算而得。由表5 3可以看出：倍数随截面的增大而减小。 “二点五下乘以九，往上减一顺号走”说的是2．5mm’及以下的各种截面铝芯绝缘线，其载流量约为截面数的9倍。如2．5mm’导线，载流量为 2．5×9＝22．5(A)。从4mm’及以上导线的载流量和截面数的倍数关系是顺着线号往上排，倍数逐次减l，即4×8、6×7、10×6、16×5、25×4。 “三十五乘三点五，双双成组减点五”，说的是35mm”的导线载流量为截面数的3．5倍，即35×3．5＝122．5(A)。从50mm’及以上的导线，其载流量与截面数之间的倍数关系变为两个两个线号成一组，倍数依次减0．5。即50、70mm’导线的载流量为截面数的3倍；95、120mm”导线载流量是其截面积数的2．5倍，依次类推。 “条件有变加折算，高温九折铜升级”。上述口诀是铝芯绝缘线、明敷在环境温度25℃的条件下而定的。若铝芯绝缘线明敷在环境温度长期高于25℃的地区，导线载流量可按上述口诀计算方法算出，然后再打九折即可；当使用的不是铝线而是铜芯绝缘线，它的载流量要比同规格铝线略大一些，可按上述口诀方法算出比铝线加大一个线号的载流量。如16mm’铜线的载流量，可按25mm2铝线计算。计算电缆载流量选择电缆（根据电流选择电缆）： 导线的载流量与导线截面有关，也与导线的材料、型号、敷设方法以及环境温度等有关，影响的因素较多，计算也较复杂。各种导线的载流量通常可以从手册中查找。但利用口诀再配合一些简单的心算，便可直接算出，不必查表。 1. 口诀铝芯绝缘线载流量与截面的倍数关系 10下五，100上二， 25、35，四、三界，. 70、95，两倍半。 穿管、温度，八、九折。 裸线加一半。 铜线升级算。 说明口诀对各种截面的载流量（安）不是直接指出的，而是用截面乘上一定的倍数来表示。为此将我国常用导线标称截面（平方毫米）排列如下： 1、1.5、 2.5、 4、 6、 10、 16、 25、 35、 50、 70、 95、 120、 150、185…… (1)第一句口诀指出铝芯绝缘线载流量（安）、可按截面的倍数来计算。口诀中的阿拉伯数码表示导线截面（平方毫米），汉字数字表
一、服务器参数：
二、电暖气参数： 三、电缆参数： YJV22-4*240带铠、国标。电缆长度185米。 四、（1）栅栏参数： （一）、外观要求： 1、制作按照甲方要求。
2、镀锌钢质粉末喷漆护栏整体采用先热镀锌，然后静电粉末喷涂工艺。护栏构件喷塑层应均匀，无疤斑、滴流等表面缺陷；不得有剥落、气泡、裂纹、擦伤等表面缺陷；喷塑层应均匀无明显连接痕迹，无熔渣、色泽不一等缺陷。表面应光滑、平整、无凹陷、杂质和其他表面缺陷。型材端部应清洁、无毛刺，护栏的端头、焊接点应平滑无毛刺。 3、整体美观，表面光滑、平整、色泽均匀，无明显裂痕、毛点，焊接点平整。 4、竖杆与横杆连接点应牢固，水平杆不少于3道。 5、采用一次冲压成型镀锌钢质连接件。 6、整体牢固、结构强度高，摇晃时无明显错位变形，在合理外力影响下，表面喷塑无变形或破坏。 7、连接螺钉专用工具拆卸，产品合格证标注内容齐全。 （二）、技术要求： 1、所有钢管均采用双面热镀锌钢，表面经聚酯彩色粉未静电喷涂而成，颜色为黑色，护栏片为焊接或连接件连接，护栏片与立柱采用镀锌钢质连接件。 2、护栏立柱：采用50×50×2.0mm方钢，立柱帽采用金属冲压件；立柱安装采用镀锌钢板填砼底座，高度不小于1.8米。 3、护栏上横杆：采用25×25×1.2mm方钢，下横杆：采用25×25×1.2mm横杆。 4、竖杆：采用25×25×1.2mm方钢，每片护栏竖杆为12-14支，净距不大于12cm。每片护栏长度不大于1.8米。 （三）、总长度200米。 （2）盖板参数： 东墙外排水沟渠加固（沟渠宽约3米） 1、沟渠土方淤泥开挖清理挖掘机台班2个 2、C15砼垫层6m3 3、砌筑毛石挡土墙：毛石50立方米；成品水泥砂浆：2立方 4、200mm厚C30钢筋砼盖板30米 （3）防盗窗参数： 1、不锈钢防护窗20个（含原防护栏拆除，25*25，壁厚不小于1毫米的202不锈钢管，间距不大于12厘米，设1-2道横撑，设600*600不锈钢逃生窗。） 2、不锈钢逃生窗改造31个（25*25，壁厚不小于1毫米的202不锈钢管，间距不大于12厘米，尺寸600*600不锈钢逃生窗） 3、塑钢窗更换4个 4、铝合金大门改造2个 5、防火卷帘控制器盖板及电梯控制柜保护板加工安装31套（1毫米厚不锈钢板） 6、水表间全板铝合金门12个（洞口尺寸750*2000，板材厚度不小于1毫米，玥玛锁具） （4）乳胶漆参数： 1、乳胶漆：60桶。内墙乳胶漆，净味五合一、白色、环保、防潮、易清洗、18公斤/桶。
钢结构防腐及防火 （1）Anticorrosion of steel structure 钢结构的防腐 The requirements of steel structure surface derusting, support equipment, frame beam column beam is Sa2.5 grade, Sa3 grade (rust and other components should be used in sandblasting), component cleaning should be immediately after spraying and coating primer matching. 钢结构的表面要求除锈，除锈等级框架梁柱、支撑、设备梁为Sa2.5级，其余构件Sa3级（除锈应采用喷砂），构件除锈后应立即喷涂与涂料相配套的底漆。 Anticorrosive coatings: 防腐涂料： Epoxy zinc rich primer 2, a total of 70um thick. 环氧富锌底漆2道，共70μm厚； Epoxy cloud iron intermediate paint 1, 70um thick. 环氧云铁中间漆1道，70μm厚； High chlorinated polyethylene or polyurethane finish 2~3 channel, total is of 60~100um. 高氯化聚乙烯或聚氨酯面漆2~3道，共60~100μm， The general steel plate by hot dip galvanized anti-corrosion coating; zinc coating thickness should be greater than 85um. 一般钢格板采用热浸锌防腐涂层，锌镀层的厚度应大于85μm。 Anticorrosion service life of steel structure: 钢结构防腐使用年限： All exposed steel structures shall be protected against corrosion besides fire protection. According to the general corrosion of steel structure anticorrosion Chemical Anticorrosion Coatings by atmospheric design, anti-corrosion treatment,
精神分裂症的病因及发病机理 精神分裂症病因：尚未明，近百年来的研究结果也仅发现一些可能的致病因素。（一）生物学因素1．遗传遗传因素是精神分裂症最可能的一种素质因素。国内家系调查资料表明：精神分裂症患者亲属中的患病率比一般居民高6.2倍，血缘关系愈近，患病率也愈高。双生子研究表明：遗传信息几乎相同的单卵双生子的同病率远较遗传信息不完全相同 的双卵双生子为高，综合近年来11项研究资料：单卵双生子同病率（56.7%），是双卵双生子同病率（12.7%）的4.5倍，是一般人口患难与共病率的35-60倍。说明遗传因素在本病发生中具有重要作用，寄养子研究也证明遗传因素是本症发病的主要因素，而环境因素的重要性较小。以往的研究证明疾病并不按类型进行遗传，目前认为多基因遗传方式的可能性最大，也有人认为是常染色体单基因遗传或多源性遗传。Shields发现病情愈轻，病因愈复杂，愈属多源性遗传。高发家系的前瞻性研究与分子遗传的研究相结合，可能阐明一些问题。国内有报道用人类原癌基因Ha-ras-1为探针，对精神病患者基因组进行限止性片段长度多态性的分析，结果提示11号染色体上可能存在着精神分裂症与双相情感性精神病有关的DNA序列。2．性格特征：约40%患者的病前性格具有孤僻、冷淡、敏感、多疑、富于幻想等特征，即内向
型性格。3．其它：精神分裂症发病与年龄有一定关系，多发生于青壮年，约1/2患者于20～30岁发病。发病年龄与临床类型有关，偏执型发病较晚，有资料提示偏执型平均发病年龄为35岁，其它型为23岁。80年代国内12地区调查资料：女性总患病率（7.07%。）与时点患病率（5.91%。）明显高于男性（4.33%。与3.68%。）。Kretschmer在描述性格与精神分裂症关系时指出：61%患者为瘦长型和运动家型，12.8%为肥胖型，11.3%发育不良型。在躯体疾病或分娩之后发生精神分裂症是很常见的现象，可能是心理性生理性应激的非特异性影响。部分患者在脑外伤后或感染性疾病后发病；有报告在精神分裂症患者的脑脊液中发现病毒性物质；月经期内病情加重等躯体因素都可能是诱发因素，但在精神分裂症发病机理中的价值有待进一步证实。（二）心理社会因素1．环境因素①家庭中父母的性格，言行、举止和教育方式（如放纵、溺爱、过严）等都会影响子女的心身健康或导致个性偏离常态。②家庭成员间的关系及其精神交流的紊乱。③生活不安定、居住拥挤、职业不固定、人际关系不良、噪音干扰、环境污染等均对发病有一定作用。农村精神分裂症发病率明显低于城市。2．心理因素一般认为生活事件可发诱发精神分裂症。诸如失学、失恋、学习紧张、家庭纠纷、夫妻不和、意处事故等均对发病有一定影响，但这些事件的性质均无特殊性。因此，心理因素也仅属诱发因
脐带血造血干细胞库管理办法（试行） 第一章总则 第一条为合理利用我国脐带血造血干细胞资源，促进脐带血造血干细胞移植高新技术的发展，确保脐带血 造血干细胞应用的安全性和有效性，特制定本管理办法。 第二条脐带血造血干细胞库是指以人体造血干细胞移植为目的，具有采集、处理、保存和提供造血干细胞 的能力，并具有相当研究实力的特殊血站。 任何单位和个人不得以营利为目的进行脐带血采供活动。 第三条本办法所指脐带血为与孕妇和新生儿血容量和血循环无关的，由新生儿脐带扎断后的远端所采集的 胎盘血。 第四条对脐带血造血干细胞库实行全国统一规划，统一布局，统一标准，统一规范和统一管理制度。 第二章设置审批 第五条国务院卫生行政部门根据我国人口分布、卫生资源、临床造血干细胞移植需要等实际情况，制订我 国脐带血造血干细胞库设置的总体布局和发展规划。 第六条脐带血造血干细胞库的设置必须经国务院卫生行政部门批准。 第七条国务院卫生行政部门成立由有关方面专家组成的脐带血造血干细胞库专家委员会（以下简称专家委
员会），负责对脐带血造血干细胞库设置的申请、验收和考评提出论证意见。专家委员会负责制订脐带血 造血干细胞库建设、操作、运行等技术标准。 第八条脐带血造血干细胞库设置的申请者除符合国家规划和布局要求，具备设置一般血站基本条件之外， 还需具备下列条件： （一）具有基本的血液学研究基础和造血干细胞研究能力； （二）具有符合储存不低于1 万份脐带血的高清洁度的空间和冷冻设备的设计规划； （三）具有血细胞生物学、HLA 配型、相关病原体检测、遗传学和冷冻生物学、专供脐带血处理等符合GMP、 GLP 标准的实验室、资料保存室； （四）具有流式细胞仪、程控冷冻仪、PCR 仪和细胞冷冻及相关检测及计算机网络管理等仪器设备； （五）具有独立开展实验血液学、免疫学、造血细胞培养、检测、HLA 配型、病原体检测、冷冻生物学、 管理、质量控制和监测、仪器操作、资料保管和共享等方面的技术、管理和服务人员； （六）具有安全可靠的脐带血来源保证； （七）具备多渠道筹集建设资金运转经费的能力。 第九条设置脐带血造血干细胞库应向所在地省级卫生行政部门提交设置可行性研究报告，内容包括：
在网上下载个电缆选型软件就搞定了。导线截面积与载流量的计算一、一般铜导线载流量导线的安全载流量是根据所允许的线芯最高温度、冷却条件、敷设条件来确定的。一般铜导线的安全载流量为5~8A/mm2，铝导线的安全载流量为3~5A/mm2。 <关键点> 一般铜导线的安全载流量为5~8A/mm2，铝导线的安全载流量为3~5A/mm2。如：2.5 mm2 BVV铜导线安全载流量的推荐值2.5×8A/mm2=20A 4 mm2 BVV铜导线安全载流量的推荐值4×8A/mm2=32A 二、计算铜导线截面积利用铜导线的安全载流量的推荐值5~8A/mm2，计算出所选取铜导线截面积S的上下范围： S=< I /(5~8)>=0.125 I ~0.2 I(mm2) S-----铜导线截面积(mm2) I-----负载电流(A) 三、功率计算一般负载(也可以成为用电器，如点灯、冰箱等等)分为两种，一种式电阻性负载，一种是电感性负载。对于电阻性负载的计算公式：P=UI 对于日光灯负载的计算公式：P=UIcosф，其中日光灯负载的功率因数cosф=0.5。不同电感性负载功率因数不同，统一计算家庭用电器时可以将功率因数cosф取0.8。也就是说如果一个家庭所有用电器加上总功率为6000瓦，则最大电流是 I=P/Ucosф=6000/220*0.8=34(A) 但是，一般情况下，家里的电器不可能同时使用，所以加上一个公用系数，公用系数一般0.5。所以，上面的计算应该改写成 I=P*公用系数/Ucosф=6000*0.5/220*0.8=17(A) 也就是说，这个家庭总的电流值为17A。则总闸空气开关不能使用16A，应该用大于17A的。估算口诀：二点五下乘以九，往上减一顺号走。三十五乘三点五，双双成组减点五。条件有变加折算，高温九折铜升级。穿管根数二三四，八七六折满载流。说明： (1)本节口诀对各种绝缘线(橡皮和塑料绝缘线)的载流量(安全电流)不是直接指出，而是“截面乘上一定的倍数”来表示，通过心算而得。由表5 3可以看出：倍数随截面的增大而减小。“二点五下乘以九，往上减一顺号走”说的是2.5mm’及以下的各种截面铝芯绝缘线，其载流量约为截面数的9倍。如2.5mm’导线，载流量为2.5×9=22.5(A)。从4mm’及以上导线的载流量和截面数的倍数关系是顺着线号往上排，倍数逐次减l，即4×8、6×7、10×6、16×5、25×4。“三十五乘三点五，双双成组减点五”，说的是35mm”的导线载流量为截面数的3.5倍，即35×3.5=122.5(A)。从50mm’及以上的导线，其载流量与截面数之间的倍数关系变为两个两个线号成一组，倍数依次减0.5。即50、70mm’导线的载流量为截面数的3倍;95、120mm”导线载流量是其截面积数的2.5倍，依次类推。“条件有变加折算，高温九折铜升级”。上述口诀是铝芯绝缘线、明敷在环境温度25℃的条件下而定的。若铝芯绝缘线明敷在环境温度长期高于25℃的地区，导线载流量可按上述口诀计算方法算出，然后再打九折即可;当使用的不是铝线而是铜芯绝缘线，它的载流量要比同规格铝线略大一些，可按上述口诀方法算出比铝线加大一个线号的载流量。如16mm’铜线的载流量，可按25mm2铝线计算配电电缆截面的优化选择以往在选择配电电缆时，通常都根据敷设条件确定电缆型号，再按发热条件选择电缆截面，最后选出符合其载流量要求，并满足电压损失及热稳定要求的电缆截面。若考虑经济效益，则电缆最佳截面应是使初投资和整个电缆经济寿命中的损耗费用之和达到最少的截面。从这一点考虑选择电缆截面时，约需在按发热条件选出的截面基础上，再人为地加大4～5级截面，称此截面为最佳截面。由于加大了电缆截面，提高了载流能力，使电缆的使用寿命得以延长;由于截面增大，线路电阻降低，使线路压降减少，从而大大提高了供电质量，电能损耗降低，使运行费用降低，这样，可保证在整个电缆经济寿命中总费用最低。下面将用总拥有费用法来论证，电缆最佳截面应是在按常规方法选出的截面基础上，再加大
精神分裂症的发病原因是什么 精神分裂症是一种精神病，对于我们的影响是很大的，如果不幸患上就要及时做好治疗，不然后果会很严重，无法进行正常的工作和生活，是一件很尴尬的事情。因此为了避免患上这样的疾病，我们就要做好预防，今天我们就请广州协佳的专家张可斌来介绍一下精神分裂症的发病原因。 精神分裂症是严重影响人们身体健康的一种疾病，这种疾病会让我们整体看起来不正常，会出现胡言乱语的情况，甚至还会出现幻想幻听，可见精神分裂症这种病的危害程度。 (1)精神刺激：人的心理与社会因素密切相关，个人与社会环境不相适应，就产生了精神刺激，精神刺激导致大脑功能紊乱，出现精神障碍。不管是令人愉快的良性刺激，还是使人痛苦的恶性刺激，超过一定的限度都会对人的心理造成影响。 (2)遗传因素：精神病中如精神分裂症、情感性精神障碍，家族中精神病的患病率明显高于一般普通人群，而且血缘关系愈近，发病机会愈高。此外，精神发育迟滞、癫痫性精神障碍的遗传性在发病因素中也占相当的比重。这也是精神病的病因之一。 (3)自身：在同样的环境中，承受同样的精神刺激，那些心理素质差、对精神刺激耐受力低的人易发病。通常情况下，性格内向、心胸狭窄、过分自尊的人，不与人交往、孤僻懒散的人受挫折后容易出现精神异常。 (4)躯体因素：感染、中毒、颅脑外伤、肿瘤、内分泌、代谢及营养障碍等均可导致精神障碍，。但应注意，精神障碍伴有的躯体因素，并不完全与精神症状直接相关，有些是由躯体因素直接引起的，有些则是以躯体因素只作为一种诱因而存在。 孕期感染。如果在怀孕期间，孕妇感染了某种病毒，病毒也传染给了胎儿的话，那么，胎儿出生长大后患上精神分裂症的可能性是极其的大。所以怀孕中的女性朋友要注意卫生，尽量不要接触病毒源。 上述就是关于精神分裂症的发病原因，想必大家都已经知道了吧。患上精神分裂症之后，大家也不必过于伤心，现在我国的医疗水平是足以让大家快速恢复过来的，所以说一定要保持良好的情绪。
l Applications and Design l Engineering Analysis l Engineering Basics l Engineering Calculators l Engineering Materials Corrosion Definition - Corrosion and Galvanic Compatibility Corrosion and Galvanic Compatibility Knowledge Corrosion Testing Equipment Corrosion is the deterioration of a material due to interaction with its environment. It is the process in which metallic atoms leave the metal or form compounds in the presence of water and gases. Metal atoms are removed from a structural element until it fails, or oxides build up inside a pipe until it is plugged. All metals and alloys are subject to corrosion. Even the noble metals, such as gold, are subject to corrosive attack in some environments. The corrosion of metals is a natural process. Most metals are not thermodynamically stable in the metallic form; they want to corrode and revert to the more stable forms that are normally found in ores, such as oxides. Corrosion is of primary concern in engineering and design Corrosion occurs in every metal is subject to it. Even though this corrosion cannot be eliminated, it can be controlled. ? Copyright 2000 - 2009, by Engineers Edge, LLC All rights reserved. Disclaimer Engineering Solutions Industrial Project Management for critical applications https://www.doczj.com/doc/229370229.html, Corrosion damage?The specialist in surface treatment of stainless steel and mild steel! www.inox-ferro.nl Cortec Corporation Prevent, remove rust & corrosion VCI/VpCI film, emitters, paper, etc https://www.doczj.com/doc/229370229.html, Tankinetics Fiberglass Engineered FRP Equipment ASME RTP 1, Section X, tanks, pipe https://www.doczj.com/doc/229370229.html, Material Characterization Providing solutions for over 25 yrs SIMS, XPS, TOF-SIMS, SEM & more. https://www.doczj.com/doc/229370229.html,
精神分裂症的病因是什么 精神分裂症是一种精神方面的疾病，青壮年发生的概率高，一般 在16～40岁间，没有正常器官的疾病出现，为一种功能性精神病。 精神分裂症大部分的患者是由于在日常的生活和工作当中受到的压力 过大，而患者没有一个良好的疏导的方式所导致。患者在出现该情况 不仅影响本人的正常社会生活，且对家庭和社会也造成很严重的影响。 精神分裂症常见的致病因素： 1、环境因素：工作环境比如经济水平低低收入人群、无职业的人群中，精神分裂症的患病率明显高于经济水平高的职业人群的患病率。还有实际的生活环境生活中的不如意不开心也会诱发该病。 2、心理因素：生活工作中的不开心不满意，导致情绪上的失控，心里长期受到压抑没有办法和没有正确的途径去发泄，如恋爱失败， 婚姻破裂，学习、工作中不愉快都会成为本病的原因。 3、遗传因素：家族中长辈或者亲属中曾经有过这样的病人，后代会出现精神分裂症的机会比正常人要高。 4、精神影响：人的心里与社会要各个方面都有着不可缺少的联系，对社会环境不适应，自己无法融入到社会中去，自己与社会环境不相
适应，精神和心情就会受到一定的影响，大脑控制着人的精神世界， 有可能促发精神分裂症。 5、身体方面：细菌感染、出现中毒情况、大脑外伤、肿瘤、身体的代谢及营养不良等均可能导致使精神分裂症，身体受到外界环境的 影响受到一定程度的伤害，心里受到打击，无法承受伤害造成的痛苦，可能会出现精神的问题。 对于精神分裂症一定要配合治疗，接受全面正确的治疗，最好的 疗法就是中医疗法加心理疗法。早发现并及时治疗并且科学合理的治疗，不要相信迷信，要去正规的医院接受合理的治疗，接受正确的治 疗按照医生的要求对症下药，配合医生和家人，给病人创造一个良好 的治疗环境，对于该病的康复和痊愈会起到意想不到的效果。
卫生部办公厅关于印发《脐带血造血干细胞治疗技术管理规 范(试行)》的通知 【法规类别】采供血机构和血液管理 【发文字号】卫办医政发[2009]189号 【失效依据】国家卫生计生委办公厅关于印发造血干细胞移植技术管理规范(2017年版)等15个“限制临床应用”医疗技术管理规范和质量控制指标的通知 【发布部门】卫生部(已撤销) 【发布日期】2009.11.13 【实施日期】2009.11.13 【时效性】失效 【效力级别】部门规范性文件 卫生部办公厅关于印发《脐带血造血干细胞治疗技术管理规范（试行）》的通知 （卫办医政发〔2009〕189号） 各省、自治区、直辖市卫生厅局，新疆生产建设兵团卫生局： 为贯彻落实《医疗技术临床应用管理办法》，做好脐带血造血干细胞治疗技术审核和临床应用管理，保障医疗质量和医疗安全，我部组织制定了《脐带血造血干细胞治疗技术管理规范（试行）》。现印发给你们，请遵照执行。 二〇〇九年十一月十三日
脐带血造血干细胞 治疗技术管理规范（试行） 为规范脐带血造血干细胞治疗技术的临床应用，保证医疗质量和医疗安全，制定本规范。本规范为技术审核机构对医疗机构申请临床应用脐带血造血干细胞治疗技术进行技术审核的依据，是医疗机构及其医师开展脐带血造血干细胞治疗技术的最低要求。 本治疗技术管理规范适用于脐带血造血干细胞移植技术。 一、医疗机构基本要求 （一）开展脐带血造血干细胞治疗技术的医疗机构应当与其功能、任务相适应，有合法脐带血造血干细胞来源。 （二）三级综合医院、血液病医院或儿童医院，具有卫生行政部门核准登记的血液内科或儿科专业诊疗科目。 1.三级综合医院血液内科开展成人脐带血造血干细胞治疗技术的，还应当具备以下条件： （1）近3年内独立开展脐带血造血干细胞和（或）同种异基因造血干细胞移植15例以上。 （2）有4张床位以上的百级层流病房，配备病人呼叫系统、心电监护仪、电动吸引器、供氧设施。 （3）开展儿童脐带血造血干细胞治疗技术的，还应至少有1名具有副主任医师以上专业技术职务任职资格的儿科医师。 2.三级综合医院儿科开展儿童脐带血造血干细胞治疗技术的，还应当具备以下条件：
日成首页 / 新闻中心 / 日成新闻 / 电缆线径和最大载荷电流关系 电缆线径和最大载荷电流关系 日期：2016-12-27 文章来源：RCCN 访问： 电缆线径和最大载荷电流关系 1mm2的电源线最大能过多少安的电流，多大的功率？例如2.5平方的电线，工程施工中怎样算要用多大的电线？ ①对于1.5、2.5、4、6、10mm2的导线可将其截面积数乘以5倍。 ②对于16、25mm2的导线可将其截面积数乘以4倍。 ③对于35、50mm2的导线可将其截面积数乘以3倍。 ④对于70、95mm2的导线可将其截面积数乘以2.5倍。 ⑤对于120、150、185mm2的导线可将其截面积数乘以2倍。 工作温度30℃，长期连续90％负载下的载流量如下： 1.5平方毫米――18A 2.5平方毫米――26A) 4 平方毫米――26A 6平方毫米――47A 10平方毫米――66A 16 平方毫米――92A 25平方毫米――120A 35平方毫米――150A 功率P=电压U×电流I＝220伏×18安＝3960瓦 国标GB4706.1-1992/1998规定的电线负载电流值（部分） 铜芯电线：铜芯线截面积.. 允许长期电流 2.5平方毫米(16A～25A) 4平方毫米(25A～32A) 6平方毫米(32A～40A) 铝芯电线：铝芯线截面积..允许长期电流 2.5平方毫米(13A～20A) 4平方毫米( 20A～25A) 6平方毫米(25A～32A) 举例说明： 1、每台计算机耗电约为200～300W(约1～1.5A)，那么10台计算机就需要一条2.5平方毫米的铜芯电线供电，否则可能发生火灾。 2、大3匹空调耗电约为3000W(约14A)，那么1台空调就需要单独的一条2.5平方毫米的铜芯电线供电。 3、现在的住房进线一般是4平方毫米的铜线，因此，同时开启的家用电器不得超过25A(即5500瓦)，有人将房屋内的电线更换成6平方毫米的铜线是没有用处的，因为进入电线是4平方毫米的。 4、早期的住房(15年前)进线一般是2.5平方毫米的铝线，因此，同时开启的家用电器不得超过13A(即2800瓦)。 5、耗电量比较大的家用电器是：空调5A(1.2匹)，电热水器10A，微波炉4A，电饭煲4A，洗碗机8A，带烘干功能的洗衣机10A，电开水器4A在电源引起的火灾中，有90％头发热造成的，因此所有的接头均要焊接，不能焊接的接触器件5～10年必须更换(比如插座、空气开关等)。 国标允许的长期电流
不銹鋼常見腐蝕種類 1. 2.電流腐蝕（galvanic corrosion）或稱二金屬腐蝕（two-metal corrosion） 兩不同金屬在電解質溶液中接觸，當兩者的電位不同時，活性較大者將成為陽極，活性較小者將成為陰極，形成一個封閉回路，兩極間即有電流流動，造成電流腐蝕。電流腐蝕的大小，取決於兩不同金屬的電位差大小。 3.裂隙腐蝕（crevice corrosion） 裂隙腐蝕是發生在裂隙處的局部腐蝕，常見的裂隙處為搭接面（lap joint），止洩墊面（gasket）螺絲丁頭下，以及沈積物（deposit）下等。不論是金屬與金屬或金屬與非金屬接合面間隙，都可能發生裂隙腐蝕。 4.孔蝕（pitting） 孔蝕是局部的穿孔腐蝕，在金屬表面生成一個個或是許多密集的坑坑洞洞，深淺不一，使金屬表面看起來粗糙，但也只是一區一區的，並不是整個表面。 孔蝕的生成原因很多，最普通的一個是不清潔，金屬表面有灰塵、鐵銹、污垢等沈積物。 5.粒界腐蝕（intergranular corrosion） 晶粒邊界是液態金屬最後凝固的部分，其熔點最低，固體金屬熔解時，此部分也最先熔解。晶粒邊界也是高能量區，富有化學活性，所以金屬腐蝕時，也容易先由晶粒邊界開始。 6.選擇腐蝕（或稱分離腐蝕） 選擇固體合金中某一合金元素腐蝕。最常見的例子是黃銅（30﹪Zn＋70﹪Cu）因腐蝕而失去鋅，失去鋅的部位表面顯現出銅原有的紅色，肉眼即可辨別出紅色和黃色。所以也稱為失鋅（Dezincification）。 7.應力腐蝕（stress corrosion） 內有應力，外有J腐蝕媒體，聯合造成的金屬腐蝕，叫做應力腐蝕。應力腐蝕大多會發生裂紋，所以又稱為應力蝕裂（stress corrosion cracking，簡寫成SCC）。 應力腐蝕可能有兩種情況： (1) 應力促進的腐蝕（stress-accelerated corrosion ） (2) 應力蝕裂（SCC），是比較重要的一種情況。 8.沖蝕（erosion corrosion） 機件遇到流動的腐蝕流體（corrodent）所造成的腐蝕，叫做沖蝕。形成的要件有二，一是腐蝕媒體是流體（fluid），一是腐蝕媒體是流動的。腐蝕流體包括氣體，水溶液，有機溶液，和液態金屬。 與沖蝕有關的因素是： (1) 媒體的腐蝕性強弱。 (2) 流體中有無懸浮的固體顆粒，如泥漿（slury）。 (3) 流體的流動是穩定流（steady flow）或是亂流（turbulent flow），以及流速的大小。 9.其他腐蝕 腐蝕的種類很多有些少見的現象，是在無法觀察處漸漸進行，並非由顯著外力造成的物質敗壞，也可歸類於腐蝕。下面列出的就是此類。 (1)刃狀腐蝕（knife-line attack），簡寫為KLA (2)磨蝕（fretting corrosion） (3)熱變（thermal gradient） (4)絲狀腐蝕（filiform corrosion）
铜线截面积（平方）：1.0，1.5，2.5，4，6，10， 聚氯乙烯绝缘电线穿塑料管时（三根并排穿），安全载流量为11，15，21，28，36，49。单位：安。（按上面顺序） 穿铁管时比穿塑料管的大三安左右！ 如果是塑料绝缘电线的话又和这不一样啦！只比这种再大点！但一般情况下，塑料绝缘电线很少用，通用的是聚氯乙烯绝缘电线！ 10下五，100上二，16、25四，35、50三，70、95两倍半。 穿管、温度八、九折，裸线加一半。铜线升级算。 口诀中的阿拉伯数字与倍数的排列关系如下： 对于1.5、2.5、4、6、10mm2的导线可将其截面积数乘以5倍。 对于16、25mm2的导线可将其截面积数乘以4倍。 对于35、50mm2的导线可将其截面积数乘以3倍。 对于70、95mm2 的导线可将其截面积数乘以2.5倍。 对于120、150、185mm2的导线可将其截面积数乘以2 塑料铜芯线载流量(安)表 导线截面(mm2) 1 1.5 2.5 4 6 10 16 25 35 50 70 95 120 硬线BV 根数/单根直径1/1.13 1/1.37 1/1.76 1/2.24 1/2.73 7/1.33 7/1.68 7/2.11 7/2.49 19/1.81 19/2.14 19/2.49 37/2.01 软线BVR 根数/单根直径7/0.43 7/0.52 19/0.41 19/0.52 19/0.64 19/0.82 49/0.64 98/0.58 133/0.58 133/0.68 189/0.68 259/0.68 259/0.76 开启式载流量(安) 5 10 15 25 35 60 90 113 140 177 268 288 314 封闭式载流量(安) 4 8 12 20 28 48 72 93 115 145 220 240 258 导线截面积与载流量的计算 一、一般铜导线载流量导线的安全载流量是根据所允许的线芯最高温度、冷却条件、敷设条件来确定的。一般铜导线的安全载流量为5~8A/mm2，铝导线的安全载流量为3~5A/mm2。如：2.5 mm2 BVV 铜导线安全载流量的推荐值2.5×8A/mm2=20A 4 mm2 BVV铜导线安全载流量的推荐值4×8A/mm2=32A 二、计算铜导线截面积利用铜导线的安全载流量的推荐值5~8A/mm2，计算出所选取铜导线截面积S 的上下范围：S=< I /（5~8）>=0.125 I ~0.2 I（mm2）S-----铜导线截面积（mm2）I-----负载电流（A） 三、功率计算一般负载（也可以成为用电器，如点灯、冰箱等等）分为两种，一种是电阻性负载，一种是电感性负载。对于电阻性负载的计算公式：P=UI 对于日光灯负载的计算公式：P=UIcosф，其中日
Pitting Corrosion G.S.Frankel,The Ohio State University Fig.1 Deep pits in a metal MANY ENGINEERING ALLOYS,such as stainless steels and aluminum alloys,are useful only because of passive ?lms,which are thin (nanometer-scale)oxide layers that form natu-rally on the metal surface and greatly reduce the rate of corrosion of the alloys.Such passive ?lms,however,are often susceptible to localized breakdown,resulting in accelerated dissolution of the underlying metal.If the attack initiates on an open surface,it is called pitting corrosion;at an occluded site,it is called crevice corrosion.These closely related forms of localized corro-sion can lead to accelerated failure of structural components by perforation or by acting as an initiation site for cracking.Figure 1shows an example of deep pits on a metal surface. It should be noted that,whereas localized dis-solution following breakdown of an otherwise protective passive ?lm is the most common and technologically important type of pitting corro-sion,pits can form under other conditions as well.For instance,pitting can occur during ac-tive dissolution if certain regions of the sample are more susceptible and dissolve faster than the rest of the surface.This section concentrates on the better-known and widely studied phenome-non of pitting corrosion of passive metals. Pitting corrosion is in?uenced by many dif-ferent parameters,including the environment,metal composition,potential,temperature,and surface condition.Important environmental pa-rameters include aggressive ion concentration,pH,and inhibitor concentration.Other phenom-enological aspects of localized corrosion include the stochastic nature of the processes and the stages of localized attack,including passive ?lm breakdown,metastable attack,stable growth,and perhaps eventual arrest. Phenomenology of Pitting Corrosion Environment and Development of Local Environment.Classical pitting corrosion caused by passive ?lm breakdown will only occur in the presence of aggressive anionic species,and chlo-ride ions are usually,although not always,the cause.The severity of pitting tends to vary with the logarithm of the bulk chloride concentration (Ref 1).The reason for the aggressiveness of chloride has been pondered for some time,and a number of notions have been put forth.Chlo-ride is an anion of a strong acid,and many metal cations exhibit considerable solubility in chlo-ride solutions (Ref 2).Chloride is a relatively small anion with a high diffusivity;it interferes with passivation,and it is ubiquitous as a con-taminant. The presence of oxidizing agents in a chlo-ride-containing environment is usually ex-tremely detrimental and will further enhance lo-calized corrosion.It should be noted that chromate is an oxidizing agent that typically in-hibits corrosion by reducing to form Cr(III)?lm.Most oxidizing agents enhance the likelihood of pitting corrosion by providing extra cathodic re-actants and increasing the local potential.Of course,dissolved oxygen is the most common oxidizing agent.One of the reactions by which oxygen reduction occurs is: O H O 4OH pH vs. SHE 22rev ++=???241230059e E →() ..(Eq 1) where SHE is standard hydrogen electrode.Removal of oxidizing agents,such as removal of dissolved oxygen by deaeration,is one pow-erful approach for reducing susceptibility to lo-calized corrosion.The in?uence of potential on pitting corrosion is described subsequently.Pitting is considered to be autocatalytic in na-ture;once a pit starts to grow,the local condi-tions are altered such that further pit growth is promoted.The anodic and cathodic electrochem-ical reactions that comprise corrosion separate spatially during pitting (Fig.2).The local pit en-vironment becomes depleted in cathodic reactant (e.g.,oxygen),which shifts most of the cathodic reaction (such as is given by Eq 1)to the boldly exposed surface outside of the pit cavity,where this reactant is more plentiful.The pit environ-ment becomes enriched in metal cations as a re-sult of the dissolution process in the pit (written for a generic metallic element,M): M r M n ??ne ? (Eq 2) The concentration of an anionic species such as chloride must also increase within the pit in order to balance the charge associated with the cation concentration and to maintain charge neu-trality.This enrichment of anions occurs by elec-tromigration from the bulk solution in response to the potential gradient that develops as a result of the ohmic potential drop along the current path between the inside of the pit and the cath-odic sites on the boldly exposed surface.The ?-nal aspect of the local pit environment that must be considered is the pH,which decreases,owing to cation hydrolysis: M H O M OH H O M OH H 22e e e 2222++ ++ ++Η++→()→()(Eq 3) The common cathodic reactions that must ac-company the dissolution occurring in the pit,such as the oxygen reduction reaction (Eq 1),result in a local increase in the pH at the cathodic sites.The acidity developed in the pit is not neu-tralized by the cathodic reaction because of the spacial separation of the anodic and cathodic re-actions.In summary,the local pit environment is depleted in the cathodic reactant,such as dis-solved oxygen;enriched in metal cation and an anionic species,such as chloride;and acidi?ed.This acidic chloride environment is aggressive to most metals and tends to prevent repassivation and promote continued propagation of the pit.