26:
105:
The proportion of iron oxide is low due to its reduction with cobalt. The bond strength is highly dependent on the oxide layer thickness and character. The presence of cobalt makes the oxide layer easier to melt and dissolve in the molten glass. A grey, grey-blue or grey-brown color indicates a good seal. A metallic color indicates lack of oxide, while black color indicates overly oxidized metal, in both cases leading to a weak joint.
104:
Kovar not only has thermal expansion similar to glass, but its nonlinear thermal expansion curve can often be made to match a glass, thus allowing the joint to tolerate a wide temperature range. Chemically, it bonds to glass via the intermediate oxide layer of nickel(II) oxide and cobalt(II) oxide.
62:(~5 × 10 /K between 30 and 200 °C, to ~10 × 10 /K at 800 °C) to allow a tight mechanical joint between the two materials over a range of temperatures. It finds application in glass-to-metal seals in scientific apparatus, and conductors entering glass envelopes of electronic parts such as
101:
is not the same as glass; as the joint cools after fabrication the stresses due to the different expansion rates of the glass and metal cause the joint to crack.
244:
108:
The name Kovar is often used as a general term for Fe–Ni alloys with these particular thermal expansion properties. The related particular Fe–Ni alloy
97:, and in vacuum systems in chemistry and other scientific research. Most metals cannot seal to glass because their
98:
316:
375:
414:
419:
294:
195:
17:
399:
272:
8:
82:
59:
55:
29:
Assortment of Kovar metal shapes from an advertisement in a 1950 electronics magazine
94:
373:
258:
230:
408:
305:
25:
63:
283:
90:
86:
190:
151:
75:
71:
216:
202:
146:
51:
44:
141:
136:
131:
41:
37:
109:
67:
47:
126:
374:
USPTO United States Patent and
Trademark Office (1993).
81:Kovar was invented to meet the need for a reliable
85:, which is required in electronic devices such as
36:(trademark of CRS Holdings, inc., Delaware) is a
406:
54:1, designed to have substantially the same
353:
345:
337:
329:
321:
310:
299:
288:
277:
24:
407:
115:
112:exhibits minimum thermal expansion.
13:
14:
431:
393:
120:Given in percentages of weight.
99:coefficient of thermal expansion
376:"Trademark Assignment Abstract"
367:
1:
360:
317:thermal expansion coefficient
179:
50:compositionally identical to
7:
350:
342:
334:
326:
10:
436:
15:
319:/10 K (25 – 200 °C)
400:Kovar specification page
295:electrical resistivity
30:
18:Kovar (disambiguation)
247:at fracture / %
28:
273:thermal conductivity
16:For other uses, see
116:Typical composition
83:glass-to-metal seal
58:characteristics as
60:borosilicate glass
31:
358:
357:
284:Curie Temperature
245:reduction of area
177:
176:
95:cathode ray tubes
56:thermal expansion
427:
387:
386:
384:
382:
371:
351:(25–500 °C)
343:(25–450 °C)
335:(25–400 °C)
327:(25–300 °C)
184:
183:
123:
122:
435:
434:
430:
429:
428:
426:
425:
424:
405:
404:
396:
391:
390:
380:
378:
372:
368:
363:
182:
118:
74:tubes and some
21:
12:
11:
5:
433:
423:
422:
417:
415:Ferrous alloys
403:
402:
395:
394:External links
392:
389:
388:
365:
364:
362:
359:
356:
355:
352:
348:
347:
344:
340:
339:
336:
332:
331:
328:
324:
323:
320:
313:
312:
309:
302:
301:
298:
291:
290:
287:
280:
279:
276:
269:
268:
265:
262:
259:yield strength
255:
254:
251:
248:
241:
240:
237:
234:
231:Youngs Modulus
227:
226:
223:
220:
213:
212:
209:
206:
199:
198:
193:
188:
181:
178:
175:
174:
171:
168:
165:
162:
159:
155:
154:
149:
144:
139:
134:
129:
117:
114:
9:
6:
4:
3:
2:
432:
421:
420:Nickel alloys
418:
416:
413:
412:
410:
401:
398:
397:
377:
370:
366:
349:
341:
333:
325:
318:
315:
314:
307:
306:specific heat
304:
303:
296:
293:
292:
285:
282:
281:
274:
271:
270:
266:
263:
260:
257:
256:
252:
249:
246:
243:
242:
238:
235:
232:
229:
228:
224:
221:
218:
215:
214:
210:
207:
204:
201:
200:
197:
194:
192:
189:
186:
185:
172:
169:
166:
163:
160:
157:
156:
153:
150:
148:
145:
143:
140:
138:
135:
133:
130:
128:
125:
124:
121:
113:
111:
106:
102:
100:
96:
92:
88:
84:
79:
77:
73:
69:
65:
61:
57:
53:
49:
46:
43:
39:
35:
27:
23:
19:
379:. Retrieved
369:
119:
107:
103:
91:vacuum tubes
80:
64:vacuum tubes
33:
32:
22:
167:< 0.01%
87:light bulbs
409:Categories
361:References
180:Properties
76:lightbulbs
66:(valves),
297:Ω mm / m
187:Property
72:microwave
275:/ W/K∙m
217:Hardness
191:sintered
158:balance
381:18 June
203:Density
52:Fernico
45:ferrous
308:J/g∙K
261:/ MPa
233:/ GPa
219:/ HV1
205:g /cm
42:cobalt
38:nickel
311:0.46
300:0.49
286:/ °C
211:8.35
196:HIPed
173:0.3%
170:0.2%
110:Invar
68:X-ray
48:alloy
34:Kovar
383:2014
354:6.2
346:5.3
338:4.9
330:5.1
322:5.5
289:435
267:270
264:270
239:138
236:138
225:150
222:160
208:8.0
164:17%
161:29%
78:.
70:and
278:17
253:30
250:30
411::
152:Mn
147:Si
137:Co
132:Ni
127:Fe
93:,
89:,
385:.
142:C
40:–
20:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
