國際千克原器

國際千克原器（粵拼：gwok3 zai3 cin1 hak1 jyun4 hei3）（International Prototype of the Kilogram，簡稱IPK）係世界質量單位「千克」嘅標準砝碼，目前存放喺法國巴黎郊區嘅國際度量衡局（BIPM）。

國際公斤原器以鉑銥合金鑄造，因為鉑銥合金有膨脹率低、唔易氧化等特點。

國際千克原器[編輯]

自1889年起，國際單位制將千克嘅大細定義為同國際千克原器嘅質量相等。IPK由一種鉑合金製成，呢種合金叫「Pt‑10Ir」，即百分之九十鉑及百分之十銥（按質量比）；然後將呢種合金用機器造成39.17mm嘅直立圓柱體（高度=直徑），噉樣做可以將表面積減至最低^[1]。比起純鉑嘅檔案局千克，新加入去嘅百分之十銥改善咗硬度，但同時保留鉑嘅好多長處：對氧化嘅高度抵抗性、極高密度、良好嘅導電與導熱性以及低磁化率。IPK同佢六件姐妹複製品都被存放喺國際度量衡局（BIPM）位於巴黎郊區嘅總部下層嘅儲藏室之中，有環境監控嘅夾萬入面。開夾萬需要三條被分開保管嘅鎖匙。IPK嘅正式複製品可以畀第二啲國家作佢哋嘅全國標準之用。呢啲複製品大概每五十年就要同IPK比對一次。

IPK係1879年製造嘅三個圓柱體之一。1883年，IPK嘅質量被發現同八十四年前嘅檔案局千克嘅一致，並喺1899年嘅第一屆國際度量衡大會中被正式指定為千克^[1]。維也納標準海水（有嚴格同位素控制嘅純淨水）密度嘅現代測量指出一立方分米嘅水，喺最大密度時（3.984°C）比一千克只差25.05ppm^[2]。呢個微小嘅差別，同IPK同檔案局千克質量一致呢個事實，說明咗超過209年前班科學家喺量度水密度及製造檔案局千克嘅技藝係相當高超嘅。

國際千克原器嘅穩定性[編輯]

定義來上話，IPK質量嘅量度值誤差為整零；IPK就係千克。然而，IPK因時間而成嘅質量變量，可經由比對世界各地正式複製品質量判定出來，呢個過程被稱為「定期核準」。例如，美國擁有四個90%鉑/10%銥嘅千克標準儀，其中K4同K20係1884年製嘅原批四十個複製品嘅其中兩個^[4]。K20被指定為美國嘅國家首席標準。呢兩個原器，同第二啲國家嘅一樣，都要定期送返BIPM作質量核準^[5]。

冇一個複製品嘅質量準確地等於IPK；佢哋嘅質量經過校準，得出嘅偏差值會被存檔。譬如，美國嘅國家首席標準K20，1889年最初嘅正式質量為1kg − 39µg；亦即係話K20比IPK輕39µg。1999年嘅上一次核準指出佢質量準確地等於1889年嘅原值。同呢種小差異相當唔同嘅係，美國嘅檢核標準，K4嘅質量持續地相對於IPK下降——噉都係有原因嘅。檢核標準比首席標準常用得多，所以好容易被刮及受到各種磨損。K4最初送抵時嘅正式質量為1kg − 75µg，但到1989年經正式校準後質量為1kg − 106µg，而十年後就係1kg − 116µg。喺呢一百一十年間，K4相對於IPK輕咗41µg^[6]。

除檢核標準可能受到嘅一般磨損外，就算被小心收藏嘅國家原器都會因為唔同原因，而產生相對於IPK嘅質量變動，當中原因有已知嘅，亦有未知嘅。由於IPK同佢嘅複製品都被存放於空氣中（雖然有兩層或以上嘅鐘罩），佢哋都係會經由表面吸附大氣層中嘅灰塵而獲得質量。因此會用一種稱為「BIPM清潔法」嘅方式來清潔佢哋，呢種方法係BIPM喺1939至1946年間開發嘅，步驟包括用沾有等量乙醚同乙醇嘅油鞣革輕抹，用蒸餾過兩次嘅水進行蒸氣清潔，以及畀原器喺核準前先放七至十日^[7]。

至2011年，國際千克原器嘅重量可能少咗大約五十微克^[8]。

全球各地嘅原器[編輯]

臺灣[編輯]

目前喺國立臺灣高雄科學工藝博物館中有一公斤副原器，係日治時期所遺留，原交由臺灣度量衡檢驗所管理，轉由經濟部標準檢驗局，之後喺2001年捐贈畀科學工藝博物館。

臺灣國家度量衡標準實驗室喺1995年向國際度量衡局買到國際質量最高標準嘅鉑銥公斤原器，編號七十八，係而家臺灣嘅國家質量標準。

中國大陸[編輯]

中國大陸嘅千克原器係1965年從英國引入，編號60，1986年被批准為國家質量基準，編號：GJJ（力）0101。

千克作證基準砝碼係質量基準嘅組成部分，1984年從英國引入，編號64，1986年批准為質量作證基準，編號：GJJ（力）0151。

千克副基準砝碼係1967年由中國計量科學研究院自行研製，編號9，佢係直徑同高度相等嘅直圓柱體，用不銹鋼造，體積為126.6006cm³，質量標稱值為1kg。1967年首次檢定結果為1公斤-1.94mg，檢定精度為0.04mg。1986年批准為質量副基準，編號：GJJ（力）0152^[9]。

香港[編輯]

香港政府創新科技署轄下嘅標準及校正實驗所擁有國際千克原器嘅第75號複製本，用作香港嘅質量參考標準及普及質量單位^[10]。

參考[編輯]

↑ ^1.0 ^1.1 New Techniques in the Manufacture of Platinum-Iridium Mass Standards, T. J. Quinn, Platinum Metals Rev., 1986, 30, (2), pp. 74–79
↑ Water Structure and Science, Water Properties, Density maximum (and molar volume) at temperature of maximum density, a (by London South Bank University). Link to Web site.
↑ The Third Periodic Verification of National Prototypes of the Kilogram (1988–1992), G. Girard, Metrologia 31 (1994) 317–336
↑ The other two Pt‑10Ir standards owned by the U.S. are K85, which is used for watt balance experiments (see Watt balance, above), and K650, which was an early attempt with a new series of prototypes (K64–K80) that were diamond-turned directly to a finish mass. K650 has a density of 7004215353700000000♠21.53537 g/ml, which is normal for Pt‑10Ir alloy. However, as its finished mass was roughly 2000 µg less than one kilogram, it is unsuitable for use as a national prototype and is instead known as a mass -{“standard”—not a “prototype”. However, it serves well for special duties, such as a stability reference when K4 and K20 are transported to the BIPM and back. There are three other diamond-turned, Pt‑10Ir replicas that are not formally considered to be “prototypes”}-: K651, K690, and K691.
↑ 運輸原器需要極其小心。1984年，原器K4同K20就被人手帶入商業客機嘅客艙。
↑ The Kilogram and Measurements of Mass and Force, Z. J. Jabbour et al., J. Res. Natl. Inst. Stand. Technol. 106, 2001, 25–46 (3.5 MB PDF, here 互聯網檔案館嘅歸檔，歸檔日期2011年6月4號，.)
↑ Before the BIPM’s published report in 1994 detailing the relative change in mass of the prototypes, different standard bodies used different techniques to clean their prototypes. The NIST’s practice before then was to soak and rinse its two prototypes first in benzene, then in ethanol, and to then clean them with a jet of bi-distilled water steam.
↑ 秋凌 (2011-01-28). 〈科學家發現國際千克原器減少約五十微克〉. 《科學網》. 喺2011-01-30搵到.
↑ 國家計量院NIM質量基準^{[失咗效嘅鏈]}
↑ 標準及校正實驗

睇埋[編輯]

出面網頁[編輯]

中國計量科學研究院力聲學基標準

[Quinn-1] 1.0 ^1.1 New Techniques in the Manufacture of Platinum-Iridium Mass Standards, T. J. Quinn, Platinum Metals Rev., 1986, 30, (2), pp. 74–79

[2] Water Structure and Science, Water Properties, Density maximum (and molar volume) at temperature of maximum density, a (by London South Bank University). Link to Web site.

[Girard-3] The Third Periodic Verification of National Prototypes of the Kilogram (1988–1992), G. Girard, Metrologia 31 (1994) 317–336

[4] The other two Pt‑10Ir standards owned by the U.S. are K85, which is used for watt balance experiments (see Watt balance, above), and K650, which was an early attempt with a new series of prototypes (K64–K80) that were diamond-turned directly to a finish mass. K650 has a density of 7004215353700000000♠21.53537 g/ml, which is normal for Pt‑10Ir alloy. However, as its finished mass was roughly 2000 µg less than one kilogram, it is unsuitable for use as a national prototype and is instead known as a mass -{“standard”—not a “prototype”. However, it serves well for special duties, such as a stability reference when K4 and K20 are transported to the BIPM and back. There are three other diamond-turned, Pt‑10Ir replicas that are not formally considered to be “prototypes”}-: K651, K690, and K691.

[5] 運輸原器需要極其小心。1984年，原器K4同K20就被人手帶入商業客機嘅客艙。

[Recalibration-6] The Kilogram and Measurements of Mass and Force, Z. J. Jabbour et al., J. Res. Natl. Inst. Stand. Technol. 106, 2001, 25–46 (3.5 MB PDF, here 互聯網檔案館嘅歸檔，歸檔日期2011年6月4號，.)

[7] Before the BIPM’s published report in 1994 detailing the relative change in mass of the prototypes, different standard bodies used different techniques to clean their prototypes. The NIST’s practice before then was to soak and rinse its two prototypes first in benzene, then in ethanol, and to then clean them with a jet of bi-distilled water steam.

[8] 秋凌 (2011-01-28). 〈科學家發現國際千克原器減少約五十微克〉. 《科學網》. 喺2011-01-30搵到.

[9] 國家計量院NIM質量基準^{[失咗效嘅鏈]}

[10] 標準及校正實驗

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