X射線熒光光譜儀樣品制備方法：壓片法介紹和注意事項

樣品制備技術(shù)對于在分析樣品時獲得更好的結(jié)果至關(guān)重要。樣品制備技術(shù)會影響X射線熒光分析結(jié)果的準確性。

樣品（簡稱標樣）的配制

X射線熒光分析與化學分析不同，熒光分析儀是一種相對測量儀器，它是通過測量一定數(shù)量已知結(jié)果的標準樣品，建立相應的正確的數(shù)學模型后，才能得到準確的測量。也就是說：要達到好的測量效果，一組好標樣與一臺好儀器同樣重要。好儀器由我公司提供，好標樣得由用戶化驗室提供。好標樣的標準是：有代表性，有一定的跨度范圍，有準確的化學分析結(jié)果。具體要求如下：

●樣品量：5-10.每個質(zhì)量：50-100克

●具有代表性：樣品可以代表您工廠的實際產(chǎn)品，是來自實際生產(chǎn)線的瞬時樣品，盡量避免人為準備的樣品，這會帶來主觀因素。并且不使用國標樣品，每個工廠使用不同的原材料和不同的配方，會得到不同的數(shù)學模型。

●主要化學成分的含量范圍。

壓片制備步驟

標準樣品中主要化學成分的含量范圍應涵蓋正常產(chǎn)品主要化學成分含量的變化范圍，且應保持距離，分布均勻。以水泥原料為例：正常情況下，在原料（白色原料）中，如果CaO含量目標值為42%，那么，為了保持距離，CaO含量的最小值約為39 %，值高為45%左右，為使CaO含量分布均勻，CaO含量應為39%、40%、41%、42%、43%、44% ,45%。您可以額外準備幾個此類標準樣品，其含量在正常變化范圍內(nèi)（41%~43%）。 （表 1）

是一系列白色原料的標準樣品，主要化學成分的目標值分別如下：

Al2O3：3.1%，SiO2：13%，CaO：41.5%，F(xiàn)e2O3：3.5%

在表1中，我們可以得到：主要原料的含量之間保持一定的距離，分布均勻。 Al的變化范圍為2.5%，Si的變化范圍為4-6%，Ca的變化范圍為4%-6%，F(xiàn)e的變化范圍為3%。有鋁與硅、硅與鈣、鈣與鐵之間沒有人為的規(guī)律性。

一般來說，高含量元素的變化幅度大于低含量元素的變化幅度，含量越低，變化幅度越小

表1.白生料標樣結(jié)果

一般，系列標樣中對于含量為40%、50%、60%、70%、80%左右的元素（或其氧化物），其跨度范圍應為：5%-10%左右；含量為10%、20%、30%左右的元素，其跨度范圍應為：4%-8%左右；含量為1%-10%左右的元素，其跨度范圍應為：3%-5%左右。即：含量較高的元素，跨度范圍應相應增大；含量較小的元素，跨度范圍應相應減小。

l        系列標樣里高低樣的制備：

系列標樣中，對于目標值附近的樣品，直接從生產(chǎn)線上留??；而對于系列標樣中的高低樣品，一般很難從正常生產(chǎn)中的生產(chǎn)線上取出，這種情況下，我們只好人為配制高低樣品。仍以表1中的白生料為例，正常生產(chǎn)時白生料CaO的含量一般控制在41.0%-42.0%左右，要達到45%的高CaO含量，我們在留取的正常生產(chǎn)樣中，按一定比例添加少量石灰石原料，以使CaO含量升高、同時使Al2O3、SiO2、Fe2O3含量降低，可達到高CaO、低SiO2、低Fe2O3的目的。同理，可制備出高SiO3、高Fe2O3標樣。CaO含量在正常范圍內(nèi)（40.0%-43.0%左右）的樣品必須從生產(chǎn)線上留取，不可人為配制！

注意：應盡量減少人為配制標樣。當需要人為配制標樣時，應采用在大量的實際生產(chǎn)樣中添加少量原材料的方法，而且所添加的原材料必須是實際生產(chǎn)中所使用的同種原料。不要用同一結(jié)果的實際生產(chǎn)樣去配制若干個標樣（一個生產(chǎn)樣最多只能配制一個人工標樣），以減少人為的規(guī)律性。

l        混料：

當人為配制標樣后，必須充分混合均勻。我們發(fā)現(xiàn)：許多廠家在混料方面都做得不夠好。在樣品本身不均勻的情況下就進行化學全分析和儀器測量，即使是同一種樣品，化學分析時所取的樣與儀器測量時所取的樣很可能不一致，這樣必將導致儀器測量值與化學分析值之間存在很大的誤差，直接影響儀器測量的準確性?；炝鲜且粋€比較枯燥但又十分關(guān)鍵的工作，混料是否均勻?qū)竺娴墓ぷ髦陵P(guān)重要。如果這一環(huán)節(jié)做得不好，那么下面的工作即使做得再嚴格、再細致，也無濟于事?；炝弦?封閉的環(huán)境下進行，以減少輕基體元素含量的損失，避免造成標樣與待測生產(chǎn)樣品不一致。一般人工混合一個樣品至少要15-30分鐘。

l        化學分析：

熒光分析儀是以化學分析為基礎(chǔ)的，如果化學分析本身不很準確，將來做出的數(shù)學模型誤差就會很大甚至不能用。所以，為使化學分析結(jié)果準確，應由至少兩名優(yōu)秀分析人員各自做全分析，其分析結(jié)果誤差在GB/T176-1996允許誤差范圍內(nèi)時取其平均值作為最終結(jié)果。超差時應進行復驗、刪除錯誤值。分析過程中必須避免兩人互相對比、修改分析結(jié)果。

l 保存：系列標樣配制好后，用磨口玻璃瓶密封保存，貼上標簽，注明編號、日期，以備長期使用。

二． 標準樣品及待測樣品的成型

用X射線熒光儀精確分析礦物樣品需要適當?shù)臉悠分苽洌核袠悠方?jīng)粗磨后還必須進一步細磨，在30MPa 壓力下加壓成型，以減小顆粒效應、礦物效應、元素間吸收-增強效應。

l 細磨

白生料：稱量30g樣品（精確到0.05g），0.2g硬脂酸（精確到0.0001g）（助磨劑，以防止細磨過程中結(jié)塊，提高研磨效率），放入振動磨中，細磨2分鐘。

熟料：稱量30g樣品（精確到0.05g），放入振動磨中，往磨中加10滴乙醇，細磨2分鐘。

石膏、鐵粉：稱量30g樣品（精確到0.05g），1g硬脂酸（精確到0.0001g），放入振動磨中，細磨3分鐘。

砂巖、頁巖、粉煤灰：稱量20g樣品（精確到0.05g），2g硬脂酸（精確到0.0001g），放入振動磨中，細磨1分鐘。

上述細磨時間僅供參考。用戶應該根據(jù)本廠振動磨的研磨效率，通過實驗來確定研磨時間。一般可用一參考樣品，不斷增加對它的研磨時間，同時測量其特征X射線強度，直至測得的強度不再升高（或降低）趨于恒值為止。注意：在細磨每個樣品前，必須將振動磨的料缽清洗干凈。細磨后的樣品，放入小磨口瓶中保存，貼上標簽，注明樣品編號、日期。

助磨劑系分散劑，細磨時可防止結(jié)塊，提高研磨效率，降低電耗。助磨劑種類較多，如硬脂酸、甘油、乙醇、丙醇、異丙醇、三乙醇胺、尿素等。標樣和待測樣必須使用同一種助磨劑，更換助磨劑種類時應重新制備標樣細粉，重新壓片后制作工作區(qū)。

l        壓片

1. 磨具底座的上表面與模具套、隔套的內(nèi)外表面擦拭干凈，確保上面沒有殘留的樣品和硼酸，并按（圖1）組裝好模具。

2. 稱量7g（精確到0.05g）研磨均勻的樣品，倒入隔套的中間，并用整平桿把樣品攤均勻。

3. 稱量7g（精確到0.05g）的硼酸，并將其中的1/2均勻地倒入模具套與隔套的中間；輕輕地取出隔套，并將剩余的硼酸倒在樣品的上面，用整平桿將其攤平。

4. 按（圖2）將模具桿裝上。

5. 托著模具底座將整套模具放在壓力機工作臺的中間，將壓力加到30MPa并停留30s后，把模具卸下。

6. 取下模具底座，按（圖3）將模具倒置，并在上面放上退模套；手扶著退模套的中部，同時用膠皮榔頭猛擊退模套就可把樣品退出（也可將模具放在壓片機工作臺的中間同時旋下壓片機絲杠即可）。

7. 樣品表面不得有沾污、擦痕、裂紋，否則重新壓制，壓片背面用彩色軟筆注明編號、日期，然后正面朝上放入干燥器內(nèi)。

8. 擦凈模具等用具。模具長期不用時，應將其表面涂上一層黃油，以防止模具生銹。取放模具時要平穩(wěn)，以免劃傷底座，使壓片表面不平。

The technique of sample preparation is essential for obtaining a better result when analyzing samples. the technique of sample preparation will affect the accuracy of the result of the X-ray fluorescence analyzing.

1.the preparation of standard samples

the X-ray fluorescence analyzing method is different from the chemical method, it is a comparative measuring method ,which gets the accurate result by establishing the corresponding mathematical model after measuring a certain mount known samples(standard samples) .in another word, a series of good standard samples is as important as a good instrument. a good instrument is provided by us, while a good series of standard samples is provided by the users’ laboratory. A good series of standard samples be of the following features: Be representative, Be of certain content range, and Be of accurate chemical analyzing result, the details are as follows:

●Sample amount:5-10.each mass:50-100gram

●Be representative: the samples can represent the actual products of your factory, and is the instantaneous samples from the actual production line, and try to avoid the artificial prepared samples, which will bring in subjective factors. and do not use national standard samples, for each factory use different raw materials and different formula, and will get different mathematical model.

●The content range of main chemical constituents.

The content range of main chemical constituents in standard samples should cover the variation range of content of main chemical constituents in normal products, and should keep distance with each other and be well-distributed. take the cement raw material as an example: in normal condition, in raw material (white raw material) if the target value of content of CaO is 42%, then, to keep distance, the minimum of the content of CaO will be about 39%,and the maximum of it will be about 45%,to make the content of CaO well-distributed, the content of CaO should be 39%(minimum),40%,,41%,42%,43%,44%,45%(the maximum). You may prepare extra several this kind of standard samples of which the content be in the normal variation range(41%~43%). (Tab 1)

It’s a series of standard sample of white raw material, and the target value of main chemical constituents is as following respectively:

Al2O3:3.1%,   SiO2:13%,    CaO:41.5%,    Fe2O3: 3.5%

In tab.1, we can get that: the content of main raw material keep a certain distance from each other and be well-distributed. the variation range of Al(the maximum subtract the minimum) is2.5%, the variation range of Si is 4-6%, the variation range of Ca is 4%-6%, the variation range of Fe is 3%.there is no factitious regularity between Al and Si, Si and Ca, Ca and Fe.

Generally speaking, the variation range of high content element is larger than the variation of low content element, and the lower the content is , the smaller the variation range 

●Preparation of the high content samples and low content samples.

In the series of samples, the samples whose content is near the target value can be collected from the production line. Those samples whose content is much higher or lower than the target is hardly available directly from the normal production line. We must prepare those sample by ourselves. Take the white raw material as example (Tab.1). In normal conditions, the content of CaO is controlled in 41%~42%，If we want to get the samples above 45%, we must add limestones in the raw material to increase the content of CaO and decrease the content of Al2O3, SiO2, Fe2O3, in the same way, we can prepare high SiO2 samples and high Fe2O3 samples. the samples whose content is near the target value must be collected directly from the production line.

NOTICE: try to avoid preparing artificial samples. When sample has to be prepared manually, you should add only a little raw material to a mass of practical 

manufacture samples, and the raw material must be same as the manufacture samples. In order to reduce factitious regularity, users must not use the same manufacture material to prepare different samples(one manufacture sample can be use to prepare for only one manual sample).

●mixing material:

When users prepare sample manually, it must be well-distributed. We discovered that many users don't do well in mixing material .If the materials are not well distributed, even for the same sample, the parts for total-chemical analysis may be different from the parts for instrumental analysis, this may lead to large error between the chemical analytical values and instrumental analytical values, and then influence the accuracy of the instrument. Mixing material is critical for subsequent process though dreary, however, If this step is not done well, even if subsequent processes is done so strictly, so meticulously, the result will be beyond remedy. Mixing material must be done in a entirely sealed environment, for lessening the loss of light matrix element content. and avoiding the variance between sample and the things which will be tested. Generally, it needs 15-30 minutes to mix a sample manually.

●Chemical analysis:

fluorescence spectrometer analysis is based on chemical analysis, if chemical analysis is not accurate, the mathematical model will have great errors, even can not be used. So, for the sake of accuracy of chemical analysis, this step must be done by two excellent operator, and adopt the average as the final result when the error of each result is within the allowable range of the GB/T176-1996. if the error is oversized, users should check and delete and wrong value. In this process, the operaters must not compare with each other, nor juggle the results.

● storage:

when sample series is prepared well, seal them in ground glass bottles,and lable them for long-term use.

2：molding of standard samples and unknown samples

Mineral samples for XRF require proper sample preparation, all the samples need both coarse grinding and subsequent fine grinding, and molded under 30Mpa pressure to correct the granular effect, grain effect and matrix effect.

●Fine grinding

Raw material: Weight 30g samples(accurate to 0.05g),0.2g stearic acid(accurate to 

0.0001g)(grinding aids, preventing caking and improving grinding efficiency), fill in vibration mill, grind for 2 minutes.

Clinkers: weight 30g clinkers(accurate to 0.05g),1g stearic acid(accurate to 0.0001g),fill in vibration mill, grind 3 minutes.

Gypsum, iron powder: weight 30g sample(accurate to 0.05g),1g stearic acid(accurate to 0.0001g),fill in vibration mill, grind 3 minutes.

Sand stone , shale, fly-ash: weight 20g sample(accurate to 0.05g),1g stearic acid(accurate to 0.0001g),fill in vibration mill, grind 1 minutes.

All the above grinding time is for reference only. Users should fix the best grinding time according to actual grinding efficiency. user can increase the grinding time of a reference sample, and at the same time, measure the intensity of the characteristic X-ray, until the right time that the intensity do not rise with the increase or decrease of grinding time.

 NOTES: users must have the container of the vibration mill cleaned before grinding every sample. and the-grinded sample must be stored in ground bottle flasks, and labled with sample number, and date.

Grinding aid plays the role as dispersant, preventing caking, improving grinding efficiency and reduce energy consumption. there are many sorts of grinding aid, such as stearic acid, glycerol and alcohol, propanol, isopropanol, 

triethanolamine,and urea etc. Standard samples and unknown samples must use the same grinding aid. changing the grinding aid must change the standard sample powder, and squash again and establish new work area.

●Squashing

1. The upper surface of the base of mill, the inner and outer surface of mill sleeve, must be cleaned and make sure that no residues and boric acid left. Assemble the mill according to Fig 1.

2. Weight 7g(accurate to 0.05g) grinded sample, and fill in the sleeve gasket and level the sample by leveling rod.

3. weight 7g(accurate to 0.05g)boric acid, fill half of it into the middle of the mill sleeve and sleeve gasket. drop out the sleeve gasket carefully, and fill in the left boric acid and level it.

4. Assemble the mill rod.(Fig 2)

5. Carry the mill to the center of the working platform of the presser, set the pressure to 30MPa, keep for 30s and disassemble the mill.

6. take the mill base out and invert the mill（Fig.3）. Put on removal, and buttress the middle of the removal, then beat on the top of the removal with rubber hammer. you can take out the sample.

7. The sample should not be contaminated, scraped, or splitted, otherwise, you need to do it again. It is suggested to write the number, date on the back of the sample with the pastel.

8. Clean the mill. if the mill was left unused for a long time, grease should be smeared on the surface to prevent rusting. The mill should be carried carefully to avoid base scrape.