Claims:
We Claim:

1) A method of analyzing the impurities in alumina sample, comprising:

a) contacting said alumina sample with a reagent mixture comprising ortho phosphoric acid, hydrofluoric acid and water;
b) heating mixture of step (a) at a temperature in the range of 200oC to 230oC for a duration of 10 to 20 minutes; and
(c) analyzing the heated sample of step (b) for impurities.

2) The method as claimed in claim 1, wherein ramping time of heating of step (b) is in the range of 25 to 40 minutes.

3) The method as claimed in claim 1, wherein said heating is performed in a microwave.

4) The method as claimed in claim 3, wherein the power of vessel distribution of microwave is in the range of 1100 W to 1200 W.

5) The method as claimed in claim 1, wherein the ratio of ortho phosphoric acid, hydrofluoric acid in reagent mixture is in the range of 7: 0.4 to 9: 1 and the remaining being water.

6) The method as claimed in claim 1, wherein ratio of alumina sample to reagent mixture in step (a) is in the range of 0.07: 1.2 to 0.05: 0.5.

7) The method as claimed in claim 1, wherein said analyzing of samples is performed by inductively coupled plasma mass spectrometry or inductively coupled plasma optical emission spectroscopy.

Dated this 16 September 2021
M. Kisoth
IN/PA-2259
Agent for the Applicant
, Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2006

COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE OF THE INVENTION
METHOD OF ANALYZING THE IMPURITIES IN HIGH PURITY ALUMINA

APPLICANTS
Aditya Birla Science and Technology Company Private Limited
of address
Plot No.1 & 1-A/1, MIDC Taloja, Panvel
Navi Mumbai - 410208
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
[1] The present invention in general relates to material elemental analysis, in particular the invention relates to a non-invasive method for analyzing quantities in high purity alumina.
BACKGROUND OF THE INVENTION
[2] High purity aluminium oxide (Alumina) of different grades is used in various microelectronic devices and structural materials. Alumina is considered to be one of the most refractory ceramic materials. High purity alumina is a requirement for production of sapphire crystal, fluorescent powder, electronic ceramics, fine ceramics, structural ceramics, fire resistive material, stainless steel polishing grinding, high-voltage switch gear, semiconductors etc.
[3] The HPA are very stringent as compared to commercial grade alumina. Alumina with significantly higher purities of 99.99% (4N) and 99.999% (5N) indicates that the concentration of all the impurities are limited only to 100 ppm and 10 ppm respectively. Accurate analysis of these impurities at ppm & ppb levels is major challenges. Critical impurities are Na, Ca, Mg, K, Fe, Si, Cr, Zn, As, etc. In this context, effective & systematic analysis of impurities measurement in HPA is crucial.
[4] The application of alumina in different industries is based on the purity of the materials such as 99.9%, 99.99%, & 99.999% etc. In particular, the need for the determination of trace impurities in high-purity alumina is of high importance in semiconductor industry. Since the properties of alumina is directly proportional to impurities, determination of impurities in high purity alumina is essential.
[5] Analysis of trace impurities in alumina is performed either by solid sampling or solution-based methods. Solid sampling includes by Glow Discharge Mass Spectrometry (GD-MS), and Wavelength Dispersive X-Ray Fluorescence & Energy Dispersive X-ray fluorescence (WD & ED XRF).
GD-MS is providing complete material characterization. The ideal tool for the direct analysis of metals, high purity conductive and semi-conductive materials, the system can detect and routinely quantify almost all the elements present in a solid sample at the ppm or below the ppb range. But this technique is very expensive and low limitation of sample size < 5ug only. In this case particle size also criteria for accurate measurement of analysis.
WD & ED XRF techniques are using for major chemical analysis i.e. ppm to % level, maybe it is not accurate in ppm and ppb levels.
[6] Solution based methods can be realized either by fusion or by open acid digestion techniques. Solution based method includes, inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectroscopy (AAS) requires a complete analysis of the samples.
[7] Open digestion techniques are known (common technique) to be more reliable, but they are more time consuming, cross contamination & loss of trace metals concentrations etc. and their efficiency strongly depends on different physicochemical parameters of the sample. Conventionally, the hydrochloric acid, nitric acid and sulfuric acids were used in order to confirm the purity of the alumina. Several methods have been used for the digestion of this material for trace element analysis by inductively coupled plasma optical emission spectrometry (ICP-OES). However, the impurity analysis using acid digestion is not completely efficient since the complete dissolution of alumina in acid is a challenge. Further, the samples are also susceptible to contamination in fusion technique and acid digestion methods.
[8] Microwave digestion of alumina has been extensively studied with various acids and acid mixtures. The performance of microwave digestion methods is less time consuming, contamination free and there is no loss of the analytes during the digestion process.
SUMMARY OF THE INVENTION
[9] An object of the invention is to provide a simple and practical non-invasive method to analyze impurity in a high purity alumina sample.
[10] Another object of the invention is to provide method to analyze impurities, which is capable to minimize contamination and detecting and analyzing the trace level impurities with high level of accuracy & precision.
[11] In an aspect, the invention provides a method of analyzing the impurities in alumina samples, mixing an alumina sample with a reagent mixture comprising ortho phosphoric acid, hydrofluoric acid and water. The reaction mixture of alumina sample and reagent is heated at a temperature in the range of 200oC to 230oC for a duration of 10 to 20 minutes. The heating results in digestion of samples by the reagents. The digested sample is analyzed by spectroscopy techniques for measurement of elemental impurities like Fe, Cr, Ni, Cu, Sb, B, Mn, Zn, Cd, As, Hg, Pb, Na, Ca, Mg, K & Si etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[12] The foregoing summary, as well as the following detailed description of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of assisting in the explanation of the invention, the details are shown in the drawings embodiments which are presently preferred and considered illustrative. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown therein. In the drawings:
[13] Figure 1 is the data on comparison study with CRM.
[14] Figure 2 is the data on comparison study with spiked concentration.
[15] Figure 3 is the data on % elemental recovery achieved by present process.
[16] Figure 4a-4c are elemental linearity graphs for quantification of elemental concentrations in HPA
DESCRIPTION OF THE INVENTION
[17] In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual process parameters, substituents, and ranges are for illustration only; they do not exclude other defined values or other values falling within the preferred defined ranges.
[18] As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.
[19] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention
[20] As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e. to mean including but not limited to.
[21] As used herein, “microwave digestion” as used herein refers to microwave digestion system is used to digest the metals in a closed vessel allows, heating the acids above its boiling point by using microwave energy (electromagnetic waves).
[22] As used herein, “Inductively coupled plasma optical emission spectroscopy (ICP-OES)” as used herein refers to a technique, when plasma energy is given to sample, the atoms/ions can absorb energy and move electrons from the ground state to an excited state, those excited atoms emit electromagnetic radiation at wavelength of a particular element as they transition to lower energy level.
[23] As used herein, the term “Inductively coupled plasma mass spectrometry (ICP-MS)” as used herein refers to a technique, which uses plasma to ionize the sample for determination of trace multi elemental and isotopic concentrations (ppb & ppt) in a sample, each ion has a particular mass to charge ratio i.e. m/z.
[24] In an embodiment, the method of analyzing the impurities in alumina sample, comprising:
a) contacting said alumina sample with a reagent mixture comprising ortho phosphoric acid, hydrofluoric acid and water;
b) heating mixture of step (a); and
(c) analyzing the heated sample of step (b) for impurities.
[25] In the first step, the hydrofluoric acid and orthophosphoric acid are mixed in a ratio of 7: 0.4 to 9: 1 (V/V) and the remaining being water. This reagent mixture serves as a catalyst for digestion of the high purity alumina sample. The ratio of alumina sample to reagent mixture is in the range of 0.07: 1.2 to 0.05: 0.5.
[26] To the reagent mixture, high purity alumina sample is added. The mixture of reagent and alumina sample is taken in a Teflon vessel (suitable container).
[27] Microwave digestion of the sample is carried out by placing the container having reagent and alumina sample in a microwave digester for digesting the sample. The digestion of sample is performed by microwaving the container at a temperature in the range of 200oC to 230oC for a duration of 10 to 20 minutes. The ramping time of microwave digestion is in the range of 25 to 40 minutes. In an embodiment, the power of vessel distribution of microwave digester is in the range of 1100 W to 1200 W.
[28] In an embodiment, analyzing of samples is performed by inductively coupled plasma mass spectrometry or inductively coupled plasma optical emission spectroscopy.
DETAILS OF ICP-OES OR ICP-MS PROCESS PARAMETERS:
Instrument: ICP-OES
Make & Model: Agilent 5110 SVDV.
Instrument Conditions: (Operating parameters)
Parameters Values
Torch Standard DV torch (1.8 mm ID injector)
Nebulizer Standard Sea spray
Spray chamber Standard double-pass glass cyclonic spray chamber
Read Time (s) 5
Replicates 3
Sample uptake delay (s) 0
Stabilization time (s) 15
Rinse time (s) 3
Fast pump (80 rpm) Yes
Background correction Left and/or right background correction
RF power (kW) 1.4
Nebulizer flow (L/min) 0.70
Plasma flow (L/min) 12.0
Aux flow (L/min) 1.0
Pump Speed (rpm) 12.0
Viewing height (mm) 8.0

SELECTION OF WAVELENGTH (?):
[29] Wavelength selection followed by trails and error basis with known concentration of reference standards, which are took into the consideration: (a) the freedom from spectral interferences; (b) the different sensitivities and expected concentration in the samples. The selected analytical wavelengths are compiled below.
[30] Elemental wavelengths (nm) selected/used for measurement of elemental concentrations in the samples., Iron 238.204, Potassium 766.491, Lithium 670.783, Magnesium 279.553, Manganese 257.610, Sodium 589.592, Nickel 231.604, Lead 220.353, Zinc 213.857, Silver 328.068, Boron 249.772, Barium 455.403, Calcium 396.847, Cadmium 214.439, Cobalt 238.892, Chromium 267.716, Copper 327.395, Antimony 206.833, Arsenic 193.691, Beryllium 313.042, Molybdenum 203.843, Phosphorus 214.912 Selenium 196.022, Silicon 251.607, Titanium 334.936 Vanadium 292.399 & Yttrium (Internal standard) 371.024, 324.221.

[28] ICP-MS PROCESS PARAMETERS:

Make & Model: Perkin Elmer NexION 350x.
Instrument Conditions: (Operating parameters)
Parameters Values
Nebulizer Glass concentric
Spray chamber Glass cyclonic
Cones Nickel
Plasma gas flow 18.0 L/min
Auxiliary gas flow 1.2 L/min

Nebulizer gas flow 0.98 L/min
Sample uptake rate 300 µL/min
RF power 1600 W
Total integration time 0.5 (1.5 seconds for As, Se, Hg)
Replicates per sample 3
Universal Cell Technology Collision mode

WORKING EXAMPLES
EXAMPLE 1: High purity alumina CRM determination by ICP-MS
[31] 0.5 gm of an alumina sample was taken in a teflon vessel. To the alumina sample, 8.0 ml of ortho phosphoric acid of concentration 85% and 0.5ml of hydrofluoric acid of concentration 40% were added. The teflon vessel is placed in a microwave digester.
The temperature of microwave was gradually increased over a duration of 20 minutes to a temperature of 220oC. The temperature of 220oC was maintained for a duration of 20 minutes. The microwave digestion of samples resulted in complete dissolution of high purity alumina. The microwave digested alumina was analyzed for impurities by ICP-OES or ICP-MS.
[32] Sample digested on Microwave Digestion system and sample analyzed by ICP-MS., Calibration linearity range: (1.0ppb to 100.0 ppb) 1.0, 2.5, 5.0, 10.0, 25.0, 50.0 & 100ppb. The results of the sample values are very close to the CRM (certified reference material) value are provided in table 1.

Table: 1
[33] Recovery study on ICP-MS & ICP-OES with known concentration of spike standard solution and CRM of Alumina- Al2O3. The recovery obtained in the range of 90 to 105% for all the elements are shown in table 2 and table 3 (concentration in ppm).

EXAMPLE 2: High purity alumina in house samples for determination of trace metals by ICP-OES
[34] 0.5 gm of an alumina sample was taken in a teflon vessel. To the alumina sample, 8.0 ml of ortho phosphoric acid of concentration 85% and 0.5ml of hydrofluoric acid of concentration 40% were added. The teflon vessel is placed in a microwave digester.
The temperature of microwave was gradually increased over a duration of 20 minutes to a temperature of 220oC. The temperature of 220oC was maintained for a duration of 20 minutes. The microwave digestion of samples resulted in complete dissolution of high purity alumina. The microwave digested alumina was analyzed for impurities by
ICP-OES.
Calibration linearity range: (0.05ppm to 5.0 ppm) 0.05, 0.1, 0.5, 1.0, 2.5 & 5.0ppm. Results in ppm (Elemental concentrations in ppm) are shown in Table: 4

Table 4
[35] One of the major challenges of prior analytical method are sample digestion and accurate measurement of elemental impurities in ppm & ppb level. It was observed that, in the claimed method, alumina samples are digested by using microwave digestion system in the ratio of orthophosphoric acid and hydrofluoric acid, in this combination the samples are completely digested. The claimed method is accurate and reliable for measurement of trace metal concentration in high purity alumina products by using ICP-MS & ICP-OES.