A methodology for developing nanomaterial testing standards

Nanomaterial testing standards play a crucial role in the international standardization of nanotechnology within ISO. These standards specify the characteristics of nanomaterials that need to be measured, as well as the methods and procedures used for conducting such measurements. This paper presents a methodology for the development of nanomaterial testing standards, which addresses raw nanomaterials and intermediate materials like composites, suspensions, films, and coatings containing raw nanomaterials. The methodology is outlined as a scenario comprising several stages towards the goal, where essential actions to be conducted in standardization are identified and integrated into the standard. Furthermore, this paper highlights the significance of these testing standards as a technical foundation for material specification and certification, with the ultimate aim of facilitating the industrialization of nanomaterials by ensuring consistent quality and enabling reliable performance.


Introduction
Nanotechnology has made significant progress thanks to the production of various new nanoscale materials and the development of measurement techniques that enable detailed and easy characterization of these materials.Carbon nanotubes and graphene are examples of important nanoscale materials.Additionally, several types of scanning probe microscopy, including scanning tunnelling microscopy and atomic force microscopy, have been developed as measurement techniques.
As industrialization has progressed, many nanomaterials have moved from basic research to application development and the market transaction phase.Standardization plays a crucial role in promoting the dissemination of technology and growth of markets by establishing agreed-upon technical terminology and practices in industry and society.The International Organization for Standardization (ISO) initiated the international standardization of nanotechnology in 2005 by establishing the technical committee TC 229 for nanotechnologies.Academic societies also exhibited interest in nanomaterial standardization.Productive discussions were made across research and standardization spheres for nanomaterials between American Chemical Society NANO and international nanotechnology standards developing organizations [1,2].
The primary objective of nanotechnology standardization is to facilitate the responsible and early industrialization of the technology.Developing nanomaterial testing standards is one of the most critical components of this process.These standards serve the purpose of accurately assessing the quality of nanomaterials by specifying their important characteristics, as well as the applicable measurement methods and procedures.Additionally, nanomaterial testing standards play an essential role in establishing a solid foundation for nanomaterial specification and certification.Consequently, these standards make a significant contribution to the industrialization of nanomaterials by ensuring consistent quality, enabling reliable performance, and facilitating market acceptance.In this regard, it is important to establish a methodology for the development of nanomaterial testing standards.
The 4th Working Group (WG4) was established in 2008 within ISO TC 229 with the responsibility of developing material specifications in the field of nanotechnology.Collaborating with other TC 229 working groups responsible for standardization related to terminology, measurement, and characterization, as well as environment, health, and safety, WG4 directed its efforts towards developing nanomaterial testing standards.
During the inception of TC 229, when novel nanomaterials were emerging, the methodology to develop testing standards for such materials was not yet established.Nonetheless, through expert dialogues during WG4's standardization activities, a refined methodology for developing high-quality nanomaterial testing standards took shape.The primary idea behind this methodology was elucidated in general [3] and specific contexts [4,5].
This paper comprehensively presents the methodology, emphasizing the development of high-quality nanomaterial testing standards.It also describes how nanomaterial testing standards are utilized for the industrialization of nanomaterials through material specification and certification, while incorporating the latest outputs from WG4.Specifically, essential actions needed for standardization are identified and integrated into the framework.The presented methodology is intended to be used not only by international and national standard-developing organizations but also by other entities such as consortia, industrial associations, and companies involved in the phases planning, developing, and revising nanomaterial testing standards.
In this paper, the term "nanomaterial" refers to raw nanomaterials and intermediate materials such as composites, suspensions, films, and coatings containing raw nanomaterials."To specify" means giving exact instructions, while "being in conformance with a standard" means following the instructions given by the standard as required."Nanomaterial testing standard" refers to an agreed-upon technical document that specifies the characteristics to be measured for nanomaterials and their measurements."Nanomaterial specification" refers to a technical document that specifies the values of characteristics of nanomaterials."Measurement procedure standard" refers to an agreed-upon technical document that specifies the measurement procedure for a specified measurement method.

Market relations and nanomaterial testing standards
This chapter describes the relationship between the market and testing standards in the field of nanomaterials, which serves as a prerequisite for this paper.

Production chain and standards
Figure 1 illustrates a typical production chain for nanomaterials.At the top layer of the chain, source material manufacturers provide the materials needed to make nanomaterials.Nanomaterial manufacturers produce their own nanomaterial products by using the source materials.Intermediate manufacturers then procure nanomaterials from the nanomaterial manufacturers to make their own products such as composites, coatings, films, suspensions and others.Product manufacturers make finished products such as electronics, transportation equipment, optical goods, medical products, food additives, and cosmetics for consumers by using the intermediate materials.
As a product is transacted between the adjacent layers of the production chain, the buyer and seller generally agree on the product specification.The testing  standard can contribute to the assessment of product quality at every transaction in the production chain.

Market growth and standards
Figure 2 illustrates the general market growth of a new material, from the basic research stage to maturity, through application development and market expansion.It is assumed that many nanomaterials follow similar processes.During the basic research stage, researchers conduct various experiments to create new nanomaterials and clarify their characteristics.At this stage, standardization is not necessary; instead, researchers should freely explore different scientific endeavours.
Promising nanomaterials are selected from the results of basic research and move on to the application development stage.During this stage, various development possibilities are explored for industrial use, and manufacturers and users engage in trial and error by providing sample materials.Candidate nanomaterials are then screened and traded in the market.Furthermore, when multiple manufacturers offer nanomaterials with distinct characteristics, it becomes necessary for users to select an appropriate manufacturer for procurement.Testing standards for nanomaterials can help manufacturers and users at this stage.
Manufacturers must specify the key characteristics of nanomaterials and report their measurement results using specified methods.At this stage, nanomaterials are differentiated fairly and transparently based on testing results, allowing users to select the most suitable materials for their purposes.Competition among manufacturers over the quality of nanomaterials will activate the market.
As nanomaterials are accepted by the market, the number of buyers will increase.When nanomaterials are used in large quantities for specific applications, those with guaranteed characteristic values are preferred.Standardized material specifications are required at this stage, and materials that satisfy certain function and performance criteria will benefit users.Once nanomaterial specifications are standardized, the emphasis will likely shift from quality competition to price competition.As a result, nanomaterials that have become more convenient due to standardized specifications will expand their application fields, grow the market, and reach maturity.
If appropriate testing standards are developed during the application development stage, fair and transparent assessment of nanomaterials will ensure smooth business transactions.Without such standards, the market would possibly be chaotic, with inferior products and de facto standards proliferating, leading to the trading of misplaced nanomaterials by business operators.Nanomaterial specifications in the expansion stage promote mass production of nanomaterials.It is worth noting that most steel materials have already reached this stage.

Transactions and testing standards
This section provides an example of how material testing standards are utilized in market transactions.Figure 3 demonstrates that initially, the buyer (user) of a nanomaterial provides a procurement specification to the seller (manufacturer), which can use the testing standard as a procurement model.The procurement specification outlines the desired characteristics of the nanomaterial as specified by the buyer.When the seller confirms that it can provide nanomaterials that meet the procurement specifications, the buyer and seller reach an agreement, and a business contract is formed.
The seller produces the nanomaterial to meet the procurement specifications and measures its required characteristics.A test report is provided to the buyer along with the produced material.When the test report satisfies the procurement specification, the transaction is completed.If necessary, the buyer conducts acceptance inspection of the nanomaterial using the agreed-upon measurement methods and procedures to ensure that the reported results are reasonable.Another example of the use of nanomaterial testing standards is the catalog that sellers provide to the public.The catalog provides the characteristics specified by the testing standard, as well as representative measurement results obtained using the specified measurement methods and procedures.The sellers produce the nanomaterials in large quantities and provide the required quantity to the buyers, who can have confidence in the quality of the nanomaterials based on the nanomaterial testing standard.

Flexible use of testing standards
When a buyer and a seller agree to conduct business in accordance with a testing standard, the seller must implement all the requirements of that standard.However, it is possible to deviate from the provisions of the standard if they agree, as shown in Figure 4(a).For instance, the parties may add other characteristics or exclude some of the existing characteristics, or they may agree to change the measurement method or procedure from the standard.Unlike laws, standards can be used flexibly by agreement between the buyer and the seller.It should be noted, however, that if any deviations from the standard occur, it can no longer be said that the product assessment is in conformance with the standard.
Figure 4(b) schematically shows the case where there is no established testing standard for a nanomaterial.In this situation, in order to conclude a transaction contract, the buyer and seller must negotiate all characteristics, their definitions, and how to measure them from the beginning.Such negotiations for each new contract would be a great loss for the business when transactions are frequent in the market.Testing standards have the effect of avoiding such individual negotiations, enabling smooth and reliable transactions.

Scenario for nanomaterial testing standards
This chapter presents a methodology in the form of the scenario for developing high-quality nanomaterial testing standards.The term "high quality" refers to standards that are well-organized and user-friendly, while also providing practical value to the relevant industrial communities working with nanomaterials.

Developing the scenario
Figure 5 illustrates the devised scenario for developing nanomaterial testing standards, which consists of a series of stages leading towards the goal.Each stage includes a list of standardization items to be considered and/or conducted, and these standardization items are progressively integrated into the final goal as the scenario unfolds.
The scenario comprises the following stages: (a) surveying markets and literature, (b) identifying key issues, (c) defining the scope, (d) specifying standardization items, (e) finalizing the overall framework, and (f) achieving the ultimate goal of establishing a highquality nanomaterial testing standard.It is important to note that the standardization process does not always follow a linear path from (a) to (f); discussions often occur back and forth between stages within WG 4 as progress is made towards the overall goal.Critical issues may necessitate a comprehensive review of the entire scenario for resolution.Through this iterative approach, it has been recognized that careful consideration and conduction of each standardization item listed in Figure 5 are essential to ensure the development of high-quality standards.

Surveying markets and literature
In the initial stage of the scenario, a survey is conducted on commercially available nanomaterials in relevant markets.Assessing the market maturity of these nanomaterials is crucial as it directly impacts the standardization process.To address health and safety concerns, the survey also includes consumers and regulators.Nanomaterials that are solely of interest to academic communities are excluded from this survey.
The survey also involves identifying the manufacturers (sellers) and users (buyers) involved in the production chains of these commercialized nanomaterials, as depicted in Figure 1.Gathering information from users can provide valuable insights into the potential applications of the nanomaterials.Additionally, it is important to consider the availability of testing laboratories specializing in measuring relevant characteristics.These laboratories can be either independent organizations or in-house facilities of the manufacturers.
A comprehensive review of relevant literature is conducted, encompassing existing standards and scientific papers that focus on the characteristics and measurements of relevant nanomaterials.It is advisable to consider international, regional, and national standards, as well as peer-reviewed journal articles.

Identifying key issues
In the second stage of the scenario, the survey results are used to identify key issues concerning the nanomaterial testing standard.This allows for the appropriate definition of the standard's scope in the next stage.The key issues include selecting industrially significant nanomaterials, identifying promising application products that utilize nanomaterials, and anticipating the performance of these application products.
When selecting nanomaterials for standardization, priority should be given to those of global interest that are already commercialized.Nanomaterials that are solely of academic interest should be excluded, while those deemed promising from an industrial perspective should be prioritized.It is also important to clarify the major applications of the nanomaterials, as the characteristics to be measured depend on the desired performance of the application products.
The referencing includes existing standards and scientific papers relevant to the standardization process.Normative references, which are standards essential for conducting the requiring provisions of the nanomaterial testing standard, should be identified.Informative references should not be included in the category of normative ones, as users would be required to purchase all of these standards to comply with the standard.Instead, informative references can be cited in the Bibliography to assist users in better understanding the provisions of the standard.

Defining the scope
The third stage of the scenario deals with defining the scope of the nanomaterial testing standard.This establishes the extent to which the standard will be applied and what will be standardized within it.The scope is determined based on the key issues identified in the previous stage.The standardization items are identified and organized into the scope.Typically, these include the category of nanomaterials with their intended applications, as well as the characteristics to be measured with their corresponding measurement methods and procedures.Additionally, if necessary, the intention or purpose of the standard can be mentioned.Any specific items not covered by the standard should also be explicitly stated.

Specifying standardization items
At the fourth stage of the scenario, the standardization items are specified in detail and organized into the nanomaterial testing standard, based on the scope defined in the previous stage.This includes identifying the specific nanomaterial to be standardized, the characteristics to be measured, the measurement methods and procedures to be adopted, and the items to be reported.

Nanomaterials
The selection of the nanomaterial to be standardized is a crucial aspect of the nanomaterial testing standard.Typically, the following attributes need to be specified: chemical composition, morphology (whether it is a nano-object or a nanostructured material), and form (such as dry powder, suspension, composite, porous material, etc.).For nano-objects, the morphology can be further specified as nanoparticle, nanofiber, or nanoplate.Surface modifications of nano-objects can also be mentioned.In the case of nanostructured materials, the morphology can be specified based on whether the nanostructures exist on the material surface or inside the material.The material type of the nanostructures and the base materials should also be specified, such as metal oxide nanoparticles in polymer, cellulose nanofibers in water, nanopores in amorphous silica, etc.General attributes of the nanomaterial to be standardized are typically specified in the scope, while specific attributes are further detailed in separate clauses.

Characteristics
The characteristics to be measured are the physical or chemical parameters of the nanomaterial that significantly influence the desired performance of the application products.These characteristics are desired to be specified along with the intended application products and their desired performance.
To ensure clarity and scientific accuracy, the characteristics are defined in a scientifically rigorous manner.They can be either intrinsic parameters or parameters defined by the measurement method for the nanomaterial.
The importance of the characteristics varies depending on the application of the target nanomaterial.Therefore, the characteristics can be classified into two categories: core characteristics that are universally important for general applications and must be measured, and optional characteristics that are specifically relevant to individual applications and are recommended to be measured.The specified characteristics are typically presented in a table format.Example formats for the core and optional characteristics are provided in Tables 1 and 2, respectively.

Measurement methods
Measurement methods refer to the principles of measurement and the fundamental measurement conditions that significantly impact the measurement results.The selection of measurement methods to be adopted is based on the accuracy as well as industry usage and global commercial availability.Preferably, inexpensive equipment and simple operations are prioritized.In a nanomaterial testing standard, there are three options for specifying the measurement method(s): requirement, recommendation, and information supply.
When a nanomaterial testing standard requires the adoption of a specific measurement method(s), it means that measurement methods other than that are excluded.This option is chosen when the required measurement method(s) is firmly deemed the most suitable among others for the nanomaterial and characteristic.
When a nanomaterial testing standard recommends the adoption of one or more measurement methods, standard users have the flexibility to select the most suitable measurement method from the recommended ones or choose other methods based on mutual agreement among involved parties.This option is chosen when the recommended measurement method(s) are equally suitable to others, or when the most appropriate measurement method depends on specific nanomaterials, measurement conditions, or intended applications.
When a nanomaterial testing standard supplies information on potentially applicable measurement methods, standard users are responsible for selecting a measurement method based on their specific situations or agreeing on alternative measurement methods with involved parties.This option is chosen when the suitability of the measurement methods varies entirely depending on the specific nanomaterials or intended applications.
Regardless of the chosen option, nanomaterial manufacturers should report the adopted measurement method to users when providing the measurement results of nanomaterial characteristics.

Measurement procedures
Measurement procedures refer to the detailed technical processes adopted to determine values of nanomaterial characteristics according to the specified measurement methods.This includes sample preparation, operation of measuring equipment, measurement conditions, data analysis, and more.The validity of the measurement procedure can be evaluated through interlaboratory comparisons, reference standards, reference materials, and other means.Generally, measurement procedures widely accepted by the industrial community are preferred, unless there are serious issues.
The nanomaterial testing standard specifies the measurement procedures for each individual measurement method of a nanomaterial characteristic.Similar to the three options mentioned in 3.5.3for specifying the measurement method, there are three options for specifying the measurement procedure in the nanomaterial testing standard: requirement, recommendation, and information supply.The descriptions given in 3.5.3for the measurement method options apply similarly to the options for the measurement procedure.Regardless of the chosen option, manufacturers should report the adopted measurement procedure to users whenever requested.
Measurement procedures can be described in a separate document or incorporated into the nanomaterial testing standard.Organizations preferably document the measurement procedures for their own stakeholders, such as individual companies, industrial associations, consortia, national organizations, and international organizations.

Reporting
The nanomaterial testing standard requires manufacturers to report to users the measurement results, measurement methods and procedures adopted, and general information about the supplied nanomaterial.
Furthermore, when the shelf life of a nanomaterial is an important characteristic, the nanomaterial testing standard can also require manufacturers to report it to users.The shelf life is defined as the recommended time period during which a product can be stored, maintaining acceptable quality of specified characteristics under expected or specified conditions of distribution, storage, display, and usage.
It is important to note that the testing standard does not specify a specific value for the shelf life of the nanomaterial, as it is not a material specification standard.Instead, it can require manufacturers to report the shelf life of the target nanomaterials by specifying the characteristics to be assessed and their acceptable variations as well as measurement methods and procedures to be adopted for the assessment.The following are examples of reporting items for the shelf life: The manufacturer's guaranteed shelf life (if requested), along with the measurement results of homogeneity, dry solid content, and viscosity at the end of the shelf life, with agreed storage conditions and any acceleration test method used (if applicable).The supplier's guaranteed shelf life and the method used to determine it.

Finalizing the framework
The fifth stage in the scenario involves finalizing the overall framework, as depicted in Figure 5(e).During this stage, the normativity and flexibility of the standard are determined, while its reliability and integrity are assessed.

Normativity
The nanomaterial testing standard comprises technical provisions, each specifying standardization items."Normativity" of these standardization items refers to their normative status, which can be categorized as requirements, recommendations, or information supplies.These standardization items within the nanomaterial testing standards encompass the characteristics of nanomaterials to be measured, as well as the methods and procedures to be adopted for measuring each characteristic.
A "requirement" statement mandates the implementation of the standardization item, excluding any alternatives.A "recommendation" statement allows user discretion, with an emphasis on the recommended item.An "information-supplying" statement provides valuable or interesting information without requiring or recommending any specific standardization items.Statements carrying requirements are deemed "normative," while those without requirements are labelled as "informative."When describing a provision in the nanomaterial testing standard, a clear definition of the intended normativity for each standardization item is crucial.
In general, the overall normativity of a nanomaterial testing standard advances from a primitive level to a mature one as technology progresses and the market expands.Table 3 presents provision normativity levels (PNL) in ascending order, indicating the normativity for each standardization item.
Symbols "N" and "I" in Table 3 indicate that standardization items are stated in a normative and informative manner, respectively.A dash (-) indicates that a standardization item is not specified in the testing standard.For example, the symbol "N" or "I" in the "Characteristic" column indicates that the characteristic must be measured, or may or may not be measured, respectively.The symbols "N" or "I" in the "Measurement method" and "Measurement procedure" columns indicate that the specified methods and procedures must be adopted or alternatives are allowed, respectively.A nanomaterial testing standard can select an appropriate PNL for each provision based on technical maturity and market demand.
A nanomaterial testing standard usually addresses multiple characteristics.Then, it may include provisions with different normativity levels, such as PNL 2 and PNL 7 for different provisions, depending on the significance of the characteristics in applications and the maturity of measurement techniques.It is worth noting that specific measurement procedures can be specified in a separate measurement procedure standard, distinct from the main testing standard, or they can be incorporated into the main testing standard.
PNL 10, where characteristic values are specified, falls beyond the scope of testing standards and belongs  to another standard category known as material specification standards, distinct from testing standards.ISO has developed numerous material specification standards for steels due to the well-established technology and matured market.However, it is worth mentioning that in contrast, ISO TC 229 has not yet formulated a nanomaterial specification standard due to the ongoing development of nanomaterial technology and the nascent state of the market.

Flexibility
Flexibility in the nanomaterial testing standard refers to the ability to change the application of provisions through an agreement between the manufacturer and the user.Since the significance of characteristics and measurement methods varies depending on the type of nanomaterial and its application, it is possible that a specific requirement may not align well with the specific needs of standard users.Therefore, it is desirable for the nanomaterial testing standard to be flexible in its implementation of provisions.
There are two common ways incorporate flexibility into nanomaterial testing standards.The first is to allow deviations from the standard if there is a technically justified reason.For instance, the reporting clause can specify that if there are any deviations from the document, the name, detailed information, and justification of the measurement methods used should be provided.
The second way is to include flexibility within the testing standard itself by incorporating different provision normativity levels (PNLs).For example, a testing standard can include both core characteristics that must be measured and optional characteristics that are recommended to be measured.The manufacturer and user can then decide, based on their agreement, whether to measure the optional characteristics or not.This approach enables more standard users to adopt the nanomaterial testing standard without deviating from its requirements.ISO has published many nanomaterial testing standards that utilize different normativity levels for the characteristics.

Reliability
Reliability in the context of nanomaterials encompasses two aspects: the reliability of the testing standard itself and the stability of the nanomaterial.
Reliability in the nanomaterial testing standard refers to the uncertainty in the characteristic measurement results when they are measured according to the specified measurement methods and procedures.It can be evaluated through interlaboratory comparisons of characteristic measurement results using typical nanomaterials, instrument calibration using reference standards, utilization of reference materials for the characteristics, and other methods.
Most of the nanomaterial testing standards developed by ISO are Technical Specifications (TS) rather than full International Standards (IS).In such cases, it is likely that the validity of the specified measurement methods and procedures in the TS has not been fully assessed through interlaboratory comparisons using the target nanomaterials.Instead, their validity is estimated based on their current use and reputation within relevant industrial communities.Thus, the majority of nanomaterial testing standards published by ISO require manufacturers to report at least the repeatability and reproducibility of measured data to validate the adopted measurement methods and procedures.
The stability of a nanomaterial can be expressed as the ratio between the characteristic value measured after a specified treatment and the value measured before the treatment.The nanomaterial testing standard can define the stability by specifying the target characteristic and providing details of the treatment.

Integrity
Integrity in the context of the nanomaterial testing standard refers to the level of acceptance and usage within the relevant industrial communities.International Standard (IS) documents are published by ISO based on their integrity.However, Technical Specification (TS) documents can be published with the intention of delivering them earlier to obtain feedback from the relevant industrial communities, even if their integrity is not yet fully established.
Nanomaterial technology is still in the developmental stage, and there is not yet a universally accepted technical consensus.Therefore, it is understandable that most of the nanomaterial testing standards published by ISO are in the form of TS documents.As the nanomaterial technology advances and the market matures, these TS documents may be upgraded to IS documents.When publishing an IS document, a mandatory validation of the measurement methods and procedures through interlaboratory comparisons may be required.
Overall, this section provides insight into the importance of integrity in the nanomaterial testing standard and acknowledges the current state of the field, where TS documents play a significant role in facilitating feedback and further development.

Publication of nanomaterial testing standards
The references [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] encompass the comprehensive outcomes of nanomaterial testing standards developed by ISO TC 229 as of June 2023.A total of 20 standards have been developed or are currently under development, based partially or entirely on the scenario outlined in Chapter 3.This scenario is expected to guide the revision of these standards during ISO's periodic systematic review.Figure 6 shows the hierarchical model of nanomaterial testing standards.The upper layers encompass generic standards that address nanomaterials in general for widespread applications.The middle layer focuses on specific substances for general applications, while the lower layer addresses specific substances intended for particular applications.It is crucial for standards developers to position their nanomaterial testing standards appropriately within this hierarchical model.

Upgrading nanomaterial testing standards
As discussed in Section 3.6.1,nanomaterial testing standards encompass provisions with varying levels of normativity.The normativity of a testing standard increases as measurement techniques advance, leading to improved reliability.
Figure 7 illustrates the process of upgrading nanomaterial testing standards in correlation with advancements in measurement techniques.When a new nanomaterial emerges, the documentation of measurement methods and standardization of measurement procedures are typically in their early stages.As basic research progresses, measurement techniques for nanomaterial characteristics become more sophisticated and widely shared among academic and industrial communities.This enables the comparison of measurement data obtained by different organizations and individuals.As measurement methods are documented and measurement procedures are standardized from Stage A to Stage C in Figure 7, the deviation in measured characteristic data decreases significantly.
Advancements in measurement techniques drive the upgrading of nanomaterial testing standards by increasing normativity as shown in Figure 7.In Stage A, where both documented measurement methods and standardized measurement procedures are not available, the business catalogues of new nanomaterial products provided by manufacturers generally contain lowquality data, as the characteristic data can vary significantly and are not sufficiently comparable.
In Stage B, where measurement methods have been documented, the business catalogues of new nanomaterial products can display more comparable characteristic data by incorporating the documented measurement methods.ISO/TC229 has already reached Stage B, with many well-defined measurement methods for nanomaterials [6][7][8].
In Stage C, where measurement procedures have been standardized, the business catalogues of new nanomaterial products can exhibit maximized comparability of characteristic data by implementing standardized measurement procedures in industries.
These advancements in measurement methods and procedures enhance the reliability of nanomaterial testing standards, as shown in Figure 7, by increasing normativity.The ISO nanomaterial testing standards already published range from Level 2 to Level 9, depending on the maturity of the measurement technology.These standards can usually be upgraded during ISO's periodic Systematic Review.

Nanomaterial specification and certification
A nanomaterial certification system can greatly support the industrialization of nanomaterials.This chapter explains how nanomaterial testing standards are utilized within the nanomaterial certification system.In this context, nanomaterial certification refers to the third-party attestation that a nanomaterial meets the requirements outlined in the nanomaterial specification.The nanomaterial certification system provides nanomaterial users with confidence in the quality of the nanomaterial.
Figure 8 presents a schematic representation of the nanomaterial certification system.Firstly, the nanomaterial testing standard is employed to establish a nanomaterial specification, which defines the desired values for specific characteristics.The selection of characteristics with specified values is based on the characteristics list provided by the nanomaterial testing standard, ensuring that the nanomaterial product performs as intended in various applications.Multiple organizations, including individual nanomaterial manufacturers, relevant industrial associations, or national and international standardization organizations, can develop the nanomaterial specifications for their own purposes.
In Figure 8, the nanomaterial manufacturer requests a testing laboratory to measure certain specified characteristics of a nanomaterial in accordance with the nanomaterial testing standard.The testing laboratory then provides the requester with a report detailing the measurement results (indicated by 1 ).The testing laboratory performs the measurements using the measurement methods and procedures specified in the nanomaterial testing standard.The testing laboratory can be either an independent laboratory or an in-house facility within the manufacturer's organization.
The testing laboratory can be accredited for proficiency by the accreditation body ( 2 ) or evaluated and recognized by the certification body ( 3 ) based on ISO 17025 [29].The certification body can also be accredited by the accreditation body ( 4 ) in accordance with ISO/IEC 17065 [30].The certification body is responsible for certifying the nanomaterial product of the manufacturer ( 5 ) as meeting the requirements outlined in the nanomaterial specification, following product certification standards such as ISO/IEC 17067 [31] and the quality management system requirements like ISO 9001 standards [32].
Nanomaterial users can purchase nanomaterials from the manufacturer ( 6 ) with confidence in the specified characteristics.They can achieve this by either verifying the testing laboratory's report for a lot that meets the requirements of the nanomaterial testing standard or by confirming the certification body's report for a batch that complies with the requirements of the nanomaterial specification.
Hence, the nanomaterial testing standard serves as the fundamental basis for the nanomaterial certification system, which greatly facilitates the industrialization of nanomaterials.

Conclusions
The field of nanomaterial technology is rapidly advancing in the industry, and nanomaterial testing standards play a crucial role in facilitating industrialization of these materials.The scenario described in Chapter 3 helps stakeholders identify key standardization items and effectively integrate them into the standards.This scenario is useful overall, not only for developing these standards but also for advanced planning and subsequent revisions.
This paper also emphasizes the role of nanomaterial testing standards in the certification system, providing third-party attestation that a nanomaterial meets specific requirements.These standards provide a technical foundation for fair and transparent market transactions involving nanomaterials.Specifically, nanomaterial users can have confidence in the quality of the nanomaterials they purchase, thereby facilitating the nanomaterial market growth.

Figure 2 .
Figure 2. Market growth and standards development.

Figure 3 .
Figure 3. Use of testing standards for market transactions.

Figure 4 .
Figure 4. Flexible use of testing standards.

Figure 5 .
Figure 5.A scenario for developing nanomaterial testing standards.
and I: informative.

Figure 6 .
Figure 6.Hierarchical model of ISO nanomaterial testing standards.

Figure 8 .
Figure 8.A schematic of nanomaterial certification system.

Table 1 .
An example table format for core characteristics and their measurements.

Table 2 .
An example table format for optional characteristics and their measurements.

Table 3 .
Provision normativity levels in nanomaterial testing standards.