Visual Analysis of Carbon Emissions in Steel Industry Based on CiteSpace

This paper analyzes the research characteristics and development context of carbon emissions in the steel industry, which will provide reference for future carbon emissions research and practice in the steel industry in China. Based on the “Web of Science Core Collection” (hereinafter referred to as SCIE) database, this paper used CiteSpace software to make a bibliometric analysis of the literatures related to carbon emissions in the steel industry from 1991 to 2020 in terms of countries and regions, major publishing institutions, high-yield authors, keywords and time zone views. The results show that: 1) Scholars and research institutions in different countries and regions form a close cooperation network according to their geographical location;2) The research forces with China, the United States, the United Kingdom and Japan as the core have provided key research support and contributed major research results to the carbon emission eld of the steel industry;3) Climate change, production technology and future scenario analysis are the three main research topics;4) In the future research stage, the comprehensive application of various disciplines such as technical and economic analysis, scenario analysis and environmental climatology will become the forefront of the research on carbon emissions in the steel industry. The attribute method, etc.


Introduction
The Fifth Assessment Report of IPCC pointed out that man-made greenhouse gas emissions lead to the continuous deterioration of global climate, which poses a serious threat to the stable development of human beings and nature (Stocker 2014). Industry is the main body of economic activities, plays an important role in the greenhouse gas emissions, according to BP world energy statistics yearbook (2019) data statistics, in 2019, industry accounted for 33% of the world's energy consumption and 40% of CO 2 emissions in turn (Yu et al. 2021), and the iron and steel industry as one of resource-intensive industries, is a key eld of greenhouse gas emissions, accounting for about 33.8% of the total industrial emissions and7% of the world's total CO 2 emissions (Yuan et al. 2020).Therefore, carbon emission reduction activities of the steel industry play a vital role in its own sustainable development and global carbon emission control (Talaei et al. 2020). At present, China is the world's largest steel producer and consumer. In 2019, China's steel consumption totaled 907.5 million tons, accounting for 51.3% of the world's total consumption. Crude steel production totaled 996.3 million tons, ranking rst in the world, accounting for 53.3% of the world's total production. Pig iron production totaled 809.4 million tons, accounting for 63.2% of the total pig iron production in the world (BP Company 2019).In addition, China's steel industry mainly consumes coal and coke energy, accounting for 89.18% of the total energy consumption of the steel industry (Wang et al. 2017), which makes the steel industry become one of the key sources of China's CO 2 emissions, accounting for about 15% of the total national CO 2 emissions (Zhang et al. 2018). In recent years, with the annual increase of CO 2 emissions in China's steel industry, its development has also been faced with serious environmental problems (Xu et al. 2017). In order to cope with China's increasingly severe environmental challenges and achieve the goal of carbon peak and carbon neutral before 2030 and 2060 in turn (Hu 2021), it is necessary to conduct in-depth research on carbon emissions in the steel industry. What is the collaborative network of research journals, institutions, authors, and countries that have been involved in the analysis of carbon emissions from the steel industry for nearly three decades?
How do the research topic evolve? How do they relate to each other? What are the latest research frontiers? The discussion of these problems is of great theoretical and practical signi cance for researchers to grasp the research hotspots in this eld systematically and to enhance the e ciency of scienti c research.
With the help of CiteSpace visualization analysis software, this paper adopted the method of bibliometric analysis to make a visual metrological analysis of the relevant literatures on carbon emissions of steel industry from 1991 to 2020 in SCIE database by using cooperative network map, keyword co-appearing, clustering and Timezone time map. This paper revealed the research hotspot and development trend of the current and future, aiming to provide reference for future prospective research on carbon emissions in China's steel industry.

Materials And Methods
In order to comprehensively analyze the characteristics and frontier hot of carbon emission research in iron and steel industry, this paper usedCiteSpace (version 5.7.R3) software to conduct scienti c econometric analysis on related literature. CiteSpace is gradually developed under the background of scientometrics, data and information visualization, and is a visual analysis software for visual description and trend display of literature (Li and Chen 2016).By using CiteSpace to draw the map of cooperative network, keyword clustering and time zone view, the basic characteristics of research in this eld and the evolution path of the topic can be explored (Huang et al. 2020), and the research hotspots and trends can be sought.
Generally speaking, the main stages of research development in each eld are determined according to the evolution process of the research topic, which in turn is promoted by both the knowledge base and the research frontier (Chen 2020).Therefore, this paper usedCiteSpace software to draw a visual analysis map. Through detailed interpretation and analysis of each map, this paper explored the evolution process and rules of carbon emission research in the steel industry, found out its active themes and frontier hotspots, and objectively analyzed and commented on the research panoramic view in this eld.
In this paper, an advanced retrieval was conducted on CNKI database, with "steel industry" and "carbon emissions" as the retrieval topics, the time set as "unlimited year" to "2020", and the journal source categories set as "SCI source journals", "EI source journals" and "CSSCI". A total of 20 related literatures were retrieved. Due to the small number of domestic literatures and considering the representativeness of samples, this paper used Web of Science as the literature retrieval system and selected SCIE database for advanced retrieval. The relevant literature retrieved was downloaded and saved as a plain text le in the form of "full record", which was used as the data sample for analysis in this paper.

Overview of Research Characteristics
Through the analysis of the basic characteristics of carbon emission research in the steel industry, the development of the research in this eld can be grasped as a whole, and the academic circles' attention to this eld and its research value can be understood.

Research Records Distribution
Through sorted out the published papers from 1991 to 2020, it is found that the distribution of the published papers related to carbon emissions in the iron and steel industry showed an overall increasing trend. As shown in Figure 1 below, some researchers began to pay attention to carbon emissions in the steel industry in the early 1990s, and corresponding research results emerged. In recent years, it has attracted widespread attention. In 1991, Italian scholar Gretz, J, et al rst made relevant research in this eld and put forward their opinions, and they thought that steel production is one of the most important source of carbon dioxide pollution, as a large user of coal and other forms of energy, in order to cope with the threat of global warming, it is necessary to control coal consumption and seek alternative energy

Analysis of the Major Sources
The continuous development and growth of carbon emission research in the steel industry in the past 30 years has bene ted from the continuous support of international journals of various disciplines. Table 1 lists the journals that published more than 4 research articles in this eld, including energy, environmental engineering, metallurgy and ecology, etc., with strong comprehensive disciplines. More than half of the major source journals are in JCR 1 area, among which the number of publications of Energy is the highest with an impact factor above 6. Other top six journals, such as Energy Policy and Journal of Cleaner Production, all have an impact factor above 7. The most prominent one is that the 5-year impact factor of Applied Energy has reached 9.086. This indicated that the carbon emission research of iron and steel industry has been widely concerned by the mainstream academic journals, especially the authoritative energy journals. Thus it can be seen that although the carbon emission research eld of the steel industry started late, with the increasingly severe global climate change situation (Isson et al. 2020), scholars and authoritative professional journals from all walks of life are gradually paying more attention to it.

Analysis of Main Research Forces and Cooperation
In order to have a deeper understanding of the speci c research situation in the eld of carbon emissions in the steel industry, this part made a bibliometric and statistical analysis on the major publishing regions, publishing institutions and high-yield authors, and explored the internal relationship between the literatures in this eld.

Analysis of Main Publishing Countries and Regions
In order to explore the cooperation characteristics of publishing countries in the carbon emission research of the steel industry, CiteSpace software was used to conduct a quantitative analysis of the literature extracted from SCIE. Country was selected in the Node Type and the distribution network map of publishing countries and regions was obtained as shown in Figure 2 below. After statistics, it is found that a total of 41 countries and regions have published relevant literatures (due to the small nodes in some regions with a small number of published papers, they are not shown in the gure), mainly distributed in Asia, Europe, Oceania and North America. The top ten countries and regions were sorted out. As shown in Figure 3, all countries except China are developed countries, which also echoes the economic and cultural development pattern of the world today.
The size of the node (circle) in the network map of the country and region where the paper is issued represents the amount of the paper it publishes and the size of nodes means the number of articles it publishes. In addition, the thickness of the connection lines indicates the degree of cooperation. In the picture, we can see obviously, China has the largest number of nodes. It is the only country that has published more than 100 papers on carbon emissions in the steel industry, up to 157 papers, and it is the core force of research in this eld. As the world's largest energy user in the steel industry and one of the  Table 2   In addition, this paper uses CiteSpacebibliometric software to generate a network map of research institutions of carbon emission in the steel industry (Fig.4), which can indicate the cooperation between major publishing institutions and further explore the distribution of scienti c research forces in this eld.
In the network graph, nodes represent the number of articles published by research institutions, and the connecting lines between nodes represent the degree of cooperation among research institutions. As can be seen from Figure 4, on the whole, there is a certain degree of cooperation among major scienti c research institutions, and the closely connected scienti c research institutions are geographically close to each other. For example, China and Japan in Asia, the United States and Mexico in the Americas and other countries and regions have close cooperative relations. Only some underdeveloped countries and regions have weak cooperative relations between their research institutions.

Analysis of Main High-yield Authors
In this paper, the authors of carbon emissions research in the steel industry are sorted out and summarized, and the number of published papers, nationality, institution and research scope keywords of the top 10 most productive authors in this eld are statistically analyzed, as shown in Table 3 below.It is intuitive to nd that nearly half of these major proli c authors are from China, led by Professor Lin  In addition, several collaboration groups of authors have been formed in the eld of carbon emission research in the steel industry, among which the collaboration among the highly productive authors is more prominent. In order to more intuitively represent the cooperation system among scholars, this paper usedCiteSpace software to generate a map of author cooperation network (Fig.5) for analysis. It can be seen from this map that only a few scholars have formed a cooperative network, among which the most extensive group is centered on E Worrell of Lawrence Berkeley National Laboratory, including L Price and N Martin, etc. They looked at the low cost energy e ciency and carbon reduction opportunities in the US steel industry (Worrell et al. 2001). The most closely collaborated group is Lin Boqiang and Xu Bin. They identi ed the key in uencing factors of carbon dioxide emissions in China's steel industry from the perspective of regional geographical differences, and provided certain theoretical support and practical guidance for realizing carbon emission reduction in China's iron and steel industry and formulating Running CiteSpace, set Node Type as Keyword, and the time range was 1991-2020, the network cutting method was Path nder, Pruning networks and Pruning the merged network, selected 1 year time slice, selected keywords for Node Type, defaulted for other options, imported the selected literature data, and got Keyword co-emerging map (Fig.6). As shown in Fig. 6, the co-occurrence graph of key words in carbon emission research of the steel industry has a total of 451 nodes, 918 connections, and a network density of 0.009. Among them, the size of the keyword node corresponds to its frequency.
In addition, the mediating centrality of each keyword can be obtained from the keyword co-occurrence graph. The node with high centrality is the bridge connecting each keyword, and the higher the value of the keyword is, the more critical the keyword is in its research hotspots. The top ten keywords with the highest frequency and the highest intermediary centrality were sorted out through the keyword cooccurrence map of carbon emissions research in the steel industry, as shown in Table 4. Summing up the two overlapping keywords, divided into three categories: carbon emissions, e ciency and China, they can be regarded as the most important connecting hub of hot keywords in the research eld of carbon emissions in the steel industry.

Analysis of Hot Research Topics
Keywords clustering can deepen the co-occurrence relationship of keywords and calculate a group of keywords with a closer relationship, so as to form a topic clustering containing multiple groups of words.In order to further investigate the knowledge structure of carbon emissions in the steel industry and explore the research hotspots, this paper conducted cluster analysis on the key words. Run the software to obtain the correlation clustering map (Fig. 7).From the clustering map, we can see that the Modularity module value (Q value) is 0.8166, greater than 0.3, indicating that the clustering results are signi cant. And Mean Silhouette: the Mean contour value (S value) of the clustering is 0.9306, greater than 0.7, indicating that the clustering is highly credible. Scholars closely focused on carbon dioxide emissions and steel industry research, formed a total of 10 keywords cluster research hotspots. In the following, the clustering shown is sorted out and analyzed, and three hot research topics are formed. threats to human habitat, and changing it will require fundamental changes in our daily social and economic lives. Steel production is a special case of economic activity, which is not only related to combustion, but also closely related to greenhouse gas emissions (Mayer et al. 2019). In many developed countries, global climate change has been widely concerned. In order to protect the environment, they have taken more and more measures to deal with greenhouse gases in heavy industries such as steel In the future, with the rapid development of the global economy, the demand for steel will greatly increase, and the research and development of new technologies and the adjustment of energy structure to cope with the future climate change situation are urgent. Carbon emission reduction in the steel industry needs long-term regulation and control. It is an important strategic measure to forecast the future scenario and make corresponding adjustments in time, and it is also a hot topic of research at the present stage.

Frontier Analysis
In order to further explore the future research frontier hot spots in the eld of carbon emissions in the steel industry, it is necessary to analyze the evolution trend of the research hot spots. In this paper, CiteSpace software was used to generate the Timezone map (Fig.8). and Japan as the core, they have provided key scienti c research support and contributed major research results to the carbon emission eld of the steel industry. In particular, the Chinese Academy of Sciences and Xiamen University in China have led the way in the number of published papers, and they are an important driving force for the research in this eld. However, the cooperation between their institutions still needs to be improved. Therefore, in the future, we can strengthen the participation and cooperation of other research institutions and enterprises, expand the scope of research, and learn from each other's research experience and results.
(2) In terms of hot spots and frontiers of carbon emissions research in the steel industry, they are mainly classi ed into three research orientations: climate change-oriented research, production technologyoriented research and future scenario analysis-oriented research on carbon emissions in the steel industry. From 1991 to 2020, the research focus of carbon emissions in the steel industry continued to focus on four major issues, namely carbon dioxide emissions, energy use, air pollution and climate policy.
The research levels and methods have been continuously deepened. And the carbon peak and carbon neutral targets have attracted wide attention from scholars in this eld. Therefore, in the future research stage, there will be an outbreak period in the eld of carbon emissions in the steel industry, and the research direction can focus on the comprehensive application of various technical and economic analysis, scenario analysis and environmental climatology.

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Competing interests
The authors declare that they have no competing interests. All of the funding bodies play a partin the design of the study and collection, analysis, and interpretation of data and in writing the manuscript play.